IADR Abstract Archives
Cuspal deflection in model dental cavities during resin-composite photopolymerization
Objectives: The intention was to establish a model cavity system as an adjunct to dental MOD cavities for time-dependent measurements of cuspal deflection (CD), especially with bulk fill (BF) resin-composites.
Methods: Multiple cavity molds were machined in Aluminium alloy blocks, with cavities of 4 mm slot depth & width and 8 mm slot length. Cavity walls & floor were sandblasted and primer/adhesive applied. Cuspal widths were designed to have comparable stiffness to representative enamel/dentin cusps. Seven Bulk Fill materials were studied, and assigned the following codes: TECBF, FBR, FBF, SDR, VBF, XB, EX. The BF composites were placed in the vertically-oriented test blocks, mounted in a precision measurement assembly with a LVD transducer contacting the upper surface of the thinner (2 mm) Al cusp to facilitate real-time cuspal deflection (CD) measurement from 0-60 min. Polymerization was initiated by 20 s irradiation 1200 mW/cm2 from an Elipar S10 LCU, occlusally, at 0 mm from target. The measurement system was itself modelled by Finite Element Analysis. Subsequently, CD specimens were also imaged by X-ray micro-CT and VHN microhardness measured on occlusal composite surfaces. Data were statistically analysed by ANOVA and post-hoc tests.
Results: Cuspal deflection/time plots were comparable in form to stress/time kinetics. After 1 h, the deformations ranged between 5 and 20 μm (p <0.01). That range was comparable with the FEA predictions and micro-CT images of strain at the thinner wall. Cuspal deformations could be normalized with reference to the measured occlusal hardness, yielding an additional CD/VHN parameter.
Conclusions: Bulk-fill composite transferred shrinkage-stress to the bonded retaining cavity walls, causing cantilever cuspal strain. Cuspal deflection was reduced with low modulus BF composites.
Methods: Multiple cavity molds were machined in Aluminium alloy blocks, with cavities of 4 mm slot depth & width and 8 mm slot length. Cavity walls & floor were sandblasted and primer/adhesive applied. Cuspal widths were designed to have comparable stiffness to representative enamel/dentin cusps. Seven Bulk Fill materials were studied, and assigned the following codes: TECBF, FBR, FBF, SDR, VBF, XB, EX. The BF composites were placed in the vertically-oriented test blocks, mounted in a precision measurement assembly with a LVD transducer contacting the upper surface of the thinner (2 mm) Al cusp to facilitate real-time cuspal deflection (CD) measurement from 0-60 min. Polymerization was initiated by 20 s irradiation 1200 mW/cm2 from an Elipar S10 LCU, occlusally, at 0 mm from target. The measurement system was itself modelled by Finite Element Analysis. Subsequently, CD specimens were also imaged by X-ray micro-CT and VHN microhardness measured on occlusal composite surfaces. Data were statistically analysed by ANOVA and post-hoc tests.
Results: Cuspal deflection/time plots were comparable in form to stress/time kinetics. After 1 h, the deformations ranged between 5 and 20 μm (p <0.01). That range was comparable with the FEA predictions and micro-CT images of strain at the thinner wall. Cuspal deformations could be normalized with reference to the measured occlusal hardness, yielding an additional CD/VHN parameter.
Conclusions: Bulk-fill composite transferred shrinkage-stress to the bonded retaining cavity walls, causing cantilever cuspal strain. Cuspal deflection was reduced with low modulus BF composites.
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