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Implants for Orthodontic Anchorage
Chapter
17
Implants for Orthodontic Anchorage: Temporary Anchorage Device Joyce T. Lee
O
ver the past 3 decades, successful application of dental endosseous implants has been well established in oral and maxillofacial surgery. Since the late 1980s to early 1990s, the use of endosseous implants has expanded to the treatment of orthodontic patients. The principle of placing implants as anchorage devices to facilitate orthodontic movement of teeth, as well as to affect skeletal growth, has broadened the clinical applications of dental implants. Conventional orthodontics for the treatment of dental and facial skeletal discrepancies often involves cumbersome intraoral appliances, such as full arch braces, interarch elastics, and Nance appliances, in addition to extraoral appliances such as headgear. In situations in which patients are partially edentulous or have oligodontia, the lack of teeth can often pose challenges for the orthodontist in devising a treatment plan with the existing dentition to provide sufficient anchorage. Implants placed into the maxillo-mandibular skeleton enable the orthodontist to provide additional anchorage and exert predictable force in all three spatial planes: transverse, vertical, and sagittal. There is a vast amount of literature on the use of implants in orthodontics to treat malaligned teeth by uprighting, extrusion, intrusion, mesialization, and distalization. Early after their introduction, the literature has been filled with descriptions of different types and designs of anchorage devices for orthodontic purposes that have various shapes and sizes of screws, plates, cylinders, and other components. Some of these implants required a healing period for osseointegration before orthodontic forces could be applied, whereas others were designed to be left and restored with a prosthetic crown on completion of the orthodontic treatment. Several different classifications of osseous anchorage devices have been described by Creekmore and Eklund, Kanomi and Costa, and Cope. Devices with different designs that served the same purpose of assisting in orthodontic treatment lacked uniformity and thus made the nomenclature extremely confusing. In 2005, a metaanalysis conducted by Labanauskaite and colleagues attempted to clarify and further classify these implant devices according to their shape and size (cylindrical, screws, miniplates, and disk shaped), fixation of the implant to the surface of the bone (osseointegrated versus mechanical locking), and clinical applications (orthodontic, orthodontic and restorative/prosthetic, and orthopedic). In a more contemporary approach, the definition of these implants has been narrowed so that it refers specifically to titanium alloy miniscrews or miniplates that are placed as removable temporary anchorage devices (TADs) in the maxilla and mandible to facilitate orthodontic movement. For the purpose of this chapter, we will discuss the type of implants placed solely for the purpose of temporary orthodontic anchorage. Unlike its predecessor, the conventional endosseous osseointegrated implant, a TAD differs from it in many ways. A TAD is designed to be placed for orthodontic anchorage purposes, and on completion of treatment the implant device is always removed. In addition, the success criteria for TADs are defined differently. The capacity to withstand orthodontic forces throughout treatment, lack
146
of clinically detectable mobility, presence of soft tissue health, and lack of painful symptoms are defined as success. In other words, these anchorage devices do not need to be osseointegrated. One of the early implant devices on the market for orthodontic anchorage was the palatal implant. In 1995, Block and Hoffman designed a disk-shaped subperiosteal implant with a roughened hydroxyapatite undersurface that could be placed in the hard palate for orthodontic anchorage. This implant required surgical placement through a palatal tunneling technique and a latency period for osseointegration before loading. Although studies documented its success in providing anchorage, this implant did not gain broad application because of multiple disadvantages, including cost, lengthy osseo integration period, and need for a surgical procedure to place and remove the implant. Similarly, Wehrbein and associates devised a cylindrical palatal implant in 1996 for the same purpose. Without doubt, these devices have achieved success and safety in providing anchorage for the placement of implants in the palatal area.
ANATOMIC CONSIDERATIONS Since 2006, the U.S. Food and Drug Administration has approved the use of TADs in patients who are 12 years and older. Pretreatment planning for these patients includes serial lateral cephalograms or hand-wrist films to assess growth cessation. Placement of anchorage implants in the mid-palatal suture may affect skeletal growth of the maxilla. Recently, cone beam computed tomography (CT) techno logy has drastically reduced the cost and increased the accessibility and ease of obtaining a three-dimensional volumetric study of areas where bone volume, quality, and proximity to vital structures may be questionable for the placement of palatal implants. CT analysis has revealed that bone density is thickest at the level between the first and second premolars and the first and second molars, thus making these areas ideal for placement. If a situation warrants placement of the anchorage more anteriorly, paramedian placement in the area of the premolars may be more suitable because this will avoid potential injury to the incisive neurovascular bundle. Generally, the incisive canal should be kept at a minimum distance of 1 cm from placement of the implant. Although classified as a temporary ortho dontic anchorage device, the early generation of palatal implants required osseointegration and indeed differed from the more recent TAD miniscrews and miniplates. TAD miniscrews are not osseointegrated. Instead, they rely on mechanical engagement of the screw threads to the cortical alveolar bone. Because of this very crucial difference, loading can be performed immediately at orthodontic forces of less than 2 N. An increase in length and hence surface area of TADs does not add to their stability since they do not engage by the principles of osseointegration. Any screw length greater than 5 to 6 mm and up to 12 mm appears to be sufficient. Unlike screw length, screw diameter is significant in determining the stability of TADs. Miyawaki and co-authors, in an article on the optimal screw dimensions and design
Implants for Orthodontic Anchorage: Temporary Anchorage Device of TAD miniscrews, reported that a diameter of no less than 1.2 to 1.4 mm in the maxilla and no greater than 1.4 to 1.8 mm in the mandible provides adequate stability. The recommended difference in screw diameter in the maxilla versus the mandible is due to differences in corticocancellous bone composition. The amount of cortical bone and its density are crucial factors in providing stability to TADs. The thickest portion of the alveolar bone is located between the lateral incisors and canines anteriorly and adjacent to the first molars posteriorly. These sites are ideal for the placement of TADs. Although placement of TADs is possible in areas where there is a high cancellous-to-cortical bone ratio, the hard palate, the infranasal spine, and the maxillary buttress, symphysis, parasymphysis, and retromolar region tend to be more optimal sites given their higher cortical bone content. The TAD miniplate carried over the traditional principles of plating for trauma and osteotomy fixation in oral and maxillofacial surgery. These plates are low profile with one end fixed to bone via screws while the other end emerges transmucosally and has tubes, buttons, notches, and grooves to allow orthodontic attachments (Fig. 17-1). The ideal site for placement of TADs is in an area where there is thick type D2, three-bone density, sufficient bone volume and clearance from vital structures, thin attached gingival soft tissue, and optimal location for anchorage to support the planned orthodontic forces. Three-dimensional studies indicate that the alveolar bone widens as it approaches the apical portion of the tooth roots.
A
B
C
147
Clinically, this level is often apical to the mucogingival junction. For optimal placement of TADs, the screw body should engage the thicker portion of the alveolus apically and the screw head should emerge coronally from the mucogingival junction through the attached gingiva (Fig. 17-2). TAD miniscrews and plates provide both direct and indirect anchorage for orthodontic treatment. Direct anchorage refers to situations in which the implant serves as an anchor for the ortho dontic forces applied. Indirect anchorage refers to situations in which the implant stabilizes a tooth or group of teeth, with the entire unit serving as anchorage for the orthodontic forces exerted. TADs are versatile and can readily be used for retraction, pro traction, uprighting, and intrusion of teeth. Although Sugawara reported a high relapse rate of 30% in cases in which TADs were used for the intrusion of molars, the amount of forces applied, the treatment period, and the degree of intrusion may have been contributing factors.
TREATMENT AND TECHNIQUES The surgical protocol for TAD miniplates involves gaining access to bone via a full-thickness mucoperiosteal incision. Two to three monocortical fixation screws are used to secure the plate vertically in between roots of the teeth, and the transmucosal end of the plate is positioned so that it emerges out of the attached gingiva. Placement of TAD miniscrews can be done via a flapless approach. The soft tissue gingiva can be removed with a small punch. The TAD screws can be screwed in place either with a drill or by hand, but a smaller pilot hole may need to be drilled first in dense cortical bone. The TAD miniscrew should be placed at an angle that is ideal in assisting in the planned orthodontic movement. The TAD is placed at a very slight 30- to 45-degree acute angle to the occlusal plane to engage the greatest dimension of bone available and also to allow emergence of the screw head from the attached gingiva. Loading can begin immediately with forces of less than 50 to 250 g, depending on the planned orthodontic movements. Excessive intrusive or torque forces beyond 250 g affect stability and increase the risk for failure. In addition, minimal clearance of 2 mm from any adjacent vital structures and tooth roots is recommended to avoid potential injury. TADs are absolutely contraindicated in patients with a known allergy to titanium alloy. Patients with a history of heavy tobacco use, advanced osteoporosis, uncontrolled immune or metabolic bone disorders (i.e., uncontrolled diabetes), and bisphosphonate use should be evaluated on a case-by-case basis and the underlying problem corrected before TAD placement.
POSTOPERATIVE CARE
D Fig. 17-1 n A and B, Type A titanium screws, 2.0 mm in diameter with variable lengths. C, Miniplate with screws, 2 mm in diameter and 5 mm in length. D, Clinical use of a type A screw. (A, C, D Modified from Kuroda S, Sugawara Y, Deguchi T, et al: Clinical use of miniscrew implants as orthodontic anchorage: success rates and postoperative discomfort, Am J Orthod Dentofacial Orthop 131:9-15, 2007; B, courtesy KLS Martin L.P., Jacksonville, Fla.)
Complications of TAD placement include infection, damage to adjacent teeth and neurovascular bundles, perforation of the maxillary sinus, loosening or migration of the implant, and hardware fracture. Perioperative antibiotics are recommended, as well as the use of oral chlorhexidine rinses, similar to the surgical protocol for conventional endosseous implants. Patient compliance in maintaining good oral hygiene is also important to minimize mucosal inflammation. Studies have shown peri-implant mucosal inflammation to be one of the major causes of TAD failure. Care in handling these delicate mini-implants during placement and removal is crucial to avoid shearing the screw head or fracturing the implant.
148
Current Therapy in Oral and Maxillofacial Surgery
A
B
C
D Fig. 17-2 n A, After the molar distalization phase, the temporary anchorage device is bonded to the first molars to provide anchorage for retraction of the anterior teeth. B, Lateral cephalograph of this patient showing the 6-mm intraosseous implant (and healing cap) in the standard anterior palate site and angulated 25 degrees to the vertical plane. C, An Aarhus mini-implant inserted in the buccal interproximal region mesial to the first molar and at an angulation of approximately 45 degrees to the vertical axis. This has been loaded immediately with a traction auxiliary to distalize the canine and first premolar. D, A postinsertion radiograph confirms the position of the miniimplant in the interproximal bone between the second premolar socket and the first molar roots. (From Prabhu J, Cousley RRJ: Current products and practice: bone anchorage devices in orthodontics, J Orthod 33:288-307, 2006.)
PEARLS AND PITFALLS • The overall success rate of TADs in recent years has risen predictably to 90%. • The key to success in cases involving the use of TADs is careful planning and a multidisciplinary approach, including a team composed of an orthodontist, a surgeon, and a restorative dentist. • It is through a team approach that the ideal location (dense cortical bone, emergence from attached gingiva), proper angulation (slight acute angle to the occlusal plane), and appropriate size of the TAD (screw diameter of 1.2 to 1.4 mm in the maxilla and 1.4 to 1.8 mm in the mandible) can be accurately predetermined. • Orthodontic treatment with TADs increases patients’ acceptance of treatment by minimizing the necessity of having to deal with interarch elastics and awkward orthodontic gear.
• TADs offer the possibility of a shorter course of treatment while force is continuously being exerted, whereas conventional orthodontics requires headgear or elastics; the choice may depend heavily on patient compliance. • Both the placement and removal of TADs are minimally invasive procedures and can often be performed with the patient under local anesthesia. • Because TADs provide adequate stability, the orthodontist can use these implants immediately after insertion. • The cost of TADs is far lower than that for conventional osseointegrated implants.
Implants for Orthodontic Anchorage: Temporary Anchorage Device
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BIBLIOGRAPHY Bae SM, Park HS, Kyung HM, et al: Clinical application of micro-implant anchorage, J Clin Orthod 36:298-302, 2002. Baumgaertel S: Quantitative investigation of palatal bone depth and cortical bone thickness for mini-implant placement in adults, Am J Orthod Dentofacial Orthop 136:104-108, 2009. Block MS, Hoffman DR: A new device for absolute anchorage for orthodontics, Am J Orthod Dentofacial Orthop 107:251-258, 1995. Celenza F, Hochman MN: Absolute anchorage in orthodontics: direct and indirect implantassisted modalities, J Clin Orthod 34:397-402, 2000. Chen Y, Kyung HM, Zhao WT, et al: Critical factors for the success of orthodontic miniimplants: a systematic review, Am J Orthod Dentofacial Orthop 135:284-291, 2009. Chen YJ, Chang HH, Lin HY, et al: Stability of miniplates and miniscrews used for orthodontic anchorage: experience with 492 temporary anchorage devices, Clin Oral Implants Res 19:1188-1196, 2008. Cheng SJ, Tseng JY, Lee JJ: A prospective study of the risk factors associated with failure of mini-implant used for orthodontic anchorage, Int J Oral Maxillofac Implants 19:100-106, 2004. Cope JB: Temporary anchorage devices in orthodontics: a paradigm shirt, Semin Orthod 11:39, 2005. Cornelis MA, Scheffler NR, Mahy P, et al: Modified miniplates for temporary skeletal anchorage in orthodontics: placement and removal surgeries, J Oral Maxillofac Surg 66:1439-1445, 2008. Costa A, Pasta G, Bergamaschi G: Intraoral hard and soft tissue depths for temporary anchorage devices, Semin Orthod 11:10-15, 2005. Costa A, Raffini M, Melsen B: Miniscrews as orthodontic anchorage: a preliminary report, Int J Adult Orthod Orthognath Surg 13:201209, 1998. Creekmore TD, Eklund MK: The possibility of skeletal anchorage, J Clin Orthod 17:266-269, 1983.
Gapski R, Wang HL, Mascarenhas P, et al: Critical review of immediate implant loading, Clin Oral Implants Res 14:515-527, 2003. Heymann GC, Camilla Tulloch JF: Implantable devices as orthodontic anchorage: a review of current treatment modalities, J Esthet Restor Dent 18:68-80, 2006. Janssen KI, Raghoebar GM, Vissink A, et al: Skeletal anchorage in orthodontics—a review of various systems in animal and human studies, Int J Oral Maxillofac Implants 23:7588, 2008. Kanomi R: Mini-implant for orthodontic anchorage, J Clin Orthod 31:763-767, 1997. Kravitz ND, Kusnoto B, Tsay TP, et al: The use of temporary anchorage devices for molar intrusion, J Am Dent Assoc 138:56-64, 2007. Kuroda S, Sugawara Y, Deguchi T, et al: Clinical use of miniscrew implants as orthodontic anchorage: success rates and postoperative discomfort, Am J Orthod Dentofacial Orthop 131:9-15, 2007. Labanauskaite B, Jankauskas G, Vasiliauskas A, et al: Implants for orthodontics anchorage. Meta-analysis. Stomatologica 7:128-132, 2005. Leung MT, Lee TC, Rabie AB, et al: Use of miniscrews and miniplates in orthodontics, J Oral Maxillofac Surg 66:1461-1466, 2008. Miyawaki S, Koyama I, Inoue M, et al: Factors associated with the stability of titanium screws placed in the posterior region for orthodontic anchorage, Am J Orthod Dentofacial Orthop 124:373-378, 2003. Ohashi E, Pecho OE, Moron M, et al: Implant vs screw loading protocols in orthodontics: a systematic review. Angle Orthod 76:721-727, 2006. Papadopoulos MA, Tarawneh F: The use of miniscrew implants for temporary skeletal anchorage in orthodontics: a comprehensive review, Oral Surg Oral Med Oral Pathol Oral Radiol Endod 103:e6-e15, 2007. Park HS, Bae SM, Kyung HM, et al: Microimplant anchorage for treatment of skeletal class I bialveolar protrusion, J Clin Orthod 35:417-422, 2001.
Park HS, Jeong SH, Kwon OW: Factors affecting the clinical success of screw implants used as orthodontic anchorage, Am J Orthod Dentofacial Orthop 130:18-25, 2006. Poggio PM, Incorvati C, Velo S, et al: “Safe zones”: a guide for miniscrew positioning in the maxillary and mandibular arch, Angle Orthod 76:191-197, 2006. Prabhu J, Cousley RRJ: Current products and practice: bone anchorage devices in orthodontics, J Orthod 33:288-307, 2006. Reynders R, Ronchi L, Bipat S: Mini-implants in orthodontics: a systematic review of the literature, Am J Orthod Dentofacial Orthop 135:564.e1-564.e19, discussion 564-565, 2009. Sándor GK, Daskalogiannakis J, Carmichael RP: Facilitation of orthodontics and orthognathic surgery using dental implants, Atlas Oral Maxillofac Surg Clin North Am 16:125-135, 2008. Straumann USA. 510(k) Summary. Available at: www.fda.gov/cdrh/pdf4/k040469.pdf. Acces sed Oct. 24, 2006. Tseng YC, Hsieh CH, Chen CH, et al: The application of mini-implants for orthodontic anchorage, Int J Oral Maxillofac Surg 35:704-707, 2006. Viwattanatipa N, Thanakitcharu S, Uttraravichien A, et al: Survival analysis of surgical miniscrews as orthodontic anchorage, Am J Orthod Dentofacial Orthop 136:29-36, 2009. Wehrbein H, Glatzmaier J, Mundwiller U, et al: The Orthosystem—a new implant system for orthodontic anchorage in the palate, J Orofac Orthop 57:142-153, 1996. Wu TY, Kuang SH, Wu CH: Factors associated with the stability of mini-implants for ortho dontic anchorage: a study of 414 samples in Taiwan, J Oral Maxillofac Surg 67:1595-1599, 2009.
17
Implants for Orthodontic Anchorage: Temporary Anchorage Device Joyce T. Lee
O
ver the past 3 decades, successful application of dental endosseous implants has been well established in oral and maxillofacial surgery. Since the late 1980s to early 1990s, the use of endosseous implants has expanded to the treatment of orthodontic patients. The principle of placing implants as anchorage devices to facilitate orthodontic movement of teeth, as well as to affect skeletal growth, has broadened the clinical applications of dental implants. Conventional orthodontics for the treatment of dental and facial skeletal discrepancies often involves cumbersome intraoral appliances, such as full arch braces, interarch elastics, and Nance appliances, in addition to extraoral appliances such as headgear. In situations in which patients are partially edentulous or have oligodontia, the lack of teeth can often pose challenges for the orthodontist in devising a treatment plan with the existing dentition to provide sufficient anchorage. Implants placed into the maxillo-mandibular skeleton enable the orthodontist to provide additional anchorage and exert predictable force in all three spatial planes: transverse, vertical, and sagittal. There is a vast amount of literature on the use of implants in orthodontics to treat malaligned teeth by uprighting, extrusion, intrusion, mesialization, and distalization. Early after their introduction, the literature has been filled with descriptions of different types and designs of anchorage devices for orthodontic purposes that have various shapes and sizes of screws, plates, cylinders, and other components. Some of these implants required a healing period for osseointegration before orthodontic forces could be applied, whereas others were designed to be left and restored with a prosthetic crown on completion of the orthodontic treatment. Several different classifications of osseous anchorage devices have been described by Creekmore and Eklund, Kanomi and Costa, and Cope. Devices with different designs that served the same purpose of assisting in orthodontic treatment lacked uniformity and thus made the nomenclature extremely confusing. In 2005, a metaanalysis conducted by Labanauskaite and colleagues attempted to clarify and further classify these implant devices according to their shape and size (cylindrical, screws, miniplates, and disk shaped), fixation of the implant to the surface of the bone (osseointegrated versus mechanical locking), and clinical applications (orthodontic, orthodontic and restorative/prosthetic, and orthopedic). In a more contemporary approach, the definition of these implants has been narrowed so that it refers specifically to titanium alloy miniscrews or miniplates that are placed as removable temporary anchorage devices (TADs) in the maxilla and mandible to facilitate orthodontic movement. For the purpose of this chapter, we will discuss the type of implants placed solely for the purpose of temporary orthodontic anchorage. Unlike its predecessor, the conventional endosseous osseointegrated implant, a TAD differs from it in many ways. A TAD is designed to be placed for orthodontic anchorage purposes, and on completion of treatment the implant device is always removed. In addition, the success criteria for TADs are defined differently. The capacity to withstand orthodontic forces throughout treatment, lack
146
of clinically detectable mobility, presence of soft tissue health, and lack of painful symptoms are defined as success. In other words, these anchorage devices do not need to be osseointegrated. One of the early implant devices on the market for orthodontic anchorage was the palatal implant. In 1995, Block and Hoffman designed a disk-shaped subperiosteal implant with a roughened hydroxyapatite undersurface that could be placed in the hard palate for orthodontic anchorage. This implant required surgical placement through a palatal tunneling technique and a latency period for osseointegration before loading. Although studies documented its success in providing anchorage, this implant did not gain broad application because of multiple disadvantages, including cost, lengthy osseo integration period, and need for a surgical procedure to place and remove the implant. Similarly, Wehrbein and associates devised a cylindrical palatal implant in 1996 for the same purpose. Without doubt, these devices have achieved success and safety in providing anchorage for the placement of implants in the palatal area.
ANATOMIC CONSIDERATIONS Since 2006, the U.S. Food and Drug Administration has approved the use of TADs in patients who are 12 years and older. Pretreatment planning for these patients includes serial lateral cephalograms or hand-wrist films to assess growth cessation. Placement of anchorage implants in the mid-palatal suture may affect skeletal growth of the maxilla. Recently, cone beam computed tomography (CT) techno logy has drastically reduced the cost and increased the accessibility and ease of obtaining a three-dimensional volumetric study of areas where bone volume, quality, and proximity to vital structures may be questionable for the placement of palatal implants. CT analysis has revealed that bone density is thickest at the level between the first and second premolars and the first and second molars, thus making these areas ideal for placement. If a situation warrants placement of the anchorage more anteriorly, paramedian placement in the area of the premolars may be more suitable because this will avoid potential injury to the incisive neurovascular bundle. Generally, the incisive canal should be kept at a minimum distance of 1 cm from placement of the implant. Although classified as a temporary ortho dontic anchorage device, the early generation of palatal implants required osseointegration and indeed differed from the more recent TAD miniscrews and miniplates. TAD miniscrews are not osseointegrated. Instead, they rely on mechanical engagement of the screw threads to the cortical alveolar bone. Because of this very crucial difference, loading can be performed immediately at orthodontic forces of less than 2 N. An increase in length and hence surface area of TADs does not add to their stability since they do not engage by the principles of osseointegration. Any screw length greater than 5 to 6 mm and up to 12 mm appears to be sufficient. Unlike screw length, screw diameter is significant in determining the stability of TADs. Miyawaki and co-authors, in an article on the optimal screw dimensions and design
Implants for Orthodontic Anchorage: Temporary Anchorage Device of TAD miniscrews, reported that a diameter of no less than 1.2 to 1.4 mm in the maxilla and no greater than 1.4 to 1.8 mm in the mandible provides adequate stability. The recommended difference in screw diameter in the maxilla versus the mandible is due to differences in corticocancellous bone composition. The amount of cortical bone and its density are crucial factors in providing stability to TADs. The thickest portion of the alveolar bone is located between the lateral incisors and canines anteriorly and adjacent to the first molars posteriorly. These sites are ideal for the placement of TADs. Although placement of TADs is possible in areas where there is a high cancellous-to-cortical bone ratio, the hard palate, the infranasal spine, and the maxillary buttress, symphysis, parasymphysis, and retromolar region tend to be more optimal sites given their higher cortical bone content. The TAD miniplate carried over the traditional principles of plating for trauma and osteotomy fixation in oral and maxillofacial surgery. These plates are low profile with one end fixed to bone via screws while the other end emerges transmucosally and has tubes, buttons, notches, and grooves to allow orthodontic attachments (Fig. 17-1). The ideal site for placement of TADs is in an area where there is thick type D2, three-bone density, sufficient bone volume and clearance from vital structures, thin attached gingival soft tissue, and optimal location for anchorage to support the planned orthodontic forces. Three-dimensional studies indicate that the alveolar bone widens as it approaches the apical portion of the tooth roots.
A
B
C
147
Clinically, this level is often apical to the mucogingival junction. For optimal placement of TADs, the screw body should engage the thicker portion of the alveolus apically and the screw head should emerge coronally from the mucogingival junction through the attached gingiva (Fig. 17-2). TAD miniscrews and plates provide both direct and indirect anchorage for orthodontic treatment. Direct anchorage refers to situations in which the implant serves as an anchor for the ortho dontic forces applied. Indirect anchorage refers to situations in which the implant stabilizes a tooth or group of teeth, with the entire unit serving as anchorage for the orthodontic forces exerted. TADs are versatile and can readily be used for retraction, pro traction, uprighting, and intrusion of teeth. Although Sugawara reported a high relapse rate of 30% in cases in which TADs were used for the intrusion of molars, the amount of forces applied, the treatment period, and the degree of intrusion may have been contributing factors.
TREATMENT AND TECHNIQUES The surgical protocol for TAD miniplates involves gaining access to bone via a full-thickness mucoperiosteal incision. Two to three monocortical fixation screws are used to secure the plate vertically in between roots of the teeth, and the transmucosal end of the plate is positioned so that it emerges out of the attached gingiva. Placement of TAD miniscrews can be done via a flapless approach. The soft tissue gingiva can be removed with a small punch. The TAD screws can be screwed in place either with a drill or by hand, but a smaller pilot hole may need to be drilled first in dense cortical bone. The TAD miniscrew should be placed at an angle that is ideal in assisting in the planned orthodontic movement. The TAD is placed at a very slight 30- to 45-degree acute angle to the occlusal plane to engage the greatest dimension of bone available and also to allow emergence of the screw head from the attached gingiva. Loading can begin immediately with forces of less than 50 to 250 g, depending on the planned orthodontic movements. Excessive intrusive or torque forces beyond 250 g affect stability and increase the risk for failure. In addition, minimal clearance of 2 mm from any adjacent vital structures and tooth roots is recommended to avoid potential injury. TADs are absolutely contraindicated in patients with a known allergy to titanium alloy. Patients with a history of heavy tobacco use, advanced osteoporosis, uncontrolled immune or metabolic bone disorders (i.e., uncontrolled diabetes), and bisphosphonate use should be evaluated on a case-by-case basis and the underlying problem corrected before TAD placement.
POSTOPERATIVE CARE
D Fig. 17-1 n A and B, Type A titanium screws, 2.0 mm in diameter with variable lengths. C, Miniplate with screws, 2 mm in diameter and 5 mm in length. D, Clinical use of a type A screw. (A, C, D Modified from Kuroda S, Sugawara Y, Deguchi T, et al: Clinical use of miniscrew implants as orthodontic anchorage: success rates and postoperative discomfort, Am J Orthod Dentofacial Orthop 131:9-15, 2007; B, courtesy KLS Martin L.P., Jacksonville, Fla.)
Complications of TAD placement include infection, damage to adjacent teeth and neurovascular bundles, perforation of the maxillary sinus, loosening or migration of the implant, and hardware fracture. Perioperative antibiotics are recommended, as well as the use of oral chlorhexidine rinses, similar to the surgical protocol for conventional endosseous implants. Patient compliance in maintaining good oral hygiene is also important to minimize mucosal inflammation. Studies have shown peri-implant mucosal inflammation to be one of the major causes of TAD failure. Care in handling these delicate mini-implants during placement and removal is crucial to avoid shearing the screw head or fracturing the implant.
148
Current Therapy in Oral and Maxillofacial Surgery
A
B
C
D Fig. 17-2 n A, After the molar distalization phase, the temporary anchorage device is bonded to the first molars to provide anchorage for retraction of the anterior teeth. B, Lateral cephalograph of this patient showing the 6-mm intraosseous implant (and healing cap) in the standard anterior palate site and angulated 25 degrees to the vertical plane. C, An Aarhus mini-implant inserted in the buccal interproximal region mesial to the first molar and at an angulation of approximately 45 degrees to the vertical axis. This has been loaded immediately with a traction auxiliary to distalize the canine and first premolar. D, A postinsertion radiograph confirms the position of the miniimplant in the interproximal bone between the second premolar socket and the first molar roots. (From Prabhu J, Cousley RRJ: Current products and practice: bone anchorage devices in orthodontics, J Orthod 33:288-307, 2006.)
PEARLS AND PITFALLS • The overall success rate of TADs in recent years has risen predictably to 90%. • The key to success in cases involving the use of TADs is careful planning and a multidisciplinary approach, including a team composed of an orthodontist, a surgeon, and a restorative dentist. • It is through a team approach that the ideal location (dense cortical bone, emergence from attached gingiva), proper angulation (slight acute angle to the occlusal plane), and appropriate size of the TAD (screw diameter of 1.2 to 1.4 mm in the maxilla and 1.4 to 1.8 mm in the mandible) can be accurately predetermined. • Orthodontic treatment with TADs increases patients’ acceptance of treatment by minimizing the necessity of having to deal with interarch elastics and awkward orthodontic gear.
• TADs offer the possibility of a shorter course of treatment while force is continuously being exerted, whereas conventional orthodontics requires headgear or elastics; the choice may depend heavily on patient compliance. • Both the placement and removal of TADs are minimally invasive procedures and can often be performed with the patient under local anesthesia. • Because TADs provide adequate stability, the orthodontist can use these implants immediately after insertion. • The cost of TADs is far lower than that for conventional osseointegrated implants.
Implants for Orthodontic Anchorage: Temporary Anchorage Device
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