Protection against minocycline pigment formation by ascorbic acid (vitamin C).

Minocycline, a member of the tetracycline family of antibiotics, is widely used in the treatment of acne. Its use has been associated with intrinsic staining of adult human teeth, bones, and soft tissues. It causes blackening of the thyroid glands in both animals and humans. It has been determined that the pigment is the product of an oxidation reaction. Laboratory studies have shown that the pigment formation can be induced by exposure to ultraviolet light in the presence of air, and that an antioxidant, such as ascorbic acid (vitamin C), can block its formation. The present study was undertaken to determine whether the antioxidant vitamin C could prevent the pigmentation of tissues of laboratory rats given minocycline. Based on other studies, one group of rats was given minocycline by stomach tube at a dose of 75 mg/kg/day, 5 days per week, for 6 weeks. A second experimental group was given the same regimen of minocycline plus a supplement of ascorbic acid at a level of 0.1% of the diet. A control group received no treatment at all; all rats were maintained on laboratory rats chow and water ad libitum. The rats were euthanized by carbon dioxide inhalation. Nasomaxillary bones, including central incisors, and thyroid glands were removed and fixed with 10% buffered formalin. Bones and teeth showed no gross signs of staining and, therefore, were not processed further. Thyroid glands were visibly darker in the minocycline group; specimens from all three groups were processed histologically. Microscopic examination revealed extensive deposits of black pigment throughout the follicles of the minocycline group, whereas the group receiving both minocycline and vitamin C showed no sign of pigmentation and were indistinguishable from controls. It is suggested that patients on long-term minocycline medication be monitored for thyroid function.

Abrasive particles in tobacco products: a possible factor in dental attrition.

Tobacco products are known to cause oral soft-tissue lesions, but they may also directly affect the teeth. Abrasive particles contained in tobacco products may contribute to dental attrition. We studied tobacco samples from 16 brands of cigars, eight brands of snuff, four brands of chewing tobacco and several unprocessed tobacco leaves used as cigar wrappers. Insoluble particulate matter made up about 0.5 percent of the weight of an average tobacco sample.

Catalase/peroxidase activity in dental pulp.

Extrinsic stains on vital teeth are bleached with 30% hydrogen peroxide (H2O2) or carbamide peroxide, H2O2 greatly inhibits the activity of several enzymes. Free H2O2 and carbamide peroxide readily enter the pulp through the coronal wall of the tooth. Nevertheless, adverse effects have been remarkably rare. This study was undertaken to determine whether dental pulp exhibits any catalase or peroxidase activity that might protect it from damage during vital bleaching procedures. Pulpal tissue from healthy human teeth was assayed for catalase and glutathione peroxidase activity. A phosphate buffer extract of the tissue served as the source of the enzymes. The rate of breakdown of H2O2 by the tissue extract was measured and the rate constant for catalase was determined. The catalase activity, defined as microM H2O2 broken down/min/mg wet tissue, was determined and found to be only 2 x 10(-2), which is very low. The fibrous pulpal tissue was found to exhibit virtually no glutathione peroxidase activity.

Penetration of the pulp chamber by carbamide peroxide bleaching agents.

Hydrogen peroxide readily penetrates the pulp chamber of freshly extracted teeth. This study was undertaken to determine whether carbamide peroxide also penetrates the pulp chamber. Freshly extracted teeth were sectioned 2 to 3 mm apical to the cementoenamel junction and the coronal pulpal tissue was removed. Acetate buffer was placed in the pulp chamber to absorb and stabilize any peroxide that might penetrate. The coronal portion of each tooth was immersed in either carbamide peroxide gel or gelled hydrogen peroxide at various concentrations for 15 min at 37 degrees C. The buffer was removed, leukocrystal violet was added, and the optical density of the resulting blue solution was determined spectrophotometrically. Amounts of peroxide found in the pulp chamber after 15 min ranged from 3.3 +/- 0.38 micrograms for the 10% sample to 40.4 +/- 3.51 micrograms for the 30% sample.

Skin tumors may imitate infectious processes.

A small nodule on the middle finger of the right hand of a right-handed dentist was removed and found to be benign. The lesion recurred and showed increased collagen deposition and vascularity; it was diagnosed as a dermatofibroma. In the absence of a specific incidence of trauma, the cause of such a lesion is a matter of speculation. Such lesions can develop as local tissue reactions to wounds that are the result of routine operatory procedures. This points to the need for careful handling of sharp instruments. Because of the serious consequences of a malignancy or infection from HIV, nodules and other lesions of unknown etiology that appear suddenly should not be ignored.

Evaluation of new gingival retraction agents.

Current gingival retraction agents are not without undesirable side-effects; there appears to be no ideal gingival retraction agent. Several sympathomimetic amines, capable of producing local vasoconstriction with minimal systemic side-effects, are available as non-prescription nasal decongestants and eye washes. The purpose of this study was to evaluate the efficacy of three of these agents for gingival tissue displacement. Mongrel dogs were used as experimental subjects, in which pulse rate and blood pressure were monitored electronically. Visine (tetrahydrozoline HCl, 0.05%), Afrin (oxymetazoline, 0.05%), and Neosynephrine (phenylephrine HCl, 0.25%) were the commercial products studied as gingival retraction agents. Plain, untreated cord was used as a mechanical control, and as a vehicle for the three experimental agents. Commercially available cords impregnated with both racemic epinephrine (8%) and alum were also used as standard retraction agents with which the test solutions were compared. Visine and Afrin produced tissue displacement greater than that of any of the other agents; Neosynephrine, epinephrine, and alum were more effective than the untreated mechanical control. Cardiovascular changes included a slight increase in systolic pressure in the Neosynephrine group, and a slightly lower mean arterial pressure and pulse rate in all three experimental groups.

In vivo studies on the carcinogenic potential of an orthodontic bonding resin.

Data from another laboratory have indicated that the individual components of an orthodontic bonding resin might contain a carcinogen. Since that report, the formulation of the product was changed. The purpose of this study was to determine whether the new product is safe. Three groups of rats were used for the experiment. One group served as a control, while the other groups ingested the sealant resin or sealant catalyst. The materials were suspended in an alcohol-aqueous mixture and the solutions were given to the animals as their only source of fluid. The exposure was for 1 year. After this period of time, all the rats were given tap water and observed until day 600. The animals were autopsied at time of death or at the end of the experiment. During the treatment, there were significant differences (p less than 0.01) in water intake among the three groups. The average intake per day for the animals in the control group, the resin group, and the catalyst group was 50.2 cc, 37.8 cc, and 42.2 cc, respectively. Several animals died during the experiment, but there was no significant differences in the life expectancy of the animals in the three groups. The autopsies uncovered one malignant neoplasm, an undifferentiated sarcoma, in a rat from the control group and four benign tumors in rats from the three groups. All of these results indicate that the new formulation of the orthodontic bonding resin is not carcinogenic when ingested at a dose level of 50 ppm.

Reevaluation of submerged vital roots.

A total of eight vital roots were submerged and retained under complete dentures in two patients. Within two to three years, each patient experienced problems of pain, re-exposure, and inflammation, resulting in the removal of the roots. Histologic evaluation showed evidence of chronic inflammation of the pulpal tissue. Because of alveolar resorption and perhaps super-eruption of the submerged roots, the likelihood of exposure and abscess is a distinct disadvantage to the procedure. Therefore, some doubt remains as to the long-term success with this technique.