Teeth and Their Types - Practice Questions & MCQ

• Teeth are the hard bone-like organs used in tearing, grinding, and otherwise mechanically breaking down food.
• Human dentition is described as:
  • Diphyodont:  Those animals in which two successive sets of teeth, initially the "deciduous" set and consecutively the "permanent" set occur. 20 deciduous teeth, or baby teeth, first begin to appear at about 6 months of age. Between approximately ages 6 and 12, these teeth are replaced by 32 permanent teeth. 
  • Thecodont: The base of the tooth is completely enclosed in a deep socket of bone.
  • Heterodont: Presence of different types of teeth.

• The Two sets are : Deciduous and Permanent

  A) DECIDUOUS TEETH 

• These are primary or milk teeth
• These are 20 in total and thus each qudrant has 5 teeth
• 5 Teeth are 2 Incisors,1 Canine and 2 Molars (Premolars are only in permanent dentition)

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  B) PERMANENT TEETH

• These are 32 in number (28 to 32) and thus each quadrant has 8 teeth
• 8 Teeth are : 2 Incisors, 1 Canine (cuspids), 2 Premolars (Bicuspids) and 3 Molars
• The eight incisors, four top and four bottoms, are the sharp front teeth are used for biting into food.
• The four cuspids (or canines) flank the incisors and have a pointed edge (cusp) to tear up food. These fang-like teeth are used for piercing tough or fleshy foods.
• The eight premolars (or bicuspids), which have an overall flatter shape with two rounded cusps useful for mashing foods. These are monophyodont as they are not present in milk teeth set.
• The most posterior and largest are the 12 molars, which have several pointed cusps used to crush food so it is ready for swallowing. 
• The third members of each set of three molars, top and bottom, are commonly referred to as the wisdom teeth. These are also monophyodont.
• Molars and premolars are hard to differentiate and collectively termed as molariform or cheek teeth

• NOTE : Thus we can say that, 2 Premolars and 1 Third molar per quadrant are seen only in permanent dentition. This means these teeth are not regarded as Diphyodont and hence are referred as Monophyodont (total teeth showing Monophyodont dentition = 3 x 4 = 12)

Dental Formula:

• It shows the arrangement of teeth in each half of the upper and lower jaws in order of incisors, canines, premolars and molars. 

• A tooth has the following three parts:
  • Crown (above the gum)
  • Neck (at the gum line)
  • Root (inside jaw bone)
• The teeth are secured in the alveolar processes (sockets) of the maxilla and the mandible. 
• Gingivae (commonly called the gums) are soft tissues that line the alveolar processes and surround the necks of the teeth.
• Teeth are also held in their sockets by a connective tissue called the periodontal ligament. It is made up of collagen fibres called Sharpey's fibres. 
• Crown is covered by enamel. Enamel is the hardest part of the human body. It is secreted by Ameloblast cells
• Below the enamel, dentine is present. It is secreted by odontoblast cells.
• Dentine forms the bulk of the teeth and is responsible for sensitivity
• Inside the dentin, pulp cavity is present. 
• Pulp cavity contains nerves and blood vessels. There are no lymphatic vessels.

Tooth and its parts are shown in the diagram below :