Exploring a three-dimensional analysis method to occlusion plane determination: A retrospective study

doi:10.21203/rs.3.rs-4708751/v1

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Exploring a three-dimensional analysis method to occlusion plane determination: A retrospective study

https://doi.org/10.21203/rs.3.rs-4708751/v1

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Background

The available literature lacks comprehensive guidance on constructing the occlusal plane within the broader facial and skeletal context. This study aims to accurately determine the occlusal plane (OP) within the normal population through three-dimensional data analysis using cone-beam computed tomography (CBCT) and specific feature points alignment.

Material and methods

One hundred patients underwent both clinical evaluation and CBCT imaging examination. A digital model was constructed based on the imaging data, delineating a virtual occlusal plane (V-OP), a virtual Frankfort plane (V-FP), and a virtual plane formed by two camper lines (V-CL) using specific feature points. Two angles, formed by V-OP and V-FP, as well as V-OP and V-CL, were computed using the angle measurement function in Geomagic Control X. The angular relationship between V-OP and the angular bisector plane (ABP) of V-FP and V-CL was determined through calculations using the aforementioned data. Ordinary two-way ANOVA with post hoc Sidak’s multiple comparisons was performed (p < 0.05).

Results

The mean ± standard deviation of the angle between V-FP and V-OP is 8.94° ± 4.22°, and it is 4.82° ± 3.07° between V-CL and V-OP. In comparison, the mean ± standard deviation of the angle between ABP and the occlusal plane was 3.12° ± 1.78°, lower than that of the former two groups.

Conclusions

The ABP and OP are nearly parallel, suggesting stability across different patients, making it a reliable reference for digital dental alignment.

Trial registration

This study was registered in the Chinese Clinical Trial Registry as “Exploring the Method of Determining the Occlusion Plane in 3D Data Analysis: A Retrospective Study” (No. ChiCTR2300077289) on November 3rd, 2023 (https://www.chictr.org.cn/searchproj.html?regno=ChiCTR2300077289).

Occlusal plane

Three-dimensional analysis

Cone-beam computed tomography (CBCT)

Anatomical landmarks

In clinics, constructing a stable and healthy occlusal plane is an important step in manufacturing complete dentures for patients needing dental treatment; such construction is achieved by cooperation between orthodontists, surgeons, and prosthodontists [1]. The occlusal plane is typically considered a surface that passes through incisal edges and occlusal surfaces of the teeth [2]. The occlusal surface is a virtually common plane established by the occlusal surfaces of the teeth. The direction of the occlusal plane in edentulous patients is crucial for achieving aesthetic results in denture treatment. For complete denture wearers, achieving functional balance occlusion is crucial, and the direction of the occlusal plane should be as close as when natural teeth are present. Therefore, the occlusal plane position of the denture wearer should simulate the previously established position of the patient's natural teeth.

With the development of digital technology, the production of fixed dentures has also transformed into computer-aided design and production[3]. Digital technology is more widely used in dental implants and restoration technologies, evident in techniques such as intraoral scanning and facial scanning. The application of cone-beam computed tomography (CBCT) is more extensive, and its three-dimensional reconstruction function greatly reduces the difficulties in the treatments of the jaw and occlusion[4].

The occlusal plane forms the foundation of the ideal tooth arrangement, meets the necessary aesthetic and mechanical requirements, and helps to achieve appropriate oral function. In the manufacturing of complete dentures, the position of the occlusal plane can be determined according to various soft and hard tissue characteristics and the judgment of clinicians. In clinical practice, the achievement of this goal is mainly determined by the experience of physicians and chair-side technicians, which are often influenced by past judgments of facial contours or intraoral soft-tissue contours[5]. The literature provides several markers of evidence for clinical dentists to determine the most acceptable position of the occlusal surface. According to reports, the occlusal plane can be repositioned through different methods, such as using anterior aesthetic considerations and parallel to the camper’s line (CL) backward; positioning it parallel to the residual ridge; orienting it to the junction of the cheek sulcus and lips; and terminating it backward in the middle or upper third of the molar pad and positioning it at the same level as the lateral boundary of the tongue in a 2-dimensional flat image[6]. However, previous methods were inaccurately used to reposition the occlusal surface, and the evaluation criteria are also relatively subjective[5].

Currently, no scientific literature agrees on which plane reference to use in constructing the occlusal plane in the facial and bone context. Moreover, the judgment of these soft tissues is imprecise enough to the extent that some patients may need to modify the occlusal relationship multiple times after completing implant repair to achieve functional perfection and aesthetic satisfaction. Thus, further studies to help clarify dentists’ decision-making process during the rehabilitative diagnosis process are urgently needed[7].

In this study, we proposed to accurately determine the occlusal surface within the normal population through three-dimensional data analysis using CBCT and matching some feature points. These feature points were selected based on the jawbone projection or approximate point positions of the body surface markers mentioned in the above literature. We hope to assist clinical physicians in more accurately constructing the occlusal surface of edentulous patients through this exploration.

1. Study design

The current cohort study was conducted in full compliance with the 2013 revision of the 1975 Helsinki World Medical Association Declaration. The protocol was approved by the Ethics Committee of Shanghai Stomatological Hospital, Fudan University (No. [2023]013). This study was registered in the Chinese Clinical Trial Registry as “Exploring the Method of Determining the Occlusion Plane in 3D Data Analysis: A Retrospective Study” (No. ChiCTR2300077289) on November 3rd, 2023.

2. Patient selection

One hundred patients were recruited in this study based on the following inclusion criteria:

(1) Systematically healthy patients with stable occlusal contact.

(2) No orthodontic treatment.

(3) A CBCT radiographic exam was necessary.

Patients with periodontal diseases were excluded, and all patients signed a written informed consent statement.

3. Sample size calculation

The sample size in this study was estimated according to the methodology used in a previous study wherein the 2-dimensional measurement of the maxillofacial angle plane was measured in 75 patients with positions similar to those in the current study[8, 9]. The data from the previous study showed that the angle between the occlusal plane was 5.12° for the MAT group and 10.6° for the FH group, and the effect size was estimated as 26. Based on the abovementioned information, a sample size of 13 per group was estimated for the present study to have a power > 90%, a significance level of α = 0.01, a group dropout rate of 20% and an effect size = 34 through a two-tailed t test using PASS software. Considering the possibility of a loss to follow-up rate, a sample size of 100 was included in this study[10].

4. Clinical procedures and data acquisition

Before implant placement surgery, the included patients received a clinical evaluation of their whole dentition and occlusion according to the above patient selection. Subsequently, each patient underwent an auricular registration during a CBCT examination. The CBCT image was output as digital imaging and communications in medicine (DICOM) format files and subsequently converted into a maxillofacial bone Standard Template Library (STL) file in Mimics software. After the conversion, the STL file was imported into the 3-dimensional model measurement software (Geomagic® Control XTM, 3D Systems, Rock Hill, South Carolina, USA) for data acquisition (Fig. 1).

5. Data acquisition and analysis

A virtual occlusal plane (V-OP) was used to evaluate the occlusal plane of dentate subjects from all digital models of patients, determined by three points, the mesial buccal cusp tip of the maxillary molars on two sides (U6) and the adjacent point of two central incisors (U1). A virtual Frankfort plane (V-FP) is composed of the most superior point of the external auditory meatus and the orbital point referring to the Frankfort plane (FP). Another virtual plane (V-CL) was determined by the camper’s lines (CL), which were composed of the portions and the outermost points on both sides of the pyriform foramen (Fig. 2).

Two angles formed by the V-OP and V-FP and by the V-OP and V-CL were calculated by the angle measurement function in the digital model software[11]. The angular relationship between the V-OP and the angular bisector plane (ABP) of the V-FP and V-CL was calculated from the above data (Fig. 2). All measurement operations were completed by two inspectors (Jiabi Xiong and Xiu Yao), and the final result was obtained by averaging the measurements of the two inspectors.

6. Statistical Analysis

Statistical analyses were performed using SPSS 26.0. Data are presented as the means ± standard deviations. An ordinary two-way analysis of variance (ANOVA) with post hoc Sidak’s multiple comparisons was performed. The significance level was set at p < 0.05.

The study is in compliance with the STROBE guidelines.

One hundred patients were recruited for this study based on the inclusion criteria. The main clinical characteristics of the patients are summarized in Table 1. The Shapiro‒Wilk test demonstrated that the descriptive statistical parameters in each group were normally distributed. The mean ± standard deviation of the angle between the V-FP and the V-OP is 8.94°±4.22°, which is 4.82°±3.07° between the V-CL and the V-OP. Compared to that of the above two groups, the mean ± standard deviation of the angle between the ABP and the occlusal plane was 3.12°±1.78°, which was lower than that of the above two groups (Table 2, Fig. 3). To estimate possible relationships between 3 angles and clinical parameters (sex and age) in the 100 candidates, correlation analyses were performed (Table 3, Fig. 4). Correlation analyses revealed a statistically significant moderate correlation between the V-CL and age and between the V-CL and sex (p < 0.01). Moreover, we found a moderate correlation between V-FP and sex (p < 0.05), whereas there was no significant correlation between ABP and age or sex.

Table 1

The main clinical indices of patients (n = 100)
Clinical indices		Results
Age (years)		41.04 ± 11.67
Gender	Male(cases)	41 41.00%)
Gender	Female(cases)	59 (59.00%)

Table 2

The mean angle between each plane and the occlusal plane (n = 100)
		Mean ± SD	95% CI	Min-Max	p-value ^b	Multiple comparison ^c
Angle (°)	V-FP	8.94 ± 4.22	8.10–9.78	0.65–20.67	< 0.001	ABP < V-FP(<0.001) ABP < V-CL༈<0.001༉ V-CL < V-FP༈<0.001༉
	V-CL	4.82 ± 3.07	4.22–5.43	0.13–15.01
	ABP	3.12 ± 1.78	2.77–3.48	0.15 − 6.59
a. V-FP: The virtual Frankfort plane, V-CL: The virtual Camper’s plane, ABP: The angular bisector plane, V-OP: The virtual occlusal plane.
b. One-way ANOVA (p < 0.05)
c. Bonferroni method was used to compare the multiple means for homogeneity of variance; Tamhane's T test was used to compare the multiple means for heterogeneity of variance.

Table 3

Correlation analysis between each plane and age or gender
Plane ^a	Age ^bc	Gender ^bc
V-FP	r = 0.12, p = 0.5085	r = 0.21, p = 0.0381
V-CL	r=-0.39, p = 0.0002	r=-0.26, p = 0.0183
ABP	r = 0.02, p = 0.8007	r = 0.15, p = 0.0742
a. V-FP: The virtual Frankfort plane, V-CL: The virtual Camper’s plane, ABP: The angular bisector plane, V-OP: The virtual occlusal plane.
b. Pearson correlation analysis (p < 0.05). The table contains the value of the correlation coefficient (r) among various variables. The correlation coefficient is generally between − 1 and 1. The positive and negative signs indicate the positive correlation and the negative correlation.
c. The general relationship strength was as follows: \|r\|>0.95: significant correlation; \|r\|≥0.8: highly correlated; 0.5≤\|r\|<0.8: moderately correlated; 0.3≤\|r\|<0.5: low correlation; \|r\|<0.3: weak correlation.

The ideal occlusal plane is crucial for the aesthetics and function of dentures and has a long-term impact on the protection of oral soft and hard tissues, as well as on the lifespan of dentures. The outcomes for both patients undergoing dental restoration treatment and those undergoing implant-supported fixed restoration are affected by the occlusal plane[12]. The traditional method in a biofunctional complete denture restoration system (BPS) for determining the occlusal plane is generally based on the FP, while for functional dentures, the camper’s line is used as a reference[13]. However, neither the FP nor the camper’s line is horizontal to the patient’s natural occlusal position. This leads to deviation when the occlusal plane is transferred. Such an error can lead to incorrect occlusal plane reproduction, prosthetic instability, reduced chewing capacity, and occasional occlusal contacts[12].

Our study utilized preoperative CBCT images taken by patients to identify skeletal landmarks and connect them into a virtual plane, which then served as a reference for the occlusal plane of implant-supported fixed dentures in patients. In this study, we measured an angle of 8.94° ± 4.22° between the V-FP and the V-OP and an angle of 4.82° ± 3.07° between the plane determined by the V-CL on both sides and the occlusal plane. Similar to previous studies, the present study determined that neither the V-FP nor the plane determined by the V-CL is horizontal to the patient’s V-OP. Interestingly, when we calculated the angle between the ABP of the two planes and the V-OP, which was 3.12° ± 1.78°, the parallelism of the natural V-OP with ABP was determined. Moreover, the anatomic relationship of the data with patient age and sex was also explored and indicated a meaningful discovery that, compared with V-CL and V-FP, the result of ABP is relatively stable and may be used as a digital technology reference for occlusal planes.

With the development of digital technology, the production of fixed dentures has also transformed into computer-aided design and production[3]. The determination of the occlusal plane has also become a challenge. Some scholars refer to the pupil line, mouth angle line, and bisected occlusal distance in patients' photographs to roughly determine the position of the occlusal plane; however, the photographs are all two-dimensional and significantly deviate from the actual situation[6]. Some scholars also use traditional methods to determine the occlusal plane by matching patients' facial scans, CBCT data, and intraoral scan data^{[14, 15]}. However, there are significant errors in data registration, and any deviation from the ideal occlusal plane may lead to functional and/or esthetic deficiency^[16]. In addition, clinical dentists create removable dentures based on their clinical experience, restoring the patient's ideal occlusal plane through actual eardrums and nasal alar connections, and then scanning and transforming it into a digital model. The digital model is then used as a reference in the computer to enable the restoration of the ideal occlusal plane. This method is relatively accurate, but the process is cumbersome, requiring repeated debugging and a more tedious time than desired.

One of the limitations of this study was the lack of consideration of the changes occurring in the morphological characteristics of skeletal tissue in different races, as the study was carried out only among Asian individuals. Moreover, due to the subtle differences in the human body structure, it is still necessary for dentists to take cephalometric variables, such as posterior facial height and curve of Spee, into account and make personalized adjustments for patients after determining the occlusal plane through digital technology. These shortcomings urgently need to be addressed through future research. Moreover, this method still needs to be further investigated and verified in future studies and clinical applications.

It is recommended that dentists should reestablish the occlusal plane in edentulous patients by using the plane between the ABP of the V-FP and the plane determined by the V-CL. This method can be used to directly devise a set of dentures that are more in line with the aesthetics, function, and biomechanics of the patients. This may prevent deviation in the digital occlusal plane due to the diverse experience of the technician and further prevent the technician from adjusting repeatedly and performing tedious scanning steps in the patient's mouth. Moreover, the data can be used as a reference for the final fabrication of the denture occlusal plane.

According to our research, the angles between the V-OP are 8.94°±4.22° with the V-FP and 4.82°±3.05° with V-CL, respectively, which results in an angle of 3.12°±1.78° between the ABP and V-OP. The ABP and occlusal plane are almost parallel. Moreover, the anatomic relationship of the data with patient age and sex indicated that the result of ABP is relatively stable in different patients. Therefore, these data could fully serve as a reference occlusal plane for digital dental alignment.

CBCT: Cone-beam computed tomography

OP: Occlusal plane

V-OP: Virtual occlusal plane

V-FP: Virtual Frankfort plane

V-CL:Virtual plane formed by two camper lines

ABP: Angular bisector plane

ANOVA: Ordinary two-way analysis of variance

Ethics approval and consent to participate

The present study was designed as a cohort study and conducted in accordance with the Helsinki Declaration of 1975 and revised in 2013. The protocol has been approved by the Ethics Committee of Shanghai Stomatological Hospital, Fudan University (No. [2023]013).

This study was registered in the Chinese clinical trial registry (No. ChiCTR2300077289, 2023-11-03).

All of the procedures were explained to each participant in a quiet room before their recruitment in the study, and patients were asked to sign a written informed consent.

Consent for publication

Not applicable.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request ([email protected]).

Competing interests

The authors declare that they have no competing interests.

Funding

This study was generously supported by Shanghai Nature Foundation (No. 202240275).

Author contributions

Jiabi Xiong and Zhengjie Dong conceived the idea and designed the experiment; Jiabi Xiong, Xiu Yao and Zhengjie Dong performed clinical operations and data collection; Jiabi Xiong and Xiu Yao analyzed the data and wrote the manuscript; Xiaoming Xu and Zhengjie Dong supervised the project and edited the manuscript; All authors have read and approved the content of the manuscript.

Acknowledgements

The authors would like to acknowledge Mr. Zhicheng Gong and Mr. Xi Zhu for their great assistances in software acquisition and data collection, respectively.

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No competing interests reported.

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You are reading this latest preprint version

Exploring a three-dimensional analysis method to occlusion plane determination: A retrospective study

Status:

Version 1

Abstract

Figures

Introduction

Materials and methods

1. Study design

2. Patient selection

3. Sample size calculation

4. Clinical procedures and data acquisition

5. Data acquisition and analysis

6. Statistical Analysis

Results

Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

Status:

Version 1