Favorable residual stress induction by resin-cementation on dental porcelain

Garry J.P Fleming,Xu Cao,Dan L Romanyk,Owen Addison

doi:10.1016/j.dental.2017.07.018

Garry J.P Fleming, Xu Cao + Show 2 more

Open Access

https://doi.org/10.1016/j.dental.2017.07.018

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Abstract

ObjectivesDespite developments in polycrystalline ceramics, glassy dental-ceramic materials provide the optimum cosmetic option in most clinical situations to mimic the natural dentition. The clinical success of glassy dental-ceramic materials is often attributed to resin-adhesive bonding techniques. In this study we explore whether shrinkage stresses generated on photo-polymerisation of the resin-cement are sufficient to induce ceramic surface defect stabilization, and we quantify the transient nature of the induced stresses. MethodsStress-induced changes in a feldspathic ceramic over a range of thicknesses (0.5–2.0mm: n=20 per thickness) were measured using a profilometric technique at baseline for each disc-shaped specimen (mean of the maximum deflection (δbaseline)) and again following polymerisation of a controlled resin-cement thickness on the contra-lateral surface. Measurements were repeated at 30, 60, 90 and 1440min following photo-polymerization (δ30, δ60, δ90 and δ1440, respectively) before bi-axial flexure strength (BFS) determination at 24h. ResultsA repeated measures ANOVA and post-hoc Bonferroni tests determined that δ1440 was significantly different from δbaseline (p=0.02), δ30 (p<0.01) and δ60 (p<0.01) but not δ90 (p=0.61). Data exploration revealed that there were differences in directionality of the independent variable (mean of the maximum deflection (δ)) with a proportion of specimens increasing in deflection and others reducing. The directionality of the effect strongly correlated with the BFS values. Where δ1440-δbaseline was low and/or negative, BFS values were also low. High BFS values were observed when δ1440-δbaseline was large and positive (indirectly inferring high shrinkage-stress-induced-deformation). SignificanceA link between shrinkage stresses associated with the photo-polymerization of dental resin-based cements and the reinforcement of dental porcelain has clearly been established.

Highlights

In 2002, a review entitled ‘Are adhesive technologies needed to support ceramics? An assessment of the current evidence’concluded that resin-cements reinforce dental ceramics, the assessment of the ‘available evidence’ was poor [1]
This consensus was predicted by John McLean who postulated that the tooth could act as a ‘reinforcing core’ for ceramic restorations with the adhesive resin-cement providing a ‘synergistic bond’ to confer system strength [12]
This study explores the link between shrinkage stresses associated with the photo-polymerisation of dental resin-based cements and the reinforcement of dental porcelain

Summary

Introduction

In 2002, a review entitled ‘Are adhesive technologies needed to support ceramics? An assessment of the current evidence’concluded that resin-cements reinforce dental ceramics, the assessment of the ‘available evidence’ was poor [1]. When adhesively coupled to the underlying tooth substrate, relatively ‘weak’ ceramic materials demonstrate significantly higher clinical survival rates compared with acid-base cement systems [2,3]. This consensus was predicted by John McLean who postulated that the tooth could act as a ‘reinforcing core’ for ceramic restorations with the adhesive resin-cement providing a ‘synergistic bond’ to confer system strength [12]. Despite the mechanical advantages of polycrystalline ceramics [13], glassy ceramics still provide the optimum minimally invasive cosmetic option for the clinician to mimic tooth structure in terms of form, shade, translucency, lustre and hue [3]. Extrapolating from McLean’s postulation, two questions arise: (1) are we close to optimising the ‘synergism’ between the ceramic/resin-cement/tooth substrate complex? and (2) with appropriate technological development could reinforcing ceramic cores be eliminated completely from the prosthodontists armamentarium to herald a truly conservative all-ceramic indirect restoration?

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