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.

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

Tooth eruption Theories

Tooth eruption occurs when the teeth enter the mouth and become visible. Although researchers agree that tooth eruption is a complex process, there is little agreement on the identity of the mechanism that controls eruption. Some commonly held theories that have been disproven over time include: (1) the tooth is pushed upward into the mouth by the growth of the tooth's root, (2) the tooth is pushed upward by the growth of the bone around the tooth, (3) the tooth is pushed upward by vascular pressure, and (4) the tooth is pushed upward by the cushioned hammock. The cushioned hammock theory, first proposed by Harry Sicher, was taught widely from the 1930s to the 1950s. This theory postulated that a ligament below a tooth, which Sicher observed on under a microscope on a histologic slide, was responsible for eruption. Later, the "ligament" Sicher observed was determined to be merely an artifact created in the process of preparing the slide.

The most widely held current theory is that while several forces might be involved in eruption, the periodontal ligaments provide the main impetus for the process. Theorists hypothesize that the periodontal ligaments promote eruption through the shrinking and cross-linking of their collagen fibers and the contraction of their fibroblasts.

Although tooth eruption occurs at different times for different people, a general eruption timeline exists. Typically, humans have 20 primary (baby) teeth and 32 permanent teeth. Tooth eruption has three stages. The first, known as deciduous dentition stage, occurs when only primary teeth are visible. Once the first permanent tooth erupts into the mouth, the teeth are in the mixed (or transitional) dentition. After the last primary tooth falls out of the mouth—a process known as exfoliation—the teeth are in the permanent dentition.

Primary dentition starts on the arrival of the mandibular central incisors, usually at eight months, and lasts until the first permanent molars appear in the mouth, usually at six years. The primary teeth typically erupt in the following order: (1) central incisor, (2) lateral incisor, (3) first molar, (4) canine, and (5) second molar. As a general rule, four teeth erupt for every six months of life, mandibular teeth erupt before maxillary teeth, and teeth erupt sooner in females than males. During primary dentition, the tooth buds of permanent teeth develop below the primary teeth, close to the palate or tongue.

Mixed dentition starts when the first permanent molar appears in the mouth, usually at six years, and lasts until the last primary tooth is lost, usually at eleven or twelve years. Permanent teeth in the maxilla erupt in a different order from permanent teeth on the mandible. Maxillary teeth erupt in the following order: (1) first molar (2) central incisor, (3) lateral incisor, (4) first premolar, (5) second premolar, (6) canine, (7) second molar, and (8) third molar. Mandibular teeth erupt in the following order: (1) first molar (2) central incisor, (3) lateral incisor, (4) canine, (5) first premolar, (6) second premolar, (7) second molar, and (8) third molar. Since there are no premolars in the primary dentition, the primary molars are replaced by permanent premolars. If any primary teeth are lost before permanent teeth are ready to replace them, some posterior teeth may drift forward and cause space to be lost in the mouth. This may cause crowding and/or misplacement once the permanent teeth erupt, which is usually referred to as malocclusion. Orthodontics may be required in such circumstances for an individual to achieve a straight set of teeth.

The permanent dentition begins when the last primary tooth is lost, usually at 11 to 12 years, and lasts for the rest of a person's life or until all of the teeth are lost (edentulism). During this stage, third molars (also called "wisdom teeth") are frequently extracted because of decay, pain or impactions. The main reasons for tooth loss are decay or periodontal disease.

The pre-dentition period.

-This is from birth to six months.

-At this stage, there are no teeth. Clinically, the infant is edentulous

-Both jaws undergo rapid growth; the growth is in three planes of space: downward, forward, and laterally (to the side). Forward growth for the mandible is greater.

-The maxillary and mandibular alveolar processes are not well developed at birth.

-occasionally, there is a neonatal tooth present at birth. It is a supernumerary and is often lost soon after birth.

-At birth, bulges in the developing alveoli precede eruption of the deciduous teeth. At birth, the molar pads can touch.

HISTOLOGY OF SALIVARY GLANDS

Parotid: so-called watery serous saliva rich in amylase
Submandibular gland: more mucinous
Sublingual: viscous saliva

Parotid Gland:  The parotid is a serous secreting gland.

There are also fat cells in the parotid.

Submandibular Gland

This gland is serous and mucous secreting.

There are serous demilunes

This gland is more serous than mucous

Also fat cells

Sublingual Gland

Serous and mucous secreting

Serous cells in the form of demilunes on the mucous acini.

more mucous than serous cells

Minor Salivary Glands

Minor salivary glands are not found within gingiva and anterior part of the hard palate
Serous minor glands=von Ebner below the sulci of the circumvallate and folliate papillae of the tongue; palatine, glossopalatine glands are pure mucus; some lingual glands are also pure mucus

Functions

Protection: lubricant (glycoprotein); barrier against noxious stimuli; microbial toxins and minor traumas; washing non-adherent and acellular debris; calcium-binding proteins: formation of salivary pellicle
Buffering: bacteria require specific pH conditions; plaque microorganisms produce acids from sugars; phosphate ions and bicarbonate
Digestion: neutralizes esophageal contents, dilutes gastric chyme; forms food bolus; brakes starch
Taste: permits recognition of noxious substances; protein gustin necessary for growth and maturation of taste buds
Antimicrobial: lysozyme hydrolyzes cell walls of some bacteria; lactoferrin binds free iron and deprives bacteria of this essential element; IgA agglutinates microorganisms
Maintenance of tooth integrity: calcium and phosphate ions; ionic exchange with tooth surface
Tissue repair: bleeding time of oral tissues shorter than other tissues; resulting clot less solid than normal; remineralization

Permanent dentition period  

-Maxillary / mandibular occlusal relationships are established when the last of the deciduous teeth are lost. The adult relationship of the first permanent molars is established at this time.

-Occlusal and proximal wear reduces crown height to the permanent dentition and the mesiodistal dimensions of the teeth

occlusal and proximal wear also changes the anatomy of teeth. As cusps are worn off, the occlusion can become virtually flat plane. -In the absence of rapid wear, overbite and overjet tend to remain stable.

-Mesio-distal jaw relationships tend to be stable,

With aging, the teeth change in color from off white to yellow. smoking and diet can accelerate staining or darkening of the teeth.

Gingival recession results in the incidence of more root caries . With gingival recession, some patients have sensitivity due to exposed dentin at the cemento-enamel junction.

Curve of Spee.

-The cusp tips and incisal edges align so that there is a smooth, linear curve when viewed from the lateral aspect. The mandibular curve of Spee is concave whereas the maxillary curve is convex.

-It was described by Von Spee as a 4" cylinder that engages the occlusal surfaces.

-It is called a compensating curve of the dental arch.

There is another: the Curve of Wilson. Clinically, it relates to the anterior overbite: the deeper the curve, the deeper the overbite.