Orthodontic treatment of eight overbite cases with a maxillary fixed lingual arch appliance with anterior biteplane involved a reduction in overbite of 4 to 7 mm between the upper and the lower front teeth and a first molar separation of 2 to 4 mm. After a treatment period of 3.5 to 5 months, occlusal contact between the upper and the lower molars was established. The appliance was then removed, and permanent overbite reduction was secured with an edgewise appliance. With the subtraction technique, 15 temporomandibular joints were radiographically investigated in the retruded position for change of condylar position on the glenoid fossa before and directly after insertion of the appliance, as well as after achieved molar contact. All condyles changed position directly after the bite opening, indicating that pure rotation did not occur. The direction of movement varied not only between subjects but also between the two condyles of each subject. With one exception, none or very small further positional changes occurred during treatment. No imaged signs of hard structure remodeling were observed. It may be concluded that other factors than change of condylar position must be responsible for the therapeutic effect of the bite-opening appliance that has been demonstrated in an earlier study.

SUMMARY The purpose of the present study was to compare the vertical change in the incisor and molar areas caused by insertion of a bite opening appliance and to analyse the occurrence of rotation and eruption during the following treatment period (mean 4.3 months). Eight patients between 15 and 24 years of age with vertical overlaps ≥ 4mm were treated by means of a maxillary fixed lingual arch appliance with an anterior bite plane. The retruded mandibular position was recorded with cold cure acrylic before treatment, immediately after insertion of the fixed appliance, and after removal of it. Vertical overlap and separation between the first molars was measured at each of these occasions. Finally, tooth movements during eruption were measured on the indices in the area of the second molar. The results showed that, independent of the amount of bite raise, the relation between frontal and molar area bite raise was approximately 2:1 for six and 5:3 for two patients. There was a significant difference in thickness of indices from registrations I and III in the second molar area indication not only eruption during bite opening therapy but also buccolingual rotation.

The "hinge axis concept" maintains that the mandible moves around a transverse horizontal axis through both condyles. Since it was introduced in the 1920s it has had a profound impact on clinical dental practices all over the world. By use of the radiographic subtraction technique, we demonstrated that an increase in the occlusal vertical dimension of 4 to 7 mm in the retruded position resulted in a small positional change (range 0.31 to 1.84 mm) in an unpredictable direction. Pure rotation did not occur; however, the condylar displacement is probably of minor clinical importance in prosthodontic restoration.

Clinical signs and symptoms of temporomandibular joint arthropathy were evaluated by comparison of clinical findings with arthroscopic findings in 62 temporomandibular joints of 55 patients. The arthroscopic frequency of osteoarthritis was high and was often combined with a mild localized synovitis.

Established radiographic criteria of temporomandibular joint osteoarthrosis were evaluated by comparison of arthroscopic and tomographic findings in the superior compartment. 34 joints of 30 patients with long-standing chronic pain and/or functional impairment were investigated according to standardized techniques. Agreement was found between arthroscopy and corrected sagittal tomography regarding diagnosis of osteoarthrosis in all advanced cases. Diagnostic accuracy as regards slight changes was, however, lower. At tomographic examination, the sensitivity was slightly higher than specificity, i.e., pathological changes were more frequently identified than normality. No radiographic sign of osteoarthrosis could be specifically associated with arthroscopic features of osteoarthrosis or synovitis. Predominant location of osteoarthrosis at both arthroscopy and tomography was the posterior slope of the eminence (latero-central part). Osteoarthrosis was more widespread in the fibrocartilage than in the subchondral bone.

The superior compartments of 42 temporomandibular joints of 38 patients with longstanding chronic pain and/or functional impairment were examined arthroscopically. Occurrence and location of osteoarthrosis and synovitis were investigated. Osteoarthrosis occurred in 31 joints (74%). In 17 of them more extensive changes were found. Predominant location of osteoarthrosis was the posterior slope of the eminence. The disk was less frequently affected and most commonly in the latero-central part. Synovitis occurred in 22 joints (52%) and was combined with osteoarthrosis in 17 of them. In 20 of them it was of mild and localised nature. The posterior disk attachment was affected in all of them.

The stretch reflex is much more complicated than the simple tendon jerk with a monosynaptic reflex pathway. Muscle stretch is not a necessary prerequisite to elicit the short latency EMG excitatory response. Long latency EMG responses are probably of greater functional importance. The silent period (SP) following the jaw jerk is prolonged in patients with symptoms of mandibular dysfunction. In the individual case, however, measurement of the SP may not be of diagnostic value. The Golgi tendon organs are highly sensitive tension receptors which play a much larger role in the proprioceptive regulation of muscle tension than has been believed in the past. So-called type P mechanoreceptors which like a large part of the periodontal receptors have their cells of origin in the mesencephalic nucleus V, have been found in the hard palate. The majority of periodontal mechanoreceptors are slowly adapting and thus able to respond with sustained discharge to long lasting stimulation, as during chenching or bruxing. The postural position has been assigned great clinical significance. It has been assumed that this position is constant throughout life. It has, however, been observed that the postural position rapidly adapts to changes of the vertical occlusal dimension.

Jaw muscle motor behaviour, however complicated, has important implications for the every day dental practice. In recent years the understanding of jaw and other skeletal muscle function has increased considerably. Direct recording of primary afferent discharge in conscious human beings and animals during normal function has caused radical changes of the concepts of muscle receptor function. Central pattern generators at segmental levels and suprasegmental programming centres are important mechanisms behind voluntary and automatic movements of different kinds. The most important proprioceptive function is probably to provide reassurance of correct movement pattern, to adjust the central programming to environmental changes and to directly influence slow movements requiring precision. Muscle spindle receptors contribute to mandibular kinesthesia. Muscle spindles are rarely present in jaw opening muscles. Despite this fact an excitatory reflex similar to the stretch reflex but with longer latency has been demonstrated. Further on a reciprocal organisation with antagonist inhibition has been shown to exist between jaw openers and closers. Motor behaviour of jaw and limb muscles thus seem to have many characteristics in common.

The ability of ten edentulous patients and one patient with a full upper removable denture and a full arch (16-26) lower fixed denture to adapt to sudden change of the interocclusal distance was tested. An upper acrylic bite splint was inserted which, on average, increased the vertical dimension of the face by approximately twice the mean interocclusal distance during relaxation. After this procedure all patients quickly acquired an unstrained new postural position of the mandible. Directly after insertion, when instructed to relax, all patients hit the lower surface of the splint. They seemed, however, to need only one such experience to adapt to the increased interocclusal distance. The second time they repeated the procedure none of them touched the splint. Instead a new postural position was established with a mean interocclusal distance of 3.3 mm. This fast re-programming of jaw muscle tonus and length is assumed to be a response to different peripheral receptor discharge converging to the cerebellum and other programming centres. The present study on edentulous patients shows that afferent discharge from periodontal receptors is not a necessary prerequisite. It also confirms that the old concept of consistency of the mandibular postural position (Thompson, 1946) is erroneous.

An autopsy study was performed on 84 left human temporomandibular joints. Frequency and location of osteoarthrosis and deviation in form were registered in each joint component. Locations of disc perforations were registered with special emphasis on involvement of the bilaminar zone. The anatomical relationship between the deep masseter muscle and the TMJ capsule was investigated in part of the material. Deviation in form was most frequent in condyles (53%) compared with temporal components (40%) and discs (15%). The relative frequencies of the three joint components were opposite for osteoarthrosis; discs (32%), temporal components (26%) and condyles (21%). Higher frequency of arthrotic changes was found in edentulous specimens than in dentulous ones. Disc perforations were located within disc tissue except for one joint where it also included part of the bilaminar zone. No correlation between sex and arthrosis and/or deviation in form was found. Insertion of the posterior fibres of the deep masseter muscle into the anterior capsule was macroscopically observed in six of ten joints.

A dissectional study of the TMJ was performed in an elderly autopsy material. The left joints of 84 cadavers were removed "en bloc" with preserved joint structures. The specimens were dissected in a fresh state. The upper and lower compartments of the TMJ were opened by circumcision of the capsule. Deviation in form, arthritic changes, disk position and perforation of the posterior disk attachment were registred and photographically documented. Observable deviation in form was noted in 69 joints (82,1%), most frequently in the condyle (76,2%). Arthrotic lesions in the fibrocartilage were predominantly seen in the fossa, where changes occurred in 22 specimens (26,2%). Disk perforationwere found in 20 cases (23,8%) most frequently in the laterocentral part of the disk. An anterior or oblique disk position was found in 27 cadavers (32,1%) and was not correlated to joint pathology. In two cases the disk were medially displaced with signs of derangement. Perforation of the posterior disk attachment was found in one joint with extensive arthrotic changes. Conclusion: Our findings are in line with earlier investigations regarding prevalence of deviation inform and arthrotic changes. Reported prevalence of disk displacement and perforation of the disk attachment could not be confirmed. Anterior disk position may be within normality. 9 :Development of mouse tooth germs in vitro. IA. HEYDENA and S.H. FROM, Dept. of Anatomy, iDental Faculty, Univ. of Oslo, Oslo, Norway. The objective of the present investigation was to establish culture conditions which allowed tooth development in defined media as a basis for later experimental manipulations. Mandibular first and second molar tooth germs from mouse embryos and newborn mice were isolated and cultured in media with or without serum substitutes for periods of three, six and nine days. In some experiments the epithelial and connective tissue parts of tooth organs were separated after enzymatical and mechanical treatment and cultured individually or after recombination. Incubation mas carried out at different oxygen tensions. Effects of culture conditions on tooth development with regard to matrix formation were assayed with histological and histochemical techniques and compared to in vivo odontogenesis. The results showed that mouse tooth germs could differentiate and produce matrix in defined media for periods up to nine days although the development always was retarded compared to the in vivo situation. Precise separation of epithelial and connective tissue compartments was achieved with newly explanted tooth organs but this was much more difficult with cultivated tooth germs. Effects on odontogenesis of growth factors, hormones and cAMP-derivates added to the media at varying concentrations and time periods are in progress. 606 Evaluation of clinical TMJ arthroscopy. i. Hellsing*and A. Holmlund. Departments of ttomatognathic Physiology and Oral Surgery, 'tarolinska Institutet, Huddinge, Sweden. rhe advantages of arthroscopy in kneie joint diigns tics compared with clinical and radiologic examination is well documented. With recently introduced so called needle scopes small body joints like the temporomandibular joint (TMJ) may be investigated. rhe present study concerns the 30 first arthroscoped patients in our clinic. Thorough clinical examination and lateral tomography were performed on all cases before the inspection and compared with our observations. RESULTS: Synovitis with hyperaemia of capsular wall and/or retrodiscal ligament with or without combination of arthrotic changes (fibrillation, eburnation, disk perforation etc.)are clearly observable phenomena. Two therapy resistant patients with severely impaired function and chronic pain exhibited no structurally observable pathology. Three patients were able to produce clicking during observation. No uniformity in disk behaviour during production of the sound was noticed. Disk perforations are easily discovered and allow entrance for the telescope into the inferior joint compartment without tissue damage. It may be concluded that TMJ arthroscopy yields information which sometimes contradicts a provisional diagnosis based on clinical and radiographic examination. 4 ;Relationship between age and dental Attrition. T. Solheim. Dept. of 1Pathology, Dental Faculty, University of Oslo, Oslo, Norway. Attrition has been used as an independent variable in methods for forensic dental age assessments. The purpose of this investigation was to study the relationship between age and attrition. One thousand teeth from a Caucasian population, 100 from each type of tooth excluding molars were studied. Attrition was assessed by various indices as well as by more objective measurements, eg. crown and tooth length and area of attrition facets. Correlation and regression analyses utilizing the SPSS statistical package were made. No left/right differences were found. Correlation varied from to 0.7 depending on type of assessment and type of tooth. Attrition of canines was least correlated with age. For some types of teeth and measurements, the independent variable with a negative sign, significantly contributed to the regression, indicating a decrease irn the progression of attrition with age. Generally, less attrition was found in females. When attrition is used for age assessment each tooth should be considered as a separate entity and individual formulas used for each. When significant, the square of the independent variable should be used and if possible, the sex of the person should be given due consideration. 5 ;Clinical studies of pain regulated deformation during loading of vital and non-vital teeth. K. RANDOW* & P-I. GLANTZ. Dpt. of Prosthetic Dent., Univ. of Lund, Malmo, Sweden. During masticatory functions such as chewing or clenching the participating teeth and their surrounding tissues will undergo deformation. As it is reasonable to assume that mechanoreceptor functions may be present and of importance is human pulpal tissue it was considered worth while to perform a series of clinical experiments of the deformation pattern of vital and non-vital teeth. Three healthy test persons with contralateral or neighbouring vital and non-vital teeth in need of crown therapy was selected. In all the persons the non-vital tooth was root-filled. Crowns were manufactured using routine procedures and buccal extension bars were then soldered to the occlusal surfaces of these crowns. Weights were then placed in different positions along these bars until the test person claimed clear pain reactions to appear. The experiments were also repeated after local anaesthesia. The results of this study show non-vital teeth with good bone support to have a pain regulated loading capacity which is 2-3 times higher than that of vital teeth. The centre (hypomoklion) of the presumably mainly rotational deformations of the loaded teeth were found to be located inside the periferi of the crowns for the vital teeth but in a markedly palatal position for the non-vital teeth. Immunohistochemical demonstration oP Igt 6 during amelogenesis. A.PIERCE*, S.LINDSKOG & L.HAMMARSTRUM. Dept. of Oral Pathology, Karolinska Institutet, Stockholm, Sweden. There are indications that dental cementum is formed following an immunological reaction with the enamel matrix-like substance on the root surface produced by the epithelial root sheath. Enamel matrix has furthermore, been shown to attract mast cells, the function of which is intimately associated with IgE. Consequently, the present study was undertaken in an attempt to assess the distribution of IgE around developing teeth. First molar sections from 5,9 and 15 day-old mice, as well as sections from 6 week-old mice incisors were incubated using the biotin-avidin technique to demonstrate IgE immunohistochemically. Results showed that post-secretory ameloblasts stained positively for IgE towards the enamel surface. Furthermore, clusters of IgE positive cells were at this stage found close to the developing molars. These observations support previous suggestions that enamel matrix is immunologically active and that mast cells may play a role during

Arthroscopy of the temporomandibular joint (TMJ) is evaluated on an autopsy material, 2 different types of arthroscope — one with a rod-lens system and one with a so-called Selfoc system — were used and compared regarding diagnostic accuracy. On 54 cadavers, it was found that the upper joint compartment may be punctured with accuracy and without damage to vital tissues. Landmarks on the skin facilitating clinical arthroscopy were defined in relation to a guideline from tragus to lateral canthus. A further 49 TMJ specimens were investigated with arthroscopy. The findings are in good agreement with subsequent observations made during dissection. Regarding arthrotic changes, 100% diagnostic accuracy was achieved with both types of arthroscope. Regarding remodelling changes, the diagnostic accuracy was approximately 57%. No significant difference was noticed between the 2 arthroscopes. Photographic documentation with the rod-lens arthroscope was found to be of superior quality.

During the past decade much interest has been focused on disorders of the TMJ. The etiology appears to be multifactorial, with signs and symptoms difficult to evaluate and radiologic investigations insufficient. This review attempted to analyze current diagnostic tools. The recent introduction of various techniques promises optimism for this diagnostic and therapeutic challenge.