Development of Occlusion PDF

Course Name: Development of Occlusion Speaker: Dr. Sharaf El Din Program: Orthodontics Orthodontics is a little different from other dental specialties, it mainly depends on knowledge not instruments nor hand skills. In the American journal there was a debate on if one of the ancient orthodontic pi...

Course Name: Development of Occlusion Speaker: Dr. Sharaf El Din Program: Orthodontics Orthodontics is a little different from other dental specialties, it mainly depends on knowledge not instruments nor hand skills. In the American journal there was a debate on if one of the ancient orthodontic pioneers is presents nowadays can he still reach the same results with the lack of instruments back then. Surprisingly YES, as we mentioned before orthodontics is all about knowledge. Occlusion Salzmann definition of occlusion: dynamic relation between mandible and maxilla through movement and interdigitation Differentiation between normal and abnormal occlusion is important for the following reasons: - Treatment planning - Expected results post treatment - Planning for post treatment retention - Follow up visits - When to refer the patient to an orthodontist Stages of development of occlusion - Predental - Primary - Mixed - Permenant 1) Predental stage: there isn’t a definite relation between mandible and maxilla during this stage it’s considered an arbitrary relation. Although neonatal teeth may be present but it’s rare and intervention depends on the severity of the case. Normally 2 gum pads usually the lower is gum pad is behind the upper gum pad, there’s no contact except at the posterior area. 2) Primary stage: there are 6 important features to consider during this stage: a. Sequence of eruption: A>B>D>C>E b. Generalized spacing: spacing between the anterior teeth which is completely healthy and normal. c. Primate space: mesial to upper canine and distal to lower canine. d. Overbite: supposed to decrease gradually during the next couple of years. e. Overjet f. Relationship of Es: based on Baume’s classification the distal surface of upper and lower E are on the same plane ( flush terminal planes ) which is completely normal during this stage. SO, based on what we know can we predict future malocclusion from deciduous dentition? Unfortunately No We can’t guarantee the patient neither normal nor abnormal occlusion just by these features for the following reasons:. The deciduous dentition isn’t static.. The possible change of the mesiodistal dimension due to the proximal wear.. Decay that may lead to loss of tooth structure.. Prolonged habits as thumb sucking.  3) Mixed dentition: Eruption of first molars intermediate period replacement of canines + + Replacement of incisors deciduous molars First transitional period second transitional period First transitional period: -eruption of molars: early mesial shift where the first permenant molars force the teeth mesially to occupy the primate space so as to gain class I position where the lower molars are ahead of the upper molars and the buccal cusp of the upper molar is in the mesiobuccal groove of the lower molar. -eruption of centrals and laterals:.the generalized spacing compensate for the size difference between primary and permenant anteriors..labial eruption of permenant anterior teeth help increase the arch length..increase in the intercanine width. Intermediate period: Only 2 important events occur during this stage:.root completion of anteriors and first permenant molars.the ugly duckling: the maxillary permenant canine develops far distant from the dental arch and close to the floor of the orbit. At the age 9 to 10 years as it moves downward and forward towards occlusion, it comes to lie against the apices of the permenant lateral and central incisors causing mesial pressure on their roots. The centrals clinically responds to this pressure by central diastema and distal crown flaring while the lateral shows labial tipping. This temporary clinical picture improves as the permenant maxillary canines continue to erupt and exerts mesial wedging action on the crowns of the lateral and central incisors. And any orthodontic intervention at this completely natural stage may cause impingent, external resorption and change of canine path causing impaction. Second transitional period: Lee way space: difference between mesiodistal width of CDE and 345 Needed for the late mesial shift. 4) Permenant dentition:.post eruption spurt..Juvenile occlusal equilibrium..Adult occlusal equilibrium which is a slow process of wear and tear throughout life. Summary of clinical consideration: A) Arch expansion: Despite the generalized growth of the child during this stage the maxillary growth ceases nearly at the age of 9, No significant increase in the intercanine width, so this is the perfect time for intervention for treatment of constricted maxilla as the sutures are still open for expansion. B) Space considerations: - Generalized space 6mm anterior spacing 1/3 with crowding 3mm anterior spacing 50:50 crowding No spacing 67 % crowding crowding 100 % crowding - Primate space. - Early and late mesial shift. - Lee way space. C) Ugly dickling: wait until canines are erupted. D) Over bite and molar angulation E) Canines: long path way of erruption so it’s common to see malocclusion. F) Late mandibular crowding 16:22 years -residual mandibular growth. -anterior component of occlusal forces. -physiologic mesial drift. -soft tissue maturation. -lack of interproximal wear. -pathologic tooth material loss causing drift and occlusal functional changes. -Third molar presence and position may contribute, however according to NICE national institute for health and care excellence Through evidence based guide stated that there’s no need to extract third molars to maintain orthodontic results nor to prevent late mandibular crowding.  Normal occlusion If we define normal as “the usual” then a beautifully straight alignment of teeth in each jaw doesn’t qualify. For the orthodontist ideal occlusion is an admirable goal but is usually a therapeutic impossibility. Practically speaking the accepted occlusion: Well balanced Stable Aesthetic Functional Andrews six keys of occlusion: Key I: Molar relation.the distal surface of the distal marginal ridge of the maxillary first permanent molar made contact and occluded with the mesial surface of the mesial marginal ridge of the mandibular second molar..the mesiobuccal cusp of the maxillary permanent first molar fell within the buccal groove located between the mesial and middle cusp of the mandibular permanent first molar..the mesiolingual cusp of the maxillary permanent first molar was seated in the central fossa of the mandibular permanent first molar. Key II: Crown angulation (mesiodistal tip) By definition the crown angulation of the mesiodistal of the long axis of the crown. It’s the angle formed between the long axis of the crown (as viewed from a facial perspective) and a perpendicular line erected from the occlusal plane. -It’s positive when the gingival portion of the long axis of the crown is distal to the incisal portion, and vice versa. -In the normal occlusion, the crown angulation is positive for all teeth. Key III: Crown inclination (faciolingual torque) By definition, the crown inclination is the faciolingual inclination of the long axis pf the crown. It’s the angle formed between the line tangent to buccal surface (as viewed from a proximal perspective) and a perpendicular to the occlusal plane. -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 the normal occlusion, the crown inclination was negative for all teeth except the maxillary central and lateral incisors. Key IV: Rotations In normal occlusion the dentition should be free from undesirable rotations. If a molar is rotated, it would occupy more space than normal within the arch. The reverse is true for the anterior teeth. Key V: Tight contacts In normal occlusion, contact areas should be tight. Key VI: Occlusal plane By definition, the 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. A deep curve of spee results in a more confined area for the maxillary teeth. On the other hand, a reverse curve of spee results in excessive room for the upper teeth. However, these keys described ideal static occlusion without taking function and movements into considerations. Roth’s keys of occlusion 1981: Key 1: Rest cuspal position (RCP) and inter cuspal position (ICP) should be coincident. A 2 or 3 mm range is normal there’s no strain on the TMJ or muscles of mastication and no need for interference. Key 2: Anterior guidance Relation of the anterior teeth, in protrusion the incisors should disocclude the posterior teeth by the guidance provided by the lower incisal edges passing along the palatal contour of the upper incisors. Key 3: Lateral excursions of the mandible - Canine guided occlusion. - Group guided occlusion. Summarized by Dr. Sally Adel