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EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

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these variables indicate more anteriorly positioned mandibular incisors and<br />

increased the likelihood that a case would be put in fixed retention.<br />

Overbite shows up at both the pretreatment and posttreatment<br />

examination as being significantly greater in the fixed retention group than the<br />

removable group. The clinical reason for this is not clear, but two possibilities<br />

are (1) that greater overbite is associated with greater Incisor Irregularity and/or<br />

(2) that greater overbite is associated with (a consequence of) incomplete<br />

orthopedic correction of the intermaxillary skeletal relationships, that is a failure<br />

of incisor coupling. Either case might be seen as a risk factor for relapse—thus<br />

the use of a fixed retainer in hopes of enhancing the chances for stability. It is<br />

difficult to determine what significance, if any, an increased overbite might have<br />

on the stability of lower incisors, although Sadowsky (1982) demonstrated that in<br />

a sample of 96 treated patients, more severe mandibular anterior crowding (> 3.0<br />

mm) usually occurred together with an excessive overjet and overbite at longterm<br />

recall. In another study by Kahl-Nieke et al. (1995), 226 cases with various<br />

Angle’s classifications of malocclusion were examined to document postretention<br />

changes and to distinguish factors that may play a role as predictors for<br />

long-term prognosis. The authors also found an association between increased<br />

pretreatment overbite and increased amounts of postretention incisor crowding<br />

and Incisor Irregularity.<br />

A greater total chin dimension persisted from the pretreatment evaluation<br />

to the posttreatment evaluation in the sample receiving fixed retainers. Indeed,<br />

this was the single most predictive measure of who received a fixed retainer. It is<br />

interesting that Merrifield (1966) recognized this as a useful clinical measure. As<br />

defined by Merrifield (1966), total chin is a millimetric measurement including<br />

the bony chin lying anterior to the NB line and measured to soft tissue Pogonion<br />

(Figure 3-22).<br />

Merrifield acknowledged that some investigators have placed great<br />

significance on the bony chin, but Merrifield himself made no association<br />

between the total chin measurement and the stability of lower incisors.<br />

Merrifield (1966) found the overall evaluation of the total chin to be more<br />

important in the study of facial esthetics and profile evaluation, and he attributed<br />

changes in total chin thickness to the individual’s growth (particularly of the<br />

mandible) and developmental changes. Stoner and Lindquist (1956) proposed<br />

that the lower incisors have a definite relationship to facial esthetics, though<br />

possibly indirectly. Holdaway (1956) emphasized the important contribution the<br />

bony chin has on facial esthetics, and further indicated that a recontouring of<br />

Point B by lingual movement of the lower incisors increased the effective bony<br />

chin and was accompanied by improvement in facial balance.<br />

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