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Fibroblasts from human periodontal ligaments were grown in vitro. The levels of collagen and total protein in these cells were compared with subject- and passage-matched gingival fibroblasts. In 3 subjects the levels of both were greater in ligament than in gingival fibroblasts. These increased levels were also associated with increased levels of proteins reacting with anti-colligin/hsp47 antibodies on SDS-PAGE. Ligament and gingival fibroblasts were subjected to heat shock, sodium arsenite and the amino acid analogue AZC. These studies showed that (a) sodium arsenite and AZC enhanced the cellular levels of hsp47 in both types of fibroblast, (b) the colligin/hsp47 levels expressed were associated with elevated levels of protein and collagen production and (c) the presence of colligin/hsp47 was decreased under conditions of serum deprivation.

Periodontal ligament cells may have a role in the regulation of hard and soft periodontal tissues, but their specific function has yet to be determined. To evaluate further their role in periodontal homeostasis, they were examined for osteoblast-like behaviour; in vitro no characteristic osteoblastic responsiveness was found. Periodontal ligament cells gave a PGE2- and isoproterenol-mediated cAMP response, but did not respond in a similar fashion to calcitonin or PTH. When exposed to PGE2, isoproterenol, or 1,25(OH)2 vitamin D3, they did not exhibit an increase in protein production, as measured by [35S]-methionine incorporation. Immunofluorescent localization indicated that periodontal ligament cells produce a bone-associated protein, osteonectin. In addition, mRNA levels for osteonectin and bone proteoglycan I (biglycan) were detected in these cells, in vitro. This information should help to clarify the role such cells play in the regulation of periodontal tissues.

Summary Dental enamel is a product of ameloblast cells, which secrete a mineralizing organic matrix, composed primarily of amelogenin proteins. The amelogenins are thought to be crucial for development of normal, highly mineralized enamel. The X-chromosomal amelogenin gene is a candidate gene for those cases of amelogenesis imperfecta, resulting in defective enamel, in which inheritance is X-linked. In this report, a kindred is described that has a C to A mutation resulting in a pro to thr change in exon 6 of the X-chromosomal amelogenin gene in three affected individuals, a change not found in unaffected members of the kindred. The proline that is changed by the mutation is conserved in amelogenin genes from all species examined to date.

Tooth eruption is a precisely timed and sequenced event that brings the tooth from within bone into a functional position in the mouth. Every part of the developing tooth has been theoretically implicated as a primary factor in this process, but it now appears that eruption is multifactorial, with the dental follicle and type I collagen playing an important part. Immunological probes were used here to investigate in vivo and in vitro the temporal and spatial expression of type I collagen and its molecular chaperone Hsp47 in the dental follicle during eruption. Mandibles were dissected from 2-, 5-, 9- and 11-day-old neonatal mice and fixed in 95% ethanol overnight. Sections of 7 μm were obtained and reacted with antibodies directed against type I collagen. Dental follicles were isolated from 2-, 5-, 9- and 11-day-old neonates and cells were grown in culture for 8 days. Slides were then reacted with antibodies directed against type I collagen and Hsp47. The production of type I collagen and Hsp47 in the follicle varied with the stage of dental development and eruption. There was a progressive decrease of type I collagen in the coronal part of the follicle, leading to an arrest of its production in these areas. These findings support the notion that cells of the coronal portion of the dental follicle stop producing type I collagen as a prerequisite to the initiation of tooth eruption and that this phenotype persists in vitro .

A hypomineralized-type of amelogenesis imperfecta was investigated with the scanning electron microscope, analyzed with an electron microprobe and compared with normal enamel. Perikymata, imbrication lines and a prismless zone were absent in the abnormal enamel. Two-hour etching of the samples with EDTA revealed the presence of cross-striations in abnormal enamel but not in normal enamel. Pathological enamel showed the presence of macroporosities and disoriented prisms which extended below the surface of enamel. In addition, hypocalciflcation of prism sheaths and surface prisms were observed. Electron microprobe analyses of formed prisms in amelogenesis imperfecta showed that the values for calcium, phosphorus and the Ca:P ratio were normal, and fibrillar disorientated surface prisms were hypomineralized. Selective aplasia of ameloblasts and hypocalcification of enamel matrices were suggested as causes of the enamel defects.