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YIJOM-3747; No of Pages 10
Int. J. Oral Maxillofac. Surg. 2017; xxx: xxx–xxx
http://dx.doi.org/10.1016/j.ijom.2017.07.004, available online at http://www.sciencedirect.com
Clinical Paper
Pre-Implant Surgery
Virtual quad zygoma implant
placement using cone beam
computed tomography:
sufficiency of malar bone
volume, intraosseous implant
length, and relationship to the
sinus according to the degree of
alveolar bone atrophy
J. Bertos Quı́lez,
R. Guijarro-Martı́nez,
S. Aboul-Hosn Centenero,
F. Hernández-Alfaro
Department of Oral and Maxillofacial Surgery,
International University of Catalonia, Sant
Cugat del Vallés, Barcelona, Spain
J. Bertos Quı́lez, R. Guijarro-Martı́nez, S. Aboul-Hosn Centenero, F. HernándezAlfaro: Virtual quad zygoma implant placement using cone beam computed
tomography: sufficiency of malar bone volume, intraosseous implant length, and
relationship to the sinus according to the degree of alveolar bone atrophy. Int. J. Oral
Maxillofac. Surg. 2017; xxx: xxx–xxx. ã 2017 International Association of Oral and
Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. The objective of this study was to investigate the malar bone volume and
length that a zygomatic implant can engage, and the relationship to the sinus
according to the degree of alveolar bone atrophy. A three-dimensional evaluation
was performed using cone beam computed tomography scans from 23 patients with
a totally edentulous maxilla; quad zygoma implants were virtually placed. The
predictor variable was the amount of malar bone volume and length that a
zygomatic implant can engage. The primary outcome variable was the relationship
to the sinus according to the degree of alveolar bone atrophy. Other variables were
the residual alveolar bone height to the floor of the sinus and the nasal cavity. The
mean volume of malar bone engaged in this sample of 92 zygomatic implants was
0.19 0.06 cm3. The implant had an extrasinus path in 60.9% of cases, a parasinus
path in 25%, and an intrasinus path in 14.1%. The results suggest that the average
volume of malar bone engaged by a zygomatic implant is constant regardless of
implant position and the degree of alveolar bone atrophy. As alveolar atrophy
increases, the trajectory of the implant becomes more parasinus and intrasinus. The
0901-5027/000001+010
ã 2017 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone
YIJOM-3747; No of Pages 10
2
Bertos Quı́lez et al.
examiners were able to find enough bone to adequately distribute the implants in all
cases.
Accepted for publication
Key words: zygoma implant; malar bone volume engaged; zygoma implant path; zygoma
implant relationship to the sinus.
Since the introduction of zygoma implants
by Brånemark in the 1990s1, several technical modifications have been proposed in
response to the disadvantages observed2–4.
These disadvantages relate to the path of
the implant, in which the platform
emerges in the palatal cortical bone of
the alveolar crest, thus rendering prosthetic rehabilitation uncomfortable, not only
for the clinician but also for the patient. It
is well acknowledged that a palatal emergence of a zygomatic implant implies
compromised cleaning and diction, which
in turn lead to a suboptimal rehabilitation
for the patient5.
With the aim of resolving this problem,
the placement of zygoma implants is now
prosthetically driven, and the emergence
of the platform, as well as the path that the
implant takes, has been modified. The
placement of the implant platform in a
more suitable position for rehabilitation
has altered the relationship between the
implant and the sinus, with the implant
being outside the sinus (extrasinus) in
most cases6,7. This has also changed the
relationship between the implant platform
and the residual alveolar crest. In fact, this
relationship is sometimes non-existent
depending on the class of alveolar bone
atrophy, as described in the literature8.
A number of study groups have focused
on the surgical technique and subsequent
modifications4,9, number of implants per
quadrant, and surgical and prosthetic complications10, but little is known about the
path of a zygomatic implant and its relationship to the alveolar crest11.
In this context, the main objective of the
present study was to investigate the
amount of malar bone volume and length
that a zygomatic implant can engage, and
the expected relationship of the implant to
the sinus depending on the degree of
alveolar bone atrophy.
Materials and methods
The Research Ethics Committee of the
International University of Catalonia approved this study. Every precaution was
taken to protect the privacy of the research
subjects and the confidentiality of their
personal information.
Radiological sample
The cone beam computed tomography
(CBCT) scans of a sample of 23 patients
with a totally edentulous maxilla were
collected. These CBCT scans had originally been taken for diagnostic purposes.
The patients were recruited from the databases of the International University of
Catalonia and the Institute of Maxillofacial Surgery at the Teknon Medical Centre
(Barcelona). The CBCT scans were
obtained with an i-CAT Cone Beam 3D
Imaging device (Imaging Sciences International, Inc., Hatfield, PA, USA) with
settings of 120 kVp, 8 mA, voxel size
0.4 mm, and a field of view of
27 14 cm.
Inclusion criteria
Patients with a fully edentulous maxilla
and with alveolar bone atrophy due to
tooth loss corresponding to class IV or
V of the classification of Cawood and
Howell were recruited12. Patients in whom
tooth loss had occurred as a result of
maxillofacial trauma or oncological resection surgery were excluded. Furthermore,
patients with alveolar bone atrophy of
class VI of the Cawood and Howell classification were also excluded.
Determination of the type of bone
atrophy (Cawood and Howell
classification)
The classification of alveolar bone atrophy
was determined according to the reference
points used in the study by Cawood and
Howell12 (Fig. 1).
A variable point ‘C’ (crest of the alveolar process) and two constant points
marked at the limit between the basal bone
and the alveolar bone labelled ‘I’ (incisive
foramen) for the anterior maxilla and ‘GP’
(greater palatine foramen) for the posterior
maxilla were identified. The distance between ‘I’ and ‘C’ and between ‘GP’ and
‘C’ allowed the determination of the precise type of alveolar bone atrophy.
A residual knife-edge ridge form that
was inadequate in width and greater than
5 mm in height was categorized as class
IV alveolar bone atrophy, and a residual
flat-ridge ridge form that was inadequate
Fig. 1. Determination of alveolar bone atrophy according to the classification of Cawood
and Howell: (a) the anterior sector; (b) the
posterior sector.
in width and less than 5 mm in height
without evident basilar loss was categorized as class V alveolar bone atrophy.
Sample preparation
Simplant Pro 16.0 software (Simplant,
Dentsply Sirona, Iberia) was used to simulate zygomatic implant placement. This
process begins with the selection of an
area of interest mask and the exclusion of
the remaining CBCT data in order to make
virtual implant planning simpler.
The mask limits were set as follows
(Fig. 2): (1) the anterior limit was set in
the coronal plane and was located at the
level of the anterior nasal spine (ANS); (2)
the posterior limit was set in the coronal
plane and was located immediately distal
Fig. 2. Delimitation of the mask in a 3D
model.
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone
YIJOM-3747; No of Pages 10
Virtual quad zygoma implant placement using CBCT
to the pterygoid plates; (3) the cranial limit
was set in the axial plane and was located
at nasion; (4) the caudal limit was set in
the axial plane and was located immediately inferior to the alveolar crest of the
upper maxilla; (5) the lateral limits were
set in the sagittal plane and were located at
the zigion points bilaterally.
A defined specific type of tissue to be
included in the mask was set with the
thresholding tool, which uses the Hounsfield unit (HU) level. This level ranges
from a minimum of 250 HU to a maximum
of 3071 HU, which is established by default as bone. Once the mask and the type
of tissue were defined, a high quality 3D
model was created.
Fig. 4. 3D model of the mask. Occlusal view,
in which the ideal emergence of the prosthetic
implants is in the alveolar ridge. Anterior
implants Z1 and Z3 emerge in an upper lateral
incisor/canine position and posterior implants
Z2 and Z4 emerge in an upper first or second
premolar position.
Virtual implant planning
Four zygoma implants were virtually
placed in each case. The panoramic curve
was used as the basis for panoramic and
sectional view calculations of implant
placement. Once this step had been accomplished, zygoma implants were
planned according to the anatomical insertion guidelines of Rossi et al. and Rigolizzo et al.13,14 (Figs 3 and 4).
The specific position (anterior or posterior) and quadrant (first or second) of each
zygomatic implant were described using
the following nomenclature: Z1 was the
first quadrant anterior implant, corresponding to the approximate position of
the upper right lateral incisor (#12) or
upper right canine (#13); Z2 was the first
quadrant posterior implant, corresponding
to the approximate position of the upper
right first or second premolar (#14 or #15);
Z3 was the second quadrant anterior implant, corresponding to the approximate
position of the upper left lateral incisor
(#22) or the upper left canine (#23); Z4
was the second quadrant posterior implant, corresponding to the approximate
position of the upper left first or second
premolar (#24 or #25).
Volume of malar bone engaged by the
implant
The ‘draw a volume’ tool enabled the
alignment of the implant perimeter in
the axial, sagittal, and coronal planes
along the portion of the zygoma implant
located within the malar bone. Once every
section of the implant had been aligned, a
high-quality 3D model (the highest possible quality that the software can create)
representing the volume of malar bone
engaged by the zygoma implant (in cubic
centimetres, cm3) was generated. The soft-
3
Fig. 3. 3D model of the mask. (a) Front view
of four zygoma implants placed, two per
quadrant, according to the anatomical insertion guidelines of Rossi et al. 2008. For the
anterior implants (Z1 and Z3), the initial
drilling point is the lowermost point of the
alveolar crest, taking a line from the lateral
margin of the nasal incisure; the final drilling
point is the lowermost point on the lateral
margin of the orbital socket. For the posterior
implants (Z2 and Z4), the initial drilling point
is the lowermost point of the alveolar crest,
taking a line at a tangent to the lateral margin
of the infraorbital foramen; the final drilling
point is located one-third of the distance between the lowermost point of the lateral margin of the orbital socket and the lowermost
point of the zygomaticomaxillary suture. (b)
Three-quarter view of first quadrant implants
Z1 and Z2 according to the anatomical anchorage guidelines of Rigolizzo et al. 2005.
Sections 5, 6, 8, and 9 are described as the
sections with the best potential for implant
anchorage. In this case, implants are anchored
in sections 8 and 9.
‘see the centric implant image’ tool enabled the evaluation of the implant in its
longitudinal axis and its relationship with
the maxillary sinus.
The reference lines on a 2D image are
shown in Fig. 7. These included the implant longitudinal axis and lines parallel to
the axial plane.
The reference points are shown in
Fig. 8. These were Za, corresponding to
the implant apex; Zb, following the im-
ware also provided the mean HU value for
this portion of bone (Figs 5 and 6).
Relationship of the zygoma implant to
the sinus according to the degree of
alveolar bone atrophy
Along its path, the implant is associated
with the maxillary sinus in different ways.
Specific reference points were defined to
establish which portions of the implant
were associated with the sinus and in what
way. These points were located at the
intersection of two axes or lines (Figs 7
and 8).
All measurements were performed on
two-dimensional (2D) CBCT images. The
Fig. 5. 2D images in the (a) frontal, (b) axial,
and (c) sagittal planes, in which the delimitation (in green) of each section of the zygoma
implants can be seen. These were used to
calculate the volume of malar bone engaged.
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone
YIJOM-3747; No of Pages 10
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Bertos Quı́lez et al.
Fig. 8. Reference points on a 2D image: point
Za (blue point), point Zb (red point), point Zc
(orange point), point Zd (green point), and
point Ze (brown point). (For interpretation
of the references to colour in this figure legend, the reader is referred to the web version
of this article.)
Fig. 6. Sequence of 3D images showing the
volume of malar bone engaged by the zygoma
implants. (a) The implants placed and the
malar bone volume engaged highlighted in
green, surrounding approximately the apical
third. (b) To determine the volume of malar
bone engaged, the implants are first hidden.
(c) The mask is then hidden so that only the
malar bone volume engaged by the zygoma
implants can be seen.
plant insertion path, corresponding to the
intersection between its longitudinal axis
and a line parallel to the axial plane at the
level where the implant penetrates the
malar bone; Zc, following the implant
insertion path, corresponding to the intersection between its longitudinal axis and a
line parallel to the axial plane at the level
Fig. 7. Linear references on a 2D image:
longitudinal axis of the implant (blue) and
lines parallel to the axial plane (green). (For
interpretation of the references to colour in
this figure legend, the reader is referred to the
web version of this article.)
where the implant penetrates the maxillary
sinus; Zd, following the implant insertion
path, corresponding to the intersection
between its longitudinal axis and a line
parallel to the axial plane at the level
where the implant leaves the alveolar
ridge; and Ze, corresponding to the implant platform.
The intra-malar length (length of the
implant within the malar bone) was defined as the distance between Za and Zb.
The intrasinus length was defined as the
distance between Zb and Zc. The parasinus
length was defined as the distance between
Zb or Zc and Zd or Ze. The extrasinus
length was defined as the distance between
Zb or Zc and Zd or Ze.
When categorizing the path of each
implant as intrasinus, parasinus, or extrasinus, it was established that the implant
had to have at least 50% of its diameter
associated with the maxillary sinus as
follows: (1) extrasinus path: the implant
is outside the maxillary sinus and has no
contact with the lateral wall, or this contact is at most less than the lateral 50% of
its diameter (Figs 9 and 10); (2) parasinus
path: the implant is in contact with the
lateral wall of the maxillary sinus in 50%
(either lateral or medial) of its diameter
(Figs 11 and 12); (3) intrasinus path: the
implant is inside the maxillary sinus without any contact with the lateral wall or at
most less than 50% of its diameter (Figs 13
and 14).
After measuring the intrasinus, parasinus, and/or extrasinus portions of the implant, the longest portion determined the
category of path for the zygomatic implant
(Fig. 15).
Fig. 9. Implants Z1 and Z2 with an extrasinus
path: (a) Z1 implant showing no relationship
with the lateral wall of the upper maxilla; (b)
Z2 implant showing a relationship with the
lateral wall of the upper maxilla and also with
the maxillary sinus.
Measurement of the residual bone height
to the floor of the maxillary sinus and the
nasal cavity
A cross-section in which the entire implant
platform could be adequately visualized
was identified. The ‘measure distance’
tool was used to measure the linear distance between the most caudal point of the
alveolar crest and the most caudal point of
Fig. 10. 3D image of the Z1 and Z2 implants
seen in Fig. 9.
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone
YIJOM-3747; No of Pages 10
Virtual quad zygoma implant placement using CBCT
5
Fig. 14. 3D image of the Z1 and Z2 implants
seen in Fig. 13.
Fig. 13. (a) Z1 implant and (b) Z2 implant
with an intrasinus path. The implants travel
totally inside the maxillary sinus to anchor in
the malar bone.
Fig. 11. (a) Z1 implant and (b) Z2 implant
with a parasinus path. The implants relate
totally with the lateral wall of the upper
maxilla, passing through the maxillary sinus
to anchor in the malar bone.
the maxillary sinus in the case of a Z2 or
Z4 implant, or of the nasal fossa in the case
of a Z1 or Z3 implant (Fig. 16).
Statistical analysis
The Student t-test for independent samples
was used to compare the mean values of a
given dimension according to the bone
atrophy group. Prior to this, the normality
of the data was corroborated with the
Kolmogorov–Smirnov test. The result of
the t-test was validated, ensuring the homogeneity of the variances with Levene’s
test; Welch’s correction was applied in the
case of deviation.
The Kruskal–Wallis test was used to
study the distribution of alveolar bone
atrophy classes according to the different
paths followed by the zygoma implants.
The association x2 test was used to evaluate the degree of dependence between two
categorical variables, such as implant path
and degree of bone atrophy. For all tests,
statistical significance was set at 0.05.
by
the
implant
was
engaged
0.20 0.06 cm3. Stratified according to
the Cawood and Howell classification of
alveolar bone atrophy, the average volume
malar
bone
engaged
was
of
0.21 0.06 cm3 in class IV and
0.19 0.06 cm3 in class V.
On comparing the volume of malar
bone engaged between class IV and class
V bone atrophy cases, no statistically significant difference was found overall
(P = 0.650), or for the anterior and posterior locations separately (P = 0.559 and
P = 0.184 for anterior and posterior, re-
Results
Volume of malar bone engaged by a
zygoma implant
Fig. 12. 3D image of the Z1 and Z2 implants
seen in Fig. 11.
For the sample of 92 zygoma implants, the
mean volume of malar bone engaged by a
zygoma implant was 0.19 0.06 cm3.
The mean volume of malar bone engaged
according to the implant position (anterior
or posterior) is shown in Table 1. In the
anterior sector (n = 46 anterior implants),
the mean volume of malar bone engaged
by the implant was 0.18 0.05 cm3.
Stratified according to the Cawood and
Howell classification of alveolar bone atrophy, the average volume of malar bone
engaged was 0.18 0.05 cm3 in class IV
and 0.19 0.06 cm3 in class V. In the
posterior sector (n = 46 posterior
implants), the mean volume of malar bone
Fig. 15. (a) 2D image of a Z2 implant: the
intrasinus portion of 18.90 mm is greater in
length than the extrasinus portion of
14.76 mm. (b) 3D image of the same Z2
implant, which clinically seems to have an
extrasinus path.
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone
YIJOM-3747; No of Pages 10
6
Bertos Quı́lez et al.
Table 2. Volume of malar bone (cm3) engaged by the zygoma implant according to the sector
(anterior and posterior) and the Cawood and Howell classification of alveolar bone atrophy
(classes IV and V).a
Total
Anterior sector
Posterior sector
a
b
Class IV
Class V
P-valueb
0.19 0.05 (0.18–0.21)
0.18 0.05 (0.16–0.20)
0.21 0.06 (0.19–0.24)
0.19 0.06 (0.17–0.21)
0.19 0.06 (0.16–0.22)
0.19 0.06 (0.17–0.21)
0.650
0.559
0.184
Results are presented as the mean standard deviation (95% confidence interval).
The t-test was used to compare the means according to the degree of alveolar bone atrophy.
Fig. 17. Volume of malar bone engaged according to the Cawood and Howell classification of
alveolar bone atrophy (classes IV and V), in cubic centimetres.
Fig. 16. (a) Distance to the floor of the maxillary sinus from the alveolar crest. (b) Distance to the floor of the nasal cavity from the
alveolar crest.
spectively) (Table 2). The results are illustrated in Fig. 17.
Intra-malar implant length
The mean intra-malar length for the total
of
92
implants
was
sample
16.95 4.73 mm. The intra-malar length
of the zygoma implant according to the
implant position (anterior or posterior) is
shown in Table 3. In the anterior sector
(n = 46 anterior implants), the mean
length of zygomatic implants situated
the
malar
bone
was
within
17.42 3.74 mm. When categorized
according to the Cawood and Howell
classification of alveolar bone atrophy,
the average intra-malar length was
17.97 4.14 mm in class IV and
16.81 3.24 mm in class V. In the posterior sector (n = 46 posterior implants), the
average length of the zygomatic implant
found within the malar bone was
16.48 5.55 mm. When categorized
according to the Cawood and Howell
classification of alveolar bone atrophy,
the average intra-malar length was
18.51 6.36 mm in class IV and
Table 1. Volume of malar bone (cm3) engaged by the zygoma implant according to the sector
(anterior and posterior) and the Cawood and Howell classification of alveolar bone atrophy
(classes IV and V).
Sector
Anterior
Total
Posterior
Total Class IV Class V Total Class IV Class V Total Class IV Class V
92
Implants, n
Mean
0.19
Standard deviation 0.06
Minimum
0.10
Maximum
0.39
Median
0.18
45
0.19
0.05
0.11
0.34
0.18
47
0.19
0.06
0.10
0.39
0.17
46
0.18
0.05
0.11
0.39
0.17
24
0.18
0.05
0.11
0.28
0.17
22
0.19
0.06
0.12
0.39
0.17
46
0.20
0.06
0.10
0.34
0.19
21
0.21
0.06
0.14
0.34
0.20
25
0.19
0.06
0.10
0.32
0.17
14.78 4.16 mm in class V. Thus, the
mean intra-malar length was greater in
class IV than in class V cases.
On comparing the zygoma implant
intra-malar length between class IV and
class V bone atrophy cases, a statistically
significant difference was found for the
posterior sector (P = 0.028) and for the
total sample (P = 0.011). These results
are summarized in Table 4 and are illustrated in Fig. 18.
Relationship of the zygoma implant to
the sinus
According to the Cawood and Howell
classification of alveolar bone atrophy
Of the whole sample of 92 implants,
60.9% had an extrasinus path (n = 56),
25% a parasinus path (n = 23), and the
remaining 14.1% had an intrasinus path
(n = 13), according to the parameters described in the Materials and methods section (Table 5).
With regard to the class of alveolar bone
atrophy, the following findings were noted
(Table 5): for class IV, of the whole
sample of 45 implants, 77.8% had an
extrasinus path (n = 35), 15.6% had a
parasinus path (n = 7), and 6.7% had an
intrasinus path (n = 3); for class V, of the
whole sample of 47 implants, 44.7% had
an extrasinus path (n = 21), 34.0% had a
parasinus path (n = 16), and 21.3% had an
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone
YIJOM-3747; No of Pages 10
Virtual quad zygoma implant placement using CBCT
Table 3. Zygoma implant intra-malar length (mm) according to the sector (anterior and
posterior) and the Cawood and Howell classification of alveolar bone atrophy (classes IV
and V).
Sector
Anterior
Total
Posterior
Total Class IV Class V Total Class IV Class V Total Class IV Class V
92
45
Implants, n
Mean
16.95 18.22
Standard deviation 4.73 5.24
Minimum
9.26 9.79
Maximum
30.22 30.22
Median
15.82 17.70
47
15.73
3.86
9.26
26.43
14.50
46
24
17.42 17.97
3.74 4.14
12.14 12.14
26.52 26.52
16.52 17.19
intrasinus path (n = 10). The results are
illustrated in Fig. 19.
The association x2 test confirmed that
the difference in the path of the implant
according to the degree of alveolar bone
atrophy was statistically significant
(P = 0.005).
The relationship of the zygoma implant
to the sinus (intrasinus, parasinus, or
extrasinus) according to the sector (anterior and posterior) is shown in Table 6. In
the anterior sector, all cases (100% of the
sample) classified as class IV (n = 24) had
an extrasinus path, compared to 72.7%
(n = 16) of class V cases; the difference
was statistically significant (P = 0.025,
Kruskal–Wallis test). In the posterior sector, a very strong trend towards statistical
significance (P = 0.067, x2 test) was also
detected: in the class IV group, 52.4%
had an extrasinus path compared to only
20% in the class V group.
Hence, as the degree of alveolar bone
atrophy increases, the implant is more
related to the maxillary sinus, acquiring
a parasinus or intrasinus path.
According to the Cawood and Howell
classification of alveolar bone atrophy and
the residual bone height to the floor of the
maxillary sinus and the nasal cavity
Since the Cawood and Howell classification of alveolar bone atrophy is based on a
visual evaluation of the residual alveolar
22
16.81
3.24
12.92
23.76
15.79
46
21
16.48 18.51
5.55 6.36
9.26 9.79
30.22 30.22
14.27 19.63
25
14.78
4.16
9.26
26.43
13.56
ridge and can therefore be subjective, an
attempt was made to objectively quantify
the residual bone. To this effect, the residual alveolar bone height to the floor of the
maxillary sinus and the nasal cavity in the
respective positions of the zygoma
implants was measured. In this way, class
IV and class V alveolar bone atrophy were
related to a specific quantifiable residual
alveolar bone height.
In the assessment of the residual bone
height to the floor of the sinus (n = 46
implants), a mean overall residual alveolar
bone height of 5.83 3.00 mm was measured. When assessed by Cawood and
Howell classification, the mean residual
alveolar bone height for class IV was
7.85 1.99 mm, while for class V this
was reduced to 4.05 2.59 mm.
In the assessment of the residual bone
height to the floor of the nasal cavity
(n = 46 implants), a mean overall residual
alveolar bone height of 9.63 4.07 mm
was found. When assessed by Cawood and
Howell classification, the residual bone
height for class IV was a mean
12.64 2.92 mm, while this height was
reduced to a mean of 6.48 2.33 mm for
class V.
These data are displayed in Table 7 and
illustrated in Fig. 20.
Regarding the residual bone height,
intrasinus and parasinus paths were found
to correspond to lower mean residual bone
to
the
maxillary
sinus
heights
Table 4. Zygoma implant intra-malar length (mm) according to the sector (anterior and
posterior) and the Cawood and Howell classification of alveolar bone atrophy (classes IV
and V).a
Total
Anterior sector
Posterior sector
*
Class IV
Class V
P-valueb
18.2 5.2 (16.6–19.8)
17.9 4.1 (16.2–19.7)
18.5 6.4 (15.6–21.4)
15.7 3.9 (14.6–16.9)
16.8 3.2 (15.4–18.2)
14.8 4.2 (13.1–16.5)
0.011*
0.297
0.028*
Significant difference.
Results are presented as the mean standard deviation (95% confidence interval).
b
The t-test was used to compare the means according to the degree of alveolar bone atrophy.
a
7
(5.39 2.34 mm and 4.74 2.99 mm, respectively)
than
extrasinus
paths
(7.34 2.93 mm). A Kruskal–Wallis test
confirmed that the difference was statistically significant (P = 0.036).
Similar results were obtained with respect to the residual bone height to the
floor of the nasal cavity: an extrasinus path
was associated with a higher mean residual bone height (P = 0.005, Kruskal–
Wallis test).
Focusing on the class of alveolar bone
atrophy, only the residual bone height to
the floor of the sinus showed similar
results for class IV, and the results did
not
reach
statistical
significance
(P = 0.260, Kruskal–Wallis test). For class
V, neither the residual bone height to the
floor of the sinus (P = 0.486, Kruskal–
Wallis test) nor the residual bone height
to the floor of the nasal cavity (P = 0.230,
Kruskal–Wallis test) showed significant
results.
Hence, the differences in the path of the
implant are perceived globally, but not
within each degree of bone atrophy. It
must be acknowledged that the samples
for each subgroup of bone atrophy were
relatively small and the statistical power is
thereby reduced. The data are displayed in
Table 8.
Discussion
The purpose of this study was to investigate the amount of malar bone volume and
length that a zygomatic implant can engage and the expected relationship of the
implant to the sinus depending on the
degree of alveolar bone atrophy. The absence of similar studies in the scientific
literature hinders comparisons with the
observations of other study groups.
Balshi et al. evaluated malar bone-toimplant contact (BIC) in zygomatic
implants15. They found a BIC of
in
men
and
15.5 6.0 mm
14.7 5.4 mm in women. These lengths
in millimetres correspond to the amount of
implant within the malar bone. In the
present study, the mean intra-malar length
for the total sample was 16.95 4.73 mm.
No differentiation was made between men
and women; rather, the sample was categorized according to the class of alveolar
bone atrophy. In this regard, it was found
that the mean intra-malar length in class
IV cases was 18.22 5.24 mm and in
class V cases was 15.73 3.86. Hence,
the average intra-malar length is greater in
positions with class IV atrophy than in
those with class V atrophy. Nevertheless,
statistical significance was reached only
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone
YIJOM-3747; No of Pages 10
8
Bertos Quı́lez et al.
Fig. 18. Intra-malar length according to the Cawood and Howell classification of alveolar bone
atrophy (classes IV and V), in millimetres.
Table 5. Relationship of the zygoma implant to the sinus (intrasinus, parasinus, or extrasinus)
according to the Cawood and Howell classification of alveolar bone atrophy (classes IV and V).
Alveolar bone atrophy
Class IV
Total
Total
Intrasinus
Parasinus
Extrasinus
Class V
Implants, n
%
Implants, n
%
Implants, n
%
92
13
23
56
100.0%
14.1%
25.0%
60.9%
45
3
7
35
100.0%
6.7%
15.6%
77.8%
47
10
16
21
100.0%
21.3%
34.0%
44.7%
for the posterior sector (P = 0.028) and the
total sample (P = 0.011).
Balshi et al. stated that the zygoma BIC
varies according to the angle at which the
implant is placed. As the angle of the
implant placement changes, the implant
contacts different anatomical portions of
the zygoma, and this can lead to an increase or decrease in the BIC. In the
present study, anterior or posterior positioning and the different classes of alveolar bone atrophy changed the angulation of
the implant and confirmed this hypothesis
with statistical evidence. Similarly, the
present results regarding the intra-malar
implant length are comparable to those
published by Balshi et al.15, with a discrepancy of 1.65 mm. This small difference may be attributable to several factors,
which include the fact that Balshi et al.
performed measurements at the lowermost
part of the implant in contact with the
malar bone, while in the present study
the longitudinal implant axis was used.
In addition, it must be taken into account
that in the study methodology, implant
planning was done virtually and it was
possible to select the ideal position three-
Fig. 19. Zygoma implant path (extrasinus, parasinus, and intrasinus) according to the Cawood
and Howell classification of alveolar bone atrophy (classes IV and V).
dimensionally in terms of the maximum
bone contact. Determining this optimal
placement in vivo is not that simple.
It is well acknowledged that the length
of the implant located in bone is a key
factor in determining osseointegration and
the success and survival of the implant.
Authors refer to this factor in terms of a 2D
linear measurement of an implant that
nevertheless has a three-dimensional
(3D) volume and is placed into a 3D
anatomical structure
the bone. Hence,
it seems much more reasonable to talk in
3D terms than in 2D terms. It is surprising,
therefore, that the volume of bone engaged
by a zygoma implant or a conventional
implant has not been covered by previous
investigations in the scientific literature.
The data from this study showed that the
average volume of malar bone engaged by
a zygoma implant was 0.19 0.06 cm3,
with no statistically significant difference
whether the implants were placed anteriorly or posteriorly (P = 0.559 and
P = 0.184, respectively), and regardless
of the degree of alveolar bone atrophy
in the area to be treated (P = 0.650). It
can, therefore, be concluded that the volume engaged is constant, regardless of the
degree of alveolar bone atrophy or position. In other words, despite severe alveolar bone atrophy, the amount of bone
volume that the malar bone offers for
zygoma implant anchorage is stable and
thus renders this therapeutic option reasonable and reliable14,16–20.
Regarding the relationship of the zygoma implant to the sinus, only one article
published by Aparicio reported the relationship of this to the anterior maxillary
wall11. A description of the morphology of
the anterior maxillary wall according to
the different degrees of concavity, defined
as flat, slightly concave, concave, very
concave, and extreme alveolar lateral
and vertical bone atrophy, was given, in
what the author called the zygoma anatomy guided approach (ZAGA) classification. However, despite the widespread use
of the Cawood and Howell classification
of alveolar bone atrophy in this field, no
relationship between the path of the implant and the different bone atrophy classes was established. In the present study,
an important finding was the fact that the
relationship of the zygoma implant to the
sinus changes depending on the degree of
bone atrophy. Indeed, more extrasinus/
extramaxillary paths were found for the
lower degrees of atrophy than for the
higher degrees of atrophy (77.8% for
Cawood and Howell class IV compared
to 44.7% for Cawood and Howell class V).
Hence, as alveolar bone atrophy increases,
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone
YIJOM-3747; No of Pages 10
25 (100)
8 (32)
12 (48)
5 (20)
46 (100)
11 (23.9)
19 (41.3)
16 (34.8)
9
Table 7. Residual height (mm) to the floor of the maxillary sinus and the nasal cavity in the
location of the zygoma implant according to the Cawood and Howell classification of alveolar
bone atrophy (classes IV and V).
Alveolar bone atrophy
Height to sinus floor
Implants, n
Mean
Standard deviation
Minimum
Maximum
Median
Height to nasal cavity
Implants, n
Mean
Standard deviation
Minimum
Maximum
Median
Total
Class IV
Class V
46
5.83
3.00
1.00
11.97
6.39
21
7.85
1.99
3.03
11.97
7.81
25
4.05
2.59
1.00
9.30
3.86
46
9.63
4.07
1.92
18.43
9.02
24
12.64
2.92
7.53
18.43
12.67
22
6.48
2.33
1.92
11.77
6.73
the relationship to the sinus tends towards
a more intrasinus path.
Another factor influencing the relationship of the zygoma implant to the sinus is
the residual alveolar bone height to the
floor of the nasal cavity and the maxillary
sinus. More intrasinus/intramaxillary
paths were found for lower residual alveolar bone heights. Thus, as the residual
bone height increases, the relationship of
the implant to the sinus tends towards a
more extrasinus/extramaxillary path.
In conclusion, the results of this study
suggest that the average volume of malar
bone that a zygoma implant engages is
0.19 0.06 cm3. This amount does not
vary regardless of the implant position
and degree of alveolar bone atrophy. All
of the cases evaluated showed enough
bone volume at the zygoma level to allow
for quadruple implant placement. In none
of the cases did the examiners fail to find
sufficient bone to adequately distribute
the implants. Although it was not the
purpose of this study, from this experience in the virtual scenario, it can be
hypothesized that any malar bone is actually appropriate for the placement of
two fixtures.
As the degree of alveolar bone atrophy
increases, the path of the zygomatic implant becomes more parasinus and intrasinus.
The absence of similar studies in the
scientific literature limits the establishment of comparisons with other study
groups. Further investigations should incorporate state-of-the-art imaging technologies and 3D implant parameters
such as minimum alveolar bone volume
engagement required for successful
osseointegration.
Total
Intrasinus
Parasinus
Extrasinus
92 (100)
13 (14.1)
23 (25.0)
56 (60.9)
45 (100)
3 (6.7)
7 (15.6)
35 (77.8)
47 (100)
10 (21.3)
16 (34.0)
21 (44.7)
46 (100)
2 (4.3)
4 (8.7)
40 (87.0)
24 (100)
0 (0)
0 (0)
24 (100)
22 (100)
2 (9.1)
4 (18.2)
16 (72.7)
21 (100)
3 (14.3)
7 (33.3)
11 (52.4)
Class V
Implants, n (%)
Class IV
Implants, n (%)
Total
Implants, n (%)
Class V
Implants, n (%)
Total
Implants, n (%)
Class IV
Implants, n (%)
Class V
Implants, n (%)
Total
Implants, n (%)
Class IV
Implants, n (%)
Posterior
Anterior
Total
Sector
Table 6. Relationship of the zygoma implant to the sinus (intrasinus, parasinus, or extrasinus) according to the sector (anterior and posterior) and the Cawood and Howell classification of alveolar bone
atrophy (classes IV and V).
Virtual quad zygoma implant placement using CBCT
Fig. 20. Residual bone height to the floor of the maxillary sinus and to the floor of the nasal
cavity according to the Cawood and Howell classification of alveolar bone atrophy (classes IV
and V).
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone
YIJOM-3747; No of Pages 10
10
Bertos Quı́lez et al.
Table 8. Relationship of the zygoma implant to the sinus (intrasinus, parasinus, or extrasinus)
according to the Cawood and Howell classification of alveolar bone atrophy (classes IV and V)
and the residual bone height to the floor of the maxillary sinus and the nasal cavity.
Total alveolar bone
atrophy
Class IV alveolar bone Class V alveolar bone
atrophy
atrophy
Relation to the sinus
Relation to the sinus
Relation to the sinus
Total Intra Para Extra Total Intra Para Extra Total Intra Para Extra
Height to sinus floor
Implants, n
46
11 19 16
21
3
7
11
25
8
12 5
Mean
5.83 5.39 4.74 7.34 7.85 8.18 6.64 8.53 4.05 4.35 3.53 4.73
Standard deviation 3.00 2.34 2.99 2.93 1.99 1.25 1.96 1.93 2.59 1.67 2.95 3.22
Minimum
1.00 2.00 1.00 1.00 3.03 6.77 3.03 6.39 1.00 2.00 1.00 1.00
Maximum
11.97 9.14 9.30 11.97 11.97 9.14 8.70 11.97 9.30 6.73 9.30 8.64
Average
6.39 4.90 5.70 7.22 7.81 8.62 7.69 8.56 3.86 4.69 2.00 5.12
Height to nasal cavity
Implants, n
46
2
4
40
24
0
0
24
22
2
4
16
Mean
9.63 5.58 5.18 10.39 12.64 –
–
12.64 6.48 5.58 5.18 7.00
Standard deviation 4.07 2.76 1.10 3.90 2.02 –
–
2.92 2.33 2.76 1.10 2.48
Minimum
1.92 3.62 3.94 1.92 7.53 –
–
7.53 1.92 3.62 3.94 1.92
Maximum
18.43 7.53 6.73 18.43 18.43 –
–
18.43 11.77 7.53 6.73 11.77
Average
9.02 5.58 4.82 10.17 12.67 –
–
12.67 6.73 5.58 4.82 7.15
Funding
None.
Competing interests
None.
Ethical approval
The Research Ethic Committee (C.E.R.)
of the International University of Catalonia approved this research (reference number CIR-ELM-2013-02).
Patient consent
Not required.
Acknowledgements. Special thanks to
Gemma Puerta López-Pastor for her great
dedication and contribution to this study,
to Juan Luı́s Gómez Martı́nez for assistance with the statistical analysis, and to
Marina Monjó and Simplant (Dentsply
Sirona, Iberia) for the technical support
in the use of the software.
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Address:
Jorge Bertos Quı́lez
Department of Oral and Maxillofacial Surgery
International University of Catalonia
C/Josep Trueta s/n
08195 Sant Cugat del Vallés
Barcelona
Spain
Tel.: +34 687 595 482
E-mail: jorgebertos@uic.es
Please cite this article in press as: Bertos J, et al. Virtual quad zygoma implant placement using cone beam computed tomography:
sufficiency of malar bone volume, intraosseous implant length, and relationship to the sinus according to the degree of alveolar bone