Bonding to dentin relies on the penetration of adhesive into the collagen fibers (polypeptides) and encapsulation of the irregular hydroxyapatite crystals at the bottom of the decalcified area, to create the resin-reinforced interdiffusion zone called the “hybrid layer�. Concerns have been raised that dentin bonding agents do not fully diffuse through the collagen network that remains after acid conditioning of dentin. This unprotected collagen may potentially be a weak physical link in the long term adhesion of dentin to resin. Hydrolysis of these bands of exposed collagen not protected by resin (non-hybridized collagen) would occur with long term exposure to water. This could lead to deterioration of the adhesion between resin and dentin, resulting in decreased bond strength. So the purpose of the present study was to investigate the effect of collagen removal using sodium hypochlorite (NaOCl) following acid conditioning of the dentin on the shear bond strength of two single bottle adhesive systems, an acetone based (Prime & Bond NT) and ethanol/water based (3M Single bond).

The effect of three Bleaching Agents (Opalscence, 30% H2O2 and 30% H2O2 mixed with Sodium Perborate) and 37% Phosphoric acid on the external surface of Human enamel were examined with the scanning Electronic Microscope. The materials were applied to the enamel surfaces of 50 specimens obtained for 10 teeth. Each test agent was applied to one specimen from each tooth. One specimen of each tooth was left untreated. Comparison to the untreated control surfaces revealed that enamel exposed to the bleaching agents underwent slight Morphologic Surface alterations. The enamel surfaces treated with Phosphoric Acid, in contrast showed severe Morphologic alterations.

Recently, the importance of light source intensity has been in the forefront of clinical practice. It is generally accepted that an intensity reading of 400 mW/cm2 or greater in the proper wave length range is needed for complete polymerization of material up to 2 mm depth with an optimal exposure time of 40 seconds. In the present study the intensity of light curing units were checked among 50 private practitioners and the effect of its variation on the compressive strength was measured. After checking the intensity with a radiometer, a posterior composite resin (Solitaire, Shade A30 was cured in a plastic mould of 4 mm depth and 5 mm diameter by placing the composite in 2mm increments. After curing. It was stored in distilled water and later compressive strength of the cured composite was measured with an Instron universing testing machine with 0.2mm/minute cross head speed. The result showed a decrease in the compressive strength with reduction in the intensity of light cure unit. To conclude, there is a relation between intensity and compressive strength and that the compressive strength reduced with decreased intensity of the curing light.

Extensive silver amalgam restorations in premolars and molars occasionally require sacrifice of healthy unsupported enamel walls or cusps. Unsupported enamel is prohibited because it may lead to cuspal fractures in large silver amalgam restorations and complicated, posterior silver amalgam restorations also lack esthetics. Inserting composite resin veneers to disguise silver amalgam restorations has been proposed. Large hybrid composite resin restorations in posterior teeth are more conservative and esthetic than are silver amalgam restorations, but researchers agree that composite resins commonly exhibit few drawbacks and they are unsuitable for stress bearing restorations. A conservative approach to the treatment of wide and deeply carious posterior teeth; an alternative to the use of retentive form, is described in this study. The technique involves reinforcing the thin cavity walls or undermined cusps for conservative restorations with a posterior composite resin. The new cavity preparation can be restored with a silver amalgam that ensures occlusal resistance and an acceptable marginal seal.

The method of reducing dentinal sensitivity by incorporation of glutaraldehyde is known. However, the effect of 2% glutaraldehyde on the hybridization and thus the bond strength is still obscure. This study was undertaken to determine the effect of use of 2% glutaraldehyde on the bond strength using 5% generation bonding agent and also the effect of same on the formation of hybrid layer. The variables tested were 5th generation bonding agent with and without application of 2% glutaraldehyde, applied before and after the application of 5th generation of bonding agent. The results showed a definite increase in bond strength in the group in which glutaraldehyde was a part of bonding protocol.

Retention of restoration in non-carious cervical lesions (NCCLs) present a challenge to the practitioners. The reasons cited for loss of restoration are multiple. Polymerization shrinkage resulting in v-shaped gap formation at the cervical margin due to questionable bonding and concentration of flexural stresses at the cervical region of tooth and inability of stiff composite resin material to flex with the flexion of tooth under occlusal loading are some of the reasons resulting in loss of restorative materials. The aim of the present study was to compare the retention of two composite resins of different modulus of elasticity, hybrid and microfilled with two different bonding agents – 5th generation dentin bonding agent and glass-ionomer based adhesive system in NCCLs in canines and premolars. 64 NCCLs were divided randomly into 4 groups of approximately 40 each and restored with 4 variables (i.e. two bonding agents and two restorative materials) interchanged with each other. 6 months follow up was carried out and retention rate was evaluated using Modified United State Public Health Service criteria. Statistically no significant difference was found between these groups (p>0.05).