19 Heidi B. Lobprise Main Street Veterinary Dental Clinic, Flower Mound, TX, USA The term orthodontics comes from the Greek language of ortho meaning correct and odontics meaning tooth. From early goals of having ideal dental occlusion and jaw relationships, modern treatment goals now involve a soft tissue paradigm in human dentistry. With an increased focus on clinical examination to obtain diagnostic information, there is emphasis on soft tissue relationships and adaptations for optimal facial appearance, as well as functional occlusion [1]. As the functional dentition and oral support tissues are at risk when the animal’s occlusion is abnormal, the assessment of the best course of treatment and whether or not to consider treatment or genetic counseling is one of the most critical points in veterinary orthodontics. Every animal both deserves and has the medical right to an occlusion that is functional and free from discomfort, as can be reasonably provided by therapy. In some dogs, and to a lesser degree in the cat, human intervention has perpetuated some occlusal aberrations. The American Veterinary Dental College (AVDC) has a position statement: “The goal of orthodontic procedures in companion animals is to provide pets with a healthy and functional occlusion. The AVDC supports the AVMA policy regarding cosmetic procedures that enhance the appearance of show or breeding animals” (http://www.avdc.org/statements.html – Orthodontic Procedures). The Principles of Veterinary Medical Ethics of the AVMA (Section I.e.) states: “Performance of surgical or other procedures in all species for the purpose of concealing genetic defects in animals to be shown, raced, bred, or sold, as breeding animals is unethical. However, should the health or welfare of the individual patient require correction of such genetic defects, it is recommended that the patient be rendered incapable of reproduction” (Section VII, Genetic Defect) (https://www.avma.org/KB/Policies/Pages/Principles‐of‐Veterinary‐Medical‐Ethics‐of‐the‐AVMA.aspx). The American Kennel Club disqualifies a dog from competition if its appearance has been changed by artificial means due to procedures, substances, or drugs that can obscure, disguise, or eliminate any congenital or hereditary abnormality or undesirable characteristic, even if absolutely necessary to the health and comfort of the dog. This includes correction of harelip, cleft palate, restorative dental procedure, the use of bands or braces on teeth, or any alteration of the dental arcade (amongst other named procedures) (http://images.akc.org/pdf/rulebooks/RREGS3.pdf). When there are reasonable indications of hereditary involvement the owner should be informed as to the possibility and, should treatment be considered, the owner or agent should acknowledge their responsibilities prior to treatment and genetic counseling should be advised. One of the major obstacles in advising clients as to dental hereditary involvement is the lack of definitive studies to distinguish hereditary from non‐hereditary conditions. It is generally conceded that orofacial skeletal length variations are hereditary, with the exception of those caused by local oral or systemic influences, and there is reasonable research on the dog to support it. When etiology can be determined, the client should be counseled as to preventive measures that may be able to be taken to help control the condition, and of the likelihood of the dentofacial deformity being passed on to offspring. Dentofacial deformity refers to abnormalities of the teeth in morphology or location, and/or of the facial support structures. These deformities typically fall into one or more of three general categories involving heredity, systemic influences, or local influences. It is not unusual for some influences to fall within several categories, or fall within one yet also cause influence within another. Heredity is concerned with traits and characteristics that are transmitted from parents or other ancestors to offspring. This can be of great concern in breeding lines and influences the determination of removing an animal from the genetic pool. Interference, including genetic and developmental ones, with neural crest cells migrating to branchial arches can result in craniofacial abnormalities. While odontoblasts also develop from the neural crest, the ectoderm of the first pharyngeal arch is also involved, so a wide variety of abnormalities may arise [2]. These may include variations in size, number, length, shape, or lack of development of the teeth, jaws, periodontium, or orofacial supporting tissues. Defects in any of these components may affect occlusion or their presence may not affect occlusal function at all. Numbers of teeth, either too few or too many, can all have effects on the occlusal pattern. With the jaws, the length, size, and development can all affect occlusion. Almost any alteration in morphology of the teeth, jaws, or supportive tissues, pattern or chronology of primary tooth exfoliation, lack of primary tooth exfoliation, and pattern, direction, or chronology of eruption of primary or permanent teeth may result in some form of orthodontic disturbance. Brachycephalic dogs with chondrodystrophy results in the underdevelopment of the base of the skull and tooth crowding is frequently found [3]. Macroglossia, a tongue that is too large, may place pressures on the lingual surface of the teeth, forcing them facially and out of position, while microglossia, a tongue that is too small, may allow the dental arch to collapse lingually. A short frenulum may lead to altered tongue posturing, which may release or apply pressures to lingual tooth surfaces. Excessively loose lips may fail to place appropriate pressures to the facial surfaces of the teeth, thereby allowing a facial or even a mesial drift of the teeth [4]. On the other hand, a tight lip, a condition of lip attachment too close to the dentition, can place excessive facial surface pressures on the teeth and jaw, resulting in linguoversion of teeth and even a shortened jaw in the effected arch [5]. Systemic influences include two groups, pre‐natal (congenital) and post‐natal (developmental). Pre‐natal problems differentiate from hereditary ones in that heredity implies a genetic origin, whereas congenital ones can be caused by various influences during pregnancy. Post‐natal problems encompass defects that develop from exposure to a systemic influence after birth, including nutritional disturbances, infectious diseases, endocrine imbalances, radiation effects, and chemical exposures. Any of these factors may alter development of the teeth or the orofacial complex. Local influences are those stimuli that may affect the orofacial complex, such as an injury that causes loss of teeth, in that the loss of the teeth allows changes in the orofacial complex to occur. Early loss of any primary or permanent tooth may allow migrational changes. Delayed loss of primary teeth can result in impactions and/or crowding. The local influence of periodontal destruction and tooth loss can affect surrounding tissues. Cysts, tumors, and other growths also can have a dramatic impact on the area [6]. Behavioral habits from cage biting, bruxing, chewing habits, and suckling habits may all likewise alter the complex [7]. Management of the local influences is necessary for successful orthodontic management. There are many pathologic possibilities, both short and long range, that may develop from untreated malocclusions. These unfavorable consequences vary with species, but include problems with mastication, temporomandibular joint (TMJ) function, caries formation, incidence of periodontal disease, effects on dentofacial growth and development, soft tissue trauma, traumatic dental fractures, and dental attrition. Each of these is a legitimate reason to initiate orthodontic treatment. Orthodontic treatment should be biologically based for a harmonious occlusion, rather than cosmetic orientation of teeth. Before attempting to assess animal occlusions, a basic understanding of the establishment of normal standards for species and breeds, as well as the nature of malocclusions, is necessary. There are three basic skull and jaw types dealt with, which may be either breed or individual specific. Dolichocephalics are individuals with long narrow facial profiles, such as Collies and Grayhounds. The brachycephalics have a short broad facial profiles, such as Boxers and Bulldogs. The mesocephalics have a more balanced facial profile somewhere between the two previously mentioned, such as in the Beagle and German Shepherd. Certain breeds (i.e., Boxers, Bulldogs, etc.) have a pronounced mandibular mesioclusion (Class III) according to dental and medical standards, but according to breed standards their occlusion is acceptable, within a certain range. When discussing occlusions there are some terms of which a general understanding may be needed at times. The American Veterinary Dental College has provided distinct definitions and examples of malocclusions on the website: http://avdc.org/nomenclature.html#occlusion. The abbreviations concerning occlusion and orthodontics can be found in Table 19.1. Table 19.1 AVDC nomenclature abbreviations (http://avdc.org/nomenclature.html#occlusion). An ideal occlusion can be described as perfect interdigitation of the maxillary and mandibular teeth. In the dog, the ideal tooth positions in the arches are defined by the occlusal, interarch and interdental relationships of the teeth of the archetypal dog (i.e., wolf). This ideal relationship with the mouth closed can be defined by the following. The maxillary incisor teeth are all positioned rostral to the corresponding mandibular incisor teeth (Figure 19.1). The crown cusps of the mandibular incisor teeth contact the cingulum of the maxillary incisor teeth. The mandibular canine tooth is inclined labially and bisects the interproximal (interdental) space (diastema) between the opposing maxillary third incisor tooth and canine tooth. The maxillary premolar teeth do not contact the mandibular premolar teeth (Figure 19.2). The crown cusps of the mandibular premolar teeth are positioned lingual to the arch of the maxillary premolar teeth. The crown cusps of the mandibular premolar teeth bisect the interproximal (interdental) spaces rostral to the corresponding maxillary premolar teeth. The mesial crown cusp of the maxillary fourth premolar tooth is positioned lateral to the space between the mandibular fourth premolar tooth and the mandibular first molar tooth. Figure 19.1 Normal occlusion in a dog – rostral view. Source: Copyright AVDC®, used with permission from https://www.avdc.org/Nomenclature/Nomen‐Occlusion.html; accessed November 2017. Figure 19.2 Normal occlusion in a dog – buccal view. Source: Copyright AVDC®, used with permission. Figure 19.3 Mandibular distoclusion (Class 2) in a dog: (a) ventral view; (b) buccal view. Source: Copyright AVDC®, used with permission. Figure 19.4 Mandibular mesioclusion (Class 3) in a dog: (a) rostral view; (b) buccal view. Source: Copyright AVDC®, used with permission. Maxillary–mandibular asymmetry describes skeletal malocclusions that can occur in a rostrocaudal, side‐to‐side, or dorsoventral direction. Maxillary–mandibular asymmetry in a rostrocaudal direction occurs when mandibular mesioclusion or distoclusion is present on one side of the face while the contralateral side retains normal dental alignment. Maxillary–mandibular asymmetry in a side‐to‐side direction occurs when there is loss of the midline alignment of the maxilla and mandible. Maxillary–mandibular asymmetry in a dorsoventral direction results in an open bite (OB), which is defined as an abnormal vertical space between opposing dental arches when the mouth is closed. The expression “wry bite” is a layman term that has been used to describe a wide variety of unilateral occlusal abnormalities. Because “wry bite” is non‐specific, its use is not recommended. Scissors bite is the normal relationship of the maxillary incisors overlapping the mandibular incisors whose incisal edges rest on or near the cingulum on the lingual surfaces of the maxillary incisors. Overbite or vertical overlap is the extension of the maxillary teeth over the mandibular in a vertical direction, when opposing teeth are in contact and in centric occlusion. Overjut, overjet, and horizontal overlap are also all basically the same thing. They are the facial projection of the maxillary teeth anterior or posterior teeth beyond their antagonist in a horizontal direction. Level bites are when the incisor teeth meet edge to edge (edge to edge bite) or the premolars or molars occlude cusp to cusp (end to end bite). This is a traumatic occlusion for the teeth, which can cause attritional wearing down of the teeth into a closed bite. Open bites are when a part or all of the teeth are prevented from closing to normal occlusal contact. Rostral open bites in the incisal region are the most universal and are seen commonly in association with unilateral occlusal abnormalities. Caudal open bites are seen most commonly in association with traumatic CB/Cs. Full open bites are seen most often in traumatic conditions of partially avulsed caudal teeth or CB/Cs. Closed bites are those that when the bite is in static occlusion the dental arches close too far. This typically is seen when excessive wear of the teeth occurs allowing excessive closure of the occlusion. Tipping, inclinations, and versions: describes a tooth in which the crown is tipped or inclined in an abnormal position. Version is a term that can also be used to describe malposition of one or more teeth. Displacement describes a tooth in which both the crown and root have moved principally in the same direction, which is sometimes described as an occlusion (i.e., mesial occlusion). Malocclusions in young dogs and cats with deciduous dentitions, which are best termed deciduous malocclusions, are not unusual. Fairly mild malpositioning of the jaw positions could be due to a temporary disproportionate relationship caused by an independent jaw growth surge. If left on its own, there is a chance that the opposing jaw will soon experience its own surge in growth to return it to the correct relationship, if genetically coded to do so. Maturation usually evens out this unique growth pattern between the jaws, with the mandible typically experiencing the later growth of the two. One problem that can result in the interim, however, is the abnormal or malevolent interlocking of deciduous teeth in a relationship opposite to their norm, or having impingement on soft tissue. One of the most common deciduous malocclusions is where the mandible grows excessively and the incisors become rostral (labial) to the maxillary incisors. While this is certainly anticipated in brachycephalic breeds, in others this interlock may have serious consequences. With a mechanical interference such as this, maxillary growth could be hindered, keeping the jaw relationship abnormal. If still in this position when the permanent maxillary incisors begin to erupt, especially if the maxillary deciduous incisors are retained, they will come in even further lingually. Deciduous mandibular canines that are contacting or indenting into the palate or other soft tissue should have treatment as soon as the condition is identified (linguoversion). With a firm holding indentation into the palate, not only can these teeth interfere with the forward growth of the mandible (even to the point of the mandible “bowing” downward) but they can also disrupt the normal lateral growth, exacerbating the width discrepancy problem (Figure 19.5). Figure 19.5 Deciduous malocclusion – linguoversion mandibular canines that are contacting the palatal mucosa. Grossly abnormal dentitions may require exodontia just to provide the patient with a functional or comfortable malocclusion. This is typically either genetic or the result of facial trauma effecting bone growth. Trauma problems vary greatly, but facial bites by the mother or littermates have been seen to cause this problem. The aims of orthodontic treatment are to provide a reasonably functional, esthetic, stable, and harmonious occlusion by altering the position or presence of the natural teeth. To attain these aims, in veterinary orthodontics there are four goals to strive to accomplish. These are: Interceptive orthodontics is generally considered to be the extraction or recontouring (crown reduction) of primary or permanent teeth that are contributing or will contribute to alignment problems of the permanent dentition. Interceptive measures are not always successful due to time interval limitations and/or hereditary influences that cannot be overcome. In these situations, interceptive orthodontics or selective extraction of the deciduous teeth that are “caught” will help to relieve this interlock and not impede any future jaw growth. The extractions ideally are done as soon as possible, between four and eight weeks of age (no later than 12 weeks), to allow any potential normalization of the growth pattern prior to eruption of the successional teeth and re‐interlocking of the bite pattern. Selection of teeth to be extracted as well as the timing of the extractions is crucial to the occlusal outcome. The extraction technique may influence the health and eventual appearance of the unerupted permanent teeth. If the hereditary influence is for a specific jaw malocclusion, this procedure will not change the outcome. It will only make a difference in those individuals with genetic potential for a normal occlusion. Particularly in younger animals, the process of exodontia should be carried out with extreme caution to minimize the potential damage to the adjacent permanent tooth buds. Gingival flaps or epithelial attachment severing are best performed gently. Elevators used to fatigue the periodontal ligament (PDL) should be small and delicate, and utilized with minimal pressure, preferably on the sides of the tooth that are furthest from the permanent bud. Excessive force or gouging should be avoided and extraction forceps should only be used to remove an extremely loose tooth from its attachment. Any fractured or retained roots tips should be retrieved if possible, especially in interceptive orthodontic cases, as the root can still deflect the permanent tooth’s eruption. Extraction of retained deciduous teeth usually occurs once the permanent tooth has begun eruption, so damage to its formative stages is less likely. When considering deciduous extraction, the owner should always be informed that while reasonable precautions are being taken to minimize potential damage to the developing permanent teeth, problems may still occur. These vary from minimal pitting of the enamel to major structural defects (gouging, disruption of the crown/root junction) to complete relocation of the tooth [8]. With skillful care and appropriate protocol the risk and degree of complications can be greatly reduced. Preventive orthodontics is the evaluation and elimination of conditions that may lead to irregularities in the developing or mature occlusal complex. Preventive orthodontics basically break down into three categories: occlusal assessment and supervision, space control, and behavioral control. Occlusal assessment and supervision includes the supervision of timely primary dental exfoliation and permanent dental eruption. Even though exfoliation and eruption supervision is considered preventive, the actual act of assisting exfoliation or eruption is an interceptive orthodontic action. The act of occlusal assessment and supervision is classified as a part of preventive orthodontics, but the treatment of the assessed problem may fall into interceptive, preventive, or corrective categories. Space control includes treatment of traumatic, congenital, or hereditary anomalies, as well as dentally destructive diseases (caries, dental resorption, periodontal disease, etc.) and maintenance of dentally voided spaces. Behavioral control deals with therapy to manage deportment, which can affect occlusion. Corrective orthodontics has two stages: active treatment and retention. The active treatment refers to the application of devices to restore dental occlusion to a reasonably functional and esthetics state. Prior to undertaking such an action the animal’s occlusion should be evaluated, as well as the effects of various apparatuses that may be selected on the dentofacial complex. Once the active treatment stage is completed, it is necessary to have the teeth stabilized in their new position to allow a harmonious state to develop, which is termed the retention stage. During active treatment the alveolar bone is induced into a state of accelerated resorption and deposition. The retention stage allows this bone to return to a more normal physiologic state, while hopefully allowing the bone to eventually provide a sound harmonious tooth support structure. The device that provides the retention is called the retainer. Retainers can be either fixed or removable, but in veterinary orthodontics the fixed retainer is more typical. Occasionally mild cases of Class II or III malocclusions are treated for cosmetic reasons, which is termed orthodontic camouflage treatment. Diagnosis and treatment planning is principally based upon visual assessment accompanied by certain aids [3]. These aids help to improve the evaluation to reduce the chance of unexpected and possibly disastrous consequences. There are five basic diagnostic tools in veterinary orthodontics. These are history, physical and oral examination, photographs, dental models and bite registrations, and radiographs. Written records and history is always important, but in orthodontics they are essential in the determination of progression and response to treatment. History provided by the owner can be helpful, but must be screened carefully due to their lack of understanding of terminology and dental normals. All aspects of previous illnesses and accidents and their treatment are important. Information concerning the line and family can be extremely useful in attempting to classify an anomalous condition as hereditary. Nothing can take the place of a good physical and oral examination in assessment of occlusion. Only first‐hand viewing of the true dental articulation can give a reasonable evaluation of the range of motion, potential attritional wear, and interferences to tooth movement. Many TMJ dysplasias can be felt or heard. Oral soft tissue health is best evaluated by visual and tactile senses. Photographs provide records of before and after treatment. Dental models and bite registrations of a patient’s dental arches and supporting tissues are an excellent source for study of abnormalities and treatment planning. The bite registration allows for a reasonable articulation of the models. With these models, orthodontic appliances can be deliberated, designed, and fabricated. Radiographs allow analysis of potential complications to treatment and from treatment. Abnormalities and lesions must be considered prior to treatment. Resorptive lesions, caries, periodontal disease, missing teeth, unerupted teeth, root abnormalities, degree of root maturity, quality of alveolar bone, etc., must all be taken into consideration, and radiology is the best tool to address many of these. Cephalometrics and computer treatment simulations are very impressive. However, the lack of cephalometric standards in animals makes this tool unreliable. Computerized treatment simulations in animal dentistry is at this time more of a toy than a tool, but will eventually be an important diagnostic device. Ideally, orthodontic treatment should be initiated as soon as possible, once favorable conditions exist for assisting orthodontic procedures. Young bone is less resistant to tooth movement, young tissues are generally more forgiving, and young animals typically accept placement of oral appliances more easily than mature animals. Tooth movement is easier to produce in younger animals due to the fact that their cells are in an active growth phase and readily adapt to changes, whereas there is a more sluggish cellular response in older individuals. Also, with interceptive orthodontic procedures involving deciduous extractions, early institution of treatment is essential for optimal effect. However, the advantages are offset to a degree due to the fact that making an accurate diagnosis becomes more difficult the younger the animal. Additionally, treatments to animals with deciduous or mixed dentition may have to be repeated for the permanent dentition, and adjustments to young permanent dentition may require prolonged supervision for retention or retreatment due to drift or recoil. Most interceptive extractions must be delayed until the teeth have erupted or until adjacent teeth will not be injured in the process. A complete treatment plan must include the control of any active dental or oral disease [9]. Periodontitis or active periodontal disease must be controlled prior to orthodontic treatment, as orthodontic tooth movements (OTMs) superimposed on periodontitis can lead to the inevitable destruction of the periodontium [10, 11]. Once controlled, the disease should continue to be treated even during orthodontics, as research in humans has shown that regular professional treatment can halt or even reverse attachment destruction [12, 13]. Clinical research has shown that orthodontic treatments in both normal and compromised periodontal tissues can be completed without loss of attachment, providing that appropriate treatment and optimal oral hygiene had been initiated prior to and during tooth movements [11, 14]. The changes that allow OTM is a biological response that is primarily a PDL process impacting a bony response, but also including growing areas distant from the dentition [15]. It is the external forces that can be managed by the practitioner, by providing the least amount of force needed to result in appropriate treatment with the lowest levels of complications or discomfort for the patient [16]. Cellular response depends upon the degree and duration of applied force. Estimation of the root surface area is important in determining anchorage and force application. In the dog some research has been done on root surface areas of the maxillary fourth premolar and mandibular first molar [17, 18], but there are variations within breeds and from individual to individual. In the first edition the authors attempted to provide some approximations of the dog root surface area to act as a general guide (Table 19.2). While these values are just approximations, they correlate with the two studies that showed a mean root surface area for a maxillary fourth premolar was 562.8 ± 124.9 mm2 and for the mandibular first molar was 497.1 ± 116.2 mm2 [17, 18], which are similar to the values for a dog up to 50 pounds in the table. When a light to mild force is applied, it acts as a stimulus to initiate cellular activity resorption and deposition of bone, which is termed the physiologic movement. When these pressures are exceeded with a heavy force there will be necrosis of periodontal tissues on the pressure side and poor to no deposition of bone on the traction side, which is labeled pathologic movement. Table 19.2 Approximate tooth root surfaces of the dog in square centimeters in relation to the relevant weight of dog. Much discussion and study has centered around the concept of the optimal force magnitude, to the extent that wide variations in the data collected have resulted in the conclusion that the optimal force may differ for each tooth and individual patient [19]. There are several proposed models for the relationship between the magnitude of applied force and rate of OTM, including an “on–off switch” model where movement occurs once a certain level of force is reached and continues at the same level of movement beyond that point [20]
Occlusion and Orthodontics
19.1 Introduction
19.2 Ethical Standard of Orthodontics
19.3 Etiology
19.3.1 Heredity
19.3.2 Systemic Influences
19.3.3 Local Influences
19.4 Sequelae of Malocclusion
19.5 Evaluation of Occlusion
19.6 Occlusion Terms
19.6.1 AVDC Occlusion Nomenclature
CB
Crossbite
CB/C
Caudal crossbite
CB/R
Rostral crossbite
CR
Crown
CR/A
Crown amputation
CR/XP
Crown reduction
D
Diastema
D/O
Open diastema
DC
Diagnostic cast
DC/D
Die
DC/SM
Stone model
DT
Deciduous tooth
DT/P
Persistent deciduous tooth
IM
Detailed imprint of hard and/or soft tissues (e.g., individual teeth or palate defect)
IM/F
Full‐mouth impression (i.e., imprints of teeth of upper and lower dental arches)
IP
Inclined plane
IP/AC
Acrylic inclined plane
IP/C
Composite inclined plane
IP/M
Metal (i.e., lab‐produced) inclined plane
MAL
Malocclusion
MAL1
Class 1 malocclusion (neutroclusion; dental malocclusion with normal upper/lower jaw length relationship)
MAL1/BV
Buccoversion
MAL1/DV
Distoversion
MAL1/LABV
Labioversion
MAL1/LV
Linguoversion
MAL1/MV
Mesioversion
MAL1/PV
Palatoversion
MAL2
Class 2 malocclusion (mandibular distoclusion; symmetrical skeletal malocclusion with the lower jaw relatively shorter than the upper jaw)
MAL3
Class 3 malocclusion (mandibular mesioclusion; symmetrical skeletal malocclusion with the upper jaw relatively shorter than the lower jaw)
MAL4
Class 4 malocclusion (asymmetrical skeletal malocclusion in a caudoventral, side‐to‐side, or dorsoventral direction)
MAL4/DV
Asymmetrical skeletal malocclusion in a dorsoventral direction
MAL4/RC
Asymmetrical skeletal malocclusion in a rostrocaudal direction
MAL4/STS
Asymmetrical skeletal malocclusion in a side‐to‐side direction
OA
Orthodontic appliance
OA/A
Orthodontic appliance adjustment
OA/AR
Arch bar
OA/BKT
Bracket, button, or hook
OA/CMB
Custom‐made OA/BKT
OA/EC
Elastic chain, tube, or thread
OA/I
Orthodontic appliance installment
OA/R
Orthodontic appliance removal
OA/WIR
Orthodontic wire
OR
Orthodontic recheck
OS
Orthognathic surgery
19.6.2 Terms of Malocclusion
19.6.2.1 Skeletal Malocclusions (Symmetrical)
19.6.2.2 Asymmetrical Skeletal Malocclusions
19.6.2.3 Dental Malocclusions
19.6.3 Additional Terminology
19.6.4 Malpositioning of Teeth Terms
19.6.5 Version Terms
19.6.6 Displacement Terms
19.6.7 Deciduous Malocclusions and Orthodontics
19.7 Aims of Orthodontic Treatment
19.8 Categories of Orthodontic Treatment
19.8.1 Interceptive
19.8.1.1 Deciduous Tooth Extraction
19.8.2 Preventive
19.8.3 Corrective
19.9 Diagnostic Aids
19.10 Age, Timing, and Treatment
19.11 Physiologic and Histologic Aspects of Tooth Movement
<10 lb
<25 lb
<50 lb
<90 lb
Maxillary
First incisor
0.7
1.0
1.3
1.7
Second incisor
0.8
1.2
1.5
1.9
Third incisor
1.2
1.6
2.25
2.6
Canine
3.4
5.4
7.8
9.5
Fourth premolar
2.5
4.15
5.25
6.75
First molar
1.5
2.25
3.25
4.25
Mandibular
First incisor
0.6
0.9
1.2
1.6
Second incisor
0.7
1.2
1.5
1.8
Third incisor
0.9
1.4
1.7
2.0
Canine
3.3
5.25
7.65
9.25
Fourth premolar
1.3
1.9
3.25
3.75
First molar
2.6
3.8
4.75
6.00
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