Date of Award
Master of Science (MS)
Thompson, Geoffrey A.
Berzins, David W.
Purpose: The purpose of this study was to evaluate the accuracy and precision of die-spacer thickness achieved by the combination of computer aided design and 3-dimension printing technology.
Materials and Methods: An ivorine maxillary central incisor was prepared for an all ceramic crown. The prepared tooth was duplicated by using poly (vinyl siloxane) duplicating silicone and 80 die-stone models were produced using type IV dental stone. Dies were randomly divided into 5 groups with assigned die spacer thickness of (25 μm, 45 μm, 65 μm, 85 μm, 105 μm) (n=16/group). The printed resin copings, obtained from 3D Systems ProJet DP 3000 printer, were cemented onto their respective die-stone models with Relyx Unicem 2 and stored at room temperature until sectioning into two halves, in the bucco-lingual direction. The internal gap was measured at 5 defined locations per side of the sectioned die: (A) facial chamfer, (B) facial mid-axial, (C) incisal, (D) lingual mid-axial, and lingual (E) chamfer. Images of the printed resin coping/die-stone model internal gap dimension were obtained with an inverted bright field metallurgical microscope at 100x magnification. The acquired digital image was calibrated and measurements were made using image analysis software. The results were compared using the mixed models ANOVA with repeated measurements to analyze the paired data and the level of significance was set at .05. The coefficients of variation (CV) were obtained by standard deviation divided by the mean and multiplied by 100.
Results: The accuracy expressed in term of mean differences between prescribed die spacer thickness and measured internal gap width (standard deviation) were 50 μm (10) for the 25 μm group simulated die-spacer thickness, 30 μm (11) for the 45 μm group, 15 μm (14) for the 65 μm group, 3 μm (24) for the 85 μm group, and - 10 μm (32) for the 105 μm group. The precision mean of the measurements, expressed in percentages, ranged between 14 - 33% per the groups.
Conclusions: The accuracy of die spacer thickness showed statistically significant difference for all the groups. The precision of the all groups was above 10% of CV.