During a 5 day period without oral hygiene, 4 groups each consisting of 3 subjects with healthy gingivae, rinsed their mouths with solutions of tetracycline, vancomycin, polymyxin B or distilled water. Gingival plaque accumulated rapidly in the group rinsing with water, while tetracycline, and to a lesser degree vancomycin and polymyxin B inhibited plaque formation. Clinical gingivitis was not observed in any of the participants, but gingival exudate and leukocyte emigration were noted and seen to increase during the experimental period, especially in the water group. Rinsing with antibiotics inhibited these signs of subclinical inflammation to varying degrees. The bacterial composition of the gingival plaque changed in the water group during the experimental period towards a higher percentage of gram‐negative bacteria, following the pattern observed in previous investigations. Tetracycline markedly reduced the numbers of gingival plaque organisms, while polymyxin B favored a proliferation of gram‐positive cocci and short rods and depressed gram‐negative bacteria. Rinsing with vancomycin resulted in a pronounced shift towards an almost pure gram‐negative plaque flora. It is concluded that local administration of antibiotics with a limited spectrum may be useful for the study of the pathogenicity of the different components of the gingival microbial flora.

The general objectives of this study were to examine the long term effects of daily chlorhexidine application on the development of dental plaque, calculus and periodontal pathology and to monitor changes in oral microbiology and any systemic or local side effects following prolonged use of chlorhexidine over a period of two years. An experimental group of 61 medical and dental students used 10 ml. of 0.2 per cent aqueous solution of chlorhexidine gluconate daily in addition to tooth brushing and interdental cleansing. A control group of 59 students used a placebo solution in addtion to tooth brushing and interdental cleansing. Assessment of selected oral and systemic parameters took place at regular intervals throughout the experiment. The results show that, when compared to the placebo solution, chlorhexidine treatment reduced plaque and gingivitis, but tended to stain teeth. Stains were readily removed by a conventional dental prophylaxis procedure. The chlorhexidine group tended to exhibit a greater amount of supragingival calculus. There were no other local side effects relative to the structure and function of the oral mucosa, tongue, salivary glands and pharyngeal complex, following the prolonged use of chlorhexidine.

Twelve male dental students with healthy gingiva were subjected to a 3 week period without oral hygiene. During this period 6 subjects rinsed their mouth 3 times daily with a 0.5 per cent solution of vancomycin, while 6 subjects rinsed with distilled water. In both groups gingival plaque accumulated rapidly and after 3 weeks all participants developed gingivitis. Clinically no difference could be detected between the two groups. The microflora of the plaque accumulating in the group rinsing with water developed according to the pattern observed in previous investigations. In the vancomycin group this pattern was not followed. Gram‐positive bacteria did not proliferate, and after 5 days rinsing with vancomycin only gram‐negative bacteria were seen in stained smears and impression preparations. Spirochetes were never observed. In cultures of bacterial plaque a few gram‐positive bacteria were found in most but not all of the samples collected at intervals during the experimental period from subjects in the vancomycin group. It is concluded that a predominantly gram‐negative bacterial flora is able to form plaque and elicit gingival inflammation in humans.

One group of 61 students rinsed once daily with 10 ml of a 0.2 per cent solution of chlorhexidine gluconate for two years and another group of 59 students rinsed with 10 ml of a placebo solution. Both groups were otherwise kept on the same oral hygiene programme. The number of total anaerobes, aerobes and streptococci in saliva was followed regularly before, during and after the treatment, in all for 2 years and 7 months. At the same time the number in saliva of large gram negative rods of the enteric types was followed, as was the presence of Streptococcus mutans. It is concluded that treatment with chlorhexidine resulted in a 30 to 50 per cent reduction in the number of bacteria in saliva without producing a detectable shift. A change in. the population of large gram negative rods was not observed, however, the number of students from whom Streptococcus mutans could be isolated from saliva decreased during the treatment.

Possible changes in the structure of human oral mucosa resulting from exposure to chlorhexidine were examined in biopsy specimens of palatal and gingival mucosa obtained from three groups of young adults who had rinsed for more than 1 year (a) once or (b) twice daily with 0.2 % chlorhexidine solution or (c) with a placebo mouthwash. Specimens were quenched in liquid nitrogen and cryostat sectioned perpendicular to the epithelial surface. Sections stained with hematoxylin and eosin were used to assess the degree of keratinization of epithelia and to measure the width of the stratum corneum. Sections treated with buffered alkaline solutions were used to expand and count the number of layers of cells in the stratum corneum. All specimens examined showed evidence of keratinization and, in keeping with previous reports, palatal specimens were more frequently orthokeratinized than gingival specimens. Mean width of the stratum corneum of gingival specimens was approximately 13 μm and of palatal specimens, 23 μm. The mean number of layers of cells in the stratum corneum of the gingiva was approximately 10 and of the palate, approximately 12. Differences in the degree of keratinization and thickness of the stratum corneum between gingival and palatal specimens was statistically significant, but no statistically significant differences were found between the chlorhexidine‐exposed and non‐chlorhexidine‐exposed palatal tissue in keratinization, layers of cells or thickness of the stratum corneum. Neither was there any statistical difference in the same parameters for the gingival specimens. The methods employed did not therefore detect any changes in the normal structure of keratinizing oral epithelia as a result of prolonged daily exposure to chlorhexidine.