Restoration of a severely atrophic jaw presents a challenge in
dentistry. Bone augmentation is usually required in the posterior
maxilla to enable placement of a sufficient number and length of
implants to support implant prosthesis due to the poor bone quality of
the posterior maxilla. The recent invention of new surgical techniques
and implant systems help circumvent the current restorative problems and
provide a solution to erstwhile un-rehabilitated cases. The use of
pterygoid implants in the pterygo-maxillary region provides posterior
bone support without sinus augmentation or supplemental grafts. This
article describes a clinical procedure for the restoration of severely
resorbed maxilla using a new pterygoid implant in combination with
conventional or cortically fixed implant system. In the present study,
the use of implants in the posterior maxilla to support a fixed
prosthesis was demonstrated to be a reliable and a good alternative to
distal cantilever prostheses or sinus-lifting procedures.
Keywords: Atrophic Jaw; Pterygoid Implants; Pterygo-maxillary Region; Edentulous Patient; Rehabilitation
Introduction
Restoration of a severely atrophic jaw presents a challenge in
dentistry. The poor bone quality of the posterior maxilla, coupled with
limited vertical bone height due to sinus pneumatisation and chronic
periodontitis often leaves insufficient bone for implant anchorage
[1,2]. Bone augmentation is usually required to enable placement of a
sufficient number and length of implants to support implant prosthesis
[3,4]. Many procedures, such as onlay grafts, free or micro vascular
bone grafts, transport distraction osteogenesis, and apposition grafts
with or without a Le Fort I osteotomy are well documented and have
success rates of between 60-90% [5-9]. These often involve invasive and
lengthy surgeries, long treatment time, and some morbidity [6-8].
Furthermore, free bone grafts are commonly associated with resorption
during healing [5,9]. Zygomatic Implants have been used to provide
support for oral rehabilitation where there has been a substantial
amount of bone loss from the upper jaw, and where ordinary dental
implants are not sufficient for prosthetic support [2,10].
Still, some severe atrophic jaw cases defile these current treatment
options. Continuous advances in dentistry have resulted in the invention
of new surgical techniques and implant systems that circumvent the
current restorative problems and provide a solution to erstwhile
un-rehabilitated cases. One of such is the use of Pterygoid implants to
rehabilitate posterior maxillal. Placement of implants in the
pterygomaxillary region provides posterior bone support without sinus
augmentation or supplemental grafts. This article describes a clinical
procedure for the restoration of severely resorbed maxilla using a new
terygoidimplant in combination with conventional or cortically fixed
implant system.
The Pterygoid Implant
The pterygoid implant is anaxial implant placed through the maxillary
tuberosity with fixation apically in the pterygoid process of the
sphenoid bone and the pyramidal process of the palatine bone. Pterygoid
implants were first proposed by Linkow in 1975 [11] and the method was
first described by JF Tulasne in 1992 [12]. These implants are
relatively long and specifically manufactured with the characteristics
of the pterygoid region in mind. The implant was introduced to solve the
problem of implants restoration in the posterior maxilla due to the
presence of the maxillary sinusand
as a result of limited quantity and poor quality of available bone in
this region [1]. Support for pterygoid implantsis derived from the
tuberosity of the maxillary bone, the pyramidal process of the palatine
bone, and the pterygoid process of the sphenoid bone [13]. The length of
pterygoid implant ensures that the implant can cross the mucosa (which
is often thick in this region) and engage the implant apex in the
cortical bone of the pterygopalatine suture.
Figure 1: Pterygoid implant.
Pterygoid implant passes through the maxillary tuberosity and the
pyramidal process of palatine bone to engage the pterygoid process of
the sphenoid bone [13,14], its length ranges from 16 to 20 mm, they have
a pointed, self-tapping apex to ensure strong anchorage when inserted.
The implant neck has a wide thread profile which provides compression in
the region of the tuberosity, where the bone is often of low density
(Figure 1). New Pterygoid implants designed under the guidance of Henri
Diederich, Luxembourg with the collaboration of the Swiss company TRATE
are surface treatedithhydroxyapatite/tricalciumphosphate (HA/ TCP) and
have a conical shape with compressive threads. The implants are of 3.5
or 4.5 mm diameter with a length of 16, 18, 20 mm respectively (Figure
2).
Figure 2: New Pterygoid implants from TRATE.
Surgical Technique
The placement of implants in the pterygoid process requires surgical
experience and detailed knowledge of the anatomy of the posterior
maxillary region. Various surgical techniques for implant insertion in
this region have been described in the literature. The standard surgical
technique involves; making a full-thickness crestal incision on an
edentulous crest as far as the back of the tuberosity, and extended by a
vestibular releasing incision after anaesthesia of the region is
achieved with a local anaesthetic solution. The incision design is such
that the entire tuberosity, including its posterior aspect, is uncovered
for visualization and instrumentation. Radiographic information is used
to determine the proper drilling angle necessary to avoid perforation
of the posterior sinus wall. The drill entry point is often marked 3-4
mm in front of the posterior region of the tuberosity. The drill axis
runs towards the palate at about 20-30° in the horizontal plane and
about 45° from the maxillary plane. Drilling with a pilot drill
continues up to the pterygopalatine-tuberosity suture, which is the
anchorage region for a pterygoid implant. Three different types of
drills are used for insertion. All preparation is done in an
underprepared mode, at a working speed of 600 rpm or manually. The
implant is then inserted manually using a bone condensation technique,
due to its self-tapping and compressive characteristics. The implant is
anchored in the pterygoid plate of the sphenoid bone, through the
maxillary and palatine bones and with distal angulation between 35° and
55°, depending on the maxillary sinus floor and the height of the bone
of the tuberosity.
Various modifications of the above surgical techniques have been
proposed by different authors. Reasons for modifications are, to reduce
surgical trauma, to increase primary stability and to reduce the failure
rate of the pterygoid implant. One of such modification was proposed by
Venturelli et al. [15]. His aim is to reduce the failure rates of
implants placed in the maxillary tuberosity with the modified technique.
In the modified technique a crestal incision was made from the
pterygomaxillary notch to the premolar area, with a releasing vertical
incision. Then the buccal and palatal flaps were carefully raised. The
site is prepared with care to minimize drilling maneuvers. Drilling
begins with a 2.0-mm round drill at 1,500 rpm through the cortical bone.
Then, a 2.0-mm twist drill at 500 rpm is used to the depth of the
superior cortical plate. The depth of the drilled site is measured with a
depth gauge, and the integrity of the sinus membrane is verified. If
damage to the sinus membrane is revealed, a new more distal site is
selected, and the described sequence is repeated. All subsequent
drilling is done with internal irrigation drills.
A pilot drill is then used to shape the whole entrance. After using a
2.5-mm shaping drill, a 3.0-mm trispade cylinder bur at 200 rpm is
recommended until the predefined depth is reached. Single-stroke
drilling is advised to avoid overextending the site in the poor quality
bone. To avoid damaging thin cortical bone, countersinking is not used.
Tapping is also avoided because of the particular quality of bone
present. Implants are then placed with standard implant mounts (3 mm). A
self-tapping implant is first placed at 15 rpm. The implant is removed
if minimal instability is seen and replaced immediately with a
4.0-mm-diameter implant without any further drilling. The proposed
variations in the standard protocol are aimed at minimizing surgical
trauma to the bone and reduce
the amount of heat generated. This is expected to reduce the high
failure rates (usually during stage 2 surgery) for implants placed in
the maxillary tuberosity according to Venturelli et al. [15]. For the
new pterygoid implants, a different insertion technique is used. The
surgical technique uses a single drill at a working speed of 600 rpm and
the implant insertion is done by hand. This technique is termed Soft
technique. The Soft technique was invented to enhance implant primary
stability and encourage early prosthodontic restoration Figure 3.
Figure 3: Clinical photo of the patient at presentation: hypo plastic upper arch can be seen.
Case Presentations
Patient 1 is a 47-year-old non-smoker, male patient with Down
syndrome, who presented at the clinic with a reason to get fixed teeth
in the maxilla and mandible. A clinical examination showed an edentulous
lower arch with resorbed ridge and an edentulous upper arch with
sagittal and transverse hypo plasia. Figure 3 shows the clinical photo
of the patient at presentation: hypo plastic upper arch can be seen. The
Radiographic examination using an orthopantomogram showed an edentulous
upper jaw with moderate vertical bone resorption in the front and
severe vertical resorption in the premolar and molar region. In the
lower jaw, there is a moderate vertical bone resorption. Figure 4 shows
the panoramic radiograph of the patient at presentation.
Figure 4: Panoramic radiograph of the patient at presentation.
a) Treatment Plan: In the lower jaw, placement of four standard
implants was advised. From a prosthetic point of view, the patient
desired a fixed prosthetic solution. For the upper jaw placement of
Zygoma implant was planned, this was changed after 3D assessment of the
upper jaw showed severe atrophic maxilla with insufficient bone and
space for zygoma implant (Figure 5), then a combination of two pterygoid
and four hybrid plates was proposed. The patient agreed to this
treatment plan.
Figure 5: Cone beam computed tomography image of patient at presentation showing shape and width of upper arch.
Figure 6: Surgical procedure and implant placement in the maxilla (a, b) and mandible (c, d).
In the maxilla, an open flap was made from the left tuberosity along
the crest till the canine region. The flap was reflected on the
vestibular side in positions 17 and 27 of the zygomatic arch; flap was
also reflected in the palate. Pterygoid implant P3.5/20mm was inserted
at the left and right pterygoid plate. Two-hybrid plates HENGG-2 (Highly
efficient no graft gear) were fixed at positions 22 and 25. The plates
were fixed with osteosynthesis screws and covered with MatriboneR. The
procedure was quite similar to the right side. Two plates HENGG-2 were
installed at position 12 and15. The flap was then closed on the left and
right with polytetrafluoroethylene polymer (PTFE) monofilament
non-absorbable suture. In the lower jaw, a crestal incision was made
from 35 to 45 and four Nobel Speedy Groovy RP 4x13 mm implants were
placed at region 35, 32, 42 and 45 with a minimum torque of 50N (Figures
6 & 7). After surgery, an impression was taken with transfer coping
in place. Weeks later, a try-in was done and a new bite registration
was taken. A laboratory technician was present at this session to decide
the smile line and aesthetic outlook. Five days
after the try-in an appointment for prosthesis delivery was given. In
the maxilla, the bridge was screwed, and in the mandible, the bridge was
fixed with temporary cement (Figure 8). The patient was reviewed after 2
weeks. Thereafter, the patient was scheduled for follow-up at 3 months
and then every 6 months.
Figure 7: Panoramic radiograph of patient after implant placement.
Figure 8: Images of prosthesis and patient at completion of treatment
Figure 9: Panoramic radiograph of patient 2 at presentation.
Patient 2 is a 49-year-old female, who lost her bridge on the right
maxilla. The patient presented at the clinic with a reason to get fixed
teeth to replace the defective bridge. A clinical examination showed
fractures of teeth retaining the bridge. Radiographic examination using
an orthopantomogram showed pin retained bridge on compromised teeth in
the right maxilla (Figure 9). In the lower jaw, several teeth were
present. The proposed treatment plan was the placement of a combination
of pterygoid and two C 3.5 /14 mm ROOTT one-piece implants. The patient
agreed to this treatment plan. In the maxilla, the broken teeth were
extracted and an open flap was made from the right tuberosity along the
crest till the canine region. The flap was reflected on the vestibular
side in positions 26 and 27 of the zygomatic arch; flap was also
reflected in the palate. Pterygoid implant P3.5/20mm was inserted at the
right pterygoid plate. Thereafter, one-piece implants of 3.5mm diameter
and height of 12mm were inserted in positions 14, 15 with a torque of
50N. The flap was then closed with polytetrafluoroethylene polymer
(PTFE) monofilament non-absorbable suture. After an implant placement,
bite registration was done. Then transfer coping was inserted and an
impression was taken with silicone immediately after the surgery
(Figures 10 & 11). Four days after the framework, a try-in was done.
Ten days after the try-in an appointment for prosthesis delivery was
given. In the maxilla, the metal-ceramic bridge was screwed. The patient
was reviewed after 2 weeks. Thereafter, the patient was scheduled for
follow-up at 3 months and then every 6 months.
Figure 10: Laboratory step.
Figure 11: Laboratory step.
Discussion
Pterygoid implants provide strong cortical anchorage in the maxilla.
It is an alternative treatment option for patients with highly atrophic
maxillae without the need for extensive augmentation procedures. The
availability of dense cortical bone for engagement of the implant
encourages its use. The location of the posterior implant is dictated by
the dimensions and quality of the tuberosity. The mesiodistal
angulation of the implant is dictated by the angle
of the posterior wall of the sinus and its proximity to the posterior
wall of the tuberosity. The bucco-palatal angulation of the implant is
dictated by the bone segments to be engaged. Previous studies show that
Pterygoid implants have high success rates, similar bone loss levels to
those of conventional implants, minimal complications and good
acceptance by patients [1,16]. Two anatomic locations in which implants
are placed in the retro molar area can be distinguished in the
literature, these are the pterygoid process and the pterygomaxillary
region.
Implant lengths and angulations vary between these two locations.
Though the results are promising, case selection is very important and a
thorough understanding of the pitfalls of the procedure should be borne
in mind. The lack of need for maxillary sinus lift and grafting
procedures shorten the treatment time considerably and allow immediate
loading of the pterygoid implant [13]. Pterygoidimplants allow the
prosthesis to have sufficient posterior extensions there by eliminate
distal cantilevers [13,16]. Because the anatomy of the posterior region
is complex and poorly described; training and experience is needed in
order to achieve a good result. Pterygoid implant is technique sensitive
and learning curve is usually required, its proximity to vital anatomic
structures and poor access for clinicians and patients are its
shortcomings [12,13,16]. In the above case reports, new Pterygoid
implants were used for patient rehabilitation with "soft technique"
described above. The use of new pterygoid implants to support a fixed
prosthesis was demonstrated to be a reliable, predictable alternative to
distal cantilever prostheses or sinus-lifting procedures. This
technique has good success rate and it ensures short treatment period.
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