Conventional restorations (fillings, crowns, and bridges) used to require the removal of a substantial amount of tooth structure to make them strong and to give them sufficient mechanical retention to the tooth.
Within the last three decades various generations of bonding agents have been developed that allow a direct adhesion of dental materials to the tooth surface. Some recent generations of these agents have a high bonding strength that give porcelain restorations better stress distribution and a long survival rate. A secure placement of porcelain restorations is therefore feasible without an extensive reduction of the tooth for mechanical retention. However, bonded restorations withstand higher pressure and tension without breaking.
While enamel bonding (developed in the 1980's) depended on retentive surface patterns etched by acidic gels within the crystalline structure of the dental enamel, dentin bonding is an entirely different treatment modality. As opposed to enamel (of ectodermal origin), dentin (of mesodermal origin) contains a high amount of collagen fibers and a variety of extra-cellular proteins. It is made up of about 70% inorganic material (mostly hydroxyapatite), 20% of organic matrix, and 10% of water by weight. The organic matrix is about 90% of collagen. Dentin is generally composed of inter- and peri-tubular dentin matrices that are permeated by dentinal tubules. These dentinal tubules harbour the so-called odontoblast processes, which are extensions of odontoblasts, which retreat away from the area of the deposition of dentin matrix.
Dentinal tubules are opened and collagen fibers exposed when exposed to acids. It is the first step for creating a hybrid layer, which is a blend of collagen fibers and resin. The hybrid layer is the retentive interface between the layers of dental materials and the untouched dentin. It is a thin layer of resin-reinforced dentin. Two dissimilar components, natural and artificial, are locked together at a molecular level. This in turn seals the dentin interface towards the dental restoration against leakage and leads to a high degree of acid resistance.
References:
Butler WT. Dentin extracellular matrix (ECM) proteins: comparison to bone ECM and contribution to dynamics of dentinogenesis. Connect Tissue Res 2003; 44: 171–178.
Schilke R. Comparison of the number and diameter of dentinal tubules in human and bovine dentine by scanning electron microscopic investigation. Arch Oral Biol 2000; 45: 355–361.
Goldberg M. Dentin: structure, composition and mineralization. Front Biosci (Elite Ed). 2011; 3: 7711-35.
Nakabayashi N. Hybrid Layer as a Dentin-Bonding Mechanism. Journal of Esthetic and Restorative Dentistry 1991, 3(4): 133-138.
All this allows to save a great amount of tooth structure. It is evident that this development does not just benefit cosmetic dentistry and smile design.
Teeth that are restored with bonded restorations have recently been shown to be more fracture resistant than healthy and intact teeth.
Once your tooth is ready and clean to receive a restoration, it will have to be conditioned to allow the bonding of the restorative material to take place. To understand the value of bonding, a few elementary things about tooth structure have to be understood. If you like to learn more, please feel free to study the graphic depiction of the creation of a hybrid layer.
Bonding makes ''invisibly" strong!
Animated bonding sequence
