Adhesion in dentistry: restorative materials

The largest application of radiation-cured adhesives is for dental procedures (see Adhesion in dentistry restorative materials). Originally UV curable, these have given way to... 

Adhesion in dentistry restorative materials M SHERRIFF Polymers as filling materials... 

Adhesion is becoming more and more important in many situations in dentistry. Effective adhesion retains restorative dental materials at proper positions of tooth structure, solves the problem of leakage around restorations, and, consequently, improves their performances. Recently, adhesion of ceramic restorative materials is attracting increasingly more attention, as ceramics are highly desirable for esthetic restoration in terms of toothlike appearance, inertness, and durability. Because of their brittle nature, however, the ceramics must be bonded steadily to tooth structure to assure endurance under continual occlusal load for practical uses as dental materials. 

The glass polyalkenoate cement uniquely combines translucency with the ability to bond to untreated tooth material and bone. Indeed, the only other cement to possess translucency is the dental silicate cement, while the zinc polycarboxylate cement is the only other adhesive cement. It is also an agent for the sustained release of fluoride. For these reasons the glass polyalkenoate cement has many applications in dentistry as well as being a candidate bone cement. Its translucency makes it a favoured material both for the restoration of front teeth and to cement translucent porcelain teeth and veneers. Its adhesive quality reduces and sometimes eliminates the need for the use of the dental drill. The release of fluoride from this cement protects neighbouring tooth material from the ravages of dental decay. New clinical techniques have been devised to exploit the unique characteristics of the material (McLean Wilson, 1977a,b,c Wilson McLean, 1988 Mount, 1990). 

In the realm of dentistry, restoration and protection of tooth enamel are of great importance in operative and conservative dentistry. Yamamoto et al. (2013) used PLD to create a freestanding flexible double-layered sheet composed of a 4 pm thin hydroxyapatite (HAp) layer coated with a 0.5 pm thin TCP layer. The adhesive strength between the HAp/TCP sheet and enamel was 5.7 MPa, decidedly higher than that between the monolayered HAp sheet and enamel (1.9 MPa). Electron microscopical observation revealed that the HAp/TCP sheet was largely fused with the enamel. Therefore, the double-layered HAp/TCP sheet can be used as a material to promote the repair of tooth eruption and to maintain healthy dentine. 

Adhesive dentistry, specifically in association with the use of composite resins, has anerged as an important component of modem restorative dentistry. These are several reasons for this. First, as a result of the research into restorative materials of improved aesthetics, there are now polymeric and also ceramic materials that provide an excellent match for the natural tissue of the tooth. This is complemented by an increasing demand for aesthetic repairs by patients [3,4]. This is part of the trend within the developed world for cosmetic dental treatments, and for cosmetic dentistry to be seen as an acceptable part of the profession. 

The largest voliune of polsrmeric materials used in dentistry is in prosthetic applications. Polymeric materials are also important in operative dentistry, being used to produce composite resins, dental cements, adhesives, cavity liners, and as a protective sealant for pits and fissures. Elastomers are employed as impression materials. Resilient prosthetic devices are oft en fabricated to restore external soft-tissue defects. Mouth protectors are fabricated to prevent injury to teeth, as well as prevent head and neck injinaes. Other polymer applications include fabricating patterns for metal castings and partial denture frameworks, impression trays, orthodontic and periodontal devices, space maintainers, bite plates, cleft palate obdurators, and oral implants. Polymeric materials may also be used to fabricate an artificial tongue, when disease results in its loss. 

After surface preparation, the restorative material is bonded to the tooth structure with auto-polymerizing adhesive resin. One prerequisite for dental adhesives is an ability to cure in the mouth that is why methaciylate-based polymer materials are used in dentistry. Initiation systems are BPO-f amine or TBB (201). Monomers used are MMA or bifunctional methacrylate monomers. The needed optical opacity (215,216) is achieved by various inorganic and metal compoimds incorporated into the formulations. 

In view of the potential importance of ceramic materials for esthetic dentistry, we have focused our attention on the development of high-performance dental adhesives for calcium metaphosphate ceramic as a novel restoration material. The calcium metaphosphate ceramic is characterized by considerable similarities of the appearance, composition, and physical... 

Modern resin-based restorative materials used in stomatology originated with the invention of the so-called Bowen s monomer and the introduction of composites [142]. This monomer is known as BisGMA, a label easier to use than chemical name of 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane.Today, both unfilled and composite resins are widely employed in dentistry—as binding agents, pit and fissure sealants, direct filling materials, orthodontic adhesives, and resin cements [143]. 

Barnes IE, Newsome PRH (1996) The adhesive revolution of restorative dentistry. Hong Kong Med J 2 181 Bascom WD (1990) Primers and coupling agents. In Brinson (ed) Engineered materials handbook adhesives and sealants, vol 3. ASM International, Metals Park, p 254... 

Abstract Adhesive techniques and materials are being used increasingly in clinical dentistry, and they are reviewed in the present chapter. Broadly speaking, there are two types of tooth-colored restorative material, the so-called composite resins and the glass-ionomer cements. There are, though, variations on these basic types, as explained in the chapter. In addition, there is the zinc polycarboxylate cement, which was the first adhesive dental restorative material to be developed, and it retains a niche in modem clinical practice. 

Zinc polycarboxylate was the first of the adhesive dental restorative materials to be described. It was invented by Smith (1968) who reported that it was fabricated from aqueous polyacrylic acid and deactivated zinc oxide, and that it had excellent adhesion to both dentin and enamel. It was also found to have other desirable properties. For example, it set rapidly with minimal shrinkage, it was bland toward the soft tissues of the mouth, and it was almost completely insoluble in saliva (Smith 1968). Zinc polycarboxylate cement can thus be considered a major development in the field of adhesive dentistry. Typical properties of zinc polycarboxylate cement are shown in Table 56.4. 

Zinc polycarboxylate cement, the first adhesive dental restorative material, is also described, though nowadays it has only niche applications in dentistry. 

The enhanced performance resin-modified glass-ionomers are high in resin, and as a result appear to have somewhat compromised adhesion. Their bioactivity appears very good. Considerable further work is required to know whether or not these materials represent a significant advance in glass-ionomer technology and restorative dentistry. 

Although some ceramics are highly attractive materials for restorative dentistry, the high potentials have not been fully explored in clinical practices because of their inert nature to adhesion. However, as we have shown here,... 

Davis, J. R., ed. 2003. Handbook of Materials for Medical Devices. Materials Park, OH ASM International. This work provides a review of the properties, processing, and selection of materials used in the environment of the human body. Among the application areas described are orthopedics (hips, knees, and spinal and fracture fixation), cardiology (stents, heart valves, pacemakers), surgical instruments, and restorative dentistry. Materials discussed include metals and alloys, ceramics, glasses, and glass-ceramics, polymeric materials, composites, coatings, and adhesives and cements. 

Dentistry is concerned with the preservation, repair, and replacement of teeth. As such, it increasingly makes use of modem adhesive materials and techniques. For example, the placement of adhesive materials to fill fissures of newly empted teeth in which decay-inducing bacteria might otherwise lodge is a widely practiced procedure in preventative dentistry (Mount and Hume 2005). In restorative dentistry, repair using the tooth-colored materials known as composite resins involves bonding to the tooth by bespoke adhesive systems, whereas repair with the alternative tooth-colored options, the glass-ionomer cements, exploits their inherently adhesive nature (Mount 2002). 

The next adhesive repair material to become available to the dental profession was the glass-ionomer cement, which was first described by Wilson and Kent in 1972 (Wilson and Kent 1972). These materials are now used in clinical dentistry for a variety of aspects of the repair of teeth damaged by dental decay. Depending on how they are formulated, they may be used as liners and bases or as full restorations, and they may also be formulated for other clinical uses, as shown in Table 56.5. They are aesthetic in that they match the natural color of the tooth and, like the zinc polycarboxylate cement, they are able to bond directly to the surface of the tooth. They have the additional advantage of being able to release fluoride, which is generally considered beneficial, as it prevents further decay of the repaired tooth. 

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