SUMMARYThis in vivo study evaluated by TEM the degradation of dentin hybrid layers in deep occlusal resin composite restorations. Caries-free premolars scheduled for extraction as part of orthodontic treatment were prepared, restored and evaluated after two and six months. The adhesive used was a single-bottle etch-and-rinse product (Single Bond Plus, 3M ESPE). Control group restorations were placed according to the manufacturer's instructions, while the experimental group received application of a 2% solution of chlorhexidine digluconate after etching. No degradation was observed in either group after two months. Slight degradation was found in the control group after six months, but none was observed in the experimental group. In vitro testing showed no significant difference in microtensile bond strength between the control and experimental adhesive protocols. INTRODUCTIONThe adhesion of resin to dentin became feasible with the advent of hydrophilic resins capable of infiltrating and polymerizing within the collagen mesh exposed through acid decalcification of dentin, forming a hybrid layer.1 Unfortunately, this adhesion degrades over time, 2-3 probably due to hydrolysis of both the resin and Degradation of dentin hybrid layers in Class I resin composite restorations is minimal over six months but is lessened by the application of 2% chlorhexidine digluconate after etching.

Objectives The lack of durability in resin–dentine bonds led to the use of chlorhexidine as MMP-inhibitor to prevent the degradation of hybrid layers. Biomimetic remineralisation is a concept-proven approach in preventing the degradation of resin–dentine bonds. The purpose of this study is to examine the integrity of aged resin–dentine interfaces created with a nanofiller-containing etch-and-rinse adhesive after the application of these two approaches. Methods The more established MMP-inhibition approach was examined using a parallel in vivo and in vitro ageing design to facilitate comparison with the biomimetic remineralisation approach using an in vitro ageing design. Specimens bonded without chlorhexidine exhibited extensive degradation of the hybrid layer after 12 months of in vivo ageing. Results Dissolution of nanofillers could be seen within a water-rich zone within the adhesive layer. Although specimens bonded with chlorhexidine exhibited intact hybrid layers, water-rich regions remained in those hybrid layers and degradation of nanofillers occurred within the adhesive layer. Specimens subjected to in vitro biomimetic remineralisation followed by in vitro ageing demonstrated intrafibrillar collagen remineralisation within hybrid layers and deposition of mineral nanocrystals in nanovoids within the adhesive. Conclusions The impact was realized by understanding the lack of an inherent mechanism to remove water from resin–dentine interfaces as the critical barrier to progress in bonding with the etch-and-rinse technique. The experimental biomimetic remineralisation strategy offers a creative solution for incorporating a progressive hydration mechanism to achieve this goal, which warrants its translation into a clinically applicable technique.

Tooth bleaching is an exciting treatment option for patients, which has many treatment options and considerations for the dentist. The purpose of this article is to answer questions in a Q&A fashion about different types of tooth bleaching and their applications to various clinical situations and patients' dental situations.

Objective To provide an update on tray bleaching for various tooth discoloration conditions, including a complete examination form as well as an information and consent form. Clinical considerations Since the bleaching process was first documented in 1989, it has become a safe, successful, and conservative treatment for consistently whitening the color of patients' natural teeth. Though initially used on a limited basis, the process has expanded to include bleaching nicotine and tetracycline stains, single dark teeth, brown spots, reducing white spots, caries control as well as color change from aging. Ten percent carbamide peroxide is the material most used in research and has shown to be the most effective with the least amount of adverse side effects, including sensitivity or gingival irritation. Bleaching overnight using a smooth nonscalloped, nonreservoir vacuum‐formed tray has been shown to be the method of choice for most clinicians, leading to greater patient compliance and an overall successful treatment. When possible, conservative bleaching treatment should be considered prior to more invasive, irreversible procedures such as veneers, or crowns to meet patients' esthetic requirements. Because of its basic pH, and potential for caries inhibition, complete restorative treatment does not have to be performed prior to initiating bleaching, making it an extremely flexible treatment. Conclusion With a thorough bleaching analysis, proper treatment of appropriate discolorations over an ideal timeframe, tray bleaching is a powerfully predictable tool in restorative dentistry. Clinical significance Tray bleaching with 10% carbamide peroxide should be the first consideration for treatment of discolorations of any type, with varying times of treatment, even in the presence of mild decay.

Clinicians need to be aware of the possible interaction between curing light barriers and curing light type in order to optimally photocure restorative materials.