تأثير طرق الإمضاج وخطوات الإلصاق للمرمات الراتنجية على المكونات الطبيعية الكيمائية للعاج المهجن"

"THE EFFECT OF CURING TECHNIQUES AND BONDING PROCEDURES OF COMPOSITE RESTORATIONS, ON THE PHYSICO-CHEMICAL STRUCTURES OF HYBRIDIZED NORMAL AND "HEBAALLA MOHAMED TAHER AHMED

EROSIVE DENTINE                                                           

                                                                "The increased esthetic demands and patients’ interest have resulted in the development of new tooth-coloured restorative materials and techniques. Composite resin materials and adhesive techniques have become the foundation of modern dentistry. Now, they are used in cases ranging from the restoration of initial decay and cosmetic correction to veneering in complex prothodontic rehabilitation. However, polymerization shrinkage of composite resins remains a challenge and still imposes limitations in the application of techniques. (1)

During the pre-gel polymerization, composite resin is able to flow, which relieves stress within the structure. (2) After gelation, flow ceases and cannot compensate for shrinkage stresses. Therefore, post gel contraction, results in clinically significant stresses in composite – tooth bond and surrounding structure. (3) These stresses may produce defects in composite tooth bond, leading to bond failure, microlcakage with associated postoperative sensitivity, (4) recurrent caries and could also cause deformation of the surrounding tooth structure. (5) This coronal deformation may result in enamel microcracks in the cervical region and postoperative hypersensitivity. (6)

The control of contractions stresses may be accomplished by different methods. (7) One approach is the technique or the manipulation of the composite resin during filling. This can be achieved by controlling the technique of insertion, (8) or modulating the curing technique. The concept is to prolong the time required for the material to approach the post-get phase. The longer the pre-gel phase the more the restoration can adapt to shrinkage.(9) One way to prolong the pre-gel time is through controlling the. curing light by using “soft-start” or two-step polymerization. (10) Pulse-delay curing mode, have been recently proposed to allow relaxation of stresses of composite resin materials during polymerization. (11)

Bonding to dentin is affected by many variables some of them are related primarily to the dentin structure perse. (12) Dentin is a dynamic substrate, (13) with regional differences in dentinal tubule density, dentin permeability, calcium concentration, presence of abnormal dentin and varying thickness of smear layer. This results in non-uniform etching of dentin, and hence a non uniform bond strength. (14) Van Meerbeek et at, in 1994(15) suggested that demineralization is more difficult in both the peritubular and intergobular regions of sclerotic dentin and they showed that, the hybrid resin layer formed in dentin bonding is much thinner and exhibited fewer or no resin tags as compared to normal dentin.

It’s worthy to mention that adherence depends on adhesive technology, material application, taken into consideration its time, the surrounding tooth structure and within the immediate vicinity of the hybridized dentin. All are factors inducing a change which mereostates its investigation."