Ralph DeLong

Development of an Artificial Oral Environment for the Testing of Dental Restoratives: Bi-axial Force and Movement Control

The integration of two closed mechanical loops was used to produce a force-movement cycle, using servo-hydraulics. Several of the parameters were of interest in clinically-simulated laboratory studies. The system represented the first phase in developing an artificial oral environment.

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.

Clinical Science Cusp Reinforcement by the Acid-etch Technique

Strain gauges were mounted on 12 maxillary pre-molars which were subjected to a sequence of restorative procedures for MOD preparations. An occlusal stress was applied using servohydraulics, and the cuspal flexure was assessed using a strain gauge. Two bonded and three non-bonded restorative procedures were tested for each tooth. The two bonded conditions showed significantly higher cuspal reinforcement when compared with the MOD preparation and the non-bonded restorative procedures. The non-bonded restorations showed some intragroup differences, with one non-bonded composite showing useful cuspal reinforcement. However, this was much less than that afforded by the bonded technique. The deformation of the cusp under occlusal force in restorations bonded by the acid-etch technique showed much less hysteresis when compared with non-bonded restorations.

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.

Biophysical stress analysis of restored teeth: experimental strain measurement

Abstract The substantial amount of literature on biophysical stress analysis of restored teeth is reviewed. Principal methods of analysis include photoelastic analogs, measurement and finite element techniques. It is asserted that although much has been learned from these activities, there is no integrated methodology for analyzing the strength of restored teeth. Such a methodology is proposed, involving both experimental and modelling components which are mutually corroborating. The rest of the paper concentrates upon the experimental component of the methodology, which is based upon strain gauge measurements obtained within the context of a servohydraulics framework. Data are reported on the strain measured in a wide variety of cavity sizes, both unrestored and utilizing a range of materials and techniques in the restored complex. It is shown that intracoronal restorations which feature hard tissue bonding and cuspal coverage yield restorations with significant recovery of stiffness.

Accuracy of two impression techniques with angulated implants

STATEMENT OF PROBLEM Accurate recording of implant locations is required so that definitive restorations are properly supported and do not place additional stress on the implants. Angulated implants may result in inaccurate impressions, and the impression technique may affect the accuracy of the definitive cast. PURPOSE The purpose of this study was to determine the effect the combined interaction of impression technique, implant angulation, and implant number has on the accuracy of implant definitive casts. MATERIAL AND METHODS One definitive stone cast was fabricated for each of 6 experimental groups and 1 control group. All 7 definitive casts had 3 implants arranged in a triangular pattern creating a plane. In the 6 experimental groups, the center implant was perpendicular to the plane of the cast while the outer implants had 5, 10, or 15 degrees convergence towards or divergence away from the center implant. The control definitive cast had all 3 implants parallel to each another and perpendicular to the plane of the cast. Five open tray and 5 closed tray addition silicone impressions were made of each definitive cast. Impressions were poured with type IV dental stone, and a fine tip measuring stylus was used to record multiple axis (X-Y-Z) coordinates on the top surface of the implant hex and on the cast base. Computer software was used to align the data sets and vector calculations determined the difference in degrees between the implant angles in the definitive cast and the duplicate casts. Statistical analysis used repeated-measures ANOVA (alpha=.05) with post-hoc tests of significant interactions. RESULTS The angle errors for the closed and open tray impression techniques did not differ significantly (P=.22). Implant angulations and implant numbers differed in average angle errors but not in any easily interpreted pattern (P<.001). The combined interaction of impression technique, implant angulation, and implant number had no effect on the accuracy of the duplicate casts compared to the definitive casts (P=.19). CONCLUSIONS The average angle errors for the closed and open tray impression techniques did not differ significantly. There was no interpretable pattern of average angle errors in terms of implant angulation and implant number. The magnitude of distortion was similar for all combinations of impression technique, implant angulation, and implant number.

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.