Chronology of deciduous & permanent teeth

Condition of teeth at different ages Mandible at different ages Significance of geometric outline form of

the crowns of teeth The role of physiologic tooth form in

protecting peridontium

Calcification of deciduous teeth begins before birth & only first permanent molar begin calcification at birth.

Eruption of the tooth means that: a- developing tooth move from the bony crypt to appear in the oral cavity. b- crown and cervical third of the tooth was completed.

Sequence of eruption of deciduous teeth A,B,D,C,E, mandibular tooth precedes the maxillary one of the same type. So by the age of two years all the deciduous teeth are erupted and the root completed at three years.

Root formation of deciduous teeth = eruption+ 1or1.5 years. Shedding means: resorption of the root of the deciduous teeth due to the

pressure produced from its successor. Shedding of the deciduous teeth begins at 6 years A and ended at 10 years

E. Date of shedding = Date of eruption of permanent. Beginning of root resorption of deciduous teeth = shedding – 3years except

lower canine – 1year.

A B C D E

A B C D E

1 2 4 3 5

Sequence of eruption of permanent teeth In the mandible 6-1-2-3-4-5-7-8. In the maxilla 6-1-2-4-3-5-7-8. Root formation date fore permanent teeth= date of eruption+ 3years. Crown completed for permanent teeth =date of eruption-3years.

The equation used to determine the formed hard part of each tooth at a specific date

Upper A beginning of calcification eruption 4MIU 7M 5m until birth + 7m=12m ( crown& 1/3 of root ) Every three month: 1/3 of the tooth is formed. At birth 5m from the beginning of calcification about ½ of the crown

is formed.

B beginning of calcification--- eruption

4.5MIU 8M=12.5M each 1/3 need 3.1M to

formed at birth less than ½ crown formed.

C beg. Of calcification ---------- eruption 5MIU 18M 4M+18M= 22M SO crown + 1/3 of root formed at 22M. Each 1/3 need 5.5 m to formed At birth ( about 4m only from the beg. Of calcification) at birth cusp tip formed. D beg. Of calcification --------eruption 5MIU 14M 4M+14M= 18M for formation of crown and 1/3 of root So each third need 4.5 M to

formed. At birth occlusal surface only formed . E beg. Of calcification ------------------eruption 6MIU 24M 3M+24M=27M each third =6.5m separate cusps of the occlusal surface is formed.

Permanent teeth The mesiolingual cusp of lower 6.

½

Less than1/2

Cusp tip

Occ.S Separate cusp

ML cusp

Beginning of calcification -----crown completed

3M 4Y(4X12=48-3=45M)

Each third formed in15M So at one year less than 1/3 of crown formed

15m15m

15m

Beginning of calcification -------crown completed

at birth 3y x12=36m

Each third formed in 12M

So at one year 1/3 of crown formed

12m

12m12m

start to eruption

Crown&1/4 root

part of crowns formed C&D&E

Incisal 1/3 of 1&2

separate cusps of 6

cusp tip

The deciduous teeth Incisors , canines and the first deciduous molars are present in the oral

cavity. Incisors are in occlusion and their roots completed. Two third of the canines and first molars roots are formed.

E beg. Of calcification ------------------eruption 6MIU 24M 3M+24M=27M each third =6.5m **So at one and half year thesecond deciduous molar is not yet erupted however the crown is completed

and less than third of the root formed.

The permanent teeth :

Upper central permanent incisor: Beginning of calcification -----crown completed 3M 4Y(4X12=48-3=45M)Each third formed in15M So at one& half year less than 1/2 of crown formed, nearly incisal third is formed.

Less than half of the crown of maxillary and mandibular central incisors.

One third of the crown of the mandibular lateral incisors.

Less than third of the upper lateral incisor. More than half of the crown of first molar. Less than half of the canine is formed.

All deciduous teeth erupted with fully formed teeth

More than ½ crown of 1&2 formed

½ crown 3

small part of 4&5

crown of 6 completed

separate cusps of 7

Root of lower A resorped

B&C&D some amount of resorption

E no resorption

crown&1/3 root formed

less than 1/3 of the root formed

crowns of 3&4&5 formed

6 is erupted

crown of 7 not completed

C&D&E most of their roots resorped

1&2 is erupted their root completed

3&4&5 not yet erupted &less than 1/3 of root formed

root of 6 completed

7 crown& less than 1/3 root formed

8 Calcified separate cusps are formed

All permanent teeth erupted except 8 .

All roots are completed except 7&8

Significance:

To accommodate interproximal gingiva. Spacing between roots allow sufficient alveolar bone,

periodontal ligament, blood vessels and nerves. Provide contact between teeth which support & stabilization of

the dental arch. Contact between upper & lower teeth which prevent over

eruption and elongation on tooth loss.

Facial and lingual aspects of all teeth is Trapezoid

Wide base cervically provides ----- more strength for the teeth & increases their stability in the jaw, this is important for the reduction of forces transmitted to the periodontium.

Tapered labial & lingual surfaces which facilitate pearcing of food.

The proximal aspect is triangular

the base is toward the cervix & apex is toward the incisal ridge

Upper teeth: * Constricted occlusal surface lead to early penetration of the food. * Decrease forces on base of the tooth. * Self cleaning. Lower teeth: * Lingual inclination of the crown of lower molar prevent traumatic

occlusion & periodontium degeneration & give proper inter cuspation and occlusion.

* Keeps the axis of maxillary and mandibular teeth parallel . * Permits the prominence of cervical ridge so protect the gingival

contour.

Upper teeth trapezoid

Lower teeth rhomboid

Condyle process at the level of the upper border of mandible. Coronoid process at higher level than condyloid. Mental foramen near the lower border under the crypt of D Mandibular canal near lower border Sigmoid notch is shallow Mandible two half till the end of the first year. Angle of the mandible 170 degree.

Symphyseal cartilage

(Symphysis of mandibule +mental ossicals) 2parts fuse at 1 year

Mental foramen Mandibular

canal

Condyloid cartilage 14WIUL-20Y give condyle+ posterior part of the ramus

Coronoid cartilage 14WIU---6MIU give coronoid process + anterior part of the ramus

Coronoid process higher than condyloid process. Mental foramen midway between upper& lower border. Mandibular canal slightly above mylohyoid line. Sigmoid notch more deeper. Angle of the mandible 140 degree. Chin is poorly developed.

Increase in length by bone remodeling make room for permanent molars

Increase in height by eruption of teeth +alveolar bone formation+ bone deposition at lower border of the mandible

Growth

Condyle cartilage

Alveolar bone

Posterior border of ramus

Increase in length of ramus

Increase in height

Increase in length

Condyle process at a higher level than coronoid process. Sigmoid notch deepest. Mental foramen mid way between upper & lower border under the

socket of lower 5. Angle of the mandible 110-120 degree. Chin is significantly prominent ----- mental protuberance.

Condyloid process

Coronoid process

Sigmoid notchRamus

Body

Mental foramen

Mental protuberance

Condyloid process at a lower level than coronoid process Sigmoid notch is shallower. Mental foramen near the upper border of the mandibule. Mandibular canal near the upper border. Angle of the mandible 140 and the ramus inclined posterior. Body of the mandible has reduction in height due to loss of teeth

and alveolar process.

Condyloid process

Coronoid process

Mental foramen

Mental protuberance

Mandibular canal

At birthAt childhood

At adult period

At old age

The periodontium: It is the system of attachment and

investing tissues surrounding the tooth that serve to attach the tooth in its socket.

This includes, the gingiva, periodontal ligament cementum and the alveolar bone.

Tooth form physiologically may affect the periodontium by. Direct factors & Indirect factors.

1- Proximal contact area. 2- Inter proximal spaces. 3- Embrasures or spill ways. 4-Facial and lingual contours of the

crown. 5- Curvature of the cervical line.

1- Cusp, crown and root form: Crown (proximal maximal contour, Facial & lingual

maximal contour and geometric outline) & root form (length, number& distribution and root outline (cone shape) ) .

2- Proportion between size of crown and root. 3-Angulation of teeth in jaw. 4-Self cleaning ability of the teeth which is achieved

by: A- Proper alignment of teeth in the dental arch. B- Normal gingival attachment. C- Brushing action of the tongue, lips & cheek. D- Washing effect of saliva & fluid intake. E- Friction of food during mastication. F- Home care of teeth as teeth brushing.

Each tooth has a mesial and distal contact areas except lower& upper 8 ( has no distal contact area).

Contact areas are small in anterior teeth and increase in size in posterior teeth.

The mesial contact area is located more incisally, while the distal one is more cervically.

Generally in anterior teeth the contact areas are near the incisal ridge and become more cervically as we go to posterior teeth.

The contact area in anterior teeth is centered labiolingually.

In posterior teeth the contact area is more buccally situated

However these relations are greatly influenced by:

1- length & width of the crown.

2- Level & height of proximal contour.

3- proximal wear.

4- malocclusion.

5- disproportional growth between teeth & jaw.

6- developmental anomalies. 7- extraction, developmental missing or unerupted teeth.

1- Stability of the dental arch by combined anchorage of all the teeth in each arch by positive contact .

2- Protects the inter dental gingiva.3- Prevents food impaction between teeth.4- distribution of masticatory force among the adjacent teeth in the

individual dental arch. If proper contact is lost: 1- Food impaction between teeth. 2- Dental caries and gingival inflammation. 3-Disturbance of proper alignment of teeth change in angulations of teeth

occlusal trauma

Destruction of periodontium and loss of teeth.

Embrasure is an open space between adjacent teeth in the same dental arch, formed by the curved smooth surfaces of teeth. They diverge from the contact area incisally, occlusally or cervically, labially, buccally or lingually.

Cervical embrasures are filled with the inter dental papilla. The size of the embrasure depend on the position of the contact area: Occlusal embrasure in posterior teeth larger than incisal embrasure of anterior teeth.

Incisal embrasure Occlusal embrasure

Cervical embrasure

1- Makes a spill way for escapement of food during mastication which lead to reduce forces on the teeth and periodontium.

2-Proper embrasure and contact prevent food from being forced between teeth & so protect the inter dental papilla.

3- Embrasure allow proper degree of frictional massage during mastication gingival stimulation

4-Embrasure and rounded surfaces of teeth ensures self cleaning ability of teeth. If there was no embrasure and teeth surfaces were not rounded stagnation of food and poor oral hygiene.

Triangular spaces filled with inter dental papilla Base at the alveolar process.

Sides proximal surfaces of teeth. Apex at the contact area.

The form of the inter proximal space depend on the tooth form & position of the contact area:

*Wide cervix of the tooth narrow inter proximal space. * Narrow cervix wide inter proximal space.

* Wide inter proximal space give considerable space between roots of teeth for bone & investing tissues including B. Vs., nerves and lymphatic.

The height of contour of the labial and buccal surfaces of all teeth is at the cervical third.

The height of curvature lingually is:

- At the cervical third in anterior teeth.

- At the middle third in posterior teeth.

The physiologic importance of the labial,

buccal& lingual contours of the crowns 1- Hold the gingiva under definite tension.2- Protect the gingival margin by deflecting

the food away during mastication which allow proper degree of gingival massage.

3- If these curvatures are absent or under developed:

* the gingiva will be pushed apically (gingival recession).

4- If the curvature is over developed this make:

* over protection to the gingiva & prevent gingival massage.

* allow food accumulation which lead to chronic inflammation.

In individual tooth the curvature of the cervical line mesially greater than distally.

Generally the curvature of the cervical line in anterior teeth greater than in posterior teeth.

In molars, it is nearly straight mesially and straighter distally .