Influence of posteruptive age of enamel on its susceptibility to artificial caries.

Epidemiologic studies and caries experiments with animals have suggested that caries susceptibility of teeth decreases with age. Observations on the changes in the dental tissues and their environment with age have pointed out that a process commonly referred to as 'posteruptive maturation' of the dental enamel may be responsible. To test this assumption 10 unerupted third molars and 56 erupted human premolar teeth of various posteruptive ages were subjected for 130 days to an acid gel for caries-like lesion formation in vitro. Sections of the teeth were examined with polarized light and 'contour maps' were drawn with the approximate porosity of the lesions. The results were: unerupted = 833 microns (+/- 261); erupted of posteruptive age 0-3 years = 561 microns (+/- 150), 4-10 years = 470 microns (+/- 136), 11-30 years = 459 microns (+/- 192) and over 30 years = 297 microns (+/- 89). These findings show a decrease in the susceptibility of enamel to artificial caries with increasing age, which was especially marked at and shortly after eruption. This may be explained by a completion of mineralization of the outer enamel at about eruption, by a maturation process of the outer enamel posteruptively and by a reduction in the permeability of enamel occurring through to old age. The fluoride content of the mid-coronal buccal surface enamel under study was found to decrease posteruptively with age, therefore not accounting for the decreasing caries susceptibility.

Simulation of natural enamel caries in vitro with methylcellulose acid gels: effect of addition of calcium and phosphate ions.

A modified acid gel technique for producing caries-like lesions in dental enamel has been developed. The decalcifying medium consists of a 10% (w/v) methylcellulose gel acidified with 0.1 M lactic acid-sodium lactate at pH 4.5 and having a hydroxyapatite content of 0.05% (w/v). This medium can produce caries-like lesions in vitro at a slow rate, which are indistinguishable from natural enamel caries when examined by polarised light microscopy and contact microradiography.

A model for the production of artificial caries in the mouth in man.

Sixteen blocks of enamel were sliced from the buccal surfaces of caries-free human premolars and mounted in an appliance worn in the mouth by one individual for 6 months. Eight of the blocks were arranged in pairs with buccal surfaces in contact. The other eight were not in contact but were able to accumulate plaque by being recessed in the appliance. Lesions formed in all specimens, the depths of which were measured in ground sections; around contact surfaces, these formed at only half the rate of those not in contact. Histologically, lesions on contact surfaces were similar to natural lesions, but the shape of the artificially-induced lesions was greatly influenced by the curvature of the buccal enamel.

The amount and distribution of sclerotic human root dentine.

In low-power photomicrographs of ground sections of canine teeth, the amount of sclerosis increased with age linearly and was not markedly affected by the function of the tooth or external stimuli encountered during life. The pattern of distribution was similar in all teeth. Sclerosis started in the apical dentine adjacent to the cementum and extended coronally and towards the root canal, with increasing age. In the plane transverse to the long axis of the root, sclerosis appeared first at the mesial and distal sides so that the sclerotic zones formed a butterfly shape.

The histology of sclerotic human root dentine.

Studies by optical microscopy, microradiography and SEM suggested that sclerosis is the result of occlusion of the dentinal tubules by a mineral substance with a refractive index similar to that of the rest of the dentine. Translucence appeared before the majority of the tubules were completely occluded. The deposition of the occluding mineral took place initially in individual tubules or in groups of tubules. The occluding material and the peritubular dentine were almost indistinguishable under SEM. Both were smooth and densely mineralized. The process of deposition of occluding mineral appeared to be more like that of in-vitro mineralization and thus different from that of peritubular dentine.

Continuous eruption of some adult human teeth of ancient populations.

It has been argued that the teeth maintain a potential for eruption throughout life and that eruption takes place whenever an opportunity occurs. Thus continuous, active eruption would be expected when the occlusal surfaces of the teeth have been affected by severe attrition. Radiographs of teeth and jaws of adult skulls with marked attrition from the Romano-British, Anglo-Saxon and Mediaeval periods were measured using the inferior alveolar canal (IAC) as a reference structure. Statistical analysis of the measurements from 164 of the specimens showed that the worn occlusal surfaces (OS) maintained a more or less constant distance from the IAC with age, and the distance from the IAC to the cemento-enamel junction increased continuously. Likewise, the distance from the IAC to the alveolar bone crest (AC) and the distance OS-AC remained almost constant. In most groups there was a slow, continuous deposition of bone at the lower border of the mandible which could account for the increased face height of older individuals. Hence continuous eruption occurs at least up to about 45 years providing that there is inter-occlusal space available into which the teeth may erupt; furthermore, there is potential for eruption whether or not attrition occurs in all human adults at a similar age.