Effects of radiant exposure and distance on resin-based composite polymerization.

PURPOSE: To evaluate the hardness profile of three resin-based restorative composites (RBC) (Filtek Z250XT, Filtek One Bulk Fill, Filtek Bulk Fill Flow) polymerized by a multi-wave curing light. METHODS: Specimens (n= 12) were prepared by inserting 2 mm RBC increments into a split-mold and polymerized from the top using either 20- or 40-second exposure times. Specimen curing was performed directly at a 1 mm distance (control-group) or through an ivorine-tooth slot preparation at a 5 mm distance (experimental-group). Specimens were stored (37 ± 1°C/24 hours), then subjected to Knoop indenter (25g/5 seconds). Specimens' KHN values were obtained from the upper and lower surfaces. Relative hardness (RH) (lower-to-upper ratio) was calculated for each specimen. Data were analyzed with three-way ANOVA and Tukey's HSD (α= 0.05). RESULTS: There was no significant RH difference among RBCs in the control group, regardless of the exposure time (P> 0.05). Average RH ratios for all RBCs tested in this group were greater than 0.80. However, the average RH values of the experimental RBC group were significantly lower. The RH for Z250 was 0.39 in the 20-second group, while RH was 0.63 in the 40-second group. BF had an RH ratio of 0.70 in the 20-second and 0.72 in the 40-second group, while One Bulk had a ratio of 0.65 in the 20-second and 0.71 in the 40-second groups. Doubled exposure time substantially increased RH of all tested materials at a 1 mm tip-to-material distance. Clinically relevant 5 mm light-tip to material-surface distance significantly reduced polymerization efficacy of RBC specimens, regardless of the exposure time. CLINICAL SIGNIFICANCE: Adequate light-polymerization of resin-based direct restoratives is necessary for long-term clinical success. Polymerizing Class 2 restorations is challenging due to a hard-to-reach location and an increased distance between the light source and the restorative material. Insufficient polymerization is often seen at the bottom of the proximal box of the Class 2 cavity, with a detrimental effect on restoration longevity.

Depth of cure of bulk fill composites with monowave and polywave curing lights.

PURPOSE: To measure and compare the depth of cure (DOC) of two bulk fill resin composites using a monowave and polywave light curing unit (LCU) according to ISO 4049 and using custom tooth molds. METHODS: The DOC of Tetric Evoceram Bulk Fill and Filtek Bulk Fill Posterior were measured using a monowave LED LCU (Elipar S10) and a polywave LED LCU (Bluephase G2). Metal molds were used to fabricate 10 mm long DOC specimens (n = 10) according to ISO 4049. Uncured composite material was scraped away with a plastic instrument and half the length of remaining composite was measured as the DOC. Custom tooth molds were fabricated by preparing > 10 mm long square- shaped (4 x 4 mm) holes into the mesial/distal surfaces of extracted human molars. Resin composite was placed into one end of the prepared tooth and light polymerized. Uncured resin composite was removed from the opposite side from which the tooth was irradiated and the tooth was sectioned mesio-distally. Half the length of remaining cured composite was measured as the DOC. Data were analyzed by three-way ANOVA (α = 0.05) for factors material, LCU, and mold. RESULTS: The main effect LCU was not significant (P = 0.58). The interaction effect between material x mold was significant (P = 0.0001). The DOC of the composites differed significantly only with the stainless steel mold in which Tetric Evoceram Bulk Fill showed a deeper DOC than Filtek Bulk Fill Posterior (4.03 ± 0.14 vs 3.56 ± 0.38 mm, P < 0.0001).