1. Errors in development. These are usually genetic.

a. Variability of the individual teeth. In general, the teeth most distal in any class are the most variable.

b. Partial or total anodontia. missing teeth in children,

c. Supernumerary teeth.

d. Microdontia

e. Macrodontia

F. Microdontia

2. Errors in skeletal alignment. Malpositioned jaws disrupt normal tooth relationships.

3. Soft tissue problems.

-Ocasionally, the proper eruption of a tooth is prevented by fibrous connective tissue over the crown of the tooth.

-In the mixed dentition, the deciduous second molars have a special importance for the integrity of the permanent dentition. Consider this: The first permanent molars at age six years erupt distal to the second deciduous molars.

-Permanent posterior teeth exhibit physiological mesial drift, the tendency to drift mesially when space is available. If the deciduous second molars are lost prematurely, the first permanent molars drift anteriorly and block out the second premolars.

An incisor diastema may be present. The plural for diastema is diastemata.

-Important: The deciduous anteriors--incisors and canines are narrower than their permanent successors mesiodistally.

-Important: The deciduous molars are wider that their permanent successors mesiodistally.

-This size difference has clinical significance. The difference is called the leeway space.

The leeway space in the lower arch is approximately 3.4 mm.

-The leeway space in the upper arch is approximately 1.8 mm. In normal development, the leeway space is taken up by the mesial migration of the first permanent molars.

Embryonic development

The parotid derives from ectoderm
The sublingual-submandibular glands thought to derive from endoderm
Differentiation of the ectomesenchyme
Development of fibrous capsule
Formation of septa that divide the gland into lobes and lobules
The parotid develops around 4-6 weeks of embryonic lofe
The submandibular gland develops around the 6th week
The sublingual and the minor glands develop around the 8-12 week

Nerve and vascular formation

Frequently, nerves and blood vessels run parallel to each other in the body, and the formation of both usually takes place simultaneously and in a similar fashion. However, this is not the case for nerves and blood vessels around the tooth, because of different rates of development.

Nerve formation

Nerve fibers start to near the tooth during the cap stage of tooth development and grow toward the dental follicle. Once there, the nerves develop around the tooth bud and enter the dental papilla when dentin formation has begun. Nerves never proliferate into the enamel organ

Vascular formation

Blood vessels grow in the dental follicle and enter the dental papilla in the cap stage. Groups of blood vessels form at the entrance of the dental papilla. The number of blood vessels reaches a maximum at the beginning of the crown stage, and the dental papilla eventually forms in the pulp of a tooth. Throughout life, the amount of pulpal tissue in a tooth decreases, which means that the blood supply to the tooth decreases with age. The enamel organ is devoid of blood vessels because of its epithelial origin, and the mineralized tissues of enamel and dentin do not need nutrients from the blood.

Periodontal ligament development

Cells from the dental follicle give rise to the periodontal ligaments (PDL).

Formation of the periodontal ligaments begins with ligament fibroblasts from the dental follicle. These fibroblasts secrete collagen, which interacts with fibers on the surfaces of adjacent bone and cementum. This interaction leads to an attachment that develops as the tooth erupts into the mouth. The occlusion, which is the arrangement of teeth and how teeth in opposite arches come in contact with one another, continually affects the formation of periodontal ligaments. This perpetual creation of periodontal ligaments leads to the formation of groups of fibers in different orientations, such as horizontal and oblique fibers.

Maxillary First Deciduous Molar.

-The notation is B or I.

-It looks a bit like an upper 1st premolar.

-There are three roots.

-It has a strong bulbous enamel bulge that protrudes buccally at the mesial.

-It is the smallest of the deciduous molars in crown height and in the mesiodistal dimension.

CONTACT POINT.:-The point on the proximal surface where two adjacent teeth actually touch each other is called a contact point.

INTERPROXIMAL SPACE.:-The interproximal space is the area between the teeth. Part of the interproximal space is occupied by the interdental papilla. The interdental papilla is a triangular fold of gingival tissue. The part of the interproximal space not occupied is called the embrasure.

EMBRASURE. :-The embrasure occupies an area bordered by interdental papilla, the proximal surfaces of the two adjacent teeth, and the contact point (fig 4-18). If there is no contact point between the teeth, then the area between them is called a diastema instead of an embrasure.

OCCLUSAL

The occlusal surface is the broad chewing surface found on posterior teeth (bicuspids and molars).

OCCLUSION.:-Occlusion is the relationship between the occlusal surfaces of maxillary and mandibular teeth when they are in contact. Many patterns of tooth contact are possible. Part of the reason for the variety is the mandibular condyle's substantial range of movement within the temporal mandibular joint.

Malocclusion occurs when any abnormality in occlusal relationships exist in the dentition. Centric occlusion, is the centered contact position of the chewing surfaces of mandibular teeth on the chewing surface (occlusal) of the maxillary teeth.

OCCLUSAL PLANE.:-Maxillary and mandibular teeth come into centric occlusion and meet along anteroposterior and lateral curves. The anteroposterior curve is called the Curve of Spee  in which the mandibular arch forms a concave (a bowl-like upward curve). The lateral curve is called the Curve of Wilson . The composite (combination) of these curves form a line called the occlusal plane, and is created by the contact of the upper and lower teeth

VERTICAL AND HORIZONTAL OVERLAP. :-Vertical overlap is the extension of the maxillary teeth over the mandibular counterparts in a vertical direction when the dentition is in centric occlusion Horizontal overlap is the projection of maxillary teeth over antagonists (something that opposes another) in a horizontal direction.

KEY TO OCCLUSION.:-The occlusal surfaces of opposing teeth bear a definite relationship to each other. In normal jaw relations and when teeth are of normal size and in the correct position, the mesiofacial cusp of the maxillary first molar occludes in the facial groove of the mandibular first molar. This normal relationship of these two teeth is called the key to occlusion.

PERMANENT DENTITION

The permanent dentition consists of 32 teeth. Each tooth in the permanent dentition is described in this section. It should be remembered that teeth show considerable variation in size, shape, and other characteristics from one person to another. Certain teeth show a greater tendency than others to deviate from the normal. The descriptions that follow are of normal teeth.