Pulp oxygen saturation measurement as a diagnostic tool for assessing pulp status in primary teeth

A systematic review and meta-analysis

Abstract

Objectives: 

This study aimed to determine the mean oxygen saturation values (SpO₂) in primary teeth using pulse oximetry.

Materials and Methods: 

This comprehensive literature search on pulse oximeter used for primary teeth in determining pulp vitality using MeSH terms in four electronic databases, including PubMed, Scopus, Cochrane Library, and Ovid^SP, from January 1990 to January 2022. Studies reported the sample size and the mean SpO₂ values (with standard deviations) for each tooth group were included. The quality assessment of all the included studies was done using the Quality Assessment of Diagnostic Accuracy Studies-2 tool and the Newcastle-Ottawa Scale. The meta-analysis included studies reporting means and standard deviations of SpO₂ values. The I² statistics were used to determine the degree of heterogeneity among the studies.

Results: 

A total of 90 studies were identified, of which five met the eligibility criteria that were qualified for the systematic review, and among them, three were included in the meta-analysis. All five included studies were of low quality due to the high risk of bias related to the patient selection, index test, and uncertainties about outcome valuation. In the meta-analysis, the mean fixed-effect measure of oxygen saturation in the pulp of primary teeth was 88.45% (confidence interval: 83.97%–92.93%).

Conclusion: 

Though most of the available studies were of poor quality, the SpO₂ in the healthy pulp can be established (minimum saturation, 83.48%) in primary teeth. Reference values established might help clinicians to assess changes in pulp status.

Introduction

Pulp tissue is a vital organ of the tooth and is clinically invisible. The dentist has to use indirect methods to determine the tooth’s vitality.[¹] Assessing tooth vitality is an essential diagnostic procedure for constructing a proper treatment plan in dental practice. Nevertheless, the most frequently used conventional pulp vitality tests detect pulp vitality by assessing neural responses. Consequently, false-negative or false-positive responses can be obtained.[²] Furthermore, these methods can produce unpleasant and painful sensations.[³] In addition, the children’s coordination is deprived due to their extreme sensitivity to noxious stimuli, particularly following the traumatic dental injury, so applying sensory tests to achieve accurate subjective responses is challenging.[⁴] Several noninvasive vitality tests have been advocated to overcome these impediments, which measure teeth vascular circulation, such as laser Doppler flowmeter (LDF), dual-wavelength spectrophotometry, pulse oximetry, and light photoplethysmography.[^5-9]

The pulse oximeter is considered one of the most reliable and noninvasive tools for assessing pulp vitality by monitoring the intensity of the light transmitted through the tooth, which measures the absorption of oxygenated and deoxygenated hemoglobin.[¹⁰] The oxygenated and deoxygenated hemoglobin absorbs different quantities of light (red and infrared), which are perceived by the photodetector diode and a microprocessor.[¹¹] Gopikrishna et al. reported that the pulse oximeter has been superior to cold and electric pulp tests (EPT) in detecting non-vital teeth.[¹²] Sharma et al. postulated that employing a pulse oximeter in diagnosing pulp vitality is essential to analyze the dental pulp’s inflammatory state, which may save many teeth with a doubtful subjective response, particularly in pediatric dentistry.[¹³]

A pulse oximeter has been used in several studies to test the vitality of teeth, with varying diagnostic outcomes.[^14-16] However, the authenticity of the pulse oximeter values is associated with the vitality of the tooth not being appropriately documented. A significant gap has been observed in the collective evidence on pulse oxygen saturation values to know the vitality of the tooth. Only one systematic review has evaluated the pulp oxygen saturation levels in permanent teeth.[¹⁷] On the other hand, using a pulse oximeter for primary teeth has been introduced as a new approach to assessing pulpal blood flow in primary teeth. There is a need to establish the oxygen saturation values using a pulse oximeter in primary teeth. Therefore, this study aimed to conduct a systematic review and meta-analysis to determine the mean oxygen saturation values (SpO₂) in primary teeth using pulse oximetry.

Materials and Methods

The present study was registered with the International Prospective Register of Systematic Reviews under registration number CRD42022306044 (accessible at www.crd.york.ac.uk/Prospero) and performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.[¹⁸]

Search strategy and study selection

The literature search on the pulp vitality devices for primary teeth was analyzed to identify all the potential studies regarding pulse oximeter as a pulp vitality device. The search strategy was confined to the following electronic databases: MEDLINE (via PubMed; www.ncbi.nlm.nih.gov/pubmed), the Cochrane Central Register of Controlled Trials (CENTRAL; http://www.thecochranelibrary.com), Scopus (https://www.scopus.com/home.uri) and Ovid^® (https://ovidsp.dc1.ovid.com/ovid-a/ovidweb.cgi). Apart from these databases, a supplementary search was performed in Google Scholar to segregate the published studies appropriate for this review from January 1990 to January 2022, limited to English. For each database, a search strategy was designed involving different combinations of restricted vocabulary identifiers such as Medical Subject Heading Terms (MeSH) or simple text words and their synonyms, as well as Boolean operators (“OR” and “AND”) and truncation to expand and narrow the search. Various combinations and variations of the keywords “pulse oximetry,” “dental pulp test,” and “primary teeth” were used. In addition, a hand search was conducted to identify other potentially relevant studies in the cross-references from all the retrieved articles.

Two reviewers (SK and SR) independently evaluated the titles of all the studies identified in the initial databases and hand searches. Later, abstracts of the studies were assessed after removing the duplicates and irrelevant titles. Finally, all the abstracts that fulfilled the inclusion criteria were included in the analysis. The abstract in the studies did not provide any meaningful information; the full text of the article was also reviewed. Any disaccord between the two reviewers was resolved by consulting a third reviewer (SN), an expert working in the subject area.

Eligibility criteria

The population, intervention, comparison, outcomes, and study design method were applied to establish this systematic search’s inclusion and exclusion criteria. Inclusion criteria: (i) Studies performed on a primary tooth involving pulse oximetry to determine the dental pulp oxygen saturation. (ii) Studies reported the sample size and the mean SpO₂ values (with standard deviations) for each tooth group. Exclusion criteria: In vitro studies, Case reports, case series, narrative reviews, systematic reviews, and letters to the editor were excluded before checking the abstract.

Data extraction and synthesis

Full-text versions were obtained for all the studies that met the eligibility criteria. A calibration exercise (using two papers) was conducted with all reviewers before commencing the data extraction and methodological or reporting quality appraisal. Disagreements, if any, were resolved by consensus, and where needed, any unresolved differences were resolved by a third reviewer. The two independent reviewers read the full-text articles. The succeeding data were collected from the included studies using a standardized form: Patient age, tooth group (incisors, canine, molars), type of pulse oximeter and probe used, sample size, SpO₂ levels (means and standard deviations), confirmation test used, and whether a control group was included or not. The authors of selected studies were contacted via E-mail to have the studies for the final analysis in case of missing data or clarification.

The I² statistic was used to determine study heterogeneity, with I² values <25%, 25%–75%, and >75%, indicating moderate, intermediate, and high heterogeneity. All meta-analyses were performed with R software version 3.5.0 (R Project for Statistical Computing, Vienna, Austria) (package, Meta; the United States Environmental Protection Agency, Corvallis, OR, USA).

Assessment of study quality

The diagnostic accuracy of each included study was assessed with the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) tool, and the Newcastle-Ottawa scale (NOS) was adapted for evaluating the quality of reporting the study.[^19,20] The study quality was evaluated as low, moderate or high.

Reliability

Cohen’s kappa (κ) for overall inter-rater agreement for the QUADAS-2 tool was 0.77 (91% agreement) and 0.75 (% agreement) for the NOS tool. These values indicate a high level of understanding. One of the included studies was selected using an online random number generator and re-evaluated 4 weeks later to establish intra-rater reliability. When utilizing the QUADAS-2 tool, the intra-rater agreement was 0.98 (98% agreement) for both SK and SR, 0.84 (95.6% agreement) for SK, and 0.73 (92.8% agreement) for SR when using the NOS criteria.

Results

Ninety studies were identified through the search strategy from all four databases (PubMed, Cochrane Library, Scopus, and Ovid^®) and Google Scholar. After eliminating the duplicates, 68 were available for further analysis. Of these, 48 studies were excluded after reading the titles with reasons being irrelevant studies (42), review articles (4), and systematic review (2). Subsequently, 20 studies were available for the abstract phase; after the screening, fifteen were excluded for not meeting the eligibility criteria, and only five studies were included for the full-text reading and qualitative analysis. Finally, only three studies were included in the quantitative analysis because of the lack of homogenous data in two studies. The inter-rater agreement corresponding to kappa statistics for the methodological quality assessments was over 0.93 for all the categories. A flow diagram of the included studies was presented, adhering to the PRISMA [Figure 1].

Figure 1: Flow diagram of study identification, selection, and inclusion

Among the included studies, two were conducted in India, and the other three were performed in Brazil, Germany, and Turkey.[^13,21-24] The study participants include both genders, ranging from 4 to 15 years. All five studies have used different pulse oximeter models (by brand name) with a custom-made or specially modified probe [Table 1]. A total of 259 (88 incisors and 171 molars) teeth were included in the analysis. The recorded values of SpO₂ levels were from 83.48% to 93%. Three studies have performed the LDF,[²³] EPT,[²⁴] and thermal test[¹³] to confirm pulp vitality, whereas confirmation tests were not performed in the other two studies [Table 2].[^21,22]

Table 1: Characteristics of the studies included in the systematic review and method of diagnostic confirmation

Table 2: Sample size, mean and standard deviations values among the included articles

For the qualitative analysis, QUADAS-2 was used for the diagnostic accuracy of the employed tool in the five studies [Table 3]. The NOS tool for cross-sectional studies was used to perform the reporting studies’ quality assessment [Table 4]. Due to the substantial risk of bias associated with the applicability and analysis of the index test, the unknown risk associated with patient selection, and concerns about general applicability, the studies were mostly of moderate quality [Table 3]. The quality of the cross-sectional studies was rated as moderate due to the high risk of bias related to the representation of the sample, lack of description of inclusion criteria of subjects and sampling strategy, a lack of justification for the sample size, whereas moderate risk of bias due to concerns about the outcome assessment and the lack of description of the laboratory methods employed or the use of non-standard methods [Table 4].

Table 3: Quality assessment of studies using the Quality Assessment of Diagnostic Accuracy Studies-2

Table 4: Quality assessment of studies with the Newcastle-Ottawa scale adapted for cross-sectional studies

Meta-analysis

Only three studies performed on the 88 incisor teeth were included in the meta-analysis.[^13,21,22] The mean fixed-effect measure of SpO₂ in the dental pulp of these teeth was 88.45% (95% confidence interval, 83.97%–92.93%). The individual study outcomes from the included studies for this analysis were displayed in Figure 2.

Figure 2: Forest plot of individual and combined effect measures of mean oxygen saturation levels in the dental pulp of the primary tooth in the included studies

Discussion

The development of a clinical diagnostic and treatment plan is complicated by inaccurate assessment of the dental pulp status.[¹] During treatment, inadvertent dental pulp removal will enhance the complexities of the teeth and lead to dental fractures. On the other hand, traumatized dental pulp may develop complications due to necrosis, leading to irreversible internal and external absorption of roots, tooth loss, and other significant complications.[²⁵]

The pulse oximeter is the foremost reliable, noninvasive diagnostic device that relies on measuring arterial blood oxygen saturation, studied extensively in recent years.[²⁶] However, several studies have reported various reference values in identifying the pulp vitality of primary, permanent, and immature permanent teeth.[^22,27,28] Hence, the present systematic review was planned to establish a proper reference value in primary teeth to identify tooth vitality using a pulse oximeter device. The mean saturation values analyzed in the present study were 88.45% for the primary incisors after considering the possible confounding factors and risk of bias among the finally available studies.[^13,21-24] These values reported in the present Systematic review may serve as a clinical reference for determining the vital pulp status in primary teeth.

The quality assessment for the included studies was done using QUADAS-2 and NOS.[^19,20] The diagnostic accuracy among the studies was assessed using the QUADAS-2 tool because of its high transparent bias rating, highlighting the strengths and weaknesses and applicability of primary diagnostic accuracy studies.[¹⁹] In contrast, cross-sectional studies were assessed to evaluate quality in reporting the studies because of the ease of use directed to incorporate quality assessments in interpreting meta-analytic results.[²⁰] However, it is essential to acknowledge that no study is perfect, especially diagnostic studies, subject to several sources of bias, such as a diagnostic review. It can also be noted that observational studies are inherently heterogeneous.

The included studies’ high heterogeneity (I² = 97%) may directly relate to the study design, as most were diagnostic studies. This heterogeneity aligns with the quality of studies assessed by the abovementioned instruments. Thus, the values observed between the included studies cannot be explained exclusively by sampling error but rather by factors related to the differences between samples (participants), ages, oximeter models and brands, measurement methods, and outcome analyses.

Although it was impossible to establish a summary value for the different tooth groups, one study on molar teeth failed to mention the mean and standard deviation for the tooth groups evaluated. This condition could be linked to the test’s sensitivity and specificity, which were both high (1.00 respectively), as mentioned by Sharma et al.[¹³] However, the other two studies have not mentioned the data on sensitivity and specificity, which will impact the quality assessment to draw the relevant conclusion.[^21,22] The weighted mean of the fixed effect measure was combined with the minimum and maximum limits for the incisor tooth group, enabling us to conclude that pulse oximetry can be used to assess dental pulp vitality and detect pulp abnormalities in a variety of clinical circumstances. To the best of the authors’ knowledge, this is the first evidence-based systematic approach to the available literature regarding the mean oxygen saturation values (SpO₂) in primary teeth using pulse oximetry. It is an effective and objective method for determining the vitality of pulp tissue in primary teeth in clinical practice.

The clinical significance of the present study is that it contributes to the development of clinical protocols that can confirm the potential of pulse oximetry as a diagnostic tool for determining pulp vitality in primary teeth. Due to the significant variations of the included studies, most were observational studies and were low-quality due to the high risk of bias. It is essential to develop studies with a design that can promote a higher level of evidence and control bias, particularly for diagnostic accuracy studies. In addition, improvements in pulse oximeters are needed to develop specific devices for teeth measurements, thus facilitating the routine use of these oximeters in clinical practice.

Conclusion

Despite the potential for confounding factors and bias in the included studies, the values revealed in this study are clinically relevant for both specialists and clinicians since they can be utilized as reference parameters for assessing changes in pulp status. The findings of this study reveal that oxygen saturation levels in the normal pulp could be established was 88.45% (minimum 83.97%, maximum 92.93%) in primary incisor teeth, which could be helpful as a clinical reference criterion.

Trail registration

This systematic review and meta-analysis was registered with the International Prospective Register of Systematic Reviews under registration number CRD42022306044 (available at www.crd.york.ac.uk/Prospero).

Ethics approval and consent to participate

Not applicable.

Data availability

The analyzed data during the current study are available from the corresponding author upon reasonable request.

Financial support and sponsorship

The present study was partly funded by Department of Science and Technology (DST), India. The funding agency had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Conflicts of interest

There are no conflicts of interest.