Key points
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The second molar tooth is usually the last functional tooth to erupt and can become impacted under the distal contour of the first molar.
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Leaving the second molar in that position can damage the first molar and cause malpositioning of teeth in the opposing arch.
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Conventional orthodontic uprighting is lengthy and not always predictable, whereas surgical intervention can expedite the completion of care.
Introduction
The prevalence of impacted second molar is estimated to be approximately 3 in every 1000 patients. They occur more frequently in the mandible than the maxilla, are usually unilateral, and are more common in females than males. The primary cause can be attributed to a discrepancy in arch length. The typical pattern of resorption-apposition during mandibular development may be associated with insufficient resorption of the anterior border of the ramus. This can cause a lack of arch length causing the third molar to be situated above and behind the second molar, which prevents the natural eruption pathway of the second molar. In addition, the lack of mesial movement of the permanent first molar after exfoliation of the primary second molar can prevent eruption. A less common cause is an excess of arch length. During normal eruption, the second molar is guided into occlusion by the distal root of the first molar. When there is space between the first and second molar the second molar tends to tip mesially during eruption and the crown becomes situated beneath the height of contour of the first molar. Iatrogenic causes have also been implicated, such as bulky first molar bands ( Fig. 1 ) and early orthodontic treatment of anterior crowding leading to insufficient space in the posterior mandible ( Fig. 2 ).
It is essential that the treating dentist recognize and treat impacted second molar in a timely manner. Failure to do so can result in prolonged treatment times for patients undergoing orthodontic therapy and more importantly can result in loss of the first and second molar because of caries and periodontal disease. After the impacted second molar is identified, a referral should be made to a specialist who is trained in complex dentoalveolar procedures. The initial evaluation should include appropriate radiologic studies, a full medical history, a clinical examination, and a discussion with the patient and referring doctor regarding treatment options and goals.
There are many different management options that are described in the literature to treat impacted second molar. These include surgical and nonsurgical approaches. A generalization can be made that nonsurgical approaches often take longer to complete treatment; require strict patient compliance; and are technically more difficult to achieve the desired result (especially in cases of severe impactions). These techniques require that the second molar be at least partially erupted so that orthodontic appliances can be applied. To circumvent this problem, a separate surgical procedure can be performed that exposes the crown of the tooth. This not only adds another procedure, but it is difficult to keep a dry field to bond a bracket and it also causes the patient discomfort because of soft tissue overgrowth over the orthodontic appliance.
Lastly, there are several purely surgical treatment options that include the following: elective extraction of the second molar to allow eruption of the third molar; transplantation of the third molar into the second molar site; and extraction of the third molar and surgically uprighting the second molar ( Fig. 3 ). The last of these options has been shown to be a safe and predictable procedure with excellent long-term results. The advantages of this approach are that only a single surgical procedure is necessary with a shorter overall treatment time compared with other nonsurgical options. Although there is a potential risk of root fracture and pulpal necrosis, these are exceedingly rare when the appropriate technique is used. This article describes the procedure so that the reader can achieve the same results.
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