ARC Journal of Dental Science Volume 4, Issue 3, 2019, PP 6-12 ISSN No. (Online) 2456-0030 DOI: http://dx.doi.org/10.20431/2456-0030.0403002 www.arcjournals.org

Understanding Anchorage in Orthodontics

Mohammed Nahidh1*, Arkan M. Al Azzawi2, Sajid C. Al-Badri3 1Assistant professor, Department of Orthodontics, College of Dentistry, University of Baghdad, Iraq 2Assistant professor, Department of POP, College of Dentistry, University of Babylon, Iraq 3Specialist orthodontist, Ministry of Health, Baghdad Iraq

*Corresponding Author: Mohammed Nahidh, Assistant professor, Department of Orthodontics, College of Dentistry, University of Baghdad, Iraq, Email: [email protected]

Abstract: Before starting active treatment of any orthodontic case, anchorage must be planned well to get rid of the problems that might accompanied the treatment procedures. This article reviewed the anchorage from all aspects starting from the definition, sources, types, planning, anchorage loss and how to avoid it.

1. DEFINITION  Parietal bone According to the third law of Newton, for every  Facial bones action there is a reaction equals in amount and opposite in direction. This can be applied in  Frontal bone orthodontics simply when retracting canine  Mandibular symphysis against posterior teeth. The expected thing is distalization of the canine in the first premolar  Back of the neck (cervical bone) extraction site against mesial (forward) 2.1. Intra-Oral Sources of Anchorage movement of the posterior teeth which called 2.1.1. Teeth anchorage unit. In orthodontics, teeth themselves are the most According to Graber (1), the term anchorage is frequently used anchorage unit to resist referred as "the nature and degree of resistance unwanted movement. Forces can be exerted to displacement offered by an anatomic unit from one set of teeth to move certain other teeth. when used for the purpose of affecting tooth Many factors related to the teeth can influence movement", while Gardiner et al. (2) defined it the anchorage like: the root form, the size as "the site of delivery from which a force is (length) of the roots, the number of the roots, the exerted". On the other hand, Lewis (3) defined anatomic position of the teeth, presence of anchorage simply as "the resistance to unwanted ankylosed tooth, the axial inclination of the tooth movement". teeth, root formation, contact points of teeth and their intercuspation. 2. SOURCES OF ORTHODONTIC ANCHORAGE Basically, the sources of orthodontic anchorage 2.1.2. Root Form can be summarized as (4-7): Generally, the root in cross section can be either A. Intra-Oral Sources round, flat (mesio-distally) or triangular. The distribution of the periodontal fibers on the root  Teeth surface aid in anchorage. The more the fibers,  Alveolar bone the better the anchorage potential. The direction  Cortical bone of attachment of the fibers also affects the  Basal jaw bone anchorage offered by a tooth. Round roots have only half their periodontal fibers stressed in any  Musculature given direction, hence offer the least anchorage. B. Extra-Oral Sources Mesio-distally flat roots are able to resist  Cranium mesiodistal movement better as compared to labio-lingual movement as more number of  Occipital bone fibers are activated on the flatter surfaces as

ARC Journal of Dental Science Page | 6 Understanding Anchorage in Orthodontics compared to the relatively narrower labial or contact with those of the opposing jaw, this is lingual surfaces. especially true for teeth in the posterior segment which also show the presence of attrition facets. Triangular roots, like those of the canines are able to provide greater anchorage. Their flatness 2.1.6. Alveolar Bone adds to resistance. The investing alveolar bone around the roots The tripod arrangement of roots like that seen offer resistance to tooth movement up to a on maxillary molars also aids in increasing the certain amount of force, exceeding which there anchorage. The round palatal root resists will be bone remodeling. Less dense alveolar extrusion and the two flat buccal roots resist bone offers less anchorage. More mature bone intrusion and the mesio-distal stresses. increases anchorage. This takes place because of two factors—one, the bone becomes more  Size (Length) of the Roots calcified and dissolution takes time and two, the The larger or longer the roots, the more is their regenerative capacity of the bone decreases. anchorage would be. The maxillary canines, Forces that are dissipated over a larger bone because of their long roots can be the most surface area offer increased anchorage. difficult teeth to move in certain clinical circumstances. 2.1.7. Cortical Bone  Number of Roots Ricketts floated the idea of using cortical bone for anchorage. The contention being that the The greater the surface area of the root, the cortical bone is denser with decreased blood greater the periodontal support and hence, supplies and bone turnover. Hence, if certain greater the anchorage potential. Multi-rooted teeth were torqued to come in contact with the teeth provide greater anchorage as compared to cortical bone, they would have a greater single rooted teeth with similar root length. anchorage potential. The idea as such remains 2.1.3. Anatomic Position of the Teeth controversial as tooth roots also show resorption in such conditions and the risk of non-vitality of Sometimes the position of the teeth in the such teeth is also more. individual arches also helps in increasing their anchorage potential. As in the case of 2.1.8. Basal Jaw Bone mandibular second molars, which are placed Certain areas of basal jaw bone such as hard between two ridges—the mylohyoid and the palate and lingual surface of anterior mandible external oblique, they provide an increased can be utilized in order to enhance the intra-oral resistance to mesial movement. anchorage. Nance palatal button uses the 2.1.4. Presence of Ankylosed Teeth anchorage provided by the hard palate to resist the mesial movement of maxillary molars. Orthodontic movement of such teeth is not possible and they can therefore serve as 2.1.9. Musculature excellent anchors whenever possible. Under normal circumstances, the peri-oral 2.1.5. Axial Inclination of the Tooth musculature plays an important part in the When the tooth is inclined in the opposite growth and development of the dental arches. direction to that of the force applied, it provides Hypotonicity of the peri-oral musculature might greater resistance or anchorage. lead to spacing and flaring of the anterior teeth. The hypertonicity of the same muscles has the  Root Formation reverse effect. Lip bumper is an appliance that Teeth with incomplete root formation are easier makes use of the tonicity of the lip musculature to move and are able to provide lesser and enhances the anchorage potential of the anchorage. mandibular molars preventing their mesial  Contact Points movement. Teeth with tight intact and/ or broad contacts 2.2. Extra-Oral Sources of Anchorage provide greater anchorage. 2.2.1. Cranium  Intercuspation Headgears derived anchorage from occipital or Good intercuspation leads to greater anchorage parietal regions of the cranium. These are used potential. This is mainly because the teeth in one along with a face bow to resist the growth of jaw are prevented from moving because of the maxilla or to move the maxillary teeth distally. ARC Journal of Dental Science Page | 7 Understanding Anchorage in Orthodontics

2.2.2. Facial Bones  Simple The frontal bone (forehead region) and  Stationary mandibular symphysis (chin area) are used as resistance units during face mask therapy so as  Reciprocal to protract the maxilla.  Reinforced 2.2.3. Back of the Neck (Cervical Bone)  Intermaxillary The cervical headgears derived anchorage from  Extra-oral. back of the neck or cervical region. They are also used to bring about changes in the maxilla 4. ACCORDING TO THE MANNER OF FORCE or maxillary teeth. APPLICATION

3. CLASSIFICATION OF ANCHORAGE 4.1. Simple Anchorage Generally, anchorage could be classified (8): In this type, the manner and application of force is such that it tends to change the axial 3.1. According to the Manner of Force inclination of the anchor tooth or teeth in the Application plane of space in which the force is being  Simple anchorage applied. In other words, the resistance of the anchorage unit to tipping is utilized to move  Stationary anchorage another tooth or teeth. In this type of anchorage,  Reciprocal anchorage the appliance usually engages a greater number of teeth than are to be moved within the same 3.2. According to Jaws Involved dental arch. Ideally, the combined root surface  Intra-maxillary anchorage area of the anchor teeth should be two times that of the teeth to be moved. The amount of force  Inter-maxillary anchorage on each anchor tooth in simple anchorage is 3.3. According to the Site of Anchorage equal to the total moving force component of the appliance divided by the number of 1. Intra-oral anchorage anchored teeth. 2. Extra-oral anchorage: 4.2. Stationary Anchorage  Cervical It is defined as dental anchorage in which the  Occipital manner of application of force tends to displace the anchorage unit bodily in the plane of space  Cranial in which this force is being applied. In this type  Facial of anchorage, the resistance of anchor teeth to bodily movement is utilized to move other teeth. 3. Muscular anchorage Stationary anchorage provides greater resistance 3.4. According to the Number of Anchorage than simple anchorage to unwanted tooth Units movement.  Single or primary anchorage 4.3. Reciprocal Anchorage  Compound anchorage The reciprocal anchorage refers to the resistance offered by two malposed units, when the  Multiple or reinforced anchorage. dissipation of equal and opposite forces tends to 3.5. According to Anchorage Demands move each unit towards a more normal (5,9,10) occlusion. In some treatment procedures, it is desirable to move teeth or groups of teeth of  Maximum anchorage (Type A anchorage). equal anchorage potential in opposite directions.  Moderate anchorage (Type B anchorage). In such cases, it is possible to utilize their anchorage forces as moving forces to achieve  Minimum anchorage (Type C anchorage). the desirable changes. A frequently used form of reciprocal anchorage is known as intermaxillary  Absolute anchorage (direct and indirect traction in which, the forces used to move the anchorage). whole or part of one dental arch in one direction Gardiner et al. (2) classified anchorage into six are anchored by equal forces by moving the categories as followed: opposite arch in opposite direction, thus, ARC Journal of Dental Science Page | 8 Understanding Anchorage in Orthodontics correcting discrepancies in both the dental 6.4. According to the Number of Anchorage arches, also seen in cases of correction of Units midline diastema, bilateral symmetrical 6.4.1. Single or Primary Anchorage expansion and correction of single tooth crossbite. Single or primary anchorage is defined as the resistance provided by a single tooth with 5. ACCORDING TO JAWS INVOLVED greater alveolar support to move another tooth 5.1. Intra-Maxillary Anchorage with lesser alveolar support, e.g. retraction of a premolar using a molar tooth. Intra-maxillary anchorage is the anchorage in which the resistance units are situated within the 6.4.2. Compound Anchorage same jaw. If appliances are placed only in It is the type of anchorage where more than one maxillary or mandibular dental arches, they are tooth with greater anchorage potential are used considered intra-maxillary resistance units. to move a tooth/group of teeth with lesser Class I elastic stretched from first molar to support. canine teeth in either of the dental arches is an example. 6.5. Reinforced Anchorage/ Multiple Anchorage 5.2. Inter-Maxillary Anchorage (Baker’s It frequently happens that the teeth available for Anchorage) simple anchorage are not sufficient in number or Inter-maxillary anchorage is the anchorage in in size to resist the forces necessary for which the units situated in one jaw are used to orthodontic treatment and that reciprocal affect tooth movement in the other jaw. Class II anchorage is not appropriate to the type of elastic stretched from upper canine to lower treatment to be carried out. In such molar to affect correction of class II circumstance, it is necessary to reinforce the malocclusion and Class III elastic stretched anchorage to avoid unwanted movements of the from upper molar to lower canine to correct anchor teeth. Anchorage is said to be reinforced class III malocclusion are good examples. when more than one type of resistance units are utilized. 6. ACCORDING TO THE SITE OF ANCHORAGE 7. ACCORDING TO ANCHORAGE DEMANDS 6.1. Intra-Oral Anchorage 7.1. Maximum Anchorage (Type A When intra-oral structures such as teeth and Anchorage) other anatomic areas are used as anchor units it A situation in which the treatment objectives is called intra-oral anchorage. Mini-screws can require that very little anchorage can be lost. be considered as an absolute intra-oral anchorage. 7.2. Moderate Anchorage (Type B Anchorage) 6.2. Extra-Oral Anchorage A situation in which anchorage is not critical Extra-oral anchorage is the anchorage and space closure should be performed by established from extra-oral structures. It reciprocal movement of both the active and the included: anchorage segment.  Cervical region: Use of cervical pull 7.3. Minimum Anchorage (Type C headgear. Anchorage)  Occipital region: Use of occipital pull A situation in which, for an optimal result, a headgear. considerable movement of the anchorage segment (anchorage loss) is desirable, during  Forehead and chin: Use of reverse pull closure of space. headgear. 7.4. Absolute Anchorage 6.3. Muscular Anchorage In this type of anchorage, mesial migration of Peri-oral musculature may be used as anchorage the anchor unit is avoided conserving 100% of units in certain cases. For example, the lip the extraction site space. In the last years, bumper utilizes the force exerted by lower lip titanium temporary skeletal anchorage devices musculature to bring about distalization of (TSAD) like mini-implants have been used in mandibular first molar. orthodontic treatment in order to provide ARC Journal of Dental Science Page | 9 Understanding Anchorage in Orthodontics absolute anchorage without patient compliance. support is required when all or most of the These mini-screws are small enough to be space created, most commonly through placed in different areas of the alveolar bone. tooth extraction, is required in order to This type of anchorage can be divided into achieve the desired tooth movements. direct anchorage when the TSAD is used  Aims of treatment; the fewer teeth that need directly to move a tooth and indirect anchorage to be moved to achieve the aims of when a tooth or group of teeth are connected to treatment then the lesser anchorage demand, TSAD that acts as periodontal-skeletal however, if treatment is complex and anchorage unit allowing for anchor tooth or multiple teeth are to be moved there will be group of teeth to be moved against this a greater anchorage demand. The aims of stabilized unit (10). treatment should be clear. In cases with a 8. PLANNING OF ANCHORAGE IN Class II molar relationship, anchorage needs ORTHODONTIC CASES will be greater if a Class I molar (and At the time of determining the space canine) relationship is to be achieved rather requirement to resolve the malocclusion in a than a Class II molar (and Class I canine) given case, it is essential to plan for space that is relationship. The need to achieve a Class I likely to be lost due to the invariable movement canine relationship is essential for the of the anchor teeth. The anchorage requirement success of all treatment, anchorage planning depends on (3, 9): should therefore focus not only on the intended molar movements but also  The number of teeth to be moved; the importantly on the required movements of greater the number of teeth being moved, the canines to achieve this goal. the greater is the anchorage demand. Moving teeth in segments as in retracting  Growth rotation and skeletal pattern; an the canine separately rather than retracting increased rate of tooth movement has been the complete anterior segment together will associated with patients who have an decrease the load on the anchor teeth. increased vertical dimension or backward growth rotation. It has been suggested that  The type of teeth to be moved; teeth with space closure or anchorage loss may occur large flat roots and/or more than one root more rapidly in these high angled cases. exert more load on the anchor teeth, hence, Conversely in a patient with reduced it is more difficult to move a canine as vertical dimensions or a forward growth compared to an incisor or a molar as rotation, space loss or anchorage loss may compared to a premolar. be slower. A possible explanation that has been proposed for this observation is the  Type of tooth movement; moving teeth relative strength of the facial muscles, with bodily requires more force as compared to reduced vertical dimensions having a tipping the same teeth. stronger musculature.  Periodontal condition of the dentition; teeth  The angulations and position of the teeth; with decreased bone support or usually, in cases where there is bi- periodontally compromised teeth are easier protrusiveness or excessive proclination of to move as compared to healthy teeth the anterior teeth, a total control of attached to a strong periodontium. anchorage will be necessary. This way we  Duration of tooth movement; prolonged can take complete advantage of the treatment time places more strain on the extraction spaces. anchor teeth. Short term treatment might  The mandibular plane angle (high or low). bring about negligible amount of change in The inclination of this angle may be the anchor teeth whereas the same teeth modified with different extra-oral anchorage might not be able to withstand the same forces adequately if the treatment becomes appliances (High Pull, Head Gear, and Face prolonged. Bow).  Speed curve depth.  Space requirements; the amount of crowding or spacing should be assessed as  Age of the patient. Depending on this we part of treatment planning. This can be done must take the growth factor of the patient using visual assessment or more formally into consideration for anchorage type using a space analysis. Maximum anchorage selection. ARC Journal of Dental Science Page | 10 Understanding Anchorage in Orthodontics

 Patient profile. In biprotrusive type patients 9.1. Anchorage with the Removable and we will need very good posterior anchorage Myofunctional Appliances in order to modify this type of profile. Removable appliances can be used alone or to  Surrounding bone characteristics; when reinforce anchorage in conjunction with a fixed teeth are located within trabecular bone, appliance. By virtue of their palatal coverage they pose less resistance to move. But, when they increase anchorage. Other design features they are located in cortical bone, their which reinforce anchorage include (3): anchorage quantity increases because this  Anteroposteriorly – by colleting around the bone is denser, laminated and much more posterior teeth with acrylic; inclined bite- compact, with a very limited blood supply. blocks, palatal bows or the use of incisor Blood supply is the key factor in dental capping. movement because the physiologic resorption process and the osseous  Transversely – the pitting of one side of the apposition are delayed, so dental movement arch against the other can reinforce is slower. transverse anchorage, typically seen where an expansion screw or coffin screw is used 9. ANCHORAGE WITH FIXED APPLIANCE for increasing the palatal transverse Many methods had been listed to increase dimension. anchorage value with the fixed appliance; these  Vertically – by either reducing the vertical included (5, 9): dimensions during treatment of a high angle  Banding or bonding the second molars. patient by intruding the posterior teeth, or increasing the vertical dimension by  Decreasing number of teeth to be moved at allowing differential eruption with the use a given time. of an anterior bite-plane.  Moving the apices of anchor teeth close to All of these three dimensional features can be the cortex incorporated into functional appliances, which  Stopper in the wire in front of the molars additionally can be used to gain anchorage in the anteroposterior direction to aid in the  Retro-ligature (figure of 8 ligation). treatment of a Class II malocclusion.  Toe-in and Tip back bends [Anchor bends 9.2. Anchorage Loss for posterior anchorage] and “Apical torque” [for anterior anchorage] in archwire. Anchorage loss is the movement of the reaction unit or the anchor unit instead of the teeth to be  Use of combined Nance bottom with trans- moved (4, 5). palatal arch in the upper and lingual arch in the lower. 9.2.1. Causes of Anchorage Loss (4,5)  Managing the timing of extraction.  Not wearing the appliance adequately.  Managing the friction between the bracket’s  Too much activation of springs or active slot and archwire. components  Inter-maxillary elastics.  Presence of acrylic or any obstruction on the path of tooth movement  Extra oral traction – occipital, occipital- cervical or cervical.  Poor retention of appliance.  Lip bumper.  Anterior bite plane: as this withdraws the occlusal interlock.  Tipping the molars and premolars distally  Anchor root area not sufficiently greater prior to retraction of the anterior teeth than the root area of tooth or teeth to be according to Tweed philosophy to increase moved. the anchorage value of the posterior  If appliance encourage tipping movement of segments, allowing further retraction of the anchor teeth and bodily movement of the canines and incisors with less anchorage loss. teeth to be moved.  Utilizing dental implants or ankylosed teeth  Using heavy force in moving teeth.  Mini-screws and mini-plates.  Poor anchorage planning. ARC Journal of Dental Science Page | 11 Understanding Anchorage in Orthodontics

9.2.2. Signs of Anchorage Loss (4,5) REFERENCES  Mesial movement of molars. [1] Graber TM. Orthodontics principles and practice. 3rd ed. Mosby: W.B. Saunders  Closure of extraction space by movement of Company; 1972. posterior teeth. [2] Gardiner JH, Leighton BC, Luffingham JK,  Proclination of anterior teeth. Valialhan A. Orthodontics for dental students. 4th ed. Delhi: Oxford: Oxford university press;  Spacing of teeth. 1998.  Increase in overjet. [3] Lewis BRK. Anchorage planning. In Littlewood SJ, Mitchell L (ed). Introduction to  Change in molar relations. orthodontics. 5th ed. Oxford: Oxford university press; 2019.  Buccal cross bite of upper posteriors. [4] Rani MS. Synopsis of orthodontics. 1st ed. 9.2.3. Means to Detect Anchorage Loss (5) Delhi: A.I.T.B.S. publishers and distributors; 1995.  Relating the position of other teeth to the [5] Alam MK. A to Z orthodontics volume 4. 1st teeth in the same and opposite arch. ed. Malaysia: PPSP publication; 2012.  Increase in overjet. [6] Phulari BS. Orthodontics Principles and Practice. 2nd ed. New Delhi: Jaypee Brothers  Checking the fitness of the removable Medical Publishers (P) Ltd; 2016. appliance in the mouth. [7] Singh G. Textbook of orthodontics. 3rd ed. New  Measurements of the distance of anchor Delhi: Jaypee Brothers Medical Publishers (P) Ltd; 2015. teeth from midline. [8] Moyers RE. Handbook of orthodontics. 4th ed.  Measurements from palatal rugae and Chicago: Year book medical publishers; 1988. frenum. [9] Yanez EER. 1001 Tips' for orthodontics and its st  Observation of the spacing mesial/distal to secrets. 1 ed. Miami: AMOLCA; 2008. the anchor teeth. [10] Miles PG, Rinchuse DJ, Rinchuse DJ. Evidence-based clinical orthodontics. 1st ed.  Inclination of the anchor teeth. Chicago: Quintessence publishing Co., Inc.; 2012.  Radiological examination (cephalometric radiograph).

Citation: Mohammed Nahidh, Arkan M. Al Azzawi, Sajid C. Al-Badri, Understanding Anchorage in Orthodontics. ARC Journal of Dental science. 2019; 4(3):6-12. doi:dx.doi.org/10.20431/2456-0030.0403002. Copyright: © 2019 Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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