AJR 2000; 174:1289-1292
© American Roentgen Ray Society
Sinus Lift Procedure of the Maxilla in Patients with Inadequate Bone for Dental Implants
Radiographic Appearance
James J. Abrahams1,
Michael W. Hayt and
Reuben Rock
1
All authors: Department of Diagnostic Radiology SP2-123, Yale University
School of Medicine, 333 Cedar St., P.O. Box 208042, New Haven, CT
06520-8042.
Received June 9, 1999;
accepted after revision October 15, 1999.
Address correspondence to J. J. Abrahams.
Abstract
OBJECTIVE. Dental implants have gained popularity for treating
edentulism, but some patients develop jaw atrophy, which leaves insufficient
bone for implants. To treat these patients, the sinus lift procedure, which
augments bone, was developed. Altered anatomy from this procedure has an
unusual radiographic appearance, confusing those unfamiliar with it. We
describe the sinus lift procedure and its radiographic appearance.
CONCLUSION. With knowledge of this surgery and some of its pitfalls,
radiographs can be more easily and accurately interpreted.
Introduction
Poor oral function and detriment to self-esteem can debilitate millions of
people who are partially or totally edentulous. Dentures, which are often used
to treat this condition, may not completely restore function because of poor
fit related to atrophy. As a result, dental implants have been developed to
improve aesthetics and the function of mastication. These implants are
metallic struts that are surgically placed in the jaw to support a dental
prosthesis. Dental implants provide an alternative to the standard removable
complete or partial dentures and improve function almost completely.
To be a candidate for the dental implant procedure, a patient must have
sufficient bone in the maxillary and mandibular alveoli to support these
posts. Unfortunately, after a prolonged period of being edentulous, the
alveolar ridge that once supported the teeth becomes atrophic and sufficient
bone may not be present for implants. To increase the amount of bone in the
maxilla, the sinus lift procedure, or subantral augmentation, has been
developed. This procedure involves placing bone-graft material in the
maxillary sinus to increase the height and width of the alveolus (Fig.
1A,1B,1C,1D).
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Fig. 1A. —Sinus lift procedure. (Reprinted from
[7]) Drawing shows that, after
incision, soft tissue in anterior maxilla has been reflected back to expose
overlying maxillary sinus (arrowheads). Note osteotomy
(arrows) in bone.
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Fig. 1B. —Sinus lift procedure. (Reprinted from
[7]) Drawing shows
cross-sectional (lateral) view of maxillary sinus. Note that bone flap created
by osteotomy has been pushed inward with maxillary sinus membrane, creating
space that is packed with bone-graft material as shown in C and
D.
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The radiographic appearance of the maxilla after the sinus lift procedure
is quite unusual because of the altered anatomy and the dense graft situated
in the sinus. To radiologists unfamiliar with this technique, the unusual
radiographic appearance can be a source of confusion and can be mistaken for
osteomas, fibrous dysplasia, tumors, and so forth. Because sinus lift has
become a common procedure, it is important for radiologists to be familiar
with this surgery and the manner in which the maxillary anatomy is altered.
Most radiologists interpret routine sinus or head CT scans without knowledge
of the dental history of the patient. Our objective is to describe the sinus
lift procedure and its radiographic appearance.
Materials and Methods
Three hundred fifty-six maxillary DentaScans (General Electric Medical
Systems, Milwaukee, WI), obtained between November 1, 1994 and November 1,
1998, and the associated clinical and surgical histories were retrospectively
reviewed to identify patients who had undergone sinus lift alveolar
augmentation. Patients who had DentaScans were identified by using the
radiology computer code for DentaScan. From this group, patients who also had
a sinus lift procedure were identified by the clinical history on the
radiology or operative report or by calling the referring dentist. A single
reviewer, with expertise in radiology of the oral cavity and awareness of the
patient's history, then reviewed the radiographs to describe the radiographic
changes resulting from this procedure.
Images were acquired using a HiSpeed Advantage CT scanner (General Electric
Medical Systems). One-millimeter axial slices of the maxilla were obtained
parallel to the alveolar ridge using a bone algorithm, dynamic mode, 15-cm
field of view, and head holder. DentaScan software (General Electric Medical
Systems) was used to display the multiple direct axial and reformatted
sagittal oblique and panoramic images. Several patients had undergone both
preoperative and postoperative scans and one patient also had undergone direct
coronal CT.
Results
Of the 356 DentaScans, six patients were identified who had undergone the
sinus lift augmentation. The procedure was unsuccessful in two patients. One
failure was caused by a postoperative infection and the the other by a lack of
integration of the graft into the residual alveolar bone. The radiographic
description that follows is best understood by first becoming familiar with
the surgical procedure (Fig.
1A,1B,1C,1D),
which is described in detail in the discussion section.
In the four patients without infection or lack of integration, the
subantral augmentation appeared on CT as an irregular high-density mass in the
maxillary sinus (Fig.
2A,2B,2C,2D,2E).
On the axial images the mass was situated in the center of the sinus. Scanty
areas of soft-tissue density were interspersed between the mass and the walls
of the sinus (Fig. 2A). The
graft filled the caudad portion of the sinus but not the more cephalad
portion.
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Fig. 2A. —67-year-old man who underwent sinus lift procedure to treat alveolar
atrophy. Axial CT scan through maxillary antrum shows bone graft appearing as
irregular dense mass (arrowheads) in center of sinus. Note scanty
soft-tissue density (arrow) between graft and wall of sinus.
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Fig. 2B. —67-year-old man who underwent sinus lift procedure to treat alveolar
atrophy. Axial CT scan slightly caudad to A shows slight concavity at
osteotomy site (arrow). Note more graft material is seen in caudad
portion of sinus than in cephalad portion.
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Fig. 2C. —67-year-old man who underwent sinus lift procedure to treat alveolar
atrophy. Panoramic (C) and sagittal oblique (D) DentaScans
(General Electric Medical Systems, Milwaukee, WI) show position of graft
(large arrow, C) adjacent to alveolar ridge (small
arrows, C) in caudad aspect of sinus better than in the axial
scans, A and B. Note convex border of graft where it bulges
through osteotomy in anterior maxillary wall (arrowheads, D).
S = nasal septum, T = turbinate, M = maxillary sinus, A = anterior, I =
inferior.
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Fig. 2D. —67-year-old man who underwent sinus lift procedure to treat alveolar
atrophy. Panoramic (C) and sagittal oblique (D) DentaScans
(General Electric Medical Systems, Milwaukee, WI) show position of graft
(large arrow, C) adjacent to alveolar ridge (small
arrows, C) in caudad aspect of sinus better than in the axial
scans, A and B. Note convex border of graft where it bulges
through osteotomy in anterior maxillary wall (arrowheads, D).
S = nasal septum, T = turbinate, M = maxillary sinus, A = anterior, I =
inferior.
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Fig. 2E. —67-year-old man who underwent sinus lift procedure to treat alveolar
atrophy. Panoramic DentaScan obtained before surgery shows atrophy of alveolar
ridge (arrowheads) and lack of soft tissue in sinus. M = maxillary
sinus.
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The panoramic and sagittal oblique reformatted images (Figs.
2C and
2D) best showed the
relationship of the bone graft to the maxillary alveolus and sinus floor. The
graft was adjacent to and indistinguishable from the floor of the sinus and
the alveolar ridge. The panoramic view also showed the height of the available
bone to be increased by the graft and the sagittal oblique views showed the
height and width to be augmented. The zones of soft-tissue density surrounding
the graft were also revealed.
The actual osteotomy in the anterior wall of the maxillary sinus was
difficult to see because it was packed with the bone graft. However, the
osteotomy could be identified as a convex
(Fig. 2D) or concave
(Fig. 2B) border to the bone
graft, depending on whether the graft material was bulging through the
osteotomy or recessed into it. In the patients who had undergone scanning
before the procedure, the maxillary sinuses were free of soft tissue and bone
density (Fig. 2E), but the
alveolar ridge was severely atrophied.
Images of the two patients in which the procedure was unsuccessful were
distinguishable from the other four patients. In the patient with the
postoperative infection, the amount of soft-tissue density in the maxillary
sinus was far greater than in the other patients. On the left side, the sinus
was completely opacified and the bone graft was more diffusely dispersed and
did not have the appearance of a mass as in the other patients
(Fig. 3). The graft itself
also was not as dense as those in the successful procedures. On the right
side, no residual bone graft could be identified and, thus, the osteotomy site
in the anterior wall of the maxillary sinus was well visualized. In the
patient who lacked integration of the graft with the alveolus, the amount of
bone graft was diminished and the density was lower than that seen in the
successful procedures. No sinus opacification was seen, and the scanty amounts
of soft-tissue density in the sinus were similar to that seen in the other
four patients.
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Fig. 3. —53-year-old man who underwent sinus lift procedure and developed
postoperative infection. Coronal CT scan shows opacified left maxillary sinus
(white arrow). Note bone graft is more diffusely disbursed on left
(arrowheads) and absent on right. Also note osteotomies (black
arrows).
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Discussion
The sinus lift procedure, developed in the mid 1970s, has been refined and
is now frequently performed
[1,2,3,4].
The surgical procedure, often performed in the office of a dentist or oral
surgeon, begins with the creation of a mucoperiosteal flap along the anterior
wall of the maxillary sinus similar to the Caldwell-Luc approach
(Fig. 1A). A rectangular
osteotomy is then cut into the lateral antral wall with the inferior
horizontal segment of the rectangle 3-4 mm above the floor of the sinus. This
helps keep the graft material in place in the floor of the sinus. The superior
horizontal segment of the rectangle is formed by drilling closely positioned
holes (Fig.
1A,1B,1C,1D).
This creates a trapdoor, which will be fractured inward and hinged along the
superior aspect of the rectangle (Fig.
1B). The in-fracturing is done carefully to prevent tearing of the
schneiderian (maxillary sinus) membrane. Tears can be repaired with pieces of
resorbable collagen (Collatape; Calcitek, Carlsbad, CA).
Next, the membrane at the inferior aspect of the osteotomy is dissected
from the floor of the maxillary sinus and elevated upward to create a space in
the floor of the sinus for the bone-graft material
(Fig. 1B). The bone flap that
was fractured inward and pushed upward will create the roof of this space.
Bone-graft material is then packed into the space and, finally, the
mucoperiosteal flap is repositioned and the mucosa is sutured closed (Figs.
1C and
1D). Healing takes 6 months
before implants are placed, but some surgeons will now place implants at the
time of surgery if enough residual bone is available to support them. For
successful implantation, most surgeons like to have bone that measures at
least 5 mm in width and 7 mm in height and the sinus lift procedure attempts
to provide at least this amount of bone.
Several types of bone-graft materials have been used
[5]: autogenous bone from the
iliac crest or maxillary tuberosity, frozen bone, freeze-dried bone,
demineralized freeze-dried bone, and hydroxyapatite. Hydroxyapatite is a
resorbable calcium phosphate material and acts as a foundation for new bone
regeneration. Some authors have found more success when this is mixed with
freeze-dried bone [6]. A
variation on this technique is to place a piece of cortical bone in the sinus,
inferior (caudad) to the bony flap, to reinforce the graft
[2,
4].
In patients without infection, we noted scanty amounts of soft-tissue
density around the graft. This appears to be a normal postoperative finding
and was not present on any scans obtained before surgery. The soft tissue may
represent granulation tissue related to postoperative scarring. In one patient
with infection, the amount of soft tissue in the sinus was markedly increased
and the graft material was dissipated
(Fig. 3); therefore, increased
soft tissue in the sinus may indicate infection. Whether infection places the
graft at risk has not been determined. It seems possible to have an intact
maxillary sinus membrane and sinusitis above the graft without affecting the
graft. However, in our patient, it appears that the infection was in the graft
itself and not from secondary sinusitis. The cause of nonintegration of the
graft in one patient is not known, but undetected infection might be a
consideration. Poor surgical technique could also result in this type of
failure.
Although the outcome of the sinus lift procedure is generally quite good,
failure may result from infection (Fig.
3) or from lack of integration of the graft into the alveolar
remnant (as noted in the other patient for whom the procedure was
unsuccessful).
In summary, the sinus lift procedure has proven to be successful and has
become popular, allowing patients with insufficient bone to undergo
implantation surgery. Eventually, many of these patients will have head CT
scans for various reasons and the findings in the maxillary sinus may be quite
confusing to the radiologist who is unfamiliar with this procedure. We have
therefore described the surgical technique and the radiographic findings in
both successful and unsuccessful procedures.
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Abstract
Introduction
