Comparing the pulp/tooth area ratio and dentin thickness of mandibular first molars in different age groups: A cone-beam computed tomography study.

CONTEXT: Mandibular first molar frequently requires endodontic treatment. Understanding age-related changes in pulp-dentin complex and root canal morphologies is essential for successful endodontic and restorative treatments. AIM: This study aimed to compare pulp/tooth area ratio (PTAR) and dentin thickness (DT) in mandibular first molars in different age groups through cone-beam computed tomography (CBCT) imaging. SUBJECTS AND METHODS: One hundred CBCT images of mandibular first molar were divided into five groups; age 20-29, 30-39, 40-49, 50-59, and 60 years old and older. Axial images were used to determine PTAR at Level A (furcation), Level B (between Levels A and C), and Level C (half distance between the furcation and apex of the root). The minimum DT of the distal wall of mesiobuccal (MB) and mesiolingual (MLi) canal and mesial wall of distal canal at 2 and 3 mm under the furcation was measured. STATISTICAL ANALYSIS USED: Analysis of variance was used to determine differences among age groups.
RESULTS: PTAR was determined to reduce as age increases, showing a significant difference among the age groups at Levels A, B, and C of both roots (P < 0.05). The minimum DT was found to increase with age, demonstrating a significant difference among the age groups of MB and MLi canal at 2 and 3 mm (P < 0.05). No statistically significant difference was observed in the mesial DT of distal canal.
CONCLUSIONS: The reduction of PTAR and the increasing DT were confirmed with advanced age. Copyright:

INTRODUCTION

Mandibular first molar has an important role in chewing and maintains the vertical dimension of the face. It is prone to dental caries because of having deep pit and fissures, in addition to poor oral hygiene during childhood.[1] With advanced age, the risk of dental caries and periodontal disease has been found to increase. Mandibular first molar frequently requires endodontic treatment in order to retain its function and prevent tooth extraction. Thus, understanding age-related changes in pulp-dentin complex and root canal morphologies is essential for successful endodontic and restorative treatments.[23]

Obliterated canal is clinically challenging in terms of locating and negotiating the root canal.[4] The obliterated canal, which is often attributed to advanced age, is a degenerative change of pulp-dentin complex caused by secondary dentin deposition, which is formed throughout life after completed root formation.[35] The relationship between secondary dentin deposition and age was examined and used for age estimation using dental radiographs. Several researchers have found that the pulp/tooth area ratio (PTAR) decreased with aging; however, the majority of the previous studies used single-rooted teeth.[678]

Strip perforation is another complication that can lead to the failure of endodontic treatment.[9] This is often caused by overinstrumentation at the furcation area, known as a danger zone.[10] In mandibular first molar, the distal wall of mesial root has limited dentin thickness (DT), around 2–4 mm under the furcation.[11121314] Data remain lacking in terms of the correlation of DT and aging.

Cone-beam computed tomography (CBCT), which has the ability to create accurate three-dimensional images, could be a powerful tool in endodontic treatment. CBCT provides accurate information of internal root canal anatomy.[15] Moreover, CBCT imaging can overcome problems related to the superimposition of image from crowding of the teeth, providing axial images traditional radiographs cannot.[816] Thus, this study aimed to compare PTAR and DT in mandibular first molars in different age groups using CBCT imaging.

SUBJECTS AND METHODS

Subjects

This study was approved by the Human Experimentation Committee of the Faculty of Dentistry, Chiang Mai University, Thailand (Clearance#26/2019). One hundred CBCT images were retrospectively collected from patients, aged 20–85 years old (mean = 44.72 ± 15.692), which were taken for the purpose of routine therapeutic and clinical evaluation from 2012 to 2019. All images were obtained using DentiScan (NSTDA, Bangkok, Thailand), which had good quality for diagnosis. The images were categorized into five groups (n = 20); age 20–29, 30–39, 40–49, 50–59, and 60 years old and older.

The inclusion criteria were right/left fully erupted mandibular first molar with complete root formation. The outline of the roots and pulp must be clearly seen with no radiopaque restorative or endodontic filling. Meanwhile, the exclusion criteria were as follows: those with large dental caries or restorative filling, excessive tooth wear, presence of periapical lesion or other odontogenic or nonodontogenic pathology, presence of root canal filling or post or crown restoration, and presence of two root canals of distal root.

Axial cone-beam computed tomography image acquisition

CS 3D imaging software (Version 3.7.1, Carestream Dental, Rochester, New York, USA) was used. The axial images were obtained at three levels of each root; Level A (furcation), Level B (between Levels A and C), and Level C (half distance between the furcation and apex of the root) to measure the PTAR and at 2 and 3 mm under furcation to measure DT. Then, the axial images were exported to ImageJ software (Version 1.50i, National Institutes of Health, Bethesda, Maryland, USA). The contrast and brightness of the images were adjusted to achieve optimal visualization.

Methods

Pulp and tooth area analysis

According to the axial images at Levels A, B, and C, twenty points of tooth outline and ten points of pulp outline were created[7] using polygon selection. The areas of pulp and tooth were measured thrice, and the mean values were recorded. The PTAR of each level was calculated for each sample.

Dentin thickness analysis

According to the axial images at 2 and 3 mm under furcation, the DT of distal wall of mesiobuccal (MB) and mesiolingual (MLi) canals and mesial wall of distal canal was measured by calculating the minimum distance from the edge of the root canal to the external surface of its root.[11] The values were measured thrice, and the mean values were recorded.

Before measurement, the calibration was performed by an examiner and an experienced oral radiologist. To test the intraexaminer reproducibility, ten samples were re-examined after an interval of 2 weeks using intra-class correlation coefficient (ICC). ICC for intraobserver agreement of PTAR was 0.816 and for DT was 0.909.

Statistical analysis

Statistical Package for the Social Sciences, version 23 (IBM Company, Chicago, IL, USA), was used for data analysis. One-way analysis of variance was used to determine significant difference among age groups and least significant difference test was performed to determine which pair was different. The significant level was set at P < 0.05.

RESULTS

Pulp/tooth area ratio

The PTAR reduced as one's age increased. The morphological changes of PTAR are shown in Figure 1. The means of PTAR of each group is shown in Table 1. Significant differences were found among age groups in each level (P < 0.05).

Figure 1

Morphological changes of pulp/tooth area ratio (Levels A, B, and C) in mesial (left) and distal (right) roots of mandibular first molars

Table 1

Mean and standard deviation of the pulp/tooth area ratio by age groups

Level	Age groups (years)					P
	20-29	30-39	40-49	50-59	60 and older
Mesial root
A	0.078±0.019X	0.085±0.034X	0.075±0.027X	0.054±0.021Y	0.052±0.021Y	0.000*
B	0.076±0.022X	0.077±0.027X	0.074±0.035X	0.048±0.024Y	0.052±0.025Y	0.001*
C	0.078±0.036X	0.067±0.029X, Z	0.073±0.042X, W	0.056±0.027Y, Z, W	0.048±0.035Y, Z	0.035*
Distal root
A	0.091±0.032X	0.091±0.030X	0.091±0.027X	0.067±0.021Y	0.061±0.030Y	0.001*
B	0.093±0.034X	0.096±0.037X	0.093±0.037X	0.062±0.029Y	0.056±0.024Y	0.000*
C	0.080±0.031X, Y	0.085±0.033X	0.092±0.038X	0.064±0.026Y	0.043±0.023Z	0.000*

*Significant difference at P<0.05. If all the letters are distinct, a significant difference between the corresponding tracks is shown using Fisher’s LSD. LSD: Least significant difference

Dentine thickness

The DT has been found to increase with age. The morphological changes of DT are shown in Figure 2. The average of DT of each group is shown in Table 2. Significant differences were found in distal DT of MB and MLi canal at 2 and 3 mm (P < 0.05) among age groups. No statistical difference was found in mesial DT of distal canal among age groups.

Figure 2

Morphological changes of dentin thickness at 2 mm (left) and 3 mm (right) below furcation of mandibular first molars

Table 2

Mean and standard deviation of distal dentin thickness in mesial root and mesial dentin thickness in distal root by age groups

Canal	Age groups (years)					Total group	Minimum	Maximum	P
	20-29	30-39	40-49	50-59	60 and older
2 mm below furcation
MB	0.728±0.150X	0.698±0.152X	0.876±0.150Y	0.851±0.189Y	0.838±0.175Y	0.789	0.461	1.335	0.002*
MLi	0.741±0.138X	0.734±0.155X	0.876±0.128Y	0.869±0.193Y	0.883±0.153Y	0.821	0.480	1.300	0.001*
Distal	0.973±0.240	0.860±0.194	0.986±0.155	0.962±0.276	0.980±0.187	0.952	0.493	1.612	0.323
3 mm below furcation
MB	0.718±0.152X	0.700±0.187X	0.839±0.139Y	0.840±0.213Y	0.869±0.215Y	0.793	0.408	1.337	0.009*
MLi	0.714±0.173X	0.695±0.131X	0.791±0.146X, Y	0.787±0.186X, Y	0.840±0.203Y	0.765	0.467	1.304	0.049*
Distal	0.801±0.213	0.790±0.170	0.899±0.169	0.891±0.207	0.871±0.141	0.850	0.497	1.286	0.182

*Significant difference at P<0.05. If all the letters are distinct, a significant difference between the corresponding tracks is shown using Fisher’s LSD. LSD: Least significant difference, MB: Mesiobuccal, MLi: Mesiolingual

DISCUSSION

Understanding the internal anatomy of the teeth plays a significant role in the success of endodontic and restorative treatments.[15] Increasing age has been observed to change of pulp-dentin complex due to the physical deposition of secondary dentin, which results in the reduced size of pulp chamber and root canal diameter.[51117]

To explore the change of PTAR among different age groups, we selected the coronal part of the root because the deposition of secondary dentin in multirooted tooth begins at the floor of the pulp chamber following the coronal part and then the apical part of the root.[5] The change of pulp space at the coronal part is strongly correlated with age than at the apex of root.[18]

PTAR has been observed to be inversely correlated with age. The mean values of PTAR showed significant differences between age groups. According to a study by Porto et al.,[19] who examined CBCT images obtained from maxillary central incisors, they reported that pulp/tooth volume varies among age groups. Kaya et al.[17] also reported the difference of pulp width of the maxillary central incisor between age groups.

At Levels A and B, a significant reduction of the PTAR was determined between 40 and 49 years old and 50–59 years old in both roots. Kaya et al.[17] reported that the greatest decrease in the pulp width of the maxillary central incisor was determined in the age group of 45–54 years. In premolars, the steepest reduction of pulp/tooth volume was in the age group of 20–50 years.[18] Therefore, this reduction could be attributed to varying tooth types and genetic and other environmental factors that may affect secondary dentin deposition.

At Level C, PTAR was observed to decline with increasing age, which is deemed similar to other levels. However, its pattern of significant difference among age groups was different from those at the Levels A and B. The possible reason could be the difficulty to clarify the boundary of the root canal.[6] Lee et al.[8] also reported that PTAR at cervical area has shown strong correlation with age than other levels.

These results suggested that locating and negotiating the calcified canals are practical challenges during endodontic treatment in patients with advanced age. Thus, endodontic treatment in older patients is more likely to be complicated than in younger patients.

Understanding DT, especially in the danger zone, plays an important role in successful endodontic and restorative treatments. The DT reduction during root canal and post space preparation is a crucial point that can lead to strip perforation.[10] As per our findings, the mean distal DT of mesial root ranged from 0.765 to 0.821 mm, while the mesial DT of distal root ranged from 0.850 to 0.952 mm. Previous studies have reported that the distal DT in mesial roots ranged from 0.789 to 1.27 mm,[12] whereas the mesial DT of distal root was at 1.3 mm.[13] The mean values could vary for many reasons, for example, usage of different measurement methods, range of the danger zone location, races, and the age of patients.

According to our study, the distal DT at two and three mm below the furcation of mesial roots was significantly different among age groups. These results were consistent with the study of Zhou et al.,[11] which examined the axial CBCT images obtained from a Chinese population. This study reported that distal DT of MB and MLi canal had significantly increased with age in every age groups.

At distal root, our study showed no significant difference in the mesial DT of distal canal among age groups. We found that 30–39 years old had the smallest DT. However, the data in terms of DT and the correlation with aging of distal root remain to be limited.

In this study, DT increased with age particularly between 30 and 39 years old and 40–49 years old. In accordance with the study of Gani et al.,[20] who examined root canal morphology of mandibular first molars, they reported that the root canals in adults over 40 years were sharply defined and narrow compared to others. Nitzan et al.[21] reported that secondary dentine has significantly increased after the age of 39. Based on these findings, it can be indicated that younger patients have larger canal and thinner root canal wall compared to older patients.

This study showed that distal DT of the mesial root was smaller in comparison with the mesial DT of the distal root. It was affirmed that the mesial root is prone to strip perforation and crack formation during root canal and post space preparations.[11121314] The lowest recommended residual DT of 1 mm is generally accepted to avoid the risk of jeopardizing root integrity.[22] However, the minimum DT after root canal instrumentation should be at least 0.2–0.3 mm in order to withstand compaction force during root canal filling, which can lead to perforation or vertical root fracture.[23] Therefore, accurate preoperative radiographs should be taken into account to help evaluate root anatomy before any treatment. Dentists may consider using CBCT imaging as it reveals more accurate three-dimensional information compared to traditional radiographs.[15]

Based on the results of PTAR and DT, we have determined that a decrease in PTAR corresponds to the increase in the DT with increasing age. It was confirmed that pulp-dentin complex changes over time due to the deposition of secondary dentin, which contributes to the narrowing of root canal and increasing DT around root canal. However, the deposition of secondary dentin was not consistent. Besides aging process, the dentin deposition may be influenced by several other factors such as tooth loss or occlusal contact.[24] Further study may be needed to explore factors related to the deposition of secondary dentin in advanced ages.

Although the sample size calculation was done and achieved, limited sample sizes might be a limitation of this study. Thus, it would be great to obtain more samples to determine the relationship between age and the changes of PTAR and DT.

CONCLUSIONS

The PTAR was found to reduce; meanwhile, the DT was found to increase with age. Clinically, the calcified canals and thin furcation area have been identified to be practical challenges in endodontic and restorative treatments. Thus, accuracy and reliability of preoperative radiographs play an essential role in evaluating root canal morphologies in order to avoid iatrogenic errors.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.