The purpose of this study was to analyse the masticatory patterns and range of motion (maximal incisal opening (MIO), protrusion and lateral excursion) in patients who have had unilateral and bilateral temporomandibular joint (TMJ) replacement with an alloplastic prosthesis, and compare them to each other and to normal controls. Mandibular motion was examined in 18 patients, who had undergone alloplastic TMJ reconstruction, 13 with a bilateral prosthesis and 5 with a unilateral prosthesis, and in 13 normal controls. A statistically significant difference ( P < 0.01) for MIO and maximum lateral excursion was observed between the bilateral group and the control group. Maximum protrusion was only statistically significantly different ( P < 0.05) between the bilateral group and the control group. For the unilateral group, a statistically significant difference ( P < 0.01) was seen only with maximum contralateral excursion when compared with controls. No statistically significant difference existed in MIO and protrusion between the unilateral and bilateral groups. Even though maximum ipsilateral lateral excursion was greater for the unilateral group than either left or right maximum lateral excursion by the bilateral group, this difference was not statistically significant. This study provided an in vivo analysis of mandibular motion following alloplastic TMJ reconstruction.
Temporomandibular joint disorder (TMD) is an inclusive term used to describe orofacial pain, masticatory dysfunction or both. Approximately 5% of the population is affected by TMD . The patient with end-stage temporomandibular joint (TMJ) disease commonly suffers from unrelenting pain and severe limitation of jaw movement. Alloplastic reconstruction of the TMJ is a mainstay in the treatment of end-stage TMJ disease ( Table 1 ).
|• Arthritic conditions: e.g. osteoarthritis, rheumatoid arthritis, or traumatic arthritis|
|• Post-excision of benign and malignant neoplasms|
|• Congenital disorders|
|• Avascular necrosis|
|• Irreparable fractures of the mandibular condyle|
|• Functional deformities|
|• Revision when previous treatments (e.g. alloplastic reconstruction, autogenous grafts) have failed|
Studies have compared mandibular motion in patients with unilateral internal derangements and bilateral internal derangements of the TMJ with normal controls . Jaw movement has also been compared in patients who have had arthroscopic lysis of adhesions and lavage, partial meniscectomy with disc repair, and total meniscectomy . Despite the long history of total alloplastic TMJ reconstruction, no studies to date have evaluated post-surgical mandibular motion patterns in these patients.
The purpose of this study is to evaluate the masticatory patterns and range of motion (maximal incisal opening (MIO), protrusion and lateral excursion) in patients who have had unilateral and bilateral alloplastic TMJ reconstruction. These groups are compared with each other and with a normal control group. The rationale to carry out the study was to establish actual reasonable functional outcome expectations for patients undergoing the procedure, to assess differences in masticatory movements between patients with unilateral and bilateral reconstruction, and potentially to identify specific mandibular motion patterns in the unilateral replacement group that may deleteriously affect the other side.
Materials and methods
Mandibular motion was examined in 31 participants. There were three study groups: 13 participants had undergone bilateral alloplastic TMJ reconstruction with the Biomet Microfixation TMJ Replacement System ® (Biomet, Warsaw, IN, USA); 5 with a unilateral prosthesis; and 13 were normal controls. This TMJ replacement system consists of a fossa component constructed from ultra-high molecular weight polyethylene (UHMWPE), and a mandibular component composed of a chrome–cobalt–molybdenum alloy with a plasma-sprayed titanium coating at the bone interface. The control group comprised individuals who had no symptoms or signs of TMD.
Each patient in the unilateral and bilateral replacement group was studied for a minimum of 6 months after surgery, to account for facial oedema and/or pain during the postoperative period that could mask true mandibular motion.
The magnetic jaw tracker, JT-3 ® , made available from BioResearch Associates, Inc. (Milwaukee, WI, USA), was used to record jaw movements ( Fig. 1 ). A magnet was fixed to the mandibular central incisors and the vertical, antero-posterior, and lateral planes of mandibular motion were evaluated.
MIO, maximum protrusion, maximum lateral excursion (right and left), the velocity of mandibular movement, and overall mandibular motion were measured ( Fig. 2 ). The mandibular motion of each patient/control was recorded three times and the mean values obtained were compared between groups. Statistical differences were calculated for each mandibular movement using one-way analysis of variance (ANOVA). Tukey’s multiple comparisons test was used to determine whether or not there was a significant statistical difference for each mandibular motion between the study groups.
The demographics and mean mandibular measurements for MIO, maximum protrusion, and maximum lateral excursion movements were obtained for each of the three test groups, and the mean values were calculated ( Tables 2 and 3 ).