- Email: [email protected]
Current concepts about the temporomandibular joint
SEC’1 >h El *1TC R
GEOKE
4. :%&.I
Current
concepts about the temporomandibular
Tore L. Hansson,
joint
D.D.S., Chbmt. Dr.*
University of .4msterdam, Scho31 of Dentistry, Ansterdam, ‘The Ne,hf,I lands
S
ymptoms and signs of crarliomandibular diaorders are frequently recognized. Single signs of pain at muscular palpation are common even z.mong young individuals,‘, z and with increasing age tanporomandibular joint (TMJ) sounds become more prelralent. In aclults., TMJ sounds are the most. common sign Iof craniomandibular disorder. Clicking is often bilateral, whereas crepitation is usually unilateral.3 Findings liom severa!. epidemiologic studies show the close rclationship between the anatomic part of the joint and its associated muscles. Results of studies indicate that the development of a craniomandibular disorder with muscular incoordination at the onset is followed by increased engagement of the associated part of the joint structures. The structure of the joint, that is, the condyle, the temporal component, the disk, and their arrangement in constituting a functioning unit, becomes disturbed. The complicated relationship between the condyle/ disk complex and the temporal component is conceptualized as rotation and translation. It took a long time for the observations of Posselt4 (posterior displacement of the condyle) and Farrars (anterior displacement of the disk) to be accepted. These authors’ diagnostic contributions ran counter to the dental profession’s equalization of a click with a derangement. It became clear that any successful treatment must be based upon an understanding of the pathogenesis of the disease. The condition in which the anatomic components of the joint exist at a particular time therefore deserves detailed consideration. Four different tissue layers, fibrous connective tissue, undifferentiated mesenchymal cells, cartilage, and bone, can be distinguished in the condyle and in the temporal component. Cellular proliferation with cartilage formation from the undifferentiated mesenchyme takes place, resulting in a thickening of the subarticular soft tissue layers. The differences in thickness point to variations in biomechanical loading in the joint. The loading stimulates the undifferentiated mesenchyme to a proliferative response and formation of cartilage.6-8 The disk mainly consists of fibrous connective tissue. Morphologically it is regarded as the passive component of the joint.
Presented before the American Academy of Restorative Dentistry, Chicago,
III.
*Professor and Chairman, Department of Masticatory 370
Function.
Functionally however, it plays an active role in intraarticular stabilization. Its sagittal biconcave shape and resemblance to a condylar cap, with its close attachments to the two condylar poles, underscore its dependence of form and function on the two other components. Only the periphery of the disk shows the presence of soft connective tissue with blood vessels and nerve endings. Reasons for TMJ pain are therefore likely to be in the region of the TMJ capsule rather than the articulating part of the disk. The undifferentiated mesenchyme of the corldyle and of the temporal component contribute to the development of deviations in form.8’9 This undifferentiated mesenthyme may be used to such an extent in cartilage formation that it subsequently disappears because the demands of normal tissue maintenance, that is, remodefing, are exceeded.” The threshold of pathology is exceeded as a result of excessive remodeling, and predegenerative changes occur. The lateral part of the joint is exposed to the largest functional/parafunctional loads. A histomorphometric analysis of the extent of changes and the amount of remaining undifferentiated mesenchymal cells in the different regions indicates that the amount of undifferentiated mesenchymal cells varies inversely with the thickness of the soft tissue layers. The disk cannot proliferate in the manner of the condyle and temporal campkent because of the lack of undifferentiated mesenchyme. The disk, therefore, passively adapts to the changes occurring in the other articulating components by becoming increasingly thinner. If this process is not interrupted, a perforation of the disk can ensue, with gradual deterioration of the other joint components. In this context the works of Hansson et al.” and Solberg et al.12 become particularly relevant. They reported the frequency of disk displacement to be 12% among 95 young TN Js at autopsy. Partial displacements were twice as common as total displacements, with the displacement anteromedial in its direction. Disk deformation was cwly assoeiated with the displacement, and changes of. soft tiss~! character in the other joint [email protected] were evident. These findings indicate the displacement to be a cons quence rather than the cause of previous hi&&& events. A divided approach that focus s on om? particular articulating part and subse+Gntly the treatment of an arthrogenous disease should therefore be avoided. MARCH
1986
VOLUME
55
NUMBER
3
CURRENT
CONCEPTS
ABOUT
TMJ
The sizes of the TMJ components vary greatly even though their mean values seem to be universal. Componential form, on the other hand, seems to be decisive in the future development of changes. Frontally flat and gable-shaped condyles articulate against flat and inverted V-shaped temporal components.‘* These joints show more changes. Totally irregular forms are also well-correlated among the three different planes. Thus it appears that there are TMJ groups morphologically at risk. In addition, each TM J component seemsto have its own capacity for maturity, adaptation, and degeneration.13 Less than half of 90 TMJs in the age group between 13 and 38 years (43%) manifested the same histologic pattern in all three articulating components. Adaptive changes followed by local degenerative changes can be expected by the third decade in life. Joints in women appear more stable morphologically, whereas those in men are more unpredictable in their development, and often show adaptive changes in the temporal component even before condylar growth has ceased. Therefore one reason for the skewed sex distribution among patients with craniomandibular disorders may be a matter of developmental background combined with differences in potential tissue compensation. Whereas occlusal factors such as interferences and tooth loss are generally acceptable etiologic considerations, emphasis on mandibular symmetry is bound to grow. Underdeveloped condyles, unilateral defects of condylar form, asymmetrical lengths of the two mandibular rami, and condylar fractures can be recognized in any orthopantomogram. Their recognition provides clinical information on the possible effect of function of the supporting muscles and deviations of mandibular movements. The existence of morphologic variants does not imply that the patient will seek immediate care. It is a common clinical impression that overt joint symptoms caused by overloading do not show up until several years after the accident or precipitating event. The symptoms then tend to be localized in the “uninjured” side of the face. The bilateral function of the mandible makes the cause, and its effect of injury on stomatognathic function, difficult to evaluate. It is possible to distinguish between two basic origins of craniomandibular pain. Criteria developed from accepted orthopedic tests can be used by any practicing dentist and applied to the TMJ.14 Manipulation makes it possible to differentiate the condition of the joint surfaces. Statistical differences between patients with myogenous origin for pain versus patients with an arthrogenous origin was found in EMG amplitude and
THE JOURNAL
OF PROSTHETIC
DENTISTRY
in silent period duration. Myogenous origin demands one sequence of treatment whereas arthrogenous origin demands another. Restorative or prosthetic dentistry is bound to remain an important part of the treatment for restoring adult stomatognathic function although dental therapy is becoming more individualized. As a result, dogmas on mandibular position for dental rehabilitation can now be regarded as past history. REFERENCES 1. Nilner M, Laming SA: Prevalence of functional disturbances and diseases of the stomatognathic system in J-14 year olds. Swed Dent J 5:173, 1981. 2. Nilner M: Prevalence of functional disturbances and diseases of the stomatognathic system in 15-18 year olds. Swed Dent J 5:189, 1981. 3. Hansson T, Nilner M: A study of the occurrence of symptoms of diseases of the temporomandibular joint, masticatory musculature, and related structures. J Oral Rehabil 2~313, 1975. 4. Posselt U: Physiology of Occlusion and Rehabilitation, ed 2. Oxford, 1964, Blackwell Scientific Publications, pp 37, 90, 187, 229. 5. Farrar W: Differentiation of temporomandibular joint dysfunction to simplify treatment. J PRO~THETDENT Z&629, 1972. 6. Blackwood HJJ: Cellular remodeling in articular tissue. J Dent Res (Suppl) 3:480, 1966. 7. Hansson T, Oberg T, Carlsson GE, Kopp S: Thickness of the soft tissue layers and the articular disk in the temporomandibular joint. Acta Odontol Stand 35177, 1977. 8. Hansson T, Nordstriim B: Thickness of the soft tissue layers and articular disk in temporomandibular joints with deviations in form. Acta Odontol Stand 35~281, 1977. 9. Lubsen CC, Hansson TL, Nordstrom, BB, Solberg WK: Histomorphometric analysis of cartilage and subchondral bone in mandibular condyles of young human adults at autopsy. Arch Oral Biol 30~129, 1985. 10. Moffett B: The morphogenesis of the temporomandibular joint. Am J Orthod 52401, 1966. Il. Hansson TL, Nordstrijm B, Solberg WK: TMJ articular disc displacement in young adults at autopsy (abstract). J Oral Rehabil 103452, 1983. 12. Solberg WK, Hansson TL, Nordstrom B: The temporomandibular joint in young adults at autopsy: A morphologic classification and evaluation. J Oral Rehabil 12~303, 1985. 13. Hansson TL, Nordstrom B, Solberg WK: Histological analysis of TMJs during late growth and maturity. J Dent Res (Special issue) 63:1984 (Abstr No. 519). 14. Naeije M, Hansson TL: Electromyographic screening of myogenous and arthrogenous TMJ dysfunction patients. J Oral Rehabil (in press). l&~/win1
reyuesls
lo:
DR. TORE L. HANSSON UNIVERSITYOF AMSTERDAM SCHOOLOF DENTISTRY AMSTERDAM THE NETHERLANDS
GEOKE
4. :%&.I
Current
concepts about the temporomandibular
Tore L. Hansson,
joint
D.D.S., Chbmt. Dr.*
University of .4msterdam, Scho31 of Dentistry, Ansterdam, ‘The Ne,hf,I lands
S
ymptoms and signs of crarliomandibular diaorders are frequently recognized. Single signs of pain at muscular palpation are common even z.mong young individuals,‘, z and with increasing age tanporomandibular joint (TMJ) sounds become more prelralent. In aclults., TMJ sounds are the most. common sign Iof craniomandibular disorder. Clicking is often bilateral, whereas crepitation is usually unilateral.3 Findings liom severa!. epidemiologic studies show the close rclationship between the anatomic part of the joint and its associated muscles. Results of studies indicate that the development of a craniomandibular disorder with muscular incoordination at the onset is followed by increased engagement of the associated part of the joint structures. The structure of the joint, that is, the condyle, the temporal component, the disk, and their arrangement in constituting a functioning unit, becomes disturbed. The complicated relationship between the condyle/ disk complex and the temporal component is conceptualized as rotation and translation. It took a long time for the observations of Posselt4 (posterior displacement of the condyle) and Farrars (anterior displacement of the disk) to be accepted. These authors’ diagnostic contributions ran counter to the dental profession’s equalization of a click with a derangement. It became clear that any successful treatment must be based upon an understanding of the pathogenesis of the disease. The condition in which the anatomic components of the joint exist at a particular time therefore deserves detailed consideration. Four different tissue layers, fibrous connective tissue, undifferentiated mesenchymal cells, cartilage, and bone, can be distinguished in the condyle and in the temporal component. Cellular proliferation with cartilage formation from the undifferentiated mesenchyme takes place, resulting in a thickening of the subarticular soft tissue layers. The differences in thickness point to variations in biomechanical loading in the joint. The loading stimulates the undifferentiated mesenchyme to a proliferative response and formation of cartilage.6-8 The disk mainly consists of fibrous connective tissue. Morphologically it is regarded as the passive component of the joint.
Presented before the American Academy of Restorative Dentistry, Chicago,
III.
*Professor and Chairman, Department of Masticatory 370
Function.
Functionally however, it plays an active role in intraarticular stabilization. Its sagittal biconcave shape and resemblance to a condylar cap, with its close attachments to the two condylar poles, underscore its dependence of form and function on the two other components. Only the periphery of the disk shows the presence of soft connective tissue with blood vessels and nerve endings. Reasons for TMJ pain are therefore likely to be in the region of the TMJ capsule rather than the articulating part of the disk. The undifferentiated mesenchyme of the corldyle and of the temporal component contribute to the development of deviations in form.8’9 This undifferentiated mesenthyme may be used to such an extent in cartilage formation that it subsequently disappears because the demands of normal tissue maintenance, that is, remodefing, are exceeded.” The threshold of pathology is exceeded as a result of excessive remodeling, and predegenerative changes occur. The lateral part of the joint is exposed to the largest functional/parafunctional loads. A histomorphometric analysis of the extent of changes and the amount of remaining undifferentiated mesenchymal cells in the different regions indicates that the amount of undifferentiated mesenchymal cells varies inversely with the thickness of the soft tissue layers. The disk cannot proliferate in the manner of the condyle and temporal campkent because of the lack of undifferentiated mesenchyme. The disk, therefore, passively adapts to the changes occurring in the other articulating components by becoming increasingly thinner. If this process is not interrupted, a perforation of the disk can ensue, with gradual deterioration of the other joint components. In this context the works of Hansson et al.” and Solberg et al.12 become particularly relevant. They reported the frequency of disk displacement to be 12% among 95 young TN Js at autopsy. Partial displacements were twice as common as total displacements, with the displacement anteromedial in its direction. Disk deformation was cwly assoeiated with the displacement, and changes of. soft tiss~! character in the other joint [email protected] were evident. These findings indicate the displacement to be a cons quence rather than the cause of previous hi&&& events. A divided approach that focus s on om? particular articulating part and subse+Gntly the treatment of an arthrogenous disease should therefore be avoided. MARCH
1986
VOLUME
55
NUMBER
3
CURRENT
CONCEPTS
ABOUT
TMJ
The sizes of the TMJ components vary greatly even though their mean values seem to be universal. Componential form, on the other hand, seems to be decisive in the future development of changes. Frontally flat and gable-shaped condyles articulate against flat and inverted V-shaped temporal components.‘* These joints show more changes. Totally irregular forms are also well-correlated among the three different planes. Thus it appears that there are TMJ groups morphologically at risk. In addition, each TM J component seemsto have its own capacity for maturity, adaptation, and degeneration.13 Less than half of 90 TMJs in the age group between 13 and 38 years (43%) manifested the same histologic pattern in all three articulating components. Adaptive changes followed by local degenerative changes can be expected by the third decade in life. Joints in women appear more stable morphologically, whereas those in men are more unpredictable in their development, and often show adaptive changes in the temporal component even before condylar growth has ceased. Therefore one reason for the skewed sex distribution among patients with craniomandibular disorders may be a matter of developmental background combined with differences in potential tissue compensation. Whereas occlusal factors such as interferences and tooth loss are generally acceptable etiologic considerations, emphasis on mandibular symmetry is bound to grow. Underdeveloped condyles, unilateral defects of condylar form, asymmetrical lengths of the two mandibular rami, and condylar fractures can be recognized in any orthopantomogram. Their recognition provides clinical information on the possible effect of function of the supporting muscles and deviations of mandibular movements. The existence of morphologic variants does not imply that the patient will seek immediate care. It is a common clinical impression that overt joint symptoms caused by overloading do not show up until several years after the accident or precipitating event. The symptoms then tend to be localized in the “uninjured” side of the face. The bilateral function of the mandible makes the cause, and its effect of injury on stomatognathic function, difficult to evaluate. It is possible to distinguish between two basic origins of craniomandibular pain. Criteria developed from accepted orthopedic tests can be used by any practicing dentist and applied to the TMJ.14 Manipulation makes it possible to differentiate the condition of the joint surfaces. Statistical differences between patients with myogenous origin for pain versus patients with an arthrogenous origin was found in EMG amplitude and
THE JOURNAL
OF PROSTHETIC
DENTISTRY
in silent period duration. Myogenous origin demands one sequence of treatment whereas arthrogenous origin demands another. Restorative or prosthetic dentistry is bound to remain an important part of the treatment for restoring adult stomatognathic function although dental therapy is becoming more individualized. As a result, dogmas on mandibular position for dental rehabilitation can now be regarded as past history. REFERENCES 1. Nilner M, Laming SA: Prevalence of functional disturbances and diseases of the stomatognathic system in J-14 year olds. Swed Dent J 5:173, 1981. 2. Nilner M: Prevalence of functional disturbances and diseases of the stomatognathic system in 15-18 year olds. Swed Dent J 5:189, 1981. 3. Hansson T, Nilner M: A study of the occurrence of symptoms of diseases of the temporomandibular joint, masticatory musculature, and related structures. J Oral Rehabil 2~313, 1975. 4. Posselt U: Physiology of Occlusion and Rehabilitation, ed 2. Oxford, 1964, Blackwell Scientific Publications, pp 37, 90, 187, 229. 5. Farrar W: Differentiation of temporomandibular joint dysfunction to simplify treatment. J PRO~THETDENT Z&629, 1972. 6. Blackwood HJJ: Cellular remodeling in articular tissue. J Dent Res (Suppl) 3:480, 1966. 7. Hansson T, Oberg T, Carlsson GE, Kopp S: Thickness of the soft tissue layers and the articular disk in the temporomandibular joint. Acta Odontol Stand 35177, 1977. 8. Hansson T, Nordstriim B: Thickness of the soft tissue layers and articular disk in temporomandibular joints with deviations in form. Acta Odontol Stand 35~281, 1977. 9. Lubsen CC, Hansson TL, Nordstrom, BB, Solberg WK: Histomorphometric analysis of cartilage and subchondral bone in mandibular condyles of young human adults at autopsy. Arch Oral Biol 30~129, 1985. 10. Moffett B: The morphogenesis of the temporomandibular joint. Am J Orthod 52401, 1966. Il. Hansson TL, Nordstrijm B, Solberg WK: TMJ articular disc displacement in young adults at autopsy (abstract). J Oral Rehabil 103452, 1983. 12. Solberg WK, Hansson TL, Nordstrom B: The temporomandibular joint in young adults at autopsy: A morphologic classification and evaluation. J Oral Rehabil 12~303, 1985. 13. Hansson TL, Nordstrom B, Solberg WK: Histological analysis of TMJs during late growth and maturity. J Dent Res (Special issue) 63:1984 (Abstr No. 519). 14. Naeije M, Hansson TL: Electromyographic screening of myogenous and arthrogenous TMJ dysfunction patients. J Oral Rehabil (in press). l&~/win1
reyuesls
lo:
DR. TORE L. HANSSON UNIVERSITYOF AMSTERDAM SCHOOLOF DENTISTRY AMSTERDAM THE NETHERLANDS