Histology of the Digestive System: Teeth

Histology of the Digestive System: Teeth

• Adult humans typically have 32 permanent teeth
• Teeth are arranged in two symmetrical arches within the maxillary and mandibular bones
• Each arch has eight teeth: two incisors, one canine, two premolars, and three molars
• Twenty permanent teeth are preceded by deciduous teeth (baby teeth)
• Permanent molars do not have deciduous precursors

Tooth Structure

• Teeth have a crown (above the gum line) and one or more roots (below the gum line)
• The crown is covered by enamel, the hardest substance in the human body (about 96% mineral)
• The roots are covered by cementum, a mineralized tissue
• The bulk of the tooth is composed of dentin, a calcified tissue harder than bone (about 70% calcium salts)
• Dentin surrounds a pulp cavity containing soft connective tissue, blood vessels, and nerves
• The pulp cavity includes a coronary portion (chamber) and root portion (canal) that extends to the apex (tip) of the root
• The apex contains an opening (apical foramen) for blood vessels and nerves to enter and exit the pulp

Dentin

• Dentin is a calcified tissue harder than bone due to its high calcium content
• Primarily composed of type I collagen fibrils, glycosaminoglycans, phosphoproteins, phospholipids, and hydroxyapatite crystals
• Dentin's organic matrix is secreted by odontoblasts, pulp cells lining the tooth's inner surface

Odontoblast

• Odontoblasts are polarized cells producing organic matrix, only at the dentin surface
• These cells have protein-secreting granules
• They have apical extensions that penetrate dentin, and these projections are known as Tomes’ fibers
• They develop gradually, becoming longer with increasing dentin thickness
• Odontoblast processes are extensively branched near the junction of the dentin and enamel

Dentin Sensitivity

• Dentin is sensitive to stimuli like heat, cold, trauma, and acidic pH, leading to pain perception
• Although the pulp is highly innervated, dentin has only a few unmyelinated nerve fibers penetrating its internal portion

Enamel

• Enamel is the hardest component of a tooth, composed of approximately 96% mineral (mostly hydroxyapatite)
• Enamel is produced by ameloblasts, cells originating from ectoderm
• Enamel’s organic matrix contains proteins amelogenins and enamelins
• Enamel consists of enamel rods (prisms) joined by interrod enamel

Pulp

• Tooth pulp consists of loose connective tissue, primarily odontoblasts, fibroblasts, thin collagen fibers, and a ground substance with glycosaminoglycans
• Pulp is richly innervated and vascularized, with blood vessels and myelinated nerve fibers entering the apical foramen
• Some nerve fibers lose their myelin sheaths and extend into dentinal tubules
• Pulp fibers are sensitive to pain, the only sensory modality recognized in teeth

Periodontium

• Periodontium is the structure maintaining teeth in the maxillary and mandibular bones; it consists of cementum, periodontal ligament, alveolar bone and gingiva

Cementum

• Cementum covers the dentin of the root and is similar to bone, albeit without Haversian systems and blood vessels
• Cementum thickens in the root's apical region, containing cementocytes (similar to osteocytes but with no canaliculi)
• Cementum derives nourishment from the periodontal ligament.

Periodontal Ligament

• The periodontal ligament is specialized connective tissue anchoring the tooth to its socket (alveolus)
• Its fibers penetrate the cementum and bind the tooth to the bone; allowing for limited movement
• The collagen in the ligament has characteristics of immature tissue
• It has a rapid turnover rate

Alveolar Bone

• The alveolar bone is closely associated with the periodontal ligament
• It is an immature type of bone (primary bone), without typical lamellar collagen arrangement
• Sharpey's fibers connect the collagen in the periodontal ligament to the cementum and alveolar bone
• Blood vessels and nerves penetrate the bone and supply the periodontal ligament and pulp

Gingiva

• Gingiva (gums) is a mucous membrane firmly attached to the periosteum of the upper and lower jawbones
• It is made of stratified squamous epithelium and lamina propria
• The junctional epithelium, a specialized portion, adheres to tooth enamel via a cuticle resembling a basal lamina
• A small sulcus separates the gingiva from the enamel of the tooth

This quiz covers the essential aspects of human teeth, including their arrangement, structure, and composition within the digestive system. Learn about the different types of teeth and their roles, as well as the materials that make up each tooth. Perfect for students studying anatomy and histology.