Teeth

Teeth are hard, calcified structures located in the oral cavity that play a crucial role in biting, chewing, and breaking down food for digestion. They are made up of multiple layers, including enamel, dentin, pulp, and cementum, each contributing to their strength and function. Teeth are anchored in the alveolar sockets of the jawbones (maxilla and mandible) and are supported by the periodontal ligament.

Humans have two sets of teeth during their lifetime – primary teeth (deciduous), also known as baby teeth, and permanent teeth (adult). The primary teeth consist of 20 teeth, while the permanent set includes 32 teeth, divided into incisors, canines, premolars, and molars, each serving different purposes. Teeth are lined with gingiva (gums), which provide structural support and protection. They also contain nerves and blood vessels that keep them nourished and responsive to external stimuli.

Location

Teeth are located within the oral cavity, embedded in the alveolar processes of the maxilla (upper jaw) and mandible (lower jaw). They are arranged in two arches – the upper dental arch in the maxilla and the lower dental arch in the mandible. The teeth are aligned along the dental ridges and are surrounded by gingiva, forming the dental occlusion where the upper and lower teeth meet when the mouth is closed.

Anatomy

Each tooth is composed of multiple layers of tissues and is supported by surrounding structures like the periodontal ligament and gingiva. Teeth are categorized into primary (deciduous) and permanent sets, with distinct shapes and functions.

Types of Teeth

1. Incisors – Located at the front of the mouth, they are flat and sharp, designed for cutting food.
2. Canines – Pointed teeth next to the incisors, used for tearing food.
3. Premolars – Broad-surfaced teeth behind the canines, used for crushing and grinding.
4. Molars – Located at the back of the mouth, they have a larger surface area for grinding food.
5. Wisdom Teeth – The third molars, often appearing later in adulthood, and sometimes require extraction if they are impacted.

Structure

Each tooth consists of three major parts:

1. Crown – The visible part of the tooth above the gum line, covered by enamel for protection.
2. Neck – The narrow region where the crown and root meet, surrounded by the gingiva.
3. Root – The portion embedded in the jawbone, anchoring the tooth securely within the alveolar socket.

Layers of Teeth

Enamel

• The outermost layer and the hardest substance in the human body.
• Composed primarily of hydroxyapatite, a crystalline form of calcium phosphate.
• Provides protection against wear, decay, and acid erosion.

Dentin

• Lies beneath the enamel, forming the bulk of the tooth structure.
• Softer than enamel but harder than bone.
• Contains microscopic tubules that transmit sensory signals to the pulp.

Pulp

• The innermost layer, containing nerves, blood vessels, and connective tissues.
• Supplies nutrients and sensations to the tooth.
• Extends from the crown to the root canal.

Cementum

• A calcified tissue covering the root of the tooth.
• Provides attachment for the periodontal ligament, anchoring the tooth to the jawbone.
• Protects the root and assists in repair processes.

Supporting Structures

Periodontal Ligament

• Connective tissue fibers that attach the tooth to the alveolar bone.
• Acts as a shock absorber, distributing forces during chewing.
• Provides sensory feedback for pressure and pain.

Alveolar Bone

• The part of the jawbone that forms the sockets for the teeth.
• Supports and holds the roots of the teeth securely in place.
• Remodels in response to pressure from chewing or orthodontic treatments.

Gingiva (Gums)

• Soft tissue covering the alveolar bone and surrounding the teeth.
• Provides protection against bacterial infections and mechanical trauma.
• Forms a seal around the teeth to prevent entry of pathogens.

Dental Arches

Teeth are arranged in two arches:

• Maxillary Arch – Upper jaw teeth, attached to the maxilla.
• Mandibular Arch – Lower jaw teeth, attached to the mandible.

Both arches meet at the occlusal surface during biting and chewing, forming the dental occlusion.

Dental Formula

• Primary Teeth (Deciduous) – 20 teeth in total.
  • Incisors (8), Canines (4), Molars (8).
• Permanent Teeth – 32 teeth in total.
  • Incisors (8), Canines (4), Premolars (8), Molars (12).

Root and Root Canal System

Root Anatomy

• Each tooth may have one or more roots, depending on its type.
• Incisors and canines typically have one root, premolars may have one or two, while molars can have two to three roots.

Root Canal

• A hollow chamber within the root that contains the pulp tissue.
• Extends into the crown through the pulp chamber and exits at the apex of the root.

Apical Foramen

A small opening at the tip of the root that allows blood vessels and nerves to enter and exit the pulp.

Blood Supply

Teeth receive blood supply through the branches of the maxillary artery:

• Superior Alveolar Arteries – Supply the maxillary teeth.
• Inferior Alveolar Artery – Supplies the mandibular teeth.
• Venous drainage occurs via the pterygoid venous plexus and facial vein.

Nerve Supply

1. Maxillary Teeth – Supplied by branches of the maxillary nerve (V2), a division of the trigeminal nerve (cranial nerve V).
2. Mandibular Teeth – Supplied by branches of the mandibular nerve (V3), another division of the trigeminal nerve.
3. Pulp Sensation – The nerves within the pulp detect pain, pressure, and temperature changes.

Lymphatic Drainage

Teeth and surrounding structures drain into:

• Submental Lymph Nodes – Drain the central incisors and adjacent soft tissues.
• Submandibular Lymph Nodes – Drain most of the remaining teeth and surrounding areas.
• Deep Cervical Lymph Nodes – Serve as secondary drainage points for all teeth.

Microscopic Anatomy

Enamel Composition

• 96% mineral content (hydroxyapatite) and 4% water and organic material.
• Non-living tissue with no regenerative capacity.

Dentin Composition

• Contains microscopic tubules extending to the pulp.
• Can regenerate and form secondary or reparative dentin in response to injury.

Pulp Tissue

• Rich in cells, blood vessels, and nerves, providing nutrients and sensation.
• Fibroblasts and odontoblasts present in the pulp produce dentin.

Cementum Composition

45–50% mineralized and supports tooth attachment via the periodontal ligament.

Function

Chewing and Mastication

Teeth play a primary role in mastication, the process of breaking down food into smaller, digestible pieces.

• Cutting and Biting – The incisors at the front of the mouth are sharp and flat, designed for cutting and slicing food.
• Tearing – The canines have pointed edges that tear and rip apart tougher foods, such as meat.
• Grinding and Crushing – The premolars and molars have broad, flat surfaces that crush and grind food into smaller particles.
• Food Mixing – Teeth work with the tongue and saliva to mix food, forming a bolus that can be swallowed easily.

This process improves digestion by increasing the surface area of food, allowing enzymes to act more effectively.

Speech and Pronunciation

Teeth are essential for speech production and articulation.

• Teeth help produce sounds by controlling airflow and providing points of contact for the tongue and lips.
• They assist in the pronunciation of specific letters and sounds, such as s, t, v, and f.
• Proper alignment of teeth ensures clarity of speech and prevents lisps or speech impediments.

Aesthetic and Facial Structure

Teeth contribute to the appearance of the face and maintain structural balance.

• Proper alignment and spacing of teeth support the cheeks and lips, giving shape to the face.
• They influence facial symmetry, contributing to an aesthetically pleasing appearance.
• Missing or misaligned teeth can affect facial features, leading to sunken cheeks or jaw misalignment.

Digestion and Enzymatic Activation

Teeth initiate chemical digestion by breaking food into smaller pieces and stimulating salivary secretion.

• Saliva contains amylase, which begins the breakdown of carbohydrates into sugars.
• The mechanical process of chewing stimulates the release of enzymes that prepare food for further digestion in the stomach and intestines.
• Smaller food particles ensure efficient absorption of nutrients during later stages of digestion.

Defense and Protection

Teeth act as barriers to protect the oral cavity and deeper tissues.

• They shield the tongue and oral mucosa from trauma caused by chewing hard or sharp objects.
• Healthy teeth prevent foreign objects from entering the airway during eating.
• Teeth also form part of the immune defense, as they are surrounded by gingiva and saliva, which contain antibodies and enzymes that inhibit microbial growth.

Supporting Jaw Function and Alignment

Teeth play a crucial role in jaw movement and alignment.

• The occlusion between upper and lower teeth ensures proper bite force distribution during chewing.
• Teeth support the temporomandibular joint (TMJ), allowing smooth movements for opening, closing, and lateral shifts of the jaw.
• Balanced alignment of teeth prevents jaw disorders and conditions like bruxism (teeth grinding).

Maintaining Bone Density

The roots of teeth are embedded in the alveolar bone, stimulating it during chewing and biting.

• Pressure exerted on the bone through the periodontal ligament maintains bone density and prevents resorption (bone loss).
• Tooth loss or absence of chewing activity can lead to alveolar bone atrophy, compromising jaw stability.

Sensory Perception

Teeth are equipped with nerves in the pulp cavity that detect pressure, pain, and temperature.

• Pain Sensation – Detects injury, infection, or excessive pressure to prevent further damage.
• Temperature Sensation – Responds to heat and cold, signaling discomfort in cases of sensitivity or enamel damage.
• Proprioception – Teeth provide feedback to the brain about positioning and force, ensuring controlled jaw movements during chewing.

Speech Development in Children

In children, primary teeth support proper speech development by acting as guides for tongue placement and phonation.

• Early loss of teeth can affect speech clarity, resulting in delays or speech therapy needs.
• Teeth help maintain space for permanent teeth, ensuring proper alignment and minimizing the need for orthodontic treatments.

Aid in Emotional and Psychological Health

Teeth influence confidence and self-esteem through their role in facial appearance and speech clarity.

• Healthy teeth improve smiles, impacting social interactions and personal image.
• Dental issues, such as misalignment, discoloration, or tooth loss, may cause emotional distress and lead to avoidance of communication.

Biting and Defense Mechanism

Historically, teeth served as a defense mechanism in animals and early humans.

• The canines provided a means for grasping and tearing, acting as tools for survival.
• While less relevant today, they still reflect the evolutionary structure of teeth.

Storage of Minerals

Teeth serve as a calcium reservoir, maintaining mineral balance in the body.

• The enamel and dentin are rich in calcium phosphate, which supports the overall mineral metabolism.
• While not actively reabsorbed, teeth mirror bone composition, linking them to systemic health.

Occlusion and Mechanical Stability

Teeth ensure proper alignment and contact during chewing, maintaining balance in the oral cavity.

• Proper occlusion distributes bite forces evenly, reducing the risk of jaw strain and fractures.
• Malocclusion, or misalignment, can cause jaw pain, headaches, and speech disorders.

Cleaning and Self-Maintenance

Teeth assist in self-cleaning processes by interacting with the tongue and saliva during chewing.

• Saliva washes away food particles and reduces the risk of plaque formation.
• The structure of molars and premolars allows food to be directed toward the tongue for clearance.

Preparation for Swallowing

Teeth prepare food for swallowing by forming it into a bolus.

• Proper chewing ensures that food particles are uniformly sized, preventing choking.
• The bolus formed by teeth and saliva slides easily through the esophagus into the stomach.

Clinical Significance

Teeth are vital for chewing, speech, and aesthetics, but they are also prone to various disorders affecting oral and overall health. Dental caries (tooth decay) is one of the most common conditions, caused by bacterial activity that leads to enamel erosion and cavity formation. If untreated, it can progress to pulpitis or dental abscesses, causing severe pain and infection. Periodontal diseases, such as gingivitis and periodontitis, affect the supporting structures of teeth, leading to gum recession, bone loss, and even tooth loss.

Malocclusion, or improper alignment of teeth, can impact chewing, speech, and jaw function, often requiring orthodontic treatments like braces. Tooth sensitivity may result from enamel erosion or gum recession, exposing the dentin. Impacted wisdom teeth can cause pain, swelling, and infection, often requiring surgical removal.

Regular dental checkups, professional cleaning, and oral hygiene practices are essential for preventing dental diseases, maintaining healthy teeth, and avoiding complications such as tooth loss and systemic infections.