Temperature rise in photopolymerized adhesively-bonded resin composite: A thermography study

ObjectivesTo assess visually and quantitatively the contributions of the adhesive layer photopolymerization and the subsequent resin composite increment to spatio-temporal maps of temperature at five different cavity locations, subjected to two irradiance curing protocols: standard and ultra-high.MethodsCaries-free molars were used to obtain 40, 2 mm thick dentin slices, randomly assigned to groups (n = 5). These slices were incorporated within 3D-printed model cavites, 4 mm deep, restored with Adhese® Universal bonding agent and 2 mm thick Tetric® Powerfill resin composite, and photocured sequentially, as follows: G1: control-empty cavity; G2: adhesive layer; G3 composite layer with no adhesive; and G4 composite layer with adhesive. The main four groups were subdivided based on two curing protocols, exposed either to standard 10 s (1.2 W/cm2) or Ultra high 3 s (3 W/cm2) irradiance modes using a Bluephase PowerCure LCU. Temperature maps were obtained, via a thermal imaging camera, and numerically analyzed at 5 locations. The data were analyzed using two-way ANOVA followed by multiple one-way ANOVA, independent t-tests and Tukey post-hoc tests (α = 0.05). Tmax, ΔT, Tint (integrated area under the curve) and time-to-reach-maximum-temperature were evaluated.ResultsTwo-way ANOVA showed that there was no significant interaction between light-curing time and location on the measured parameters (p > 0.05), except for the time-to-reach-maximum-temperature (p < 0.05). Curing the adhesive layer alone with the 10 s protocol resulted in a significantly increased pulpal roof temperature compared to 3 s cure (p < 0.05). Independent T-tests between G3 and G4, between 3 s and 10 s, confirmed that the adhesive agent caused no significant increases (p > 0.05) on the measured parameters. The ultra-high light-curing protocol significantly increased ΔT in composite compared to 10 s curing (p < 0.05).SignificanceWhen the adhesive layer was photocured alone in a cavity, with a 2 mm thick dentin floor, the exothermal release of energy resulted in higher temperatures with a 10 s curing protocol, compared to a 3 s high irradiance. But when subsequently photocuring a 2 mm layer of composite, the resultant temperatures generated at pulpal roof location from the two curing protocols were similar and therefore there was no increased hazard to the dental pulp from the immediately prior adhesive photopolymerization, cured via the ultra-high irradiation protocol

Post-irradiation surface viscoelastic integrity of photo-polymerized resin-based composites.

From PubMed via Jisc Publications RouterHistory: received 2021-09-11, revised 2021-09-13, accepted 2021-09-13Publication status: aheadofprintA class of ultra-rapid-cure resin-based composites (RBCs) exhibited immediate post-irradiation surface viscoelastic integrity using an indentation-creep/recovery procedure. The aim of this study was to determine whether such behavior is more generally characteristic of a wider range of RBCs. Eight representative RBCs were selected based on different clinical categories: three bulkfills (OBF, Filtek One Bulk Fill; VBF, Venus Bulkfill; EBF, Estelite Bulkfill), three conventional non-flowables (XTE, Filtek Supreme XTE; GSO, GrandioSo; HRZ, Harmonize) and conventional flowables (XTF, Filtek Supreme XTE Flow; GSF, GrandioSo Flow). Stainless steel split molds were used to fabricate cylindrical specimens (4mm (dia)×4mm). These were irradiated (1.2W/cm ) for 20s on the top surface. Post-irradiation specimens (n=3), within their molds, were centrally loaded with a flat-ended 1.5mm diameter indenter under 14MPa stress: either immediately (<2min) or after 24h delayed indentation. Stress was maintained for 2h, then - after removal - recovery measurements continued for a further 2h. Indentation depth (%) versus time was measured continuously to an accuracy of <0.1μm. Data were analyzed by One-way ANOVA and Tukey post-hoc tests (α=0.05). Time-dependent viscoelastic indentation was observed for all RBCs. For immediate indentation, the maximum indentation range was 1.43-4.92%, versus 0.70-2.22% for 24h delayed indentation. Following 2h recovery, the residual indentation range was 0.86-3.58% after immediate indentation, reducing to 0.22-1.27% for delayed indentation. The greatest immediate indentation was shown by VBF followed by XTF and GSF. OBF, HRZ, XTE and GSO had significantly lower indentations (greater hardness). XTE showed a significantly reduced indentation maximum compared to OBF (p<0.05). Indentations delayed until 24h post-irradiation were reduced (p<0.05) for most materials. The indentation-creep methodology effectively characterized resin-based composites within several categories. Viscoelastic properties evaluated by the indentation-creep method confirmed that highly filled RBCs were more resistant to indentation. Indentations were reduced after 24h post-irradiation due to further matrix-network development. [Abstract copyright: Copyright © 2021. Published by Elsevier Inc.