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Case Presentation: Molar Substitution for a Congenitally Missing Premolar by Saritha Chary-Reddy, DDS, PhD

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Introduction
This report describes the treatment of a 16-year-old male patient with a hyperdivergent profile and congenitally missing mandibular left second premolar. Both mandibular right and left primary second molars were ankylosed. The ankylosed mandibular left primary second molar was extracted and the mandibular first and second molars were mesialized with the help of a micro-screw. The mandibular left third molar was left in occlusion with the maxillary second molar. The micro-screw was useful as an absolute anchorage for the mesial movement of mandibular molars.

Approximately two percent to 10 percent of the population shows congenitally missing teeth. Excluding third molars, the most common missing teeth are maxillary lateral incisors and second premolars. Without the underlying permanent successors, the primary teeth show increased frequency of ankylosis and submergence.1 Ankylosis of primary teeth can result in compromised alveolar bone height, tipping of adjacent teeth and destruction of bone during the extraction. Infraocclusion due to ankylosis increases as vertical bone development occurs commensurate with facial growth.

To preserve the alveolar bone, the ankylosed primary teeth should be extracted in a timely manner. The current approach to replace congenitally missing teeth is the placement of implants. However, implants cannot be placed on individuals until the growth is completed. This can create problems with space maintenance and a possible bone graft. An alternative treatment approach is to mesialize adjacent permanent teeth in place of missing permanent teeth.2

Diagnosis and treatment plan
A 16-year-old male patient in the mixed dentition stage was referred by his general dentist for orthodontic treatment. Clinical examination showed a Class III dental malocclusion with bilateral open bite caused by ankylosed mandibular primary second molars, normal overjet and overbite (Fig. 1). Panoramic X-ray showed congenitally missing mandibular left second premolar and ankylosed mandibular right and left primary second molars (Fig. 2). Maxillary arch showed mild crowding and mandibular arch showed moderate crowding. Cephalometric analysis showed a Class I skeletal relationship, a hyperdivergent profile and a straight nasolabial angle (Fig. 3).





Different treatment options were offered. The first option was to mesialize the mandibular left first molar in place of the missing mandibular left second premolar using a micro-screw. The second option was to leave the space of the missing mandibular left second premolar for restoration with an implant and crown. The third option was to extract the maxillary right and left first premolars, mandibular right second premolar and the ankylosed mandibular left primary second molar. Parents and patient chose the first option.

Treatment progress
Bands were cemented on the molars and 0.022 brackets (MBT, 3M Unitek) were bonded in the maxillary and mandibular arches. After 10 months of alignment, 0.016x0.022 SS wires were placed in both arches and patient was referred to the oral surgeon for extraction of ankylosed mandibular primary second molars. A 10mm micro-screw (3M Unitek) was placed at the mucogingival junction distal to mandibular left first premolar. The micro-screw was activated immediately with an elastomeric chain (Fig. 4).

Patient was seen every four weeks for orthodontic adjustment appointments until the molars were mesialized. Force was maintained with an elastomeric chain until the mandibular left first and second molars were mesialized. Vertical elastics were also used to get the molars in occlusion. In five months, the molars were mesialized and the space was closed. The micro-screw was then removed. Since the mandibular right second premolar was severely rotated and the patient did not want supracrestal fiberotomy, it was decided to leave it as is. The occlusion was not affected by the rotation. The total treatment time was 23 months.

Treatment results
The right side occlusion was finished in Class I molar and canine relationship (Figs. 5-7). The left side occlusion was finished in Class III molar relationship and Class I canine relationship. The larger mesiodistal width of the rotated mandibular right second premolar did not compromise either the molar or anterior occlusion. The midlines were perfectly coordinated and ideal overjet and overbite was established. The mandibular left third molar was left in occlusion with the maxillary second molar. The maxillary right and left third molars and mandibular right third molar were referred to an oral surgeon for extraction.









Discussion
The substitution of mandibular left first molar in place of a congenitally missing mandibular left second premolar was accomplished because of the micro-screw, which provided absolute anchorage. Extraction of the ankylosed primary second molar in a timely manner has prevented the need for a bone graft. A delay in orthodontic treatment would cause a severe bony defect at the site of the ankylosed primary second molar which would require a bone graft before the first molar is mesialized. This approach has also maintained the facial profile. This approach is cost-effective to the patient since it prevented the need for a bone graft, implant and restoration in place of the congenitally missing mandibular left second premolar.

References
  1. Baccetti T. A controlled study of associated dental anomalies. Angle Orthod 1998; 68:267-74.
  2. W E Roberts, C L Nelson, C J Goodacre. Rigid implant anchorage to close a mandibular first molar extraction site. Journal of clinical Orthodontics 01/1995; 28(12):693-704.

Dr. Saritha Chary-Reddy received her DDS degree from University of Oklahoma, College of Dentistry in 2002 and pursued specialty training in Orthodontics and Dentofacial Orthopedics at University of Texas Health Sciences Center, San Antonio. She became board certified in 2006 and is currently a diplomate of the American Board of Orthodontics. Prior to her DDS degree she received a Ph.D. degree in genetics. Dr. Chary- Reddy currently is in private practice in San Antonio at VK Orthodontics.


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