Rheological properties of veneer trial pastes relevant to clinical success

Introduction The porcelain veneer is a relatively conservative means of improving the appearance of teeth. As these res­ torations are usually highly visible it is essential to gain the approval of the patient before final cementation takes place. As a result a variety of trial pastes are available that match the shades of the resins that are used ultimately to fi nally cement the veneer in place. Such restorations, by virtue of their small size and fragility, are difficult to handle and position. It is therefore important that the application of trial paste does not impede placement and retention upon the tooth surface at try in whilst the patient assesses its appearance. Objective To determine the rheological properties of three makes of trial pastes (Calibra - Dentsply Caulk, USA; Nexus – Kerr, USA; Rely X – 3M Espe, USA) and assess if temperature affected these. Design In vitro rheological measurement. Method For each product the rheological properties of three shades were determined at both 25 o C and 35 o C three times. Measurements of both the Initial Yield Stress and Shear Rate Index were undertaken using a controlled stress rheometer (Carri-med, Dorking, UK) in flow mode with a cone-and-plate test confi gu­ ration. Results One way analyses of variance of the initial yield and shear rate index for each shade of material at 25 and 35 o C demonstrated no significant effects of temperature with the exception of the initial yield of Nexus (P = 0.0024) where the yield stress of the white shade was significantly (P <0.01) higher at 35 o C than at 25 o C. In all cases the yield stress for Nexus was of the order of ten times higher than the other materials. All materials demonstrated pseudoplastic behaviour. Conclusions The variation in yield stress displayed by the materials will affect the handling of veneers and offers a poten­ tially useful choice parameter to the clinician as to which paste bests suits their requirements.