Impact of the presence of partially erupted third molars on local radiographic bone status

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The present study found that in patients with partially erupted lower 3Ms, older ages and greater angulations between the 3M and 2M were independent factors that contributed to the presence of a fuzzy bony appearance, horizontal bone loss or vertical bone loss in the alveolar bone. ridge between 3 and 2M. Additionally, older age was positively associated with radiolucency in the distal aspect of lower 3M values.

Although there is evidence that 2Ms adjacent to 3Ms may present with periodontal problems, such as gingival inflammation2.4periodontal pocket3and alveolar bone resorption3.5, to the authors’ knowledge, this is the first paper to demonstrate an association between age and alveolar bone crest status. Radiographic examination evaluating the levels of the alveolar bone crest is a very useful adjunct diagnosis to the periodontal clinical examination.12. Periodontal disease presents with radiographic signs that usually begin with a fuzzy bony appearance (“fuzziness”) or discontinuity of the lamina dura in the region of the alveolar bone crest12. Then, the destruction will extend to the interdental septa and lead to a reduction in the height of the bone crest.12. In this sense, the alteration of the bony crest must be considered as the initial process of periodontal disease.

According to the statistical results, after controlling for confounding factors, for each year of increase in the age of the individual, the risk of alteration of the alveolar bone crest increases by 15%. Therefore, age should be considered an important predictor of crest bone alterations and, therefore, an important reason to consider prophylactic removal of the third molar.1. On the other hand, sufficient space in the dental arch should be considered for decision-making on prophylactic removal of 3M once this variable can predict complete eruption of 3M.15.

The decision for prophylactic withdrawal below 3M is still a subject of wide discussion. Dental surgeons often have difficulty in decision-making: withdraw 3M as a prophylactic approach or wait for the development of associated pathologies as a reason for withdrawal? Some studies elucidate reasons for indicating 3M removal, such as caries, periodontitis, and pain1,2,5,16,17. A current systematic review concluded that the evidence comparing prophylactic removal of the impacted lower 3M with its retention is very limited.18. Although sufficient evidence is lacking, the authors suggest that prophylactic withdrawal may be the most cost-effective strategy18. However, these results relate to impacted teeth and systematic reviews evaluating the effectiveness of extracting partially erupted teeth were not found. Thus, the lack of reliable evidence hampers the decision-making process. In this sense, this study elucidates new findings based on the analysis of periapical radiographs of the alveolar bone crest in the 3M region. The results of this study are an additional consideration for surgeons and patients when deciding whether to extract or store 3Ms prophylactically.

When performing a radiological examination in an asymptomatic 3M region, at least three radiographic signs can determine hard tissue alterations and indicate the need for surgical removal of the tooth: loss of marginal bone in the distal aspect of the 2M adjacent; the increased radiolucent area surrounding the 3M crown; and bone resorption in adjacent 2M8.19. Greater angulations between 3 and 2M promote greater distances between these teeth and lead to the occurrence of food impaction20. Some studies have reported increased local inflammation and bone resorption related to this impacted food21.22what can be observed clinically9. The present study showed that for each degree of increase in 3M angulation, holding other variables constant, the probability of understanding the bony crest increases by 3%. Some studies have reported that most of the pathological changes presented in panoramic radiographs were associated with mesioangular and horizontally impacted 3Ms, considering Winter’s classification8.19, which supports the results of this study. Few studies in this area describe 3M angulation as a continuous variable. However, the literature suggests the advisability of using an objective measurement method to minimize the error introduced by the observer’s interpretation.23.

Specifically, pathological changes in radiographs such as pericoronal radiolucency greater than 2.0 mm in the distal aspect, is a generally accepted reason for extraction of impacted lower third molars.24. The present study showed that only the age variable was significantly associated with radiolucency between the distal aspect of the inferior 3M crown and the mandibular branch in the final multivariable regression model. Thus, older patients had wider radiolucency in the distal part of the lower 3M crown compared to younger patients. According to previous studies25.26, the earlier the need to remove a 3M that causes periodontal alterations distal to the adjacent 2M is diagnosed, the greater the chance of reducing local inflammatory activity. A study has shown that this inflammatory activity can decrease from 77% before surgery to 23% after 3M removal in young patients25. Thus, previous radiographic examinations in addition to the clinical examination in periodontal conditions will make it possible to orient the confirmed clinical recommendations, in particular with regard to asymptomatic teeth.

Cone-beam computed tomography is the gold standard radiographic method for analyzing third molars and related structures19, however, it has a high cost. The two most widely used methods for assessing regional bone anatomy when planning surgery are panoramic and periapical radiographs.12. However, one study compared measurements on panoramic and periapical radiographic methods with actual measurements of the 3M region and, although no statistically significant differences were found, distortions on panoramic exams were slightly greater than on periapical examinations.27.28. Another study suggested full-mouth investigation of periapical radiographs as the gold standard for periodontal diagnosis.25. Considering the exposure to radiation, a single panoramic radiograph can adequately represent an individual’s periodontal status. However, as the focus of the present study was to assess only the lower 3M region, it can be suggested that the current evidence, which is based on periapical radiographs, is sufficient to indicate the presence or absence of periodontal pathologies with considerable accuracy without exceeding radiation exposure.

Furthermore, in view of the ALARA (“as low as reasonably achievable”) principle, which states that exposing a patient to even a small dose of radiation should be avoided if there is no benefit in receiving that dose29, it is not justifiable to use a panoramic radiograph to analyze a single inferior 3M. Certain adverse events may occasionally occur, such as in patients who cannot tolerate the periapical X-ray film and therefore may require re-examination. In these cases, the three main protective measures of the ALARA principle (time, distance and shielding) must be followed precisely to avoid unnecessary exposure to X-rays.29. Additionally, X-ray positioners are also a great alternative to avoid errors when taking a periapical x-ray.

Although periapical radiography is not the best imaging test to check for pathological conditions related to the 3M region20it is a widely used method in clinical practice due to its low cost, ease and small amount of equipment needed27.28. Additionally, at the institution where this study was conducted, periapical x-rays are the required preoperative examination as they can be performed at the university at no cost to patients. Periapical radiographs were the images available to conduct this study and investigate the target conditions. In future studies, periodontal diagnosis should consider the association between radiographic and clinical findings.

Some limitations of this study should be highlighted. The prevalence rate of periodontal pockets in the distal portion of 2Ms adjacent to 3Ms was used to calculate the sample size, considered to be patients from the United States, and may not be representative of the population included in this study. Different techniques and performers can be adopted to perform the radiographic examinations, resulting in possible differences between the x-ray exposure time and the direction of incidence. Moreover, to accurately assess possible anatomical alterations caused by 3Ms would require a random sample from a generalized population, but there is a limitation to performing radiographic examinations without consistent indication, for ethical reasons. Thus, for patients with partially eruptive 3Ms, radiographic and clinical monitoring is recommended to verify the need for prophylactic or resolving extraction of these teeth. Finally, this is a cross-sectional study based solely on periapical radiographs. To further elucidate other conditions associated with the risk of broader radiolucency and bone crest involvement, longitudinal studies should be conducted. No temporal relationship between these variables can be determined with respect to our results. Additionally, further studies are needed to develop predictive equations to estimate periodontal performance when 3M is present.

In conclusion, older patients and greater angulations between 3M and adjacent 2M are more likely to develop alveolar bone crest alterations in this region. Additionally, age is associated with greater radiolucency in the distal portion of the lower 3Ms crown. It is suggested that these characteristics should be considered when evaluating a 3M for extraction due to future implications. The proposed null hypothesis was rejected and the association between the presence of a partially burst lower 3M and alterations in local bone structures was confirmed by this study.

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