EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

Based on the present results, the use of temporary fixed retention (~ 2.5
years) following orthodontic treatment does allow for slightly less changes in
Incisor Irregularity over the long-term. However, does this clinically
inconsequential amount of change over the long-term (beyond 10 years) warrant
the added time, expense, and hassle of placing a fixed retainer for such a
transient time? We propose that if the time and effort is spent to use fixed
retention at the end of treatment, plans for its indefinite use should be
considered.
Explanation for Stability
Two important tenets of Tweed treatment mechanics (Sandusky and
Gramling 1988) are to minimize mandibular canine expansion during treatment
and to upright mandibular incisors over basal bone. In the majority of cases
examined in the present study, both of these treatment goals were achieved.
Expansion of the mandibular intercanine width was minimized during
treatment. The average mandibular intercanine width for both retention groups
prior to treatment was 24.5 mm. Following treatment, this dimension increased
to 25.7 mm, resulting in an average in-treatment increase of just over 1.0 mm.
Two cephalometric measurements, FMIA and IMPA, are used to evaluate
the position of the mandibular incisors relative to the basal bone. The average
FMIA for both retention groups prior to treatment was 60.2, and 62.5 at
posttreatment, for an average intreatment change of 2.3. The average IMPA for
both retention groups prior to treatment was 93.0 and posttreatment was 91.1,
resulting in an average in-treatment reduction of 1.9.
This is compelling evidence that the orthodontists in the present study
recognized and attempted to (1) minimize the expansion of the dental arches
because expansion of lower intercanine width is the most predictable of all
orthodontic relapse (McCauley 1944; Tweed 1944; 1945; Riedel 1960; Steadman
1961; Lundström 1968; Bishara et al. 1973; Herberger 1981; Glenn et al. 1987;
Bishara et al. 1989; Vaden, Harris, and Gardner 1997; Blake and Bibby 1998;
Boley et al. 2003) and (2) maintain or upright the lower incisors because
advancing the lower incisors is unstable and may seriously compromise
posttreatment stability of the lower incisors (Lundström 1925; Tweed 1944;
1945; Riedel 1976; Shields et al. 1985; Houston and Edler 1990; Boley et al. 2003).
The important influence that these two treatment goals have on the longterm
stability of orthodontically treated cases is well documented by research
referenced previously in the current study and in the final conclusions of Blake
and Bibby (1998) in their review of the literature regarding retention and
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