Periodontal ligament

Composition

a. Consists mostly of collagenous (alveolodental) fibers.
Note: the portions of the fibers embedded in cementum and the alveolar bone proper are known as Sharpey’s fibers.

b. Oxytalan fibers (a type of elastic fiber) are also present. Although their function is unknown, they may play a role in the regulation of vascular flow.

c. Contains mostly type I collagen, although smaller amounts of type III and XII collagen are also present.

d. Has a rich vascular and nerve supply.

Both sensory and autonomic nerves are present.

(1) The sensory nerves in the PDL differ from pulpal nerves in that PDL nerve endings can detect both proprioception (via mechanoreceptors) and pain (via nociceptors).

(2) The autonomic nerve fibers are associated with the regulation of periodontal vascular flow.

(3) Nerve fibers may be myelinated (sensory) or unmyelinated (sensory or autonomic).

Cells

a. Cells present in the PDL include fibroblasts; epithelial cells; cementoblasts and cementoclasts; osteoblasts and osteoclasts; and immune cells such as macrophages, mast cells, or eosinophils.

b. These cells play a role in forming or destroying cementum, alveolar bone, or PDL.

c. Epithelial cells often appear in clusters, known as rests of Malassez.

Types of alveolodental fibers

a. Alveolar crest fibers—radiate downward from cementum, just below the cementoenamel junction (CEJ), to the crest of alveolar bone.

b. Horizontal fibers—radiate perpendicular to the tooth surface from cementum to alveolar bone, just below the alveolar crest.

c. Oblique fibers

(1) Radiate downward from the alveolar bone to cementum.

(2) The most numerous type of PDL fiber.

(3) Resist occlusal forces that occur along the long axis of the tooth.

d. Apical fibers

(1) Radiate from the cementum at the apex of the tooth into the alveolar bone.

(2) Resist forces that pull the tooth in an occlusal direction (i.e., forces that try to pull the tooth from its socket).

e. Interradicular fibers

(1) Only found in the furcal area of multi-rooted teeth.

(2) Resist forces that pull the tooth in an occlusal direction.

Gingival fibers

a. The fibers of the gingival ligament are not strictly part of the PDL, but they play a role in the maintainence of the periodontium.

b. Gingival fibers are packed in groups and are found in the lamina propria of gingiva

c. Gingival fiber groups:

(1) Transseptal (interdental) fibers

(a) Extend from the cementum of one tooth (just apical to the junctional epithelium), over the alveolar crest, to the corresponding area of the cementum of the adjacent tooth.

(b) Collectively, these fibers form the interdental ligament , which functions to resist rotational forces and retain adjacent teeth in interproximal contact.

(c) These fibers have been implicated as a major cause of postretention relapse of teeth that have undergone orthodontic treatment.

(2) Circular (circumferential) fibers

(a) Extend around tooth near the CEJ.

(b) Function in binding free gingiva to the tooth and resisting rotational forces.

(3) Alveologingival fibers—extend from the alveolar crest to lamina propria of free and attached gingiva.

(4) Dentogingival fibers—extend from cervical cementum to the lamina propria of free and attached gingiva.

(5) Dentoperiosteal fibers—extend from cervical cementum, over the alveolar crest, to the periosteum of the alveolar bone.

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.

SURFACES OF THE TEETH

Facial, Mesial, Distal, Lingual, and Incisal Surfaces

• The facial is the surface of a tooth that "faces" toward the lips or cheeks. When there is a requirement to be more specific, terms like labial and buccal are used. The labial is the surface of an anterior tooth that faces toward the lips. The buccal is the surface of a posterior tooth that faces toward the cheek.
• The mesial is the proximal surface closest to the midline of the arch. The distal is the opposite of mesial. The distal is the proximal surface oriented away from the midline of the arch.
• The lingual is the surface of an anterior or posterior tooth that faces toward the tongue. Incisal edges are narrow cutting edges found only in the anterior teeth (incisors). Incisors have one incisal edge
• Proximal Surfaces

A tooth has two proximal surfaces, one that is oriented toward the midline of the dental arch (mesial) and another that is oriented away from the midline of the arch (distal).

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.

Genetics and Environment: Introduction

The size of the teeth and the timing of the developing dentition and its eruption are genetically determined. Teeth are highly independent in their development. Also, teeth tend to develop along a genetically predetermined course.: tooth development and general physical development are rather independent of one another. Serious illness, nutritional deprivation, and trauma can significantly impact development of the teeth. This genetic independence (and their durability) gives teeth special importance in the study of evolution.

Teeth erupt full size and are ideal for study throughout life. Most important, age and sex can be recorded.

When teeth erupt into the oral cavity, a new set of factors influence tooth position. As the teeth come into function, genetic and environment determine tooth position.

In real life, however, girls shed deciduous teeth and receive their permanent teeth slightly earlier than boys, possibly reflecting the earlier physical maturation achieved by girls. Teeth are slightly larger in boys that in girls

MANDIBULAR SECOND BICUSPID

Facial: From this aspect, the tooth somewhat resembles the first, but the buccal cusp is less pronounced. The tooth is larger than the first.

Lingual: Two significant variations are seen in this view. The most common is the three-cusp form which has two lingual cusps. The mesial of those is the larger of the two. The other form is the two-cusp for with a single lingual cusp. In that variant, the lingual cusp tip is shifted to the mesial.

Proximal: The buccal cusp is shorter than the first. The lingual cusp (or cusps) are much better developed than the first and give the lingual a full, well-developed profile.

Occlusal: The two or three cusp versions become clearly evident. In the three-cusp version, the developmental grooves present a distinctive 'Y' shape and have a central pit. In the two cusp version, a single developmental groove crosses the transverse ridge from mesial to distal

Contact Points; Height of Curvature: From the facial, the mesial contact is more occlusal than the distal contact.The distal marginal ridge is lower than the mesial marginal ridge

Root Surface:-The root of the tooth is single, that is usually larger than that of the first premolar  

the lower second premolar is larger than the first, while the upper first premolar is just slightly larger than the upper second

There may be one or two lingual cusps