Cap stage

The first signs of an arrangement of cells in the tooth bud occur in the cap stage. A small group of ectomesenchymal cells stops producing extracellular substances, which results in an aggregation of these cells called the dental papilla. At this point, the tooth bud grows around the ectomesenchymal aggregation, taking on the appearance of a cap, and becomes the enamel (or dental) organ. A condensation of ectomesenchymal cells called the dental follicle surrounds the enamel organ and limits the dental papilla. Eventually, the enamel organ will produce enamel, the dental papilla will produce dentin and pulp, and the dental follicle will produce all the supporting structures of a tooth

Dental Terminology.

Cusp: a point or peak on the occlusal surface of molar and premolar teeth and on the incisal edges of canines.

Contact: a point or area where one tooth is in contact (touching) another tooth

Cingulum: a bulge or elevation on the lingual surface of incisors or canines. It makes up the bulk of the cervical third of the lingual surface. Its convexity mesiodistally resembles a girdle  encircling the lingual surface at the cervical.

Fissure: A linear fault that sometimes occurs in a developmental groove by incomplete or imperfect joining of the lobes. A pit is usually found at the end of a developmental groove or a place where two fissures intersect.

Lobe: one of the primary centers of formation in the development of the crown of the tooth.

Mamelon: A lobe seen on anterior teeth; any one of three rounded protuberances seen on the unworn surfaces of freshly erupted anterior teeth.

Ridge: Any linear elevation on the surface of a tooth. It is named according to its location or form. Examples are buccal ridges, incisal ridges, marginal ridges, and so on.

Marginal ridges are those rounded borders of enamel which form the margins of the surfaces of premolars and molars, mesially and distally, and the mesial and distal margins of the incisors and canines lingually.

Triangular ridges are those ridges which descend from the tips of the cusps of molars and premolars toward the central part of the occlusal surface. Transverse ridges are created when a buccal and lingual triangular ridge join.

Oblique ridges are seen on maxillary molars and are a companion to the distal oblique groove.

Cervical ridges are the height of contour at the gingival, on certain deciduous and permanent teeth.

Fossa: An irregular, rounded depression or concavity found on the surface of a tooth. A lingual fossa is found on the lingual surface of incisors. A central fossa is found on the occlusal surface of a molar. They are formed by the converging of ridges terminating at a central point in the bottom of a depression where there is a junction of grooves

Pit: A small pinpoint depression located at the junction of developmental grooves or at the terminals of these groops. A central pit is found in the central fossa on the occlusal surfaces of molars where developmental grooves join. A pit is often the site of the onset of Dental  caries

Developmental groove: A sharply defined, narrow and linear depression formed during tooth development and usually separating lobes or major portions of a tooth.

A supplemental groove is also a shallow linear depression but it is usually less distinct and is more variable than a developmental groove and does not mark the junction of primary parts of a tooth.

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

Tubercle: A small elevation produced by an extra formation of enamel. These occur on the marginal ridges of posterior teeth or on the cingulum of anterior teeth. These are deviations from the typical form.

Interproximal space: The triangular space between the adjacent teeth cervical to the contact point. The base of the triangle is the alveolar bone; the sides are the proximal surfaces of the adjacent teeth.

Sulcus:-An elongated valley or depression in the surface of a tooth formed by the inclines of adjacent cusp or ridges.

Embrasures: When two teeth in the same arch are in contact, their curvatures adjacent to the contact areas form spillway spaces called embrasures. There are three embrasures:

(1) Facial (buccal or labial)

(2) Occlusal or incisal

(3) Lingual

(NOTE: there are three embrasures; the fourth potential space is the interproximal space ).

Soft Oral Tissues

Oral Mucosa

The oral mucosa consists mainly of two types of tissues: the oral epithelium, which consists of stratified, squamous epithelium, and the underlying connective tissue layer, known as the lamina propria.  There are three variations of oral mucosa.

A. Oral epithelium

1. Consists of stratified, squamous epithelium.

2. Four layers (Note: Cells mature as they progress from the deepest [basal] layer to the most superficial [cornified] layer) a. Basal layer (stratum germinativum or basale)

(1) A single layer of cuboidal or columnar cells overlying the lamina propria.

(2) Contains progenitor cells and thus provides cells to the epithelial layers above.

(3) Site of cell division (mitosis).

b. Prickle cell layer (stratum spinosum)

(1) Consists of several layers of larger, ovoid-shaped cells.

c. Granular layer (stratum granulosum)

(1) Cells appear larger and flattened.

(2) Granules (known as keratohyaline granules) are present in the cells.

(3) This layer is absent in nonkeratinized epithelium.

d. Cornified layer (stratum corneum, keratin, or horny layer)

(1) In keratinized epithelium:

(a) Orthokeratinized epithelium the squamous cells on the surface appear flat and contain keratin. They have no nuclei present.

(b) Parakeratinized epithelium the squamous cells appear flat and contain keratin; nuclei are present within the cells.

(2) In parakeratinized epithelium, both squamous cells without nuclei and cells with shriveled (pyknotic) nuclei are present.

(3) In nonkeratinized epithelium, the cells appear slightly flattened and contain nuclei.

B. Lamina propria

1. Consists of type I and III collagen, elastic fibers, and ground substance. It also contains many cell types, including fibroblasts, endothelial cells, immune cells, and a rich vascular and nerve supply.

2. Two layers:

a. Superficial, papillary layer

(1) Located around and between the epithelial ridges.

(2) Collagen fibers are thin and loosely arranged.

b. Reticular layer

(1) Located beneath the papillary layer.

(2) Collagen fibers are organized in thick, parallel bundles.

C. Types of oral mucosa

1. Masticatory mucosa

a. Found in areas that have to withstand compressive and shear forces.

b. Clinically, it has a rubbery, firm texture.

c. Regions: gingiva, hard palate.

2. Lining mucosa

a. Found in areas that are exposed to high levels of friction, but must also be mobile and distensible.

b. Clinically, it has a softer, more elastic texture.

c. Regions: alveolar mucosa, buccal mucosa, lips, floor of the mouth, ventral side of the tongue, and soft palate.

3. Specialized mucosa

a. Similar to masticatory mucosa, specialized mucosa is able to tolerate high compressive

and shear forces; however, it is unique in that it forms lingual papillae.

b. Region: dorsum of the tongue.

D. Submucosa

1. The connective tissue found beneath the mucosa . It contains blood vessels and nerves and may also contain fatty tissue and minor salivary glands.

2. Submucosa is not present in all regions of the oral cavity, such as attached gingiva, the tongue, and hard palate. Its presence tends to increase the mobility of the tissue overlying it.

E. Gingiva

1. The portion of oral mucosa that attaches to the teeth and alveolar bone.

2. There are two types of gingiva: attached and free gingiva. The boundary at which they meet is known as the free gingival groove .

a. Attached gingiva

(1) Directly binds to the alveolar bone and tooth.

(2) It extends from the free gingival groove to the mucogingival junction.

b. Free gingiva

(1) Coronal to the attached gingiva, it is not bound to any hard tissue.

(2) It extends from the gingival margin to the free gingival groove.

c. Together, the free and attached gingiva form the interdental papilla.

.F. Alveolar mucosa

1. The tissue just apical to the attached gingiva.

2. The alveolar mucosa and attached gingiva meet at the mucogingival junction .

G. Junctional epithelium

1. Area where the oral mucosa attaches to the tooth, forming the principal seal between the oral cavity and underlying tissues.

2. Is unique in that it consists of two basal lamina, an internal and external . The internal basal lamina, along with hemidesmosomes, comprises the attachment apparatus (the epithelial attachment). This serves to attach the epithelium directly to the tooth.

3. Histologically, it remains as immature, poorly differentiated tissue. This allows it to maintain its ability to develop hemidesmosomal attachments.

4. Has the highest rate of cell turnover of any oral mucosal tissue.

H. Interdental papilla (interdental gingiva)

1. Occupies the interproximal space between two teeth. It is formed by free and attached gingiva.

2. Functions to prevent food from entering the (interproximal) area beneath the contact point of two adjacent teeth. It therefore plays an important role in maintaining the health of the gingiva.

3. Col

a. If the interdental papilla is cross-sectioned in a buccolingual plane, it would show two peaks (buccal and lingual) with a dip between them, known as the col or interdental col. This depression occurs around the contact point of the two adjacent teeth.

b. Histologically, col epithelium is the same as junctional epithelium

Compensating curvatures of the individual teeth.

- the gentle curvature of the long axes of certain posterior teeth to exhibit a gentle curvature.

-These are probably analogous to the trabecular patterns seen in the femur and therefore reflect lines of stress experienced during function.

Posteruptive tooth movement.

These movements occur after eruption of the teeth into function in the oral cavity. These movements, known collectively as occlusomesial forces.

A. Continuous tooth eruption eruption of teeth after coming into occlusion. This process compensates for occlusal tooth wear.. Cementum deposition and progressive remodelling of the alveolar bone are the growth processes that provide for continuous tooth movement

B. Physiological mesial drift :Tthe tendency of permanent posterior teeth to migrate mesially in the dental arch both before and after they come into occlusion. Clinically, it compensates for proximal tooth wear.

(1) It describes the tendency of posterior teeth to move anteriorly.

(2) It applies to permanent teeth, not deciduous teeth.

(3) The distal tooth have the stronger is the tendency for drift.

(4) It compensates for proximal wear.

(5) In younger persons, teeth drift bodily; in older persons, they tip and rotate.

(6) Forces that cause it include occlusal forces, PDL contraction, and soft tissue pressures. There may be other more subtle factors as well.

Height  of Epithelial Attachment

The height of normal gingival tissue . mesiallv and distallv on approximating teeth, is directly dependent upon the height of the epithelial attachment on these teeth. Normal attachment follows the curvature of the cementoenamel junction if the teeth are jn proper, alignment and contact.

Clinical importance of cementum

1) Deposition of cementum continues throughout life.
The effects of the continuous deposition of cementum are the maintenance of total length of the tooth (good) and constriction of the apical foramen (bad).
2) With age, the smooth surface of cementum becomes more irregular due to calcification of some ligament fiber bundles. This is referred to as spikes.

Behavior of cementum in pathologic conditions

Time for tooth development

Entire primary dentition initiated between 6 and 8 weeks of embryonic development.
Successional permanent teeth initiated between 20th week in utero and 10th month after birth Permanent molars between 20th week in utero (first molar) and 5th year of life (third molar)