DEVELOPMENT OF DENTITION & OCCLUSION /fixed orthodontic courses by IDA

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INDIAN DENTAL ACADEMY Leader in continuing dental education


DEVELOPMENT OF DENTITION INTRODUCTION Embryonic cavity is lined by oral ectoderm 6 th week of intra uterine life(IUL) →local proliferation of oral ectoderm →formation of dental lamina Deciduous teeth →direct proliferation of dental lamina Permanent teeth →lingual extension of dental lamina Permanent molars →distal proliferation of dental lamina


DEVELOPMENT OF TEETH Bud stage Cap stage Bell stage Root formation

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Bud stage:

Bud stage

Cap stage:

Cap stage

Bell stage:

Bell stage


PERIODS OF OCCLUSAL DEVELOPMENT Pre-dental period Deciduous dentition period Mixed dentition Permanent dentition period


PRE-DENTAL PERIOD Period after birth during which neonate does not have teeth Lasts 6 months after birth

Gum pads:

Gum pads Alveolar processes at the time of birth Firm,pink,horse shoe shaped,covered by fibrous periosteum Develops in two parts Labiobuccal portion Lingual portion Both portions separated by dental groove Gum pads are divided into 10 segments by transverse grooves Each segment has one developing deciduous tooth sac

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lateral sulcus: transverse groove between canine and first deciduous molar segment. Useful in judging inter arch relationship at a very early stage. Lateral sulcus of mandibular arch is more distal to that of maxillary arch

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birth At birth, no teeth are visible. Primary teeth are at least partially formed and development of permanent teeth has begun.

Infantile open bite:

Infantile open bite Upper and lower gum pads are similar to each other Upper gum pad is longer and wider When both are approximated, there is a complete overjet all around Contact occurs between upper and lower gum pads in first molar region and space exists in anterior region This infantile open bite is considered normal and helps in suckling


STATUS OF DENTITION Neonate is without teeth for 6 months of life. Gum pads insufficient to accommodate developing incisors that are crowded in crypts 1 st yr of life →gum pads grow rapidly permitting incisors to erupt in good alignment.

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NATAL TEETH Teeth erupted at the time of birth →natal teeth Teeth erupted during 1 st month of life →neonatal teeth

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Natal and neonatal teeth mostly in mandibular incisor region and show familial tendencies


DECIDUOUS DENTITION PERIOD 1 st 6 weeks of IUL →initiation of tooth buds Primary teeth erupt at about 6 months Eruption completed by 2 ½-3 ½ yrs Sequence of eruption →A-B-D-C-E

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6 months At six months, the four central incisors are visible, usually appearing two at a time and appearing in the lower jaw first

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7-8 months At seven or eight months, the four lateral incisors appear next to the central incisors. The primary teeth are bluish white.

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12 months At around twelve months, the primary first molars appear, leaving temporary spaces between them and the lateral incisors

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16 months At sixteen months, the primary canines erupt between the lateral incisors and first molars.

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2 years At two years, the second primary molars begin to appear, completing the primary teeth. By age three, they appear completely


SPACING IN DECIDUOUS DENTITION Spaces usually exist between deciduous teeth →physiological or developmental spaces Important for normal development of 2°dentition Absence of spaces is an indication that crowding of teeth may occur in 2°dentition

Primate spaces:

Primate spaces Also called as simian or anthropoid spaces Seen mesial to maxillary canines and distal to mandibular canines Helps in placement of canine cusps of opposing arch

Deep bite:

Deep bite May occur in initial developing stages Accentuated by the fact that deciduous incisors are more upright Lower incisal edges often contact cingulum area of maxillary incisors Later reduced by Eruption of deciduous molars Attrition of incisors Forward growth of mandible

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Flush terminal plane:

Flush terminal plane Mesiodistal relation between distal surfaces of upper and lower 2 nd deciduous molars is called as flush terminal plane Normal feature of deciduous dentition where second deciduous molars are in same vertical plane


MIXED DENTITION PERIOD Begins at approximately 6yrs.Classified into: 1 st transitional period Inter transitional period 2 nd transitional period


FIRST TRANSITIONAL PERIOD Emergence of 1 st permanent molars and exchange of deciduous incisors with permanent incisors 1 st permanent molar erupts at 6yrs-guided into the dental arch by distal surface of 2 nd deciduous molar Mesiodistal relation between distal surfaces of upper and lower deciduous molars are of 3 types Flush terminal plane Mesial step terminal plane Distal step terminal plane

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FLUSH TERMINAL PLANE Mesiodistal relation between distal surfaces of upper and lower 2 nd deciduous molars is called as flush terminal plane. Normal feature of deciduous dentition where second deciduous molars are in same vertical plane.

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Erupting first molars may be in a flush or end on relation For transition of such an end on molar to a Class I molar relation, lower molar has to move forward by about 3-5mm relative to upper molar This can occur in 2 ways. By early shift or late shift

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EARLY SHIFT Occurs during early mixed dentition period Eruptive force of permanent molar pushes deciduous 1 st and 2 nd molars in the arch to close primate space and establishing Class I LATE SHIFT Occurs during late mixed dentition period In children who lack primate space, when the deciduous molars exfoliate the permanent 1 st molars drift mesialy utilizing leeway space.


MESIAL STEP TERMINAL PLANE Distal surface of lower 2 nd deciduous molar is more mesial than that of upper. Thus permanent molars directly erupt into Angles Class I occlusion Occurs due to early forward growth of mandible

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DISTAL STEP TERMINAL PLANE Distal surface of lower 2 nd deciduous molar lies more distal to that of upper. Thus erupting permanent molars maybe in Class II relation

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INCISAL LIABILITY The exchange of lower incisors take place. The difference between the amount of space needed for the accomodation of incisors and the space available for this →incisal liability It is roughly 7mm in upper arch and 5 mm in lower arch

Incisal liability:

Incisal liability Overcome by the following factors: Utilization of interdental spaces seen in primary dentition Increase in inter- canine width Change in incisor inclination


INTER TRANSITIONAL PERIOD Maxillary and mandibular arches consists of sets of deciduous and permanent teeth Between permanent incisors and permanent 1 st molars are deciduous canines and molars This phase during mixed dentition stage is relatively stable and no change occurs


SECOND TRANSITIONAL PERIOD Replacement of deciduous molars and canines by premolars and permanent cuspids respectively

Leeway space of Nance:

Leeway space of Nance Combined mesiodistal width of permanent canines and premolars is usually less than that of deciduous canines and molars, this is Leeway space of Nance

Leeway space of Nance:

Leeway space of Nance Greater in mandibular arch [3.4mm] than in maxillary arch [1.8mm] This excess space is utilized for mesial drift of mandibular molars to establish Class I molar relation

Ugly duckling stage:

Ugly duckling stage Transient or self correcting malocclusion seen in maxillary incisor region b/w 8-9yrs seen during eruption of permanent canines

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As developing permanent canines erupt, they displace roots of lateral incisors mesially,in turn transmitting force to roots of central incisors which gets displaced mesially. Resultant divergence of crown causes midline spacing

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18 years Last teeth to appear, the third molars, or the wisdom teeth, erupt at about age 18


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