Effect of Palatal Bars on the Upper Facial Skeleton

Abstract

The palatal bar is used with a headgear in clinical orthodontics to control the vertical growth of the maxilla. We investigated the effects of two types of palatal bar on the facial skeleton by measuring the strain distribution around the maxillary first molars using triaxial rosette gauges set on dry skulls of one adult and one child.
The results obtained were as follows :
1. When the straight palatal bar was used, high compressive strain oriented at right angles to the occlusal plane was found in the buccal segments of the bone surrounding the maxillary first molars. The magnitude of the compressive strain in this region produced by the curved palatal bar was smaller than that by the straight type.
2. When the straight palatal bar was used, the lingual alveolus around the maxillary molars was subjected to high compressive strain oriented at right angles to the occlusal plane. The magnitude of the compressive strain in this region was greater with the curved palatal bar than with the straight type.
3. Both types of palatal bar produced pronounced counterclockwise rotation of the maxilla of the dry skull of the child, similar to that experienced with high-pull headgear traction.
4. Strains were found in the frontal process of the maxilla, nasal bones, infraorbital area of the maxilla, and the areas around the frontonasal and zygomaticomaxillary sutures.
5. The degree of strain on the infraorbital foramen was significant in the dry skull of the child.
Clinically, the palatal bar increases the stability of the maxillary buccal segments, and decreases their normal vertical descent. Reduction of vertical facial growth tends to close the mandibular plane angle and move the relative position of the mandible forward. The results of this experiment suggest that the palatal bar might be useful for anchorage to resist the elongation and mesial migration of the maxillary first molars produced by intermaxillary elastics in adults.