Biomedical subjects
Publications and source records attributed to R E Going.
The dentist must fully appreciate that restorative procedures, done well, are an integral part of prevention. Poorly condensed materials and poorly adapted margins of restorations are often the reasons for marginal leakage, recurrent caries and pulp involvement.
Although significant progress has been made with the advent of composite restorative materials and associated techniques, the problem of marginal leakage has been lessened but not solved. The primary aim of future work must still be directed toward preventing the formation of a gap between the restoration and the tooth.
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Twenty-two materials, including 19 dental impression elastomers, were compared in their ability to replicate microscopic detail. Some polysulfide, silicone, and polyether materials performed well. Curiously, microscopic replication ability generally correlated inversely with that expected from the nominal consistency. The test method developed appears to be a suitable microreplication evaluation standard.
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Colored, disposable applicator tubes have been said to lose color to their contents during use. Since they are used to contol the placement of a variety of accessory materials important to clinical dentistry, a selection of restorative materials and solvents was evaluated to determine which had a color-leaching potential. Neither aqueous system nor alcohol, chloroform, eugenol, xylene, or ether caused a loss of color that was clinically significant. Acetone and amyl acetate caused a visibly apparent loss of color and softening of the tube matrix. Methyl methacrylate completely dissolved specimens of celluloid tubes. Unfilled resins containing methyl methacrylate in their liquid catalysts leached sufficient red color form the test specimens to stain the restorative noticeably pink; the composite resins and cements that were evaluated did not.
Carious lesions that were covered with a pit and fissure sealant for five years yielded bacterial cultures that were predominantly negative. Sixteen of 18 test sites judged to have active caries in 1972 were found inactive in 1977; ten of 12 sites suspected to have caries in 1972 were deemed to have inactive caries in 1977. Sealant treatment resulted in an apparent 89% reversal from a caries-active to a caries-inactive state. These data confirm and extend previous observations that a limited number of cultivable organisms persist in some lesions but their numbers are few, and they do not appear capable of continuing the destruction of tooth structure.
The clinical retention of a single application of a pit and fissure sealant was evaluated on the teeth of children to determine the influence that this protective coating, or its loss, would have on caries activity during a four-year period. The sealant was fully retained on 50% of all paired permanent teeth at 48 months. Of the 689 pit regions that retained the sealant, 95% were rated as having severe loss of substance, only 5% as slight loss, and none with no loss of substance. It also was found that 53% of all paired permanent control teeth judged cariesfree at the baseline examination were found to be carious, whereas only 30% of the treated teeth examined were carious. The corresponding relative reduction in caries rates was, therefore, 43%. The actual number of teeth estimated to be saved by the sealant treatment at 48 months, as measured by net gain per 100 teeth treated, was 23. The net gain per child was estimated as 2.7 teeth saved from caries (full mouth), with a positive treatment benefit in 69% of the children. When the sealant remained intact, there was a pronounced reduction in caries initiation--the percent effectiveness being 84%.
For the study, 479 paired permanent teeth and 20 paired deciduous teeth were coated under controlled clinical conditions with Nuva-Seal. A red dye was added to assist in placement and subsequent evaluation over a two-year period. Eighty-four children (ages 10 to 14) participated in the study. Caries was evaluated 3, 6, 12, and 24 months later with the same rating scale used at the baseline examination (0, caries free, to 4, severe caries), except when the sealant was found completely present and intact; then caries evaluation was limited to visual inspection through the sealant. The caries rate for control teeth was 6.9% at 3 months, 16.1% at 6 months, 26.4% at 12 months, and 37.6% at 24 months. Corresponding percent effectiveness figures for the sealant were 63.6%, 66.6%, 61.7%, and 54.6%, respectively. At 24 months, effectiveness rates for all types of teeth were at least 52% with the exception of the maxillary second molars (only 27% sealant effectiveness). Overall, caries protection as reflected by percent effectiveness was higher for mandibular teeth and premolars than for maxillary teeth and molars. There was significant effect on the incidence of dental caries when the sealant remained completely intact. Percentage effectiveness rates in this case were 90.7% at 12 months and 90.9% at 24 months. There was little gain or loss in caries protection when the sealant was partially or completely missing. Twenty-four percent of the children had a positive net gain or treatment effect at three months. This increased to 52% at 6 months, 62% at 12 months, and 70% at 24 months. With the use of half-mouth caries rates, the corresponding figures for positive treatment effects were slightly higher (30%, 64%, 70%, and 80% respectively).
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Success in conservatively restoring Class IV and VI defects depends upon the method of retention and the restorative material chosen to best fulfill the clinical need. This need is determined by the size of the defect and its location in the arch relative to the functional load, age, vanity, and general dental appreciation of the patient.
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Three cement systems are favored for permanent luting of cast restorations. These include zinc phosphate, reinforced zinc oxide-eugenol, and polycarboxylate cements. Although others have been used in the past and new luting media are anticipated for the future, the status of currently used cement for luting is based mainly on the results of laboratory research and on clinical experience. Zinc phosphate cement, with an impressive 100-year history, currently holds the advantage. Future comprehensive clinical studies, correlated with results of physical and biological testing, may eventually direct the clinican's preference to another, newer material. It is hoped that properties and strength values that are clinically significant also will be identified, so that laboratory tests can be more predictive of clinical success.
The newer composites, although free of methacrylic acid and of a neutral pH, were still found to be toxic to the pulp. The intensity of response was increased after acid pretreatment procedures; this indicates an increase in dentin permeability. When the remaining dentin thickness was 1.0 mm or less, regardless of whether the dentin was primary dentin or primary and reparative dentin, the percentage of teeth with abscess formations increased. Use of calcium hydroxide bases or liners to coat the dentin before acid pretreatment of enamel is therefore highly recommended.
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