Clinical Orthodontic : concept and complexities

Limiting unwanted tooth movement, while producing desired positioning of other teeth, is a very important part of . In this article, Benjamin Lewis outlines the concept of orthodontic anchorage, explains why it is important, and how to manipulate anchorage techniques to produce the best possible result for your patients.

he concept of anchorage, in orthodontic terms, is complex. It relates to techniques that can be used Tby the orthodontist to limit unwanted tooth movement. This article will describe what anchorage is and why an understanding of it is important in orthodontic practice, as well as demonstrating some of the many methods that can be used to reinforce and manipulate anchorage to achieve the best orthodontic result.

What is anchorage and

why is it important? iStockphoto.com Orthodontic anchorage is a complex Newton’s Law states that for every action there is an equal and opposite reaction. concept that revolves around the The concept of anchorage is built around this. theoretical principles by which orthodontic techniques may be employed attached to the appliance; sometimes resistance of the periodontal ligament, to limit or even prevent unwanted tooth these reactionary tooth movements but the reactionary force which was movement. are not wanted by the orthodontist. produced was distributed over sufficient Newton’s Law states that: Anchorage management is the method teeth so that their periodontal ligaments ‘For every action (in this case, a by which the orthodontist attempts were not pushed over their thresholds, desired tooth movement) there is an to control these undesired tooth then this would result in the movement equal and opposite reaction’. movements. of just the tooth that was intended to be The reactionary force that is created moved (Proffit, 2000). Unfortunately, will move the other teeth that are Achieving tooth movement forces can not currently be placed with To be able to achieve tooth movement, sufficient precision for this to occur. a force needs to be applied to the This is further complicated by the fact Benjamin RK Lewis is a senior tooth that is sufficient to overcome the that the force required to overcome the specialist registrar in orthodontics at St Lukes Hospital, Bradford and resistance of the periodontal ligament periodontal ligament varies between Leeds Dental Institute, Leeds. (see the first article in the series for teeth depending on: more detail; Lewis and Jedynakiewicz, n The type of tooth—incisor, premolar Email: [email protected] 2007). Theoretically, if a force could be or molar. The larger the root surface placed on a tooth that just overcame the area of the tooth, the greater the

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Figure 3. Shows the occlusion initially and following orthodontic treatment. Figure 1. Elastic powerchain over the This involved the extraction of maxillary first premolars to relieve the severe maxillary incisors to close the anterior crowding and to align the canines into a Class I position. The extraction midline diastema. of mandibular second premolars allowed not only the relief to the anterior crowding but also enabled the mesial movement of the molars to correct the molar relationship to Class I.

Reciprocal anchorage The amount of space generated by Reciprocal anchorage occurs when a the extraction of a tooth is often not force is placed on two teeth or two exactly the same as the amount of space blocks of teeth that have roughly the required. A premolar is approximately same root surface area, providing 7 mm wide, therefore the extraction similar periodontal ligament thresholds. of a premolar from both sides of a Figure 2. Upper removable appliance to Treatment is planned so that the applied dental arch provides 14 mm space. This expand the maxillary arch. force creates equal tooth movements may be too much, exactly the right force required to move it in both blocks of teeth. This is amount, or insufficient space. Each of n Periodontal condition—a decreased demonstrated in Figures 1 and 2. Figure these outcomes has an impact on the level of periodontal attachment 1 shows a median diastema being closed orthodontist’s anchorage management results in a decreased periodontal with elastic power chain, with each of of the case. If there is still insufficient threshold to tooth movement the central incisors moving the same space, further space has to be created, n Type of orthodontic force that is distance towards the midline. Figure 2 either by additional extractions, moving placed on the tooth—tipping teeth shows an upper removable appliance the buccal teeth distally, expansion of the requires lower forces than those (URA) with a midpalatal expansion arch or interproximal enamel reduction. required to move teeth bodily (see screw. This has been designed to expand If the space created by the extractions is Table 1). the maxillary arch to correct a unilateral just sufficient, the orthodontist must Anchorage is important in orthodontic buccal with a displacement maintain the position of the posterior treatment because if it is not assessed (see the previous article in the series teeth to allow all the created space to correctly at the outset of treatment and/ for a full description of the diagnosis be used to align the teeth or correct or not carefully monitored throughout and management of crossbites; Lewis, the incisal relationship. This requires treatment, then the final dental and 2008). The teeth opposite each other absolute anchorage, which is discussed facial result could be compromised. are moved the same distance buccally in more detail below. In cases when because they have similar periodontal the extraction of teeth provides more Types of anchorage thresholds. space than is required, the orthodontist There are four basic types of anchorage must then plan the ‘loss of some of that are used in orthodontics: Planned anchorage loss the anchorage’; this will aim to move n Reciprocal anchorage The extraction of teeth is one of the the posterior teeth forwards at the n Planned anchorage loss options an orthodontist has of creating same time as aligning and retracting n Anchorage reinforcement sufficient space to relieve crowding the anterior teeth (Figure 3). This may n Absolute anchorage. or to create an optimum occlusion. be aided during the planning process

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Figure 6. A Class II elastic being used to establish a class I canine and molar relationship towards the end Figure 9. Transpalatal arch with Nance of orthodontic treatment. button.

Pitting a single tooth against multiple teeth Adding teeth together to create a block of teeth increases their root surface area Figure 4. The maxillary second and their anchorage value. This block premolar and first molar are secured of teeth can then be used to move a together to be pitted against the canine, single tooth while allowing, potentially, resulting in distal movement of the minimal movement of the block of teeth canine with little mesial movement of Figure 7. Transpalatal arch. In this case (Figure 4). the posterior teeth. it has been modified with a mesially extending arm to allow distal traction to be placed to the maxillary right Utilizing different types canine. of tooth movement Tooth movement requires varying levels of force depending on the types of tooth movement which are planned. As can be seen from Table 1, the tipping of teeth requires less force than that needed to Figure 5. Intra-arch being used achieve bodily movement. This can be to correct a centreline discrepancy. utilized by the orthodontist to control anchorage during an individual’s if teeth are extracted closest to the treatment, by allowing the teeth they teeth that the orthodontist wishes to Figure 8. Lower lingual arch. want to move, to tip, while restricting move the furthest. For example, if the orthodontist wanted the molars to move mesially during treatment, to correct TABLE 1. FORCE LEVELS USED FOR the molar relationship, the extraction of the second premolars instead of the first DIFFERENT TYPES OF TOOTH MOVEMENT premolars would make that planned tooth movement more straightforward. Type of movement Force (grams) 15–25 Anchorage reinforcement Anchorage reinforcement is required Tipping 30–60 when a large proportion of the extraction space is needed to achieve the aims of Extrusion 50–75 treatment. This reinforcement, which Rotational 50–75 restricts the unwanted tooth movement, can be created in a number of ways. Bodily 100–150

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Figure 10. Cross-sectional view showing the design of a transpalatal arch with a Nance button which rests against the palatal mucosa overlying the palatal vault.

those they do not want to move, to bodily movement. This can be achieved by using different types of orthodontic brackets/attachments and specific bends placed into the archwire. Figure 12. A NITOM safety facebow used with orthodontic headgear. (A) The Interarch elastics band on the first molar has a headgear Interarch elastics (Figure 5) allow a tube attached to it; (B) the intraoral connection between the maxilla and arm of the facebow in inserted into the . This connection can the headgear tube on the first molar; be used to pit some of the maxillary (C) the NITOM nickel titanium locking teeth against some of the mandibular attachment secures behind the first teeth, which can ‘alter the anchorage molar tube, preventing the facebow’s balance’ in a particular arch allowing accidental disengagement. the orthodontist to move the teeth they want to achieve a good interarch occlusal of teeth to increase their anchorage relationship; i.e. allowing the mesial value in addition to the maintaining movement of the mandibular molars at intermolar width. This results in any the same time as distal retraction the mesial movement of the molars leading maxillary incisors (Class II elastics, as to a potential binding of the molar in Figure 6) or moving the maxillary roots against the cortical bone of a molars more mesially and retracting narrower part of the maxilla, which has the mandibular incisors distally (Class a decreased resorptive potential than III elastics). cancellous (spongy) bone.

Transpalatal arch/lingual arch Transpalatal arch with Nance Transpalatal arches and lingual arches button are designed to maintain the intermolar Transpalatal arches with a Nance button distance by connecting the opposing (Figure 9) work on the same principle molars in an arch with a 0.9 mm diameter as the conventional transpalatal arch Figure 11. A Nance button has dug wire soldered to the molar bands. but the Nance button allows the palatal into the palatal mucosa (A), which has Figures 7 and 8 show a transpalatal arch vault to be utilized. Nance buttons are resulted in ginigival ulceration (B). and a lingual arch respectively. These designed to rest on the palatal mucosa Removal of the Nance button allows devices aim to restrict movement of the of the sloping palatal vault (Figure 10) complete gingival healing (C). individual molars by creating a block and therefore utilize the palatal vault

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a ‘blunt’ facebow tip to prevent/ minimize injury once the facebow has become detached, or to lock the facebow securely to the first molar bands to prevent its unintentional disengagement (Samuels et al, 2000) n ‘Masel’ neck strap—a rigid plastic strap designed to prevent the facebow from inadvertently coming out of the Figure 13. Orthodontic headgear. (A) High pull (occipital pull) headgear; (B) headgear tubes on the first molar low pull (cervical pull) headgear; (C) combination pull headgear (also showing a bands, and if it still became detached, ‘Masel’ rigid cervical neck strap safety device in situ). to maintain the facebow within the mouth to prevent extraoral injuries and its overlying mucosa to resist anterior–posteriorly and vertically). It is n ‘Snap away’ anti-recoil safety straps— the mesial movement of the molars. possible to achieve orthopaedic effects designed as a device to prevent recoil However, because the button rests on with headgear in addition to orthodontic injuries resulting from accidental the mucosa, which can be compressed, effects. However, to achieve an alteration disengagement or incorrect handling it does not provide absolute anchorage, of a patient’s growth requires the (Postlethwaite, 1989). and unless careful treatment mechanics headgear to apply large forces (>500 g are employed it can lead to the Nance per side, compared with 250 g per side button digging in to the soft tissue for anchorage reinforcement) for the Absolute anchorage resulting in trauma (Figure 11). duration of an individual’s growth, and Headgear can be used to move teeth most patients do not find this sustained in all directions depending on the Headgear wear practical. Protraction headgear modifications and adjustments made This is a form of extraoral anchorage can be used as an interceptive measure to the apparatus. However, its success (EOA) as it utilizes the neck and/or the to encourage additional maxillary is very much dependent on patient back of the head to resist unwanted tooth growth in patients with a skeletal Class cooperation, and other methods have movement. It is also able to produce III due to maxillary recently been introduced which offer the distal movement of the molars enabling hypoplasia. It is initiated between the potential benefits of absolute anchorage space to be created (extraoral traction; ages of 8 and 9 years and has to be worn without as much reliance on the patient. EOT). It uses a ‘facebow’, which acts as for 16 hours a day for 9–12 months. The two main developments in this an interface between the fixed appliance Although this can lead to impressive area are midpalatal implants and mini- and the extraoral headgear apparatus. skeletal correction in the short term, the implants. The facebow has intraoral arms that long term effects are unknown and are insert into the headgear tubes which currently being investigated. Midpalatal implants can be placed on the buccal aspect of An important aspect of using headgear These are an adaptation of standard the maxillary first molar orthodontic in clinical practice is the concurrent use restorative implants used for the bands (Figure 12). The extraoral arms of safety devices to prevent unwanted replacement of missing teeth. They of the facebow attach to the headgear disconnection of the headgear apparatus are designed with a smaller length (4– apparatus via elastic straps. There during sleep or play. There have been 6 mm with a 2.5–4.5 mm neck length) are four difference type of headgear reports that headgear can become than conventional restorative implants appliance (Figure 13): detached during sleep (Samuels et al, and are inserted into the bone of the n High-pull (occipital pull) headgear 1996) which may, in some cases, result palate after a ‘profile’ hole is cut using (13A) in facial trauma (Booth-Mason and a slow-speed handpiece under local n Cervical pull headgear (13B) Birnie, 1988). The British Orthodontic anaesthesia (Tinsley et al, 2004). These n Combination pull headgear (13C) Society (BOS) recommend that at least implants need to osseointegrate, similar n Protraction headgear. two safety devices are incorporated into to a standard restorative implant, so no The particular type of headgear the headgear appliance (BOS advice orthodontic traction must be placed for used depends on a number of factors sheet No. 8). These may be: at least 3 months. It is necessary to place including the patient’s skeletal type and n Safety ended or locking facebows these implants in the middle of the the desired tooth movements (both (Figure 12), designed either to provide palate to ensure there is sufficient bone

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Figure 14. Midpalatal implants which Figure 16. Placement of a mini–implant, which uses mechanical retention have osseointegrated into the palatal to remain in the alveolar bone. vault (Courtesy of Drs Jonathan O’Dwyer and David Tinsley). (A) Mini-implant anchorage . The implants range in size Midpalatal implant being used to Sometimes known as ‘temporary (6–9 mm long and 1–2 mm diameter) hold the first molars in their current position; (B) midpalatal implant being anchorage devices’, mini-implants and are screwed into the bone of the used to move the first molars in a are a relatively recent addition to the maxilla or mandible (sometimes after distal direction. orthodontist’s armoury. They are based a pilot hole has been drilled) under on the surgical screws used by maxillo- local anaesthetic (Figures 15 and 16). facial surgeons to repair fractured One benefit is that they can be placed

KEY POINTS

n Orthodontic anchorage is fundamentally ‘the resistance to unwanted tooth movement’.

Figure 15. Close up of a mini-implant n The forces needed to orthodontically move a tooth will vary (temporary anchorage device). depending on the type of tooth and its periodontal condition, as well as the type of orthodontic tooth movement desired. available to allow the implants to be n The four basic types of orthodontic anchorage are: reciprocal initially stable and then to osseointegrate anchorage, planned anchorage loss, anchorage reinforcement, (Figure 14). This can make the design and absolute anchorage. of the orthodontic attachment difficult because the dictated placement site may n There are many different mechanical techniques which may be not be close to the teeth the anchorage utilized by the orthodontist to achieve different these different types of which needs to be reinforced. When of orthodontic anchorage. the additional anchorage is no longer required, the midpalatal implants n Anchorage control needs to be properly assessed during treatment will need to be removed, which can planning and monitored throughout a patient’s treatment to obtain be difficult because of the degree the optimum aesthetic and functional results. of osseointegration.

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by the orthodontist in the exact place orthodontist to enable correct treatment Facebows. British Orthodontic Society Advice where the anchorage reinforcement is planning. Without this knowledge, Sheet Number 8 (Revised 2006) required because they are much smaller inappropriate teeth might be extracted Lewis BRK (2008) Orthodontic correction of crossbites. Dental Nurs 4 (4): 196–202. than the midpalatal implants and do not and the optimal treatment result may Lewis BRK, Jedynakiewicz N (2007) Fundamentals, need to osseointegrate; this also means not be achievable. This article has uses and benefits of orthodontics. Dental Nurs that the mini-implants are easier to provided an overview of the most 3(8): 430–9 remove than the midpalatal type once common methods that are available to Postlethwaite K (1989) The range and effec- tiveness of safety headgear products. Eur J they are no longer needed. Attachments the clinician to help them manage the Orthodont 11: 228–34 can be placed onto the mini-implants anchorage during a case and achieve the Proffit WR, Fields HW (2000) Contemporary to either prevent teeth from moving or, desired tooth movements to get the best Orthodontics 3rd edn. Mosby Inc, Missouri: conversely, to apply traction to teeth possible aesthetic and functional result. 308–11 that the orthodontist wishes to move. Samuels RHA, Willner F, Knox J, Jones ML (1996) Booth-Mason S, Birnie D (1988) Penetrating eye A national survey of orthodontic facebow inju- injury from orthodontic headgear – A case ries in the UK and Eire. Br J Orthodont 23: Conclusions report. Eur J Orthodont 10: 111–4 11–20 Anchorage control during orthodontic British Orthodontic Society (2006) Development Tinsley D, O’Dwyer JJ, Benson PE, Doyle PT, treatment can be complex. A thorough and Standards Committee of the British Sandler J (2004) Orthodontic palatal implants: understanding is required by the Orthodontic Society. The Use of Headgear and clinical technique. J Orthodont 31: 3–8

Answers to May’s Anaphylaxis questionnaire

1. Rapid breathing; evidence of poor circulation; stridor; hoarseness or wheeze; tongue swelling; pallor; clammy skin; flushed skin; rash 2. Itchy rash (urticaria); swelling to lips, tongue or throat; wheeze 3. Adrenaline 4. Intramuscular route 5. 1:1000 6. 50 micrograms (0.5 ml) 7. Panic attack; asthma; shock; heart attack 8. A severe life-threatening, generalized or systematic hypersensitivity reaction which may, or may not, be allergy related 9. Penicillin/antibiotics and many other drugs; non-steroidal anti-inflammatory drugs; latex; nuts (peanuts, tree nuts such as walnuts, cashews, brazils); sesame; fish and shellfish; dairy products and eggs; wasp and bee stings 10. Oxygen of sufficient size and also to allow adequate flow (>10 litres/min); an oxygen mask with a reservoir bag to maximize oxygen delivery; adrenaline 1 mg/ml 1:1000 for intramuscular use; salbutamol aerosol inhaler 100 microgram/actuation

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