The Gonial Angle as a Predictive Marker of Mandibular Fossa Depth: A Diagnostic Accuracy Study

doi:10.21203/rs.3.rs-1444489/v1

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The Gonial Angle as a Predictive Marker of Mandibular Fossa Depth: A Diagnostic Accuracy Study

https://doi.org/10.21203/rs.3.rs-1444489/v1

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Purpose

The aim of the study is to evaluate the relationship between submandibular fossa depth and gonial angle measurements in cone beam computed tomography examinations in terms of dental implant applications and whether the results can be transferred to panoramic radiographs.

Methods

Cone-beam computed tomography images of 51 dry human mandibles were included. Gonial angle and fossa depths were determined and evaluated separately for left and right sides. Gonial angle was measured on Cone-beam computed tomography images as the angle between the tangent line drawn posterior to the border of the ramus of the mandible and the tangent line drawn to the lower border of the mandible. Determination of the submandibular fossa depth was made with a line was drawn to connect the most dislocated upper and lower points on the inner surface of the mandible in the coronal plane sections, and the length of the line drawn at a right angle from the deepest point of the fossa to this line. Measurements were made separately for left and right sides.

Results

No statistically significant correlation was found between the angle measurement and the depth measurements from the left and right sides. There was no statistically significant correlation between mean angle measurement and mean depth measurement. No statistically significant correlation was found between all angle measurements and all depth measurements.

Conclusion

The mandibular gonial angle is not a suitable marker to be used to predict the depth of the submandibular fossa on panoramic radiographs.

Dental implants

Submandibular fossa depth

Gonial angle

Cone-beam computed tomography

Panoramic radiography

With the introduction of dental implants and the introduction of the term osseointegration, dental implants have begun to be widely used in the treatment of edentulism in an accepted and predictable manner [1, 2]. Although the osseointegration processes of dental implants are predictable today, implant planning should be carried out meticulously due to anatomical limitations and restorative requirements. Proper positioning and angling of the implants during surgery will bring success together and this success will continue in the prosthetic treatment phase to be passed after [2]. However, one of the indispensable criteria for successful surgical placement of dental implants is the preservation of anatomical structures. Damage to anatomical structures can lead to serious surgical complications and implant failure [1].

Bone mass and morphology and neighborhood to important anatomical structures are important diagnostics in preventing surgical complications that may occur. These diagnostics will determine the diameter, length and insertion angle of the implant to be selected and may alter the initial treatment plan [3].

Anatomy of the posterior mandible, which is frequently treated with dental implants due to edentulism, is a high-risk area for surgical complications due to the variable anatomy of the mandibular canal and submandibular fossa [1, 4]. Numerous severe complications have been reported concerning this are [2]. These risks include injury to the mandibular canal and lingual plate perforation and violation of these structures may cause serious complications in neighboring vital anatomical structures. Injury to the mandibular canal and the neurovascular bundle within may result with neurological defects. This may lead to temporary or permanent paralysis or numbness of the chin and corner of the mouth [1, 4]. The floor of the mouth is vascularized by the sublingual and submental arteries and associate closely with the lingual plate. Perforation of the lingual plate therefor, can cause arterial trauma, leading to hematoma formation in the sublingual and submandibular spaces, especially in patients with atrophic mandibles. Infection and in time, dental implant loss that may occur as a result of damage to these structures can also be added to these complications. The anatomical structure of the submandibular fossa should be detailed before the procedure [1, 2, 4].

During dental implant planning for the posterior mandible, various techniques for examining anatomical structures have been reported such as intraoral palpation of the alveolar ridge, using an osteometer, preparing diagnostic casts, examination of intermaxillary relations, the use of conventional radiographs and advanced imaging methods. However, today conventional intraoral (periapical) / extraoral (panoramic) radiographs are determined as the minimum requirement for dental implant assessment [2].

Presurgical imaging provides very important information in the pre-operative examination of the posterior mandible, in determining the area where dental implant will be placed and its placement angle and to avoid the surgical complications mentioned in the previous paragraphs. This information plays an important role. While determining the submandibular fossa depth, the osteometer is reported to be and inappropriate method. Similarly, dental castes are limited in use as they can only represent the area above the floor of the mouth. Clinical palpation of the submandibular fossa depth is also reported to be of variable use [2].

The aim of the present study is to evaluate the relationship between submandibular fossa depth and gonial angle measurements in CBCT (Cone-beam computed tomography) examinations. According to the results of the evaluation, it will be determined whether the width of the gonial angle gives information about the depth of the submandibular fossa. This knowledge may provide supplementary information for clinicians using solely panoramic radiographs, or when CBCT options are not present.

Ethics approval

was obtained from the Clinical Research Ethics Committee of the Faculty of Dentistry of Ankara University (Approval no: 13/1, NCT:04800003). All authors have read the Helsinki Declaration and have followed the guidelines in this investigation. The study was carried out in the Faculty of Dentistry of Ankara University during July-August 2019.

In the present diagnostic accuracy study, 75 dry human mandibles were used. 24 dry human mandibles with insufficient bone integrity to make the necessary measurements or which were dentate in the posterior region were not included in the study and the study was carried out with 51 dry mandibles. Data on age, gender, and duration of edentulism of the dry mandibles were not available. CBCT images of the 51 dry human mandibles included in the study were obtained using the Planmeca Promex-3D (Helsinki, Finland) device in our faculty Dentomaxillofacial Radiology department. CBCT scans of the mandibles were made using 13x9 cm FOV (Field of view) size 96.0 kVp, 7,1 mA, 12 seconds, 0.200mm³. All of the images were analyzed on a 21.3 inch flat-panel color active-matrix TFT medical display (MultiSync MD215MG; NEC) with a resolution of 2048x2560 at 75 Hz and 0.17 mm pixel pitch and grey scale reproduction at 11.9 bits. A senior dentomaxillofacial radiologist made all measurements. Gonial angle and fossa depths were determined and evaluated separately for left and right sides. Gonial angle was measured on CBCT images as the angle between the tangent line drawn posterior to the border of the ramus of the mandible and the tangent line drawn to the lower border of the mandible. (Fig. 1) These angle measurements were noted as 'degree' separately for left and right sides. While determining the depth of the submandibular fossa, a line was drawn to connect the most dislocated upper and lower points on the inner surface of the mandible in the coronal plane sections obtained with CBCT, and the length of the line drawn at a right angle from the deepest point of the fossa to this line was measured as the depth of the submandibular fossa. (Fig. 2) These measurements were noted as 'millimeters' separately for left and right sides.

Statistical analysis

Data analysis was performed by using IBM SPSS Statistics version 17.0 software (IBM Corporation, Armonk, NY, USA). Whether the distributions of continuous variables were normal or not was determined by Kolmogorov-Smirnov test. Descriptive statistics were expressed as mean ± SD (min - max). Degrees of association between continuous variables were evaluated by Spearman’s rank correlation analyses. A p value less than 0.05 was considered as statistically significant.

Descriptive statistics for angle and depth measurements are presented in Table 1. Correlation coefficients and significance levels between angle and depth measurements are presented in Table 2. Correlation between the submandibular fossa depths and gonial angles are presented in Fig. 3.

Table 1

Descriptive statistics for angle and depth measurements.
	n	Mean	Standard deviation	Minimum	Maximum
Angle
Right mandible	51	123,74	8,58	103,25	141,90
Left mandible	51	127,51	8,34	107,10	142,40
Mean	51	125,63	7,02	105,20	140,85
Total	102	125,63	8,63	103,25	142,40
Depth
Right mandible	51	1,78	0,92	0,30	4,88
Left mandible	51	1,55	0,82	0,20	3,82
Mean	51	1,67	0,81	0,50	3,83
Total	102	1,67	0,88	0,20	4,88

Table 2

Correlation coefficients and significance levels between angle and depth measurements.
	n	Correlation coefficients
Right mandible	51	0,038	0,790
Left mandible	51	0,054	0,708
Mean	51	0,021	0,886
Total	102	0,014	0,889
† Spearman's rank correlation analyses.

No statistically significant correlation was found between the angle measurement from the right side and the depth measurement (r = 0.038 and p = 0.790). No statistically significant correlation was found between the angle measurement from the left side and the depth measurement (r = 0.054 and p = 0.708). There was no statistically significant correlation between mean angle measurement and mean depth measurement (r = 0.021 and p = 0.886). No statistically significant correlation was found between all angle measurements and all depth measurements (r = 0.014 and p = 0.889).

The most common and serious complications in implantology occur during the surgical procedure. There may be many factors behind the development of these complications, such as inadequate preoperative preparation, implant contamination, overprocessing of the bone, and error in implant orientation [5].

Preoperative preparation includes a detailed examination of the anatomy of the bone. The submandibular fossa is a commonly encountered and important anatomical structure that should be discovered during this examination. The submandibular fossa is a bony depression located in the posterior part of the mandibular bone, on the medial surface, beneath the mylohyoid line. As the depth of the submandibular fossa increases, the risk of perforation in the lingual cortex, vascular trauma and bleeding during implant surgery increases. The subsequent formation of hematoma, persistent inflammation or infection which may result from the exposed oral environment due to perforations of the lingual oral mucosa, can bring about situations that are difficult to cope with. In daily surgeries, it is thought that the rates of perforation in the lingual cortex are much higher than reported, since most go unnoticed [5].

Although computed tomography has defined itself as an excellent method for defining the anatomy, anomalies and pathologies of the jaws, the newly introduced CBCT method has become used in dental implant surgery planning [6]. CBCT provides 3-dimensional images for presurgical evaluation but have higher radiation doses then conventional radiography [2, 7].

Panoramic radiographs give information about bone height and bone thickness to some extent, although they only provide two-dimensional information and image distortion, and magnification may occur [7]. However, some authors argue that CT (Computerized tomography) or CBCT are not necessary in all cases, and panoramic radiographs may be preferred [8]. Panoramic radiography is easier to access, have relatively shorter exposure times and a cheaper option and is used frequently for preoperative evaluation; many still evaluate the edentulous site solely on periapical and/or panoramic radiographs [2, 3, 9].

The study by Sumer et al. evaluating the relationship between visibility of the submandibular region on panoramic radiography with the depth of the submandibular fossa could not find any correlation and that panoramic radiographs were not reliable for determination of the depth of the submandibular fossa [10]. Another morphological study on lingual concavities of the mandible as determined by CBCT reported that the deep location of the inferior alveolar nerve close to the basal cortical bone was associated with a deep submandibular fossa. They also mentioned that although panoramic radiographs do not provide data on bucco-lingual bone dimensions, they are reliable in determining the position of the inferior alveolar nerve for dental implant planning [11]. Combining these two conditions, it can be concluded that the deep location of the inferior alveolar nerve on panoramic radiographs may be a marker for a deep submandibular fossa. Based on a similar logic, in the present study, a marker that could explain the depth of the submandibular fossa was searched on panoramic radiography and for this purpose the gonial angle was focused on. The reason for choosing the gonial angle as a marker is its anatomical neighborhood to the submandibular fossa and its easy measurement on panoramic radiographs, if a relationship could be established. However, this relationship could not be established. Establishing this relationship could have been used in dental implant surgery planning and increasing the safety of panoramic radiographs.

Morphological and anatomical changes occur in the mandibular bone depending on age, sex and edentulism. On panoramic radiographs, the differences in the gonial angle caused by the change of these data were investigated by Okşayan et al. and no statistically significant difference was found [12]. Nevertheless, the mean gonial angle measurement was higher in edentulous patients. The present study was conducted on dry mandibles which, data of age, gender and edentulism times were not present. The authors note the absence of these data as limitation of the study and point out that further studies involving these data should be conducted.

An oral surgeon should have a good knowledge of mandibular anatomy. Benefiting from the correct imaging methods while planning dental implant surgery will affect the success of the treatment. Careful evaluation and correct planning before surgery will prevent lingual perforations that may occur in the posterior region of the mandible. The results of the present study do not support the use of the gonial angle to assess the depth of the submandibular fossa on panoramic radiographs. In cases where deep submandibular fossa is suspected, it is recommended to add other imaging methods such as CT and CBCT to the minimum requirement panoramic radiographs.

CBCT

Cone-beam computed tomography

Computerized tomography

FOV

Field of view

Ethics Approval and Consent to participate: Ethics approval was obtained from the Clinical Research Ethics Committee of the Faculty of Dentistry of Ankara University (Approval no: 13/1). Not applicable: No human or animal subjects were recruited in the study.

Consent for publication: All authors have consented for the publication of the study.

Availability of data and material: NCT:04800003

Competing Interests: The authors declare that they have no competing interests.

Funding: No source of grant or funding was obtained for the study.

Authors’ Contributions: MEK was a major contributor in identifying the study protocol, writing the manuscript and performed analysis of the data. PB was a major contributor in identifying the study protocol, writing the manuscript and obtained the mandibles for the study. US was a contributor in writing the manuscript and performed CBCT scanning’s of the mandibles. All authors read and approved the final manuscript.

Acknowledgements: Authors would like to thank Dr. Ayhan Cömert and Dr. Selda Yıldız for their help in obtaining the dry mandibles used in the study.

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Kim MJ, Lee SS, Choi M, Ha EJ, Lee C, Kim JE, Heo MS (2020) Development of an evidence-based clinical imaging diagnostic guideline for implant planning: Joint recommendations of the Korean Academy of Oral and Maxillofacial Radiology and National Evidence-based Healthcare Collaborating Agency. Imaging Sci Dent 50(1):45.
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No competing interests reported.

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The Gonial Angle as a Predictive Marker of Mandibular Fossa Depth: A Diagnostic Accuracy Study

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Abstract

Purpose

Methods

Results

Conclusion

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Background

Materials And Methods

Results

Discussion

Conclusions

Abbreviations

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References

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