Orthodontic bone anchorage tad by almuzian
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Orthodontic bone anchorage tad by almuzian Orthodontic bone anchorage tad by almuzian Document Transcript

  • UNIVERSITY OF GLASGOW Orthodontic Bone Anchorage Devices Mohammed Almuzian 2013
  • Mohammed Almuzian, University of Glasgow, 2013 1 Contents Conventional osseointegrated implants ..........................................................................................2 Temporary bone anchorage devices (TAD’s).................................................................................2 1. Osstiointegrated retained devises....................................................................................................2 Biological response to Osseointegrated devices:....................................................................................2 Advantages and disadvantages................................................................................................................3 A. Mid-palatal implants .......................................................................................................................3 Disadvantages .................................................................................................................................3 B. Onplant............................................................................................................................................4 Advantage ...............................................................................................................................................4 Disadvantage...........................................................................................................................................4 2. Mechanically retained devises ........................................................................................................4 Biological response to Mechanically retained devices ...........................................................................4 Advantages..............................................................................................................................................5 A. Mini-plates (Maxillofacial bone plating kits) .........................................................................5 Advantages......................................................................................................................................5 Disadvantages .................................................................................................................................5 B. Mini-implants or mini-screw ..................................................................................................6 Ideal requirements for orthodontic bone anchorage systems..................................................................6 Indication of TADs .................................................................................................................................6 Contraindication of TADs.......................................................................................................................8 Some terminology use in the literature regarding TADs ........................................................................9 Direct versus indirect anchorage by TAD.............................................................................................10 Pre-drilling or self-drilling? ..................................................................................................................11 Success rate of mini-screws..................................................................................................................12 Parameters affecting bone anchorage success ......................................................................................12 A. Patient factors........................................................................................................................12 B. Mini-implant design factors..................................................................................................13 C. Operator related factors.........................................................................................................14 Mini-implant’s clinical steps.................................................................................................................15 Complications of TADs (Kravitz and Kusnoto, 2007) .........................................................................17 Evidences..............................................................................................................................................20
  • Mohammed Almuzian, University of Glasgow, 2013 2 Orthodontic bone anchorage Definition Orthodontic bone anchorage devise (BAD) can be defined as the use of implants, plates, screws or screw-retained devices inserted into bone to provide resistance to unwanted tooth movement (indirect anchorage) or a point from which traction can be applied (direct anchorage). Bone anchorage devices can broadly be divided into two categories: 1. Conventional osseointegrated implants. 2. Temporary bone anchorage devices (TAD’s). Conventional osseointegrated implants Conventional implants may provide a useful point of absolute anchorage in patients for whom an implant-born restoration is planned following pre-restorative orthodontics, or who already have an implant-born restoration in place. Orthodontic attachments can be mounted on implants using temporary copings, to allow them to be incorporated into a fixed appliance (Ödman et al., 1994). Whilst it is useful to have conventional implants available for anchorage control during pre-restorative orthodontic treatment, it is important that they are in the correct position, since they cannot easily be re-sited later on. Where the implant(s) are already in situ, the teeth will have to be positioned around them, which may not always give the best result (Fig. 2, Kesling or even “simplant” type illustration). Temporary bone anchorage devices (TAD’s) A TAD is mini-implant, plate, screws or screw-retained devices which are placed purely for the purpose of providing orthodontic anchorage and are then removed once it has served its purpose (Cope, 2005). They can be categorised as follows: 1. Osstiointegrated retained devises Biological response to Osseointegrated devices: • 1-2 day after implantation, RBCs and inflammatory cells are present between the bone and the TAD.
  • Mohammed Almuzian, University of Glasgow, 2013 3 • From 3 to 7 days after implantation, inflammatory cell infiltration gradually disappears and spindle-shaped cells (fibroblast) start to appear in the interface between pre-existing bone and orthodontic TADs. • From 2-4 weeks osteoblasts are visible at the bone-TAD interface. • 4-6 weeks after TAD placement active bone remodelling appears to decrease. • Application of orthodontic loading to the TAD causes increased bone tissue turnover and increased density of the adjacent alveolar bone. Advantages and disadvantages • Delayed loading is mandatory. Loading protocols for implants involve a minimum waiting period of 2 months before applying orthodontic forces. • Osseointegration make removal difficult • It provide the ability to withstand greater orthodontic forces • Success rates for implants were on average higher than for screws. (Ohashi 2006) A. Mid-palatal implants Mid-palatal implants are designed to osseointegrate, but are surgically removed following use. In comparison to conventional restorative implants, they tend to be shorter in length (typically 4–6 mm) and in diameter (typically 3–4 mm) (Wehrbein et al., 1999). An example is the OrthoSystem implant. Disadvantages  Cost  These dimensions limit their insertion into edentulous sites, typically the mid-palate and retromolar areas.  Invasive surgery in insertion and removal as well as the associated laboratory work.  These anchorage devices rely on osseointegration, which requires a 3 months’ delay in orthodontic loading.  High failure rate in growing patient in the midpalatal suture (Wilmes et al., 2009).
  • Mohammed Almuzian, University of Glasgow, 2013 4 B. Onplant Onplants: These are based on the impressive research of Block and Hoffman (Block and Hoffman, 1995). These authors used a subperiosteal titanium alloy disk, 2 mm thick and 10 mm wide, coated with hydroxyapatite. This disk-type ‘’onplant’’ was inserted subperiosteally and left unloaded for four months to osseointegrate before uncovering and placement of attachments. Advantage There is no need for any bone depth, so the onplant can be placed in a much wider range of sites than a conventional implant. Disadvantage  Cost  The need for two soft tissue surgical interventions.  These anchorage devices rely on osseointegration, which requires a 3 months’ delay in orthodontic loading. 2. Mechanically retained devises Biological response to Mechanically retained devices Areas of the screw in direct contact with the bone are responsible for primary mechanical stability of the device. There are also gaps hundreds of microns in size between the screw surface and bone. • 1 day after insertion, there are mineralized bone tissue contacts present between the surface of the implant and bone and the osteoblasts are also attached firmly to the titanium implant surface. • From 3 to 7 days after implantation, no invasion of inflammatory cells occurs • After 1-2 weeks, the bone is resorbed and replaced with newly formed viable bone. After this stage the screw can be loaded.
  • Mohammed Almuzian, University of Glasgow, 2013 5 Advantages • Immediate loading is possible. Loading protocols for screws involve immediate loading or a waiting period of 4-6 weeks to apply forces • Lack of osseointegration which make removal easier • Ability to withstand lesser orthodontic forces A. Mini-plates (Maxillofacial bone plating kits) Mini-plates, e.g. the Bollard and Skeletal Anchorage (SAS) systems, arose from the adaptation of maxillofacial bone plates. In particular, the orthodontic versions have transmucosal necks and customised heads to facilitate their connection to fixed appliances Advantages 1. The fixing screws are above the root apices and therefore much less of a risk to the tooth roots. 2. No need for reposition the plate when the teeth are retracted, opposite to the TAD where the screw should be replaced when their positions interfere with the prospective movement. 3. The force application can still be brought close to the occlusal plane by extending the powered arm of the plate, so it easily avoid unwanted intrusion 4. Successful for a range of en masse tooth movements (Lai et al., 2008). 5. Successful for intermaxillary skeletal traction (such as maxillary protraction in Class III cases (De Clerck et al., 2009) 6. Some authors have found slightly higher percentage success rate with miniplates than with miniscrews (Kuroda et al., 2007) Disadvantages 1. Cost 2. Their insertion is limited to extra-alveolar sites such as the zygomatic process and inferior mandibular body. Also, they are difficult use in the anterior maxillary area due to anatomical limitation 3. Require much more invasive surgical placement and removal than other devices as well as require an experienced surgical operator to insert them.
  • Mohammed Almuzian, University of Glasgow, 2013 6 B. Mini-implants or mini-screw  Orthodontic mini-implants are derived from bone plating technology, but are much more user friendly to both the orthodontist and patient. e.g. Absoanchor, Infinitas, Frostodent and Vector. They typically consist of head, neck and body sections.  Endosseous dimensions of 1.2–2.0 mm diameter and 5–10 mm length. In general, an approximate diameter of 1.5 mm is recommended for interproximal sites in order to maximise the surface area of bone engagement yet limit the proximity to dental roots (not less than 0.25 mm from the root) and the periodontal ligament. To place these dimensions in context, the mean interproximal distance between the upper second premolar and first molar mesiobuccal root is 2.5 mm.  For clarity, it is worth explaining screw insertion behaviour: all bone screws are able to form a thread within the adjacent bone, i.e. they are self-tapping (self-threading), but the addition of self-drilling properties entails more distinctive cutting (body) threads and a sharper body tip. These features frequently obviate the need for pre- drilling (except to perforate the dense mandibular cortex) but increase the risk of screw fracture during insertion. Ideal requirements for orthodontic bone anchorage systems (Prabhu and Cousley, 2006) 1. Cheap 2. Easy to use 3. Biocompatible 4. Acceptable for patients – no discomfort during insertion, use or removal. 5. Less damage to the adjacent structures. 6. Accept direct loading of force. 7. Versatile and convenient for application of orthodontic forces, and allow flexibility in means and direction of force application. Indication of TADs 1. Provision of anchorage A. Moderate to maximum anchorage need eg. full unit Class II relationship or adults and older adolescents (where functional appliances cannot be used to gain anchorage).
  • Mohammed Almuzian, University of Glasgow, 2013 7 B. Mild to moderate anchorage need when the anchor unit is limited by an inadequate number of anchor teeth (e.g early tooth loss or hypodontia) or periodontal support. 2. Specific teeth movement  En mass retraction especially in high angle class II malocclusion where the extrusive tooth movements would be unfavourable which contraindicates the use of intermaxillary traction to achieve the desired tooth movement.(Park et al., 2005)  Canine retraction. Sharma et al. compared the anchorage loss with the use of TPAs or TADs and found 2.5 mm of mesial movement of the U6s with the former while the latter provided absolute anchorage (Sharma et al., 2012).  Bimaxillary protrusion. Liu et al concluded that a better dental, skeletal and soft tissue effects of the TADs in treating these groups. For this reason, they recommended the TADs as routine anchorage device in patients with bialveolar dental protrusion (Liu et al., 2009).  Molar distalization (Sugawara et al., 2006, Sugawara et al., 2004)  For intrusion of anterior teeth (Lee et al., 2009)  For intrusion of posterior teeth (Cousley, 2010). Regarding stability of molar intrusion by TADs. It was 83% stable Lee 2008, Minimum 3 months retainer after molar intrusion  For unilateral intrusion to correct cant of occlusion (Lee et al., 2009)  To control expansion using Q helix by holding the normal side and allowing unilateral expansion (Lee et al., 2009)  Adjunctive treatment when full orthodontic appliance is not required and the aim is corrects the position of single tooth. 3. Skeletal orthopaedic correction of class III (Ballard technique) (De Clerck et al., 2009) 4. Miscellaneous  Provide attachment for artificial teeth in hypodontia cases.  To provide IMF during orthognathic surgery (Harris and Reynolds, 1991)
  • Mohammed Almuzian, University of Glasgow, 2013 8 Contraindication of TADs 1. Absolute  Bleeding Disorders  Bone Metabolism Disorders (bisphosphonate use)  Immuno-compromised  Diabetes Mellitus  Anti-coagulant treatment  Pregnancy  Xerostomia  Titanium allergy 2. Relative  When other conventional methods of anchorage are adequate.  Poor Oral hygiene  Smoking  Local Bone pathology  Inadequate bone depth and quality  Local factors like bone amount and local infection Composition of TADs 1. First attempts at using screws as skeletal anchorage-1945-Cobalt-chromium base alloy 2. High grade steel is biocompatible but also gets a layer of connective tissue around it. Currently only one miniscrew material made of SS which is the Leone. Their reasons why the SS is still used by Leone are:  Steel suffer less bending and breakage.  Osseointegration is very poor, so it is easy to be removing. 3. Today most mini-implants are made from either titanium or titanium alloy (usually with aluminium and vanadium) because: A. Biocompatible. B. Corrosion resistance (a protective, passivating oxide layer develops on the surface of the metal when in contact with oxygen and fluids)
  • Mohammed Almuzian, University of Glasgow, 2013 9 C. Forms a direct contact between the bone and the metal surface D. In comparison with pure titanium, titanium alloy (usually with aluminium and vanadium) offers more favourable mechanical properties in terms of: • Strength(yield strength several times greater) • Stress-strain behaviour • Wear resistance Some terminology use in the literature regarding TADs 1. Yield strength: stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible approximately 0.1%. 2. Tensile strength: is the maximum stress that a material can withstand while being stretched or pulled before cross-section starts to significantly contract. Tensile strength is the opposite of compressive strength and the values can be quite different. 3. Pre-drilling: some screws require a pilot hole to be drilled before insertion. This preliminary procedure is sensibly called pre-drilling. It is required for screws that are blunt at their tip and are thus not self-drilling. The only potential confusion in terminology is when referring to the creation of a very small preliminary indentation in the cortex with a round bur or specialised initiator bur. This very limited ‘pre-drilling’ is sometimes referred to as ‘pilot drilling’. This can be advisable even with self-drilling screws when the bone is dense or the intended path of insertion is very oblique to the bone surface. 4. Self-drilling: as the paragraph above infers, these screws have a sharp, pointed end and need no preliminary drilling. Again, there is a potential subdivision of design which may cause confusion of terminology, because some such screws have an additional notch or groove at their tip which adds to the bone-cutting capability. These self-drilling screws are sometimes referred to as self-cutting. This additional bone-cutting notch has previously been considered by some authors to increase the chance of fracture of the screw tip, but with current designs this is not a well-supported concern. The additional cutting power is
  • Mohammed Almuzian, University of Glasgow, 2013 10 designed to ease screw insertion, particularly in areas of more dense bone in the jaws such as the retromolar area. 5. Self-tapping: all current miniscrews are self-tapping. Whether or not they are self-drilling, they require no separate tapping of a thread. The potential confusion here is that some authors e.g. Chen et al use the term self-tapping to be synonymous with screws which require predrilling. Self-tapping is therefore not a helpful term in our view (Chen et al., 2008). Direct versus indirect anchorage by TAD A. Direct Anchorage, The implant is directly connected to the dental unit(s) to be moved. Mechanics of force system include: 1. Compression spring 2. Tension spring 3. Elastic chain 4. Lever arm 5. Wire ligature, tube and compression spring Advantages • Simple activation • Efficient mechanics • No dental anchorage loss Disadvantages • Greater load is applied to the implant than with indirect anchorage, • Poor force control in three dimensions, • Mechanics are not fail safe
  • Mohammed Almuzian, University of Glasgow, 2013 11 B. Indirect anchorage, The mini-screw stabilizes the dental anchorage unit and an implant reinforced dental anchorage unit is the result. Mechanics of force system include: 1. Cross tubes or double tube 2. Acid-etch technique 3. Connection with a TPA/QH/Horseshoe arch 4. Wire ligature Advantages • Generally less load is applied to the implant than with direct anchorage, • Fail-safe mechanics. Disadvantages • Loss of anchorage in terms of undesired dental movement of the anchorage teeth is possible, • Complicated and time consuming to install, • Breakage of appliance may go unnoticed and result in anchorage loss Pre-drilling or self-drilling? Indications of Pre-drilling A. in some cases where the bone is especially dense (most commonly the posterior mandible) B. If the intended path of insertion is significantly oblique to the bony surface – this is a situation where the screw is prone to slip up the cortical surface causing soft-tissue trauma. C. An alternative strategy to avoid this slipping is to by placing the screw at right angles to the bone surface and then altering to an oblique angle once the first ‘bite’ in the cortex has occurred.
  • Mohammed Almuzian, University of Glasgow, 2013 12 Advantages of self-drilling A. Simpler and cheaper procedure (no specialised drills required). B. Probable better overall success rate and better primary stability (Kim et al., 2005). C. Better screw-bone contact after 6 months (Heidemann and Gerlach, 1999). D. Less chance of damage to tooth roots. Success rate of mini-screws  Most studies report success rates between 80% and 96% (Park et al., 2005).  Lim reported 83% success (Lim et al., 2009).  A systematic review by Reynders identified 19 studies of sufficient quality and the success rate was mainly in excess of 80% (Reynders et al., 2009) Parameters affecting bone anchorage success A. Patient factors 1. Gender is not considered as influential factors in the success of TADs. (Miyawaki et al., 2003) 2. Age: the failure rate is significantly higher in adolescents than adults (Chen et al., 2007) because of thinner buccal plate thickness. 3. Poor oral hygiene leads to: Peri implantitis, Epithelial infiltration, Bleeding on probing, Suppuration, Loss of bony support, Mobility and finally Implant failure (Miyawaki et al., 2003). So that regular tooth-brushing and chlorhexidine (0.12%, 10 ml) mouthwash is recommended. The cationic nature of chlorhexidine allows for its sustantivitiy, or persistent adherence to the enamel and soft tissue, providing a prolonged bacteriocidal and bacteriostatic effect. However, this sustantivitiy stains enamel, frequently causing patients to want to brush immediately after rinsing. The clinician should strongly advise the patient against this for 2 reasons: the surface contact from the toothbrush can remove the chlorhexidine coating, and the anionic agents in the toothpaste can rapidly reduce the activity of the cationic rinse (Kravitz and Kusnoto, 2007). 4. Smoking is a risk factor for implant success (Melsen, 2005).
  • Mohammed Almuzian, University of Glasgow, 2013 13 5. ANB value, crowding, TMD are not considered as influential factors in the success of TADs. (Miyawaki et al., 2003) 6. Maxillo-mandibular planes angle: high angle cases have a higher failure rate for maxillary buccal mini-implants. This might be a result that a high angle cases may have thinner cortical plate causing low torque with resultant poor primary stability. On the other hand, with a thick bone, a high torque force is needed which might increase secondary failure rate (Miyawaki et al., 2003). 7. Insertion site: Variations in success rates occur depending on the location of the insertion site within the mouth because: • Upper or lower: Approximately 80% and 90% mini-implant success rates for mandibular and maxillary alveolar insertions, respectively. This is because of the different thickness of the cortical plate with variable insertion torque. If the insertion torque (the resistance encountered during insertion) is excessive then it is likely that secondary failure will occur because of ischaemic pressure effects on the adjacent alveolar bone (Miyawaki et al., 2003). • Mucosa: Studies found that non-keratinized mucosa was a risk factor for miniscrew failure (Chen et al., 2007) (Miyawaki et al., 2003(Park et al., 2005). • Bone density: Stationary anchorage failure is often a result of low bone density due to inadequate cortical thickness. Bone density is classified into 4 types D1, D2, D3 and D4. D1, D2, D3 are optimal for self-drilling miniscrews. Implant placement in D4 not recommended due to the reported high failure rate. • Proximity to the roots reduce the success rate because of the giggling effect of the occlusion that transferred to the root and cause TADs failure. • Left side success is high because of brushing bias for right handed patients, however, it is better to avoid electric brush because of the vibration and giggling effect. (Park 06). B. Mini-implant design factors 1. Diameter  A diameter less than 1.1 mm is associated with a higher failure rate (Miyawaki et al., 2003, Park et al., 2006).
  • Mohammed Almuzian, University of Glasgow, 2013 14  A diameter greater than about 1.6 mm seems to confer no advantage and clearly wider screws run an extra risk of contact with tooth roots. This consideration is now largely of historic interest because almost all screws are currently between 1.4 and 1.8 mm in maximum diameter (Park et al., 2006).  2.0 mm screws are suitable for sites such as the zygomatic ridge or retromolar pad, where avoidance of roots is not an issue (Park et al., 2006) 2. Length • This usually refers to the intraosseous threaded part of the screw. • The range of available body lengths is typically 6 - 12 mm.  This length does NOT seem to be a factor in stability if the screw is more than 5 mm long (intraosseous length) (Miyawaki et al., 2003, Park et al., 2006). • All manufacturers produce screws of different lengths and longer screws may be advocated if the mucosal thickness is greater e.g. in the palate for alveolar placement. 3. Miniscrew head: The head must be of sufficient dimension to accept and hold any coupling elements selected for a particular application. Different head designs also require different dimensions. A small diameter and lower profile of the miniscrew head are important for oral hygiene and patient comfort (Lee et al., 2009) 4. Shape • There are two basic body shapes: cylindrical and tapered. The former is typically associated with non-drilling insertion behaviour and the latter with self-drilling designs • Animal research results indicate that self-drilling techniques result in higher primary stability and better preserve the original bone (histologically) around mini-implant threads (Chen et al., 2008). • However, pre-drilling, at least through the cortical plate, may be valuable in avoiding excessive torque generation in thick/dense cortex sites e.g. the posterior mandible (Wilmes et al., 2008) C. Operator related factors 1. Selection of implant site
  • Mohammed Almuzian, University of Glasgow, 2013 15 In order to avoid root contact, implants should be placed in safe zones. The minimal space requirement between roots is 0.5 mm mesial and distal to the implant or 1 mm more than the implant diameter. In the maxilla, the more anterior and the more apical, the safer the location becomes. 2. Insertion angle  To achieve the best primary stability, an insertion angle ranging from 60° to 70° is advisable (to reduce insertion torque) while 30 degree has low stability (Wilmes et al., 2008). However the latest systematic review by Jung 2013 showed that insertion angle has no value in relation to avoid root contact.  If the available space between two adjacent roots is small, a more oblique direction of insertion seems to be favourable to minimize the risk of root contact 3. Implant placement torque  Motoyoshi et al recommended an implant placement torque range of 5 to 10Ncm. Very high insertion torques leads to higher failure rates due to excessicve bone compression (Motoyoshi et al., 2006).  There is a study show that holding the screw driver by using the index and thumb (digital torquing) is better than palm (brachial torquing) because less force would be applied and so less necrosis and failure (Estelita et al., 2012). 4. Loading protocol Chen found that completely unloaded screws had a success rate of 75% compared with 90% for screws immediately loaded with a 200 gm force (Chen et al., 2009). The explanation is that the immediate loading believed to be related to higher bone turn over and remodelling than delayed loading. 5. Sterilization and asepsis are mandatory throughout the procedure. 6. Clinician experience and skill do contribute to the success of mini implants. Mini-implant’s clinical steps 1. Determine the area of placement and the amount of the intra-radicular bone using PA radiograph
  • Mohammed Almuzian, University of Glasgow, 2013 16 2. 0.2% chlorohexidine mouth wash for 30 seconds will improve the success rate of TADs (Baek et al., 2008) 3. Few drops of LA infiltrated at the area of insertion. • Only the superficial soft tissues (gingiva/mucosa and periosteum) should be anaesthetised. The patient’s sensory feedback from the periodontal tissues can warn if the mini-implant begins to approximate the root of an adjacent tooth. • Kravitz and Kusnoto used topical anaesthesia in placing the TADs (Kravitz and Kusnoto, 2007) • TADs placement has a similar pain level to separators placement and less than the effect of 0.016NiTi wire. Almost 50% of patients require LA and 10% require postoperative analgesia. (Kuroda et al., 2007) 4. Avoiding contact of the adjacent anatomical and tooth roots which likely contribute to reduced success rates. • Several animal and clinical studies have provided clear reassurance that even when pilot drills or mini-implants have been used to directly traumatise the periodontal and root tissues, these heal without clinically detectable damage (in terms of loss of vitality, irreversible root resorption, Ankylosis). • The use of an insertion guidance stent, and oblique (rather than horizontal) insertion (Cousley, 2010)proposed advantages of stent: a) Stable insertion point, b) Prevents slippage. c) Reduces directional variation, d) Reducing fracture of the self-drilling tip. e) Reduce root trauma f) Minimizes radiation exposure of the patient, since the stent fabrication requires no additional radiographs g) Help left handed dentist to insert easily on right sude and vice versa
  • Mohammed Almuzian, University of Glasgow, 2013 17 h) Prescription for other how to use if the job is allocated to other 5. A manual insertion technique or slow motor-driven insertion may be used. The slow HP should be 128:1 torque, torqueing force 5-100Ncm and 60 RPM. 6. Direct loading • It is feasible to apply an orthodontic (unidirectional) force immediately after insertion, although it is commonly recommended that full force application be delayed for the first month, especially in adolescents (where there is a higher failure rate). 7. Once the anchorage demand has abated, the mini-implant may be left in situ or removed. There have been no clinical case reports of mini-implant osseointegration. Complications of TADs (Kravitz and Kusnoto, 2007) 1. Root trauma Cho et al reported a 13% in experience clinician to 21% in non-experience clinician incidence of root contact (Cho et al., 2010). Practical steps to minimise the chances of root contact are: a) Use screws of 1.4-1.8 mm maximum thread diameter b) Choose a favourable site. In the maxillary buccal region, the greatest amount of inter- radicular bone between the second premolar and the first molar is located at a level of 5 to 8 mm from the alveolar crest. In the mandibular buccal region, the greatest amount of interradicular bone is either between the second premolar and the first molar, or between the first molar and the second molar, approximately 11 mm from the alveolar crest. Theoretically, the more apically the miniscrew is placed, the less is the risk of root damage. c) Placing miniscrews at an angle to the bone surface puts the screw tip nearer the wider space between to root apices whilst keeping the screw head in the attached mucosa. d) Consider placing screws in the palate. e) Align the adjacent teeth thoroughly before screw insertion f) Use stent g) Pre-insertion radiograph 2. implantation in the nasal or maxillary sinus
  • Mohammed Almuzian, University of Glasgow, 2013 18 If the maxillary sinus has been perforated, the small diameter of the miniscrew does not warrant its immediate removal. Orthodontic therapy should continue, and the patient should be monitored for potential development of sinusitis and mucocele (Kravitz and Kusnoto, 2007). 3. Trauma of nerve (greater palatine, inferior alveolar, mental) Nerve injury can occur during placement of miniscrews in the maxillary palatal slope, the mandibular buccal dentoalveolus, and the retromolar region (Kravitz and Kusnoto, 2007). 4. Trauma of vessel (palatine artery) 5. Mini-screw slippage Causes a) Fail to fully engage cortical bone during placement and inadvertently slide the miniscrew under the mucosal tissue along the periosteum. b) Placement of miniscrews less than 30° (very oblique insertion) from the occlusal plane can increase the risk of slippage. Management a) The clinician can initially engage bone with the miniscrew at a right angle before reducing the angle of insertion after the second or third turn. b) Only minimal force should be used with the hand-driver, regardless of bone density. c) Predrilling d) Using stent 6. Infection/peri-implantitis Inflammation of the peri-implant soft tissue has been associated with a 30% increase in failure rate. So that regular tooth-brushing and chlorhexidine (0.12%, 10 ml) mouthwash is recommended Kravitz and Kusnoto, 2007 7. Soft tissue impingement/coverage Miniscrews placed in alveolar mucosa, particularly in the mandible, might become covered by soft tissue.
  • Mohammed Almuzian, University of Glasgow, 2013 19 8. Mini-screw migration 9. Fracture of screw Increased torsional stress during placement can lead to implant bending or fracture, or produce small cracks in the peri-implant bone, that affect miniscrew stability (Park et al., 2006). 1.2mm screw has a high fracture rate of 10%. But in general the fracture rate around 5% and the TAD must be removed. 10. Failure Failure which is either immediate success 80-95% (Park et al., 2006).. 11. Local emphysema 12. Patient discomfort 90% of pain disappears after 24h (Baxmann et al., 2010). NICE guidelines for Mini/micro screw implantation for orthodontic anchorage 2007 1. There is limited evidence that mini/micro screw implantation provides adequate orthodontic anchorage 2. There are no major safety concerns. 3. During the consent process clinicians should ensure that patients understand that there is a failure rate associated with the use of mini/micro screws and that the success of dental alignment cannot be guaranteed. 4. Evidence about optimal screw size and site of implantation (upper/lower jaw or buccal/lingual side of the bone) is limited. Therefore, further audit and research to clarify these issues would be useful 5. Efficacy: success rate 80-85% 6. Safety : breakage 3%
  • Mohammed Almuzian, University of Glasgow, 2013 20 Evidences 1. Skeggs 2008 in his Cochrane review found there is little evidence to support the use of surgical anchorage systems over conventional means of orthodontic anchorage reinforcement. However there is evidence from one recent trial by Benson 2005 that showed mid-palatal implants are an acceptable alternative to conventional techniques for reinforcing anchorage. So that Surgical anchorage via palatal onplant or miniscrew is effective with a difference of 1.75mm in term of anchorage preservation.  Sharma et al 2012 compare in their RCT compare the use of TAD with TPA and found significant difference in the anchorage control with the former (Sharma et al., 2012).  Feldmann & Bondemark (Feldmann and Bondemark, 2008) in their RCT measured the anchorage loss with Onplant (gp1), TADs (gp2), HG (gp3) & TPA (gp4). They found anchorage loss only in gp4 after levelling/aligning phase (approximately 1mm) but this had been increased to reach 2mm. additionally, gp3 showed 1.6 mm of anchorage loss while the anchorage was stable in the gp 1 & 2 from the start until the end of treatment. Three years later, the same authors measured the difference patient perception in the four groups in term of pain, discomfort, and jaw dysfunction. They concluded a very few significant differences between skeletal and conventional anchorage systems in term of patient perceptions (Feldmann et al., 2012)  For the treatment of bimaxillary protrusion, the use of TADs and TPAs to provide anchorage during En-mass retraction and space closure had been compared. The study had been conducted by Liu et al on adult Chinese. They concluded that a better dental, skeletal and soft tissue effects of the TADs in treating these groups. For this reason, the recommended the TADs as routine anchorage device in patients with bialveolar dental protrusion (Liu et al., 2009).  Salma and Hajeer 2014 TPA against TAD