bluuebunny/crossref_metadata_2025 huggingface dataset:
The interdental brush and its place in operative and crown and bridge dentistry
Authors: WÆRHAUG JENS
Published: June 2007

The effect of the interdental brush was evaluated on sixty‐seven extracted teeth which were stained and examined under the stereomicroscope. Thirty‐one of the teeth were totally covered with plaque when the interdental brush was used on them immediately before extraction. Thirty‐six of the teeth were from patients who had used the interdental brush routinely for several years. The interdental brush was found to have an excellent effect both in the central part of the interdental space and on the embrasures. However, the most noteworthy finding was that it removes plaque as far as 2‐2½ mm below the gingival margin. This means that restorations can be kept free of plaque, even if they are extended into the pocket. In modern dentistry ‘extension for prevention of dental caries’ has become a controversial principle because subgingival restorations retain plaque which induces destructive periodontal disease. In many cases this problem can be solved by introducing the interdental brush.
Soft lining to relieve soreness beneath dentures
Authors: MÄKILÄ EINO
Published: June 2007

The mandibular dentures of eighteen patients who suffered from chronic tissue soreness beneath the denture which could not be relieved by bringing the denture into a functionally faultless condition, were furnished with a soft lining. Of the patients re‐examined after 2 weeks, 89% were symptom‐free. After 6 months, 1, 2 and 3 years the percentages of the symptom‐free patients were 64, 79, 60 and 71% of the total re‐examined. However, after soft lining, some relief of the complaint was reported by all patients of the series.

The series included a woman with bronchial asthma whose oral mucosa again became sore after she had worn the denture with soft lining for a year, and a bruxist who had a definite relief.

The percentage incidence of denture stomatitis increased in the course of the 3‐year period studied. At the listed dates of re‐examination, it was 25, 46, 43, 80 and 100%, respectively.
Physical properties of a nickel‐base alloy prepared by isostatic pressing and sintering of the powdered metal*
Authors: FUYS R. A. , CRAIG R. G. , ASGAR K.
Published: June 2007

The physical and mechanical properties of samples of a nickel‐base alloy fabricated by powder metallurgy were determined. The particle sizes of the powders used to make the samples varied from –80/+ 200 mesh to –325 mesh. The compaction pressure varied from 138 to 414 MN/m2 and the sintering temperature varied from 1150 to 1250°C. The shrinkage during processing, the porosity, tensile strength, yield strength, elongation, and elastic modulus were used to characterize the samples. The strength of the samples generally increased with decreasing particle size of the powder and increasing compaction pressure and sintering temperatures. The porosity and strength, therefore, could be varied over a wide range by controlling the various parameters. The properties of the samples prepared by powder metallurgy were compared with those of the cast alloy and compact bone. Conditions can be selected that will yield equivalent or better properties by powder metallurgy than by casting.
The night guard: its uses and dangers of abuse
Authors: BRAYER LAURENTIU , ERLICH JACOB
Published: June 2007

An outline of the indications for, and construction of the night guard have been presented. Comment is made on its bio‐mechanical value and on the dangers of its abuse.
Etching of enamel prior to application of fissure sealants
Authors: WILLIAMS B. , VON FRAUNHOFER J. A. , WINTER G. B.
Published: June 2007

Acid etching has been shown to be necessary to increase the bond strength of the polymeric fissure sealants Epoxylite 9075 and Nuva Seal to enamel. For Nuva Seal or Epoxylite 9075 it would appear that it does not matter which concentration between the concentration levels of 30 and 70% is used.
Adaptation of amalgams to cavity walls
Authors: ØILO GUDBRAND
Published: June 2007

The adaptation of amalgam fillings to the cavity walls has been studied. Cavities were made in human teeth and filled with four different amalgams: (1) amalgam with an expansion of approx. 10 μm/cm after 48 h; (2) amalgam with no dimensional change after 48 h (balanced); (3) amalgam with a contraction of approx. 10 μm/cm after 48 h; and (4) amalgam with a contraction of approx. 20 μm/cm after 48 h.

The filling surface and parts of the surrounding enamel were planed, polished and studied under the microscope. The degree of contact between the amalgam and the cavity wall and the number and dimensions of the marginal defects were observed.

Fillings made from expanding or balanced amalgams mostly had good contact with the cavity wall, and the marginal defects were small and scattered. Around fillings made from contracting material, a slit formation was observed, and in these areas fractures of both the amalgam and the enamel margins had regularly changed the slit to a V‐shaped gap 10–20 μm wide. Greater defects exceeding 50 μm were also frequently observed.

The results showed a gradual decrease in the quality of adaptation from fillings made of expanding material to those made of contracting material. It was further shown that the polishing procedure caused fracturing of both the unsupported enamel and amalgam margins thus widening the defects considerably.
Pyruvic acid as an etching agent
Authors: RETIEF D. H. , BISCHOFF J. , VAN DER MERWE E. H. M.
Published: June 2007

Phosphoric acid at different concentrations has been extensively used as an etching agent to improve bonding of dental materials to enamel surfaces. Recently attention has been drawn to the possible use of polyfunctional organic acids as conditioning agents.

The object of this investigation was to determine the optimal concentration of pyruvic acid as an etching agent. A commercial composite resin with an intermediary bonding system supplied with 37% H3PO4 as an etching agent was used as the control system. In addition, a comparative study was carried out to evaluate 37% H3PO4, 20% lactic acid and the optimal concentration of pyruvic acid as conditioning solutions.

Etching enamel surfaces with 10% pyruvic acid resulted in the optimal tensile bond strength of the resin to etched enamel surfaces. The use of 10% pyruvic acid did not adversely affect the bond strength of the resin system when compared to enamel surfaces etched with 37% H3PO4 for the same time period. Significantly lower tensile bond strengths were recorded on enamel surfaces etched with 20% lactic acid. The rate and depth of etching obtained with 37% H3PO4 can be considerably reduced by using 10% pyruvic acid as the conditioning agent.
Assessment of reliability of cineradiographic recording of temporomandibular joint movements
Authors: SAXBY M. S. , FRANKS A. S. T.
Published: June 2007

As part of a cineradiographic study of temporomandibular joint movements, the reliability of the apparatus and techniques has been assessed. The areas of concern were the radiographic procedure, tracing apparatus and tracing technique.

To assess the accuracy of the radiographic procedure, anatomical and radiographic measurements of mandibular condyles were compared. A range of variation of 0.46–0.8 mm was found, which compared favourably to the only previously published investigation. The use of mechanical devices simulating the fundamentals of mandibular movements suggested that the cineradiographic record showed paths of opening and closing separated more widely than occurred in vivo.

The reliability of the tracing apparatus was assessed by calculated misalignments and found to be acceptable.

The subjective error in tracing cineradiographic films by a regular observer was investigated by a point location error method. The error was found to be small and within acceptable limits.
Some morphological aspects of the meatus acusticus externus in connection with mandibular movements
Authors: VAN WILLIGEN J.
Published: June 2007

A method is described to measure volumetric variations in the meatus acusticus externus caused by the movements of the mandible. Simultaneous registration of EMG activity and gnatho‐sounds demonstrated that after tooth contact a slight decrease in volume, followed by some increase in volume takes place within 20–30 ms. The fast volume changes, during and after tooth contact, seem to be correlated to the speed of closure.
The fallacy of facial measurements of occlusal height in edentulous subjects
Authors: TRYDE GERD , MCMILLAN D. R. , CHRISTENSEN J. , BRILL N.
Published: June 2007

A controlled trial was made using fifteen subjects and making 120 measurements with a caliper gauge between marks disposed on the upper lip and the point of the chin when maxillo–mandibular relationships were altered vertically by known amounts within a range of 6 mm. It was found that mean facial measurements could account for only half of the skeletal movement involved. The variability of soft tissue translation in relation to skeletal movement led to the conclusion that such facial measurements are inappropriate to clinical practice.
The linear model: a statistical tool applied to psychophysical research in dental prosthetics
Authors: STOLTZE K. , TRYDE GERD , MCMILLAN D.R. , MORIMOTO T. , SPANNER O. , BRILL N.
Published: June 2007

The construction of a linear model is described, and its function in analysing variations in the perception of comfortable mandibular occlusal positions is explained. In principle, the model combines analyses of variance and regression in a number of simple computer operations. Data from a clinical study were used to demonstrate the analytical capacity of a specific model, designed to estimate the effect of factors, which were supposed to influence the perception of comfortable mandibular positions.
Long‐term changes in the perception of comfortable mandibular occlusal positions
Authors: TRYDE GERD , STOLTZE K. , MORIMOTO T. , SALK D. , BRILL N.
Published: June 2007

The aim of this study was to disclose, whether use of a screw jack device to set the distance between the jaws, would contribute towards a stabilization of the magnitude and position of a comfortable zone of mandibular positions or even eliminate it. Thirteen subjects participated in each of fifteen experimental sessions distributed over a 3‐week period. Throughout the investigation the zone prevailed at an average width of 1.3 mm. The gap shrank 0.08 mm on average per experimental session. Although this latter value was found to be significant statistically, it can hardly be of clinical importance, considering the time needed for a total contraction of 0.8 mm to develop.
The construction of a crown for clasp‐bearing teeth
Authors: STERN NOAH , BEN‐LAVEE ARIE , GRAJOWER RAPHAEL
Published: June 2007

A method is described for the fabrication of clasp‐bearing crowns. The technique involves the preparation of a thin gold transfer coping, on to which the bulk of the crown is cast in a later stage.
The variation in contact angle of a fissure sealant on enamel surfaces
Authors: BREAKSPERE ROBERT J. , WILTON ALLAN
Published: June 2007

For strong adhesion of ultraviolet initiated polymeric fissure sealants to dental enamel, a well‐formed tag structure is necessary. This requires that the unpolymerized sealant must be able to flow quickly into the etched surface before polymerization is initiated. The variation in contact angle, θ, with time (the spreading ability) of unpolymerized Nuva‐Seal has been measured on unetched, etched and moist enamel surfaces. This spreading ability varies with the condition of the surface. It is estimated that, in the system investigated, the roughness of the enamel surface is increased by up to 13% on etching, but is reduced again if moisture is present, due to condensation into the etch pits. An etched, moisture free enamel surface is therefore necessary for strong adhesion of polymeric materials.
High temperature behaviour of hydroxy‐ and fluorapatite
Authors: NEWESELY HEINRICH
Published: June 2007

The application of laser rays for caries prevention as for restorative purposes in oral rehabilitation causes severe changes in the structural and textural assembly of the dental hard tissue. Electron microscopical and X‐ray investigations of the new calcium phosphate phases which arise demonstrate a deterioration of the affected tooth regions.
A comparative study of three different approaches to the comfortable zone
Authors: FUJII H. , STOLTZE K. , TRYDE GERD , McMILLAN D. R. , BRILL N.
Published: June 2007

By means of a screw jack device, applied to thirteen edentulous subjects, the comfortable zone was approached in three different ways, by the central, the internal and the external approaches. Correspondingly, the zonal borders behaved differently. Applying the central approach it was found that the initial height of the screw jack had a lingering effect upon subsequent adjustments of the screw. Moreover, lower border data collected by the external approach distinguished themselves form other zonal border data by showing a signifincantly lower susceptibility to successive adjustments. The study suggests that muscle activity is a factor on which the perceptual mechanism relies, when a zonal border is assessed subjectively by a patient.
Polymer adhesion to enamel
Authors: CATE J. M. TEN , KEIZER S. , ARENDS J.
Published: June 2007

For a four‐component acrylate adhesive system the influence of viscosity and penetration on adhesion to enamel was investigated. While low viscous monomer adhesives yield both inter‐ and intraprismatic penetration in enamel after polymerization, highly viscous adhesives result in the former type only. This difference in penetration of the adhesive in enamel is reflected quantitatively in the tensile strength values. Scanning electron microscopic measurements on the tag formation under various circumstances have been carried out. The SEM experiments show, e.g. that at polymerization times less than 1·5–2 min (a clinical necessity) polymer‐tags were usually fractured from the bulk material due to stresses generated.
Dimension discrimination at two different degrees of mouth opening and the effect of anaesthesia applied to the periodontal ligaments
Authors: CHRISTENSEN JOHN , MORIMOTO TOSHIFUMI
Published: June 2007

The dimension discrimination ability of twenty‐five young persons was tested at two different degrees of mouth opening. One reference stick of 10·0 mm and another of 45·0 mm was placed between the teeth, alternating with test sticks of different heights. The subjects were asked to assess whether a test stick felt higher or lower than the reference stick. The experiment was performed with and without anaesthesia applied to the periodontal ligaments.

Anaesthesia did not impair the discrimination ability. At dimensions in the region of the 10.0 mm stick the incorrect assessments occurred predominantly among sticks higher than the reference stick. Around the 45.0 mm stick incorrect assessments were distributed evenly detween dimensions higher or lower than the reference stick.
The effect of water on the abrasion of restorative materials
Authors: HEATH J. R. , WILSON H. J.
Published: June 2007

The effect of two testing schedules on the abrasion resistance of restorative materials has been investigated.
Tooth tapping ability of young and elderly males and females
Authors: WIDMALM SVEN‐ERIK
Published: June 2007

The ability to perform high frequency tooth tapping movements was studied in young dentulous, elderly dentulous and elderly edentulous subjects of both sexes as a possible test of the overall efficiency of the masticatory motor apparatus and related structures.

Tapping frequency was measured during a test period of 90 s by counting the number of taps per 5 s intervals. It was found that observed values of tapping frequency could be fitted to an exponential equation with a high degree of fit for 90% of the young subjects and for 60% of the elderly subjects. The values of the remaining elderly subjects were best fitted to straight lines. The elderly subjects could thus be regarded as belonging to two different populations which were differently affected by advanced age and loss of teeth regarding their tooth tapping ability.

Young dentulous subjects had the highest starting frequency (6·1 Hz) followed by elderly dentulous (5·5 Hz) and elderly edentulous subjects (4·9 Hz). The lower limits were 4·6 Hz for young dentulous subjects, 4·1 Hz for elderly dentulous and 3·7 Hz for elderly edentulous subjects.

The average group means pointed all in the same direction that increased age and loss of teeth change the functional ability by deteriorating it.
The performance of ultraviolet lights used to polymerize fissure sealants
Authors: YOUNG K. C. , HUSSEY M. , GILLESPIE F. C. , STEPHEN K. W.
Published: June 2007

The performances of ultraviolet (uv) lights used to initiate polymerization in fissure sealant systems were studied with a view to establishing recommendations for improving clinical results. The relationship between the setting time of an uv polymerized sealant (Nuva‐seal) and the intensity of radiation applied was first established. This was compared with the intensity and distribution of radiation from seven Nuva‐lites and one Quartzlite. It was found that some of the Nuva‐lites did not produce an average intensity of uv radiation sufficient to completely polymerize Nuva‐seal within the manufacturer's recommended exposure times. It is suggested that this may be a factor contributing to the large variation in sealant retention found in the different clinical trials with Nuva‐seal. Finally, a number of recommendations are made to ensure that sufficient uv radiation is applied to all sealant surfaces when Nuva‐seal system is used.
Preparation areas resisting displacement of artificial crowns
Authors: HEGDAHL T. , SILNESS J.
Published: June 2007

The areas of luting cement resisting rotation of artificial full crowns subjected to non‐axial forces were calculated for varying values of preparation diameter, height, and convergence angle. The calculations were performed for regular conical and pyramidal preparations.

The results showed that the resisting areas are larger in pyramidal than in conical preparations. Increasing the convergence angle resulted in an almost linear reduction in resisting area. The reduction was particularly pronounced for preparations of large diameters.
Occlusion between removable dentures and natural teeth
Authors: PIETROKOVSKI JAIME , MEJIAS JUDITH E.
Published: June 2007

Study casts of thirty‐five partially edentulous patients were analysed at their arch level and at the interarch levels. At the arch level the crest of the residual ridge is located lingually to the position of the remaining teeth in the maxilla as well as in the mandible.

The spatial interarch relationship between the residual edentulous ridge and the antagonist natural teeth in the buccolingual plane indicated that the crest of the residual ridge is lingual to the occlusal surfaces of the antagonist teeth.

In the maxilla the positioning of the artificial teeth in the area previously occupied by the natural extracted teeth will place the denture teeth far buccal as well as away from the crest of the residual ridge. Other possibilities are to place the artificial teeth in a cross bite relation or to eliminate the buccal cusps of the replacement teeth. In the mandible the denture teeth can be placed at the position occupied formerly by the natural teeth.
An overhead projection aid for teaching the principle of occlusion
Authors: WISE MICHAEL D.
Published: June 2007

A technique has been presented whereby models which can be animated are used to form a projected image on a screen and thereby demonstrate the principles of occlusion together with principles of articulators. The system can be used alone or in conjunction with clinical slides interjected at relevant places in the discussion. This technique has been found to be a very useful aid in the teaching of occlusion to both graduate and undergraduate students.
Biological testing of dental restorative materials
Authors: TYAS MARTIN J. , BROWNE R. M.
Published: June 2007

The problems discussed are those inherent in standardizing test procedures for dental materials, where the pulp response is studied after the materials have been placed in cavities in teeth. The advantages of cell culture methods are stressed. Standardization is only possible with in vitro methods and the development of these methods is advocated.
A colorimetric study of coffee and tea staining of four composite resins
Authors: GROSS M. D. , MOSER J. B.
Published: June 2007

Colorimetric measurements were made on four composite resins before and after controlled immersion treatments. The four composite resins were: Adaptic (Johnson and Johnson), Prestige (Lee Pharmaceuticals), Addent XV (3M Mfg. Co.) and Smile (Kerr Mfg. Co.).

Specimens of each material were prepared with mylar surfaces and with abraded finished surfaces. Separate groups of specimens of the four materials were immersed in three separate solutions for 12 days at 55°C. The three solutions used were: a control solution of distilled water, a solution of distilled water and coffee and a solution of distilled water and tea.

For all materials and surface finishes, immersion in coffee and tea produced significantly greater colour changes than distilled water. Coffee produced significantly greater colour changes than tea with the exception of ‘Prestige’ and ‘Addent XV’ with finished surfaces. When immersed in a tea solution, speciments of the same material with differing surface finishes showed greater differences in colour change than when immersed in control and coffee solutions. The relative colour changes of the four materials due to the immersion procedures were as follows: ‘Adaptic’ showed the least colour changes and ‘Smile’ showed the most. ‘Addent XV’ and ‘Prestige’ tended to vary between the former two. Comparison and correlation of colorimetry results with visual assessment scores allowed for the expression of the objective measures in subjective terms suitable for clinical purposes.
Tissue reactions to implanted vitreous carbon and high purity sintered alumina
Authors: HOBKIRK J. A.
Published: June 2007

Vitreous carbon and high purity sintered alumina implants were inserted into the iliac crests and mandibles of rabbits. The reactions of the tissues were assessed after periods up to 2 years using resin embedded histological sections.

Both types of material were well tolerated, although the alumina excited a slightly greater tissue response than did the vitreous carbon.

Electron microprobe analysis of the bone around the implants failed to show the movement of known contaminants from the alumina and vitreous carbon into the surrounding tissue.

Observations are made on the reactions of the tissues to the implants and the effect of cortical penetration and implant movement.
Connectors for mandibular partial dentures: use of the sublingual bar
Authors: BASER R.M. , TRYDE GERD
Published: June 2007

The types of connectors commonly used for mandibular partial dentures are discussed. The concept of the sublingual bar is examined and a description of the relevant clinical and technical procedures is presented.
The development of an artificial saliva for in vitro amalgam corrosion studies
Authors: DARVELL B.W.
Published: June 2007

Published data, consideration of chemical and physical properties and the requirements of amalgam corrosion testing were used to formulate an artificial saliva. A previously described method was used to determine the relevance of a number of human saliva constituents. Some results of those tests are described. Practical problems are discussed, and necessary further developments outlined. A number of other applications are suggested.
Mechanism of adhesion of polymers to acid‐etched enamel
Authors: SOETOPO  , BEECH D.R. , HARDWICK J.L.
Published: June 2007

The tensile bond strengths of composites to enamel etched with various concentrations of phosphoric acid have been shown to correlate closely with the phase diagram for the system Ca(OH)2/H3PO4/H2O. Bond strengths were independent of the adhesive used and were a maximum when using ∼20% phosphoric acid as etchant. High bond strengths were obtained with 2% phosphoric acid etchant without ‘tag’ formation, after short term water immersion. Washing the enamel for 60 s instead of 15 s after etching significantly increased the bond strengths obtained with 16 and 30% acid but not with 2%. Etching enamel with phosphoric acid results in deposition of calcium phosphates, which must be removed to give optimal bonding.
Dynamic and static recordings of the comfortable zone
Authors: BRILL N. , FUJII H. , STOLTZE K. , TRYDE G. , KATO H. , Møller E.
Published: June 2007

A dynamic and a static method of assessing the comfortable zone by means of a screw jack were compared in 12 subjects. Recorded under dynamic conditions the average width of the comfortable zone was approximately 3·0 mm, and under static conditions approximately 5·0 mm (P < 0·0001). It is suggested that in the dynamic experiments the larger output from receptors in the chewing system was responsible for the narrower zone, i.e. the more precise assessments of the comfortable zone.
Effect of the curing cycle on some properties of a polymethylmethacrylate denture base material
Authors: JAGGER R. G.
Published: June 2007

The properties of a denture base material may be modified by altering both the temperature and the time of heating during the curing cycle. In this study a polymethylmethacrylate denture base containing no crosslinking agent was polymerised using four different curing cycles. The structure of the materials so obtained was investigated by an acid etching technique. The materials were characterized with respect to degree of cure, strength and water sorption.

It was concluded that: 1. No correlation was observed between the curing cycles and polymer structure.

2. The curing cycle of 7 h at 70°C plus 1 h at 100°C produced best indentation strength and tensile strength.

3. A correlation was observed between residual monomer, indentation resistance, tensile strength and water sorption. This suggested that residual monomer concentration is the most important parameter in the determination of the properties of the material investigated in this study.
The clinical significance of median occlusal position
Authors: MCNAMARA DAVID C.
Published: June 2007

The harmony of the occlusal components of the teeth, mandibular joint and muscles, were investigated in 180 human subjects by clinical, dental articulator, radiographic and electrodiagnostic methods. Significant correlations were found between disharmony of these components at median occlusal position (MOP), and with pain‐dysfunction of the masticatory system. Using the standardized stimuli of opening the jaw wide and snapping it shut automatically into MOP, temporalis and masseter muscle co‐ordination and somesthetic reflex effects were quantified. The interval from tooth contact (s) to reinstitution of EMG activity (x), and the EMG silent‐period duration (SP), were prolonged in the patients but returned to within the control range with elimination of the pain‐dysfunction. Muscle incoordination with mandibular dysfunction was prevalent in the patients, and the incidence of osteoarthritis was greatest in those with persistent symptoms. The hypothesis was supported that disharmony of MOP exists in pain‐dysfunction patients—while successful occlusal therapy leads to the restoration of the harmony within the biologic range. This implies physiological significance to this hitherto clinically neglected occlusal position.
Microhardness studies on the setting characteristics of fissure sealants
Authors: YOUNG K.C. , CUMMINGS A. , MAIN C. , GILLESPIE F.C. , STEPHEN K.W.
Published: June 2007

The hardness of five fissure sealants was measured using a Wallace Microhardness Tester and found to continue to increase long after the initial setting. The effect of the intensity of radiation and exposure time on the setting of two u.v. activated sealants (Nuva‐seal and Alphaseal) was also investigated, with higher intensities producing both a more rapid set and greater final hardness. Alphaseal required longer exposure at a given intensity of u.v. radiation to achieve the same hardness as Nuva‐seal, and displayed relatively slow setting in depth, which could give rise to incomplete polymerization during clinical use, resulting in early sealant loss. Thus special care must be taken to ensure that Alphaseal receives an adequate exposure to u.v. radiation, and sources which are suitable for setting Nuva‐seal may not be sufficiently powerful when applying Alphaseal.
Viscoelastic properties of elastomeric impression materials
Authors: INOUE K. , WILSON H. J.
Published: June 2007

The variation of torsional shear modulus with time for several commercial elastomeric impression materials has been determined. The effects of mixing proportions and temperature on rheological properties are presented. The relevance of these properties to the actual use of these materials are discussed.
Charecterization of hydroxyapatite powders and compacts at room temprature and after sintering at 1200°C
Authors: ROOTARE HILLAR M. , CRAIG ROBERT G.
Published: June 2007

Synthetic HAP made in the laboratory as ‘synthetic bone’ may be a possible replacement or repair material, since the mineral phase of dental hard tissue and bone is essentially hydroxyapatite in form. Hydroxyapatite or modified compositions of HAP appear to offer possibilities as a substitute for the original material provided by nature.

A high surface area (70·4 m2sol;g) commercially available hydroxyapatite (HAP) of poor crystallinity was converted to a highly crystalline HAP through sintering at 1200°C in an atmosphere of steam and nitrogen. Compacts were made of the powdered HAP from 500 to 25,000 psi and sintered under the same conditions. The changes in the resulting pore volumes, pore sizes, pore size distributions, densities, and surface areas of the sintered compacts were determined by mercury porosimetry. A 20‐fold reduction in open pore volume for sintered compacts was observed. For compacts made at pressures above 5000 psi, the reduction in open pore volume was compensated for by the formation of closed pore volume. The sintering mechanism was attributed mainly to neck formation, growth between particles, diffusion, and plastic deformation.
Activity of temporal and lip muscles during swallowing and chewing
Authors: INGERVALL BENGT
Published: June 2007

The activity of the anterior and posterior portions of the temporal muscle and in the upper and lower lips were studied electromyographically in 50 girls, aged 9–13 years with normal occlusion.

The recordings were made during swallowing of water, saliva, apple and peanuts as well as during chewing of apple and peanuts.

The maximal mean voltage amplitudes during swallowing varied notably with the test medium and were larger for solid than for fluid media. The amplitudes were the same for both portions of the temporal muscle, but always greater for the lower lip than for the upper. Many girls swallowed fluid media without demonstrable activity of the anterior portion of the temporal muscle, while absence of demonstrable activity in the lips was rare. No correlation was found between the degree of activity of the lips during swallowing of fluid and solid substances.

The amplitudes during chewing were the same for both portions of the temporal muscle, but larger for the lower lip than for the upper.

The amplitudes found for the two portions of the temporal muscle and for the upper and lower lips were intercorrelated both during swallowing and chewing.

No correlation was found between the amplitudes from the lower lip and from the temporal muscle during swallowing. The amplitude from the upper lip during swallowing was correlated only with that from the posterior portion of the temporal muscle. Palpation of muscular activity of the temporal muscle during swallowing is of little or no value for estimating the degree of activity of the lip during swallowing.
In vitro toxicity tests of zinc phosphate cement
Authors: TYAS M. J.
Published: June 2007

BHK‐21 (C‐13) cells were exposed to freshly mixed zinc phosphate cement for 0·5, 1 and 2 h in a simulated cavity apparatus. The effect on the cells was evaluated by quantitative measurement of acid phosphatase and succinic dehydrogenase reaction product in order to determine organelle membrane permeability. After 0·5 h cellmaterial contact there was no significant effect. After 1 h cell‐material contact, there was slight labilization of the lysosomal membranes, and a significant decrease in succinic dehydrogenase activity. The mean overall stain density in the experimental cells was 109% and 57% of the control values for acid phosphotase and succinic dehydrogenase respectively. After 2 h cell‐material contact, there was significant labilization of the lysosomal membranes, and also labilization of the mitochondrial membranes. The mean overall stain densities were 114 % and 75 % of the control values for acid phosphatase and succinic dehydrogenase respectively. The relevance of these findings to the in vivo situation is discussed.
Age changes in the perception of comfortable mandibular occlusal positions
Authors: MCMILLAN D.R. , TRYDE G. , STOLTZE K. , MAEDA T. , BRILL N.
Published: June 2007

It has been shown that a zone of comfort in maxillo‐mandibular relationships in edentulous subjects can be identified with some precision. Whilst the neurophysiological mechanism involved has not been explained fully, the phenomenon is influenced by starting position and by fatigue. This experiment was set up to test the hypothesis that age is another significant factor in perception of the comfortable zone.

A group of seventeen subjects with a mean age of 62 years and an equivalent younger group, the mean age of which was 28 years, were tested with Timmer screw jacks applied using the central approach to record the upper and lower limits of the zone fifteen times in succession for each subject.

A linear statistical model was used to analyse the data from upper and lower borders separately. The results showed that the effect of making successive adjustments, whilst not significant statistically in the young group, was significant in the more elderly. Regression lines from the young group data were horizontal signifying the high degree of accuracy with which their perceptual mechanisms worked: the upwards inclination of those from the more elderly was interpreted as showing that initial appreciations were subjected to constant correction.
Copper in dental amalgams
Authors: SARKAR N.K.
Published: June 2007

The relationship between microstructure and physical and electro‐chemical properties of copper‐containing dental amalgams has been discussed in an attempt to understand the role of copper in currently used dental amalgams.
Comparison of the accuracy of denture bases by a non‐parametric method
Authors: SONI P. M. , POWERS J. M. , CRAIG R. G.
Published: June 2007

A comparison of the accuracy of denture bases made from a conventional acrylic and four modified acrylic resins was made with the use of a non‐parametric method. Twenty‐five identical maxillary stone casts were made and five dentures for each resin were processed by conventional compression moulding techniques. The fit of each denture at the molar‐to‐molar region on its cast was evaluated by five evaluators who independently ranked the twenty‐five dentures from best to worst fit after processing, after polishing, and after storage in water at 37°C for 42 days. The ranking data were analysed by Kendall's coefficient of concordance, the Kruskal‐Wallis statistic, and the Mann‐Whitney test. Excellent agreement among observers was obtained. After storage in water, two modified acrylic resins, Hydrocryl and Vitalon II, had a better fit on their casts than the conventional acrylic, Lucitone Hypro. Lucitone 199 had the same and Hircoe had a poorer fit than Lucitone Hypro.
The effect of silicate cement on the mitochondria and lysosomes of cultured cells assessed by quantitative enzyme histochemistry
Authors: TYAS M. J.
Published: June 2007

The cytotoxic effect of the silicate cement ‘Silicap’ was evaluated in an in vitro system which simulates the clinical usage of the material. BHK‐21 (C‐13) cells on cover slips were exposed to the freshly mixed material for 1h, and stained for the demonstration of succinic dehydrogenase and acid phosphatase. The mean stain density for succinic dehydrogenase and acid phosphatase in the experimental cells was 77% and 153% of the control values respectively. The mechanism of cytotoxicity of ‘Silicap’ is discussed.
A clinical study of marginal integrity and tarnish behaviour of three Cu‐rich amalgam systems
Authors: LARSON T. H. , SABOTT D. , COOLEY R. , GREENER E. H.
Published: June 2007

Three high Cu‐γ2 free amalgams and one conventional amalgam were used in a clinical study to evaluate degree of marginal integrity and surface discoloration occurring for time periods of up to two years. Two hundred and seventy restorations were placed in Class I and II cavities in sixty‐two paedodontic patients. Amalgams were prepared from conventional alloy, Cu admixed, Dispersalloy and three parts 50Ag‐20 Sn‐30Cu mixed with one part conventional alloy. Restorations were evaluated by three groups of clinicians. Ridit means obtained from all three groups of evaluations were in good agreement. The lower ridits indicate better marginal integrity and less tarnish. Marginal integrity of amalgams prepared from Cu‐admix did not differ appreciably (0.41) from the ridit associated with initial placement (0.39). Conventional amalgams had the highest ridit (0.65) for marginal integrity whereas the ternary/conventional and Dispersalloy restorations were intermediate (0.55 and 0.52). The ridit for tarnish and surface discoloration was decidedly higher for the Cu‐admix (0.73) than for the other systems investigated which had ridits of the order of 0.50 compared to an initial ridit for tarnish of 0.28.
A comparison of two methods of quantifying masticatory pressures developed under dentures with variable occlusal widths
Authors: ROEDEMA WILLIAM H.
Published: June 2007

Pressures developed during mastication with removable dental prostheses have beer quantified by two methods. This pilot study (1) compares the peak pressure method of pressure quantification with the integrated curve method of quantification and (2) continues the exploration of the effect of the width of the occlusal table on pressures developed under dentures.

A set of specially designed experimental dentures was constructed for one individual. The mandibular experimental denture contained a series of pressure transducers by which masticatory pressures were recorded. These pressures were monitored between the denture base and the residual ridge tissues. Several interchangeable posterior occlusal segments, varying only in the width of the occlusal table, were fabricated for the opposing maxillary denture.

Masticatory pressure and total ridge pressure were quantified by the integrated curve method and the peak pressure method. Both methods indicated a direct relationship between masticatory pressures produced and the width of the occlusal table. A similar direct relationship between total ridge pressure and occlusal width was suggested statistically by the integrated curve method, and graphically by both methods.
The Langerhans cell density of palatal epithelium in denture and non‐denture wearers, as correlated with other parameters of the palatal mucosa
Authors: VAN MENS P. R. , JAMES J.
Published: June 2007

A quantitative histological investigation was carried out on biopsy specimens taken from patients suffering from denture sore mouth. The results were compared with those obtained in investigations on denture and non‐denture wearers. The sections were studied by standardized quantitative morphometric methods. After 4 years the denture bearing palatal epithelium from both groups, normal denture wearers and the patients suffering from denture sore mouth did not show changes in mean thickness of the epithelium as compared with the controls. The mitotic index in denture bearing epithelium from patients suffering from denture sore mouth was three times lower than in the epithelium of the normal denture wearers. The number of Langerhans cells correlated with the mitotic indices of the group of denture wearers and nondenture wearers. The group of denture sore mouth patients showing a low mitotic index showed a high number of Langerhans cells in their palatal epithelium. The three groups of patients investigated did not show differences in density of mast cells in the lamina propria of their palatal epithelium.
Evaluation of endosseous implant abutments as a base for fixed prosthetic appliances. A preliminary clinical study
Authors: WIE H. , LARHEIM T. A. , KARLSEN K.
Published: June 2007

In the present 2‐year report nineteen Linkow blade implants with a total of twentyseven perforating posts were assessed. All implants included were considered functionally successful and served as abutments for fixed prosthetic appliances. Periodontal probe and radiographic measurements of bone loss around the perforating implant posts, and registratration of plaque and gingival index scores were performed every 6 months.

During the first 4–6 weeks after implantation a vertical bone loss approximating an average of 1–2 mm occurred in the neck area of the implants. After this initial resorption, bone loss proceeded at a slower rate. The mean annual crest reduction was approximately 0.1 mm from the first to the fourth examination, as assessed from radiographic measurements.

Periodontal probe measurements, showing a mean annual crest reduction of 0.2 mm, usually exhibited higher values than corresponding radiographic measurements at both implants and abutment teeth.

At implants there was a significant positive correlation between plaque and gingivitis after 18 and 24 months, but not before that time. No correlation was seen between gingival index scores and the degree of bone resorption.
Book Reviews and Notices
Authors: Rock W. P. , Foster T. D.
Published: June 2007

Books reviewed in this article.

Preventive Dentistry By Leon Silverstone.

The European Journal of Orthodontics Vol. 1 No. 1 January 1979.

Textbook of Oral Biology Ed. by J. H. Shaw E. A. Sweeney C. C. Cappucino and S. M. Meller..

Sectional Dentures By E. Pullen‐Warner and P. R. L'Estrange.

Elements of Dental Materials By R. W. Phillips.
Short term evaluation of counselling and occlusal adjustment in patients with mandibular dysfunction involving the temporomandibular joint
Authors: KOPP S.
Published: June 2007

The effect of counselling and occlusal adjustment was investigated in thirty patients with mandibular dysfunction involving the temporomandibular joint (TMJ). The patients were examined at three visits 6 weeks apart. At the first visit all patients received counselling. At the second visit they were divided into two groups, one receiving occlusal adjustment and the other not receiving treatment. The degree of mandibular dysfunction was assessed by the patients according to a five grade scale and by the clinical dysfunction index according to Helkimo (1974a). The score of subjective dysfunction was reduced significantly during the period following counselling and 60% of the patients improved. No effect was found on the clinical dysfunction score. The score of clinical dysfunction was reduced significantly during the period following occlusal adjustment and 67% of the patients improved. No further effect could be detected on the subjective dysfunction score. The correlation between changes in subjective and clinical dysfunction was poor, but changes in the subjective score were generally associated with changes in the clinical score. It was concluded that counselling may reduce the subjective symptoms; and occlusal adjustment the clinical signs of mandibular dysfunction involving the TMJ, but that the individual variation in response is substantial.
Roentgenological detection of casting defects in cobalt‐chromium alloy frameworks
Authors: WICTORIN L. , JULIN P. , MÖLLERSTEN L.
Published: June 2007

A method for non‐destructive X‐ray investigation of casting defects in cobalt‐chromium prosthetic frameworks has been developed and tested. The attenuation properties of a cobalt‐chromium alloy were studied. A dental X‐ray machine with a tube voltage working at 70 kVp and a focus‐film distance of 45–50 cm on dental ultraspeed film made it possible to detect defects representing 10% or less of the thickness of cobalt‐chromium details with dimensions between 0.6 and 3.0 mm.

The frequency and site of internal defects in sixty‐six frameworks were investigated. Of the sixty‐six frameworks only two were without roentgenologically visible defects. In the other sixty‐four frameworks 294 pores or cracks were recorded. The defects were mostly situated in the saddles. Porosities occurred in 53% of the saddlebar regions. The results confirmed the need for a non‐destructive routine test of prosthetic frameworks.
Diametral tensile strength of twenty‐three hardened commercial amalgams
Authors: VRIJHOEF M. M. A. , VERMEERSCH A. G. , SPANAUF A. J.
Published: June 2007

In view of the ever increasing number of high copper alloys, it was the aim of this study to investigate the tensile strength property of some of the new alloy systems. The factors alloy system and heat treatment were investigated in relation to the tensile strength. The factors alloy system as well as the heat treatment turned out to be significant. The study suggests that the introduction of ‘dispersion’ alloys did not change the dental picture as to the property of the tensile strength. The selection of strength values in the range of 35–55 MN/m2 for the diametral tensile strength probably have no clinical relevancy as to the prevention of bulk fractures of amalgam restorations under oral conditions.
Influence of muscle pain tolerance on muscle pain threshold in experimental tooth clenching in man
Authors: CHRISTENSEN L. V.
Published: June 2007

Ten adults and ten children exercised maximal voluntary tooth clenching until pains appeared in the jaw muscles, i.e. the muscle pain threshold of tooth clenching was determined. Subsequently, the subjects were instructed to exercise tooth clenching until they were forced to stop because of intolerable pains and exhaustion of the contracting muscles, i.e. the muscle pain tolerance of tooth clenching was recorded, and during these bouts of clenching the pain threshold was also determined. In adults, determination of the pain tolerance decreased the pain threshold by 19%, and in children it either decreased the pain threshold by 20%, or increased it by 56%. It is proposed to introduce the muscle pain tolerance of tooth clenching as an adjunct in the clinical examination of cases of facial pains presumed to originate from the jaw muscles, but the test should be interpreted with caution.
Accidental perforation of the roots of teeth
Authors: TIDMARSH BRIAN G.
Published: June 2007

The causes, prevention and treatment of various types of accidental perforation are discussed.
Investigation of the strain produced in maxillary complete dentures in function
Authors: STAFFORD G. D. , GRIFFITHS D. W.
Published: June 2007

An experiment has been completed to investigate the strain levels obtained on polymethylmethacrylate dentures in function when biting and swallowing. The use of stacked, rosette strain gauges enabled the magnitude of strain in the material underlying the gauge to be calculated and, in addition, the direction of the principal maximum and minimum strain was also calculated.

Strain in the denture base was measured in biting and swallowing with a normal occlusion, when the occlusal contact area was narrowed, and with the rosette gauges.