Development of a novel dental thermal imaging application

Thermography is a process where a thermal camera captures and generates an image by using infrared radiation, emitted from an object. Thermography has had limited use in dentistry, but with recent technological advances, thermography has been employed for the production of digital images. An Android software application was developed, called the Dental Thermal App (DTA), to facilitate a simple, cost-effective, systematic and clinically-based workflow. The application functions on a mobile device and requires the use of a connected Flir camera, which has 19 200 pixels of thermal image resolution, measures temperatures between -20 to 120ºC and can detect differences in heat as little as 0.01 ºC. Thermal imaging provides an alternative method for visualization for identification and assessment, with applications in patient records, documentation, infection control, education and laboratory clinical work. DTA has been developed, tested and launched and is a novel, low-cost, portable, non-invasive digital tool for dentistry. DTA provides an alternative mobile tool that provides improved accessibility for clinicians and patients.


Introduction
Thermography is a process where a (thermal) camera captures and generates an image by using infrared radiation, emitted from an object [1]. The image provides an opportunity to visibly record invisible (to the human eye) infrared energy or heat. Thermography is noninvasive, non-contact, user-friendly and a portable imaging method and has been used in various industrial fields, such as engineering and construction.
Thermography is now an evolving and expanding field in medicine [2] as a diagnostic tool, currently used to diagnose vascular malformations [3], thyroid nodules [4] and differentiating different intraocular tumors [5]. Specific to medicine, thermography is a field of science that analyzes and records the biothermal changes in various structures to assess health or disease [6]. Using infrared radiation, a pixel map, also known as thermogram, is generated to record biothermal change. Each temperature change is defined with a different color [7]. A thermogram with less colors due to less heat production may suggest areas of poor blood circulation, and vice versa [6].
Thermography has had limited use in dentistry [8], but with recent technological advances, thermography has been employed for the production of digital images [8,9] to assess changes in the temperature of (1) restorations, (2) inflamed periodontal tissues, (3) disease of the temporomandibular joints and (4) detecting intraosseous temperature changes during dental implant placement [10,11]. Thermography has recently been used to monitor inflammation after dental surgeries [10] and has shown promise as a tool to diagnose pathological conditions [10].
Digital dentistry technologies tend to have limited use, due to the high cost of equipment [12], software [13], and the challenging workflow [14]. Dental thermography has also faced these challenges.
This report explores the development of a novel dental thermal imaging application that is simple, cost-effective and efficient.

Materials and Methods
An Android software application was developed, called the Dental Thermal App (DTA), to facilitate a simple, cost-effective, systematic and clinically-based workflow. The application functions on a mobile device and requires the use of a connected Flir camera.

Functionality
The application is compatible with any Android-based mobile de- To begin, tap the Start button ( Figure 2). Connect and turn on and the Flir camera (either One Pro or the One Pro LT) and allow DTA to access the camera (select OK). The DTA functions as an imaging app, similar to any smart phone camera. The image is based on heat and has a slight lag; therefore, it is recommended to move the phone slowly, allowing the image to process and then gently pressing the shutter release to take the thermal image. There are several selectable icons across the top of the screen (Figure 4), such as Visual, MSX, Thermal Palettes and Temperature.
The Visual feature ( Figure 4) provides a standard nonthermal image, which is useful as a comparison or orientation image.
Thermal images can be generated selecting the Thermal icon ( Figure   5). There are several thermal palettes or filters to choose from, which drop down when the Palette icon is selected ( Figure 6      This app also provides draw on and write on features (Figure 9).
For drawing, select the brush, desired colour and opacity ( Figure 10). Labels can also be attached to images by selecting the Text icon ( Figure   11), typing in the text and then simply sliding the label to the desired location. An eraser, other filters and emojis are also available, should the need arise. When the thermal image is ready to be saved, tap the download icon ↓ (Figure 11). A section for the Patient or Project name will drop down ( Figure 12) with a section for Notes.
Type in the required information and then tap the Save button. The image, the name and notes and all relevant information will now be saved as a png file. The saved image can now be transfer or shared through any pathway for communication (text, email, etc.).

Discussion
It is recognised in dentistry that proper visualization remains a key component to the examination [16]. Thermal imaging provides an alternative method for visualization, providing an unconventional method of identification and assessment. This permits the invisible to be visible, which presents several immediate fields of application.
The first application is patient records and documentation. In dentistry, it is essential to document certain aspects of the patient visit. Prescreening, utilizing surface temperature, has been and still remains a common practice. DTA provides a simple, accurate and cost-effective method to determine the patient's surface temperature [17] and provides the proper documentation, with the patient's name and date, ideal for records and documentation ( Figure 13).
The second application is infection control. Hard surface disinfection is critical to dentistry, but it can be difficult to confirm or recall if it was completed. Figure 14 contains images of the same countertop at approximately the same time. Figure 14 (left) is a photo image, while Figure 14 (right) is the thermal image. The thermal image depicts the energy from a recently placed hand, demonstrating that it just touched the countertop. In a dental setting, it would be prudent to disinfect that surface again. Properly fitted masks are also critical in dentistry, especially during the pandemic. The N95 fit test is quite subjective [18] and the DTA app could provide an alternative evaluation.     Education is the third application. The training of dental students involves several peripherals and materials, to provide additional information for the diagnosis and treatment of disease [19].
Many peripherals and materials are sensitive and are influenced by how they are handled by the student/operator. Improper handling and use can result in inaccurate diagnoses. The DTA app provides guidance for instruction and confirmation of appropriate operator performance. For example, Figure 16 is a thermal image of a drill performing a preparation on a model. The thermal image illustrates that substantial heat has been generated, which is detrimental to the health of the tooth [20]. DTA can be used to identify these situations and rectify the procedure before an iatrogenic problem occurs [21]. Similarly, testing a tooth's vitality may require thermal testing (with cold). If performed improperly, the wrong diagnosis could be concluded. Figure 17 illustrates this procedure and the thermal image demonstrates whether an adequate testing scenario has occurred.
A final application is laboratory clinical work. Prostheses must be properly evaluated before they are delivered to the patient.
A specific evaluation is establishing a proper bite, which is typically performed with sprays and papers. Figure 18 is a thermal image of a mandibular prosthesis. The image illustrates high temperatures at the lower front area. This was due to excessive heat caused by biting, or occluding, with the upper teeth. This energy seems concentrated in a localized area and should be equalized to the other teeth. DTA could be used as a novel visualization record to assess and document how the teeth come together prior to patient delivery.
DTA is a fluid and dynamic application. Further research is required to explore novel applications and develop research investigations. Although DTA has been developed as an application for clinicians, there is the possibility that it could be expanded as a tool for teledentistry and connected oral health.

Conclusions
A novel software application, called Dental Thermal App, has been developed, tested and launched onto Google Play. The application has been revised and approved by the Teledyne FLIR Developer Community is now available for download and use. DTA is a novel, low-cost, portable, non-invasive digital tool for dentistry. The software could provide limitless applications in imaging, assessment, identification and documentation. DTA provides an alternative mobile tool that provides improved accessibility for clinicians and patients.

Acknowledgments
A very special thank you to Lina Kalman (CDA II), for the countless hours of input and advice during development, and to Arti Saxena for Figure 17: Cold test thermography.