Purpose: To compare the mechanical properties and fracture behaviour of laser-sintered/3D-printed cobalt chromium (LS CoCr) with soft-milled cobalt chromium (SM CoCr) to assess their suitability for use in high-stress areas in the oral cavity. Material and Method: Two computer-aided manufacturing methods were used to fabricate dumbbell specimens in accordance with the ASTM standard E8. Specimens were fractured using tensile testing and elastic modulus, and proof stress and ultimate tensile strength were calculated. Fracture surfaces were examined using scanning electron microscopy. Plate specimens were also fabricated for the examination of hardness and elastic modulus using nanoindentation. Unpaired t-test was used to evaluate statistical significance. Results: LS CoCr specimens were found to have significantly higher ultimate tensile strength (UTS) and proof stress (PS) (p < 0.05) but not a significantly higher elastic modulus (p > 0.05). Examination of the dumbbell fracture surfaces showed uniform structure for the LS CoCr specimens whilst the SM CoCr specimens were perforated with porosities; neither showed an obvious point of fracture. Nanoindentation also showed that LS CoCr specimens possessed higher hardness compared with SM CoCr specimens. Conclusion: LS CoCr and SM CoCr specimens were both found to exhibit uniformly dense structure; although porosities were noted in the SM CoCr specimens. LS CoCr specimens were found to have superior tensile properties, likely due to lack of porosities, however both had mean values higher than those reported in the literature for cast CoCr. Uniformity of structure and high tensile strength indicates that LS CoCr and SM CoCr fabricated alloys are suitable for long-span metallic frameworks for use in the field of prosthodontics.

Bulk-fill restorative material has gained popularity in clinical practice, due to their perceived timesaving aspect. Objective was to compare the properties of bulk-fill direct restorative materials. Filtek Z350 (CR), Filtek One Bulk Fill Restorative (BF), Fuji IX and EQUIA Forte (EF) were compared. Thirty specimens from each material were prepared according to ISO 4049 for three-point flexural strength. Elastic moduli and hardness (n = 20) were evaluated using nanoindentation. Depth of cure (DC) (n = 20) was measured for BF at three different depths (2, 3, 4 mm) and at two irradiation times (20 and 40 s). Wear testing was carried out for three different periods (3, 6, 12 month(s)). All specimens were stored in 37 °C water for 24 h prior to testing. Results were evaluated using one-way ANOVA followed by a post hoc Bonferroni test (p < 0.05). BF and CR showed a significantly higher flexural strength than other groups (p < 0.05), and the highest Weibull modulus was found in CR. BF showed sufficient DC with at least 85%, at all thicknesses. CR and BF also had a high level of translucency than EF and Fuji IX. Significant differences in flexural strength were found among all materials except between Fuji IX and EF. While all material tested are suitable for use clinically, BF and CR have superior properties than GIC based bulk-fill.

Removable partial denture (RPD) frameworks have traditionally been produced by conventional impression making and casting. Due to the popularity of intraoral scanning (IOS) and digital manufacturing, RPD frameworks can be produced by alternative workflows. The purpose of this in vitro study was to assess the seating-related adaptation and deformation of components of RPD frameworks fabricated by different workflows. A partially edentulous mandibular arch was used as the master model. Three RPD framework manufacturing workflows were evaluated: the conventional impression making and casting (Imp-Cast) group, conventional impression making and digital fabrication by selective laser melting (Imp-SLM) group, and IOS and digital fabrication (IOS-SLM) group. According to each workflow, 10 frameworks were produced. The virtual superimposition of seated and unseated frameworks was executed to determine component adaptation (retentive arm, reciprocating arm, and occlusal rest) and component deformation (retentive arm and framework body). The 1-way analysis of variance (ANOVA) test was used to determine the differences among the groups (α=.05). No difference in component adaptation was observed for Imp-Cast and Imp-SLM (P>.05), and both were better than IOS-SLM (P<.001). The least retentive arm deformation was observed for Imp-SLM. Imp-Cast and Imp-SLM showed no difference in framework body deformation (P=.92), and both were better than IOS-SLM (P<.05). The IOS-SLM frameworks appeared narrower than the master model. Frameworks fabricated from conventional casts exhibited comparable adaptation of components. In some comparisons, SLM fabrication was associated with less deformation than casting. Frameworks fabricated from IOS had the greatest adaptation error and deformation. As all the frameworks were seated on the master model without adjustment, the clinical relevance of this study's finding is yet to be determined.

We investigated the effects of lithium disilicate ceramic thickness and translucency on the degree of polymerization of light-cured resin cement using the measure of hardness. Lithium disilicate specimens of three translucencies (low, medium and high) were prepared to four thicknesses (0.5, 1.0, 2.0 and 3.0 mm). A light-cured resin cement was cured through each of the ceramic specimens using a handheld curing light for 50 s. A 3D printed jig was used to achieve a uniform thickness of the resin cement. Directly cured resin cement was used as the control. Hardness was measured using nano-indentation to determine the degree of polymerization of the resin cement. Two-way ANOVA and Tukey post hoc tests were used to evaluate interaction between translucency and thickness. Hardness values from control specimens were assessed using the two-tailed t-test with the Bonferroni approach. The translucency of the specimens significantly influenced the hardness (p < 0.001), where a negative linear relationship between cement hardness and ceramic thickness was present for low translucency and high translucency. However, at a 0.5 mm thickness, all specimens showed similar hardness regardless of the translucency. The translucency of ceramics affected the hardness, and hence polymerization, of light-cure resin cement. However, the effect of increased thickness was a more significant factor.

The purpose of this study was to evaluate and measure the microleakage inhibiting quality of provisional restorations manufactured using computer-aided manufacturing, 3D printing, and chairside molded provisional restorative materials. Fifteen provisional restorations each from 3D printed, milled, and chairside molded were manufactured. All restorations were cemented onto sintered zirconia abutment dies and adhered with zinc-oxide non-eugenol temporary cement. Artificial aging was conducted by thermocycling for 800 cycles to simulate 1 month of clinical use. All specimens were submerged in 2% (w/w) methylene blue for 24 hours at 37°C, sectioned, and analyzed digitally for the distance of dye penetration through image analysis. The data were analyzed using the Kruskal-Wallis test with Dunn-Bonferroni post-hoc. Significant differences in dye penetration depth were observed between all groups except milled vs chairside molded. Light microscopy revealed differences in mean cement thickness for 3D printed, milled, and chairside molded of 83.6 µm (1σ = 31.9 µm), 149.1 µm (1σ = 88.7 µm) and 137.9 µm (1σ = 67.2 µm) respectively. Conclusion: 3D printed provisional restorations were found to have the least amount of microleakage compared to milled and chairside molded provisional restorations.