Part 4 - AQB Implant Prosthesis
Chapter 1 - Esthetic restoration and attachment techniques with CAD/CAM
Department of Crown and Bridge, School of Dentistry, Tokyo, Nippon Dental University
Professor Akiyoshi Shinya
I.

Esthetic restoration

The recent development in dentistry is the need for esthetic restoration that implements the ideology ofminimal intervention (MI). The main focus of this practice is to treat by leaving the enamel that has theability to treat itself as much as possible, and any deficiencies in the enamel or dentin structures isrecovered by adhesion treatment with the application of adhesives. This allows the prevention of any
leakages by increasing its resistance to acidic conditions, consequently inhibiting the progress of tooth
decay or discoloration of the ceramic restoration margins. The application of adhesives to fuse the esthetic
restoration apparatus and the dentin not only aids its long-term functions in the oral cavity, but also
plays a role in extending the life-time of the tooth. The uses of metal-bonded ceramic crowns or bridges
have typically been employed to achieve esthetic restoration thus far. To meet the increased demand in
the esthetics, the clinical uses of all-ceramic restorative methods are currently under investigation.
The ceramic restorative materials have been utilized in a variety of appliances from the initial inlay,
onlay, laminated veneer, crown, to bridges that replaces one to two missing teeth. The zirconia frame
produced with CAD/CAM, currently in its developmental stages, has become the centre of attention withthe expectations as a ceramic material with high tensile strength that is the same or superior to the metalframe that has been used as the bridge material. In a similar manner, the hybrid resin has been applied
widely in the clinical settings, ranging from the crown of the molar regions to the bridges strengthened
with fiber.
In the following sections, the esthetic restoration materials and the technological developments are
discussed.
A.

Thermo-metal restoration

1.

Manufacturing methods for porcelain fused restorative appliances

In 1960s, Ceramco, lnc. produced a metal-bonded ceramic crown that plated the ceramics onto the metal
and initiating its application to the clinical practices. The unfaltering attempts at research and its
application to clinical practices, as well as the development of technology have led to the production ofesthetic restoration appliances which are highly appraised. As an example, to a defective central incisor(Fig. 4-1-1), porcelain plated onto multi-purpose alloy (Fig. 4-1-2) for final attachment to the oral cavity as
the metal-fused metal crown (Fig 4-1-3) is displayed. Current growthing demand for esthetic finish has
progressed to require all-ceramic restoration.

Fig 4-1-1 Loss of esthetics in the right incisor by dental caries

Fig 4-1-2 Metal-bonded ceramic crown constructed with multi-purpose alloys

Fig 4-1-3 Restorative device of porcelain and gold-alloy, in the oral cavity
2.

All-ceramic restorationa.

Fabrication with refractory investment by direct sintering

The working model is fabricated in pouring extra hard gypsum, after the impression of the preparedabutment has been taken with the silicon rubber impression material. Then a refractory model isfabricated by duplicating the trimmed indirect working model, and pouring the phosphate bonded
investing material.
Apply multiple layers of porcelain directly onto this model, and place this in the furnace.
A clinical example is given below (Fig. 4-1-4 to -12).

Fig. 4-1-4 Masticatory dysfunction

Fig. 4-1-5 Fabrication ofFig. 4-1-6 Inlay attachment todue to secondary caries ofporcelain inlay with refractory

the enamel and dentin to

mandibular right first molar

investment

restore esthetics

Fig. 4-1-7 Tooth discoloration

Fig. 4-1-8 Laminated shell by

Fig. 4-1-9 Laminated veneer

bythe application and baking ofthat is glued to the enameltheadministration

tetracyclineofporcelain

Fig. 4-1-10 Crown fabricated by

Fig. 4-1-11 Porcelain crownFig. 4-1-12 Porcelain crown

the application of porcelain toafter its baking step

attached to the dentin,
improving the aesthetics

the refractory investmentb.

Glass casting method

Cast the molten state of the glass by the lost wax process that follows on from the method of dental
precision casting. The casted ceramic restoration undergoes crystallization heat treatment in order toimprove its mechanical properties and restore its natural color at the same time. The glass cast crown iscasted after the fabrication of the crown with wax to the abutment on the working model, invested in its
molten state. A transparent glass crown removed off the investment is shown in Fig. 4-1-13. The glass
cast crown that has been colored to mimic that of the natural tooth by crystallization heat treatment isfeatured in Fig. 4-1-14.
Its clinical application is presented in Fig. 4-1-15.

Fig. 4-1-13 Glass cast crownFig.4-1-14 Crown reinstatedFig. 4-1-15 Attached glassthat has been removed fromwith mechanical property andcasting crown

the investment

color tone by crystallization
heat treatmentc.

Compression molding technique

The recovery of its form is conducted with the lost wax method as with the glass casting technique, butwith this technique, the block of which its color tone already has been chosen is inserted into the ring.
This is then placed into the furnace for it to melt and the construct the shape by applying pressure to theheated, softened form. The compression molded crown is kneaded into its shape in its softened form after
the crown has been constructed with wax onto the abutment teeth on the working model as shown in Fig.
4-1-17. The porcelain crown fabricated is shown in Fig 4-1-17, which has been taken out from theinvesting materials that has been restored with the natural color tone of teeth. Its clinical application isfeatured in Fig. 4-1-18.

Fig. 4-1-16 Wax patternFig. 4-1-17 Ceramic crownFig. 4-1-18 The fitted

waxed up on the working

molded with compression

pressure molding ceramicmodel

and restored with natural

crown

color toned.

CAD/CAM method

The fabrication of ceramic restoration is facilitated with computer-aided design and computer-aided
manufacturing. In order to apply the CAD/CAM technology, the scanner has been set up in the dental
clinics to enable sending the CAD information to the CAM center on the internet. By applying this novel
system into clinical practice, the ceramic restoration appliances have improved the quality of the products,
simplified the production process, as well as of the laboratory environment. The CAD/CAM crown isconstructed by the measurement of the abutment tooth, and designing the shape of the crown with CAD
then this information is used to mechanically reproduce this shape with CAM. The process of crownconstruction with the application of oil with CAM is featured in Fig. 4-1-19. The fabrication of the
CAD/CAM crown is as shown in Fig. 4-1-20, and its clinical application is given in Fig. 4-1-21. The
CAD/CAM bridge with zirconia is fabricated by first constructing a zirconia frame (Fig. 4-1-22) aided by
CAD/CAM system to which the porcelain is applied, and burned in the furnace (Fig. 4-1-23). The
application of this to the clinical setting is featured in Fig. 4-1-24.

Fig. 4-1-19 Ceramic block

Fig.

crown

Fig. 4-1-21 CAD/CAM

processing

produced by CAD/CAM systemceramic crown attachedFig. 4-1-22 Zirconia bridge

Fig. 4-1-23 Interior of zirconia

Fig. 4-1-24 Fitted zirconia

fitted onto the working model

bridgebridge3.

Composite resin restorationa.

Hybrid resin crown

4-1-20

Ceramic

The mechanical property of the composite resin has been reinforced to the extent that it is applied tomolar crowns. The dimensions of the abutment tooth has been set to be 1.0 to 1.5 mm at the occlusal
plane, a clearance of 1.0 mm at the tooth cervix, with margins with the deep chamfer (Fig. 4-1-25). The
construction process is conducted by placing the various materials onto the indirect working model in theorder of opaque, cervical, dentin and enamel, then project photopolymerization and heat curing before thefinal polishing step (Fig. 4-1-27). The crown in the oral cavity is featured in Fig. 4-1-30.
b.

Fiber reinforced hybrid resin bridge

Place the fiber 0.1 mm from the bottom of the junction and the pontic (Fig. 4-1-28). The amount of thefiber is 1/2 - 1/3 of the dentin material that was removed. The hybrid resin should be applied in the sameaway as the crown onto the fiber, undergo photopolymerization and heat curing to finish off (Fig. 4-1-29).
Its placement in the clinical setting is shown in Fig. 4-1-30.

Fig.4-1-25 Abutment preparation

Fig. 4-1-26 Hybrid resin

Fig. 4-1-27 Fitted hybridof the right mandibular secondary

crown applied with gloss

resin crownFig. 4-1-28 Fitted onto theFig. 4-1-29 Glossed hybrid

Fig. 4-1-30 Fitted hybrid

working model with glass fiber

resin bridge reinforced withresin bridge reinforced withas the frame

glass fiber

glass fiber

molar

4.

Clinical evaluation strengthen

In prosthetic appliance with excellent esthetic properties, materials such as enamel, dentine, composite
resin, metal, and ceramics are an adherend. The success of achieving firm adherence with thepolymerization and protection of the dentins lies in the selection of surface processing material and theadhesives with regards to the attachment surfaces. The abutment tooth is created by the resin
impregnated dentin by the bonding treatment that has been aimed to protect the dentin and dental pulp
complex.
Sufficient adhesive strength could not be achieved with the ceramics with the application of adhesive
agent alone. The use of an organic functional monomer, -methacryloxypropyltrimethoxysilane (-MPTS)
has been valued as a measure to strengthen the adhesive strength of the ceramics in the clinical practice.
In the silane reaction, the stable siloxane bonding is formed on the silica or the glass to achieve strong
adhesion. By the application of Rocatec method and the adhesion to provide adhesive strength, as well asprevention of marginal leakage, it should be possible to create a composite dentin that is able to endureharsh intraoral environment. This can also be applied to the high strength alumina or zicornia crownbridge. The application of adhesive agent is also effective in preventing the development of secondary
dental caries and discoloration of the crown margin.
A case illustrating the importance of the adhesives is presented here.
The optic porcelain crown was attached as shown in Fig. 4-1-31, but issues arose with the cervical region
becoming sensitive to cold water, and appearance of black line. Upon removal of the crown, the toothcervix showed that it had turned black in color (Fig. 4-1-32). The marginal leakage resulting from theinsufficient adhesion was the cause of this complication (Fig. 4-1-33). This kind of issue should be able tobe prevented by a careful operation to apply adhesives.

Fig. 4-1-31 Attached

Fig 4-1-32 Porcelain crown with

Fig. 4-1-33 Coloration of theporcelain crowntheabutment tooth presenting

toothcervix

becoming

sensitive to cold water, andafter the removalwith discoloration
5.

Structure of ceramic restoration

The structure of the ceramic restoration is shown in Fig. 4-1-34. There are four types of esthetic
restorative devices that are currently being employed. The ceramic restorative system that iscommercially available is featured in Table 4-1-1. Ceramic metal crown (Fig. 4-1-1 to 3) is fabricated bylayering the bonding agent, opaque, cervical, dentin, incisal and enamel porcelain built up on the metalframe. It is completed by adjusting its shape, and grazing to give a glossy finish. The structure of the
all-ceramic crown and bridges are created by the application of each layering-porcelain onto the ceramicframe, then to be placed in the furnace (Fig. 4-1-1 to 30). The compositions that have been employed forthe ceramic frames include leucite which is used for a refractory model, mica for glass casting, lithium
disilicate for pressure injection, and alumina zirconia for CAD/CAM. This is a system to recover esthetics
burning porcelain applied onto the high intensity ceramic frame.
Dental prosthetic restorative devices such as inlays, crowns and bridges are artificial internal organs andbiomaterials that have excellent affinity, functional and esthetic properties. These can even be applied topatients with metal allergies, and it has become a growing interest in the recent years. Implant
treatment has been placed as a first-line therapy for the restoration to the area that lacks teeth. The
clinical application of the ceramic crown onto osseointegrated implant that can achieve esthetic outcome
without the need to mill natural healthy teeth as required for the bridge placement has been muchappreciated. Implant has been referred to as the third tooth, and is a system that contributes topreservation of teeth. With the notion of maintaining healthy teeth, it has consequently contributed to theimprovement of the quality of life (QOL) of the nation and giving a helping hand in meeting the goal of
the 8020 movement.

Transparent
porcelain
Surfacecoloring
porcelain

Enamelporcelain

Incisalporcelain

Transparent
porcelain
Incisalporcelain
Coloring
porcelain

Dentinporcelain
Enamelporcelain

Coloring
porcelainCoreporcelain

Opaqueporcelaincervicalcolor
porcelaincervicalcolor
porcelainCoreporcelainCoreporcelain

Alumina

Metal casting

Glass casting

Zirconia

Pressure
injection

Impregnated glass

Fig 4-1-34 The structures of ceramic restorations
Manufacturing Methods Name of product1. Direct firing of

Maker

Elemental composition

Lamina porcelain

Shohu

LeuciteG-cera cosmotech II

GC

LeuciteVintage

Shohu

LeuciteVITA VM7

GC

LeuciteIn-Ceram Alumina

VidentPorous alumina, Glass infiltration

In-Ceram Ziruconia

VidentPorous aluminal, zirconia and glass infiltration

In-Cream Spinell

VidentPorous spinel, Glass infiltration

Dicor

Dentsply

Mica

OCC

OlympusMica・βspodumene

Kurisera

Kyutai-dentceram

β-calcium metaphosphate

Finesse All Ceramic

Dentsply

LeuciteIPS Empress

Ivoclar

LeuciteIPS Empress 2

IvoclarLithium・Tokuyama Dental

Diopside

Procera AllCeram

Nobel biocare

Alumina

Procera AllZircon

Nobel biocare

Zirconia

CerconDeguDent

Zirconia

Lava

3M ESPE

Zirconia

In-Cream YZ CUBES

VidentZirconia

refractory model

2. Glass casting

3. Pressure molding

4. CAD/CAM

Table 4-1-1 The manufacturing methods, the product name, manufacturers and the basic compositions of
the ceramic restorations

II. CAD/CAM crown
The recent acceleration in the development of IT has not only promoted industrial development but also
contributed greatly to the technological innovation in the field of dentistry. The current main focus is on
the lost wax method that has represented the dental craftsmanship so far in the field of restorative crown,
and similarly on the CAD/CAM system that is believed to be the next generation of dental technology. The
implementation of dental CAD/CAM system have led to improvements in the quality of the restorative
devices; allowed the processing precision to be standardized; simplified the processing steps; and led to
improvements in the working environment. The dental technology of the 20th Century had mainly
involved the combination of the dental crown material with the precision casting, such as with metalmaterials, for the construction of the restorative apparatuses. The 21st century dental technology has
become focused on the esthetic restoration using the ceramics with the application of the precise
mechanical processing with the CAD/CAM system.
The dental CAD/CAM system in the past had often limited the material that could be used, but with therecent models that have become commercially available, have overcome this issue, with its ability toadjust the processing conditions and therefore enabling machining of hard resin, titanium and porcelain.
For this reason, the materials can now be selected based not only on their functionality, but also theiresthetics. Additionally, by implementing the information gained from the jaw tracking device controlledwith the computer, this could lead to further understanding of occlusion specific to each patient therefore
allowing for improved accuracy of the prosthetic appliances.
Problems still remain that needs to be clarified with the prosthetic appliances constructed with
CAD/CAM system, before they can be safely applied in clinical practices. In particular, when fabricating
the crown, the processing precision of the overall structure of the crown concerning factors have to be
fully acknowledged such as: the internal and external of the occlusal plane, proximal plane, cervix andthe abutment surfaces; as well as the processing properties of each work materials.
Coupled with the development of IT and network systems CAD/CAM network system that transfer the
CAD information to the CAM center on the internet has been developed and the computers equipped witha scanner and image processing software have been increasingly placed in the dental clinics. This systemallows the CAD information to be transmitted from the dental clinics, therefore enabling fabrication of
the restorative devices with only the CAD data that has been derived from the measurements of theworking model. This indicates that the working model does not have to be used at the CAM center andthat the restorative appliances can be fabricated with the application of digital data. Such application of
the innovative IT technology in the field of dental care is discussed in the following sections.
A. The types of CAD/CAM systems on the market
A wide variety of CAD/CAM systems are available on the current market, therefore in an attempt toclarify each of their properties, the simplified explanations have been summed up in Table 4-1-2. The
typical models that are in current use are Cadim (ADVANCE), CERCON (Degu Dent), DECSY (Nissan
digital process), EVEREST (KAVO), GN-1 (GC Co.), Prosera (Nobel Biocare), three of which are
manufactured in Japan and three remaining are from overseas. Fig. 4-1-35 illustrates the general flow of
CAD/CAM system.
For the measurement of abutment tooth, there are contact and non-contact methods, wax pattern andmeasurement data /computer image for the design, and exclusive CAM for the processing. The times forthe production of the restorative appliances are 2 h 10 mins for Cadim, 8 h in total for CERCON that
includes firing time, 75 mins for DECSY, 40 mins for EVERST, 90 mins for GN-1, and three days in total
for Prosera for the actual measurement time added with the time required for data transmission.
The materials that are used in the CAD/CAM system include hard resin, porcelain, titanium, and zirconia,
and although the compositions of these materials are different, they can all be processed in the sameequipment. There has been a growing interest in the use of zirconia, but the downsides to using thismaterial is that its processing can take a long time needed to machine its half sintering block, and in thesintering after the milling step. The time required in the furnace can vary in each model, but six to eight
hours is the standard. All these factors have to be taken into account when selecting the suitableequipment.
Product Name
Manufacturer
Plan

MeasuringsystemProcessing
Number of
revolutions (rpm)Auto changer
Price (Yen)
Measuring time(min, except wherestated)CAD time(min, except wherestated)CAM time (min)Production time(min)

CadiumCadiumCERCONDECSY
EVEREST
GN-I
ProceraDental system Center system
ADVANCE
Degu Dent
KAVO
GC
Nobel Biocare
Waxing up
ComputerWaxing up
MeasuredComputerComputer
Measured data
abutment
virtual design
abutment
data
virtualvirtual design Abutment tooth
tooth model
tooth model Crown data
designmodel
Contact type Non-contact Non-contact Non-contact Non-contact Non-contact
Contact type
type
type
type
type
type
CAM
CAM
CAM
CAM
CAM
CAM exclusive CAM exclusive
exclusive
exclusive
exclusive
exclusive
exclusive
20,00020,00010,000-20,000
12,0005,000-8,000
50,000No
6,980,000

No
10,482,800

Yes
9,800,000

Yes
2,200,000

Yes
12,800,000

1,850,000

30No
Ordering
system5

15 secs

15

2-6

10-15

2-3

1

15

45 secs

10 secs

10

5-15

70
110

40
60

40-60
55
(Excludesintering)

60
75

30
40

70- 100
90

Table 4-1-2 Commercial CAD/CAM systems

Form abutment tooth
Impression taking

Take a picture of intraoral with CCD camera, etc

Produce plaster cast

Design with computer
Waxing up
Scan waxing up
Design with computer
Processing/Shaving

Scan plaster cast
Design with computer
Possessing/ shaving

Fig.4-1-35 Flow chart of CAD/CAM system
B. Machining accuracy of the CAD/CAM crown
The dental CAD/CAM system (Cadim, ADVANCE) is featured in Fig. 4-1-36. The machining accuracy ofthis system was analyzed with different materials by comparing the dimensions of the shape derived withthe three dimensional coordinate measurement system to the molds of the abutment tooth and the crown.
The materials that were employed as work materials for comparison were: resin block (Hybrid resin, GC
Co., code HR), pure titanium JIS second block (JIS H 4650 Daido Steel, code Ti), and 2 types of porcelain
blocks [(Cadim Porcelain, ADVANCE, code CP), (Vita porcelain block・Mark II Vita, code VO)]. The
cervical margin was observed with the scanning electron microscope.
1.

The molds of the abutment tooth and for the crown

The molds employed in the experiments for the abutment tooth and the crown (SUS-304), and theirrespective dimensions are as indicated in Fig. 4-1-37.
The abutment with the dimensions: the base diameter of 0.5 mm, diameter of the occlusal plane of 6.0mm, height of 6.0 mm and the tapered angle on the axial wall to be 8.0, a cervical margin, and thecorners on both axial wall and the occlusal plane were rounded with 0.5 mm radii. As for the crown that
corresponds with the above structure, the base diameter of 11.0 mm, diameter of the occlusal plane of 8.0mm, height of 7.0 mm, and tapered angle of the lateral wall as 8.0 was fabricated. The corners for
occlusal plane and the axial wall were given a curvature of 0.5 mm radii.
2.

Measurement system

The state at the time of measuring the dies of the abutment and the crown are illustrated in Fig. 4-1-38.
The abutment die was fixed on the Cadim working surface held with a holder. The holder consisted of acylindrical and a planar section, with the diameter of 6.0 mm for the plane. The base of the abutment die
was first attached to the planar section of the holder before connecting the cylinder to the maincomponent. The two dimensional (2D) measurement of the X-Y flat plane was done at the height that
included the maximum height of the contour. The standard measuring range was determined using theseoutlines obtained from the captured 2D data to conduct the 3D measurement. The crown die was thenattached to the abutment tooth, after conducting the crown die measurements, to scan in the samemanner.
In this study, a cylinder ruby type with 1.0 mm diameter was used as the stylus of probe tip and wasscanned using the following parameters: bidirectional probing; radial scanning; 0.05 mm pitch count; 170
mm / min scanning speed; and contact pressure of 70 g. The measuring times for the abutment die, andthe crown die, were 25 min and 30 min, respectively.
The production of tool paths were conducted as follows, first the crown data was gained by merging thedata of abutment die and the external dimensions of crown die gained from the three dimensional
measurement on the computer. The internal structures were expanded by 50.0 m for a cement layer. In
order to ease the removal of data, one expressed with sprue lines was created and adopted as the model
data for the milling process. The tool path was generated implementing the data gathered and using soft
trace cut (Renishaw). Two types of toolpaths, coarse and one that was finished to completion, were
produced to suit the work materials and the tools employed. The crown data and each tool paths thatwere employed in generating the sprue lines are featured in Fig. 4-1-39 a to d. The processing apparatus
in Fig. 4-1-40 and the CAD/CAM crown that was processed to completion is shown in Fig. 4-1-41,
respectively.

Fig. 4-1-36 The dental CAD/CAM system (Cadim)

Fig. 4-1-37 The molds of the abutment tooth andfor the crownFig. 4-1-38-a,b Measuring the crown die

Fig.4-1-39 Constructing the tool patha. Crown model datab. Processing of the terracec. Parallel processing
d. Radial processing

Fig. 4-1-40 Processing apparatus

Fig. 4-1-41 Completed crown(Left to right) 2.0 mm, 1.0 mm(Left) HR, Ti, CP, VP

super hard end-mills; 2.0 mm, 1.0
mm electroplated diamond burs
3.

Resultsa.

The machining accuracy of the internal and external structures of the crown

The means and standard deviations (SD) of the difference between the dimensions, internal and externalsurfaces, of each crown against the die model and the crown model are presented in Fig. 4-1-42.
With respect to the resin block, HR as an example, the machining accuracy of the inner surfaces were as
follows: occlusal plane 42.7 (9.0) m to 35.6 (9.7) m at the position 5.0 mm away from the occlusal plane;
and 74-2 (7.7) m was indicated for the height, suggesting the machined product was larger with all thedimensions. On the exterior, -0.6 (102) m at the occlusal plane to 23.4 (182) m at the cervical region,and 109.9 (172) m was indicated for the external height, showing a decline in accuracy from the occlusal
plane to the cervical region.
The internal dimensions for each of the four working materials were shown to expand linearly. The
external planes of the CP were shown to reduce from the occlusal plane to the cervix as with the HR.
However, this trend was not seen in VP or Ti, where the slight expansion was demonstrated only on theocclusal plane, and then a decrease from the 1.2 mm mark to the cervix was seen with VP. Meanwhilewith Ti, an expansion was seen from the occlusal plane to the 3.0 mm mark, but declining after that to 6.0mm mark where a slight increase was illustrated again.
The machine accuracy in all four of the working materials showed an increase in the heights of both theinternal and external surfacesOcclusal
surfacepart

Insidecrown
Inside ofof
thethecrown
Outside ofof
thethecrown
Outsidecrown

Occlusal
surfaceparttooth cervix

tooth cervix

HeightHeightstandard
deviation

Occlusal
surfacepart

Insideof crown
the crown
Insideof theOutsideof theOutsideofcrown
the crown

standard
deviation.

Insideofcrown
the crown
Insideof theOutsideof theOutsideofcrown
the crown

tooth cervix

Occlusal
surfacepart

Inner crownOuter crowntooth cervix

HeightHeightstandard
deviation

standard
deviation

Fig 4-1-4-2 Machining accuracy of the internal and external surfaces of the crownb.

The observation of the surface topography with SEM.

The SEM photomicrographs featuring the internal cervical region of HR, Ti, CP and VP are shown in Fig.
4-1-43. The surface of HR is shown to be coarse, covered with the passage marks of the tools, and in someareas a continuous filing of roughly 200 m could be observed. In Ti, the machining marks were clearlyvisible and in contrary to those of HR, CP or VP, presented with sharp angles. CP and VP showed sharp
angles on the cervical region with signs of chippings.

Heavy chamfer portion
Cervical region
Exterior

Fig. 4-1-43 SEM observation of crown cervix margin in each working materials
C.

Machining accuracy of CAD/CAM crown fabricated with repeated machining

The repeated usage of one processing tool to fabricate multiple CAD/CAM crowns with high accuracy
would indicate reduction in the cost and limit the number of tools in the manufacturing process. In thisstudy, the machining accuracy of CAD/CAM crown was investigated with repetitive machining to clarify
the limit of the tools to determine the durability of the tools, an issue often faced in the daily clinicalpractice.
1.

Experimental method

To evaluate the machine accuracy, 51 CAD/CAM crowns were fabricated with using one processing tool,and in total fabricated 153 crowns with the use of three processing tools. Amongst these, the interior
surfaces of the crown numbers 1, 11, 21, 31, 41 and 51 were measured for comparison.
2.

Results

The machining accuracy of 1, 11, 21, 31, 41 and 51 have been shown in Fig. 4-1-44. The machine accuracy
from crown numbers 1 to 51 were shown to decrease from 78 m at the occlusal plane to 36 m in thesurface 5 mm away from the occlusal plane, indicating that the surface towards the cervix was becoming
narrower. The results also showed that even after fabricating 51 crowns, the dimensions were shown tostill be larger than the die, and the cement space had been preserved. The images of the cervical form of
the ceramic crown, shown in Fig. 4-1-45, indicated the processing to have retained the reproducibility
from numbers 1 to 11, but in the latter fabricated crowns presented with slight chippings. The surface ofthe bur showed no changes in its structures throughout the experiment.

Fig.

4-1-44Inner

surfacemachiningaccuracy of CAD/CAM crown with repetitivemachining

Fig. 4-1-45 Inner surface machining state of
CAD/CAM crown which with repetitivemachining
D. Machining accuracy with the application of the CAD/CAM system connected to the internet
Coupled with the development of IT and network systems, CAD/CAM network system have developedthat can transfer the CAD information to the CAM center via the internet, and computers equipped witha scanner and image processing software have been placed in the dental clinics. The data sent from thedental clinic is only the CAD information derived from the measurement of the working model, therefore
the fabrication of the restorative appliances must be done in the CAM center solely relying on the digital
data without the working model. In order to fabricate precise restorative appliances, the accuracy in themeasurement with CAD is inevitable. A major factor influencing the accuracy in CAD measurements isthe step-over, the distance between the lines when obtaining the data. The closer the distance between
each of these lines, the more precise the data obtained. The problem that arises as the result of this is theincrease in the size of the data and thus increasing the time required to obtain the measurements andprocessing of the CAD data. In order to overcome this complication, the parameters for an efficientfabrication of crowns with high accuracy need to be clarified.

A study was conducted to enable fabrication of crowns with high machining accuracy with the application
network linked CAD/CAM system by comparing the dimensions of the resulting crown and the original
die scanned using 3D coordinate measuring machine. The various parameters that were employed tofabricate the studies were: three settings of step-over, 0.01, 0.11, and 0.21 mm, to fabricate crowns fromblocks of titanium, porcelain and composite resin.
1.

CAD system

Dental Cadim (Cadim 107D, ADVANCE, is abbreviate to Cadim thereafter) was adopted as the CAD
system for this study. Cadim consists of personal computer equipped with software (Tracecut24,
Renishaw) that controls CAD and CAM contact-type measurement.
2.

Measurements using the step-over of the molds

Scanning parameters adopted were as follows: step-over of 0.01, 0.11, 021; scanning speed, 1000 mm/min;
pitch of the abutment surface, 0.05 mm; and pitch of the crown outer surface, 0.1 mm; contact pressure,
30g; and measurement direction to be bidirectional. Cylinder-type tungsten carbide with diameter of 1.0
mm was used as the stylus at the probe tip.
The scanning times for St 0.01, St 0.11 and St 021 were, 2 hours and 55 minutes, 18 minutes and nine
minutes, respectively for the abutment die; and 3 hours 3 minutes, 35 minutes and 10 minutes,
respectively for the crown die (Fig. 4-1-46).

Fig. 4-1-46 Measuring with step-over3.

Transmission of data

The scanned data was then compressed into the LZH form, and was then sent to the CAM center with the
Cadim mailing software (Advance Co., Ltd.) The data capacity for St 0.01, St 0.11, and St 0.21 were 11.8
MB, 957 KB and 500 KB, respectively.
4.

Resultsa.

The difference in the interior and exterior dimensions with the die

The differences in the internal and external dimensions with respect to St 0.01 and St 0.11 were greaterthan that with the St 0.21 at the distances of 1.2 mm, 2.0 mm and 3.0 mm away from the occlusal plane,
respectively. In the regions 4.0 mm and 5.0 mm away, the dimensions became greater in the order of St
0.11, St 0.01, St. 0.21, and with respect to the height, the difference in St 0.01 was greater than both St
0.11 and 0.21. These differences were found to be significant. The least amount of scattering was observedwith St 0.01. The differences were shown to decrease from the occlusal plane to 5.0 mm, reduction from 65
μm to 40 μm was observed in St 0.01; 67 μm to 47 μm with St 0.11; and 52 μm to 32 μm withrespect to St 0.21 (Fig. 4-1-47).
The difference in the crown exterior and the die with the step-over values were found to be small with St
0.11 at the occlusal plane relative to St 0.01 or St 0.21; in terms of height, St 0.11 was found to have been
reduced more than both St 0.01 and St 0.21. The differences were found to be significant. Furthermore,
the decrease in the difference from the occlusal plane to the tooth cervix region were found in all step-overvalues: 23 μm to 1 μm with St 0.01; 11 μm to 5 μm with St 0.11; and 20 μm to -1 μm with St 0.21.

Fig. 4-1-47 Machining accuracy of CAD/CAM with step-over
E. The properties of commercialized internet-based CAD/CAM system
The process of internet-based CAD/CAM system is shown in Fig. 4-1-48. As evident from the diagram, theprocess is fundamentally the same as those that have been mentioned in this chapter, and the only
novelty is that the measured data is transmitted on the internet in its digital form. This indicates the
reduction in the costs that was spent on purchasing and maintaining CAM, purchasing and storing theblocks and also on the cutting tools. This should result in an overall cut down in the expenses spent on
CAM and eliminate the space used for its operation and storage. The CAD/CAM devices of the past werelarge and therefore were only limited for use in large laboratory centers. The incorporation of internet
data transmission should override this past notion. The only space required for CAD is the size of astandard cardboard box, and to set up the personalized computer. This system enables the dentist
him/herself to incorporate the finishing touches on those that require high accuracy, and gingival
structures onto the computer which are vital steps in the development of dentistry. The internet based
CAD/CAM system can be accessed from any part of the world, enabling clinical practice to incorporate thelatest technology.
① Abutment preparation
The preparative steps are similar to those for the basic all-ceramics crown but conducted by employing
the methods recommended by each company to suit the properties of each CAD/CAM system. The errors
in CAD measurements arise where the corners are at acute angles. The size of the abutment has to belarger than the diameter of the milling bur otherwise it would not be able to be applied.
② Impression taking
Gingival displacement is critical for creating a definitive finishing line to avoid undercut being formed on
the axial and occlusal plane when obtaining impression for the fabrication of fixed restorations.
③ Constructing an indirect working model
A particular type of extra hard gypsum for a contact-type measure; and dark extra hard gypsum,
recommended by the manufacturer that does not reflect light, employed for the non-contact type (laser)
measure. Fabricate the indirect working model with the usual procedure, partition the model and clarify
the margin line.
④ Scanning
The questions often asked by the dentists are whether this can be operated by themselves and whether it
demands time and effort. There are numerous CAD/CAM systems available in Japan, and at least one ofthese will likely be suitable for your practice. There are contact and non-contact types to scanning. Stylus(probing through physical touch) is usually required for the contact type, with a tip diameter of 1 mm,
made of ruby or tungsten carbide, enabling precise measurements to be conducted (Fig. 4-1-49). For the
non-contact type scanning, laser is the typical means. Amongst the techniques employed for this type,there is the multi-light band recording method that utilizes the plaster specific for scanning, andphotographs once projecting light and shadow. In the methods where the model is optically digitized toprecision, there are those in which the complex forms, and obscured sections such as undercut of theworking model can be measured and recorded as it is, and be modified on computer to result in a 3Dmodel. With optical impression taking method that is based on technique of triangulation, its mainfeature is the ability to conduct structural measurement of the abutment immediately within the oralcavity. Simultaneous measurement of the abutment and the adjacent teeth is possible by adopting a
specialized channel tray, as well as preparing the devices that can shorten the processing time.
⑤ Construction
The construction process from the collected data have been designed that can simply be conducted withthe software equipped by each manufacturer that enables simple operation with just a few clicks on theicons displayed on the screen. It is highly user-friendly and will be able to be operated by those who areless apt with IT. It is equipped with functions that can automatically recognize the marginal lines orchoose it as an optional setting. For instance, the pontic structure can be selected for a bridge denture, as
well as the area of contact in the connector portion; and freely set the distance to the mucosal surface. The
setting of the finishing line is shown in Fig. 4-1-50.
⑥ Data transmission
Upon finishing the reconstruction procedure, the data is sent in LZH format via the internet.
⑦ Milling and processing
At the laboratory centers, milling process is conducted as CAM in accordance with the CAD data sent.
The milling tools for each manufacturer are specific with regards to the diamond bur, carbide bur, eachwith various diameters. In addition, the methods are diverse, including milling from blocks; aluminumoxide powder compacted under high pressure sintering onto the coping; or a powder-slip application
method with the electroforming effect with the whole of the denture as the conducting body where theworking model is dipped into the electrolyte solution.

① Form abutment tooth② Impression taking③ Make a model④ Scanning⑥ Send data via
internet⑤ Design⑦ Processing/Shaving⑧ Mail restoration

Arrival ofrestoration device

Fig. 4-1-48 Internet-based CAD/CAM system

Fig. 4-1-49-a,b Measuring
procedure of the abutment andcrown with scana. Contact-type abutment
scanningb. Contact-type crown scanning

MarginFig. 4-1-50 Setting the line of the margin

F. The machining accuracy of each internet-based CAD/CAM system
The processing accuracies of CAD/CAM systems, listed in Table 4-1-3, were investigated. The actual
fabrication of crown was conducted using four different routes. First, Dental Cadim 107D measuring
device (ADVACE Co., Ltd.) was used to perform contact-type scan. The data was subsequently sent to theprocessing center, in which the prosthetic crown was also fabricated. Second, a contact-type scan with
Procera (Nobel Biocare) measuring device, from which obtained data was sent to the product center in
Sweden, in which the alumina crown restoration device was fabricated in the same facility. Third, laser

scanning with GN-1 device (GC Co.) was conducted after which the data was transmitted to the sameprocessing device, to fabricate an In-Ceram crown restoration device. Lastly, laser scanning with Cercon
scanning device (Dentsply International) was performed to fabricate a zirconium crown restoration
appliance.
For this investigation, stainless steel abutment die was employed that was fabricated with consideration
to the all-ceramic crown for the molars. Five crown restoration devices were constructed at eachmanufacturing sites based on these transmitted data.
The restoration devices produced are shown in Fig. 4-1-51. The milling tools for each of these restoration
devices: Dental Cadim 107D porcelain crown, Procera alumina crown, GN-1 porcelain crown, GN-1
In-Ceram crown, Cercon zirconia crown (each will abbreviated to CA, PN, GR-Po, GN-In, CE, respectively,
thereafter) are shown in Fig. 4-1-52. A flat end-mill reamer with 1 and 2 mm diameter were used for
Dental Cadim 107D; flat end-mill reamer with 2 mm diameter for GN-1; and fine milling cutter with a 1
mm diameter and rough milling cutter with 2.8 mm diameter for Cercon were employed. The
reconstruction with Procera was conducted with the sintering of aluminum oxide at high pressure insteadof the method to that mills from a piece of block, thus no tools were required.

Table 4-1-3 CAD/CAM system and restoration materials

Fig. 4-1-51 The fabricated restoration devices

Fig. 4-1-52-a,b,c The milling tools for CAD/CAM
a.

Dental Cadim 107 D

b. Cerconc. GN-I

The processed crown interior is shown in Fig. 4-1-53. The mechanical marks from the milling procedure
were visible in GN-Po, GN-In and CE crowns out of the five that were inspected. The images of theinternal surfaces of GN-In and CE crowns have been given in Fig.4-1-53. Horizontal markings werevisible in the interior of GN-In, whereas both horizontal and longitudinal markings were observed in CE
interior.
The processing accuracy of the interior of the fabricated crown was analyzed with 3D coordinate
measuring device and the results are shown in Fig. 4-1-55. The accuracy with CA decreased from 73 μm
near the occlusal portion to 20μm in the abutment. The accuracy values at each measured surfaces were
found to be the greatest in PR that resulted in a straight line graph varying around the 110μm. The
values for both GN-Po and GN-In were largest closest to the occlusal surfaces with 45.6 μm and 67.2 μm, respectively, but smallest at the point 5 mm away from the occluding surface. The values for CE were
the smallest amongst the other crown types.
The degree of fit of the crown and the die are displayed in Fig. 4-1-56. A slight gap could be observed with
PR that showed the largest differences as shown on the machine accuracy graph. On the contrary, there
were no obvious gaps seen with CA, GN-Po or GN-In, indicating a relative accuracy in the fit. The CE
crown with the negative values as indicated in the accuracy graph, showed a slight rise above the othertypes with large gap with the original die.
The processing of titanium, ceramics, and hard resin materials were conducted using the internet based
CAD/CAM system (Cadim 107D).
The crown was fabricated with cement space in the interior of the crown from 1 mm above the cervix
region to the occlusal surface with a 50 μm off-set. From the results of the machine accuracy, as shownin Fig. 4-1-58, at points 1.2 mm, 4.0 mm and 5.0 mm away from the occlusion surface, the significant
differences in the machine accuracies were evident between the various materials. The machine accuracyof titanium was roughly 60 μm in all of the measured portions, but the accuracy tended to become lesstowards the cervix region with ceramics and hard resin materials. In addition, significant differences in
the machine accuracy between the materials with regards to the crown exterior were also found at all of
the measured points. The precision of the CAD/CAM with which crowns were fabricated were shown to be
extremely high and thus was concluded there would be no difficulties for it to be applied in the clinicalpractice.

Fig. 4-1-53

Interiors of each crownFig. 4-1-54 Magnified images of mechanically processed internal surface

Fig. 4-1-55 Machining accuracy of each crownFig. 4-1-45

Degree of fit for each crownFig. 4-1-57 Blocks of titanium, porcelain and resin used

Fig. 4-1-58 Machining accuracy with titanium, porcelain and resin
G. Restoration of color tone
The varieties of CAD/CAM blocks provided amongst the different manufacturers are diverse but
generally the basic colors referred to as A1, A2 or A3, or a gradation block that combines these are
adopted. It is also possible to mill from a basic color block then add staining later onto the dental cleft or
to the tooth cervix, for the restoration of natural crown tone. The transparency varies for different
materials. With regards to the all-ceramics crown, due to the absence of the opaque material that is often
used to mask the metal coping used in the metal ceramic crown, it has more transparency than the lattercrown type. This may be an important factor for consideration for some of the treatments or depending on
the region.
A range of colors for coping are also available for its fabrication with the CAD/CAM system (Fig. 4-1-59)
and there is also a sintering method utilized whereby a specialized solution is applied before placing the
coping into the furnace. There is even a manufacturer that offers ten different shades for those structurescolored with this method. The porcelain is then applied on top of this, thus producing one with a naturalappearance (Fig.4-1-60).

Fig. 4-1-59 Alumina porcelain crown incorporating copinga. Coping was fabricated with CAD/CAM systemb. Occlusal plane applied with porcelainc. Porcelain interiorFig. 4-1-61 All ceramic crown fabricated with CAD/CAM system
H. Installation costs
There are devices needed for vacuum, high frequency dissolution and casting devices used in dental
precision casting that are relatively expensive. Generally speaking, CAD/CAM systems therefore are notcheap. As shown in Fig. 4-1-2, the prices vary among the different manufacturers, but roughly ten million
yen is required to purchase a set, consisting of measuring device, CAD, PC equipped with the softwareand CAM. However, as mentioned at the beginning, the cost for the CAM can be omitted in incorporating
the internet-based system, therefore limiting the expenditure to few million yen to purchase CAD on its
own. The added bonus of this system is that the past waxing and casting processes by hand can be
entrusted on the machine with a few simple operational settings. The reduction in cost is possible if therestoration devices such as inlay, crown, conus crown, implant superstructure, and plate dentures can beprocessed, and there will come a period where one system will be installed per dental clinic. The notion of
CAD/CAM system has become well known in the dental community, but it has not yet been thoroughly
distributed in all of the dental practice settings. The past CAD/CAM system had its limitations, but withthis newly developed internet-based system, there are advantages such as reduction in the costs andspace; high precision in scanning and processing; and ease in operation of the computer and the devices
for the reconstruction without the need for specialized knowledge that make it such an accessible system.
The current market demands are treatments with white teeth instead of metals, and one that iscost-effective as a private treatment. The all-ceramics used in this CAD/CAM system has stablecharacteristics as a block, is less expensive than the metal-bonded porcelain, and can overcome the issuesof esthetics encountered with metals due to the development of metal shadows on the gingivae.
1. The search continues for new materials that meet the estheticism requirements as well as instrength and resistance, combined with cost effectiveness to be applied in clinical practice, in such
ways as with the Kaguya-block® (ADVANCE Co., Ltd.) (Refer to Chapter 6 – „The method to mountthe superstructure fabricated with CAD/CAM system to the AQB implant‟ for further details).

I believe that the restoration devices will not be able to fulfill the demand for high precision/ high qualitythat is also cost effective in devoid of the internet-based CAD/CAM system. I highly recommend the use to
many of the dental practitioners and assistants.

Fig. 4-1-61 The all ceramic crown fabricated with CAD/CAM system
III. The science behind adhesion and its clinical applications
As mentioned previously, the importance of leaving the enamel portion untouched is emphasized by thenotion of minimal intervention with estheticism. It has become possible to treat the milled enamel,
having regenerating ability, and dentin surfaces by applying adhesive agents. The pH is consequently
increased, inhibiting the leakage of ions and thus preventing tooth decay and discoloration of the ceramic
restoration devices.
The application of the adhesive agents to fuse the esthetic restoration devices with the tooth has been not
only been suggested to affect its long-term functions but also in the lengthening the life-time of teeth. The
metal-bonded crown bridge, that has sintered porcelain on the metal, has often been applied as esthetic
restoration device. The use of all-ceramics restoration has been considered in the clinical practice to meetthe rise in demand for estheticism. The science of adhesion and its clinical applications that provides with
estheticism are discussed in the following sections.
A. Products of adhesive agents
Japan has been at the forefront adhesive resin research, in particular with regards to the surface
treatment and the adhesion mechanisms to the enamel and dentin. The adhesive agents in the current
commercial markets are shown in Fig. 4-1-62, and the product names listed in Table 4-1-4. The
commercial adhesive agents are: resin reinforced glass ionomer, MMA-TBB type resin cement andcomposite resin cement; and the luting agents including, zinc phosphate cement, polycarboxylate cement,
and glass ionomer cement. The properties of these luting agents and adhesive materials in terms ofchemical engineering are shown in Table 4-1-5. Generally, the time required for it to set range from six tonine minutes, but a longer time of 12 minutes is required for the MMA-TBB type. The pressure required
for the composite-type resins is the greatest with 200 to 380 MPa. The key property is its adhesion ability

to teeth, and is the line that has been used to differentiate between the adhesive and luting agents.
The properties of adhesive agents, as listed in Table 4-1-6 are, its high mechanical properties, its
insolubility in saliva, the ease in operability, not an irritant to dental pulp, and its impermeability to
X-ray.
The term adhesion is referred to here as the state whereby the adherend (enamel, dentin, resin, metal,
and ceramics) are chemically bonded to the cement through adhesive monomers. Cementing, on the other
hand, describes a mechanical bonding of the adherend and cement through anchoring with their unevensurfaces as shown in Fig. 4-1-62.

Fig.4-1-62 a-i the different bonding materials that are commercially available

Table 4-1-4 A selection of commercial bonding agents

Cementing
agent

Adhesive

Setting
Film
Compressive
time
thickness
strength(Minute)(μm)（MPa）
Zinc phosphate
6-8Middle77-147
cement18-20
Polycarboxylate
7-9
Middle53-95
cement12-17
Glass ionomer
5-7
Middle102-206
cement15-20
Reinforced resin
3-5
Thin
133-155
Glass ionomer
10-18
cement
MMA-TBB type
11-12
Thin
(49)
resin cement
20-30
Composite resin
6-7
Thin
206-378
type
10-19
resin cement

Tensile Decay rate Floride
Bonding
Toxicitystrength (In distilled removal strength toto（MPa）water) (%)
teeth
dental pulp
4-6
Low
No
No
Middle0.03-0.05
5-6
Low
No
Rare
Low
0.02-0.04
6-10
MiddleYes
Yes
Low-middle
0.06-0.28
23-24
Low
Yes
Yes
Low
0-0.07-

Low0.04

No

Yes

Low

34-65

Low
0.01-0.03

No

Yes

Low

Table 4-1-5 A table of bonding materials (Taken from „Restorative Preservation, 4th ed‟.) the materials canbe divided into 6 classes, and are provided in powder and solution, or paste/paste forms
1) Mechanical performance must be high2) Scientific stability must be high and it must be insoluble to oral fluid3) Coating thickness must be thin4) Operability must be well and setting time is moderate
Powder and liquid must stick well and easy to mix withOperation has time relatively also, and it should harden rapidly after cementing5) Wet well with Dentin and restoration and it should keep adhesiveness after harden
6) It should not toxicate dental pulp or soft tissue
7) Shrinkage during hardening must be small
8) Thermal expansion coefficient must to close to dentin`s and nonconductor of thermoelectricity
9) It should have X-ray impermeabnility10) A color tone must to close to dentin

Abutment tooth

Cementing agent

Prosthesis

Table 4-1-6 The list of bonding material properties

Fig. 4-1-63 Mechanical bonding through the irregular surface structures
B. The bonding technique
Measure out the adhesive material onto the mixing slab as shown in Fig. 4-1-64 for bonding the inlay.

After applying the bonding material onto the dentin, insert the inlay as shown in Fig. 4-1-65. Then,
carefully remove the hardened adhesive first from the occlusal plane and then the adjacent plane. Inspect
the state of the inlay and the tooth after the adhesive removal (Fig. 4-1-67).

Fig. 4-1-64 a,b Operating with the cement material

Fig. 4-1-65 a,b Insertion of cementing agent, and inlay

Fig. 4-1-66 a,b Removal of the cementing material, fromthe occlusal surface, and between the adjacent teeth.

Fig. 6-1-67 Cementing completed
C. Bonding to enamel
The effects of the dental surface treatment are listed in Table 4-1-7. The improvements in the level ofhygiene, prevention of resin leakage and polarization can be expected. The surface treatment of theenamel with phosphoric acid convert it into the mould for the resin to seep through the uneven surface asshown in Fig. 4-1-68, becoming polymerized and set for the two surfaces to be fused together. The
phosphoric acid treatment as conducted in Fig. 4-1-69 modifies the surface to become rough as illustrated
in Fig.4-1-70. Adhesion is formed after the bonding treatment.

1) The improvements in hygiene and wetting of the tooth plane
The dentin surface was decalcified by phosphoric acid treatment, which also gave rise to a smear
layer, thus preventing the resin leakage can be expected
2) Polarization of dental surface
Hydrogen bonds form between the polarized group of the resin and the terminal groups (-OK, -NH2,-COOH) of the dentin components polarized by phosphoric acid.
Table 4-1-7 Effects of treatment to the dentin surfacea.

b.
Enamel surface after the

The state of the enamel surface

phosphoric acid treatment (SEM

after the self-etchgin primer

image)

treatment (SEM image)Fig. 4-1-68 a, b
Adhesion with the enamel surfaces

Solubilization and removal of smear layer

Formation of enamel trabeculae resulting in rough edged surfacesFormation of rough microscopic projections due to the apatite crystals.



Significant enlargement of the surface area

Infiltration and setting of the bonding resinStrong support is exhibited with the application of masticatory forceFig. 4-1-69 Etching the dental surface with phosphoric acid
Fig. 4-1-70 Acid treatment of enamelsurface
Most of the enamel is solubilized bytreating with acid solution resulting inheight reduction. However new enamelthat is rich organic components arecontinuously generated on the surface
that is dense and low in transparency.

D. Bonding to dentin
The bonding materials used for dentin surface is shown in Fig. 4-1-71. The adhesive properties of thesebonding materials are listed in Table 4-1-8. The adhesion processes to the dentin surface include,
solubilization of the smear layer, exposure of collagen, and impregnation of the dentin with resin (Fig.
4-1-72). The smear layer that coats the dentin surface prevents adhesion from being formed. In order toremove this smear layer, a series of steps are taken as illustrated in Fig. 4-1-74. First an etching agent(citric acid) is applied then rinsed with water, and the surface is dried. The collagen surface becomes
exposed with the application of primer, ready to form dentin surface imbedded with resin by applicationof the bonding material, polymerized with light. The adhesion is finally established between the dentin
and the resin that consists of hardened 4-META, by its infiltration into the intertubular dentin that has
been decalcified by the citric acid that contains ferric chloride.

Fig. 4-1-71 a-g
Commercially available
Bonding material

Solubilization of smear layer and decalcification of the dentin surfaceSolubilization of smear plugDecalcification also occurs to the dental tubules and the interior of the tubulesThe remaining collagens become exposed onto the surfaceResin-impregnated dentin provides subtle mechanical supportMechanical strength of the resin tag, hardened after infiltrating into the dentin tubule.

Table 4-1-8 Adhesion with the dentin

Fig. 4-1-72 The adhesion interface between
the resin and the dentin surface

Fig. 4-1-73 The acid treatment of the dentin surface
The acid treatment strips away inorganic content of the dentin surface, but the mass remains unchanged.
This results in the exposure of organic substances, mainly the water molecules and collagen, onto theadhesion surface, giving rise to a state referred to as “softened dentin”.

Fig.4-1-74 Dentin bonding mechanism
E. The difference between total etching and self-etching
The formation of resin-impregnated dentin and adhesive strength is largely influenced by the dentin
treatment used. The smear layer that results from the phosphoric acid treatment is completely
solubilized with etching and removed from the cavities by the subsequent rinsing step with water.
Whereas with self-etching primer, although the smear layer is solubilized with the acid treatment, thewater rinsing does not result in its full removal from inside the crevices. Furthermore the degree of
decalcification is less than that with the total etching method, as well as the formation of honeycomb
structure or opening of the dentin tubule
F. Mechanism of wet-bonding
The wet-bonding adhesion as shown in Fig. 4-1-75, prevents the collagen structure from crushing byremoving the excess moisture with blow drying, or by blotting with cotton wool or absorbing paper. The
bonding material consisting of hydroxyethyl methacrylate (HEMA) is hardened by photopolymerization,and then the resin is applied to this.
The present adhesion mechanisms adopted in dentin bonding are aimed to avoid the collagen frombecoming constricted with drying after the decalcification of dentin surface. By preventing the surface
from becoming dry, the dentin bonding material infiltrating into the structure and hardening, can bondwith the collagen fibers that have remained moist

Fig. 4-1-75 Wet-bonding adhesion mechanism
The collagen fibers remain suspended in its original structure by removing
the excess moisture with slight air blow, cotton wool or absorbing paper
G. Observation of marginal leakage
To observe marginal leakage, first, crevices in the external and internal surfaces of natural teeth wereformed. To the external cavity, resin cement (Superbond C&B), and acidic cement such as: Vitremer
luting cement (3M) or Elite cement (Kerr) were applied before placing the crown. Composite resin wasapplied to the internal cavity after its bonding with Megabond self-etching primer.
The test subject was placed into water set at 37ºC for 24 hours, then preserved in staining solution forfurther 24 hours at 37ºC, it was separated, and then monitored. The leakage from the cervical region thatwas observed is shown in Fig. 4-1-76. The crown and whole of the dentin surface with the Elite cement
was stained in red showing a large area of leakage. With Vitremer cement, leakage was shown to result
from the crown margin and slight staining of the dentin surface. There were no areas of staining seen
with either the Superbond C&B (Fig. 4-1-79) or the Megabond (Fig. 4-1-80).

Fig. 4-1-76 a,b Leakage from the margin of the tooth cervix

Severe leakage

Moderate leakage

Fig. 4-1-77 a,b Stained Elite cement

Fig. 4-1-78 a,b Stained Vitremer cement

No leakage

CRNoleakage

Tooth

Fig. 4-1-79 a,b Stained Superbond C&B

Fig. 4-1-80 Megabond

H. Adhesion with ceramics
It had been considered difficult to achieve chemical bonding due to the inactive surface of ceramics. Silane
coupling was considered an effective method for surface treatment, and is applied in current practice. A
selection of silane coupling agent that are commercially available, classified into one, two or three bottle
types, is listed in Table 4-1-9. The silane chemical structure is shown in Fig. 4-1-81. The silane coupling
agent of three-bottle type is featured in Fig. 4-1-82. The bonding strength of the newer adhesive bonding
materials such as Panavir EX and Superbond C&B has increased if applied with the silane couplingmaterial (Fig. 4-1-83), but significantly decreased if placed in 70 º C water bath. To examine thedifferences in strength with the addition of silane coupling agent, the porcelain blocks were attached
together with Panavir EX or Superbond C&B with or without the adjuvant, then was pulled apart. The
state of the porcelain after the strength test without the adjuvant resulted in the separation of thebonding material from the ceramics surface with only affect to the interface (Fig. 4-1-84). On the contrary,
the destruction state after the test showed the bonding agent to be attached firmly to the ceramics, andresulting in disruption of the adherent (Fig. 4-1-85). The handling of silane coupling agent for its clinicalapplication is shown in Fig. 4-1-86. Add a drop of catalyst solution, universal solution and the activator
solution into a dappen-dish (Fig. 4-1-87 to 89), mix well before applying onto the ceramics (Fig.4-1-90).
Only apply the bonding agent once the surface has been dried.

Liquid 1

Liquid 2

Liquid 3

PrimerManufacturer

Lamina bond, Porcelain primer

Shohu

Imperva, Porcelain primer

Shohu

Scotch prime, Ceramic primer

3M

Porcelain liner M

Sun Medical

GC, Cosmotec primer

GC

Tokuso, Ceramic primer

Tokuyama

Clear fill, Porcelain bond

Kuraray

Table 4-1-9 Silane coupling agents commercially available

Fig. 4-1-81 The structure of γ-methacryloxypropyltrimethoxysilane (MPTS)

Bonding strength

Bonding strength

Fig. 4-1-82 Silane coupling agent

Without silane

Without silane

With silane

With silane

Without silane

With silane

Fig. 4-1-83 Comparison of bonding strength with or without the different silane coupling agent

Fig. 4-1-84 a,b The disrupted state ofceramics without the addition of silane
coupling agent (after 24 hours at 37ºC)
a. Panavir EX
b. Superbond C&B

Fig. 4-1-85 a,b The disrupted state ofceramics with the addition of silane
coupling agent (after 24 hours at 37ºC)
a. Panavir EX
b. Superbond C&B

Fig. 4-1-86 ceramics before undergoing silane treatment

Fig. 4-1-87 Catalyst solution Fig. 4-1-88 Universal solution Fig. 4-1-89 Activator solution
Mix the above solutions wellFig. 4-1-90 Application of silane coupling agent
I.

Adhesion of metals

Another issue is encountered when attempting to form chemical bonding with metals, and was the reason
for which metals had not been bonded to resins and adhesive materials in the past.
In the current practice a primer is applied as a material used to prepare the surface for the subsequentadhesion step. Five types of primers specifically for metals that are readily available on the market arelisted in Table 4-1-10. The properties of the primers vary according to the adhesion monomer types. The
distinct properties of these primers (Fig.4-1-11) include those for gold-alloy (noble metals), Ni-Cr(non-metals), extraoral technical use, and intraoral biological use. Thus, the selection must be madeaccordingly. As shown in Fig. 4-1-91, the bonding strength is improved with the primer treatment in all of
the primer agents with the two materials of hard resins tested.

Name

Maker

AdhesivemonomerContents
(ml)

Price
(Yen)

Sun medical

VTD

6

8,000

GC
Kuraray
Tokuyama

MEPS
VDY/MDP
MTU 6

5
5
5

6,400
5,500
7,500

Sun Medical

VTD

8

6,400

Resin set
Super bond C&B cementing
set
Axis
Secede II-

V-Primer
Metal primer II
Alloy Primer
Metal tightInfes・opaqueprimerNew meta color・infes

Table 4-1-10 Comparisons of commercially available primers

Name

Application
Noble metal

Nonprecious metal

Intraoral

Extraoral

○
○
○
○
○

×
○
○
×
×

○
○
○
○
×

○
○
○
○
○

V- Primer
Metal primer II
Alloy primer
Metal tightInfes・opaque Primer

Table 4-1-11 Properties and application of commercially available primers

Heat cycle O times

20,000times

Heat cycle
Heat
cycle

20,000times

Bonding strength

Bonding strength

Heat cycle

Heat cycle
Heat
cycle O times

No
Metal
VAlloyPrimer Primer Primer primer

Metal
tight

No
Metal
Alloy
VMetal V-Primer
Alloy
Primer Primer
Primer Primer primer
primer

No Primer

Metal
Metal
tight
tight

Fig. 4-1-91 The difference in bonding strength with different primers on hard resins.
J. Removal of adhesion inhibitors
The suitability of the testing agent is evaluated with instruments such as fitting checker (Fig.4-1-92) orrouge (Fig. 4-1-93) for the attachment of prosthetic restoration devices. During the process, the interior of
the restoration device usually becomes soiled with layer of silicon oil which can subsequently inhibit theadhesion from being formed. Such inhibitory materials are referred to as adhesion inhibitors. Other
examples of inhibitors include finger tip dirt, plaque, tartar, saliva (Fig. 4-1-94), blood, exudates, water,
temporary adhesive materials, temporary sealing material, and oils from turbines. These polluting
substances from the processes should be removed retain the surface ready to enable the formation of firmbonding to be achieved. There are mechanical means for removal such as sand blast, tooth cleaning device,cotton wool; chemical removal means, such as treatment with acetone, ethanol, etching agents,
surfactants. The interior surface of the tooth after removal of inlay, secondary tooth decay anddiscoloration can be observed from ineffective bonding. The bonding strength and the falling rate ofSuperbond (Fig. 4-1-96) and Panavir (Fig. 4-1-97) were observed. The adhesive strength was measured
once the adjuvants: saliva (SA), fit checker (FC) or green rouge that was solubilized in chloroform (SP)were applied onto the tooth surface, and dried.
In comparison to the strength of the control, #600, the reductions in the bonding strength in the presenceof inhibitors are clear.

Fig. 4-1-92 Bridge trial placement

Fig. 4-1-94 The addition of saliva

Fig. 4-1-93 Application of rouge

Fig. 4-1-95 The interior of the tooth
after the removal of the inlay

Fig. 4-1-96 Bonding strength and theFig. 4-1-97 Bonding strength of PE andrate of reduction

the rate of reductionReferences
1) Okada T, Shinya A, Yokozuka S. Effects of load and loading time on fracture toughness withindentation method. Shigaku 1990; 78(3): 460-486. (in Japanese)
2) Watari K, Shinya A，Yokozuka S. Study of adhesive strength and mechanical character of Al2O3.
Adhesive Dentistry. 1990; 8: 53-73. (in Japanese)3) Kuroda A, Shinya A, Matsuda T, Katagiri S. The Mechanical Properties of the Pressable Ceramics and
its Optimal Crystalization. Dent Mater J. 2003; 22: 221-230. (in Japanese)
4) Matsuda T, Shinya A, Tomita S, Shinya A, Mitobe T, Hasebe S, et al: A clinical report and a small
study of fitness on Procera AllCeram crown. J J Prosthondont Soc 2004; 48: 543-548.
5) Tomita S, Shinya A, Gomi H, Matsuda T, Ogura H, Miyazaki T, et al: Machining accuracy of CAD/CAM
ceramic crowns fabricated with repeated machining using the same diamond bur. Dent Mater J 2005;
24(1): 123-133.
6) Tomita S, Shinya A, Gomi H, Shinya A, Yokoyama D: Machining accuracy of crowns by CAD/CAM
system using TCP/IP. Influences of restorative material and scanning condition. Dent Mater J 2007;
26(4): 549-560.
7)Lassila LVJ, Tezvergil A, Lahdenpera M, Alander P, Shin-ya A, et al: Evaluation of some properties of
two fiber-reinforced composite materials. Acta Odontol Scand 2005; 63(4): 196-204.
8) Shinya A, Matsuda T, Shinya A, Nakasone Y. Hybrid Resin Fixed Partial Dentures Reinforced with
Glass Fiber-Optimum Posterior Fiber Frame Design with Finite Element Analysis- Dent Mater J. 2004;
23: 186-192. (in Japanese)
9) Ootaki M, Shin-ya A, Gomi H, Shin-ya A, Nakasone Y: Optimum design for fixed partial dentures madeof hybrid resin with glass fiber reinforcement by finite element analysis. Effect of vertical reinforced
thickness on fiber frame. Dent Mater J. 2007; 26: 280-289.