Dental Adhesive Systems

Surface topography its influence on wetting and adhesion in a dental adhesive system. Journal of Dental Research, 51, 780-8. 

C. de Souza Costa, M. Vaerten, C. Edwards, C. Hanks, Cytotoxic effects of current dental adhesive systems on immortalized odontoblast cell line MDPC-23, Dent. Mater. 15 (1999)434 1. 

Table 9.1 Contemporary dental adhesive systems and their composition...

Fig. 9.1 a Typical monomer molecules used in dental adhesive systems, b Schematic of the resin dentin interface... 

The clinical technique can also affect the performance of dental adhesive systems. Significant reduction in the degree of conversion and mechanical properties of adhesive systems was observed when solvents were not properly evaporated [23-26]. The application of simplified-step adhesive systems to an excessively wet dentin surface may lead to phase separation and a hydrophobic-poor and hydro-philic-rich zone may be formed, lowering the stability of the adhesive interface [13]. Acidic monomers remain active when poorly polymerized resulting in continuous etching of the underlying dentin [27]. 

Sparked a need to acknowledge the biology nature of the tissue as well as new directions in the resin chemistry that has been used in dental adhesive systems for the past 40 years. Some of the emerging and future concepts are detailed in the two sub-items below. 

Braga RR, Ballester RY, Daronch M. Influence of time and adhesive system on the extrusion shear strength between feldspathic porcelain and bovine dentin. Dental Materials 2000 16(4) 303-310. 

A.R. Yazici, Q. (Jelik, G. Ozgunaltay, B. Dayanga9, Bond strength of different adhesive systems to dental hard tissues, Oper. Dent. 32 (2007) 166-172. 

J. Hecbing, E.M. Aparecida Giro, C.A. Costa de Souza, Biocompatibility of an adhesive system apphed to exposed human dental pulp, J. Endod. 25 (1999) 676-682. 

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. 

Adhesion of restorative dental biomaterials to tooth substrates is primarily based on micromechanical interlocking of resin monomers to the components of the hard tissue. In addition to micromechanical retention, chemical bonding can be achieved via functional monomers, which are able to chemically and mechanically bond to the tooth [10, 11]. While commonly classified as generations by industry, the most appropriate way to classify the current adhesive systems is by the dentin surface treatment and application techniques. The application techniques recommended by manufacturers is greatly influenced by the composition of the adhesive polymer [12]. A summary of the current adhesive systems is shown in Table 9.1. 

The basic components of a dental bonding system include a primer, the adhesive resin, an organic solvent and polymerization initiators. Primers contain hydrophilic blends of resin monomers/co-monomers. Adhesive resins contain blends of hydrophobic monomers/co-monomers. Solvents are added to the systems to enhance resin infiltration into the tissue, whereas photoinitiators are commonly used for convenient operator-controlled photopolymerization of the adhesive. Other ingredients such as fluoride, glutaraldehyde, antimicrobials are also commonly added to the mixture in an attempt to further protect or strengthen the adhesive interface. 

Additional improvements on the degree of conversion of the adhesive systems were observed with new and less hydrophobic initiators of polymerization. Camphorquinone and aromatic amines are the most commonly used photoinitiator systems for light-activated dental resins, but they can be excessively hydrophobic making it difficult to activate the more hydrophilic monomers at the adhesive systems. The addition of alternative initiators such as 1-phenyl-1,2-propanedione (PPD), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (Lucerin-TPO) and bisacylphosphine oxide (BAPO) improve resin polymerization within hydrophilic domains and reduce susceptibility to inactivation by... 

The oxirane rings are responsible for the physical properties and the low shrinkage, while the hydrophobic properties of the material are related to the siloxanes [61]. As a consequence, exogenous discolouration and water absorption are reduced. All these reported advantageous characteristics serve to enhance the potential of silorane monomers to be used successfully in dental composite materials. Weinmann et al. [54] observed a low shrinkage rate (<1 %) and seven times more light stability for the silorane in comparison with resin-based methacrylates. The clinical application of siloranes is limited to the posterior teeth because only a few low translucent colours are available. Additionally, due to its hydrophobic properties, a special adhesive system must be used for silorane restorations. 

Shinp M, Shinya A, Lassila LVJ, Gomi H, Varrela J, Vallittu PK, Shinya A (2008) Treated enamel surface patterns associated with five orthodontic adhesive systems-surface morphology and shear bond strength. Dental Mater J 27(1) 1... 

May KN, Swift JR, Bayne SC (1997) Bond strengths of a new dentin adhesive system. Am J Dent 10 195 McCabe JF, Walls AWC (2008) Applied dental materials, 9th edn. Blackwell, Oxford... 

Organic peroxide-aromatic tertiary amine system is a well-known organic redox system 1]. The typical examples are benzoyl peroxide(BPO)-N,N-dimethylani-line(DMA) and BPO-DMT(N,N-dimethyl-p-toluidine) systems. The binary initiation system has been used in vinyl polymerization in dental acrylic resins and composite resins [2] and in bone cement [3]. Many papers have reported the initiation reaction of these systems for several decades, but the initiation mechanism is still not unified and in controversy [4,5]. Another kind of organic redox system consists of organic hydroperoxide and an aromatic tertiary amine system such as cumene hydroperoxide(CHP)-DMT is used in anaerobic adhesives [6]. Much less attention has been paid to this redox system and its initiation mechanism. A water-soluble peroxide such as persulfate and amine systems have been used in industrial aqueous solution and emulsion polymerization [7-10], yet the initiation mechanism has not been proposed in detail until recently [5]. In order to clarify the structural effect of peroxides and amines including functional monomers containing an amino group, a polymerizable amine, on the redox-initiated polymerization of vinyl monomers and its initiation mechanism, a series of studies have been carried out in our laboratory. 

The performance of polyelectrolyte materials is determined by several factors, including the extent to which the dental material adheres to the tooth, cario-static properties of the restoration, pulpal and tissue sensitivity in the vidnity of the restorative material, long-term stability of the dental material, and perhaps most importantly, the aesthetic appeal of the restorative material. Poor adhesion leads to the formation of gaps, which become sites for infection. Biodegradation of the cement can cause increased pulpal and oral-tissue sensitivity, as well as systemic responses. Several recent reviews on the performance of GICs [121,173,230-232] are available, so the subject is only briefly discussed here. 

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