Mixed Dentition Period.

-Begins with the eruption of the first permanent molars distal to the second deciduous molars. These are the first teeth to emerge and they initially articulate in an 'end-on' (one on top of the other) relationship.

-On occasion, the permanent incisors spread out due to spacing. In the older literature, is called by the 'ugly duckling stage.' With the eruption of the permanent canines, the spaces often will close.

-Between ages 6 and 7 years of age there are:

20 deciduous teeth

4 first permanent molars

28 permanent tooth buds in various states of development

Permanent teeth

1. The permanent teeth begin formation between birth and 3 years of age (except for the third molars)

2. The crowns of permanent teeth are completed between 4 and 8 years of age, at approximately one- half the age of eruption

The sequence for permanent development

Maxillary                     

First molar → Central incisor → Lateral incisor → First premotar → Second pmmolar  → Canine → Second molar → Third molar

Mandibular

First molar → Central incisor → Lateral incisor → Canine → First premolar → Second premolar → Second molar → Third molar

Permanent teeth emerge into the oral cavity as

                                      Maxillary                       Mandibular

Central incisor               7-8 years                        6-7 years

Lateral incisor                8-9 years                        7-8 years

Canine                           11-12 years                    9-10 years

First premolar                10-Il years                      10-12 years

Second premolar            10-12 years                  11-12 years

First molar                       6-7 years                      6-7 years

Second molar                 12-13 years                    11-13 years

Third molar                      17-21 years                    17-21 years

The roots of the permanent teeth are completed between 10 and 16 years of age, 2 to 3 years after eruption

Deciduous dentition period.

-The deciduous teeth start to erupt at the age of six months and the deciduous dentition is complete by the age of approximately two and one half years of age.

-The jaws continue to increase in size at all points until about age one year.

-After this, growth of the arches is lengthening of the arches at their posterior (distal) ends. Also, there is slightly more forward growth of the mandible than the maxilla.

1. Many early developmental events take place.

-The tooth buds anticipate the ultimate occlusal pattern.

-Mandibular teeth tend to erupt first. The pattern for the deciduous incisors is usually in this distinctive order:

(1) mandibular central

(2) maxillary central incisors

(3) then all four lateral incisors.

-By one year, the deciduous molars begin to erupt.

-The eruption pattern for the deciduous dentition as a whole is:

(1) central incisor

(2) lateral incisor

(3) deciduous first molar

(4) then the canine

(5) then finally the second molar.

-Eruption times can be variable.

2. Occlusal changes in the deciduous dentition.

-The overjet tends to diminish with age. Wear and mandibular growth are a factor in this process.

-The overbite often diminishes with the teeth being worn to a flat plane occlusion.

-Spacing of the incisors in anticipation of the soon-to-erupt permanent incisors appears late. Permanent anterior teeth (incisors and canines) are wider mesiodistally than deciduous anterior teeth. In contrast, the deciduous molar are wider mesiodistally that the premolars that later replace them.

-Primate spaces occur in about 50% of children. They appear in the deciduous dentition. The spaces appear between the upper lateral incisor and the upper canine. They also appear between the lower canine and the deciduous first molar.

Clinical importance of cementum

1) Deposition of cementum continues throughout life.
The effects of the continuous deposition of cementum are the maintenance of total length of the tooth (good) and constriction of the apical foramen (bad).
2) With age, the smooth surface of cementum becomes more irregular due to calcification of some ligament fiber bundles. This is referred to as spikes.

Behavior of cementum in pathologic conditions

THE DECIDUOUS DENTITION

I. The Deciduous Dentition

-It is also known as the primary, baby, milk or lacteal dentition.

diphyodont, that is, with two sets of teeth. The term deciduous means literally 'to fall off.'

  There are twenty deciduous teeth that are classified into three classes. There are ten maxillary teeth and ten mandibular teeth. The dentition consists of incisors, canines and molars.

HISTOLOGY OF THE ODONTOBLAST

Formation of Dentin

Mantle dentin: First formed dentin
Type I collagen with ground substance
Formation of the odontoblast process

Matrix vesicles
Appearance of hydroxyapatite crystals
 

Predentin
Primary physiologic (circumpulpal) dentin
All organic matrix is formed from odontoblasts
Smaller collagen fibers
Presence of phosphophoryn

Mineralization
Globular calcification
Interglobular dentin: Areas of incomplete calcification
Incremental lines of von Ebner: Daily, 4mm of organic matrix is deposited. Also every 5 days the arrangement of collagen fibers changes. This creates the incremental lines of von Ebner.
Intratubular dentin

Dentin tubules
S-shaped in the coronal aspect, straight in root dentin

Von Korff fibers
They are an artifact