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This is a review of the literature concerning wear related to the following materials used in dentistry: dental amalgam, composite resins, and glass-ionomer cements, as well as natural tooth substance. Discussions are included on both in vivo and in vitro studies in which various methods were used to help determine wear resistance.
This study determined the effect of castable ceramic, with and without shading porcelain applied, on enamel wear. The wear produced by conventional dental porcelain was used as a control. Cusp tips from extracted human third molars were precision-machined into cones of enamel approximately 1 mm long. Three groups of nine cones each were abraded against rotating disks of (1) castable ceramic with shading porcelain, (2) castable ceramic without shading porcelain, and (3) conventional dental porcelain. Enamel wear was calculated from microscopic measurements of the enamel cones before and after abrading. Mean and standard deviation values were 1.220 +/- 0.218 for castable ceramic with shading porcelain, 0.639 +/- 0.218 for castable ceramic without shading porcelain, and 0.785 +/- 0.311 for glazed conventional dental porcelain (all values are X 10(-3) cm3). Significant differences were found between castable ceramic with and without shading porcelain and between conventional dental porcelain and castable ceramic with shading porcelain (p less than 0.001 ANOVA and 0.05 Scheffe's test). These findings suggest that castable ceramic with shading porcelain should not be used in regions that will function against opposing natural teeth.
Inlay-onlay composite resin restorations have been introduced to the profession as alternatives to amalgam and direct composite resins. Two-body wear testing was performed on three inlay-onlay resins and one direct composite resins using a machine designed to produce sliding wear. The composite resins were opposed by human enamel, type III gold alloy, and porcelain. Of the investigated materials, the homogeneously microfilled inlay-onlay material showed significantly less wear. The direct composite resin showed significantly the greatest wear. The hybrid inlay-onlay resins showed intermediate wear. The hybrid inlay-onlay resins and the direct composite (small particle, heavily filled) resin created wear tracks in the opposing surfaces while the homogeneous microfill inlay-onlay resin did not. The depth of the observed wear tracks in the opposing surface was sufficiently substantial to warrant further investigation into the wear of materials that oppose composite resin restorations.
Rehabilitation of patients with severe dental wear is a complex diagnostic and restorative problem. As wear occurs, space for restorative materials is lost, and unique treatment techniques are needed to provide good esthetics and function. Use of orthognathic surgery to reposition mandibular anterior teeth and supporting alveolar bone can create a more ideal environment for restorative procedures.
Dental factors commonly associated with signs and symptoms of temporomandibular disorders were investigated in a group of nonpatients. A highly sensitive technique was used to establish the presence of temporomandibular joint (TMJ) sounds. In a discriminant analysis nonworking side interferences, attrition, molar contacts, horizontal range of jaw movement, and morphologic occlusion contributed significantly to the prediction of sounds. Further study of morphologic aspects of the joint and stress-related parafunctions may contribute to the understanding of the development of TMJ sounds. We concluded that TMJ sounds are a fairly common sign associated with mild deviations in certain morphologic and functional aspects of the stomatognathic system.
The wear of ceramic inlay materials and antagonist enamel cups was measured in vitro. Per group, six MOD inlays were adhesively cemented in extracted molars. Castable glass ceramic, pressed glass ceramic, and feldspathic porcelain were used as inlay materials. A microfilled and a fine hybrid composite served as luting agents. The restorations were exposed to an in vitro wear test that corresponds to approximately 5 years of clinical service. The wear in the occlusal contact area was quantified during and at the end of the test with a three-dimensional scanner. Final wear measurements on the inlays (mean +/- SD) ranged from 21.8 +/- 8.8 microns for pressed glass ceramic to 59.0 +/- 37.9 microns for castable glass ceramic. The mean wear of the enamel antagonists ranged from 74.6 +/- 32.9 microns for pressed glass ceramic to 153.2 +/- 61.5 microns for feldspathic porcelain. The wear of the luting composites at the end of the test ranged from 4.9 +/- 5.1 microns for microfilled to 12.3 +/- 6.3 microns for fine hybrid.
This study investigated the influence of occlusal contacts on the location and severity of occlusal wear during various mandibular movements. The study population consisted of 80 dental students with a mean age of 22 years, within the age range of 19 to 25 years. A dentition wear index--in addition to anterior, canine, and posterior subindexes--was derived from a tooth-by-tooth evaluation of casts. Lateral excursive and protrusive contact relationships were obtained by clinical examination. There was no correlation between the distribution of occlusal wear and the type of lateral excursive contact scheme. The location of contacts in protrusive movement demonstrated a distinct correlation with occlusal wear in overall severity and distribution according to segmental wear subindexes. The results indicate that the role of "disclusive protection" in the occurrence of occlusal wear may be questioned; the efficacy of "mutual protection" is similarly unsubstantiated, and the results lend further support to the concept of multifactorial etiology of occlusal tooth wear.
The wear of human dental enamel against amalgam, Concise composite, SR-Isosit Inlay/Onlay composite, Vitadur-N glazed porcelain, unglazed IPS Empress ceramic, and enamel (control) was investigated by use of a modified stress cycling machine. Testing was carried out in water and in citric acid (pH 4) and the enamel-material couples were subjected to 25,000 cycles of wear with a maximum load of 40 N. Tooth profile reduction was measured at baseline and at 5000 cyclic intervals with a computer image analysis program. The depth of the wear scars on material specimens was analyzed with a profilometer. All materials produced increased enamel wear in acid. Vitadur-N glazed porcelain was found to be the most destructive to human dental enamel, and this was closely followed by Empress and enamel.
MOD inlays were made with conventional, coarse hybrid, fine hybrid, and two microfilled composite resins. They were adhesively luted in six extracted human molars for each group and were subjected to longitudinal, in vitro testing. Final wear ranged from 46.8 +/- 18.6 microns for fine hybrid composite resin to 132.0 +/- 39.3 microns for conventional composite resin for the inlays and from 19.3 +/- 6.6 microns for homogeneous microfilled composite resin to 136.3 +/- 65.1 microns for coarse hybrid composite resin on enamel antagonists. The wear of the luting composite resins ranged from 11.2 +/- 11.2 microns to 20.0 +/- 23.6 microns. Marginal adaptation at the beginning of the test exceeded 88.7% of "continuous margin" for all groups in enamel. However, marginal gaps were evident in dentin without dentinal adhesives. Marginal adaptation of the microfilled composite resin inlays deteriorated during loads even when a dentinal adhesive and an inlay primer were used. The margins of the other composite resin inlays remained stable during load application.
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Vital staining of monkey incisor teeth with the incisal dentin exposed to the oral environment by attrition was carried out, with the use of a number of dyes (pH and redox indicators). There was a distinct staining of the coronal dentin, regardless of which dye was introduced into the pulpal cavity. The exposed dentin was stained like the unaffected dentin, with the exception of a narrow centrally located zone that extended from the tip of the original pulp horn to the incisal edge of the tooth. The suggestion is that this zone is not unstained because of exposure of the dentin to the oral environment, but because it coincides with an area of the tissue where the pulpal ends of the dentinal tubules are blocked by atubular hard tissue normally laid down in the pulp horn of incisor teeth.
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The wear of enamel when opposed by different ceramic systems was investigated by use of an artificial oral environment. Cerestore, Dicor, and Ceramco discs were opposed by recently extracted natural teeth. The samples were exposed to 300,000 defined masticatory cycles under physiologic conditions. It was found that the wear mechanisms for Cerestore and Ceramco porcelains were similar, but were distinctly different from that of Dicor. The total volume loss of enamel was 50% less when opposed by Dicor, than when opposed by either the Cerestore or Ceramco porcelains. None of the samples had any external shade applied to their surfaces.
A study was conducted to determine whether the wear resistance of a posterior composite could be improved by maximizing filler particle-to-particle contacts. This was expected to reduce stress concentrations on the resin matrix and thus reduce occlusal wear. A self-curing quartz-filled composite with this design, P-10, was used to restore 90 Class I and II cavity preparations in adult teeth. Restorations were recalled after baseline at six months, one year, two years, and three years to measure wear by direct and indirect evaluation methods. There was no apparent advantage for this material compared with other previously evaluated posterior composites. The average cumulative wear for P-10 after three years was 145 microns. In addition, the restorations were evaluated for color-matching, interfacial staining, secondary caries, marginal adaptation, surface texture, and postoperative sensitivity. This material was not significantly different in those ways from other posterior composite products except in terms of more rapid color change, because it is self-cured.
The influence of variation in contact stress on the sliding-water behaviour of a dispersed amalgam has been investigated. The results demonstrate that: (1) the rate of wear of the amalgam in sliding contact with pins fashioned from human enamel remains virtually constant (0.39 +/- 0.06 micrometer/h-1) throughout the range of stresses encountered in vivo; and (2) the wear process involves adhesive transfer of amalgam to the contacting face of the enamel pin during sliding.
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