Mitchell Dental Materials in Operative Dentistry

1. Auflage 2019
ISBN: 978-1-85097-351-5
Verlag: Quintessenz Verlag
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, Band 33, 140 Seiten

Reihe: QuintEssentials of Dental Practice

In such a rapidly changing field, dental students and practitioners need up-to-date information on a wide range of restorative materials available for use in operative dentistry. This book concisely outlines the clinical advantages and disadvantages as well as indications and contraindications of different materials. Topics include finishing and polishing restorations and the use of dental curing lights.

Autoren/Hrsg.

Mitchell, Christina

Leseproben

Chapter 2
Compomers and Giomers
Aim
The aim of this chapter is to increase comprehension of compomers and giomers, including how they relate to other tooth-coloured, adhesive, restorative materials. Outcome
Readers will become familiar with how the composition and physical properties of these newer materials differ from those of resin composites, together with their clinical indications and contraindications. Compomers
Compomers are polyacid modified composite resins. These materials derive their name from merging parts of the descriptors “composite” and “glass-ionomer”. The idea was to suggest that these new materials were a hybrid between composite resins and glass-ionomer cements, retaining the benefits of both while minimising their respective disadvantages. Thus, composite resins have superior strength, fracture toughness and aesthetics compared with glass-ionomer cements, but in general lack the ability to bond chemically to tooth substance and release fluoride. Compomers have been a successful addition to the range of direct restorative materials. Their popularity is largely attributed to their excellent, non-sticky handling. In appearance and performance, compomers are more closely related to composite resins than glass-ionomer cements. Trends in material properties for resin composites, compomers, conventional and resin-modified glass-ionomer cements are set out in Fig 2-1. Fig 2-1 Trends in properties of tooth-coloured restorative materials. Indications
Compomers are recommended by manufacturers for the restoration of: all types of cavities in deciduous teeth cervical cavities (carious or non-carious) in adults anterior proximal restorations in adults small load-bearing restorations in adults, and also: as a temporary or transitional restorative material as a core build-up material if at least 50% of coronal dentine is still available. In addition, one compomer (Dyract AP, Dentsply) is recommended by the manufacturer for the restoration of all types of cavities in children and adults, including stress-bearing occlusal surfaces, where the cavity is less than two-thirds the intercuspal distance. The presentation of a compomer material is shown in Fig 2-2. The clinical placement of a compomer material in a cervical cavity in an upper left central incisor tooth is illustrated in Figs 2-3 to 2-9. Fig 2-2 A compomer restorative material, showing the compule and applicator gun. Fig 2-3 Prepared cervical cavity on the labial aspect of an upper left central incisor tooth. Fig 2-4 Orthophosphoric acid etchant being applied to the enamel and dentine of the prepared cavity. The etchant is then washed and lightly dried. Fig 2-5 Enamel and dentine adhesive system being applied to the cavity with an applicator brush. Fig 2-6 Placement of compomer in the cavity. Fig 2-7 Photopolymerisation of the compomer restoration. Fig 2-8 Polishing the compomer with small-diameter aluminium oxide abrasive discs. Fig 2-9 The finished compomer restoration. Contraindications
Compomers have been contraindicated in the following clinical situations: where a direct or indirect pulp cap is required a core build-up for an all-ceramic crown where a dry field cannot be achieved where the patient has an allergy to dimethacrylate resins where the restoration will be in contact with a eugenol-containing lining or base material, which will interfere with the polymerisation of the compomer. Composition
Compomers are resin-based materials but their composition varies between brands. In general, compomers contain: polymerisable resins with methacrylate and polycarboxylate groups glass filler particles, such as fluoroaluminosilicate, strontium fluorosilicate or barium fluorosilicate glass photoinitiators (camphorquinone/amine system) stabilisers. The polymerisable resins of some commercially available compomers contain significantly more carboxylate groups than other compomers, which contain more methacrylate groups. Materials with methacrylate groups behave predominantly like composite resins. Those with a high proportion of carboxylate groups behave more like glass-ionomer cements. The first commercially available compomer (Dyract, Dentsply) contained the polymerisable resins urethane dimethacrylate (UDMA) and TCB resin, an acid monomer – a biester of 2-hydroxyethyl methacrylate (2-HEMA) and butane tetracarboxylic acid – which contained both carboxylate and methacrylate groups. Initially, the filler particles were strontium fluorosilicate glass with a mean particle size of 2.5 µm and 70% filler loading by weight (47% by volume). Thus, this compomer contained the components of glass-ionomer cement – acidic polycarboxylate groups and basic strontium fluoroaluminosilicate glass (see Chapter 4, pages 53–54) together with the methacrylate groups that undergo light-activated free radical polymerisation, as occurs with most composite resins (see Chapter 1, pages 3–4) (Burke et al., 2002). This material has been replaced by a newer version (Dyract AP, Dentsply), which has a similar chemistry but has been modified by the addition of smaller glass filler particles (0.8 µm) and a new, more highly cross-linked monomer. These changes are stated by the manufacturer to give the material increased strength, fracture toughness, wear resistance and fluoride release and improved polishability. An alternative compomer material (F2000, 3M ESPE) contains the polymerisable resin CDMA, a dimethacrylate functional oligomer derived from citric acid, which acts as the acidic hydrophilic matrix former, and glyceryl dimethacrylate (GDMA), which acts as a hydrophilic co-monomer and CDMA diluent. An additional high molecular weight, hydrophilic polymer is added to modify material handling properties and aid the transport of water and fluoride in the compomer. This compomer contains 3–10 µm fluoroaluminosilicate glass filler particles (84% filler by weight). Hytac (3M ESPE) contains the polymerisable resins methacrylated phosphoric acid ester (MPAE) and UDMA. This compomer contains zinc-calcium-alumino-fluoro-silicate glass and ytterbium trifluoride glass fillers (81% filler by weight) of average particle size 5 µm. The compomer Compoglass F (Ivoclar Vivadent) contains the polymerisable resins UDMA, tetraethylene glycol dimethacrylate and cycloaliphatic dicarboxylic acid dimethacrylate (DCDMA). The glass filler particles are barium aluminofluorosilicate glass, ytterbium trifluoride and spheroid mixed oxides. The particle size is 0.2–3.0 µm, 55% filler by volume (77% by weight). Setting Reaction
Compomer is exposed to a curing light and the free radical polymerisation reaction is initiated by a camphorquinone/amine system. The polymerisable resin molecules intermingle to become a resin matrix reinforced with glass filler particles. Later, when exposed to saliva in the mouth, water is absorbed by the matrix over a period of days and weeks, and permits the acidic polycarboxylate groups and basic glass filler particles to react, creating further ionic cross-linking of the matrix and release of small amounts of fluoride (Burke et al., 2002). Fluoride Release
Compomers are part of a spectrum of materials that release fluoride (Fig 2-1). Fluoride release is related to water content, and in general there is an inverse relationship between fluoride release and physical properties. The ability to release fluoride ...