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Clinical Methodologies for Achieving Primary Dental Implant Stability
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Clinical Methodologies for Achieving Primary Dental Implant Stability: The Effects of Alveolar Bone Density John Cavallaro, Jr., Ben Greenstein and Gary Greenstein JADA 2009;140(11):1366-1372 10.14219/jada.archive.2009.0071 The following resources related to this article are available online at jada.ada.org (this information is current as of December 13, 2014): Updated information and services including high-resolution figures, can be found in the online version of this article at: http://jada.ada.org/content/140/11/1366
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Clinical methodologies for achieving primary dental implant stability The effects of alveolar bone density John Cavallaro Jr., DDS; Ben Greenstein, DMD; Gary Greenstein, DDS, MS
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® Purpose. The authors conducted a literature review to determine the effects of local alveolar bone density on clinical techniques designed to N C U U achieve primary implant stability. A ING ED 2 RT Types of Studies Reviewed. The authors ICLE reviewed articles in the literature that addressed attaining primary stability of dental implants. They combined their findings with their own clinical experiences to produce the information provided in this article. Results. The authors present practical information regarding bone density to delineate for clinicians instances in which modifications of the drilling protocol are needed. They also correlate measures to enhance primary stability with the alveolar bone density at the implantation site. Clinical Implications. To enhance primary implant stability, modifications of the drilling protocol are necessary in different bone densities. Key Words. Clinical protocols; dental implants. JADA 2009;140(11):1366-1372. I
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he density of bone found in the mandible and maxilla often is related to the arch position being evaluated.1,2 For instance, the densest bone frequently is located in the anterior aspect of the mandible, followed by the premaxilla and the posterior mandible. The least dense bone usually is situated in the posterior maxilla.3 However, variations in osseous density can occur in all locations in the mouth.4 Therefore, clinicians should validate their assumptions regarding osseous density at the time of osteotomy development, because bone density at an implant site is a critical factor with respect to surgical protocol and osseointegration (Figure 1).5,6 In particular, clinicians use their tactile assessments of of bone density to make decisions concerning the depth and width of the osteotomy, implant design,7 healing time,8,9 countersinking, immediate loading of implants,10 platform switching11 and time at which to load implants.
Dr. Cavallaro is a clinical associate professor, Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York City. He also maintains a private practice in surgical implantology and prosthodontics in New York City. Address reprint requests to Dr. Cavallaro at 315 Ave. W, Brooklyn, N.Y. 11223, e-mail “[email protected]”. Dr. Ben Greenstein maintains a private practice in surgical implantology and periodontics in Freehold, N.J. Dr. Gary Greenstein is a clinical associate professor, Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York City. He also maintains a private practice in surgical implantology and periodontics in Freehold, N.J.
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Classifications of bone density in the literature often describe four different levels of osseous quality (Table)12-16; however, the clinician cannot differentiate clearly between all these gradations of bone density when developing an osteotomy. For example, Trisi and Rao17 compared clinicians’ perceptions of bone density at implant sites with histomorphometric assessment of bone cores. Clinicians could distinguish between type 1 bone (dense) and type 4 bone (soft); however, they could not distinguish reliably between the other types of bone (type 2 and type 3). Therefore, we deemed it important to differentiate between three readily identifiable bone densities—hard, medium and soft—found in the maxilla and mandible. On the basis of these findings, we present in this article recommendations to modify the drilling protocol relative to osseous densities. In addition, we describe how clinicians can determine the degree of osseous density with a 2-millimeter twist drill and ways in which they can use this information to alter osteotomy development and subsequent prosthetic design. TYPES OF BONE AND THEIR EFFECTS ON DRILLING PROTOCOLS
We discuss three common scenarios relative to osseous density that have an effect on drilling procedures. The following recommendations are practical and predicated on the clinician’s tactile perception of the bone quality encountered while developing an osteotomy. The 2-mm twist drill provides this feedback, facilitating delineation of the amount of cortical bone and the density of the trabecular bone. dDense type (Td) is cortical bone that spans the entirety or the majority of the length of the intended implant or a layer of cortical bone followed by a medullary compartment that provides notable drilling resistance when the clinician applies the 2-mm twist drill. This type of bone usually exists in the anterior region of the mandible. dMedium type (Tm) is a layer of cortical bone approximately 2 to 3 mm in length followed by a medullary compartment that provides limited drilling resistance when the 2-mm twist drill is applied. Clinicians often detect Tm in the maxillary anterior region and the posterior mandible but sometimes find it in the anterior region of the mandible. dSoft type (Ts) is a minimal or indiscernible cor-
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Figure 1. Intraoral depiction of a 2-millimeter twist drill in an osteotomy. Tactile feedback from the twist drill can provide critical information regarding bone density at the implant site.
tical bone layer and poor-quality medullary bone. Ts occurs most often in the posterior region of the maxilla. The criteria for defining Tm as approximately 2 to 3 mm of cortical bone are based on several factors. The results of several studies have indicated that primary implant stability, which is critical to achievement of osseointegration,18,19 is directly related to the thickness of the cortical bone.20-24 In this regard, Motoyoshi and colleagues,25,26 studying orthodontic mini-implants (1.6 mm in diameter), recommended a 1.0-mm cortical bone thickness as the minimum threshold for implant stability and success. Accordingly, if the clinician places an implant platform at the level of the alveolar crest and attaches an abutment to the platform, 1.5 to 2 mm of bone resorption will occur apically to the microgap to facilitate reformation of the biological width.27,28 Therefore, it is necessary that approximately 3.0 mm of cortical bone be present initially to ensure that 1.0 mm of cortical bone will remain after an abutment is connected to an implant platform. In addition, another author indicated that type 2 (D2) and type 3 (D3) bone are associated ABBREVIATION KEY. D1: Dense cortical bone. D2: Dense-to-porous cortical bone and dense trabecular bone. D3: Porous cortical bone and fine trabecular bone. D4: Little cortical bone and fine trabecular bone. Td: Dense type. Tm: Medium type. Ts: Soft type. JADA, Vol. 140
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supracrestally. As previously stated, this is the reason we chose 2.0 to 3.0 mm of Bone density and common locations.* cortical bone as a defining criterion for a BONE HISTOLOGY USUAL LOCATION TACTILE designation of Tm bone. If 1.5 to 2.0 mm DENSITY SENSE of vertical bone resorbs as the biological LEVEL† width re-forms and approximately 1.0 D1 Dense cortical Anterior mandible (6 percent), Drilling into mm of cortical bone remains crestally, bone posterior mandible (3 percent) oak or maple the implant will retain the support it D2 Dense to porous Anterior mandible (66 percent), Drilling into cortical bone and posterior mandible (50 percent), pine or spruce needs to remain stable during the period dense trabecular anterior maxilla (25 percent) of osseointegration. bone Countersinking. The crestal D3 Porous cortical Anterior maxilla (65 percent), Drilling into bone and fine posterior maxilla (50 percent) balsa wood module or implant platform is the part trabecular bone of the dental implant body that holds D4 Little cortical Posterior maxilla (40 percent) Drilling into the prosthetic component. It often is bone and fine styrofoam smooth so as to inhibit bacterial attachtrabecular bone 14 16 ment and includes a polished cervical * Sources: Misch and Misch. † D1: Dense cortical bone. D2: Dense-to-porous cortical bone and dense trabecular bone. collar. Some implants have a crestal D3: Porous cortical bone and fine trabecular bone. D4: Little cortical bone and fine module that is wider than the implant trabecular bone. body. If the clinician decides to place respectively with 2.5 to 4 mm and 1.5 to 2 mm of the implant platform at the level of the osseous cortical bone.29 crest, he or she can use a countersink drill to Distinguishing between three types of bone is enlarge the osteotomy in the cortical bone to facilrelatively easy, and using this information can itate its placement. However, this may diminish help guide the clinician in creating an osteotomy. the implant’s primary stability.31 If the clinician In general, regional differences in cortical bone places the implant platform subcrestally, then the occur more regularly than do variations in the biological width will develop subcrestally and 1.5 cancellous bone, and may be more significant to to 2.0 mm of cortical bone will be lost apically initial implant stability.18 Before correlating the from the microgap.27-28 altered drilling protocols with regional bone denPlatform switching. The technique of platsities, we provide some information regarding form switching involves use of an abutment that several relevant concepts: biological width, counis smaller than the platform of the implant.32 This tersinking and platform switching. Then we disprocedure facilitates the development of part of cuss the practical implications of Td, Tm and Ts. the biological width on the implant platform and results in less bone loss.32 Thus, if the patient has TERMINOLOGY AND TECHNIQUES a limited amount of cortical bone, the clinician Biological width. The term “biological width” may find platform switching beneficial, because it refers to the epithelial attachment and connective may help preserve cortical bone and thereby tissue found coronal to the bone surrounding a enhance primary stability.11 Using platform dental implant. It usually is 1.5 to 2.0 mm in switching can be beneficial in any bone type, but height. Investigators also have referred to a “horiit may be of particular benefit when the patient zontal biological width,” which is approximately has a dearth of cortical bone because this method1.3 mm.30 This term refers to lateral loss of bone ology results in less bone loss (Figure 2).33 In this that occurs around an implant if implants are regard, Cappiello and colleagues34 found that verplaced less than 3 mm apart. tical bone loss for implants placed with platform The vertical biological width can form either switching varied between 0.6 and 1.2 mm (mean, subcrestally or supracrestally. This depends on the 0.95 mm), whereas for implants placed without implant’s type and its initial positioning in bone. platform switching, bone loss was between 1.3 For instance, if a clinician inserts an implant at and 2.1 mm (mean, 1.67 mm). the osseous crest and places a healing abutment, DRILLING PROTOCOLS AND CLINICAL the bone will resorb 1.5 to 2.0 mm to accommodate IMPLICATIONS 27-28 development of a subcrestal biological width. On the other hand, if the clinician uses a transginTd bone. In Td bone, the dentist should use a gival implant design, the biological width will form round bur or pilot drill to initiate an osteotomy
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Figure 2. The abutment attached to the most posterior implant (site no. 19) is an example of a platform switch (use of an abutment smaller than the implant platform). The reduced amount of crestal bone resorption associated with platform switching as the biological width re-forms is beneficial in this instance, because there is a limited amount of cortical bone over the inferior alveolar canal.
Figure 3. The platform placed supracrestally on the distal implant (site no. 30, red arrows) and inserted subcrestally on the mesial implant (site no. 29, yellow arrows). Note that the bone level is more coronal around site no. 30, where the biological width formed supracrestally. In contrast, the bone level is more apical around site no. 29, where the biological width formed subcrestally.
and then use a 2-mm twist drill at the proposed implant site. He or she should measure the amount of cortical bone before penetrating into the cancellous bone. In the case of Td, the operator will find that the bone is difficult to penetrate throughout the length of the osteotomy. The operator may note a point of cortex penetration, but the medullary compartment still provides significant drilling resistance. This type of bone overheats easily; therefore, the operator should use new sharp drills, copious irrigation and intermittent drilling pressure.35 In addition, Td bone type expands minimally. Therefore, the final osteotomy must closely approximate the diameter of the implant to be inserted. Bone tapping may be required, but it usually is not needed with contemporary self-tapping implants. If the clinician is using a handpiece to insert an implant into the bone, the implant should not cease progression into the osteotomy (or “torque out”) at 40 newton centimeters before the majority of it has been inserted. Hand-ratcheting two to three threads is reasonable, but generating high hand-torque forces to seat the entire implant is not advisable. If the clinician notes excessive resistance to implant insertion, he or she should remove the implant and enlarge the osteotomy. Implants placed in Td bone can be left supracrestal, placed level with the osseous crest or countersunk (Figure 3). Apicocoronal implant placement depends on several factors, such as the
need for running room, requirements for interocclusal space and the type of restoration to be fabricated.36 Because Td bone initially is mechanically supportive for the majority or the entire length of the implant, biological width formation does not jeopardize the initial stability of placed implants. Accordingly, these implants are suitable for immediate nonocclusal loading and immediate occlusal loading (particularly in cases involving cross-arch splints).10,37 In addition, since the amount of boneto-implant contact is high in this bone type, implants do not have to be excessively long to provide resistance to occlusal forces.12 Tm bone. In medium-quality bone, the clinician can observe a distinct drop in drilling resistance beyond the cortical layer of bone; however, the twist drill meets with resistance as it penetrates the cortex. The clinician should note the distance from the osseous crest to the marrow compartment, which he or she can measure with a round-ended implant probe. When the cortical bone is approximately 3 mm, and the remaining medullary bone provides distinctly less drilling resistance, we recommend that clinicians use the following modifications to the drilling and insertion protocol: devenly undersize the osteotomy relative to the final implant diameter (as described by Bahat38); dinsert an evenly tapered implant into an undersized or straight-stepped osteotomy, because in less dense bone, this provides bone compression JADA, Vol. 140
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Figure 4. Periapical radiograph of an implant placed in a fresh extraction socket at site no. 13. The clinician used several strategies to enhance primary stability: drilling the osteotomy 5.0 millimeters apical to the base of the socket, undersizing the apical portion of the osteotomy relative to the diameter of the implant, placing a flared healing abutment to wedge against the side walls of the socket and not loading the implant at insertion.
(as described by Turkyilmaz and colleagues39 ); deliminate countersinking from the process to avoid reducing cortical bone and, possibly, primary stability; dplace the implant supracrestally to avoid losing cortical bone; dprepare the coronal portion of the osteotomy with a bur having a diameter that approximates the width of the implant, and prepare the apical portion of the osteotomy minimally. If the clinician follows these recommendations, a healing abutment or a nonocclusally loaded provisional restoration often can be placed. Nonocclusal loading reduces the risk that would be associated with immediate occlusal loading for single-unit or straight-line splinted restorations. Ts bone. In soft bone, the 2-mm twist drill penetrates the length of the osteotomy with little resistance. As soon as the clinician realizes this, he or she must consider undersizing the osteotomy substantially. For example, the clinician can place an implant 4 mm in diameter by 10 mm long in an osteotomy drilled to a 3-mm diameter in its coronal one-half but to a diameter of only 2 mm in the remainder. When undersizing the osteotomy, the clinician drills its coronal aspect a little wider than the rest of the implant to facilitate inserting the implant into the orifice of the osteotomy. For a 5-mm diameter implant, which tapers evenly to an apical diameter of 4 mm, the entire osteotomy can be 1 to 2 mm narrower, and the implant generally will thread into place and provide bone compression 1370
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as it is seated. Alternately, the clinician can use hand instruments (osteotomes) to prepare the osteotomy after using the 2-mm twist drill in poorquality bone.40 This will provide bone compression, which can enhance primary implant stability. In soft bone, the clinician must make a distinction between a “spinner” (an implant that continues to turn in an osteotomy after being fully seated) and an implant with buccolingual or mesiodistal mobility.41 The former still can integrate, while the latter should be removed because it will not integrate predictably.42 Often, if the patient’s anatomy permits, the clinician can use a wider implant to replace a mobile implant without additional drilling.43 The clinician may consider these additional strategies when working with Ts bone: dsubmerge the implant to protect it during osseointegration (as described by Adell and colleagues9); dallow a longer time frame (as much as six months) for osseointegration (as described by Ostman and colleagues44); duse an implant with a flared coronal portion for additional bone compression (as described by Akkocaoglu and colleagues45); dplace a flared healing abutment to aid in stabilizing the implant, as the healing abutment will bind at the osseous crest (Figure 4); dprovide meticulous relief of any prosthesis that lies over an implant placed in soft bone; dplace the implant slightly subcrestally to protect against any transmucosal loading; dplace additional implants (even as many as one per tooth) to provide additional resistance to occlusal forces (as described by Bidez and Misch46); dafter the period of submergence, load the implant with the provisional prosthesis to test the integrity of osseointegration; dsplint implants to distribute forces across multiple implants; dat the time of abutment connection, use a torque of 20 to 35 Ncm to tighten the prosthetic abutment screws appropriately (this provides an additional piece of information about the stability of the implants and helps prevent the potential disruptions to osseointegration that can occur during reverse-torque tests).47 OTHER DECISIONS BASED ON BONE TYPE
Length and width of osteotomy. When using the 2-mm twist drill to initiate the osteotomy, the clinician may find the bone density to be softer
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than expected. If bone is available, the clinician should modify the drilling protocol by developing the osteotomy deeper or wider than planned initially. This allows the insertion of a larger implant, 48,49 which increases the implant-bone contact area and reduces the occlusal load to the bone.50 If the clinician places an implant that is 1 mm wider than planned originally, the implant surface area increases by 20 to 30 percent.15 To attain this same increase in implant surface area with respect to length, the clinician must place an implant that is 3 mm longer.15 Immediate placement of implants in extraction sockets and immediate provisionalization. Immediate insertion of an implant after extraction is a rational choice if Td or Tm bone is present.51,52 Additionally, in the esthetic zone, immediate insertion into fresh extraction sockets is possible if other factors are favorable (a low smile line, no buccal recession, presence of buccal plate, healthy attached gingiva). Immediate placement of implants in Ts bone also is possible, but submergence of the implant is prudent. When the clinician determines that Ts bone is present, he or she should consider placing longer or wider implants than if Td or Tm bone was present, because such implants will provide additional resistance to displacement.53 In addition, in Ts bone, if the clinician can undersize the osteotomy or use osteotomes to compact the bone, immediate implant placement will be facilitated. The clinician can consider immediate implant placement with provisionalization if he or she can achieve primary stability during implant placement with a torque of 30 to 40 Ncm insertion force.54 However, if while drilling with the 2-mm twist drill the clinician notes that the bone is soft, he or she should avoid—or accept as having a higher risk—immediate provisional restoration (nonocclusal loading) of the implants, unless he or she can protect the implants by means of splinting or cross-arch stabilization.55 Duration of time to achieve osseointegration. Research and consensus have suggested that for osseointegration to occur, three to six months should elapse between implant placement and implant loading.56 The time needed to achieve osseointegration has been shortened with the advent of textured implant surfaces.57 Nevertheless, a 2-mm twist drill can provide the clinician with tactile feedback that can help him or her predict how much time is needed for an implant to osseointegrate. With soft bone, it may be pru-
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dent for the clinician to wait four to six months before loading the implant; with dense bone, the clinician can load the implant three months (or less) after its placement.17,58-59 Bone recontouring. In Td or Tm bone, which most often is found in the anterior portion of the mandible, the clinician can reduce the ridge to gain a wider osseous platform for implant insertion. This approach does not lessen the implant’s stability, because the buccal and lingual cortical plates and trabecular bone furnish firm support.16 CONCLUSION
The clinician can use information ascertained from tactile feedback during osteotomy development to verify osseous density. He or she then can use these data to modify the drilling protocol to optimize an implant’s primary stability and help ensure successful implant placement. In this article, we have presented clinical recommendations related to osseous density at the implant site to demarcate when clinicians should alter their drilling protocol. ■ Disclosure. None of the authors reported any disclosures. 1. Friberg B, Jemt T, Lekholm U. Early failures in 4,641 consecutively placed Brånemark dental implants: a study from stage 1 surgery to the connection of the completed prostheses. Int J Oral Maxillofac Implants 1991;6(2):142-146. 2. van Steenberghe D, Lekholm U, Bolender C, et al. Applicability of osseointegrated oral implants in the rehabilitation of partial edentulism: a prospective multicenter study on 558 fixtures. Int J Oral Maxillofac Implants 1990;5(3):272-281. 3. Jaffin RA, Berman CL. The excessive loss of Brånemark fixtures in type IV bone: a 5-year analysis. J Periodontol 1991;62(1):2-4. 4. Truhlar RS, Orenstein IH, Morris HF, Ochi S. Distribution of bone quality in patients receiving endosseous dental implants. J Oral Maxillofac Surg 1997;55(12 suppl 5):38-45. 5. Truhlar RS, Farish SE, Scheitler LE, Morris HF, Ochi S. Bone quality and implant design-related outcomes through stage II surgical uncovering of Spectra-System root form implants. J Oral Maxillofac Surg 1997;55(12 suppl 5):46-54. 6. Truhlar RS, Morris HF, Ochi S, Winkler S. Second-stage failures related to bone quality in patients receiving endosseous dental implants: DICRG Interim Report No. 7. Dental Implant Clinical Research Group. Implant Dent 1994;3(4):252-255. 7. Morris HF, Ochi S. The influence of implant design, application, and site on clinical performance and crestal bone: a multicenter, multidisciplinary clinical study. Dental Implant Clinical Research Group (Planning Committee). Implant Dent 1992;1(1):49-55. 8. Misch CE. Density of bone: effect on treatment plans, surgical approach, healing, and progressive bone loading. Int J Oral Implantol 1990;6(2):23-31. 9. Adell R, Lekholm U, Rockler B, Brånemark PI. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981;10(6):387-416. 10. Tarnow DP, Emtiaz S, Classi A. Immediate loading of threaded implants at stage 1 in edentulous arches: ten consecutive case reports with 1- to 5-year data. Int J Oral Maxillofac Implants 1997;12(3):319-324. 11. Hürzeler M, Fickl S, Zuhr O, Wachtel HC. Peri-implant bone level around implants with platform-switched abutments: preliminary data from a prospective study (published correction appears in J Oral Maxillofac Surg 2008;66[10]:2195-2196). J Oral Maxillofac Surg 2007;65 (7 suppl 1):33-39. 12. Misch CE, Qu Z, Bidez MW. Mechanical properties of trabecular bone in the human mandible: implications of dental implant treatment planning and surgical placement. J Oral Maxillofac Surg 1999;57(6):700-706.
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13. Misch CE. Bone density: a key determinant for clinical success. In: Misch CE, ed. Contemporary Implant Dentistry. 2nd ed. St Louis: Mosby; 1999:113-114. 14. Misch CE. Bone density: a key determinant for clinical success. In: Misch CE, ed. Contemporary Implant Dentistry. 2nd ed. St Louis: Mosby; 1999:134-137. 15. Misch CE. Available bone and dental implant treatment plans. In: Misch CE, ed. Contemporary Implant Dentistry. 3rd ed. St Louis: Mosby; 2008:181. 16. Misch CE. Density of bone: effects on surgical approach and healing. In: Misch CE, ed. Contemporary Implant Dentistry. 3rd ed. St. Louis: Mosby; 2008:645-667. 17. Trisi P, Rao W. Bone classification: clinical-histomorphometric comparison. Clin Oral Implants Res 1999;10(1):1-7. 18. Brunski JB. Biomechanical factors affecting the bone-dental implant interface. Clin Mater 1992;10(3):153-201. 19. Albrektsson TO, Johansson CB, Sennerby L. Biological aspects of implant dentistry: osseointegration. Periodontol 2000 1994;4:58-73. 20. Sennerby L, Thomsen P, Ericson LE. A morphometric and biomechanic comparison of titanium implants inserted in rabbit cortical and cancellous bone. Int J Oral Maxillofac Implants 1992;7(1):62-71. 21. Nkenke E, Lehner B, Fenner M, et al. Immediate versus delayed loading of dental implants in the maxillae of minipigs: follow-up of implant stability and implant failures. Int J Oral Maxillofac Implants 2005;20(1):39-47. 22. Huja SS, Rao J, Struckhoff JA, Beck FM, Litsky AS. Biomechanical and histomorphometric analysis of monocortical screws at placement and 6 weeks postinsertion. J Oral Implantol 2006;32(3):110-116. 23. Ivanoff CJ, Grondahl K, Bergstrom C, Lekholm U, Brånemark PI. Influence of bicortical or monocortical anchorage on maxillary implant stability: a 15-year retrospective study of Brånemark System implants. Int J Oral Maxillofac Implants 2000;15(1):103-110. 24. Miyamoto I, Tsuboi Y, Wada E, Suwa H, Iizuka T. Influence of cortical bone thickness and implant length on implant stability at the time of surgery: clinical, prospective, biomechanical, and imaging study. Bone 2005;37(6):776-780. 25. Motoyoshi M, Yoshida T, Ono A, Shimizu N. Effect of cortical bone thickness and implant placement torque on stability of orthodontic mini-implants. Int J Oral Maxillofac Implants 2007;22(5):779-784. 26. Motoyoshi M, Inaba M, Ono A, Ueno S, Shimizu N. The effect of cortical bone thickness on the stability of orthodontic mini-implants and on the stress distribution in surrounding bone. Int J Oral Maxillofac Surg 2009;38(1):13-18. 27. Cochran DL, Hermann JS, Schenk RK, Higginbottom FL, Buser D. Biologic width around titanium implants: a histometric analysis of the implanto-gingival junction around unloaded and loaded nonsubmerged implants in the canine mandible. J Periodontol 1997;68(2):186-198. 28. Hermann JS, Buser D, Schenk RK, Schoolfield JD, Cochran DL. Biologic width around one- and two-piece titanium implants. Clin Oral Implants Res 2001;12(6):559-571. 29. Hahn J. Clinical uses of osteotomes. J Oral Implantol 1999;25(1): 23-29. 30. Tarnow DP, Cho SC, Wallace SS. The effect of inter-implant distance on the height of inter-implant bone crest. J Periodontol 2000; 71(4):546-549. 31. Akça K, Fanuscu MI, Caputo AA. Effect of compromised cortical bone on implant load distribution. J Prosthodont 2008;17(8):616-620. 32. Lazzara RJ, Porter SS. Platform switching: a new concept in implant dentistry for controlling postrestorative crestal bone levels. Int J Periodontics Restorative Dent 2006;26(1):9-17. 33. Luongo R, Traini T, Guidone PC, Bianco G, Cocchetto R, Celletti R. Hard and soft tissue responses to the platform-switching technique. Int J Periodontics Restorative Dent 2008;28(6):551-557. 34. Cappiello M, Luongo R, Di Iorio D, Bugea C, Cocchetto R, Celletti R. Evaluation of peri-implant bone loss around platform-switched implants. Int J Periodontics Restorative Dent 2008;28(4):347-355. 35. Watanabe F, Tawada Y, Komatsu S, Hata Y. Heat distribution in bone during preparation of implant sites: heat analysis by real-time thermography. Int J Oral Maxillofac Implants 1992;7(2):212-219. 36. Cavallaro J, Greenstein G. Prosthodontic complications related to non-optimal implant placement. In: Froum S, ed. Complications in Implant Dentistry: Both Common and Uncommon. Ames, Iowa: WileyBlackwell (in press).
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37. Ottoni JM, Oliveira ZF, Mansini R, Cabral AM. Correlation between placement torque and survival of single-tooth implants. Int J Oral Maxillofac Implants 2005;20(5):769-776. 38. Bahat O. Brånemark system implants in the posterior maxilla: clinical study of 660 implants followed for 5 to 12 years. Int J Oral Maxillofac Implants 2000;15(5):646-653. 39. Turkyilmaz I, Aksoy U, McGlumphy EA. Two alternative surgical techniques for enhancing primary implant stability in the posterior maxilla: a clinical study including bone density, insertion torque, and resonance frequency analysis data. Clin Implant Dent Relat Res 2008;10(4):231-237. 40. Saadoun AP, Le Gall MG. Implant site preparation with osteotomes: principles and clinical application. Pract Periodontics Aesthet Dent 1996;8(5):453-463. 41. Orenstein IH, Tarnow DP, Morris HF, Ochi S. Factors affecting implant mobility at placement and integration of mobile implants at uncovering. J Periodontol 1998;69(12):1404-1412. 42. Orenstein IH, Tarnow DP, Morris HF, Ochi S. Three-year postplacement survival of implants mobile at placement. Ann Periodontol 2000;5(1):32-41. 43. Langer B, Langer L, Herrmann I, Jorneus L. The wide fixture: a solution for special bone situations and a rescue for the compromised implant—part 1. Int J Oral Maxillofac Implants 1993;8(4):400-408. 44. Ostman PO, Hellman M, Sennerby L. Direct implant loading in the edentulous maxilla using a bone density-adapted surgical protocol and primary implant stability criteria for inclusion. Clin Implant Dent Relat Res 2005;7(suppl 1):S60-S69. 45. Akkocaoglu M, Uysal S, Tekdemir I, Akca K, Cehreli MC. Implant design and intraosseous stability of immediately placed implants: a human cadaver study. Clin Oral Implants Res 2005;16(2):202-209. 46. Bidez MW, Misch CE. Force transfer in implant dentistry: basic concepts and principles. J Oral Implantol 1992;18(3):264-274. 47. Jividen G Jr, Misch CE. Reverse torque testing and early loading failures: help or hindrance? J Oral Implantol 2000;26(2):82-90. 48. Ochi S, Morris HF, Winkler S. The influence of implant type, material, coating, diameter, and length on periotest values at secondstage surgery: DICRG interim report no. 4. Dental Implant Clinical Research Group. Implant Dent 1994;3(3):159-162. 49. Misch CE. Wide-diameter implants: surgical, loading, and prosthetic considerations. Dent Today 2006;25(8):66-71. 50. Ding X, Liao SH, Zhu XH, Zhang XH, Zhang L. Effect of diameter and length on stress distribution of the alveolar crest around immediate loading implants (published online ahead of print Sept. 9, 2008). Clin Implant Dent Relat Res. 51. Misch CE, Wang HL, Misch CM, Sharawy M, Lemons J, Judy KW. Rationale for the application of immediate load in implant dentistry: part I. Implant Dent 2004;13(3):207-217. 52. Misch CE, Wang HL, Misch CM, Sharawy M, Lemons J, Judy KW. Rationale for the application of immediate load in implant dentistry: part II. Implant Dent 2004;13(4):310-321. 53. Winkler S, Morris HF, Ochi S. Implant survival to 36 months as related to length and diameter. Ann Periodontol 2000;5(1):22-31. 54. Saadoun AP. Immediate implant placement and temporization in extraction and healing sites. Compend Contin Educ Dent 2002;23(4): 309-318. 55. Misch CE, Hahn J, Judy KW, et al. Workshop guidelines on immediate loading in implant dentistry. J Oral Implantol 2004;30(5): 283-288. 56. Cochran DL, Morton D, Weber HP. Consensus statements and recommended clinical procedures regarding loading protocols for endosseous dental implants. Int J Oral Maxillofac Implants 2004; 19(suppl):109-113. 57. Le Guéhennec L, Soueidan A, Layrolle P, Amouriq Y. Surface treatments of titanium dental implants for rapid osseointegration. Dent Mater 2007;23(7):844-854. 58. Trisi P, Rebaudi A. Peri-implant bone reaction to immediate, early, and delayed orthodontic loading in humans. Int J Periodontics Restorative Dent 2005;25(4):317-329. 59. Nelson K, Semper W, Hildebrand D, Ozyuvaci H. A retrospective analysis of sandblasted, acid-etched implants with reduced healing times with an observation period of up to 5 years. Int J Oral Maxillofac Implants 2008;23(4):726-732.
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Clinical Methodologies for Achieving Primary Dental Implant Stability: The Effects of Alveolar Bone Density John Cavallaro, Jr., Ben Greenstein and Gary Greenstein JADA 2009;140(11):1366-1372 10.14219/jada.archive.2009.0071 The following resources related to this article are available online at jada.ada.org (this information is current as of December 13, 2014): Updated information and services including high-resolution figures, can be found in the online version of this article at: http://jada.ada.org/content/140/11/1366
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Clinical methodologies for achieving primary dental implant stability The effects of alveolar bone density John Cavallaro Jr., DDS; Ben Greenstein, DMD; Gary Greenstein, DDS, MS
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® Purpose. The authors conducted a literature review to determine the effects of local alveolar bone density on clinical techniques designed to N C U U achieve primary implant stability. A ING ED 2 RT Types of Studies Reviewed. The authors ICLE reviewed articles in the literature that addressed attaining primary stability of dental implants. They combined their findings with their own clinical experiences to produce the information provided in this article. Results. The authors present practical information regarding bone density to delineate for clinicians instances in which modifications of the drilling protocol are needed. They also correlate measures to enhance primary stability with the alveolar bone density at the implantation site. Clinical Implications. To enhance primary implant stability, modifications of the drilling protocol are necessary in different bone densities. Key Words. Clinical protocols; dental implants. JADA 2009;140(11):1366-1372. I
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he density of bone found in the mandible and maxilla often is related to the arch position being evaluated.1,2 For instance, the densest bone frequently is located in the anterior aspect of the mandible, followed by the premaxilla and the posterior mandible. The least dense bone usually is situated in the posterior maxilla.3 However, variations in osseous density can occur in all locations in the mouth.4 Therefore, clinicians should validate their assumptions regarding osseous density at the time of osteotomy development, because bone density at an implant site is a critical factor with respect to surgical protocol and osseointegration (Figure 1).5,6 In particular, clinicians use their tactile assessments of of bone density to make decisions concerning the depth and width of the osteotomy, implant design,7 healing time,8,9 countersinking, immediate loading of implants,10 platform switching11 and time at which to load implants.
Dr. Cavallaro is a clinical associate professor, Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York City. He also maintains a private practice in surgical implantology and prosthodontics in New York City. Address reprint requests to Dr. Cavallaro at 315 Ave. W, Brooklyn, N.Y. 11223, e-mail “[email protected]”. Dr. Ben Greenstein maintains a private practice in surgical implantology and periodontics in Freehold, N.J. Dr. Gary Greenstein is a clinical associate professor, Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York City. He also maintains a private practice in surgical implantology and periodontics in Freehold, N.J.
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Classifications of bone density in the literature often describe four different levels of osseous quality (Table)12-16; however, the clinician cannot differentiate clearly between all these gradations of bone density when developing an osteotomy. For example, Trisi and Rao17 compared clinicians’ perceptions of bone density at implant sites with histomorphometric assessment of bone cores. Clinicians could distinguish between type 1 bone (dense) and type 4 bone (soft); however, they could not distinguish reliably between the other types of bone (type 2 and type 3). Therefore, we deemed it important to differentiate between three readily identifiable bone densities—hard, medium and soft—found in the maxilla and mandible. On the basis of these findings, we present in this article recommendations to modify the drilling protocol relative to osseous densities. In addition, we describe how clinicians can determine the degree of osseous density with a 2-millimeter twist drill and ways in which they can use this information to alter osteotomy development and subsequent prosthetic design. TYPES OF BONE AND THEIR EFFECTS ON DRILLING PROTOCOLS
We discuss three common scenarios relative to osseous density that have an effect on drilling procedures. The following recommendations are practical and predicated on the clinician’s tactile perception of the bone quality encountered while developing an osteotomy. The 2-mm twist drill provides this feedback, facilitating delineation of the amount of cortical bone and the density of the trabecular bone. dDense type (Td) is cortical bone that spans the entirety or the majority of the length of the intended implant or a layer of cortical bone followed by a medullary compartment that provides notable drilling resistance when the clinician applies the 2-mm twist drill. This type of bone usually exists in the anterior region of the mandible. dMedium type (Tm) is a layer of cortical bone approximately 2 to 3 mm in length followed by a medullary compartment that provides limited drilling resistance when the 2-mm twist drill is applied. Clinicians often detect Tm in the maxillary anterior region and the posterior mandible but sometimes find it in the anterior region of the mandible. dSoft type (Ts) is a minimal or indiscernible cor-
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Figure 1. Intraoral depiction of a 2-millimeter twist drill in an osteotomy. Tactile feedback from the twist drill can provide critical information regarding bone density at the implant site.
tical bone layer and poor-quality medullary bone. Ts occurs most often in the posterior region of the maxilla. The criteria for defining Tm as approximately 2 to 3 mm of cortical bone are based on several factors. The results of several studies have indicated that primary implant stability, which is critical to achievement of osseointegration,18,19 is directly related to the thickness of the cortical bone.20-24 In this regard, Motoyoshi and colleagues,25,26 studying orthodontic mini-implants (1.6 mm in diameter), recommended a 1.0-mm cortical bone thickness as the minimum threshold for implant stability and success. Accordingly, if the clinician places an implant platform at the level of the alveolar crest and attaches an abutment to the platform, 1.5 to 2 mm of bone resorption will occur apically to the microgap to facilitate reformation of the biological width.27,28 Therefore, it is necessary that approximately 3.0 mm of cortical bone be present initially to ensure that 1.0 mm of cortical bone will remain after an abutment is connected to an implant platform. In addition, another author indicated that type 2 (D2) and type 3 (D3) bone are associated ABBREVIATION KEY. D1: Dense cortical bone. D2: Dense-to-porous cortical bone and dense trabecular bone. D3: Porous cortical bone and fine trabecular bone. D4: Little cortical bone and fine trabecular bone. Td: Dense type. Tm: Medium type. Ts: Soft type. JADA, Vol. 140
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supracrestally. As previously stated, this is the reason we chose 2.0 to 3.0 mm of Bone density and common locations.* cortical bone as a defining criterion for a BONE HISTOLOGY USUAL LOCATION TACTILE designation of Tm bone. If 1.5 to 2.0 mm DENSITY SENSE of vertical bone resorbs as the biological LEVEL† width re-forms and approximately 1.0 D1 Dense cortical Anterior mandible (6 percent), Drilling into mm of cortical bone remains crestally, bone posterior mandible (3 percent) oak or maple the implant will retain the support it D2 Dense to porous Anterior mandible (66 percent), Drilling into cortical bone and posterior mandible (50 percent), pine or spruce needs to remain stable during the period dense trabecular anterior maxilla (25 percent) of osseointegration. bone Countersinking. The crestal D3 Porous cortical Anterior maxilla (65 percent), Drilling into bone and fine posterior maxilla (50 percent) balsa wood module or implant platform is the part trabecular bone of the dental implant body that holds D4 Little cortical Posterior maxilla (40 percent) Drilling into the prosthetic component. It often is bone and fine styrofoam smooth so as to inhibit bacterial attachtrabecular bone 14 16 ment and includes a polished cervical * Sources: Misch and Misch. † D1: Dense cortical bone. D2: Dense-to-porous cortical bone and dense trabecular bone. collar. Some implants have a crestal D3: Porous cortical bone and fine trabecular bone. D4: Little cortical bone and fine module that is wider than the implant trabecular bone. body. If the clinician decides to place respectively with 2.5 to 4 mm and 1.5 to 2 mm of the implant platform at the level of the osseous cortical bone.29 crest, he or she can use a countersink drill to Distinguishing between three types of bone is enlarge the osteotomy in the cortical bone to facilrelatively easy, and using this information can itate its placement. However, this may diminish help guide the clinician in creating an osteotomy. the implant’s primary stability.31 If the clinician In general, regional differences in cortical bone places the implant platform subcrestally, then the occur more regularly than do variations in the biological width will develop subcrestally and 1.5 cancellous bone, and may be more significant to to 2.0 mm of cortical bone will be lost apically initial implant stability.18 Before correlating the from the microgap.27-28 altered drilling protocols with regional bone denPlatform switching. The technique of platsities, we provide some information regarding form switching involves use of an abutment that several relevant concepts: biological width, counis smaller than the platform of the implant.32 This tersinking and platform switching. Then we disprocedure facilitates the development of part of cuss the practical implications of Td, Tm and Ts. the biological width on the implant platform and results in less bone loss.32 Thus, if the patient has TERMINOLOGY AND TECHNIQUES a limited amount of cortical bone, the clinician Biological width. The term “biological width” may find platform switching beneficial, because it refers to the epithelial attachment and connective may help preserve cortical bone and thereby tissue found coronal to the bone surrounding a enhance primary stability.11 Using platform dental implant. It usually is 1.5 to 2.0 mm in switching can be beneficial in any bone type, but height. Investigators also have referred to a “horiit may be of particular benefit when the patient zontal biological width,” which is approximately has a dearth of cortical bone because this method1.3 mm.30 This term refers to lateral loss of bone ology results in less bone loss (Figure 2).33 In this that occurs around an implant if implants are regard, Cappiello and colleagues34 found that verplaced less than 3 mm apart. tical bone loss for implants placed with platform The vertical biological width can form either switching varied between 0.6 and 1.2 mm (mean, subcrestally or supracrestally. This depends on the 0.95 mm), whereas for implants placed without implant’s type and its initial positioning in bone. platform switching, bone loss was between 1.3 For instance, if a clinician inserts an implant at and 2.1 mm (mean, 1.67 mm). the osseous crest and places a healing abutment, DRILLING PROTOCOLS AND CLINICAL the bone will resorb 1.5 to 2.0 mm to accommodate IMPLICATIONS 27-28 development of a subcrestal biological width. On the other hand, if the clinician uses a transginTd bone. In Td bone, the dentist should use a gival implant design, the biological width will form round bur or pilot drill to initiate an osteotomy
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Figure 2. The abutment attached to the most posterior implant (site no. 19) is an example of a platform switch (use of an abutment smaller than the implant platform). The reduced amount of crestal bone resorption associated with platform switching as the biological width re-forms is beneficial in this instance, because there is a limited amount of cortical bone over the inferior alveolar canal.
Figure 3. The platform placed supracrestally on the distal implant (site no. 30, red arrows) and inserted subcrestally on the mesial implant (site no. 29, yellow arrows). Note that the bone level is more coronal around site no. 30, where the biological width formed supracrestally. In contrast, the bone level is more apical around site no. 29, where the biological width formed subcrestally.
and then use a 2-mm twist drill at the proposed implant site. He or she should measure the amount of cortical bone before penetrating into the cancellous bone. In the case of Td, the operator will find that the bone is difficult to penetrate throughout the length of the osteotomy. The operator may note a point of cortex penetration, but the medullary compartment still provides significant drilling resistance. This type of bone overheats easily; therefore, the operator should use new sharp drills, copious irrigation and intermittent drilling pressure.35 In addition, Td bone type expands minimally. Therefore, the final osteotomy must closely approximate the diameter of the implant to be inserted. Bone tapping may be required, but it usually is not needed with contemporary self-tapping implants. If the clinician is using a handpiece to insert an implant into the bone, the implant should not cease progression into the osteotomy (or “torque out”) at 40 newton centimeters before the majority of it has been inserted. Hand-ratcheting two to three threads is reasonable, but generating high hand-torque forces to seat the entire implant is not advisable. If the clinician notes excessive resistance to implant insertion, he or she should remove the implant and enlarge the osteotomy. Implants placed in Td bone can be left supracrestal, placed level with the osseous crest or countersunk (Figure 3). Apicocoronal implant placement depends on several factors, such as the
need for running room, requirements for interocclusal space and the type of restoration to be fabricated.36 Because Td bone initially is mechanically supportive for the majority or the entire length of the implant, biological width formation does not jeopardize the initial stability of placed implants. Accordingly, these implants are suitable for immediate nonocclusal loading and immediate occlusal loading (particularly in cases involving cross-arch splints).10,37 In addition, since the amount of boneto-implant contact is high in this bone type, implants do not have to be excessively long to provide resistance to occlusal forces.12 Tm bone. In medium-quality bone, the clinician can observe a distinct drop in drilling resistance beyond the cortical layer of bone; however, the twist drill meets with resistance as it penetrates the cortex. The clinician should note the distance from the osseous crest to the marrow compartment, which he or she can measure with a round-ended implant probe. When the cortical bone is approximately 3 mm, and the remaining medullary bone provides distinctly less drilling resistance, we recommend that clinicians use the following modifications to the drilling and insertion protocol: devenly undersize the osteotomy relative to the final implant diameter (as described by Bahat38); dinsert an evenly tapered implant into an undersized or straight-stepped osteotomy, because in less dense bone, this provides bone compression JADA, Vol. 140
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Figure 4. Periapical radiograph of an implant placed in a fresh extraction socket at site no. 13. The clinician used several strategies to enhance primary stability: drilling the osteotomy 5.0 millimeters apical to the base of the socket, undersizing the apical portion of the osteotomy relative to the diameter of the implant, placing a flared healing abutment to wedge against the side walls of the socket and not loading the implant at insertion.
(as described by Turkyilmaz and colleagues39 ); deliminate countersinking from the process to avoid reducing cortical bone and, possibly, primary stability; dplace the implant supracrestally to avoid losing cortical bone; dprepare the coronal portion of the osteotomy with a bur having a diameter that approximates the width of the implant, and prepare the apical portion of the osteotomy minimally. If the clinician follows these recommendations, a healing abutment or a nonocclusally loaded provisional restoration often can be placed. Nonocclusal loading reduces the risk that would be associated with immediate occlusal loading for single-unit or straight-line splinted restorations. Ts bone. In soft bone, the 2-mm twist drill penetrates the length of the osteotomy with little resistance. As soon as the clinician realizes this, he or she must consider undersizing the osteotomy substantially. For example, the clinician can place an implant 4 mm in diameter by 10 mm long in an osteotomy drilled to a 3-mm diameter in its coronal one-half but to a diameter of only 2 mm in the remainder. When undersizing the osteotomy, the clinician drills its coronal aspect a little wider than the rest of the implant to facilitate inserting the implant into the orifice of the osteotomy. For a 5-mm diameter implant, which tapers evenly to an apical diameter of 4 mm, the entire osteotomy can be 1 to 2 mm narrower, and the implant generally will thread into place and provide bone compression 1370
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as it is seated. Alternately, the clinician can use hand instruments (osteotomes) to prepare the osteotomy after using the 2-mm twist drill in poorquality bone.40 This will provide bone compression, which can enhance primary implant stability. In soft bone, the clinician must make a distinction between a “spinner” (an implant that continues to turn in an osteotomy after being fully seated) and an implant with buccolingual or mesiodistal mobility.41 The former still can integrate, while the latter should be removed because it will not integrate predictably.42 Often, if the patient’s anatomy permits, the clinician can use a wider implant to replace a mobile implant without additional drilling.43 The clinician may consider these additional strategies when working with Ts bone: dsubmerge the implant to protect it during osseointegration (as described by Adell and colleagues9); dallow a longer time frame (as much as six months) for osseointegration (as described by Ostman and colleagues44); duse an implant with a flared coronal portion for additional bone compression (as described by Akkocaoglu and colleagues45); dplace a flared healing abutment to aid in stabilizing the implant, as the healing abutment will bind at the osseous crest (Figure 4); dprovide meticulous relief of any prosthesis that lies over an implant placed in soft bone; dplace the implant slightly subcrestally to protect against any transmucosal loading; dplace additional implants (even as many as one per tooth) to provide additional resistance to occlusal forces (as described by Bidez and Misch46); dafter the period of submergence, load the implant with the provisional prosthesis to test the integrity of osseointegration; dsplint implants to distribute forces across multiple implants; dat the time of abutment connection, use a torque of 20 to 35 Ncm to tighten the prosthetic abutment screws appropriately (this provides an additional piece of information about the stability of the implants and helps prevent the potential disruptions to osseointegration that can occur during reverse-torque tests).47 OTHER DECISIONS BASED ON BONE TYPE
Length and width of osteotomy. When using the 2-mm twist drill to initiate the osteotomy, the clinician may find the bone density to be softer
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than expected. If bone is available, the clinician should modify the drilling protocol by developing the osteotomy deeper or wider than planned initially. This allows the insertion of a larger implant, 48,49 which increases the implant-bone contact area and reduces the occlusal load to the bone.50 If the clinician places an implant that is 1 mm wider than planned originally, the implant surface area increases by 20 to 30 percent.15 To attain this same increase in implant surface area with respect to length, the clinician must place an implant that is 3 mm longer.15 Immediate placement of implants in extraction sockets and immediate provisionalization. Immediate insertion of an implant after extraction is a rational choice if Td or Tm bone is present.51,52 Additionally, in the esthetic zone, immediate insertion into fresh extraction sockets is possible if other factors are favorable (a low smile line, no buccal recession, presence of buccal plate, healthy attached gingiva). Immediate placement of implants in Ts bone also is possible, but submergence of the implant is prudent. When the clinician determines that Ts bone is present, he or she should consider placing longer or wider implants than if Td or Tm bone was present, because such implants will provide additional resistance to displacement.53 In addition, in Ts bone, if the clinician can undersize the osteotomy or use osteotomes to compact the bone, immediate implant placement will be facilitated. The clinician can consider immediate implant placement with provisionalization if he or she can achieve primary stability during implant placement with a torque of 30 to 40 Ncm insertion force.54 However, if while drilling with the 2-mm twist drill the clinician notes that the bone is soft, he or she should avoid—or accept as having a higher risk—immediate provisional restoration (nonocclusal loading) of the implants, unless he or she can protect the implants by means of splinting or cross-arch stabilization.55 Duration of time to achieve osseointegration. Research and consensus have suggested that for osseointegration to occur, three to six months should elapse between implant placement and implant loading.56 The time needed to achieve osseointegration has been shortened with the advent of textured implant surfaces.57 Nevertheless, a 2-mm twist drill can provide the clinician with tactile feedback that can help him or her predict how much time is needed for an implant to osseointegrate. With soft bone, it may be pru-
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dent for the clinician to wait four to six months before loading the implant; with dense bone, the clinician can load the implant three months (or less) after its placement.17,58-59 Bone recontouring. In Td or Tm bone, which most often is found in the anterior portion of the mandible, the clinician can reduce the ridge to gain a wider osseous platform for implant insertion. This approach does not lessen the implant’s stability, because the buccal and lingual cortical plates and trabecular bone furnish firm support.16 CONCLUSION
The clinician can use information ascertained from tactile feedback during osteotomy development to verify osseous density. He or she then can use these data to modify the drilling protocol to optimize an implant’s primary stability and help ensure successful implant placement. In this article, we have presented clinical recommendations related to osseous density at the implant site to demarcate when clinicians should alter their drilling protocol. ■ Disclosure. None of the authors reported any disclosures. 1. Friberg B, Jemt T, Lekholm U. Early failures in 4,641 consecutively placed Brånemark dental implants: a study from stage 1 surgery to the connection of the completed prostheses. Int J Oral Maxillofac Implants 1991;6(2):142-146. 2. van Steenberghe D, Lekholm U, Bolender C, et al. Applicability of osseointegrated oral implants in the rehabilitation of partial edentulism: a prospective multicenter study on 558 fixtures. Int J Oral Maxillofac Implants 1990;5(3):272-281. 3. Jaffin RA, Berman CL. The excessive loss of Brånemark fixtures in type IV bone: a 5-year analysis. J Periodontol 1991;62(1):2-4. 4. Truhlar RS, Orenstein IH, Morris HF, Ochi S. Distribution of bone quality in patients receiving endosseous dental implants. J Oral Maxillofac Surg 1997;55(12 suppl 5):38-45. 5. Truhlar RS, Farish SE, Scheitler LE, Morris HF, Ochi S. Bone quality and implant design-related outcomes through stage II surgical uncovering of Spectra-System root form implants. J Oral Maxillofac Surg 1997;55(12 suppl 5):46-54. 6. Truhlar RS, Morris HF, Ochi S, Winkler S. Second-stage failures related to bone quality in patients receiving endosseous dental implants: DICRG Interim Report No. 7. Dental Implant Clinical Research Group. Implant Dent 1994;3(4):252-255. 7. Morris HF, Ochi S. The influence of implant design, application, and site on clinical performance and crestal bone: a multicenter, multidisciplinary clinical study. Dental Implant Clinical Research Group (Planning Committee). Implant Dent 1992;1(1):49-55. 8. Misch CE. Density of bone: effect on treatment plans, surgical approach, healing, and progressive bone loading. Int J Oral Implantol 1990;6(2):23-31. 9. Adell R, Lekholm U, Rockler B, Brånemark PI. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981;10(6):387-416. 10. Tarnow DP, Emtiaz S, Classi A. Immediate loading of threaded implants at stage 1 in edentulous arches: ten consecutive case reports with 1- to 5-year data. Int J Oral Maxillofac Implants 1997;12(3):319-324. 11. Hürzeler M, Fickl S, Zuhr O, Wachtel HC. Peri-implant bone level around implants with platform-switched abutments: preliminary data from a prospective study (published correction appears in J Oral Maxillofac Surg 2008;66[10]:2195-2196). J Oral Maxillofac Surg 2007;65 (7 suppl 1):33-39. 12. Misch CE, Qu Z, Bidez MW. Mechanical properties of trabecular bone in the human mandible: implications of dental implant treatment planning and surgical placement. J Oral Maxillofac Surg 1999;57(6):700-706.
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