NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

311.05-11-3110561 April 29, 1971

NBS REPORT

10 587

Progress Report

on A REVIEW OF RECENT STUDIES OF

IN VITRO REACTIVITY OF SURFACES OF CALCIFIED TISSUES

by

G. M. Brauer

Chemist, Dental Research Section

National Bureau of Standards

Washington, D. C. 20234

This work was supported by the National Institute

of Dental Research.

IMPORTANT NOTICE NATIONAL BUREAU OF ST/

for use within the Government. Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

;s accounting documents intended

subjected to additional evaluation

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! Office of the Director, National

y the Government agency for which

opies for its own use.

and review. For this reason, the whole or in part, is not authori Bureau of Standards, Washingtoi

the Report has been specifically |

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

A REVIEW OF RECENT STUDIES OF

IN VITRO REACTIVITY OF SURFACES OF CALCIFIED TISSUES

G. M. Brauer

Dental Research Section

National Bureau of Standards

Washington, D. C. , U. S. A.

Much scientific data have been accumulated on the chemical organization of the organic matrix and the chemistry of the mineral phase of

enamel, dentin and bone.

^ ^ Relatively little information is available, however, regarding the chemical and physical characteristics of

the surfaces of the components of tooth structure. Furthermore, in vitro

techniques to modify calcified tissue surfaces under an environment approximating conditions that are likely to be encountered clinically have

received only scant attention. Such studies are of utmost importance

not only in gaining more basic knowledge, but also in the solution of a wide spectrum of clinical problems such as improved anti-cariogenic

agents, remineralization, speedier wound healing techniques, more

compatible implants and the development of efficient medical and dental

tissue adhesives and biodegradable sutures.

The effectiveness of potential surface conditioning agents can be

demonstrated by changes in the surface properties of the substrate.

Physico-chemical methods to detect these surface modifications include

scanning electron microscopy, infrared spectroscopy using multiple internal

reflectance techniques, as well as measurements of (1) the effective

surface area, (2) adsorption isotherms, (3) heat of immersion and heat

of reaction, (4) contact angle and critical surface tension, (5) oil

wettability under water, and (6) adhesionability

.
The following discussion emphasizes the efforts made in various

laboratories to modify tooth surfaces to obtain an adhesive bond

between the restorative material and tooth structure so that the interface between the restoration and the tooth would support a mechanical

load in addition to preventing the ingress of oral fluids. Potential

adhesive systems are summarized in Table 1 and include both application

of surface conditioning agents and various polymeric materials cured

in situ. The evaluation of the resinous materials as adhesives will be

discussed by other participants in this symposium. The usefulness of inorganic polymers and bioadhesives (such as barnacle cement) for clinical

applications has not been demonstrated.

ADSORPTION

1. From the Gaseous Phase

Adsorption of a gas on tooth surface presents the simplest

example of adhesion. Studies of the interaction of gases by Beebe and

coworkers have provided considerable insight into the details of the

surfaces and structures of hard tissues Dry anj Beebe have demonstrated the strong affinity of hydroxyapatite surfaces for water and the

( 9 ) dependence of apparent surface areas on water content . A significant

decrease in specific surface area (determined from gas adsorption measurements by the BET method) occurred when chemisorbed layers of water blocked

the very narrow pores or grain boundaries of the substrate and thus

effectively reduced the area accessible to nitrogen adsorption. From

adsorption isotherms and calorimetric heats of adsorption of methanol on

mineral surfaces, it was possible to separate the total adsorption into

chemisorbed and physisorbed fractions. In the case of water, such a
- 3 -

separation was not as clearly delineated. Relatively high heats of adsorption in the first monolayer for both methanol and water indicate a high energy of binding by hydroxyapatite and may be attributed to hydrogen

bond formation involving exposed oxygen atoms at the surface.

The structures and surface properties of bone and tooth mineral have

also been studied by Loebenstein, utilizing the low temperature nitrogen

adsorption BET technique . Surface areas of powdered dentin ranged

2 between 6.8 and 11.1 m /gm, while powdered and defatted bovine femur shaft

2 revealed a surface area of only 1.47 m /gm. Samples of dentin and bone

rendered anorganic by treatment with ethylene diamine presented specific

2 surfaces of 130 and 114 m /gm, respectively. This increase in surface area

was attributed to the removal of dried collagen that denied access of nitrogen

molecules to the micropores of dentin and bone. The low surface area of de2

fatted bone (1.47 m /gm) supports the concept of pore blockage by collagenous

material

.

Loebenstein developed a simple apparatus for obtaining, gravimetrically

,

water vapor adsorption measurements at ambient temperatures

.

For components of teeth, typical Type II BET isotherms resulted which could be used

to calculate surface areas available to water. Well-developed hysteresis

loops extending over the entire range of humidities were found on comparison

of the adsorption and desorption isotherms.

Results of pore size experiments indicate that some of the detailed

pore-volume profile patterns for anorganic bone are shared by both hydroxyapatite and octacalcium phosphate, while others are more closely aligned

with hydroxyapatite . The relative amplitudes of peaks and troughs for the

mineral component of bone and teeth, as well as their location, along the

pore diameter axis, were found to be dependent, not upon their organic matrix,

but rather upon their crystallographic makeup.
To provide information regarding the mechanism and chemistry of surface forces by which tooth structure and adhesive interact, Loebenstein

studied the adsorption of carbon dioxide and ammonia on tooth components

These two reactive gases were chosen because they should indicate the

presence of acidic and basic groups, respectively, as possible bonding

sites for an adhesive. The extent of the surface area available after preconditioning the solid substrate was compared for each of these gases, as well as for nitrogen. Presence of collagen in dentin exerted a profound

influence on the BET area depending on the gas used.

By making measurements near the boiling point of the adsorbate, but

at different temperatures, the isosteric heat of adsorption (the heat

liberated per constant number of moles of gas adsorbed per gram of adsorbant) was determined. From the magnitude of the heat of adsorption,

the intensity of the reaction between adsorbate and adsorbent can be

estimated. The isosteric heats of adsorption of carbon dioxide and ammonia to about two statistical layers on anorganic whole tooth powders

and dentin powders fell within the van der Waals physical adsorption range;

that is, below 12 kcal, although in most instances they were greater than

for hydrogen bonding. The isosteric heat fell off rapidly until a monolayer was formed and at higher coverage generally did not change appreciably

This work demonstrates the use of adsorption and area of coverage measurements as criteria for the selection of chemically reactive groups for incorporation in potential adhesives. Extrapolation of these findings would

suggest that amino groups incorporated into a dental adhesive may provide

better bonding than carboxylic acid groups.
5

2. From Solution

Studies of adsorption on hydroxyapatite and tooth surfaces

from solution are required to determine quantitatively the effectiveness of tooth conditioning procedures and to ascertain the effect of application variables such as concentration of conditioner in the solvent,

exposure time to the solution, and rinsing time. Furthermore, adsorption

studies may assist in the disclosure of those materials that would serve

most effectively as surface conditioners.

A number of investigators have studied adsorption from solution

to tooth surfaces and hydroxyapatite in order to determine the nature

and magnitude of the interfacial chemical interactions occurring between

teeth and selected model organic compounds. In addition to the complex

structural characteristics of enamel and dentin, the deposition and

smearing of organic debris accompanying operative cutting and grinding

procedures render hard tooth tissues poor substrates for such studies.

Bertolucci and Chamberlain studied interfacial reactions of

synthetic and natural hydroxyapatites, as well as other calcium phosphates,

( 12 ) using infrared attenuated total reflection (ATR) techniques . The

organic adsorbates were applied to the finely divided solids from aqueous

and non-aqueous solutions. The infrared spectra were recorded before and

after adsorption. Shifts in the infrared absorption bands are indicative

of the nature and degree of interaction between apatite and the organic

compounds. Adsorption of citric acid and oxytetracycline (as the HC1

salt) on synthetic hydroxyapatite produced shifts of between 5 to 9 cm

1

in the asymmetric P-0 stretching frequency in the vicinity of 1027 cm

J".

Similar shifts were not observed on exposure of commercially available
- 6 -

hydroxyapatites, natural apatite, fluorapatite or calcium phosphate

to these adsorbates. From a fundamental point of view, it is likely that

complete interpretation of infrared spectra should give absolute information about the interaction with the surface and therefore of the

wetting. The technique is limited at the present time mainly because

it has not been investigated in detail.

The adsorption isotherms for water on bovine tooth powder and

on synthetic hydroxyapatite have been determined gravimetrically by

(13) Pitt . Although the amount of water absorbed by the hydroxyapatite

was apparently not considered, it appears that a relative humidity of

about 25% is necessary to adsorb a monolayer of water on bovine tooth

(14) powder. Based on the values given in the literature for the adsorption of moisture on collagen (kangaroo tail tendon) , the quantity of water

sorbed on tooth powder is somewhat lower than that computed on the assumption

that dentin is comprised of 80% hydroxyapatite and 20% collagen by weight.

This discrepancy may be the result of the partial inaccessibility of the

collagen caused by its bonding to the mineral component of tooth structure.

Citric acid treatment of tooth surfaces produces little change in the

isotherm. Treatment of bovine tooth powder with aqueous silver nitrate

decreases the total amount of moisture that is reversibly adsorbed. At

high relative humidity, where multilayer adsorption is likely to occur,

this treatment reduces the uptake of water to half that of untreated tooth

powder. Assuming that the mineral portion of the composite was not significantly affected by the aqueous silver nitrate, adsorption of moisture

on the protein must have been greatly reduced.
- 7 -

Schwartz and Galligan studied the equilibrium adsorption of

aqueous solutions of linoleic acid and sorbic acid on hydroxyapatite

having a particle size of 2 to 16 ym^“^. The amount of conditioner

that could be removed on exposure of the apatite substrate to fresh

solvent was also determined. Adsorbed linoleic or sorbic acid

could not be removed by the solvent. This behavior, as well as similarities in the adsorption isotherms at 20°C and 37°C, are

characteristic of chemical adsorption or reaction rather than

physical adsorption.

Patrick et al determined the adsorption isotherms of a commercial hydroxyapatite with a series of polymers dissolved in

methylene chloride A typical rubbery interliner that interacts with the physiologic substrate as well as the resin, and

thus should provide a zone that would absorb stresses, was

selected. The greatly increased adsorptivity , and thus the

strongest interaction with the hydroxyapatite, of this partially

saponified acrylonitrile-butyl acrylate copolymer as compared to

the other copolymers studied was clearly indicated from the isotherms

obtained. Furthermore, the adsorption isotherms for this polymer

were nearly the same when human or bovine dentin or enamel were used

as substrates.

(18) Eric.son and Ericson reported that protein adsorption was less
- 8 -

on fluoride-containing hydroxyapatite- than on fluoride-free hydroxyapatite. Glantz and Nyquist assume that fluoride ions cause a reduction

in the free surface energy of hydroxyapatite crystals immediately after

(19) topical application of fluorides . Mannerberg hypothesized that if

the free surface energy of enamel is decreased by fluorides, the possibility

for adhesion of an organic pellicle or plaque may also be decreased ^0)

HEATS OF IMMERSION

The forces of attraction can vary greatly in the case of two different substances spread on the same solid even if the wetting angle is

( 21 ) zero in both cases. Greatest adhesion occurs when chemical bonds are

formed and the wetting is truly complete. Enthalpies of adhesion give a direct measure of the forces of interaction and hence the "wetting" irrespective of the contact angle. Furthermore, it has been pointed out

by Zettlemoyer that a study of heats of immersion will indicate if adhesion between two contacting surfaces will be maintained or disrupted

( 21 ) by water or saliva . The measurement and evaluation of these heats

of immersion and heats of reaction therefore facilitates the study of

any modification of tooth structure necessary to achieve a chemical bond

and aids in the determination of those groups that will bond effectively

to the components of tooth structure in an aqueous environment.

Calorimetric measurements of the heats of immersion of wellcharacterized powders of the components of human tooth structure have

been used by the author and coworkers to assess the nature and degree of

modification of well-characterized tooth surface produced by the presence

(22-24a) of various ions and functional groups in an aqueous environment
9

The specific surfaces (BET) of the dentin, enamel and anorganic whole

tooth powders used in these experiments were obtained from nitrogen ad2 sorption measurements and were 10.5, 3.9, and 75 m /gm, respectively.

Comparison of the apparent heats of immersion values (-AH ) of dry

tooth powders (Table 2) illustrates the reactive nature of the organic

(23) constituents when present in tooth substance . The specific surface

of dry anorganic whole tooth tissue was approximately 7.2 times that of

dry dentin. The apparent heat of immersion value for dentin, however,

was higher than that of anorganic whole tooth tissue by a factor of 4.9

per gram of substrate, and by a factor of 35 on a unit area basis. The

magnitude of the value obtained for powdered dentin suggests that more

than simple wetting occurs when this substance is immersed in water.

(25) Heats of wetting values of +37 cal/gm have been reported by Kanagy

for purified bovine corium collagen. Since the -AH values for anorganic

w

whole tooth are low (2.06 cal/gm), it is likely that the unexpectedly large

-AH values obtained for dentin were caused by the presence of collagenous w

material at the surface of the powder particles.

The apparent -AH values obtained for dentin greatly exceeded the

w

2

-AH values for inert solids (0.007 to 0.15 cal/m ) previously reported w

/ r\ r \ by other investigators for other substances v

. Therefore, the collagenous

component of dentin binds water through hydrophilic groups and may further

absorb, dissolve or react upon contact with water. The observed -AH

w

values for anorganic whole tooth, however, were found to be within this

range.

The observed heats of immersion of odontic powders with solutions

containing disodium EDTA, in contrast to the observed heats of immersion
- 10 -

of these powders with ammonium

citrate and methacrylic acid, are more dependent upon the calcium available

for chelation than upon the presence of organic matter (Tables 3.5 Examination of the apparent heats of immersion values on a unit area basis

reveals that the reactions of disodium EDTA with odontic powders appear to

be independent of available surface area.

The presence of NO^, NC^, CNS , S0^, and I at pH 5 lowered the heat of

immersion of dentin. Other anions (F and Cl ) had no effect. At pH 8 , however, anions did not alter the heat of immersion values of dentin (Table 6).

The depressed -AH^ values observed for powdered dentin upon immersion

in dilute aqueous solutions containing certain anions at pH 5 suggest the

•f direct endothermic interaction of these anions with R-NH groups. An

J

alternative mechanism may involve the preferential binding of these anions

to positively charged sites on the dentinal collagen at the expense of water.

Chloride and fluoride ions apparently possess a low affinity for dentinal

collagen.

In vitro studies have shown a decrease in the acid solubility of tooth

(27) structure after treatment with dilute fluoride solutions . If an enamel

or dentin surface can be modified. In such a way that it will resist acid

attack, it is reasonable to assume that the substance producing the modification must first react with the surface of tooth. Values observed for the

heats of Immersion of dentin (23.4 cal/gm), enamel (3.0 cal/gm) and anorganic

whole tooth (1.09 cal/gm) with 8 % stannous fluoride solution indicate that

this reagent reacts mainly with the organic matter of the powdered samples

(23)

of these tissues; The immersion of dentin in dilute aqueous solutions of

sodium fluoride yielded values similar to those observed upon the immersion

of dentin in water. The marked change in the heat of immersion value obtained
- 11 -

when dentin was immersed in stannous fluoride solution was therefore probably dependent on the presence of stannous ions.

The addition of aldehyde groups to the liquid adsorbate at pH 8

resulted in the lowering of the heat of immersion of dentin, although

addition of aldehyde groups to the aqueous phase at pH 5 had only a

slight effect upon the observed -AH of dentin and anorganic whole tooth

powders

.

Reductions in the -AH^ values of dentin in aqueous phenol and urea

from those obtained in water suggest that these compounds react either

endothermically with the dentinal protein or are bound preferentially to

( 24a) charged sites at the expense of water v

. Exposure of dentin to dilute

hydrogen peroxide yielded values similar to those obtained on immersion

of this powder in water. The 2% aqueous potassium permanganate, a stronger oxidizing agent than 3% hydrogen peroxide solution, reacted exothermically with

dentin.

/This reaction is probably an exhaustive process that results in destruction

of the organic matrix. Dentin also reacted exothermically with silver

nitrate. The reactions, however, were erratic and prolonged and possibly

were caused by a reduction of the silver nitrate at the surface. Precise

-AH measurements, therefore, could not be made. For anorganic whole

w

tooth, the apparent heat of immersion in water did not differ appreciably

from the values obtained on exposure to the aqueous solutions investigated.

Thus, the organic matrix of dentin presents active sites at which

bonding may occur with certain ions and functional groups under proper

environmental conditions. Furthermore, the reactions which occur at the

surface of dentin are similar to those exhibited by purified collagen.
12 -

The surface of dentin may be modified by treatment with nonpolar

(24) solvents . A decrease in the heat of immersion value of dentin also

occurs on immersion in 2-40% aqueous solutions of organic solvents (ethanol,

acetone, butanol, ethylene glycol), suggesting strengthening of electrostatic bonds between polar groups of the collagenous matrix of dentin and

also reflects the presence of a coating of collagenous material at the

surfaces of the powder particles. In absolute ethanol and hexane, dentin

absorbs heat, indicating the weakening of hydrophobic bonds. Values for

anorganic whole tooth in aqueous solutions of organic solvents, however,

are not appreciably different from those obtained in water.

A precise explanation for the decrease in the -AH values of dentin

w

as the solvent medium becomes more organic in nature cannot be offered.

This behavior may be attributed to the strengthening of electrostatic

linkages of the dentinal collagen which, in turn, could result in (1) the

reduction of the number of sites accessible to water, or (2) a slight decrease in the surface area of the specimen through tightening of the

structure of collagen. An endothermic interaction of the substrate with

compounds such as butanol or ethylene glycol could also be a possible

cause. The apparent absorption of heat which was observed when dentin

was immersed in absolute ethanol and hexane could also be the result of

the endothermicity of the transfer of the non-polar side chains of the

collagenous matrix of dentin from the aqueous environment provided by its

residual water content to an overwhelmingly hydrophobic environment ^8)

Water-vapor-saturated samples of dentin powders more closely approximate the native or physiologic state of intact dentin. Therefore, expanded
- 13 -

investigations of the heats of reaction of water-vapor-saturated tooth

powders would be appropriate from a clinical point of view.

Pitt has shown that the integral heats of immersion as a function

of moisture sorption are similar for both untreated bovine tooth powder

(13)

and citric acid treated powder . The values for hydroxyapatite are

considerably lower. Silver nitrate treated powder is intermediate at low

amounts of presorbed moisture. Silver nitrate treatment reduces the immersion energy by a factor of two with some values approximating those of

hydroxyapatite, indicating the formation of a significantly altered surface

by this treatment. Analysis of the energy of immersion of bovine tooth

powder indicates a significant concentration of adsorption sites having an

energy in the region of 3 kcal per mole of water adsorbed.

WETTABILITY

Formation of a strong adhesive joint requires: (1) good wetting, (2)

solidification of the liquid adhesive, and (3) sufficient def ormability to

(29) reduce the build-up of elastic stresses in the formation of the joint

The wetting of biological surfaces has been reviewed by Zisman et al

(31,31a) (32) Baier et al and Huntsberger

(30)

Intimate interfacial contact between the adhesive and its substrate is

the most important requirement for good adhesive performance. When the

maximum possible number of interfacial "contacts" is achieved between a given adhesive-substrate pair, the adhesive completely wets the substrate.

Electron photomicrogiaphs of dentin and enamel show that their cut surfaces

exhibit roughness with grooves of the order of a few hundred angstroms

.

This roughness Is important in determining the extent of wetting. A finite

time interval may be required to achieve complete wetting of the surface.
14 -

Young provided the first good description of wetting and spreading

of a liquid on a solid, as well as the relation of these characteristics

(34)

to the equilibrium contact angle . This relationship is expressed by

the equation: y o-y-,=y, o cos 0 , where y o, y 1 and y _ o are the

surface tensions at the solid-vapor, solid-liquid and liquid-vapor interface at equilibrium, respectively. The contact angle 0 is the angle between solid-liquid and liquid-vapor interface. When 0=0, the liquid

spreads over the surface of the solid spontaneously. On a sufficiently

smooth and homogeneous solid, 0 is independent of the volume of the liquid

drop. Since the tendency for a given mass of liquid to spread and adhere

increases as 0 decreases, the contact angle is a useful inverse measure

of wettability, whereas cos 0 is an obvious direct measure.

Contact angles above 0° occur primarily between liquids and low energy

surfaces. For this reason, contact angle measurements do not provide

differentiation for high energy surfaces. Under normal conditions,

a high energy surface seldom retains its hydrophilic properties. Such a surface, because of its high free surface energy will attract and be

covered by low energy substances.

If the adhesive behaves as a Newtonian liquid, the wetting rates will

be directly related to the product of the liquid-vapor interfacial tension

and the cosine of the advancing contact angle. Wetting rates will also

be inversely proportional to the viscosities of the adhesives. Huntsberger

showed a reasonable correlation between the values of y. o cos 0 , lv adv.

(32) and adhesive performance . His data indicate that good adhesive performance can be attained with adhesives that exhibit relatively large

contact angles.
15

The difficulty in measuring accurately small contact angles was

offset by Zisman's concept of critical surface tension y , the maximum

surface tension of a liquid which will form a zero contact angle. Provided the molecules in the solid surface do not form hydrogen bonds or

otherwise associate strongly with the liquid, a rectilinear relationship

was shown to exist between the cosine of the contact angle and the sur-

_ • c u -i v , (30,35,36) face tensions of a homologous series of organic liquids . The

critical surface tension y

c for wetting was defined as the intercept of

the horizontal line where cos 6 is equal to one with the extrapolated

straight-line plot of cos 0 against y o. Even when cos 0 is plotted

against y^ o f°r a variety of non-homogeneous liquids, the plotted points

fall close to a straight line or collect around it in a narrow rectilinear

band. Although this intercept is less precisely defined than the critical

surface tensions of a homologous series of liquids, it is a more useful

parameter because it is solely a characteristic of the solid and a good,

but not complete, criterion for predicting adhesive bonding. The y

c values are also useful for ranking the surface energies of solids. Completely fluorinated polymers have the lowest y^ values. Values of Y

£

for

a series of hydroxyl-rich surfaces ranged from 40 to 45 dyne/cm, and

Nylon 66, with its many exposed amide groups, yielded the highest y

(31)

value (46 dyne /cm)

To obtain strong adhesion, it is advantageous to use an adhesive with

a surface tension slightly less than the critical surface tension of the

adherent . Thus, a value for y^ of 30 dyne/cm would permit the organic

liquids used in most common liquid adhesive compositions to spread readily
- 16 -

over the surface without void formation or excessive trapping of air

bubbles

Because of the highly localized nature of the forces between each

solid surface and the molecules of the organic liquid, and also between

the molecules of each liquid, a monolayer of adsorbed molecules is usually

sufficient to give the high energy surface the same wettability properties

as the low-energy solid having the same surface constitution. Thus, the

value of the critical surface tension of solids is dependent upon the

nature and packing density of the outermost or exposed atoms and functional

groups at the surface. To obtain maximum adhesive strength, the adhesiveadherent interface must be kept free from exposure to low-energy organic

films. In this way, the number and size of interfacial voids is kept to

a minimum. Adsorbed water greatly decreases the surface energy

The adsorption of water molecules on clean high-energy surfaces results

in the formation of only a fraction of a monolayer, yet, as low as at 0.6%

relative humidity, this fraction drastically lowers the critical surface

tension of wetting. The increased amount of water adsorbed at 95% relative

humidity forms a film comprising little more than a condensed monolayer

and further lowers y to a value somewhat above that of bulk water . Thus

after exposure to a humid atmosphere, the surface energy of any clean,

smooth, high-energy hydrophilic surface (glass, sapphire, metal, or metal

oxide) or low-energy surface such as keratin, depends mainly on the concentration of water or other contaminants adsorbed on the surface. The

chemical nature of the underlying hydrophilic substrate has little effect

on wetting and spreading properties.
17

Schwartz and Galligan used water insoluble liquids to displace

water from prepared tooth surfaces

The wetting characteristics

of freshly ground tooth surfaces depended on the method of preparation.

Air and alcohol-dried surfaces were not readily wetted by organic liquids.

Soap or detergent washing "conditioned" tooth surfaces so that they were

wetted under water by organic liquids of widely ranging polarities. Alcohol washing or mild abrasive cleaning removed the conditioned layer.

Tooth surfaces can, however, be more durably conditioned by substances

containing free carboxylic acid groups. Critical surface tension values

of tooth sections that had been allowed to dry were influenced by the

relative humidity during the drying period.

The contact angles between various liquids and human enamel, dentin

(39) and whale dentin are given in Table 7 . The liquids were chosen because

their different specific free-surface energies made them useful for deter-

(40 41) mining the critical surface tensions of low-energy solids ’

. The

results indicated that untreated teeth have low-energy surfaces consisting of organic membranes. These surfaces are apparently derived from the

organic constituents of teeth since synthetic hydroxyapatite is hydrophilic

and, therefore, does not participate in the formation of the low-energy

surfaces. The mechanism of the formation of these low-energy surfaces can

be explained on the assumption that at least some parts of the organic

(42) phases of enamel and dentin are mobile and exist in the form of a gel

The observation of Uy and Chang that the contact angle increases

during the first hour after grinding and varies with relative humidity (43)

(39) could not be confirmed by Glantz . It is likely that traces of organic
18 -

matter were leached out from the embedded teeth used by Uy and Chang. j This may have modified both the wetting characteristics of the surface,

- as well as the adhesive properties.

The calculated mean critical surface tensions at 23° C for human dentin,

I whale dentin and enamel show that these substances have roughly the same

(39) specific free-surface energies (Table 7) . Uy and Chang, however, gave

values for y at 37°C of 31.5, 24-29, and 39.5 dyne/cm, respectively, for

c (43) human enamel, bovine enamel and dentin . The fairly large discrepancy

in the critical surface tensions for enamel reported in these two studies

I may be the result of differences in surface preparation procedures and points

out the difficulty in obtaining reproducible results, even under relatively

well-controlled conditions. Comparison of these values with those of y in

c Table 7 suggests that enamel and dentin have surface energies similar to

polyethylene and poly (methyl methacrylate), respectively. Thus, a nonhydrogen bonding adhesive applied to enamel should wet and spread on this

low-energy surface.

On the conventional cos 0 versus y^ o plot, there are distinct differences between the location of the contact angles for methylene iodide and

(39) 1-bromonaphthalene and those of the other liquids used . The surface

tension of the former two liquids is made up almost entirely of van der

Waal’s dispersion forces, whereas those of the other test liquids also con-

(44) tain polar forces and hydrogen bonds . The value of the contact angle

is determined by the magnitude of the interacting forces of both the liquid

and the solid phases. The position of the cosines of the contact angles of the tw<

liquid groups in the cos 0 vs. y o plot indicates that the free-surface energies

of both enamel and dentin are partially built up of polar forces and/or hydrogen

bonds. The values for the total work of adhesion and the work of adhesion

resulting from the interaction of non-dispersion forces (Table 8) also bear
19 -

out this point. The total work of adhesion VJ was calculated from the

A

Dupre equation = y^o(l + cos 0). The work of adhesion resulting from

interaction of non-dispersion forces was obtained from the following

equation

= y_ o (1 + cos 0) - (yf o + y^ o) A lv lv sv

where y!j o and y^o are respectively the free-surface energies (or freesurfacc tensions) at the liquid-saturated vapor and solid-saturated vapor

interface resulting from van der Waals dispersion forces. From contact

angle measurements on enamel and dentin surface, the van der Waals dispersion

(39) forces were calculated to be about 43 dyne/cm . Among the test liquids

used, water appeared to have the greatest work of adhesion from interactions

with the non-dispersion forces. The linear relation between the work of adhesion and the surface tensions of the liquids suggests that many attractive

forces interacting within the liquids also interact with enamel and dentin

surfaces on adhesion.

By studying the influence of stannous fluoride solutions on EDTA decalcified human dentin, and on hydroxyapatite, the observed decrease in wettability

could be attributed to the organic component of dentin.

Fluorides of tin, silver and nickel changed the wetting characteristics

of enamel and dentin. Chromium, copper, zinc and sodium fluoride did not appreciably lower the surface free energy. Glantz assumed from these results

that the resistance of fluoridized enamel surfaces to acids may be partially

dependent on the formation of fluorocarbon derivatives which are produced

on the enamel and dentin on catalytic reaction with fluorine.

Measurement of the contact angles demonstrated that the wettability
20 -

(39) of hard tissues is affected by lactic acid (Table 9) . The effect

varied in degree with the concentration of the acid solution, the exposure time and the type of hard tissue. Human enamel surfaces could

be made hydrophilic (water spreads when applied) by 0.02% lactic acid

treatment within five hours. Similar treatment, however, did not render

the surfaces of human or whale dentin hydrophilic. Those tooth surfaces

which were not rendered hydrophilic by the treatment, reverted to their

original wettability status when the attack by lactic acid had ceased.

Table 9 indicates that pretreatment of tooth surfaces with stannous

fluoride delayed the effect of lactic acid on the wettability of enamel

and dentin. Presumably, the gradual solubilization of the low-energy

fluoride containing surface layer is required before significant changes

in wettability characteristics occur.

Tooth surfaces can also be made hydrophilic by treatment with 85%

(45) phosphoric acid . These surfaces give essentially zero contact angles

with both water and epoxy resins. The tooth surfaces could be restored

to their original hydrophobic condition by polishing with dental pumice.

Snyder et al . measured contact angles of a methyl methacrylatepoly(methyl methacrylate) system (without initiator and accelerator) before

and after treatment of tooth surfaces with 50% phosphoric acid^^). Contact

angles were determined in a nitrogen atmosphere saturated with methyl methacrylate vapor to prevent evaporation of the monomer from the liquid drop.

Phosphoric acid treatment drastically lowered the observed contact angles.
21

The contact angles rose steadily on untreated surfaces as the percentage

of polymer in the mix was increased. This was to be expected since the

surface tension of methyl methacrylate monomer (28 to 29 dyne/cm at 20° C)

was considerably lower than the critical surface tension of wetting for

poly(methyl methacrylate) (y *= 39 dyne/cm). After phosphoric acid treatment, the

contact angles for the monomer-polymer mixes were nearly the same, suggesting

that there was little difference in the surface wetting ability of the adhesive

studied. Since the phosphoric acid treatment drastically improved bond

strengths in a closely related system, it was clearly demonstrated that

surface wetting was an important factor in improving adhesion.

Immersion of dentin in aqueous silver nitrate solution and subsequent

reduction of the silver nitrate by light is accompanied by a distinct change

(13,47)

in the wettability of the dentin . The contact angle of water is increased from 13° for freshly polished dentin to 46° after silver nitrate

treatment. The critical surface tension of dentin, which may be as high as

49 dyne/cm, is correspondingly decreased to 33 dyne/cm. This transformation

in hydrophilic character is reflected by a greatly reduced water vapor adsorption on silver nitrate treated powder. The surface treatment, which

presumably makes the surface less polar by occupying polar adsorption sites,

results in increased adhesion. The resulting bond strength depends on the

duration of the treatment, concentration of the reagent and exposure of the

dentin surface to light prior to bond formation. This treatment, however,

must be considered solely as a prototype means of obtaining adhesion to dentin.

Dark unaesthetic staining resulting from the inclusion of silver salts within

the dentinal tubules precludes the use of this procedure in clinical dentistry.
22

SURFACE TREATMENTS

1 . Etching

Chemical treatment of teeth to provide a modified surface offers

an attractive approach for the improvement of adhesion between tooth structure and dental restorative materials. In 1955, Buonocore reported that

treatment of enamel with 85% phosphoric acid increased adhesion to acrylic

, (48) n . , (49,50,51 ,51a) filling materials . Since then, Buonocore ana coworkers , Gwinnett an(j Fookson^^, Lee, Cupples , Swartz and Schubert ,

f C £ \ and Eden, Craig and Peyton have demonstrated improved bonding by pretreatment of tooth surfaces with acids and sequestering agents prior to placement of the restorative. The acids used in these studies included phosphoric-,

hydrochloric-, and citric acid and the sodium salts of ethylene diamine tetraacetic acid (EDTA)

Brauer et al. have determined the relative efficiency of simple surface treatments of enamel using a variety of polyfunctional acids and chelating

agents to obtain bonding between tooth surfaces and commercially available

-i . . (57,58) acrylic resins

Bond strengths of dental resins to tooth structure, as evaluated in

(59) the tensile test of Lee, Swartz and Culp , were determined after pretreatment of yearling calf anterior teeth specimens with more than 40 different

chelating or acidic substances. To minimize variations in results, the following procedure was employed. Resin-mounted teeth which had been stored in

water were: (1) patted dry with tissue, (2) swabbed with a solution for a specified time, (3) rinsed with water, and (4) the pretreatment repeated

after a specified time to obtain reproducible results. The curing cycle of

the resin to be bonded to the tooth surface was rigidly controlled. Coefficients
23 -

of variation of the bond strengths after 24-hour water exposure were of

the order of 20 to 40%—an order of magnitude generally associated with

values obtained in adhesion testing of non-homo geneous surfaces. Representative results are given in Table 10. Bonding was not obtained without

pretreatment

In these initial studies, Brauer employed a 5% aqueous tetrahvdrofuran-2 , 3 ,4 ,5-tetracarboxylic dianhydride (TTAD) pretreatment. This compound

on hydrolysis yields a polycarboxylic acid that may also react as a chelating

agent. Bonding was not obtained without the treatment, whereas a single treat2

ment gave a tensile adhesion of 21 kg/cm and a repetition of this treatment

2 applied in approximately 3 minutes raised the bond strength to 28 kg/cm . If

the second application is delayed, e.g., as much as an hour, a significant

2 increase in bond strength occurs (e.g., 50 kg/cm ). Further delay in the

second application of this acid did not increase the tensile adhesion, nor did

further applications of the acid. A 5% solution of TTAD appeared to give

optimum results. A longer application of the solution (for 30 seconds, instead

of 10 seconds) , mechanical roughening of the surface or cleaning the enamel in

an ultrasonic bath did not further increase adhesion. Enamel pretreatment

with TTAD neutralized to pH 7 did not result in measurable adhesion. A 5% solu2 tion of tetrahydrofuran-2 , 3 ,4 ,5-tetracarboxylic acid (TAA) gave a 64 kg/cm

tensile strength value even if the second pretreatment took place after 3 minutes.

Thus, the repeated application of the free acid within a short period of time

promotes improved adhesion, as compared to the anhydride treatment. This result may be caused by the time required to hydrolyze the anhydride to the free

acid, which is the effective adhesion promoter.

To correlate chemical structure of the acid with bonding efficiency,
24 -

the effect of the treatment of bovine enamel surfaces with simple acids,

as well as higher molecular weight acids and chelating agents, containing polyfunctional groups on adhesive strength was studied (Table 10)

The 50% phosphoric, formic or citric acid treatments did not yield improved adhesion compared to 5% TTA solutions. Five percent citric or

phosphoric acid solutions gave inferior adhesion values. Lactic acid

treatment yielded very promising results. A 20% lactic acid treatment

2

gave a bond strength of 61 kg/cm , which was similar to the value obtained for a 42.5% solution of the same acid. Addition of 1% methacrylic acid to the monomer to obtain a more polar polymer, or treatment with a wetting agent before the etch to possibly increase the rate

of ingress of acid into the enamel, actually decreased adhesion. Use

of 50% phosphoric acid containing 7% zinc oxide gave a significantly lower

bond strength than the 20% lactic acid. A solution of a carboxylated

polyester, which improved adhesion of coatings to metal and plastic substrates because of the presence of a large number of free acid groups ^0)

,

when applied to the enamel surface after the lactic acid treatment^ gave

only a low tensile adhesion value.

By substitution of ethanol for water, 5% ethanolic solutions of

water insoluble compounds were obtained. The lack of adhesion found

when enamel surfaces were treated with 5% ethanolic solutions of various

acids is caused by the decreased dissociation of the acid in ethanol. The

lower concentration of hydrogen ions reduces the etching effect of the

acid on the enamel surface. Because of the insolubility of many organic

acids in water, selection of acids with the required structural differences
25

to pinpoint structure-adhesive properties relationships was possible

only on a very limited scale.

A number of aliphatic acids, besides lactic acid, such as

citric-, dihydroxytar taric- , dihydroxymaleic- and 1 , 3 ,5-pentane tricarboxylic-acid , gave adequate adhesion. Some cyclic and aromatic

compounds also improved adhesion. With both the cis , cis , cis , cis-l ,2 ,3 ,4-

cyclopentanetetracarboxylic dianhvdride or the corresponding acid,

significant adhesion was obtained. No correlation was found between

the number of carboxylic acid groups attached to the benzene ring and

adhesive properties. Thus, treatment with 5% aqueous 1 ,2 ,4-benzenetricarboxylic acid induced bonding; the pentacarboxylic acid treatment re2 suited in a bond strength of 56 kg/cm , but saturated solutions of (

f 5%)

1,2,4,5-benzenetetracarboxylic acid and benzenehexacarboxylic acid were

ineffective for this purpose.

While only nominal bonding was obtained on treating the enamel

surface with a saturated EDTA solution, a somewhat stronger adhesive

bond was developed on application of disodium EDTA. Treatment with a

5% solution of tetrasodium EDTA in 0.001 N NaOH, which should more readily

chelate calcium present in the tooth enamel, did not produce evidence

of bonding. However, some chelating agents such as N- (2-hydroxyethyl)

ethylenediamine triacetic acid and phosphonomethyliminodiacetic acid

promoted bonding probably by the reaction of the carboxylic acid groups

with calcium.

The improved adhesion gained as a result of acid treated enamel

surfaces was not restricted to resins containing amine accelerators.
26 -

Similar results were observed with resins cured with other accelerators

and with a representative composite resin. For these restoratives,

bonding was not obtained when untreated enamel surfaces were used.

For the enamel surfaces treated with 5% TTAD, 5% TTA, and 5%

or 20% lactic acid, the bond strength to the resin was not reduced after

storage in an aqueous environment for periods as long as 90 days.

Most of the 5% acid solutions gave pH values in the 1.3 to 2.3

range. Especially interesting are the pH values of 20% lactic and 5%

tetrahydrofurantetracarboxylic acid which were 1.5 and 1.4, respectively.

A fairly large number of wafer soluble acids, especially those

containing polyfunctional groups, induced bonding to enamel surfaces.

Perhaps most significant were the results obtained after treatment with

20% lactic acid, an acid which apparently has not been used by previous

investigators to increase adhesion. Treatment of enamel with an aqueous

solution of the acid resulted in adhesion values greater than were obtained with a 50% phosphoric acid solution containing 7% zinc oxide.

The latter solution had a considerably more acidic pH. This solution has been used clinically by Buonocore as an efficient pretreatment

for pits and fissure sealants without any apparent deleterious effect on

(51) the tissues . Thus, it is likely that the less acidic lactic acid

treatment can be tolerated by the oral tissues and may actually be

more desirable for this application. It must also be realized that

the total amount of acid applied to the enamel is probably less than

0.1 ml and under clinical conditions is partially neutralized within a few seconds on contact with the enamel surface.
27 -

It is unfortunate that the effect of the application of the solutions of many of the effective adhesion promoters to dental tissues is

unknown

.

Pretreatment with chelating agents such as ethylene diamine

J . (52,61) tetraacetic acid is reported to improve adhesion . Treatment of

the tooth surface with the tetrasodium salt of this acid in 0.001 M NaOH,

a highly effective chelating agent for calcium, did not produce evidence

of bonding. Thus, it appears that adhesion to enamel is not promoted

markedly by application of an efficient chelating agent for calcium.

Acid treatment removes surface debris, etches enamel and makes

its surface more wettable. The improved adhesion is not caused by strong

chemical bonding of the resin to the modified enamel surface. Mechanical

retention plays a most important role in adherence of resins to treated

enamel surfaces. The penetration of uncured resin into the enamel pores

improves retention. Etching creates an increased surface area and opens

up pores into which the resin can flow. Since acid treatment makes the

surface more wettable, the extent of penetration will depend greatly on the

number of pores into which the resin can flow. Greater porosity allows an

easier ingress of uncured resin and therefore better mechanical interlocking

of the hardened resin with the enamel phase.

Scanning electron micrographs (SEM) of enamel before and after

acid treatment prove beyond doubt that this treatment leads to preferential dissolution of portions of the enamel surface and to exposure of

the enamel rods^^’^ 5 ^

^). ^ typical SEM photograph of bovine enamel

surface before (bottom, Fig. l) , and after (top, Fig. l) , two 30-second
28

applications of a 5% tetrahydrofuran-2 ,3 ,4 ,5-tetracarboxylic dianhydride solution shows clearly the removal of debris and the exposure

of the rod structure of the enamel V

. This acid treatment also removes the debris and exposes the tubular structure of dentin. Similar

(54) results have been obtained with human tooth tissue . The removal

of loose debris remaining in the cavity preparation with a 50% solution

/o\

of citric acid appears to be complete within a 3-minute period^

Similar treatment with water leaves the surface substantially unchanged.

Hoffman et al found that etching of sound human enamel for 15

minutes with 0.2M acetate buffer, pH 4, causes demineralization of prism

cores, whereas treatment with 0.12M ethylenediamine tetraacetic acid (EDTA)

//: c\

neutralized to pH 7.9 attacks their peripheral boundaries v

. EDTA

action on enamel appears to follow a specific selective pattern, which

starts at the peripheral borders of the prisms and progresses centrally,

so that at first only portions of the peripheral prism boundaries are

delineated

with prolonged action there is more complete prism isolation until only prismatic cores remain after 24 hours. Furthermore,

surface coatings seem to diminish with progressive loss of mineral.

Topical stannous fluoride treated enamel inhibited surface alterations

rr on when subjected to acetate buffer v '

. This supports the concept that

fluoride protection involves a reduction in enamel solubility.

Wei used the electron microprobe to analyze the calcium and

phosphorous concentration of sound, acetic acid-potassium acetate (pH 5.5)

acid-etched and remineralized human enamel

Acid etching of enamel

produced a decrease in calcium and phosphorous concentration with a rise
29

in the Ca :P ratio. Under the experimental conditions, the mineral loss

was mainly confined to the first 9 to 12 pm from the surface.

2 . Enzymes

The abrasive or etching pretreatment of dentin prior to the application of dental restoratives leaves the protein component of tooth

structure substantially untouched. This predominantly collagenous surface

appears to interfere with the adhesion of the inorganic constituent of

dentin to organic adhesives.

To provide a completely inorganic substrate, dissolution of the

(54 64 69) collagenous matrix of dentin by enzymatic treatment has been suggested * 5

Collagenase , which is capable of attack on native collagen at or near physiological pH, was employed > 70 )

. This enzyme is stable in "tris" buffer

containing calcium chloride and hydrolyzes collagen to peptides. The collagenase was effective in reducing the collagen level on the surface of acidetched dentin ^0). ^ thirty-minute immersion time in the 5% collagenase

solution at pH 7 was required. The enzyme treatment, however, did not improve

adhesion to bovine dentin. Lee et al used bovine pancreas trvpsin, a proteolytic enzyme that preferentially catalyzes the hydrolysis of peptide bonds

formed between the carboxyl group of arginine or lysine and the amino group

(64 69)

of any other amino acid in denatured non-native collagen ’

. The trypsin

solution was found quite effective in removing surface debris, as judged from

photomicrographs. Subsequent etching of the inorganic substrate with citric

acid and then treating with silane primer was attempted. The application of

a 10% trypsin solution, however, had only a slight effect on adhesion.

Ellison and Fookson employed a 1.5% papain or 1% alcalase solution
30 -

at pH 7 which were applied for 5, 10 and 20 minutes to bovine dentin

(54) surfaces . Scanning electron micrographs indicated that the fiveminute papain treatment had a negligible effect, while the twenty-minute

treatment produced more extensive changes. The enzymatic treatments under

certain conditions enhanced adhesion of bovine dentin to methacrylate

resin using a titania filled urethane adhesive, but the improvements were

not as significant as those obtained by acid etching and subsequent silane

pretreatment

3. Coupling Agents

Coupling agents are multi-functional molecules that promote adhesion

of the solid substrate to the restorative. These adhesion promoters function

by adsorbing on and altering the surface of the mineralized tissue to facilitate interaction with the restorative by either chemical or physical processes.

The portion of the molecule which is not directly responsible for its adsorption

presents a surface which can be more easily wetted by the restorative. An adhesion promoter is ideally adsorbed as a monomolecular layer and will prevent

contamination of the solid by organic substances. It should be inert chemically, should have a low surface energy and should form a hydrophobic barrier film to avoid the accumulation of water which could prevent efficient

wetting by an uncured liquid restorative ;

’ a 'Since its small size, highsurface mobility and short relaxation time makes permeation of organic coatings

by water a constant threat to the integrity and longevity of the adhesive joint,

the outer surface of the coupling agent film should be more hydrophobic

then hydrophilic. The reacted film of the coupling agent should be as
31

coherent and impermeable to water as possible, have a minimum water

solubility and have optimum resistance to hydrolysis.

The choice of the group of the coupling agent to be adsorbed

to the solid surface will depend on the nature of that solid and on

whether or not chemical interaction with the adherent surface can provide high resistance to water degradation of the joint. Molecules which

should give optimum results, with an outermost surface specifically designed to have good wetting by most liquid adhesives, are reported to

have a p-chlorophenyl and mono- or polycarboxyl groups; the two portions

being connected by a sufficiently long aliphatic chain which serves as a

( 72 ) hydrophobic spacer . The carboxylic acid groups should be particularly effective in promoting adsorption and adhesion to cationic surfaces such

as hydroxyapatite.

Perhaps the earliest application of coupling agents in dentistry

is the use of glycerophosphoric acid dimethacrylate as a component of a cavity seal liquid

5

. Application of this compound modifies

dentin as shown by staining of the dentin layers adjacent to the

adhesive 5

. The compound, when incorporated into methyl methacrylate

( 49 ) autopolymerizing resin, adheres to some degree to tooth surfaces and

is used in a commercial cavity liner. Bowen has synthesized a number of

potential coupling agents

(^lj75 ^7)

^ An adduct of N-phenylglycine

and glycidyl methacrylate produced a statistically significant increase

in adhesive strength after short-term water exposure of dentin or enamel

joined to methacrylate resins. The adhesion was enhanced after pretreatment of the tooth surface with dilute acid, base or a 10% solution
32

of EDTA. Similarly, Masuhara and co-workers have synthesized chelating

agents that are capable of bonding to calcium and contain polymerizable

methacrylate groups v J

. Among these, 2-methacryloyloxy ethyl

phthalate, N-methacryloyl-N'-dicarboxymethyldiaminobenzene and 2-hydroxyethyl methacrylate improved adhesion to enamel. The resulting bond strength was

rapidly weakened in the presence of water. However, a tributyl borane

initiated methacrylate polymer adhered well to enamel after the surface had

/ yg\

been pretreated with a phosphoric acid solution and a silanizing agent v

Heth^crylato chromic chloride (Volan L) and a saturated solution of phosphono-

/gi \ methyliminodiacetic acid also improved adhesion of enamel to acrylic resins" . Bonding was not obtained with trans- jsoeugenol , 4-hydroxy-3-methoxystyrene, 4-hydroxy-3-nitros tyrene and its methacrylate ester, 4-hydroxy-3 ,5-

dinitrostyrene , allylphosphonic acid and ’its hydroxyethyl methacrylate ester

and N-allylimino-N ,N-dimethylene diphosphoric acid. Thus, many ligands that

chelate calcium do not bond strongly to enamel.

Organo-functional silanes appear to improve adhesion of tooth substrate to dental restoratives. Lee (55,64,82)

usecj silanes such as glycidoxypropyltrimethoxysilane hydrolyzed in acetic acid as adhesion promoting

primers to improve rigid or flexible liners formulated from epoxy resins,

epoxy-polyurethane blends or catalyzed polyurethane resins. As shown in

Figure 2, silanes (such as y-aminopropyltriethoxysilane) theoretically should

be capable of performing two functions: 1. react with water adsorbed on the

surface of the dentin, and 2. react with the inorganic constituents of the

dentin and the resin to provide a chemical link between

the tooth and restorative. On incorporation into a polyurethane of 1% (based
33 -

on total resin solids) of N-beta- (aminoethyl)-gamma-aminopropyltrif c o \ methoxysilane , the silane reacts instantaneously with the isocyanate v '

.

Major improvement in bond strength does not result from the use

(54) of silanes prior to placing a polyurethane liner . When other coupling

agents were incorporated into the polyurethane, however, improved adhesion

was obtained. The coupling agents used were 2-hydroxyethyl- , 2-hydroxypropyl- and 2-t-butylaminoethyl methacrylate and 1 , 3-di (allyloxy) -2-ethyl2- (hydroxymethyl) propane. Optimum adhesion was obtained when the bovine

enamel test surfaces were treated for one minute with 50% formic acid,

rinsed and air-dried before application of the thin polyurethane liner

(formulated from a titanium dioxide filled polymethylene polyphenyl isocyanate-castor oil resin) and an acrylic rod. To insure that the acrylic

moiety of the coupler would bond to the rod, its surface was wetted with

a drop of monomer prior to assembling the joint. Best results, with bond

2

strength up to 900 kg/cm , were obtained with 2 to 5% concentration of the

coupling agent. Similar values resulted when the coupling agent was

added to the monomer used to wet the acrylic rod instead of adding it to

the polyurethane formulation. In this test, the hydroxyethyl methacrylate

coupler was especially effective.

The use of a partially saponified acrylonitrile-butyl acrylate copolymer rubbery liner resulted in some improvement in restoration shear

strength^^. This value was enhanced by the addition of a silane (yaminopropyltriethoxysilane) to the liner. Silane treated specimens

exhibited improved moisture resistance and provided some protection

when the joint was subjected to vigorous thermocycling. The
34 -

synergistic effect of the silane and the rubbery polymer indicated pronounced interaction of the silane with the physiologic substrate, as well as interaction of the silane and the polymer.

4. Surface Grafting

During the past few years, significant progress has been made

in the chemical modification of proteinaceous materials with the aim

of improving the physico-chemical properties in the resulting products.

The grafting of organic monomers to collagen, dentin or bone (so that

after polymerization of the monomer the proteinaceous surface is bonded

chemically to the polymer chains) offers an attractive technique of improving surface characteristics. Employment of the proper monomer in

the grafting procedure may make it possible to vary widely or even control

the surface properties of the resulting substrates.

Rao and coworkers have described experimental conditions for

grafting methyl methacrylate, acrylonitrile and acrylamide to insoluble

collagen^^ 5 ^ . Collagen powder was reacted with monomer in water or

dimethylformamide in the presence of ceric ammonium nitrate. The reaction presumably involves the hydroxy groups in the side chains of hydroxyproline, hydroxylysine , serine and threonine residues.

IV \ III + * Ce + R CH^OH 5— Ceric alcohol complex —> Ce + H + R CHOH

Mino and Kaizerman have shown that the ceric ion-alcohol complex reacts

reversibly with alcohols and glycols v

. Dissociation of this complex

is the rate-determining step. Thus, the hydroxyl group in the collagen

molecule is the reducing agent. If the reaction is carried out in the

presence of a vinyl monomer, the free radical formed on the carbon atom
35

attached to the hydroxyl group of the polymeric backbone acts as the

initiator for the polymerization of the graft side chain.

Brauer and Termini reacted purified steer hide collagen powders

or collagen films with over twenty monomers in water in the presence of 1

_3 (86 87)

to 2 x 10 M ceric ammonium nitrate in IN nitric acid v *

. Maximum

grafting was attained after soaking collagen in 2% wetting agent, deaerating

the solution and allowing the reaction to proceed for 3 hours. Product

yields were highly dependent on the monomer used. However, with reactive

monomers such as methyl methacrylate or glycidyl methacrylate, an increase

in weight of over 15% (based on the original weight of collagen after extraction of the homopolymer with suitable solvent) was obtained even after a 15-minute

reaction time. Generally, the lower molecular weight acrylates and methacrylates gave higher yields (over 100% increase in the original weight of collagen)

than the higher homologs (Tables 11 and 12). The yield of the graft polymer

is greatly reduced if the reaction is conducted in air. A marked increase in

graft polymer yield is obtained using a 2% concentration of wetting agent.

Among these dioctyl sodium sulfosuccinate , an anionic agent, proved most successful. Probably the hydrophobic portion of the wetting agent interacts with

the hydrophobic portion of the collagen. Possibly partial unfolding of the

collagen structure occurs with an accompanying increase in the number of reactive sites. Reduced yields of graft polymer on employing higher molecular

weight monomers may have been caused by steric hindrance of the more bulky

monomer, the decreased solubility of the monomer in the reaction mixture, as well as the slower rate of diffusion of monomer into the collagen.

Methacrylate monomers containing glycidyl, hydroxyethvl , dimethylamino or tert-butylamino groups could be grafted to collagen.
36 -

These functional groups may provide additional centers for further

surface modification. Dimethacrylates such as ethylene- or 1,3-butylene

dimethacrylate, can be grafted to collagen in excellent yield. The

polymers may be crosslinked and would therefore be likely to decrease

the solubility and increase chemical resistance of the resulting products.

Grafting of collagen to monomers such as styrene, acrylonitrile and

vinv3pyrroli.done is also possible.

Grafting yields vary, but are likely to depend on the solvent system

employed. Amount of homopolymer formed, as determined by weight loss on

extraction with a suitable solvent such as acetone or ethylene dichloride

for poly (methyl methacrylate), was generally less than 5%. Only the butylene

dimethacrylate graft product had a large weight loss (22.1% on extraction

with chloroform) , which may be caused by the presence of unreacted monomer

adsorbed on the reaction product. Especially promising are grafts with

glycidyl methacrylate. Infrared absorption curves of the product indicate

that the glycidyl group is not affected during polymerization. Since

this group can be converted to the highly reactive hydrophilic hydroxyl

group using mild alkaline hydrolysis, a whole new field of investigation

is opened up.

Appearance of the products often varied considerably from the original

collagen powder. The grafted materials consisted of powders after reaction

with some monomers, but formed loose mats and even tough films with others.

The large variety of monomers (acrylates, methacrylates, methacrylic

acid, styrene, vinyl acetate and vinylpyrrolidone , and others)
37 -

graftable to collagen indicates that surfaces with the desired degree

of hydrophilic-hydrophobic balance to fit specific applications can

be obtained. Monomers were also grafted to powdered bone that had

/ o y

\ been presoaked in 2% dioctyl sodium sulfosuccinate for one hour v

On grafting glycidyl methacrylate, dime thylaminoethyl methacrylate,

1,3-butylene dimethacrylate or isobutyl methacrylate to powdered bone,

an increase in weight of 60%, 27%, 19% and 11%, respectively, was obtained after acetone and chloroform extraction. Infrared spectra show

the presence of the oxirane ring of the glycidyl group (899 cm ^ and

843 cm ^) , as well as a C=0 stretching band at 1730 cm \ a C=0 stretching band at 1270 cm ^

, and an absorption band at 747 cm ^

, characteristic

of the methacrylate group indicating the glycidyl methacrylate was grafted

to bone. The presence of 1,3-butylene dimethacrylate and dime thy laminoethyl methacrylate could alsoi. be detected by this technique. Grafting

to bone surface is possible within one hour reaction time, as indicated

by a slight increase in weight. However, a number of monomers such as (methyl

methacrylate, ethyl acrylate) do not appear to react with bone.

Methyl methacrylate was also grafted to dentin . An 8%

weight increase was obtained after removal of the homopolymer by acetone

extraction, whereas a 21% weight reduction was noted for powder treated

in the absence of monomer. Presence of the poly (methyl methacrylate)

grafts was established from the -COOCH^ absorption at 1720 cm

1

. No appreciable amounts of polymer grafts or increase in weight could be detected after reacting the dentin with ethyl methacrylate, isobutyl

methacrylate, glycidyl methacrylate, dimethylaminoethyl methacrylate,
38 -

vinyl acetate or 1,3-butylene dimethacrylate. These results seem to

indicate that the dentin surface is not as susceptible to grafting as

the surface of powdered bone.

Experiments with calfskin indicate a less reactive surface for

grafting than is available in collagen powder v. The epidermal layer

of the calfskin being keratinous in nature, may provide a much less reactive surface for this purpose. Thus, the relative grafting efficiency

of monomers to the solid substrate decreases in the following order:

Powdered collagen > collagen film > powdered bone > epidermal calfskin > powdered dentin.

Although this grafting procedure is conducted in an acid environment at a pH around 2.2 that may not be tolerated by living tissues,

suitable in vivo techniques for modifying tooth and bone surfaces may

eventually be developed. Characteristics that could presumably be improved

by such treatment are better adhesive properties of tooth surfaces to restorative materials, greater resistance of teeth to caries formation, and

increased resistance of bone and skin to fungal and bacterial diseases.

Grafting to collagen, other proteinaceous materials and polypeptides has also been accomplished through polymerization of methyl

(78 88—90) methacrylate with tri-n-butyl borane v

’

. The following mechanism

has been suggested:
39 -

0 2R *B

r

3

b —

2

boor -

>

9

2R* + R

2

BOBR

2

* + other products.

R' *+ -NH - CH - C - NH - CH - C

t

’>

t 'I CH 0 R” 0

C - NH - CH - C -

II | II 0 R" 0

methyl methacrylate

(MMA)

V/

| (MMA)

t

°

- NH -*C - C -

I ll CH

3 0

NH - CH - C -

I /I R" 0

Tri-n-butyl borane is not suitable for use as a dental material because it is very unstable in air. Complexes of tributyl borane with ammonia

or primary and secondary amines are, however, easily reactivated by the

(91) action of isocyanates, acid chlorides and sulfonyl chloride . The complex

of tributyl borane with ethylene diamine is stable and can be reactivated with

£-toiuenesulfonyl chloride. It reduces the curing time at room temperature

to half that obtained with tri-n-butyl borane and does not affect adversely

other properties of the cured resin. Bond formation of the borane-cured resin

to dentin appears to be enhanced by .the presence of moisture and bond strength

is retained rather well after water immersion. An experimental restorative

that exhibits a somewhat variable degree of adhesiveness to dentin has been

(92,93) (92) evaluated. Lenz and Viohl reported a setting time of 12 minutes for

this material which was too long for clinical use. Adhesion was not adequate

in 20% of the cases.
- 40 -

SUMMARY

Studies of the reactivity and modification of surfaces of calcified

tissues offer an attractive approach for obtaining useful information which

may be applied toward reduced dental caries and improved adhesion between

tooth structure and restoratives. Investigation of the interaction of gases

on such surfaces provides considerable insight into the structural details

of surfaces of hard tissues. Effectiveness of potential conditioning agents

can be demonstrated from alterations of the surface properties of teeth or

bone as indicated by changes in: critical surface tension, oil-wettability,

adsorption isotherms and adhesionability . Measurement and evaluation of heats

of immersion and heats of reaction are useful for observing modifications and

determining those groups that bond to tooth structure in aqueous environments.

Dissolution of the collagenous matrix of dentin by enzymatic treatment

enhances adhesion under certain conditions, but the improvements are not as significant as those obtained by acid etching.

Coupling agents comprising multifunctional molecules promote adhesion of

the solid substrate to restoratives. These adhesion promoters function by adsorbing on and altering the surface of the mineralized tissue to facilitate

interaction with the restorative by either chemical or physical processes.

Coupling agents, especially organo-functional silanes, improve adhesion of

tooth substrate to dental restoratives.

Application of dilute polyfunctional acids removes debris, etches enamel

and increases surface wettability. Etching creates an increased surface area

and opens pores into which resin can flow. Excellent adhesion is obtained

after hardening because of mechanical interlocking of resin at the enamel-resin

interface
- 41 -

Long side chains have been grafted to collagenous surfaces (collagen

powder or film, bone). Grafting monomers containing additional functional groups that are potential reactive centers for further modification is

feasible. Surfaces with the desired degree of hydrophil-lipophii balance

to suit specific applications can be prepared.
42 -

REFERENCES

1. Biology of Hard Tissues , A. M. Budy, ed. ; New York Academy of Sciences,

New York, N. Y. , 1967.

2. Calcification in Biological Systems , R. F. Sognnaes, ed.; Publication No.

64, American Association for the Advancement of Science, Washington, D. C. , 1960.

3. W. F. Neuman and M. W. Neuman, The Chemical Dynamics of Bone Mineral ; University of Chicago Press, Chicago, 111., 1958.

4. Bone and Teeth , H. J. J. Blackwood, ed . ; Pergamon Press, Oxford, 1964.

5. The Biochemistry and Physiology of Bone , G. H. Bourne, ed.; Academic

Press, New York, 1956.

6. Tooth Enamel, Its Composition Properties and Fundamental Structure , M. V.

Stack and R. W. Fearnhead, eds.; Wright, Bristol, 1965.

7. Structural and Chemical Organization of Teeth , A. E. W. Miles, ed . ; Vol. II, Academic Press, New York, 1967.

8. R. A. Beebe, in Adhesive Restorative Dental Materials , R. W. Phillips and

G. Ryge, eds.; Owen Litho Service, Spencer, Ind . , p. 75, 1961.

9. M. E. Dry and R. A. Beebe, J. Phys . Chem. , 64 , 1300 (1960).

10. W. V. Loebenstein, in Adhesive Restorative Dental Materials - II ; Public

Health Service Publication No. 1494, U. S. Government Printing Office,

Washington, D. C. , p. 213, 1966.

10a. W. V. Loebenstein, Program and Abstracts of Papers ; International Association for Dental Research, 49th General Meeting, Chicago, 111. 1971, No. 672.

11. W. V. Loebenstein, Program and Abstracts of Papers , International Association for Dental Research, 48th General Meeting, New York, 1970, No. 178.

12. M. Bertolucci and D. L. Chamberlain, Jr., Annual Comprehensive Report , March 17 , 1966 to May 16 , 1967 , Contract A2 (320) PH 43-65-15'*,

Clearinghouse for Federal Scientific and Technical Information, Springfield,

Va., 1967.

13. D. A. Pitt, Research on the Mechanism of Adhesion to Teeth , Contract No.

PH 43-65-15, PB 17 5780; Clearinghouse for Federal Scientific and Technical

Information, Springfield, Va.

,

1967.

14. W. F. Harrington and W. F. von Hippel, Adv. Protein Chem. , 16 , 92 (1961).

A. M. Schwartz and J. D. Galligan, in Adhesive Restorative Dental Materials - II

Public Health Service Publication No. 1494, U. S. Government Printing Office,

Washington, D. C., 1966, p, 132.

15 .
- 43 -

References (Confd.)

16. R • L. Patrick and C. M. Kaplan, in Adhesive Restorative Dental

Materials - II ; Public Health Service Publication No. 1494, 0T S.

Government Printing Office: Washington, D.C., 1966; p. 156 . 17. R. L. Patrick, C. M. Kaplan and E. R. Beaver, J . Dent . Res. ; 4£, 12 ( 1968 ),

18« T. Ericson and Y. Ericson, Helv. Odont. Acta ; 11 , 10 ( 1967 )*

19. P. 0. Glantz and G. Nyquist, Odont. Rev* ; 17 > 332 ( 1966 ).

20® F. Mannerberg, Odont . Rev* ; 19 * 271 (1968).

21. 0. A. C. Zettlemoyer, in Adhesive Restorative Dental Materials , R. W. Phillips and G. Ryge ed.; PB 17 3009; Clearinghouse for

Federal Scientific and Technical Information: Springfield, Va.

,

1961; p. 95.

22. Go M. Brauer, in Adhesive Restorative Dental Materials - II:

Public Health Service Publication No. 1494, U. S. Government

Printing Office: Washington, D.C., 1966 ; p. 203.

23 . E. F. Huget, G. M. Brauer, and W. V. Loebenstein, J. Dent. Res.;

42, 291 (1968).

'

24.

E. F. Huget and G. M. Brauer, J. Coll, and Interface Sci.;

22, 714 ( 1968 ). —

24a. G. Mo Brauer and E. F. Huget, J. Dent. Res. , 50 , June-July 1971.

25 • R* Je Kanagy, J. Am. Leather Chemists Assoc. ; 49 » 646 (1954).

26. S. J. Greg, The Surface Chemistry of Solids , 2nd ed.; Reinhold:

New York, I 96 I; p. 288.

27. J.

29

M. Boyd, and G. Van Huysen, J a Dent. Res.;

28. W. Kauzman, Advan. Protein Chem. ; 14, 1 ( 1959 ).

29* Jc Wo McBain and D. G® Hopkins, J. Phvs. Chem. ; 29, 88 (1925).

30o W. A. Zisman, in Adhesive Restorative Dental Materials. R. W. Phillips and G, Ryge.ed*; PB 17 3009, Clearinghouse for Federal Scientific and Technical Information: Soringfiela , Va e , I 96 I;

p. 106 .

V -Le R* E« baier, E. G. Shairin and W. A. Zisman, Science; 162*

1360 ( 1968 ). — —

32o J. R. Huntsberger, in Adhesive Restorative Dental Materials - II , Public Health Service Publication No. 1494, Uo S. Government

Printing Office: Washington, D.C., 1966; p. 7*

31a. R. E. Baier, in Adhesion in Biological Systems , (R. S. Manley, ed . ) , Academic Press, New York, 1970, pp. 225-254.
- 44

References (ConfcL)

33. D. V. Provenza and R. C. Sardana, in Adhesive Restorative Dental

Materials - II ; Public Health Service Publication No. 1494, U. S.

Government Printing Offices Washington, D. C., 1966; p. 68.

34. T. Young, Phil. Trans. Roy. Soc. London ; 95 > 65 (1805).

35 . W. A. Zisman, in Contact Angle, Wettability and Adhesion , R. F.

Gould, ed.; Adv. Chem. Series No. 43; American Chemical Society:

Washington, D.C., 1964; p. 1.

36 . E 0 G

Shafrin and W. A. Zisman, J. Phys. Chem.; 66, 740 ( 1962 ) 37- M. K. Berne tt and W. A. Zisman, J. Colloid and Interface Sci.;

22,413 ( 1969 )

«

«

CO M. K. Berne tt and W. A. Zisman, J. Colloid and Interface Sci .

28, 243 (1968).

39* Eh 0* Clantz, Qdont. Rev. ; 20 (Suppl. 17) 1-124 ( 1969 )

40. Ho W. Fox and W. A. Zisman, J . Colloid Sci

; 514 (1950).

41. N. L. Jarvis, R. Bo Fox and W, A. Zisman in Contact Angle, Wettability and Adhesion , R. F. Gould, ed.; Adv. CTRem. Series

No. 43; American Chemical Society; Washington, D.C., 1964;

P* 317.

42. J. E. Eastoe, Arch. Oral Biol. ; 8, 633 ( 196 3 )

43c K. C. Uy and R. Chang, Adhesive Restorative Dental Materials - IT:

Public Health Service Publication No. 1494", U. ^''"Government

Printing Offices Washington, D.C., 1966 ; p. 103 . 44. F. M. Fowkes, Ind. Eng. Chem. ; 56 , 40 (1964).

45. G. V. Newman and L. H. Sharpe, J. N.J. Dental Soc. ; 37 , 289 (1966),

46. W. H. Snyder, C. E. Wilson, G. V. Newman and J. Semen, J. Appl.

Poly. Sci

; 11, 1509 ( 1967 ).

' "

47« D. E. Cadwell and B « Johannessen, Research on the Mechanism of Adhesion to Teeth ; Contract No. PH 43-65-15, PB T78T727~ Clear inghouse for Federal Scientific and Technical Informations Springfield, Va, , 1967 . 48. M. G. Buonocore, J «, Dent » Res

; 34 , 849 (1955)®

49. M. Buonocore, W. Wileman and F. Brudevold, J. Dent. Res.; 33.

846 (1956). ~ ~

50o M. G. Buonocore, A. Matsui and A. J. Gwinnett, Archs. Oral

Biolo ; 12, 61 (1968).

M. G. Buonocore, J. Am. Dent. Assn., 80, 324 (1970). 51.
- 45 -

References (Cont*d.)

51a. M. G. Buonocore, in Adhesion in Biological Systems , (R. S. Manley, ed.).

Academic Press, New York, 1970, pp. 225-254.

52. A. J. Gwinnett and NI. G. Buonocore, Brit. Dent. J. ; 119 * 77

(1965).

53« A. J. Gwinnett and A. Matsui, Archs. Oral Biol. ; 12 , 1615 (1967).

54. A. H. Ellison and A. Fookson, Gillette Research Institute Report

1969; P.D. 188 781; Clearinghouse for Federal Scientific and

Technical Information: Springfield, Va., 1969 . 55* H. L. Lee, A. L. Cupples, M. L. Swartz and R. J. Schubert,

Epoxvlite Research Report , 6 9-132 ; P.D. 185 829; Clearinghouse

for Federal Scientific and Technical Information: Springfield,

Va., 1969 . 56 . G. T. Eden, R. G. Craig and F. A. Peyton, J « Dent. Res

; 49 . 428

(1970).

57- D. J. Termini, G. M. Brauer and R. H. Adams, Program and Abstracts

of Papers ; 48th General Meeting, International Association for

Dental Research: New York, 1970; No. 405

58.

59

60 .

61 . 62 O 63 .

64.

65.

66 a

67 . 68 .

G. M. Brauer and D. J. Termini, submitted for publication, J. Dent. Res.

H. L. Lee, Jr. , M. L. Swartz and G. Culp, J . Dent. Res

; 48 , 211 ( 1969 ).

W. J. Jackson and J. R. Caldwell, Polymer Preprints; 11, (No. 1)

359 (1970).

R. L. Bowen, J, Dent. Res. ; 44, 1369 (1965)*

R. Borasky and G. M. Brauer - unpublished results.

H. Lee, M. Swartz and R. Schubert, Epoxylite Research Report , 70-116

Clearinghouse for Federal Scientific and Technical

Information: Sprmgiield, Va.

H. Lee, J. Biomed. Mater. Res. ; S. Hoffman, W. S. McEwan and C.

1242 (1969)

S. Hoffman, W. S. McEwan and C.

1234 ( 1969 ).

S. H e Y Wei, J. Dent. Res. ; 4£,

S. Hoffman, G. Rove Istad, W. S.

Res . ; 48, 1296 ( 1969 )*

1970.

1, 349 (1969).

M. Drew, J. Dent. Res. ; 48 ,

M. Drew, J. Dent. Res. ; 48 ,

621 ( 1970 ).

McEwan and C. M. Drew, J. Dent.
- 46 -

References (Cont f d.)

69 * H. L. Lee, A. L. Cupples and M* L. Swartz, Epoxylite Researcn

Report, 68-140; P.D. 179 420; Clearinghouse for Federal Scientific

and Technical Informations Springfield, Va., 1968.

70, A. Fookson, Program and Abstracts of Papers ; International

Association for Dental Research, 48th General Meeting: New

York, 1970 ; No. 403

71* W. A. Zisman, NRL Report 6911 ; Naval Research Laboratory:

Washington, D.£., 19&9.

72. E. ,G. Shafrin and W. A. Zisman, in Interaction of Liquids at

Solid Substrates a R. F. Gould, ed.j Adv. Chem. Series No. 87 ; American Chemical Society: Washington, D.C., 1968; p. 20.

73. I. R. H. Kramer and J. W. McLean, Brit. Dent. J. ; 93 , 150 (1952).

74.

75®

76.

77®

780

1. R. H. Kramer and K. W. Lee, J ® Dent. Res. ; 39 , 1003 (i960).

R 0 L. Bowen, J® Dent® Res.; 44, 895 (1965).

R © L. Bowen, J. Dent. Res.; 44, 903 (1965).

R 0 L. Bowen, J

Dent. Res.; 44, 906 (1965).

•< E. Masuhara, Deut. Zahnarzt. Zeitschr® ; 24 , 620 (1969).

79 0 E. Masuhara, K. Kojima, N. Tarumi, No Nakabayashi and H. Hotta,

Iyo Kinzai Kenkyusho Hokoku ; 1, 29 (1967) through Chem. Abstr

; 6£, 3409 (1968).

80 . E. Masuhara, K. Kojima, N® Tarumi and N. Nakabayashi, Shika

Zairyo Kenkyusho Hokoku ; 2, (9) 7 82 (1966) through Chem® Abstr. ; 68, 50454 (1968)

81. Fc C e M. Driessens, G® M e Brauer and D® J* Termini, Program

and Abstracts of Papers ; International Association for Dental

Research, 47th General Meeting: Houston, Texas, 19691 No® 137®

82® H e L® Lee, Adhesive Restorative Dental iMaterials - II ; Public

Health Service Publication No® 1494, U. S* Government Printing

Office; Washington, D.C., 19665 p® 232®

I 83 © K® Pq Rao, K. T® Joseph and Y® Nayudamma, Leather Sci*; 14,

73 (1967)®

84® K. P. Rao, K 0 T. Joseph and Y® Nayudamma, Das Leder; 19.

77 ( 1968)

1 85® G. Mino and S 0 Kaizerman, Jo Polymer Sci. ; 31 , 242 (1958)

71a. H. L. Lee and M. L. Swartz, in Adhesion in Biological Systems , (R. S. Manley, ed

Academic Press, New York, 1970, pp . 269-289.
- 47 -

References (Cont ' d)

86. G. M. Brauer , D. J. Termini and A. 0

f Grady, Program and Abstracts of

Papers; International Association for Dental Research, 48th General

Meeting, New York, 1970, No. 404.

87. G. M. Brauer and D. J. Termini, Program and Abstracts of Papers ; International Association for Dental Research, 49th General Meeting,

Chicago, 111., 1971, No. 438.

88. E. Masuhara, K. Kojima, N. Tarumi, T. Hirasawa and D. Sanjo, Shika Zairyo

Kenkyusho Hokoku ; _2 (6) 511 (1964) through Chem. Abstr. ; 63 , 16541 (1965)

89. E. Masuhara, K. Kojima, N. Tarumi, T. Hirasawa and D. Sanjo, Shika Zairyo

Kenkyusho Hokoku ; 2^, (7) 622 (1965) through Chem. Abstr. ; 63 , 16541 (1965).

90. E. Masuhara, K. Kojima, N. Tarumi and N. Nakabayashi, Shika Zairyo Kenkyusho

Hokoku ; 2., (9) 788 (1966) through Chem. Abstr. ; 68 , 50455 (1968)

91. S. Fujisawa, Y. Imai and E. Masuhara, Rept. Inst. Med. Dent. Eng. ; Tokyo

Med, and Dent. Univ. ; _3 , 64 (1969)

ii 92. H. Lenz and J. Viohl, Deut . Zahnarzt. Zeitschr. ; 23 , 218 (1968).

93. D. Sanjo, J . Dent . Res

, 50 , 60 (1971).
- 48 -

Table 1

Potential Adhesive Systems

A. Surface Treatments

lo Etching agents

2. Enzymes

3« Coupling agents

4# Surface grafting

B* Polymers

1. Acrylics

2« Zinc polyacrylate

3. Alkyl cyanoacrylate

4. Epoxy resins

5* Polyurethanes

6. Inorganic polymers

7» Bioadhesives
- 49 -

Table 2

APPARENT HEATS OF IMMERSION OF COMPONENTS OF

TOOTH STRUCTURE AND SYNTHETIC FLUORAPAT ITSV>'

Apparent Heats of Immersic

Powder Samples Conditioned

-AH

w

Average

( calories/gm)

Average

(calories/

sq meter)

Dent 5 r. (400 mesh) Anhydrous CaSC>4 -7.71 - 0.734

Dentin (400 mesh) 10--*- mm Hg

1 -10.29 - 0.980

Dentin (200 mesh) 10~1 mm Hg -10.00 -0.952

Dentin (400 mesh) 10”3 mm Hg -12.11 -1.15

Dentin (400 mesh) Saturation

H2O vapor

v/ith -0.31 -0.029

Anorganic dentin (400

mesh)

Saturation

H2O vapor

with - 0.995 -0.009

Enamel (400 mesh) 10”-*- mm Hg 0 . 58

^

+0.148\>'

Enamel (400 mesh) 10“3 mm Hg +0 . 64\^ +0.l64\>'

Enamel (400 mesh) Saturation

H 2 O vapor

with +0 . 07^/ +0.02 ^

Anorganic whole tooth 10”-*- mm Hg - 2.06 -0.02S

(120 mesh)

Anorganic whole tooth 10”3 mm Hg -1.85 -0.024

(120 mesh)

Anorganic whole tooth

(120 mesh)

Saturation

H 2 O vapor

with -0 .66 -0.009

X/^Reprinted (23. j p. 296)

The small endothermic values obtained for enamel may be artifacts induced because

of lack of sufficient surface area.
50

Table 3 (23)

Apparent Hi ATS Of Witting and Heats ok Reaction of Dentin

(40() Mesh) in Aqueous Solution

Apparent Heat of Wetting Apparent Heat of Reaction

Solution

I mil victual Run*

(calorin/gm)

Average

(caloriei /g m)

Average

(calorie*/

tq meter) Average

(cainries/gm)

Average

(calorie*/

• q meter) Sample powders stored at /0~l mm Hg Ammonium citrate —45.52

(0.044M) -46.15

-45.27

-45.65 -4.43 -35.35 -3.37

Disodium EDTA

(0.0067M)

-25.99

-25.86

-25.92 -2.46 -15.64 -1.49

Malonic acid (0.02M) -56.54

-55.48

-56.01 -5.33 -45.72 -4.35

Ascorbic acid (0.56M) -39.37

-39.60

-39.48 -3.76 -29.20 -2.78

Citric acid (0.047M) -42.40

-42.75

-42.58- -4.05 -32.29 -3.07

Glacial methacryiic acid

(1.2M)

-66.29

-66.06

-66.18 -6.30 -55.89 -5.32

Methyl methacrylate

(0.094 M)

-9.87

-9.78

-9.82 -0.945 negligible negligible

Cola beverage (1 vol

cola + 3 vol H20)

-17.91

-18.00

-17.96 -1.70 -7.66 -0.729

Powders saturated with water Ammonium citrate (0.044 M)

vapor-16.25

-15.83

-16.04 -1.52 -15.73 -1.49

Disodium EDTA

(0.0067 M)

-8.01

-7.62

-7.82 -0.743 -7.50 -0.714

Table 4 (23)

Apparent Heats of Wetting and Apparent Heats of

Reaction of Enamel (400 Mesh) in Aqueous Solution

Apparent Heat of Wetting Apparent Heat of Reaction

Solution

I ndividual Runs

(calories/gm)

Average

(caiorics/gm)

Average

(calories/

sq meter) A vera ge (calorics/gm)

Average

(calories/

sq meter) Sample powders stored at 10~ Ammonium citrate (0.044 M)

1 mm Hr

-10.51

-10.47 ' -10.49 -2.68 - 1 1 .07 -2.83

Disodium EDTA

(0.0067 M)

-17.52

-17.95

-17.74 -4.54 -18.32 -4.69

Glacial methacryiic acid (1.2M)-19.63

-19.10

-19.36 -4.96 -19.95 -5.11

Methyl methacrylate

(0.094 M)

+0.86

+0.56

+0.71 +0.18 negligible negligible

Cola beverage (1 vol cola 4- 3 vol H20)

-16.78

-16.45

-16.62 -4.26 -17.20 -4.41

Powders saturated with water Ammonium citrate (0.044 M)

vapor-2.49

-2.29

-2.39 -0.61 -2.46 -0.63

Disodium EDTA

(0.0067 M)

-8.91

-8.90

-8.90 -2.28 -8.98 - 2.30
51

Table 5 (23)

Apparent Heats of Wetting and Apparent Heats of Reaction

of Anorganic Whole Tooth Tissue (120 Mesh) in Aqueous Solution

Solution

Apparent Heat of Wetting Apparent Heat of Reaction Run*I mli vidual

* (caloriea/gm)Average

(caloriet/gm)

Average

(calorie*/

• q meter) Average

(calorir*/gm)

Average

(calorie*/ q meter) Sample powders stored at I0~l mm H%

Ammonium citrate -10.04 -10.08 -0.134 -8.02 -0.106

(0.044 M) -10.11

Disodium EDTA -20.51 -20.50 -0.273 -18.44 -0.245

(0.0067 M) -20.48

Glacial methacrylic acid -22.79 -22.71 -0.302 -20.65 -0.275

(1.2M) -22.63

Cola beverage (1 vol -19.57 -19.48 -0.259 -17.43 -0.232

cola +3 vol H?0) -19.40 k Powders saturated with water vapor Ammonium citrate -4.52 -4.76 -0.063 -2.70 -0.036

(0.044 M) -5.03

Disodium EDTA -16.88 -17.04 -0.227 -14.98 -0.199

(0.0067 M) -17.20

Table 6 (24)

Ukats of I mm fusion of Odontic Powders in Dilute Aqueous Salts Solutions at 3000

Heats of immersion ( — A//r)

Solution Dentin Anorganic: whole tooth pH 5 pH 8 pH 5 pH 8 cal/gm ergs/cm'1 cal/gm ergs/cm1 cal/gm ergs 'em5 cal/gm ergs cm!

11,0 10.20 . 4100 8.32 3300 2.00 117 1.00 104 NnCl 2% 10.34 4100 8.00 3430 1.72 02 1.70 100 XaF 2% 10.10 4020 8.70 3510 2.02 108 1.01 104 NaNO;, 2% 5.04 2230 8.13 3230 1.10 00 1.41 75 NaNO, 2% 0. 15 2430 8.48 3300 1.22 00 1.40 75 Na^SO* 2% 0.20 2510 8.04 3180 1.01 87 1.00 87 NaCNS 2% 5.21 2070 8.19 3260 1.80 100 1.81 100 Nal 2% 4.81 1910 8.39 3350 1.22 00 1.40 75

' Specific surface of dentin powders (BET) = 10.5 m2/grn. Specific surface of anorganic whole tooth

• wder« 'BE'!') “5 ni 2 /gm. Powders stored at 10-1 mm Tig prior to immersion.
Advancing

Contact

Angles

Using

Plano

Tooth

Surfaces

C3Q

)

52
The

Work

of

Adhesion

between

Pure

Liquids

and

Plane

Tooth

Surfaces ct •

<r CM I CM AJ

A • E tr O • • • 1 | c. rH CJ Ci a rH O r" CO j | < > H <D <C \ X CA CM rH o a •JZ * 3

>• > > o CD CD X) vO 0

(1> -H

r>. 0 1 o C H

CM X

VC r | CM rH r-l E • • • • • O 1A CO 3 CO rH (N

<2 \ ro

CM c> o O' O' 00

II *3 rH rH

rH p-

<H E

-3-a CM ‘cj \ E O' rH cc

*71 II 0 O X • • • | | H c Pm \ o r' CO 1 1 p O >i c »0> CM CM rH g > 05

05 CO ac c

x- un 0

G- l Z c ' CM

rH VC rr' O vr O' E X • • • • • < \ cc 00o 3O

O'

O'

rHO' PCO

rH rH

CM

rH 3

rH E 3 O

i--l / CM o

-h II <D CG E -3 O o CD G < O X • • • i 1 E Vv O > \ o 3 CM i 1 cop5 > 05 0) CM CM CM C'

>1 ' 00 lA r

-1 0

c:3 A

CM o

rH CO O' O' 00 3 E • • • • • o X p- 3 rH o P> \ CM o O O O' 00

0> rH rH

CO

CMrH . A o Eo $> / > \ 00 O vr vr

0J rH 0 • • • • 1 1 - >~ C rH O' 00 1 1 >> CM O' CO

03E O VO -3 CM o 00 VC > <D • • • • • • rH C CM CP CC 3 o _-A- >> 03 P- VC vr vr vr 3

CDC

CD <D CD

r*l 03 rH H 1 rH O •r— O 0) O Cl? n G E CJ rH a) E 3

•H G o ci 1 > >>05 O -P 0 o E O rH 3*H G 3 U 4* > G • H b. 4-> TO cq a

*cH CJ rH O «C «H <D O » ri o Pm 6h 05 S«H rH C

W)

tj) r"Ah

JO' •r-l •H 4-> 4 3 «H

rH 'J

0! 00 11 CD

CD 5-r 5m 0

dr’ c> y 0 # •0 0

CD ao 4-* 4* o G 0 5t •H

•H op G g O o p P

a, o 0 0 • c-i > > 0

5m 05 05 ao 0

CD Pm P 4J 0 0 0 •H G

5) 05 3 2 1 4-5 -P G 0

Cl) O 0

CO P 1 1 05

TO o? •rH •rH 0 r—

0 o c •; CO •rH P

rH ao 0

rO -C

CD p

X? c P o p

•rH 0 P p 0 o •»—

0 r

-1 5m O c 0 •rH o 4J CO • rH G

r~* CO •rH 0 0 P

CD • o P G 4 3 0 o o 0 • H 0 0 o 0 3 Pi

cd • 0 05 G • P CO r~* 3 0

5-) CD 'P C 0 CJ 3 o 0 o O

CO 5i •rH G G o P CO O O

5h P O 0 ^P O 3 W c 05 >5 G o 5m 0 bD o

0>1»H o G •H • bD co > P 0 CO ^ * 5m 5m o G G 0 0 0 0 0 0 Pa i—

‘.M Pr • 0 CO & 1m a co P

•H •H O O *H 0 0 'O 0 5 0 TJ G o 5m p

cd co 0 o 5i CO e P r—

> rH 3 H O

5m Cj 0 rO CO 0 G 3 Cd 5m • rH 0 P

co S- CO 0 Si

r-l G a C O Sm 0 0 5. G 0 a o P > P P >'

5m 'O O o 05 0

Pm Eh r\ J

j; 4J G G

II 0 II it O 0 0 > > > P O < P< 0JCO 0 0 > E ~

X- 6 a

rH O o

i> P >

fr $
54

On3

PQ<

e-«

On

'D•HO<O

-H

J-J b

Cvj "0C yo

*00 ^ O

<D o s°^ XC -P;

CL) • r— I f <D *- rOO

4-» ciO

)ri

fcr

tooo

ctf

COX

-Poo

o'c

ctf rH

Ph 4 4
55

Table 10

EFFECT OF SURFACE PRETREATMENT ON ADHESION

OF ACRYLIC RESTORATIVES TO BOVINE ENAMEL (58)

Surfaces treated twice for 10 seconds.

Treatment

Bond Strength*"

Mean S.D.

kg/cm2 kg/cm2

None

5% Phosphoric acid

50% Phosphoric acid

50%o Formic

20%0 Citric acid

5%° Succinic acid

5%o Lactic acid

20% Lactic acid

20% Lactic acid

42o5% Lactic acid

100% Methacrylic acid

5%° Dihydroxymaleic acid

5% Tartaric acid

5%o Dihydroxytartaric acid

5% 1, 2, 3-Propanetricarboxylic acid

5%o 1> 3 >5”Pentane tricarboxylic acid

5% cis, cjls, els, cis-l,2,3,4-cyclopentanetetracarboxylic dianhydride

5%<> 1, 2,4-Benzenetricarboxylic acid

5% Benzene pentacarboxylic acid

5%o Benzenehexacarboxylic acid

5%o Tetrahydrofuran-2-3,4,5-tetraearboxylic acid (TTA) 5% Tetrahydrofuran-2, 3,4,5 -tetracarboxylic acid Sat 0 sol {<5%) EDTA

5% Na2 EDTA

5% Na^ EDTA in 0.001N NaOH

5% Methacrylate- Chromic chloride

0

22

49

20

39

6l

63/

58

0

43

33

66

29

51

6 o 36

56

0

64

42/

7

21

0

24

0

22

27

2 6

13

21

21

21

12

0

21

13

18

17

26

10

30

23

0

21

18

6

15

0

11

Mean vaxue 01 at least 5 specimens stored in water for 24 hours at 3?°

/ Storage time 43 days

/ Storage time 30 days
56

Table XI

Grafting to Steer Hide Collagen

Reaction Time: 3 hours

Monomer

* Increase in Weight

Appearance

of Product

Ethyl acrylate

%

82 powder

Butyl acrylate 11 powder

2-Ethylhexyl acrylate 14 powder

Methyl methacrylate 81-103 powder

Ethyl methacrylate 75 powder

Isobutyl methacrylate 87 loose mat

Lauryl methacrylate 6 loose mat

Ethylene dimethacrylate 41 loose mat

1,3-Butylene dimethacrylate 58 loose mat

Hydroxyethyl methacrylate 26 powder

Glycidyl methacrylate 92 powder

t-Butylaminoethyl methacrylate 3 loose mat

Dimethylamionoethyl methacrylate 16 tough film

Vinyl acetate 21 film

* After extraction of homopolymer
- 57

Table 12

Grafting to Steer Hide Collagen

Reaction Time: 3 hours

it Increase in Weight

Styrene

%

14

Acrylonitrile 2

Chloroacrylonitrile 49

Vinylpyrrolidone 12

Vinylpyridine 9

* After extraction of homopolymer with appropriate

solvent
1 0 Mm

Fig, i : Scanning electron microscope photograph of bovine enamel surface. Bottom: before acid treatment; top, after two 30-second

applications of 5% aqueous tetrahydrofuran -

2 , 3 ,4 ,5-tetracarboxylic dianhydride. (105).