Dental implants have been successfully used to restore
edentulous mandibles with implant-supported fixed bridges,
hybrid prosthetic dentures and removable overdenture prosthetics.
However, many completely edentulous patients desire
a fixed restoration rather than a removable prosthesis. A fixed
restoration provides the psychological advantage of acting and
feeling similar to natural teeth, whereas an overdenture, even if
fully implant supported, remains a removable prosthesis.1 This
article focuses on the techniques implemented when restoring a
patient with a fixed lower bridge supported by implants.
A female patient presented to the office with an existing set
of dentures that were about 23 years old. Her chief complaint
was that her mandibular denture was very loose and painful,
even though it had been relined multiple times over several years.
The patient was evaluated preoperatively with respect to jaw
size, bone quality and volume, jaw relations, maxilla-mandibular
distance and occlusion. Preoperative analysis of the anatomic
conditions was performed with a CT scan (i-CAT). Upon clinical
examination and radiographic interpretation, the anterior mandibular
ridge had severe undercuts (Fig. 1) as well as posterior
bone loss that would prevent dental implant placement without
extensive block grafting. She had already consulted with other
dentists and specialists about dental implant options prior to
presenting to my office, but was not satisfi ed with the treatment
duration and prognosis regarding block grafting. Although block
grafts (and other non-block grafts) represent the accepted treatment
standard for fortifying or augmenting bone tissue, there is
another method for creating a foundation of adequate width and contour that many dentists may not be completely aware of yet that
is taught in some of today's popular post-graduate training programs.
My consultation with the patient focused on the advantages
of having the ability to restore the lower arch with implants and
a fixed cantilever bridge after bone leveling. Some of the advantages
included less extensive surgery, shortened treatment time and reduced
cost. Once the patient was educated about these advantages, she
quickly agreed to the proposed treatment plan, which included
fabrication of a new upper complete denture, alveoplasty of the
mandibular ridge, and placement of five dental implants with a
cantilevered fixed bridge.
The arch form and the position of the mental foraminae are
important criteria when placing implants in the anterior segment
to replace the entire mandibular arch. The anterior arch form and
foraminae position affects the position of the distalmost implants
and the anterior arch form (square, oval or tapering) is relative to
the anteriomost implant position. The distance from the center of
the most anterior implant to a line joining the distal aspect of the
two most distal implants on each side is called the "A-P Distance" or
the "A-P Spread." The greater the A-P Spread, the further the distal
cantilever may be extended to replace the missing posterior teeth.1
The most common number of implants used today in the
Branemark treatment option is five. This number allows as great
an A-P Spread as six implants, with greater inter-implant distance,
so that if bone loss occurs on one implant, the loss would not automatically
affect the adjacent implant site."1 As a general rule, when
five implants are placed in the anterior mandible between the
foramina, the cantilever should not exceed 2.5 times the A-P Spread
with all other force factors being low.
Before the surgical appointment, a CBCT scan (Fig. 2) was
taken to accurately treatment plan this case to make certain no
complications would arise from doing the guided bone leveling
procedure and dental implant placement at the same time. Sim-
Plant software (Materialise Dental) was used through 3D Diagnostix
virtual assistance to precisely plan the placement of fi ve
Engage (OCO Biomedical) dental implants in the mandibular arch
after bone leveling. A bone leveling guide as well as a pilot implant
guide were fabricated from Materialise in developing the most
stable confi guration of implants possible and, as demonstrated in this case, define the amount of and location of leveling to create a uniform modified ridge.
Engage dental implants were selected because I have personally
experienced their high implant stability at placement, which is a
critical success factor during the early healing process of osseointegration
with these types of cases. The Engage implant body creates
a tapping pattern when threaded for an enhanced mechanical
lock in the bone. Other dental implant systems with aggressive
threading may include but are not limited to: Nobel Active (Nobel
Biocare), Seven (MIS), ETIII (Hiossen), I5 (AB Dental USA) and
Any Ridge (Megagen).
The patient was anesthetized and a full thickness flap reflected
using a mucoperiosteal elevator. Soon afterwards, the floor of the
mouth was temporarily sutured to ensure it would not be traumatized
by the bone-leveling bur during reduction. The bone level
guide was inserted onto the mandible and inspected to insure complete
seating (Fig. 3). Once stable, bone was reduced through the
bone leveling guide using a surgical handpiece and bur with the
Aseptico surgical motor (AEU 7000) at a speed of 1,200rpm with
copious amounts of sterile saline (Fig. 4).
Once the bone level guide established an optimal level of
bone, the pilot implant guide was seated and secured with retention
pins (Fig. 5). Using the pilot surgical guide provided by 3D
Diagnostix, the sites for the implants were begun with a 1.95mm
longstop pilot drill.
Paralleling pins were placed in the sites of the osteotomies to
confirm the accuracy of the surgical guide (Fig. 6) and X-rays were
taken to check the angulations of the pins within the mandible.
Once the osteotomies were complete, an implant finger driver
was used to place the dental implants, until increased torque was
necessary (Fig. 7). The ratchet wrench was then connected to the
adapter and the implants torqued to final depths reaching a torque
level of about 40-50Ncm.
Extended healing caps were hand-tightened to the implants. A
post-operative radiograph was made of the implants and the healing
caps to ensure complete seating (Fig. 8). The lower denture
was soft relined with a silicone based soft denture relining material
Ufi Gel Soft (VOCO America). By using the extended healing
caps with the soft reline, the immediate dentures were much more
retentive. The soft tissue and implants were evaluated clinically
after one week. The patient stated she had very little post-operative
discomfort or swelling.
Approximately nine weeks after the initial placement of the
dental implants, the patient returned for the definitive porcelain fused
to metal restoration impressions. Adequate implant osseointegration
was verified using an Osstell ISQ implant stability
meter (Osstell), which uses resonance frequency analysis (RFA)
as a method of measurement (Fig. 9). Several studies have been
conducted based on RFA measurements and the implant stability
quotient scale. They provide valid indications that the acceptable
stability range lays above 55 ISQ
Using impression posts, full arch impressions were taken using
Instant Custom C&B Trays (Goodfit). These custom trays can be
adapted and fitted in minutes, eliminating the need for models,
light cure materials, monomers and extra laboratory time in custom
impression tray fabrication, because they are made of a material
(PMMA) that becomes adjustable when heated and maintains
its shape while cooling. Once molded for the patient, an access
window was created to take an open tray impression (Fig. 10) and
full arch impressions were taken using a polyvinylsiloxane impression
material (Take 1 Advance by Kerr). Bite relations as well as
instructions for size, shape and color for the full arch fixed restoration
was forwarded to the dental laboratory.
Within a couple weeks, the custom abutments and final
bridgework were forwarded to the dental office. The custom
abutments were inserted and torqued to 25Ncm (Fig. 11). The
access openings were sealed with some cotton and Temposil
cement (Coltene Whaldent).
The patient was very satisfied with the look of her fixed
bridge restoration and approved them for final cementation.
The crown restorations were seated with Premier Implant Cement.
Premier Implant Cement is a non-eugenol resin cement
that features a unique, two-stage cure that makes seating the
restoration and removing excess cement a quick and simple process.
The rigid final set and low solubility in oral fluids provide
an excellent marignal seal and superior retention. The overall
health and structure of the soft tissue and restoration was very
good (Fig. 12). The patient was very pleased with the restorations
and her new enhanced smile.
The advent of cone CT scans and 3D treatment planning
software has not only improved yesterday's dentistry, it
is responsible now for the development of treatment plans that
would not otherwise be available today. Time-honored concepts
of trial and error and wait and see dentistry is rapidly
becoming a historical event within the dental profession. More
importantly, virtual planning is within the reach of nearly any
dentist or specialist. In addition, 3D dentistry does not automatically
determine that treatment costs will be higher. As in
this case, it was used to create a mandibular reconstruction
treatment plan that cut costs by 30 percent and made it immediately
affordable for the patient.
- Contemporary Implant Dentistry, Third Edition. Carl E. Misch. Mosby. Pages 327-364. 2008.