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

As root and cementum formation begin, bone is created in the adjacent area. Throughout the body, cells that form bone are called osteoblasts. In the case of alveolar bone, these osteoblast cells form from the dental follicle. Similar to the formation of primary cementum, collagen fibers are created on the surface nearest the tooth, and they remain there until attaching to periodontal ligaments.

Like any other bone in the human body, alveolar bone is modified throughout life. Osteoblasts create bone and osteoclasts destroy it, especially if force is placed on a tooth. As is the case when movement of teeth is attempted through orthodontics, an area of bone under compressive force from a tooth moving toward it has a high osteoclast level, resulting in bone resorption. An area of bone receiving tension from periodontal ligaments attached to a tooth moving away from it has a high number of osteoblasts, resulting in bone formation.

Age changes in the dentition

I. After the teeth have reached full occlusion, microscopic tooth movements occur to compensate for wear at the contact area (Mesial Drift) and occlusal surfaces (by Deposition of cementum at the root apex)

2. Attrition of incisal ridges and cusp tips may be so severe that dentin may become exposed and intrinsically stained

3. Secondary dentin may be formed in response to dental caries, trauma, and aging and result in decreased pulp size and tooth sensation

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.

MAXILLARY CUSPIDS (CANINE)

The maxillary cuspid is usually the longest tooth in either jaw. canines are considered the corner stones of the dental arch They are the only teeth in the dentition with a single cusp.

Facial Surface:- The facial surface of the crown differs considerably from that of the maxillary central or lateral incisors. In that the incisal edges of the central and lateral incisor are nearly straight, the cuspid has a definite point, or cusp.  There are two cutting edges, the mesioincisal and the distoincisal. The distoincisal cutting edge is the longer of the two. The developmental grooves prominent on the facial surface  extending two-thirds of the distance from the tip of the cusp to the cervical line.  The distal cusp ridge is longer than the mesial cusp ridge

Lingual Surface:  Distinct mesial and distal marginal ridges, a well-devloped cingulum, and the cusp ridges form the boundries of the lingual surface. The prominent lingual ridge extends from the cusp tip to the cingulum, dividing the lingual surface into mesial and distal fossae.

Proximal: The mesial and distal aspects present a triangular outline. They resemble the incisors, but are more robust--especially in the cingulum region

Incisal: The asymmetry of this tooth is readily apparent from this aspect. It usually thicker labiolingually than it is mesiodistally. The tip of the cusp is displaced labially and mesial to the central long axis of this tooth.

Root Surface:-The root is single and is the longest root in the arch. It is usually twice the length of the crown.

MAXILLARY LATERAL INCISORS

it is shorter, narrower, and thinner.

Facial: The maxillary lateral incisor resembles the central incisor, but is narrower mesio-distally. The mesial outline resembles the adjacent central incisor; the distal outline--and particularly the distal incisal angle is more rounded than the mesial incisal angle (which resembles that of the adjacent central incisor. The distal incisal angle resembling the mesial of the adjacent canine.

Lingual: On the lingual surface, the marginal ridges are usually prominent and terminate into a prominent cingulum. There is often a deep pit where the marginal ridges converge gingivally. A developmental groove often extends across the distal of the cingulum onto the root continuing for part or all of its length.

Proximal: In proximal view, the maxillary lateral incisor resembles the central except that the root appears longer--about 1 1/2 times longer than the crown. A line through the long axis of the tooth bisects the crown.

Incisal: In incisal view, this tooth can resemble either the central or the canine to varying degrees. The tooth is narrower mesiodistally than the upper central incisor; however, it is nearly as thick labiolingually.

Contact Points: The mesial contact is at the junction of the incisal third and the middle third. The distal contact is is located at the center of the middle third of the distal surface.

Root Surface:-The root is conical (cone-shaped) but somewhat flattened mesiodistally.