Effects of Polymerization Mode and Interaction with Hydroxyapatite on the Rate of pH Neutralization, Mechanical Properties, and Depth of Cure in Self-Adhesive Cements.

OBJECTIVE: The aim of the study was to evaluate the physicochemical properties of self-adhesive resin cements associated with hydroxyapatite (HAp) according to the polymerization activation. MATERIALS AND METHODS: Specimens of cements (PermaCem 2.0 [DMG]; MaxCem Elite [Kerr], and RelyX U200 [3M ESPE]) were distributed into three groups: activation mode; self-cured and dual-cured modes; and association or not with HAp powder mode. The pH neutralization was evaluated as a function of time. Flexural strength and elastic modulus were also tested (0.5 mm/min.). The depth of cure was also analyzed using the scraping test (ISO 4049). Infrared spectroscopy was also used to collect the spectra of specimens to evaluate the chemical bonds. Statistical comparisons were conducted at 5% of significance. RESULTS: The aggressiveness of the self-adhesive resin cements evaluated varied among the materials with a tendency for neutralization. Self-cure groups exhibited lower pH throughout the entire evaluation when compared with that of the dual-cure ones, irrespective of the addition of HAp. MaxCem Elite when photoactivated was the only cement influenced by the addition of the HAp in terms of mechanical properties. The self-adhesive cements tested presented equivalent depth of cure based on the ISO 4049 requirements, regardless of the evaluated factors. CONCLUSIONS: Based on the parameters evaluated, the results demonstrated that most of the self-adhesive cements remained unaltered or improved when mixed with HAp, regardless of the activation mode.

Synthesis and Characterizations of a Collagen-Rich Biomembrane with Potential for Tissue-Guided Regeneration.

OBJECTIVES: In this study, a collagen-rich biomembrane obtained from porcine -intestinal submucosa for application in guided bone regeneration was developed and characterized. Then, its biological and mechanical properties were compared with that of commercial products (GenDerm [Baumer], Lumina-Coat [Critéria], Surgitime PTFE [Bionnovation], and Surgidry Dental F [Technodry]). MATERIALS AND METHODS: The biomembrane was extracted from porcine intestinal submucosa. Scanning electron microscopy, spectroscopic dispersive energy, glycosaminoglycan quantification, and confocal microscopy by intrinsic fluorescence were used to evaluate the collagen structural patterns of the biomembrane. Mechanical tensile and deformation tests were also performed. STATISTICAL ANALYSIS: The results of the methods used for experimental membrane characterizations were compared with that obtained by the commercial membranes and statistically analyzed (significance of 5%). RESULTS: The collagen-rich biomembrane developed also exhibited a more organized, less porous collagen fibril network, with the presence of glycosaminoglycans. The experimental biomembrane exhibited mechanical properties, tensile strength, and deformation behavior with improved average stress/strain when compared with other commercial membranes tested. Benefits also include a structured, flexible, and -bioresorbable characteristics scaffold. CONCLUSIONS: The experimental collagen-rich membrane developed presents physical-chemical, molecular, and mechanical characteristics similar to or better than that of the commercial products tested, possibly allowing it to actively participating in the process of bone neoformation.

Influence of light-curing sources on polymerization reaction kinetics of a restorative system.

PURPOSE: To determine the effect of using a variety of commercial light-curing units on polymerization of a dentin-bonding agent (Adper Single Bond) and of a resin composite (Filtek Z250). METHODS: Infrared (IR) spectra were obtained kinetically at one scan/second at 2 cm(-1) resolution for a period of 5 minutes and were analyzed for: maximum conversion rate (%/s), time into exposure when maximum rate occurred (seconds), conversion at maximum rate (%), and total conversion (%) at 300 seconds by comparison of aliphatic-to-aromatic absorption IR peak ratios, before and after polymerization. Light units used were: QTH 540 mW/cm2 (XL3000); LED 750 mW/cm2 (Elipar FreeLight 2); PAC 2,130 mW/cm2 (ARC II). Exposure followed manufacturers' recommendations: dentin bonding agent for 10 seconds, RC for 20 seconds (QTH), and 10 seconds (LED and PAC). Polymerization kinetics was evaluated at the bottom surface (2.5 mm thick) for the resin composite and as a thin film for the dentin bonding agent on the diamond surface of an attenuated total reflectance accessory in the IR spectrometer. Values (n = 5) were compared using ANOVA and Tukey's pairwise post-hoc test: pre-set alpha 0.05. RESULTS: PAC produced the highest total conversion and conversion rate for the resin composite (P < 0.05). Total conversion was lower for dentin bonding adhesive using PAC than with LED or QTH (P < 0.05). LED provided the highest proportion of conversion at the maximum rate with respect to conversion at 300 seconds for both materials. QTH demonstrated the lowest maximum rate value that occurred at a longer time into exposure (P < 0.05). Polymerization kinetic parameters varied greatly between the restorative materials as well as among light-curing unit types when compared to values observed when using a QTH light as control.

A new technique for assessing hybrid layer interfacial micromorphology and integrity: two-photon laser microscopy.

PURPOSE: This study describes a two-photon laser fluorescence microscopy technique developed to evaluate the interfacial micromorphology of the hybrid layer in bonded restorations. MATERIALS AND METHODS: Micropermeability of the hybrid layer was characterized by means of simultaneously contrasting a dye-containing adhesive with a differently colored dye placed into the pulp chamber and allowed to diffuse toward the different-colored hybrid layer. A fluorescent red dye (rhodamine B) was incorporated into a commercial dentin bonding agent. Class I preparations (margins in enamel) were made on extracted human third molars. The teeth were restored using conventional methods: bonding agent, composite, finishing, and polishing. An aqueous solution of a yellow/green dye (fluorescein) was then placed into the pulp chamber for 3 h, allowing time to diffuse toward the different-colored bonded interface. The teeth were then embedded, sectioned, and microscopically analyzed using two-photon laser microscopy at 40X magnification. RESULTS: Subsurface fluorescent imaging using this technique enabled interfacial micromorphology to be characterized at submicrometer resolution and provided high-contrast images. The quality of surrounding structures and potential presence of gaps were also precisely assessed. CONCLUSION: Two-photon laser microscopy provided high quality, high-resolution images of the bonded interface and surrounding areas, allowing accurate qualitative and quantitative analysis of the structure and integrity of the hybrid layer.

Factors affecting use of fluorescent agents in identification of resin-based polymers.

PURPOSE: The present study is a compilation of methodologies developed in order to evaluate the effects of addition of a fluorescent agent, rhodamine B, to resin-based materials. The intent of the work was to develop a systematic methodology that accounts for variables not shown to be of concern in past testing, but may significantly affect interpretation of the resulting images and material properties. MATERIALS AND METHODS: Different methodologies were specifically developed to evaluate factors affecting the use of the fluorescent agent rhodamine B in the identification of resin-based materials. The influence of dye concentration was evaluated with respect to adhesive polymerization reaction kinetics and bond strength of the resin into which the dye is added. The pH of the dye-solvent solution was also considered. Additionally, the mass and percentage of rhodamine B leached into different media over time was determined. RESULTS: It was demonstrated that a specific dye must be used with caution, and the concentration of a fluorescent agent is important with respect to both the conversion and bond strength of the resin to which the dye is added. An alcohol-based dye solution also produced an extremely high amount of dye leaching from polymerized specimens. The adhesive pH was not altered. CONCLUSION: The standardized methodology developed here to analyze restoration interfaces using a fluorescent dye can lessen the impact of variables when interpreting results.

Bond strength of resin-based restorations polymerized with different light-curing sources.

PURPOSE: To evaluate the influence of different light-curing units on microtensile bond strength of resin composite restorations. MATERIALS AND METHODS: Standardized Class I preparations (6.0 x 4.5 mm, 2.5 mm deep) were made in extracted human third molars after abrading the cusps. Resin was inserted in bulk using a 3M ESPE restorative system [Adper Single Bond (DBA)/ Filtek Z250 (RC)]. Both materials were polymerized using different light-curing units: QTH at 540 mW/cm(2) (XL 3000, 3M ESPE); LED at 750 mW/cm(2) (Elipar FreeLight2, 3M ESPE); PAC at 2130 mW/cm(2) (Arc Light II, Air Techniques). Nine different light combinations were developed to polymerize both DBA and RC: QTH/QTH; QTH/LED; QTH/PAC; LED/LED; LED/QTH; LED/PAC; PAC/PAC; PAC/QTH; PAC/LED. Restored teeth were stored in distilled water for 24 h at 37 degrees C and then sectioned, yielding stick-shaped specimens with a bonded area of approximately 0.9 mm(2). Specimens were assessed in a testing machine at a crosshead speed of 1 mm/min. The results were analyzed using two-way ANOVA and Tukey's test at a pre-set alpha = 0.05. RESULTS: The combinations PAC/QTH and QTH/QTH presented the highest bond strength values, and LED/QTH the lowest (p < 0.05). Significantly lower values were observed in combinations when the LED light was used to polymerize DBA compared to QTH and PAC lights, irrespective of the light source used to polymerize RC (p < 0.05). Same light combinations presented similar bond strength values. CONCLUSIONS: Different light sources influence restoration bond strength. Bond strength is more dependent on the light source used for DBA than for curing RC.

Use of fluorescent compounds in assessing bonded resin-based restorations: a literature review.

OBJECTIVES: This work reviews fundamental concepts involved with fluorescent imaging in the dental materials field. DATA: Fluorescent dyes have been widely used: incorporated into adhesive system components, placed in the pulp chamber and allowed to diffuse toward the restorative interface, as well as used as a visible tracer in microleakage tests. CONCLUSIONS: Although use of fluorescent imaging has substantially contributed to the existing knowledge base, there is no standardized methodology used, and as a result, interpretation of study results as well as comparison of results among studies remains questionable.

Evaluation of compatibility between different types of adhesives and dual-cured resin cement.

PURPOSE: The objective of this in vitro study was to evaluate the bonding compatibility between different adhesives and a dual-cured resin cement, using a conventional tensile bond test. MATERIALS AND METHODS: The adhesives used were: Prime & Bond (PB) (Dentsply) (PB), Scotchbond Multi Purpose (SB) (3M), and the activator Self Cure (SC) (Dentsply). The dual-curing resin cement used was Enforce (EF) (Dentsply). Six groups with five specimens in each were tested: G1: EF/PB/EF (light cured); G2: EF/SB/EF (light cured); G3: EF/PB+SC/EF (light cured); G4: EF/PB+SC/EF (only chemically cured); G5: EF/EF (light cured); G6: EF/EF (only chemically cured). The resin cement was applied in two stainless steel molds with a cone-shaped perforation measuring 4 mm in diameter and 1 mm in thickness, and the adhesive was applied between them. Ten minutes after specimens were cured, the tensile strength was measured in a universal testing machine at a crosshead speed of 0.5 mm/min. RESULTS: The mean values (MPa) +/- SD obtained in each experimental group were: G1: 1.4 +/- 0.2; G2: 1.3 +/- 0.2; G3: 1.2 +/- 0.4; G4: 0.8 +/- 0.2; G5: 1.2 +/- 0.1; G6: 0.7 +/- 0.1. The results were statistically evaluated using nonparametric Kruskal-Wallis and Dunn tests (p < or = 0.05). Statistically significant differences among groups were found only between G1 and G4, and G1 and G6. CONCLUSION: There was no incompatibility among the different adhesives used with dual-cured resin cement. The lowest tensile bond strength values occurred in the absence of photoactivation.