OVERCORRECTION

Figure 2. Overcorrected Class III molar position following 14 weeks of therapy. Note distal drifting of upper buccal segments upon eruption.

Indications for Use:

Commonly indicated as the sole method of correction where the Class II malocclusion is very mild. If the upper molar can be moved distally and tipped back early in the eruption sequence of the upper teeth, the erupting bicuspids will have a tendency to drift distally, also. Although much of this overcorrection comes by virtue of upper molar tipping, in the strong growth patterns the inclined-plane effect uprights these teeth with little or no mechanical intervention. In more severe Class II malocclusions, the molars are greatly overcorrected and used in conjunction with other anchorage techniques mentioned herein. It is axiomatic that the farther you need to go, the more you need to overcorrect. Simply put, just moving the upper molar back into a Class I occlusion is most often not enough. Moving it back into a Class III relationship is more desirable.

Technique:

The more the upper molar moves distally in a Class II malocclusion, the more it must be expanded to prevent crossbite. The midpalatal jackscrew is activated one turn every third day to create this expansion in the molar region. As the molar is tipped distally, it has atendency to rotate mesially - a phenomenon quite commonly seen when using reverse curve Ni-Ti archwires. This is thought to be due to the nature of the cortical bone surrounding these teeth, but other mechanical factors no doubt come into play. This can be compensated for somewhat by placing approximately 30 degrees of distal rotation in the terminal legs of the Pendulum springs.

Considerations:

Since the distal movement of the upper molars occurs so rapidly (10-12 weeks), there is a transient bite opening due to driving these teeth back into the wedge of occlusion. This is commonly not a problem with brachyfacial types, as muscular rebound and growth more than compensate for this initial bite opening. In fact, in extremely strong muscular patterns, this response can be very beneficial in the bite opening process. But in vertical growth patterns with weak muscular rebound, bite opening can be a harbinger of further negative side effects. Once the bite opens, the tongue goes into the interspace, sometimes initiating a reverse swallow/tongue thrust (if it doesn’t already exist). Severely tipping the upper molar only aggravates this problem because the bite can be propped open on the inclines of these teeth, allowing the buccal segments to supererupt. The answer: choose this type of appliance only in mesofacial and brachyfacial types where the muscular pattern, growth and subsequent mechanics can compensate for this response. Fortunately, approximately 65% of all Class II malocclusions fall into this category. In the others, a more conservative approach should be utilized.