EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

1 mm expansion of the intermolar width provides only a 0.25 mm increase in
arch perimeter.
De La Cruz et al. (1995) evaluated records of 45 Class I patients and 42
Class II, division 1 patients to evaluate the long-term stability of orthodontically
induced change in arch form. Dental casts were analyzed at pretreatment,
posttreatment and a minimum of 10 years posttreatment. These researchers
concluded that arch form tends to return toward its pretreatment shape and that
the patient’s pretreatment arch form appears to be the best guide to future
stability. Although the researchers found a positive correlation between degree
of treatment arch change and degree of posttreatment relapse, they claimed that
minimizing treatment arch form change was no guarantee of postretention
stability.
Vaden, Harris and Gardner (1997) quantified changes in tooth
relationships in a sample of 36 extraction patients at 6 years and again at 15 years
posttreatment. Although the maxillary intercanine width was expanded more
than the mandibular intercanine width during treatment, both arches were
expanded slightly, but to a statistically significant extent. An interesting
observation noted during this study was that with any study of this type, “it is
difficult to determine whether intercanine ‘expansion’ occurred by a transverse
movement of the teeth or retraction of the canines in to the premolar extraction
spaces, a broader part of the arch” (p 545). Posttreatment results indicated that a
significant amount of the maxillary expansion was maintained, while half of the
expansion that occurred in the mandible during treatment was lost. Maxillary
and mandibular arch length was reduced an average of 5.7 mm during treatment
as a result of tooth extraction, but it also continued to decrease an average of 1
mm throughout the two recall periods even though no spacing was left following
active treatment. This continued reduction in arch length was attributed to the
mesial migration of teeth in the buccal segment. Both arches become shorter and
narrower with age. These results reiterate the conclusions of previous
researchers who found that posttreatment arch dimension changes and dental
crowding can be minimized and kept similar to changes seen in untreated
samples by maintaining pretreatment arch dimension and keeping alterations in
the intermolar and intercuspid distances to a minimum during treatment
(Steadman 1961; Lundström 1968; Glenn et al. 1987; Bishara et al. 1989).
Burke et al. (1998) applied a meta-analysis technique of literature review to
a total of 26 studies to assess the longitudinal stability of posttreatment
mandibular intercanine width. Glass (1976, p 3) defines meta-analysis as “the
statistical analysis of a large collection of results from individual studies for the
purpose of integrating findings.” Weighted averages and standard deviations
for the means of 1,233 patients were analyzed for changes in intercanine width at
9