Orthopantomography is the standard exam used in surgery of included teeth, however, there is a concern to assess the diagnostic capacity that OPG has to determine the relationship of the roots of the lower third molar with the mandibular canal and the types of radiographic signs, because some types of signs such as the apex on an island, which constitutes a "danger signal" of a true relationship between the tooth and the mandibular canal 7. The literature has sought to determine the sensitivity and specificity of OPG to validate the diagnosis.28–30 Gomes (2001)31 verified, when performing a clinical trial, that the sensitivity of OPG was 50% and the specificity was 72.11%, values that are considered low. Sedaghatfar et al25 obtained a sensitivity of 79% and specificity of 86%. In the present study, the value typified from the sensitivity was 100%, the value that may be altered due to the low prevalence. Since the lesion of the lower alveolar nerve resulting from surgery of the lower third molar is a pathology of low prevalence, and the high search a low low, result of 97.6% false positives, that is, a good part of the positive evaluation of the dental relationship with the mandibular canal belongs to the healthy group. Therefore, the positive results are due to the diagnostic failure. On the other hand, the negative predictive value was high (100%) due also to the low pre-valence. In these situations, the negative exams will be almost universally healthy, with few false negatives, that is, in the present study it was 0%, so the radiographic exam for this modality was a success. With regard to the relationship of the lower third molar with the mandibular canal seen in OPG, manifesting as radiographic signs of various types, it is extremely important to remember that these observations and concerns have been in the 1960s, being part of the literature classical radiological. The practical value of radiographic signs is that their presence makes it possible to interpret the existence of an intimate contact between the root and the mandibular canal, information that is otherwise valuable for surgery. The types of radiographic signs seen on orthopantomography are: darkening, narrowing, or deflection of the root, a dark and bifid apex of the root, interruption of the cortical outline of the canal, diversion or narrowing of the canal, and an island-shaped apex.19–21 Although knowing that the knowledge of radiographic sign types comes from remote times and is a topic of concern in classical literature, its interpretation is still not a usual practice, leaving only a few radiologists and surgeons qualified for interpretation, even so, with difficulties related to the limitations of orthopantomography and the classification itself. With regard to the type of radiographic signal related to the appearance of nerve injuries, in the literature consulted, the radiographic signs most commonly related to the appearance of a lesion in the lower alveolar nerve are: darkening of the roots, narrowing of the mandibular canal, deviation of the mandibular canal and interruption of white lines.3,7,16 As in this study, the sample included teeth in stages of rhizogenesis, and the radiographic image can be presented in close relationship with the mandibular-home canal, however, not being in the classification of signs proposed by the literature, a new classification was proposed. This new classification was created with the objective of elucidating for radiologists’ evaluators the situations of radiolucency of the pericoronary hood over the mandibular canal, suggesting an intimate contact. The most frequent type of radiographic signal found in the research was the Darkening of the roots with (40.0%), followed by rhizogenesis (33.9%) and interruption of white lines (14.8%). The other types had frequencies that varied from one to four cases. The majority (84.7%) of the cases had a radiographic relationship with the lower alveolar nerve, highlighting that of the 127 cases with close relationship, 12 did not show a radiographic sign. However, only darkening of the apexes was associated with lesion of the lower alveolar nerve in two cases, and in one case, it was closely related to the mandibular canal, but without radiographic signal.
The interpretation of radiographic signs seems, in fact, to be a difficult task, considering that in the current research, the examiners had many doubts about the type of signal to classify, even in the case of experienced radiologists. Certainly, some signs may suggest others, such as the signal of the reflection of the apexes and the diversion of the canal, however, when one must perceive the anatomy of the roots and the canal and check if the intimate relationship was what changed its development. In cases classified as narrowing of the roots, it is important to observe whether it is really an obscuration or a failure in the nuances of the radiography, and, for this differentiation, there is radiopacity of the rest of the root. This signal can also be confused with the interruption of the white line of the upper cortex of the mandibular canal. Another situation, which is confused with narrowing of the roots and interruption of the white line, is the process of rhizogenesis, which is shown with different nuances due to the cellular activity of dental development. In the type of island-shaped apex, one root presents with greater radiopacity than the other, this fact occurs, as one is through the buccal and the other through the lingual, and in the final portion of the root, they converge around the mandibular canal. In this study, the evaluation of orthopantomography seems to be more effective in evaluating radiographic signs because the surgeon and the radiologist are already calibrated, in other studies developed, in this evaluation.
When the radiographic image shows an intimate relationship between the tooth and the mandibular canal, however it needs to be confirmed, other imaging tests are used, with computed tomography as the best and most accurate method for anatomical identification of the mandibular canal.32–33
Better et al.34 stated, in their study, that the use of computed tomography in the preoperative evaluation of lower third molar surgery should not be routine, being reserved only in cases where proximity to the roots of the third molar with mandibular canal in the orthopantomography are less than 1 mm, further states that the use of tomography influences decision-making, although it does not have surgical outcome effects in relation to morbidity, and its use is justified for medico-legal considerations. For Miller et al35, Kaeppler36, Tyndall and Brooks37, conventional tomography should be the technique of choice for verifying the true relationship between the roots of the third molar and the mandibular canal, because although the sharpness of the computed tomography is incomparably better, its financial cost is 4 to 10 times higher than that of conventional tomography, in addition to the radiation dose. for the study, conventional tomography was used for cases in which close proximity to the mandibular canal was observed as an auxiliary diagnostic measure.
In cases where this assessment is positive, it is necessary to verify the relationship type, since, in the presence of the apex on the island type, the lower alveolar nerve is trapped, and the tooth excision can cause neurotmesis.6,16 Some authors believe that in cases where the lower alveolar nerve is found between the roots of the third molar, the coronectomy technique seems to minimize postoperative surgical morbidity, decreasing the possibility of iatrogenic injury.20
When surgical exposure of the lower alveolar nerve occurs during tooth excision, the relationship is considered to be true, and in these cases, there seems to be a significant contribution to the appearance of nerve injuries and transoperative pain.22,29 In the present study of the three cases of nerve injury only, in one, the lower alveolar nerve was seen transoperatively and in this case there was pain during the surgery. However, even without visualizing the inferior alveolar nerve transoperatively, 12 more cases had pain during the surgery.
The age at which patients undergo surgery for excision of the included lower molar thirds seems to be a risk factor for the appearance of nervous complications. Merril39, in 1979, stated that injury to the lower alveolar nerve is uncommon in patients under the age of eighteen. Gülicher and Gerlach38 state that in patients over 25 years of age, and especially in those older than 35 years, there is a greater propensity for nerve injury with an increase in the prevalence of surgical morbidity in older adult patients. Chiapasco et al40 observed that patients over the age of 24 have a higher risk of postoperative complications, a fact that seems to be related to the complete formation of the third molar roots. Black41 mentions that the lesion of the lower alveolar nerve is significantly related to age, this percentage being higher in patients over 21 years of age. The author correlates this fact to the incomplete formation of the roots of the lower third molar, associated with greater bone elasticity, compared to older age groups, in which hypercementosis of developed roots can occur, with a greater anatomical relationship of the roots as a mandibular canal. One of the advantages of performing germectomy is that it has a lower risk of producing paresthesia of the lower alveolar nerve, since the roots of the third molar are not fully formed and, therefore, the relationship with the lower alveolar nerve is nonexistent or much less evident than in adults.40 Gomes31 corroborates the findings of these authors, stating that when complete rhizogenesis of the third molar occurs, there is a greater probability of close relationship between the roots and the mandibular canal. For Gülicher and Gerlach38 when there is radiographic evidence of complete tooth development, the depth of inclusion and the vertical proximity of this to the mandibular canal are factors that are significantly associated with the appearance of sensory changes in the lower alveolar nerve. For the authors, there is an increase in the prevalence of nerve damage in patients aged 35 years, the increase in is closely related to the increased risk of complications after surgery of the third molars.
In this research, the nerve injury resulting from the surgery of the third molars in the different radiographic stages of Nolla (1960) was evaluated, as there are few studies that highlight the risk of nerve injury, intervening surgically in the lower third molar, in the different stages. of tooth root formation, this is because the literature only compares the lesion after germectomy or after tooth excision with complete or almost complete rhizogenesis. However, it is known that orthopantomography has up to 26% distortion and is not the exam indicated to assess the stages of rhizogenesis, being, on the other hand, the exam indicated to visualize the third molar. Thinking about the evaluation biases regarding the stage of root formation of the third molar involved in the research, the maroscopic evaluation was adopted as the gold standard after tooth excision. The percentage of nerve damage was 2% (3 cases), being classified radiographically according to Nolla's stages: one case in stage 7, one in stage 8 and the other in stage 9. However, it is known that the radiographic evaluation of Nolla used in the research presents stages 6, 7, 8, 9 and 10, and the standard used for macroscopic evaluation only presents four stages, being the crown, 1/3 of the root, 2/3 of the root (8 and Radiographic 9) and closed apex. This meant that, since the scale was not the same, it became impossible to determine the degree of coincidence (Kappa). Due to the high number of null or very low frequencies, the Chi-square test was not valid, Fisher's Exact test was applied due to the number of categories, although the results indicated a significant association, since, depending on the degree in maroscopic evaluation, there is a higher percentage in the radiographic evaluation. However, when starting with the gold standard, that is, the clinical classification, all cases presented in incomplete rhizogenesis with 2/3 of the formed root. Only one case, that of stage 7, was not compatible with the macroscopic evaluation. The fact that the root is from 2/3 formed in relation to the mandibular canal, seems to be a risk factor for the appearance of nerve damage. Thus, it is recommended that, in future studies, the macroscopic evaluation be used as an instrument for measuring the rhizogenesis stages of the included lower third molar, with indication of exeresis, as it has proved to be more reliable.
As for the variables of the type of inclusion, with regard to the spatial relationship and degree of depth, according to the classification of Pell and Gregory and the angular position, according to that of Winter, there seems to be an agreement in the literature that the higher the degree of operative difficulty, that is, deeper inclusions, with more bone involved and more difficult to ostectomy and odontossection, the risk of sensory alterations will be greater.22–38 The three injury cases in our study had a higher degree of surgical difficulty compared to the aforementioned classifications.
An important condition to note is the surgical maneuver performed during the excision of the lower third molar, which radiographically shows a sign of close relationship with the mandibular canal. In the presence of positive signs, the movements of tooth dislocation and traction should be in the extrusive direction and never be in the intrusive sense, as the appearance of paresthesia may be due to the compression of the lower alveolar nerve during exodontic maneuvers. In some cases, there is still no intimate contact relationship, only a thin papyraceous blade separating the tooth from the mandibular canal and this can be broken as an intrusive movement caused during the use of elevators. For Hausamen42 axonotmesis it can occur during a third molar exercise due to traumatic action on the mandibular canal, which causes intense compression on the nerve by a hematoma or by direct action by the root or bone fragment to the product of the tooth dislocation. With the appearance of current studies that return to consecrate old techniques, as is the burial of the root, when coronectomy is suggested, consecrating techniques is believed that, despite the low prevalence of sensory changes. de-current from lower third molar surgeries, this fact can characterize a permanent disorder, that is, of minimum values, such as, for example, 0.06%, one can reach 100% of permanent discomfort. Therefore, knowing the limitations of the study, but certain of the attempt to minimize the bias and the seriousness of the research development, it is believed that the greatest contribution is to make knowledge and the importance of the correct interpretation of the results clear. radiographic signs in surgical planning and medico-legal parameters. It is also suggested to implement the recognition of the relationship between the teeth and the mandibular canal and the types of radiographic signs in the current classic literature for radiologists, as well as the interpretation of the signs in the radiological reports. Knowing, also, the risks of nervous complication in the surgery of the included lower third molars, associated with the process of complete or almost complete rhizogenesis, it is recommended to consecrate the new classification of the types of radiographic signs, which allows to relate the tooth in rhizogenesis that presents a relationship with the mandibular canal. In view of the above, it is believed that in this way it will be possible to draw the attention of dentists and oral and maxillofacial surgeons to assess the possible risks of nerve damage associated with the surgical procedure, preserving the professional-patient relationship when le-san is an inevitable condition.