In-depth morphological evaluation of tooth anatomic lengths with root canal configurations using cone beam computed tomography in North American population

Abstract Objective This study aimed to assess the association between tooth size and root canal morphology by using CBCT analysis. Methodology In this retrospective study, tooth anatomic lengths (crown and root lengths, buccolingual and mesiodistal dimensions) of 384 patients were assessed and correlated with Vertucci’s root canal morphology classification. Data was analyzed for gender-related differences using the independent sample t-test, ANOVA, and the Pearson’s correlation for a possible relation between anatomic lengths and canal morphology. Results The maxillary first and second premolars showed a greater predilection for Type IV and II variants, respectively, while the mandibular first premolar showed a greater predilection for Type II canal system. The root canal system of the mandibular second premolar showed maximal diversity (47% Type I, 30% Type II, and 20% Type III). The dimensions were greater in men regardless of tooth type. The most significant relation (p<0.05) between the anatomic size and canal morphology was observed in the maxillary first premolars, followed by the mandibular canines (buccolingual dimension) and the lower second premolars (crown length). Negative correlations existed between the crown length and the patient’s age for the anterior teeth and mandibular second premolar (r=−0.2, p<0.01). Conclusions The most common canal formation for anterior teeth was the Type I. The anatomic lengths had the strongest influence on the canal configuration of the maxillary first premolar, with Type IV being the most common root canal system. The mandibular second premolars showed maximal diversity in the canal classification terms and had a significant correlation with their crown lengths. Clinical Relevance The complex relationship between the canal morphology and anatomic tooth sizes need meticulous awareness and recognition during endodontic procedures, in conjunction with the demographic variabilities.


Introduction
Root canal morphology varies greatly from tooth to tooth and is not a single uniform canal in many cases, but it can be highly complex from orifice to apex. Tooth canal heterogeneities have been reported, including but not limited to: apical ramifications, loops, C-shaped canals, double "s-shaped" canal curvatures and accessory canals. 1 One of the fundamental prerequisites for a successful endodontic treatment is a comprehensive knowledge about the anatomy of the tooth; typically, the root canal shape and its diversities. Undetected root canals are reported as the primary reason for endodontic retreatment in 42% of the cases. An investigation on root canal geometry reported that variations in canal conformations have much more influence on the changes occurring during canal preparation when compared with those due to instrumentation techniques, thereby reiterating the significance of canal anatomy. 2 Considering the vast individual, genetic, and ethnic variations, it becomes particularly essential to understand and gauge the morphologic details of root canals. 3,4 This can help in minimizing failure rates and ensure longterm prognosis of a tooth undergoing endodontic retreatment.
A study evaluating 1400 permanent teeth in Turkish population reported more than one canal in 22% of maxillary lateral incisors. 5 Maxillary anterior teeth have been found to have a lower prevalence of extra roots and extra canals compared with mandibular anterior teeth. The estimated prevalence for a second canal is 11% for mandibular central incisors and from 7% to 11% for mandibular lateral incisors. [6][7][8][9] Root canal treatment for mandibular incisors is deemed harder than that of molars, and it is as difficult as that of mandibular two-canal premolars because of their small dimension and the high prevalence of two canals.
A study assessing the root anatomy of mandibular anterior teeth found two previously unidentified root canal types. The first variant consisted of two separate canals extending from the pulp chamber to the midroot region, where the lingual canal was divided into two, followed by the joining of all three canal elements in the apical third as one canal. In their second category, a single canal from the pulp chamber was divided into two in the middle third of the root, which then rejoined to form one canal that split again, exiting as three separate canals with separate foramina. 10 A possible association between crown size and the pervasiveness of bifid canals in mandibular incisors has been documented. Therefore, having a comprehensive knowledge of the pulpal anatomy is critical.
Likewise, the mandibular first premolars are equally difficult to treat endodontically, because of its wide canal morphology variety and difficulty in accessing the second canal, with an approximate 12% treatment failure rate. More so the lingual propensity of its crown and the angled separation of the secondary canal can hamper the detection of the second canal, both radiographically and via tactile examination. The incidence of mandibular premolars with the prevalence of more than one canal in the first and second premolars is 27.8% and 8.9%, respectively. 11 An accurate interpretation of the crown and root morphology of such teeth is warranted for precise diagnostic radiography. In a case study, the cervical half of the root in mandibular premolars with more than one canal is often wider. 12 The facio-lingual curvatures of the root canal system, which are not often visualized by two-dimensional radiographs, may make cleaning and shaping procedures more difficult.
This requires a simpler, yet more accurate method to diagnose and visualize the root canal morphology. As cone beam computed tomography technique (CBCT) has an excellent resolution and capacity to visualize root anatomy in three dimensions and a much lower patient radiation dose compared with the multislice computed tomography, it is considered more precise in providing details about extra canals, apical deltas, and canal type than the digital radiography, with a highly strong correlation between data acquisition via CBCT in all spatial planes, for histology specimens. 13 Its precision is comparable to the canal staining and clearing technique, which is considered the gold standard for gauging canal morphology, in addition to its utility in in vivo application. 14 Very few studies have evaluated the root and canal morphology of the anterior and premolar teeth with CBCT to establish any possible correlation with tooth crown and root lengths.
However, because of the small sample size of those studies, the findings cannot be generalized to larger populations. 14,15 Thus, this study seeks to fill adequate knowledge voids regarding canal morphology, with the ultimate goal to increase the success of the endodontic treatment by decreasing procedural errors. This retrospective and cross-sectional study aims to establish reference data for normal tooth lengths In-depth morphological evaluation of tooth anatomic lengths with root canal configurations using cone beam computed tomography in North American population J Appl Oral Sci. 2020;28:e20190103 3/10 (including crown and root lengths) and common root canal system for the maxillary and mandibular anterior teeth and premolars, and to correlate the relationship between anatomic lengths and canal morphology using CBCT analysis. This study also aimed to detect significant differences in CBCT measurements between demographic factors (gender and age), and tooth anatomic lengths and canal classification relationships.

Methodology Study samples
This study was approved by the Institutional Review

Results
The study sample consisted of 384 patients (n=233 females and n=151 males), providing a total of 447 CBCT scans (n=280 mandibular and n=167 maxilla)  Type II and Type III, respectively. The detailed canal topology percentage distribution for each tooth is shown in Figure 2.
The cumulative mean of crown and root lengths, and buccolingual and mesiodistal dimensions for anterior and premolar teeth of the right and left quadrants are noted in Table 1 (maxilla) and in Table 2 (mandible). When the mean tooth anatomic lengths (TL, CL, RL, BL, MD) were compared between men and women for both the arches, almost all the anatomic measurements were higher for men than for women (p<0.05; Tables 1, 2). Additionally, there was no significant age-related differences between genders (p=0.1). Statistically significant relations between the tooth anatomic lengths and the Vertucci's canal system type are shown in Table 3 (maxillary arch) and in Table 4 (mandibular arch). The most significant relation (p<0.05) between the anatomic size and canal topology was observed in maxillary first premolars, followed by the buccolingual dimension for mandibular canines and crown length for mandibular second bicuspids (in Tables 3 and 4). The mean tooth length was greatest with the Vertucci Type IV canal system for both maxillary right and left first premolar.
The buccolingual dimension was the lowest with the Vertucci's Type I when compared with Type III and IV

Discussion
To account for the possible root canal variations, this study was designed to expand the understanding of the anatomic morphology of the maxillary and mandibular   Type I, 3% Type II, 4% Type III, and 2% Type IV.
Likewise, in this study, 99% of the maxillary canines demonstrated type I configuration with approximately 1% Type II. The root canal morphology of mandibular incisors is reported to vary greatly, and the difference in prevalence is affected by factors such as sample size, examination methods, and ethnic diversity. 6,8,10 Studies using staining and clearing techniques 20,21 have reported that the prevalence of a single canal in mandibular incisors is around 65.6%, and 36.25% with two canals. This is consistent with the results of this study. In a total of 280 mandibular scans, 58% of the lower incisors have the Vertucci Type I followed by 41.5% Type II, and 0.5% Type III configuration.
The mandibular canines showed a greater predilection for the Type I (85%) canal configuration, followed by the Type II (14%), and the Type III (1%) variants, with the buccolingual dimension increasing with these    accordingly, such as further removal of the pulp chamber roof of the lingual part to access the canal to avoid the likelihood of pulpal necrosis due to partial endodontic treatment.
Gender has been invariably reported as an important factor to be considered in the preoperative evaluation of the canal morphology for root canal treatment. 19 In this study, all the anatomic measurements were higher in males than in females. The pulp cavity generally decreases in size as an individual ages 4 with nonuniform dentine and cementum formation occurring throughout life and is more rapid on the roof and floor than on the pulp chamber walls of the posterior teeth. These calcifications result in a flattened pulp chamber. In accordance with previous studies, 4 a weak negative correlation was noticed between crown lengths and increasing age. This study did not examine the correlation between tooth lengths and persons' stature.

Clinical relevance
The data obtained in this study can be used as a reference for evaluating CBCT based measurements of: tooth, crown and, root lengths, as well as buccolingual/mesio-distal dimensions of anterior and premolar teeth. Considering the apparent relationship between the tooth anatomic lengths and the root canal variants, meticulous radiographic interpretation, proper access preparation, and a detailed tooth exploration with age and gender consideration are essential prerequisites for a successful treatment outcome.

Limitations and future directions
The proportion of women in this study was higher than that of men (60% versus 40%). Additionally, subtle incongruities were observed in the findings of this study when compared with other studies, due to differences in geographic location (ethnic and genetic factors) and assessment methods. Future studies using CBCT-based measurements with larger sample size can help augment these findings.

Conclusions
In summary, maxillary and mandibular anterior teeth prevalence is higher for Type I canal configuration.
Anatomic lengths (crown and root length, buccolingual and mesiodistal dimension) had the strongest influence on the root canal configuration of maxillary first premolars. Additionally, mandibular second premolars showed maximal diversity concerning the type of canal classification and a significant correlation with their crown lengths.