PubMed · 11495570
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J Nicholls. Remember when?. https://pubmed.ncbi.nlm.nih.gov/11495570/
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OBJECTIVES: This study evaluated the ultra-morphological effects of maleic and citric acid on human dentin by means of a field emission in-lens scanning electron microscope (FEISEM). Both acids were tested on human dentin at pH 0.7 and 1.4 in aqueous solutions. METHODS: Each of 12 dentin disks were divided into four groups and exposed to either maleic acid at pH 0.7, maleic acid at pH 1.4, citric acid at pH 0.7 and citric acid at pH 1.4. All samples were then fixed and dehydrated in a critical point drying apparatus. Observations were carried out by means of a FEISEM (JEOL 890) after coating with a carbon-platinum film. RESULTS: Both acids removed smear layer and partially removed smear plugs. Details of fine structures measuring from 5 to 15 nm were shown on the intertubular demineralized dentin. Maleic acid at pH 0.7 showed the highest depth of demineralization of all the tested samples; citric acid, showed a higher depth of demineralization values when tested at pH 1.4 than at pH 0.7. SIGNIFICANCE: The FEISEM reveals ultra-structural aspects of the demineralization process of the dentin tissue of the both acids tested. Differences related to the pH of the acids were found. Images obtained at high magnification clarify the dentin collagen structure of both peritubular and intertubular dentin. Small periodic structures associated with collagen fibrils were also imagined.
OBJECTIVES: This study investigated the effect of two factors: conditioning methods and light-curing techniques on the marginal adaptation of Dyract AP (Dentsply DeTrey, Germany). The 'pulse activation' curing technique was compared with a conventional light-curing technique for their effectiveness in reducing marginal gaps in restorations that were conditioned with three different protocols. MATERIALS AND METHODS: Cylindrical cavities, 3mm in diameter, were prepared in extracted human molar teeth. They were restored with Dyract AP using Prime&Bond NT (PBNT; Dentsply DeTrey) as the adhesive. Cavities were etched with: Conditioner36/PBNT (group 1), Non-Rinse Conditioner (NRC)/PBNT (group 2), and PBNT only (group 3). Either conventional or the 'pulse activation' technique was used for light-curing of the material. Epoxy resin replicas were obtained from longitudinal sections of the specimens, and the restoration-tooth interfaces were examined using scanning electron microscopy. Marginal qualities along the resin-dentin interfaces were further measured using image analysis and analyzed using nonparametric statistical methods. RESULTS: With the conventional curing technique, enamel margin fractures were frequently observed. Marginal gaps were found along the compomer-dentin interfaces irrespective of the conditioning protocol. A significantly lower percentage of gap-containing margins were found in cavities that were conditioned with 36% phosphoric acid. With the 'pulse activation' technique, no marginal gap was found along compomer-dentin interfaces that were etched with either Conditioner36 or NRC. More than 90% of the total margin length were excellent. No cohesive failure of enamel could be observed along cavosurface margins. SIGNIFICANCE: The 'pulse activation' curing technique significantly improves the marginal integrity of Dyract AP when Conditioner36/Prime&Bond NT and NRC/Prime&Bond NT are used as conditioning/bonding systems. The use of Prime&Bond NT without etching is not recommended, as marginal gaps are present irrespective of the curing techniques employed.
OBJECTIVES: The purpose of this study was to evaluate the effects of thickness and adhesion of three resin cements on the fracture resistance of indirect resin composite bonded to dentin. METHODS: A disk of resin composite used for indirect restorations was bonded to a disk of bovine dentin using three kinds of resin cements with various bonding procedures. The bonding procedures were planned into five groups according to the materials and methods, and subsequently subdivided into three groups according to the cement thickness (50, 150 and 500 microm) in each bonding procedure. The thickness of the resin cement and that of the resin composite disk was changed simultaneously while maintaining a total specimen thickness of 2 mm. The prepared specimens were then stored in water at 37 degrees C for 24h at which time they were trimmed to a size of 2 x 2 x 8 mm. The trimmed specimens were subjected to a three point bending test and the fracture load determined. The tensile bond strength of each bonding procedure was measured and the correlation to the fracture load evaluated. RESULTS: The fracture load was affected by the dentin bond strength. The effect of cement film thickness on the fracture load was negligible. SIGNIFICANCE: When an indirect restoration is adhered to the tooth substrate, the adhesion of the luting cement to the tooth substrate is very important for the fracture resistance of indirect resin composite.