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Insertion and removal of orthodontic miniscrew implants
Insertion and removal of orthodontic miniscrew implants
14
Fadi Tarawneh and Moschos A. Papadopoulos
INTRODUCTION In general, insertion of miniscrew implants (MIs) should be as noninvasive as possible, in order to reduce postoperative patient discomfort and to avoid irritation and inflammation of the peri-implant tissues. The insertion procedure for a MI is usually given by the manufacturer; however, certain general issues should be taken into consideration and these are outlined in this chapter
PREPARATIONS BEFORE INSERTION
ANESTHESIA Soft tissue anesthesia is usually sufficient for the insertion of MIs and can usually be achieved with topical anesthetics, gels or creams; some patients may need a small amount of local anesthetic. Block anesthesia is rarely required and should be avoided as it could mask signs of root contact during insertion, which could lead to root injury.1
SOFT TISSUE PREPARATION Self-drilling MIs can usually be inserted directly through the gingival tissue or the mucosa without any need for soft tissue or bone manipulation. In contrast, non-self-drilling MIs are inserted only after removal of the soft tissue covering the insertion site, either through a gingival flap incision or a soft tissue punch (see Fig. 11.1).1–3 Raising a gingival flap has been associated with pain, discomfort and inflammation that might last up to a week after surgery but use of the procedure does not influence success rates.4 Use of a flap has been advocated in some circumstances, such as for insertion in the mandibular symphysis. When a MI has to be inserted in the frenum area, a frenectomy is suggested to prevent possible mechanical irritation around the implant during function.2 If possible, these areas should be avoided to simplify the soft tissue issues.
PILOT DRILLING Self-drilling MIs do not require pilot drilling except when they have to be inserted in sites presenting with thick cortical bone where the high force required can cause excessive bone compression, which might decrease secondary stability of MIs or lead to MI fracture during insertion. In
general, buccal cortical bone thickness seems to be greater in the mandible than in the maxilla, and increases gradually in the apical direction.5,6 Males and adults have thicker cortical bone than females and adolescents.5,6 A pilot hole is most important for inserting self-drilling MIs in the mandible and in an apical location, more specifically between the first and second mandibular molars.5 A pilot drill is always necessary for insertion of non-self-drilling MIs. The procedure is performed in a surgical environment and if possible by an oral surgeon. The soft tissue from the site is either incised or removed using a soft tissue punch (see Fig. 11.1). Then, the pilot hole is drilled, usually using a handpiece (see Fig. 18.6D). A speed of 500–1000 rpm is usually sufficient for cortical bone perforation but should not exceed 1500 rpm.1,2 Copious irrigation and cooling with sterile saline helps to minimize overheating, which can lead to bone necrosis and implant failure. Cortical bone can be predrilled manually with a sharp drill of high cutting efficiency to minimize heat production. Pilot drilling is an invasive procedure with the potential to introduce microbial contamination and so it is recommended that the drill is not reinserted into the hole once it is made. To avoid fractures and high bone stresses, optimum predrilling diameters should be chosen: the pilot drill must be approximately 0.2–0.3 mm thinner than the diameter of the MI to be used. Although drilling a pilot hole makes the procedure more complicated and more time consuming, it provides a fixed path of insertion for the MI, which, in turn, minimizes the risk of injuring adjacent roots or insertions into the sinus.
INSERTION OF MINISCREW IMPLANTS Insertion of implants can be performed either manually with the use of screwdrivers (Fig. 14.1A) or mechanically with a specially angled handpiece that permits adjustment of torque through altering the speed of the handpiece (see Fig. 16.5C). For implant insertion, a speed up to 30 rpm is usually adequate and should not exceed 60 rpm.1,2 Ratchets are also available that help to work with MIs in different locations (Fig. 14.1B). Some even provide an adjustable torque control ranging from 5 to 30 Ncm. Once the desired torque is reached, the ratchet bends preventing further force application.1 Insertion torque magnitude depends on factors such as bone thickness, bone quality, size and design of the MI, as well as method and velocity of insertion.1 It is recommended that insertion of MIs should be carried out at a slow and steady rate, with low and continuous forces so that the load
Fig. 14.1 Manual insertion of a MI using a screwdriver (A) and a rachet (B).
A
B
83
84 SECTION IV: SURGICAL CONSIDERATIONS IN THE USE OF SKELETAL ANCHORAGE DEVICES IN ORTHODONTICS
on both the MI and bone is kept low. Motoyoshi et al.7 have recommended an insertion torque of 5–10 Ncm to avoid bone damage. Controlling torque magnitude, particularly for insertion, seems to be clinically very significant but is not always easy to achieve, particularly when using self-drilling MIs inserted manually.1 Insertion torque and direction is easier to control with non-self-drilling MIs, which require a pilot hole. The required insertion torque is also lower and so there is less risk of bone compression or MI fracture.8,9 However, both non-self-drilling and self-drilling MIs show similar resistance to lateral forces.10 There is still the potential for trauma if the predrilling procedure is not carefully controlled to avoid overheating. There is more risk of root injury with self-drilling MIs because of the increased difficulty in controlling the insertion path. There is also a greater risk of excessive bone compression because of the higher torque values needed, particularly when the cortical bone is thicker than 1.5 mm, leading to loss of secondary stability.8,11 Some reports suggest that self-drilling MIs have less mobility and more bone–implant contact than the non-selfdrilling types.1,12 As a general guideline, self-drilling MIs are favored by most clinicians, particularly when cortical bone is thin, such as in several sites in the maxilla, while non-self-drilling MIs are preferable in sites where the cortical bone is thick, as in the mandible. Placement recommendations according to cortical bone thickness are shown in Table 14.1.
DIRECTION OF MINISCREW IMPLANT INSERTION Placing MIs perpendicular to the bone surface is not always possible, particularly when teeth are present and root injury is to be avoided.13 Many authors recommend a more oblique insertion rather than perpendicular if this achieves better implant–cortical bone contact.14 Inter-radicular space increases in an apical direction but so does movable mucosa. If the available space between two adjacent roots is small, a more oblique direction of insertion seems to be favorable to minimize the risk of root contact.2 In the maxilla, it is recommended to insert MIs at an oblique angle in an apical direction with an angulation of 30–45° to the long axes of the
Table 14.1 Placement recommendations according to cortical bone thickness
A
Cortical bone thickness (mm)
Recommendation
<0.5
Implant placement not recommended
0.5–1.5
Predrilling not necessary
1.5–2.5
Predrilling of the cortical plate recommended in order to decrease compression and unwanted effects to the bone
teeth, except in the area of the maxillary sinus, where a more perpendicular angulation is favored in order to avoid any damage to the sinus.15 In the mandible, the MIs should be inserted as parallel to the roots as possible if teeth are present, or with a 10–20° angulation.15,16
POSSIBLE SITES FOR PLACEMENT OF MINISCREW IMPLANTS Determination of the best site for placement of a MI is made using radiography, casts and clinical examination to assess buccolingual depth and thickness of the cortical bone, soft tissue characteristics, inter-radicular distance, sinus morphology, nerve location, biomechanical considerations and accessibility.5
MAXILLA Possible sites for MI placement in the maxilla include the area below the nasal spine, the palate (on the median or paramedian area), the infrazygomatic crest, the maxillary tuberosities and the alveolar process (both buccally and palatally between the roots of the teeth) (Fig. 14.2). In the maxilla, the more anterior and the more apical the location, the safer for insertion of a MI.5,16 The optimal site in the anterior region is between the roots of the central and the lateral incisor, approximately 6 mm from the cementoenamel junction. Buccally, the optimal sites are between the second premolars and the first molars and between the first and second molars (see Fig. 40.1C,D). Palatally, the best site is between the first and second premolars, since it presents the highest cortical bone thickness. The least amount of bone was found to be in the tuberosity and at the wisdom teeth, which was not considered suitable for MI insertion. Within the palate, the paramedian region is considered as the safest site for MI placement as it has the greatest amount of ossified tissue in the palate and is away from the roots of neighboring teeth. Alternative to the median region of the palate, the greatest amount of bone support was found 6–9 mm posterior to the incisive foramen and 3–6 mm paramedially;19 a more recent study showed that orthodontic MIs could be effectively inserted in palatal areas if placed approximately 3 mm posterior to the incisive foramen and 1–5 mm the paramedian.20 The midpalatal suture has sufficient bony support for implants with a diameter ranging from 4 to 6 mm (see Fig. 16.5).19,20 However the suture is sinuous and interdigitized and may not be fully ossified (closed) even in adults;19,22 consequently, since MIs are provided with a maximum diameter of 2.3 mm, their insertion in the midpalatal suture area should be avoided since there is an increased possibility that a significant part of their endosseous surface would be within the suture and so not in contact with bone.
B
Fig. 14.2 Examples of possible sites for miniscrew implant placement and direction of insertion in the maxilla in frontal (A) and lateral (B) view.
Insertion and removal of orthodontic miniscrew implants
A
85
B
Fig. 14.3 Examples of possible sites for miniscrew implant placement and direction of insertion in the mandible in frontal (A) and lateral (B) view.
A
B
C
Fig. 14.4 Determination of insertion location for a miniscrew implant using a surgical guide. (A) The surgical guide equipped with several custom-made wire extension arms in the mouth of the patient. (B,C) Periapical radiographs of the anterior teeth of the same patient depicting the position of the wire extensions for the evaluation of the quality of the bone, the dimensions of the inter-radicular spaces and the height of the alveolar bone in the possible insertion areas.
MANDIBLE Possible sites for the insertion of MIs in the mandible include the symphysis or parasymphysis, the alveolar process (between the roots of the teeth) and the retromolar area (Fig. 14.3).15 The safest sites are between the lateral incisor and the canine at 6 mm from the cementoenamel junction, between the first molar and second premolars, and between the first and second molars (see Fig. 40.1C,D).5,23 However, while adequate bone is located more than halfway down the root length, this area is likely to be covered by movable mucosa and so there is more risk of soft tissue irritation. To overcome this problem, modification of the MI head design or placement technique (such as using an oblique insertion direction) may be necessary.23
SOFT TISSUE CONSIDERATIONS FOR MINISCREW IMPLANT INSERTION Placement within the attached gingiva, where proper soft tissue sealing can occur, has been associated with fewer soft tissue complications and failure risks in comparison with placement in the movable mucosa.1,7
INTER-RADICULAR SPACE CONSIDERATIONS FOR MINISCREW IMPLANT INSERTION It is considered that a minimum of 3 mm space is needed for the safe placement of MIs when they are inserted inter-radicularly.16,23,24 Taking an intraoral radiograph with a surgical guide greatly assists in identification and assessment of a specific inter-radicular region for MI
insertion site (Fig. 14.4).15 An adjustable surgical guide, usually fabricated from wires, silicone and acrylic material, or a stent can be used for placement of MIs.25,26 Chapters 16–18 contain more details of the use of surgical guides.
INFECTION CONTROL AFTER INSERTION Infection control is vital to avoid peri-implantitis and consequent premature loss and failure of MIs (see Fig. 9.3).1,27 The risk of infection and inflammation can be reduced by ensuring a sterile environment during MI insertion, placing the implants in attached gingiva and following the advised insertion procedures. After this, the patient must maintain an immaculate oral hygiene, similar to that after tooth extraction, but with specific instructions on attention to the MI during teeth brushing and how to properly clean the area surrounding the MI as well as the head of the MI. Antibiotics are not needed, but mouthwashes and disinfectant rinses help the patient to maintain good oral hygiene. The patient must be instructed to avoid manipulating the MI with fingers, tongue or lips, or with foreign objects such as pens or pencils. Healing and health of the peri-implant gingival tissues and the status of the patient’s oral hygiene must be regularly reviewed by the clinician throughout the time that the MI remains in function.
REMOVAL OF MINISCREW IMPLANTS Usually, the removal of MIs is uncomplicated and easily accomplished in one appointment using the same screwdriver as for the insertion. Local
86 SECTION IV: SURGICAL CONSIDERATIONS IN THE USE OF SKELETAL ANCHORAGE DEVICES IN ORTHODONTICS
Fig. 14.5 The wound seen immediately after removal of two miniscrew implants that were inserted in the paramedian region of the anterior palate.
anesthetic is not usually needed, although it might be used to avoid patient discomfort or if there is tissue covering the MI. The linking elements of the orthodontic mechanism are first removed and then the MI is simply unscrewed. The resulting small wound requires no special care beyond normal dental hygiene and can be gently swabbed with 0.2% chlorhexidine. The wound left from the removal of a MI is minimal and usually closes within a few days (Fig. 14.5). In most cases, healing continues uneventfully. If a MI is very tight and cannot be removed at once, it is advised to wait 3 to 7 days before retrying as microfractures or bone remodeling at the peri-implant surfaces following the initial attempt at removal will lead to loosening of the MI. If during removal the MI fractures flush with the bone, the shaft might need to be removed with a trephine. In such cases, referral to an oral surgeon or periodontist might be needed to remove the retained fractured part of the MI.2
REFERENCES 1. Ludwig B, Baumgaertel S, Bowman J. Mini-implants in orthodontics: innovative anchorage concepts. Hanover Park, IL: Quintessence; 2008. 2. Lee J, Kim J, Park Y, et al. Applications of orthodontics mini-implants. Hanover Park, IL: Quintessence; 2008. 3. 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 2007;131:9–15. 4. Moon CH, Lee DG, Lee HS, et al. Factors associated with the success rate of orthodontic miniscrews placed in the upper and lower posterior buccal region. Angle Orthod 2008;78:101–6.
5. Fayed MM, Pazera P, Katsaros C. Optimal sites for orthodontic mini-implant placement assessed by cone beam computed tomography. Angle Orthod 2010;80:939–51. 6. Ono A, Motoyoshi M, Shimizu N. Cortical bone thickness in the buccal posterior region for orthodontic mini-implants. Int J Oral Maxillofac Surg 2008;37:334–40. 7. Motoyoshi M, Hirabayashi M, Uemura M, et al. Recommended placement torque when tightening an orthodontic mini-implant. Clin Oral Implants Res 2006;17: 109–14. 8. Sowden D, Schmitz JP. AO self-drilling and self-tapping screws in rat calvarial bone: an ultrastructural study of the implant interface. J Oral Maxillofac Surg 2002;60: 294–9. 9. Wilmes B, Drescher D. Impact of insertion depth and predrilling diameter on primary stability of orthodontic mini-implants. Angle Orthod 2009;79:609–14. 10. Su YY, Wilmes B, Hönscheid R, et al. Comparison of self-tapping and self-drilling orthodontic mini-implants: an animal study of insertion torque and displacement under lateral loading. Int J Oral Maxillofac Implants 2009;24:404–11. 11. Böhm B, Fuhrmann R. Clinical application and histological examination of the FAMI screw for skeletal anchorage: a pilot study. J Orofac Orthop 2006;67:175–85. 12. Kim JW, Ahn SJ, Chang YL. Histomorphometric and mechanical analyses of the drillfree screw as orthodontic anchorage. Am J Orthod Dentofacial Orthop 2005;128: 190–4. 13. Dalstra M, Cattaneo PM, Melsen B. Load transfer of miniscrews for orthodontic anchorage. Orthodontology 2004;1:53–62. 14. Motoyoshi M, Yoshida T, Ono A, et al. Effect of cortical bone thickness and implant placement torque on stability of orthodontic mini-implants. Int J Oral Maxillofac Implants 2007;22:779–84. 15. Carano A, Velo S, Leone P, et al. Clinical applications of the Miniscrew Anchorage System. J Clin Orthod 2005;39:9–24. 16. Poggio P, Incorvati C, Velo S, et al. Safe zones: a guide for miniscrew positioning in the maxillary and mandibular arch. Angle Orthod 2006;76:191–7. 17. Bernhart T, Vollgruber A, Gahleitner A, et al. Alternative to the median region of the palate for placement of an orthodontic implant. Clin Oral Implants Res 2000;11: 595–601. 18. Moon SH, Park SH, Lim WH, et al. Palatal bone density in adult subjects: Implications for mini-implant placement. Angle Orthod 2010;80:137–44. 19. Henriksen B, Bavitz B, Kelly B, et al. Evaluation of bone thickness in the anterior hard palate relative to midsagittal orthodontic implants. Int J Oral Maxillofac Implants 2003;18:578–81. 20. Gahleitner A, Podesser B, Schick S, et al. Dental CT and orthodontic implants: Imaging technique and assessment of available bone volume in the hard palate. Eur J Radiol 2004;51:257–62. 21. Melsen B. Palatal growth studied on human autopsy material: A histologic microradiographic study. Am J Orthod 1975:68:42–54. 22. Persson M, Thilander B. Palatal closure in man from 15 to 35 years of age. Am J Orthod 1977;72:42–52. 23. Schnelle MA, Beck FM, Jaynes RM, et al. A radiographic evaluation of the availability of bone for placement of miniscrews. Angle Orthod 2004;74:832–7. 24. Chaimanee P, Suzuki B, Suzuki EY. “Safe Zones” for miniscrew implant placement in different dentoskeletal patterns. Angle Orthod 2011;81:397–403. 25. Kitai N, Yasuda Y, Takada K. A stent fabricated on a selectively colored stereolithographic model for placement of orthodontic mini-implants. Int J Adult Orthodon Orthognath Surg 2002;17:264–6. 26. Suzuki EY, Buranastidporn B. An adjustable surgical guide for miniscrew placement. J Clin Orthod 2005;39:588–90. 27. Park HS, Jeong SH, Kwon OW. Factors affecting the clinical success of screw implants used as orthodontic anchorage. Am J Orthod Dentofacial Orthop 2006;130:18–25.
14
Fadi Tarawneh and Moschos A. Papadopoulos
INTRODUCTION In general, insertion of miniscrew implants (MIs) should be as noninvasive as possible, in order to reduce postoperative patient discomfort and to avoid irritation and inflammation of the peri-implant tissues. The insertion procedure for a MI is usually given by the manufacturer; however, certain general issues should be taken into consideration and these are outlined in this chapter
PREPARATIONS BEFORE INSERTION
ANESTHESIA Soft tissue anesthesia is usually sufficient for the insertion of MIs and can usually be achieved with topical anesthetics, gels or creams; some patients may need a small amount of local anesthetic. Block anesthesia is rarely required and should be avoided as it could mask signs of root contact during insertion, which could lead to root injury.1
SOFT TISSUE PREPARATION Self-drilling MIs can usually be inserted directly through the gingival tissue or the mucosa without any need for soft tissue or bone manipulation. In contrast, non-self-drilling MIs are inserted only after removal of the soft tissue covering the insertion site, either through a gingival flap incision or a soft tissue punch (see Fig. 11.1).1–3 Raising a gingival flap has been associated with pain, discomfort and inflammation that might last up to a week after surgery but use of the procedure does not influence success rates.4 Use of a flap has been advocated in some circumstances, such as for insertion in the mandibular symphysis. When a MI has to be inserted in the frenum area, a frenectomy is suggested to prevent possible mechanical irritation around the implant during function.2 If possible, these areas should be avoided to simplify the soft tissue issues.
PILOT DRILLING Self-drilling MIs do not require pilot drilling except when they have to be inserted in sites presenting with thick cortical bone where the high force required can cause excessive bone compression, which might decrease secondary stability of MIs or lead to MI fracture during insertion. In
general, buccal cortical bone thickness seems to be greater in the mandible than in the maxilla, and increases gradually in the apical direction.5,6 Males and adults have thicker cortical bone than females and adolescents.5,6 A pilot hole is most important for inserting self-drilling MIs in the mandible and in an apical location, more specifically between the first and second mandibular molars.5 A pilot drill is always necessary for insertion of non-self-drilling MIs. The procedure is performed in a surgical environment and if possible by an oral surgeon. The soft tissue from the site is either incised or removed using a soft tissue punch (see Fig. 11.1). Then, the pilot hole is drilled, usually using a handpiece (see Fig. 18.6D). A speed of 500–1000 rpm is usually sufficient for cortical bone perforation but should not exceed 1500 rpm.1,2 Copious irrigation and cooling with sterile saline helps to minimize overheating, which can lead to bone necrosis and implant failure. Cortical bone can be predrilled manually with a sharp drill of high cutting efficiency to minimize heat production. Pilot drilling is an invasive procedure with the potential to introduce microbial contamination and so it is recommended that the drill is not reinserted into the hole once it is made. To avoid fractures and high bone stresses, optimum predrilling diameters should be chosen: the pilot drill must be approximately 0.2–0.3 mm thinner than the diameter of the MI to be used. Although drilling a pilot hole makes the procedure more complicated and more time consuming, it provides a fixed path of insertion for the MI, which, in turn, minimizes the risk of injuring adjacent roots or insertions into the sinus.
INSERTION OF MINISCREW IMPLANTS Insertion of implants can be performed either manually with the use of screwdrivers (Fig. 14.1A) or mechanically with a specially angled handpiece that permits adjustment of torque through altering the speed of the handpiece (see Fig. 16.5C). For implant insertion, a speed up to 30 rpm is usually adequate and should not exceed 60 rpm.1,2 Ratchets are also available that help to work with MIs in different locations (Fig. 14.1B). Some even provide an adjustable torque control ranging from 5 to 30 Ncm. Once the desired torque is reached, the ratchet bends preventing further force application.1 Insertion torque magnitude depends on factors such as bone thickness, bone quality, size and design of the MI, as well as method and velocity of insertion.1 It is recommended that insertion of MIs should be carried out at a slow and steady rate, with low and continuous forces so that the load
Fig. 14.1 Manual insertion of a MI using a screwdriver (A) and a rachet (B).
A
B
83
84 SECTION IV: SURGICAL CONSIDERATIONS IN THE USE OF SKELETAL ANCHORAGE DEVICES IN ORTHODONTICS
on both the MI and bone is kept low. Motoyoshi et al.7 have recommended an insertion torque of 5–10 Ncm to avoid bone damage. Controlling torque magnitude, particularly for insertion, seems to be clinically very significant but is not always easy to achieve, particularly when using self-drilling MIs inserted manually.1 Insertion torque and direction is easier to control with non-self-drilling MIs, which require a pilot hole. The required insertion torque is also lower and so there is less risk of bone compression or MI fracture.8,9 However, both non-self-drilling and self-drilling MIs show similar resistance to lateral forces.10 There is still the potential for trauma if the predrilling procedure is not carefully controlled to avoid overheating. There is more risk of root injury with self-drilling MIs because of the increased difficulty in controlling the insertion path. There is also a greater risk of excessive bone compression because of the higher torque values needed, particularly when the cortical bone is thicker than 1.5 mm, leading to loss of secondary stability.8,11 Some reports suggest that self-drilling MIs have less mobility and more bone–implant contact than the non-selfdrilling types.1,12 As a general guideline, self-drilling MIs are favored by most clinicians, particularly when cortical bone is thin, such as in several sites in the maxilla, while non-self-drilling MIs are preferable in sites where the cortical bone is thick, as in the mandible. Placement recommendations according to cortical bone thickness are shown in Table 14.1.
DIRECTION OF MINISCREW IMPLANT INSERTION Placing MIs perpendicular to the bone surface is not always possible, particularly when teeth are present and root injury is to be avoided.13 Many authors recommend a more oblique insertion rather than perpendicular if this achieves better implant–cortical bone contact.14 Inter-radicular space increases in an apical direction but so does movable mucosa. If the available space between two adjacent roots is small, a more oblique direction of insertion seems to be favorable to minimize the risk of root contact.2 In the maxilla, it is recommended to insert MIs at an oblique angle in an apical direction with an angulation of 30–45° to the long axes of the
Table 14.1 Placement recommendations according to cortical bone thickness
A
Cortical bone thickness (mm)
Recommendation
<0.5
Implant placement not recommended
0.5–1.5
Predrilling not necessary
1.5–2.5
Predrilling of the cortical plate recommended in order to decrease compression and unwanted effects to the bone
teeth, except in the area of the maxillary sinus, where a more perpendicular angulation is favored in order to avoid any damage to the sinus.15 In the mandible, the MIs should be inserted as parallel to the roots as possible if teeth are present, or with a 10–20° angulation.15,16
POSSIBLE SITES FOR PLACEMENT OF MINISCREW IMPLANTS Determination of the best site for placement of a MI is made using radiography, casts and clinical examination to assess buccolingual depth and thickness of the cortical bone, soft tissue characteristics, inter-radicular distance, sinus morphology, nerve location, biomechanical considerations and accessibility.5
MAXILLA Possible sites for MI placement in the maxilla include the area below the nasal spine, the palate (on the median or paramedian area), the infrazygomatic crest, the maxillary tuberosities and the alveolar process (both buccally and palatally between the roots of the teeth) (Fig. 14.2). In the maxilla, the more anterior and the more apical the location, the safer for insertion of a MI.5,16 The optimal site in the anterior region is between the roots of the central and the lateral incisor, approximately 6 mm from the cementoenamel junction. Buccally, the optimal sites are between the second premolars and the first molars and between the first and second molars (see Fig. 40.1C,D). Palatally, the best site is between the first and second premolars, since it presents the highest cortical bone thickness. The least amount of bone was found to be in the tuberosity and at the wisdom teeth, which was not considered suitable for MI insertion. Within the palate, the paramedian region is considered as the safest site for MI placement as it has the greatest amount of ossified tissue in the palate and is away from the roots of neighboring teeth. Alternative to the median region of the palate, the greatest amount of bone support was found 6–9 mm posterior to the incisive foramen and 3–6 mm paramedially;19 a more recent study showed that orthodontic MIs could be effectively inserted in palatal areas if placed approximately 3 mm posterior to the incisive foramen and 1–5 mm the paramedian.20 The midpalatal suture has sufficient bony support for implants with a diameter ranging from 4 to 6 mm (see Fig. 16.5).19,20 However the suture is sinuous and interdigitized and may not be fully ossified (closed) even in adults;19,22 consequently, since MIs are provided with a maximum diameter of 2.3 mm, their insertion in the midpalatal suture area should be avoided since there is an increased possibility that a significant part of their endosseous surface would be within the suture and so not in contact with bone.
B
Fig. 14.2 Examples of possible sites for miniscrew implant placement and direction of insertion in the maxilla in frontal (A) and lateral (B) view.
Insertion and removal of orthodontic miniscrew implants
A
85
B
Fig. 14.3 Examples of possible sites for miniscrew implant placement and direction of insertion in the mandible in frontal (A) and lateral (B) view.
A
B
C
Fig. 14.4 Determination of insertion location for a miniscrew implant using a surgical guide. (A) The surgical guide equipped with several custom-made wire extension arms in the mouth of the patient. (B,C) Periapical radiographs of the anterior teeth of the same patient depicting the position of the wire extensions for the evaluation of the quality of the bone, the dimensions of the inter-radicular spaces and the height of the alveolar bone in the possible insertion areas.
MANDIBLE Possible sites for the insertion of MIs in the mandible include the symphysis or parasymphysis, the alveolar process (between the roots of the teeth) and the retromolar area (Fig. 14.3).15 The safest sites are between the lateral incisor and the canine at 6 mm from the cementoenamel junction, between the first molar and second premolars, and between the first and second molars (see Fig. 40.1C,D).5,23 However, while adequate bone is located more than halfway down the root length, this area is likely to be covered by movable mucosa and so there is more risk of soft tissue irritation. To overcome this problem, modification of the MI head design or placement technique (such as using an oblique insertion direction) may be necessary.23
SOFT TISSUE CONSIDERATIONS FOR MINISCREW IMPLANT INSERTION Placement within the attached gingiva, where proper soft tissue sealing can occur, has been associated with fewer soft tissue complications and failure risks in comparison with placement in the movable mucosa.1,7
INTER-RADICULAR SPACE CONSIDERATIONS FOR MINISCREW IMPLANT INSERTION It is considered that a minimum of 3 mm space is needed for the safe placement of MIs when they are inserted inter-radicularly.16,23,24 Taking an intraoral radiograph with a surgical guide greatly assists in identification and assessment of a specific inter-radicular region for MI
insertion site (Fig. 14.4).15 An adjustable surgical guide, usually fabricated from wires, silicone and acrylic material, or a stent can be used for placement of MIs.25,26 Chapters 16–18 contain more details of the use of surgical guides.
INFECTION CONTROL AFTER INSERTION Infection control is vital to avoid peri-implantitis and consequent premature loss and failure of MIs (see Fig. 9.3).1,27 The risk of infection and inflammation can be reduced by ensuring a sterile environment during MI insertion, placing the implants in attached gingiva and following the advised insertion procedures. After this, the patient must maintain an immaculate oral hygiene, similar to that after tooth extraction, but with specific instructions on attention to the MI during teeth brushing and how to properly clean the area surrounding the MI as well as the head of the MI. Antibiotics are not needed, but mouthwashes and disinfectant rinses help the patient to maintain good oral hygiene. The patient must be instructed to avoid manipulating the MI with fingers, tongue or lips, or with foreign objects such as pens or pencils. Healing and health of the peri-implant gingival tissues and the status of the patient’s oral hygiene must be regularly reviewed by the clinician throughout the time that the MI remains in function.
REMOVAL OF MINISCREW IMPLANTS Usually, the removal of MIs is uncomplicated and easily accomplished in one appointment using the same screwdriver as for the insertion. Local
86 SECTION IV: SURGICAL CONSIDERATIONS IN THE USE OF SKELETAL ANCHORAGE DEVICES IN ORTHODONTICS
Fig. 14.5 The wound seen immediately after removal of two miniscrew implants that were inserted in the paramedian region of the anterior palate.
anesthetic is not usually needed, although it might be used to avoid patient discomfort or if there is tissue covering the MI. The linking elements of the orthodontic mechanism are first removed and then the MI is simply unscrewed. The resulting small wound requires no special care beyond normal dental hygiene and can be gently swabbed with 0.2% chlorhexidine. The wound left from the removal of a MI is minimal and usually closes within a few days (Fig. 14.5). In most cases, healing continues uneventfully. If a MI is very tight and cannot be removed at once, it is advised to wait 3 to 7 days before retrying as microfractures or bone remodeling at the peri-implant surfaces following the initial attempt at removal will lead to loosening of the MI. If during removal the MI fractures flush with the bone, the shaft might need to be removed with a trephine. In such cases, referral to an oral surgeon or periodontist might be needed to remove the retained fractured part of the MI.2
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