The Difference Between Primary & Permanent Dentition

Human beings develop two sets of teeth during the course of their lifetime. These are divided into the primary and permanent teeth. The term "dentition" is used to describe the development of teeth and the manner in which they are arranged in the mouth. The two sets of human teeth have certain unique characteristics which differentiate them from each other.

Period of Development

• The period of the eruption of primary teeth is measured in months while that of the permanent teeth is measured in years. The process by which a tooth emerges is known as an eruption. The eruption of teeth in infants usually starts with the lower central incisor. The clinical timing for the onset of this eruption is 6 1/2 months, and 7 months for the lateral incisor. The upper central incisor usually erupts by 7 1/2 months. The full set of primary teeth is usually formed by 2 1/2 years of age. The permanent teeth start erupting by the age of 6 and continue until the third molars are formed, usually by the age of 21.

Physical Characteristics

• Primary teeth are usually whiter in color than permanent teeth due to the fact that the enamel of permanent teeth are more mineralized, giving them a vaguely yellowish tint. The enamel of the primary teeth is also thinner than that of the permanent teeth. The second molar is usually larger than the first molar in primary teeth. The opposite is true in permanent teeth.

Number of Teeth

• Primary teeth are 20 in number while permanent teeth are 32. There are 10 primary teeth on each jaw. Primary teeth are divided into eight primary molars, four canines and eight incisors. There are 16 permanent teeth on the upper and lower jaws respectively. Permanent teeth are divided into eight premolars, eight incisors, four canines and 12 molars. Twenty-eight out of the total 32 primary teeth should erupt by the time a child reaches the age of 13 years.

Wisdom Teeth

• The last set permanent teeth to erupt in adults are the upper and lower molars, also known as "wisdom teeth." Wisdom teeth may erupt without any problem. However, there are some unique issues associated with the eruption of wisdom teeth. Sometimes, the jaw is not be large enough to accommodate them as they try to erupt. This causes the wisdom teeth to become stuck against the preceding teeth, or to remain below the jawline. This is referred to as "impacted" wisdom teeth. Another problem associated with wisdom teeth is a condition known as pericoronitis. This is a situation where a partially erupted wisdom tooth causes food, bacteria and plaque to be trapped under the flap of gum which covers a part of the tooth. Since the set of primary teeth do not have wisdom teeth, this is not an issue with primary teeth.