Mammalia: Dentition | Zoology Optional Notes for UPSC PDF Download

Dental Arrangement in Mammals

Teeth in Vertebrates

1. Origin of Teeth:

   • Teeth are bony dermal armor derivatives.
   • Unique among vertebrate animals.
   • Composed of dentin, topped by enamel or enameloid (similar to placoid scales).

2. Development:

   • Inductive interaction between embryonic epidermis and neural-crest-derived mesenchyme.
   • Epidermis cells contribute to enamel, while mesenchyme cells form dentine.

3. Functions:

   • Assist in catching and holding prey.
   • Provide strong surfaces for crushing hard shells.
   • Initiate mechanical digestion in the mouth.

Tooth Anatomy

1. Crown and Base:

   • Crown: Projects above the gum line.
   • Base: Fits into a socket (alveolus) in the jaw bone.

2. Pulp Cavity and Root Canal:

   • Pulp cavity narrows into the root, forming the root canal.
   • Apical foramen opens at the root tip.

1. Hard Tissues:

   • Enamel: Hardest substance, forms crown surface.
   • Dentin: Harder than bone, beneath enamel and cementum.
   • Cementum: Cellular and acellular regions, covers dentin on roots.

2. Periodontal Ligament:

   • Connects cementum-covered root to the jaw bone.

Development of Teeth

1. Inductive Interaction:
   • Epidermis and neural-crest-derived mesenchyme interaction for enamel and dentine formation.
2. Tooth Formation Process:
   • Dental lamina ingrowth into dermis.
   • Dermal papillae formation indicating future teeth sites.
   • Odontoblasts organize, forming dentin.
   • Enamel organ formation from dental lamina.
   • Ameloblasts secrete enamel.
   • Cementum anchors the tooth to the jaw bone.
3.  Crown and Root Development:
   • Crown forms first, root develops shortly before eruption.
   • Cementum and periodontal ligament development last.

Types of Dentition in Mammals

1. Monophyodont Dentition:

   • One set of teeth.
   • Examples: Platypus, toothless whales, freshwater manatee, Australian Rock Wallaby.

2. Thecodont Dentition:

   • Teeth in bony sockets (alveoli), deepest in mammals.
   • Heterodont dentition prevalent, with incisors, canines, premolars, and molars.

3. Varieties of Teeth:

   • Incisors, Canines, Premolars, Molars.

Morphological Variants of Teeth

1. Incisors:

   • Vary in size, shape, and growth patterns across species.

2. Canines:

   • Spear-like in carnivores.
   • Absent in lagomorphs.

3. Premolars and Molars:

   • Vary in cusp numbers and arrangement.
   • Categories: Secodont, Selenodont, Lophodont, Bunodont, Tricodont, Trituberculate.

4. High and Low Crowned Teeth:

   • Hypsodont: High-crowned teeth (e.g., horse).
   • Brachyodont: Low-crowned teeth (e.g., human, pigs).

5. Specialized Teeth in Whales:

   • Crab eater whales use teeth to strain small crustaceans from sea water.

6. Rodent Teeth Variety:

   • Exhibit diverse teeth forms based on diet.
   • E.g., squirrels with low crowned and long-rooted teeth.

Dental Formula

• Represents the number and type of teeth in one side (quadrant) of the mouth.
• Incisors (I), Canines (C), Premolars (P), Molars (M).
• Notation: I:C:P:M. E.g., 2.1.2.3 indicates 2 incisors, 1 canine, 2 premolars, and 3 molars.

Dental Eruption Sequence

• Specific sequence in which teeth emerge.
• Wisdom teeth (third molars) erupt last in higher primates.

Epidermal Teeth in Monotremes

• Monotremes, like platypus, have temporary horny egg teeth for shell cracking.
• After bony teeth loss, horny teeth replace them and persist throughout life.