Extreme distal migration of premolar in association with an unusual fracture of the mandible Stuart Clark, BDS,” and Nicholas J. Maiden, BDS, FDS, RCP and S,b West Lothian and Edinburgh, Scotland

BANGOUR GENERAL HOSPITAL AND ROYAL INFIRMARY OF EDINBURGH

A case of an unerupted mandibular premolar, discovered as an incidental finding during investigation of a fracture of the mandible, is described. The possible mechanisms and outcome of migrations of such teeth

are reviewed. (ORAL SURC ORAL MED ORAL PATHOL 1989;68:563-4)

T he following case involves the migration of a premolar associated with a fracture of the mandi- ble.

CASEREPORT

A 32-year-old woman came to the Department of Plastic and Maxillofacial Surgery, Bangour General Hospital, West Lothian, Scotland, with a complaint of an ill-fitting lower denture; the onset of symptoms was coincident with an assault that occurred some 5 weeks previously.

On examination, a step deformity of the right alveolar ridge was noted, as was some preauricular tenderness on the left side. No mobility across the step deformity was elicited and no trigeminal nerve damage was detectable, but because of the patient’s history a malunited fracture was suspected.

Radiographic investigation confirmed a displaced frac- ture of the right body of the mandible and revealed the unusual fracture of the left condyle and coronoid process in association with a migrated tooth (Fig. 1).

Because of the relative lack of morbidity encountered by the patient as the result of her injuries, a conservative treatment plan was adopted. The bony step was smoothed down, with the patient under local anesthesia, to aid the construction of an additional lower prosthesis. This minor procedure was carried out on an outpatient basis, and after a postoperative review was conducted, long-term radio- graphic surveillance was planned. The patient, however, has thus far failed to keep her follow-up appointments.

“Department of Plastic and Maxillofacial Surgery, Bangour Gen- eral Hospital, Broxburn, West Lothian, Scotland. bDepartment of Oral and Maxillofacial Surgery, Royal Infirmary of Edinburgh, Lauriston Place, Edinburgh, Scotland. 7/U/11455

DISCUSSION

“Migration,” when used in the context of tooth movement, should, in the author’s view, be restricted in use to describe bodily movements of a partially or fully formed tooth within the bone prior to its erup- tion.

The actual mechanisms that produce unerupted tooth migration are poorly understood, although certain patterns of preeruptive tooth movements have been described. The direction of migration is normally in that which the tooth is pointing, that is, crown first.’ Mesial migration is most common. However, the mandibular premolar is unusual in its preference for distal migration.* In a review of 62 cases of mandibular premolar migration, 58 involved distal movement.3 A common predisposing factor was postulated by one author, who concluded that “distal mandibular bicuspid migration, to a greater or lesser extent, can be expected in 5% to 10% of cases when the first permanent molar is lost prior to the eruption of the bicuspids.“4 A recent report, however, demonstrated that early loss of molar teeth is not the only initiating factor.’

Migrations continue until an obstacle is reached, commonly the second molar root, when self-righting and eruption can be expected. If no molar teeth are present, then further migration can be expected, although it has been clearly demonstrated that migration of premolars in the bone buccal to the roots of standing molars’ or inferiorly to the roots both above and below the inferior dental cana13*s-6 can occur.

Migration on the lingual aspect of the lower

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564 Clark and Malden ORAL SURG ORAL MED ORAL PATHOL November 1989

Fig. 1. Bilateral fractured mandible showing position of migrated premolar.

molars has yet to be demonstrated, but this is not surprising when one considers the comparative lack of cancellous bone lingually.

Once into the ascending ramus, a more vertical trajectory appears to be preferred; this leads the tooth toward the coronoid, rather than the condylar area. Whether teeth in this position will perforate the cortical plate and migrate into the soft tissues has yet to be documented.

The arguments for and against the removal of such misplaced teeth will not be discussed in this article; suffice it to say that in the case described there was mutual agreement between patient and surgeon to leave the tooth alone. Removal of such teeth with an intraoral as well as an extraoral approach has been described.3*6

A fracture of the condyle as well as the coronoid process accounts for 1% of mandibular fractures.’ This particular case, in our opinion, demonstrates an uncommonly high migrated tooth as a predisposing factor in this rare fracture.

We thank Mr. J. Wallace for his permission to publish details of this case and Mrs. J. MacIntyre and Mr. D.

Franklyn for their assistance in the preparation of this article.

REFERENCES

I. Stafne EC. Oral roentgenographic diagnosis. Philadelphia: WB Saunders Company, 1963:53-8.

2. Rose JS. Variations in the developmental position of un- erupted premolars. Dental Practitioner 1962;12:212-8.

3. Sutton P. Migrating nonerupted mandibular premolars: a case of migration to the coronoid process. ORAL SURG ORAL MED ORAL PATHOL 1968:25:87-98.

4. Matteson SR. Extreme distal migration of the mandibular second bicuspid. Angle Orthod 1982;52:1 l-8.

5. Loh HS. Migration of unerupted mandibular premolars. Br Dent J 1988;64:324-5. _

6. Loh HS, Ho KH. Unerupted and ectopic mandibular premo- lam. ORAL SURG ORAL MED ORAL PATHOL 1986:62:358.

7. Hopkins R. Mandibular fractures. In: Rowe NL, Williams JLL. Maxillo-facial injuries. London, New York: Churchill Livingstone, 1985:232-92.

Reprint requests to: Dr. Stuart Clark Department of Plastic and Maxillofacial Surgery Bangour General Hospital Broxburn West Lothian Scotland