Histological evaluation of the temporomandibular joint after bilateral vertical ramus mandibular distraction in a canine model

[Congenital malformations of the temporo-mandibular joint and the mandibular ramus: Grafting vs distraction osteogenesis]

Congenital deformities of the mandibular ramus and of the temporo-mandibular joint are treated by surgery since the early 20th century. However, morphological and functional results are often disappointing, accounting for iterative operations. Today, a clear consensus concerning the type of intervention to be proposed, and at what age it should be carried out does not yet exist. For mild cases, "conventional" orthognathic or osteogenic distraction procedures seem to work well, especially if they are carried out at the end of growth. In severe cases, it is often necessary to proceed in several surgical steps, usually starting with a chondrocostal graft, especially when interceptive surgery, performed before the end of growth, is preferred in order to improve the patient's quality of life.

Changes in growth and morphology of the condyle following mandibular distraction in minipigs: overloading or underloading?

OBJECTIVE

Loading of temporomandibular tissues during mandibular distraction may cause changes in condylar growth and cartilage thickness. This study examines the effects of distraction on the condyle in a large animal model by explicitly measuring growth and in vivo loading.

DESIGN

Unilateral mandibular distraction was carried out on 20 growing minipigs divided into three groups. One group underwent distraction but not consolidation, whereas the other two groups were allowed a period of consolidation of either 1 or 2 weeks. Animals received fluorochrome and 5-bromo-2'-deoxyuridine (BrdU) labelling and masticatory strain was measured from the condylar neck. Condylar strain was also recorded in an age-matched sample of eight animals that received no distraction surgery. Immunohistochemical procedures were used to identify dividing prechondroblasts and histological analysis was used to measure mineral apposition rate, count dividing cells, and measure the thickness of condylar cartilage.

RESULTS

Strain magnitude, particularly compressive strain, was much larger on the non-distraction side compared to the distraction side condyle. Compared to normal loading levels, the distraction side condyle was underloaded whereas the condyle on the intact side was overloaded. Mineral apposition and cartilage thickness were greater on the distraction side condyle compared to the opposite side. Differences between the sides were most pronounced in the group with no consolidation and became progressively reduced with consolidation time.

CONCLUSIONS

Increased mineralisation and cartilage thickness on the distraction side condyle are associated with reduced, not increased loading, perhaps because of disruption of the distraction side masseter muscle.