Pedo 13 Development of Dental Arch and Occlusion PDF

Development of dental arch and occlusion Pedodontic Lec 13 Dr. Rawaa B. Fadhel B.D.S M.Sc. Development of dental arch and occlusion  At birth, the alveolar ridges are plain firm tissue with no teeth on them  As the child grows, the alveolar ridge grows and enlarges while the teeth develop to attai...

Development of dental arch and occlusion Pedodontic Lec 13 Dr. Rawaa B. Fadhel B.D.S M.Sc. Development of dental arch and occlusion  At birth, the alveolar ridges are plain firm tissue with no teeth on them  As the child grows, the alveolar ridge grows and enlarges while the teeth develop to attain their final shape and size within the jaws The usual sequence of primary dentition eruption is: central incisor (A) lateral incisor (B) first primary molar (D) canine (C) second primary molar (E) The typical sequence is A-B-D-C-E Development of occlusion can be divided into the following developmental periods: 1- pre-dental/dentate period:  after birth  The neonate does not have any teeth  Lasts for 6 months after birth  The alveolar ridge called gum pad  The upper anterior gum pad (intercuspid width) is wider than lower anterior pad and protrude (overjet) 5mm relative to lower anterior gum pad and overlap the lower anterior gum pad (overbite) by about 0.5mm  In the first 6 months of postnatal life, there is marked palatal width increase and overjet decrease rapidly  Gum pad relationship at birth cannot be used as reliable diagnostic criteria for predicting subsequent arch relationship 2- The deciduous dentition period  The initiation of primary tooth buds occurs during the first 6 weeks of intrauterine life  The primary teeth begin to erupt about 6 months  The eruption of all primary teeth is completed around 3 years of age when (E) come into occlusion and their roots complete development  By age 3 years, the relationship of maxilla to mandible is well established and maxillomandibular pattern dose not change their after 3- The mixed dentition period  Begin at 6 years of age with eruption of first permanent molar  The deciduous teeth with some permanent teeth present 4- The permanent dentition period  The presence of all permanent teeth Ideal occlusion at a young age predispose to an ideal adult occlusion The most desirable occlusion is an class 1 interdigitation By age of 7 years, primary central and lateral incisors have been or on process of been replaced by their permanent successor and permanent first molar already erupted The primary dentition remaining usually include canine and first and second molar of both arches The criteria of ideal occlusion at 7 years old age:  Class 1 molar and incisor interdigitation  2mm anterior and posterior overjet  2mm anterior overbite  Coincident dental midline Deciduous dentition period 1- Spacing in deciduous dentition (physiological spacing with the most prevalent space mesial to primary canine in maxilla and distal in primary canine in mandible (primate space) or (anthropoid space) which is helpful in canine positioning and relationship with opposing arch  Two consistent morphologic arch forms of primary dentition: A- type I : generalized spacing between teeth present B- type II: teeth were in proximal contact without spacing  The other space in primary dentition are called (developmental space) play important role in development of permanent dentition  Some children don’t have physiological spaces referred to (closed space or non spaced dentition, which highly prone to malocclusion during development of permanent dentition 2- Shape of dental arch  In deciduous dentition dental arch wider and (U) shape with spaces between teeth 3- Terminal plane relation to deciduous molar  The relationship of the distal terminal plane of opposing second primary molar teeth can be classified into one of 3 categories: A- a flush terminal plane (flush terminus) mean that anteroposterior position of distal surface of opposing primary second molars are in the save vertical plane B- mesial-step terminus: a lower second primary molar terminal plane that mesial to maxillary primary terminus C- The distal-step terminal plane is a situation in which mandibular second primary molar terminus is distal to upper second primary molar terminus 4- deep bite 5- flat curve of spee 6- shallow cuspal interdigitation 7- incisor are more vertically placed Mixed dentition period Divided into 3 phases:  first transitional period  inter transitional period  second transitional period 1- First transitional period  The emergence of first permanent molar and exchange of deciduous incisor with permanent incisor A- eruption and occlusion of first permanent molar Erupt about 6 years of age The location and relationship of first permanent molar depend upon distal surface relationship between upper and lower second deciduous molars, 6 guided into dental arch by distal surface of E Three distinct types of molar adjustment can occur:  Mesial shift during first permanent molar eruption occurs at the expense of any posterior spacing that might have been present including breakdown spaces resulting from interproximal caries, proximal breakdown of crown and/or premature loss of primary teeth the occlusion forming a mesial step (distal surface of lower E is mesial to same surface of maxillary molar) is ideal for cl I development  Distal step (distal surface of lower E is distal to same surface of maxillary molar) indicate a developing class II malocclusion  Proper permanent molar occlusion was achieved from straight terminal plane by a second mesial shift of molar as second primary molar are exfoliated. B- Exchange of incisor  During first transitional period of deciduous incisors are replaced by permanent incisors  Lower central are first to erupt  Permanent incisor larger than deciduous they replaced  Incisal liability: the difference between amount of space needed for accommodation of incisors and amount of space available about 7 mm in upper and 5 mm in lower  The mean increase of intercanine width was greater in upper (3- 4)mm than in lower (2-3)mm  In lower, the greater tendency to increase during eruption of lower lateral , whereas in upper during eruption of upper central  The spaced arch result in favorable alignment of permanent incisors  40% of arches without primary dental spacing result in crowded anterior segment The regulatory factors controlling the arrangement of four permanent incisors  utilization of physiologic spaces that exists in primary dentition  Increase intercanine width  Increase anterior length in dental arch will provide space to accommodate the larger permanent incisor  Both maxillary and mandibular permanent incisor show labial inclination much more than primary incisors making permanent dental arch circumference wider for arrangement of large permanent incisor 2- Intertransitional period  it is lag phase with no active tooth movement to occur  The dental arches are comprised of both primary and permanent teeth.  The upper and lower arches consist of permanent incisors and molars that sandwich the deciduous canines and molars.  This phase last for 1.5 years and relatively stable  Only few changes in morphology of deciduous teeth are seen because they undergo attrition 3- Second transitional period  Also called late mixed dentition  Between 9-12 years of age, involve exfoliation of primary canines and molars in conjugation with eruption of permanent canines, premolars and second permanent molars A- exchange of canines and premolars The space is limited as the mesial surface of first permanent molar forms its distal limit and the distal surface of permanent lateral incisor forms its mesial limit The factors considered during this period are: 1- leeway space of Nance 2- ugly duckling stage 1- Leeway space of Nance  The combined mesiodistal width of permanent canines and premolars is usually less than that of deciduous canines and molars  The surplus space called leeway space of Nance  The amount of leeway space is greater in mandibular arch than in maxillary arch, it is about 1.8mm (0.9 mm on each side of the arch) in maxillary arch and 3.4 mm (1.7mm on each side of the arch) in mandibular arch  This excess space available after the exchange of deciduous canines and molars is utilized for mesial drift of mandibular molars to establish class I molar relation  The most favorable dental arch pattern is one in which leeway space is excessive (combined size of unerupted canine and premolars is smaller than arch space available)  If leeway space is deficient, dental crowding result 2- Ugly duckling stage  Also called broadbond phenomenoun  Indicate unesthetic appearance of the child  It is transient or self-correcting malocclusion seen in maxillary incisors region between 8-9 years of age seen during eruption of permanent canines  As the permanent canines erupt, they displace the roots of lateral incisor mesially, this result in transmitting of force onto roots of central incisors which displaced mesially  A resultant distal divergence of crown of incisors occur which result in creation of diastema B- Eruption of second permanent molar  After the exchange of lateral completed and dental arch up to first molar is established, the second permanent molar begin to erupt  With eruption of second permanent molar , the arch circumstances may become shorter than that of primary arch by utilization of leeway space