developement of dentition

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study material for undergraduate dental students

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DEVELOPMENT OF DENTITION & OCCLUSION : 

DEVELOPMENT OF DENTITION & OCCLUSION Dr Lakshmi Ravi Reader St.Gdc

INTRODUCTION : 

INTRODUCTION The development of dentition is an important part of craniofacial growth as the formation, eruption, exfoliation and exchange of teeth take place during this period. This is an assimilation of facts, predictions, studies, in both static and dynamic situations; the factors influencing them and their clinical implications.

PRE-NATAL DEVELOPMENTOF TEETH : 

PRE-NATAL DEVELOPMENTOF TEETH Initiation Bud stage Cap stage Bell stage

THEORIES OF TOOTH ERUPTION : 

THEORIES OF TOOTH ERUPTION Bone remodeling Root growth Vascular pressure Periodontal ligament traction

BIRTH TO COMPLETE PRIMARY DENTITION 1ST INTERTRANSITIONAL PERIOD 1ST TRANSITIONAL PERIOD 2ND INTERTRANSITIONAL PERIOD 2ND TRANSITIONAL PERIOD ADULT DENTITION POST-NATAL DEVELOPMENT OF DENTITION

BIRTH TO COMPLETE PRIMARY DENTITION (Birth- 3yrs) : 

BIRTH TO COMPLETE PRIMARY DENTITION (Birth- 3yrs) The tooth buds of all primary teeth are present and in various stages of development at the time of birth. About 7 to 8 months after birth, all the teeth except the 7’s & 8’s are present in some stage of development. In a mandible which is less than 1yr of age, a line drawn along the occlusal surfaces passes through the condyle suggesting the lack of ramal growth. By the 1st year, a normal & desirable dentition will usually exhibit spacing.

Slide 7: 

The 1st primary tooth to erupt is the lower central incisor between 6&8 months of age, followed by the U.Centrals, U.Laterals & L.Laterals. The 1st primary molar erupts by about the 14th month. The primary cuspids & 2nd primary molars erupt by about 21/2 yrs of age. There is evidence of vertical growth as signified by the superior positioning of the condyle to the occlusal plane.

FIRST INTERTRANSITIONAL PERIOD( 3-6 yrs ) : 

FIRST INTERTRANSITIONAL PERIOD( 3-6 yrs ) This is the period between the completion of eruption of Primary dentition & the emergence of the Permanent teeth. According to Baume(1950) Primate Space(Type I Spacing) Terminal plane Space for the 6’s is achieved by Tuberosity apposition in the maxilla. Ramal resorption in the mandible. The tooth buds of the 4’s & 5’s begin to form.

FIRST TRANSITIONAL PERIOD( 6-8 yrs ) : 

FIRST TRANSITIONAL PERIOD( 6-8 yrs ) Eruption of the 1st permanent molars : The Terminal plane is very important in determining the interocclusal relationship of the 1st permanent molars. -Vertical plane -Mesial step -Distal step

Slide 10: 

Exchange of incisors : The primary incisors begin to exchange with the permanent incisors before & after the eruption of the 6’s. The total sum of the M-D width of the 4 permanent incisors is > that of the primary incisors by about 7mm in the maxilla & 5mm in the mandible. Incisor liability(Mayne 1968 ) -Interdental spacing in primary incisors should exist. -Intercanine archwidth growth should occur. - Intercanine archlength should increase through anterior positioning of the permanent incisors. -Favourable size ratio between the primary & permanent teeth.

SECOND INTERTRANSITIONAL PERIOD( 8-10 yrs ) : 

SECOND INTERTRANSITIONAL PERIOD( 8-10 yrs ) This period is referred to as the “Mixed Dentition period”/ “Ugly Duckling stage” ( Broadbent 1937 ) . Vertical dimension of the face increases thus increasing the alveolus to accommodate the roots. Max. Tuberosity& Mand. Ramal activity makes room for the 7’s. Max. cuspids are lateral to the nose, mand. cuspids close to the mand. borders.

Slide 12: 

Premolars are in the bifurcation of their antecedents with evidence of their resorption. The “GABLE EFFECT” : The mand. cuspids & bicuspids are in the shape of a ‘V’, in sequence, in relation to the occlusal plane. The sequence of eruption being 3,4,5 in the mandible, 3 makes its way much ahead of 4 & 5.

SECOND TRANSITIONAL PERIOD( 10- 12 yrs ) : 

SECOND TRANSITIONAL PERIOD( 10- 12 yrs ) Here, exchange of teeth occurs between c,d,e & 3,4, 5. Emergence of 7’s takes place by virtue of increase in arch-circumference, after the Dental arch upto 6, is established .(mixed to permanent ) During the exchange & emergence, smooth utilization of “Leeway space” & “Primate space” takes place. The sequence of eruption of the buccal teeth in: Maxilla - 4, 3, 5 ( 3,4,5 /4,5,3 are exceptions ). Mandible - 3,4, 5.

ADULT DENTITION : 

ADULT DENTITION This is considered to be between 18 & 25 yrs, when the roots of the permanents are completed and the 8’s have erupted. Nose & chin become more prominent to enhance profile. Cranio-facial growth gives finishing touches to the face by pneumatization of the Sinuses & apposition at the Glabella. Increase in jaw growth continues ( mandible ) to accommodate the 8’s.

FACTORS AFFECTING OCCLUSAL DEVELOPMENT : 

FACTORS AFFECTING OCCLUSAL DEVELOPMENT GENERAL FACTORS 1.Skeletal Factors 2.Muscle Factors 3.Dental factors LOCAL FACTORS

General Factors : 

General Factors Skeletal factors : Conditions that affect jaw growth are ; 1. Any pathological condition 2. Inherited & acquired congenital malformation 3. Trauma or infection during the growing years

Slide 17: 

The teeth are set in the jaws and hence jaw relationship will have an influence on that of the dental arches. Jaw relationships can be considered as : 1. Jaws in relation to the cranial base 2. Jaws in relation to each other -Skeletal Cl.I, II & III -Buccal cross-bite/ lingual occlusion -High gonial angle-increased V.D Low gonial angle-decreased V.D 3. Alveolar bone in relation to basal bone

Slide 18: 

Muscle factors : Final tooth position is largely governed by muscle action, particularly muscles of the lips, cheeks & tongue. Lip form Lip activity Tongue size, resting position & function Adaptive resting posture or adaptive swallowing Endogenous tongue thrust Thumb & finger sucking Neutral zone

Slide 19: 

Dental factors : The third major factor affecting occlusal development is the relationship between the size of the dentition & the size of the jaws. But it is more realistic to consider dentition size in relation to the dental arch size, than to jaw size. Effects of excessive dentition size -Overlapping & displacement of teeth -Impaction of teeth -Space closure after extractions

Slide 20: 

Effects of early loss of primary teeth -Function & oral health -Over-eruption of opposing teeth -Psychological effects on child & parent -Position of permanent teeth Effects of asymmetric loss of primary teeth -Mid line shift Space maintenance

Local Factors : : 

Local Factors : Aberrant developmental position of individual teeth -Trauma -Malposed crown -Dilacerated root -Unknown etiology( perm. Max. canines ) Presence of supernumerary teeth -Supplemental (teeth of normal form ) -Conical (the mesiodens ) -Tuberculate (usually palatal to the upper centrals, delaying their eruption )

Slide 22: 

Developmental Hypodontia Hypodontia can modify the occlusion & position of the teeth by virtue of its effects on : -The form of the teeth -The position of the teeth -The growth of the jaw The Upper Labial Frenum This may cause median diastema. Other possible causes are : -Hypodontia -Supernumerary teeth -Generalized spacing -Proclination of upper incisors -Heredity

Slide 23: 

Buccal Crossbite : -Bilateral Crossbite -Unilateral Crossbite -The Incisal Overbite

Possible questions : 

Possible questions Development of dentition from 6-12yrs(essay) Transient malocclusion/ugly duckling stage Leeway space/primate space Incisor liability Flush terminal planes