The first most popular and significant application of this technique is the monitoring of two physiological parameters – the pulse rate and oxygen saturation, during dental treatment of paediatric patients under general anesthesia and sedation, most commonly nitrous oxide sedation. In accordance with the American Academy of Pediatric Dentistry (AAPD) Guideline on the use of nitrous oxide for pediatric dental patients (2018) and Practice Guidelines for Moderate Procedural Sedation and Analgesia (2018) by the American Society of Anesthesiologists, continuous monitoring of the patient by pulse oximetry along with sound alarms during sedation is recommended.^[9,10] In contrast, European Academy of Paediatric Dentistry (EAPD) considers that pulse oximetry is not required for conscious sedation with nitrous oxide but is preferable in benzodiazepine sedation. They report a significant number of false positive alarms and an increased anxiety in paediatric patients to the placement of the pulse oximeter.^[11] During the sedation, administration and immediate recovery phase, the continuous pulse oximeter monitoring of oxyhemoglobin saturation must be recorded at a minimum of 15-minute intervals.^[12]

The American Dental Association (ADA) recommends baseline vital signs such as pulse rate, blood pressure, and oxygen saturation to be obtained and recorded by pulse oximeter during dental treatment under general anesthe- sia.^[13] Oxygen saturation by pulse oximetry may be clinically useful and should be considered.^[13]

Oxygen saturation and pulse rate monitoring during local anesthesia

Due to the low cost and easy use of this technology, Gandy reported it as a standard of patient care and a useful method in the dental office during local anesthesia for monitoring of hypoxia.^[14] In a systematic review of local anesthetic-related methemoglobinemia, Guay pointed out that the use of a pulse oximeter was required when infants had undergone local anesthesia, especially in children under 3 years old.^[15] Usually, it is associated with compromised patients or children with special needs. In 2019, Lu et al. compared the response of pulse oximetry and regional cerebral oxygen saturation to hypoxia in preschool children and found that pulse oximetry allowed rapid identification of hypoxic state.^[16] The authors considered this technique as an alternative to intermittent arterial blood sampling owing to its non-invasive and consecutive mechanism of monitoring.

The aforementioned articles reported the required use of pulse oximetry during dental treatment of paediatric patients when sedation and different types of anesthesia must have been used.^[9–16]

Another use of pulse oximetry in paediatric dentistry is as an objective method of assessing the patients’ dental anxiety by measuring their pulse rate at different time points of dental visit: 1. patient staying in the waiting room; 2. when the patient is sitting on the dental chair; 3. during oral examination; 4. during the dental treatment; and 5. at the end of the dental procedure.

Finger pulse oximeter has been accepted as a reliable device for direct measurement of pulse rate in dental settings which is considered as a physiological indicator of dental anxiety.^[17–19] The increase in the pulse rate corresponds to high levels of dental anxiety and stress during the dental visit.^[18] Yadav et al. found it an objective, non-invasive technique for the evaluation of physiological changes caused by the subjective nature of anxiety.^[18] The results of numerous studies are in line with their findings and using a finger pulse oximeter remains the most acceptable method to measure a patient’s heart rate.^[17,20,21] The data were recorded and analysed by a specially developed digital processing and graphic visualization software. Heart rate was chosen for analysis because it is the simplest biological parameter to measure and because an increase in heart rate is the most common physiologic indicator of anxiety and fear.^[22] It has been shown that this parameter is more in line with the anxiety experienced in dental visits than the other physiological parameters.^[23,24] There was an investigation that found a correlation indicating that self-report anxiety degree as a subjective method for assessment is comparable to heart rate as a physiological stress indica- tor.^[25] Despite these findings, for reliable assessment of dental anxiety in paediatric dental patients, researchers usually used a combination of subjective (a facial or numeric scale) and objective method (a physiological indicator).^[19,26]

In recent years, direct implementation of the mecha- nism of action of pulse oximetry in dentistry has been achieved. Several studies reported the use of this technique to monitor arterial blood oxygen saturation of dental pulp.^{[1,2,4,27-30]} Kakino et al. found that the function and vitality of dental pulp depend more on the microcirculatory system of the tissue rather than its sensory nerve respon- se.^[31] Due to the false negative results when immature traumatized teeth are inspected and the subjective response of the patient, pulp tests used to determine neural response are not suitable to be used in paediatric dentistry.^[1,3,31] Thus, the innovative methods for pulp vitality testing in attending paediatric dental patients are based on the state of the blood supply of pulp tissue. Despite the reliability and accuracy of the laser Doppler flowmetry, the latest studies emphasized several limitations of the obtained results.^[32–34] Akpinar et al., Polat et al., and Gopikrishna et al. reported false positive results due to the interference of laser transmission in case of discolouration of the crown of the tooth or contamination of the backscattered light from the periodontal tissues.^[32–34]

In searching for a non-invasive, more reliable and objective method, several researchers found that pulse oximetry is a successful technique in the monitoring of arterial blood supply of dental pulp.^{[1,2,4,27-30]} The results obtained by a significant number of studies showed that this method could be successfully used in everyday dental practice as a reliable and accurate vitality test.^[27–34] However, until 2021 no devices have been particularly developed and adjusted for dental use – modified versions of rubber dam clamps, different custom-made stainless steel or plastic adapters to the finger or earlobe sensor were reported.^[2,4,28,29] Summarising the articles evaluating arterial oxygen saturation of dental pulp in the field of pediatric dentistry, only one research conducted by Sharma et al. was identified. The authors tested a customized pulse oximeter for pulp vitality diagnostics of primary and permanent teeth and found it a valuable adjunct to diagnosing.^[35] In 2021, Grabliauskienė et al. described a new universal pulse oximeter probe holder developed at the Lithuanian University of Health and Science, Kaunas, Lithuania.^[36] Using software for 3D CAD (Computer-aided design) and a 3D printer, a sample of the holder was designed and made of thermoplastic polyester. The authors demonstrated perfect adaptation of the holder to the specific characteristics associated with the tooth type and group, anatomy, shape, size and parallel maintenance of the two photodiodes and photodetector to ensure precise measurement. The results of the study over 128 healthy asymptomatic teeth with complete root development confirmed the opportunity for the potential use of the newly developed tool for pulp test vitality in adults.^[36] However, further investigations should be conducted to identify the accuracy and reliability of the universal pulse oximeter probe holder in immature teeth.