Pacific Coast Society of Orthodontists Bulletin Spring 2023 - 30

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Table 1. Mean Speeds (mm/month) of Distolateral Tooth Movement for Five Applied Stresses
(kPa) in Growing (G) and Nongrowing (NG) Subjects
Stress (kPa)
Teeth Moved in G Subjects
4
13
26
52
78
Overall
a,b,c,d
Speed ± SD (mm/month)
1.05 ± 0.42a,b,c
1.56 ± 0.51d
2.25 ± 0.60a,d
2.13 ± 0.48b
2.61 ± 0.87c,d
1.86 ± 0.78
16
16
12
16
12
72
Teeth Moved in NG Subjects
Number Speed ± SD (mm/month) Number
0.90 ± 0.63
0.75 ± 0.27
1.20 ± 0.60
1.65 ± 0.42
1.59 ± 0.54
1.23 ± 0.57
4
4
4
4
4
20
P*
.535
.006
.007
.089
.046
.001
Significant differences (P < .0001) within growing subjects using the Tukey honestly significant difference
post hoc test.
*Results of t tests between growing and nongrowing subjects within each stress level, with significant
results shown in bold font.
related over time for all stresses (Figure 2). Average
speeds for 4 to 78 kPa showed a logarithmic
relation (R2
on speed (partial η2
for teeth moved by 26 and 78 kPa versus 13 kPa
(Table 1).
= 0.962), where stress had a large effect
= 0.376), and teeth moved by
the two highest compared with the two lowest
stress levels moved significantly faster (Figure 3;
all P ≤ .022). Side effects of extrusion, labial crown
torque, and distal crown tip fluctuated over time,
were relatively small, and at the end of the study averaged
0.15 ± 1.45 mm, −1.29° ± 5.66°, and 2.39° ±
4.50°, respectively. Distopalatal rotations were also
relatively small for stresses ≤52 kPa (3.86° ± 6.83°)
but were notably larger for teeth moved by 78 kPa
(18.03° ± 9.50°).
The average speeds of distolateral tooth movement
overall for G versus NG subjects were 1.86 ± 0.78
versus 1.23 ± 0.57 mm/month, which was significantly
different (P = .001). For applied stresses of 13,
26, and 78 kPa, teeth in G versus NG subjects moved
significantly faster (Table 1, all P ≤ .046). Because
growth status was a significant factor, the 72 teeth
moved in G subjects were analyzed separately and
showed that stress had a large effect on the speed
of tooth movement (partial η2
= 0.495), where
speeds were significantly faster (all P < .0001) for
teeth moved by 26, 52, and 78 kPa versus 4 kPa and
Discussion
This study series measured the three-dimensional
movement of 92 maxillary canines in 46 subjects
using controlled and quantified mechanics for distolateral
maxillary canine translation with definitive
posterior anchorage. The range of applied stresses
of 4, 13, 26, 52, and 78 kPa were equivalent to
average applied forces of 18, 60, 110, 240, and 360
cN (~gm-force). For question 1 (how is the speed
of tooth translation affected by stress magnitude?),
the results showed that the effect is logarithmic (R2
= 0.962); stress magnitude explained 38% of the
variability in speed, independent of sample size
(partial η2
= 0.376), and teeth moved by 26, 52, and
78 kPa (approximately 110-360 cN) translated faster
distolaterally than teeth moved by ≤13 kPa (≤60
cN). The highest applied stress (78 kPa) showed
faster tooth movement but also notable distopalatal
rotation, outstripping the ligation (stainless-steel
plus elastomeric ties) compared with teeth moved
by the lower stresses. These results support the hypothesis
that the rate of tooth movement increases
with applied stress up to a relatively optimum
magnitude and that further increases do not show
30
PCSO Bulletin Spring 2023

Pacific Coast Society of Orthodontists Bulletin Spring 2023

Table of Contents for the Digital Edition of Pacific Coast Society of Orthodontists Bulletin Spring 2023

Pacific Coast Society of Orthodontists Bulletin Spring 2023 - 1
Pacific Coast Society of Orthodontists Bulletin Spring 2023 - 2
Pacific Coast Society of Orthodontists Bulletin Spring 2023 - 3
Pacific Coast Society of Orthodontists Bulletin Spring 2023 - 4
Pacific Coast Society of Orthodontists Bulletin Spring 2023 - 5
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