EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

larger ANB at the recall examination. Clinically, it is unlikely that these subtle
differences can be detected (e.g., Sloss et al. 2008).
Retention Differences
The central theme of this study, discussed in this section, is the effect of
the kind of retention—either a removable Hawley or a fixed 3-3 or 4-4 retainer—
influenced the stability of the case when evaluated at long-term. As noted
before, complete records are available on 97 and 69 cases, respectively.
Appendix B lists the results of two-way analysis of variance that partitioned the
sample by sex and type of retention. An ANOVA table was produced for each of
the 13 cephalometric and 19 dental cast variables. These lengthy results are used
to identify which variables exhibited statistical significance when considering the
type of retention. Appendix A lists descriptive statistics for all variables
separated according to type of retention. These statistics (sexes pooled) are
supplied here so the nature of the significant differences can be interpreted.
Variables exhibiting statistical significance are denoted with an asterisk.
We reviewed differences in the pretreatment variables with the intent of
finding any variables that may have been thought informative by the
orthodontist relative to the type of retention to be used when treatment was
complete. That is, if differences exist at the pretreatment examination, this
would suggest that the orthodontist had decided early-on, based on the nature of
the malocclusion, to use a fixed appliance based on some distinguishing criteria.
Table A-1 lists the four variables (each denoted with an asterisk) with significant
differences dependent on retention, and these are described as follows.
Overjet was appreciably greater in those subsequently treated with a fixed
retainer. Average overjet at the start of treatment was more than 6 mm in the
fixed group and slightly over 5 mm in the Hawley-only group.
Greater maxillary incisor procumbency is reflected too in incisor depth at
the start of treatment, where cases with greater incisor depth ( x = 26 mm) were
more likely to be treated with fixed retention than those with shorter depths ( x =
22 mm).
The difference in SNA at the pretreatment examination was marginally
significant as evaluated by the two-way analysis (P = 0.04), and it is likely that
when the patient’s sex is ignored, the retention difference would go away, even
though the sex-by-retention interaction term was not significant.
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