Skeletal Class II high-angle open bite is often accompanied by osteoarthrosis of the temporomandibular joint (TMJ-OA). This type of malocclusion is challenging to correct, and it has been reported that patients with TMJ-OA treated with orthognathic surgery often experience skeletal relapse and a poor prognosis. This case report describes the treatment of a 25-year-old woman with retrognathia and TMJ-OA, whose masseter and temporal muscle activities were weak. Temporary anchorage devices were placed in the maxilla and the mandible, and the first molars were intruded. We used improved superelastic nickel-titanium alloy wires with tip-back bends for both arches, and intermaxillary elastics were used to upright the molars. After treatment, intrusion of the maxillary and mandibular first molars, counterclockwise rotation of the mandible, and improvement of occlusion and profile had been achieved. The patient’s condyles were repositioned into ideal positions, and masticatory muscle activity was augmented and balanced. After 2 years of retention, the mandibular and condylar positions were stable, and acceptable occlusion was maintained without recurrence of TMJ symptoms; harmonious activity of the masticatory muscles was retained. The findings of this case report suggest that molar intrusion using temporary anchorage devices for a patient with severe anterior open bite and TMJ-OA may be useful for improving stomatognathic function, occlusion, and facial esthetics.
Highlights
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We treated a patient with a skeletal Class II high-angle open bite and osteoarthrosis of temporomandibular joint.
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Molar intrusion using temporary anchorage devices achieved mandiblar counterclockwise rotation.
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Occlusion, facial profile, masticatory muscle activity, and joint symptoms were improved.
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After 2 years of retention, the mandibular and condylar positions and occlusion were stable.
A skeletal Class II malocclusion with an anterior open bite is difficult to treat orthodontically in adults and frequently requires surgical intervention. It often results in clockwise rotation of the mandible (due to molar elongation) and the long-face tendency, followed by compensatory eruption of the anterior teeth to correct the resultant open bite. However, excessive eruption of the incisors is unstable during retention. Therefore, in adults, a skeletal Class II malocclusion with severe anterior open bite is primarily considered an indication for orthognathic surgery of both the maxilla and the mandible with counterclockwise rotation.
Class II retrognathia is occasionally accompanied by osteoarthrosis of the temporomandibular joint (TMJ-OA). Although TMJ-OA is common among young women, its etiology is not fully understood; internal derangement, trauma, and parafunctional habits are all known to be contributing factors. Condylar resorption causes morphologic collapse of the TMJs, and the subsequent decrease in ramus height results in progressive mandibular retrusion and development of an anterior open bite. Previous studies have suggested that the maxillofacial skeletal discrepancies in patients with TMJ-OA treated with orthognathic surgery often had poor outcomes and skeletal relapse. Alternatively, several reports have shown that improvements in facial profile and occlusion can be achieved with counterclockwise rotation of the mandible by intruding the molars using temporary anchorage devices (TADs). However, there are few reports describing functional improvement after treatment of skeletal Class II malocclusion and anterior open bite by inducing a counterclockwise rotation of the mandible.
Electromyographic (EMG) analysis of the masticatory muscles, which has good reproducibility, provides useful data regarding the functional impact of morphologic discrepancies and permits functional evaluation of the treatment of occlusal relationships. Most patients with an open bite have masticatory muscle dysfunction and require harmonious stomatognathic function after orthodontic treatment to achieve long-term stability of the occlusion.
This case report illustrates the successful nonsurgical treatment of a skeletal Class II malocclusion with anterior open bite and TMJ-OA, resulting in both occlusal and functional improvements.
Diagnosis and etiology
The patient was a 25-year-old woman with the chief complaint of a frontal open bite; she admitted to having a tongue-thrusting habit. A convex profile due to a retrognathic mandible was noted. Her maxillary dental midline was coincident with the midsagittal plane, whereas her mandibular midline was deviated by 2.0 mm to the right ( Fig 1 ). She had Angle Class II molar and canine relationships. Arch length discrepancies were estimated to be –5.0 mm in the maxillary arch and –3.0 mm in the mandible. Overbite was estimated to be –6.0 mm and overjet was +13.0 mm. Both the maxillary and mandibular third molars were erupted, and the mandibular left lateral incisor was missing. She had no occlusal contact from the left second premolar region to the right second premolar region ( Fig 2 ).
Cephalometric analysis showed a skeletal Class II malocclusion (SNA, 79.9°; SNB, 66.3°; ANB, 13.6°) and a large mandibular plane angle (FMA, 52.5°; Fig 3 ). Both the maxillary and mandibular incisors were proclined ( Table I ). Cone-beam computed tomography (CBCT) of the TMJs showed flattening and erosion of the condyles bilaterally, and an osteophyte on the left condyle ( Figs 4 , A , and 5 , A ). The CBCT images were obtained with the patient’s head positioned so that the Frankfort and midsagittal planes were perpendicular to the floor. The selected imaging slices were processed as previously reported. There was a large posterior joint space between the condyle and the posterior wall of the mandibular fossa, and a large superior joint space between the condyle and the most superior point of the mandibular fossa. Magnetic resonance imaging of the TMJs showed severe anterior disc displacement without reduction, and the disc contour indicated deformation. The patient reported no current muscular or TMJ pain during mandibular movements, but she had experienced pain and clicking 6 years previously and was aware of her mandibular recession.
| Variable (°) | Japanese norm (°) | Pretreatment (°) | Posttreatment (°) |
|---|---|---|---|
| SNA | 82.3 ± 3.5 | 79.9 | 79.8 |
| SNB | 78.9 ± 3.5 | 66.3 | 70.3 |
| ANB | 3.4 ± 1.8 | 13.6 | 9.5 |
| FMA | 28.8 ± 5.2 | 52.5 | 48.9 |
| U1 to SN | 104.5 ± 5.2 | 102.8 | 82.8 |
| FMIA | 58 | 41.2 | 43.0 |
EMG recordings were taken bilaterally from the masseter, anterior and posterior temporal, and anterior digastric muscles during maximum clenching in centric occlusion. To investigate the activity of all muscles noninvasively, we used bipolar surface electrodes with an interpolar distance of 25 mm. The electrodes were applied as parallel as possible to the muscle fibers. Muscle activity was analyzed during isometric voluntary contractions, with the subject performing maximum-strength occlusion for approximately 5 seconds. The activity of the elevator muscles was low, especially in the masseter muscles ( Fig 6 , A ). The mean muscular potentials in the 5-second span were computed, and the activity index (ratio between the mean potentials of the temporal and masseter muscles) was calculated. This index ranges between –100% and +100%; a positive value indicates masseter muscle dominance, and a negative value indicates temporal muscle dominance.
This patient was diagnosed with an Angle Class II malocclusion with a skeletal Class II base, a large mandibular plane angle, 3 mandibular incisors, and a severe anterior open bite.
Treatment objectives
The treatment objectives were to (1) increase masseter muscle activity and improve tongue protrusion; (2) align and level the dental arch; (3) obtain intrusion of the maxillary and mandibular molars, and counterclockwise rotation of the mandible for improvement of the facial profile; (4) upright the maxillary and mandibular posterior teeth and (5) establish ideal overjet and overbite and (6) achieve a functional and stable occlusion with a full Class II relationship.
Treatment objectives
The treatment objectives were to (1) increase masseter muscle activity and improve tongue protrusion; (2) align and level the dental arch; (3) obtain intrusion of the maxillary and mandibular molars, and counterclockwise rotation of the mandible for improvement of the facial profile; (4) upright the maxillary and mandibular posterior teeth and (5) establish ideal overjet and overbite and (6) achieve a functional and stable occlusion with a full Class II relationship.
Treatment alternatives
For this patient, 2 treatment alternatives were considered. The first was orthognathic surgery with a LeFort I osteotomy for maxillary impaction and a bilateral sagittal split ramus osteotomy for mandibular advancement, which would be a suitable choice for correction of the skeletal problem. However, patients with TMJ-OA and resultant maxillofacial skeletal discrepancies who are treated with orthognathic surgery often experience a significant relapse. For this reason, surgical treatment is not strongly recommended for patients with progressive mandibular protrusion associated with TMJ-OA.
In camouflage treatment of Class II malocclusions, the use of TADs for intrusion of mandibular and maxillary molars is an effective method, and the resultant counterclockwise rotation of the mandible reduces the skeletal discrepancy. However, we did not want to close the anterior open bite by extruding the incisors, since the skeletal pattern was a high-angle severe Class II, and anterior tooth extrusion is generally an unstable movement.
Therefore, this patient was treated according to the following plan: (1) myofuntional therapy to increase masseter muscle activity and improve tongue protrusion, (2) extraction of both maxillary first premolars and both maxillary and mandibular third molars, (3) placement of multibracket appliances on both arches, (4) placement of TADs bilaterally on the posterior maxilla and mandible to intrude the molars and induce counterclockwise rotation of the mandible, (5) use of transpalatal and lingual arch appliances to prevent posterior molar buccal tipping, and (6) stripping of the maxillary incisors to compensate for the missing mandibular lateral incisor.
Treatment progress
Before the orthodontic treatment, we followed the patient for a year to confirm that there was no progressive resorption of the TMJ or change in the occlusion. On the CBCT images, there was no change in condylar shape, and cephalometric superimposition showed no change in mandibular position. The patient attempted to repeat “spot position” as myofunctional therapy to correct the tongue-thrusting habit and clenching to strengthen her masseter muscles. A 0.47-in lingual arch appliance and a 0.59-in transpalatal arch appliance were placed between the first molars of the mandibular and maxillary arches, respectively, to maintain the widths of the arches and prevent buccal tipping of the molars during intrusion. Under local anesthesia, Y-shaped anchor plates (Orthoanchor Super-Mini Anchor-plate System; Dentsply-Sankin, Tokyo, Japan) were implanted bilaterally onto the zygomatic processes of the maxilla and the buccal mandibular alveolar bone through the buccal mucosa, with the arm and 3 holes exposed to the oral cavity. The plates were contoured to fit the bone surface and positioned outside the dentition. After a month to allow for healing and integration, the maxillary first premolars and third molars, and the mandibular third molars were extracted. The 0.018 × 0.025-in slot, preadjusted edgewise appliances (Dentsply-Sankin; Tomy, Tokyo, Japan) were then bonded from the canines to the second molars in both arches, and 0.016 × 0.022-in improved superelastic nickel-titanium alloy wires (L&H Tomy International, Tokyo, Japan) were used to level and intrude the molars. Then maxillary canine retraction began. Elastic power chains were placed bilaterally between the hole of the miniplate and the first molar buccal tube to create a vertical intrusive force.
After 5 months of active treatment, the maxillary incisors were bonded, and leveling began with 0.016 × 0.022-in wires. Molar intrusion lasted for 8 months, and a positive overbite was obtained. After 13 months of orthodontic treatment, the mandibular incisors were bonded, and leveling was initiated, while the maxillary incisors were retracted. After 2 years and 4 months, nickel-titanium alloy wires with tip-back bends in both arches and intermaxillary elastics were used to upright the molars after the transpalatal and lingual arch appliances were removed; nickel-titanium alloy wires of 0.018 × 0.025 in (L&H Tomy International) were used for detailing. After 3 years and 2 months of edgewise-appliance treatment, a circumferential retainer was placed in the maxillary arch, and both Hawley-type and fixed retainers were placed in the mandibular arch.
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