For correction for skeletal Class III malocclusion, there are three main treatment options: growth modification, orthodontic camouflage therapy, and surgical-orthodontics. Growth modification by dentofacial orthopedic appliances is an effective method to resolve skeletal Class III jaw discrepancies in children.2-5 Proffit indicated the criteria of case selection to enhance the outcome of orthodontic camouflage therapy, including: (1) average or short facial pattern; (2) mild anteroposterior jaw discrepancy; (3) crowding less than 4-6 mm; (4) normal soft tissue features (nose, lips, chin); (5) no transverse skeletal problem.1 Tseng et al. used the receiver operating characteristic analysis of cephalometric variables to distinguish the skeletal Class III malocclusions who requiring orthognathic surgery. There should meat 4 of these 6 measurements that indicated for surgical treatment: (1) overjet, ≦ –4.73 mm; (2) Wits appraisal, ≦ –11.18 mm; (3) L1-MP angle, ≦8 0.8°; (4) Mx/Mn ratio, ≦ 65.9%; (5) overbite, ≦ –0.18 mm; and (6) gonial angle, ≧120.8°.6 For this patient, only 2 of these 6 measurements (L1-MP angle=79°; gonial angle=122°) met the surgical indication. Besides, this patient had average facial pattern, mild anteroposterior jaw discrepancy with upper dentition crowding, no transverse skeletal problem; patient’s incisors could be shifted to edge to edge position with relative normal soft tissue features in this position; so, this patient was arranged for camouflage orthodontic treatment.
For correction of the anterior crossbite, disoccluding the bite for unrestricted pathway in the initial tooth movement is essential. Various treatment methods have been proposed to correct anterior dental crossbite, such as tongue blades, reversed stainless steel crowns, fixed acrylic planes, bonded resin-composite slopes and removable acrylic appliances with finger springs.7-10 The aforementioned appliances might be huge, uncomfortable, and only applicable in young patients. For adult patients, fixed appliances with Class III elastics and bondable resin bites for disocclusion was effective to correct the anterior crossbite. The anterior resin bites also help to intrude the supra-eruptive lower anterior teeth. The upper teeth show was insufficient before treatment. By flaring of upper anterior incisors, the crowding in upper dentition was relived and the pleasing smile curve was also achieved. The patient’s upper lip rests on the gingiva margin of upper incisors when smile. The tooth show exceeds the proposed minimum of 0 to 2 mm of upper lip coverage of the anterior teeth for posed smile in Asian female standard.11
In treating anterior crossbite with camouflage orthodontic treatment, lingual tipping of lower anterior teeth may result in wash-board appearance and periodontal damage. The cephalometric analysis indicated the change of lower incisor inclination was few ( L1-MP: 78° to 77°). The reasons for the few change in the lower incisors may be attributed to: (1) light force and short distance of Class III elastics (3/16” 2 oz) were applied when small-sized initial working NiTi wires (0.013 / 0.014 inch) were used to avoid unwanted side effect of over-retraction in lower anterior teeth; (2) gradually increase the size of working wires with appropriate amount of buccal crown torque in lower anterior teeth when closing lower dental space; (3) the combination of pre-torque NiTi wire (.017 x .025 NiTi with 20 degree lingual root torque) for torque control of lower anterior teeth.
The mandibular second premolars are the most frequent congenitally missing teeth followed by mandibular and maxillary lateral incisors.12 The etiology of tooth agenesis is considered to involve the disturbance of dental development by genetic factors, environmental factors, or combination of both. Many researchers have reported that tooth size is often smaller in patients with tooth agenesis than in patients without tooth agenesis.13-18 Two treatment approaches are available to solve the missing tooth space: (1) close the spacings and allow the permanent first molar drift mesially and then complete the space closure orthodontically; (2) retain or regain the spaces for prothesis.19 As for this patient, the dental spacings were small (< 3mm) and the lower anterior teeth retraction was required for the cross bite correction, the space was closed for camouflage treatment and no further prosthesis. To finish in Class III molar occlusion, the occlusion should be evaluated for the existence of mandibular third molars to make sure that there are antagonist teeth to occlude the maxillary second molars. Some adjustment might be required to occlude the mandibular first with maxillary premolars in finishing a good Class III molar relationship, including positioning the mandibular first molars lingually than normal; no offset in mandibular first molar; more offset in the maxillary premolars and molars; no toe-in in maxillary molars; lingual crown torque in mandibular molars; reduced palatal crown torque in maxillary premolars and molars. Some contouring or occlusal adjustment was required for better intercuspation, such as reduction of the palatal cusps in the maxillary premolars and molars or the augmentation of the buccal cusps of the mandibular molars with restortion.20
When reviewing the long treatment duration (32M) for this patient, the main time was spent on correction of anterior crossbite. The time to use the lower anterior resin bite blocks was not long enough, so the patient still could move the mandible forward as the upper anterior teeth were still locked within the lower anterior teeth while biting or eating. The anterior crossbite was further corrected after the use of .017 x .025 pre-torque NiTi (20-degree, buccal crown torque) combined short Class III elastics. When remove the resin bite block, the mandible position should be re-evaluated and confirmed for stability.