Mandibular Growth and Disc displacement of TMJ
Mandibular condyle functions as a growth center of facial bones and provides the kinetic energy for mandible to grow forward and downward. Unilateral dysplasia of mandibular condyle may lead to mandibular asymmetry and malocclusion. Impaired growth of bilateral mandibular condyle may lead to mandibular retrognathia and following disorders in bite and narrow airway (Enlow DH, 1996)。
The growth and bone morphology of mandibular cartilage is different from other cartilages located in long bones in human body. The completion of mandibular growth is only about 50% at birth and ends late during adolescence (Buchbinder D,1991). Condylar growth cartilage exhibits adaptive growth property, which undergoes adaptive remodeling in response to external stimuli during and after growth stage (Shen G, 2005). Hence the TMJ motion and functioning during childhood and adolescence have significant influence on the growth of TMJ and mandible (Enlow DH,1996; Meikle MC, 2007)。
Trauma in facial bones and jawbones during childhood and adolescence may affect the growth of condylar head, resulting in growth inhibition of the entire mandible (Schellhas KP, 1990; Skolnik J, 1994). Similarly, the inflammation or degenerative bone changes in TMJ may also affect mandibular growth (Stabrun A. 1988; Schellhas KP, 1993; Kjellberg H, 1995)。
Many clinical studies showed that the development of craniofacial asymmetry is related to unilateral non-reducing TMJ disc displacement(Yamada K, 1999; Isberg A, 2000; Nakagawa S, 2002; Gidarakou IK, 2003). Long-term follow-up clinical trial also found that TMJ disc displacement without reduction happened during the growth stage may hinder the afterwards mandibular growth (Legrell PE, 1998; 1999. Displaced TMJ disc can cause changes in condylar cartilage while the extent of the changes is proportional to the level of disc displacement (Berteretche MV, 2001)。. As the disc displacement lasts longer, the damage to the condylar cartilage becomes more prominent ( Ali AM, 1995; Legrell PE, 1999), which affects the normal mandibular growth and causes mandible deviation, retrognathia and malocclusion.
The growth of facial bones and jawbones is closely relative to TMJ disorders, which represents the functional influence on bone growth. In particular TMJ disc displacement or TMJ trauma during adolescence should not be overlooked. For patients with facial asymmetry, mandibular retrognathia or mandibular asymmetry, clinicians should comprehensively evaluate the TMJ conditions and the past history in order to develop custom made treatment and surgical plan to ensure the best outcome (i.e. joint stability and health).
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