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

AGE CHANGES

Progressive apical migration of the dentogingival junction.
Toothbrush abrasion of the area can expose dentin that can cause root caries and tooth mobility.

Histology of the alveolar bone

Near the end of the 2nd month of fetal life, mandible and maxilla form a groove that is opened toward the surface of the oral cavity.
As tooth germs start to develop, bony septa form gradually. The alveolar process starts developing strictly during tooth eruption.

The alveolar process is the bone that contains the sockets (alveoli) for the teeth and consists of

a) outer cortical plates
b) a central spongiosa and
c) bone lining the alveolus (bundle bone)

The alveolar crest is found 1.5-2.0 mm below the level of the CEJ.
If you draw a line connecting the CE junctions of adjacent teeth, this line should be parallel to the alveolar crest. If the line is not parallel, then there is high probability of periodontal disease.

Bundle Bone

The bundle bone provides attachment to the periodontal ligament fibers. It is perforated by many foramina that transmit nerves and vessels (cribiform plate). Embedded within the bone are the extrinsic fiber bundles of the PDL mineralized only at the periphery. Radiographically, the bundle bone is the lamina dura. The lining of the alveolus is fairly smooth in the young but rougher in the adults.

Clinical considerations

Resorption and regeneration of alveolar bone
This process can occur during orthodontic movement of teeth. Bone is resorbed on the side of pressure and opposed on the site of tension.

Osteoporosis
Osteoporosis of the alveolar process can be caused by inactivity of tooth that does not have an antagonist

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.

Abnormalities

There are a number of tooth abnormalities relating to development.

Anodontia is a complete lack of tooth development, and hypodontia is a lack of some tooth development. Anodontia is rare, most often occurring in a condition called hipohidrotic ectodermal dysplasia, while hypodontia is one of the most common developmental abnormalities, affecting 3.5–8.0% of the population (not including third molars). The absence of third molars is very common, occurring in 20–23% of the population, followed in prevalence by the second premolar and lateral incisor. Hypodontia is often associated with the absence of a dental lamina, which is vulnerable to environmental forces, such as infection and chemotherapy medications, and is also associated with many syndromes, such as Down syndrome and Crouzon syndrome.

Hyperdontia is the development of extraneous teeth. It occurs in 1–3% of Caucasians and is more frequent in Asians. About 86% of these cases involve a single extra tooth in the mouth, most commonly found in the maxilla, where the incisors are located. Hyperdontia is believed to be associated with an excess of dental lamina.

Dilaceration is an abnormal bend found on a tooth, and is nearly always associated with trauma that moves the developing tooth bud. As a tooth is forming, a force can move the tooth from its original position, leaving the rest of the tooth to form at an abnormal angle. Cysts or tumors adjacent to a tooth bud are forces known to cause dilaceration, as are primary (baby) teeth pushed upward by trauma into the gingiva where it moves the tooth bud of the permanent tooth.

Regional odontodysplasia is rare, but is most likely to occur in the maxilla and anterior teeth. The cause is unknown; a number of causes have been postulated, including a disturbance in the neural crest cells, infection, radiation therapy, and a decrease in vascular supply (the most widely held hypothesis).Teeth affected by regional odontodysplasia never erupt into the mouth, have small crowns, are yellow-brown, and have irregular shapes. The appearance of these teeth in radiographs is translucent and "wispy," resulting in the nickname "ghost teeth"

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.

Deciduous dentition period.

-The deciduous teeth start to erupt at the age of six months and the deciduous dentition is complete by the age of approximately two and one half years of age.

-The jaws continue to increase in size at all points until about age one year.

-After this, growth of the arches is lengthening of the arches at their posterior (distal) ends. Also, there is slightly more forward growth of the mandible than the maxilla.

1. Many early developmental events take place.

-The tooth buds anticipate the ultimate occlusal pattern.

-Mandibular teeth tend to erupt first. The pattern for the deciduous incisors is usually in this distinctive order:

(1) mandibular central

(2) maxillary central incisors

(3) then all four lateral incisors.

-By one year, the deciduous molars begin to erupt.

-The eruption pattern for the deciduous dentition as a whole is:

(1) central incisor

(2) lateral incisor

(3) deciduous first molar

(4) then the canine

(5) then finally the second molar.

-Eruption times can be variable.

2. Occlusal changes in the deciduous dentition.

-The overjet tends to diminish with age. Wear and mandibular growth are a factor in this process.

-The overbite often diminishes with the teeth being worn to a flat plane occlusion.

-Spacing of the incisors in anticipation of the soon-to-erupt permanent incisors appears late. Permanent anterior teeth (incisors and canines) are wider mesiodistally than deciduous anterior teeth. In contrast, the deciduous molar are wider mesiodistally that the premolars that later replace them.

-Primate spaces occur in about 50% of children. They appear in the deciduous dentition. The spaces appear between the upper lateral incisor and the upper canine. They also appear between the lower canine and the deciduous first molar.