ABSTRACT
This chapter presents commercial and proposed dental applications within the biomaterials literature based on chemically bonded bioceramics (CBBCs). 9.1 Chemically Bonded Bioceramics for Dental
Applications: An IntroductionThe existing dental materials are mainly based on amalgam, resin composites, or glass ionomers. Amalgam, originating from the Tang dynasty in China, was introduced in the early 19th century as the first commercial dental material. It is anchored in the tooth cavity by undercuts in the bottom of the cavity to provide mechanical retention of the metal. Although it has excellent mechanical characteristics it is falling out of favour in most dental markets because of health and environmental concerns. One exception is the United States, in which amalgam still (2013) has a large market share. The second-generation material is the resin composites, first introduced in the late 1950s. These are attached to the tooth using powerful bonding agents which glue them to the tooth structure. After technical problems over several decades, these materials today have developed to a level where they work quite well and provide excellent aesthetic results. Despite the improvements, resin composites have some drawbacks related to shrinkage, extra
bonding, irritant components, a risk of post-operative sensitivity, and technique sensitivity in that they require dry field treatment in the inherently moist oral cavity. The key problem, due to shrinkage or possible degradation of the material and the bonding, is the margin between the filler material and the tooth, which often fails over time, leading to invasion of bacteria and secondary caries. Secondary caries is a leading cause of restorative failure and one of the biggest challenges in dentistry today. As a significant number of dental restorations today are replacement of old, failed tooth fillings, it is clear that tackling this problem is a major market need [1]. Secondary caries occurs not only after filling procedures but also following other restorative procedures such as the cementation of crowns and bridges. Glass ionomers were first introduced in 1972 and today are an established category for certain restorations and cementations. Their main weakness is the relatively low strength and low resistance to abrasion and wear. Various developments have tried to address this, and in the early 1990s resin-modified ionomers were introduced. They have significantly higher flexural and tensile strength and lower modulus of elasticity and are therefore more fractureresistant. However, in addition to the problems of resin composites highlighted above, wear resistance and strength properties are still inferior to those of resin composites. Alternative dental materials and implant materials based on bioceramics are found within all the classical ceramic families: traditional ceramics, special ceramics, glasses, glass-ceramics, coatings, and chemically bonded ceramics (CBCs) [2]. The CBC group, also known as inorganic cements, is based on materials in the system CaO-Al2O3-P2O5-SiO2, where phosphates, aluminates, and silicates are found. Depending on in vivo chemical and biological stability, CBC biomaterials can be divided into three groups: stable, slowly resorbable, and resorbable. The choice for dental and stable materials is the Ca-aluminate (CA)- and Ca-silicate (CS)-based materials [3], discussed in detail in Chapter 3. The stable biomaterials are suitable for dental applications, long-term load-bearing implants, and osteoporosis-related applications. For trauma and treatment of younger patients, the preferred biomaterial is the slowly resorbable materials, which can be replaced by new bone tissue [4].
