Time-dependent decrease and seasonal variation of the porosity of recently erupted sound dental enamel in vivo

Recently erupted teeth are more sensitive to dental caries than teeth that have remained free from caries lesions for a few years after eruption. It has been hypothesized that this may be ascribed to differences in enamel porosity. The objective of the present work was to assess the time-dependence of electrical conductance, as an indication of porosity, of occlusal enamel in recently erupted permanent molar teeth. Fifty children aged 5-15 years of age, receiving regular dental care at six-month intervals, participated in the study when their first molar teeth (in 5- to 6-year-olds) or their second molar teeth (in 11- to 15-year-olds) had not been exposed to the oral environment for more than six months. On the first semi-annual check-up after eruption of a first or second molar, baseline diagnostic measurements, i.e., visual inspection and electrical conductance measurements (ECMs), were made at three or four pre-defined sites in the fissures. Subsequently, data collection was repeated every six months for three years. Sites were excluded from ECMs when a caries lesion was observed at a site by visual inspection. After 36 months, there were 257 sites in teeth considered sound upon visual examination. The ECM values of these sound sites showed a clear decrease with time after the first examination. The conductance decreased on average from 0.13 (M Omega)(-1) to 0.059 (M Omega)(-1). Since the conductance is assumed to be proportional to the porosity of the enamel, the latter decreased by a factor of 2.2 over the 36-month period. The results furthermore indicated a higher conductance for maxillary than for mandibular enamel. Almost all sites in that sample appeared to be in teeth that were observed for the first time during the months September to December. Electrical conductance, and therefore enamel porosity, of the sites showed a periodic variation with season of observation. In the fall, the conductance was higher than in the spring. This implies that a dentist should be more prudent in the fall than in the spring when indicating restorative treatment of an incipient caries lesion.