Comparison of fracture strength of implant-supported immediate restorations with different polymeric structures fabricated by additive and subtractive manufacturing.

Statement of problem: Additive manufacturing is a rising trend in fabrication of polymeric restorations, but fracture strengths are uncertain especially for polyetheretherketone (PEEK) materials.

Purpose: The purpose of the in vitro study was to compare the fracture strength of the 3-unit immediate restorations fabricated by subtractive and additive manufacturing.

Material and methods: Three-unit immediate prostheses, restoring the maxillary first and second premolar and first molar, were designed digitally. Eight groups were created according to the abutment, the material, and the manufacturing techniques. Titanium and PEEK abutment-supported 3-unit immediate restorations were fabricated by additive and subtractive manufacturing from polymethyl methacrylate (PMMA) and PEEK materials (n=12). After cementation, the specimens were subjected to dynamic loading (1.6 Hz, 50 N) with 60 000 thermal cycles (5 to 55 °C) in distilled water by using a dual-axis mastication simulator. After the dynamic loading, all specimens were statically loaded by using a universal testing machine and maximum values were recorded. All specimens were classified according to failure type. The normal distribution was checked with the Shapiro Wilk test, the variance homogeneity with the Levene test, and the sphericity assumption with the Mauchly W test. The 3-way ANOVA test was used to examine the difference between the independent groups that met the normality assumption with the interaction effect. Post hoc Bonferroni tests were used to reveal the group or groups that created the difference (α=.05).

Results: For titanium-supported immediate restorations, specimens fabricated by the subtractive manufacturing showed higher failure load values compared to the additive manufacturing for both PMMA and PEEK material (P<.05). For PEEK-supported immediate restorations, the subtractive manufacturing showed higher values for PMMA materials but had lower values for PEEK material compared to the additive manufacturing (P<.05). Additionally, PEEK material had higher values compared to PMMA (P<.05). Titanium abutments showed higher failure load values compared to PEEK abutments (P<.05).

Conclusions: PEEK immediate restorations showed higher fracture strength values compared to PMMA immediate restorations. Subtractive manufacturing showed higher fracture strength values than additive manufacturing in all groups except PEEK immediate restorations supported by PEEK abutments. Fracture strengths of all specimens were within physiological occlusal forces and additive manufacturing is promising in the fabrication of implant-supported immediate restorations.