Iatrogenic pulpal reactions to orthodontic extrusion.

A careful review of the literature reveals an absence of studies about the reactions of dental pulp to orthodontic extrusion. The purpose of the present research investigation is to study the pulpal reactions and the sequence of histologic events in human dental pulp after orthodontic extrusion. The sample consisted of 36 intact maxillary first premolars of young adult orthodontic subjects. The mean age of the subjects was 18 years. Eighteen maxillary first premolars were extruded, under controlled conditions with the aid of fixed edgewise orthodontic appliances, for either 1, 2, or 4 weeks. The contralateral maxillary first premolars were not extruded and were used as controls. Immediately after removal of the appliances, all the maxillary first premolars were extracted. The pulps were histologically examined in a double-blind experiment. The results obtained from this study indicate that certain characteristic pulpal reactions arise from orthodontic extrusion. These reactions involve circulatory disturbances with congested and dilated blood vessels, odontoblastic degeneration, vacuolization and edema of the pulp tissues, and (by the fourth week) manifestation of fibrotic changes. It is speculated that the vacuolization of the pulp tissues (which occurred after the application of extrusive orthodontic forces in young adult subjects) resulted from a prolapse of the pulp, made possible by the relatively wide apical foramina. However, the odontoblastic degeneration is most probably the result of a compromised blood supply. The authors believe that this study constitutes a building block for establishing a more complete biologic foundation for orthodontic tooth movement. Further studies are suggested to reach more definitive conclusions.