new-true-dentalloy and Dental-Caries

Artificially induced carious lesions on either side of in vitro un/restored amalgam cavities were examined to establish the degree of randomness of caries development. Class I cavities were cut in 132 extracted premolars: twelve teeth were not restored, and 120 teeth were restored with one of 20 different restoration combinations of silver amalgam, base and varnish. After ageing for periods of 3 months and 1 year, the 12 unrestored teeth and 80 of the restored teeth were subjected to an in vitro bacterial challenge for 36 days, while the other 40 specimens were challenged in acidified broth (pH 4.0). Sections were then prepared for polarized light microscopy. Carious lesion configuration on either side of the cavity was noted, and outer, wall and dentine lesions measured. Data underwent Fisher's exact test, a chi-squared goodness of fit test and a Student's paired t-test with P<0.05. Except for dentine lesions, acid broth and unrestored specimens showed carious lesions having similar size and occurrence on either side of the cavity. Two unrestored cavities showed caries resistance. Restored, bacterially challenged specimens were significantly different regarding total and wall lesion distribution and wall lesion width and area on either side of the cut cavity. Acid broth challenge will promote regular caries development at the tooth-restoration interface. The random caries pattern which developed in restored bacterially challenged specimens indicates that the tooth-restoration interface forms a diverse environment providing sites of varying susceptibility to caries.

Topics: Bicuspid; Chi-Square Distribution; Dental Alloys; Dental Amalgam; Dental Caries; Dental Caries Susceptibility; Dental Cavity Lining; Dental Cavity Preparation; Dental Enamel; Dental Restoration, Permanent; Dentin; Humans; Lactic Acid; Microscopy, Polarization; Streptococcus mutans; Time Factors

The surface margin of a restoration is where the restored tooth is subjected to aggressive oral attack. Any resistance to this attack will have favorable consequences on the clinical performance and longevity of the restoration. In this study, Black's class I classic cavity preparations were completed in 120 extracted intact human premolars that were restored with one of two silver amalgams, six different base conditions, and with or without cavity varnish, resulting in 20 different restoration combinations. The cavities were aged for 3 months and 1 year in 1% NaCl at 20 degrees C. A resin cast impression was made of the restoration margin for each specimen. Thereafter 80 restored teeth were subjected to an in vitro bacterial challenge for 36 days. The other 40 specimens were placed in an acidified (pH = 4.0) broth for the same length of time. A second cast impression was then made of the margin of each specimen. The casts were examined with a scanning electron microscope and the widest gap of the margin opening and the length of margin showing a discrepancy were measured. Specimens were ranked first on the basis of the gap size and then on percent of margin discrepancy length. Results were evaluated with one-way ANOVA and Turkey's Student range test with a critical level of statistical significance (p < 0.05). Base type significantly affected aged margin quality. Cariogenic challenge caused a significant breakdown of the amalgam margin although the type of challenge was not significant. A shorter aging time, varnish, and high copper amalgam exacerbated the breakdown. Margin breakdown can be reduced by judicious selection of restoration material combinations.

Topics: Analysis of Variance; Calcium Hydroxide; Dental Alloys; Dental Amalgam; Dental Caries; Dental Cavity Lining; Dental Cavity Preparation; Dental Marginal Adaptation; Dental Materials; Dental Restoration, Permanent; Drug Combinations; Eugenol; Formaldehyde; Humans; Minerals; Organic Chemicals; Polycarboxylate Cement; Streptococcus mutans; Zinc Oxide

Replacement of amalgam restorations may lead to more destruction of sound dental tissue, is often a time-consuming chair procedure, and it does not always provide a favorable risk/benefit balance for the patient. This article reviews the clinical alternative of repairing instead of completely replacing old amalgam restorations. During a 2-year period, 45 repaired restorations were monitored every 6 months by direct (clinical) and indirect (color slides and stone casts) methods. Findings of this study reveal broad clinical success when based on proper indications.

Topics: Dental Alloys; Dental Amalgam; Dental Caries; Dental Polishing; Dental Restoration, Permanent; Evaluation Studies as Topic; Follow-Up Studies; Humans; Recurrence; Surface Properties

Topics: Acrylates; Adolescent; Adult; Bisphenol A-Glycidyl Methacrylate; Child; Child, Preschool; Cost-Benefit Analysis; Dental Alloys; Dental Amalgam; Dental Bonding; Dental Caries; Dental Restoration, Permanent; Fluoridation; Humans; Infant; Infant, Newborn; Methacrylates; Middle Aged; Pit and Fissure Sealants; Retrospective Studies; Surface Properties; Time Factors