Background
Occlusion is closely related to oral health and considered as an important indicator of the functional status of the masticatory system [
1,
2]. Occlusal analysis plays an important role in the diagnosis, treatment and prognosis evaluation in the field of prosthodontics [
3,
4], orthodontics [
5‐
7], implants [
8], maxillofacial surgery [
9], etc.
Every improvement in occlusal analysis methods has brought great changes to dental practice. Generally, the content of occlusion analysis should include occlusal contact area (OCA), occlusal contact number (OCN) and occlusal force. The articulating paper has always been a traditional tool for occlusal analysis, and is widely used in clinical practice because of its simplicity and intuitiveness. However, the size and distribution of occlusal contact can only be determined according to the doctor's experience [
10]. It can not be used for quantitative analysis.
In recent years, the advent of occlusal analysis systems such as the T-scan system [
11], Dental Prescale system [
12], Blue Silicone system [
13], etc. makes quantitative measurement possible. These systems use a media, such as silicone, PTE film or piezoelectric transducers, to analyze occlusal contact. For example, Dental Prescale occlusion analysis system uses a pressure-sensitive film with polyethylene terephthalate (PET) shells, which contains a pigment layer which consists of small dye capsules and a colour development reagent layer. When pressure is applied to film, the dye capsule ruptures and releases the colourless dye to mix with the substance in the colour development layer, thus presenting colour changes at where under the pressure [
14]. The colour changes can be interpreted in the software to calculate the occlusal force value of each occlusal contact point. It can obtain the OCA values and absolute values of occlusal forces [
15‐
17]. However, the data obtained on the two-dimensional level of these systems can not directly correspond to the tooth surface with three-dimensional profile, therefore the clinical guidance value is limited.
The rise of digital technology has brought new ideas to the development of dental analysis instruments [
18‐
22]. The intra-oral scanners allow dentists to obtain three-dimensions digital models of the dentition directly [
23,
24], with the advantages of high accuracy, enhanced patients’ comfort and possibility of quantitative analysis [
25,
26]. As an important part of digital workflow, digital analysis software provides powerful function for the measurement of distances, areas, coordinates, errors, etc. [
27,
28]. In recent years, the integration of digital technology into occlusal analysis has led to the development of occlusal analysis methods based on 3D dental models [
29]. The advent of these methods has made it easier to quantify OCA, etc., however, the analysis of bite force is still lacking.
A combination of the 3D dental models obtained by intraoral scanning and quantitative data from 2D occlusal contact analysis, make it possible for quantitative analysis of occlusal contact and force simultaneously. This study constructed a novel digital occlusal analysis method which can not only be used to locate the occlusal contact on the tooth surface, but also to make quantitative analysis of OCA, OCN and occlusal contact force of each teeth, or part of dentition.
This study consists of two parts. Firstly, the consistency of used 2D and 3D methods was evaluated in vivo. After confirming the consistency, these two methods were used to construct a novel occlusal analysis system.
Discussion
Occlusal contact analysis, including the location of contact, OCA, OCN and occlusal force of each tooth, is essential in dentistry, especially in prosthetics and orthodontics, as maintaining the balance of occlusal contact and force of the teeth or prosthesis is the goal of the occlusal adjustment. However, there is still a lack of a convenient and reliable method which can achieve the abovementioned occlusal contact information simultaneously. In this study, after verifying the consistency between the 2D and 3D occlusion analysis systems, we have developed a novel occlusion analysis method to locate occlusal contact and quantitatively analyze OCA, OCN and occlusal forces of each tooth.
In evaluation trial, the reliability and validity of two analysis techniques were evaluated. The results indicated that the ICC values obtained from two systems were higher than 0.9, which indicated high stability for both two systems. Paired t-tests demonstrated no significant difference in the OCN values obtained from the DP and SA analysis. The following Bland–Altman test showed good consistency between the results of the two systems. Therefore, it can be considered that these two methods have a high consistency in measuring the OCN. In measuring OCA, although paired t-test showed that a significant difference between the data obtained from these two analysis systems, a significant correlation was indicated by Pearson correlation analysis. The result that the OCNs were the same while the OCAs were proportionally enlarged may be due to the influence of the media used in the analysis systems. The pressure sensitive film of DP comprises three layers of PET, which is more resistant to compression deformation than articulating papers. In addition, the dye of the articulating paper has spreading ability in the presence of saliva [
30,
31]. Thus, the stained area of articulating paper might extend beyond the actual occlusal contact area. From this point of view, the difference OCA values did not affect the distribution of the occlusal contact as similar OCN values were found. In clinical demonstration, analysis of the occlusal forces showed that the occlusal forces changed in response to the tooth position. Usually, the first molar is subjected to the greatest force. However, for this patient with bruxism, the second molar is subjected to the greatest occlusal force during occlusion. This anomaly results in more wear of the cusps of the second molar. Furthermore, we can clearly see from the data how the teeth are subjected to forces in different directions. For example, the patient's second molar teeth on the left and right side have opposite directions of force in the
y-axis, which cannot be identified in a two-dimensional force analysis. Many oral diseases are caused by imbalance in occlusal forces and it is easy to misdiagnose the two forces as the same based on the force values alone. The identification of the direction of force will be of great help in the treatment and diagnosis of diseases.
The difference between the 2D analysis results and the 3D dentition, caused by the loss of spatial information, will cause inconvenience in the clinical application of these occlusal analysis systems [
32]. For example, quantitative analysis results (OCA or occlusal contact force) from T-scan and DP can not be used directly to locate the occlusal contact on the surface of teeth in clinical practice. In recent years, with the introduction of digital technology into dental practice, some 3D occlusal analysis systems were designed [
33,
34]. For example, the occlusal contact analysis function that comes with the intraoral scanner, the transillumination technique used in the study by DeLong et al. [
32] and the virtual occlusion analysis system proposed by Li et al. [
35]. These methods achieved quantitative analysis of the OCA in three dimensions, however, they did not include the function of occlusal force analysis. After verifying the consistency between the two systems in detect occlusal contact, we constructed a 3D occlusal analysis method system by combining the advantages of respective systems. This new method not only achieved a 3D spatial location of occlusal contact points, but also combined the force analysis function to make a powerful and quantitative evaluation of occlusal contact of nature teeth or prosthesis. These innovations provide clinicians with more realistic and comprehensive information on occlusal contact, which would improve the accuracy of clinical diagnosis and treatment, as well as improve their clinical decision-making ability.
Another potential advantage of this novel occlusal analysis method is that it is more accurate and flexible in occlusal force analysis. It can not only decompose the bite force, but also specify the direction of force division as required. These characteristics have not been reported in previous studies. Prado et al. [
36] applied T-scan to three-dimensional dentition analysis with the help of oral appliances. However, oral appliances increase the inconvenience of occlusion collection. In addition, due to the limitations of the T-scan [
37], it can only display the relative value of the force and cannot obtain the absolute magnitude of the occlusal force, let alone the decomposition of the occlusal force. The study by Hattori et al. proposed a method to set the occlusal force value and direction and initially constructed a 3D occlusal force analysis system. However, its arithmetic is quite complicated and cannot be flexibly adjusted to clinical needs [
38]. In our study, the constructed method could allow analytical calculations of the magnitude of the occlusal forces in the proximal-distal or buccolingual directions or any other direction required, as well as the magnitude of the fractional forces on individual tooth or combinations of several teeth in different directions, as required. It is worth noting that the calculation of the magnitude of forces in directions specific direction, such as proximal, distal, buccolingual and others, is of great importance in clinical practice, especially in prosthetic treatment, because abnormal forces can lead to occlusal instability and damage.
In addition, as the pressure-sensitive film and intraoral scanning techniques used in this method are simple to operate, this new occlusal analysis method has the potential advantages of simple operation and intuitive analysis results. Occlusal contact analysis methods in previous studies are unable to visualize the direction and magnitude of the occlusal forces. In the constructed method in this study, the length of the line segment to simulate the magnitude of the occlusal force and the direction of the line segment to illustrate the direction of the occlusal force. This allows for a more visual presentation of the results of the occlusal analysis and facilitates clinical work, for example, in presenting and explaining the abnormal occlusal conditions to patients.
Although the new method system has several potential advantages mentioned above, there are also some limitations that need to be further studied. At this stage, this 3D occlusal force analysis method needs to be constructed manually and the simulation of occlusal forces at each occlusal contact point repeats the same operational steps. In future research, we will try to apply artificial intelligence and other methods to realize the automation of these operations, and further improve the efficiency and automation level of the new method. Besides, the inability to obtain dynamic occlusal force changes throughout mandibular movements is also the limitation of the system. To address this issue, more computer-aided simulation and occlusal analysis tools are needed.
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