Influence of placement techniques on Vickers and Knoop hardness of class II composite resin restorations

Objectives. To analyze the influence of two placement techniques on Knoop and Vickers hardness of class II cavities restored using packable (A.L.E.R.T., Solitaire 2, SureFil) and conventional microfilled and hybrid (Filtek A110 and Z250, respectively) resin composites. Methods. Fifty standardized class II cavities (5×3×1.5 mm3) were prepared in human premolars. They were divided into ten groups (n=5) and restored according to each resin composite material (A.L.E.R.T., Solitaire 2, SureFil, Filtek A110 and Z250) and placement technique (incremental or bulk). After storage in distilled water at 37 °C for 24 h, they were thermal cycled (700 cycles/5–55 °C, 1 min dwell time) and sectioned longitudinally. One section from each specimen was embedded and polished for Knoop and Vickers hardness measurements. Sixteen indentations were performed for each restoration, eight on the occlusal and eight on the cervical surfaces. Results. Results were submitted to ANOVA and demonstrated that all materials presented lower hardness values at the cervical surfaces when the bulk placement technique was employed, when compared to the occlusal surfaces (p<0.001), whereas the same did not occur with the incremental technique. Pearsonʹs correlation test demonstrated a positive correlation between Vickers and Knoop hardness numbers. Significance. The use of bulk placement technique resulted in lower values of hardness at the cervical surfaces of class II restorations. Values obtained using Knoop hardness test showed a high correlation with Vickers hardness measurements.