Investigation of fracture strength and trueness of resin crowns produced with three-dimensional printers on different framework materials

Aim: The aim of this thesis study is to evaluate the effect of different material-manufacturing techniques on trueness, fracture toughness (KD) and fracture types in framework and crown restoration groups. Material and Method: Seventy-two maxillary premolar die (framework) specimens were fabricated using Computer Aided Design-Computer Aided Manufacturing (CAD-CAM) technology, subtractive manufacturing (SM) techniques as polyetheretherketone (Dental PEEK; SM_PEEK), titanium (Titanium tube; SM_TI) and additive manufacturing (AM) as cobalt chrome (Scheftner CoCr; AM_CoCr) (n=24). Seventy-two maxillary premolar crown restoration specimens were fabricated using polymethylmethacrylate (DuoCad Temp; SM_PMMA) as SM, a temporary crown-bridge resin (C&B MFH; AM_CB) and a permanent crown resin (Crowntec; AM_CT) as AM (n=24). Randomly selected 10 samples from each framework and crown group were scanned with an intraoral scanner (Trios 3; 3 Shape AG) and accuracy analyses were performed using a reverse engineering program (Geomagic Control X; 3D Systems) against the main design model reference, and deviations for different regions of the samples were recorded as root mean square (RMS) values (µm). After all framework samples were embedded in acrylic blocks, the connection surfaces of the crown and framework samples were roughened with 50 and 110 μm Al₂O₃ sand, and after primer applications, the samples were cemented with a self-adhesive dual cure resin cement (PANAVIA™ SA Cement). Then, these samples were stored in 37 ºC distilled water for 24 hours and then the fracture strength (KD) test was performed at a head speed of 1 mm/min in a universal testing machine. Accuracy analysis and KD test data were statistically analyzed with one- and two-way analysis of variance (ANOVA) and Tukey HSD test (α=.05). Pearson chi-square test was used to analyze the fracture types of the test groups, and Pearson Correlation test was used to evaluate the correlation between KD and fracture types. Results: According to the results of one and two-way analysis of variance (ANOVA) tests, it was seen that different material-production techniques and their interactions had significant effects on the mean trueness, KD values and fracture types (P<.001). According to multiple Tukey HSD comparison analyses, the highest trueness among the framework groups was observed in the AM_CoCr group on marginal, internal and overall, while in the crown restoration groups, the highest trueness was observed in the marginal region in the AM_CB group, and in the internal, external and overall in the AM_CB and AM_CT groups (P<.05). The highest KD value in the framework groups was determined in the SM_PEEK group (1250.1 ± 87.8 N), in the crown restoration groups, the SM_PMMA group (1237 ± 96.6 N) group and in the framework-crown combination (test) groups, the TI_CB group (1352.62 ± 120.94 N) group (P<.05). It was observed that there was a statistically significant correlation between KD and failure types (P<.001; r2=0.549). Conclusion: It has been observed that different materials and production techniques affect the trueness, KD values and fracture types of framework and crown restorations. CoCr frameworks and resin crowns made with AM technique have higher trueness, more compatible results can be obtained by preferring them in hybrid prostheses and large-complex fixed prosthetic applications. It can be said that KD increases on frameworks obtained from high-performance biopolymer PEEK material of resin crowns made with AM technique. Considering the KD test results of this thesis study in hybrid prosthesis and large-complex fixed prosthetic applications, the clinical use of CB crowns prepared with AM technique on TI frameworks made with SM technique can be recommended. Considering that the failure types of CT crown restorations result in less material loss and are in the form of localized fractures, repairability is more possible in refuse cases when preferred as crown material in hybrid prostheses and large-complex fixed prosthetic applications. Keywords: 3D Printer, CAD-CAM, additive manufacturing, subtractive manufacturing, fracture strength testing.