Developmental Anomalies of the Temporomandibular Joint R. Bruce Ross, DDS, MSc, FRCD he processes by which the human face develops in the Division of Orthodontics embryo are exceedingly complex, but they work out per- The Hospital for Sick Children fectly—-almost every time. Occasionally, however, the Toronto, Ontario, Canada T development of structures such as those comprising the temporo- mandibular articulation is disturbed, leading to an anomalous Professor Faoulty of Dentistry morphology in later life. It is important to note that an anomaly is University of Toronto not necessarily an undesirable condition requiring treatment. It Toronto, Ontario, Canada may be benign, with no associated problems, and therefore of no consequence; in fact, it may never be identified. Ross and Correspondence to: Johnston' have published a review of the developmental processes Dr R. B. Ross and etiology of undesirable conditions affecting the temporo- Faculty oS Dentistry mandibular joint (TMJ). University of Toronto Craniofacial anomalies may be caused by genetic faults (eg, 124 Edward Street Treacher Collins syndrome) or caused by a teratogenic agent (eg, Toronto, Ontario thahdomide), but most often it appears the cause is multifactorial M5G lG6 0anads Fax:416-813-6375 (eg, cleft hp and palate). When the entire human genome is avail- E-mail: [email protected] able and studied in persons with congenital anomalies, there may well be indicators for, or at least a demonstrable predisposition to, developmental problems. Problems involving the TMJ can be acquired or congenital (developmental). Tbe vast majority seen in a dental office are acquired dysfunctions, traumatic injuries, or pathologic condi- tions. Developmental anomalies appear to be rare because most of them arc asymptomatic and never come to the patient's or den- tist's attention. Others are associated with syndromes, and the patients are referred to centers where treatment is provided by muJtidiscipiinary teams of specialists. Diagnosis The standard approach to any suspected morphologic or func- tional anomaly of the temporomandibular articulation is a radio- graph or series of radiographs, which provides an excellent image of the bony elements. Dysmorphologies of the condyle and fossa are frequently detected in panoramic films that are part of a gen- eral examination of "normal" patients. There is thus much experi- ence and information available on the skeletal elements. The soft tissue elements are not as well documented. The enor- mous variety of developmental anomalies that occur in the cranio- facial region suggests that anomalies occur in virtually every Key words: temporomandibular joint, developmental anomalies, hemifacial microsomia J OROFAC PAIN lS99;13:262-272, 262 Volume 13. Number4. 1999 Ross component of every structure, even if most go morphology, TMJ function is not abnormal in undetected. If this is true, mild and even severe these cases. Another form of unilateral hypertro- anotnalies of the soft tissue components of rhe phy is part of a generalized hemihypertrophy TMJ undoubtedly do occur, producing symptoms involving the entire mandible and the teeth, many that are difficult ro diagnose. Assessment of joinr other facia! structures, and even rhe enrire body, dysfunctions or dysplasias is usually limited to the Tbe TMJ on the enlarged side may be well for- interpretation of radiographs, clinical observa- ward of the external auditory canal. The affected tions, and occasional arthroscopic examination. condyle is longer but not increased in diameter We do nor routinely search with other sophisti- (Eig 2). cated imaging techniques. Abnormalities of the synovial membrane, tbe capsule, and the support- Hemifacial Microsomia ing ligaments may not produce recognizable pri- mary symproms but may lead to secondary bony Almost all the developmental anomalies of the symptoms. Absence of the capsule, for example, if TMJ belong to a group of anomalies generally it occurs, would probably remain undiagnosed termed hemifacial microsomia, although the condi- until it resulted in inflammation and bony destruc- tions are not always unilateral—nor are rhey often tion or ankylosis of the joinr. microsomia. They include Goldenhar syndrome Developmental bony ankylosis is very rare, if it and orber variations.^-^ In the severe expression of occurs at all. A decreased mobility of tbe mandible this condition there is a dysmorphology of most of is most probably caused by the soft tissue elements the structures in the region, including the of the joint. In an unpublished survey of 107 chil- mandibular condyle and ramus, the middle and dren with hemifacial microsomia, we found only 2 external ear, orbit, zygoma, and maxilla (Fig 3). patients who had a severe restriction of opening The affected condyle and ramus are often severely (less than 15 mm). If developmental processes dysplastic or even absent or displaced medially; m cause a dysmorphology of the bony elements, they very severe cases there may be no temporal fossae will almost certainly cause dysmorphology of tbe or middle ear (Fig 4}. The muscles of mastication associated soft tissues. Surgeons operating in rhe are severely hypoplastic or may be virtually absent. The abnormalities of the TMJ range from com- region of a dysmorpbic condyle often note gross plete agenesis to subtle differences in form or size defects of the disc and supporting structures. with few deformities (Fig 5). Invariably, bowever, One would suspect that there are developmental the dysplasia is botb a deficiency and a malforma- defects limited to the soft tissues, but this is specu- tion. A significant feature is that in 70% of cases lation, because access ro study sucb joints is rare. the condition appears to be unilateral, while in However, disc displacement problems in adults bilateral cases asymmetry is tbe rule, with only could be a developmental malformation of the subtle dysmorphology on the less affecred side. capsule and ligaments, or abnormal disc morpbol- Rarely are borh sides severely affecred. Alrhough ogy. When the joint is not functioning well in a there is evidence of a generic etiology in a few congenital problem, in my experience the bone is cases, it is not a major factor. always recognizably involved. There may or may not be involvement of rhe muscles and soft tissues. Surprisingly, there are almost no problems asso- ciated with the grossly abnormal temporo- Micrognathia mandibular articulation in these cases. There is no dysfunction, in the general sense of function, Tbese The mandible in any of the recognized micro- patients have no associared pain or discomfort, gnathias invariably has a normal appearance of the can cbew and swallow comfortably and well, can speak with normal articulation and nasal reso- condyle and a normally functioning articulation. nance, and can breathe adequately (the mandible Tbere is a posterior displacement of the condyle in provides snpport for maintenance of the airway, so mandibulofacial dysostosis (Treacher Collins syn- that obstructive sleep apnea is very rare). There is drome), which may be responsible for the limited no dysfunction except in the narrowest of defmi- mobility and unusual shape of tbe lower border tions^that is, the mandible and TMJ do not func- witb time (Fig 1), True condyiar hyperplasia with tion in the normal way. There is often a deviation enlargement of the condyle does occur but has of rhe mandible toward the affected side on open- only heen seen in our clinic in cases of unilateral ing, indicating a restriction of movemenr in rhe condylar hyperplasia, a condition of unknown eti- affected joint. This is probably due ro an absence ology thar occurs in young adults between approx- or virtual absence of the lateral pterygoid muscle imately 19 and 23 years of age. Despite the dys- Joumal of Orofacial Pain 263 Ross Figs la and lb Child with typical Trcacher Collins syndrome. Figs lc and Id Two affected individuals in whom che condyie appears to be adhering to the posterior of the glenoid fossa. This may be an abnormality of the distomalleolar iiga- ment cbaratteristic of tbis condition. or ro hypoplasia of contiguous soft tissues. The Timing of Treatment affected mandible can often he freely advanced manually (Pig 6), When should treatnient he instituted in these There are, however, psychosocial problems cases? The parenrs would like treatment completed relared Co the facial asymmetry that is invariabiy in the neonatal period, if that were possible. The present. One side of the mandible is greatly speech pathologist would iike the speech mecha- reduced, usually in all 3 dimensions: vertical nism corrected in rhe first year, the psychologist heighr, anCeroposterior length, and bicondylar/ wouid like the facial appearance Creaced before bigonial width. Although poor facial esthetics are school age ar least, che orthodontist would like a a serious problem for the patient and che family, corrected jaw relationship stabilized in the primary one couid even argue that facial esthetics are not a dentition, and the surgeon might like to wait as biologic characteristic hut a sociologie one, and in long as possibie to avoid facial changes with a society that did not care about physiognomy, growth after surgery. As an example, the surgical there would be no problem with having this faciès. protocois for cleft iip and palate usually are: lip 264 Volume 13. Number 4. 1999 Ross Fig 2a Child with typical hetnifa- Fig 2b Radiographic view. The soft tissties are more cial hypertrophy, featuring gross affected than the skeleton. overdevelopment of many structures of tbe right side of the face, includ- ing the ear and rhe teeth. Figs 2c and 2d The right condyle \left) is tubular in shape and the TMJ is the extertial anditory canal, compared to the unaffected side {right). repair in the early postnatal period for esthetics, ately. If tbe condition will gradually worsen if left hard and soft palate repair later in the first year untreated, for example with mandibular ankylosis, for speech, alveolar cleft bone grafting at 9 to 11 then early intervention is mdicated.