Influence of the Light Curing Tip Distance and Material Opacity on Selected Physical Properties of a Pit and Fissure Sealant

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Purpose: The purpose of this study was to evaluate the influence of the light curing to distance and material opacity on hardness (KHN), degree of conversion (DC), and crosslink density (CLD) of a resin-based fissure sealant (Fluroshield). Methods: One-millimeter-thick white opaque and clear sealant specimens, photoactivated at 1-, 2-, and 3-mm distances, were fabricated (8 groups, N=5). KHN and DC were evaluated 24 hours after polymerization. Specimens were subjected to a new KHN reading after 24-hour immersion in absolute ethanol to indirectly assess the CLD. Results: Samples of clear sealant cured at longer distances presented lower KHN, although there were not differences between opacities at all distances. The mean DC of the opaque white material, however, was lower than that of the clear one at higher distances. There were no differences among CLD for all experimental conditions analyzed. Conclusions: KHN of the clear sealant was affected by increased distances. The clear sealant showed higher DC at increased distances, although CLD was not influenced by the factors under study. Since physical properties of sealing materials are directly related to their clinical efficacy, the clear sealant tested may present a better clinical performance than the opaque one. (Pediatr Dent 2011;33:505-9) Received April 20, 2070 vertical bar Last Revision July 4, 2010 vertical bar Accepted July 7, 2010337505509Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [07/02800-3

Thermo-mechanical degradation of composite restoration photoactivated by modulated methods-a SEM study of marginal and internal gap formation

Objective. To evaluate the influence of thermal-mechanical degradation on superficial and internal gap formation of composite restorations photoactivated using modulated methods. Materials and methods. An experimental composite was prepared using a resin matrix containing 65wt% Bis-GMA and 35wt% TEGDMA. Camphorquinone (0.5wt%) and dimethylaminoethyl-methacrylate (0.5wt%) were dissolved in the resin as a photo-initiator system and 65wt.% silanized glass fillers were added to the matrix. Ground buccal surfaces of bovine lower incisors were used to make 160 preparations (3 mm x 3 mm x 2 mm in depth). An adhesive system (Adper Single Bond 2) was applied and the specimens were assigned into 16 groups (n = 10), according to the photoactivation method [high intensity (HI), low intensity (LI), soft-start (SS) and pulse-delay (PD)] and the degradation protocol [(control/no degradation; thermal cycling (TC); mechanical loading (ML); thermo-mechanical loading (TC+ML)]. Marginal and internal interfaces of bonded restorations were replicated in epoxy resin and analyzed by SEM. Gaps were expressed as a percentage of the total length of the margins. Data were submitted to 2-way ANOVA and Tukey's test (alpha = 0.05). Results. For the control group no significance was noted among the photoactivation methods. TC had no effect in gap formation. ML and TC+ML increased the incidence of superficial gaps for both HI and SS groups as well as increased the internal gaps for all groups. Conclusion. Although photoactivation methods do not influence gap formation at first, composite restoration photoactivated by low intensity or modulated methods showed improved resistance to thermo-mechanical degradation. Mechanical loading is determinant for interfacial degradation of composite restorations, while thermal cycling has no effect on gap formation.7151341134

Effect of irradiation times on the polymerization depth of contemporary fissure sealants with different opacities

The aim of this study was to evaluate the depth of curing of 10 contemporary blue light-activated dental flowable materials at several opacities, influenced by different irradiation times using FT-IR spectroscopy. Fifty-five specimens (n = 5) with a 5-mm diameter and 1-mm thickness of translucent (Opallis Flow T), yellowed (Master Flow A2; Opallis Flow A2; Natural Flow A2; Fluroshield Yellowed), and opaque materials (Master Flow OA2; Natural Flow O; Opallis Flow OA3.5; Opal lis Flow OP; Fluroshield White) were obtained at six curing times (10s, 20s, 30s, 40s, 50s, and 60s) using a high-intensity LED (Coltolux, Coltene/Whaledent). The degree of conversion (DC) (%) was obtained using the Nexus 470 FTIR Spectrometer (Nicolet Instruments, USA). The FTIR-ATR spectra for uncured and cured samples were analyzed using a ZnSe crystal. The top and bottom surfaces of the cured specimens were analyzed to obtain the depth of curing. Two-way ANOVA was used to analyze the data. The highest curing depth was obtained by Natural Flow OA2, while the lowest was shown by Master Flow OA2. The shortest curing time generated similar depths of cure in comparison with the most extensive for Opallis Flow A2 and Fluroshield Yellowed. Therefore, depth of curing, influenced by the irradiation time, was dependent on the materials. Using the Natural Flow OA2 opaque sealant and the 10-s curing time for Opallis Flow A2 and Fluroshield Yellowed may represent alternative approaches to sealing tooth fissures.25213514