The All-on-4 Shelf: Maxilla

(1)

All-on-4 treatment of the maxilla requires presurgical prosthetic treatment planning for high smile line es-thetics to be acceptable.1,2 _{This requires bone}

re-moval in the vast majority of dentate or edentulous patients who undergo full arch treatment. This is particularly important in the female population, who have greater gingival display to avoid exposure of the restoration margin during animation.3,4 _{Because of}

this, the surgeon is faced with the dilemma of removal of supporting bone for dental implant placement, often to such an extent that axial implant placement becomes impossible without significant bone graft-ing, especially sinus floor augmentation.5-7

Since the Sinus Consensus Conference of 1996,8

most treatment plans involving atrophic maxillae have involved sinus bone grafting and placement of multiple posterior implants. However, within the past decade, a simple innovation, that of nonaxial implant placement, with implant placement angulations of up to 30°, has led to a new concept, that of “graftless” surgical management.9-13

Surgical care for the maxilla, therefore, stands at a crossroads, that of subtraction of bone mass versus addition of bone graft for osseointegration. Driving this controversy is the desire for immediate function, something nearly impossible to do when significant bone grafting is performed.

The use of angulated implants for short-span bridges or even long-span reconstructions to avoid bone grafts has now been used for 10 years, although many of these were not immediately loaded.13-16 However, with the advent of the All-on-4 immediate function, this became consistently possible using a graftless protocol.

Immediate function is based on earlier studies, some-times using up to 10 implants per arch until biomechani-cal analysis demonstrated that when 2 implants are placed sufficiently close together, they function as if there were only 1 implant present (B. Rangert, personal communication, March 2007). This discovery first be-came important in the mandible, where fixed denture prosthetics using 5 implants had been (and still is) pre-scribed as optimal. However, when 5 implant distribu-tion was studied biomechanically it was found that the

middle implant took no measurable loadin function and therefore could be eliminated. This same biome-chanical finding was observed for the maxilla.17-21

Another important aspect of maxillary care is ex-traction of diseased teeth followed by simultaneous implant placement with immediate function.22-24The surgeon is therefore faced with the challenge of re-moving failing teeth, trimming back bone stock, avoiding bone grafting procedures, inserting dental implants at angulations, and placing the patient into an immediately loaded provisional restoration; all of these procedures are counterintuitive to traditional surgical management, if not biomechanical under-standing of maxillary treatment.25-27Antemolar reduc-tion in the number of implants, restricted to available bone anterior to the sinus cavities, further compli-cates the surgical difficulty.28

Given this controversy, 3 questions must be asked in the face of reduced bone stock: 1) Can osseointegration occur without significant grafting?

2) Can full arch prosthetic loading be obtained with only 4 implants placed at angulation? 3) Can

imme-*Director, Colorado Tissue Engineering Institute, Denver, CO. †Private Practice, Denver, CO.

‡Fellow, Colorado Tissue Engineering Institute, Denver, CO. §Private Practice, Dallas, TX.

㛳Private Practice, Dallas, TX.

Address correspondence and reprint requests to Dr Jensen: Implant Dentistry Associates of Colorado, 8200 East Belleview Avenue, Suite 520E, Greenwood Village, CO 80111; e-mail:

[email protected]

doi:10.1016/j.joms.2010.05.082

(2)

diate load biomechanics be established using the limited bone stock of the anterior maxilla?

The somewhat oblique answer to these questions is found in the development of a simple surgical solution in which bone is leveled by prosthetic prescription creating a flat surface termed the All-on-4 shelf (Fig 1A). Placed “on” this shelf are im-plants directed at angulations emerging from spe-cific end points likely to gain primary fixation (Fig 1B). The implant positions on the shelf are based in part on compensating angled abutments that must emerge through tissue at or lingual to the midoc-clusal axial plane.29The shelf facilitates the anteri-or-posterior (A-P) spread maximum by identifying the anterior sinus wall and lateral nasal wall.14

There are numerous other advantages to using a shelf approach, which affirm that adequate os-seointegration capacity of only 4 load-bearing im-plants can biomechanically sustain immediate pro-visionalization.

Here, then, are 10 technical advantages for the surgical-prosthetic team to consider in the use of the maxillary All-on-4 shelf:

1. Creates prosthetic restorative space 2. Establishes the alveolar plane

3. Shelf width determines implant diameter selec-tion

4. Shelf reduction proximates piriform bone fixa-tion

FIGURE 1. A, Bone leveling of the alveolus creates a new alveolar plane that functions as a “shelf” on which to place dental implants. The

All-on-4 technique must take advantage of available bone, which is best observed using the All-on-4 shelf approach for which angled implants and compensating angled abutments are placed. B, The All-on-4 shelf provides several advantages for the surgical-prosthetic team, including determining optimal sites for implant placement and helping to avoid pneumatized structures to derive maximum anterior-posterior spread.

(3)

5. Shelf findings suggest convergent or divergent implant placement strategy

6. Establishes optimal osseous sites for implant placement

7. Defines secondary fallback sites for implant placement

8. Exposes palatal plate cortical anatomy for im-plant fixation

9. Facilitates posterior implant placement (A-P spread) in relation to anterior sinus wall 10. Provides bone stock for bone grafting Prosthetic Restoration Space

One of the most difficult surgical prosthetic errors to manage is insufficient interocclusal space, that is, inadequate interrestorative space between opposing arches.27,30,31 _{This can be due to inadequate bone}

removal in full arch cases. Therefore, the most impor-tant function of the All-on-4 shelf is adequate bone

reduction, especially in dual-arch cases which require 22 mm of interarch prosthetic space. The use of bone reduction guides (Fig 2) or windowed denture guides (Fig 3) helps facilitate adequate bone removal.

When the junction of the prosthesis and tissue is visible, there is esthetic failure. A flange is required to hide the junction. Use of a flange on a fixed prosthesis creates an oral hygiene access problem. By locating the prosthesis tissue junction a minimum of 3 mm beyond the visible gingiva, the surgeon and restor-ative dentist are assured of hiding the prosthesis-tissue junction. This is perhaps the greatest advantage of using the All-on-4 shelf. Although not yet pub-lished, alveolar reduction to this extent has not led to bone-level instability, greater tendency for bone loss, or gingival hyperplasia around implants.

Alveolar Plane

Using the interpupillary plane as a guide, a new “alveolar plane” is established, which avoids a cant in the positioning of implants and creates level place-ment of implant platforms; this is difficult to do with-out creating the All-on-4 shelf.16,32When upper and lower jaw shelves parallel each other (Fig 4), there is less likely to be prosthetic problems with implant positioning.

The alveolar plane must also be level front to back. A common error in making the shelf is to taper the shelf too much toward the alveolar crest posteriorly, leaving the prosthodontist with inadequate interarch space. This leads to an “alligator bite” effect and can result in a thin prosthesis in the bicuspid-molar re-gion. Therefore, the All-on-4 shelf must not only cre-ate an alveolar plane parallel to the interpullary line FIGURE 2. A clear acrylic bone reduction guide ensures there is

adequate restorative space for abutments and titanium bar housed within the prosthesis.

Jensen et al. The All-on-4 Shelf: Maxilla. J Oral Maxillofac Surg 2010.

FIGURE 3. The provisional appliance can be “windowed” to

determine adequate bone removal and used to determine appro-priate abutment angulation.

FIGURE 4. Bimaxillary All-on-4 surgery should have at least

22 mm of interarch space for the final provisional restoration. The planes should be parallel front to back.

(4)

but a plane, when viewed laterally, that is parallel to Frankfort horizontal.

Shelf Width

After bone reduction, the width of the shelf be-comes defined at the level of the desired implant platform vertical dimension. Alveolar concavities be-come evident, and optimal diameter of implants can be assessed.33When the ridge is thin (Fig 5), small-diameter implants are placed; if it is wide and osteoporotic, a wide-diameter implant may be prescribed.34

Midalveolar constriction, the so-called hourglass ef-fect, seen on cross-sectional computed tomography in the anterior maxilla can sometimes be pronounced. If the alveolar plane is established at the constriction, a narrow implant is needed to avoid fracturing the al-veolus. The width of the shelf is another factor that can be addressed at the time the shelf is made by sometimes removing more bone than necessary to optimize the width of implants used.

Piriform Rim Proximation

When there is alveolar crest atrophy, vertical di-mension may still be present but at reduced width such that reduction of height will not only widen the shelf but bring the created alveolar plane in closer approximation to the piriform rim, the most desirable site for implant fixation using an M-4 placement strat-egy (Fig 6).35 Shelf reduction then determines the position and length of posterior implant placement with a maximum available implant length of 18 mm (Nobel Biocare, Zurich, Switzerland). Inadequate bone reduction may force the clinician to anteriorize the placement of the posterior implant or even pre-vent adequate fixation. Optimal implant fixation for the atrophic maxilla is frequently obtained using an M-4 placement strategy fixing implants at what has been called M-point (Fig 7), the point of maximum bone mass at the lateral piriform rim just above the nasal fossa.35 Even in highly atrophic cases, the posterior implant can often be placed 10 mm or more posterior to this point.

Implant Angulation Strategy

More than any surgical procedure, the All-on-4 shelf helps determine the angulation strategy em-ployed for implant placement. Long face syndrome patients, after shelf reduction, may still have ade-quate bone for axial placement of implants,36 whereas short face patients after bone reduction require all implants to be angled, usually using the M-4 strategy.35,37

Optimal Osseous Implant Sites

After alveolar crest reduction, the surgeon is of-ten faced with the prospect of implant placement FIGURE 5. A thin residual maxillary alveolar process will split

unless small-diameter implants are used as shown. The shelf width helps determine implant diameter selection.

FIGURE 6. Using an angulated placement strategy, paranasal

cortical bone is able to anchor an implant placed at some distance away. When subnasal bone is reduced in height, anterior implants are angled posteriorally to engage bone in this same area.

FIGURE 7. M-Point, the area of maximum lateral pyriform rim

bone mass above the nasal fossa, enables using the “M”-shaped (when viewed on Panorex) placement strategy, including fixation of longer implants placed at a favorable distribution for anterior-posterior spread.

(5)

extraction. Following bone reduction, the surgeon is able to identify either visually or tactically the best load bearing sites possible for implant place-ment.

Determine Fallback Implant Sites

Before preparation of final implant sites, secondary, or fallback, sites are assessed. Oftentimes, there are a limited number of sites available, and therefore, it is important for the surgeon to address this ahead of time. In the process of creating 4 receptor sites, one or more sites may need to be abandoned because of a lack of bone quality or quantity for fixation. A sequen-tial (and careful) preplanned placement strategy with secondary fallback sites can salvage treatment for an immediate-load strategy best facilitated by use of the All-on-4 shelf.

This process of selecting sites is important lest the surgeon paint himself or herself into a corner. The first site selected is the posterior site, not the anterior site. If that site does not work, moving slightly for-ward is the secondary site. After posterior implants are placed, anterior sites are selected in a distributed fashion.

Palatal Cortical Plate

Although a computed tomographic scan can delin-eate width of the palatal plate,39,40after bone reduc-tion, the specific site of placement is more easily assessed for cortical thickness because implants will likely need to engage the palatal plate because of the complete loss of facial bone that is often seen in periodontally involved dental extraction cases.40 Gen-erally, the palatal plate can be difficult to engage, but with shelf reduction, it usually is clear to the surgeon how best to gain access through the alveolus and engage at least a portion of the palatal cortex. The thicker the plate, the more likely adequate insertion torque will be obtained (Fig 8).41

Posterior Implant Placement and Anterior-Posterior Spread

The All-on-4 shelf clearly shows the maximum al-lowable posterior position where the posterior im-plant can be placed because shelf reduction fre-quently exposes the sinus membrane, which can then FIGURE 8. The All-on-4 shelf established a visual cue by exposing

the palatal cortical bone thickness for optimal placement for high insertion torque implants.

FIGURE 9. The All-on-4 shelf frequently exposes the sinus cavity or

brings it into close approximation such that the exact visual location of the anterior sinus wall (S-point) can be identified to place the posterior implant as far back in the arch as possible without sub-jecting the patient to sinus floor bone grafting.

(6)

be directly visualized (or reflected) for placing the implant just anterior to the anterior sinus wall (Fig 9). When the sinus is not exposed, a lateral punch hole into the sinus is made at the most anterior inferior extent of pneumatization to serve as a guide for im-plant placement and angulation.14This point is called S-Point, for sinus point, in All-on-4 nomenclature. This is the most anterior inferior projection of the sinus

where implants must bypass to not traverse the sinus cavity and where posteriorly, no load-bearing bone is present36(Fig 10A).

The vertical alveolar bone available from S-Point to the alveolar plane of the All-on-4 shelf often deter-mines how far posteriorly the implant can be in-serted. For example, if there is 5 mm of bone from S-Point to the All-on-4 shelf, implant insertion can usually be accomplished about 5 mm posterior to S-Point when the implant is angled 30° (Fig 10B).

When S-Point and M-point converge, A-P spread is reduced proportionately; when there is confluence between the nasal fossa and maxillary sinus (1 cavity), no fixation points are available and the alveolar All-on-4 procedure may be contraindicated in favor of a zygomatic All-on-4 strategy.42,43

Bone Stock Source

Although the All-on-4 procedure is considered a “graftless” procedure, it often is not.13Bone removal in creation of the All-on-4 shelf is ground up for use in grafting fenestrations, extraction wall defects, cystic cavities, exposed implant threads in narrow alveolar placements, and sometimes even for sinus grafting.44-46

FIGURE 10. A, When the shelf is well away from the sinus, the

most anterior sinus deflection (S-point) is identified using a lateral antrostomy burr hole. The space from this point to the shelf is measured. This same distance posterior of the S-point perpendicu-lar should be the entrance location of the posterior implant site (when placed at 30°) to avoid the sinus. B, The vertical alveolar bone available from S-Point to the alveolar plane of the All-on-4 shelf often determines how far posteriorally the implant can be inserted.

FIGURE 11. Variants of the natural orifice of the nasolacrimal duct

that may occur intraossesously below the inferior turbinate and can be close to piriform rim bone used to place “M”-shaped distribution implants. Care should be taken not to cause nasolacrimal damage inadvertently when the duct is near M-point for All-on-4 implant placement.

(7)

Nasolacrimal Duct

One final anatomic structure to be aware of is the nasolacrimal duct, which exits below the inferior tur-binate sometimes anatomically near where M-point implant fixation is desirable in the piriform (Fig 11).4-9 Implants that penetrate the piriform and enter into the nasal fossa can on rare occasions disturb nasolac-rimal drainage.47

Discussion

The overall benefit of the All-on-4 shelf is one of technical, biological, and biomechanical advantage to the surgical prosthetic team.13 The use of the shelf ensures that implants are placed at the right level, at the most optimal angles, at maximum A-P spread, and with the most favorable insertion torque obtainable for immediate load restorations. Recall the three questions of controversy: 1) Can osseointegration occur in the maxilla without bone grafting? 2) Can full arch prosthetic loading be accomplished with only 4 implants placed at angu-lation? 3) Can full arch immediate load biomechan-ics be satisfied by the often limited bone stock of the anterior maxilla? All of these questions are more

ment scheme.

References

1. Garber DA, Belser UC: Restoration-driven implant placement with restoration-generated site development. Compend Contin Educ Dent 16:796, 798, 804, 1995

2. McFadden DD, Australas AR: Pre-prosthetic surgery options for fixed dental implant reconstruction of the atrophic maxilla. Coll Dent Surg 15:61, 2000

3. Jivraj S, Chee W: Treatment planning of implants in the aes-thetic zone. Br Dent J 201:77, 2006

4. Berson PJ: The functionally fixed restoration: A third modality of treatment. Compend Contin Educ Dent 23:157, 164, 166, 2002

5. Kahnberg KE, Wallström M, Rasmusson L: Local sinus lift for single-tooth implant. I. Clinical and radiographic follow-up. Clin Implant Dent Relat Res, 2009

6. Raja SV: Management of the posterior maxilla with sinus lift: Review of techniques. J Oral Maxillofac Surg 67:1730, 2009 7. Huang HL, Fuh LJ, Ko CC, et al: Biomechanical effects of a

maxillary implant in the augmented sinus: A three-dimensional finite element analysis. Int J Oral Maxillofac Implants 24:455, 2009

8. Jensen OT, Shulman L, Block M, et al: Report of the Sinus Consensus Conference of 1996. Int J Oral Maxillofac Implants 139(Suppl.):11, 1998

9. Aparicio C, Perales P, Rangert B: Tilted implants as an alterna-tive to maxillary sinus grafting: A clinical, radiologic, and peri-otest study. Clin Implant Dent Relat Res 3:39, 2001

10. Capelli M, Zuffetti F, Del Fabbro M, et al: Immediate rehabili-tation of the completely edentulous jaw with fixed prostheses supported by either upright or tilted implants: A multicenter clinical study. Int J Oral Maxillofac Implants 22:639, 2007 11. Testori T, Del Fabbro M, Capelli M, et al: Immediate occlusal

loading and tilted implants for the rehabilitation of the atrophic edentulous maxilla: 1-year interim results of a multicenter pro-spective study. Clin Oral Implants Res 19:227, 2008

12. Francetti L, Agliardi E, Testori T, et al: Immediate rehabilitation of the mandible with fixed full prosthesis supported by axial and tilted implants: Interim results of a single cohort prospec-tive study. Clin Implant Dent Relat Res 10:255, 2008 13. Krekmanov L, Kahn M, Rangert B, et al: Tilting of posterior

mandibular and maxillary implants for improved prosthesis support. Int J Oral Maxillofac Implants 15:405, 2000 14. Calandriello R, Tomatis M: Simplified treatment of the atrophic

posterior maxilla via immediate/early function and tilted im-plants: A prospective 1-year clinical study. Clin Implant Dent Relat Res 7(Suppl. 1):S1, 2005

15. Aparicio C, Rangert B, Sennerby L: Immediate/early loading of dental implants: A report from the Sociedad Espanola de Im-plantes World Congress consensus meeting in Barcelona, Spain. Clin Implant Dent Relat Res:5:57-60, 2003

16. Naylor CK: Esthetic treatment planning: The grid analysis sys-tem; J Esthet Restor Dent 14:76-84, 2002

17. Jemt T: Fixed implant-supported prostheses in the edentulous maxilla. A five-year follow-up report. Clin Oral Implants Res 5:142, 1994

FIGURE 12. A, Reduction alveoloplasty of the All-on-4 shelf

pro-vides enough interarch space for the esthetic prosthetic reconstruc-tion. B, The use of M-4 placement, as shown in the panographic x-ray, was facilitated by the All-on-4 shelf.

(8)

18. Palmqvist S, Sondell K, Swartz B: Implant-supported maxillary overdentures: Outcome in planned and emergency cases. Int J Oral Maxillofac Implants 9:184, 1994

19. Marshall JA, Hansen CA, Kreitman BJ: Achieving a passive fit for a screw-retained implant-supported maxillary complete arch cera-mometal prosthesis: Clinical report. Implant Dent 3:31, 1994 20. Simons AM, Campbell Z: The implant-supported overdenture

prosthesis for the edentulous maxilla. J Oral Implantol 19:39, 1993

21. Mijiritsky E, Mardinger O, Mazor Z, et al: Immediate provision-alization of single-tooth implants in fresh-extraction sites at the maxillary esthetic zone: Up to 6 years of follow-up. Implant Dent 18:326, 2009

22. Younis L, Taher A, Abu-Hassan MI, et al: Evaluation of bone healing following immediate and delayed dental implant place-ment. J Contemp Dent Pract 10:35, 2009

23. Kahnberg KE: Immediate implant placement in fresh extrac-tion sockets: A clinical report. Int J Oral Maxillofac Implants 24:282, 2009

24. Balshi TJ, Wolfinger GJ: Teeth in a day for the maxilla and mandible: Case report. Clin Implant Dent Relat Res 5:11, 2003 25. Kinsel RP, Lamb RE: Development of gingival esthetics in the terminal dentition patient prior to dental implant placement using a full-arch transitional fixed prosthesis: A case report. Int J Oral Maxillofac Implants 16:583, 2001

26. Kosinski TE, Skowronski R Jr: Immediate implant loading: A case report. J Oral Implantol 28:87, 2002

27. Lin CL, Wang JC, Ramp LC, et al: Biomechanical response of implant systems placed in the maxillary posterior region under various conditions of angulation, bone density, and loading. Int J Oral Maxillofac Implants 23:57, 2008

28. Kao HC, Gung YW, Chung TF, et al: The influence of abutment angulation on micromotion level for immediately loaded dental implants: A 3-D finite element analysis. Int J Oral Maxillofac Implants 23:623, 2008

29. Park C, Raigrodski AJ, Rosen J, et al: Accuracy of implant placement using precision surgical guides with varying occlu-sogingival heights: An in vitro study. J Prosthet Dent 101:372, 2009

30. Aboul-Ela LM: The evaluation of the inter-occlusal distance in complete dentures. Egypt Dent J 13:56, 1967

31. Owen WD, Douglas JR: Near or full occlusal vertical dimension increase of severely reduced interarch distance in complete dentures. J Prosthet Dent 26:134, 1971

32. Eskelsen E, Fernandes CB, Pelogia F, et al: Concurrence be-tween the maxillary midline and bisector to the interpupillary line. J Esthet Restor Dent 21:37; discussion: 42, 2009

33. Ding X, Liao SH, Zhu XH, et al: Effect of diameter and length on stress distribution of the alveolar crest around immediate load-ing implants. Clin Implant Dent Relat Res 11:279, 2008 34. Aguilar-Meimban CO: Available bone is the foremost criterion

in the insertion of endosteal implants. J Philipp Dent Assoc 47:3, 1996

35. Jensen OT, Adams MW: The maxillary M-4: A technical and biomechanical note for all-on-4 management of severe maxil-lary atrophy—Report of 3 cases. J Oral Maxillofac Surg 67: 1739, 2009

36. Schendel SA, Eisenfeld J, Bell WH, et al: The long face syn-drome: Vertical maxillary excess. Am J Orthod 70:398, 1976 37. Freihofer HP: Surgical treatment of the short face syndrome.

J Oral Surg 39:907, 1981

38. Dreiseidler T, Neugebauer J, Ritter L, et al: Accuracy of a newly developed integrated system for dental implant planning. Clin Oral Implants Res 20:1191, 2009

39. Horwitz J, Zuabi O, Machtei EE: Accuracy of a computerized tomography-guided template-assisted implant placement system: An in vitro study. Clin Oral Implants Res 20:1156, 2009

40. Valente F, Schiroli G, Sbrenna A: Accuracy of computer-aided oral implant surgery: A clinical and radiographic study. Int J Oral Maxillofac Implants 24:234, 2009

41. Roze J, Babu S, Saffarzadeh A, et al: Correlating implant stability to bone structure. Clin Oral Implants Res 20:1140, 2009 42. Araújo MG, Wennström JL, Lindhe J: Modeling of the buccal

and lingual bone walls of fresh extraction sites following im-plant installation. Clin Oral Imim-plants Res 17:606, 2006 43. Misch KA, Yi ES, Sarment DP: Accuracy of cone beam

com-puted tomography for periodontal defect measurements. J Peri-odontol 77:1261, 2006

44. Thor A, Wannfors K, Sennerby L, et al: Reconstruction of the severely resorbed maxilla with autogenous bone, platelet-rich plasma, and implants: 1-year results of a controlled prospective 5-year study. Clin Implant Dent Relat Res 7:209, 2005 45. Cordaro L: Bilateral simultaneous augmentation of the

maxil-lary sinus floor with particulated mandible. Report of a tech-nique and preliminary results. Clin Oral Implants Res 14:201, 2003

46. McAllister BS, Haghighat K: Bone augmentation techniques [review]. J Periodontal 78:377, 2007

47. You ZH, Bell WH, Finn RA: Location of the nasolacrimal canal in relation to the high Le Fort I osteotomy. J Oral Maxillofac Surg 50:1075, 1992