Maria R. Pintado

The wear of a posterior composite in an artificial mouth: a clinical correlation

Abstract The wear of a posterior composite against a maxillary palatal cusp was studied in an artificial mouth. The coefficient of wear for the composite was 2.58×10 −5 . A retrospective clinical correlation with composite wear in the artificial mouth showed a correlation coefficient of 0.84 at 1 year of wear. The artificial mouth studies support a parabolic relationship between depth of composite wear and time. The ratio of 6 months depth of wear compared to 3 years was found to be 41% which supports the Leinfelder finding (5) of 49%. However, the correlation with the linear studies of Braem (2,3) was good as far as the mean depth of wear at 1 year was concerned. The disagreement between the linear and parabolic studies is small during the early wear process, but becomes serious during a longer term. It is important for future clinical wear studies to resolve the question of the nature of the wear rate curve in posterior composites, if accurate prediction of long term performance is to be achieved.

Variation in tooth wear in young adults over a two-year period

STATEMENT OF PROBLEM Although all the processes of loss of hard tissue are important, attrition on the occlusal surfaces commands our attention. PURPOSE OF STUDY The enamel wear rate of 18 young adults over 2 consecutive years was measured independently by volume loss and mean depth loss. Any significant differences in tooth wear resulting from gender and a clinical diagnosis of bruxism were identified. MATERIAL AND METHODS A strict protocol for dental impressions provided epoxy models, which were digitized with a null point contact stylus. AnSur software provided a complete morphologic description of changes in the wear facets. RESULTS The mean loss for all teeth measured was 0.04 mm3 by volume and 10.7 microns by depth for the first year. CONCLUSIONS These numbers were approximately doubled at 2 years of cumulative wear.

The wear of dental amalgam in an artificial mouth: a clinical correlation

Abstract The wear of dental amalgam by a smear mechanism and amalgam transfer onto the opposing cusp was confirmed by simulated studies in an artificial mouth. The coefficient of wear for dental amalgam was 4.89×10−5. Calculation of the coefficient of friction for the enamel/amalgam couple indicated that friction was overcome by shallow slippage and shear within the amalgam. On the basis of these facts, the good wear performance of both the amalgam and the opposing enamel was rationalized. A retrospective clinical correlation of amalgam wear in an artificial mouth showed a correlation coefficient of 0.938 as far as the mean wear values were concerned. Further the wear rates in both studies were linear except in a narrow region at time zero. The variances, however, in the 2 studies were very different. The desirability of in vitro studies to reproduce the same variance, as well as the same mean values, is a point for further discussion and experimentation.

Measurement of change in surface contour by computer graphics

Abstract Change in anatomic contour due to wear is an important criterion in the evaluation of new restorative materials. This report describes a method of capturing and displaying anatomic surface contours using a combination of computer graphics and servohydraulics. The method can be used to measure the volume change following a change in surface contour. The accuracy of the method was assessed using a sample containing two small depressions of volumes 0.006 mm 3 and 0.0281 mm 3 . The recorded accuracies of the method were 12% and 2.5% respectively. A useful feature of the method is that the graphics enable the operator to visualize the wear in relation to the surface anatomy in addition to quantitatively measuring it.

Wear of enamel and veneering ceramics after laboratory and chairside finishing procedures

PURPOSE This in vitro study compared the wear of enamel against 3 types of ceramics with high esthetic potential (designed for layering techniques): feldspathic porcelain (Creation), aluminous porcelain (Vitadur alpha), and low-fusing glass (Duceram-LFC). Laboratory finishing (glazing/polishing) and chairside polishing with a Dialite kit were simulated to compare their respective effects on wear. METHODS Tooth-material specimen pairs were placed in an artificial mouth using closed-loop servohydraulics. Constant masticatory parameters (13.5 N occlusal force, 0.62 mm lateral excursion; 0.23 second cuspal contact time) were maintained for 300, 000 cycles at a rate of 4 Hz. The occlusal surface of each pair was mapped and digitally recorded before and after each masticatory test. Quantitative changes were measured in terms of depth and volume of wear. Quantitative wear characteristics were assessed by SEM. RESULTS Significant differences were observed (2-factor ANOVA, P <.05). Duceram-LFC generated increased volume loss of enamel (0.197 mm(3)) compared with Creation (0.135 mm(3)) and Vitadur alpha (0.153 mm(3)). Creation exhibited the lowest ceramic wear and lowest combined volume loss (0.260 mm(3); the sum of the data for enamel and the opposing material) compared with Duceram-LFC (0.363 mm(3)) and Vitadur alpha (0.333 mm(3)). The most significant differences among materials were observed in volume loss, not in depth of wear. For all 3 ceramic systems, qualitative SEM evaluation revealed an abrasive type of wear. Wear characteristics of chairside polished specimens were similar to those of laboratory finished specimens (glazed and polished). CONCLUSION Duceram-LFC was the most abrasive ceramic for the antagonistic tooth. Creation ceramic was the least abrasive material and most resistant to wear. Defects, brittleness, and the possibly insufficient toughness of LFC may explain its increased abrasiveness. Laboratory and chairside finishing procedures generated similar results.

The wear of dental porcelain in an artificial mouth

Abstract Simulated occlusal wear studies in an artificial mouth involving enamel occluding on porcelain demonstrated a high coefficient of wear for dental porcelain; in agreement with other workers, an abrasive wear process is postulated. Volume loss due to wear showed good linearity as a function of the number of masticatory cycles with slight flattening at higher masticatory levels. However, the depth of wear curve showed a pronounced deviation from linearity with flattening of the wear rate with time. A parabolic relation exists between volume and depth of wear and correspondingly between time and depth. Based on the coefficient of wear, the intrinsic wear of porcelain appears to be about one order of magnitude greater than that experienced by dental amalgam.

The wear of enamel when opposed by ceramic systems

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.

Comparison of two measurement techniques for clinical wear.

OBJECTIVES Clinical wear of restorations is generally evaluated by marginal integrity over time. In this study, both a subjective and an objective method for wear assessment are compared, and the relative advantages and disadvantages of each are considered. METHODS A surface evaluation technique for quantitative measurement of wear, as developed at the University of Minnesota (UMN) has been compared to the commonly employed method of wear assessment used by Leinfelder (LF). Measurements were made by comparing suitable casts of restored teeth before and after clinical function. Semi-quantitative wear assessment was studied in comparison with detailed quantitative information about the topology of the pre- and post-wear occlusal surfaces obtained from stylus profilometry and processed by imaging techniques. Fourteen model sets of baseline, 2, 3 and 5 year old Class II composite restorations from a Danish clinical trial were evaluated using both techniques. RESULTS In general, after 5 years of function, the digitizing method (UMN) generated wear values that were twice as high, indicating that general wear of restorative materials is underestimated by the LF-method. CONCLUSIONS The comparison clearly revealed the advantages and limitations of each technique. Evaluation of wear by means of the LF technique provides global semi-quantitative data on restoration margins relative to enamel, underestimating general wear of the restorative material. Advanced 3-D measuring techniques such as the UMN method provide extensive quantitative data regarding wear patterns of the entire occlusal surface, i.e. restoration and enamel. Such a highly accurate technique is capable of differentiation between wear behavior of restorative materials early on in clinical studies. In addition, through its digital alignment procedure, the UMN method provides data on accuracy of the replication process used in clinical studies.

The wear of enamel opposing shaded ceramic restorative materials: An in vitro study

The wear rate of intact human enamel opposed by Olympia porcelain gold, Dicor, Ceramco porcelain, and externally shaded Dicor and Ceramco was investigated with an artificial oral environment. The enamel-material couples were subjected to 300,000 masticatory cycles at a maximal occlusal force of 13.4 N while they were continuously bathed with 37 degrees C deionized water. Both the enamel and material surfaces were analyzed by use of a three-dimensional surface monitoring computer program, AnSur, to record the removal of the material and the maximal loss of vertical height. The enamel opposing the externally shaded materials abraded two to five times more than that opposing the unshaded materials and 10 to 15 times more than enamel opposing gold. The wear rates for enamel opposing the gold and unshaded Dicor were similar both in the removal of material and in the loss in vertical height.

Enamel abrasion from ceramic orthodontic brackets under an artificial oral environment

The purpose of this investigation was to examine the potential enamel abrasion on contact with stainless steel and various ceramic orthodontic brackets under a simulated oral environment. Three groups of eight lower premolar ceramic brackets and one group of eight stainless steel brackets were used from four different manufacturers. An upper premolar was brought in contact with the bracket bonded to a lower premolar tooth and subjected to a lateral excursion type of movement by the artificial oral environment. A constant load of approximately 2 lb was used for the masticatory force. The rate of chewing was 1 cycle/sec. The teeth were subjected to 15, 60, and 100 masticatory cycles. The before-and-after occlusal surfaces of the upper premolars were compared by means of a computerized profiling system and the enamel volume loss was calculated. Qualitative changes, such as rate of enamel wear, were examined visually by means of computer graphics and the scanning electron microscope. Abrasion scores (mean +/- SD) in mm3 were 0.015 +/- 0.01 from the metal brackets and 0.135 +/- 0.103, 0.255 +/- 0.242, and 0.581 +/- 0.524 from the three ceramic bracket groups. The abrasion scores were significantly different at p less than 0.05. Ceramic brackets caused significantly greater enamel abrasion than stainless steel brackets. Artificial mouth in vitro testing gave a good indication of clinical performance of orthodontic brackets.