The rate of plaque growth was assessed using daily Plaque Index measurements over a 7-day period in eleven dental students with an initial mean Gingival Indes of 1.21 (+/- 0.05). The mean Gingival Index was then reduced to 0.27 (+/- 0.04) and the rate of plaque growth assessed in the same way. Bacterial smears were taken from the teeth at intervals during both experimental periods and percentage counts of various morphological types of bacteria made. The rate of plaque growth was found to be significantly greater when the Gingival Index was high compared with when the Gingival Index was low (P less than 0.001). There was also an earlier development of a complex bacterial flora when the Gingival Index was high. The hypothesis is presented that gingival exudate has no inhibitory action on the formation of dental plaque, but contains substances which enhance bacterial aggregation and the colonization of the tooth surfaces by these aggregates.
The prevalence of chronic periodontitis was investigated in six hundred and two 14-year-old English schoolchildren using a standardised radiographic technique. The interproximal spaces on the mesial and distal aspects of the first molar teeth were examined. Oral cleanliness and gingivitis for the anterior teeth and caries prevalence were also recorded. Radiographic evidence of chronic periodontitis was detected in 51.5% of the children examined. No significant relationship was demonstrated between bone loss associated with the first molars and any of the other parameters measured.
Measurements have been made of the root areas of forty five extracted teeth. These have been used to calculate the theoretical pressures that may occur in the region of the alveolar crest and their increase with progressive loss of alveolar bone when a lateral force is applied to the crown of the tooth. Pressures generated in the periodontal ligament as a result of axial loadings have also been calculated and compared with those due to lateral loadings. The results suggest that a very rapid increase in pressures in the periodontal ligament would occur with bone losses in excess of 55 per cent in the case of lateral loadings and over 80 per cent in the case of axial loading. The implications for clinical practice are discussed.
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