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Published on: December 20, 2024
Fracture strength of conventional versus digital interim crowns after thermal cycling
Işıl Sarıkaya1, Tuğçe Koç2, İlknur Usta Kutlu1
1Department of Prosthodontics, Faculty of Dentistry, Gaziosmanpaşa University, Tokat, 60100, Turkey.
Background:
Provisional restorations are essential components of fixed prosthodontic treatment. This study compared the fracture strength and failure modes of provisional crowns fabricated using conventional direct, conventional indirect, CAD/CAM 3D printing, and CAD/CAM milling techniques after thermal aging.
Methods:
A total of 48 provisional crowns were fabricated across four groups (n = 12 per group): conventional direct technique using dual-cured composite resin (Tempsmart DC, GC Corporation, Tokyo, Japan), conventional indirect technique using autopolymerized PMMA (Temdent Classic, Schütz Dental GmbH, Rosbach, Germany), CAD/CAM 3D printing using light-cured resin (ResMach Interim, ResMach, Istanbul, Turkey), and CAD/CAM milling using pre-polymerized PMMA (Acryx, Akrodent, Istanbul, Turkey). All crowns were cemented onto standardized cobalt-chromium dies and subjected to 10,000 thermocycles alternating between 5 °C and 55 °C (30-second dwell time; 5-second transfer time). Fracture strength testing was performed using a universal testing machine at a crosshead speed of 1 mm/min until failure, with maximum loads recorded in Newtons. Fracture modes were classified using Burke's classification through visual and photographic analysis. Statistical analysis was performed using one-way ANOVA and Tamhane's T2 post-hoc test (p < 0.05).
Results:
The highest fracture strength was recorded in the Acryx group (1511.67 ± 140.73 N), significantly higher than all other groups (p < 0.001). The ResMach Interim group showed the lowest fracture strength (581.62 ± 51.86 N). Conventional groups (Tempsmart DC: 716.58 ± 104.81 N; Temdent Classic: 792.85 ± 83.70 N) had intermediate values. One-way ANOVA revealed a large effect of fabrication technique on fracture strength (η² = 0.857). Acryx exhibited predominantly Class II fractures (75.0%), while other groups showed Class I fractures (83.3-100%).
Conclusions:
CAD/CAM-milled PMMA crowns demonstrated superior fracture resistance and more favorable ductile fracture patterns compared to conventional and 3D-printed crowns after thermal aging, suggesting these materials may be preferred for long-term provisional use in high-stress clinical scenarios such as posterior region applications.