Fate of vital pulps beneath a metal-ceramic crown or a bridge retainer.

AIM: To investigate the incidence of and factors associated with pulpal necrosis in vital teeth restored with metal-ceramic crowns (CMCs) or crowned as part of a fixed-fixed bridge. METHODOLOGY: Patients who had a CMC or bridge retainer (BR) placed on a tooth with no previous history of root canal treatment from 1981 to 1989 were retrieved from computer records. The collated patients were randomly selected and their clinical records examined. Those who satisfied the inclusion criteria were contacted and offered a review. After clinical examination, long-cone paralleling periapical radiographs were taken of the selected teeth, which were then assessed by two precalibrated operators to ascertain the pulpal status. Factors that might contribute to loss of pulp vitality and the tooth type were also recorded. The collected data were analysed statistically using the chi-square test and subject to Bonferroni adjustment where indicated. RESULTS: The numbers of preoperatively vital teeth in the CMC and BR groups were 122 and 77, and the mean observation periods were 169 +/- 25 (SD) and 187 +/- 23 months, respectively. In the CMC group, 19 failed cases (15.6%) were due to an endodontic reason; total number of failures was 34. In the BR group, 25 (32.5%) showed signs of pulpal necrosis; a significant association with maxillary anterior teeth was noted. The survival rates for pulp vitality were 84.4% (CMC) and 70.8% (BR) after 10 years, and 81.2% (SC) and 66.2% (BR) after 15 years. The difference between the two groups was significant. CONCLUSION: The survival of the vital pulp in teeth restored with a single-unit CMC was significantly higher than those serving as an abutment of a fixed-fixed bridge. Maxillary anterior teeth used as bridge abutments had a higher rate of pulpal necrosis than any other tooth types.

Aggressiveness of self-etch adhesives on unground enamel.

Manufacturers of mild self-etch adhesives advocate the adjunctive use of phosphoric acid etching when bonding to unground enamel. This study tested the null hypothesis that there is no difference between the recently introduced, more aggressive self-etch adhesives and a total-etch adhesive in bonding to unground enamel. The ultrastructure and microtensile bond strengths (microTBS) of Xeno III (Dentsply) and Simplicity (Apex Dental Materials), bonded to unground enamel, were examined after thermocycling. Clearfil SE Bond (Kuraray), a mild self-etch adhesive, was used as the negative control, and One-Step (BISCO), a total-etch adhesive bonded to phosphoric acid-etched unground enamel, was used as the positive control. Differences in the thickness of enamel hybrid layers were observed and the aggressiveness of apatite dissolution in the four adhesives.

Integrating oxalate desensitizers with total-etch two-step adhesive.

Compromised bonding of total-etch adhesives to dentin treated with oxalate desensitizers results from the interference of a surface layer of acid-resistant crystals of calcium oxalate. We hypothesize that effective tubular occlusion and dentin bonding may be simultaneously achieved by depleting dentin surfaces of calcium with acids before desensitizer application. Dentin specimens treated with 4 oxalate desensitizers before or after being acid-etched were bonded with a two-step adhesive. Microtensile bond strengths ( micro TBS) were significantly lower, compared with the control, when oxalates were used before the specimens were acid-etched; in contrast, when oxalates were used after acid-etching. micro TBS were similar to nonoxalate-treated controls. Dentin surfaces and tubular orifices were covered with a surface layer of crystals when desensitizers were applied to fractured dentin and smear-layer-covered dentin before specimens were acid-etched. However, when the dentin was acid-etched prior to the application of oxalate desensitizers, the crystals were largely limited to the subsurface of dentinal tubules, where they did not interfere with subsequent resin bonding.

Aging affects two modes of nanoleakage expression in bonded dentin.

Water sorption into resin-dentin interfaces precedes hydrolytic degradation. We hypothesized that these processes are morphologically manifested by the uptake of ammoniacal silver nitrate, which is thought to trace hydrophilic domains and water-filled channels within matrices. Water sorption is thought to be nonuniform and can be traced by the use of silver nitrate. Human teeth bonded with an experimental filled-adhesive were aged in artificial saliva (experimental) or non-aqueous mineral oil (control). Specimens retrieved for up to a 12-month period were immersed in 50 wt% ammoniacal silver nitrate and examined by transmission electron microscopy for identification of the changes in their silver uptake. Reticular silver deposits initially identified within the bulk of hybrid layers in the experimental group were gradually reduced over time, but were subsequently replaced by similar deposits that were located along the hybrid layer-adhesive interface. Silver uptake in water-binding domains of the adhesive layers increased with aging, resulting in water tree formation. These water-filled channels may act as potential sites for hydrolytic degradation of resin-dentin bonds.

A nanoleakage perspective on bonding to oxidized dentin.

The mechanism responsible for sodium-hypochlorite-induced reduction in dentin bond strength and its reversal with reducing agents is unknown. This study examined the relationship between nanoleakage and reversal of compromised bonding to oxidized dentin. Acid-etched dentin was completely depleted of demineralized collagen matrix when sodium hypochlorite was used. Specimens were bonded with two single-bottle dentin adhesives. They were immersed in ammoniacal silver nitrate for 24 hrs before being processed for transmission electron microscopy. For both adhesives, tensile bond strengths of acid-etched dentin were significantly reduced after sodium hypochlorite treatment, but were reversed when sodium ascorbate was used. After sodium hypochlorite application, reticular nanoleakge patterns in hybrid layers were replaced by vertical, shag-carpet-like patterns along the demineralization front. This type of nanoleakage was completely eliminated after sodium ascorbate treatment with the materials tested. Residual sodium hypochlorite within the porosities of mineralized dentin may result in incomplete resin polymerization, and hence compromised bond strength.

Reversal of compromised bonding in bleached enamel.

Oxygen inhibits polymerization of resin-based materials. We hypothesized that compromised bonding to bleached enamel can be reversed with sodium ascorbate, an anti-oxidant. Sandblasted human enamel specimens were treated with distilled water (control) and 10% carbamide peroxide gel with or without further treatment with 10% sodium ascorbate. They were bonded with Single Bond (3M-ESPE) or Prime&Bond NT (Dentsply DeTrey) and restored with a composite. Specimens were prepared for microtensile bond testing and transmission electron microscopy after immersion in ammoniacal silver nitrate for nanoleakage evaluation. Bond strengths of both adhesives were reduced after bleaching but were reversed following sodium ascorbate treatment (P < 0.001). Resin-enamel interfaces in bleached enamel exhibited more extensive nanoleakage in the form of isolated silver grains and bubble-like silver deposits. Reduction of resin-enamel bond strength in bleached etched enamel is likely to be caused by a delayed release of oxygen that affects the polymerization of resin components.