Abstract

Orthodontic and Orthopedic Expansion of the Transverse Dimension: A 45-year Perspective

by McNamara James A.

This presentation by Dr. James McNamara can be viewed as a prologue to the 2025 SIDO International Spring Meeting. The general focus of this conference is on skeletal versus conventional anchorage in dentofacial orthopedics. Dr. McNamara and his colleagues have studied changes in the transverse dimension of the face for over four decades One of their initial investigations was to answer the simple question of what causes crowding; teeth that are too large, jaws that are too small or a combination of the two? In a comparison of orthodontic normals compared to severely crowded dentitions, there was no difference in tooth size between the two groups, In contrast, measures of transpalatal width indicated that the crowded cases were 5-6 mm narrower that the normals. The two appliances used to treat problems in the early mixed dentition are the removable lower Schwarz appliance and the bonded acrylic splint expander. The protocols used are explained briefly in the presentation. The long-term impact of orthopedic expansion of the maxilla in comparison to controls is 6 mm of increased arch perimeter in the maxilla and 4.5 mm in the mandible. If the patient is treated at an earlier stage of dental development, expansion still occurs, but the gain in arch perimeter is reduced in both arches. An unanticipated finding from these studies was evidence of spontaneous improvement in Class II malocclusion following orthopedic expansion of the maxilla. In comparison to matched untreated controls, spontaneous improvement was observed in 20% of the controls and 92% of the expansion group. Improvement in Class II relationships of 2 mm or greater was observed in 48% of the expansion patients. Conclusions that can be drawn from the results of these studies indicate that: • Rapid maxillary expansion may be used effectively in patients with narrow dental arches but who do not present with a crossbite • Transpalatal width is a critical indicator of maxillary transverse deficiency. • A maxillary central incisor with a mesiodistal width of 10 mm or greater may indicate the need for extraction treatment. • Spontaneous improvement in Class II relationship following expansion may be observed in the majority of RME patients.

Learning Objectives

After this lecture, you will be able to understand the rationale behind using rapid maxillary expansion in patients who do not have a preexisting crossbite.
After this lecture, you will be able to understand how to used transpalatal width and maxillary central incisor width as diagnostic data on which to base treatment decisions.
After this lecture, you will be able to prevedere che si possa verificare un miglioramento spontaneo della malocclusione di II classe dopo l’espansione della dimensione trasversale delle arcate.