Evaluation of the mechanical properties of implant-supported permanent crowns manufactured by additive and subtractive techniques: an in vitro study

Background The development of composite resin materials that can be used with additive manufacturing techniques has contributed to the widespread use of 3D printers for producing implant-supported permanent crowns. The number of studies evaluating the surface roughness and fracture resistance of these materials is limited. This study aims to evaluate these features of implant-supported crowns produced by additive manufacturing using an experimental setup as close to clinical conditions as possible, and to compare the results with those of crowns produced by subtractive manufacturing methods. Crowns produced in three different thicknesses were used to determine the optimal wall thicknesses applicable in clinical practice. Methods In this in vitro study, two composite resins and one hybrid ceramic were used. A total of 180 crowns, produced in three different thicknesses (1.0, 1.5, and 2.0 mm), were cemented onto titanium abutments. Half of the crowns were designated as experimental, whereas the other half served as control groups (n = 10 for each material and thickness group). The samples in the experimental group were subjected to thermal aging to simulate one year of clinical aging. Surface roughness measurements were taken using a profilometer, and a universal testing machine was employed to assess fracture resistance. Two-way ANOVA was used to compare group means, Duncan’s post-hoc test was used for the comparative evaluation of subgroups, and a t-test was used to compare surface roughness results before and after thermal aging. Results Compared with those produced by the subtractive manufacturing technique, the crowns produced via the additive manufacturing technique presented lower surface roughness and lower fracture resistance values. Thermal aging did not significantly affect these parameters across all test groups (p > 0.05). There was no difference between the two manufacturing techniques at 1.0 mm (p > 0.05), whereas crowns produced using the subtractive manufacturing technique at thicknesses of 1.5 and 2.0 mm presented greater fracture resistance than those produced with the additive manufacturing technique (p < 0.01). Conclusions It was concluded that implant-supported permanent crowns produced by the additive manufacturing technique using composite resin meet clinical requirements regarding surface roughness and fracture resistance.