الفهرس 
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Abstract
This in vitro study was conducted to evaluate the effect of three different fabrication techniques on trueness and internal fit of custom-made Polyetheretherketone (PEEK) posts.
Materials and Methods: 10 extracted single root mandibular second premolars were selected for this study. The inclusion criteria for teeth were caries free, fully developed root ends, and closed apical foramina. Teeth were prepared and post space preparation was done to length 8mm. Then teeth were scanned using primescan intraoral scanner and After scanning was completed, the digital model was created after rendering the acquisition phase. The data were exported with STL format. then the custom-made PEEK posts were designed by dental CAD software (CEREC, Dentsply Sirona). In addition, the designed virtual posts were extracted as a stereolithography (STL) file to enable its use as the base data for the trueness evaluation (STLDe).
Designs will be divided into three groups according to the proposed fabrication technique: (group A: milled post and core restorationss), (group B: pressed post and core restorations) and (group C: additively manufactured post and core restorationss). The designed posts (De) were then exported into a stereolithography file (STLDe) which is then transferred to the milling machine for the direct fabrication of milled post and core restorationss as well as milling of CAD wax for pressing and to a desktop 3D printer for the production of additively manufactured post and core restorationss (10 posts for each group). To evaluate the trueness of each custom-made post produced from different techniques, each post is scanned using a desktop scanner and is stored as an STL file (STLMi 1-10, STLPr 1-10, STLAm 1-10). The designed virtual posts were also stored as an STL file during the CAD process (STLDe). The STL files of the scanned and designed virtual posts were loaded on the 3-dimensional (3D) inspection software (Geomagic Control X 3D systems, Rockhill, SC). The designed virtual posts were set as the reference data then the scanned virtual posts were superimposed on the reference data. The difference values of the superimposed data were analyzed through the 3D compare function in the inspection software.
While to evaluate the internal fit of each post, The post space was coated with a thin layer of petroleum jelly and the fitting surface of each post was coated with light body impression material and it was carefully seated on its corresponding tooth. After complete polymerization, the excess silicone was carefully removed with a scalpel; therefore, the space between the post and post space was filled with the silicone replica then the post was carefully separated from the tooth so that the impression material didn’t fall off the post.
Each post covered with impression material is scanned using the same intraoral scanner (primescan) and stored as STL file named STLR. Then the STL files were loaded on the 3D inspection software (Geomagic Control X) and superimposed on the STL files of the scanned posts of each subgroup in the order of initial alignment and best-fit alignment. The difference values of the superimposed data were analyzed through the 3D compare function in the inspection software.
A color-difference map (qualitative data) and a report (quantitative data) of the projections were obtained for every single superimposition process.
Data was recorded, tabulated and analyzed. Internal fit at different measurement areas data were analyzed using two-way mixed model ANOVA. Comparison of simple effects were done utilizing Bonferroni correction with the pooled error term from the main ANOVA model. Other data were analyzed using one-way ANOVA followed by Tukey’s post hoc test. Correlations were analyzed using Spearman’s rank order correlation coefficient.
Results: Regarding the 3D trueness, the 3D surface-to-surface comparison denoted that the highest deviation from the reference design was in the additively manufactured post and core restorations group, followed by the pressed and milled post and core restorations groups with insignificant difference between the two groups. For the internal fit, the 3D comparison denoted that the additively manufactured post and core restorations group showed the highest deviation of the posts covered by silicon replica from the reference posts while the wasn’t a statistically significant difference between the milled and pressed post and core restorations groups. The internal fit of posts fabricated by pressing and milling techniques at different measurement areas didn’t show a significant difference however, for the additively manufactured post and core restorations, the internal fit at the apical area was significantly lower than other areas.