Marginal and internal adaptation of composite restorations using a resin liner on deproteinized substrate

Objective. The purpose of this study was to evaluate the use of resin liner on deproteinized substrate on marginal and internal adaptation of composite restorations. Material and methods. Twenty-four recently extracted 3rd molars were selected. The crowns were sectioned in a mesio-distal direction, and the specimens were ground to expose a flat enamel area of at least 6 mm in diameter. Cavities were prepared on the central area of flattened surfaces. The specimens were randomly assigned into four groups (n=12): SB – 1. Acid etch, 2. Single bond application (SB); NaOCl/SB – 1. acid etch, 2. 10% sodium hypochlorite solution application for 60 s (NaOCl), 3. SB; SB/PL – 1. acid etch, 2. SB, 3. protect liner F (PL); NaOCl/SB/PL – 1. acid etch, 2. NaOCl, 3. SB, 4. PL. All cavities were restored with Filtek Z250 and polished. The outer and internal margins were stained using Caries Detector® (Kuraray), observed under the stereomicroscope, and transferred to a computer measurement program. The length of the gap was expressed as a percentage of the total length of the margins observed. Data (internal adaptation) were submitted to ANOVA and Tukey's test. Results. There were no gaps at enamel outer margins in any specimen of any group. There was no statistically significant difference in internal adaptation between SB (18%) and NaOCl/SB (18%). NaOCl/SB/PL showed the worst internal adaptation (21%), with the higher percentage of internal gaps, statistically differing from SB/PL, which showed the best internal adaptation (12%). Conclusions. Resin liner can effectively enhance internal adaptation on demineralized dentin. However, on demineralized and deproteinized dentin it affects the internal adaptation of composite restorations negatively.     

Association of photoactivation methods and low modulus liners on marginal adaptation of composite restorations

The aim of this study was to evaluate the effect of photoactivation methods, resin liners, and the association of these techniques on the marginal adaptation of composite restorations. One-hundred-and-twenty bovine incisors were selected. A circular cavity was prepared in a flat dentin area on the buccal surface and the Scotchbond Multi Purpose system was applied. These teeth were assigned to four groups in accordance with lining technique: control (one adhesive layer), three adhesive layers individually photoactivated, Filtek Flow, and Protect Liner F. Each group was subdivided depending on the photoactivation method: continuous light, soft-start, or intermittent light. All cavities were restored with Filtek Z250 and then polished. Caries detector was applied on each specimen for 5 s in order to verify marginal adaptation through dye-staining of the gaps formed on the outer margins. Images of the stained gaps were observed under the stereomicroscope, and transferred to a computer measurement program in order to determine gap length. Data were submitted to ANOVA and Tukey's test (P < 0.05). Significant differences among the lining techniques were only observed using the photoactivation method with continuous light. In this case, the lining technique with Filtek Flow significantly increased marginal adaptation of the composite to the outer dentin margins compared with the results of the control group. The other lining techniques showed intermediate values and no statistical difference from the other groups. For the photoactivation methods, intermittent light showed the best marginal quality of all the methods. This was statistically significant only for the control lining technique.     

Effect of different photo-initiators and light curing units on degree of conversion of composites

The aim of this study was to evaluate: (i) the absorption of photo-initiators and emission spectra of light curing units (LCUs); and (ii) the degree of conversion (DC) of experimental composites formulated with different photo-initiators when activated by different LCUs. Blends of BisGMA, UDMA, BisEMA and TEGDMA with camphorquinone (CQ) and/ or 1-phenyl-1,2-propanedione (PPD) were prepared. Dimethylaminoethyl methacrylate (DMAEMA) was used as co-initiator. Each mixture was loaded with 65 wt% of silanated filler particles. One quartz-tungsten-halogen - QTH (XL 2500, 3M/ESPE) and two lightemitting diode (LED) LCUs (UltraBlue IS, DMC and UltraLume LED 5, Ultradent) were used for activation procedures. Irradiance (mW/cm2) was calculated by the ratio of the output power by the area of the tip, and spectral distribution with a spectrometer (USB 2000). The absorption curve of each photo-initiator was determined using a spectrophotometer (Varian Cary 5G). DC was assessed by Fourier transformed infrared spectroscopy. Data were submitted to two-way ANOVA and Tukey's test (5%). No significant difference was found for DC values when using LED LCUs regardless of the photo-initiator type. However, PPD showed significantly lower DC values than composites with CQ when irradiated with QTH. PPD produced DC values similar to those of CQ, but it was dependent on the LCU type.     

In vitro evaluation of microleakage of different materials used as pit-and-fissure sealants

The aim of this study was to evaluate in vitro the marginal microleakage of different materials used as pit-and-fissure sealants (Delton, Filtek Flow, Dyract Flow and Vitremer). Fifty-six extracted sound human third molars were randomly assigned to 4 groups (n=14). After sealant placement, the teeth were thermocycled (500 cycles; 5 degrees C, 37 degrees C and 55 degrees C), isolated, immersed in 2% buffered methylene blue dye for 4 h, included in acrylic resin and sectioned longitudinally in a buccolingual direction. The sections were analyzed for leakage using an stereomicroscope. A 4-criteria ranked scale was used to score dye penetration. All materials exhibited dye penetration to some extension and no statistically significant difference was observed among the groups (p>0.05). In conclusion, the findings of this study showed that a flowable composite resin, a flowable compomer and resin-modified glass ionomer placed on occlusal pits and fissures had similar marginal sealing as the unfilled self-cured resin-based sealant.     

Compressive strength recovery by composite onlays in primary teeth. Substrate treatment and luting agent effects

OBJECTIVES: To evaluate 1% NaOCl treatment and two resin luting agent effects on compressive strength recovery in composite onlays on primary teeth and to analyze the fractures type. METHODS: Forty sound primary molars crowns were prepared in the standard machine and randomly divided into four groups (n=10): G1 (1% NaOCl/ 30 min+EnForce); G2 (without 1% NaOCl EnForce); G3 (1% NaOCl/ 30 min+Rely X); G4 (without 1% NaOCl+Rely X). The onlays were made using Z250 composite on plaster models. Ten sound teeth were used as control group (CG). All groups were submitted to compression mechanic test in a universal test machine INSTRON at 1mm/min cross-head speed. After that, the data (kgf) were submitted to ANOVA test (alpha=0.05). Finally, the fracture types were classified in a crescent scale (1-5) related with severity degree and submitted to Fisher's Exact Test (p<0.05). Scanning electronic microscope analysis was done in order to illustrate the fractures sites. RESULTS: The values of compressive strength of experimental groups did not differ each others neither from control group (p>0.05). The results from fracture type showed that types 5 and 4 fractures (most severe) present the highest percentage to experimental groups. Conversely, the CG showed higher percentage of fracture types 2 and 3. CONCLUSIONS: This research found that the composite onlays recovered the compressive strength compared to sound teeth, regardless of the substrate treatment and cement agent used. Nevertheless, no group showed similar type of fractures to CG, which had more frequency of less severe fracture types.     

Light-activation of resin cement through ceramic: relationship between irradiance intensity and bond strength to dentin

This study investigated the relationship between the irradiance transmitted through ceramic and the bond strength of a resin cement to dentin. After application of an adhesive system, elastomer molds with cylindrical orifices (1.2 mm in diameter) were placed onto bovine dentin surfaces and filled with a photoactivated luting agent (Enforce; Dentsply Caulk). Light-activation was performed through a 0.6-mm-thick ceramic disc using different intensities: 250, 400, 550, 700, or 850 mW/cm(2). Control specimens were irradiated without ceramic (1050 mW/cm(2)). The radiant exposure was kept at 30 J/cm(2). Light spectral distribution was analyzed with a spectrometer. Microshear test was conducted and modes of failure were classified under SEM. Bond strength data were analyzed with ANOVA and Student-Newman-Keuls' test (alpha < or = 0.05), and failure scores with the Kruskal-Wallis test (alpha < or = 0.05). A linear regression model assessed the relationship between irradiance and bond strength. Groups light-cured at 250 and 400 mW/cm(2) presented lower bond strengths than groups activated at 850 and 1050 mW/cm(2). The linear regression showed that a decrease in light irradiance predicts a decrease in bond strength (r(2) = 0.955; p = 0.004). A predominance of mixed failures was observed. No significant alteration in the spectral wavelengths was observed. Despite the constant energy dose, the bond strength was dependent upon the irradiance level.