Comparability of clinical wear measurements by optical 3D laser scanning in two different centers.

OBJECTIVE: The purpose of this study was to compare the use of different variables to measure the clinical wear of two denture tooth materials in two analysis centers. METHODS: Twelve edentulous patients were provided with full dentures. Two different denture tooth materials (experimental material and control) were placed randomly in accordance with the split-mouth design. For wear measurements, impressions were made after an adjustment phase of 1-2 weeks and after 6, 12, 18, and 24 months. The occlusal wear of the posterior denture teeth of 11 subjects was assessed in two study centers by use of plaster replicas and 3D laser-scanning methods. In both centers sequential scans of the occlusal surfaces were digitized and superimposed. Wear was described by use of four different variables. Statistical analysis was performed after log-transformation of the wear data by use of the Pearson and Lin correlation and by use of a mixed linear model. RESULTS: Mean occlusal vertical wear of the denture teeth after 24 months was between 120µm and 212µm, depending on wear variable and material. For three of the four variables, wear of the experimental material was statistically significantly less than that of the control. Comparison of the two study centers, however, revealed correlation of the wear variables was only moderate whereas strong correlation was observed among the different wear variables evaluated by each center. SIGNIFICANCE: Moderate correlation was observed for clinical wear measurements by optical 3D laser scanning in two different study centers. For the two denture tooth materials, wear measurements limited to the attrition zones led to the same qualitative assessment.

Wear of two denture teeth materials in vivo-2-year results.

OBJECTIVE: (1) To quantify wear of two different denture tooth materials in vivo with two study designs, (2) to relate tooth variables to vertical loss. METHODS: Two different denture tooth materials had been used (experimental material=test; DCL=control). In study 1 (split-mouth, 6 test centers) 60 subjects received complete dentures, in study 2 (two-arm, 1 test center) 29 subjects. In study 1 the mandibular dentures were supported by implants in 33% of the subjects, in study 2 only in 3% of the subjects. Impressions of the dentures were taken and poured with improved stone at baseline and after 6, 12, 18 and 24 months. Each operator evaluated the wear subjectively. Wear analysis was carried out with a laser scanning device. Maximal vertical loss of the attrition zones was calculated for each tooth cusp and tooth. A mixed linear model was used to statistically analyse the logarithmically transformed wear data. RESULTS: Due to drop-outs and unmatchable casts, only 47 subjects of study 1 and 14 of study 2 completed the 2-year recall. Overall, 75% of all teeth present could be analysed. There was no statistically difference in the overall wear between the test and control material for either study 1 or study 2. The relative increase in wear over time was similar in both study designs. However, a strong subject effect and center effect were observed. The fixed factors included in the model (time, tooth, center, etc.) accounted for 43% of the variability, whereas the random subject effect accounted for another 30% of the variability, leaving about 28% of unexplained variability. More wear was consistently recorded in the maxillary teeth compared to the mandibular teeth and in the first molar teeth compared to the premolar teeth and the second molars. Likewise, the supporting cusps showed more wear than the non-supporting cusps. The amount of wear did not depend on whether or not the lower dentures were supported by implants. The subjective wear was correct in about 67% of the cases if it is postulated that a wear difference of 100µm should be subjectively detectable. SIGNIFICANCE: The clinical wear of denture teeth is highly variable with a strong patient effect. More wear can be expected in maxillary denture teeth compared to mandibular teeth, first molars compared to premolars and supported cusps compared to non-supported cusps. Laboratory data on the wear of denture tooth materials may not be confirmed in well-structured clinical trials probably due to the large inter-individual variability.

Laboratory methods for evaluating the wear of denture teeth and their correlation with clinical results.

OBJECTIVE: To correlate different laboratory wear simulation protocols for three denture tooth materials with clinical wear results of the same materials. METHODS: Three denture tooth materials were evaluated for which clinical wear data of posterior denture teeth were available: DCL (double cross-linked PMMA with organic fillers; Ivoclar Vivadent), experimental material EM (double cross-linked PMMA with organic fillers; Ivoclar Vivadent), and NFC (PMMA with inorganic nanofillers, Candulor). The clinical data on the three denture tooth materials (10 subjects for each material) came from clinical studies conducted at three different locations. The investigators sent the impressions to one center where they were analyzed with the same methodology and by the same operator. Four different wear simulation protocols were evaluated in a chewing simulator (Willytec) with integrated thermocycling (5 °C/55 °C) and 8 specimens for each group: (A) molar denture tooth against premolar denture tooth with 1 mm sliding, lifting, 5 kg load; (B) standardized conical ceramic stylus (Ø2.3 mm); (C) standardized ball-shaped ceramic stylus (Ø6 mm); (D) standardized conical stylus (Ø2.3 mm) cut with a special bur from the denture tooth material to be tested. For the protocols B, C and D, the stylus slid under a load of 3 kg for 3 mm on the flat specimen without lifting. All the tests were run for 100,000 chewing cycles. The maximum vertical wear of the material and stylus was quantified on replicas of improved white stone with the etkon es1 scanner and the match 3-D software. RESULTS: The ranking of the materials according to mean clinical vertical wear after 1 year was as follows: DCL=EM>NFC. The ranking of the materials according to the mean vertical wear was as follows (ANOVA post hoc Tukey B, p<0.05): group A: NFC>DCL=EM; group B: NFC>DCL>EM; group C: NFC>DCL=EM; group D: DCL=EM>NFC. SIGNIFICANCE: Only the results of the experimental setup with standardized antagonists of the same denture tooth material against flat specimens were similar to the clinical wear results with a comparable relative difference in mean vertical wear between the materials. When evaluating denture teeth for wear in the laboratory, a protocol should be applied that matches the clinical wear results.