Occlusion And EMG Activity Change In Intruding Supraerupted Maxillary Molars Using Composite Resin

In clinical practice, severely defected mandibular first molar with supraerupted antagonist(s) was frequently seen. Restoration of the mandibular first molar was difficult mainly due to its limited restorative space. To regain space, modalities such as enameloplasty, extra coronal cast metallic restoration, intentional root canal therapy and crown reduction, temporary anchorage devices (TADs), posterior segmental osteotomy and extraction can be used. Among them, extra coronal cast metallic restoration and TADs were more popular because of their minimal damage to the remaining tissue. Recently, resin restoration comes up as a novel modality to regain restorative space under the same principle of extra coronal cast metallic restoration. Though better for final restoration and cheaper, application of this new modality is limited on account of the occlusal interference introduced at the beginning of the treatment.OBJECTIVEDefected mandibular first molars of the recruited subjects were resin restored to intrude the supraerupted antagonist by occlusal force. T-scan and electromyographic (EMG) tests were performed to trace the changes of bite and EMG activities of the masticatory muscles during the treatment to figure out effects the treatment would have on the subjects. Meanwhile, periapical films were taken using parallel technology to observe the changes of periodontal tissues during treatment.METHODS7 subjects between 18 to 50 years old (mean age:29) visiting Nanjing Stomatological Hospital in 2013 were recruited.2 of them were male, and the other 5 were female. All the subjects have one severely defected mandibular first molar with supraerupted antagonist(s) on either right or left side. Casts of the subjects were poured and mounted onto an articulator to make diagnostic wax-up. Then a silicon mock-up was made and dual-cured composite resin was used to restore the crown of the defected mandibular first molar. T-scan and EMG tests were performed on the baseline, the first, the second, the fourth week and before final restoration. Periapical films of the defected mandibular first molar and supraerupted antagonist(s) were taken using parallel technology on the baseline, the fourth week and before final restoration to observe changes of periodontal tissue. Final restoration were made when restorative space was regained and the bite was stabilized again.RESULTS1. Clinical inspection:The whole treatment allowed 2 to 4 months to regain restorative space. Usually, the treatment took 2 weeks for the subjects to get used to their new bite. Only one subject complaint about loosening of the defected mandibular first molar on the third week after resin restoration. Taken the advice to eat slower, the syndrome relieved two weeks later. At the same time, periapical film of the defected mandibular first molar revealed no signs of occlusal trauma happened to the mandibular tooth. Otherwise, no other symptom was reported. At the end of the treatment, all subjects’bite had rehabilitated to intercuspal occlusion. Compared with baseline, casts measurement showed the restorative space was gained by intrusions of both defected mandibular first molar and its antagonist(s).2. T-scan tests:A fixed pattern for bite rehabilitation during treatment was revealed by t-scan data:1) the last molars were the very first area to regain contacts; 2) contacts regained faster on contralateral side than ipsilateral side. The occlusal force between the defected mandibular first molar and its antagonist(s) decreased immediately after resin restoration then mounted afterwards. When bite was stabilized, the value even exceeded the baseline.3. EMG tests:There was a rise of the peak activity of the MM and TA observed on the ipsilateral side whereas a fall on the contralateral side immediately after resin restoration. Besides, Astot increased then fell to the baseline level. Peak percentage value of Astot appeared at the time contacts of the molar region on both sides regained.4. Periapical films:Lamina dura of the defected mandibular first molar and its antagonist broadened at the end of the treatment. Apart from that, no widening of periodontal ligament, alveolar resorption nor root resorption was observed.CONCLUSION1. Resin restoration regained restorative space by intrusion of the supraerupted antagonist as well as the defected mandibular first molar;2. There’s a fixed pattern for bite rehabilitation observed by t-scan data:1) the last molars were the very first area to regain contacts; 2) contacts regained faster on contralateral side than ipsilateral side.3. Transient Astot change was observed during treatment. A deduction of mandible rotatory movement could be draw due to rise of MM and TA peak activities on the ipsilateral side and fall on the contralateral side after resin restoratio;4. The occlusal force between the defected mandibular first molar and its antagonist decreased immediately after resin restoration then mounted afterwards. When bite was stabilized, the value even exceeded the baseline.5. Adaptive changes of periodontal tissue was observed at the end of the treatment whereas no occlusal trauma was observed.