Fracture strength of additively manufactured implant-supported resin-based crowns on polyetheretherketone and titanium abutments.

Statement Of Problem
Implant-supported crowns can be fabricated using additive (AM) or subtractive manufacturing (SM) with resin-based materials. However, their fracture strength on different implant abutments remains unclear.Purpose
The purpose of this in vitro study was to evaluate the fracture strength (FS) and failure modes of AM interim crowns cemented on polyetheretherketone (PEEK) or titanium (Ti) abutments and compare them with SM crowns.Material And Methods
Sixty-four implant-supported crowns were fabricated from 3 AM resins (Crowntec [AM_CT], FREEPRINT temp [AM_FP], Varseosmile Crown Plus [AM_VS]) and one SM resin (M-PM Disc [SM_MPM]) (N=16). The crowns were cemented on 1-piece PEEK or Ti abutments (n=8) using dual-polymerizing self-adhesive resin cement after standardized surface treatments. All specimens were subjected to thermomechanical aging (5000 thermal cycles, 250 000 cycles at 49 N, 1.7 Hz) followed by FS testing. Failures were classified as repairable crown crack or fracture, catastrophic crown fracture without abutment damage, abutment distortion without crown damage, or crown and abutment damage. One-way analysis of variance with Tukey test and chi-squared test were used for statistical analysis (α=.05).Results
All specimens survived cyclic loading. While Ti-supported crowns fractured consistently through catastrophic crown failure without abutment damage, most PEEK-supported crowns exhibited inconsistent failure patterns involving abutment distortion or combined crown-abutment damage. Only 6 crowns on PEEK abutments (4 AM_CT and 2 AM_FP) failed without abutment damage, making statistical comparison unreliable. Therefore, PEEK-supported crowns were excluded from statistical analysis. Among Ti groups, SM_MPM crowns demonstrated the highest FS, followed by AM_CT, while AM_FP and AM_VS showed significantly lower FS values (P≤.003). The distribution of failure modes differed significantly among crown materials, abutment types, and their combinations (P≤.014).Conclusions
Crowns on Ti abutments fractured without abutment damage, with SM_MPM resulting in the highest FS, followed by AM_CT. In contrast, most PEEK-supported crowns exhibited abutment distortion without crown damage or simultaneous crown and abutment damage.