Study Notes on Dentition: Form and Function

Introduction to the Form and Function of Dentition

• Two main sections discussed:

  • Tooth type

  • Function of teeth

Tooth Type and Function

• The design and shape of teeth are determined by their function.

• Example with a sheep:

  • Presence of a large diastema (gap between teeth)

  • No incisors on the maxillary arch, only on the mandibular arch

  • The design allows the sheep to grasp grasses or hay using its tongue, pulling it with its incisors against the gum pad.

  • The diastema accommodates uncut grass, moving it back to molars for chewing.

• Example with a bear:

  • Bears have large incisors and very small vestigial incisors.

  • Different tooth shapes for different diets.

  • Canine teeth sharpen against each other like a sword in a scabbard with every mouth movement.

• Importance of diet and activity in tooth form:

  • Incisors primarily cut and grasp.

  • Canines used for prehension, communication, and fighting (e.g., Western gorilla).

  • Molars and premolars are designed for grinding and crushing food.

• Dolphin dentition:

  • Teeth function differently; they interdigitate.

  • Dolphin catches fish and swallows it without chewing.

Families of Teeth

• Multiple classifications of teeth based on type and production:

  • Rodents have continuously growing teeth (modified monophyodont).

  • Humans, cats, and dogs have diphyodont teeth (two sets of teeth).

  • Polyphyodont (many families of teeth) continuously produce teeth, focusing on quantity over quality (e.g., sharks).

• Homodont teeth:

  • All teeth in a species share the same shape (e.g., certain fish).

  • Haplodont refers to simple, conical curved teeth that interdigitate for efficient food capture.

• Heterodont teeth:

  • Different shapes and sizes for varied functions among teeth.

Dental Formula

• Standard mammalian dental formula is:

  • 3 upper incisors

  • 3 lower incisors

  • 1 canine upper and lower

  • 4 premolars upper and lower

  • 3 molars upper and lower

Tooth Attachments

• Different types of tooth attachments:

  • Polyphyodont and homodont sharks have membranous attachment leading to easy shedding and replacement of teeth.

  • Thecodont (crocodilians): teeth located in deep sockets without periodontal ligaments.

  • Acrodont: teeth attached to the top of the bone in shallow sockets, seen mostly in reptiles.

  • Pleurodont: teeth attached to the medial aspect of the bone; they move forward through shedding.

  • Isonathous: teeth symmetrically aligned in the arch.

  • Asenathous: teeth asymmetrically aligned.

  • Ankylosed teeth: embedded in bone, particularly seen in reptiles or as a pathological condition in humans.

  • Gomphosis: socketed teeth supported by periodic ligaments (typical in humans).

Continuous Tooth Growth

• Hypsodont teeth: high crown, low root ratio, continuously growing.

• Ipsalodont teeth: continuously growing teeth, such as in rodents

• Brachydont teeth: low crown with long roots, socketed within the alveolus.

  • Example of horses: high crowns that grow slowly (2-3 mm per year).

• Elephant molars:

  • Weigh around 3-4 kg each.

  • Continuously growing, with anterior growth and replacement from the back.

  • Characteristic of mesial drift as teeth wear down and shift forward.

Differential Wear and Grazing Adaptations

• Grazing animals exhibit differential wear patterns:

  • Two enamel layers with softer dentine in between, exposing dentine quickly as enamel wears down.

  • Example: Horses and elephants demonstrate adaptations for grinding plant material.

Adaptations of Teeth in Different Animal Types

• Comparison of herbivores and carnivores:

  • Herbivores: eyes placed laterally for broader peripheral vision while grazing.

  • Carnivores: forward-facing orbits for focused hunting/surveillance.

• Adaptations discussed:

  • Incisors: used for cutting (e.g., horses) and cropping (e.g., sheep).

  • Canines adapted for gripping (e.g., elephants have large incisors).

  • Molars: specific shapes and patterns adapted for crushing (omnivores), grinding (herbivores), or slicing (carnivores).

  • Carnassial teeth:

  • Specialized for shearing action, interdigitating with the opposite jaw (e.g., seen in felids and canids).

  • Bunodont teeth:

  • Adapted for crushing with multiple cusps, typical in omnivores.

Conclusion

• Understanding the diverse adaptations of dentition is essential for comprehending animal behavior, feeding strategies, and ecological roles within their respective environments.