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INTRODUCTION ETIOLOGY SYMPTOMS OF CLASS III MALOCCLUSION FUNCTIONAL AND CEPHALOMETRIC ANALYSIS CEPHALOMETRIC CLASSIFICATION OF MALOCCLUSION TIMING OF CLASS III MALOCCLUSION TREATMENT OF TYPE A CLASS III TREATMENT OF TYPE B CLASS III TREATMENT OF TYPE A AND B CLASS III BIOMECHANICS AND GENERAL ASPECTS OF PERMANENT DENTITION TREATMENT RETENTION OF CLASS III www.indiandentalacademy.com
The true genetic Class III growth pattern is the opposite of the most common orthodontic problem which is retrusion of the lower jaw. In the Class III the lower jaw is protrusive and it may be mistakenly referred to as an "under bite". In reality, the lower jaw is too long relative to the rest of the face, and the chin appears to protrude too far in front of the rest of the face. The true Class III is a genetically directed problem which may express itself at an early age, but usually becomes more apparent as the child approaches the teenage growth spurt. Generally, we will find a parent or grandparent with the exact same problem on one side of the family. www.indiandentalacademy.com
The true Class III is not an all or none problem. There are varying degrees in the amount of abnormal growth which can occur in the lower jaw. Once the lower teeth move out in front of the upper incisors, the muscles influence their position and the size of the chin comes into play to determine how "bad" the condition looks.
According to ANGLE class III malocclusion is defined as class III molar relation with the mesio – buccal cusp of the maxillary first permanent molar occluding in the inter dental space between the mandibular first and second molars. Or lower permanent molar is ahead of the upper first molar by a distance of the width of a premolar or half the width of a molar.
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Although it is difficult to know the precise cause of most malocclusions, we do know in general what the possibilities are, and these must be considered during treatment. 1.TERATOGENS: Cleft lip and palate result in maxillary deficiency in most occasions a class III malocclusion is established. Teratogens causing cleft lip and palate are aspirin, cigarette smoke (hypoxia), Dilantin, 6Mercaptopurine, valium etc Vitamin D excess causes premature closure of sutures and might lead to class III malocclusion. www.indiandentalacademy.com
2. ACROMEGALY AND HEMI MANDIBULAR HYPERTROPHY: Acromegaly is caused by anterior pituitary tumour that secretes excessive amount of growth harmone. Here excessive mandibular growth occurs creating a skeletal class III malocclusion. Often the mandibular growth accelerates to levels seen in the adult growth spurt, years after the adolescent growth spurt is completed. The reason for hemimandibular hypertrophy is unknown. Formerly called condylar hypoplasia it is know called a hemi mandibular hypertrophy as a body of mandible is affected. This condition leads to a class III with asymmetry www.indiandentalacademy.com
3. GENETIC INFLUENCES: Best known examples of genetic influences are the classic HAPSBURG JAW and the prognathic mandible of Austrian royal family. The influence of inherited tendencies is strong for mandibular prognathism in particular (most inherited condition followed by long face pattern which is second. Litton et al (ajo 1970) concluded that one third of a group of children who presented with a severe class III malocclusion had a parent with the same problem and one sixth had an affected sibling.
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4.ENVIRONMENTAL INFLUENCES: Large tongue as in the case of thyroid deficiency can contribute to a mandibular prognathism by causing the mandible to be positioned forward all times. Rakosi and Schilli suggested mouth breathing in the etiology of class III malocclusions. They hypothesized that excessive mandibular growth could arise as a result of abnormal mandibular posture because constant distraction of the mandibular condyle from the fossa may be a growth stimulus.
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5.The posterior ‘squeezing out’ effect of molar crowding There has been discussion of posterior crowding as a factor in the development of Class III malocclusions. The theory suggests that a squeezing out effect can occur because of crowding in the molar regions, which can contribute to an anterior open-bite malocclusion in a mandible with poor vertical growth in the ramus area . Alternatively, good ramus growth can lead to a Class III malocclusion. This concept is not well understood, and has not been fully investigated
The incidence of skeletal Class III malocclusion in the white population is approximately 5%. The mid face deficiency is high in Asian population which increases the frequency of malocclusion. The incidence of this malocclusion ranges between 4%and 13% among the Japanese and 4% and 12% among the Chinese. A lesser incidence of class III malocclusion is seen among African- Americans. The incidence has been reported to be significantly higher in the Scandinavian and Japanese populations.
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Early signs of true progressive mandibular prognathism occasionally can occur in infancy. In the first months of life a sequential development of the class III condition may be observed as: Eruption of the maxillary central incisors in a lingual relationship and the mandibular incisors in a forward position with no overjet. Development of an incisal crossbite during the eruption of the lateral incisors into a normal relationship. www.indiandentalacademy.com
Full incisor cross bites some weeks later. Flattening of the tongue as it drops away from the palatal contact and postures forward, pressing against the lower incisors Habitual protraction of the mandible by the child into the protruded functional and morphologic relationship
The configuration and form of the forehead and nose in relation to the lower face are significant for esthetic evaluation and prognosis. A well formed Naso labial angle is important for esthetic improvement. If the angle is acute, the premaxilla segment can be retracted if the angle is obtuse; the segment must be protracted to improve facial esthetics. The soft tissue of the chin can compensate for or accentuate a skeletal class III relationship depending on its thickness. Gingival retraction or dehiscence can often be seen in early class III malocclusion. This damage is irreversible and is an indication for early treatment
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The next step is examination of the dentition, including the morphology and number of teeth. Congenital absence in the maxilla (e.g., missing canine or first premolar teeth) makes treatment more difficult. When evaluating tile axial inclination of the teeth, certain disadvantageous irregularities such as labial tipping of the upper incisors and lingual tipping of the lower incisors still in anterior cross bite should be noted. A concavity of the lingual alveolar structure in the mandible also is a clue to future difficulties in the correction of Class III malocclusion.
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Crowding of maxillary teeth also enhances treatment problems; treatment may require extraction of the counterpart teeth in the lower arch, leading to great difficulty in closing spaces and maintaining proper incisor axial inclination. To make treatment easier if extractions are required, the clinician should perform extractions in the mandible before proceeding to those in the maxilla. Depending on the state of development, enucleation or germectomy may be feasible for the lower first premolars. The molar occlusal relationship is usually Class III, but the plane of occlusion also should be evaluated because its correction may be necessary before surgery www.indiandentalacademy.com
The path of closure is from the postural rest position to occlusion must be carefully studied. The mandible may slide anteriorly into a forced protrusion because of premature contact and tooth guidance when the jaw closes into full occlusion. Such anterior displacements have more favorable prognosis. In contrast, patients with problems caused by an anterior rest position with respect to habitual occlusion are difficult to treat and usually require orthognathic surgery.
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In addition to this pseudo-forced bite category also exists. This is a skeletal class III with a dental compensation arising from labial tipping of the upper incisors on a deficient maxillary base and lingual tipping of the lower incisors on an excessively long mandible. Orthodontic pre surgical treatment must decompensate these malpositions before surgical procedures can be performed.
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If the condyle occupies the most posterior position in the temporal fossa the likelihood of its riding over the posterior periphery of the articular disk is increased with concomitant clicking and lateral crepitus,. Abnormal tongue function, size and posture must be considered. The tongue may be postured low in the mouth and be flat and elongated, especially in cases of mouth breathing. In cases of Macroglossia the tongue is not contained within the dentition and the scalloping effect of the tooth contact may be visible on the periphery. www.indiandentalacademy.com
A short hypotonic retrusive upper lip is often seen in combination with a heavy, redundant, everted lower lip. A closed lip position will produce the appearance of a long lower lip, as the lip elongates to close over the class III incisor relationship. The closed lip length is misleading and should not be used for treatment planning. Relaxed lip appearance is deceiving due to hypotonicity of lower lip --- this causes elevation and apparent lengthening. The lower lip length should be verified with the lower incisor tip to soft tissue menton which is not influenced by posture www.indiandentalacademy.com
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Maxillary retrusion is associated with upper lip retrusion and a straight maxillary sulcus curve. Upper lip retrusion is treated with labial crown torque.
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An increased gonial angle Antegonial notching Backward direction of condylar growth Thin mandibular symphysis Compensation in position of upper and lower incisors in response to disproportionate jaw growth. Mandibular incisors are retroclined as child becomes older there roots tend to press against the labial plate producing a WASH BOARD EFFECT. Maxillary incisors are usually flared anteriorly.
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Several studies have expanded on these findings in an attempt to compare Class III malocclusion with Class I controls relative to the morphology of the maxilla, the mandible, and the cranial base. These differences include the following:
1. The SNA angle is significantly lower in the Class III samples, indicating a greater degree of maxillary retrusion. 2. Mandibular protrusion is greater in the Class III samples. 3. The mean ANB angle in the Class III samples is negative. www.indiandentalacademy.com
4. The gonial angle is more obtuse in the Class III samples. 5. The mandibular plane angle is steeper than normal in the Class III samples. 6. Lower anterior face height is significantly greater in the Class III samples. 7. The sella angle and articular angle were smaller in class III samples. 8. Anterior position of the mandible is seen.
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CLASS III MALOCCLUSION CAUSED BY A DENTO ALVEOLAR MALRELATIONSHIP No basal sagittal discrepancy is apparent The sub spinale -nasion-supra mentale (ANB angle) is within normal limits. Maxillary incisors tipped lingually and mandibular incisors tipped labially
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CLASS III MALOCCLUSION WITH A STRONG MANDIBULAR BASE 1. Mandibular base and ascending ramus are large 2. SNA angle is normal 3. SNB angle is larger than normal. 4. ANB angle is negative 5. Gonial angle is usually large 6. Articular angle is usually small. 7. Anteriorly positioned mandible 8. The tongue is postured forward and lies low in the mouth 9. The upper incisors are tipped labially 10. The lower incisors are inclined lingually 11. Lateral cross bites are often evident 12. Maxillary arch appears to be narrowed. www.indiandentalacademy.com
CLASS III MALOCCLUSION WITH AN UNDER DEVELOPED MAXILLA 1. Maxillary base is small and retrognathic 2. Smaller SNA angle 3. Normal SNB angle 4. Mid face deficiency and some cases of associated cleft palates are seen
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CLASS III MALOCCLUSION WITH A COMBINED UNDERDEVELOPED MAXILLA AND A PROMINENT MANDIBLE SNA angle is small and maxillary base is short SNB angle is large and the mandibular base is large
In a patient with short ramus: 1. Growth pattern is vertical and the gonial angle is large. 2. Often open bite is seen 3. Crowding in the upper arch
In a patient with long ramus: 1. Growth pattern is horizontal and gonial angle is small 2. Reversed over bite is apparent
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CLASS III MALOCCLUSION WITH A PSEUDO FORCED BITE OR ANTERIOR DISPLACEMENT  The condition known as class III skeletal dysplasia is partially compensated by the labial tipping of the upper incisors and the lingual inclination of the lower incisors  This tooth mal position results in additional anterior guidance of the mandible on the path from postural rest to the habitual occlusion as the lingual aspect of the lower incisors rides on the maxillary incisor margins after initial contact
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Moyer’s suggested pseudo–Class III malocclusion as a positional mal relationship with an acquired neuro-muscular reflex. Pseudo–Class III malocclusion has been identified with anterior crossbite as a result of mandibular displacement. Premature contact between the maxillary and mandibular incisors results in forward displacement of the mandible in pseudo Class III malocclusion so as to disengage the incisors and permit further closure into the position in which the posterior teeth occluded. Several reports attributed the incisor interference to the retroclined upper incisors and proclined lower incisors in pseudo–Class III malocclusion. Based on clinical assessment, Turley and Lin reported that pseudo Class III malocclusion showed some degree of hereditary tendency www.indiandentalacademy.com
Habitual occlusion
Centric relation www.indiandentalacademy.com
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Clinical Examination (RABIE 2000 AJO) Clinical examination of pseudo–Class III malocclusion revealed that 75% of the examined cases showed a mesial step, which corresponds to Angle’s Class I at HO and showed a normal relationship of the primary molar that is a flush terminal plane at CR. Diagnostic characteristics of pseudo–Class III malocclusion could be summarized as: Majority showed no family history. Class I molar and canine relationships at HO and Class II or end to end relationship at CR. Decreased midface length. Forward position of the mandible with normal mandibular length. Retroclined upper incisors and normal lower incisors. Retrusive upper lip. www.indiandentalacademy.com
Early correction of mandibular Displacements These should be identified at dental age 8 or 9, soon after the permanent incisors erupt. This incisor relationship has the potential to restrict maxillary development and encourage mandibular growth, thereby worsening the Class III problem. This is similar to the effect of a functional appliance in Class II treatment. Normally, such displacements can be corrected by simple tooth movements, and it is important for treatment to be provided at an early age. Subsequently, unrestricted maxillary development can resume, and if the condyles are centered in the fossae, this will eliminate the potential ‘functional appliance’ effect of the original mandibular displacement. www.indiandentalacademy.com
Maxillary retrognathism Growing patients who present with maxillary retrognathism should be considered for early expansion and development of the maxilla. This may involve the use of rapid maxillary expansion and a reverse headgear. Subsequently, a palatal bar can be used to stabilize the skeletal change, and then full fixed appliance treatment can be commenced at approximately 12 years of age. Borderline surgical cases In some cases with mandibular excess, the diagnosis will suggest that mandibular surgery may be needed. It is helpful to delay orthodontic treatment for such cases, if possible. This will allow assessment of growth patterns, using regular cephalometric radiographs, so that a more informed surgical/non-surgical decision www.indiandentalacademy.com
Class III surgical cases Some cases are clearly Class III surgical cases from the outset, and should not be treated until all growth has ceased. Timing will be beyond the age of 20 years in males and a little earlier in females.
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The surgical/non-surgical decision in Class III treatment As with Class III treatment, it is important to recognize those Class III cases which have a major skeletal disproportion, either at the time of assessment, or where there is a probability of unfavorable growth. For such individuals, it will be necessary to consider a surgical/orthodontic solution. Treatment on the basis of orthodontics alone should be delayed, or discarded as a :
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Situation A – A Surgical/ orthodontic correction to an ideal result: Determined that mandibular surgery will be required, then the surgeon will normally wait until all growth has finished, which may be as late as 22 years of age in males. The surgeon will then require the orthodontist to decompensate the incisors. Correction will be achieved by A/P realignment of the mandible and/or maxilla, with transverse correction of the maxilla if necessary. This should lead to an optimal facial and dental result.
A 6-mm mandibular set-back will result in measurements to true vertical line (TVL) which are within 1 SD of the ideal.
Situation B – orthodontic masking of a mild Class III skeletal case. As an alternative to ‘A’ above, if the underlying skeletal discrepancy is mild, it may be decided to follow a treatment plan based on orthodontics alone. This will allow correction to be commenced much earlier, and the patient will be informed of the possibility of late mandibular growth. The orthodontist will then solve the problem by ‘masking’ the underlying Class III discrepancy by dental compensation.
In this theoretical representation, the upper incisors were proclined 2° and the lowers were retroclined 8°.
This will involve proclination of upper incisors and retroclination of lower incisors. Good patient cooperation with Class III elastics and/or a face mask will normally be needed in this type of treatment. This should lead to an acceptable dental and facial outcome without the need for orthognathic surgery.
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Situation C – late mandibular growth: After orthodontic masking of a mild Class III malocclusion, late mandibular growth can occur, especially in males. This is a difficult situation to manage. Sometimes the patient will find the late change in dental and facial outcome acceptable, and seek no further treatment. However, if mandibular surgery is deemed necessary, there is limited scope for facial improvement from the surgery, because of the dentally compensated teeth.
In some cases, late mandibular growth occurs after the type of treatment shown in ‘B’ above. This is difficult to manage.
The incisors will need to be decompensated by orthodontics before surgery, if there is to be an optimal facial benefit from the surgery. The treatment of Class III malocclusions is relatively easy when the problem is confined to the alveolar bone, but when the deformity is in the basal bone such as in a deficient maxilla or overgrowth of the mandible, and then the malocclusion does not respond readily to treatment and tends to recur after treatment.
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The “Doctrine of limitations” was in full swing in the 40”s and 50”s.Early treatment was condemned except for serial extractions. The view that prevailed then was that skeletal alteration was impossible and that the dominance of genetic morphologic pattern was so great that it included unaltered muscle patterns. Further any treatment on the deciduous dentition was held to be so temporary that it had no effect on the permanent dentition. But evidence based researches have led to many favorable conclusions for early treatment. Class III malocclusion, in particular gets the nod from many authors in favor of early treatment .Starting with Tweed, treatment timings can be as early as 4 years of age. www.indiandentalacademy.com
Rickets (AJO 2000) has summarized the main objectives of early treatment lying in five concepts 1. Obtaining a skeletal change (structural) 2. Providing the opportunity of a functional change in the environment 3. Utilization of the individual growth towards the correction. 4. Elimination of the detrimental habits (breathing etc) 5. Taking advantage of the forces of the occlusal development towards the correction.
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Turpin has developed a list of positive and negative factors to aid in deciding when to interrupt a developing class III malocclusion POSITIVE FACTORS: Good facial esthetics Mild skeletal disharmony No familial prognathism Antero posterior functional shift Convergent facial type Symmetric condylar growth Growing patients with expected good cooperation. If the above factors are not present in the patient , they are listed as negative and treatment can be delayed until growth is completed. www.indiandentalacademy.com
Joondeph, after Turpin’s thesis, also pointed out the goals of early intervention: 1. Reduce the skeletal discrepancy and provide a more favorable environment for normal growth. 2. Achieve as much relative maxillary advancement as possible. 3. Improve occlusal relationships. 4. Improve facial esthetics for more psychosocial development. 5. Reduce or simplify, phase II or surgical treatment.
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Another treatment consideration is that extraction therapy may have limited applicability in Class III treatment. For example, we would not want to limit extractions to the lower arch because many times the incisors are generally inclined lingually and extraction treatment tends to increase this inclination, possibly beyond the limits of the lingual plate of bone. Also, extractions may be contraindicated when orthodontic treatment must be combined with surgical treatment.
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Another consideration is that many of the forces in conventional orthodontics carry risks because of the unfavorable growth pattern in patients with Class III malocclusions. For example, many patients with Class III malocclusions have an increased vertical face height, particularly of the lower anterior part of the face, with an open-bite. In these patients, Class III elastics and second-order bends in the posterior regions cannot be used conveniently because the extrusive force components on posterior teeth can open the bite and increase the vertical dimension further. Particular attention must be paid to the use of Class III elastics because they can also extrude the mandibular incisors, and there is frequently excessive vertical dentoalveolar development in the incisor region. Since many of the conventional treatment procedures have limitations, we should consider the use of extra oral traction because appropriate force systems can be placed with fewer deleterious side effects.
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There are three important diagnostic principles which merit attention.  First, it is particularly important to determine whether the mandible, on closure, is in centric relation or in a "convenient" anterior position. The practical implication is that a Class I problem can appear to be a Class III malocclusion (pseudo-Class III malocclusion) when the mandible is forced anteriorly . Even a true Class III malocclusion can appear much more serious if there is an anterior path of closure of the mandible
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Type
Anterior Centric relation and centric position of mandible occlusion Significance
Pseudo-Class III
Present
Not coincident
Problem is less difficult than it appears ( in a Class I) actually.
True Class III
Present
Not coincident
Not coincident Problem is less difficult than it appears
True Class III
Absent
Coincident
Problem is as difficult as it appears
The second principle is that the nature of the skeletal discrepancy must be defined because treatment, to a large extent, is based on this differential diagnosis. Class III malocclusions can be classified as An under developed maxilla---TYPE A An over developed mandible--TYPE B A combination of TYPE A and TYPE B
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Third, a malocclusion reflects the interplay of many conditions that may be impossible to evaluate singularly. One important variable is the potential growth and development of a patient with a Class III malocclusion. In this context, at least two factors may be detrimental and aggravate Class III malocclusions with time. One is the differential growth of the jaws, carrying the mandible more anteriorly relative to the maxilla. Also, local conditions (such as low tongue posture) may adversely influence the growth pattern. Since the amount and the timing of growth of the mandible cannot be assessed accurately, we cannot consider a Class III malocclusion fully resolved until facial growth has ended. www.indiandentalacademy.com
Characteristic of this type in which the maxilla appears retrognathic is a concave profile which represents underdevelopment of the middle part of the face, rather than prominence of the mandible. Treatment should be started early, as early as 4 years of age, for two fundamental reasons. One is that extraoral traction which pulls the maxilla anteriorly functions in the same direction as the direction of development. Second, unlike posterior movement of the mandibular arch, anterior movement of the maxillary arch appears to have a greater chance of remaining stable. With this kind of treatment, we can expect to achieve: www.indiandentalacademy.com
An orthopedic protraction of the maxilla with a strong force (500 to 1,000 Gm per side). This change appears to be limited especially if treatment is started after 6 years of age, An increase in the inclination of the maxillary incisors to obtain a sufficient overjet, associated more or less with Bodily movement of all the teeth in an anterior direction, advancing point A, Both an improvement in function and a more esthetic profile.
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The use of protraction headgear in the treatment of Class III malocclusion was described more than 100 years ago, with other descriptions appearing early in this century. Early orthopedic intervention provides a non surgical alternative in the treatment of Class III malocclusion with maxillary retrusion. Protraction headgear provides directed, forward growth of the maxilla at an early age. An extra oral force of 300 gm or more per side, when applied, can cause significant changes in the circum maxillary sutures and in the maxillary tuberosity. Tension produced within the sutures was believed to cause an increase in vascularity and a concomitant differentiation of the cellular tissues resulting in increased osteoblastic activity. www.indiandentalacademy.com
In an animal study with tantalum implants and oxytetracycline dyes, heavy intermittent maxillary protraction was found to produce forward displacement of the mid face, anterior relocation of the inferior border of the orbit, and gross osseous alterations extending superiorly to the area of the fronto maxillary suture. The study also found that post treatment skeletal rebound was minimal and was observed only during the first month after discontinuation of mechanical forces. Clinically, the maxilla can be advanced 2 to 4 mm over a 12 to 15-month period of headgear treatment. The use of protraction headgear has been shown to be most effective in the full deciduous or early transitional dentition, with less skeletal changes after 9 years of age. A recent longitudinal study suggested that orthopedic effects of protraction headgear on dentofacial structure was possible in young girls as late as during the acceleration phase of pubertal growth spurt.
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DESIGN: The orthopedic facial mask consists of three basic components. The facial mask, a bonded maxillary splint and elastics. The facial mask is an extra oral device composed of a fore head pad and a chin pad that are connected with a heavy steel support rod. To this support rod is connected a cross bow to which are attached rubber bands to produce a forward and downward elastic traction of the maxilla. The position of the pads and the cross bow can be adjusted simply by loosening and tightening set screws within each part of the appliance. The major modification in the appliance is the addition of facial mask hooks in the upper first deciduous molar. In patients in whom treatment is started before the eruption of the upper first molars, the appliance is designed to incorporate the first and second deciduous molars as well s deciduous canines. www.indiandentalacademy.com
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The splint is activated once per day until the desired increase in transverse width has been achieved. In patient in whom no increase in transverse dimension is desired, the appliance still activated for 8-10 days to disrupt the maxillary sutural system and to promote maxillary protraction (HASS 1965) After the patient has been accustomed to wearing the maxillary splint, the facial mask treatment is initiated. The current version of the petit facial mask is one universal size and can be adjusted to fit the facial contours of most patients.
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SEQUENCE OF ELASTICS: At the time of delivery 3/8” 8 oz 2 weeks After 2 weeks 1/2” 14 oz Increased to a max of 5/16” 14 oz Young patients (4-9) years should wear the mask on a full time basis except during meals. Duration is 4-6 months. They can be retained with only night time wear or with a maintenance plate, chin cup or FR III. In older patients, it is worn at all times except during school.
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SKELETAL EFFECTS OF MAXILLARY PROTRACTION ( sutures involved): The maxilla articulates with nine other bones of the craniofacial complex: frontal, nasal, lacrimal, ethmoid, palatine, vomer, zygoma, inferior nasal concha, opposite maxilla, and occasionally sphenoid. Palatal expansion had been shown to produce a forward and downward movement of the maxilla by affecting the intermaxillary and circummaxillary sutures. The disruption of these sutures may help initiating cellular response in the sutures, allowing a more positive reaction to protraction forces.
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Kambara found changes at the circummaxillary sutures and at the maxillary tuberosity attributable to posteroanterior traction, including the opening of sutures, stretching of sutural connective-tissue fibers, new bone deposition along the stretched fibers, and apparent tissue homeostasis that maintained the sutural width. Nanda and Hickory showed how the histologic modifications in the zygomatico maxillary suture after maxillary protraction varied according to the orientation of the force system applied.
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Biomechanical studies on dry human skulls have demonstrated further that the application of an anteriorly directed force results in forward movement of the maxilla. These investigations also showed that the direction of the force is critical in controlling rotation of the upper jaw. A force generated parallel to the maxilla or above the palatal plane produces counterclockwise rotation of the palatal plane.
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BIOMECHANICS: The centre of resistance of the maxilla is located at the distal contacts of the maxillary first molars, one half the distance from the functional occlusal plane to the inferior border of the orbit.( Lee AJO 1997) Protraction of maxilla below the Centre of resistance produces counter clock wise rotation of the maxilla. Also Hata et al (AJO 1987) found using human skulls that protraction forces at the level of the maxillary arch produces forward but counter clock wise rotation unless a heavy downward vector of force was applied.
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A heavy force at 300 -450 gms downward to the occlusal plane is accepted.10 degree of counter clock wise rotation being acceptable .Force levels of 300-500 gms on either side in both primary and mixed dentition is recommended by most authors. Direction of force being downward, the point of application is 5 mm above the palatal plane in the canine region. Hata et al suggested that an effective forward displacement of the maxilla can be obtained with this point of application
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EFFECTS OF THE FACE MASK: 1. The maxillary incisors moved in the anterior direction, whereas the mandibular incisors moved posteriorly. 2. After maxillary protraction, the maxilla was displaced anteriorly, whereas the mandible rotated posteriorly. 3. The mandibular plane angle and anterior lower and total face heights increased. 4. There is no change in SN-palatal plane angle during growth period. 5. These changes were reflected in the profile, whereby the skeletal profile convexity increased and soft tissue facial angle and facial convexity increased; and the Class III concave profile became more balanced, with the upper lip area becoming more marked. www.indiandentalacademy.com
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Position of the posterior nasal spine remained stable Over bite was improved by eruption of maxillary and mandibular molars. Anchorage loss was observed during maxillary protraction with mesial movement of the maxillary molars. An average of 5.68 mm anterior movement of the upper incisors resulted in a significant amount of upper lip protraction. The ratio of upper lip protraction to upper incisor protraction relative to the vertical reference line was 1:1.26. A significant decrease in upper lip thickness to vermilion was caused by the fact that during the treatment period, total anterior movement of the upper incisors was approximately 1 mm more than that of the upper lip. www.indiandentalacademy.com
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A significant decrease in the upper lip sulcus depth can be evaluated as another favorable effect of the appliance on the soft tissue profile. The lower lip moved posteriorly to lie behind the Steiner S line, After the correction of the crossbite in Class III cases, the lower lip most often contacts both lower and upper incisors and would therefore be influenced not only by the retraction of the lower incisors but by protraction of the upper incisors as well. Backward repositioning of the pogonion soft, and slight inhibition of anterior migration of the lower lip was seen. upward and forward rotation of the maxilla occurs when protraction force on molars is applied parallel to the occlusal plane. This type of maxillary rotation can be minimized when the force is applied in the canine area, 20째 to 30째 below the occlusal plane.
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Maxillary advancement, Mandibular rotation, Labial tipping of the maxillary incisors, Lingual tipping of the mandibular incisors, Mesial movement of the maxillary molars, Changes in ANB differences towards a more positive value
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One other aspect of Class III malocclusions is that a retrognathic maxilla is often associated with a narrow maxillary arch which is in bilateral cross-bite. Expansion of the maxillary arch can be done at the same time as protraction of the maxilla (which brings it into a narrower portion of the mandible), or it can be done later. For this purpose, a rapid maxillary expansion appliance is used.
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Rapid maxillary expansion is the corner stone of increasing the transverse dimension in growing individual. In general there are three types of expansions are there to increase the transverse dimension 1.ORTHODONTIC EXPANSION 2.PASSIVE EXPANSION 3.ORTHOPEDIC EXPANSION
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RME is an indication of an orthopedic expansion Indications for RME.
Patients who have lateral discrepancies that result in either unilateral or bilateral posterior crossbites involving several teeth are candidates for RME. The constriction may be skeletal (narrow maxillary base or wide mandible), dental, or a combination of both skeletal and dental constriction. Anteroposterior discrepancies. For example, patients with skeletal Class II, Division 1 malocclusions with or without a posterior crossbite, patients with Class III malocclusions, and patients with borderline skeletal and pseudo Class III problems are candidates if they have maxillary constriction or posterior crossbite. Cleft lip and palate patients with collapsed maxillae . Procedure to gain arch length in patients who have moderate maxillary crowding. www.indiandentalacademy.com
Contraindications for RME. Patients who cannot cooperate with the clinician are not candidates for RME. Patients who have a single tooth in crossbite probably do not need RME. Patients who have anterior open bites, steep mandibular planes, and convex profiles are generally not well suited to RME. Patients who have skeletal asymmetry of the maxilla or mandible, Adults with severe anteroposterior and vertical skeletal discrepancies are not good candidates for RME
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The following factors need to be considered during treatment planning to determine whether to expand the dental arches conventionally or with RME: The magnitude of the discrepancy between the maxillary and mandibular first molar and premolar widths; if the discrepancy is 4 mm or more, one should consider RME, The severity of the crossbite, that is, the number of teeth involved, and The initial angulations of the molars and premolars— when the maxillary molars are buccally inclined, conventional expansion will tip them further into the buccal musculature; and if the mandibular molars are lingually inclined, the buccal movement to upright them will increase the need to widen the upper arch. www.indiandentalacademy.com
The increase in mandibular plane angle with treatment may be due to incomplete compensation of the shortterm downward displacement of maxilla by the vertical growth of the ramus. One year after protraction, the mandibular plane angle decreased, and this value was significantly smaller than that of the untreated group of age 12 . The increase in the mandibular plane angle with treatment may be due to The relapse of the treatment that induces vertical increase of anterior facial height and clockwise rotation of the mandible, and Chin cup effects after protraction.
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Correction of cross bite Increase in arch perimeter (approx .7 times the change in premolar width) Correct cuspal inclinations Improves airway function Encourage more rapid tooth movement in mixed dentition patients Broaden the smile Produces spontaneous correction of class II and class III malocclusions. www.indiandentalacademy.com
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Implant studies in expansion confirmed 50% dental movement and 50% skeletal movement in children and in adolescents only 35% movement was skeletal and 65% was dental. As the patient grows older tipping becomes greater which puts the teeth at higher risk of gingival recession (Lindhe 1989). He stated that “during orthodontic treatment tooth is moved through the envelope of alveolar process at sites with thin and inflamed gingiva and there is a risk that gingival recession may occur.
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The labial plate of bone in maxilla is extremely thin on the facial surface of the teeth. The extensive bodily movement of the incisors in a labial direction through the alveolar bone resulted in a small apical displacement of gingival margin which appeared to thin by tooth movement and reduction of alveolar bone height but no loss of connective tissue attachment was apparent when there were no signs of inflammation . Gingival graft can be used to prevent this gingival recession
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A modified protraction headgear design and the biomechanical considerations of its clinical use are presented by Nanda (1980 AJO). The clinical results show that a modified protraction headgear with a chin cup helps in the correction of moderately severe Class III malocclusions by the anterior displacement of the maxilla and maxillary dentition, and possibly restricting or changing the direction of the growth of the mandible. This headgear can also be used to correct axial inclinations and or mesial displacement of posterior teeth www.indiandentalacademy.com
Mc NAMARA AND SARVER ET AL (AJO 2003) In the cephalometric investigation, authors compared the long-term effects of an initial phase of rapid maxillary expansion and facemask (RME/FM) therapy followed by comprehensive edgewise therapy with the effects of growth in untreated, matched controls. During the post treatment period, the treated and untreated Class III subjects generally grew similarly, although the skeletal relationship of the maxilla to the mandible remained unchanged in the RME/FM group, whereas the controls had an increased skeletal discrepancy of 3.0 mm. Over the long term, there was a slightly greater increase in midfacial length (1.6 mm) in the treatment group than in the controls. www.indiandentalacademy.com
Similarly, the distance from Point A to nasion perpendicular decreased by 1.2 mm in the treated group. The overall increase in mandibular length was 2.4 mm less in the RME/FM group than in the controls, and mandibular projection relative to nasion perpendicular was 3.0 mm less in the treated group. The change in the Wits appraisal was substantial between groups (6.1 mm), with an improvement in the inter maxillary relationship in the treated group (3.4 mm. No clinically significant differences were observed between the groups in the vertical dimension.
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Overjet increased significantly in the treated group relative to the controls (4.4 mm), whereas the molar relationship decreased significantly (–3.9 mm During the post treatment period that includes the pubertal growth spurt, craniofacial growth in RME/FM patients is similar to that of untreated Class III controls. Aggressive over-correction of the Class III skeletal malocclusion, even toward a Class II occlusal relationship, appears to be advisable, with the establishment of positive overbite and overjet relationships essential to the long-term stability of the treatment outcome. www.indiandentalacademy.com
It is an example of passive expansion INDICATION: This appliance has been used during the deciduous, mixed, and early permanent dentition stages to correct Class III malocclusion characterized by maxillary skeletal retrusion, and not mandibular prognathism.
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According to Frankel, the vestibular shields and upper labial pads function to counteract the forces of the surrounding muscles that restrict forward maxillary skeletal development and retrude maxillary tooth position. Frankel has also stated that the vestibular shields stand away from the alveolar process of the maxilla but fit closely in the mandible, thus stimulating maxillary alveolar development and restricting mandibular alveolar development. Frankel reported a study of 74 severe Class III cases treated with the FR-3, comparing these cases to 58 Class II cases treated with the FR-1 appliance. He noted greater forward movement of maxillary landmarks in the Class III cases than in the Class II cases. He also stated that the changes in maxillary position in the Class II cases were minimal in comparison to what would normally occur during growth. He concluded. from this study that the forward development of the maxilla is stimulated by the FR-3 www.indiandentalacademy.com appliance.
Another use of the FR-3 has been suggested by Petit in the treatment of severe Class III cases. Petit advocates the use of heavy orthopedic forces generated by the facial mask to achieve the initial correction of the malocclusion. Further, he suggests that an FR-3 may be used to retrain the maxillary anteroposterior correction and to retrain the associated musculature. Eirew has stated that the FR-3 is an excellent retraining device and aid to muscular reeducation following surgical correction of mesiocclusion.
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Construction bite A horseshoe wafer of medium hard wax is used to orient the upper and lower dental arches in all three planes of space (horizontal, transverse, and vertical). Any arbitrary adjustments in work-model orientation during appliance fabrication can lead to an appliance that does not fit properly. The bite registration is taken with the patient's mandible in the most comfortably retruded position. It is necessary to allow 1 to 2 mm of inter occlusal space in the molar region for the construction of the lower and, when necessary, upper occlusal rests. A wide open-bite registration should be avoided. In cases with an anterior open bite, only 1 mm of vertical bite-opening in the posterior region is necessary. www.indiandentalacademy.com
A second method involves the use of removable appliances which are placed in the deciduous dentition stage of development or in the mixeddentition stage when certain teeth have exfoliated or are carious. If retention of the removable appliance is adequate, we can apply up to 500 Gm. per side.
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The orthodontic effect, moving the maxillary teeth forward, can be achieved at any time. However, there appear to be ''more optimum'' situations for this procedure. One is when there is insufficient room for the canines. In this instance, maxillary incisors can be moved forward to make space. If orthopedic protraction of the maxilla is also indicated, it is generally done immediately after space has been gained for the canines by moving the incisors anteriorly. In addition, the maxillary teeth are protracted when the potential for an orthopedic effect is diminished (age 9 to 10+, that is, at the end of the mixed-dentition stage of development or later) and when the basal discrepancy is not severe. www.indiandentalacademy.com
The movement of the maxillary teeth can be associated with reverse torque to stimulate the most anterior part of the maxilla to move in an anterior direction (point A). Since the force requirements for moving the teeth are modest, the buccal and palatal areas of the teeth are not united and extraoral traction, pulling in an anterior direction, can be attached to the labial arch either on loops mesial to the canines or distal to the first molars. Another type of appliance is a reverse headgear . This functions to produce anterior movement to the maxilla and to redirect the anterior movement of the mandible. This appliance can be used when strong forces are not necessary. Under these conditions, however, the orthopedic effect may be limited. www.indiandentalacademy.com
REVERSE HEAD GEAR www.indiandentalacademy.com
Characteristic of this type of malocclusion is the overdevelopment of the mandible, especially in relation to the maxilla. The profile is flat or concave, reflecting the hyper development of the lower third of the face rather than the underdevelopment of the middle third of the face. The treatment of choice would be to inhibit or redirect the growth of the mandible. For this purpose, a few appliances are available. CHIN CUP : Orthopedic force is used to protract the maxilla, while the chincap or mental anchorage serves to redirect mandibular growth www.indiandentalacademy.com
REVIEW OF LITERATURE: Appliances resembling chin cups have been in use since the early 1800's. According to Graber, the early attempts with the chin cup were not successful because of incomplete knowledge of mandibular and facial growth, its use on non growing patients, and an inadequate understanding of the forces generated by the chin cup. Armstrong applied 500 Gm. of force via chin cups on 100 adolescent patients with mandibular prognathism. He reported that half of his patients showed improvement in the Class III profile, whereas none of the control, non treated patients showed any favorable change. www.indiandentalacademy.com
Thilander treated sixty patients with chin cups for 1 to 6 years. A significant percentage of patients did not improve. The patients who showed improvement were comparatively young and showed favorable dental changes. The force generated by the chin cup in his study was only 150 to 200 Gm. Graber, Chung, and Aoba reported results in patients treated with chin cups for 12 to 14 hours each day with a force of 1.5 to 2 pounds on each side. They showed that mandibular growth could be redirected with a chin cup. They asserted that continuous use of the appliance for a long period or through active growth was necessary to achieve stable results. Graber treated 35 Class III malocclusions in children between the ages of 5 and 8 years with chin cup therapy for 3 years. He found that the therapy was particularly effective in patients with increased vertical growth of the face. www.indiandentalacademy.com
Chin cup therapy primarily works on the hypothesis that a force directed through the condyles will inhibit as well as redirect the condylar growth. However, this therapy alone may not be indicated for a fair percentage of patients in skeletal Class III who show a small midfacial bone or a retropositioned maxilla with relatively normal mandibular dimensions. Jacobson and associates studied 149 Class III patients and noted that in approximately one fourth of the sample the problem was due to maxillary deficiency. Several clinical studies in the past have noted that treatment of patients in skeletal Class III should include protraction of the maxilla with or without chin cups. Oppenheim suggested a technique for moving the maxilla forward. He noted that restriction of growth or distal movement of the mandible was impossible www.indiandentalacademy.com
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Kettle and Burhapp reported an appliance for cleft lip and palate which successfully inhibited forward growth of the mandible and simultaneously caused anterior movement of the maxilla. Chin cup therapy may improve the following variables of dental and skeletal Class III morphology: retrusive maxilla, moderate to severe protrusive mandible, anterior crossbite, and concave profile. www.indiandentalacademy.com
Both animal and clinical studies of chin cap treatment have reported and confirmed numerous statistically significant changes in the craniofacial complex as a result of treatment: 1. A decrease in the mandibular plane angle. 2. A decrease in the gonial angle. 3. A decrease in the SNB angle. 4. A redirection in the downward vertical growth of the midface. However, as Mitani and Fukazawa and other investigators have reported, when the Class III malocclusion is characterized by maxillary retrusion, chincap force may have inconsistent results and may not be the treatment of choice. In these cases, the use of a protracting appliance, either alone or in conjunction with a chincap, may be the treatment of www.indiandentalacademy.com choice.
In dealing with the correction of the Class III malocclusion with an anterior crossbite, there are two approaches - (1) correction by adjustment of the skeletal bones, and (2) correction by adjusting the dentoalveolar bone. The two approaches are radically different and diametrically opposite in basic principle. One stimulates alveolar bone and the other inhibits alveolar bone. Apparently, when we try to prevent forward growth of the mandible by applying posterior and superior force with a chin cap, it has an adverse effect on the gonion angle - causing the angle to increase instead of decrease. Apparently, this posterior and upward force from the chin cap reverses the natural tendency of the gonion angle to reduce as it grows. This involves basic biologic phenomena, about which we have no knowledge at the present time. www.indiandentalacademy.com
However, its application is limited to an extent because part of the force can be dispersed as it pushes against the soft tissue and also because there is no control of tooth position, which is possible with other types of extraoral traction. If we are trying to depict changes of the maxilla, it would seem desirable to include the entire maxilla. In the illustrations shown, only the anterior superior approximately one-half of the maxilla (the "northeast" one-half) is included in the maxillary triangle, while the "southwest" approximately onehalf of the maxilla, including the dentoalveolar portion, is not included in the maxillary triangle.
The growth of the non-included portion of the maxilla establishes the vertical dimension of the maxilla, and along with that of the mandible establishes the vertical dimension of the face. The mandibular triangle includes only the basal portion of the mandible and dentoalveolar processes. " If the "relative positions" of the maxilla and the mandible are not rigidly specified, then vertical growth of the upper and lower dentoalveolar processes cannot be accounted for. As pointed out above, there are two gonion angle phenomena, (1) reduction due to growth and (2) reduction due to Class III treatment. Also there is a third phenomenon of mandibular change. This involves the bending of the neck of the condyle. This backward bending of the condyle is in response to Class II treatment with removable appliances.
1. 2. 3. 4.
As the neck of the condyle reverts back toward its former position post treatment, as it usually does (DeVincenzo 1991), one of four post treatment reactions must occur; The molar relation must revert back toward Class II occlusion, The lower molars must move forward on the mandible, There must be a change in the temporal mandibular joint, or There must be a dual bite. The authors of the Class III study speak of�shrinkage" of the condylion-pogonion distance, but this is a misnomer. The distance does not become smaller, it only fails to increase in proportion to the growth of the condyle, because of the reduction of the gonion angle. The backward bending of the neck of the condyle followed by a reversion to its former position must be related in some unknown way to maintaining the constancy of the axis of the ramus. www.indiandentalacademy.com
EXTRA ORAL TRACTION: By means of extraoral traction we hope to obtain a) A repositioning of the mandible posteriorly so that the condyle enters the glenoid fossa if there is an anterior path of closure of the mandible; b) Orthodontic movement, inclining the teeth posteriorly; c) Control of the anterior bite depth; d) Better control of the vertical dimension; and e) Influence over the potential growth and development of the mandible. www.indiandentalacademy.com
There are two types of extra oral traction that can be applied to the lower arch. 1. Kloehn type of face-bow that is placed against the first molars. 2. The other consists of facial wires placed against the incisor segment by means of ''J" hooks or loops on the arch wire Practically, the Kloehn type appliance has limited applicability in open bite cases because tipping can lead to clockwise rotation of the mandible and it cannot control the position of the incisor segment. On the other hand with the use of facial wires there are a number of beneficial effects that can be obtained. One is that mandibular incisors can readily be retracted without straining anchorage since Class I forces are not necessary for incisor retraction. Second is the control of anterior bite depth . For example, in open-bite problems, a highwww.indiandentalacademy.com pull headgear can be used.
A straight-pull headgear can be applied when bite depth is shallow , whereas in the presence of a deep bite a low-pull gear is suggested . In addition, it is possible to place the force directly against the first molars by incorporating molar stops into the wire. In this manner, the molars can be held in situ, as when the deciduous second molar exfoliates and the second premolar is erupting, or the molars can be moved distally. Also, with facial wires, mandibular clockwise rotation with possible increase in vertical dimension can be avoided in open-bite cases. Further, there is the possible restraint of forward growth.
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This generally requires a combination type of therapy to produce anterior movement of the maxilla and posterior movement of the mandible. This is chosen when the malocclusion reflects underdevelopment of the maxilla associated with hyper development of the mandible. It can also be done when, during treatment, to accept a compromise result between relationships of the mandible and maxilla. Maxillary protraction and mandibular retraction can be achieved by using, in successive treatment periods, two types of extraoral traction. For example, initially, a facial mask may be used to gain space for the maxillary teeth and to protract the maxillary arch. In a subsequent treatment period, an extraoral appliance can be used to move the mandibular arch distally or, at least, to control the incisor region and possibly influence mandibular growth and development www.indiandentalacademy.com
Somchai Satravaha, (AJO 1999) The activator was introduced by Andresen and has been long served for correction of skeletal Class II malocclusions. Rakosi suggested modification of the activator for use in Class III treatment. The appliance consists of wire and acrylic parts. The wire components are 4 stop-loops located mesial to all first molars to prevent mesial tipping of the molars and to stabilize the appliance, lower labial bow to stabilize the appliance, upper labial pads to remove the force of the upper lip and create periosteal pull to induce bone formation, and tongue crib to correct anterior tongue thrusting habit.
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The goal of using a Class III activator was to achieve posterior positioning of the mandible or maxillary protraction. The construction bite is taken by retruding the lower jaw. The upper labial pad of the activator is intended to protract the maxilla Treatment Changes Effect on a backward positioning of the mandible. There were significant increases of the ANB angle and the Wits values. The SNB and SNPog became smaller resulting in increasing facial convexity (NAPog). The articular angle was significantly enlarged, thus augmenting the sum of the saddle, articular, and gonial angles. The facial axis opened significantly. There were significant differences in the upper face height (N-ANS), mandibular length (Co-Gn), and ramus length (ArGo). Dentoalveolar adaptations included labial tipping of the www.indiandentalacademy.com
Posttreatment Changes
ANB angle as well as the Wits value remained quite stable. The SNA, SNB, SNPog, and NAPog became larger. The articular angle was increased The gonial angle exhibited a compensatory decline resulting in decreasing of the sum angle
Long-term Results
The Class III activator produced a more posterior position of the mandible and changed direction of the mandibular growth. Both alterations remained through the post activator period. The maxilla and the mandible grew with an increase in maxillo mandibular differential; the maxilla remained in a more forward position There was significant difference in the degree of change of angle OP/Go-Gn during the treatment but disappeared in the post activator period due to compensatory reduction of the gonial www.indiandentalacademy.com angle.
(JCO 1997) The Two-Piece Corrector was designed by Gerald.R.Eganhouse to apply biological forces that will counteract any Class III developmental vectors, whether skeletal or dentoalveolar, and correct or minimize their effects on the patient . It is a removable acrylic appliance that simultaneously applies an anterior force to the maxilla and an equal posterior force to the mandible. The flat, sliding surfaces of the two pieces create almost no friction as the dentition is disoccluded during movement, but provide both lateral and anteroposterior stability www.indiandentalacademy.com
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Appliance construction: A construction bite of 4-6 mm thick is taken using an “Exacto Bite” registration jig. This gives an accurate centric relation, since the mandibular incisors can be positioned precisely. In the laboratory, a slide is created on the articulator, with the male(guide) portion in the maxillary acrylic plate and the female (groove) potion in the mandibular plate. The male portion is extended about 15 mm distal to allow for anteroposterior sliding and to ensure lateral stability as correction progresses. The anterior portion of the two pieces will flush when the appliance is inserted, but the maxillary piece will gradually slide forward on the mandibular piece
Elastics provide the force between two parts of the appliance – one hook on each side of the maxillary plate on the disto buccal aspect of the maxillary first molar, two located in the maxillary first bicuspid – canine area, and the fourth placed between the mandibular canine and lateral incisor www.indiandentalacademy.com
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The shorter elastics (1/8 ” 6oz ) are attached from the mandibular hook to the most anterior hook on the maxilla. As treatment progresses, it is moved to the posterior hook. The longer elastic on each side stretched from the mandibular hook to the molar hook can be ¼”, or 3/16” depending on the comfort. DURATION: 12 hours a day in conjugation with face mask. 11 months of treatment time and 18 -24 months of retention INDICATION: Mild skeletal class III where future surgery would not be indicated. And used during preadolescent and adolescent growth www.indiandentalacademy.com periods
CLASS III BIONATOR (GARATINNI ET AL AJO 1998) BALTERS BIONATOR III can be used in patients with skeletal Class III malocclusion. The use of this appliance causes some skeletal changes through neuromuscular modifications. CRITERIA Angle Class III molar relationship; Edge-to edge incisor position or anterior cross bite; Concave profile; Head hyperextension posture; Static and dynamic Class III neuromuscular attitude; Hypertonic upper lip; Low and forward tongue rest position. www.indiandentalacademy.com
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CONSTRUCTION BITE: The construction bite was taken by gently repositioning the mandible distally in centric relation technique. The mandible is positioned distally, applying as little force as possible in order to put the condyle in centric relation, avoiding compression in the retrodiscal pad. The vertical thickness of the bite, corresponding to the interocclusal acrylic between upper and lower first molar should not exceed 3 to 4 mm, Patients had to wear this appliance for at least 22 hours a day.
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RESULTS: Mean increase in the upper jaw length Advancement of point A Palatal and mandibular plane angles widened Increase of the anterior facial height Reduced Antero posterior mandibular growth Therefore, the Bionator III is helpful in Class III malocclusion treatment in growing patients with midfacial deficiency, hypo divergent growth pattern, and reduced facial height.
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THE FOUR-STAGE TREATMENT PLANNING PROCESS FOR CLASS III CASES Stage 1 – setting a PIP for the upper incisors The first stage in Class III treatment planning concerns upper incisor position. It is necessary to determine an ideal position and then decide whether it can be achieved. If not, a modified position may be appropriate, which is less than ideal, but acceptable. In this way a ‘planned incisor position’, or PIP, is determined.
Stage 2 – the lower incisors The second stage of treatment planning involves positioning of the lower incisors. This is frequently a key concern in Class III cases with mandibular excess
Stage 3 – the remaining upper teeth It is beneficial to evaluate the remaining upper teeth at stage 3. If upper premolar extractions are necessary (usually second premolars) then it is normally logical to extract lower first premolar, in a Class III case. However, if the upper arch can be treated without extractions, then a range of lower arch options needs to be considered. The third stage therefore involves deciding how to position the rest of the upper teeth to fit the PIP for the upper incisors. It normally assists Class III treatment mechanics if upper arch extractions can be avoided. The dental VTO will confirm the required movement of molars and canines.
Stage 4 – the remaining lower teeth Lower premolar extractions assist in the retraction of lower incisors, and are helpful to Class III treatment mechanics in many cases. The dental VTO can be used to reach a correct decision. In some Class III marginal extractions cases, second molars may be considered
UPPER INCISOR MOVEMENT IN CLASS III TREATMENT In mild Class III cases, with a normal maxilla but mandibular excess, the pre-treatment upper incisor position may be close to the PIP. In this situation, the case may require relatively little movement of the upper incisors. However, in many Class III cases, there will be a requirement to move the upper incisors mesially. In some maxillary deficiency Class III cases, it can be a challenge to achieve the required mesial movement without excessive Proclination. If a Class III case requires mesial movement of upper incisors, it can be achieved in two ways: www.indiandentalacademy.com
1. By proclination and mesial movement of upper incisors within the available bone . Many Class III cases require mesial movement of upper incisors, to keep pace with the growing mandible. When upper incisors are proclined forwards, each 2.5째 of proclination creates approximately 1mm of space per side, or 2mm in total. For this reason upper premolar extractions are not advisable in many Class III cases. If upper premolars are extracted it can be difficult or impossible to procline upper incisors. 2. By mesial movement of the maxillary bone as a result of normal growth or orthodontic procedures.
Mesial movement of upper incisors within the bone During tooth leveling with the opening wires, there is a tendency for upper incisors to move mesially due to bracket tip, In Class III cases, this is normally beneficial, and moves the upper incisors towards PIP. Likewise, at the rectangular HANT and the rectangular steel wire stages, the A/P expansion and torque effects tend to produce beneficial changes for most Class III cases. This can be further augmented by the use of Class III elastics. Because of these spontaneous tooth movements during tooth leveling and aligning, the early management of the upper arch in mild Class III cases is normally straightforward www.indiandentalacademy.com
Limits to mesial movement of upper incisors 1. Excessive proclination. It is necessary to avoid excessive proclination of the upper incisors, otherwise unesthetic appearance and inadequate function will result. As a general rule, proclination of the upper incisors beyond 120째 to the maxillary plane should be avoided, although there is individual variation . In some cases, less proclination than 120째 may be appropriate. Gingival recession and long clinical crowns can result from excessive proclination. 2. Failure to fully achieve a positive overjet. This can be due to the forward position of the lower incisors, or other reasons, and the resulting bite can be difficult to manage If this is allowed to persist, then there is a risk of enamel damage and/or root resorption. Accordingly, it is unwise to attempt to correct a Class III incisor relationship by orthodontic procedures alone, unless it is clear from the outset that full correction can be achieved, and a near normal overjet obtained. www.indiandentalacademy.com
Mesial movement of maxillary bone due to growth Maxillary growth cannot be relied on as a useful factor in correction of Class III malocclusions. Generally in this type of case, maxillary growth will not be favorable or helpful in reaching the PIP for the upper incisor. Mesial movement of maxillary bone due to orthodontic treatment In growing individuals who have maxillary deficiency, consideration can be given to treatment procedures which will encourage orthopedic change within the maxillary bone These can include rapid maxillary expansion, and the use of reverse headgear www.indiandentalacademy.com
LOWER INCISOR MOVEMENT IN CLASS III CASES Distal movement of the lower incisors can be achieved by distal movement of the teeth within the mandibular bone, or by distal movement of the mandible itself, when there is a displacement. Unfavorable mesial movement of the lower incisors can occur because of mandibular growth
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Inter-maxillary Class III elastics are most helpful in orthodontic (non-surgical) correction of Class III cases. They tend to produce lower incisor retroclination, upper incisor proclination, and A/P correction of the molar relationship. All components of the Class III elastic force can therefore be helpful in reaching treatment goals in average or low angle cases.
Distal movement and retraction of the lower incisors within the mandibular bone In most non-surgical Class III treatments, it is helpful to retract and retrocline the lower incisors . This can compensate for mild mandibular prognathism or mild maxillary retrognathism, and hence mask the underlying skeletal discrepancy. The anatomy of the mandibular bone in the lower incisor region places limits on what should be attempted. Retraction and retroclination beyond a figure of approximately 80째 to the mandibular plane is undesirable, because of the risk of dehiscence and lack of bone support for the over-retracted incisors. Also, dental esthetics and function will be adversely affected www.indiandentalacademy.com
The required retraction and retroclination of the lower incisors is normally achieved with the assistance of Class III elastics, and treatment mechanics are easier in cases where lower teeth have been extracted. Lower first premolar extractions are most favorable in assisting lower incisor distal movement, but loss of lower second molars can also be considered .If the lower arch is managed on a non-extraction basis, Class III mechanics can be used to produce some retraction and retroclination of the lower incisors.
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This can produce distal tipping of the lower premolars and molars, which in turn reduces the available space for the lower third molars . Early removal of lower third molars can be considered in some cases. A nonextraction approach to Class III treatment may not achieve sufficient lower incisor movement for the needs of the case. Correction of the malocclusion may be possible, but not over-correction. Thus, there is no provision in the result for any late growth changes, which occur relatively frequently in Class III cases, especially among male patients.
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Distal movement of mandibular bone – distal repositioning In many Class III cases, there is a mesial displacement of the mandible at the start of treatment. As treatment progresses, the mandible repositions distally, to a position with the condyles centered in the fossae. This favorable change can be predicted at the treatment planning stage, and is a useful adjunct to distal movement of the lower incisors within the facial complex.
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Mesial movement of mandibular bone – Class III growth This is a major factor in the treatment and subsequent retention of Class III patients, especially males. If a decision is made to treat the malocclusion with orthodontics alone, every patient should be informed of the unpredictable nature of Class III growth, and of the implications of any unfavorable growth which may occur in the retention period.
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Class III malocclusion worsens with the continuing mandibular growth. Relapse from continuing mandibular growth is likely to occur and such growth is extremely difficult to control. Applying a restraining force to a mandible as from chin cap is not effective in controlling growth in a class III patient. In mild class III problems a functional appliance or a positioner may be enough to maintain the occlusal relationship during post treatment growth. www.indiandentalacademy.com
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