Development Of Normal Occlusion PDF

DEVELOPMENT OF NORMAL OCCLUSION Mohamed Abd El Rahim Abuelazayem Lecturer of Orthodontics BDS, MSc, PhD Orthodontics Cairo University  STAGES OF DEVELOPMENT OF NORMAL OCCLUSION: 1. Gum Pad Stage: from birth till completion of the d...

DEVELOPMENT OF NORMAL OCCLUSION Mohamed Abd El Rahim Abuelazayem Lecturer of Orthodontics BDS, MSc, PhD Orthodontics Cairo University  STAGES OF DEVELOPMENT OF NORMAL OCCLUSION: 1. Gum Pad Stage: from birth till completion of the deciduous dentition (0-2.5 years) 2. Deciduous dentition stage: from the completion of eruption of deciduous teeth till eruption of 1st permanent tooth (2.5-6years). 3. Mixed dentition stage: from eruption of 1st permanent tooth till shedding of last deciduous tooth (6-12 years). 4. Early permanent dentition: from the eruption of permanent canines, premolars and permanent second molars (12 years and thereafter). 5. Adult dentition stage: by the eruption of 3rd molars (17 -21 and onward).  STAGE 1 From birth to completion of deciduous dentition ( from 0 to 2.5 years) A) At birth (gum pads) the bone of newly born infant is covered by gum pads. Stage 1 B) Eruption of deciduous teeth.  MAXILLARY GUM PADS Horse shoe shaped with a very shallow vault The alveolar part is separated from hard palate by a continuous horizontal gingival groove.  MANDIBULAR GUM PADS U shaped, The alveolar part is limited lingually by a continuous groove. The alveolar part of both maxillary and mandibular gum pads is divided by transverse grooves into 10 segments to accommodate for the development of deciduous teeth. The groove distal to the canine segment continues to the buccal side of the gum pad and is called lateral sulcus.  RELATIONSHIP BETWEEN UPPER AND LOWER GUM PADS. I) Anteroposterior: the lateral sulcus of the maxillary gum pads is mesial to the mandibular this referes to the backward position of the mandible to the maxilla at that time. II) Vertically: Anteriorly there is rarely any contact which gives space for: Sucking and feeding. Eruption of anterior teeth. Posteriorly they touch at the first deciduous molars region.  ERUPTION OF THE DECIDUOUS TEETH In the 4th month of I.U.L., calcification of the deciduous teeth begins. At birth ¼ to ½ of the deciduous crowns has been calcified & the tips of the first permenant molar cusps. The sequence of eruption is 1. A from 6 to 7 m. 2. B from 7 to 8 m. 3. C 18-20 m. 4. D from 12 to 15 m. 5. E 24-36 m.  STAGE 2 ( DECIDUOUS DENTITION STAGE) It starts from completion of eruption of deciduous dentition till the eruption of first permanent tooth (2.5 to 6 years). Arch shape usually ovoid with no crowding or malocclusion.  SPACING IN THE DECIDUOUS TEETH. 1- generalized spacing in the the incisor region. Allows for the difference between the size of the smaller deciduous teeth and their larger permanent successors.  SPACING IN THE DECIDUOUS TEETH. 2- primate space: - Mandibular primate space is distal to the canine & closes by the eruption of lower 6. - Maxillary primate space is mesial to maxillary canine & closes by the eruption of permanent maxillary incisors.  CHANGING OCCLUSION OF DECIDUOUS TEETH Anterior teeth At 3 years: there may be excessive overbite (upper incisors almost covers the lower incisors). this overbite is reduced by rapid attrition of the incisors. At 6 years: there may be edge to edge incisor relationship that facilitates the forward shift of the mandible.  CHANGING OCCLUSION OF DECIDUOUS TEETH posterior teeth Mesial cup of the mandibular D is ahead of the maxillary D. the mandibular E is wider than the maxillary E leading to flush terminal plane of the distal surfaces of upper and lower E. If the flush terminal plane remains this will lead to end to end relationship of the first permanent molars.  CHANGING OCCLUSION OF DECIDUOUS TEETH posterior teeth But: (early mesial shift) a) The natural occlusal wear of the incisal edges & cusps of the deciduous teeth allows the mandible to shift forward by growth. b) Closure of primate space distal to mandibular canines by mesial movement of mandibular posterior teeth during eruption of mandibular 6s.  STAGE 3 MIXED DENTITION STAGE From the eruption of the 6s to the shedding of the Es (6 to 12 years). 1) Calcification of the permanent dentition starts after birth except for the MB cusps of the 6s. 2) Permanent teeth starts eruption when crowns are completed. 3) They pierce through the crest of the alveolar process when 3/4 of root is formed. 4) The germ of all permanent teeth are formed on the lingual side of their deciduous predecessors.  ERUPTION OF PERMANENT INCISORS Permanent incisors remain lingual to the deciduous throughout their development then tend to move to the line of the dental arch causing the deciduous to shed and if a deciduous incisor fails to shed the permanent one will erupt in a lingual position.  ERUPTION OF PERMANENT INCISORS The permanent incisors are often rotated before eruption to occupy less space, as they are wider mesiodistally then their predecessors but at the time of their eruption they improve their position.  ERUPTION OF PERMANENT INCISORS Some or all of the following growth mechanics accommodate for the difference in the size between small deciduous incisors and larger permanent ones. 1- the normal spaces present between deciduous teeth.  ERUPTION OF PERMANENT INCISORS Some or all of the following growth mechanics accommodate for the difference in the size between small deciduous incisors and larger permanent ones. 2- proclination of permanent incisors is more than deciduous ones giving a wider arch with more space for them.  ERUPTION OF PERMANENT INCISORS Some or all of the following growth mechanics accommodate for the difference in the size between small deciduous incisors and larger permanent ones. 3- primate space (in upper arch).  ERUPTION OF PERMANENT INCISORS Some or all of the following growth mechanics accommodate for the difference in the size between small deciduous incisors and larger permanent ones. 4- increase in the ICW which increase 1-2 mm in deciduous dentition, & it also increases by 3-5 mm in maxilla, 2-3 mm in the mandible during eruption of permanent canines.  How do the larger permanent incisors fit in place of the smaller ones?  ERUPTION OF PERMANENT CANINES AND PREMOLARS Leeway space: - The combined mesiodistal width of CDE is greater than 345, this difference in size is called ‘leeway space’ - It measures 3.4 mm in the mandible bilaterally, & 1.8 mm in maxilla bilaterally. - When the second primary molars are lost, the first permanent molars move forward (mesially) using the leeway space (late mesial shift). This decreases both arch length & perimeter. the late mesial shift of the mandibular molars in order to establish a normal molar relationship. Molar moves into FTP this space... Class I  UGLY DUCKLING PATTERN - The maxillary canine develops far from the dental arch (close to the orbital floor), at 9-10 years it moves downward and forward towards occlusion. - It comes to lie against the apices of erupting centrals and laterals causing mesial pressure on their roots. - The centrals responds to the pressure clinically by central diastema & distal crown flaring,& The laterals show labial tipping. - This diastema tend to close as the permanent canines erupt.  THE UPPER PERMANENT MOLARS The upper first molar develops in the tuberosity of the maxilla with its occlusal surface facing somewhat distally. It moves downwards and forwards as growth takes place by bone apposition on the tuberosity until it erupts, its former position being occupied by the second molar and finally the third molar. LENGTHENING OF THE MAXILLA BY APPOSITION OF BONE TO THE MAXILLARY TUBEROSITIES  THE LOWER PERMANENT MOLARS Similarly the lower permanent first molar develops in the ascending ramus of the mandible with its occlusal surface tilted mesially. This tooth moves forward as growth takes place by bone remodeling of the mandible. The second and then the third molar replace it in the ascending ramus.  STAGE 4 (EARLY PERMANENT DENTITION STAGE) After eruption of permanent premolars, canines, & 2nd molars (12-13 y). All teeth are in good intercuspation, normal molar relation, but there is - some proclination of incisors. - fullness of lips. This may be due to large tongue size in relation to the skeleton of the jaw. As the jaws catch up with tongue in growth they give rise to: - more upright position of the incisors which leads to decrease in lip fullness.  STAGE 4 (EARLY PERMANENT DENTITION STAGE) Late teen crowding: - the mandible continue to grow more than maxilla (late mesial shift). - the mandibular incisors are locked lingual to the maxillary incisors so they tip lingually leading to decrease in mandibular arch perimeter.  STAGE 5 (ADULT OCCLUSION) After eruption of 8s. There is little change in size and relations of the dental arch. DIMENSIONAL CHANGES IN THE DENTAL ARCH ARCH WIDTH  1- ARCH WIDTH Maxillary inter-canine width increases between the ages of 3-14 by 5 mm, Mandibular intercanine width increases to a lesser degree (2-3) between 3-14 years of age. less increase in width is observable in the intermolar width in both arches. ARCH LENGTH AND ARCH PERIMETER  2- ARCH LENGTH AND ARCH PERIMETER In the maxilla: Between 6-10 years there is an increase in both to accommodate for the larger erupting permanent incisors while deciduous molars are still present. This is followed by a decrease in length and perimeter as the deciduous molars are replaced by the smaller premolars.  2- ARCH LENGTH AND ARCH PERIMETER In the mandible: There is no increase in either but a noticeable decrease after the age of 10 which is attributed to the following: Late mesial shift of lower molars as the Leeway space is utilized. Interproximal wear of teeth. Mesial shift tendency of all teeth throughout life. Lingual tipping of mandibular incisors as the mandible grows forward. ARCH LENGTH AND ARCH PERIMETER