Citation Information :
Edgerley PD, Versluis A, Tantbirojn D, Cagna DR. Impact of Overdried Preparation and Thermocycling on the Fracture of CAD–CAM Hybrid Ceramic Occlusal Veneer Restorations. Int J Prosthodont Restor Dent 2019; 9 (2):38-42.
Aim: To study the impact of overdried preparations prior to cementation with a self-adhesive resin cement and thermocycling on the fracture of hybrid ceramic occlusal veneer restorations.
Materials and methods: Sixty extracted maxillary molars were mounted and sectioned to remove the coronal structure 4 mm above the cementoenamel junction, leaving a flat area of exposed dentin and peripheral enamel. Ultrathin occlusal veneers with 0.3 mm central fossa thickness were milled from CAD–CAM hybrid ceramic (Vita Enamic). Teeth were randomly divided into three groups. After a selective enamel etching with phosphoric acid, groups I and II were blot-dried using cotton pellets; group III was desiccated with pressurized air for 15 seconds prior to cementation with a self-adhesive resin cement (Rely-X Unicem). Groups II and III were thermocycled between 5/55°C for 5000 cycles. The restored teeth were loaded axially until fracture. Fracture patterns were classified as fracture in the veneers only or fracture involving the tooth structure.
Results: The fracture strengths (mean ± standard deviation) were 1672 ± 585, 1789 ± 722, and 1586 ± 711 N for groups I (control), II (thermocycled), and III (overdried and thermocycled), respectively. No statistically significant differences were indicated (one-way ANOVA, p = 0.6426). Fracture patterns were significantly different (the Kruskal–Wallis rank sum test for multiple independent samples, p = 0.01315, followed by the Dunn post hoc test), where group III had more fractures in the veneer only than groups I and II.
Conclusion: Thermocycling of samples and overdrying of preparations did not show a significant difference in failure strength. However, fracture patterns indicated more veneer-only fractures under desiccated conditions, suggesting compromised restoration bonding.
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