2010 RWISO Journal - Roth Williams International Society of ...

Figure 8 Left horizontal MI/CR discrepancy.
Figure 9 Left vertical MI/CR discrepancy.
Figure 10 Transverse MI/CR discrepancy.
Discussion
Results of the present study indicate a statistically significant
improvement in MI-CR discrepancy in the right horizontal,
right vertical, left vertical, and transverse planes
with 2 months of gnathologic positioner wear. The condylar
axis distraction differences in the left horizontal planes
were not statistically significantly different. Before positioner
wear, the mean right horizontal, right vertical, left vertical,
and transverse measurements were 1.306 mm, 1.217 mm,
1.162 mm, and 1.031 mm respectively, and fell outside the
± 1.0 mm vertical and horizontal as well as the ± 0.5 mm
transverse distraction envelope proposed by Crawford, Utt
et al, and Slavicek. 12,13,14 Following 2 months of positioner
wear, the amount of condylar distraction in these 4 measurements
showed statistically significant improvement and
came within the distraction envelope. Before positioner wear,
3 patients (11.5%) had MI-CR discrepancy that fell within
the envelope of susceptibility in all 5 of the measurements
examined, while 11 patients had all 5 measurements within
the envelope after positioner wear (42.3%). Reducing MI-
CR discrepancies is an important treatment goal in the gnathological
philosophy, and the use of gnathologic positioner
is essential to achieving this goal.
Although these changes were nonsignificant when compared
to change in the control group, the level of significance
in the right horizontal, right vertical, and left vertical
planes was very close to the significance level of 0.01 used
for this study, and below the more common 0.05 level of
significance. Figures 6, 7 and 9 show a similar pattern with
reduction in MI-CR discrepancy over time with positioner
wear, while the group with the Hawley retainers shows an
increase in MI-CR discrepancy. This trend is observed in 3 of
the 5 measurements studied (right horizontal, right vertical,
and left vertical planes). The positioner and control groups
tend to change differently over time in the vertical and horizontal
planes, with the positioner group improving and the
control group getting worse. This is consistent with Roth’s
claim that general retention protocols with Hawley-type appliances
following orthodontic therapy will tend to make
MI-CR discrepancy worse, while gnathologic positioners
will improve MI-CR discrepancy. Interestingly enough, all
mean vertical and horizontal CPI measurements for the control
group started within the distraction envelope of ± 1.0
mm and finished outside the envelope following 2 months of
Hawley retainer wear.
The small sample size of the control group is a limitation
of this study. A larger sample size would eliminate type II error
and might show a statistically significant difference in the
change in MI-CR discrepancy over time between the control
and the positioner group. However, the p-values are below
80 Chiang, Freeland, et al | Effect of Gnathologic Positioner Wear on Maximum Intercuspation CR Disharmony