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J Oral Maxillofac Surg67:1503-1509, 2009

All-on-4 Treatment of Highly AtrophicMandible With Mandibular V-4: Report of

2 CasesOle 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 resorbedmandible. The use of 4 angled implants directed toward the midline of the mandible at 30° anglesprovides the advantage of increased implant length and adequate insertion torque for immediatetemporization. The technique engages or perforates the inferior border with implants placed in a spaceddistribution to avoid fracture of the mandible. The technique is proposed as an alternative to bone graftreconstruction.© 2009 American Association of Oral and Maxillofacial Surgeons

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he markedly atrophic edentulous mandible, the so-alled Cawood Class IV-V mandible, in which thevailable vertical basal bone is 5 to 7 mm, can still bereated without bone grafting for dental implantlacement and immediate loading in a modified “all-n-4” technique.1-6

A typical all-on-4 protocol uses posterior implantsilted at 30° (posteriorly) that pass just anterior to theental foramen; anterior implants are placed verti-

ally in the canine-lateral incisor area. In the case ofarked atrophy, vertically placed anterior implants7,8

equire placement of 8- to 10-mm implants that arellowed to perforate the inferior border.5,6 Four 4-mmoles placed through the anterior hoop of the mandiblean lead to stress risers, especially when perforatingoles converge or come too close together.7 This can

ead to mandibular fracture.9-11

To avoid fracture complications, most cliniciansrefer to place a bone graft to gain vertical height at

mplant placement12-14 or before implant surgery15-17

o have enough bone height to sustain at least 10-mmmplants, especially if a favorable anterior-posteriorpread is difficult to obtain.18,19

An early site classification system suggested that theone mass requirement for sustained osseointegrationhould be no less than 10 mm.20 However, the use of

*Asssociate Professor, Department of Oral and Maxillofacial Sur-

ery, Ann Arbor, MI.

†Private Practice, Greenwood Village, CO.

Address correspondence and reprint requests to Dr Jensen: 8200

Belleview Ave, Suite 520, Greenwood Village, CO 80111; e-mail:

[email protected]

2009 American Association of Oral and Maxillofacial Surgeons

278-2391/09/6707-0023$36.00/0

aoi:10.1016/j.joms.2009.03.031

1503

his cutoff was arbitrary and not determined fromiomechanical mathematics, which must take intoccount moment loads and cyclical loading for anxtended period.21,22 Also, during that formative pe-iod, implant surfaces were not as improved as theyre today,23,24 such that, given current technologynd improved biomechanical understanding, the usef even a 4- or 5-mm-length implant is thought to beufficient (mathematically) for load bearing in a well-istributed scheme.25,26 However, most cliniciansave not been willing to accept the use of short

mplants that could lose 1 to 2 mm of bone supportver time, leaving only a few millimeters of residualeight for continued function.27 Therefore, the issuef implant length remains intuitively and experien-ially valid, rather than mathematically determined.

Given the dilemma of the markedly atrophic man-ible in a patient group not highly amendable to boneraft reconstruction and a profession still in the de-elopmental phase for the use of bone morphogeneticrotein-alloplast augmentation,28-30 the question muste asked whether we can simply use the bone that isvailable and avoid a complicated grafting procedure.

In the all-on-4 technique, tilting the posterior im-lant increases the length in the bone by 50%.31 Ifnterior implants are also tilted 30°, this same figurelso applies. By tilting all 4 implants toward the mid-ine in a V formation, 5-mm vertical bone can house0-mm-length implants if the implants are allowed tolightly perforate inferiorly, a significant improvementor osseointegration potential.

This technique has been designated the “V-4” ap-roach for the all-on-4 technique and has allowed

mmediate fixed provisionalization for even highlytrophic mandibles without bone grafting. The great

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1504 TREATMENT WITH MANDIBULAR V-4

ass generally found more toward the midline can beaken advantage of, and, despite implant convergenceoward the midline, the holes perforating the inferiorortex remain well distributed and relatively far apartrom each other, reducing the fracture potential. Thearasymphyseal area, where a mandibular fracture isostly likely to occur, is avoided altogether.32,33

ase Reports

CASE 1

A 72-year-old woman had worn dentures for longerhan 30 years and presented with severe mandibulartrophy with 8 to 10 mm of alveolar height as viewedn the Panorex (Fig 1). However, because of reverserchitecture only 4 to 5 mm of vertical dimension wasresent in the mid-alveolar (axial) dimension. Theental foramina were dehisced and relatively forward

n the arch. The nerves were partially exposed poste-iorly.

A full-thickness crestal incision was made anteriorlyut only through the mucosa posteriorly to avoidutting the nerves. Using blunt dissection, the nervesere located and deflected laterally, leaving the fora-en free of neural tissue. Anteriorly, the mentalisuscle attachment was left undisturbed to preventtosis. The mandible appeared very fragile overall,ut it had been especially resorbed in the parasym-hyseal regions. Although all-on-4 fixture placementad been planned on the computer, the surgicallacement criteria dictated placing the implant visu-lly to not fracture the mandible. The first fixture waslaced directly into the right mental foramen (Fig 2A)nd angled forward 30°. The anterior implants werevenly spaced and also directed toward the midline at0° (Fig 2B). This created an overall V-shape place-ent appearance on Panorex designated a “V-4” all-

n-4 placement (Fig 3). Additionally, the implantlacement angles were tilted anteriorly to avoid lin-

IGURE 1. Preoperative Panorex view of 72-year-old woman whoresented with severe alveolar atrophy.

ensen et al. Treatment With Mandibular V-4. J Oral Maxillofacurg 2009.

ual plate perforation (Fig 4). Finally, 30° abutmentsJS

ere placed to compensate for implant angulation formmediate prosthetic rehabilitation.

CASE 2

An 81-year-old female patient with a history ofearing full dentures for 35 years who had been

IGURE 2. A, Using the all-on-4 technique, posterior fixture waslaced directly through mental foramen after deflecting dehisced

nferior alveolar nerve laterally. B, This was done bilaterally.

ensen et al. Treatment With Mandibular V-4. J Oral Maxillofacurg 2009.

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JENSEN ET AL 1505

aking an oral bisphosphonate (Fosamax; Merck,hitehouse Station, NJ) for 7 years for osteoporosis

resented for dental implant rehabilitation. The re-ults from a fasting C-terminal telopeptide study wereatisfactory (315 pg/mL).

The mandible was highly atrophic with 3 to 4 mmf vertical bone in the right symphysis and 5 to 6 mm

n the left. In preparing the implant sites, the verticalvailable bone was a maximum of 5 to 7 mm (Fig 5).

After reflection of a flap, taking care to avoid nervenjury and preserving the mentalis muscle attach-

ent, posterior implants were placed through theoramen sites after deflection of the dehisced nerves.ecause the mandible resorbs, the mental foramenften presents in a mid-crestal location. These im-lants were placed at 30°, angling forward (Fig 6).

IGURE 3. Placement of 2 anterior implants angled at 30° to midlinereated a V shape for “all-on-4” placement, designated V-4.

ensen et al. Treatment With Mandibular V-4. J Oral Maxillofac Surg009.

IGURE 4. All implants angled slightly anteriorly to avoid perfo-ation of lingual plate.

sensen et al. Treatment With Mandibular V-4. J Oral Maxillofacurg 2009.

The front implants were well-distributed andlaced at somewhat less than 30° but still angledoward the midline (Fig 7). The overall distributionnd display on the Panorex was a V shape (Fig 8). Theatient was immediately provided, after placement ofhe 30° abutments, with a fixed provisional bridge.

iscussion

Patients who have worn dentures for 3 or moreecades may seek implant reconstruction because ofhe pain from exposed inferior alveolar nerves owingo complete alveolar loss from atrophy. Denture com-ression of exposed nerves is best treated in thisetting by dental implants; however, the lack of jawone height is a concern. Although a 10-mm verticaleight may be present mid-symphysis, the parasym-hyseal areas are often one half the height of theymphysis. Also, in this setting, the mid-alveolar areas often of a reverse architecture, such that the actual

id-axial alveolar height is much less than seemspparent on a Panorex. Although the lateral boneeight can be relatively high, it cannot be accessed for

mplant placement; thus, often implants must belaced where bone is relatively deficient. Therefore,ost experienced clinicians prefer to place implantsith a careful minimal torque technique but still per-

orating through the inferior border. Using this ap-roach, an 8- or 10-mm fixture is still placed into a 5-o 7-mm site.

The value of angulation of implants in a V-4 distri-ution strategy is that bone grafting can be avoided,ecause fixtures are favorably directed toward the

ocation of maximal bone mass. This approach is alsoxcellent to use without inferior border perforation ifomewhat greater bone mass is available.

The V-4 technique is biomechanically favorable in 3ays: 1) mandibular continuity preservation; 2) a

reater length of implants; and 3) the V-shape is very

IGURE 5. View of 81-year-old woman who presented with severeandibular atrophy with 5 to 7 mm of bone available in desired

mplant sites.

ensen et al. Treatment With Mandibular V-4. J Oral Maxillofacurg 2009.

table biomechanically.

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1506 TREATMENT WITH MANDIBULAR V-4

MANDIBULAR CONTINUITY PRESERVATION

A 4-mm hole drilled into the anterior tibia, a weight-earing bone, reduces bone strength by 40%.34 A-mm hole drilled into the mandible, especially into a

ow-bone-volume atrophic mandible, may consider-

FIGURE 6. A, B, Posterior implants placed at 30° angulation.

ensen et al. Treatment With Mandibular V-4. J Oral Maxillofacurg 2009.

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bly weaken the jaw, even though it is not a weight-earing bone.35 The placement of 4 holes through theoop of the mandible, especially if they are not centrallylaced, risks a discontinuity fracture intraoperatively36

r during the demineralization phase of healing.37 Atbout 3 weeks after surgery, it is possible for a jawracture to occur under normal functional loading38 ow-ng to the relative weakening of the jaw caused by theegional acceleratory phenomenon.39 However, therea at the greatest risk of this is the parasymphysis,hich is avoided using V-4 angulation.The implants should be placed using a screw tapethod, even using self-tapping implant protocols to

ecrease insertion torque values and not overload theone.38,40

IGURE 7. Anterior implants angled forward at approximately0° such that adjacent implants are parallel to each other and doot converge at inferior border.

ensen et al. Treatment With Mandibular V-4. J Oral Maxillofacurg 2009.

FIGURE 8. Overall presentation on Panorex was a V-4 display.

ensen et al. Treatment With Mandibular V-4. J Oral Maxillofacurg 2009.

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JENSEN ET AL 1507

GREATER LENGTH OF IMPLANTS

What is important is not simply to have a greatermplant length, but also to have the implant primarilyxated into compact bone.41 Bone grafting to gain

mplant length is an alternative strategy; however,ertical bone grafts are the earliest to fail under stress,nd implants secured mainly by bone grafts can some-imes fail with time.42 The incidental elevation ofnferior border periosteum to gain periosteal prolifer-

IGURE 9. A, Implant insertion through inferior border. B, Periostertical bone growth of 2 to 3 mm compared with preoperativecclusion and posterior disclusion during 6-month provisional load

ensen et al. Treatment With Mandibular V-4. J Oral Maxillofac

tive bone must also be considered as potential sec- t

ndary support, although it does not always occur43

Fig 9). Therefore, the most dependable bone forong-term osseointegration is compact bone, more of

hich is encountered by implant angulation using a-4 strategy.These compromised sites should probably use

-mm diameter implants or less rather than trying toain more surface osseointegration using shorter,ider (5-mm) implants, which considerably increases

e apposition observed 6 months later. C, Panorex demonstratingfter 6 months of function. D, Occlusal scheme with anteriorizedase.

09.

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he risk of jaw fracture.

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1508 TREATMENT WITH MANDIBULAR V-4

V-SHAPE BIOMECHANICS

The reason the V shape is favorable biomechani-ally is the greater length of implants into more denseone. Also, the angulated implant pull-out strength insplinted configuration is intuitively greater for an-

led implants. In the V-4 strategy, this is multiplied byfactor of 4, although this has not been studied

xperimentally. Finite element analysis of the tiltedmplants that are splinted in a full-fixed prosthesisevealed a decreased peri-implant “bone strain” com-ared with vertical implants, supporting a cantile-ered prosthesis and implying better load-bearing bi-mechanics.44

The highly atrophic mandible in the elderly patientan be treated with an all-on-4 technique withoutone grafting with an immediate loading protocoly distributing the implants in a V shape, desig-ated the V-4 technique. The V-4 is protective ofandibular continuity, derives increased implant

ength with acceptable insertion torque values, andaintains a standard all-on-4 pattern of prosthetic distri-

ution despite the angulated placement. A splinted V-4istribution has highly favorable biomechanics. Overall,he V-4 permits the use of a conservative nongraftingpproach in what might otherwise require significantone graft reconstruction in a commonly elderly popu-

ation.

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