Bilateral TMJ disk displacement induces mandibular retrognathia.

Unilateral non-reducing TMJ disk displacement has been shown to retard mandibular growth on the ipsilateral side, with facial asymmetry a sequela. We hypothesized that bilateral affliction would impair mandibular growth bilaterally, generating mandibular retrognathia. Non-reducing TMJ disk displacement was surgically created in 10 growing New Zealand White rabbits. Ten additional rabbits served as a sham-operated control group. Facial growth was followed in serial cephalograms, with tantalum implants, during a period corresponding to childhood and adolescence in man. The results verified that bilateral non-reducing TMJ disk displacement retarded mandibular growth bilaterally, the extent corresponding to mandibular retrognathia in man. Maxillary growth was also retarded, but to a lesser degree. Growth impairment fluctuated over time, the most striking retardation occurring during periods of general growth acceleration. This should be taken into consideration when orthodontic treatment, aimed at stimulating mandibular growth, is initiated in adolescent individuals with non-reducing TMJ disk displacement.

Bone graft remodelling and implant success rate in the treatment of the severely resorbed maxilla: a 5-year longitudinal study.

A total of 30 patients, 10 in a developmental group and 20 in a routine group, with extremely resorbed maxillae were treated with bone grafting from the hip and implant placement in a one-stage procedure. All patients were followed for a minimum of 5 years and were examined regarding the long-term success rate of the implants and marginal bone level. The implant success rate was 74.6% for the whole patient group and 85.8% for the routine group, after 5 years. The marginal bone along the implant surface decreased continuously, up to 3 years and thereafter the bone level stabilized. In the routine group, changes in bone graft dimensions over time were also evaluated by computerized tomography. The mean height of the bone graft postoperatively at all implant sites was 8.3 mm. The total mean bone height, including bone graft and residual alveolar crest, was 12.4 mm. After 5 years the total bone height had decreased to a mean of 10 mm. The mean width of the bone graft was 12 mm postoperatively and 8.7 mm at the 5-year examination. A substantial amount of bone can be gained in patients with extremely resorbed maxillae, when treated with bone graft according to the procedure described in this study.

Validity of identification of gonion and antegonion in frontal cephalograms.

This study was designed to develop a method of transferring gonion from lateral to frontal cephalograms, and to use this method as gold standard when evaluating observer performance in identifying gonion in frontal cephalograms. Observer ability to identify antegonion was also evaluated. There was a range of 28 mm in the observers' identification of gonion and a statistically significant deviation from gold standard. The factors "observer" and "cephalogram," regarded as random effects in an ANOVA analysis, and their interaction, each influenced the result, P < .001. The deviation from the mean of all observations for antegonion ranged 8 mm with "cephalogram" having a statistically significant influence. The results suggest that neither gonion nor antegonion can be routinely used as valid landmarks in frontal cephalograms. Gonion can, however, be used if first identified in a lateral cephalogram and transferred to a paired frontal cephalogram aided by radiographic indicators combined with a bilateral scrutiny of projection geometry in different planes through gonion and indicator.

Temporomandibular joint condyle changes after surgically induced non-reducing disk displacement in rabbits: a macroscopic and microscopic study.

Experimentally induced displacement of the temporomandibular joint (TMJ) disk has previously been shown to induce shortening of the mandibular ramus on the ipsilateral side. The aim of this investigation was to reveal whether this shortening develops due to primary influence on condyle growth or by secondary loss of condyle mass due to degenerative tissue breakdown. Disk displacement was created in the right TMJ in seven 3-month-old rabbits, the posterior disk attachment kept intact. Seven rabbits underwent surgical opening of the TMJ without disk intervention. Seven additional animals served as references. After a 3-month experimental period, the animals were sacrificed. Previous analysis revealed shortening of mandibular height and length caused by ipsilateral TMJ disk displacement. The condyles were examined macroscopically and by histologic sectioning or scanning electron microscopy. All condyles were covered with smooth articulating soft tissue and without visible signs of degenerative changes. Four condyles from joints with disk displacement demonstrated substantial regressive remodeling resulting in a change of condyle shape with forward/downward rotation of an enlarged articulating surface. It was concluded that TMJ disk displacement in a growing individual can induce reduction of mandibular height and length before a stage where visible osteoarthrotic changes develop. It implies a primary adverse effect on condyle growth.

Mandibular length and midline asymmetry after experimentally induced temporomandibular joint disk displacement in rabbits.

The purpose of the present investigation was to test the hypothesis that permanent disk displacement in the temporomandibular joint (TMJ) is one causal factor in the development of mandibular midline asymmetry. Unilateral, nonreducing disk displacement was therefore created in growing rabbits. The right TMJ in seven experimental animals was surgically opened, and the disk was anteriorly displaced with the posterior disk attachment kept intact above the condyle. The right TMJ in seven sham animals was surgically opened and closed without any disk manipulation. Seven additional rabbits served as reference animals. For identification of mandibular growth, tantalum implants were inserted into the mandibular body, and lateral cephalograms were exposed at the beginning and at the end of the experimental period. After the animals had been sacrificed, the mandibles were dissected and measurements were performed on the mandibular specimens. Axial radiographs of the mandibles were then exposed and measurements of mandibular length and midline shift were performed in the radiographs. The mandible in the experimental animals was consistently shorter on the disk displacement side resulting in a midline shift to the ipsilateral side. No mandibular asymmetry was observed in the sham and reference groups. The hypothesis was verified; disk displacement in the TMJ with an onset during the growth period can cause mandibular length and midline asymmetry in growing rabbits.

Mandibular height asymmetry following experimentally induced temporomandibular joint disk displacement in rabbits.

OBJECTIVE: The purpose of this study was to test the hypothesis that nonreducing disk displacement of the temporomandibular joint causes mandibular asymmetry. STUDY DESIGN: Unilateral anterior temporomandibular joint disk displacement with intact posterior disk attachment was surgically created in the right joints of seven growing rabbits. In each of seven sham animals, the right temporomandibular joint was surgically opened without any disk manipulation. Seven animals served as references. For identification of ramal growth and inferior growth at the mandibular base, tantalum implants were inserted into the mandibular body. Lateral cephalograms were exposed repeatedly throughout the 3-month investigation period. Kruskal-Wallis one-way analysis of variance was used to compare the groups. RESULTS: Compared with the sham and reference groups, the experimental group exhibited a deviant growth pattern, with inferiorly directed growth along the mandibular base and in the gonial area. The ramal height was significantly shorter on the side with disk displacement. No significant side difference was present in the sham and reference groups. CONCLUSIONS: Disk displacement can cause mandibular asymmetry in growing rabbits, including shortening of the mandibular ramus and excessive inferiorly directed bone growth along the lower border of the mandible.

Combined use of bone grafts and implants in the severely resorbed maxilla. Postoperative evaluation by computed tomography.

Combined horseshoe-shaped iliac bone grafts and Brånemark fixtures were used to rehabilitate patients with severely resorbed maxillae. Twenty patients were followed-up by computed tomography (CT) examination with axial slices to assess the fixture sites and to study the changes in height and width of the bone graft 3 weeks and 3, 6, 12, and 24 months postoperatively. The mean height of the bone graft at the 3-week postoperative examination was 8.2 mm; after 2 years the mean value had decreased to 6.2 mm. The height reduction occurred mainly between the 3-month and 1-year examinations. The mean width of the bone graft at the 3-week postoperative examination was 12.2 mm, and it decreased to 8.6 mm after 2 years. Most of the width reduction took place during postoperative months 1-3. From 1 year after the grafting procedure, the rate of reduction of both height and width was very low.

A technique for the accurate administration of corticosteroids in the temporomandibular joint.

A new technique for intra-articular injection of a corticosteroid in the temporomandibular joint (TMJ) is presented. The corticosteroid is mixed with contrast medium and the administration visualized and controlled using fluoroscopy. When superior and inferior joint spaces have been filled and the soft tissues of the joint have been identified in the fluoroscopic image, additional corticosteroid can be administered to selected sites within the TMJ.

Radiographic study of structural changes in the temporomandibular joint after oblique sliding osteotomy: comparison between the extra-oral and intra-oral approaches.

Oblique sliding osteotomy of the mandibular rami was performed on 41 patients by either an intra-oral (21 patients) or extra-oral (20 patients) approach. The temporomandibular joints were radiographed preoperatively and then immediately and 18 months postoperatively. Signs of structural changes were recorded so as to compare the two approaches to osteotomy. The most common findings following the operation were signs of sclerosis and bone remodelling in 85% and 73% respectively of the two groups but these differences were not statistically significant.

Standard forms of dentition and mandible for applications in rotational panoramic radiography.

Mathematical expressions describing the average form and size of the dentition and the mandible are presented. These expressions should be of value in applications of panoramic radiography when reference to an average standard jaw form is of interest. Data were collected from axial radiographs of 35 males and 35 females of three ethnic groups: Mexican-Americans, black Americans and American and Scandinavian Caucasians. Curves were traced on the axial radiographs representing the dentition and the mandible and points along these curves digitized. Mathematical expressions were established using advanced algorithms for orthogonal polynomial curve fitting, i.e. perpendicular distances to the curved dentition and mandible were minimized rather than distances parallel to the y-axis in an arbitrarily chosen coordinate system. The standard deviations around the polynomials defining the average curves are demonstrated and expressions for calculating the continuously varying standard deviations are given.