THIRD MOLARS :
IT’S SIGNIFICANCE IN ORTHODONTIC
TREATMENT AND RELAPSE
Third molars are the teeth which are most often missing, impacted
and with altered morphology .Advances in dental anthropology states that there is a reduction in the number of teeth and size of jaws on evolutionary basis for the past 1,00,000 years .Third incisors ,third premolars and fourth molars have disappeared already. At present human third molars often fail to develop, which indicate that these teeth may be on their way out. Although there are some who advice the early removal of the third molars , many strongly believe that the retention of asymptomatic third molars may be useful in later years as a substitute for badly decayed teeth or may even be useful as a transplant.
DEVELOPMENT AND ERUPTION
There is great variation in the timing of development, calcification,and eruption of third molars. Development may begin as early as 5 years or as late as 16 years,with the peak formation period at 8 or 9 years.Calcification can start at age 7 years in some children and as late as age 16 years in others.Enamel formation is normally complete between 12 and 18 years and root formation is normally completed between 18 and 25 years. Hellman reported that the average age of eruption was 20.5 years. In 1962,Fanning reported average ages of eruption of 19.8 years for females and 20.4 years for males.Early formation of third molars is generally regarded as predictive of early maturation but not always of early eruption. Most surveys report that more than 17% of lower third molars become impacted.
Lower third molars normally have their occlusal surfaces tilted slightly forwards and lingually during early calcification.As the mandible increases in length,with bone resorption at the inner angulation between the body and the ascending ramus of the mandible,the third molars become more upright.
In contrast, upper third molars erupt downwards, backwards, and often outwards. There is, therefore, a possibility of crossbite, but tongue pressure on lower crowns and buccinator pressure on upper crowns will often correct this. If there is a lack of space,then normal eruptive paths cannot be followed,and crossbites can result.
THIRD MOLARS AND CROWDING
Lower arch crowding after establishment of the permanent dentition during teenage period (post adolescent crowding) is a common orthodontic problem. This late lower arch crowding is caused by pressure from the back of the arch. Whether this pressure results from a developing third molar, physiologic mesial drift or the anterior component of force derived from the forces of occlusion on mesially inclined teeth is not clear. There is also a school of thought holding the view that in the absence of third molar, the dentition has room to settle distally under anterior pressures caused by late growth or soft tissue changes. Thus the third molar plays, at the very least, a passive role in the development of late lower arch crowding
EXTRACTION OF THIRD MOLARS
The third molars need to be considered as part of overall treatment planning,and this may include a recommendation for extraction.The timing of extractions requires an understanding of the various techniques available.
EXTRACTION BEFORE TREATMENT
It is not common practice for third molar teeth to be enucleated before orthodontic treatment of adolescents. Orthodontists are normally reluctant to make surgical extractions a prerequisite of providing treatment. They may feel that ramus growth and lower third molar eruptive pattern cannot be predicted, and take the view that the third molars may erupt eventually.