Comparison of two Impression Methods for Clinical Wear Measurement

Objective: To test the hypothesis that an individually fitted partial impression tray (IT) provides more accurate replicas for the wear measurement in vivo than conventional partial trays (CT). Methods: Thirty posterior restorations (5 Class I, 25 Class II, 13 premolars, 17 molars) were placed in 29 patients using Tetric EvoCeram and Syntac Classic. One week and 6 months after placement impressions were taken with a CT (Systemp Trays Posterior/Virtual light & putty) and with an IT (Light Tray/Virtual light) which reached until the tooth equator and had an uniform impression space of 0.5 mm. The impressions were poured with white plaster (Fuji Super Hardrock). The replicas were scanned (step distance 30µm) and matched with the Laserscan 3D device/Match 3D software (Willytec). The reference enamel areas were selected by means of intraoral pictures with marked stops in centric occlusion. The criterion for an acceptable matching was if the standard deviation (SD) was less than 20µm after repeated automatic matching (8000 iterations, 1200 points). Results: The threshold value of 20µm was not reached in 5 cases in the CT group and 8 cases in the IT group; this difference was not statistically significant (Wilcoxon test, p>0.05). Mean SD for valid cases was 14.7±2.7µm for IT and 13.9±2.1µm for CT. The not matchable cases were mainly in molars (CT 5/5, IT IT 6/8) and in situations with the adjacent tooth being absent (CT 3/7, IT 3/7). In only two cases both methods failed to show acceptable matching. Conclusion: Replicas from impressions made with an individually fitted tray did not result in a better match result for the wear analysis in vivo. The probability of a good match result was higher in premolars than in molars and in teeth with an adjacent tooth than in teeth whose adjacent tooth was absent.