EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

more stable (i.e., the mean change was close to zero) compared to greater change
in the removable sample. The amount of change in the fixed sample was 1.46
mm versus 2.30 mm in the removable group.
Maxillary Intermolar Width (Table C-9) also shows up as a significant
variable (P = ~ 0.01). The sample with fixed retention experienced slight
expansion, while cases with just Hawley retainers experienced slight constriction
(Figure 4-23). Maxillary Intermolar Width decreased in both groups, but
significantly more so in the group with just removable retainers. It is difficult to
determine why this effect on maxillary intermolar width shows up between the
groups during the recall period. Any attempts at explaining this difference
would be purely conjecture.
Incisor segment ratio (Table C-6) shows up as significant variable (P = ~
0.01). In the sample that received just the Hawley retainers, incisor segment ratio
is closer to zero, which indicates that the incisor arch form became more curved
and decreased in width after treatment as viewed occlusally (Figure 4-21) more
so than in the fixed retention sample.
Incisor Aspect Ratio (Table C-7) reveals only borderline significance (P =
~ 0.05). Figure 4-22 illustrates that Incisor Aspect Ratio is greater in the fixed
group, indicating that incisors remained more upright in cases retained with a
fixed retainer as compared to those retained with a Hawley retainer following
treatment.
Incisor segment depth (Table C-13) shows up as significant variable (P = ~
0.01). Figure 4-24 illustrates that the sample with fixed retention was more stable
(i.e., the median hovered on zero) compared to the removable sample.
Extraction Pattern
Three different extraction patterns proved common enough in the data to
allow for statistical analysis (Appendix E). These are (1) nonextraction, (2)
extraction of maxillary and mandibular first bicuspids (4-4/4-4), and (3)
extraction of maxillary first bicuspids and mandibular second bicuspids (4-4/5-
5). Table E-1 lists the results of two-way ANCOVA tests evaluating whether the
amount of relapse was associated with a particular extraction pattern while
controlling for the time out of treatment. That is, there is little chance that the
occlusion is continuing to change since no one less than 10 years out of treatment
was included. Still, partly out of curiosity and partly to confirm the situation,
time-out-of-treatment was used as the covariate. In fact, 3 of the 33 variables did
show a significant age effect (i.e., ISR, LCW, and ISD).
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