Accuracy of milled restorations fabricated from direct tooth scans and scans of cast from polyether impression
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Objectives: Compare the accuracy of milled restorations fabricated from direct tooth scans to those made by scans of casts from polyether impressions, measure the total space volume between the restoration and original tooth preparation, and compare the marginal gap and total space volume of milled restorations fabricated with digital CEREC AC to those fabricated with laser inLab. Materials and methods: The right mandibular second molar tooth in an odontofom was prepared for a full I coverage crown. Two acrylic model teeth, #29 and #31 were prepared for Zirconia FPD restoration with chamfer finish lines. Using impression material (Impregum Penta, polyether) the 'master models' were replicated to produce identical stone models. A total of four groups each containing 10 specimens were fabricated. A Cerec inLab Sirona and Cerec inLab MC XL were used to fabricate Vita MarkII crowns, and Zircona frameworks. Each restoration was subsequently cemented on the corresponding die (RelyX[TM] Unicem, 3M ESPE) under 30N of static force. Cemented specimens were embedded in epoxy resin and sectioned Bucal-lingually and mesio-distally. The marginal fit between the restoration and the corresponding individual model was examined utilizing a Metallurgical microscope (Carl Zeiss) at a magnification of 50X. A silicone fit checker (GC Corporation, Tokyo) was used to determine the volume of space between the restoration and the "patient" tooth preparation. The fit checker was applied to the crowns and copings. Each restoration was placed on corresponding die. The weights of the fit checkers were measured (in grams) using an analytical balance (Electronic Analytical, Mettler). The overall gap volume for each sample was determined by dividing the mass of each sample in grams by density. Statistical analysis was conducted for all tests using ANOVA and Tukey-Kramer HSD test at p=0.05. Results: The results were recorded as means [plus or minus] standard deviations and coefficients of variance. The relationship between 8 groups A, B, C, D, E, F, G, H, were analyzed with 2-way analysis of variance (ANOVA). Tukey method was used in conjunction with one-way ANOVA to find which means are significantly different from one another. The significance level (Alpha-[alpha]) was set at 0.05. Comparisons for all pairs were performed using Tukey-Kramer HSD test. A 2-way ANOVA indicated a statistically significant difference in marginal fit was found among the test groups (p[less than]0.05). All statistical analyses were performed using JMP 8.02 software (SAS Institute Inc., Cary, NC). The marginal gaps for laser scan of groups A and B were significantly different from each other, and the same significant difference in marginal fit was found between groups C and D. The marginal gaps for CEREC AC scan of groups E and G were significantly different from each other, and the same significant difference in marginal was found between groups F, and H. CEREC AC scan had significantly better marginal fit than laser scan. CONCLUSIONS: (1) Direct laser scans showed larger marginal gap discrepancy than the laser indirect scans when examined using cross sections (2) Margin gaps measured using cross sectioned specimens fabricated with direct CEREC AC (blue beam) scans and indirect CEREC AC scan showed no significant difference (3) The total volume of the gap between the restoration and preparation was significantly smaller with the direct laser (inLab) scans as compared to laser indirect scans (4) The total volume of the gap between the restoration and preparation was significantly smaller with the direct CEREC AC (blue beam) scans as compared to the CEREC AC indirect scans (5) The marginal gap and the overall volume of the gap between the restoration and preparation was significantly smaller with the digital CEREC AC (blue beam) impressions as compared to digital laser (inLab) impressions.
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact email@example.com.Thesis (MSD) --Boston University, Henry M. Goldman School of Dental Medicine, 2012 (Department of Restorative Sciences and Biomaterials).Includes bibliography: leaves 105-113.
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