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News Bulletin : ADA News Bulletin May 2011
38 MAY 2011 aesthetic update Compiled by Geoffrey M Knight Open and closed SANDWICHES The occurrence of proximal caries indicates a susceptibility to decay that will require an environmental modification in the region to prevent further recurrence of caries at this site. Although improvements in oral hygiene will reduce the chance of further decay, the placement of a restoration with cariostatic properties is a more predictable way of preventing ongoing caries than relying on behavioural changes by a patient. Metallic, ceramic and resin restorative materials have no ability to protect adjacent tooth structure from recurrent caries. Furthermore, self etching bonding systems have a reduced bond strength to enamel that can lead to marginal debonding and dentine caries (Fig 1). Auto cure and resin modified glass ionomer cements have been shown to prevent the demineralization of tooth structure adjacent to the restorative interface, either by pH buffering or the perfusion of fluoride into the tooth. Whilst it is the opinion of many Australian dentists that glass ionomer cement restorations protect teeth from recurrent caries there are a number of clinical studies suggesting recurrent caries is the most observed reason for replacement of these restorations. The buffering ability of glass ionomer cements results in the slow breakdown of the surface cement that can give the clinical impression of caries even though closer examination reveals no softening of dentine at the restorative interface. Fig 1. Self etching bonding systems have a reduced bond strength to enamel that can lead to marginal debonding and dentine caries. Fig 2. The main benefit of the 'open sandwich' is the large surface area of glass ionomer cement available for buffering any changes in acidic pH. OPEN SANDWICH The 'open sandwich' technique involves the placement of a glass ionomer cement restoration into the base of a proximal cavity and filling the preparation with glass ionomer up to the level of the dento enamel junction. The final portion of the restoration is placed with composite resin to provide wear resistance and aesthetics on the occlusal surface. The main benefit of the 'open sandwich' is the large surface area of glass ionomer cement available for buffering any changes in acidic pH. Figure 2 shows an 'open sandwich' restoration. The resin modified glass ionomer cement bond (dyed blue to identify the interface) chemically bonds the glass ionomer cement to the composite resin overlay. The problem here is that over time the glass ionomer cement succumbs to acid breakdown over the surface resulting in food packing and giving the impression of recurrent caries within the glass ionomer (Fig 3). CLOSED SANDWICH The traditional 'closed sandwich' technique involves placing the glass ionomer at the base of the proximal box so as it falls just short of the external cavo surface. After setting, the glass ionomer cement is etched with phosphoric acid and a dentine bonding agent applied before placing a composite resin into the proximal
ADA News Bulletin April 2011
ADA News Bulletin June 2011