Introduction

Dental treatment chairs, as essential equipment in the oral treatment process, are designed to support patients and adjust their positions to facilitate procedures performed by doctors during diagnosis and treatment1,2. Due to the nature of dental care, patients are typically required to remain in the same position for extended periods, often leading to feelings of discomfort, anxiety, and fatigue3,4. Therefore, it is crucial to analyze and improve dental treatment chairs from an ergonomic perspective, ensuring that patients are more comfortable and relaxed during dental procedures. This is an urgent issue that must be addressed in modern dental care.

Jack software is a tool for human body modeling, simulation, and human–machine efficiency evaluation, widely used in industrial design and the medical industry5,6. By creating virtual environments and digital human models, Jack software helps designers assess the ergonomic performance of products, thereby improving designs and enhancing user comfort. It is commonly used in industrial design to evaluate the ergonomic performance of tools and equipment, ensuring that designs meet user needs and enhance operational efficiency and comfort. For example, Peng et al.7 used Jack software to evaluate the comfort level of a CNC grinding machine control box design, selecting optimal design solutions to improve operator comfort and work efficiency. Fu et al.8 employed Jack software for human–machine engineering analysis and the improved design of walking aids for preschool children with cerebral palsy. Their analysis showed that the posture load indices, including the trunk bending moment, L4/L5 spinal compression force, and shear force, were reduced by 53%, 47%, and 81%, respectively, compared to pre-improvement measurements, thereby enhancing the comfort of the children. Fan et al.9 simulated and analyzed the comfort and pressure of the electric locomotive driver’s seat using Jack software, leading to improvements in the shape of the seat back to increase comfort. In research related to dental treatment chairs, Liu et al.10 used Jack simulation software to simulate and analyze the dimensions of the main components of dental chairs and patient comfort. They developed a dental chair model tailored to the patient’s body size, although simulation studies on other modules were not conducted. Mo et al.11 designed and analyzed a children’s dental chair using Jack simulation software, studying the size, angle, and layout of the chair. Zhang et al.12 established a comprehensive treatment table evaluation system for children’s dentistry using sensory engineering methods combined with the DE-BP algorithm, analyzing the multisensory experience of children during diagnosis and treatment. The aforementioned studies indicate that there are relatively few simulation studies on dental treatment chairs, and those that exist primarily focus on improving the design of pediatric dental treatment chairs, without fully addressing the comfort and psychological anxiety of adult patients. Therefore, analyzing the current shortcomings of dental treatment chairs and improving their design to ensure patient comfort during treatment is an urgent issue that must be addressed.

Based on the above summary of the current research on dental treatment chairs, it is evident that there is limited research in this area, particularly regarding patients’ subjective experiences. Therefore, to enhance both comfort and efficiency for dental patients during their use of dental treatment chairs, this study analyzes dental treatment chairs using Jack simulation software in combination with ergonomics.

Process of human–machine engineering simulation analysis for dental treatment chairs

During dental treatment, patients must either lie or sit in a dental treatment chair and cooperate with the dentist to complete the procedure13. To enhance the effectiveness and comfort of dental patients during treatment, Jack simulation software is used to analyze patient behavior, identify shortcomings, and propose improvements in the treatment process.

In Jack’s virtual simulation experiments, tasks are assigned to virtual patients and simulated treatment scenarios to mimic their behavior and actions in a real treatment environment. Relevant data from the treatment process is collected and analyzed using the software to guide the design process14. The first step involves constructing a human body model of the dental patient, a dental treatment chair model, and a human–machine simulation environment for dental treatment. Human–machine simulation analysis is then conducted to evaluate both the treatment and operation processes from the perspective of ergonomics. The simulation process is shown in Fig. 1.

Fig. 1
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Simulation operation flowchart: (a) Build a virtual model, (b) JACK simulation analysis content, (c) Improve design.

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Simulation analysis of ergonomics for dental treatment chairs

Establishment of virtual human model for dental patients

Jack simulation software creates digital human models using standard digital humans or precise dimensions, ensuring that the designed product dimensions align with human physiology15. To construct a virtual human model for dental patients, a 50th percentile human body model is built in Jack software, based on the GB/T 10000-2023 "Chinese Adult Body Dimensions" standard issued in 202316. This model is shown in Fig. 2.

Fig. 2
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The 50th percentile human body model.

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Establishment of simulation environment

To construct a human–machine simulation environment for dental treatment chairs, it is essential to match the position and spatial relationship between the virtual human body model of the dental patient and the dental treatment chair. A specific model of a dental treatment chair is selected as the research object, and a 3D model of the chair is created using modeling software and imported into Jack software. This setup, combined with the virtual human model, forms a dental treatment simulation system. Based on the typical dental treatment workflow, a collaborative operation scenario is created to simulate real treatment conditions, as shown in Fig. 3.

Fig. 3
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Construction of a simulation environment for dental treatment chairs.

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Simulation task analysis

Visual field analysis

During the process of dental patients spitting water, visibility plays a crucial role in ensuring the accuracy of spitting and maintaining patient hygiene. The View Cones tool in Jack software was utilized to determine the viewing angle and cone of vision for dental patients during the spitting process, and to assess whether the spittoon falls within the patient’s line of sight. A visual field simulation was performed for dental patients. According to the design specifications for the cone parameters, the cone angle was set to 40° and the line of sight distance was set to 30 cm to simulate the visual field, as shown in Fig. 4. The simulation results indicated that the visual field of dental patients was adequate for the spitting process. Patients demonstrated good visibility when sitting upright or bending forward to spit, successfully supporting the completion of the treatment task.

Fig. 4
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Visual ___domain analysis of dental patients.

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Comfort analysis of homework operation

According to the usage requirements of dental treatment chairs, patients must perform a series of treatment-related movements during the treatment process, and their comfort during these activities is an important consideration in chair design. To enhance patient comfort during treatment, a simulation analysis was conducted using the Dreyfuss and Krist comfort modules in Jack software. The virtual simulation analysis of dental patient comfort is shown in Fig. 5. The simulation results indicated that the comfort levels for regions such as Upper Arm Flexion (Right/Left), Humeral Rotation (Right/Left), Foot-Calf Inclusive (Right/Left), and Knee Inclusive (Right/Left) were relatively low during treatment. Krist comfort analysis for patients in a reclining position revealed a fatigue value of approximately 56 and a comfort value of around 59. Significant discomfort was observed in the back, arms, and legs when patients were reclining or spitting, highlighting substantial deficiencies in the current dental chair design that urgently need to be addressed to improve patient comfort.

Fig. 5
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Comfort analysis of dental patients.

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Analysis of lower back force

The Lower Back Analysis tool in Jack software was used to analyze the patients, as shown in Fig. 6. The results indicated that the lower back force of dental patients while lying down was approximately 900 N. During spitting, the torques in the Y- and Z-directions at the L4/L5 lumbar vertebrae were relatively high, and the lower back force increased to about 1000 N. At this stage, the elevated pressure on the lower back could lead to increased fatigue or a higher risk of lower back injury.

Fig. 6
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Analysis of lower back stress in dental patients.

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Static strength analysis

Through static strength analysis of dental patients, as shown in Fig. 7, the results indicated that in the Percent Capables percentage test, 100% of dental patients were able to perform wrist, elbow, ankle, and shoulder movements while lying down. However, the percentage of patients capable of achieving trunk, hip, and knee positions was less than 100%. Similarly, in the analysis of joint torsion angles and joint torques, the torsion angle values of the patient’s elbows and knees during the spitting posture were relatively large, which significantly impacted the patient’s body load. Therefore, it is necessary to improve the design of the dental treatment chair to reduce patient fatigue and the risk of injury during the treatment process.

Fig. 7
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Static strength analysis of dental patients.

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Design and simulation analysis of dental treatment chair

Improvement of dental treatment chair ergonomics

Based on the simulation results of patient behavior and posture during dental treatment, combined with the comfort analysis of dental patients’ lying and spitting positions, improvements were made to the headrest, backrest, leg pads, spittoon, and armrests of the dental treatment chair. The redesigned dental treatment chair is shown in Fig. 8. To ensure the headrest conforms to the curvature of the head, a concave structure was incorporated, and space memory foam material was used to inhibit mold growth and eliminate the odor caused by mold reproduction. The pressure distribution of the backrest is focused on both sides of the scapula and lumbar spine, so support was specifically designed for these areas. Circular armrests were added on both sides of the leg pads, allowing patients to grip them when getting up or feeling mentally tense.

Fig. 8
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Improved design of dental treatment chair.

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To further reduce back pressure and discomfort during the spitting process, the spittoon was designed with a rotating mechanism that allows it to adjust its position according to the patient’s posture. This rotation function reduces the twisting angle of the lumbar spine when the patient tilts to spit water, thereby decreasing pressure on the lower back. Fixed spittoons, especially for long-term treatments, may cause repetitive twisting of the body, leading to increased muscle fatigue and spinal strain. In contrast, an adjustable spittoon design effectively addresses this issue, making it easier and more comfortable for patients to spit water. Additionally, the rotating mechanism enhances the flexibility of the treatment process, facilitating medical staff operations and improving the overall efficiency of diagnosis and treatment, as well as patient satisfaction.

Analysis of simulation results of improved dental treatment chair

Improved visual field analysis

A visual field simulation analysis was conducted on the improved dental treatment chair to determine the patient’s visual field range when spitting water and assess whether visibility had been enhanced. Using the View Cones tool for simulation analysis, the patient’s visual field was obtained, as shown in Fig. 9. After adjusting the direction of the spittoon, the visual field for dental patients was significantly improved. This adjustment effectively reduces discomfort, such as the need to twist the body sideways, and enhances patient comfort.

Fig. 9
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Improved visual ___domain analysis.

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Comfort analysis of improved homework posture

The simulation analysis of the comfort level of the improved dental treatment chair was conducted using the Dreyfuss and Krist tools, as shown in Fig. 10. The results showed that dental patients experienced a more relaxed head and back posture when lying down, naturally fitting the contours of the dental chair, and their hands could easily rest on the circular armrests. Compared with the previous dental chair, the improved design provided better support for the patient’s hands and elbows, helping to relieve fatigue. The Krist analysis of the patient’s lying posture indicated that the fatigue value was approximately 32 and the comfort value around 27; during the water-spitting posture, the fatigue value was about 59 and the comfort value about 68. Compared with the original chair, the fatigue values were significantly reduced, making dental patients less likely to experience tiredness and progressively enhancing their overall treatment experience.

Fig. 10
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Improved comfort analysis.

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Analysis of lower back force after improvement

A force analysis of the lower back for the improved dental treatment chair was conducted, as shown in Fig. 11. The results indicated that the X-direction torque at the L4/L5 lumbar spine of dental patients in the lying position was approximately 400 Nm, which represents a reduction compared to the pre-improvement design. When patients adopt the spitting posture, they can grasp the circular handrails on both sides with both hands, allowing them to leverage their upper body strength to assist in sitting up, thereby reducing strain on the lumbar spine. After the improvements, the force exerted on the L4/L5 vertebrae during treatment and spitting tasks was noticeably decreased, making it easier and more comfortable for patients to spit water. Additionally, the rotatable spittoon design enables the spittoon to move in front of the patient, eliminating the need for significant lateral torso twisting, further alleviating lower back stress.

Fig. 11
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Improved analysis of lower back stress.

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Improved static strength analysis

A static strength analysis of the improved dental treatment chair was conducted, as shown in Fig. 12. When patients use the enhanced chair, the spittoon rotates to the front of the patient, facilitating a more comfortable and convenient spitting action. The results of the static strength analysis indicate that nearly 100% of the population is able to perform this action comfortably, thanks to the improved ergonomic design.

Fig. 12
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Improved static strength analysis.

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Comparison of simulation results of dental treatment chairs before and after improvement

Comparing the simulation data of the dental treatment chair before and after improvement, as shown in Fig. 13, it was found that the improved dental treatment chair resulted in a decrease in elbow angle from 145° to 125° in the lying posture, according to the Dreyfuss comfort analysis module, which is well below the limit standard of 165°. The upper arm flexion decreased from 20.9° to 16.6°, and the wrist load, including the Wrist Ulnar and Knee Included, was also reduced. In the Dreyfuss analysis of the spitting posture, the Head, Elbow, Wrist Ulnar, Leg Splay, and other areas showed a decrease in load after improvement. However, there were still some areas, such as forearm torsion and humeral rotation, where values increased and require further evaluation. Overall, the improvements to the dental treatment chair have led to significant optimization in most key areas, aligning with the ergonomic optimization goals.

Fig. 13
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Comparison of simulation data before and after improvement of dental treatment chairs.

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Conclusion

Virtual simulation analysis was conducted on dental treatment chairs and patients’ lying and spitting postures during the treatment process. Based on simulation results, improvements and designs were made to the headrest, backrest, armrest, and spittoon components of the dental treatment chair, and improvement plans were analyzed. The results indicate that the comfort level of dental patients is greatly improved, providing ideas for the product design of dental treatment chairs. This study provides support for improving the patient experience in dental clinical treatment. However, this study still has limitations. Due to the fact that Jack software mainly focuses on static simulation and lacks simulation analysis of dynamic postures, there has been no comprehensive research on the doctor’s operating interface. Therefore, in-depth research on the doctor interface is needed in the future to provide a theoretical basis for the development of the medical and mechanical fields.