Andrew's Six Keys of Normal Occlusion PDF

Andrew’s six keys of occlusion  The first key of normal occlusion: Molar interarch relationship Above: Diagram showing examples of occlusions with poor Class I molar relationships, according to Andrews, caused by insufficient crown angulation of the upper first molar. Bottom left: Diagram...

Andrew’s six keys of occlusion  The first key of normal occlusion: Molar interarch relationship Above: Diagram showing examples of occlusions with poor Class I molar relationships, according to Andrews, caused by insufficient crown angulation of the upper first molar. Bottom left: Diagram showing an improved Class I molar relationship. Bottom right: Diagram showing the correct Class I molar relationship according to Andrew's first key of occlusion. According to Andrew's occlusal concept: - The mesiobuccal cusp of the upper first molar should occlude in the groove between the mesial and medial buccal cusp of the lower first molar. - The mesiolingual cusp of the upper first molar should occlude in the central fossa of the lower 6- year molar. - The crown of the upper first molar must be angulated so that its distal marginal ridge occludes with the mesial marginal ridge of the lower second molar (Andrews, 1972).  Long axis of the crown Vertical line = Long axis of the clinical crown (= LACC) LA spot = Center of the long axis of the clinical crown Unlike other concepts, it is not the long axis of the tooth which serves as the plane of reference, but rather the long axis of the clinical crown. It passes through the central, vertical ridge of the tooth, i.e. through the most prominent part in the center of the labial or buccal surface. This applies to all teeth, except molars.  Mesiodistal angulation of the crown --- Perpendicular to the occlusal plane —— Long axis of the crown The angulation of the crown is defined as the angle which the tooth forms with a line drawn perpendicular to the occlusal plane. Right: Drawing showing the mesiodistal angulation of the crown of the upper left central incisor (Andrews, 1972). Second key of normal occlusion: Mesiodistal crown angulation For the occlusion to be considered normal, the gingival part of the long axis of the crown must be distal to the occlusal part of the axis. The degree of angulation depends on the type of tooth. Right: Diagrammatic view of the mesiodistal angulation of the crowns when the occlusion is normal (Andrews, 1972). Mesiodistal crown angulation for various types of upper teeth Horizontal plane of reference = Line passing through all LA spots (Andrews plane) Vertical plane of reference = Perpendicular to the horizontal plane According to Andrews, in he upper jaw the crowns of the canines exhibit the greatest degree of angulation and the premolars the least.  Third key of occlusion: Labiolingual crown inclination --- Tangent on the crown of the tooth —— Perpendiculartotheocclusal plane The third key defines the angle between a tangent to the LACC at its center and a line perpendicular to the occlusal plane. If the gingival area of the crown is more toward the lingual, the result is expressed in positive values; should the opposite apply, the result is negative. Labiolingual crown inclination between upper and lower incisors (crown torque) --- Tooth crown tangent ––– Perpendicular to the occlusal plane –––– Long axes of the incisors The upper incisors form a positive angle with the crown tangent and the line perpendicular to the occlusal plane (+7°) and an angle of 18° between the crown tangent and the long axis of the tooth. The crown torque of the lower incisor is -1° and the angle between its crown tangent and the axis of the incisors is 16°. The interincisal angle between the crown tangents of the upper and lower incisors is 174° for normal occlusions (unlike the interincisal angle between the axes of the incisors which is considered to be, on average, 139°) (Andrews, 1972). Incorrect crown torque and occlusal findings Should the upper anterior teeth be in a too upright position (the labiolingual crown inclinations of the upper incisors have negative values), the occlusion is unstable. The canine guidance is insufficient and there is a risk that the posterior teeth will drift toward the mesial (Andrews, 1972).  Anterior and posterior occlusion in case of incorrect crown torque If the posterior occlusion is correct, but the upper incisors are in linguoversion, this can result in interdental spacing of the anterior teeth which then is often incorrectly associated with a discrepancy in the intermaxillary tooth-size (Andrews, 1972).  Occlusal changes after orthodontic treatment Clinical picture of the situation schematically Occlusal relations in the postretention stage after orthodontic treatment. The long-term result is a dentally supported bite with lingually inclined upper incisors and a space posterior to the upper right canine. The canines are no longer in Class I relationship. Labiolingual inclination of the posterior teeth in optimal occlusion The tangents on the facial surfaces of the crowns form negative values with the line drawn perpendicular to the occlusal plane, i.e. the gingival portions of the teeth are more pronounced buccally than the occlusal portions. The upper canines and premolars are inclined at virtually the same angle, whereby the molars are tilted slightly more. In the lower arch, the inclination increases progressively from the canine to the second molar.  Fourth key of occlusion: Rotations In order to achieve correct occlusion, none of the teeth should be rotated. Rotated molars and premolars occupy more space in the dental arch than normal. Rotated incisors may occupy less space than those correctly alignd. Rotated canines adversely affect esthetics and may lead to occlusal interferences. Fifth key of occlusion: Tight contacts, no spacing If there are no anomalies in the shape of the teeth, or intermaxillary discrepancies in the mesiodistal tooth size, the contact points should abut in normal occlusion. Clinical picture of a poor example, with spaces between the upper teeth and a Class I relationship of the canines. These findings are indicative of a Bolton discrepancy. Sixth key of occlusion: Curve of Spee a- An excessive curve of Spee restricts the amount of space available for the upper teeth, which must then move toward the mesial and distal, thus preventing correct intercuspation. b- A normal occlusion has a flat occlusal plane (according to Andrews, the mandibular curve of Spee should not be deeper than 1.5 mm). c- A reverse curve of Spee creates excessive space in the upper jaw, which prevents development of a normal occlusion (Andrews, 1972). Curve of Spee - Occlusion-Case examples- Reverse curve of Spee This panoramic radiograph shows the occlusal relationship resulting from a reverse sagittal compensating curve. When compared to the upper jaw, insufficient space is available in the lower dental arch and the anterior teeth are crowded. The bite is open anteriorly.  Flat curve of Spee Flat sagittal compensating curve with good intercuspation around the premolars and molars. This type of curve is considered to be "normal" according to Andrews.  Excessive curve of Spee Pronounced sagittal compensating curve with excessive space in the upper dental arch and inadequate space in the lower arch. The lower incisors are crowded and the overbite is increased. Every upper tooth occludes against two opposite teeth except lower centrals. Maxillary midline coincides with mandibular midline. Overbite is 1/3 the crown heights of the lower incisors. In normal adult occlusion ,spaces and crowding are not present. The neighbouring teeth are aligned without Overbite is one third the crown height of the lower incisors and overjet is about the thickness of the incisal edges of the upper incisors in normal adult Upper third molar occludes against the lower one only in normal adult occlusion. In normal adult occlusion the mid lines are on. Upper arch shape Lower arch shape is is horseshoe in parabolic or U-shaped normal adult in normal adult occlusion occlusion A, ideal intercuspation, buccal view. B, ideal intercuspation, lingual view of normal adult occlusion. Occlusion at 13 years. There are few changes except the tendency to less dental procumbency. CLASSIFICATION OF MALOCCLUSION PRESENTER: SAPEEDEH AFZAL. ROLL # 10 GROUP : A  ROAD MAP WHAT IS MALOCCLUSION? NEED OR USES FOR CLASSIFICATION. SYSTEMS OF CLASSIFICATION & TERMINOLOGIES. – ANGLE’S CLASSIFICATION. MODIFICATIONS OF ANGLE’S CLASSIFICATION. – ANDREW’S SIX KEYS. – SKELETAL CLASSIFICATION. – BRITISH STANDARD CLASSIFICATION OF INCISOR RELATIONSHIP. – CANINE CLASSIFICATION. – SIMON’S CLASSIFICATION. – ACKERMAN & PROFFIT CLASSIFICATION.  OCCLUSION WHEN THE TEETH IN THE MANDIBULAR ARCH COME INTO CONTACT WITH THOSE IN THE MAXILLARY ARCH IN ANY FUNCTIONAL RELATION, ARE SAID TO BE IN OCCLUSION. (WHEELER’S) WHAT IS MALOCCLUSION..?? A CONDITION IN WHICH THERE IS A DEFLECTION FROM THE NORMAL RELATION OF THE TEETH TO OTHER TEETH IN THE SAME ARCH AND/OR TO TEETH IN THE OPPOSING ARCH. (GARDINER, WHITE & LEIGHTON)  NEED FOR CLASSIFICATION Grouping of orthodontic problems. Location of problems to be treated. Diagnosis & treatment plan. Comparison of different types of malocclusion. For self-communication. Documentation of problems. Used for epidemiological studies. Assessment of treatment effects of orthodontic appliances. QUESTIONNAIRE, INTERVIEW CLASSIFICATION CLINICAL DATA PROBLEM LIST = EXAMINATION BASE DIAGNOSIS ANALYSIS OF DIAGNOSTIC RECORDS METHODS OF CLASSIFICATION OF MALOCCLUSION CAN BE BROADLY DIVIDED INTO TWO TYPES QUANTITATIVE INTRA-ARCH & & QUALITATIVE INTER- ARCH TYPES OF PROBLEMS MALOCCLUSION  MALOCCLUSION: QUALITATIVE & QUANTITATIVE METHODS QUALITATIVE METHODS QUANTITATIVE METHODS Angle’s classification. The PAR index. Modification of Angle’s The IOTN index by Shaw. classification. Massler & Frankel. Simon’s classification. Malalignment index by van Kurt Bennett’s classification. and Pennel. Skeletal classification. Ackerman-Proffit classification. WHO/FDI classification. Aetiological classification. Incisor classification. Canine classification. MALOCCLUSION: INTRA-ARCH & INTER-ARCH PROBLEMS INTRA-ARCH PROBLEMS (INDIVIDUAL OR GROUPS OF TEETH) (i) SAGGITAL PROBLEMS: (ii) VERTICAL PROBLEMS: LABIOVERSION SUPRAVERSION LINGUOVERSION INFRAVERSION MESIOVERSION DISTOVERSION (iii) ROTATED TEETH (iv) TRANSPOSITION OF TEETH MALOCCLUSION: INTRA-ARCH & INTER-ARCH PROBLEMS INTER-ARCH PROBLEMS (i) SAGGITAL: (ii) TRANSVERSE: CLASS II MALOCCLUSION. CROSSBITES, SCISSOR CLASS III MALOCCLUSION. BITE. MIDLINE SHIFT. (iii) VERTICAL: DEEP BITE. OPEN BITE.  ANGLE’S CLASSIFICATION OF MALOCCLUSION In 1899 Edward H. Angle published the first classification of malocclusion. The classifications are based on the relationship of the mesiobuccal cusp of the maxillary first molar and the buccal groove of the mandibular first molar.  ANGLE’S CLASSIFICATION OF MALOCCLUSION CLASS I CLASS II CLASS III MALOCCLUSION MALOCCLUSION MALOCCLUSION DIVISION 1 DIVISION SUB-DIVISION 2 CLASS III PSEUDO SUB-DIVISION CLASS III CLASS I MALOCCLUSION THE MESIOBUCCAL CUSP OF THE UPPER FIRST PERMANENT MOLAR OCCLUDES WITH THE MESIOBUCCAL GROOVE OF THE LOWER FIRST MOLAR, BUT LINE OF OCCLUSION IS INCORRECT BECAUSE OF MALPOSED TEETH, ROTATIONS OR OTHER DISCREPANCIES.  CLASS II MALOCLUSION THE MESIOBUCCAL CUSP OF THE LOWER FIRST PERMANENT MOLAR OCCLUDES DISTAL TO THE CLASS I POSITION.  CLASS II DIVISION 1 Condition when class II molar relationship is present with proclined upper central incisors. There is an increase in overjet.  CLASS II DIVISION 2 Condition when class II molar relationship is present with retroclined upper central incisors, upper lateral incisors may be proclined or normally inclined. Overjet is usually minimal or may be increased.  CLASS II SUB-DIVISION Condition when the class II molar relationship exists on only one side with normal molar relationship on the other side. CLASS III MALOCCLUSION THE MESIOBUCCAL CUSP OF THE LOWER FIST MOLAR OCCLUDES MESIAL TO THE CLASS I POSITION. PSEUDO CLASS III MALOCCLUSION Due to occlusal prematurity, when the mandible moves from rest position to occlusion, it slides forward into a pseudo class III position. It’s also known as postural class III. CLASS III SUB-DIVISION Condition in which class III molar relationship is present only on one side with normal relation on the other side.  VALIDITY OF ANGLE’S CLASSIFICATION MERITS: DE-MERITS: Easy & most practical method. Incorrect hypothesis. Rapid. Angle considered only saggital Requires no instrumentation. dimension. Easy to communicate. Not applicable in deciduous Widely used for teaching dentition. purpose. Not applicable when first permanent molars are missing. Skeletal problems are not considered. Didn’t elaborate the etiology of malocclusion.  MODIFICATIONS OF ANGLE’S CLASSIFICATION There are two modifications of Angle’s classification 1.Lischer’s modification. 2.Dewey’s modification.  LISCHER’SMODIFICATION He introduced following names to the Angle’s classification: – Neutrocclusion- Class I. – Distocclusion- Class II. – Mesiocclusion- Class III DEWEY’S MODIFICATION (1915) Martin Dewey divided Angle’s class I & III into further types: – CLASS I: Type 1: Crowded maxillary anterior teeth. Canines may be abnormally positioned. Type 2: Proclined or labioversion of maxillary incisors. Type 3: Anterior cross bite present. Type 4: Posterior cross bite present. Type 5: Mesioversion of molars. DEWEY’S MODIFICATION – CLASS III: Type 1: Well aligned teeth & dental arches. Edge-edge relationship. Type 2: Crowded mandibular incisors. Type 3: Crowded maxillary incisors, underdeveloped maxilla. Anterior cross bite present.  ANDREW’S SIX KEYS (1970) Andrew extended Angle’s classification: 1. Correct molar relationship. 2. Correct crown angulations. 3. Correct crown inclination i.e. Class I incisor relationship. 4. No rotation present. 5. Teeth in tight contact with no spacing. 6. Occlusal plane/ curve of spee should be flat i.e. it should not be deeper than 1.5mm. 7. No tooth size discrepancies. (Bannet & McLanghlan’s)  SKELETAL CLASSIFICATION It considered relationship between maxilla & mandible, in antero-posterior direction. CLASS I: Maxilla & mandible are in harmony with each other. SKELETAL CLASSIFICATION CLASS II: Maxilla lies ahead of mandible with refrence to anteroir cranial base. In other words maxilla is prognated. SKELETAL CLASSIFICATION CLASS III: Maxilla lies posterior to mandible with reference to anterior cranial base. In other words maxilla is retrognathed.  BRITISH STANDARD CLASSIFICATION OF INCISOR RELATIONSHIP (1983) Based upon incisor relationship, proposed in 1983. Do not consider molar relationship in some cases. CLASS I: The lower incisor edges occlude with or lie immediately below the cingulum plateau of upper central incisors.  BRITISH STANDARD CLASSIFICATION OF INCISOR RELATIONSHIP CLASS II: The lower incisor edges lie posterior to the cingulum plateau of the upper incisors. There are two sub-divisions: – DIVISION 1: The upper central incisors are proclined or of average inclination & there is an increase in overjet. – DIVISION 2: The upper central incisors are retroclined. The overjet is usually minimal or may be increased. BRITISH STANDARD CLASSIFICATION OF INCISOR RELATIONSHIP CLASS III: The lower incisor edges lies anterior to the cingulum plateau of the upper incisors. The overjet is reduced or reversed. CANINE CLASSIFICATION CLASS I : When the mesial slope of upper canine coincides with the distal slope of lower canine. CANINE CLASSIFICATION CLASS II : When the mesial slope of upper canine is ahead of the distal slope of lower canine.  CANINE CLASSIFICATION Class III : When the mesial slope of the upper canine lies behind the distal slope of the lower canine. SIMON’S CLASSIFICATION (1926) In Simon’s classification system, the dental arches are related to three anthropologic planes. PLANES USED: – Frankfort horizontal plane or eye-ear-plane. – Orbital plane. – Raphe median plane or mid-saggital plane. SIMON’S CLASSIFICATION FRANKFORT HORIZONTAL PLANE: -Helps detect deviations in the vertical plane. -Dental arch closer to the plane is called attraction and farther away is called abstraction. SIMON’S CLASSIFICATION ORBITAL PLANE: -Helps to detect deviations in the transverse plane. -Dental arch more anteriorly placed is called protraction and posteriorly placed dental arch is called retraction. SIMON’S CLASSIFICATION MID-SAGGITAL PLANE: - Helps to detect deviations in the saggital plane. - Dental arch closer to mid- saggital plane is called contraction and farther away is called distraction.  ACKERMAN & PROFFIT CLASSIFICATION (1960) It was proposed to overcome the drawbacks of Angle’s classification. This system includes Angle’s classification & five characteristics of malocclusion within a Venn diagram. FIVE MAJOR CHARACTERISTICS ADDITION TO THE FIVE-CHARACTERISTICS CLASSIFICATION SYSTEM Two things particularly help this more thorough analysis: 1. Esthetic line of occlusion. 2. Rotational axes. 1. ESTHETIC LINE OF OCCLUSION In modern analysis, another curved line characterizing the appearance of the dentition is important. – Esthetic line of occlusion, follows the facial edges of the maxillary anterior and posterior teeth.  2. ROTATIONAL AXES In addition to relationship in the transverse, antero- posterior and vertical planes of space used in traditional 3-D analysis, rotations around axes perpendicular to three planes also must be evaluated. It’s a useful way to evaluate the relationship of the teeth to the soft tissues that frame their display. – Pitch. – Roll. – Yaw.  ROTATIONAL AXES PITCH: ROLL: The vertical relationship of the Roll describes the vertical position of teeth to the lips & cheeks can be the teeth when this is different on conventionally described as up-down the right & left sides. deviations around the antero- Viewed as up-down deviations posterior axes. around the transverse axes. Evaluated clinically & from It’s seen with lips relaxed and more cephalometric radiographs. clearly on smile, in both frontal and oblique views. YAW: Rotation of the jaw or dentition to one side or the other, around a vertical axes, produces a skeletal or dental midline discrepancy. Viewed as left-right deviations around the vertical axes.  VALIDITY OF ACKERMAN & PROFFIT CLASSIFICATION MERITS DE-MERITS Explained complexities of malocclusion. Etiological considerations not All three dimensional problems included. included. Based on static occlusion only. Differentiation between skeletal & dental problems are made. Profile of the patient is given. Arch length problems are evaluated. Helps in complete diagnosis & treatment planning.  REFRENCES CONTEMPORARY ORTHODONTICS, WILLIAM R. PROFFIT (5TH. EDITION) INTRODUCTION TO ORTHODONTICS, LAURA MITCHELL (3RD. EDITION) ORTHODONTICS, PREM KUMAR (2ND. EDITION)