The isolated mandibular ramus - a hitherto rarely described anomaly of the mandible. Pathogenesis and treatment

INTRODUCTION: A very famous paper by Sam Pruzansky, published in 1969, was entitled "Not all dwarfed mandibles are alike". This is the topic of this paper: to describe the shape and discuss the possible pathogenesis of an extremely rare congenital dysplasia found in a unilaterally hypoplastic mandible, namely the isolated mandibular ramus.

MATERIAL AND METHODS: A unique malformation of the lower jaw was found in more than 75 patients with developmental abnormalities of the mandible diagnosed and treated by the two authors in two different university hospitals over the last 40 years. We performed the following teratological experiments with laboratory rodents in order to try to understand the pathogenesis of this special dysplasia (and others): at first the normal development of the lower jaw was studied in rat and mouse foetuses. Then a variety of teratogenic drugs were applied to pregnant females and then the foetuses of these pregnancies were studied following Caesarian section.

RESULTS: One rat foetus was identified which presented the identical dysplasia that had been noted in the patient described here. The dam pregnant with this foetus had been given 25 mg/kg bodyweight of 6-mercaptopurine on day 12 of pregnancy. The explanation found for the pathogenesis of this anomaly was deducted from the scientific literature regarding normal development of the mandibular condyle.

CONCLUSION: The nucleus of the so-called secondary cartilage that will produce the ascending ramus (plus condyle and coronoid) is a separate growth centre which fuses a short time later with the dental bone which becomes the mandible proper by this fusion.