Paranasal Bone: The Prime Factor Affecting the Decision to Use Transsinus vs Zygomatic Implants for Biomechanical Support for Immediate Function in Maxillary Dental Implant Reconstruction Ole T. Jensen, DDS, MS1/Mark W. Adams, DDS, MS2/Edmund Smith, MSc3 Paranasal bone affects the decision-making process for placement of implants for immediate function in the highly resorbed maxilla. The most important bone for apical fixation of implants in this setting is the lateral nasal bone mass. Maximum available bone mass found at the pyriform above the nasal fossa, designated M point, can most often engage two implants placed at 30-degree angles. The second most important area of paranasal bone mass is the subnasal bone of the premaxilla, which is required to engage an angled implant at the alveolar crest. However, only 4 to 5 mm in height is needed when implants are angled posterior to engage M point. The third most important paranasal bone site for implant fixation is the midline nasal crest extending upward to the vomer. This site, which is usually type 1/2 bone, can engage implants apically and provide enough fixation for immediate function even if implants are short. These anatomical bone sites enable placement of implants to obtain a 12- to 15-mm anterior-posterior spread, which is favorable for immediate function. Int J Oral Maxillofac Implants 2014;29:e130–e138. doi: 10.11607/jomi.te52 Key words: anterior-posterior spread, immediate function, M-4, M point, pyriform rim, V point, vomer/nasal crest, zygomatic implants
T
reatment planning decisions made from computed tomography (CT)-scan images for maxillary reconstruction in conditions of severe atrophy will be affected by available bone mass, the need for anterior-posterior (A-P) spread, and desire for immediate function.1–3 The surgical-prosthetic team needs to know whether immediate function is possible or if bone grafting is necessary, as well as whether transalveolar placement of implants is possible or if zygomatic implants will be required.4–6 If implants can be placed with sufficient insertion torque and A-P spread, then immediate loading is possible; if not, a submerged technique will be necessary.7–9 The number of implants required will vary, with 1Clinical
Assistant Professor, Department of Oral and Maxillofacial Surgery, University of Michigan; Private Practice, ClearChoice, Denver, Colorado, USA. 2P rosthodontist, ClearChoice, Denver, Colorado, USA. 3 B iomechanical Engineer, ClearChoice, Denver, Colorado, USA. Correspondence to: Dr Ole T. Jensen, 8200 East Belleview Avenue, Suite 500, Greenwood Village, CO 80111, USA. Email: [email protected] ©2014 by Quintessence Publishing Co Inc.
a minimum of four implants recommended.10–13 Despite the high incidence of severe maxillary atrophy, zygomatic implants remain relatively infrequently used since the advent of the transsinus implant approach.14 The key decision factor for when or when not to prescribe zygomatic implants is largely based on the presence of paranasal bone, especially the lateral pyriform rim, which historically has been used for craniofacial fixation in orthognathic surgery and now apical fixation of dental implants.14–16 Important features of paranasal bone mass include the thickness of the lateral nasal wall, the presence of subnasal bone, and the height of the midline suture including the vomer/ nasal crest bone mass.17 In a four-implant scheme, such as All-on-4 (Nobel Biocare), posterior implants rely on cortical bone found anterior at the lateral nasal wall. Because the alveolar crest remnant is often reduced to form the All-on-4 bone shelf, alveolar cortical bone is removed, making crestal fixation difficult, if not impossible.18 The two anterior implants are optimally angled posteriorly to also engage the lateral pyriform rim, but they can sometimes be angled toward the midline bone mass for fixation there when vertical bone mass is insufficient.18
e130 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Fig 1 In this atrophic maxilla with the sinus and nasal fossa exposed, the posterior implant is inserted to pass transsinus into the pyriform rim.
Fig 2 The anterior implant is angled 30 degrees posteriorly to avoid the nasal fossa and insert into the pyriform rim; this creates an M-4 pattern when viewed on a panoramic radiograph postplacement.
A-P spread is also an important factor for biomechanical stability.19 Implants must be 12 to 15 mm apart, anterior to posterior, to gain adequate A-P spread for a fixed maxillary restoration.20 To achieve this amount of spread, the posterior implants need to be placed in areas where fixation cannot be obtained, due to loss of alveolar crest and proximity to the sinus cavity. Implants placed as such have little or no insertion torque as they pass transsinus and will require bone grafting (Fig 1). Though four implants could be placed in a relatively straight line in available subnasal bone, there would be minimal A-P spread, which would not be favorable biomechanical support for extended cantilever function.21 Insertion torque, therefore, takes a back seat to A-P spread despite lack of fixation of the posterior implants. These posterior implants angle anteriorly to engage the lateral pyriform rim even as anterior implants angle posteriorly to the pyriform (Fig 2), the implants often touching apically (described previously as the M-4 configuration for Allon-4 therapy).14,22 Implant reconstruction to gain adequate insertion torque for immediate loading is determined by the lateral nasal cortical bone, the subsinus alveolar crest bone residuum, available subnasal bone mass, and the nasal crest, all used to develop a favorable A-P spread. The occlusal scheme of the provisional prosthesis is also an important biomechanical factor to consider, as fragile primary implant stability can be overcome by occlusal load.
LATERAL NASAL WALL Midface osseous atrophy follows a pattern of volumetric reduction in all dimensions, with the alveolus lost first, then basal bone, and then lateral pyriform rim.23 But the pyriform, nasal crest, and zygomatic bones are somewhat unaffected by disuse atrophy of the maxilla, with the zygomatic bone least affected.22 In patients with severe maxillary atrophy and a reduced alveolar bone stock combined with reduced lateral nasal wall thickness of 1 mm or less, there may be insufficient bone to engage using a transsinus approach; in such cases, a zygomatic implant can be considered.23 In the vast majority of patients, however, the lateral nasal wall will be 2 mm or greater, enough to engage an implant transsinus, but only if there is also sufficient bone at the alveolar crest to stabilize the implant.14 In situations where there is confluence between the nasal fossa and the sinus cavity, the zygomatic implant is a good choice.23
SUBSINUS ALVEOLAR CREST BONE HEIGHT Subsinus bone residuum after reduction for the bone shelf must be of sufficient height to warrant transsinus implant placement. Implants placed at 30degree angles anteriorly into the lateral pyriform above the nasal fossa will gain stability even if there is very The International Journal of Oral & Maxillofacial Implants e131
© 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
M point
V point
Fig 3 M point is the maximum bone mass at the lateral pyriform rim above the nasal fossa, where implant apices can engage cortical bone for primary stability.
Fig 4 V point is the maximum bone mass found at the nasal crest in the midline, where midline-directed implants can engage cortical bone for anterior implant stability.
little bone available, as stability is assisted by implant splinting.12 When there is an absence of bone at the lateral pyriform, consideration should be given to the use of zygomatic implants.23 Alternatively, when there is minimal crestal bone available but enough bone at the lateral pyriform to gain primary stability, the implant can still be placed and grafted within the transsinus passage, though it may be considered too unstable for immediate loading. Experienced surgeon/prosthodontist teams have determined that even if an implant is mobile and can be hand turned, as long as it is vertically stable, having a vertical stop, it can be splinted into an immediate-function provisional restoration (Jensen OT, Adams MR, unpublished data, 2012).24 In maxillae that have very thin alveolar width as well as insufficient subsinus bone height, the entry point for implant placement is palatal, then directed transalveolar (medial to lateral transsinus) to engage cortical bone at the lateral pyriform at M point. This method provides bicortical engagement and higher torque values, and may not require sinus grafting despite transsinus passage.24
way are generally short—approximately 10 mm—but often well fixed, with insertion torques above 50 Ncm (Jensen OT, Adams MR, unpublished data, 2012).17,25 When there is minimal subnasal bone available and the entire maxilla is extremely atrophic except for the midline, two 30-degree–angled vomer/nasal crest implants can be complemented by bilateral posterior zygomatic implants.26 However, when there is complete absence of both M point and V point bone mass, a quad zygomatic approach is suggested if immediate function is desired.23,26
SUBNASAL ALVEOLAR HEIGHT In the highly atrophic maxilla, the alveolus can be almost absent subnasally; however, implant fixation can often still be obtained by directing angled implants laterally into the nasal wall, where there is generally enough bone to secure both posterior and anterior implants at M point (Fig 3).14 When this is not possible, two anterior implants can be angled toward V point at the midline into the vomer/nasal crest area (Fig 4).17 This is done without entering the nasal fossa. Implants placed in this
ANTERIOR-POSTERIOR SPREAD Implants placed into available bone mass in an atrophic maxilla with a relatively anterior sinus cavity deflection will lead to a short A-P span between implants, sometimes only 5 to 6 mm if implants are placed vertically. The consequence of this is a long, biomechanically unfavorable cantilever. A narrow spread is generally inadequate for a full-arch fixed restoration.27 Angulation of the posterior implants facilitates increased A-P spread (Figs 5 and 6). The minimum A-P spread should be 12 mm, but 15 mm is optimal.19 This will provide adequate support for the titanium bar to enable an approximate 10-mm cantilever for first-molar occlusion (Figs 7 and 8). Adequate A-P spread is one reason the transsinus implant approach was developed; if not transsinus, zygomatic implant placement facilitates A-P spread for immediate provisionalization.14,25 Ectomorphic individuals with small overall bone dimension can sometimes be treated with a threeimplant scheme, as a reduced A-P spread may be acceptable in both jaws.
e132 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Anterior-posterior spatial mandible
Anterior-posterior spatial maxilla
Fig 5 Anterior-posterior spread is improved in the mandible by tilting the posterior implants 30 degrees distally.
10 mm
10 mm
Fig 6 Anterior-posterior spread is improved in the maxilla by tilting the posterior implants 30 degrees distally.
10 mm
10 mm
Fig 7 Once bone reduction is completed to create a level bone shelf (a total bone reduction of approximately 14 to 15 mm in each arch), there is enough room for a 4-mm titanium bar. However, without tilting the back implants, the bar will need to support a longer cantilever and bar fracture may occur.
Fig 8 Following bone reduction and placement of posterior tilted implants, the bar is well supported and results in a shorter cantilever than for vertical implant placement.
OCCLUSAL SCHEME
in lateral movements to eliminate interferences, and cusps are flattened slightly to minimize lateral forces and distribute them over a large area.30 Along with a limited occlusal scheme, there is a requirement for a mechanical soft diet until the implants undergo early osseointegration from bone modeling at about 6 weeks.29 When sinus grafting for low–insertiontorque transsinus implants is done, 4 to 6 months of an occlusion-sparing regimen should be prescribed.12
In the provisional stage for immediate function, the occlusion should be limited to equal contacts and equal, symmetric distribution of contacts between the implants,25 avoiding both anterior and posterior cantilever extensions.27 Cantilevers are not used in the provisional restoration so as to reduce bone strain from lever moments of force.28,29 Adjustments are made
The International Journal of Oral & Maxillofacial Implants e133 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Fig 9 The “M” pattern of M-4 implant placement as seen on a postoperative panoramic radiograph is an excellent method to gain adequate A-P spread using cortical bone found at the lateral pyriform rim.
CASE STUDY A 36-year-old man presented with an edentulous maxilla, having worn a maxillary complete denture for 3 years. There was moderate to severe alveolar-width atrophy but still adequate height for placement of implants. Implants were placed at 30-degree angles using the M-4 technique, engaging M point with implant apices bilaterally (Fig 9). This enabled placement of the implants into wider bone so that facial dehiscence grafting was not required. The M-4 angulation strategy easily avoided the nasal and sinus cavities. Long implants, which gain high insertion torque (greater than 50 Ncm) and an A-P spread of 12 to 15 mm for immediate function (Figs 10a to 10c), were used. Following placement of the implants, a provisional restoration was placed to splint all of the implants into cross-arch stabilization (Fig 11).
DISCUSSION Several factors affect decision-making regarding immediate function in the edentulous maxilla, one of the most important being engagement into cortical bone. Because the alveolar crest is frequently removed to create a bone shelf, the search for cortical bone becomes complicated and there are few options available in a well-aerated midface. Though pterygoid and zygomatic cortex are possibilities, the use of paranasal
bone remains the most easily accessed in the majority of cases. But how much cortical fixation is required for dependable full-arch provisionalization? For single implants placed into extraction sites and temporized on the same day, it has been suggested that a minimum of 6 mm of apical cortical bone is required for immediate function.31 In cross-arch splinted schemes, the absolute requirement of cortical fixation has not been determined, though it must be substantially less, as evidenced by multiple All-on-4 maxillary
e134 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
a
b
Figs 10a to 10c By using an M-4 strategy with four 30-degree angled implants instead of sinus grafting for vertical implant placement, A-P spread is found to be 12 to 15 mm, as demonstrated in this patient.
c Fig 11 The provisional restoration remains stable after 6 weeks of loading.
treatments done successfully with minimal bone availability.11,32 In fact, full-arch splinted restorations often are based on a relatively low composite torque (the sum of all four insertion torque values). Our studies suggest that a composite torque value of 120 Ncm, allowing for a maximum value of 50 Ncm for any single implant, is sufficient for immediate loading. This has been done even when two of four implants are somewhat mobile (Jensen OT, Adams MR, unpublished data, 2012).
One study demonstrated that an implant placed completely out of contact with bone but splinted to adjacent implants in a mandibular fixed prosthesis still osseointegrated.31 In the maxilla, with the economy of four implants in type 3/4 bone, it would seem that all four implants need to be fixed for osseointegration to occur. This has been shown clinically not to be required.31 However, when adjacent implants are of low insertion torque and have minimal cortical bone contact, the entire appliance can be overcome by occlusal The International Journal of Oral & Maxillofacial Implants e135
© 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Fig 12a The medical model of a maxilla showing ideal placement of zygomatic and M-4 distribution implants.
a Fig 12b The emergence of the zygomatic and transsinus implants are both near the second premolar area, giving a near equivalent A-P spread for prosthetic stability.
b
load, leading to catastrophic failure of all four implants (Jensen OT, Adams MR, unpublished data, 2012). The key is to use available bone mass in creative ways, such that insertion torque is maximized and a favorable A-P spread is still realized. Implant angulation accomplishes this, with the most favorable angle— surgically and prosthetically—being 30 degrees. Implant angulation at 30 degrees does three things: 1. It increases the length of the implant in bone by 50%.33,34 2. It increases occlusal load resistance form.34–36 3. In splinted configurations, it leads to subosseous conformation that is highly resistant to shear force.35,36
Increased length will increase load-bearing capacity, both for immediate function and once osseontegration occurs (Jensen OT, Adams MR, unpublished data, 2012). Since there is an absence of cortical bone at the crest after bone reduction, resonance frequency analysis is generally not helpful. The surgeon must therefore rely on insertion torque as the main clinical guide. By placing longer angled implants, there is potentially greater implant surface area to gain insertion torque, though it still may be relatively low (Jensen OT, Adams MR, unpublished data, 2012). In addition, implants lying “sideways” have potentially more resistance form to compression and pullout force as well as shear force.35 In this setting, cancellous bone may actually contribute to load-bearing capacity when compared to vertically placed (shorter) implants.
e136 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Adjacent implants placed at 30-degree angles can be as much as 60 degrees convergent/divergent from each other within bone. In most cases, four implants placed with various divergence angles will add complex secondary resistance form to augment prosthetic splinting.14,36 However, the major determinant of load-bearing capacity of newly placed implants in a maxilla with deficient bone mass is finding cortical bone to fix four implants apically for adequate A-P spread, as there is seldom substantial bone contact available anywhere else except apically. Though bone contact may be minimal at the alveolar crest, the prosthesis will serve to immobilize the implants by what could be termed secondary stabilization.37–40 In summary, the residual cortical areas of commonly available paranasal bone, including subnasal basal bone, the vomer/nasal crest, and the lateral pyriform rim, should be considered prior to selecting the zygo matic implant option. The clinician should remember that transsinus implant emergence in the alveolar process is nearly equivalent with that of the zygomatic implant (Figs 12a and 12b) and that the transsinus implant does not have as high an incidence of oroantral fistulae as the zygomatic implant.14,34,41–43 It is only when paranasal sites have inadequate bone that extramaxillary bone stock should be considered for All-on-4 immediate function.
Acknowledgments The authors reported no conflicts of interest related to this study.
REFERENCES 1. Tyndall DA, Brooks SL. Selection criteria for dental implant site imaging: A position paper of the American Academy of Oral and Maxillofacial Radiology. Oral Surg Oral Med Oral Path Oral Radiol Endod 2000;89:630–637. 2. Harris D, Buser D, Dulka K, et al. E.A.O. guidelines for the use of diagnostic imaging in implant dentistry. A consensus workshop organized by the European Association for Osseointegration at Trinity College Dublin. Clin Oral Implants Res 2002;13:566–570. 3. Mozzati M, Arata V, Gallesio G, Mussano F, Carossa S. Immediate postextraction implant placement with immediate loading for maxillary full-arch rehabilitation: A two-year treatment analysis. J Am Dent Assoc 2012;143:124–133. 4. Bedrossian E, Rangert B, Stumpel L, Indresano T. Immediate function with the zygomatic implant: A graftless solution for the patient with mild to advanced atrophy of the maxilla. Int J Oral Maxillofac Implants 2006;21:937–942.
5. Maló P, Nobre Md, Lopes A, Francischone C, Rigolizzo M. Three-year outcome of a retrospective cohort study on the rehabilitation of completely edentulous atrophic maxillae with immediate loaded extra-maxillary zygomatic implants. Eur J Oral Implantol 2012;5:37–46. 6. Chiapasco M, Brusati R, Ronchi P. Le Fort I osteotomy with interpositional bone grafts and delayed oral implants for the rehabilitation of extremely atrophied maxillae: A 1-9-year clinical follow-up study on humans. Clin Oral Implants Res 2007;18:74–85. 7. Lundgren S, Rasmusson L, Sjöström M, Sennerby L. Simultaneous or delayed placement of titanium implants in free autogenous iliac bone grafts. Histological analysis of the bone graft-titanium interface in 10 consecutive patients. Int J Oral Maxillofac Surg 1999;28:31–37. 8. Sbordone L, Levin L, Guidetti F, Sbordone C, Glikman A, Schwartz-Arad D. Apical and marginal bone alterations around implants in maxillary sinus augmentation grafted with autogenous bone or bovine bone material and simultaneous or delayed dental implant positioning. Clin Oral Implants Res 2011;22:485–491. 9. Zoghbi SA, de Lima LA, Saraiva L, Romito GA. Surgical experience influences 2-stage implant osseointegration. J Oral Maxillofac Surg 2011;69:2771–2776. 10. Parel SM, Phillips WR. A risk assessment treatment planning protocol for the four implant immediately loaded maxilla: Preliminary findings. J Prosthet Dent 2011;106:359–366. 11. Krekmanov L, Kahn M, Rangert B, Lindstrom H. Tilting of posterior mandibular and maxillary implants for improved prosthesis support. Int J Oral Maxillofac implants 2000;15: 405-414. 12. Damghani S, Masri R, Driscoll CF, Romberg E. The effect of number and distribution of unsplinted maxillary implants on the load transfer in implant-retained maxillary overdentures: An in vitro study. J Prosthet Dent 2012;107:358–365. 13. Schley JS, Wolfart S. Which prosthetic treatment concepts present a reliable evidence-based option for the edentulous maxilla related to number and position of dental implants? Eur J Oral Implantol 2011;4:31–47. 14. Jensen OT, Cottam JR, Ringeman JL, Adams MW. Transsinus dental implants, bone morphogenetic protein 2, and immediate function for All-on-4 treatment of severe maxillary atrophy. J Oral Maxillofac Surg 2012;70:141–148. 15. Rinehart GC. Mandibulomaxillary fixation with bone anchors and quick-release ligatures. J Craniofac Surg 1998;9: 215–221. 16. Jensen OT, Cottam JR, Ringeman JL, et al. Experience with bone morphogenetic protein-2 and interpositional grafting of edentulous maxillae: A comparison of Le Fort I downfracture to full-arch (horseshoe) segmental osteotomy done in conjunction with sinus floor grafting. Oral Craniofac Tissue Eng 2011;1:123–140. 17. Jensen OT, Cottam JR, Ringeman JL, Graves S, Beatty L, Adams MW. Angled dental implant placement into the vomer/ nasal crest of atrophic maxillae for All-on-Four immediate function: A 2-year clinical study of 100 consecutive patients. Oral Craniofac Tissue Eng 2012;2:66–71. 18. Jensen OT, Adams MW, Cottam JR, Parel S, Phillip W. The All-on-Four shelf: Maxilla. J Oral Maxillofac Surg 2010;68: 2520-2527. 19. Rodriguez AM, Aquilino SA, Lund PS, Ryther JS, Southard TE. Evaluation of strain at the terminal abutment site of a fixed mandibular implant prosthesis during cantilever loading. J Prosthodont 1993;2:93–102.
The International Journal of Oral & Maxillofacial Implants e137 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
20. Benzing UR, Gall H, Weber H Biomechanical aspects of two different implant-prosthetic concepts for edentulous maxillae. Int J Oral Maxillofac Implants 1995;10:188–198. 21. Hobkirk JA, Havthoulas TK. The influence of mandibular deformation, implant numbers, and loading position on detected forces in abutments supporting fixed implant superstructures. J Prosthet Dent 1998;80:169–174. 22. Jensen OT, Adams MW. The maxillary M-4: A technical and biomechanical note for all-on-4 management of severe maxillary atrophy—Report of 3 cases. J Oral Maxillofac Surg 2009;67:1739–1744 [erratum 2009;67:2554]. 23. Richard MJ, Morris C, Deen BF, Gray L, Woodward JA. Analysis of the anatomic changes of the aging facial skeleton using computer-assisted tomography. Ophthal Plast Reconstr Surg 2009;25:382–386. 24. Butura CC, Galindo DF. Combined immediate loading of zygomatic and mandibular implants: A preliminary 2-year report of 19 patients. Oral Craniofac Tissue Eng 2012;2:58–65. 25. Bedrossian E, Sullivan RM, Fortin Y, Malo P, Indresano T. Fixed-prosthetic implant restoration of the edentulous maxilla: A systematic pretreatment evaluation method. J Oral Maxillofac Surg 2008;66:112–122. 26. Graves S, Mahler BA, Javid B, Armellini D, Jensen OT. Maxillary all-on-four therapy using angled implants: A 16-month clinical study of 1110 implants in 276 jaws. Dent Clin North Am 2011;55:779–794. 27. Bellini CM, Romeo D, Galbusera F, et al. Comparison of tilted versus nontilted implant-supported prosthetic designs for the restoration of the edentulous mandible: A biomechanical study. Int J Oral Maxillofac Implants 2009;24:511–517. 28. Gapski R, Wang HL., Mascarenhas P, Lang P: Critical review of immediate implant loading. Clin Oral Implants Res 2003; 14:515–527. 29. Kinsel RP, Liss M: Retrospective analysis of 56 edentulous dental arches restored with 344 single-stage implants using an immediate loading fixed provisional protocol: Statistical predictors of implant failure. Int J Oral Maxillofac Implants 2007;22:823–830. 30. Achilla A, Tura F, Euwe E. Immediate/early function with tapered implants supporting maxillary and mandibular posterior fixed partial dentures: Preliminary results of a prospective multicenter study. J Prosthet Dent 2007;97 (6 suppl):S52–S58. 31. Becker CM, Wilson TG Jr, Jensen OT. Minimum criteria for immediate provisionalization of single-tooth dental implants in extraction sites: A 1-year retrospective study of 100 consecutive cases. J Oral Maxillofac Surg 2011;69:491–497.
32. Romanos GE, Nentwig GH. Immediate functional loading in the maxilla using implants with platform switching: Five-year results. Int J Oral Maxillofac Implants 2009;24:1106–1112. 33. Villa R, Polimeni G, Wikesjö UM. Implant osseointegration in the absence of primary bone anchorage: A clinical report. J Prosthet Dent 2010;104:282–287. 34. Jensen OT, Adams MW. All-on-4 treatment of highly atrophic mandible with mandibular V-4: Report of 2 cases. J Oral Maxillofac Surg 2009;67:1503–1509. 35. Demenko V, Linetskiy I, Nesvit K, Hubalkova H, Nesvit V, Shevchenko A. Importance of diameter-to-length ratio in selecting dental implants: A methodological finite element study. Comput Methods Biomech Biomed Engin 2012 May 22 [Epub ahead of print]. 36. Lee JS, Lim YJ. Three-dimensional numerical simulation of stress induced by different lengths of osseointegrated implants in the anterior maxilla. Comput Methods Biomech Biomed Engin 2012 Mar 8 [Epub ahead of print]. 37. Ueda C, Markarian RA, Sendyk CL, Laganá DC. Photoelastic analysis of stress distribution on parallel and angled implants after installation of fixed prostheses. Braz Oral Res 2004;18:45–52. 38. Lan TH, Huang HL, Wu JH, Lee HE, Wang CH. Stress analysis of different angulations of implant installation: The finite element method. Kaohsiung J Med Sci 2008;24: 138–143. 39. Burak Özcelik T, Ersoy E, Yilmaz B. Biomechanical evaluation of tooth- and implant-supported fixed dental prostheses with various nonrigid connector positions: A finite element analysis. J Prosthodont 2011;20:16–28. 40. Makary C, Rebaudi A, Mokbel N, Naaman N. Peak insertion torque correlated to histologically and clinically evaluated bone density. Implant Dent 2011;20:182–191. 41. Nissan J, Gross O, Ghelfan O, Priel I, Gross M, Chaushu G. The effect of splinting implant-supported restorations on stress distribution of different crown-implant ratios and crown height spaces. J Oral Maxillofac Surg 2011;69:2990–2994. 42. Jensen OT, Adams MW, Cottam JR, Ringeman JL. Occult peri-implant oroantral fistulae: Posterior maxillary periimplantitis/sinusitis of zygomatic or dental implant origin. Treatment and prevention with bone morphogenetic protein-2/ absorbable collagen sponge sinus grafting. Oral Craniofac Tissue Eng 2011;1:340–348. 43. Chrcanovic BR, Abru MH. Survival and complications of zygomatic implants: A systematic review. Oral Maxillofac Surg 2012 May 6 [Epub ahead of print].
e138 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
T
reatment planning decisions made from computed tomography (CT)-scan images for maxillary reconstruction in conditions of severe atrophy will be affected by available bone mass, the need for anterior-posterior (A-P) spread, and desire for immediate function.1–3 The surgical-prosthetic team needs to know whether immediate function is possible or if bone grafting is necessary, as well as whether transalveolar placement of implants is possible or if zygomatic implants will be required.4–6 If implants can be placed with sufficient insertion torque and A-P spread, then immediate loading is possible; if not, a submerged technique will be necessary.7–9 The number of implants required will vary, with 1Clinical
Assistant Professor, Department of Oral and Maxillofacial Surgery, University of Michigan; Private Practice, ClearChoice, Denver, Colorado, USA. 2P rosthodontist, ClearChoice, Denver, Colorado, USA. 3 B iomechanical Engineer, ClearChoice, Denver, Colorado, USA. Correspondence to: Dr Ole T. Jensen, 8200 East Belleview Avenue, Suite 500, Greenwood Village, CO 80111, USA. Email: [email protected] ©2014 by Quintessence Publishing Co Inc.
a minimum of four implants recommended.10–13 Despite the high incidence of severe maxillary atrophy, zygomatic implants remain relatively infrequently used since the advent of the transsinus implant approach.14 The key decision factor for when or when not to prescribe zygomatic implants is largely based on the presence of paranasal bone, especially the lateral pyriform rim, which historically has been used for craniofacial fixation in orthognathic surgery and now apical fixation of dental implants.14–16 Important features of paranasal bone mass include the thickness of the lateral nasal wall, the presence of subnasal bone, and the height of the midline suture including the vomer/ nasal crest bone mass.17 In a four-implant scheme, such as All-on-4 (Nobel Biocare), posterior implants rely on cortical bone found anterior at the lateral nasal wall. Because the alveolar crest remnant is often reduced to form the All-on-4 bone shelf, alveolar cortical bone is removed, making crestal fixation difficult, if not impossible.18 The two anterior implants are optimally angled posteriorly to also engage the lateral pyriform rim, but they can sometimes be angled toward the midline bone mass for fixation there when vertical bone mass is insufficient.18
e130 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Fig 1 In this atrophic maxilla with the sinus and nasal fossa exposed, the posterior implant is inserted to pass transsinus into the pyriform rim.
Fig 2 The anterior implant is angled 30 degrees posteriorly to avoid the nasal fossa and insert into the pyriform rim; this creates an M-4 pattern when viewed on a panoramic radiograph postplacement.
A-P spread is also an important factor for biomechanical stability.19 Implants must be 12 to 15 mm apart, anterior to posterior, to gain adequate A-P spread for a fixed maxillary restoration.20 To achieve this amount of spread, the posterior implants need to be placed in areas where fixation cannot be obtained, due to loss of alveolar crest and proximity to the sinus cavity. Implants placed as such have little or no insertion torque as they pass transsinus and will require bone grafting (Fig 1). Though four implants could be placed in a relatively straight line in available subnasal bone, there would be minimal A-P spread, which would not be favorable biomechanical support for extended cantilever function.21 Insertion torque, therefore, takes a back seat to A-P spread despite lack of fixation of the posterior implants. These posterior implants angle anteriorly to engage the lateral pyriform rim even as anterior implants angle posteriorly to the pyriform (Fig 2), the implants often touching apically (described previously as the M-4 configuration for Allon-4 therapy).14,22 Implant reconstruction to gain adequate insertion torque for immediate loading is determined by the lateral nasal cortical bone, the subsinus alveolar crest bone residuum, available subnasal bone mass, and the nasal crest, all used to develop a favorable A-P spread. The occlusal scheme of the provisional prosthesis is also an important biomechanical factor to consider, as fragile primary implant stability can be overcome by occlusal load.
LATERAL NASAL WALL Midface osseous atrophy follows a pattern of volumetric reduction in all dimensions, with the alveolus lost first, then basal bone, and then lateral pyriform rim.23 But the pyriform, nasal crest, and zygomatic bones are somewhat unaffected by disuse atrophy of the maxilla, with the zygomatic bone least affected.22 In patients with severe maxillary atrophy and a reduced alveolar bone stock combined with reduced lateral nasal wall thickness of 1 mm or less, there may be insufficient bone to engage using a transsinus approach; in such cases, a zygomatic implant can be considered.23 In the vast majority of patients, however, the lateral nasal wall will be 2 mm or greater, enough to engage an implant transsinus, but only if there is also sufficient bone at the alveolar crest to stabilize the implant.14 In situations where there is confluence between the nasal fossa and the sinus cavity, the zygomatic implant is a good choice.23
SUBSINUS ALVEOLAR CREST BONE HEIGHT Subsinus bone residuum after reduction for the bone shelf must be of sufficient height to warrant transsinus implant placement. Implants placed at 30degree angles anteriorly into the lateral pyriform above the nasal fossa will gain stability even if there is very The International Journal of Oral & Maxillofacial Implants e131
© 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
M point
V point
Fig 3 M point is the maximum bone mass at the lateral pyriform rim above the nasal fossa, where implant apices can engage cortical bone for primary stability.
Fig 4 V point is the maximum bone mass found at the nasal crest in the midline, where midline-directed implants can engage cortical bone for anterior implant stability.
little bone available, as stability is assisted by implant splinting.12 When there is an absence of bone at the lateral pyriform, consideration should be given to the use of zygomatic implants.23 Alternatively, when there is minimal crestal bone available but enough bone at the lateral pyriform to gain primary stability, the implant can still be placed and grafted within the transsinus passage, though it may be considered too unstable for immediate loading. Experienced surgeon/prosthodontist teams have determined that even if an implant is mobile and can be hand turned, as long as it is vertically stable, having a vertical stop, it can be splinted into an immediate-function provisional restoration (Jensen OT, Adams MR, unpublished data, 2012).24 In maxillae that have very thin alveolar width as well as insufficient subsinus bone height, the entry point for implant placement is palatal, then directed transalveolar (medial to lateral transsinus) to engage cortical bone at the lateral pyriform at M point. This method provides bicortical engagement and higher torque values, and may not require sinus grafting despite transsinus passage.24
way are generally short—approximately 10 mm—but often well fixed, with insertion torques above 50 Ncm (Jensen OT, Adams MR, unpublished data, 2012).17,25 When there is minimal subnasal bone available and the entire maxilla is extremely atrophic except for the midline, two 30-degree–angled vomer/nasal crest implants can be complemented by bilateral posterior zygomatic implants.26 However, when there is complete absence of both M point and V point bone mass, a quad zygomatic approach is suggested if immediate function is desired.23,26
SUBNASAL ALVEOLAR HEIGHT In the highly atrophic maxilla, the alveolus can be almost absent subnasally; however, implant fixation can often still be obtained by directing angled implants laterally into the nasal wall, where there is generally enough bone to secure both posterior and anterior implants at M point (Fig 3).14 When this is not possible, two anterior implants can be angled toward V point at the midline into the vomer/nasal crest area (Fig 4).17 This is done without entering the nasal fossa. Implants placed in this
ANTERIOR-POSTERIOR SPREAD Implants placed into available bone mass in an atrophic maxilla with a relatively anterior sinus cavity deflection will lead to a short A-P span between implants, sometimes only 5 to 6 mm if implants are placed vertically. The consequence of this is a long, biomechanically unfavorable cantilever. A narrow spread is generally inadequate for a full-arch fixed restoration.27 Angulation of the posterior implants facilitates increased A-P spread (Figs 5 and 6). The minimum A-P spread should be 12 mm, but 15 mm is optimal.19 This will provide adequate support for the titanium bar to enable an approximate 10-mm cantilever for first-molar occlusion (Figs 7 and 8). Adequate A-P spread is one reason the transsinus implant approach was developed; if not transsinus, zygomatic implant placement facilitates A-P spread for immediate provisionalization.14,25 Ectomorphic individuals with small overall bone dimension can sometimes be treated with a threeimplant scheme, as a reduced A-P spread may be acceptable in both jaws.
e132 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Anterior-posterior spatial mandible
Anterior-posterior spatial maxilla
Fig 5 Anterior-posterior spread is improved in the mandible by tilting the posterior implants 30 degrees distally.
10 mm
10 mm
Fig 6 Anterior-posterior spread is improved in the maxilla by tilting the posterior implants 30 degrees distally.
10 mm
10 mm
Fig 7 Once bone reduction is completed to create a level bone shelf (a total bone reduction of approximately 14 to 15 mm in each arch), there is enough room for a 4-mm titanium bar. However, without tilting the back implants, the bar will need to support a longer cantilever and bar fracture may occur.
Fig 8 Following bone reduction and placement of posterior tilted implants, the bar is well supported and results in a shorter cantilever than for vertical implant placement.
OCCLUSAL SCHEME
in lateral movements to eliminate interferences, and cusps are flattened slightly to minimize lateral forces and distribute them over a large area.30 Along with a limited occlusal scheme, there is a requirement for a mechanical soft diet until the implants undergo early osseointegration from bone modeling at about 6 weeks.29 When sinus grafting for low–insertiontorque transsinus implants is done, 4 to 6 months of an occlusion-sparing regimen should be prescribed.12
In the provisional stage for immediate function, the occlusion should be limited to equal contacts and equal, symmetric distribution of contacts between the implants,25 avoiding both anterior and posterior cantilever extensions.27 Cantilevers are not used in the provisional restoration so as to reduce bone strain from lever moments of force.28,29 Adjustments are made
The International Journal of Oral & Maxillofacial Implants e133 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Fig 9 The “M” pattern of M-4 implant placement as seen on a postoperative panoramic radiograph is an excellent method to gain adequate A-P spread using cortical bone found at the lateral pyriform rim.
CASE STUDY A 36-year-old man presented with an edentulous maxilla, having worn a maxillary complete denture for 3 years. There was moderate to severe alveolar-width atrophy but still adequate height for placement of implants. Implants were placed at 30-degree angles using the M-4 technique, engaging M point with implant apices bilaterally (Fig 9). This enabled placement of the implants into wider bone so that facial dehiscence grafting was not required. The M-4 angulation strategy easily avoided the nasal and sinus cavities. Long implants, which gain high insertion torque (greater than 50 Ncm) and an A-P spread of 12 to 15 mm for immediate function (Figs 10a to 10c), were used. Following placement of the implants, a provisional restoration was placed to splint all of the implants into cross-arch stabilization (Fig 11).
DISCUSSION Several factors affect decision-making regarding immediate function in the edentulous maxilla, one of the most important being engagement into cortical bone. Because the alveolar crest is frequently removed to create a bone shelf, the search for cortical bone becomes complicated and there are few options available in a well-aerated midface. Though pterygoid and zygomatic cortex are possibilities, the use of paranasal
bone remains the most easily accessed in the majority of cases. But how much cortical fixation is required for dependable full-arch provisionalization? For single implants placed into extraction sites and temporized on the same day, it has been suggested that a minimum of 6 mm of apical cortical bone is required for immediate function.31 In cross-arch splinted schemes, the absolute requirement of cortical fixation has not been determined, though it must be substantially less, as evidenced by multiple All-on-4 maxillary
e134 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
a
b
Figs 10a to 10c By using an M-4 strategy with four 30-degree angled implants instead of sinus grafting for vertical implant placement, A-P spread is found to be 12 to 15 mm, as demonstrated in this patient.
c Fig 11 The provisional restoration remains stable after 6 weeks of loading.
treatments done successfully with minimal bone availability.11,32 In fact, full-arch splinted restorations often are based on a relatively low composite torque (the sum of all four insertion torque values). Our studies suggest that a composite torque value of 120 Ncm, allowing for a maximum value of 50 Ncm for any single implant, is sufficient for immediate loading. This has been done even when two of four implants are somewhat mobile (Jensen OT, Adams MR, unpublished data, 2012).
One study demonstrated that an implant placed completely out of contact with bone but splinted to adjacent implants in a mandibular fixed prosthesis still osseointegrated.31 In the maxilla, with the economy of four implants in type 3/4 bone, it would seem that all four implants need to be fixed for osseointegration to occur. This has been shown clinically not to be required.31 However, when adjacent implants are of low insertion torque and have minimal cortical bone contact, the entire appliance can be overcome by occlusal The International Journal of Oral & Maxillofacial Implants e135
© 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Fig 12a The medical model of a maxilla showing ideal placement of zygomatic and M-4 distribution implants.
a Fig 12b The emergence of the zygomatic and transsinus implants are both near the second premolar area, giving a near equivalent A-P spread for prosthetic stability.
b
load, leading to catastrophic failure of all four implants (Jensen OT, Adams MR, unpublished data, 2012). The key is to use available bone mass in creative ways, such that insertion torque is maximized and a favorable A-P spread is still realized. Implant angulation accomplishes this, with the most favorable angle— surgically and prosthetically—being 30 degrees. Implant angulation at 30 degrees does three things: 1. It increases the length of the implant in bone by 50%.33,34 2. It increases occlusal load resistance form.34–36 3. In splinted configurations, it leads to subosseous conformation that is highly resistant to shear force.35,36
Increased length will increase load-bearing capacity, both for immediate function and once osseontegration occurs (Jensen OT, Adams MR, unpublished data, 2012). Since there is an absence of cortical bone at the crest after bone reduction, resonance frequency analysis is generally not helpful. The surgeon must therefore rely on insertion torque as the main clinical guide. By placing longer angled implants, there is potentially greater implant surface area to gain insertion torque, though it still may be relatively low (Jensen OT, Adams MR, unpublished data, 2012). In addition, implants lying “sideways” have potentially more resistance form to compression and pullout force as well as shear force.35 In this setting, cancellous bone may actually contribute to load-bearing capacity when compared to vertically placed (shorter) implants.
e136 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
Adjacent implants placed at 30-degree angles can be as much as 60 degrees convergent/divergent from each other within bone. In most cases, four implants placed with various divergence angles will add complex secondary resistance form to augment prosthetic splinting.14,36 However, the major determinant of load-bearing capacity of newly placed implants in a maxilla with deficient bone mass is finding cortical bone to fix four implants apically for adequate A-P spread, as there is seldom substantial bone contact available anywhere else except apically. Though bone contact may be minimal at the alveolar crest, the prosthesis will serve to immobilize the implants by what could be termed secondary stabilization.37–40 In summary, the residual cortical areas of commonly available paranasal bone, including subnasal basal bone, the vomer/nasal crest, and the lateral pyriform rim, should be considered prior to selecting the zygo matic implant option. The clinician should remember that transsinus implant emergence in the alveolar process is nearly equivalent with that of the zygomatic implant (Figs 12a and 12b) and that the transsinus implant does not have as high an incidence of oroantral fistulae as the zygomatic implant.14,34,41–43 It is only when paranasal sites have inadequate bone that extramaxillary bone stock should be considered for All-on-4 immediate function.
Acknowledgments The authors reported no conflicts of interest related to this study.
REFERENCES 1. Tyndall DA, Brooks SL. Selection criteria for dental implant site imaging: A position paper of the American Academy of Oral and Maxillofacial Radiology. Oral Surg Oral Med Oral Path Oral Radiol Endod 2000;89:630–637. 2. Harris D, Buser D, Dulka K, et al. E.A.O. guidelines for the use of diagnostic imaging in implant dentistry. A consensus workshop organized by the European Association for Osseointegration at Trinity College Dublin. Clin Oral Implants Res 2002;13:566–570. 3. Mozzati M, Arata V, Gallesio G, Mussano F, Carossa S. Immediate postextraction implant placement with immediate loading for maxillary full-arch rehabilitation: A two-year treatment analysis. J Am Dent Assoc 2012;143:124–133. 4. Bedrossian E, Rangert B, Stumpel L, Indresano T. Immediate function with the zygomatic implant: A graftless solution for the patient with mild to advanced atrophy of the maxilla. Int J Oral Maxillofac Implants 2006;21:937–942.
5. Maló P, Nobre Md, Lopes A, Francischone C, Rigolizzo M. Three-year outcome of a retrospective cohort study on the rehabilitation of completely edentulous atrophic maxillae with immediate loaded extra-maxillary zygomatic implants. Eur J Oral Implantol 2012;5:37–46. 6. Chiapasco M, Brusati R, Ronchi P. Le Fort I osteotomy with interpositional bone grafts and delayed oral implants for the rehabilitation of extremely atrophied maxillae: A 1-9-year clinical follow-up study on humans. Clin Oral Implants Res 2007;18:74–85. 7. Lundgren S, Rasmusson L, Sjöström M, Sennerby L. Simultaneous or delayed placement of titanium implants in free autogenous iliac bone grafts. Histological analysis of the bone graft-titanium interface in 10 consecutive patients. Int J Oral Maxillofac Surg 1999;28:31–37. 8. Sbordone L, Levin L, Guidetti F, Sbordone C, Glikman A, Schwartz-Arad D. Apical and marginal bone alterations around implants in maxillary sinus augmentation grafted with autogenous bone or bovine bone material and simultaneous or delayed dental implant positioning. Clin Oral Implants Res 2011;22:485–491. 9. Zoghbi SA, de Lima LA, Saraiva L, Romito GA. Surgical experience influences 2-stage implant osseointegration. J Oral Maxillofac Surg 2011;69:2771–2776. 10. Parel SM, Phillips WR. A risk assessment treatment planning protocol for the four implant immediately loaded maxilla: Preliminary findings. J Prosthet Dent 2011;106:359–366. 11. Krekmanov L, Kahn M, Rangert B, Lindstrom H. Tilting of posterior mandibular and maxillary implants for improved prosthesis support. Int J Oral Maxillofac implants 2000;15: 405-414. 12. Damghani S, Masri R, Driscoll CF, Romberg E. The effect of number and distribution of unsplinted maxillary implants on the load transfer in implant-retained maxillary overdentures: An in vitro study. J Prosthet Dent 2012;107:358–365. 13. Schley JS, Wolfart S. Which prosthetic treatment concepts present a reliable evidence-based option for the edentulous maxilla related to number and position of dental implants? Eur J Oral Implantol 2011;4:31–47. 14. Jensen OT, Cottam JR, Ringeman JL, Adams MW. Transsinus dental implants, bone morphogenetic protein 2, and immediate function for All-on-4 treatment of severe maxillary atrophy. J Oral Maxillofac Surg 2012;70:141–148. 15. Rinehart GC. Mandibulomaxillary fixation with bone anchors and quick-release ligatures. J Craniofac Surg 1998;9: 215–221. 16. Jensen OT, Cottam JR, Ringeman JL, et al. Experience with bone morphogenetic protein-2 and interpositional grafting of edentulous maxillae: A comparison of Le Fort I downfracture to full-arch (horseshoe) segmental osteotomy done in conjunction with sinus floor grafting. Oral Craniofac Tissue Eng 2011;1:123–140. 17. Jensen OT, Cottam JR, Ringeman JL, Graves S, Beatty L, Adams MW. Angled dental implant placement into the vomer/ nasal crest of atrophic maxillae for All-on-Four immediate function: A 2-year clinical study of 100 consecutive patients. Oral Craniofac Tissue Eng 2012;2:66–71. 18. Jensen OT, Adams MW, Cottam JR, Parel S, Phillip W. The All-on-Four shelf: Maxilla. J Oral Maxillofac Surg 2010;68: 2520-2527. 19. Rodriguez AM, Aquilino SA, Lund PS, Ryther JS, Southard TE. Evaluation of strain at the terminal abutment site of a fixed mandibular implant prosthesis during cantilever loading. J Prosthodont 1993;2:93–102.
The International Journal of Oral & Maxillofacial Implants e137 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Jensen et al
20. Benzing UR, Gall H, Weber H Biomechanical aspects of two different implant-prosthetic concepts for edentulous maxillae. Int J Oral Maxillofac Implants 1995;10:188–198. 21. Hobkirk JA, Havthoulas TK. The influence of mandibular deformation, implant numbers, and loading position on detected forces in abutments supporting fixed implant superstructures. J Prosthet Dent 1998;80:169–174. 22. Jensen OT, Adams MW. The maxillary M-4: A technical and biomechanical note for all-on-4 management of severe maxillary atrophy—Report of 3 cases. J Oral Maxillofac Surg 2009;67:1739–1744 [erratum 2009;67:2554]. 23. Richard MJ, Morris C, Deen BF, Gray L, Woodward JA. Analysis of the anatomic changes of the aging facial skeleton using computer-assisted tomography. Ophthal Plast Reconstr Surg 2009;25:382–386. 24. Butura CC, Galindo DF. Combined immediate loading of zygomatic and mandibular implants: A preliminary 2-year report of 19 patients. Oral Craniofac Tissue Eng 2012;2:58–65. 25. Bedrossian E, Sullivan RM, Fortin Y, Malo P, Indresano T. Fixed-prosthetic implant restoration of the edentulous maxilla: A systematic pretreatment evaluation method. J Oral Maxillofac Surg 2008;66:112–122. 26. Graves S, Mahler BA, Javid B, Armellini D, Jensen OT. Maxillary all-on-four therapy using angled implants: A 16-month clinical study of 1110 implants in 276 jaws. Dent Clin North Am 2011;55:779–794. 27. Bellini CM, Romeo D, Galbusera F, et al. Comparison of tilted versus nontilted implant-supported prosthetic designs for the restoration of the edentulous mandible: A biomechanical study. Int J Oral Maxillofac Implants 2009;24:511–517. 28. Gapski R, Wang HL., Mascarenhas P, Lang P: Critical review of immediate implant loading. Clin Oral Implants Res 2003; 14:515–527. 29. Kinsel RP, Liss M: Retrospective analysis of 56 edentulous dental arches restored with 344 single-stage implants using an immediate loading fixed provisional protocol: Statistical predictors of implant failure. Int J Oral Maxillofac Implants 2007;22:823–830. 30. Achilla A, Tura F, Euwe E. Immediate/early function with tapered implants supporting maxillary and mandibular posterior fixed partial dentures: Preliminary results of a prospective multicenter study. J Prosthet Dent 2007;97 (6 suppl):S52–S58. 31. Becker CM, Wilson TG Jr, Jensen OT. Minimum criteria for immediate provisionalization of single-tooth dental implants in extraction sites: A 1-year retrospective study of 100 consecutive cases. J Oral Maxillofac Surg 2011;69:491–497.
32. Romanos GE, Nentwig GH. Immediate functional loading in the maxilla using implants with platform switching: Five-year results. Int J Oral Maxillofac Implants 2009;24:1106–1112. 33. Villa R, Polimeni G, Wikesjö UM. Implant osseointegration in the absence of primary bone anchorage: A clinical report. J Prosthet Dent 2010;104:282–287. 34. Jensen OT, Adams MW. All-on-4 treatment of highly atrophic mandible with mandibular V-4: Report of 2 cases. J Oral Maxillofac Surg 2009;67:1503–1509. 35. Demenko V, Linetskiy I, Nesvit K, Hubalkova H, Nesvit V, Shevchenko A. Importance of diameter-to-length ratio in selecting dental implants: A methodological finite element study. Comput Methods Biomech Biomed Engin 2012 May 22 [Epub ahead of print]. 36. Lee JS, Lim YJ. Three-dimensional numerical simulation of stress induced by different lengths of osseointegrated implants in the anterior maxilla. Comput Methods Biomech Biomed Engin 2012 Mar 8 [Epub ahead of print]. 37. Ueda C, Markarian RA, Sendyk CL, Laganá DC. Photoelastic analysis of stress distribution on parallel and angled implants after installation of fixed prostheses. Braz Oral Res 2004;18:45–52. 38. Lan TH, Huang HL, Wu JH, Lee HE, Wang CH. Stress analysis of different angulations of implant installation: The finite element method. Kaohsiung J Med Sci 2008;24: 138–143. 39. Burak Özcelik T, Ersoy E, Yilmaz B. Biomechanical evaluation of tooth- and implant-supported fixed dental prostheses with various nonrigid connector positions: A finite element analysis. J Prosthodont 2011;20:16–28. 40. Makary C, Rebaudi A, Mokbel N, Naaman N. Peak insertion torque correlated to histologically and clinically evaluated bone density. Implant Dent 2011;20:182–191. 41. Nissan J, Gross O, Ghelfan O, Priel I, Gross M, Chaushu G. The effect of splinting implant-supported restorations on stress distribution of different crown-implant ratios and crown height spaces. J Oral Maxillofac Surg 2011;69:2990–2994. 42. Jensen OT, Adams MW, Cottam JR, Ringeman JL. Occult peri-implant oroantral fistulae: Posterior maxillary periimplantitis/sinusitis of zygomatic or dental implant origin. Treatment and prevention with bone morphogenetic protein-2/ absorbable collagen sponge sinus grafting. Oral Craniofac Tissue Eng 2011;1:340–348. 43. Chrcanovic BR, Abru MH. Survival and complications of zygomatic implants: A systematic review. Oral Maxillofac Surg 2012 May 6 [Epub ahead of print].
e138 Volume 29, Number 1, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
