A Consideration for Locating a Mandible in Centric Relation during Orthodontic Treatment

Abstract

R. H. Roth and others have incorporated mandibular function analysis using C.P.I. (Condylar Position Indicator) and Axi-Path Recorder as part of orthodontic diagnosis to achieve the treatment goal of establishing centric occlusion with the condyles seated in centric relation. Their approach is to stabilize the mandibular position with a splint prior to orthodontic treatment in patients with unstable mandibular positions due to Temporo-Mandibular Disorder, major CO-CR discrepancy based on C.P.I. data, or facial asymmetry. The treatment procedures are simplified by utilizing the Straight Wire Appliance or SWA with necessary anatomical information built into the brackets, which are directly bonded to tooth surfaces. This comprehensive system integrating all the steps from diagnosis to treatment has improved the accuracy, reliability and simplicity of orthodontic treatment, contributing greatly to the advancement of modern orthodontics.
However, the loss of mandibular stability during orthodontic treatment is unavoidable due to difficulty of wearing a splint with an orthodontic appliance. This paper introduces the mini occlusal splint developed by the authors to compensate for this shortcoming.
The patient had no midline deviation initially. The C. P. I. data showed no discrepancy. There was no difference in the amount of cuspid overjet between the right and left sides. Space closure was accomplished equally on both sides. However, the midline deviation was noticed with a difference in the amount of cuspid overjet between the two sides at the time of space closure or 6 months after the beginning of orthodontic treatment. The midline deviation increased further 9 months into treatment. The most probable cause was “mandibular displacement.” However, the patient was in the midst of maxillary anterior retraction, making it difficult to wear a regular splint. The mini occlusal splints were bonded onto the occlusal surfaces with an adhesive resin so that a maximum number of teeth could come into equal occlusal contact in CR. The mandibular position was stabilized and the midline deviation was eliminated approximately 3 months after the placement of the occlusal splints.
1. GC pattern resin is mixed. Pour in a small amount of water and mix to the consistency of a dough.
2. Take an anterior bite with the resin. Trim the resin to leave shallow indentations of incisal edges of the lower anterior teeth. Replace it in the mouth to check its reproducibility.
3. Take posterior bites with a quick-cure resin. Mark an outline of each splint and the tooth number on the upper side of the posterior bite and lower cusp tips on the bottom side with an indelible pen. Trim the resin to leave only cusp tip indentations. Grind each splint along the recorded outline.
4. Bond the splints to the occlusal surfaces of the upper molars.
1) It is very important to make a differential diagnosis to determine if the problem is skeletal or not. For this purpose, it is necessary to achieve a stable mandibular position prior to orthodontic treatment with a centric splint.
2) This case effectively demonstrates the effectiveness of the mini occlusal splints when midline deviation is caused by mandibular displacement.
3) In our practice, 30 patients have developed TMD symptoms during orthodontic treatment. The symptoms were eliminated in 28 patients of these patients.