Fracture resistance of ceramic and polymer-based occlusal veneer restorations

doi:10.1016/j.jmbbm.2017.06.013

Journal of the Mechanical Behavior of Biomedical Materials

Volume 74, October 2017, Pages 245-250

https://doi.org/10.1016/j.jmbbm.2017.06.013 Get rights and content

Abstract

Objectives

The purpose of this in vitro study was to evaluate the influence of thermodynamic loading on the durability and fracture resistance behavior of occlusal veneers fabricated from different biomedical dental CAD/CAM materials.

Methods

The occlusal surfaces of 64 extracted premolars were prepared in the enamel layer and restored with occlusal veneers with a fissure/cusp thickness of 0.5/0.8 mm made from four different dental CAD/CAM materials: group LD lithium disilicate (e.max CAD), group LS zirconia-reinforced lithium silicate (Vita Suprinity), group PI polymer-infiltrated ceramic (Vita Enamic), and group PM polymethylmethacrylate PMMA (Telio CAD). The prepared teeth were etched with phosphoric acid. The occlusal veneers were then bonded using an adhesive luting system (Multilink Primer A/B and Multilink Automix luting resin). Half of the specimens were subjected to thermodynamic loading in a chewing simulator (1.2 million cycles at 98 N). All specimens were quasi-statically loaded until fracture. The statistical analysis was made using the t-test and one-way ANOVA followed by the Tukey HSD test (α = 0.05).

Results

All aged specimens survived the thermodynamic loading. Thermodynamic loading significantly raised the fracture resistance in groups LS, PI, and PM (P < 0.03). Occlusal veneers made from lithium disilicate and zirconia-reinforced lithium silicate recorded higher fracture resistance than those made from polymer-infiltrated ceramic and PMMA resin.

Conclusions

All tested dental CAD/CAM biomaterials exhibited a fracture resistance considerably exceeding the average occlusal force in the posterior dentition. Therefore, they might present a viable long-term treatment for restoring the occlusal surfaces of posterior teeth.

Introduction

Conservation of tooth structures is the main objective in restorative dentistry. Unfortunately, the loss of natural occlusal contacts between maxillary and mandibular teeth may occur because of wear, caries, or malposition. The treatment of such problems is complicated and challenging as removal of undamaged hard dental tissues has to be done to accept conventional restorative materials (Edelhoff and Sorensen, 2002, Tsitrou and van Noort, 2008). Moreover, loss of occlusal contact may be compensated by tooth over-eruption (Tsitrou and van Noort, 2008), which in turn restricts the thickness of the planned restorations. Minimally invasive procedures in prosthetic dentistry aim to preserve sound tooth substance, maintain the vitality of the tooth, and reduce postoperative sensitivity (Edelhoff and Sorensen, 2002).

Lithium disilicate ceramic has been considered the strongest glass-ceramic. The high number of microstructural, interlocking, needle-like lithium disilicate crystals that are embedded in the glassy matrix gives this type of ceramic higher mechanical properties than other types of glass- based ceramic materials (Oh et al., 2000). Lithium disilicate ceramic has shown promising results in terms of structural integrity when used in the anterior or posterior area as veneers, inlays, onlays, crowns, partial coverage restorations, and three-unit fixed dental prostheses (Attia and Kern, 2004a, Guess et al., 2013, Kern et al., 2012, Sasse et al., 2015). In an attempt to improve the mechanical and optical properties of glass-ceramic restorative materials, new generations have been developed for computer-aided design and computer-aided manufacturing (CAD/CAM) technology. For instance, dissolving 10% zirconia into the lithium silicate glass matrix claimed to be more translucent and stronger material than the conventional lithium disilicate ceramic (Elsaka and Elnaghy, 2016). In another approach, a ceramic network structure was infiltrated with a polymer material to combine the advantages of the two materials to obtain better mechanical properties and better machinability for CAD/CAM than those of glass-ceramics (Coldea et al., 2013). Likewise, the mechanical and physical properties of CAD/CAM polymer restorative materials have been continually improved to be used as an alternative to glass-ceramics, especially when thin restorations with high masticatory loads are required because of their high resistance to dynamic fatigue (Schlichting et al., 2011). For that reason, the longevity, stability, and behavior of these new biomedical dental materials should be investigated when they are used for minimally invasive occlusal veneer restorations.

In the current study, the influence of thermodynamic loading on the durability and fracture resistance of four different dental CAD/CAM occlusal veneer restorative biomaterials with a fissure/cusp thickness of 0.5/0.8 mm was evaluated. The null hypotheses of this study were as follows: (1) different dental CAD/CAM occlusal veneers will survive thermodynamic loading equally; (2) thermodynamic loading will not affect the fracture resistance of each material itself; and (3) no differences will be found in fracture resistance between the different dental CAD/CAM biomaterials before and after thermodynamic loading.

Section snippets

Tooth preparation

Sixty four intact, noncarious, unrestored human maxillary first premolars, recently extracted for orthodontic reasons, were collected anonymously. They were cleaned of both calculus deposits and soft tissues and then stored at room temperature in 0.1% thymol solution (Caelo, Hilden, Germany). The teeth in this study were selected to be as similar as possible in dimension. The mesiodistal and buccolingual as well as the buccal and lingual cusp slopes of the tooth occlusal surfaces were measured

Results

All aged specimens in all groups survived the thermodynamic loading without fracture, ceramic chipping, or cracks. The results of the quasi-static load to fracture test of all groups are listed in Table 1. Thermodynamic loading increased the fracture resistance significantly for groups LS, PI, and PM (P ≤ 0.031).

Without thermodynamic loading, group LD showed significantly higher fracture resistance than groups PI and PM (P ≤ 0.015) but not group LS (P = 0.051). No statistically significant

Discussion

Little information is available on the reliability and longevity of recent dental CAD/CAM biomaterials as minimally invasive restorations when bonded to natural tooth structures with nonretentive preparation designs (Clausen et al., 2010, Guess et al., 2013, Sasse et al., 2015). To ensure a close simulation of the clinical situations, all procedures in the recent study were designed to follow clinically applied protocols. In fact, several factors influence the fracture resistance of all-ceramic

Conclusion

Considering the survivability and the fracture resistance of the tested occlusal veneers, all materials may be considered as a viable treatment for restoring the occlusal surfaces of posterior teeth.

Acknowledgements

The authors gratefully acknowledge Ivoclar Vivadent, Schaan, Liechtenstein, and Vita Zahnfabrik, Bad Säckingen, Germany for providing their materials free of charge.

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To study the stress distribution and bonding performance in posterior occlusal veneers and tooth bodies under different preparation forms and materials.
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This in-vitro study is planned to analyze the effect of different thicknesses of ceramic occlusal veneers and different surface treatments on fracture resistance.
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To evaluate the influence of the type of preparation and mechanical cycling on the fracture load and failure mode of semi-direct posterior resin composite restorations.
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¹: The first and second author contributed equally to this work.

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