Development and Application of a Simplified Bite Force Measuring Device

In orthodontic treatment for children, a method has been recommended to strengthen bite force by chewing a tube in a certain rhythm for five minutes every day. However, ensuring that children keep the training daily is difficult due to repetitive, monotonous movements. Additionally, it is not easy for guardians to keep monitoring and ensure that children are doing the training properly, biting the tube with appropriate force. Therefore, we aim to develop an interactive serious game that utilizes bite force as an input device, allowing children to continue training properly and allowing guardians to monitor their training situation easily. This study introduces a simplified tube-based bite force measurement device to assess and record the force of the bites, as well as training games using the device.


ABSTRACT
In orthodontic treatment for children, a method has been recommended to strengthen bite force by chewing a tube in a certain rhythm for five minutes every day.However, ensuring that children keep the training daily is difficult due to repetitive, monotonous movements.Additionally, it is not easy for guardians to keep monitoring and ensure that children are doing the training properly, biting the tube with appropriate force.Therefore, we aim to develop an interactive serious game that utilizes bite force as an input device, allowing children to continue training properly and allowing guardians to monitor their training situation easily.This study introduces a simplified tube-based bite force measurement device to assess and record the force of the bites, as well as training games using the device.

CCS CONCEPTS
• Human-centered computing → Interface design prototyping.

INTRODUCTION
Orthodontic treatment is efficacious in improving teeth' alignment and facial distortions, jaw movements, oral functions, and social adaptability [4].It pulls great interest in this area.In addition, it is known that the treatment is particularly effective in childhood compared to adulthood [5,6].In Japan, the number of patients aged 5-14 years who received orthodontic treatment doubled between 2017 and 2020, and this age group will account for about 51 % of all patients in 2020 [11,12].In orthodontic treatment, masticatory training, such as Tube training, is sometimes performed simultaneously with dental movement using a mouthpiece, especially in childhood.Masticatory training aims to improve bite force, balance occlusion, shift jaw position, and promote jawbone growth.These effects are considered to contribute to promoting orthodontic treatment and stabilizing the dentition after treatment [15].Tube training is a popular method that uses tubes with a diameter of about 6 mm with a certain hardness.Tube training is a set of exercises, such as biting and relaxing the tube at regular intervals for 5 minutes, recommended to be performed at least twice a day [15].Although tube training is considered effective in orthodontic treatment, several months to years of continuous training may be required for satisfactory results [15].However, keeping this monotonous training daily may be challenging for children.Furthermore, cheating is easy in this training, such as biting the tube with extra light force and making a biting sound.Monitoring by guardians might prevent children from those issues.Unfortunately, it is also challenging for guardians to keep checking that they bite the tube with appropriate force and to keep watching children's training for five minutes twice a day.
Therefore, this study aims to develop a system that encourages children to keep training at home.The system should also help guardians check the children's training status easily.To achieve this, we developed a device to measure bite force during tube training.This device also contributes to visualizing the occlusal information, including bite force and rhythm.Such information can be provided to guardians for monitoring, as well as to dentists as supplemental information for making personalized treatment plans.Then, we also composed serious games that gamified the training by using the device.The game is played through the occlusal movements that are detected by the device.The gamified training should motivate children to keep training correctly and spontaneously.This report describes details of the developed bite force measurement device and composed serious games based on the device.

RELATED WORKS
Kosaka et al. [2] developed a serious game that uses mastication as a trigger.They suggest that this game could promote an increase in the number of chews and improve children's mastication behavior.Sugita et al. [14] proposed an application to promote mastication behavior using myoelectric information.The study utilized an electromyograph to measure the number of mastications and mastication time.Visual and auditory feedback was then provided to the user through the application.The results showed an improvement in the mastication time during meals.These efforts are expected to improve mastication behavior and mastication ability.On the other hand, the combination of mastication training and interactive techniques has not been sufficiently studied.In addition, little attention has been paid to devices that can easily measure the number of chews and the chewing force at home.The Dental Prescale II (DB2) is a device used to measure bite force in the field of treatment [3].It can measure static bite force distribution in the entire dentition with high precision.This is achieved by biting a pressure-sensitive sheet and analyzing it using dedicated software and a scanner.However, it does not support real-time measurements of repetitive occlusal movements.The training game developed in this research requires real-time measurement of bite force, so this device cannot be used for this purpose.Additionally, current measuring devices, such as DB2, are designed for use by medical professionals and may not be affordable for home use.In this study, we develop an easy-to-use bite force measurement system and introduce gamification into mastication training to induce children's occlusal movement appropriately.Furthermore, by visualizing occlusal information, we aim to create an environment where both children and their parents can easily monitor the training progress.

BITE FORCE MEASURING DEVICE 3.1 Requirements for the Proposed Device
The bite force measurement device developed in this study is intended to be used for daily training at home.Therefore, the device should easily and safely be used by general persons, including children.To simplify the system, the minimum requirement for the device is to distinguish "weak bite" and "strong bite" in real time.Among various existing types of tube training methods [1,15], most of them instruct trainees to bite the tube weakly or strongly in a certain rhythm.
In addition, it is preferable for the device to be capable of distinguishing whether the trainee is biting the tube with only one side of the teeth or both sides of the teeth.The situation in which the bite force of either one of the left or right teeth is extremely strong during occlusion is called "one-sided mastication".One-sided mastication causes jaw distortion, which distorts the alignment of teeth during orthodontic treatment [7,8], and it is desirable to correct it appropriately.

Structure of the Device
The developed bite force measurement device consists of a tube to be bitten and a measurement component.Figure 2a shows the developed device.The tube is sealed with a silicone rubber stopper, and the pressure inside the tube is measured by the pressure sensor AP40R-100KG.The pressure inside the tube changes when bitten.The tube can be easily replaced to maintain hygiene.The transition of the pressure represents the bite force.The pressure inside the tube is measured with the pressure sensor embedded with M5StickC Plus.The measured value is displayed on the M5StickC Plus display and, at the same time, transmitted to the PC via Bluetooth for recording and playing games.This device can measure the bite force but is not capable of distinguishing one-sided mastication or not.Then, this system is referred to as TBMS-S (Tube-based Bite-force Measurement System -Single).
The system's configuration prioritizes easy cleaning and tube replacement, but unfortunately, it cannot detect one-sided mastication.To address this issue, we modified the system to distinguish one-sided mastication from another.The developed device is shown in Figure 2b.The tubes are sealed at the center, and the pressure variation in the tubes is measured by two pressure sensors installed at both ends of the tube.The tube compartment is separated into two, then this system can identify which side of the teeth is used during occlusion to detect one-sided mastication.This device is called TBMS-D (TBMS-Dual), following TBMS-S.Replacing the tube is still easy for everyone.However, the tube needs to bond to make two compartments, which might bother users.This issue needs to be addressed in the future.

Measurement Performance
This section briefly describes the result of the evaluation of bite force measurement by using the developed device.A dental manikin installed with a force sensor is used in this evaluation.By biting the tube of the TBMS-S using the manikin, the relationship between From the above, we regard that the device can provide reasonable bite force between a range of 0.5kPa to 4.0kPa, which is identical to bite force from 4.5N to 14.5N, respectively.We define this range as a "measurable range."Unfortunately, the measurable range is limited to a relatively weaker area compared to the maximum bite force of children aged 3 to 5 years, which is approximately 160N to 250N [13].However, it can still distinguish between "weak bite" and "strong bite" by using the measurable range as a threshold.Therefore, this device adopts 14.5N (4.0 kPa) as the threshold value for judging the strength of occlusion, as it is the maximum value of the measurable range.Firstly, the children should be able to reproduce the proper method for the tube training in the game without being explicitly instructed.This will contribute to focusing on playing the game, not the training.Previous cases of gamification have suggested that using the desired exercise as a control input action for gameplay can improve the training effect, as users naturally perform that exercise when they focus on the game [2,9,14].In this game, we aim to induce the typical appropriate method of tube training shown in 3.1, which is repeating weak and strong bites in a well-balanced manner.In our prototype games, several items to indicate the biting type and well-planned item appearance rhythm are designed to implicitly make game players follow this training while playing the game.It is expected that the game can be easily extended, which should improve the children's motivation for playing the game.
Secondly, occlusal information during gameplay should be visualized.Under visualization, guardians can easily monitor the children's playing status, and players can modify their mastication method to fit the game/training in real time.By recording the visualized data, it will also contribute to the post-evaluation of the game/training.

Game Details
Figure 1b 1c shows the developed games played in conjunction with the tube training.Both TBMS-S and TBMS-D can be used as the input interface for either game.The main character in the game is controlled using occlusal movements as input.Both games provide real-time graphical display of bite force during gameplay and output of occlusal information files after the game.The real-time display of bite force during gameplay allows the user to distinguish between weak and strong bites visually.Also, the occlusal information file output is prepared for the sake of sharing with dental professionals, guardians, and users to enable more accurate verification of training status.In the following section, the details of the two games are described.1b is a game in which the user jumps the character by occlusion to avoid objects scrolling from the right side of the screen.(hereinafter referred to as "Chew Chew Jumper") The character jumps each time the user bites to avoid the coming objects.Each object requires a different occlusion action to be avoided.The details of bite type, character motion, and related objects are illustrated in Table 1.A rock object requires a weak jump, a tree object requires a strong jump, and a pond object requires a strong jump at a time that avoids hitting a jumping fish.The weak/strong bite motion is detected through TBMS-S.If the user uses TBMS-D, they are required to bite equally using their both side of teeth.By designing the timing of the appearance of those objects, it induces users to perform the appropriate occlusion action at the desired rhythm.Objects appear once per second on average.The game engine counts the number of each occlusion type and controls the occurrence of each bite by changing the objects' type to appear so that weak/strong occlusions occur equally.

Fruit Munch
Master. Figure 1c depicts a game where the user controls the character's movement by biting the tube with their left teeth to move left and biting the tube with their right teeth to move right.Then eats fruits falling from the tree to obtain a score.This game is named "Fruit Munch Master".The game adds the elements of left/right momentary bite to achieve the appropriate tube training method.Specifically, this game intended to follow the bite training method that "randomly repeats momentary strong  In this game, the character moves left and right by weak and momentarily biting either the left or right side of the TBMS-D tube.When using TBMS-S, the character's left/right motion is controlled by an alternative method, such as a keyboard.Through such bite actions, the character is moved to the position where the fruit drops.The character can eat the fruit by simultaneously biting the tube multiple times quickly when it reaches the character.The number of bites required to eat a fruit depends on the type of fruit.Table 2 shows the list of bite types and related game motions.For the apple, pear, and dregs shown in the table, the fruit appearance interval is adjusted so that the user's biting motion occurs about once every 0.5~0.8seconds.In addition, to allow the user to interweave left/right bites and simultaneous bites, the game is designed to require positional movement operations and fruit-eating operations alternately by constantly changing the position of each fruit's appearance.The appearance position of the fruit is designed so that left/right bites occur equally to prevent one-sided mastication from becoming dominant.Furthermore, to maintain a balance between weak and strong bites, the probability of the appearance of apples and pears is adjusted to a ratio of 2:1, using the same method described in Section 4.2.1 for "Chew Chew Jumper".

Demonstration
The developed devices and games are demonstrated at our open laboratory event.Both the TBMS-D and TBMS-S devices described in section 3.2 were used in the demonstration.To keep hygiene among participants in such public events, players are not allowed to bite the tube with their mouths.Instead of it, they were allowed to apply pressure to the tube to play the game.
When playing the 'Chew Chew Jumper', most participants tended to apply excessive pressure to avoid obstacles.In addition, many participants hit obstacles more frequently due to inappropriate timing of applying pressure.However, the appropriate instructions from the developer make the play of such games smoother.Thus, a clearer but implicit instructional message should be integrated into the game for easier play.
Most players who play 'Fruit Munch Master' also tended to apply excessive pressure, the same as players of 'Chew Chew Jumper'.Different from the 'Chew Chew Jumper', the timing issue was not observed in this game because the game structure does not require players' subtle bite timing control.However, players tend to produce unnecessary bites often to play the game.From the view of appropriate tube training, reducing unnecessary bites and improving bite timing control is the critical issue to be solved.

CONCLUSIONS AND FUTURE WORKS
This study presents the development of a tube-type bite force measuring device and serious games that use bite force as an input.The device is intended to measure and provide bite force information to users of general people, to be used in tube training games.It shows the capability of the device to measure the bite force easily and with hygiene.
As a prospect, improvements are still necessary for the TBMSs' bite force measurement range and information display method.To expand the measurable range, using a harder tube can be one of the solutions.Using such a tube may contribute to improving the bite force measurement range.However, the long-term effects of using such tubes must be investigated because harder tubes may have more impact on teeth, which might lead to improper biting conditions.Currently, the bite force information is presented as a numerical value on the file and a graph on the game.A more intuitive way of information display is necessary to understand the biting condition easily for general people.

Figure 1 :
Figure 1: Overview of the TBMS(a) and training games(b)(c) using TBMS to play

Figure 3 :
Figure 3: Relationship between Air Pressure and Bite Force weak bites at an interval of once every 0.5-0.8seconds[10], mixing left/right bites and simultaneous bites".

Table 2 :
Occlusal correspondence table for "Fruit Munch Master"