|Year : 2016 | Volume
| Issue : 3 | Page : 113-121
Root and root canal morphology of third molars in a Jordanian subpopulation
Ibrahim Ali Ahmad1, Manal Mahmoud Azzeh2, Abdalwahab M.A. Zwiri3, Mohd Ashraf Shakib Abu Haija4, Maha Methqal Diab5
1 Department of Dentistry, Al Wakra Hospital, Al Wakra, Qatar
2 Private Dental Clinic, Amman, Jordan
3 Department of Oral Medicine and Periodontics, Faculty of Dentistry, Aljouf University, Aljouf, Saudi Arabia
4 Private Dental Clinic, Ostrava, Czech Republic
5 Private Dental Center, Doha, Qatar
|Date of Web Publication||29-Aug-2016|
Ibrahim Ali Ahmad
Department of Dentistry, Al Wakra Hospital, Hamad Medical Corporation, P.O. Box. 82228, Al Wakra
Source of Support: None, Conflict of Interest: None
Introduction: The aims of this study were to (1) investigate the root and root canal morphology of human third molars in a Jordanian subpopulation and (2) determine the effect of age, gender, and tooth location on the morphology of these teeth. Materials and Methods: A total of 159 maxillary and mandibular third molars were used in this study. After canal staining and tooth clearing, the specimens were examined, and the following morphological features were recorded: Number of roots and presence of roots fusion, number of canals and their configurations in each root, total number of canals per tooth, and incidence of lateral canals and intercanal communications. Results: The majority (74.2%) of maxillary molars had 3 roots and 3 (55.1%) or 4 (27%) canals while the majority (74.3%) of mandibular molars had 2 roots and 2 (38.6%) or 3 (45.7%) canals. Roots fusion was found in 70.1% of maxillary molars and 40.7% of mandibular molars. Type I canal configuration was the predominant type in distal roots of mandibular molars and distobuccal and palatal roots of maxillary molars. Multiple canals were evident in 36% of the maxillary mesiobuccal roots and 56% of mandibular mesial roots. Single/fused roots showed a wide range of canals number and configurations. The number of roots and canals in both molars did not differ with gender, age, and tooth location. Females had a higher incidence of roots fusion than males and this difference was significant in mandibular molars (P = 0.034). Conclusions: Third molars showed a range of root and canal morphologies. Careful preoperative assessment is essential before commencing root canal treatment on these teeth.
Keywords: Clearing technique, Jordanian population, root canal system, third molars
|How to cite this article:|
Ahmad IA, Azzeh MM, Zwiri AM, Abu Haija MS, Diab MM. Root and root canal morphology of third molars in a Jordanian subpopulation. Saudi Endod J 2016;6:113-21
|How to cite this URL:|
Ahmad IA, Azzeh MM, Zwiri AM, Abu Haija MS, Diab MM. Root and root canal morphology of third molars in a Jordanian subpopulation. Saudi Endod J [serial online] 2016 [cited 2019 Sep 19];6:113-21. Available from: http://www.saudiendodj.com/text.asp?2016/6/3/113/189350
| Introduction|| |
Sound knowledge of the internal anatomy of different teeth groups is a cornerstone for successful outcome of root canal treatment., Therefore, the clinicians should be familiar with the common root canal morphology and its possible variations before commencing endodontic treatment. The permanent first and second molars are the most commonly root canal-treated teeth and they have been extensively studied in the dental literature. On the other hand, third molars are nonstandard teeth that have variable and unpredictable morphology.,,,,,, Consequently, endodontically-involved third molars are extracted and rarely considered for root canal treatment.,,
The major objectives of contemporary dental practice are the minimum intervention and retention of every functional tooth in the dental arch including third molars. Indeed, fully erupted and functional third molars may serve as abutments for fixed or removable prosthesis when the first and/or second molars are missing. Furthermore, these molars may be auto-transplanted to replace badly decayed or missed first or second molars.,
During the last two decades, the internal and external morphology of third molars was investigated by a number of clinical , and laboratory ,,,,,,,,,, studies [Table 1]. In addition, several clinical case reports showing successful management of third molars were published.,, Collectively, these studies showed that:
|Table 1: Summary of previous studies that investigated the morphology of permanent third molars|
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- Maxillary third molars may have 1–5 roots and 1–6 root canals
- Mandibular third molars may have 1–4 roots and 1–6 root canals
- Both molars may have a high incidence of roots fusion (RF).
A number of factors contribute to variations in root and root canal morphology including ethnic background, gender, and age of the studied population. The majority of third molars studies were conducted in Europe, America, and East Asia and, therefore, their results may not be applicable to Middle Eastern countries including Jordan. In addition, none of them evaluated the effect of age, gender, and tooth location on the root and root canal anatomy. Therefore, the aims of the present study were to (1) evaluate the external and internal morphology of third molars in a Jordanian subpopulation using canal staining and clearing technique; (2) evaluate the effect of patient's age, gender, and tooth location on the morphology of these teeth.
| Materials and Methods|| |
The study sample included maxillary and mandibular third molars extracted from Jordanian patients and collected from public and private dental practices in Amman, the capital of Jordan. Teeth were included in the study if they had no fractured or surgically separated roots, had complete root formation, and had no previous root canal treatment. After extraction, each tooth was washed with water and kept individually in a labeled container containing 10% formalin solution. For each sample, the patient's age, gender, and tooth location (right or left) were recorded. The collected teeth were rinsed under running tap water for 2 h. Then, they were immersed for 1 h in a 2.6% sodium hypochlorite (NaOCl) to remove any soft tissue adherent to their root surfaces. In some cases, calculus was present and it was removed using hand scalers.
Assessment of root and canal morphology
For each tooth, the number of roots and presence of RF were recorded. Roots fusion was defined as the union of two or more roots over more than half their lengths or union of two roots at their apical thirds. Then, access cavities were prepared and pulp tissue was dissolved by immersing teeth in 2.6% NaOCl overnight. Next, the teeth were rinsed with water, dried and injected with black Indian ink (Sanford rotring GmbH, Hamburg, Germany) using a 27 gauge needle. The diffusion of ink into the teeth was assisted by connecting the root tip to vacuum suction until ink existed through apical foramen. After the ink has dried, the teeth were decalcified using 5% citric acid for 5–7 days. Following decalcifification, the samples were washed under running water for 3 h and dehydrated using successive concentrations of ethyl alcohol (70%, 95% and 99%) for 12 h each. Finally, teeth were cleared by immersion in methyl salicylate for 2 days. The cleared teeth were inspected under magnification and the following anatomical features were recorded:
- Total number of canals per tooth
- Number of canals and their configurations in each root following Vertucci's classfication and its modifications. When two or more roots were fused, they were evaluated as a single root
- Presence of intercanal communications (ICCs) and lateral canals (LCs).
Data were tabulated and analyzed with SPSS (Version 20.0; SPSS Inc., Chicago, IL, USA) software. The relationships between the roots/root canals number and patient's gender and tooth location were assessed using the Student's t-test; the relationship between canals number and age was assessed using Pearson's correlation test, while the relationships between RF and patient's gender and tooth location were assessed using Chi-square test. The statistical level of significance was set at P < 0.05.
| Results|| |
During the study period, a total of 203 third molars were collected. Of these teeth, 159 molars (89 maxillary and 70 mandibular) met the inclusion criteria. The included teeth were extracted from 90 female and 69 male patients with a mean age of 31.1 years (range: 20–52 years).
The majority (74.2%) of maxillary molars had 3 roots and 13.5% were single-rooted. Two- and four-rooted variants were the least common (5.6% and 6.7%, respectively). Of the mandibular molars, 74.3% had 2 roots, 12.9% had 1 root, and 8.7% had 3 roots. C-shaped and four-rooted molars comprised 4.3% of the sample. Roots fusion was reported in 70.1% and 40.7% of maxillary and mandibular molars, respectively [Table 2]. [Figure 1] and [Figure s2] illustrate some of the root morphologies observed in the current study for maxillary and mandibular third molars.
|Table 2: Number of roots and presence of roots fusion in permanent third molars|
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|Figure 1: Samples of root morphologies observed in this study for maxillary molars. (a) Single root; (b) two fused roots with severe curvature; (c) three separate roots; (d) four roots (the mesiobuccal root bifurcated into two roots in the apical third)|
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|Figure 2: Samples of root morphologies observed in this study for mandibular molars. (a) C-shaped root; (b) two roots fused in the apical third; (c) three separate roots; (d) four separate roots|
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The statistical analysis showed that the number of roots in maxillary and mandibular molars did not differ significantly with patient's gender and tooth location. While the incidence of RF was not affected by tooth location, females had a higher incidence of RF than males. This difference was statistically significant in mandibular molars only (P = 0.034).
Root canal morphology
Over than half of the maxillary molars had 3 canals, 27% had 4 canals, 9% had 1 canal, 6.7% had 2 canals, and 2.2% had 5 canals [Table 3]. Of the 34 separate mesiobuccal roots (MBRs), 64% had 1 canal and 32% had 2 canals of which types IV (16%) and VI (12%) were the most prevalent. One root (4%) had 3 canals (type 3-2-1). All separate distobuccal roots (DBRs) and palatal roots (PRs) had type I configuration [Table 4] and [Figure 3].
|Table 3: Total number of root canals per tooth in permanent third molars|
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|Figure 3: Sample of root canal configurations observed in this study. (a) Type I (1-1); (b) Type II (2-1); (c) Type III (1-2-1) with an intercanal communication; (d) Type IV (2-2); (e) Type V (1-2); (f) Type VII (1-2-1-2); (g) Type VIII (3-3); (h) Type 2-3-2-1; (i) Type 1-2-3; (j) Type 1-3; and (k) Type 5-5|
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The majority of the mandibular molars had either 2 (38.6%) or 3 (45.7%) canals and about 10% had either 1 or 4 canals [Table 3]. The majority (56%) of separate mesial roots (MRs) had 2 canals of which types IV and II were the most dominant configurations (26.5% and 20.6%, respectively). Type I configuration was reported in 94.3% of separate distal roots (DRs), 100% of distolingual roots in three-rooted molars, and separate roots in four-rooted molars [Table 5] and [Figure 3]. The number of root canals in both molars did not differ significantly with patient's age, gender, and tooth location.
About 9% of the roots in maxillary molars and 10% in mandibular molars had LCs while ICCs were found in 8.9% and 7.1% of roots in maxillary and mandibular molars, respectively. Lateral canals were most common in the apical third of the roots while ICCs predominated in multi-canalled and fused roots.
| Discussion|| |
Root canal treatment of third molars is challenged by their limited accessibility and variable morphology. Nevertheless, with proper diagnosis and treatment planning, endodontically-involved third molars may be successfully treated and retained as a functional component in the dental arch.
Many techniques have been used to investigate the internal anatomy of the teeth including root sectioning, canal remodeling, canal staining and clearing, review of clinical records, and radiographic techniques such as conventional radiographs, microcomputed tomography, and cone-beam computed tomography (CBCT)., The tooth staining and clearing technique was used in the current study because it allows three dimensional evaluation of the root canal system and maintains the original shape of the root canals and their relationship to the external tooth surface., The vacuum-assisted ink injection allowed diffusion of ink throughout the root canal system including canal complexities such as LCs and ICCs.
The number of roots in both molars ranged from 1 to 4, and the majority of mandibular (74.3%) and maxillary (74.2%) molars had 2 and 3 roots, respectively. This finding is consistent with previous studies of maxillary ,,,,, and mandibular ,,,,, molars. In contrast, some studies found that the single-rooted variant was the predominant type in maxillary  and mandibular , molars. This variation in roots number may be caused by differences in sample sizes and study methods or may reflect true differences among the investigated populations. Statistical analysis revealed that the number of roots did not differ significantly with patient's gender and tooth location. This finding is agreement with the results of Park et al. 2013 who investigated root morphology of mandibular third molars in a Korean subpopulation.
In the current study, about 70% of maxillary molars and 40% of mandibular molars had RF. These figures are generally higher than the corresponding figures in previous studies ,,, but lower than the findings of Ross and Evanchik. This difference may be attributed to the different criteria used to define RF. In the present study, roots with fusion occurring over than half of their lengths or two roots joining in the apical third were classified as fused roots while Ross and Evanchik considered single-rooted teeth and roots fused over less than one-third of their lengths as having RF. The statistical analysis showed that while the incidence of RF was unaffected by tooth location, teeth extracted from females had a higher incidence of RF than those extracted from males. This finding is consistent with the findings of Ross and Evanchik.
Root canal morphology
Most of the maxillary molars had 3 (55.1%) or 4 (27%) canals while the majority of mandibular molars had 2 (38.6%) or 3 (45.7%) canals. The patient's age, gender, and tooth position had no effect on a number of root canals. Several studies evaluated whether these parameters affected the number of canals in permanent first and second molars.,,, The results showed that while the number of canals was not affected by gender and tooth location, young patients (particularly those 20–40 years old) had a higher incidence of additional canals than older patients. The majority (88.1%) of teeth in our sample were extracted from patients younger than 40 years (mean age 31.1 years), and this may account for the insignificant effect of age on the number of root canals.
The individual roots exhibited a variety of root canal configurations depending on the root type and presence of RF. Type I configuration was the predominant type in DBRs and PRs of maxillary molars and DRs of mandibular molars. These findings are consistent with previous studies of maxillary ,,,,, and mandibular ,, third molars. On the other hand, 32% of maxillary MBRs and 56% mandibular MRs had 2 canals. These results are comparable to the findings of other investigators ,,,, who used a similar clearing technique. In contrast, a lower incidence of 2 canals was reported in studies that used a conventional radiographic technique  or evaluated the clinical records of root canal-treated teeth. Fused and, to a lesser extent, single roots demonstrated a range of root canals number and configurations [Table 4] and [Table 5], a finding that supports the results of other studies.,,
A number of previous studies compared the morphology of maxillary and mandibular third molars with their corresponding first and second molars.,,,, Collectively, these studies showed that the majority of maxillary first and second molars had 3 separate roots and 3 or 4 root canals while the majority of mandibular first and second molars had 2 separate roots and 2 or 3 root canals. On the other hand, the maxillary and mandibular third molars demonstrated a wide range of roots and root canals number (1–4 and 1–5, respectively). In addition, they had a high incidence of RF (46.3–69% in maxillary molars and 21.6–46.6% in mandibular molars). A search of the literature identified two studies that evaluated the morphology of permanent molars in the Jordanian population., Although these studies used a similar evaluation technique to the current study (i.e, canal staining and tooth clearing), they did not include third molars in their samples. Therefore, we compared the results of these studies with our findings to show the morphological similarities and differences between the third molars and other molars. Khraisat and Smadi  evaluated 97 three-rooted maxillary first molars and found RF in 3.1% of the sample. In addition, the majority of MBRs (77.3%) had 2 canals with types II (27.8%) and IV (35.1%) being the most common confifigurations. In contrast, 69.7% of the 3-rooted maxillary third molars in the present study had RF, and the majority of separate MBRs had type I (55%) canal configuration followed by types IV (20%) and VI (15%). In another study, Al-Qudah and Awawdeh  reported that the majority of mandibular first (96.1%) and second (87.4%) molars had 2 roots. Roots fusion was reported in 0.9% and 6.1% of first and second molars, respectively. The majority of first molars demonstrated 3 (48.2%) or 4 (45.8%) canals while most of second molars had 2 (18.9%) or 3 (58.3%) canals. Although the majority (74.3%) of mandibular third molars in the current study had 2 roots, a wide range of roots number (1–4) and a high incidence of RF (40%) were also observed in these teeth. The number of canals ranged from 1 to 4 and the majority of the teeth had either 2 (38.6%) or 3 (45.7%) canals. Careful clinical and radiographic assessment of individual third molars is essential before commencing root canal treatment to ensure a successful treatment outcome.
There are several limitations of in vitro morphological studies. First, they include only sound teeth and exclude those with fractured or separated root(s) leading to selection bias in the study sample. Second, the majority of these studies classify extracted teeth into different teeth groups (i.e., first, second, or third molars) based on their external morphological features which may lead to identification errors. Third, the majority of these studies do not provide information about the ethnicity, age, and gender of the study sample. In the current study, teeth were collected prospectively with specific instructions to save only those from Jordanian patients. Each extracted tooth was stored individually, and its related data (gender, age, and location) were recorded immediately after extraction. Nevertheless, the final number of included molars was relatively low as some of the collected teeth were excluded due to the presence of fractured or separated roots. Further studies using a larger sample of third molars are warranted to confirm the findings of the present study. In this regard, the use of CBCT technique is recommended because it allows three-dimensional evaluation of teeth morphology and enables simultaneous comparison of their anatomy with adjacent and contralateral counterparts.
| Conclusions|| |
The third molars of the investigated Jordanian subpopulation showed a range of root and root canal morphologies. The number of roots and root canals was not affected by patient's gender, age, or tooth location. Females had a higher incidence of RF compared to males, and the difference was significant in mandibular molars. Careful assessment of individual third molars is essential before commencing root canal treatment to ensure a favorable treatment outcome.
The authors would like to thank all colleagues who participated in collecting the teeth used in this study. The authors would like also to acknowledge the contribution of Dr. Ashwin Shetty who assisted with the statistical analysis.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]