Stationary Relationship

a) .Centric Relation is the most superior relationship of the condyle of the mandible to the articular fossa of the temporal bone as determined by the bones ligaments. and muscles of the temporomandibular joint; in an ideal dentition it is the same as centric occlusion.

(b) Canines may also be used to confirm the molar relationships to classify occlusion when molars are missing; a class I canine relationship shows the cusp tip of the maxillary canine facial to the mesiobuccal cusp of the first permanent molar

c) Second primary molars are used to classify the occlusion in a primary dentition

(d) In a mixed  dentition the first permanent molars will erupt into a normal occlusion if there is a terminal step between the distal  surfaces of maxillarv and mandibular second primary molars; if these surfaces are flush, a terminal plane exists and the first permanent molars will first erupt into an end-to-end relationship until there is a shifting of space or exfoliation of the second primary molar

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

Tooth development is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth.. For human teeth to have a healthy oral environment, enamel, dentin, cementum, and the periodontium must all develop during appropriate stages of fetal development. Primary teeth start to form between the sixth and eighth weeks in utero, and permanent teeth begin to form in the twentieth week in utero.

 Overview

The tooth bud (sometimes called the tooth germ) is an aggregation of cells that eventually forms a tooth.These cells are derived from the ectoderm of the first branchial arch and the ectomesenchyme of the neural crest.The tooth bud is organized into three parts: the enamel organ, the dental papilla and the dental follicle.

The enamel organ is composed of the outer enamel epithelium, inner enamel epithelium, stellate reticulum and stratum intermedium.These cells give rise to ameloblasts, which produce enamel and the reduced enamel epithelium. The location where the outer enamel epithelium and inner enamel epithelium join is called the cervical loop. The growth of cervical loop cells into the deeper tissues forms Hertwig's Epithelial Root Sheath, which determines the root shape of the tooth.

The dental papilla contains cells that develop into odontoblasts, which are dentin-forming cells. Additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth. Mesenchymal cells within the dental papilla are responsible for formation of tooth pulp.

The dental follicle gives rise to three important entities: cementoblasts, osteoblasts, and fibroblasts. Cementoblasts form the cementum of a tooth. Osteoblasts give rise to the alveolar bone around the roots of teeth. Fibroblasts develop the periodontal ligaments which connect teeth to the alveolar bone through cementum.

MAXILLARY SECOND BICUSPID

smaller in dimensions. The cusps are not as sharp as the maxillary first bicuspid and have only one root.

Facial: This tooth closely resembles the maxillary first premolar but is a less defined copy of its companion to the mesial. The buccal cusp is shorter, less pointed, and more rounded than the first.

Lingual: Again, this tooth resembles the first. The lingual cusp, however, is more nearly as large as the buccal cusp.

Proximal: Mesial and distal surfaces are rounded. The mesial developmental depression and mesial marginal ridge are not present on the second premolar.

Occlusal: The crown outline is rounded, ovoid, and is less clearly defined than is the first.

Contact Points; When viewed from the facial, the distal contact area is located more cervically than is the mesial contact area.

FORMATION OF THE PERMANENT DENTITION

Twenty deciduous tooth buds are formed initially.
Proliferative activity of the dental lamina during the bell stage that leads to formation of permanent tooth buds (cap stage) lingual of each deciduous tooth germ.
Molars have no predecessors; they are formed by posterior proliferation of the dental lamina.

HARD TISSUE FORMATION

Hard tissue formation starts at the late stages of the bell stage.
Differentiatioin of cells into odontoblasts and ameloblasts.
The cells of the inner dental epithelium will become ameloblasts.
The cells of the dental papilla opposite to the inner dental epithelium will become odontoblasts.
Dentin is formed before enamel.
Dentin initiates the formation of enamel.

ROOT FORMATION

The root of the tooth is composed by dentin and cementum.
Dentinogenesis is initiated by the odontoblasts.
Odontoblasts are formed as epithelial cells continue to proliferate from the cervical loop as a double layer of cells known as Hertwig's root sheath.

TOOTH SHAPE

The shape of the crowns results from the interaction of inner dental epithelium and the dental papilla.
The cells of the inner dental epithelium have a programmed proliferation.
This internal program determines the tooth form.

The fate of the dental lamina

Rests of Serres
The rest of Serres are rests of the dental lamina identified in the gingival soft tissues.
They are round to ovoid aggregates of epithelial cells that have clear cytoplasm (glucogen rich).
They result from early breakup of the dental lamina during bell stage.

Rests of Malassez
The rests of Malassez result from breakup of the Hertwig's root sheath during root formation.
They can be identified in the periodontal ligament and are responsible for the development of radicular cysts.

Dental Formula, Dental Notation, Universal Numbering System

A. Dental Formula. The dental formula expresses the type and number of teeth per side

The Universal Numbering System. The rules are as follows:

1. Permanent teeth are designated by number, beginning with the last tooth on the upper right side, going on to the last tooth on the left side, then lower left to lower right

2. Deciduous teeth are designated by letter, beginning with the last tooth on the upper right side and proceeding in clockwise fashion