|Year : 2021 | Volume
| Issue : 3 | Page : 63-70
Prevalence of distal caries in the second mandibular molar among the general population in Mexico and its relationship with the position and angulation of the adjacent third molar
Elan Ignacio Flores-Orozco1, Diaz-Pena Rogelio1, Victor Melesio Barron-Crespo1, Bernat Rovira-Lastra2, Jordi Martinez-Gomis2
1 Departments of Prosthodontics and Orthodontics, Faculty of Dentistry, Autonomous University of Nayarit, Mexico
2 School of Dentistry, Faculty of Medicine and Health Sciences, University of Barcelona; Oral Health and Masticatory System Group (Bellvitge Biomedical Research Institute) IDIBELL, L'Hospitalet de Llobregat, Barcelona, Catalonia, Spain
|Date of Submission||30-Nov-2021|
|Date of Decision||30-Nov-2021|
|Date of Acceptance||11-Dec-2021|
|Date of Web Publication||13-Jan-2022|
Elan Ignacio Flores-Orozco
Department of Prosthodontics, Faculty of Dentistry, Autonomous University of Nayarit, Edificio de la Unidad Académica de Odontología, Ciudad de la Cultura Amado Nervo, Tepic, C.P. 63155, Nayarit
Source of Support: None, Conflict of Interest: None
Aims: This study aimed to estimate the prevalence of distal caries in the mandibular second molar (M2M) in a general population and to determine the strength of the association of several factors related to the adjacent mandibular third molar (M3M). Subjects and Methods: This retrospective cross-sectional study assessed digital panoramic radiographs of 753 individuals prescribed for screening and/or diagnostic purposes by different specialists. From these radiographs, 1358 M2Ms/M3Ms were included in the analysis. Age, sex, position, and inclination of the M3Ms with respect to the M2Ms and presence of distal caries in the M2Ms were assessed. Continuous variables were dichotomized using optimal cutoff values using receiver operating characteristic curve analysis. Statistical Analysis Used: A multivariate logistic regression model was performed. Results: In total, 8.2% (95% confidence interval 6.7 to 9.6%) of the M2Ms had distal caries. Multivariate logistic regression analysis showed that >22.5 years of age (odds ratio [OR] 3.42), >4.2 mm between the M2M and M3M (OR 2.67), >31.6° inclination of the M3M (OR 2.12) and the right side (OR 1.61) were positively associated with M2M distal caries. Conclusions: The prevalence of M2M distal caries can range from 6.7% to 9.6% in the general population. M3Ms separated more than 4.2 mm and mesioangulated more than 31.6° with respect to their adjacent M2Ms were 2.7- and 2.1-fold more likely to develop distal caries in their adjacent M2Ms.
Keywords: Dental caries, impacted tooth; panoramic radiograph, wisdom tooth
|How to cite this article:|
Flores-Orozco EI, Rogelio DP, Barron-Crespo VM, Rovira-Lastra B, Martinez-Gomis J. Prevalence of distal caries in the second mandibular molar among the general population in Mexico and its relationship with the position and angulation of the adjacent third molar. J Oral Maxillofac Radiol 2021;9:63-70
|How to cite this URL:|
Flores-Orozco EI, Rogelio DP, Barron-Crespo VM, Rovira-Lastra B, Martinez-Gomis J. Prevalence of distal caries in the second mandibular molar among the general population in Mexico and its relationship with the position and angulation of the adjacent third molar. J Oral Maxillofac Radiol [serial online] 2021 [cited 2022 Sep 30];9:63-70. Available from: https://www.joomr.org/text.asp?2021/9/3/63/335735
| Introduction|| |
Dental caries is a multifactorial disease, and untreated caries in permanent teeth affect more than 2 billion people. Among the different types of dental caries, proximal enamel lesions are highly prevalent in both adult and teenage populations. Biological and nonbiological factors, such as age, genetics, lifestyle, behavior, diet, and socioeconomic status, are related to caries. Furthermore, recent systematic reviews have concluded that local factors such malocclusion or impacted third molars might be associated with the incidence or prevalence of dental caries, although the quality of evidence supporting these associations is not high.,,
Third molars usually erupt between the ages of 18 and 24 years, but this eruption may be blocked by either soft tissue or bone, and impactions are more frequent in the mandible than in the maxilla. The degree of eruption of the mandibular third molar (M3M) and its position and inclination in reference to its adjacent mandibular second molar (M2M) are risk factors for the presence of distal caries in the M2M.,,, However, a great diversity in the range of distances or angulations has been reported to be associated with distal caries in the adjacent M2M. For example, ranges of angulations between M3Ms and their adjacent M2Ms, which were found to be significantly associated with M2M distal caries, were found to be more than 11°,, more than 20°, 30–75°, 31–90°, 30–108°, 40°–80°,, 43°–73°, and more than 90°. On the other hand, the ranges of distance between the cementoenamel junction (CEJ) in the distal part of the M2M and the CEJ in the mesial part of the M3M associated with distal caries in the M2M were found to be 3–10 mm, 6–8 mm, 7–9 mm, and 7–12 mm. The criteria for establishing cut points or ranges in these quantitative variables have not been described in most studies,,,, which makes it difficult to compare these studies to obtain evidence that can be applied in clinical situations.
Dichotomizing a quantitative variable using a cutoff point helps to better interpret this variable as a risk factor for a condition or disease. This cutoff point can be designated a priori and based on the knowledge that distinct groups of individuals exist, which facilitates the comparison between studies. Another approach is to establish the cutoff point a posteriori at the sample median to obtain a high and a low group with similar sample sizes. Alternatively, this cutoff point can be established according to the sensitivity and specificity of correctly identifying a person with a disease or condition. A receiver operating characteristic (ROC) curve is a mapping of this sensitivity by 1 minus the specificity across a spectrum of possible cut-points not only for assessing diagnostic tests but also for constructing a predictive model with a binary outcome. The area under the ROC curve can be interpreted as the probability of correct classification or prediction. Using a ROC curve analysis to establish the cut point on the variables of angulations or distances of the M3M could help to better interpret their association with distal caries in the M2M.
Another important aspect in this field is to know the strength of the association, expressed as the odds ratio, between each risk factor and the prevalence of distal caries in the M2M. Odds ratio values range from 1.8 to 2.5 for age,, 2.9 to 9.4 for M3M mesioangulation,, and from 2.9 to 19.6 for CEJ distance.,, These differences may be due not only to the characteristics of the population studied but also to the cut point established for the quantitative variables. Furthermore, the interrelationship between some of these factors means that the prevalence of distal caries in the M2M should be studied using multivariate techniques to obtain the adjusted odds ratio. This knowledge would help both clinicians when counseling patients whether to retain or remove the M3M in order to prevent M2M distal caries.
The prevalence of distal caries in M2Ms associated with the presence of their adjacent M3M ranges from 4% to 52%.,,,,,,,,, This great variation is mainly explained by the different populations studied, with low values from the general population and higher values from people who are indicated for their M3M to be removed. To determine the true prevalence of distal caries in the M2M and the strength of the association of risk factors, participants from the general population should be considered. This study aimed to estimate the prevalence of distal dental caries in M2Ms in a general population and to determine the strength of the association between several factors related to the adjacent M3M and the prevalence of distal caries in the M2M in this population.
| Subjects and Methods|| |
This retrospective cross-sectional study assessed the radiographic records of patients who attended the Radiology Department of the Dental School of the Autonomous University of Nayarit, Tepic, Mexico, from January 2017 to December 2017. The main indication for the panoramic radiograph was for screening and for diagnostic purposes indicated by different specialists, including orthodontists, prosthodontists, endodontists, and oral surgeons. Inclusion criteria included individuals aged 17 to 65 years with at least one M3M and the presence of an M2M on the same side. Buccolingualized M3M molars were not taken into account. The protocol was approved by the Ethics Committee of the Faculty of Dentistry, Autonomous University of Nayarit, and all experiments were conducted in accordance with the principles of the Helsinki Declaration.
Digital panoramic radiographs were taken with the Vatech unit device (Gyeonggi-do, Korea) PaX-i3D model PHT-6500; to make the images, it was necessary that the subject's head be stabilized using a cephalostat orienting the Frankfort plane parallel to the floor. All linear and angular measurements were performed by a single examiner using tools available in the software program MicroDicom (MicroDicom, Sofia, Bulgaria). Prior to measurements, calibration of the width of 50 M3Ms was performed by comparing the values obtained in cast models using a caliper with respect to the values obtained using MicroDicom software. The mean correction factor was 0.22 and was applied in all digital linear measurements.
Age and sex were obtained by reviewing dental records, and the number of teeth was determined using panoramic radiographs. The distal space in relation to the ramus and the impaction depth with respect to the occlusal plane of the M3M were determined using the Pell and Gregory classification as described in [Figure 1]. The eruption status was assessed and considered nonimpacted if the M3M was classified as IA and impacted if it was classified as other than IA. The inclination of the M3M in relation to the M2M was measured as the angle formed by their longitudinal axes and classified according to Winter's classification as vertical 10° to −10°; mesioangular at 11° to 79°; distoangular at −11° to −79°; and horizontal at 80° to 100°. Inclination of the occlusal surface of the M3M in relation to the occlusal surface of the second molar was also measured and classified according to the Shiller method as mesioangular at 11° to 69°; vertical at 0° to −10°; distoangular at −11° to −69°; and horizontal at ≥70°. The distance between the distal part of the CEJ of the M2M and the mesial part of the CEJ of the M3M was measured and classified according to the method described by Leone et al. To determine the retromolar space, the distance between the anterior border of the mandibular ramus and the most distal point of the second molar was measured. The width of the crown of the third molar was obtained by measuring the mesiodistal length of the line drawn in the widest area of the crown of the M3M. Distal caries in the M2M were assessed as the presence of distal radiolucency in the enamel and/or dentine and an absence of contact between the M2M and M3M at that level.
|Figure 1: (a) Pell and Gregory classification for impaction depth of the M3M. (b) Pell and Gregory classification with respect to the distal space|
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The sample size was determined based on the primary aim considering a type I error of 0.05, a precision of ±2%, an estimated prevalence of distal caries in the 2M of 15%, and an expectation that approximately half of the molars would not be included. Therefore, 2444 M2Ms had to be included, corresponding to 1222 panoramic radiographs. To evaluate the reproducibility of the main parameters used in this study, a test-retest assessment was performed in 30 M2Ms/M3Ms of 15 panoramic radiographs. Test-retest reliability for quantitative parameters was examined using the intraclass correlation coefficient calculated according to the two-way random effects and absolute agreement for single measures, and the values ranged from 0.94 for crown width to 0.99 for winter mesioangulation [Supplementary Digital Content, [Table 1]]. Test-retest reliability for categorical parameters was determined using Cohen's kappa statistics and ranged from 0.71 for lack of space according to the Pell and Gregory classification to 1 for impaction depth according to the Pell and Gregory classification [Supplementary Digital Content, [Table 1]].
|Table 1: Test-retest reliability of parameters related to distal caries in the M2M and characteristics of the mandibular third molar|
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To simplify the data analysis, categories B and C of “Impaction depth” (Pell&Gregory) were grouped and named “Impacted in depth,” and categories II and III of “Impaction in mandibular ramus” (Pell&Gregory) were grouped and named “Impacted in ramus.” Since most quantitative parameters were not distributed normally (Shapiro–Wilk's test), descriptive data are presented as the median and interquartile range (IQR). Side differences regarding the impaction of M3Ms and the presence of distal caries in M2Ms were analyzed by McNemar's test. To test the predictive performance of continuous variables for caries in the 2M, the sensitivity, specificity, and the area under the curve (AUC) were calculated from the ROC curve. When the ROC AUC was ≥0.6, the continuous variables were dichotomized using the optimal cutoff point (cutoff points) according to the closest-to-(0,1) criterion. The bivariate relationships between the presence of distal caries in the M2M and the different variables were examined with the Pearson Chi-square test. Multiple logistic regression was used to explore the relative importance of the risk factors for the presence of distal caries in the M2M as the outcome variables (forward selection strategy by using the likelihood ratio statistic). Potential risk factors were selected either because they showed a significant relationship in the bivariate analysis or because they had been reported as significant in other studies. Statistical analysis was performed using the SPSS program (IBM SPSS Statistics, version 27, Chicago, IL) and P < .05 was considered statistically significant.
| Results|| |
Among the 1236 panoramic X-rays revised, 483 did not satisfy the inclusion criteria and were excluded. These included 168 panoramic radiographs of individuals younger than 17 years, 73 of individuals older than 65, and 242 of individuals who did not have an M3M with the presence of the M2M on any of the two sides. Therefore, the final sample consisted of 753 individuals, 266 men (35%) and 487 women (65%), with a median age of 24 years (IQR 21 to 32) ranging from 17 to 65 years and a median of 30 teeth (IQR 28 to 32).
Among the 753 individuals, 605 showed M2Ms and M3Ms on both sides according to the inclusion criteria, but 72 3Ms from the right side and 76 3Ms from the left side were not considered because they were absent, buccolingualized, or with missing adjacent second molars. Thus, 1358 molars were included in the final analysis. The M3M had a median width crown of 10.3 (IQR 9.8 to 10.9) and a retromolar space of 9.1 mm (IQR 7.4 to 11.1). The 605 participants who had bilateral M2Ms/M3Ms showed more impacted M3Ms on the right side than on the left side (P = 0.040; McNemar's test). Data regarding the position and angulation of the M3M and the presence of distal dental caries in the M2M are shown in Supplementary Digital Content, [Table 2]. Regardless of the side, 8.1% (95% CI 6.7 to 9.6%) of the M2Ms had caries in their distal surface. Among the 605 participants who had bilateral M2Ms/M3Ms, 15 had caries in the M3Ms on both sides; 25, only on the left side; 45, only on the right side; and 520, no caries on any side (P = 0.022; McNemar's testAmong the six quantitative variables that could be explored as risk factors for distal caries in the M2M, 4 were converted into dichotomic variables using the cut points obtained in the area under the ROC curve (AUROC curve) analysis [[Figure 2]; Supplementary Digital Content, [Table 3]]. The bivariate relationships between the characteristics of the M3M and the presence of distal caries in the M2M are shown in Supplementary Digital Content, [Table 4]. Univariate logistic regression analysis revealed that mesioangulation higher than 31.7° (Winter), mesioangulation higher than 25.8° (Shiller), CEJ distance higher than 4.2 mm, age older than 22.5 years, impaction, location on the right side, and distal impaction with respect to the mandibular ramus (Class II or III, Pell and Gregory) were positively related to the presence of distal caries in the M2M. Multivariate logistic regression analysis showed that age (older than 22.5 years), CEJ distance (higher than 4.2 mm), presence of mesioangular inclination of the M3M (higher than 31.7°), and location on the right side were the parameters positively associated with the presence of distal caries in the M2M [Supplementary Digital Content, [Table 4]]. Adjusted by age and side, the strength of the association expressed as an odds ratio was 2.12 for mesioangular inclination of the M3M higher than 31.7° and 2.67 for CEJ distance higher than 4.2 mm (Nagelkerke R2 coefficient = 0.14).
|Table 2: Position and angulation of third molars and presence of distal dental caries in the 2nd molar|
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|Table 3: Bivariate relationship of quantitative variables with dental caries in the 2M (area under the receiver operating characteristic curve analysis)|
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|Figure 2: Receiver operating characteristic curves for each quantitative variable|
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|Table 4: Bivariate and multivariate logistic regression models of demographic and mandibular third molar-related variables as risk factors for the presence of distal caries in the mandibular second molar|
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| Discussion|| |
The results of this study suggest that the prevalence of distal caries in the M2M related to the presence of the M3M ranges from 6.7% to 9.7% in adults from a general population in Mexico. Among the risk factors studied, people older than 22.5 years with an M3M separated by more than 4.2 mm and mesioangulated by more than 31.7° with respect to the adjacent M2M were more likely to present distal caries in the M2M. People with an M3M separated more than 4.2 mm and mesioangulated more than 31.7° with respect to the adjacent M2M were 2.7- and 2.1-fold more likely to develop distal caries in their adjacent M2M, respectively, adjusted by age and side.
In the present study, the prevalence of distal caries in the M2M was similar to that observed in British military personnel, at 4.2%, although it reached 7% when the M2M was associated with a partially erupted M3M. In contrast, a higher prevalence of distal caries in the M2M (between 10 and 52%) was reported in those studies that recruited participants referred for assessment or extraction of the M3M.,,,,,,, To determine the actual prevalence of distal caries in the M2M related to the presence of an M3M, all people should be considered whether with or without symptomatology. Another aspect that could affect the true prevalence of distal caries in the M2M is the age of the population. Age was positively associated with distal caries of the M2M related to the presence of an adjacent M3M, in agreement with other studies.,,,, The cut point found using the ROC curve was 25 years of age, similar to the cut point value used in other studies.,,, It is known that the formation of caries needs time to progress, and with adequate monitoring, such caries could be detected in the initial phase. Otherwise, it has been suggested that if the M3M had to be extracted, the best timing to perform this procedure is before 23 years of age to minimize the risk not only of distal caries but also of other diseases in the second molar.
Mesioangulation of the third molar has been reported to be associated with distal caries in the adjacent M2M in several studies conducted in different countries.,,,,,,,, Furthermore, the results of the present study establishing 30° as a cut point agree with similar cut points used in other studies.,, This is perhaps the first study using an ROC curve analysis to establish the cut point for the mesioangulation of the M3M and could help dental clinicians advise patients about different treatment options. Although the distance between the M2M and the M3M was positively associated with mesioangulation of the M3M in the present study and other studies, this distance was still significantly associated with the presence of dental caries in the 2nd molar after adjusting for mesioangulation of the M3M in multiple logistic regression analysis. Therefore, both intermolar distance and mesioangulation of the 3M may contribute to retaining more dental plaque and consequently be more likely to promote the formation of caries.
Interestingly, a higher prevalence of distal caries was observed on the right side than on the left side. Although there were also more impacted M3Ms on the right side than on the left side, the side of the dental caries was still significant in the multivariate model after adjusting for “impacted” M3M. It has been reported that right-handers brush the teeth of their left side better and left-handers brush their right teeth better, and it is known that the majority of the population consists of right-handers., Unfortunately, the proportion of right-handed and left-handed people who presented distal caries on one side in the present study is unknown. In addition, biological variability and sample selection error could also have contributed to these side differences. Further well-controlled studies are warranted to clarify this relationship.
Whether asymptomatic impacted third molars need to be removed remains a dilemma among dental clinicians. The present results suggest that only up to 14% of the risk for distal caries in the M2M can be explained by angulation and position of the M3M, and therefore, most causality should be attributed to individual factors, both those related to genetics and those related to lifestyle. Moreover, distal caries in the M2M seem to be treatable in most cases,,, and long-term clinical and radiographic checks are recommended. Measures such as sugar reduction, regular oral hygiene, fluoride exposure, salivary enhancement, and the use of pre- and probiotics remain essential to prevent dental caries and promote oral health., Using floss or interdental brushes in addition to toothbrushing may reduce gingivitis or plaque, or both, more than toothbrushing alone. On the other hand, third molar removal can result in various types of morbidity, such as pain, swelling, bleeding, infection, dry socket, trismus, paresthesia, and temporomandibular disorders. When dental clinicians inform and advise patients on deciding whether to remove M3Ms, it should be noted that the general risk of developing distal caries in their adjacent M2Ms is approximately 8%, and this risk increases at least two-fold in cases where the M3M is separated more than 4 mm and mesioangulated more than 30° with respect to the adjacent M2M. This issue may be discussed along with other potential benefits (e.g., reducing the risk of other pathologies associated with an impacted M3M) and costs (e.g., financial burden, risks, and complications).
This study has several limitations. First, because of its cross-sectional design, a direct causal relationship cannot be attributed between the factors and distal caries. Moreover, the incidence of distal caries can be better assessed in cohort studies with a follow-up period of several years. Therefore, further longitudinal observational studies are required to better understand the incidence and the factors that increase the risk of distal caries in the M2M. Another weakness of the present study was that panoramic radiography is not the gold standard for detecting interproximal caries because only gross caries lesions can be reliably detected. On the other hand, the strength of the present study is the use of ROC curves, which enables identification of the best cut point in the angulation and the distance of the M3M with respect to the M2M as a risk factor for distal caries in M2M.
| Conclusions|| |
The prevalence of distal caries in the M2M might be estimated as 6.7%–9.6% in the general population. Regardless of age and side, people with an M3M separated by more than 4.2 mm and mesioangulated by more than 31.6° with respect to the adjacent M2M were 2.7- and 2.1-fold more likely to develop distal caries in their adjacent M2M.
The authors sincerely thank Hugo Francisco Martínez García for taking the panoramic radiograph.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]