Treatment of ankylosed and submerged primary molars without permanent successors is challenging, as normal vertical dentoalveolar growth is compromised. Thus, grafting techniques and distraction osteogenesis are performed for ridge augmentation before implant restoration. However, these techniques are invasive with limited success. Another treatment for implant site development is noninvasive forced eruption. This case report describes long-term follow-up of alveolar ridge augmentation in the submerged mandibular primary second molars using subluxation and orthodontic forced eruption for implant site development. A 19-year old female had Class II molar relationships, upper anterior crowding with large overjet, missing four second premolars and submerged mandibular primary second molars with inadequate vertical development of alveolar bone. For the vertical alveolar bone alterations in the mandible, forced eruption with subluxation of ankylosed lower primary second molars was applied. Treatment outcome was evaluated over 5 years with stable occlusion, healthy periodontal tissues, and successful radiographic results.

Tooth ankylosis is the fusion of the cementum or dentin with the alveolar bone.1  Primary molar ankylosis without successors can cause severe clinical problems, including a submerged tooth with or without a vertical bone defect, tipping of adjacent teeth into the submerged tooth space, and supraeruption of opposing teeth. The longer the ankylosed primary tooth exists, the higher the possibility of a long-term periodontal defect.2  Therefore, when the ankylosed primary molar is submerged, correction of the vertical bone discrepancy is critical for successful results.

If the primary molar is ankylosed without a permanent premolar, normal vertical dentoalveolar growth is compromised. Therefore, treatment of a submerged primary molar without a permanent successor is challenging. The viable options for ridge augmentation include grafting techniques3  and distraction osteogenesis.4,5  However, these techniques are invasive with limited success.6 

Another alternative for recovery of the vertical bone defect is orthodontic forced eruption,710  which is a viable nonsurgical alternative for implant site development.1119  The application of a controlled orthodontic force stimulates angiogenic factors for the formation of new bone by applying mechanical stresses to the alveolar bone.20  This additional bone generation enhances the site for a more esthetic implant prosthesis. Previous clinical reports have shown forced eruption as a successful nonsurgical alveolar ridge augmentation technique for implant site development.1113,16,17,19 

This case report describes long-term follow-up of alveolar ridge augmentation in the submerged mandibular primary second molars using subluxation and orthodontic forced eruption for implant site development.

Diagnosis and Etiology

A female aged 19 years visited the Department of Orthodontics at the Chonnam National University Dental Hospital, with a chief concern of large overjet and upper anterior crowding. Extraoral examination revealed a straight and high-angle profile. Lip incompetence at rest and mentalis strain on lip closure were noted (Figure 1). On dental cast analysis, the patient had Class II molar relationships, upper anterior crowding with large overjet (9.5 mm), and four congenitally missing second premolars with submerged lower primary second molars (Figure 2). In the panoramic radiograph, the primary second molars, especially in the mandible, showed inadequate vertical development of the alveolar bone due to ankylosis of the lower primary second molars. Cephalometric analysis revealed a skeletal Class I relationship (ANB 3.0°). The upper incisors were proclined and protrusive (U1-SN 114.0°, U1-NA 11.0 mm). The inclinations of the mandibular incisors were almost normal (IMPA 89.0°, L1-NB 5.0 mm; Figure 3).

Figure 1.

Pretreatment facial and intraoral photographs.

Figure 1.

Pretreatment facial and intraoral photographs.

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Figure 2.

Pretreatment dental casts.

Figure 2.

Pretreatment dental casts.

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Figure 3.

Pretreatment panoramic and lateral cephalometric radiographs and lateral radiograph tracing. Note the lower submerged primary second molars with vertical alveolar bone defects in the panoramic radiograph.

Figure 3.

Pretreatment panoramic and lateral cephalometric radiographs and lateral radiograph tracing. Note the lower submerged primary second molars with vertical alveolar bone defects in the panoramic radiograph.

Close modal

Treatment Objectives

The treatment objectives were (1) to achieve normal overjet and overbite, (2) to relieve the crowding of teeth, and (3) to achieve ideal occlusion.

Treatment Alternatives

There were two treatment options considered. The first was the extraction of primary second molars, which had no successors. Considering the upper anterior crowding with large overjet, Class II molar relationships, and normal position of mandibular incisors, protraction of lower molars and retraction of upper anteriors and first premolars would be needed. However, the treatment period was expected to be prolonged due to the inadequate vertical alveolar bone level at the ankylosed lower primary second molars.

The second treatment option proposed was extraction of the upper primary second molars and finishing with a Class II molar relationship. Implants placement would be planned to replace the ankylosed lower primary second molars. For vertical alveolar bone development in the mandible, forced eruption with subluxation of the ankylosed lower primary second molars was planned.

Treatment Progress

Upper primary second molars were extracted and Damon clear brackets (Ormco Corporation; Glendora, CA, USA) were bonded. The wire sequence included 0.016-inch nickel-titanium (Niti) wire, 0.016 × 0.025-inch Niti wire, and 0.019 × 0.025-inch stainless steel wire (Ormco). Next, space closure was performed using sliding mechanics in the upper arch. Alignment and leveling of the lower arch were performed, bypassing the lower primary second molars. Open coil springs were used bilaterally to regain space around the lower primary second molars (Figure 4A). After alignment and leveling, subluxation was performed on the lower primary second molars and 0.019 × 0.025-inch stainless steel wire with L-loops was inserted in the lower arch for forced eruption of the teeth (Figure 4B).

Figure 4.

Intraoral photographs of the lower primary second molars in the process of (A) space regaining and (B) forced eruption after subluxation.

Figure 4.

Intraoral photographs of the lower primary second molars in the process of (A) space regaining and (B) forced eruption after subluxation.

Close modal

Orthodontic force was applied to move the lower primary second molars occlusally. In the panoramic radiograph, although spontaneous root resorption occurred in the form of replacement root resorption of the lower primary second molars, it was confirmed that the vertical bone loss of the lower primary second molars was improved compared to the initial state (Figure 5). At the finishing stage of orthodontic treatment, the patient was referred for extraction of lower primary second molars and placement of implant prostheses. The orthodontic devices were then debonded (Figure 6).

Figure 5.

Panoramic radiograph after forced eruption with subluxation of lower primary second molars.

Figure 5.

Panoramic radiograph after forced eruption with subluxation of lower primary second molars.

Close modal
Figure 6.

Posttreatment facial and intraoral photographs.

Figure 6.

Posttreatment facial and intraoral photographs.

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Treatment Results

The posttreatment records showed significant improvement in occlusion with normal overjet and overbite (Figure 7). The profile remained straight, similar to the initial presentation, and lip incompetence was improved (Figure 8). The panoramic radiograph taken after orthodontic treatment showed that the vertical defects of the alveolar bone were improved (Figure 9). Cephalometric analysis demonstrated the maxillary incisors were retracted (U1-SN 99.0°), while the mandibular incisors were slightly flared (IMPA 97°; Figure 10). The patient was followed for 5 years. Five years after the end of the treatment, the occlusion and periodontal tissues around the implants were still stable (Figure 11).

Figure 7.

Posttreatment dental casts.

Figure 7.

Posttreatment dental casts.

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Figure 8.

Superimposition of initial (black) and final (gray) cephalometric radiographs.

Figure 8.

Superimposition of initial (black) and final (gray) cephalometric radiographs.

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Figure 9.

Improvement of vertical alveolar bone defects guided by forced eruption in the lower primary second molar areas. (A) Before treatment, (B) after forced eruption, and (C) after implant prostheses.

Figure 9.

Improvement of vertical alveolar bone defects guided by forced eruption in the lower primary second molar areas. (A) Before treatment, (B) after forced eruption, and (C) after implant prostheses.

Close modal
Figure 10.

Posttreatment panoramic and lateral cephalometric radiographs and lateral radiograph tracing.

Figure 10.

Posttreatment panoramic and lateral cephalometric radiographs and lateral radiograph tracing.

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Figure 11.

5-year follow-up. Intraoral photographs and panoramic radiograph.

Figure 11.

5-year follow-up. Intraoral photographs and panoramic radiograph.

Close modal

In the present case, the patient had two upper primary second molars and two submerged lower primary second molars without permanent successors. The first treatment option considered was the extraction of four primary second molars along with space closure, as the four permanent second premolars were missing. For its execution, a slight forward movement of the lower first and second molars was required to improve the bilateral Class II molar relationships. However, the protraction of lower permanent molars would have been difficult since the alveolar bone defects were vertical and buccolingual in the primary second molar areas.

As an alternative, the extraction of two upper primary second molars and the maintenance of two lower primary second molars was planned in consideration of the Class II molar relationships with large overjet. However, the severe infraocclusion and inadequate vertical dentoalveolar growth at the lower second premolars occurred because of tooth ankylosis. The extraction of ankylosed deciduous molars is often the treatment of choice for submerged primary molars without permanent successors.2124  Thus, extraction of the lower primary second molars was planned. For prosthetic restoration in the lower second premolar areas, implant prostheses or autotransplantation was considered. Since the upper third molars were missing and lower third molars were horizontally impacted bilaterally, autotransplantation could not be planned and implant prostheses for the lower second premolar areas was selected. Ostler and Kokich25  investigated alveolar ridge changes in patients who were congenitally missing mandibular second premolars and reported that ridge width decreased 25% within 3 years after primary molar extraction. In fact, serious bone loss was experienced after extraction of the ankylosed and submerged primary molars as shown in Figure 12.

Figure 12.

Substantial bone loss after extraction of ankylosed and submerged primary molars. (A) Before extraction and (B) after extraction.

Figure 12.

Substantial bone loss after extraction of ankylosed and submerged primary molars. (A) Before extraction and (B) after extraction.

Close modal

Esthetic and successful implant prosthesis requires special focus on the recovery of vertical alveolar bone defects. Alveolar ridge reconstruction can be performed using various procedures, such as grafting3  and distraction osteogenesis.4,5  However, these techniques are invasive with limited success.6  Thus, alveolar bone regeneration was performed with forced eruption, because it is less invasive and more effective in repairing vertical alveolar bone defects.719  In addition, subluxation was performed before orthodontic forced eruption to extrude the ankylosed lower primary second molars.26 

Orthodontic forced eruption is widely applied for implant site development as it facilitates soft and hard tissue remodeling.1119  Orthodontic forced eruption is a physiological response that naturally produces the surrounding bone without any other surgical treatment. As shown in Figure 13, when a displaced tooth is corrected orthodontically after removing a large cyst, bone is spontaneously developed. However, previous studies have been focused on permanent teeth with fractured crowns for esthetic and functional recovery. In this case, the subluxation and orthodontic traction of primary molars developed alveolar bone volume in the buccolingual and vertical dimensions. The oral surgeon who placed the implants did not consider bone grafting, as there was sufficient bone during the surgery. Considering that the extraction of submerged primary molars without permanent successors is one of the recommended methods for ankylosed primary teeth, this report suggesting orthodontic forced eruption for submerged primary teeth without permanent successors to stimulate vertical bone regeneration may be very interesting and valuable. In addition, good 5-year follow-up results also give strength to this attempt.

Figure 13.

Bone regeneration after orthodontic forced eruption. (A) A large cyst resorbed the bone and displaced the lower left second premolar and first molar. (B) After orthodontic forced eruption, the teeth were well aligned and the bone was spontaneously developed.

Figure 13.

Bone regeneration after orthodontic forced eruption. (A) A large cyst resorbed the bone and displaced the lower left second premolar and first molar. (B) After orthodontic forced eruption, the teeth were well aligned and the bone was spontaneously developed.

Close modal
  • This case showed that, despite ankylosed lower primary second molars having vertical alveolar bone defects, the vertical occlusal discrepancy can be successfully recovered using orthodontic forced eruption and the treatment results can be maintained long term.

  • Additionally, recovery of bone defects in the submerged primary molar area without a permanent successor can be achieved by orthodontic forced eruption. In particular, it is meaningful in that recovery of bone defects in the submerged primary molar, not permanent teeth, can be achieved by orthodontic forced eruption.

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Author notes

The first two authors contributed equally to this work.

a

Assistant Professor, Department of Orthodontics, School of Dentistry, Dental 4D Research Institute, Dental Science Research Institute, Chonnam National University, Gwangju, Korea.

b

Postdoctoral Researcher, Department of Orthodontics, School of Dentistry, Chonnam National University, Gwangju, Korea.

c

Professor, Department of Prosthodontics, School of Dentistry, Dental Science Research Institute, Chonnam National University, Gwangju, Korea.

d

Professor, Department of Oral and Maxillofacial Surgery, School of Dentistry, Dental 4D Research Institute, Dental Science Research Institute, Chonnam National University, Gwangju, Korea.

e

Professor and Chair, Department of Orthodontics, School of Dentistry, Dental 4D Research Institute, Dental Science Research Institute, Chonnam National University, Gwangju, Korea.