University of Palestine College of Dentistry

Human Dentition ILandmarks & Life Cycle of the toot

Tooth Identification

As the dental team performs a complete oral examination on a patient, it is necessary to use a standardized system, not only for tooth numbering, but also for tooth surface annotation. By combining both of these forms of communication, it becomes easy to identify a specific location on a tooth with dental decay, a fracture, or a restoration.

In a dental office the correct identification of teeth is important for treatment and record keeping. Correct identification of teeth relates directly to patient treatment planning, treatment, insurance claim forms, malpractice suits, and forensic identification purposes. The anatomy of any individual tooth may vary among patients.

Standard characteristics are common to most teeth. A complete understanding of the anatomy of a specific tooth is necessary to ensure correct identification of the tooth.

• Concave:

A curvature that leans inward.

• Convex:

A curvature that extends outward. Opposite of concave.

Anatomical Landmarks

A lobe:It is the primary center of growth and

calcification of the developing tooth. Each tooth begins to develop from four or more growth centers. These centers are known as Developmental Lobes then unite together to form the crown of the tooth. Cusps and mamelons are representative of lobes.

A mamelon is anyone of the three rounded protuberances found on the incisal ridges of newly erupted incisor teeth. Incisors and Canines are developed from 4 lobes, they have 3 lobes labially and one lobe lingually (cingulum). Premolars are developed from 3 lobes buccaly and 1 or 2 lobes lingually (lingual cusp or lingual cusps), while molars are developed from 3, 4, 5 lobes according to their cusp numbers.

Crown Elevations: Mamelon:

A round prominence at the incisal edge of newly erupted teeth that wears away with use.

Cusps:

These are conical or pyramidal projections on the crown portion of the tooth. Cusps are found on premolars & molars as well as canines. It denotes the primary lobe during development. When the crown matured the cusp is formed of enamel, dentine and pulp horn.

Tubercle:It is a small elevation of enamel on some

portion of the crown of the tooth. It is produced by an extra formation of enamel and dose not represents a lobe. These are deviations from the typical form.

It is found on the palatal surface (mesio-palatal cusp) of the upper first molar and called tubercle cusp or Carabelle.

A cingulum (Latin word for girdle):

It is the lingual lobe of an anterior tooth. It makes up the bulk of the cervical third of the lingual surface (a prominence of enamel). Its convexity mesiodistally resembles a girdle encircling the lingual surface at the cervical third.

A ridge is any linear elevation on the surface of a tooth and is named according to its location (e.g., buccal ridge, incisal ridge. marginal ridge).

Several types can be identified as follows:

Marginal ridges: are those rounded borders of the enamel that form the mesial and distal margins of the occlusal surfaces of premolars and molars and the mesial and distal margins of the lingual surfaces of the incisors and canines.

Triangular ridges descend from the tips of the cusps of molars and premolars toward the central part of the occlusal surfaces. They are so named because the slopes of each side of the ridge are inclined to resemble two sides of a triangle. They are named after the cusps to which they belong. e.g., the triangular ridge of the buccal cusp of the maxillary first premolar.When a buccal and a lingual triangular ridge join, they form a transverse ridge. A transverse ridge is the union of two triangular ridges crossing transversely the surface of a posterior tooth.

Triangular ridges

Triangular ridges

Transverse ridge

The oblique ridge is a ridge crossing obliquely the occlusal surfaces of maxillary molars. It is formed by the union of the triangular ridges of the distobuccal cusp and the mesiopalatal cusp.

Oblique ridge

Crown Depressions A fossa is an irregular depression or concavity, and is named according to its shape and location.

Lingual fossa are on the lingual surface of incisors.

Central fossa are on the occlusal surface of molars. They are formed by the converging of ridges terminating at a central point in the bottom of the depression, where there is a junction of developmental grooves.

Triangular fossa are found on molars and premolars on the occlusal surfaces mesial or distal to marginal ridges. They are sometimes found on the lingual surfaces of maxillary incisors at the edge of the lingual fossae where the marginal ridges and the cingulum meet.

Lingual fossae

Central fossae Triangular fossa

A sulcus is a long depression or valley in the surface of a tooth between ridges and cusps, the inclines of which meet at an angle. A sulcus has a developmental groove at the junction of its inclines. (The term sulcus must not be confused with the term groove.)

A sulcus

• A developmental groove is a shallow groove or line between the primary parts or lobes of the crown or root.

• A supplemental groove, less distinct, is also a shallow linear depression on the surface of a tooth, but it is supplemental to a developmental groove and does not mark the junction of primary parts.

• Buccal and lingual grooves are developmental groove found on the buccal and lingual surfaces of posterior teeth.

Fissure:

It is a narrow channel or cleft which is formed at the depth of a developmental groove and result from the incomplete union of the primary lobes. It is considered as a fault or abnormalities in enamel. Decay (caries) often begins in a deep fissure.

Pits are small pinpoint depressions located at the junction of developmental grooves or at terminals of those grooves. For instance, central pit is a term used to describe a landmark in the central fossa of molars where developmental grooves join.

Contact area:

The area of a tooth that physically touches the abutment tooth; the contact areas occur n the proximal surfaces of teeth.

Life Cycle of the teeth

The teeth developed in their crypts and passing in several stages of development till they appear in the oral cavity, functioning and lasted till the end of their life. These stages are known as life cycle of a tooth and they are 5 stages:

1. Soft growth stages.

2. Mineralization stage.

3. Eruption.

4. Attrition.

5. Shedding and loss.

1.Soft growth stages:

A. Formation of the tooth band of primary teeth: At 5 week in utero (WIU) basal cell layer of mucous membrane lined the primitive oral cavity undergo cell division and extends in the underlying connective tissue to form a band of epithelium named tooth band or dental lamina.

B. Formation of enamel organ: the tooth band shows cell division at labial surface to give rise to epithelial bulge called enamel organ.

C. Formation of dental papilla: the connective tissue divides inside this bulge and forms the dental papilla.

D. Formation of dental sac: the connective tissue divides and surrounds the enamel organ and the dental papilla by complete delicate fibrous layer called dental sac. The enamel organ, dental papilla and dental sac are called tooth germ.

• The enamel organ after development gives rise to enamel structure, while the dental papilla gives rise to dentin and pulp. The dental sac gives rise to cementum, periodontal ligament and alveolar bone.

• During the development of deciduous teeth the dental lamina divides lingually to give the enamel organ of permanent successor. Also the dental lamina grows back in the developing jaw to give the tooth germ of the permanent molars.

2.Mineralization stage:

During the soft growth stage the enamel, dentin and cementum undergo calcification by deposition of calcium salts in the soft organic matrix.

3.Eruption:

It is the physiological process by which the tooth moves from its bony crypt towards the oral cavity. When the crown and nearly 1/3 of the root portion are calcified, the tooth penetrates the oral mucous membrane. The process of eruption continues until the tooth reaches its occlusal plane at the time to be in contact with its opponents in the opposite jaw. At this time the root is nearly completed.

4.Attrition:

It is the physiological loss of the hard dental structure due to the continuous friction of the teeth with each other during mastication. This attrition is more pronounced in the occlusal, incisal surfaces and at the contact areas. The attrition is clearer in the permanent dentition than in the primary one because of the short time the primary teeth stay in the function.

5.Shedding and loss:

Shedding is the physiological loss of the primary dentition and is replaced by permanent dentition. After few years functioning, the primary teeth present resorption of their roots apically and continuous until the whole roots are resorped and the crowns are exfoliated.

The causes of root resorption during shedding are due to:

Differentiation of gaint cells called osteoclasts and odontocalasts which resorp bone, dentin and cementum. These cells are differentiated as a result of pressure of the erupted permanent successor.

The periodontium of the primary teeth dose not tolerate the growth of the masticatory muscles.

The loss of the permanent dentition is pathological as the diseased teeth are extracted.

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