Comparison of wear and fracture resistance of additively and subtractively manufactured screw-retained, implant-supported crowns

Statement of problem. Additively manufactured resins indicated for fixed definitive prostheses have been recently marketed. However, knowledge on their wear and fracture resistance when fabricated as screw-retained, implant-supported crowns and subjected to artificial aging is limited. Purpose. The purpose of this in vitro study was to evaluate the volume loss, maximum wear depth, and fracture resistance of screwretained implant-supported crowns after thermomechanical aging when fabricated using additively and subtractively manufactured materials. Material and methods. Two additively manufactured composite resins (Crowntec [CT] and VarseoSmile Crown Plus [VS]) and 2 subtractively manufactured materials (1 reinforced composite resin, Brilliant Crios [BC] and 1 polymer-infiltrated ceramic network, Vita Enamic [EN]) were used to fabricate standardized screw-retained, implant-supported crowns. After fabrication, the crowns were cemented on titanium base abutments and then tightened to implants embedded in acrylic resin. A laser scanner with a triangular displacement sensor (LAS -20) was used to digitize the pre-aging state of the crowns. Then, all crowns were subjected to thermomechanical aging (1.2 million cycles under 50 N) and rescanned. A metrology-grade analysis software program (Geomagic Control X 2020.1) was used to superimpose post-aging scans over pre-aging scans to calculate the volume loss (mm3) and maximum wear depth (mm). Finally, all crowns were subjected to a fracture resistance test. Fracture resistance and volume loss were evaluated by using 1-way analysis of variance and Tukey Honestly significant difference (HSD) tests, whereas the Kruskal-Wallis and Dunn tests were used to analyze maximum wear depth. Chisquared tests were used to evaluate the Weibull modulus and characteristic strength data (alpha=.05). Results. Material type affected the tested parameters (P .001). CT and VS had higher volume loss and maximum wear depth than BC and EN (P .001). EN had the highest fracture resistance among tested materials (P .001), whereas BC had higher fracture resistance than CT (P=.011). The differences among tested materials were not significant when the Weibull modulus was considered (P=.199); however, VE had the highest characteristic strength (P .001). Conclusions. Additively manufactured screw-retained, implant-supported crowns had higher volume loss and maximum wear depth. All materials had fracture resistance values higher than the previously reported masticatory forces of the premolar region; however, the higher characteristic strength of the subtractively manufactured polymer-infiltrated ceramic network may indicate its resistance to mechanical complications. (J Prosthet Dent 2024;132:154-164)