EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

acceptable postretention stability at the long-term (80%) than previously
reported (Little et al. 1981, 1988). The authors attributed much of this stability to
meeting specific evidence-based treatment objectives during treatment. The
present study and others, as reviewed by Boley (2007, p 16), also document that
acceptable long-term stability is possible and can be linked to several common
characteristics of these “satisfactory stable” samples—including minimal
alteration of the mandibular arch form and the retraction and uprighting or
maintenance of mandibular incisors in their original position (Boley et al. 2003).
Mandibular Incisor Irregularity often is used as an important indicator of
a case’s stability (Little 1977), partly because it is a condition obvious to the
patient. Figure 5-1 illustrates that group averages do not differ at the
pretreatment examination, but at the end of treatment, the fixed group has a
significantly greater amount of irregularity. However, by the recall examination,
this difference not only disappears, but becomes statistically significant in the
other direction, as the removable group now has a statistically significant greater
Incisor Irregularity than does the fixed group. This is also evident in the
significant difference noted in the rate of change of Incisor Irregularity between
the two groups following treatment (Table A-5).
Patients receiving only Hawley removable retainers displayed ~ 2.5 mm
of Incisor Irregularity, while patients receiving an upper Hawley retainer in
combination with a temporary fixed lower retainer displayed only ~ 1.9 mm
irregularity. This difference between the groups (~ 0.6 mm) at the recall
examination was found to be statistically significant, but from a clinical
standpoint, these differences are minimal, and likely would not be detected by
the patient or practitioner. Overall incidence of long-term stability of both groups
( x ~ 2.2 mm) was greater than previously reported by most studies (Table 5-1).
Other statistically significant changes after treatment occurred in Incisor
Segment Ratio and Incisor Aspect Ratio. These two ratios reflect the proclination
of the lower incisors. There was a net decrease in Incisor Segment Ratio ( x = -0.8
for the removable group), while there was a net increase ( x = 0.7 for the fixed
group). There was a greater positive change in Incisor Aspect Ratio in the fixed
retention group ( x = 5.8 mm) compared to the removable group ( x = 3.1 mm).
Considered together, these changes suggest that the lower incisors tipped
forward more in the removable group than in the fixed group. This does not
necessarily mean that alignment deteriorated, only that there was a greater
proclination. There was also a greater decrease in maxillary intermolar width
during this period in the removable group than in the fixed group. It is unclear
why this might be.
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