Marginal adaptation and fracture resistance of CAD/CAM-fabricated PMMA, PEEK, and PEKK three-unit provisional fixed dental prostheses: an in vitro comparative study

Abstract

Background: Although polymethyl methacrylate (PMMA) is widely used for computer-aided design and computer-aided manufacturing (CAD/CAM) provisional restorations, high-performance polymers such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) have been proposed as alternatives. However, limited data are available comparing these materials in multi-unit provisional fixed dental prostheses (FDPs). This in vitro study aimed to evaluate and compare the marginal adaptation and fracture resistance of CAD/CAM-fabricated three-unit provisional FDPs constructed from PMMA, PEEK, and PEKK. Materials and Methods: A total of 48 sound human maxillary teeth (24 second premolars and 24 second molars) were prepared to receive 24 CAD/CAM-fabricated three-unit provisional FDPs. Specimens were randomly assigned into three groups (n = 8) according to material: PMMA, PEEK, and PEKK. Marginal adaptation was initially measured before cementation using a stereomicroscope. Following cementation, all specimens underwent standardized thermomechanical aging (10,000 thermal cycles and 240,000 mechanical loading cycles), after which marginal adaptation was reevaluated. Fracture resistance was then assessed using a universal testing machine, followed by analysis with scanning electron microscopy. Data were statistically analyzed using two-way repeated-measures analysis of variance (ANOVA), one-way ANOVA, Tukey’s post hoc test, and Fisher’s exact test (P ≤ 0.05). Results: Following cementation and aging, PMMA showed significantly lower marginal discrepancy than PEEK and PEKK (P < 0.001). PEEK exhibited a significant improvement in marginal adaptation after thermomechanical aging (P = 0.002), whereas PMMA and PEKK showed no significant changes. Fracture resistance differed significantly among groups (P < 0.001), with PEKK recording the highest mean fracture load (2,669 ± 204 N), followed by PEEK (1,849 ± 183 N), while PMMA showed the lowest mean value (1,072 ± 127 N). Conclusions: Under the tested experimental conditions, material type significantly affected both marginal adaptation and fracture resistance. Among the tested materials, PMMA demonstrated the lowest marginal discrepancy, and PEKK exhibited the highest fracture resistance, whereas PEEK provided a balanced performance.