Dental Library- Bonding
Bonding is extremely versatile and therefore can be used to do many types of dentistry. Bonding is the chemical preparation of hard tooth structure, both enamel and dentin, to cause micro pores that the bonding agent fills and locks into. Then the restorative material is chemically bonded to the bonding agent. This allows bonding procedures to give very strong adhesion of the restoration to the remaining tooth structure that is not possible to achieve with non-bonded restorations. Bonding can be used in direct restorations (fillings) that are done entirely in the patient's mouth. Bonding can also be used to bond laboratory fabricated indirect restorations like inlays, onlays, crowns and laminate veneers in place.
All bonding procedures involve isolating the tooth with a rubber dam. This is essential to achieve maximum bond strength since any contamination from saliva or blood will significantly reduce the ultimate bond strength. Isolation also prevents the chemicals used to prepare the tooth structure for bonding procedures from irritating the patient's gums, tongue or cheeks and from being swallowed by the patient. Bonding isolation also prevents the patient's gums, tongue or cheeks from being inadvertently cut by the drilling that is needed to prepare the tooth for the restoration.
Bonding always requires the chemical etching of the tooth structure. All the hard tooth structure, both enamel and dentin, are exposed to a mild acid etching agent for 15 to 30 seconds. This causes micro pores to form in the hard tooth structure. The tooth surface is rinsed with water, dried and then a liquid bonding agent, an unfilled resin, is placed on the tooth surface and is exposed to curing light that initiates the polymerization reaction that causes the liquid to become a solid. This layer of bonding agent locks into the micro pores on the tooth surface, seals the micro pores, which helps reduce tooth sensitivity, and is what the restoration will chemically bond to.
With direct bonding restorations (fillings) light cured restorative material is placed in small increments and exposed to the curing light. When the light cured bonding material is initially placed it has putty like consistency that allows the dentist control of placement and shaping of the material. Then it is exposed to the curing light to facilitate the polymerization reaction that changes it into a solid. The light cured bonding material gives the dentist the greatest flexibility in creating the cosmetically desired effect the patient is looking for. The dentist can use several different materials that have different hardness, color and translucent properties. Translucency is the property of light passing through the material rather than being reflected back from its surface and is the physical property that most imparts life to a restoration. Since teeth are not one color nor have a singular translucency light cure bonding filling materials are superior to chemically cured bonding filling materials. The chemically cured bonding materials are bulk placed and therefore are monochromatic and have only one translucency.
Bonding can also be used to bond indirect restorations such as inlays, onlays, crowns and laminate veneers into place. The process is very similar to what has already been described. The teeth are isolated, chemically prepare and an unfilled bonding agent is placed on the tooth structures. The indirect laboratory restoration is also prepared, either chemically or mechanically, and then the unfilled bonding agent is placed on the indirect restoration. A thin layer of cement is then placed on the restoration. The restoration is then placed on the tooth and this "bonding sandwich" is exposed to the curing light to bond the restoration into place. There are many applications for bonding in modern adhesive dentistry and as time goes on and the technology progresses there will be more and more in the future.