Background
Every aspect of life has been influenced by an outbreak of the new coronavirus disease (COVID-19) in China [
1] which greatly changed the routine in dental clinics. Due to the COVID-19 pandemic, the Centers for Disease Control and Prevention (CDC) recommended in principle, avoiding aerosol-generating procedures in the dental environment whenever possible, not using equipment that produces aerosols, and prioritizing the use of hand instruments only [
2].
However, many of the instruments used in dentistry are rotary, such as handpieces, water syringes, and ultrasonic scalers. The spray created by these instruments can carry, in addition to water, droplets of saliva, blood, and microorganisms, which can pose a risk of infections for healthcare professionals and patients [
3].
Particles formed by liquids and solids dispersed and suspended in the air are aerosols, which become bioaerosols when microorganisms excreted by the body dissolve with the aerosols through the act of coughing, breathing vigorously, sneezing, or speaking loudly [
4,
5].
Micik et al. used the terms “aerosol” and “splatter” in 1969, in which they were defined as particles smaller and larger than 50 micrometers (µm) in diameter, respectively. The first term refers to small particles that remain in the air for a period of time before being deposited on surfaces or entering the airways. The second are particles or droplets that are forcibly ejected from the operating site, reaching a trajectory similar to that of a bullet until they come into contact with a surface or fall to the ground [
6].
With a simulation using computational fluid dynamics to quantify the transport of large droplets and aerosols in dental clinic environments, we better understand the risks associated with a common dental procedure such as ultrasonic scaling. Aerosols below 15 μm remain in the air for up to 7.13 min on average and can travel up to 25.45 m on average from their source, potentially contaminating entire clinics [
3].
The water spray droplets produced during ultrasonic scaling are extremely light in weight and release large numbers of microorganisms into the air [
7]. The bacterial challenge appears to be considerable and it is likely that viruses and bacteria can be spread in this way [
8]. It should also be taken into account that particles ranging from 0.3 to 5
µm increase significantly after instrumentation with an ultrasonic scaler [
9] and the variation in ultrasonic frequency causes an increase in surface contamination, as well as the type of suction used, influences the degree of contamination [
10].
Due to the fact that ultrasonic scaler is one of the equipment that produces the most aerosol and can be responsible for spreading the SARS-CoV-2 virus during dental care, which is a major concern among dentists, especially periodontists, this work aimed to carry out a systematic review of the evidence of the reach of the aerosol, produced by ultrasonic scaler during scaling and prophylaxis, in the contamination of the dental environment and the influence of the use of intraoral suction devices in the reduction of this contamination.
Materials and methods
The present systematic review was registered in the PROSPERO (International Prospective Register of Systematic Reviews) [
11] under the number #CRD42020191209 and conducted in accordance with the recommendations of the “Cochrane Handbook for Systematic Reviews of Interventions” [
12] and following the guidelines of the PRISMA checklist [
13]. Clinical questions were organized using the “PECO” (Population, Exposition, Comparison and Outcome) strategy.
Objective
The objective of this study was to carry out a systematic review of the evidence of the reach of the aerosol in distance traveled, produced by ultrasonic scaler during scaling and prophylaxis, in the contamination of the dental environment and the influence of the use of intraoral suction devices in the reduction of this contamination.
Focus question
What is the evidence of the reach of the aerosol in distance traveled produced by scaling with ultrasonic scaler in the contamination of the dental environment and the influence of intraoral suction devices in the reduction of this contamination?
Search strategy
Scientific literature was searched in six electronic databases until June 19, 2021 through Pubmed (
https://pubmed.ncbi.nlm.nih.gov), EMBASE (
https://www.embase.com), Web of Science (
www.webofscience.com), Scopus (
www.scopus.com), Virtual Health Library (VHL - in the LILACS, BBO, and IBECS databases) (bvsalud.org), and Cochrane Library (
www.cochranelibrary.com). No restrictions on language or publication date were imposed. In addition to the electronic search, a manual search was performed using the reference lists of the selected articles. In addition, information was searched in the OpenGrey open access database [
14] for unpublished studies (grey literature) using the same terms.
The following MeSH terms (Medical Subjects Headings) [
15] were used for the search: “dental care”, “dental prophylaxis”, “ultrasonic therapy”, “dental scaling” and “aerosols”. In addition, other synonyms of DeCS (Health Sciences Descriptors) [
16] and free terms were applied in the search, they are: “delivery of dental care”, “dental treatment”, “ultrasonic instrumentation”, “ultrasonic dental scale”, “ultrasonic scaling”, “dental cleaning”, “subgingival scaling”, “supragingival scaling”, “splatter”, “aerosol contamination”, “bioaerosol”, “bio-aerosol”, “airborne”, “dental aerosols”. All descriptors were connected through the Boolean operators “AND” and “OR”. The search strategy is described in Tables
1 and
2. The Endnote web software was used to organize the studies [
17].
Table 1
Search strategy associated to Population and Exposition
Population | #1 | (dental care [MeSH] OR dental prophylaxis [MeSH] OR ultrasonic therapy [MeSH] OR dental scaling [MeSH] OR delivery of dental care OR dental treatment OR Ultrasonic instrumentation OR ultrasonic dental scale OR ultrasonic scaling OR dental cleaning OR subgingival scaling OR supragingival scaling) |
Exposition | #2 | (aerosols [MeSH] OR Splatter OR aerosol contamination OR bioaerosol OR bio-aerosol OR airborne OR dental aerosols) |
Search combination | #1 AND #2 | | | | | | |
Table 2
Specific search strategy for each Database
Pubmed | #1 “dental care“[MeSH Terms] OR “dental care“[Title/Abstract] OR “delivery of dental care“[Title/Abstract] OR “dental treatment“[Title/Abstract] OR “ultrasonic therapy“[MeSH Terms] OR “ultrasonic therapy“[Title/Abstract] OR “ultrasonic scale*“[Title/Abstract] OR “ultrasonic instrumentation“[Title/Abstract] OR “ultrasonic dental scale*“[Title/Abstract] OR “ultrasonic scaling“[Title/Abstract] OR “dental prophylaxis“[MeSH Terms] OR “dental prophylaxis“[Title/Abstract] OR “dental cleaning“[Title/Abstract] OR “dental scaling“[MeSH Terms] OR “dental scaling“[Title/Abstract] OR “subgingival scaling“[Title/Abstract] OR “supragingival scaling“[Title/Abstract] |
#2 “aerosols“[MeSH Terms] OR “aerosols“[Title/Abstract] OR “splatter“[Title/Abstract] OR “aerosol contamination“[Title/Abstract] OR “bioaerosol“[Title/Abstract] OR “bio-aerosol“[Title/Abstract] OR “airborne“[Title/Abstract] OR “dental aerosols“[Title/Abstract] |
#1 AND #2 |
Web of Science | #1 “dental care” OR “Delivery of dental care” OR “dental treatment” OR “ultrasonic therapy” OR “ultrasonic scale*” OR “ultrasonic instrumentation” OR “ultrasonic dental scale*” OR “ultrasonic scaling” OR “dental prophylaxis” OR “dental cleaning” OR “dental scaling” OR “subgingival scaling” OR “supragingival scaling” |
#2 aerosols OR splatter OR “aerosol contamination” OR bioaerosol OR bio-aerosol OR airborne OR “dental aerosols” |
#1 AND #2 |
Scopus | #1 TITLE-ABS-KEY ( ( “dental care” OR “Delivery of dental care" OR “dental treatment" OR “ultrasonic therapy" OR “ultrasonic scale*" OR “ultrasonic instrumentation" OR “ultrasonic dental scale*" OR “ultrasonic scaling" OR “dental prophylaxis" OR “dental cleaning" OR “dental scaling" OR “subgingival scaling" OR “supragingival scaling" ) ) |
#2 TITLE-ABS-KEY ( ( aerosols OR splatter OR “aerosol contamination" OR bioaerosol OR bio-aerosol OR airborne OR “dental aerosols" ) ) |
#1 AND #2 |
BVS | #1 mh:“dental care” OR “dental care” OR “Delivery of dental care” OR “dental treatment” OR mh: “ultrasonic therapy” OR “ultrasonic therapy” OR “ultrasonic scale*” OR “ultrasonic instrumentation” OR “Ultrasonic dental scale*” OR “ultrasonic scaling” OR mh:“dental prophylaxis” OR “dental prophylaxis” OR “dental cleaning” OR mh:“dental scaling” OR “dental scaling” OR “subgingival scaling” OR “supragingival scaling” |
#2 mh:aerosols OR aerosols OR splatter OR “aerosol contamination” OR bioaerosol OR bio-aerosol OR airborne OR “dental aerosols” |
#1 AND #2 |
Embase | #1 dental procedure’/exp/mj OR ‘dental procedure’:ab,ti OR ‘delivery of dental care’:ab,ti OR ‘ultrasound therapy’/exp/mj OR ‘ultrasound therapy’:ab,ti OR ‘ultrasonic scaler’/exp/mj OR ‘ultrasonic scaler’:ab,ti OR ‘ultrasonic instrumentation’:ab,ti OR ‘ultrasonic dental scale*’:ab,ti OR ‘dental prophylaxis’/exp/mj OR ‘dental prophylaxis’:ab,ti OR ‘dental scaling’/exp/mj OR ‘dental scaling’:ab,ti OR ‘subgingival scaling’:ab,ti OR ‘supragingival scaling’:ab,ti |
#2 ‘aerosol’/exp/mj OR aerosol:ab,ti OR splatter:ab,ti OR ‘aerosol contamination’:ab,ti OR ‘bioaerosol’/exp/mj OR bioaerosol:ab,ti OR ‘bio aerosol’:ab,ti OR ‘airborne particle’:ab,ti |
#1 AND #2 |
Cochrane | #1 MeSH descriptor: [Dental Care] explode all trees OR delivery of dental care OR dental treatment OR MeSH descriptor: [Ultrasonic Therapy] explode all trees OR ultrasonic scale* OR ultrasonic instrumentation OR ultrasonic dental scale* OR ultrasonic scaling OR MeSH descriptor: [Dental Prophylaxis] explode all trees OR dental cleaning OR MeSH descriptor: [Dental Scaling] explode all trees OR subgingival scaling OR supragingival scaling |
#2 MeSH descriptor: [Aerosols] explode all trees OR splatter OR aerosol contamination OR bioaerosol OR bio-aerosol OR airborne OR dental aerosols |
#1 AND #2 |
Selection criteria
The eligibility requirements were outlined according to the PECOS strategy:
P (Population of interest): patients undergoing dental scaling treatment with ultrasonic scaler were included;
E (Exposure): Aerosol produced by ultrasonic scaler;
C (Comparison): comparison of contamination reduction with the use of different intraoral suction devices;
O (Outcome): contamination of the environment caused by aerosol from ultrasonic scaler;
S (Study design): randomized controlled trials (RCT) were included.
Exclusion criteria were studies that use manual scaling; studies that included prior use of mouthwashes and studies that used external air decontamination systems.
The eligibility requirements considered for studies to be included in this review were: human studies; studies that evaluated the range of the aerosol produced by ultrasonic during scaling procedures; studies that evaluated the contamination of the environment by the aerosol produced by dental ultrasonic and studies that used intraoral suction reduction devices to control the aerosol.
Screening process
At first, two reviewers (PGL and MCN) independently selected titles and abstracts. Disagreements were resolved through discussion with a third reviewer (TRSA). Studies that appeared to meet the inclusion criteria or that did not have sufficient information in their titles and abstracts were selected for evaluation of the full article at a later stage. The same reviewers independently assessed full texts to determine whether studies were eligible. Data extraction and risk of bias were performed in studies that met the inclusion criteria.
All data were extracted individually by two reviewers (PGL and MCN) and discrepancies were discussed by a third reviewer (TRSA). Reviewers were calibrated in applying the inclusion and exclusion criteria applied to a sample of 20% of the studies to determine inter-rater agreement (Kappa = 0.80). All necessary data were found in the studies, and it is not necessary to contact the authors for clarification.
The synthesis of the extracted data was organized in table with the following variables: first author, year of publication, country of origin, type of clinic, patient involved, type of suction device, collected distances, type of incubation, outcome measure and results.
Outcome measures
The outcome measure was the count of bacterial colony forming units (CFU) present in the oral aerosol, produced by ultrasonic scaler during scaling and prophylaxis, collected through plates with culture media positioned at different distances around the patient and/or the clinic.
Assessment of the risk of bias and quality
The quality assessment of the studies was performed by the same reviewers (PGL and MCN) independently and any disagreement between them was resolved through consultation with a third party (TRSA).
The Cochrane Collaboration Tool was used to assess the risk of bias using the updated Risk of Bias 2 (RoB 2) tool [
18].
This tool evaluates five domains that can be classified as: low risk of bias, some concerns or high risk of bias. The domains are:
D1: Randomization process;
D2: Deviations from intended interventions;
D3: Missing result data;
D4: Measurement of the result; and.
D5: Selection of reported result.
This tool also allows for ranking the overall risk of bias, which receives the least favorable ranking among the assessed risks for the domains. The judgment about the risk of bias resulting from each domain is proposed by an algorithm, based on signaling questions, which help the reviewer to assess the important factors for the evaluation of each domain.
Statistical analysis
Meta-analyses were performed using the Review Manager software, Version 5.4.1 (Nordic Cochrane Center, Cochrane Collaboration) [
19]. A meta-analysis of the reach of the aerosol in the contamination of the environment and a meta-analysis of the reduction of the contamination of the environment were performed, comparing the use of high-volume evacuation (HVE) and low-volume evacuation (LVE), both expressed in mean and standard deviation of CFU/m³. The inverse variance statistical method was used, with a random effects analysis model. Forest plots were calculated for 95% confidence intervals (CI) and
P values. Heterogeneity between study results and quantification of inconsistency was assessed using the I
2 test. Results were expressed as standardized mean difference. Subgroups were established according to the distance of the aerosol reach in relation to the patient’s oral cavity.
Analysis of certainty of evidence
The quality of evidence (certainty in effect estimates) was analyzed by two reviewers (PGL and PA) using the assessment, development and assessment of recommendations (GRADE) approach [
20]. The domains evaluated in clinical studies were: risk of bias, inconsistency, indirectness, imprecision and publication bias.
GRADE defines the quality of scientific evidence in a clearer and more objective way, and can be classified as high, moderate, low or very low.
Discussion
Aerosols and splashes are the main sources of environmental contamination during dental procedures [27]. This fact has become one of the biggest concerns among dentists during the COVID-19 pandemic. In order to review the evidence related to air contamination generated by the reach of the aerosol produced during the use of ultrasonic scaler for scaling and prophylaxis, a detailed search was carried out in six databases and five randomized controlled trials who met the inclusion criteria were found.
The high bacterial counts (log10 5.0 CFUs/mL) indicate that there is a worrying contamination of the air after the use of ultrasonic scaler, even when using a high volume suction combined with another device [
22]. This contamination was shown in the first meta-analysis (Fig.
3) carried out on the results of randomized controlled studies [
23‐
25], in which even with the use of high-volume suction, there was a significant difference in the increase of bacteria in the air (
P < 0.00001/CI 0.99, [0.67, 1.31]).
Of the five randomized controlled trials included, only two [
23,
24] found a statistically significant reduction in the mean CFUs (
p < 0.001) collected during the use of ultrasonic scaler when using two different suction methods, where one used the high-pressure suction cannula volume attached directly to the ultrasonic pen [
23], and the other the high volume suction combination added plus a high volume suction hose [
24]. The other RCTs [
21,
22] did not find significant differences (
p > 0.05) between the two suction methods studied. However, the number of bacteria in the air tends to be higher when conventional suction devices are used, that is, low volume ones [
25]. Furthermore, the high-volume suction device used separately, without any modification, does not appear to be as effective in reducing the amount of aerosol formed [
21]. Despite this, when a meta-analysis (Fig. 4) was performed comparing the use of high and low volume suction devices in three RCTs [
21,
23,
25], there was no significant difference in the amount of aerosol formed during the use of ultrasonic scaler.
As limitations of the study, a difference was observed in the methodologies used by the studies, which makes a more accurate comparison difficult, as the distance at which the agar plates are placed to collect the samples, the plate exposure time and the different dental environments, can influence the comparison of results. Two RCTs [
22,
23] placed the sample collection plates six inches (15.24 cm) from the patient’s mouth and the others used different distances such as 40 and 150 cm [
25]; 12 and 20 inches (approximately 30 and 50 cm) [
21] and at three different distances between 2 and 4 feet (approximately 60–120 cm) (24). Regarding the exposure time of the plaque during the use of ultrasound, there was a variation between 5 min [
23,
25] and 20 min [
24]. Therefore, the shorter the plate exposure time and the greater the distance, the lower the chance of CFU collection. And regarding the dental environments just one study used a multi-chair environment [
24].
Another limitation of the study refers to the fact that it was not possible to assess publication bias as only five studies were included for meta-analysis, with low power to detect possible bias.
Conclusions
There is an increase in the concentration of bioaerosol in the dental environment during the use of ultrasonic scaler in scaling/prophylaxis, reaching up to 2 m away from the patient’s mouth.
The use of good suction, whether low volume, high volume or a combination of different devices, can be effective in reducing air contamination in the dental environment, with no important difference between different types of suction devices.
Final considerations: To minimize the risk of infection for the operator, it is recommended to use adequate precautions, such as the use of adapted masks. And to minimize the risk of cross-infection, especially between patients, and contamination of surfaces, it is recommended to space appointments by at least 30 min and always use suction devices respectively.
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