Temporomandibular joint (TMJ) Resorption
Why Condylar Resorption (CR) happens?
ling is mainly divided into 2 types: functional remodeling and dysfunctional remodeling.
Functional bone remodeling refers to changes in joint bony structure in response to the movement of soft tissue and joint without affecting the originally stable relationship between TMJ and occlusion or normal growth of TMJ. Functional bone remodeling usually happens during the early or moderate stage of TMJ internal derangement.
Dysfunctional bone remodeling refers to bone remodeling that gravely affects the relationship between TMJ and occlusion, including obvious changes in joint bony structure (e.g. decreased condylar head volume), decreased ramus height, retrognathia in adults and slowing TMJ joint growth in adolescents. Dysfunctional remodeling is also called progressive condylar resorption (PCR) or idiopathic condylar resorption (ICR).
Correlation between condylar resorption and hormones Factors affecting condylar resorption are divided into two categories: 1) abnormal TMJ forces and 2) reduced TMJ adaptability. Reduced TMJ adaptability is related to age, gender (in particular refer to female hormones, e.g. estrogen and prolactin), and systemic diseases (e.g. autoimmune diseases and hyperparathyroidism). In general women show a higher risk of developing condylar resorption（Mercuri LG.2007）。
Correlation between condylar resorption and occlusal force 有許多國內外研究指出顳顎關節受力(例如吃東西的力量)、及關節軟組織變化(例如關節盤位置跑掉)，都會造成關節骨頭順應性的形態改變（Wolford LM.2015）。這是關節自我保護的機制之一，可避免持續產生不必要的應力而造成發炎疼痛。但若關節長期接受超過它可負荷的壓力，如不穩定的咬合、磨牙緊咬、嚴重關節盤異位、外傷撞擊或矯正治療、接受正顎手術等情形，關節產生髁頭吸收(condylar resorption)的比例便會上升。
Correlation between condylar resorption and disc displacement TMJ disc displacement may combine with TMJ bony remodeling and condylar resorption. Disc displacement occurs during mandible growth period in adolescence may have adverse effects on mandibular growth (Nebbe B, 1997) resulting in a higher risk of developing mandibular hypoplasia, retrognathia and facial deviation. These conditions associated with poor mandibular position and shape will also affect maxillary growth and result in unproportional face shape.
Correlation between condylar resorption and orthodontic treatment or orthognathic surgery Most patients with condylar resorption exhibit clinical signs, e.g. joint pain and functional restriction. However 25% of the patients, even with pathological condylar resorption, show no clinical signs (Wolford LM, 2015). This type of patient usually visits doctors for receding chin, open bite and facial symmetry problems. As they show no signs of TMD, it is difficult to discover the existing condylar resorption, which may lead to unstable outcome of orthodontic treatment and orthognathic surgery, or trigger signs of TMD such like pain or difficulty in mouth opening. Many researchers have published cases of condylar resorption occured after orthognathic surgery or during orthodontic treatment（Kerstens HC,1990. Crawford JG,1994. Arnett GW,1990. Wolford LM,2003. Goncalves JR,2008）。
Management of TMJ condylar resorption during orthodontic treatment include:
The occurrence of TMJ condylar resorption or TMD symptoms during orthodontic treatment or after orthognathic surgery, resulting in premature termination of treatment, prolongation of treatment time, or adoption of compromised treatment is a nightmare for both the clinician and the patient. Orthodontic treatment and orthognathic surgery are therapeutic options that will change dental occlusion and joint bony structure, and therefore the clinician should carefully perform evaluation of TMJ conditions to provide the most suitable and customized treatment plan for the patient.
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All Written Contents and Pictures Created by Dr. Adrian M. Hsieh and Dr. Scott H. Jiang
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