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CHAPTER 4. RESULTS<br />

The sample used in the present study consisted of the diagnostic records<br />

from 166 orthodontically treated patients. All cases had recall records available<br />

at a minimum of 10 years posttreatment (Figure 4-1), and the average case was<br />

16.0 years out of treatment (sd = 4.5 years). Treatment records of these subjects<br />

had been collected from the offices of experienced orthodontic specialists from<br />

across North America who use standard Edgewise mechanics (Harris 1985). The<br />

mean age at the beginning of treatment was 13.9 years, with patients remaining<br />

in active treatment for an average of 2.9 years. Recall records were taken at an<br />

average 16.0 years posttreatment (Table 3-1).<br />

The paramount question in this study was whether the type of retention—<br />

either Hawley retainers or Hawleys in combination with a fixed lingual<br />

retainer—provided greater long-term stability. This raises the issue of whether<br />

the cases (those with a fixed retainer and those without) were comparable at the<br />

start of treatment. Table 4-1 lists the results of testing whether the chronological<br />

ages are comparable between the two groups. One-way factorial analyses of<br />

variance were used for each of the three examinations plus the two changes<br />

between examinations to test for comparability between the types of retention.<br />

Table 4-1 shows that none of the 15 F-ratios achieved statistical significance.<br />

This means that the chronological ages at the start and at the end of treatment<br />

were statistically equivalent between the two sorts of retention. The same holds<br />

for the ages at the long-term recall examination (about 16 years out of treatment).<br />

These tests show that, insofar as the age at treatment affects the amounts of<br />

growth during and after the active phase of treatment (e.g., McKinney and Harris<br />

2001), the present samples are comparable. Any difference in outcomes would<br />

seem to be attributable to factors other than differences in the ages at treatment<br />

or at the follow-up examination.<br />

Cephalometric and Cast Analysis<br />

For the present study, we analyzed 32 variables (19 dental cast variables;<br />

13 cephalometric variables). Descriptive statistics for the dental variables were<br />

generated for each of the five examinations (Appendix A), namely (1) status at<br />

the start of treatment, (2) status at the end of treatment, (3) status and the recall<br />

examination, (4) the in-treatment changes, and (5) the posttreatment changes.<br />

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