No abstract

– A method is presented which allows the average daily rate of enamel apposition to be estimated based on measurements of the length of prisms in longitudinal ground sections, and on available data for the time of formation of the tooth crown. The method was applied on 21 sections of human maxillary premolars. The reproducibility of the method was satisfactory, the error of measurement being in the order of 3.8%. After corrections having been made for the deviation of prisms from a radial direction, the average daily rate of enamel apposition along the prisms for any maxillary premolar was estimated to be within a range of from 2.0 to 6.1 μm, while a more probable rate would be 2.7–4.6 μm. These results are in agreement with experimental data, and are also compatible with the observed cross‐striation prism periodicity. The present study supports the theory that there exists a relationship between the prism periodicity and a 24‐h rhythm in enamel apposition in human teeth.

Ribozymes are small RNA structures capable of cleaving RNA target molecules in a catalytic fashion. Designed ribozymes can be targeted to specific mRNAs, blocking their expression without affecting normal functions of other genes. Because of their specific and catalytic mode of action ribozymes are ideal agents for therapeutic interventions against malfunctioning or foreign gene products. Here we report successful experiments to ‘knock out’ a major translation product in vivo using synthesized, chemically modified ribozymes. The ribozymes, designed to cleave amelogenin mRNA, were injected close to developing mandibular molar teeth in newborn mice, resulting in a prolonged and specific arrest of amelogenin synthesis not caused by general toxicity. No carriers were required to assist cellular uptake. Amelogenins are highly conserved tissue‐specific proteins that play a central role in mammalian enamel biomineralization. Ultrastructural analyses of in vivo ribozyme‐treated teeth demonstrated their failure to develop normally mineralized enamel. These results demonstrate that synthesized ribozymes can be highly effective in achieving both timed and localized ‘knock‐out’ of important gene products in vivo, and suggest new possibilities for suppression of gene expression for research and therapeutic purposes.

Enhancement of storage phosphor images improved detection of approximal caries in this in vitro study compared with unenhanced images and Ektaspeed film.