Phosphoric acid concentration affects dentinal MMPs activity.

OBJECTIVES: To evaluate whether the concentration of phosphoric acid (PA) has an effect on the proteolytic activity of sound human demineralized dentin. It is hypothesized that the activity of matrix-bound and extracted enzymes depends on the PA concentration used to demineralize dentin. METHODS: One-gram aliquots of mid-coronal human dentin powder were demineralized with 1wt%, 10wt% and 37wt% PA. Concentrations of released calcium were measured for each set of demineralization. Extracted MMP-2 was immunologically identified by western blot and its activity was determined by conventional gelatin zymography. Analysis of released hydroxyproline (HYP) and in situ zymography were performed to evaluate the activity of insoluble, bound-matrix enzymes. RESULTS: The amount of released calcium from dentin powder treated with 37wt% PA was significantly higher (p≤0.05) than that obtained by dentin demineralization with 10wt% and 1wt% PA. Expression and activity of endogenous enzymes, extracted from or bound to dentin matrix, were detected for all samples regardless of the PA concentration. However, the expression and activity of extracted MMP-2 were significantly higher when dentin was treated with 10wt% PA (p<0.05), followed by 1wt% and 37wt% PA. Similarly, the highest concentration of released HYP (i.e. meaning higher percentage of collagen degradation) and the highest activity in in situ zymography were observed when dentin samples were treated with 10wt% PA (p<0.05). CONCLUSIONS: It was confirmed that PA does not denature endogenous enzymes of dentin matrices, but it may somehow modulate the expression and activity of these enzymes in a concentration-dependent manner. CLINICAL SIGNIFICANCE: Endogenous proteases have been identified and suggested to be responsible for the digestion of dentin matrix when activated by the acidic components of dental adhesives. Proteolytic activity of dentinal MMPs showed to be dependent on phosphoric acid concentration. The clinically-used concentration (37%) does not inhibit MMPs activity, but slows it.

Temperature increase at the light guide tip of 15 contemporary LED units and thermal variation at the pulpal floor of cavities: an infrared thermographic analysis.

In this study, a comprehensive investigation on the temperature increase at the light guide tip of several commercial light-emitting diode (LED) light-curing units (LCUs) and the associated thermal variation (ΔT) at the pulpal floor of dental cavities was carried out. In total, 15 LEDs from all generations were investigated, testing a quartz-tungsten-halogen (QTH) unit as a reference. The irradiance level was measured with a power meter, and spectral distribution was analyzed using a spectrometer. Temperature increase at the tip was measured with a type-K thermocouple connected to a thermometer, while ΔT at the pulpal floor was measured by an infrared photodetector in class V cavities, with a 1-mm-thick dentin pulpal floor. The relationship among measured irradiance, ΔT at the tip, and ΔT at the pulpal floor was investigated using regression analyses. Large discrepancies between the expected and measured irradiances were detected for some LCUs. Most of the LCUs showed an emission spectrum narrower than the QTH unit, with emission peaks usually between 450 and 470 nm. The temperature increase at the tip followed a logarithmic growth for LCUs with irradiance ≥1000 mW/cm(2), with ΔT at the tip following the measured irradiance linearly (R(2)=0.67). Linear temperature increase at the pulpal floor over the 40-second exposure time was observed for several LCUs, with linear association between ΔT at the pulpal floor and measured irradiance (R(2)=0.39) or ΔT at the tip (R(2)=0.28). In conclusion, contemporary LED units show varied irradiance levels that affect the temperature increase at the light guide tip and, as a consequence, the thermal variation at the pulpal floor of dental cavities.

Polymerization stress, flow and dentine bond strength of two resin-based root canal sealers.

AIM: To compare two resin-based root canal sealers (AH Plus and dual cure Epiphany) in terms of flow, polymerization stress and bond strength to dentine. METHODOLOGY: Flow was evaluated by measuring the diameter of uncured discs of sealer (0.5 mL) after 7 min compression (20N) between two glass plates (n = 5). Polymerization stress was monitored for 60 min in 1-mm thick discs bonded to two glass rods (Ø = 5 mm) attached to a universal testing machine (n = 3). Bond strength was analyzed through micropush-out test (n = 10) and failure mode was examined with scanning electron microscope (100x and 2500x). Data were statistically analyzed using the Student's t-test (alpha = 0.05). RESULTS: Polymerization stress was 0.32 +/- 0.07 MPa for Epiphany self-cure, 0.65 +/- 0.08 MPa for Epiphany light-cure and zero for AH Plus (P < 0.05). Flow data and bond strength values were 30.9 +/- 1.1, 28.6 +/- 0.7 mm and 6.3 +/- 5.3, 17.8 +/- 7.5 MPa for Epiphany and AH Plus, respectively (P < 0.001). Failure mode was predominantly cohesive in the sealer for both materials. CONCLUSIONS: Epiphany had higher flow and polymerization stress and lower bond strength values to dentine than AH Plus. In view of these findings it can be implied that AH Plus would provide a better seal.

Influence of photoactivation protocol and light guide distance on conversion and microleakage of composite restorations.

PURPOSE: To evaluate the effect of light guide distance and the different photoactivation methods on the degree of conversion (DC) and microleakage of a composite. METHODS AND MATERIALS: Three photoactivation protocols (600 mW/cm2 x 40 seconds; 400 mW/cm2 x 60 seconds or 200 mW/cm2 x 20 seconds, followed by 500 mW/cm2 x 40 seconds) and three distances from the light source (0, 3 or 7 mm) were tested. Cylindrical specimens (5 mm diameter; 2 mm tall; n=3) were prepared for the DC test (FT-Raman). Class V cavities were made in 90 bovine incisors to conduct the microleakage test. The specimens were conditioned for 15 seconds with phosphoric acid (37%), followed by application of the adhesive system Prime & Bond NT (Dentsply/Caulk). The preparations were restored in bulk. The specimens were stored for 24 hours in distilled water (37 degrees C) before being submitted to the silver-nitrate microleakage protocol. The restorations were sectioned and analyzed under 25x magnification. RESULTS: Statistical analyses (two-way ANOVAs and Tukey test, alpha=0.05) found significance only for the factor distance (p=0.015) at the top of the composite for the DC test. Conversion was statistically lower for the 7 mm groups compared to the 0 and 3 mm groups, which were equivalent to each other. At the bottom of the specimens, none of the factors or interactions was significant (p<0.05). The Kruskal-Wallis test showed that, in general, the soft-start method led to lower microleakage scores when compared to the continuous modes, mainly when associated with a distancing of 7 mm (p<0.01). With the exception of specimens irradiated with 400 mW/cm2 that did not demonstrate variations on scores for the distances tested, higher microleakage was observed for shorter distances from the light source. CONCLUSIONS: Soft-start methods may reduce microleakage when the light guide distancing provides a low level of irradiance, which also causes a discrete reduction in the DC.

Microtensile bond strengths of one-bottle dentin adhesives.

PURPOSE: To investigate the in vitro performance of three one-bottle adhesives by measuring their dentin microtensile strength. MATERIALS AND METHODS: Extracted human molars had the dentin exposed on the occlusal surface. The teeth were randomly assigned to three dentin adhesives: Group 1 - Prime & Bond 2.1; Group 2 - Prime & Bond NT; and Group 3 - Experimental (unfilled NT). All materials were applied as recommended by the manufacturer. A high-density resin composite (Surefil) was packed on the bonding area in five increments. Specimens (sticks) were obtained using a diamond disc and were stored in distilled water for 24 hrs. The microtensile bond strengths were measured with a universal testing machine. RESULTS: Group 1: 54.3+/-15.6 MPa; Group 2: 62.0+/-17.6 MPa; Group 3: 54.6+/-16.8 MPa. Although no statistically significant difference was found between pairs of means, Prime&Bond NT showed a tendency for higher bond strengths.

Fluoride release from restorative materials and its effects on dentin demineralization.

As the use of adhesive restorative materials has increased during the last several years, interest in adhesive materials that release fluoride has also grown. The purpose of this study was to measure fluoride release from several adhesive restorative materials and to evaluate its effect on dentin resistance to demineralization and on bacterial metabolism in a modified in vitro system. Standardized cavities (1.8 mm in diameter) were prepared in bovine teeth that had been ground to dentin. One cavity in each tooth was restored with one of the following restorative systems: (a) Single Bond and Z100; (b) Single Bond and Tetric Ceram; (c) Fuji Bond LC and Z100; (d) Fuji Bond LC and Tetric Ceram; (e) Fuji II LC; or (f) Fuji IX GP. The other cavity in each tooth was "restored" with wax as a control. For each restorative system, 12 specimens were evaluated for fluoride release during the first 24 hrs after restoration placement. Dentin adjacent to the restored sites was subjected to lactic acid challenge (pH 4.3) for 3 hrs, after which calcium release was measured. Another 12 specimens in each group were stored for 24 hrs in de-ionized water, and were exposed to an S. mutans suspension (1:1 THB/de-ionized water and 50 mM glucose, A660 = 0.2) for 6 hrs, followed by calcium release and pH measurement. Bulk specimens of each material were also made and stored in water. Fluoride released from Fuji Bond LC, Fuji IX GP, and Fuji II LC in bulk was significantly greater than from the other materials. In the restored dentin specimens, increased resistance to demineralization from a lactic acid challenge was directly related to fluoride release. The same effects were seen as a result of the S. mutans challenge. While fluoride release from restorative materials increased the resistance of dentin to demineralization in this system, the clinical relevance of the findings is not known.

Microleakage of Class V resin-based composite restorations using five simplified adhesive systems.

PURPOSE: To evaluate microleakage at enamel and dentin margins of Class V resin-based composite (RBC) restorations using five simplified adhesive systems, one self-etching adhesive, three commercial one-bottle adhesives and one experimental one-bottle adhesive. MATERIALS AND METHODS: Class V cavities (3 mm x 2 mm x 2 mm) were prepared in sound human molars with occlusal margins in enamel and gingival margins in dentin/cementum. Etch & Prime 3.0 (Degussa), Single Bond (3M), PQ1 (Ultradent), Prime & Bond NT (Dentsply) and Experimental BEH (Dentsply DeTrey) were applied strictly according to manufacturers instructions. All adhesive systems were applied on etched substrates, except for the self-etching adhesive Etch & Prime 3.0. Cavities were restored with Z100 RBC. After finishing and polishing, teeth were thermo-cycled (x 700, 5-55 degrees C, 60 s dwell time). Specimens were coated with nail varnish, immersed in silver nitrate for 2 hours and sectioned longitudinally with a diamond disc. The extent of leakage was measured and ranked using a 0-4 scale. RESULTS: Statistical analysis using Kruskal-Wallis test revealed significantly higher leakage scores (P < 0.001) for Etch & Prime 3.0 on enamel when compared to all other adhesive systems. Regarding dentin margins none of the systems completely eliminated microleakage. PQ1 had significantly lower scores (P < 0.05) when compared to Etch & Prime 3.0 and Single Bond. No statistically significant difference was observed for the other groups.