Abstract

To evaluate debonding mechanism of zirconia and lithium disilicate cemented to dentin mimicking what could occur in a clinical setting. A null hypothesis of no difference in tensile bond strength between groups of zirconia and lithium disilicate cemented with resin cements was also tested. Zirconia rods (n = 100) were randomly assigned to two different surface treatment groups; air borne particle abrasion and hot etching by potassium hydrogen difluoride (KHF2). Lithium disilicate rods (n = 50) were surface etched by hydrofluoric acid (HF). Five different dual cure resin cements were used for cementing rods to bovine dentin. Ten rods of each test group were cemented with each cement. Test specimens were thermocycled before tensile bond strength testing. Fracture morphology was visualized by light microscope. Mean surface roughness (Sa value) was calculated for randomly selected rods. Cohesive fracture in cement was the most frequent observed fracture morphology. Combination of adhesive and cohesive fractures were second most common. Fracture characterized as an adhesive between rod and cement was not observed for KHF2 etched zirconia. Highest mean tensile bond strength was observed when cementing air borne particle abraded zirconia with Variolink Esthetic (Ivoclar Vivadent). All surface treatments resulted in Sa values that were significant different from each other. The number of cohesive cement fractures observed suggested that the cement was the weakest link in bonding of zirconia and lithium disilicate.

Highlights

  • Zirconia has become one of the most used ceramic in prosthetic dentistry the last decades [1].The material has a high flexural strength [2] due to its crystal content and transformation toughening from crystal transformation [3]

  • The aim of the present study was to evaluate debonding mechanism of zirconia and lithium disilicate cemented to dentin mimicking what could occur in a clinical setting, and to test the null hypothesis that no difference in tensile bond strength between groups of zirconia and lithium disilicate cemented with resin cements would be found

  • Fracture characterized as adhesive between rod and cement was not observed for KHF2 etched zirconia

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Summary

Introduction

Zirconia has become one of the most used ceramic in prosthetic dentistry the last decades [1]. The material has a high flexural strength [2] due to its crystal content and transformation toughening from crystal transformation [3]. These characteristics make it appropriate for use as both core material in bi-layered restorations or as monolithical restorations with smaller dimension [4]. Despite excellent mechanical properties of zirconia there are complications related to clinical use. Many approaches have been studied with the aim to increase bond strength between resin cement and zirconia [5]. The results varied when it came to both tensile and share bond strength in laboratory tests, and storage in water or thermocycling showed low predictability of a stable bond [7]

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