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J Cosmet Med 2022; 6(1): 27-33

Published online June 30, 2022

https://doi.org/10.25056/JCM.2022.6.1.27

Application and limitations of facial computed tomography and three-dimensional scanner images for patient-specific three-dimensional printing of a nose mask

Jung-Gwon Nam, MD, PhD1 , Don Han Kim, PhD2 , Tae-Hoon Lee, MD, PhD1

1Department of Otolaryngology-Head and Neck Surgery, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan, Rep. of Korea
2Department of Digital Contents, College of Architecture and Design, University of Ulsan, Ulsan, Rep. of Korea

Correspondence to :
Tae-Hoon Lee
E-mail: thlee@uuh.ulsan.kr

Received: May 11, 2022; Revised: May 26, 2022; Accepted: May 26, 2022

© Korean Society of Korean Cosmetic Surgery & Medicine

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Background: The applications of three-dimensional (3D) printing are expanding in personalized medicine. The image data used for 3D printing modeling include 3D scanners and medical image data such as computed tomography (CT) and/or magnetic resonance imaging data.
Objective: To compare 3D scanner images with CT 3D images for fabricating a patient-specific nasal pillow positive airway pressure (PAP) mask using 3D printing technology.
Methods: Personalized PAP masks were designed using 3D printing based on image data obtained using a low-dose facial CT scan or a 3D scanner. After converting the extracted nose shape data into a standard tessellation language file format, it was transferred to mesh-based modeling software (3-matic) to produce a PAP mask matching the shape of the nose. A questionnaire was used to evaluate the wearing sensation, degree of air leakage, and delivery ability of positive pressure for the customized and conventional nasal type masks. Each mask was rated between 0 and 4.
Results: The ultra-low-dose CT scan with a 1-mm slice distance was adequate to obtain the clear images required to produce a 3D printed nasal pillow PAP mask. The wearing sensation of the 3D printed nasal pillow PAP masks tended to be more comfortable than that of the conventional nasal masks (p=0.056). However, the least amount of air leakage was observed with the conventional nasal mask (p=0.003). The positive pressure delivery ability was slightly lower in the 3D nasal pillow mask group (p=0.054).
Conclusion: The nasal pillow type 3D printed PAP masks used in this study did not demonstrate satisfactory results to justify its use as a replacement of the conventional nasal-type mask. An ultra-low-dose CT scan was sufficient to produce a 3D printed mask.

Keywords: continuous positive airway pressure, image, three-dimensional, nasal mask, obstructive sleep apnea, stereolithography, three-dimensional printing

The applications of three-dimensional (3D) printing are expanding in personalized medicine. The use of 3D printed models to prepare for head and neck surgery, including paranasal sinus surgery, or to educate doctors and patients is currently available in clinical practice [1]. The image data used for 3D printing modeling include 3D scanners and medical image data such as computed tomography (CT) and/or magnetic resonance imaging data. Among these, the face CT scan is a noninvasive, general test for evaluating obstructive sleep apnea (OSA) that enables internal structural visualization; however, the patient is exposed to radiation. Although the method that uses a 3D scanner is noninvasive, with no radiation exposure, it cannot be easily used to evaluate internal structures and is challenging to implement in a general medical environment. This method generally has a poor resolution, precision, and scanning speed. Image data can be obtained using a 3D scanner for visible parts of the face and using CT for internal parts. In general, a 3D scan is mainly used for guide production or simulation model production for rhinoplasty, and CT is used for surgical model or customized plate production for facial bone fracture surgery, endoscopic sinus surgery, nasal cavity or sinus tumor removal and reconstruction.

Sleep apnea is a common disease that occurs in 26% of adults aged 30–70 years [2]. Positive airway pressure (PAP) treatment is initially recommended for sleep apnea. However, compliance with PAP treatment is relatively low [3-6]. Compared to the nasal type mask, the pillow type PAP mask is associated with lower sweat generation and skin trouble because it has fewer face-contact parts, but greater discomfort. Mask fit is an important factor influencing compliance. To increase the adhesion of the mask, the mask should be fabricated considering individual anatomical characteristics, such as the size and shape of the patient’s nose and nostril. 3D printing technology can be used to develop such masks.

It is sufficient to use a 3D scan when customizing the nasal mask required for patients with sleep apnea. However, when manufacturing a patient-customized pillow-type mask, the shape of the nostrils and the part inserted into the nose must be considered. Therefore, a 3D scan alone may not be able to provide sufficient image data. In this study, we compared 3D scanner images with CT 3D images for fabricating a patient-specific nasal pillow PAP mask using 3D printing technology.

Subjects

This study adhered to the tenets of the Declaration of Helsinki and institutional review board approval was obtained (UUH 2018-04-027). All the subjects were enrolled between June and December 2018. Patients (over 19 years of age) diagnosed with OSA on polysomnography and recommended for PAP treatment were enrolled in this study. Informed consent was obtained from all patients. The number of clinical study participants was calculated using the G*Power program. An alpha value of 0.05, beta value of 0.20, and effect size of 1 were set, the number was calculated as 17 by the t-test and 15 by the analysis of variance (ANOVA). Thirty patients with sleep apnea were selected as the study subjects by additionally considering the dropout rate, possibility of subject recruitment, and research cost. Patients who had difficulty scanning their face with a 3D scanner, refused to undergo CT, or refused to use 3D masks were excluded from the study.

Facial CT scan

A CT was performed using a 256-slice multi-detection CT scanner (Brilliance iCT; Philips Healthcare, Andover, MA, USA). The range from the lower boundary of the bilateral eye to the tip of the chin was acquired from the supine position such that the eyes and thyroid glands, which are highly radiosensitive, were not included. To minimize the risk of radiation exposure, an ultra-low-dose CT (UCT; 100 kVp 10mAs) protocol with an effective radiation dose of approximately 6%, compared to the general facial CT protocol, was used.

Facial 3D scan

Using a 3D scanner, image data were obtained by scanning the range from the lower boundary of the bilateral eyes to the tip of the chin, as in the CT scan. First, the face to be photographed was positioned at a distance of approximately 60 to 70 cm from the scanner and subsequently photographed in the following order: front, right side, left side, and lower jaw. After photographing, the reference point was set for each surface, and the images were sequentially registered to extract the 3D shape. During this time, the reference points were the lateral canthi, the margin of both nasal alar, and both lateral angles of the lips. The resolution of the 3D scanner was 0.1 mm or more, the 3D point accuracy was 0.03 mm, the light source was a blue diode, and the output was stored in an OBJ or standard tessellation language (STL) format.

Mask making

Personalized PAP masks were fabricated by 3D printing based on image data obtained using a low-dose facial CT scan or 3D scanner. The image data acquired through the CT scan were converted into a 3D shape using medical image-processing software (Mimics; Materialise, Leuven, Belgium). Subsequently, the area required for mask-making was extracted. After converting the extracted nose shape into an STL file format, it was transferred to mesh-based modeling software (3-matic; Materialise) to design a PAP mask matching the shape of the nose. The thickness was created by Offset after extracting the shape of the feature required for mask-making. After producing the basic section using Boolean subtraction and Boolean union, additional segments were arranged to complete the mask (Fig. 1).

Fig. 1.Mask reverse engineering using mimics (3-matic) software.

The nasal pillow-type PAP mask was composed of a nasal adhesion piece, base piece, and connection piece (Fig. 2). To provide the appropriate hardness and elasticity, the nose contact piece was fabricated with an 80:20 mixture of VeroCyan and Agilus30, which provides a rubbery feeling. An Objet260 Connex3 (Stratasys Ltd., Eden Prairie, MN, USA) stereolithography apparatus (SLA) 3D printer was used. The base and connection pieces were fabricated using Accura ClearVue and a Projet 7000 (3D Syntems, Rock Hill, SC, USA) SLA 3D printer. These printers are harmless to the human body and have high output resolution. Based on each image, a laser beam was illuminated into a tank containing liquid photo-polymerizing resin, and a pillow-type patient-specific mask was manufactured in a layer-by-layer manner (Fig. 3, 4).

Fig. 2.Composition of the positive airway pressure mask. (1) Nose adhesion piece; (2) base piece; (3) connection piece.

Fig. 3.Three-dimensional (3D) printed positive airway pressure mask made using 3D scanner images.

Fig. 4.Three-dimensional printed positive airway pressure mask made using computed tomography scan images.

Data collection and analysis

We compared patient-specific 3D printed pillow masks made with low-dose facial CT imaging data or 3D scanner imaging data. Subjective evaluation of the masks was performed after each mask was worn for 10 minutes at a continuous positive airway pressure of 6 cm H2O. A questionnaire was used to evaluate the wearing sensation, degree of air leakage, and positive pressure delivery ability of the customized patient-specific nasal pillow PAP mask based on the imaging data. Each mask was rated between 0 and 4 (4=optimal/very high; 3=suboptimal/high; 2=general; 1=poor/low; and 0=very poor/very low). The masks were analyzed using the Kruskal-Wallis test. Statistical significance was determined based on p<0.05 and analyzed using IBM SPSS Statistics ver. 24 (IBM Corp., Armonk, NY, USA).

Thirty participants were enrolled in our study, and three participants quit during the study. The average age of the participants was 49 years, being 23 males and 4 females. When the CT scan image of the general 3-mm cut was used for the preparation of the PAP mask, the slice interval was too large, and many defects were observed in the 3D shapes inside the nostrils. After adjusting the slice distance to 1 mm, excellent 3D images of the soft tissues inside the nostrils scanned with CT were obtained. The ultra-low-dose CT scans were sufficient to acquire the clear images needed to produce 3D printed PAP masks. A comparison of the mesh data converted from the 3D scanner to the STL file and the actual face sections, left and right, and up and down, showed that the error range was within 0.1 mm. This indicates that the mask manufacturing method using the 3D scanner is effective.

Table 1 shows the subjective satisfaction scores of the masks for each item. The wearing sensation of the mask made with the 3D scan image was the best; the wearing sensation of the mask made with the CT image was better than that of the conventional nasal mask. In contrast, the lowest amount of air leakage was observed with the conventional nasal mask, and the highest amount was observed with the 3D scan mask. This difference was statistically significant (p=0.003). The positive pressure delivery ability was similar between the nasal mask and CT 3D mask; however, it was slightly lower in the 3D scan mask (Fig. 5).

Fig. 5.Subjective outcomes. 3D, three-dimensional; CT, computed tomography.

Table 1 . Subjective outcomes

Variable (point)NasalPillow 3DPillow CTp-value
Wearing sensation2.22±0.752.74±0.892.44±0.930.056
Air leakage1.37±0.492.33±1.181.96±0.980.003*
Positive pressure1.52±0.701.19±0.481.56±0.850.054

Values are presented as mean±SD.

3D, three-dimensional; CT, computed tomography.

*Statistically significance (p<0.05).


The expanded applications of 3D printing technology have been employed to medical care in various manners. Currently, medical 3D printing can be employed to fabricate life-size training models, surgical guiding tools, patient-specific implants, and tissue scaffolds [7]. Prior to fracture surgery or complex anatomical structure intervention, 3D printing is used to model and simulate the surgical site, which is very useful for surgical planning prior to the operation [8]. Surgical guiding tools are primarily used in cosmetic or reconstructive surgeries, where patient-specific implants and customized plates are widely used. Dental prostheses, hearing aids, or prostheses for reconstruction after trauma or tumor surgery are also widely utilized. 3D printing is faster and more sophisticated than traditional casting methods. In addition, bioprinting, which uses living cells to produce tissues or organs, has been actively investigated [9,10], and it will soon become a new field in medical 3D printing.

Patient-specific implants made using 3D printing are particularly effective at reducing the discomfort associated with traditional production appliances. In particular, new and innovative designs can be used to dramatically improve existing products. For example, conventional arm splints are heavy and lack ventilation, resulting in shoulder and back pain, perspiration, itching, and skin disease. The 3D printed arm splint solves all these problems by producing openings of various sizes and shapes. In particular, by adding an organic shape opening design, the resistance of the splint is strengthened to prevent breakage, and closing button-enabled attachment and detachment of the prosthesis improves hygiene, skin care, and early rehabilitation, and improves the patient’s quality of life [11].

Sleep apnea results in sleep segmentation and daytime sleepiness, causing diseases such as cerebral cardiovascular disease, metabolic disorders, and dementia [12-14]. Among the treatments available for moderate-to-severe sleep apnea, PAP treatment is recommended. Factors affecting compliance include a variety of physiological problems, such as a stuffy nose or skin irritation, mechanical problems, such as mask fit, and psychiatric problems, such as claustrophobia [15]. The mask is the most important point of contact between the patient and the PAP machine, and has been refined to reduce air leakage and discomfort experienced by the patient [16]. Mask types included pillow, nasal, and full-face types. Nasal masks are often initially used because of high patient adherence [17,18].

A PAP mask for the treatment of sleep apnea is initially slightly uncomfortable and requires a period of compliance. In general, the greater the strength of the positive pressure, the greater the discomfort. The compliance also depends on the type of mask used. Oronasal masks have more leakage, higher residual apnea-hypopnea index (AHI), and lower durability than nasal masks [19]. A nasal pillow-type mask is more uncomfortable than a nasal-type mask because of the severe pressure on the nasal tips and nostrils. In particular, a severely deviated nose or severe facial deformities can lead to air leakage, resulting in even greater discomfort. Fabricating patient-specific masks using 3D printing increases adhesion and reduces air leakage and discomfort.

In this study, when the mask was fabricated using CT scan images, soft tissue shapes of up to 1 cm inside the nostrils could be reproduced, resulting in better adhesion of the mask to the nostrils than when the mask was fabricated using 3D scanner images. This advantage led to a superior reduction in air leakage compared with masks made with 3D scanners. Ultra-low-dose CT was used for facial imaging because radiosensitive eye lenses were included in the scanning field. Although the image quality was lower than that of conventional CT, it was sufficient to obtain images of the face and nostril openings required for mask fabrication. Ultra-low-dose CT generates only 6% of the effective radiation dose of conventional CT [20]. Therefore, there is less risk of lens opacification and radiation-induced cataracts, even with repeated imaging. Thus, ultra-low-dose CT may be a good option for recreating fractured bones or organ models for surgical simulation.

Several problems arise during the mask-making process. First, in the segmentation using Mimics, noise was included in the shape of the target soft tissue. In addition, designing the internal structure of the nostrils using 3-matic is time consuming. To improve productivity, it is necessary to optimize the design of the patient-customized section, mass-produced piece, shape optimization, and mechanical design considering the air flow. With regard to the commercialization of masks, it is more efficient to manufacture masks using 3D scanners than using facial CT; however, structural improvements that can enhance mask adhesion are required. The plastic smell from 3D printed masks is also a major limitation that makes them difficult to use. The mask applied directly to the nose should be odorless; however, with current 3D printing technology, odorless materials such as silicon are difficult to use. Making a mold for a silicon mask with 3D printing can be considered the next best solution, but it is not efficient in terms of time and cost.

For these reasons, this study did not yield the expected results for patient-specific 3D printed masks. The patient’s wearing sensation and/or air leakage were worse than those of the conventional nasal mask; however, both masks exhibited a similar performance with regard to delivering positive pressure. This is due to the nasal tip and alar being applied to the 3D printed masks. These are not fixed shapes but soft tissues, and the cartilage can be changed in volume and shape by positive pressure. In this respect, the nasal type is more effective than the pillow type in producing a 3D printed PAP mask.

This study was conducted with conscious subjects, not as an actual sleep study, under uniform positive pressure. After analyzing the problems found in this study, in the future, we will enhance the design of the mask to improve air leakage and wearing sensation. We will also examine the objective amount of AHI and air leakage at an optimal positive pressure for each subject during actual sleeping state. As the mask is in direct contact with the nose, a method for eliminating odor from the 3D printing material must be developed.

In conclusions, the nasal pillow type 3D printed PAP masks used in this study showed a better wearing sensation than conventional PAP masks. However, they did not show satisfactory results to justify their use as a replacement of the conventional nasal pillow-type mask. Ultra-low-dose CT was effective to produce 3D printing and was particularly useful for the fabrication of custom implants required for embedded structures.

This study was supported by a grant from the Korean Ministry of Trade, Industry and Energy (No. 10077827).

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Article

Original Article

J Cosmet Med 2022; 6(1): 27-33

Published online June 30, 2022 https://doi.org/10.25056/JCM.2022.6.1.27

Copyright © Korean Society of Korean Cosmetic Surgery & Medicine.

Application and limitations of facial computed tomography and three-dimensional scanner images for patient-specific three-dimensional printing of a nose mask

Jung-Gwon Nam, MD, PhD1 , Don Han Kim, PhD2 , Tae-Hoon Lee, MD, PhD1

1Department of Otolaryngology-Head and Neck Surgery, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan, Rep. of Korea
2Department of Digital Contents, College of Architecture and Design, University of Ulsan, Ulsan, Rep. of Korea

Correspondence to:Tae-Hoon Lee
E-mail: thlee@uuh.ulsan.kr

Received: May 11, 2022; Revised: May 26, 2022; Accepted: May 26, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: The applications of three-dimensional (3D) printing are expanding in personalized medicine. The image data used for 3D printing modeling include 3D scanners and medical image data such as computed tomography (CT) and/or magnetic resonance imaging data.
Objective: To compare 3D scanner images with CT 3D images for fabricating a patient-specific nasal pillow positive airway pressure (PAP) mask using 3D printing technology.
Methods: Personalized PAP masks were designed using 3D printing based on image data obtained using a low-dose facial CT scan or a 3D scanner. After converting the extracted nose shape data into a standard tessellation language file format, it was transferred to mesh-based modeling software (3-matic) to produce a PAP mask matching the shape of the nose. A questionnaire was used to evaluate the wearing sensation, degree of air leakage, and delivery ability of positive pressure for the customized and conventional nasal type masks. Each mask was rated between 0 and 4.
Results: The ultra-low-dose CT scan with a 1-mm slice distance was adequate to obtain the clear images required to produce a 3D printed nasal pillow PAP mask. The wearing sensation of the 3D printed nasal pillow PAP masks tended to be more comfortable than that of the conventional nasal masks (p=0.056). However, the least amount of air leakage was observed with the conventional nasal mask (p=0.003). The positive pressure delivery ability was slightly lower in the 3D nasal pillow mask group (p=0.054).
Conclusion: The nasal pillow type 3D printed PAP masks used in this study did not demonstrate satisfactory results to justify its use as a replacement of the conventional nasal-type mask. An ultra-low-dose CT scan was sufficient to produce a 3D printed mask.

Keywords: continuous positive airway pressure, image, three-dimensional, nasal mask, obstructive sleep apnea, stereolithography, three-dimensional printing

Introduction

The applications of three-dimensional (3D) printing are expanding in personalized medicine. The use of 3D printed models to prepare for head and neck surgery, including paranasal sinus surgery, or to educate doctors and patients is currently available in clinical practice [1]. The image data used for 3D printing modeling include 3D scanners and medical image data such as computed tomography (CT) and/or magnetic resonance imaging data. Among these, the face CT scan is a noninvasive, general test for evaluating obstructive sleep apnea (OSA) that enables internal structural visualization; however, the patient is exposed to radiation. Although the method that uses a 3D scanner is noninvasive, with no radiation exposure, it cannot be easily used to evaluate internal structures and is challenging to implement in a general medical environment. This method generally has a poor resolution, precision, and scanning speed. Image data can be obtained using a 3D scanner for visible parts of the face and using CT for internal parts. In general, a 3D scan is mainly used for guide production or simulation model production for rhinoplasty, and CT is used for surgical model or customized plate production for facial bone fracture surgery, endoscopic sinus surgery, nasal cavity or sinus tumor removal and reconstruction.

Sleep apnea is a common disease that occurs in 26% of adults aged 30–70 years [2]. Positive airway pressure (PAP) treatment is initially recommended for sleep apnea. However, compliance with PAP treatment is relatively low [3-6]. Compared to the nasal type mask, the pillow type PAP mask is associated with lower sweat generation and skin trouble because it has fewer face-contact parts, but greater discomfort. Mask fit is an important factor influencing compliance. To increase the adhesion of the mask, the mask should be fabricated considering individual anatomical characteristics, such as the size and shape of the patient’s nose and nostril. 3D printing technology can be used to develop such masks.

It is sufficient to use a 3D scan when customizing the nasal mask required for patients with sleep apnea. However, when manufacturing a patient-customized pillow-type mask, the shape of the nostrils and the part inserted into the nose must be considered. Therefore, a 3D scan alone may not be able to provide sufficient image data. In this study, we compared 3D scanner images with CT 3D images for fabricating a patient-specific nasal pillow PAP mask using 3D printing technology.

Materials and methods

Subjects

This study adhered to the tenets of the Declaration of Helsinki and institutional review board approval was obtained (UUH 2018-04-027). All the subjects were enrolled between June and December 2018. Patients (over 19 years of age) diagnosed with OSA on polysomnography and recommended for PAP treatment were enrolled in this study. Informed consent was obtained from all patients. The number of clinical study participants was calculated using the G*Power program. An alpha value of 0.05, beta value of 0.20, and effect size of 1 were set, the number was calculated as 17 by the t-test and 15 by the analysis of variance (ANOVA). Thirty patients with sleep apnea were selected as the study subjects by additionally considering the dropout rate, possibility of subject recruitment, and research cost. Patients who had difficulty scanning their face with a 3D scanner, refused to undergo CT, or refused to use 3D masks were excluded from the study.

Facial CT scan

A CT was performed using a 256-slice multi-detection CT scanner (Brilliance iCT; Philips Healthcare, Andover, MA, USA). The range from the lower boundary of the bilateral eye to the tip of the chin was acquired from the supine position such that the eyes and thyroid glands, which are highly radiosensitive, were not included. To minimize the risk of radiation exposure, an ultra-low-dose CT (UCT; 100 kVp 10mAs) protocol with an effective radiation dose of approximately 6%, compared to the general facial CT protocol, was used.

Facial 3D scan

Using a 3D scanner, image data were obtained by scanning the range from the lower boundary of the bilateral eyes to the tip of the chin, as in the CT scan. First, the face to be photographed was positioned at a distance of approximately 60 to 70 cm from the scanner and subsequently photographed in the following order: front, right side, left side, and lower jaw. After photographing, the reference point was set for each surface, and the images were sequentially registered to extract the 3D shape. During this time, the reference points were the lateral canthi, the margin of both nasal alar, and both lateral angles of the lips. The resolution of the 3D scanner was 0.1 mm or more, the 3D point accuracy was 0.03 mm, the light source was a blue diode, and the output was stored in an OBJ or standard tessellation language (STL) format.

Mask making

Personalized PAP masks were fabricated by 3D printing based on image data obtained using a low-dose facial CT scan or 3D scanner. The image data acquired through the CT scan were converted into a 3D shape using medical image-processing software (Mimics; Materialise, Leuven, Belgium). Subsequently, the area required for mask-making was extracted. After converting the extracted nose shape into an STL file format, it was transferred to mesh-based modeling software (3-matic; Materialise) to design a PAP mask matching the shape of the nose. The thickness was created by Offset after extracting the shape of the feature required for mask-making. After producing the basic section using Boolean subtraction and Boolean union, additional segments were arranged to complete the mask (Fig. 1).

Figure 1. Mask reverse engineering using mimics (3-matic) software.

The nasal pillow-type PAP mask was composed of a nasal adhesion piece, base piece, and connection piece (Fig. 2). To provide the appropriate hardness and elasticity, the nose contact piece was fabricated with an 80:20 mixture of VeroCyan and Agilus30, which provides a rubbery feeling. An Objet260 Connex3 (Stratasys Ltd., Eden Prairie, MN, USA) stereolithography apparatus (SLA) 3D printer was used. The base and connection pieces were fabricated using Accura ClearVue and a Projet 7000 (3D Syntems, Rock Hill, SC, USA) SLA 3D printer. These printers are harmless to the human body and have high output resolution. Based on each image, a laser beam was illuminated into a tank containing liquid photo-polymerizing resin, and a pillow-type patient-specific mask was manufactured in a layer-by-layer manner (Fig. 3, 4).

Figure 2. Composition of the positive airway pressure mask. (1) Nose adhesion piece; (2) base piece; (3) connection piece.

Figure 3. Three-dimensional (3D) printed positive airway pressure mask made using 3D scanner images.

Figure 4. Three-dimensional printed positive airway pressure mask made using computed tomography scan images.

Data collection and analysis

We compared patient-specific 3D printed pillow masks made with low-dose facial CT imaging data or 3D scanner imaging data. Subjective evaluation of the masks was performed after each mask was worn for 10 minutes at a continuous positive airway pressure of 6 cm H2O. A questionnaire was used to evaluate the wearing sensation, degree of air leakage, and positive pressure delivery ability of the customized patient-specific nasal pillow PAP mask based on the imaging data. Each mask was rated between 0 and 4 (4=optimal/very high; 3=suboptimal/high; 2=general; 1=poor/low; and 0=very poor/very low). The masks were analyzed using the Kruskal-Wallis test. Statistical significance was determined based on p<0.05 and analyzed using IBM SPSS Statistics ver. 24 (IBM Corp., Armonk, NY, USA).

Results

Thirty participants were enrolled in our study, and three participants quit during the study. The average age of the participants was 49 years, being 23 males and 4 females. When the CT scan image of the general 3-mm cut was used for the preparation of the PAP mask, the slice interval was too large, and many defects were observed in the 3D shapes inside the nostrils. After adjusting the slice distance to 1 mm, excellent 3D images of the soft tissues inside the nostrils scanned with CT were obtained. The ultra-low-dose CT scans were sufficient to acquire the clear images needed to produce 3D printed PAP masks. A comparison of the mesh data converted from the 3D scanner to the STL file and the actual face sections, left and right, and up and down, showed that the error range was within 0.1 mm. This indicates that the mask manufacturing method using the 3D scanner is effective.

Table 1 shows the subjective satisfaction scores of the masks for each item. The wearing sensation of the mask made with the 3D scan image was the best; the wearing sensation of the mask made with the CT image was better than that of the conventional nasal mask. In contrast, the lowest amount of air leakage was observed with the conventional nasal mask, and the highest amount was observed with the 3D scan mask. This difference was statistically significant (p=0.003). The positive pressure delivery ability was similar between the nasal mask and CT 3D mask; however, it was slightly lower in the 3D scan mask (Fig. 5).

Figure 5. Subjective outcomes. 3D, three-dimensional; CT, computed tomography.

Table 1 . Subjective outcomes.

Variable (point)NasalPillow 3DPillow CTp-value
Wearing sensation2.22±0.752.74±0.892.44±0.930.056
Air leakage1.37±0.492.33±1.181.96±0.980.003*
Positive pressure1.52±0.701.19±0.481.56±0.850.054

Values are presented as mean±SD..

3D, three-dimensional; CT, computed tomography..

*Statistically significance (p<0.05)..


Discussion

The expanded applications of 3D printing technology have been employed to medical care in various manners. Currently, medical 3D printing can be employed to fabricate life-size training models, surgical guiding tools, patient-specific implants, and tissue scaffolds [7]. Prior to fracture surgery or complex anatomical structure intervention, 3D printing is used to model and simulate the surgical site, which is very useful for surgical planning prior to the operation [8]. Surgical guiding tools are primarily used in cosmetic or reconstructive surgeries, where patient-specific implants and customized plates are widely used. Dental prostheses, hearing aids, or prostheses for reconstruction after trauma or tumor surgery are also widely utilized. 3D printing is faster and more sophisticated than traditional casting methods. In addition, bioprinting, which uses living cells to produce tissues or organs, has been actively investigated [9,10], and it will soon become a new field in medical 3D printing.

Patient-specific implants made using 3D printing are particularly effective at reducing the discomfort associated with traditional production appliances. In particular, new and innovative designs can be used to dramatically improve existing products. For example, conventional arm splints are heavy and lack ventilation, resulting in shoulder and back pain, perspiration, itching, and skin disease. The 3D printed arm splint solves all these problems by producing openings of various sizes and shapes. In particular, by adding an organic shape opening design, the resistance of the splint is strengthened to prevent breakage, and closing button-enabled attachment and detachment of the prosthesis improves hygiene, skin care, and early rehabilitation, and improves the patient’s quality of life [11].

Sleep apnea results in sleep segmentation and daytime sleepiness, causing diseases such as cerebral cardiovascular disease, metabolic disorders, and dementia [12-14]. Among the treatments available for moderate-to-severe sleep apnea, PAP treatment is recommended. Factors affecting compliance include a variety of physiological problems, such as a stuffy nose or skin irritation, mechanical problems, such as mask fit, and psychiatric problems, such as claustrophobia [15]. The mask is the most important point of contact between the patient and the PAP machine, and has been refined to reduce air leakage and discomfort experienced by the patient [16]. Mask types included pillow, nasal, and full-face types. Nasal masks are often initially used because of high patient adherence [17,18].

A PAP mask for the treatment of sleep apnea is initially slightly uncomfortable and requires a period of compliance. In general, the greater the strength of the positive pressure, the greater the discomfort. The compliance also depends on the type of mask used. Oronasal masks have more leakage, higher residual apnea-hypopnea index (AHI), and lower durability than nasal masks [19]. A nasal pillow-type mask is more uncomfortable than a nasal-type mask because of the severe pressure on the nasal tips and nostrils. In particular, a severely deviated nose or severe facial deformities can lead to air leakage, resulting in even greater discomfort. Fabricating patient-specific masks using 3D printing increases adhesion and reduces air leakage and discomfort.

In this study, when the mask was fabricated using CT scan images, soft tissue shapes of up to 1 cm inside the nostrils could be reproduced, resulting in better adhesion of the mask to the nostrils than when the mask was fabricated using 3D scanner images. This advantage led to a superior reduction in air leakage compared with masks made with 3D scanners. Ultra-low-dose CT was used for facial imaging because radiosensitive eye lenses were included in the scanning field. Although the image quality was lower than that of conventional CT, it was sufficient to obtain images of the face and nostril openings required for mask fabrication. Ultra-low-dose CT generates only 6% of the effective radiation dose of conventional CT [20]. Therefore, there is less risk of lens opacification and radiation-induced cataracts, even with repeated imaging. Thus, ultra-low-dose CT may be a good option for recreating fractured bones or organ models for surgical simulation.

Several problems arise during the mask-making process. First, in the segmentation using Mimics, noise was included in the shape of the target soft tissue. In addition, designing the internal structure of the nostrils using 3-matic is time consuming. To improve productivity, it is necessary to optimize the design of the patient-customized section, mass-produced piece, shape optimization, and mechanical design considering the air flow. With regard to the commercialization of masks, it is more efficient to manufacture masks using 3D scanners than using facial CT; however, structural improvements that can enhance mask adhesion are required. The plastic smell from 3D printed masks is also a major limitation that makes them difficult to use. The mask applied directly to the nose should be odorless; however, with current 3D printing technology, odorless materials such as silicon are difficult to use. Making a mold for a silicon mask with 3D printing can be considered the next best solution, but it is not efficient in terms of time and cost.

For these reasons, this study did not yield the expected results for patient-specific 3D printed masks. The patient’s wearing sensation and/or air leakage were worse than those of the conventional nasal mask; however, both masks exhibited a similar performance with regard to delivering positive pressure. This is due to the nasal tip and alar being applied to the 3D printed masks. These are not fixed shapes but soft tissues, and the cartilage can be changed in volume and shape by positive pressure. In this respect, the nasal type is more effective than the pillow type in producing a 3D printed PAP mask.

This study was conducted with conscious subjects, not as an actual sleep study, under uniform positive pressure. After analyzing the problems found in this study, in the future, we will enhance the design of the mask to improve air leakage and wearing sensation. We will also examine the objective amount of AHI and air leakage at an optimal positive pressure for each subject during actual sleeping state. As the mask is in direct contact with the nose, a method for eliminating odor from the 3D printing material must be developed.

In conclusions, the nasal pillow type 3D printed PAP masks used in this study showed a better wearing sensation than conventional PAP masks. However, they did not show satisfactory results to justify their use as a replacement of the conventional nasal pillow-type mask. Ultra-low-dose CT was effective to produce 3D printing and was particularly useful for the fabrication of custom implants required for embedded structures.

Acknowledgments

This study was supported by a grant from the Korean Ministry of Trade, Industry and Energy (No. 10077827).

Conflicts of interest

The authors have nothing to disclose.

Fig 1.

Figure 1.Mask reverse engineering using mimics (3-matic) software.
Journal of Cosmetic Medicine 2022; 6: 27-33https://doi.org/10.25056/JCM.2022.6.1.27

Fig 2.

Figure 2.Composition of the positive airway pressure mask. (1) Nose adhesion piece; (2) base piece; (3) connection piece.
Journal of Cosmetic Medicine 2022; 6: 27-33https://doi.org/10.25056/JCM.2022.6.1.27

Fig 3.

Figure 3.Three-dimensional (3D) printed positive airway pressure mask made using 3D scanner images.
Journal of Cosmetic Medicine 2022; 6: 27-33https://doi.org/10.25056/JCM.2022.6.1.27

Fig 4.

Figure 4.Three-dimensional printed positive airway pressure mask made using computed tomography scan images.
Journal of Cosmetic Medicine 2022; 6: 27-33https://doi.org/10.25056/JCM.2022.6.1.27

Fig 5.

Figure 5.Subjective outcomes. 3D, three-dimensional; CT, computed tomography.
Journal of Cosmetic Medicine 2022; 6: 27-33https://doi.org/10.25056/JCM.2022.6.1.27

Table 1 . Subjective outcomes.

Variable (point)NasalPillow 3DPillow CTp-value
Wearing sensation2.22±0.752.74±0.892.44±0.930.056
Air leakage1.37±0.492.33±1.181.96±0.980.003*
Positive pressure1.52±0.701.19±0.481.56±0.850.054

Values are presented as mean±SD..

3D, three-dimensional; CT, computed tomography..

*Statistically significance (p<0.05)..


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