Development of occlusion Dr Lamis Elsharkasi

occlusion Occlusion simply means “contact between teeth” The human dentition is in dynamic state constantly changing throughout life. Period of occlusion : Pre-dental period Deciduous dentition period Mixed dentition period Permanent dentition period

Pre-dental period The period after birth which the neonate does not have teeth Lasts for 6 months The alveolar processes at the time of birth are known as gum pads

Gum pad Gum pad are: Pink Firm Horse-shoe shaped Covered by a dense layer of fibrous periosteum Developed in two parts labio-buccal portion and lingual portion Dental groove separates the two portions

Gum pad The gum pad is divided into 10 segments by transverse grooves Each segment consists of one developing deciduous tooth sac Gum pad are separated from the palate and the floor of the mouth by gingival grooves Lateral sulcus: present between the canine and 1st molar Transverse groove Gingival groove Lateral sulcus

Gum pad The upper gum pad is larger and wider than the lower, so when approximated there is a complete overjet all around. Contact between upper and lower gum pad occurs in the molar region A space is exist in the anterior region (infantile open bite). It is normal and helps in suckling

Gum pad State of dentition: At birth the gum pad are not sufficiently wide to accommodate the developing incisors During the first year of life a rapid growth happened which permits the incisors to erupt in good alignment

Gum pad Natal teeth : presents at time of birth Neonatal teeth: erupts during the first month of age Both located in the mandibular incisor region

Deciduous dentition period Initiation of primary tooth buds occurs during the first 6 weeks of intra-uterine life Eruption of primary teeth begin around 6 months Establishment of primary dentition is usually by the age of 3years 3-5 years – no significant change Sequence of eruption: A-B-D-C-E

Decidous teeth development and eruption time MAXILLARY TEETH A B C D E HARD TISSUE FORMATION( months intrauterine) 13-16 15-17 15-18 17-20 CROWN FORMATION 1.5 months 2.5 months 9 months 6 months 11 months ERUPTION 8 months 2 years 1.5 2.5 ROOT 3 3.5 4

MANDIBULAR TEETH A B C D E HARD TISSUE FORMATION( months intrauterine) 13-16 15-17 16-18 17-20 CROWN FORMATION 2 months 3 9 6 10 ERUPTION years 1.5 2.5 ROOT 2.5-3 3.5 2.8 Variation in eruption of deciduous teeth +/- 6 months

Molar relation ship in deciduous dentition Distal step Flash terminal Mesial step

Characteristics of deciduous dentition Flash terminal plane Deep bite: may occur in the initial stage of deciduous dentition . This is later reduced by these factors: Eruption of deciduous molars Attrition of primary incisors Forward movement of mandible due to growth Upright inclination of incisors Spacing in deciduous teeth

Spacing in deciduous dentition 1. interdental spaces: also called physiological spaces and developmental spaces These spaces are important for normal development of permanent dentition Absence of spaces in deciduous dentition, leads to crowding in permanent dentition

Spacing in deciduous dentition 2. primate space(arthropoid space): Spacing seen mesial to the maxillary deciduous canine (1.7 mm) and distal to the Mandibular canine (1.5 mm). Importance: early mesial shift

Mixed dentition Begin around 6 years of age with the eruption of the first permanent molars Mixed dentition = deciduous teeth + permanent teeth Divided into 3 phases: 1st transitional period Inter-transitional period 2nd transitional period

1st transitional period Characterized by the eruption of 1st permanent molar and exchange of deciduous incisors with permanent incisors 1st permanent molar erupts at 6 yrs. and its location depends on the deciduous molar relation ship Mesial step Flash terminal Distal step Class I molar If excess mandibular growth –class Ⅲ Edge to edge Class I Class Ⅱ

Early mesial shift Early shift occurs during early mixed dentition period Eruption force of 1st permanent molar is sufficient to push deciduous 1st & 2nd molar forward to close the primate space

Exchange of incisors During the 1st transitional period the deciduous incisors are replaced by the permanent incisors Mandibular incisors erupt first The permanent incisors are larger than the deciduous teeth they replace The amount needed for the accommodation of the permanent incisors and the amount available for this is called Incisal liability 7mm in maxilla 5mm in mandible

Incisal liability The incisal liability is overcomed by the following factors: Interdental dental spaces Inter canine width Incisor inclination

Incisal liability 1. utilization of interdental spaces: Physiological spaces that exist in deciduous dentition are utilized to account for incisal liability In spaced deciduous dentition, alignment of permanent teeth in arch is easier than in closed dentition 2. intercanine width: Width growth creates more room for the permanent incisors 3. incisor inclination: Permanent incisors erupt more labially which tend to increase the dental arch perimeter

Inter-transitional period this period started when 1st permanent molar & permanent incisors are erupted Consists of set of deciduous and permanent teeth This period is relatively stable and no change occur 6 E D C 2 1 1 2 C D E 6 6 E D C 2 1 1 2 C D E 6

2nd transitional period This period characterized by the replacement of deciduous molar and canine by the premolars and permanent canine respectively Late shift of permanent molar occur in this period by utilizing leeway space to establish class Ⅰmolar.

Late mesial shift In cases when the primate space is absent, the permanent 1st molar shift drift mesially utilizing the leeway space. Premolars are smaller than primary molar teeth they replace The extra space is called leeway space C+D+E > 3+4+5 Maxilla : 1.5mm Mandible: 2.5mm

Ugly duckling stage Characterized by spacing between maxillary central incisors Parents often apprehensive during this stage and consult the dentist It is a transient or self correcting malocclusion which seen between 8-9 yrs. During the eruption of permanent canine

Ugly duckling stage As the developing canines erupt, they displace the roots of the lateral incisors mesially This results in transmitting the force on to the roots of central incisors which also displaced mesially.

Permanent dentition Permanent dentition forms within the jaw soon after birth except the cusps of the first permanent molar which forms before birth Permanent incisors develop lingual or palatal to the deciduous teeth and move labially as they erupt Premolars develop below the diverging roots of deciduous molars

Permanent dentition Sequences of eruption of permanent teeth: Maxilla : 6 – 1 – 2 – 4 – 3 – 5 – 7 Or : 6 – 1 – 2 – 3 – 4 – 5 – 7 Mandible: 6 – 1 – 2 – 3 – 4 – 5 – 7 or : 6 – 1 – 2 – 4 – 3 – 5 – 7

Permanent teeth development and eruption time MAXILLARY TEETH 1 2 3 4 5 6 7 8 HARD TISSUE FORMATION 4 months 11 months 5 months 20 months 26 months 7 months intra- uterine years CROWN FORMATION 3.5 4.5 6.5 2.5-3 13 ERUPTION 7-8 10 10.5 12 18 ROOT 9-10 10-11 12.5 12-13 12-14 9.5 13-15 21.5

Variation in eruption of permanent teeth +/- 2 years MANDIBULAR TEETH 1 2 3 4 5 6 7 8 HARD TISSUE FORMATION months 20 26 7 months intra- uterine years 9 CROWN FORMATION 4.5 6.5 2.5 13 ERUPTION 6-7 7-8 10 10-11 11 12 18 ROOT 8-9 9-10 11-13 12-14 8-10 14-15 Variation in eruption of permanent teeth +/- 2 years

Characteristics of permanent dentition Class i molar relationship ( mesiobuccal cusp of upper 1st molar occludes with the mesiobuccal groove of lower 1st molar) No crowding No rotated teeth No spacing Appropriate inclination of teeth The occlusal plane should be flat or have only a mild curve of spee ( 1.3mm)

Essential factors of smooth transition from primary to permanent dentition Primate space Physiological spacing Preservation of leeway space Tooth size and jaw in harmony