Tooth adhesion is a frequently performed operation in dental clinics. In addition, the basis of crown restoration is the integration of the tooth substance and crown restoration, and the adhesive operation has a marked influence on the clinical prognosis. At this symposium, we gave a lecture on adhesion to the tooth substance.

The restoration technique for caries treatment, which was conceptualized by Black GV at the beginning of the 20th century, has replaced the MID （Minimal Intervention Dentistry） concept-based minimum reduction of tooth structure and adhesive material-dependent technique. It has also been transformed into a typical restoration technique. Adhesive techniques are now used in all areas of dentistry, not just caries treatment. On the other hand, unlike cavity preparation with a retention form, it is difficult to visually capture the adhesion technique performed at the chair side in the treatment method. However, it is necessary to always be aware of how to detect and eliminate various factors that may adversely affect the adhesive condition, since the quality of this condition is directly linked to the clinical results. This paper mainly discusses how to deal with the various factors adversely affecting bonding between resin-based adhesives and tooth structures in clinical situations, based on previous reports regarding the influence of a remaining smear layer, remaining solvents contained in the adhesive material, the adhesive environment, light-curing units used, and the contamination of the adherend surface.

Adhesion is closely associated with coronal restoration, pit and fissure sealant, temporary fixation of a luxated tooth, and occlusal guidance in pediatric dentistry. Although better adhesion is a desired clinical factor, attention to moisture exclusion is more important. Oral cavities of children are small and saliva secretion is abundant. Therefore, rubber dam isolation is always carried out in pediatric dentistry. It is necessary to consider the smallness of adhesion areas caused by thin enamel and dentin and the attrition of enamel. Caries activity of a primary tooth is higher than that of a permanent tooth due to calcified conditions, etc. Moreover, when oral hygiene is poor, secondary caries develop around the restorative material, and then the restorative material easily detaches from the primary tooth. Based on the above, even if better adhesion is a necessary factor, the selection of materials well-adapted to the oral condition of each child is the most important factor.

Zirconium dioxide (zirconia) ceramics have excellent biocompatibility, superior mechanical properties, and favorable esthetics. Zirconia is therefore used as an alternative to metal alloy framework materials in tooth- and implant-supported fixed dental prostheses (FDPs), and implant abutments. To replace a missing anterior tooth, some treatment options are available, such as conventional FDPs, resin-bonded fixed dental prostheses (RBFDPs), and implant-supported fixed dental prostheses. Tooth preparation for RBFDPs is significantly less invasive compared with conventional FDPs. A number of clinical studies demonstrated that zirconia-based RBFDPs led to positive clinical outcomes being suggested as a conservative treatment modality. To achieve long-term stability of zirconia-based RBFDPs, strong and durable bonds between abutment teeth and zirconia frameworks are mandatory. The aims of the present article are to clarify clinical outcomes of the zirconia-based RBFDPs and describe clinical approaches including selection of the case, tooth preparation, and bonding procedures for the long-term success of zirconia-based RBFDPs.

It is difficult to bond an artificial material to the“tooth substance”with marked defects and make them function clinically. Dental materials are manufactured under strict control, and their qualities are almost uniform. Nevertheless, the physical characteristics of tooth substances differ from individual to individual, and are affected by factors such as species, heredity, and the environment. Even within the same individual, the quality varies greatly depending on whether it is devitalized. It is extremely difficult to select the best material for each individual and each tooth.Adhesive techniques are essential for tooth crown restoration. Advances in adhesive techniques have brought esthetics and functionality to dental practice. Crown restoration set using bonding material or resin cement with high adhesive strength can function for a long time without failure. However, an excessive adhesive strength should lead to adherend failure, and in the worst case, to tooth substance fracture.The clinical theory of crown restoration and adhesive system for the prevention of tooth substance fracture should be discussed.