Management of a Mutilated Dentition with a Palatally Impacted Canine, Hypoplastic Lower First Premolars, and Missing Lower First Molars

The maxillary midline was shifted 1mm to the right of the facial midline, and the mandibular midline was shifted 2mm to the left of the maxillary dental midline. Occlusal caries were observed in both the upper first and lower second permanent molars. The anterior Bolton ratio was 62.3% (norm = 77.2% ± 1.6%), and the overall Bolton ratio was 81.1% (norm = 91.3% ± 1.9%). Severe crowding was found in the upper arch, with a space discrepancy of 14mm, while mild crowding (3mm discrepancy) was present in the lower arch (Fig. 1B).

The panoramic radiograph revealed that the upper left canine was palatally impacted and that the lower second molars had tipped mesially into the extraction spaces of the lower first molars, but with no indication of bone loss in the edentulous regions. All third molars except for the upper left were present. Cephalometric analysis (Table 1) indicated a skeletal Class I relationship (ANB = 2°) with a hyperdivergent growth pattern (SN-GoMe = 35°) and a deficient interincisal angle (128°).

Treatment goals were to alleviate the crowding, incorporate the impacted upper left canine into the arch, close the spaces left by extraction of the lower first molars, and achieve a satisfactory occlusion. Additional objectives were to align both arches and to achieve coincident midlines and an ideal overjet and overbite, while preserving the profile and optimizing facial esthetics.

Following recommendations in the literature, the position of the canine was analyzed to determine its prognosis (Fig. 2).^5-8 The canine cusp tip was in sector II, according to Ericson and Kurol’s system,⁵ close to the midline and overlapping the adjacent lateral incisor but not the central incisor. Although this position suggested a fair prognosis, the crown was above the halfway point of the central-incisor root, and the horizontal position of the canine root apex was higher than normal, both indicating a better prognosis. Finally, the canine had a mesial angulation of 30° in relation to the midline, which suggested a fair prognosis. Based on the overall favorable prognosis for the impacted left canine, a guided orthodontic eruption after surgical exposure was determined to be the most suitable approach.

Since the impacted canine was positioned high in the palate, well above the mucogingival junction, a closed-eruption surgical technique was deemed appropriate.⁹ To address the remaining concerns, one treatment option would involve extracting all four first premolars and using prosthetic implants to replace the missing lower first permanent molars, resulting in a Class I molar relationship. The second option would be to extract the upper first premolars and upright the lower second permanent molars, resulting in a Class II molar relationship. After an explanation of the prolonged treatment time either course would require, the patient chose the second option to avoid the need for prosthetic implants.

Treatment Progress

The upper first premolars were extracted to alleviate the upper crowding. Two weeks later, the upper arch was banded and bonded with MBT^*-prescription .022" x .028" preadjusted edgewise brackets, except for the blocked-in upper lateral incisors. Leveling and alignment were performed using a series of progressively larger nickel titanium wires (.012", .014", .016", and .016" × .022"), changed every five weeks.

After five months of treatment, an open-coil spring was inserted between the upper right central incisor and canine on an .017" × .025" stainless steel archwire to open space for the blocked-in upper right lateral incisor (Fig. 3A). To align the left lateral incisor, an .012" “piggyback” nickel titanium archwire was inserted. Posterior bite blocks were cemented to the lower arch to prevent interference and facilitate tooth movement. At the same time, the closed-eruption technique was used to surgically expose the impacted upper left canine (Fig. 3B). A lingual button was bonded to the canine for attachment of an .011" ligature wire, with its ends emerging from the sutured flap of gingival tissue. To preserve the extraction space and prevent tipping of the neighboring teeth during traction, a sleeve was placed between the upper left lateral incisor and second premolar.

Since immediate traction is generally beneficial after surgical exposure of palatally impacted canines in late adolescents and young adults, orthodontic eruption was initiated as soon as inflammation from the surgery had subsided. A K-9 extrusion spring was bent from .017" × .025" TMA^** wire to guide the impacted canine into the extraction space.¹⁰ The spring was engaged in the auxiliary slot of a buccal tube on the upper left first molar and activated by bending its vertical arm upward and attaching it to the button on the impacted canine, thus applying a light extrusive force. With a pattern of alternating activation and deactivation, the spring also exerted the buccal component of force needed to bring the canine into the arch. While the reactive force of activation with the vertical arm of a K-9 spring applies an intrusive force and a clockwise moment to the molars and premolars, any side effects are generally minor.^10,11 Movement of the canine was facilitated by cinching the spring back about 2mm.

Over the next eight months, the progress of canine eruption was monitored with monthly appointments. No complications were observed at the surgical site, and the gingiva remained healthy. After the crown of the impacted canine had erupted, it was bonded and engaged in the archwire. For another eight months, progressively larger stainless steel wires (.016", .017" × .025", and .019" × .025") were securely tied for leveling and alignment.

After the upper arch was aligned, the bite blocks were removed (Fig. 4), and leveling and alignment of the lower arch were initiated with an .012" nickel titanium archwire. The wires were changed three times, every four weeks, progressing up to .016" × .022" nickel titanium.

Four months later, bilateral helical uprighting springs were fabricated from 15-20mm lengths of .017" × .025" TMA wire on an .017" x .025" stainless steel base (Fig. 5). The springs were passed through buccal tubes on the lower second molars, with the helices distal to the tubes. Hooks were added at the mesial ends of the springs for attachment to the archwire between the lower canines and lower first premolars, so that each uprighting spring applied 50g of force. The force exerted on the anchor units was assessed every four weeks using a Dontrix gauge, and the springs were reactivated if necessary. After four months of treatment with the springs, uprighting of the lower second molars was complete.

Another month later, a 1.5mm x 8mm mini-implant was inserted between the upper right first molar and second premolar to provide skeletal anchorage for Class III elastics (3⁄16", 4.5oz); at the same time, to close the remaining space and correct the midline shift, Class II elastics (3⁄16", 4.5oz) were worn between a hook distal to the upper left lateral incisor and a hook on the lower left second-molar tube (Fig. 6).

Two months later, after complete closure of the extraction space, final settling was performed on an .014" nickel titanium archwire, and zirconia crowns were cemented on the hypoplastic lower first premolars.

After a total 32 months of treatment, the fixed appliances were removed, and upper 4-4 and lower 3-3 lingual retainer wires were bonded.

Treatment Results

All treatment objectives were accomplished. An acceptable occlusion was achieved, with Class II molar relationships and Class I canine relationships on both sides, good intercuspation, coincident dental and facial midlines, and appropriate overjet and overbite (Fig. 7A).

The crowding was relieved in both arches, and the crossbite was corrected. The impacted upper left canine was successfully integrated into the arch. Post-treatment panoramic radiographs revealed satisfactory root parallelism without significant resorption. Cephalometric analysis (Table 1) indicated an improved incisor inclination (U1-NA = 6mm, 24°; L1-NB = 4mm, 25°; SN-GoMe = 36°; IMPA = 91°). To prevent further complications, the patient was advised to have the upper right third molar extracted,¹² but she expressed satisfaction with the treatment results and declined any further surgical procedures (Fig. 7B).

Discussion

It is unusual to encounter a mutilated dentition in which an impacted canine, missing molars, enamel hypoplasia, crowding, and crossbite occur together. Management of such a complex case must consider space creation for the impacted canine, restoration of the hypoplastic teeth, and options for replacement of the absent molars, among other factors.