The National Institute of Health (NIH) has published the conclusions of the consensus development conference held in 1979 and, while waiting for an overall consensus on the indications for extractions, made the following recommendations:
• Evidence of hypertrophy, cyst or tumor development of the dental follicle
• Repeated episodes of pericoronitis
• Irreversible carious lesions
• Distal periodontal defect on the second molar
• Distal carious lesion of the second molar in relation to the third molar
Despite the accumulated experience in dealing with diagnosis and treatment of developmental anomalies concerning the third molars, extraction still remains controversial when patients are asymptomatic. Indeed, the proportion of prophylactic extractions is increasing and represents from 18% to 40% of the overall third molar extractions carried out in developed countries (Liedholm et al; Lysel and Rohlin). The majority of third molar extractions take place between the ages of 20 and 29 years (Liedholm et al). The main reasons for deciding on this course of action are:
• To reduce the risk of sequelae, surgical morbidity, and complications involving the neighboring teeth in the elderly patients
• To improve oral health in younger patients who have completed their growth phase
The quality of the outcome of this procedure is determined by a series of factors:
• The relevance of the indication for the prophylactic extraction of one or several third molars
• The stage at which this decision is made, the type of surgical procedure selected, and the skill of the surgeon and the surgical team
However, as yet it has not been possible to establish universal guidelines concerning the relevant indications for prophylactic extractions because of the widely varying criteria used in different countries by different practitioners and different scientific communities (Worrall et al).
Furthermore, even from a review of the current literature, it is not possible to establish a significant risk-benefit ratio. In addition, the decision to proceed with an extraction is often made during a single consultation using only one radiographic examination in young patients who have completed their growth phase.
In order to establish a diagnosis it is essential to fully understand and be able to estimate the stage of eruption of the third molar. The latter is related to the evaluation of the prognosis in terms of impaction, partial retention or enclavement, tooth and periodontal lesions on the second and/or third molar, and the risk of anterior tooth crowding, which should always be avoided.
• The age of the patient
• The angle formed between the great axis of the tooth and the occlusal plane, as well as the uprighting dynamics of this axis•
• The eruptive position
Some additional factors should also be taken into account:
• Oral hygiene
• Carious and periodontal indexes
The angulation of the axis of the third molar can be classified as follows, depending on the degree of distortion (Liedholm et al; Winter; see chapter 4):
• Mesially inclined
• Horizontal
• Vertical
• Distally inclined
Additionally, the eruptive stage can be specified as follows (Liedholm et al; see chapter 2):
• Totally erupted
• Partially covered with soft tissue
• Totally covered with soft tissue
• Totally covered with bone
The NIH has established that (NIH; Worrall et al):
• The surgical procedure and postoperative effects are more favorable in the case of younger patients.
• However, in the young adolescent, the indication for enucleation of the third molar buds before root formation becomes evident radiographically is not recommended because of the surgical risk that would be incurred.
• Distally inclined molars are more likely to develop complications during eruption than are molars with other angulations.
• Molars that are partially or totally covered with soft tissue are more prone to complications than are totally impacted molars.
In the context of orthodontic treatment, the extraction indication ratios for so-called prophylactic extractions are continually increasing, which naturally leads us to question this indication.
In orthodontics, an indication for third molar extraction usually refers to the third mandibular molar. Many practitioners support the current view of the relationship between the occurrence of anterior mandibular crowding and the eruption of the third molars at the end of adolescence and will therefore often recommend extraction. Once the decision has been made to extract the mandibular molar, this invariably implies the removal of the maxillary molars in order to create a Class I occlusion.
Embryology and eruption of the third molars
Like all human molars, the third molar is an accessional tooth, as distinct from the other teeth, which are known as replacement or successional teeth. The third molar originates from the primitive dental lamina and the bud only becomes evident at around the age of 4 or 5 years. Calcification occurs between 9 and 10 years of age, with full completion of the crown taking place between the ages of 12 and 15 years. As the eruptive movement begins, the tooth establishes an upright axis. The space available for its eruption depends on the growth of the posterior region of the arch. Emergence into the oral cavity occurs between 17 and 21 years of age. The tooth drifts along the distal aspect of the second molar in order to reach the level of the occlusal plane. Root formation is completed between the ages of 18 and 25 years.
The third molar encounters some difficulty in correcting its eruptive curve to the upright position because the direction of its growth often brings it under th/>
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