Dentistry in New Zealand from the pioneer era to the present.

As a final year undergraduate dental student at the University of Manchester, I visited the school of dentistry at the University of Otago in Dunedin, New Zealand (South Island) for the month of July, 1991 to do research for my non-clinical elective. This article is a description of some of the history of dentistry, dental education and the local way of life I glimpsed during this visit.

Immunocytochemical localisation of tenascin during the development of scleral papillae and scleral ossicles in the embryonic chick.

We have used a polyclonal antibody against tenascin (a 240 kDa extracellular matrix glycoprotein) and indirect immunofluorescence to investigate the distribution of tenascin in cryostat sections of the chick sclera during the six stages of scleral papilla development (Murray, 1943) and formation of membrane bone anlagen (mesenchymal condensations between 6-12 days of incubation - HH Stage 29-37). At Stages 1 and 2, when the papilla was a slight thickening in the conjunctival epithelium and mesenchymal condensation formation was initiated, tenascin was sparse in the sclera. At Stage 3, when the papilla had an epithelial mass intruding into the mesenchyme, there was an accumulation of tenascin fibrils along the subsurface of the papilla with fibrils extending from this region into the mesenchymal condensation. Interestingly, tenascin was sparse between papillae and between mesenchymal condensations. The Stage 4 papilla had a similar localisation of tenascin fibrils and in addition fine arborizing fibrils of tenascin were observed within the basal epithelia of the papilla adjacent to the epithelial-mesenchymal interface (which suggested that the fibrils infiltrated through the basement membrane region). The Stage 5 and 6 papillae had a column of vertical tenascin fibrils extending from the subsurface of the papilla to the interior mesenchyme corresponding exactly to the location of the mesenchymal condensation which was then forming the anlage of the ossicle in a flat bed about 100 microns from the conjunctival surface. The column of tenascin disappeared as the osteoid appeared in the ossicular bed on the 12th day of incubation but a dense accumulation of tenascin remained along the subsurface of the papilla. With the exception of tenascin fluorescence in the basal region of the Stage 4 papilla, tenascin fibrils were not observed in the other stages of papilla development in the epithelium covering areas between the mesenchymal condensation. This restricted distribution of tenascin may be important in the morphogenesis of scleral papillae and scleral ossicles.

Surgical manipulation of the developing chick embryo in ovo after the 4th day of incubation.

Surgical manipulations were performed on the eyes of the developing chick embryo between 6 1/2-12 days of incubation at stages when operations had to be performed through the shell and the extra-embryonic membranes. A sufficient proportion of the embryos survived a postoperative incubation period of 6-10 days to analyse the effects of surgical intervention on development.

The origin of the ectomesenchymal condensations which precede the development of the bony scleral ossicles in the eyes of embryonic chicks.

The origin of neural crest-derived ectomesenchymal condensations located subjacent to scleral papillae and the development of the more deeply situated scleral ossicles were investigated in scleral tissues explanted from the eyes of chick embryos at Hamburger & Hamilton (1952) stages 30-38 (6 1/2-12 days of incubation). Explants were pulse labelled with [3H]thymidine for 4h in vitro. Nuclear counts and % labelling indices were calculated for standardized areas within and between the condensations. At all stages exhibiting condensations, the % labelling indices were higher within the condensations than in tissues between condensations. % labelling declined with maturity, but the decline was greater between than within condensations. Regional differences in intensity of proliferation in the ectomesenchyme centred about the scleral papillae seemed to be the best explanation for the development of these condensations. The condensations disappeared concomitant with the complete degeneration of the adjacent papillae. A new distribution of labelled nuclei 70-100 micrometer deep in the tissue and beneath the original sites of the condensations preceded the appearance of ossicle primordia. The roles of the scleral papillae, the ectomesenchymal condensations and deeper primordia in the development of scleral ossicles are discussed.

A scanning electron microscopic study of the developing epithelial scleral papillae in the eye of the embryonic chick.

Eyes of early embryonic chicks possess 14 scleral papillae, derived from the conjunctival epithelium and present as transient structures between seven and 11 days of incubation. These papillae induce the formation of the 14 scleral ossicles, which develop in the adjacent, neural crest-derived ectomesenchyme. Each papilla undergoes a predictable series of developmental changes, divided by Murray ('43) into six morphological stages (M stages 1-6). We have confirmed his staging, and provide a scanning electron microscopic (SEM) evaluation of papilla development. The earliest stage that can be visualized with the S.E.M. is M stage 2. We describe the initial modifications of the surface of papilla cells, the presence of large microvilli and the asymmetrical morphogenesis and growth of the papillae. Papillae are shed by a mechanism that involves elongation of the cells at the base of the papilla. Such moribund papillae consist of necrotic cells coated with fibers.

Lack of association between avian cartilages of different embryological origins when maintained in vitro.

The possibility that cartilages of differing embryological origins behave as separate types with respect to cell-to-cell associations was tested by placing the cut ends of transversely sectioned embryonic chick tibial cartilages (of mesodermal origin) in apposition to transversely sectioned Meckel's cartilages (neural crest (ectodermal) cartilage) on the surface of a semi-solid organ culture medium and maintaining the combinations in vitro for five to ten days. Tibia-tibia and Meckel's cartilage-Meckel's cartilage (homotypic) combinations, which served as controls, became united by a common extracellular matrix and by the proliferation of chondroblasts. Analysis of combinations where one partner had been prelabelled with 3H-thymidine indicated that chondroblasts intermingled at the contact zone. In contrast, tibia-Meckel's cartilage (heterotypic) combinations became separated by a layer of fibrous tissue. The chondroblasts at the contact zone failed to intermingle. We conclude that avian embryonic chondrocytes are not all equivalent and that part of their nonequivalence could be related to their embryological origin either from the mesoderm or from the ectodermal neural crest.