The All-on-4 Shelf: Maxilla

Transcription

1 J Oral Maxillofac Surg 68: , 2010 The All-on-4 Shelf: Maxilla Ole T. Jensen, DDS, MSc,* Mark W. Adams, DDS, MSc, Jared R. Cottam, DDS, MD, Stephen M. Parel, DDS, MSc, and William R. Phillips III, DDS, MD All-on-4 treatment is facilitated by bone reduction to create prosthetic restorative space, establish maximum anterior posterior spread of implants, and to avoid pneumatized sites. Unlike a reduction alveloplasty for denture placement, the All-on-4 shelf enables optimal surgical prosthetic management of implant placement for the fixed hybrid prosthesis American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 68: , 2010 All-on-4 treatment of the maxilla requires presurgical prosthetic treatment planning for high smile line esthetics to be acceptable. 1,2 This requires bone removal 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 grafting, 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 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. *Director, Colorado Tissue Engineering Institute, Denver, CO. Private Practice, Denver, CO. Fellow, Colorado Tissue Engineering Institute, Denver, CO. Private Practice, Dallas, TX. 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; ole.jensen@clearchoice.com 2010 American Association of Oral and Maxillofacial Surgeons /10/ $36.00/0 doi: /j.joms 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 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, sometimes using up to 10 implants per arch until biomechanical 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 became important in the mandible, where fixed denture prosthetics using 5 implants had been (and still is) prescribed as optimal. However, when 5 implant distribution was studied biomechanically it was found that the middle implant took no measurable load in function and therefore could be eliminated. This same biomechanical finding was observed for the maxilla Another important aspect of maxillary care is extraction of diseased teeth followed by simultaneous implant placement with immediate function The surgeon is therefore faced with the challenge of removing 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 understanding of maxillary treatment Antemolar reduction in the number of implants, restricted to available bone anterior to the sinus cavities, further complicates 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- 2520

2 JENSEN ET AL 2521 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 anteriorposterior spread. 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 Allon-4 shelf (Fig 1A). Placed on this shelf are implants directed at angulations emerging from specific 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 midocclusal axial plane. 29 The shelf facilitates the anterior-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 osseointegration capacity of only 4 load-bearing implants can biomechanically sustain immediate provisionalization. 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 selection 4. Shelf reduction proximates piriform bone fixation

3 2522 THE ALL-ON-4 SHELF: MAXILLA FIGURE 2. A clear acrylic bone reduction guide ensures there is adequate restorative space for abutments and titanium bar housed within the prosthesis. 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 implant 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 important function of the All-on-4 shelf is adequate bone FIGURE 3. The provisional appliance can be windowed to determine adequate bone removal and used to determine appropriate 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. 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 restorative dentist are assured of hiding the prosthesistissue junction. This is perhaps the greatest advantage of using the All-on-4 shelf. Although not yet published, 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 placement of implant platforms; this is difficult to do without creating the All-on-4 shelf. 16,32 When 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 region. Therefore, the All-on-4 shelf must not only create an alveolar plane parallel to the interpullary line

4 JENSEN ET AL 2523 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. but a plane, when viewed laterally, that is parallel to Frankfort horizontal. Shelf Width After bone reduction, the width of the shelf becomes defined at the level of the desired implant platform vertical dimension. Alveolar concavities become evident, and optimal diameter of implants can be assessed. 33 When 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 effect, 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 alveolus. 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. 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 anteriorposterior spread. Piriform Rim Proximation When there is alveolar crest atrophy, vertical dimension 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 strategy (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 prevent 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 employed for implant placement. Long face syndrome patients, after shelf reduction, may still have adequate 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 often faced with the prospect of implant placement

5 2524 THE ALL-ON-4 SHELF: MAXILLA into marrow space, often a difficult task to do and still obtain insertion torque values adequate for immediate load. Therefore, computer guidance systems are inadequate to the task, having no ability to assess bone reduction or implant torque. 34,38 Alternatively, the shelf provides the surgeon with an opportunity to specifically select optimal sites for placement without the constraint of computer generated guides. 39 This applies especially to dental extraction cases in which there are often multiple defects present or created during the course of extraction. Following bone reduction, the surgeon is able to identify either visually or tactically the best load bearing sites possible for implant placement. 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 sequential (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 forward is the secondary site. After posterior implants are placed, anterior sites are selected in a distributed fashion. 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 subjecting the patient to sinus floor bone grafting. Palatal Cortical Plate Although a computed tomographic scan can delineate width of the palatal plate, 39,40 after bone reduction, 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 Generally, 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 allowable posterior position where the posterior implant can be placed because shelf reduction frequently exposes the sinus membrane, which can then

6 JENSEN ET AL 2525 where implants must bypass to not traverse the sinus cavity and where posteriorly, no load-bearing bone is present 36 (Fig 10A). The vertical alveolar bone available from S-Point to the alveolar plane of the All-on-4 shelf often determines how far posteriorly the implant can be inserted. 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 Allon-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. 13 Bone 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 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 perpendicular 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. 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 implant placement and angulation. 14 This point is called S-Point, for sinus point, in All-on-4 nomenclature. This is the most anterior inferior projection of the sinus 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 2526 THE ALL-ON-4 SHELF: MAXILLA likely to be answered affirmatively by use of the All-on-4 shelf. In summary, the All-on-4 shelf is a surgical prosthetic tool not unlike reduction alveoplasty for denture placement that aids in optimal surgical-prosthetic management of the All-on-4 restoration (Figs 12A,B). After the surgeon can accept the idea of nonaxial implant placement as well as a reduced number of implants, the All-on-4 shelf becomes a necessary tool to optimize what is a highly efficient, although counterintuitive, maxillary implant placement scheme. FIGURE 12. A, Reduction alveoloplasty of the All-on-4 shelf provides enough interarch space for the esthetic prosthetic reconstruction. B, The use of M-4 placement, as shown in the panographic x-ray, was facilitated by the All-on-4 shelf. Nasolacrimal Duct One final anatomic structure to be aware of is the nasolacrimal duct, which exits below the inferior turbinate 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 nasolacrimal 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 angulation? 3) Can full arch immediate load biomechanics be satisfied by the often limited bone stock of the anterior maxilla? All of these questions are more References 1. Garber DA, Belser UC: Restoration-driven implant placement with restoration-generated site development. Compend Contin Educ Dent 16:796, 798, 804, McFadden DD, Australas AR: Pre-prosthetic surgery options for fixed dental implant reconstruction of the atrophic maxilla. Coll Dent Surg 15:61, Jivraj S, Chee W: Treatment planning of implants in the aesthetic zone. Br Dent J 201:77, Berson PJ: The functionally fixed restoration: A third modality of treatment. Compend Contin Educ Dent 23:157, 164, 166, Kahnberg KE, Wallström M, Rasmusson L: Local sinus lift for single-tooth implant. I. Clinical and radiographic follow-up. Clin Implant Dent Relat Res, Raja SV: Management of the posterior maxilla with sinus lift: Review of techniques. J Oral Maxillofac Surg 67:1730, 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, Jensen OT, Shulman L, Block M, et al: Report of the Sinus Consensus Conference of Int J Oral Maxillofac Implants 139(Suppl.):11, Aparicio C, Perales P, Rangert B: Tilted implants as an alternative to maxillary sinus grafting: A clinical, radiologic, and periotest study. Clin Implant Dent Relat Res 3:39, Capelli M, Zuffetti F, Del Fabbro M, et al: Immediate rehabilitation 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, 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 prospective study. Clin Oral Implants Res 19:227, 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 prospective study. Clin Implant Dent Relat Res 10:255, 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, Calandriello R, Tomatis M: Simplified treatment of the atrophic posterior maxilla via immediate/early function and tilted implants: A prospective 1-year clinical study. Clin Implant Dent Relat Res 7(Suppl. 1):S1, Aparicio C, Rangert B, Sennerby L: Immediate/early loading of dental implants: A report from the Sociedad Espanola de Implantes World Congress consensus meeting in Barcelona, Spain. Clin Implant Dent Relat Res:5:57-60, Naylor CK: Esthetic treatment planning: The grid analysis system; J Esthet Restor Dent 14:76-84, Jemt T: Fixed implant-supported prostheses in the edentulous maxilla. A five-year follow-up report. Clin Oral Implants Res 5:142, 1994

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