The prevalence of mandibular lingual concavity among the Saudi population of Eastern Province: A CBCT evaluation

Abstract

Background

Anatomic variations can make placing implants in the mandible more complex. Exploring the variation in the presence of ridges and lingual concavity among different races and ethnicities is of therapeutic significance. The current study evaluates the prevalence and size of mandibular lingual concavity, which can cause surgical complications while inserting dental implants in the mandibular first molar area.

Methods

Two hundred and fifty-six cross-section images of the edentulous first molar region were examined. Within this geographical area, the structure of the lower jaw was categorized into three distinct types: C-configuration (convex), P-configuration (parallel), and U-configuration (with an undercut). The study was conducted at IAU College of Dentistry, Dammam. Data was gathered on the depth of the lingual concavity, the angle of the concavity, and other relevant factors. The data were analyzed with SPSS 20. A p-value ≤ 0.05 was considered significant.

Results

Of 256 subjects included in the study, 144 were males (M), and 112 were females (F). Various variables measured complimenting the lingual concavity showed no difference between the genders, except for the VCB “The vertical distance from the alveolar crest to line A” (p-value = 0.005). The division of ridges morphology as a whole was as follows: Convex (C), 70 (27.34 %), Parallel (P) 51 (19.92 %), and Undercut (U) type, 135 (52.73 %). The angle of concavity was 69.28 ± 14.41 % (M) and 67.09 ± 13.04 %. (F). Angle depth was 2.40 ± 1.72 % (M) and 2.36 ± 1.46 % (F); together, 2.38 ± 1.6 %.

Conclusion

It was concluded that U-type ridges were predominant (52.73%) with more chances of occurrence of lingual concavity. There were no differences between the genders except in one parameter. (VCB) Further studies are required to explore lingual concavity in more detail.

1. Introduction

A mandible is a bony unit that houses many anatomical structures that are considered to be of surgical importance. These anatomical structures include muscle attachments, spaces, foramen with their contents, and bony physiological growth (Chu et al., 2014). Additionally, in the back part of the lower jaw, the Submandibular and Sublingual Fossae hold significant importance (Greenstein et al., 2008). The submandibular fossa is a concave indentation at the inner side of the lower jaw, below the mylohyoid line, positioned on both sides of the mental spine and above the mylohyoid line.

It is necessary to feel the submandibular and sublingual fossae prior to osteotomy; if there is a large undercut (lingual concavity), the lingual bony plate can be perforated inadvertently, with resultant hemorrhage (Sferlazza et al., 2022). Various prior studies have reported the presence of lingual concavities with varying depths and measures (Almarghlani et al., 2023, Chan et al., 2011, Salemi et al., 2018).

Although routinely used panoramic and periapical radiographs help evaluate edentulous regions in the posterior mandible, the two-dimensional radiographs are not enough to explore the three-dimensional details like buccolingual or horizontal dimensions Magat, (2020) especially the concavity or convexity in the bony cavities. The Cone Beam Computed Tomography (CBCT) and Computed Tomography (CT) are commonly used in clinical practice, especially for implant surgical operations, to obtain accurate diagnostic outcomes (Magat, 2020).

The perforation and placement of implants outside the bony housing are rare and not reported or underreported. Only a few case reports have been published in the literature (Kalpidis and Konstantinidis, 2005, Law et al., 2017, Leong et al., 2011). Though reported prevalence studies using CBCT in various other populations are available at present (Almarghlani et al., 2023, Alqutaibi et al., 2024), considering the possible variation in the anatomical landmarks in different regional and ethnic populations (Altwaim and Al-Sadhan, 2019). Here, we examined the frequency and severity of lingual concavity in toothless individuals in the first molar area using CBCT.

2. Materials and Methods

2.1. Ethical Consideration and approval

The experiment was conducted as per the guidelines of the declaration of Helsinki, for human subject’s research. The IRB of Imam Abdulrahman Bin Faisal University, Dammam, granted approval for the study (# IRB-PGS-2024–02-129).

2.2. Sample size

The study employed CBCT scans of patients who sought dental treatment at dental clinics from June 2022 to June 2023. A database with 432 CBCT scans has been generated by the Radiology Department of the University Dental Hospital of Imam Abdulrahman bin Faisal University, Saudi Arabia.

2.3. Calculation of sample size

The WHO sample size calculator was used, developed by the National University of Singapore, assuming the prevalence of lingual concavity given a power of 80 %, a confidence interval of 95 %, and a significance level of 5 %.

2.4. Inclusion Criteria

The CBCT scans of the jaw should clearly show the missing of at least one mandibular first molar, whereas it is essential to observe the existence of the neighboring second premolar. According to (Sammartino et al., 2008), in order for a 10 mm implant to be supported, the experimental site must have a vertical bone height of at least 12 mm, measured from the alveolar crest to the upper margin of the inferior alveolar nerve canal (IAN). According to (Monje et al., 2019), the horizontal bone width at the experimental site should be at least 3.5 mm.

2.5. Exclusion Criteria

The images of medically compromised patients, such as endocrine diseases, e.g., osteoporosis, hyperparathyroidism, Paget’s disease, metabolic disorders, and renal osteodystrophy were excluded. Data regarding the edentulous time was not available. Furthermore, local oral, and periodontal conditions that may affect bone quantity and quality at the posterior mandible, e.g., moderate to severe periodontal disease, cyst, neoplasm, prior trauma, or history of surgery, were also excluded.

2.6. Analysis of Radiographic Images: Close-up of (CBCT)

All CBCT images chosen were captured using the same machine. The (Orthophos imaging system, Sirona Dental Systems, Bensheim (Germany), was used with the specified exposure setting. The imaging parameters selected were a peak kilovoltage of 120 kVp and a current of 5 mA. The field of view was 16 × 13 cm, the acquisition time was 26.9 s, and the voxel size was 0.25 mm. “As low as reasonably achievable” (ALARA) was the guiding approach for determining the imaging parameters. The photos were created and analyzed using Horos 3.0 software, Annapolis, Maryland, USA). To ensure consistency in the data, the jaw was reconstructed using coronal, sagittal, and axial perspectives. Coronal plane cross-sections were taken for the tooth under evaluation. The coronal segment closest to the tooth's mesiodistal midpoint was measured to determine the cross-sectional morphology. The reference points for the examination in these locations were the alveolar crest, mandibular lingual concavity, and inferior alveolar canal (Fig. 1, Fig. 2).

Fig. 1.

CBCT data for measurement of lingual concavity.

Fig. 2.

Data measurement for lingual concavity.

2.7. Scan measurements

2.7.1. Inter and Intra-Examiner calibration

Two calibrated examiners did the measurements on the CBCT scans. Twenty CBCT images were used for calibration for inter and intra examiner calibration. The kappa score ranged from 0.82 to 0.85.

2.7.2. Ridge categorization and measurement of lingual concavity

After selecting appropriate cross-sectional pictures of the mandibular first molar's edentulous area, we measured the specific area of interest. The lingual concavity is located 2 mm above the inferior alveolar canal (IAC). This area was categorized as either convex (C) parallel (P) or undercut (U) type (Chan et al., 2011). The U-shaped crest is wider at the top than at the base. A ridge is said to be of the C type if the width between its two points is less than half.

In contrast, a ridge is considered a P ridge if the breadth of its highest and lowest points is equal. The concavity angle, depth, and undercut type in U were utilized to quantify lingual concavity. The guidelines and markings on the CBCT that were used to assess the required data are depicted in (Fig. 1, Fig. 2) (Alqahtani et al., 2021).

2.8. Data analysis

The data were analyzed using SPSS version 20. A p-value ≤ 0.05 was considered statistically significant. The Chi-square test was used to compare categorical variables, and the Mann-Whitney U test was used to compare the continuous variables.

3. Results

3.1. Demographic data

The study included 256 images of 144 males and 112 females with a mean age of 53 years (range: 23.7–70.4), and 51.2 (range: 20.4–69.9), respectively.

3.2. Variables Related to lingual concavity

Various variables measured complimenting the lingual concavity showed no difference between the genders, except for the VCB. The average width of the Bucco-lingual dimension, measured 2 mm below the alveolar crest, was 7.03 mm ± 2.1 mm for males and 7.43 ± 2.09 mm for females. The width of the mandibular cross section 2 mm above the inferior alveolar nerve (IAN), referred to as WB, was measured to be 10.69 ± 1.94 mm for males and 10.57 ± 1.88 mm for females. The vertical measurement from the alveolar crest to a point 2 mm above the inferior alveolar nerve (IAN) was measured. The average height for (M) was 14.12 ± 2.65 mm, while for (F), it was 12.99 ± 2.17 mm. The VCB compared between the genders was significant (P ≤ 0.005) (Table 1).

Table 1.

Parameters used to measure the lingual concavity in total.

	Landmarks	Mean ± SD	Median	Range	95 % CI	Sig.
Male (n = 144)	WC	7.03 ± 2.12	6.98	3.27 – 14.3	6.68 – 7.38	0.202
	WB	10.69 ± 1.94	10.37	6.11–15.80	10.37 – 11.01	0.931
	VCB	14.11 ± 2.65	14.02	8.48–21.48	13.68 – 14.54	0.005*
	VC	10.36 ± 4.72	10.33	1.80–28.34	9.589 – 11.13	0.375
	VB	17.16 ± 4.69	17.11	4.58–27.03	16.39 – 17.93	0.143
	Angle (o)	69.28 ± 14.41	69.48	39.0–93.55	66.93 – 71.63	0.265
	Angle depth	2.40 ± 1.72	2.02	0.00–6.85	2.12 – 2.68	0.840
Female (n = 112)	WC	7.43 ± 2.09	7.35	3.51––13.50	7.04 – 7.82
	WB	10.57 ± 1.88	10.35	6.75–15.70	10.22 – 10.92
	VCB	12.99 ± 2.17	12.80	10.0–21.38	12.59 – 13.39
	VC	9.50 ± 4.36	9.57	2.46–23.04	8.69 – 10.31
	VB	16.39 ± 3.81	15.55	5.49–29.36	15.68 – 17.10
	Angle (o)	67.09 ± 13.14	66.00	43.0–90.0	4.66 – 69.52
	Angle depth	2.36 ± 1.46	2.11	0–6.25	2.09 – 2.63
Total (n = 256)	WC	7.21 ± 2.11	7.00	3.27–14.30	6.952 – 7.468
	WB	10.64 ± 1.91	10.37	6.11–15.80	10.406 – 10.87
	VCB	13.62 ± 2.50	13.45	8.48–21.48	13.31 – 13.93
	VC	9.99 ± 4.57	10.10	1.80–28.34	9.43 – 10.55
	VB	16.82 ± 4.33	16.28	4.58–29.36	16.29 – 17.35
	Angle (o)	68.32 ± 13.87	68.26	39.0–93.55	66.62 – 70.02
	Angle depth	2.38 ± 1.61	2.10	0–6.85	2.183 – 2.58

* Significance of landmarks between males and females at 5% level of significance.

3.3. Division of ridge morphology

Among 256 images examined, the division of ridges morphology was as follows: Convex (C), 70 (27.34 %), Parallel (P) 51 (19.92 %), and Undercut (U) type 135 (52.73 %). The gender-wise distribution of these ridges was as follows: Out of 70 Convex ridge types (C), 39 (55.71 %) were males, and 31 (44.28 %) were females. Parallel type ridges were (P) 26 (50.98 %) males and 25 (49.01 %) females, and the Undercut types 79 (58.51 %) (M) and 56 (41.49 %) (F) (Table 2.). Fig. 3.

Table 2.

Type of ridges and comparison between the genders.

		Gender				Total		P-value
		Male		Female
		N	%	N	%	N	%
Type of the ridge as a whole(U/P/C)	Convex(C)	39	27.0	31	27.7	70	27.3	0.86
	Parallel(P)	26	18.0	25	22.3	51	19.9
	Undercut(U)	79	54.8	56	50.0	135	52.7
Type of ridge above the nerve	Convex(C)	54	37.5	43	38.4	96	37.5	0.613
	Parallel(P)	32	22.2	36	32.1	61	23.8
	Undercut(U)	58	40.3	43	38.4	99	38.7

Fig. 3.

Type of ridges and its comparison among gender.

3.4. Details of the lingual concavity

The angle of concavity was 69.28 ± 14.41 (M), and 67.09 ± 13.04. (F). angle depth was found to be 2.40 ± 1.72 (M) and 2.36 ± 1.46 (F), and all together it was 2.38 ± 1.61. (Table 1).

4. Discussion

The current study evaluates the prevalence and size of mandibular lingual concavity, which can cause surgical complications while inserting dental implants in the mandibular first molar area. The study determines the lingual undercut in the mandible to prevent complications of perforating the lingual cortical plate (bone).

The clinical implication of lingual concavity during implant placement is essential (Leong et al., 2011). The change in lingual concavity in different ethnicities and races encouraged us to study this aspect. So far, only two studies have been reported in this region (Almarghlani et al., 2023, Alqutaibi et al., 2024). Both studies are contemporary to our study. Besides some resemblance in the results of these two studies, compared to our study, there is variation too. Further, they have not included the population from our province. Thus, the outcome of this study is expected to provide newer information about the prevalence of lingual concavity in the Eastern Province of Saudi Arabia.

The study aimed to determine the prevalence of different types of ridges, the presence of lingual concavity, and their depth. The findings of our study are by(Almarghlani et al., 2023, Alqutaibi et al., 2024), with the predominant U type of ridges. (Herranz-Aparicio et al., 2016) identified a higher prevalence of U-shaped mandibles than P and C types.

Furthermore, our results agree with (Huang et al., 2015, Sun et al., 2023). However, in reports published by (Tan et al., 2021), a greater frequency of type C ridges was noted in the first and second molar areas, as in (Watanabe et al., 2010). (Chan et al., 2011) reported more P ridges than convex and U-type ridges. Differences in the prevalence of the ridges and lingual concavity in these studies depend upon the area of the tooth examined (first or second molar), or it may be because of differences in the race and ethnicity of the population studied. Also, dentulous and edentulous areas differ in their morphology and presence of concavity (Nickenig et al., 2015, Salemi et al., 2018).

The angle of concavity was like the study results of Almarghlani et al., (2023), where the maximum subjects (445/600) were reported to have an angle of more than 60 degrees. However, the angle reported in the study by Alqutaibi et al., (2024) was slightly lower range (44.9 ± 2.3 to 54.0 ± 12.4). The difference in the reported angle may be due to the age group studied; the depth was somewhat smaller (1.7) than our study's.

A gender-wise comparison of the data collected did not show any difference in the measurements except for the VCB. Our findings agree with Alqutaibi et al., (2024), who reported similar results with all the measurements except for the ridge height of the second molars, which exhibited a statistically significant increase in males. Yoon et al., (2017) have reported similar findings, indicating no statistically significant variations in the mandibular lingual concavity across genders. Nevertheless, other published findings did not concur with our analysis. Tan et al., (2021) found that males had significantly greater length and depth of lingual concavities than females.

On the other hand, females had greater base, crest breadth, and ridge height than males. Similar reports were published by (Kamburoğlu et al., 2015, Larrabee and Bevans, 2016). Differences in the outcome among the studies could be due to sample size, race and ethnic variation, and area of tooth studied.

U-type ridges in the molar area are a matter to be considered. In the present study, we have studied the first molars. If there are lingual concavities in this region, it may lead to untoward consequences. Severe bleeding may occur upon implant implantation in undercut kinds due to the lingual cortical plate (Leong et al., 2011). The infection may also extend to the retropharyngeal and parapharyngeal areas, with untoward consequences (Jaworsky et al., 2013). Airway blockage and death may result from vascular trauma-induced hemorrhage occurring after a period of inactivity (Leong et al., 2011). Thus, careful planning is needed during implant placement (Chan et al., 2011).

Our study is the first of its kind conducted in the Eastern Province of Saudi Arabia. Thus, the study's outcome is expected to help the clinician while planning an implant in the lingual concavity area of the mandible. However, there are limitations in the study. It was a cross-sectional study, and the sample was limited to the Saudi population from the Eastern Province of the Kingdom of Saudi Arabia. Increasing the sample size and comparing the Saudi vs non-Saudi population would have provided better clarity in the outcome. The different age group inclusion and age-wise categorization of the subject may have improved further understanding of the lingual concavity. Similarly, dentulous and edentulous category separation may allow comparison in the lingual concavity occurrence and variation. The findings of this study would be helpful for the presurgical treatment planning for Implant placement and avoiding bleeding, injury to the neurovascular structures, and lingual plate perforation in the mandibular lingual concavity area.

5. Conclusion

Within the limitations of the study, it can be concluded that:

• 1.U-type ridges were predominant (52.73 %) with more chances of occurrence of lingual concavity in the mandible.
• 2.There were no differences between the genders except in one parameter (VCB).
• 3.Further studies are required to explore more details about lingual concavity in the mandible.

Ethical Statement

The study was approved by the Ethical committee of Institutional Review Board (IRB) IRB # PGS-2024-02-129.

Funding statement

The study did not receive any specific grant from funding agencies in the Public, Commercial, or Not-for-Profit Sector.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.