The debate over the removal of asymptomatic impacted third molars still continues. The very high prevalence of this condition (up to 80%!) and its possible associated complications led me to write the present post.
The main reason for third molars impaction is the lack of space in the jaws, a situation most commonly found in the mandible. When it´s retained or partially retained, the wisdom teeth may cause several pathological changes including pericoronitis, periodontitis, caries, and development of cysts or tumors. Moreover, they were also associated with caries, external root resorption (ERR) and periodontal lesions in the adjacent second molars. The most common symptoms related to some of these signs include pain, edema and trismus. When these signs and/or symptoms are present, there is usually a general agreement that surgical removal is one of the best choices, depending on the peculiarities of the case (coronectomy, repositioning and transplantation can also be considered for indicated cases).
The controversies arise regarding the management of “asymptomatic” disease-free wisdom teeth. First of all, I think it´s important to emphasize that the term “asymptomatic” is an insufficient description of the clinical status of the third molar. Just as in many other disease courses, such as diabetes and cardiovascular disease, the absence of symptoms in a third molar does not always reflect true absence of disease. Periodontitis, small caries, ERR, cysts and tumors associated with impacted third molars are usually asymptomatic and they are often identified incidentally on panoramic radiographic examinations.
Especially in cases of ERR in adjacent second molars, the lack of pathognomonic symptoms and its hidden position could result in a belated diagnosis, which highlights the relevance of identifying the risk factors for this condition. According to recent CBCT studies,1-2 the prevalence of ERR is high (around 30% in maxillary and 50% in mandibular second molars). The severity of ERR is generally higher in maxillary second molars, and the apical region is the most affected area in these teeth, while the ERR of mandibular second molars was most frequently detected at the cervical third. Another common finding of these studies is that mesially inclined third molars (mesioangular and horizontal) have a greater potential of being associated with ERR in second molars. Moreover, both studies found a relatively high prevalence and a higher risk of ERR for patients older than 25 years. Taken together, these results indicate that active surveillance, a prescribed program of follow-up and reassessment at regular intervals are recommended for retained third molars rather than waiting for the onset of symptoms to initiate follow-up, mainly in the cases mentioned above.
Fact or myth?
In orthodontics, one of the most controversial roles of the third molars is whether they can contribute to the development of malocclusion, particularly in the anterior segment of the dental arch. It has been hypothesized that, while erupting, the tooth could transmit an anterior component of force down the dental arch concentrating in the areas of canines and incisors, which results in tooth rotation and misplacement. To my knowledge, most of the studies do not support this cause-and-effect relationship, so the third molar extraction to prevent anterior tooth crowding or post-orthodontic relapse is not justifed. However, I´ve found a recent meta-analysis3 that recommends the removal of the mandibular third molars for alleviating or preventing long-term incisor irregularity. This strong and unexpected recommendation led me to a careful reading of this study. Only 3 retrospective studies were included in this review, and the only outcome measure with a significant result was the Little´s irregularity index. Surprisingly, all the 3 selected studies DID NOT show ANY significant effects related to the presence or absence of the third molars. The unexpected conclusion came when the authors pooled out the data from these studies and
conducted a meta-analysis. According to the authors, different results were indicated as the sample numbers increased. The confidence intervals were very wide, which means that there is a large amount of uncertainty in this data. Moreover, a risk of bias and quality assessment in individual studies were not performed in this meta-analysis. Therefore, I am not convinced that this result is clinically significant, even though they reported that it was statistically significant. As a teacher friend told me, statistics is the art of torturing data until it shows what you want to see. I really think we need to be very critical about the excess of systematic reviews and meta-analyzes published recently.
– To conclude, in my opinion, the impacted wisdom tooth will never be an angel, because I don´t know any beneficial effect of it. At the best, it will be quiet if any signs and/or symptoms do not arise. Following the best evidence based practices guidelines I´ve found,4-5 current data are not sufficient to refute or support prophylactic removal of third molars in patients WITHOUT any symptoms AND signs.
– In situations in which third molars are associated with a disease, or are at high risk of developing diseases, the surgical removal should be considered according to each individual case.
– Removal should also be considered in the following conditions: when there is an overlying removable prosthesis, when orthodontic removal is justifed -such as when the tooth is preventing the eruption of the second molar- and in the case of planned orthognathic surgery.
The present post recognizes that while not all third molars require surgical management, given the documented high incidence of problems associated with third molars over time, all patients should be evaluated by someone experienced and expert in third molar management. These are the best recommendations to prevent this tooth from turning into a devil.
1- Oenning AC, Neves FS, Alencar PN, Prado RF, Groppo FC, Haiter-Neto F. External root resorption of the second molar associated with third molar impaction: comparison of panoramic radiography and cone beam computed tomography. J Oral Maxillofac Surg. 2014 Aug; 72(8):1444-55.
2- Li D, Tao Y, Cui M, Zhang W, Zhang X, Hu X. External root resorption in maxillary and mandibular second molars associated with impacted third molars: a cone-beam computed tomographic study. Clin Oral Investig. 2019 [Epub ahead of print]
3- Cheng HC, Peng BY, Hsieh HY, Tam KW. Impact of third molars on mandibular relapse in post-orthodontic patients: A meta-analysis. J Dent Sci. 2018 Mar;13(1):1-7.
4- Ghaeminia H, Perry J, Nienhuijs ME, Toedtling V, Tummers M, Hoppenreijs TJ, Van der Sanden WJ, Mettes TG (2016) Surgical removal versus retention for the management of asymptomatic disease-free impacted wisdom teeth. Cochrane Database Syst Rev 8:CD003879. https://doi.org/10.1002/14651858.CD003879.pub4
5- American Association of Oral and Maxillofacial Surgeons: The management of impacted third molar teeth. White paper available at: https://www.aaoms.org/docs/govt_affairs/advocacy_white_papers/management_third_molar_white_paper.pdf. Accessed September 25, 2019