The mandibular complex

Abstract

Die Wahrheit mag uns zu allem moglichen fuhren Brecht: Leben des Galilei The mandible can be called the orthodontist's complex. A complex often defies reason and this is true of many orthodontists' views on this bone. Voluminous literature exists about the lower jaw but one issue, namely the mandibular amenability to our mechanotherapy, is still the subject of great debate, dividing the orthodontic world into two opposite camps, in spite of the fact that the evidence for the solution has been there for a long time in the numerous clinical observations and research findings. The mandible is also complex from the biological viewpoint since it consists of several relatively independent structural and functional parts. As regards its adaptability, especially where intermaxillary relationships are concerned, the key region is perhaps the evolutionary newcomer, the ramus-condyle region. It is the purpose of this presentation to review some of the most recent findings related to the condyle and the ramus in the hope that every clarification of the complex mandible will reduce the mandibular complex of the orthodontists. Let us first consider the condylar cartilage. How does the condylar cartilage grow? It is commonly accepted to-day that the condylar cartilage, unlike the so-called growth cartilages proper, grows appositionally, not interstitially and that the mitotic cells are not cartilage cells, as in the growth cartilages, but undifferentiated mesenchymal cells (Fig. 1). Figure 1 The top of the condyle of a 30-day-old rat. The mitotic cells form a dense band underneath the fibrous covering layer, then follow the chondrocytes, which soon become hypertrophic; in the lower edge of the view the erosion front. H & E, original magnification ×133. These cells are apparently multipotential, as are similar cells elsewhere. Specifically, they can become either chondrogenic or osteogenic, depending on environmental stimuli (Meikle, 1973). This makes it …