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Computer Aided Surgery
3:108 ?114 (1998)
Clinical Paper
Accuracy of Cephalometric and Video Imaging
Program Dentofacial Planner Plus? in Orthognathic
Surgical Planning
Gu?nter Schultes, M.D., D.D.S., Alexander Gaggl, M.D., D.D.S., and Hans Ka?rcher, M.D., D.D.S., Ph.D.
Clinical Department of Oral and Maxillofacial Surgery, University Hospital, Graz, Austria
ABSTRACT The prediction of profile changes after surgery poses a problem due to the variability
of the soft tissue and the differences in soft-tissue translations relative to osseous changes. This study
examined the accuracy of computer predictions of such soft-tissue changes. Twenty-five patients
with mandibular retrognathia were examined before and after orthognathic surgery. Changes in
soft-tissue reference points were correlated to translations of hard-tissue references in the sagittal
and vertical planes, and the measurements from these patients were compared to results predicted
in preoperative planning by the cephalometric and video imaging program Dentofacial Planner?. In
surgical treatment involving advancement of the mandible, the mean operative advancement of the
osseous pogonion was 6.06 mm. The corresponding movements of soft-tissue references, expressed
as percentages relative to the movement of the osseous pogonion in the sagittal plane, were 98.4%
for the soft-tissue pogonion, 93.6% for the soft-tissue menton, and 49.0% for the soft-tissue labral
inferior. The same measurements were carried out in the vertical plane and the changes in soft-tissue
references were compared to those predicted in preoperative planning using the Dentofacial Planner?. The predicted images were perceived as agreeing with the actual image most frequently in the
lip and nasal area, while the highest degree of error was seen in the submental region. An overall
predictability of more than 80% can be attained by planning mandibular advancement operations for
correction of mandibular retrognathia using the Dentofacial Planner?. Comp Aid Surg 3:108 ?114
(1998).
�98 Wiley-Liss, Inc.
Key words: video imaging, orthognathic surgery, accuracy
INTRODUCTION
The accurate prediction of profile changes following orthognathic surgery is problematic because of
the variability of the soft tissue and the differences
in soft-tissue translations relative to osseous
changes. Numerous studies were published about
the predictability of profile changes in relation to
osseous translations.2? 4,6 ?13,16,17,22 These studies
were based on manually repositioning acetate trac-
ings of skeletal segments over the original cephalometric tracing in order to simulate the proposed
treatment.13 The posttreatment soft-tissue outline
was then added, based on accepted ratios of softtissue to hard-tissue changes. Currently, the prediction technique often involves using a digitized
image of a lateral cephalometric tracing in conjunction with a video image of the patient.11,19,20,23,24
Received original December 11, 1997; accepted July 27, 1998.
Address correspondence/reprint requests to: Dr. D. Gu?nter Schultes, Clinical Department of Oral and Maxillofacial Surgery,
Auenbruggerplatz 7, A-8036 Graz, Austria.
�98 Wiley-Liss, Inc.
Schultes et al.: Orthognathic Surgical Planning
The orthodontic and surgical predictions produced
from the digitized cephalometric tracing are combined with the video image so that the prediction
includes a line drawing and a corresponding facial
image.18,20,21 Images of treatment options can then
be displayed on the computer terminal.
There are two significant advantages to using
video imaging preoperatively. First, the communication between doctor and patient is facilitated by
involving the patient in the selection of treatment
options; there are fewer surprises, fewer unrealistic
expectations, and a greater ?bonding? between the
doctor and patient during treatment. The second
advantage of video imaging is its ability to aid in
treatment planning19,23,24; it provides the orthodontist and surgeon with a manipulable image so that a
consensus can be reached on the desired soft-tissue
outcome and a decision made as to whether monomaxillary or bimaxillary osteotomies and further
corrections should be performed.
The main question about the predictability of
soft-tissue changes by computer aided planning
concerns its accuracy. Because there are so many
possible differences in profile, depending on the
direction of shift of the mandible and due to postoperative tension with either extension or compression of connective tissue, we asked ourselves
whether our computer planning program could give
a true prediction of the operative outcome. Therefore, the aim of this study was to compare the
actual changes in profile observed following mandibular surgical advancement with the outcome
predicted by the Dentofacial Planner? (Dental Facial Software Inc., Toronto, Canada).
109
Fig. 1. Preoperative cephalogram of a patient with mandibular retrognathia.
diographs were digitized using the Scriptel RDT1212, a transparent, backlit model that can be used
with IBM Software (International Business Machines Corp., Armonk, NY). The manufacturer
specifies an accuracy of ?0.025 in. over the entire
surface and an accuracy of ?0.01 in. and a resolution of 0.001 in. (1000 lines/in.) over the anterior
90% of the digitized area. A Steiner analysis was
produced for each computerized tracing.
While taking each lateral skull radiograph, a
metal device of 10-mm height and 10-mm breadth
was fixed in the glabella abutment. Comparison of
its measurements in reality and on the radiograph
showed that there was no enlargement or reduction
of the real dimensions within a range of error of no
more than 0.1 mm.
PATIENTS AND METHODS
Registration of Operative Changes
in Hard- and Soft-Tissue Structures
Twenty-five patients with skeletal mandibular retrognathia were examined pre- and postoperatively.
The orthodontic treatment of all patients entailed
using a fixed appliance technique. The average
preoperative therapy lasted 26 months, and treatment following surgery lasted 9 months. All patients were ?18 years of age and received a sagittal
splitting of the mandible as described by Obwegeser and Trauner15 and Dal Pont.5
Fifty lateral cephalograms, 25 preoperative
and 25 postoperative, were taken in centric occlusion with the patients? heads fixed in a natural
position by a Siemens Cephalostat (Siemens Medical Systems Inc., Iselin, NJ) and with the lips
relaxed. The cathode to object distance was 5?, and
the object to film distance was 13 cm. Each radiograph was duplicated, and 35 landmarks were permanently marked with pin holes. The marked ra-
Lateral cephalograms were performed preoperatively and 12 weeks postoperatively. Both cephalograms were digitized with the Prescription
Dentofacial Planner? software program25 (Fig. 1)
using the Scriptel RDT-1212. To show the real
operative translations and the relationship of softtissue changes to osseous changes pre- and postoperative cephalograms were superimposed and
changes in hard- and soft-tissue references in the
sagittal and vertical planes were recorded. The sagittal translations were registered parallel to the NSe
line (nasion-sella-entrance line), and the vertical
translations were registered perpendicular to this.
Initially, the sagittal and vertical translations were
registered in the region of hard-tissue structures
such as the pogonion (oss. po), menton (oss. men),
B point (B pt.), incisal point in the maxilla and
mandible (inc. max. and inc. mand.), and the spina
110
Schultes et al.: Orthognathic Surgical Planning
Fig. 2. Preoperative lateral video image of the same patient with mandibular retrognathia.
nasalis anterior. Similarly, the translations in relation to soft-tissue references, such as the pronasal
(pronas.), subnasal (subnas.), stomion (sto), superior labral (lab. sup.), inferior labral (lab. inf.),
soft-tissue pogonion (po. soft), and soft-tissue menton (men. soft) were recorded. Changes of softtissue reference points were correlated to translations of three hard-tissue references; the oss. po,
oss. men., and inc. mand. in the sagittal and vertical
plane. The percentage relationships of relative position alterations were calculated and standard deviations determined. Thus, the basic translations of
hard- and soft-tissue structures could be demonstrated in all patients.
Registration of Differences in Computer
Aided Planning and Real
Postoperative Profile
On the basis of preoperative cephalograms and
profile videos, preoperative video imaging (Figs. 2,
3) was performed in order to plan the surgical
treatment by simulating the posttreatment profile
situation. This simulated cephalogram was superimposed on the postsurgical one, and the hardtissue cephalometric prediction was superimposed
on the digitized posttreatment hard-tissue cephalogram (Fig. 4). Thus, with the computerized hardtissue prediction and the actual hard-tissue final
result superimposed (Figs. 5, 6), it was possible to
compare and analyze the line drawings of cephalometric soft-tissue outlines in order to determine the
accuracy of the soft-tissue line-drawing prediction
(Fig. 4). Furthermore, it was possible to compare
the preoperative, planned, and postoperative profile
by video imaging (Fig. 7).
Fourteen linear soft-tissue measurements
(Fig. 4) were obtained from the digitized posttreat-
Fig. 3. Superimposition of the cephalogram to the lateral
video imaging preoperatively. Hard structures are demonstrated in correlation to soft-tissue structures.
ment cephalogram and from the prediction line
drawing. The differences between the actual posttreatment soft tissue and the predicted posttreatment soft-tissue line drawing were analyzed in the
sagittal and vertical planes in order to show the
differences between the computer predictions and
the actual outcomes.
Soft-Tissue Prediction Algorithms
of Dentofacial Planner Plus
Dentofacial Planner Plus (DFP Plus) is a software
application that allows clinicians to link digitized
lateral cephalograms to lateral facial images and
visualize facial soft-tissue responses to orthodontic
treatment and orthognathic surgery. DFP Plus simulates soft-tissue changes using a proprietary series
of algorithms developed by Dentofacial Software
Inc. and based on retrospective studies of predictive
reliability. Earlier versions of DFP Plus used a
Fig. 4. Preoperative computer aided planning of mandibular advancement. The picture shows the predicted changes
of soft-tissue and hard-tissue structures.
Schultes et al.: Orthognathic Surgical Planning
111
Fig. 5. Superimposition of the cephalogram to the lateral
video imaging postoperatively. New positions of hard-tissue
structures in correlation to soft-tissue structures are demonstrated.
predictive model wherein ratios or linear regression
equations were used to predict the location of softtissue landmarks relative to hard-tissue change. The
current version of DFP Plus employs a nonlinear
predictive approach, using a pattern-recognition
scheme to categorize the class of facial deformity
and then establish movement thresholds prior to
which little or no soft-tissue change may be elicited. This nonlinear approach is used for predicting
soft-tissue response to maxillary surgery, mandibular rotational changes, mandibular advancement
and setbacks, and genioplasties.
Accuracy of Cephalometric Radiographs
and Measurements
While taking each lateral skull radiograph, a metal
device of 10-mm height and 10-mm breadth was
fixed in the glabella abutment. Comparison of the
measurements in reality and on the radiograph
Fig. 7. The hard- and soft-tissue cephalometric primary
landmarks and the horizontal and vertical reference lines. N,
soft tissue nasion; Ns, pronasal; Snu, subnasal upper; Sn,
subnasal; Ls, labral superior; Stos, stomion superior; Stoi,
stomion inferior; Li, labral inferior; sBu, soft-tissue B upper; sB, soft-tissue B; sBl, soft-tissue B lower; sPg, softtissue pogonion; sGn, soft-tissue gnathion; sMe, soft-tissue
menton.
showed that there was no enlargement or reduction
of the real dimensions within a range of error of no
more than 0.1 mm. The main error was that resulting from the reproduction of cephalometric landmarks. After marking the same cephalogram 25
times a mean error of 0.4 mm was recorded in the
menton, but in all other points the error was low.
The precision of the digitizer itself is high with a
resolution of 1000 lines/in.
RESULTS
Registration of Operative Changes
in Hard- and Soft-Tissue Structures
Fig. 6. Video images of the preoperative, planned, and
postoperative profile.
The mean ventral displacement for all patients was
6.06 mm for the osseous pogonion, 6.19 mm for the
osseous menton, and 5.05 mm for the lower incisal
point. In the vertical plane, the caudal dislocation
of the oss. po. was 3.48 mm, that of the oss. men.
was 2.96 mm, and that of the inc. mand. was 2.90
mm (Table 1). For confirmation purposes, the accuracy of the superimposition translation of the
anterior nasal spine and the inc. max. was determined and found to be congruent up to two decimal
places.
Following translation of the osseous pogo-
112
Schultes et al.: Orthognathic Surgical Planning
Table 1. Direction and Extent of Movement
of Osseous and Soft Tissue Structures with
Mandibular Advancement
Ventral
Osseous transposition (mm)
Spina nasalis anterior
Incisal point, maxilla
Osseous pogonion
Osseous menton
Incisal point, mandible
Caudal
0
0
6.06
6.19
5.05
Ventral
Soft-tissue transposition (mm)
Pronasal
Subnasal
Stomion
Labral superior
Labral inferior
Pogonion (soft)
Menton (soft)
0
0
2.73
1.78
2.96
6.15
5.65
Table 3. Mean Differences between
Predicted and Actual Line Drawing SoftTissue Values
0
0
3.48
2.96
2.90
Caudal
Cranial
0
0
0.9
1.15
1.46
2.71
3.13
N
Ns
Snu
Sn
Ls
Stos
Stoi
Li
sBu
sB
sBl
sPg
sGn
sMe
Sagittal
(mm)
SD
Vertical
(mm)
SD
0
0.16
0.38
0.11
0.16
0.16
0.16
0.66
1.00
1.16
1.22
1.44
1.55
1.55
0
0
0
0
0.39
0.49
0.58
0.83
1.06
1.09
1.22
1.10
1.04
1.07
0
0
0.44
0.27
0
0
0.11
0.11
0.27
0.33
0.38
0.166
0.72
1.00
0
0
0
0
0.51
0.70
0.88
0.93
1.43
1.15
1.34
1.24
1.30
1.38
N, soft tissue nasion; Ns, pronasal; Snu, subnasal upper; Sn, subnasal; Ls,
labral superior; Stos, stomion superior; Stoi, stomion superior; Li, labral
inferior; sBu, soft-tissue B upper; sB, soft-tissue B; sBl, soft-tissue B lower;
sPg, soft-tissue pogonion; sGn, soft-tissue gnathion; sMe, soft-tissue Menton.
nion, the relative soft-tissue changes in the sagittal
plane were 98.4% for the soft-tissue pogonion,
93.6% for the soft-tissue menton, 29.6% for the
labral superior, 45.2% for the stomion, and 49.0%
for the labral inferior (Table 2). The relationships
of these soft-tissue references to the osseous menton (oss. men.) and lower incisal point (inc. mand.)
in the sagittal plane are also recorded in Table 2.
Upon correction of mandibular retrognathia,
the percentage change for the soft-tissue pogonion
relative to the osseous pogonion in the vertical
plane was 78%. The relative percentage changes
for other soft-tissue references were 90% for the
soft tissue menton, 51% for the labral superior,
26% for the stomion, and 42% for the labral inferior (Table 2). Further percentage changes for soft-
tissue references relative to the osseous menton and
lower incisal point are also recorded in Table 2.
Registration of Differences in Computer
Aided Planning and Real
Postoperative Profile
The mean difference between actual postsurgical
and predicted line drawing soft-tissue values is
recorded in Table 3. The predicted images were
perceived as agreeing with the actual image most
frequently in the upper lip and nasal area, while the
labiomental fold and mental areas showed the poorest correlation with a mean error of 1.5 mm. Overall lower differences but higher standard deviation
Table 2. Percentage Distribution of Soft-Tissue Versus Osseous Transposition after Mandibular
Advancement
Changes in sagittal
relationship
po. (soft)/oss. po.
sto./oss. po.
lab. sup./oss. po.
lab. inf./oss. po.
men. (soft)/oss. po.
Changes in vertical
Relationship
lab. sup./oss. po.
sto./oss. po.
lab. inf./oss. po.
po. (soft)/oss. po.
men. (soft)/oss. po.
Percent
s
98.4
45.2
29.6
49.0
93.6
7.3
6.4
6.5
6.9
7.2
11.3
12.0
11.1
8.9
12.3
51
26
42
78
90
Percent
s
Percent
s
men. (soft)/oss. men.
po. (soft)/oss. men.
lab. inf./oss. men.
sto./oss. men.
lab. sup./oss. men.
91.3
99.3
47.8
44.0
28.8
6.4
6.7
7.0
5.7
6.3
lab. sup./inc. mand.
sto./inc. mand.
lab. inf./inc. mand.
po. (soft)/inc. mand.
men. (soft)/inc. mand.
35
54
58
82
89
8.1
7.3
7.5
7.4
7.7
lab. sup./oss. men.
sto./oss. men.
lab. inf./oss. men.
po. (soft)/oss. men.
men. (soft)/oss. men.
39
30
49
92
94
12.4
11.4
12.1
12.4
14.3
lab. sup./inc. mand.
sto./inc. mand.
lab. inf./inc. mand.
po. (soft)/inc. mand.
men. (soft)/inc. mand.
40
31
50
93
93
13.3
12.5
11.9
10.8
14.3
Schultes et al.: Orthognathic Surgical Planning
were noted in the vertical plane. In contrast to this,
there were higher values but lower standard deviation in the sagittal plane.
Statistics
The paired t test was employed to determine the
significance of the stated relationships. The determined values were plotted according to the probability net. For every average value, the standard
deviation (s) was determined as shown in Tables 2
and 3. By means of the paired t test, the concordance of the calculated averages and standard deviations was compared to the actual postoperative
average. A change in the sagittal relationship was
found, revealing a probability of error of p ? 0.15.
For changes in the vertical relationship, a slightly
lower probability of error of p ? 0.1 was determined.
DISCUSSION
It is still problematic to give a prognosis of the
postoperative profile of patients undergoing orthognathic surgery that is due to the differences
in soft-tissue translations relative to osseous
translocations. The assumption of a 1:1 relationship of osseous to soft-tissue references is actually only valid near the pogonion. Several investigators2? 4,8,12,14,16 reported this when examining
the chin regions of patients following mandibular
advancement.
In our study a relationship of 0.98:1.0 was
determined upon comparing soft- and hard-tissue
pogonion in patients after mandibular advancement. The main error of the computer prediction
was about 20% in the sagittal plane. Thus, the
Dentofacial Planner? showed a larger and more
protrusive prediction than the actual value in the
chin area. The more caudal the reference point, the
larger and more protrusive the value became. This
was contrary to the results of Sinclair et al.21 who
demonstrated the greatest probability of errors in
the upper lip region using the video imaging program Prescription Planner/Portrait software (Rx
Data Inc., Ooltewah, TN). In our study the cranial
reference points showed a low margin of error
when using the DFP Plus. The midface and upper
lip region showed an error of less than 0.2 mm and
the lower lip region an error of 0.6 mm, demonstrating a high significance of prediction for the lip
area. Lines and Steinha?user12 found a ratio of 0.67:
1.0 and Mommerts and Marxer14 reported a ratio of
0.55:1.0 for the lower lip after operative mandibular advancement, but our study showed an even
smaller ratio for similar patients. We recognized a
113
lesser degree of sagittal movement in the lip area
and therefore a higher predictability of soft-tissue
changes compared to the chin region. This difference was confirmed by the relation of the lower
incisal point and the labral inferior. The absolute
values of the changes in stomion relation were
found to lie between the average values of the
superior and inferior labral in the sagittal plane.
In the vertical plane different percentages
were found for the relationship of soft-tissue to
hard-tissue references: with a ratio of 0.92:1.0 there
was a strong relative dependency of upper lip position on the vertical position of the osseous pogonion, the lower lip following the osseous pogonion
in a ratio of 1:1 after operative mandibular advancement. Here again the prediction in the pogonion area was very accurate. Furthermore, there
was a lower level of mean error in the vertical plane
than in the sagittal plane, comparing all reference
points. Only in the submental area could errors
greater than 0.5 mm be recorded. This may be
explained by the thickness of the soft-tissue structures that were being stretched in this area, making
prediction more difficult.
Significant changes in lip contour were found
postoperatively, as well as a new configuration of
the chin. For operative mandibular advancement,
the soft tissue structures of the pogonion and menton followed the corresponding osseous references
in ratios of less than 1:1 (0.78:1.0 and 0.94:1.0,
respectively). In video imaging contour changes in
chin area in comparison to preoperative chin contour were not as severe as in postoperative reality.
The reason for this may be the relatively high
probability of prediction errors in the submental
area, which can be explained by the high portion of
fat tissue in this region. Therefore, it seems to be
difficult to predict movements in fat tissue following mandibular translocation but muscular displacement should be easier to predict; this was
demonstrated in the lip region where a closer correlation of video imaging and postoperative situation was recorded in the lip contour. In contrast to
our experiences with the DFP Plus, Sinclair et al.21
reported better predictability for the chin region
using another planning program produced by Rx
Data Inc., although they did not discuss submental
changes.
It can be concluded that mandibular advancement in correction of mandibular dysgnathia results
in significant changes in the lower face, which can
be predicted in the vertical and horizontal plane
with only a small degree of error, provided that
transduction of cephalograms has been performed
114
Schultes et al.: Orthognathic Surgical Planning
accurately, as shown by Baskin and Cisneros.1 This
statement is valid for the DFP Plus and the Quick
Ceph program (Orthodontic Processing, Coronado), according to Baskin and Cisneros,1 because
the reliability and reproducibility of landmarks is
similar in both programs. Overall, a predictability
of more than 80% can be stated. The highest degree
of error was determined to occur in the submental
area, and the error grows as the extent of mandibular advancement increases. The less the soft tissue
structures follow this advancement, the smaller the
error. Exceptions to this statement in bimaxillary
and further complex osteotomies should be examined in the future. For an accurate prediction of all
changes in the face, a 3-dimensional examination
must be performed, so differences between our
results and those reported elsewhere in the literature could have arisen because a 2-dimensional
examination cannot explore a 3-dimensional movement and its consequences.
11.
12.
13.
14.
15.
16.
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