Ole Jensen Article on all on 4 V4 modification for dental implant placement in atrophic maxilla and mandible

1. J Oral Maxillofac Surg
67:1503-1509, 2009
All-on-4 Treatment of Highly Atrophic
Mandible With Mandibular V-4: Report of
2 Cases
Ole T. Jensen, DDS, MSc,* and Mark W. Adams, DDS, MSc†
This report contains a technical note and 2 case reports of the “all-on-4” treatment of the highly resorbed
mandible. The use of 4 angled implants directed toward the midline of the mandible at 30° angles
provides the advantage of increased implant length and adequate insertion torque for immediate
temporization. The technique engages or perforates the inferior border with implants placed in a spaced
distribution to avoid fracture of the mandible. The technique is proposed as an alternative to bone graft
reconstruction.
© 2009 American Association of Oral and Maxillofacial Surgeons
J Oral Maxillofac Surg 67:1503-1509, 2009
The markedly atrophic edentulous mandible, the so-
called Cawood Class IV-V mandible, in which the
available vertical basal bone is 5 to 7 mm, can still be
treated without bone grafting for dental implant
placement and immediate loading in a modified “all-
on-4” technique.1-6
A typical all-on-4 protocol uses posterior implants
tilted at 30° (posteriorly) that pass just anterior to the
mental foramen; anterior implants are placed verti-
cally in the canine-lateral incisor area. In the case of
marked atrophy, vertically placed anterior implants7,8
require placement of 8- to 10-mm implants that are
allowed to perforate the inferior border.5,6
Four 4-mm
holes placed through the anterior hoop of the mandible
can lead to stress risers, especially when perforating
holes converge or come too close together.7
This can
lead to mandibular fracture.9-11
To avoid fracture complications, most clinicians
prefer to place a bone graft to gain vertical height at
implant placement12-14
or before implant surgery15-17
to have enough bone height to sustain at least 10-mm
implants, especially if a favorable anterior-posterior
spread is difficult to obtain.18,19
An early site classification system suggested that the
bone mass requirement for sustained osseointegration
should be no less than 10 mm.20
However, the use of
this cutoff was arbitrary and not determined from
biomechanical mathematics, which must take into
account moment loads and cyclical loading for an
extended period.21,22
Also, during that formative pe-
riod, implant surfaces were not as improved as they
are today,23,24
such that, given current technology
and improved biomechanical understanding, the use
of even a 4- or 5-mm-length implant is thought to be
sufficient (mathematically) for load bearing in a well-
distributed scheme.25,26
However, most clinicians
have not been willing to accept the use of short
implants that could lose 1 to 2 mm of bone support
over time, leaving only a few millimeters of residual
height for continued function.27
Therefore, the issue
of implant length remains intuitively and experien-
tially valid, rather than mathematically determined.
Given the dilemma of the markedly atrophic man-
dible in a patient group not highly amendable to bone
graft reconstruction and a profession still in the de-
velopmental phase for the use of bone morphogenetic
protein-alloplast augmentation,28-30
the question must
be asked whether we can simply use the bone that is
available and avoid a complicated grafting procedure.
In the all-on-4 technique, tilting the posterior im-
plant increases the length in the bone by 50%.31
If
anterior implants are also tilted 30°, this same figure
also applies. By tilting all 4 implants toward the mid-
line in a V formation, 5-mm vertical bone can house
10-mm-length implants if the implants are allowed to
slightly perforate inferiorly, a significant improvement
for osseointegration potential.
This technique has been designated the “V-4” ap-
proach for the all-on-4 technique and has allowed
immediate fixed provisionalization for even highly
atrophic mandibles without bone grafting. The great
advantage of this approach is that the greater bone
*Asssociate Professor, Department of Oral and Maxillofacial Sur-
gery, Ann Arbor, MI.
†Private Practice, Greenwood Village, CO.
Address correspondence and reprint requests to Dr Jensen: 8200
E Belleview Ave, Suite 520, Greenwood Village, CO 80111; e-mail:
Ole.jensen@Clearchoice.com
© 2009 American Association of Oral and Maxillofacial Surgeons
0278-2391/09/6707-0023$36.00/0
doi:10.1016/j.joms.2009.03.031
1503

2. mass generally found more toward the midline can be
taken advantage of, and, despite implant convergence
toward the midline, the holes perforating the inferior
cortex remain well distributed and relatively far apart
from each other, reducing the fracture potential. The
parasymphyseal area, where a mandibular fracture is
mostly likely to occur, is avoided altogether.32,33
Case Reports
CASE 1
A 72-year-old woman had worn dentures for longer
than 30 years and presented with severe mandibular
atrophy with 8 to 10 mm of alveolar height as viewed
on the Panorex (Fig 1). However, because of reverse
architecture only 4 to 5 mm of vertical dimension was
present in the mid-alveolar (axial) dimension. The
mental foramina were dehisced and relatively forward
in the arch. The nerves were partially exposed poste-
riorly.
A full-thickness crestal incision was made anteriorly
but only through the mucosa posteriorly to avoid
cutting the nerves. Using blunt dissection, the nerves
were located and deflected laterally, leaving the fora-
men free of neural tissue. Anteriorly, the mentalis
muscle attachment was left undisturbed to prevent
ptosis. The mandible appeared very fragile overall,
but it had been especially resorbed in the parasym-
physeal regions. Although all-on-4 fixture placement
had been planned on the computer, the surgical
placement criteria dictated placing the implant visu-
ally to not fracture the mandible. The first fixture was
placed directly into the right mental foramen (Fig 2A)
and angled forward 30°. The anterior implants were
evenly spaced and also directed toward the midline at
30° (Fig 2B). This created an overall V-shape place-
ment appearance on Panorex designated a “V-4” all-
on-4 placement (Fig 3). Additionally, the implant
placement angles were tilted anteriorly to avoid lin-
gual plate perforation (Fig 4). Finally, 30° abutments
were placed to compensate for implant angulation for
immediate prosthetic rehabilitation.
CASE 2
An 81-year-old female patient with a history of
wearing full dentures for 35 years who had been
FIGURE 1. Preoperative Panorex view of 72-year-old woman who
presented with severe alveolar atrophy.
Jensen et al. Treatment With Mandibular V-4. J Oral Maxillofac
Surg 2009.
FIGURE 2. A, Using the all-on-4 technique, posterior fixture was
placed directly through mental foramen after deflecting dehisced
inferior alveolar nerve laterally. B, This was done bilaterally.
Jensen et al. Treatment With Mandibular V-4. J Oral Maxillofac
Surg 2009.
1504 TREATMENT WITH MANDIBULAR V-4

3. taking an oral bisphosphonate (Fosamax; Merck,
Whitehouse Station, NJ) for 7 years for osteoporosis
presented for dental implant rehabilitation. The re-
sults from a fasting C-terminal telopeptide study were
satisfactory (315 pg/mL).
The mandible was highly atrophic with 3 to 4 mm
of vertical bone in the right symphysis and 5 to 6 mm
in the left. In preparing the implant sites, the vertical
available bone was a maximum of 5 to 7 mm (Fig 5).
After reflection of a flap, taking care to avoid nerve
injury and preserving the mentalis muscle attach-
ment, posterior implants were placed through the
foramen sites after deflection of the dehisced nerves.
Because the mandible resorbs, the mental foramen
often presents in a mid-crestal location. These im-
plants were placed at 30°, angling forward (Fig 6).
The front implants were well-distributed and
placed at somewhat less than 30° but still angled
toward the midline (Fig 7). The overall distribution
and display on the Panorex was a V shape (Fig 8). The
patient was immediately provided, after placement of
the 30° abutments, with a fixed provisional bridge.
Discussion
Patients who have worn dentures for 3 or more
decades may seek implant reconstruction because of
the pain from exposed inferior alveolar nerves owing
to complete alveolar loss from atrophy. Denture com-
pression of exposed nerves is best treated in this
setting by dental implants; however, the lack of jaw
bone height is a concern. Although a 10-mm vertical
height may be present mid-symphysis, the parasym-
physeal areas are often one half the height of the
symphysis. Also, in this setting, the mid-alveolar area
is often of a reverse architecture, such that the actual
mid-axial alveolar height is much less than seems
apparent on a Panorex. Although the lateral bone
height can be relatively high, it cannot be accessed for
implant placement; thus, often implants must be
placed where bone is relatively deficient. Therefore,
most experienced clinicians prefer to place implants
with a careful minimal torque technique but still per-
forating through the inferior border. Using this ap-
proach, an 8- or 10-mm fixture is still placed into a 5-
to 7-mm site.
The value of angulation of implants in a V-4 distri-
bution strategy is that bone grafting can be avoided,
because fixtures are favorably directed toward the
location of maximal bone mass. This approach is also
excellent to use without inferior border perforation if
somewhat greater bone mass is available.
The V-4 technique is biomechanically favorable in 3
ways: 1) mandibular continuity preservation; 2) a
greater length of implants; and 3) the V-shape is very
stable biomechanically.
FIGURE 3. Placement of 2 anterior implants angled at 30° to midline
created a V shape for “all-on-4” placement, designated V-4.
Jensen et al. Treatment With Mandibular V-4. J Oral Maxillofac Surg
2009.
FIGURE 5. View of 81-year-old woman who presented with severe
mandibular atrophy with 5 to 7 mm of bone available in desired
implant sites.
Jensen et al. Treatment With Mandibular V-4. J Oral Maxillofac
Surg 2009.
FIGURE 4. All implants angled slightly anteriorly to avoid perfo-
ration of lingual plate.
Jensen et al. Treatment With Mandibular V-4. J Oral Maxillofac
Surg 2009.
JENSEN ET AL 1505

4. MANDIBULAR CONTINUITY PRESERVATION
A 4-mm hole drilled into the anterior tibia, a weight-
bearing bone, reduces bone strength by 40%.34
A
4-mm hole drilled into the mandible, especially into a
low-bone-volume atrophic mandible, may consider-
ably weaken the jaw, even though it is not a weight-
bearing bone.35
The placement of 4 holes through the
hoop of the mandible, especially if they are not centrally
placed, risks a discontinuity fracture intraoperatively36
or during the demineralization phase of healing.37
At
about 3 weeks after surgery, it is possible for a jaw
fracture to occur under normal functional loading38
ow-
ing to the relative weakening of the jaw caused by the
regional acceleratory phenomenon.39
However, the
area at the greatest risk of this is the parasymphysis,
which is avoided using V-4 angulation.
The implants should be placed using a screw tap
method, even using self-tapping implant protocols to
decrease insertion torque values and not overload the
bone.38,40
FIGURE 6. A, B, Posterior implants placed at 30° angulation.
Jensen et al. Treatment With Mandibular V-4. J Oral Maxillofac
Surg 2009.
FIGURE 7. Anterior implants angled forward at approximately
30° such that adjacent implants are parallel to each other and do
not converge at inferior border.
Jensen et al. Treatment With Mandibular V-4. J Oral Maxillofac
Surg 2009.
FIGURE 8. Overall presentation on Panorex was a V-4 display.
Jensen et al. Treatment With Mandibular V-4. J Oral Maxillofac
Surg 2009.
1506 TREATMENT WITH MANDIBULAR V-4

5. GREATER LENGTH OF IMPLANTS
What is important is not simply to have a greater
implant length, but also to have the implant primarily
fixated into compact bone.41
Bone grafting to gain
implant length is an alternative strategy; however,
vertical bone grafts are the earliest to fail under stress,
and implants secured mainly by bone grafts can some-
times fail with time.42
The incidental elevation of
inferior border periosteum to gain periosteal prolifer-
ative bone must also be considered as potential sec-
ondary support, although it does not always occur43
(Fig 9). Therefore, the most dependable bone for
long-term osseointegration is compact bone, more of
which is encountered by implant angulation using a
V-4 strategy.
These compromised sites should probably use
4-mm diameter implants or less rather than trying to
gain more surface osseointegration using shorter,
wider (5-mm) implants, which considerably increases
the risk of jaw fracture.
FIGURE 9. A, Implant insertion through inferior border. B, Periosteal bone apposition observed 6 months later. C, Panorex demonstrating
vertical bone growth of 2 to 3 mm compared with preoperative view after 6 months of function. D, Occlusal scheme with anteriorized
occlusion and posterior disclusion during 6-month provisional loading phase.
Jensen et al. Treatment With Mandibular V-4. J Oral Maxillofac Surg 2009.
JENSEN ET AL 1507

6. V-SHAPE BIOMECHANICS
The reason the V shape is favorable biomechani-
cally is the greater length of implants into more dense
bone. Also, the angulated implant pull-out strength in
a splinted configuration is intuitively greater for an-
gled implants. In the V-4 strategy, this is multiplied by
a factor of 4, although this has not been studied
experimentally. Finite element analysis of the tilted
implants that are splinted in a full-fixed prosthesis
revealed a decreased peri-implant “bone strain” com-
pared with vertical implants, supporting a cantile-
vered prosthesis and implying better load-bearing bi-
omechanics.44
The highly atrophic mandible in the elderly patient
can be treated with an all-on-4 technique without
bone grafting with an immediate loading protocol
by distributing the implants in a V shape, desig-
nated the V-4 technique. The V-4 is protective of
mandibular continuity, derives increased implant
length with acceptable insertion torque values, and
maintains a standard all-on-4 pattern of prosthetic distri-
bution despite the angulated placement. A splinted V-4
distribution has highly favorable biomechanics. Overall,
the V-4 permits the use of a conservative nongrafting
approach in what might otherwise require significant
bone graft reconstruction in a commonly elderly popu-
lation.
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