DENT 4 DERS 2 Orthodontics.pdf

DENT 4005-ORTHODONTICS II Characteristics of Normal Occlusion Lect. Kübra SUCU, DDS Bahçeşehir University School of Dental Medicine Department of Orthodontics [email protected] References Contemporary Orthodontics William R. Proffit Elsevier Orthodontics is the speciality of dentist...

DENT 4005-ORTHODONTICS II Characteristics of Normal Occlusion Lect. Kübra SUCU, DDS Bahçeşehir University School of Dental Medicine Department of Orthodontics [email protected] References Contemporary Orthodontics William R. Proffit Elsevier Orthodontics is the speciality of dentistry concerned with the management and treatment of malocclusion. In the majority of cases, a malocclusion does not in itself represent a disease state, but rather a variation from what is considered ideal. It is therefore important for the orthodontist to have a clear definition of ideal occlusion, as this will form a basis for diagnosis and treatment planning. Ideal occlusion • The ideal relationship of the teeth can be defined in terms of static (or morphological) and functional occlusion. Edward Angle felt the key to normal occlusion was the relative anteroposterior position of the first permanent molars, which he used to define the dental arch relationship. He also recognized the importance of good cuspal interdigitation to provide mutual support for the teeth in function (Angle, 1899). Edward Hartley Angle • Edward Angle was an American dentist born in 1855. Originally trained as a prosthodontist, he developed an interest in occlusion and was instrumental in developing orthodontics as a specialty of dentistry. • Amongst his many achievements, including developing the principles upon which most modern fixed appliances are based, Angle proposed a classification of malocclusion that is still relevant today. • He suggested that normal occlusion was based fundamentally around the position of the first permanent molar teeth. If these teeth were in the correct relationship and the remaining teeth occupied a smoothly curved line of occlusion, a normal occlusion would result. • Angle’s molar classification is still used today but it is now realized that first molar position is not immutable and the position these teeth come to occupy in the dental arch can be influenced by the environment. Normal Occlusion Acording to Angle; The cusp of the upper first permanent molar must occlude in the groove between the mesial and middle buccal cusps of the lower first permanent molar. • Almost one hundred years after Angle, • Lawrence Andrews redefined the concept of an ideal static occlusion by describing it in terms of six individual keys, including an updated ideal relationship for the first molars (Andrews, 1972) Normal Occlusion Andrews who is the first one studied normal occlusion in 120 (untreated) cases with the following criteria: 1. Correct bite 2. Did not have orthodontic treatment 3. Straight teeth and pleasing appearance Normal Occlusion During the periods of 1960-1964, 120 nonorthodontic normal models were acquired with the cooperation of local dentists, orthodontists, and a major university. Normal Occlusion The crowns of this multisource collection were then studied intensively to ascertain which characteristics, if any, would be found consistently in all the models. Normal Occlusion Angle’s molar cusp groove concept was validated still again. Normal Occlusion At the end of the study, other findings emerged. Angulation (mesiodistal tip) and inclination (labiolingual or buccolingual inclination) began to show predictable natures as related to individual tooth types. These 120 non-orthodontic normals had no rotations. There were no spaces between teeth. The occlusal plane was not identical throughout the battery of examples but fell neatly into so limited a range of variation that it clearly was a differential attribute. Normal Occlusion The six keys The six differential qualities were thus validated. As follows: 1. Molar relationship. The distal surface of the distobuccal cusp of the upper first permanent molar made contact and occluded with the mesial surface of the mesiobuccal cusp of the lower second molar. The mesiodistal cusp of the upper first permanent molar fell within the groove between the mesial and middle cusps of the lower first permanent molar. (The canines and premolars enjoyed a cuspembrasure relationship buccally, and a cusp fossa relationship lingually.) Normal Occlusion The mesiobuccal cusp of the upper first molar should occlude within the mesiobuccal groove of the lower first molar. Normal Occlusion Key I. Molar Relationship Normal Occlusion Key I. Molar Relationship Normal Occlusion Key I. Molar relationship. The first of the six keys is molar relationship. The nonorthodontic normal models consistently demonstrated that the distal surface of the distobuccal cusp of the upper first permanent molar occluded with the mesial surface of the mesiobuccal cusp of the lower second molar Therefore, one must question the sufficiency of the traditional description of normal molar relationship. It is possible for the mesiobuccal cusp of the upper first molar to occlude in the groove between the mesial and middle cusps of the lower first permanent molar (as sought by Angle) while leaving a situation unreceptive to normal occlusion. Normal Occlusion Key I. Molar relationship The closer the distal surface of the distobuccal cusp of the upper first permanent molar approaches the mesial surfaces of the mesiobuccal cusp of the lower second molar, the better the opportunity for normal occlusion. In every one of the 120 nonorthodontic normal models; that is, the distal surface of the upper first permanent molar contacted the mesial surface of the lower second permanent molar. Normal Occlusion The six keys Key 2. Crown angulation (the mesiodistal Tip) Normal Occlusion The six keys Key 2. Crown angulation (the mesiodistal Tip) As orthodontists, we work specifically with the crowns of teeth and, therefore, crowns should be our communication base or referent, just as they are our clinical base. Normal Occlusion The six keys Key 2. Crown angulation (the mesiodistal Tip) The gingival portion of the long axis of each crown was distal to the incisal portion, varying with the individual tooth type. The long axis of the crown for all teeth, except molars, is judged to be the middevelopmental ridge, which is the most prominent and centermost vertical portion of the labial or buccal surface of the crown. The long axis of the molar crown is identified by the dominant vertical groove on the buccal surface of the crown. Normal Occlusion Normal Occlusion Key III. Crown inclination (torque) It’s the faciolingual inclination of the long axis of the crown. Its angle formed between the facial long axis of the crown and a perpendicular to the occlusal plane. (viewed from proximal surface) Normal Occlusion When the gingival portion of the long axis of the crown is lingual to the incisal portion , the crown inclination is positive. (and vice versa) In normal occlusion, the crown inclination for all teeth was negative except maxillary central and lateral incisors Normal Occlusion Lingual crown inclination was similar in maxillary canines and premolars, and more pronounced in the maxillary molar • •Lingual crown inclination progressively increased from mandibular canine through the mandibular second molars. Normal Occlusion Key IV. Rotations. There were no rotations. In normal occlusion, the dentition should be free from undesirable rotations. If the molar rotated, it would occupy more space than normal within the arch. The reverse is true for the anterior teeth. Normal Occlusion IV. Rotations. There were no rotations. This arch can not be ideal because there is a rotation in 33 Normal Occlusion IV. Rotations. There were no rotations. Normal Occlusion Key V. Spaces. There were no spaces; contact points were tight. In normal occlusion, contact area should be tight. Without exception, the contact points on the nonorthodontic normals were tight. Normal Occlusion VI. Occlusal plane. The plane of occlusion varied from generally flat to a slight curve of Spee. Occlusal plane: is the imaginary plane on which the teeth meet in occlusion. In normal occlusion, the occlusal plane should be flat or nearly flat. Deep curve of Spee, result in a more confined area for the maxillary teeth Normal Occlusion The six keys to normal occlusion contribute individually and collectively to the total scheme of occlusion and, therefore, are viewed as essential to Successful orthodontic treatment. Normal Occlusion Key VI. Occlusal plane. The planes of occlusion found on the nonorthodontic normal models ranged from flat to slight curves of Spee. Even though not all of the nonorthodontic normals had flat planes of occlusion, it is believed that a flat plane should be a treatment goal as a form of overtreatment. Normal Occlusion Key VI. Occlusal plane. There is a natural tendency for the curve of Spee to deepen with time, for the lower jaw’s growth downward and forward sometimes is faster and continues longer than that of the upper jaw, and this causes the lower anterior teeth, which are confined by the upper anterior teeth and lips, to be forced back and up resulting in crowded lower anterior teeth and/or a deeper overbite and deeper curve of Spee. Normal Occlusion Box 1.2 Andrews Six Keys of Occlusion • Dynamics of occlusion • Orthodontists have traditionally based their treatment upon these static goals, with little consideration for the dynamics of occlusion or temporomandibular joints and associated musculature that forms the masticatory system. However, over the past few decades there has been a greater interest in the principles of gnathology and aspects of an occlusion in function . Much has been written about what constitutes an ideal functional occlusion and why it is important; however, an essential concept is one of mutual protection, whereby teeth of the anterior and posterior dentitions protect each other in function. Mutual protection is thought to be achieved in the presence of : • An immediate and permanent posterior disclusion in lateral and protrusive contact with no associated non-working side interferences (tooth contacts); this is achieved by the presence of canine guidance or group function in lateral excursion, and incisal guidance in protrusion. Thus, the anterior teeth protect the posteriors. • Multiple, simultaneous and bilateral contacts of the posterior teeth in intercuspal position (ICP) with the incisor teeth slightly out of contact; thus, the posterior teeth protect the anteriors. • Intercuspal position (or centric occlusion, CO) coincident with the retruded contact position (RCP) (or centric relation, CR) but with some limited freedom for the mandible to move slightly forwards in the sagittal and horizontal planes from ICP. Ideal untreated occlusion. The incisor, canine and molar relationship are class I, the dental arches are well aligned and there are no transverse discrepancies. In lateral excursion there should be either canine guidance or group function. Thank you...