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

to adjust for experimentwide error by reducing our desired
significance level to 0.001.
Measurements
Table 1 Mean values of the two face-bow techniques.
Table 1 shows the means and standard deviations for
the arbitrary face-bow technique and the true hinge facebow
technique in the vertical, A-P, and transverse dimensions
with respect to the maxillary right and left first molars and
the maxillary right central incisor. The mean measurements
taken on the cast mounted with a true hinge face-bow were
significantly smaller than those measured on the arbitrary
earpiece face-bow mountings. The standard deviations for
the true hinge face-bow were also one-half to one-third
smaller, indicating less variation around the sample mean.
Results of the paired t-test are shown in Table 2.
Table 2 Paired t-tests for differences between
estimated and true hinge technique.
The two face-bow techniques differed significantly in
all three planes of space. The mean vertical discrepancy of
the maxillary right first molar between the estimated and the
true hinge face-bow was 2.19 +/- 2.31 (t = 6.76, df = 50, p
< .001). The mean vertical discrepancy for the maxillary left
first molar was 2.45 +/- 2.21 (t = 7.90, df = 50, p < .001).
The mean vertical discrepancy for the upper right central
was 1.90 +/- 1.75 (t = 7.76, df = 50, p < .001).
The mean difference in the A-P dimension was 3.82 +/-
5.51 (t = 8.163, df = 50, p < .001) for the maxillary right first
molar and 3.10 +/- 2.63 (t = 8.28, df = 50, p < .001) for the
maxillary left first molar. The maxillary right central incisor
showed a mean difference of 3.05 +/- 2.62 (t = 8.25, df = 50,
p < .001). Finally, the transverse dimension was evaluated.
The mean difference for the maxillary right first molar was
2.23 +/- 1.33 (t = 12.11, df = 50, p < .001). The mean differ-
ence for the maxillary left first molar was 2.60 +/- 1.49 (t =
11.57, df = 50, p < .001).
The measurement differences in the vertical direction of
the maxillary right first molar ranged from 0.0 to 3.0 mm.
The measurement differences in the vertical direction of the
maxillary left second molar ranged from 1.0 mm to 3.0 mm.
The measurement differences in the vertical direction of the
maxillary upper right central incisor ranged from 0.0 to 5.0
mm. The differences in the A-P dimension of the upper right
molar ranged from 0.0 to 13.1 mm; of the upper left molar
from 0.0 to 15.0 mm; and of the upper central incisor from
0.0 to 13.0 mm. The differences in the transverse dimension
ranged from 0.0 to 7.0 mm for the upper right first molar
and from 0.5 to 7.9 mm for the upper left first molar.
Discussion
Mounting dental casts on an articulator allows the clinician
to simulate maxillo-mandibular position in centric relation
and makes possible a visible simulation of mandibular border
movements. It has been recommended that mounting
diagnostic dental casts on an articulator should be incorporated
into routine clinical orthodontic practices. 3,46 Recording
the hinge axis and transferring it to an articulator is of
considerable value in the diagnosis and treatment of occlusal
malfunction. 42 In this diagnostic process, a face-bow transfer
is one of the first steps in taking accurate intermaxillary
records. Many face-bow techniques are in use today. 20,21
However, this study conducted a comparison of only two
face-bow techniques, an arbitrary earpiece face-bow and a
true hinge face-bow.
The null hypothesis for this study: “There is no difference
in the vertical, horizontal, or transverse position of the
maxillary cast mounted with a true hinge face-bow versus an
arbitrary earpiece face-bow” was rejected. Paired t-tests indicated
that the maxillary cast position using an arbitrary facebow
transfer was significantly different in all three planes of
space from the maxillary cast position mounted using a true
hinge face-bow transfer.
In previous comparison studies when the arbitrary earpiece
face-bow is located anywhere along a 5-mm radius of
the true hinge axis point, some authors have found that the
mandibular arc of closure may not be very different from the
true hinge arc of closure. 21,26,39,40,42 However, Lauritzen and
Bodner found that in only 33% of the 50 patients they examined
did the arbitrary hinge point fall within 5 mm of the
true hinge point. In the other 67%, the arbitrary hinge points
were 5 mm to 13 mm away from the true hinge points. Arbitrary
markings of the hinge axis introduce severe errors
in mounting casts on an articulator, which may introduce
occlusal errors in the centric jaw relation record. 30 Ricketts
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