COMPARISON OF THE EFFECTS OF GROWTH-HORMONE, INSULIN-LIKE GROWTH-FACTOR-I AND FETAL CALF SERUM ON MOUSE MOLAR ODONTOGENESIS IN-VITRO

The effects of growth hormone, its mediator insulin-like growth factor -I (IGF-I), and fetal calf serum on odontogenesis were compared to tho se of serum-free medium. Explanted, 16-day, fetal mouse first molar to oth germs in early bell stage were grown on semisolid, serum-free medi um supplemented with ascorbic and retinoic acids. Recombinant human gr owth hormone at 50 or 100 ng/ml, IGF-I at 100 or 200 ng/ml, or fetal c alf serum at 20% concentration were added to the media. Volumetric cha nges in serial sections of six tooth germs per treatment over 3 days o f treatment (4, 5, 6 days in vitro) were compared by digitized morphom etry. Mitotic indices were also compared and the cell densities of the dental papillae recorded. Qualitative ratings of differentiation were ascribed to each tooth germ by light microscopy. Differences in volum e, mitotic activity and cell densities were found. The growth hormone- treated tooth germs were not larger than the serum-free ones but had i ncreased mitotic indices and higher cell densities in the dental papil lae. IGF-I-treated tooth germs had larger volumes than with all other treatments, e.g. germs treated with 200 ng/ml of IGF-I, after 6 days i n culture, were significantly larger than with all other treatments (p < 0.01 - < 0.001). Whilst IGF-I-treated germs displayed the greatest extent of differentiation, growth hormone-treated germs also showed ad vanced differentiation compared to those on serum-free medium. These r esults suggest that growth hormone and IGF-I are involved in odontogen esis of murine teeth in vitro by affecting mitotic activity, tissue vo lume and cell differentiation. In conjunction with previous immunohist ochemical studies that show expression of growth hormone receptor and IGF-I in developing teeth, these results provide evidence that both gr owth hormone and its mediator play a part in odontogenesis.