Anatomical morphology of maxillary first premolars in a Chinese population assessed using Cone-beam Computed Tomography

doi:10.21203/rs.3.rs-2608443/v1

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Anatomical morphology of maxillary first premolars in a Chinese population assessed using Cone-beam Computed Tomography

https://doi.org/10.21203/rs.3.rs-2608443/v1

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The aim of this research was to study the anatomical shape of the maxillary first premolars in Chinese people using cone-beam computed tomography (CBCT). The anatomical morphology of root canals and crowns of 637 first premolars from China was observed by CBCT. In this study, 73.3% of the 637 maxillary first premolars were single roots, 26.7% were double roots, and 41.8%(n = 266) of the 637 maxillary first premolars were type IV in the light of Vertucci. The most frequent distance between two root canal orifices was 2-3mm (n = 257, 47.6%). There was a range in distance from the top of the medullary chamber to the central fossa (from 4.25mm to 4.45mm), with a mean distance of 4.35 ± 0.62mm. The incidence of mesial depression was 65.6%, and the mean angle of the mesial depression was 151.8 ± 10.5 degrees. In conclusion, the root canal system and anatomical morphology of the maxillary first premolar in the Chinese population exhibit a wide range of morphologies based on CBCT.

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The success of endodontic treatment owes to the complete cleaning and shaping and obturation of the root canal system[1]. The omission of root canals or incomplete obturation may be due to the technical competence and the lack of thorough understanding of the root canal of the clinician [2]. The maxillary first premolars seem to be frequently endodontic treated teeth attributing to the wedge-shaped defect and lesion [3]. Much research has been conducted on the morphology and number of root canals in maxillary first premolar teeth[4–7], but the effectiveness of the root canal treatment and subsequent crown restoration is also influenced by the morphology of the crown, which is very intimately related to each other from the standpoint of evolution[3]. The opening of the dental pulp cavity is a critical step in obtaining a straight path for endodontic treatment, and ignorance of tooth morphology may result in Pulp floor perforation [3]. Endodontic treatment of maxillary first premolars can be particularly arduous owing to their complicated anatomic variations [3, 8]. There has been considerable diversity observed in root anatomy and root canal morphology [9–11], which suggested that the prevalence of the single root from 30–60%, that of double roots varies from 41.7–70%, and of three roots varies from 0–6% [12]. Geographical disparities, evaluation techniques, and sample sizes were used to explain the discrepancy.

Periodontitis is one of the most widespread infectious diseases worldwide [13]. The development of periodontitis is to be blamed on the plaque, and the managing of plaque levels can have a significant impact on the treatment of periodontitis [14]. There is often a depression in the proximal part of the maxillary first premolars, which is favorable for plaque accumulation. A smaller angle of the mesial middle depression in the maxillary may accelerate the progression of periodontitis [15], which might associate with the deep periodontal pockets and attachment loss detected in the maxillary first premolar [16]. Although current studies have shown that the proximal mesial depression in the maxillary first premolar has a significant effect on the periodontal situation, there are fewer studies related to the angle of the proximal mesial depression in the maxillary first premolars.

Radiography is necessary during root canal treatment [17]. The photographs produced via CBCT imaging are shown concurrently in the axial, sagittal, and coronal planes, which helps to prevent structure overlap and offers better views of the target items [18]. When compared with two-dimensional imaging methods, three-dimensional imaging is more favorable at cleaning, shaping, and obturating the complete canal system in root canal treatment [19], which helps to offer a deeper comprehension of the multifarious structure of canals and roots [20]. CBCT provides a useful technique for studying and analyzing the crown and root canal morphology of maxillary first premolar teeth. Thus, in this study, using CBCT equipment, we tried to investigate the relationship between the number of roots and gender in the Chinese population. In addition, we also attempted to analyze the link between the anatomy of the root canal and the crown morphology as well as the angle of mesial middle depression in light of the difficulties in treating periodontitis and endodontics of the maxillary first premolars.

Sample Selection

This study was processed at the Affiliated Hospital of Hangzhou Normal University. CBCT images of a total of 637 first premolar teeth were obtained from 18 to 80-year-old patients who needed CBCT examination for adjunctive treatment from November 2021 to March 2022. In addition, the patients have at least one fully developed maxillary first premolar.

Samples were excluded based on the following criteria:

The maxillary first premolar with restorations or fillings.

The maxillary first premolar with incompletely developed roots.

Teeth with unclear images compromise the assessment.

The root has undergone external or internal resorption.

The maxillary first premolar has undergone root canal treatment.

Image Acquisition

A CBCT scanner (Galileos, Sirona, Germany) acquired the images. Sirona Dental System (D-64625 Bensheim, Germany) operated at 85 kVp and 7 Ams were used to obtain the images. A proven hybrid 3D solution with a perfectly designed cylinder volume of 8cm x 8cm and a standard resolution of 160µm. We obtained transverse images in the axial, coronal, and sagittal planes, the reconstruction was dependent on GALAXIES 1.9 (SICAT GmbH & Co. KG, Bonn, Germany) on a 17-inch personal computer (PC) monitor.

Image analysis

The images of CBCT were measured and analyzed by an oral radiologist and an endodontist. In case of a disagreement between the two doctors, another endodontic doctor will perform an assessment and discuss until a consensus was reached. The Kappa test was applied to confirm the inter-rater consensus. All the figures of CBCT were evaluated and measured in the following details.

The number of roots[21]: a) Single-rooted teeth: teeth with a single root that is visible and teeth with roots that are fused despite having two roots. (Fig 1a). b) Bifurcated teeth: teeth with double roots, whether they are either completely or partially, even if the bifurcation located close to the root tip is also bifurcated (Fig 1b). c) Triple-rooted teeth: teeth with three separate roots.

The type of root canals was classified in the light of Vertucci [12] a) Type I (1-1): the pulp chamber gives off a single canal to the apical foramen; b) Type II (2-1): two independent canals branching out from the pulp chamber but merging into a single canal before reaching its apical foramen; c) Type III (1-2-1): two canals that split off from the pulp chamber and merged at the apical foramen; d) Type IV (2-2): there are two separate canals from the pulp chamber to the apical end of the tooth; e) Type V (1-2): separation of one pulp chamber canal into two separate canals with distinct apical foramina; f) Type VI (2-1-2): there are two distinct canals leaving the pulp chamber that merge in the middle of the root before branching into two separate canals again; g) Type VII (1-2-1-2): an individual root canal splits into two canals as it exits the pulp chamber, merges again in the middle of the root, and then branches again into two different canals at the apices.; h) Type VIII (3-3): in addition to the pulp chamber, three different root canals run to the apices.

Incidence and angle of proximal mesial depression happened in the maxillary first premolar. The measurement position of proximal mesial depression was taken at the enamel-cementum boundary. The angle was obtained by connecting the most convex point of the buccal tongue on each side and the most concave point in the middle. The angle of proximal mesial depression detected from the image of the axial segment is shown in Figure 2.

Morphological analysis of maxillary first premolar: a) The width of the buccolingual diameter of the maxillary first premolar was detected as the maximum buccolingual diameter of the cross-section. The measurement method was shown in Figure 3. b) the proximal and distal mesial width of the maxillary first premolar was measured off the maximum proximal and distal mesial diameter taken in the axial section. Figure 4 showed the way to detect the distance c) The ratio of the maximum buccolingual diameter to the proximal and distal mesial diameters represents the morphology of the teeth. d) Distance from the roof of the medulla to the central fossa (Figure 4). e) Distance between two pipe openings (Figure 5).

Statistical analysis

All the data were analyzed using SPSS 24.0 software (SPSS Inc, Chicago, IL). Differences were statistical significance at P <0.05. To ensure the reliability of the test results, all measurements were executed thrice and the mean value was taken. The Chi-square test was used to analyze the correlations between the number of roots and gender, and the correlation between mesial cervical concavity and different tooth positions. Kruskal-Wallis test was used to analyze the flowing, which disobeys the normal distribution: (1) the relationship between root canal type to buccolingual diameter ratio, and (2) the relationship between age and the distance from the roof of the medulla to the central fossa.

The numbers of roots of maxillary first premolar teeth were classified by gender in Table 1. The majority (n = 467, 73.3%) of the maxillary first premolar had a single root, and nearly (n = 170, 26.7%) of the maxillary first premolar had double roots. Of the 637 maxillary first premolars, 333 were from males, there were 234 (70.3%) maxillary first premolars displayed 1 root, and 99 (29.7%) maxillary first premolars displayed 2 roots. In the meantime, out of 637 maxillary first premolars 304 were from females, 233 (76.6%) maxillary first premolars displayed 1 root, and 71 (23.4%) maxillary first premolars displayed 2 roots. There was no gender difference regarding the number of roots (P > 0.05).

Table 1

The proportion of Roots (% of Teeth) According to Gender
Gender	1 root (%)	2 roots (%)	Total	p-value
Male	234 (70.3%)	99(29.7%)	333
Female	233(76.6%)	71(23.4%)	304	0.069
Total	467(73.3%)	170(26.7%)	637

The prevalence of the type of canal configuration in line with Vertucci was shown in Table 2, the majority (n = 266, 41.8%) of maxillary first premolar teeth were Vertucci types IV, followed by type II (n = 192, 30.1%), type I (n = 106, 16.6%), type III (n = 45, 7.1%), and type V (n = 25, 3.9%). The least number of maxillary first premolar teeth was Vertucci VI.

Table 2

Proportion of Root Canal Types
Type of canal configuration	Vertucci I	Vertucci II	Vertucci III	Vertucci IV	Vertucci V	Vertucci Vl	total
Number(n)	106	192	45	266	25	3	637
Percentage (%)	16.6	30.1	7.1	41.8	3.9	0.5	100

Table 3 showed the distance between the roof of the medulla to the central fossa by age of the maxillary first premolar teeth. The mean distance to the central fossa at different ages was 4.35 ± 0.63mm. The distance between the roof of the medulla to the central fossa of the maxillary first premolar teeth showed no significant difference between different ages (P > 0.05).

Table 3

Distance from the roof of the medulla to the central fossa by age
Age	Number	Distance from the roof of the medulla to the central fossa	p-value
18–29	132	4.41 ± 0.59
30–39	119	4.33 ± 0.60
40–49	84	4.25 ± 0.59
50–59	159	4.34 ± 0.57	0.226
60–69	92	4.45 ± 0.79
༞70	51	4.39 ± 0.63
Total	637	4.35 ± 0.63

The distance between the orifices in the root canals for the 540 teeth with 2 root canals was shown in Table 4. We found the distance between the root canal orifices in the majority (n = 484, 89.63%) of teeth of the maxillary first premolar was 2–4mm. There were 257 teeth (47.6%) of the distance between the orifices in the root canals ranged from 2-3mm, 227 teeth (42.0%) ranged from 3-4mm, 28 teeth (5.2%) ranged from 1-2mm, 27 teeth (5%) from 4-5mm and 1 tooth from 5-6mm.

Table 4

An analysis of the distance between the 2 root canal orifices of maxillary first premolars with 2 root canals
Distribution (mm)	1–2	2–3	3–4	4–5	5–6
Number	28	257	227	27	1
Percentage (%)	5.2	47.6	42.0	5	0.01

The ratio of crown buccal-lingual diameter to proximal-distal by different root canal type diameters of maxillary first premolars was shown in Table 5. As listed in Table 5, the ratio is 1.39 in 106 types I; types II was 1.42, type III was 1.39; type IV was 1.42; type V was 1.39, and types VI was 1.41. which showed a significant difference according to different root canal types by the Kruskal-Wallis test (P <0.05).

Table 5

The ratio of crown buccal-lingual diameter to proximal-distal diameter of maxillary first premolars by different root canal type
type	I	II	III	IV	V	VI	p-value
number	106	192	45	266	25	3	0.039
The ratio	1.39	1.42	1.39	1.42	1.39	1.41	0.039

The incidence of proximal mesial depression of the maxillary first premolar was shown in Table 6. The incidence of proximal mesial depression in the left maxillary first premolar was 61.7% in the right was 70.2%. The mean angle of the left maxillary first premolar was 152.1 ± 11.3, while the right is 151.4 ± 9.7. By using the Kruskal-Wallis test, it was shown that there was a significant difference based on where the maxillary first premolar was located (P< 0.05).

Table 6

Incidence of proximal mesial depression of maxillary first premolar
Position	Left	Right	p-value
Number	345	292	-
Number of occurrences	213	205	-
Percentage(%)	61.7	70.2	0.026
The mean Angle	152.1 ± 11.3	151.4 ± 9.7	-

Table 7

Comparison of the number of root canals in first premolars in previous studies and those in this study
Author(year)	Population (sample size)	One root (%)	Two roots (%)	Three roots (%)
K. Olczak (2022)[22]	Polish (n = 350)	99 (28.3)	242 (69.1%)	9 (2.6%)
Mashyakhy(2022)[23]	Kingdom of Saudi Arabia (n = 2314)	657 (35.5)	1170(63.2)	24(1.3)
Faraj,B.M.(2022)[24]	n = 142	42(29.57)	97(68.31)	3(2.12)
Liu, X. (2021)[25]	Chinese (n = 880)	618(70.22)	258(29.32)	4(0.46)
Al-Zubaidi(2021)[26]	Saudi arabian (n = 500)	199(39.8)	293(58.6)	8(1.6)
Wu, D.(2020)[27]	Chinese (n = 1268)	855(67.4%)	406(32%)	7(0.55)
Buchanan, G.D.(2020)[28]	South African (n = 316)	139(44.0)	171(54.1)	6(1.9)
de Lima, C.O. (2018)[29]	Australian (n = 496)	90(18.2)	398(80.2)	8(1.6)
Nazeer, M.R.(2018)[30]	Pakistani (n = 114)	36(31.5)	74(68.6)	4(3.5)
Bürklein (2017)[31]	German (n = 644)	234(36.4)	402(62.4)	8(1.2)
Abella, (2016)[33]	Spanish (n = 430)	198(46)	221(51.4)	11(2.6)
This study	Chinese (n = 637)	467(73.3)	170(26.7)	-

Ethics approval.

The study protocol was reviewed and approved by the Ethics Committee of Hospital of Hangzhou Normal University (number: 2022(E2)-KS-107). The Helsinki Declaration and its revisions, as well as other related ethical norms, guided the conduct of the study.

Informed approval.

Participants received information about the study and completed informed permission forms before the trial began. Participants and any identifiable persons gave their agreement for their images to be published.

Informed consent.

All patients or their guardians gave their informed consent for this kind of investigation.

A great deal of variation in maxillary first premolar had been reported in root anatomy and root canal morphology in several studies [9-11]. Table 7 shows a comparison between the number of maxillary first premolar roots in previous studies in different regions[22-33]. Ethnicity may be the greatest contributor to the variation, especially between Chinese and other populations. The incidence of one-root teeth is substantially higher in the Chinese population than in Spanish and South Africa. The lowest incidence of one-root teeth was in Australia and Polish. Meanwhile, the two-root teeth and three-root teeth were far less common in the Chinese population [25]. It might be the result of differences in dental evolution due to the different living environments of different ethnic groups. Gender is also one of the factors that contribute to the discrepancy. A research study about the Australian population and the German population found a statistical difference (P＜0.05) between gender and the number of roots, and when compared to female patients, male patients had a larger percentage of two roots (62.1% vs. 41.3%)[29, 31]. In this study, we did not find a statistical difference between male and female patients in the number of roots in maxillary first premolars in the east of China. However, in a similar study of Chinese, in which the samples were collected in the north of China, a significant difference could be seen in the number of roots in maxillary first premolars [34]. Knowing the number of roots of the maxillary first premolar helps the doctor avoid missing roots during root extraction and provides force during orthodontic operations.

Great root canal variations were found in the maxillary first premolar in this study, but double root canals were the most prevalent (n=531, 83.34%). A distance of 2-4mm was most commonly found between two root canal openings in maxillary first premolars, the results were similar to Yang's research suggesting that there were 250 maxillary first premolars with double root canals, 46.4% of which had a 2-3 mm distance between their root canal orifices, and 30% of which had a 3-4 mm distance [5]. Since one root canal aperture can be discovered within 2-4 mm of another in the buccolingual direction, the clinicians are encouraged to take note of the characteristics when planning the pulp chamber access and locating the root canal orifices. Concerning the root canal configuration of the maxillary first premolar, in this study, 41.76% of tooth canals were subordinated to type IV, followed by type II, which is comparable with the research conducted by Awawdeh et al. using the clearing technique [35]. The proportion of the morphology of the root canal in different races is not the same, for example, maxillary first premolars with type IV canal structure were more common in Polish and Brazilian patients than in Chinese [22, 36]. Human tooth development is a continuous process, the various stages of tooth development are regulated by epithelial-mesenchymal interactions [37-40]. Kulkarni et al. conducted a survey that evaluated the tooth anatomic length with root canal configurations in the North American population, which found the maxillary first showed a great incidence for Type IV, and the first premolars in the maxilla showed a significant relationship (P＜0.05) between anatomic size and canal morphology. [41]. In addition, for maxillary first premolars, the Vertucci Type IV canal system had the longest tooth length. Maryam evaluated the relationship between crown size and root canal morphology of mandibular incisors and found Type III had a substantially larger mean maximum mesiodistal and buccolingual diameter than Type I [42]. The results of the study we conducted were consistent with the previous, the ratio of crown buccal-lingual diameter to proximal-distal diameter of maxillary first premolars was related to different canal types indicating a significant difference, and the ratio was greatest for type IV. Being aware of the important connections between the anatomical details of the crown and root canal configurations was advised, during the root canal treatment the larger buccolingual diameter may suggest its root canal morphology is type IV.

With time, the pulp weakens, its volume shrinks, and the dentin surrounding the pulp chamber hardens. Additionally, dental wear with age is an important reason for the reduction of tooth thickness. The continual deposition of secondary dentin is widely thought to be responsible for the decrease in pulp chamber capacity [3, 43]. The distance from the roof of the medulla to the central fossa we had detected to assess the variation with the ages. We found the mean distance from the roof of the medulla to the central fossa was 4.35±0.63mm. Concerning the distance from the roof of the medulla to the central fossa was no significant statistical difference in age (P＞0.05). It indicates that the secondary dentin will offset the abrasion of the crown with age.

In this study, we have further investigated the crown morphology, the pulp chamber is the cavity in which the pulp is located [3]. The palatal furcation groove and the mesial concavity can be seen in the maxillary first premolars [25]. A high frequency (62%-100%) of mesial concavities in the maxillary first premolars was reported in the previous research [44-46], which might encourage the accumulation of plaque and promote the development of periodontitis. Zhao's analysis in 99 periodontitis patients found the incidence of mesial depression in the maxillary first premolar was 100% (n=112) [46]. In this study, the incidence of proximal mesial depression in the maxillary first premolar was 65.6% (n=418) and the mean angle of the mesial depression was 151.8±10.5 degrees. The outcomes of this research were comparable to those of Fan, who examined the prevalence of mesial cervical concavity in maxillary first premolars and discovered that it was 68.8%. Additionally, the findings demonstrated that mesial cervical concavity was more common in two-root teeth than single-root teeth [47].

To show the anatomical morphology of the crown and root of the maxillary first premolar, in this study, CBCT was used to scan 637 locations, which contributes to a clear understanding of the maxillary first premolar in the Chinese population.

Most of the maxillary first premolars in the Chinese population are mainly one-rooted, possessing two root canals (predominantly Type IV). The distance from the roof of the medulla to the central fossa was no different with the age. The angle and prevalence of proximal mesial depression of the maxillary first premolar are both high. These results indicated that endodontic and periodontal treatment of the maxillary first premolar seems to be more challenging.

Data availability

On reasonable request, the corresponding author will provide the datasets created and/or used in the current study.

Author contributions

F.C. and X.Z.H. drafted the manuscript. L.J.Z. and C.D. designed the study and edited the manuscript. Q.L and X.Y.L performed the statistical analysis. R.L. B.X.Z and Z.S. collected the data and contributed to the analysis of the results. All authors read and approved the manuscript.

Competing interests

The authors declare no competing interests.

Additional information

Correspondence and requests for materials should be addressed to L.J.Z

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No competing interests reported.

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Anatomical morphology of maxillary first premolars in a Chinese population assessed using Cone-beam Computed Tomography

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