Advancements in adhesive restorative dental materials.
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A simple in vitro method has been described for quantitatively measuring the rate at which isotopically labeled substances permeate through dentin in occlusal cavity preparations. The presence or absence of pulp tissue had only a minor effect on the kinetics of permeation. As the dentin was made thinner there was a resulting increase in the rate of iodide permeation. The relative rates of permeation were 3H2O greater than 131I greater than 99mTc greater than 14C-urea, a sequence that follows the molecular dimensions of these substances.
The sealing properties of resin-composite resin material applied to acid-etched cavities and adjacent enamel were studied in 40 contralateral tooth pairs. This treatment was found to reduce considerably the risk of ingrowth of microorganisms from the surface of the tooth. The resin material did not have any appreciable irritative effect on the pulp; the same was true for the etching procedure. Etching of lateral enamel walls and margins with an acid gel after the application of a liner on dentinal walls was considered to be the procedure recommended before the application of the combination of unfilled resin and composite resin.
The most frequent complaints registered against composite restorations are stained margins and a rough surface. The stained margins have many causes such as (1) fracturing or crazing of enamel during preparation of the cavity, (2) using a composite having an excessive curing shrinkage, (3) manipulating too slowly, which permits a loss of plasticity during placement, (4) maintaining inadequate pressure during setting or curing of the composite, and (5) using finishing instruments which cause defects in the margin area of the tooth and/or composite. All of these the operator can control, and if not, the defect will be built into the restoration. The roughness of composites can be reduced by polishing with the finest grit available in disks and by coating with a glaze. Today's composite restorations placed with care will provide long lasting esthetic restorations providing they are not placed in areas subjected to load bearing abrasion.
Experimental marginal leakage of high- and low-Cu amalgam restorations placed in acrylic teeth, where the cavities were untreated or painted with denatured collagen and/or a CaP slurry, was assessed after specimens were stored in a 1% NaCl solution for ten days and for one yr. All specimens stored for ten days showed severe marginal leakage. High- and low-Cu amalgam restorations placed in untreated acrylic teeth cavities formed seals after a storage period of one yr, indicating that these materials are able to form a seal without interacting with a natural tooth cavity interface. Cavities treated with denatured collagen also formed seals in the long-term group. It was apparent that, when the CaP slurry was used, generally more leakage resulted after the year's storage period than when amalgam restorations were placed in uncoated acrylic cavity surfaces or in those painted with denatured collagen.
Since the 1950s, clinicians have relied on various formulations of Ca(OH)2 to stimulate dentin bridge formation. Various studies (Kozlov and Massler, 1966; Massler, 1967; Brännström, 1978; Cox et al., 1987; Snuggs et al., 1993) have demonstrated that pulp healing and dentin bridging can occur against a pH spectrum of materials. Recent studies (Akimoto et al., 1998; Cox et al., 1998, 1999; Tarim et al., 1998; Kitasako et al., 1999; Hafez et al., 2000) have reported successful pulp healing and dentin bridging using adhesives for direct capping of exposed pulps. However, others (Costa et al., 1997; Stanley and Pameijer, 1997; Pameijer, 1998; Hebling et al., 1999; Carvalho et al., 2000) have reported unsatisfactory results when exposures were direct-capped with adhesives. Biological and technical factors, or a combination of both, might be postulated to explain these differences. Recent studies have demonstrated that biological success is dependent upon proper hemorrhage control at the exposure site. This review explores the differences and common factors influencing successful dentin bridging, focusing on data derived from animal studies conducted according to ISO usage guidelines for cavity preparation and material placement. In the past, there has been concern that etching of vital dentin leads to immediate pulp death due to low pH. Recent studies have reported that acidic cements cause breakdown of only the smear layer and fail to seal the restoration interface, leading to inflammation and necrosis. A properly hybridized dentinadhesive interface provides a "bacteriometic" seal to both dentin and pulp tissues. Recent ISO usage studies have shown a high incidence of dentin bridging with adhesives following proper hemorrhage control and removal of both operative debris and biofilm at the dentin-pulp interface by agents such as NaOCl. These are important technique-sensitivity factors to be considered for pulp healing and dentin bridge formation.
The exciting treatment possibilities arising from tissue engineering approaches are still some years away from involvement in dentistry. Meanwhile, it is important to optimize conventional treatments, although precise information on pulp responses to cavity preparation and restoration variables are limited. Odontoblast survival, pulp inflammation, and tertiary dentine area are used as measures of pulp injury and repair.
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The purpose of these studies was to compare pulpal inflammatory responses induced by cementation of precision amalgam inlays with zinc phosphate cement, with and without a Hydroxyline liner, Durelon cement, and ZOE controls. Hydraulic force was induced by the inlay insertion procedure. Cavilax, water, and polyacrylic acid were compared with ZOE controls. Both studies also used untreated teeth for comparison. The use of zinc phosphate luting cement in the 48-hour inlay study was the only condition provoking moderate to severe responses. Zinc phosphate cement over Hydroxyline liner and Durelon cement in the study of inlays and Cavilax cleaner, water, and polyacrylic acid in the study of cleaners showed mild responses comparable to the ZOE control in the 48-hour and in the 45-day periods.
Today's dental patient concerned about attractive restorations is looking for a dentist who incorporates the newest and best techniques into practice. This article discusses a newer concept that pleases both the patient and dentist: restorations that are bonded into acid-etched tooth preparations with composite resin cement--tooth-colored inlays and onlays. Basic questions asked by practitioners about these esthetic restorations are addressed; characteristics, performance expectations, comparisons with cast gold inlays and onlays, and comparisons with amalgam are presented, in addition to other relevant information for today's dental practitioner.
Composite resins have been improved dramatically over the last few years. Some of the newest formulations are nearly as wear resistant as amalgam. Under the appropriate conditions, they may be used to restore Class I and Class II cavity preparations. Their use, however, must be in accordance with the conditions described in this paper. The following conditions should be followed: The selection of a posterior composite resin should be based on well-documented clinical data, not physical and mechanical properties. Complete moisture control is essential for the successful restoration of posterior teeth with composite resin. Always use a glass ionomer as a liner. The material should cover all the dentin. Cavity preparations should be minimal in dimension. Avoid unnecessary removal of tooth structure. Do not bevel the occlusal cavosurface margin. Insert the composite in increments. Minimize introduction of trauma during the finishing procedure. Use a surface penetrating sealant to reduce wear rate and to enhance margin integrity. Evaluate carefully the clinical performance of the restored tooth at least once a year. Discuss possible limitations of posterior composite resins as compared with amalgam restorations.
The rapidly changing area of dental composites can confound practitioners if they ignore material selection and correct techniques. The complex steps involved in placing composite restorations are explained to avoid potential problems and ensure complete success.