Coronavirus spread during dental procedures could be reduced with slower drill rotation

IMPERIAL COLLEGE LONDON

Research News

    SHARE

 PRINT  E-MAIL

Dental procedures can pose a high risk of viral transmission because the tools that are used often produce aerosols, which can contain high numbers SARS-CoV-2 virions, copies of the virus causing COVID-19.

The aerosols are generated when saliva mixes with water and air streams used in dental procedures. As a result, access to routine dentistry continues to be limited during the current COVID-19 pandemic.

Dental practices, which are now back in operation, have had to introduce new room decontamination processes and personal protective equipment measures which have dramatically reduced the number of patients that can be treated in a single day. In particular, dentists need to leave long intervals between treatments, leaving rooms unoccupied to allow aerosols to dissipate. This is limiting patient access and challenging financial feasibility for many dental practices worldwide.

Now, researchers at Imperial College London and King's College London have measured and analysed aerosol generation during dental procedures and suggested changes to prevent contamination in the first place to improve safety for both patients and the dental practice workforce.

They suggest that dentists avoid using dental drills that use a mixture of air and water as the abrasion coolants, and carefully select and control drill rotation speeds for those instruments that only use water as a coolant. Parameters have been identified that would allow some procedures such as dental fillings to be provided whilst producing 60 times fewer aerosol droplets than conventional instrumentation.

Lead author Dr Antonis Sergis of Imperial's Department of Mechanical Engineering said: "Aerosols are a known transmission route for the virus behind COVID-19, so, with our colleagues at King's, we have tested suggested solutions that reduce the amount of aerosols produced in the first place. These could help reduce the risk of transmission during dental procedures."

Co-author Professor Owen Addison of King's College London's Faculty of Dentistry, Oral & Craniofacial Sciences said: "This important work describes the basic mechanisms that lead to the features of dental aerosols that we currently consider to be high risk. This has enabled us to choose drill parameters to keep our patients and the dental team safe at this difficult time. Although we cannot provide every procedure, because slowing our drills is much less efficient, we now have the basis to do more than we have done in the last 6 months."

The results are published today in Journal of Dental Research and are already being included as evidence in guides for dental practices in the UK during the pandemic. The collaborative research used the engineering expertise at Imperial and clinical expertise at King's College London's Faculty of Dentistry, Oral & Craniofacial Sciences.

The researchers used dental clinical rooms at Guy's Hospital in London to test how aerosols are generated during procedures such as decay removal, applying and polishing fillings and adjusting prostheses. They measured the aerosol generation using high speed cameras and lasers. They then used these findings to suggest modifications.

They found that using air turbine drill types, which are the most common type of dental drill, creates dense clouds of aerosol droplets that spread as fast as 12 metres per second and can quickly contaminate an entire treatment room. Just one milliliter of saliva from infected patients contains up to 120 million copies of the virus, each having the capacity to infect.

They tested a different type of drill, known as high torque electric micromotor, with and without the use of water and air streams. They found that using this drill type at low speeds of less than 100,000 rpm without air streams produced 60 times fewer droplets than air turbine drill types.

In addition, they found that aerosol concentration and spread within a room is dependent on the positioning of the patient, presence of ventilation systems, and the room's size and geometry. It is also influenced by the initial direction and speed of the aerosol itself, which can be affected by the type of cutting instrument (burr), and the amount and type of cooling water used.

The researchers say that by understanding how to reduce the amount of aerosol generated in the first place, their suggestions could help dentists practice more and help patients get the treatment they need.

They also note that patients should still not attend dental appointments if they have symptoms of COVID-19.

Professor Owen Addison from King's said: "Because of the COVID-19 pandemic, dentistry has become a high-risk practice - but the need for treatments hasn't gone away. Our suggestions could help begin to open up dentistry to patients once again."

Their suggestions have been included in the evidence appraisal in dentistry document entitled "Rapid Review of Aerosol Generating Procedures in Dentistry", published by the Scottish Dental Clinical Effectiveness Programme (SDCEP). The results from the study have also been considered by an expert task force convened by the Faculty of General Dental Practice (FGDP (UK)) and the College of General Dentistry and published in their guide entitled "Implications of Covid-19 for the safe management of general dental practice."

Co-author Professor Yannis Hardalupas of Imperial's Department of Mechanical Engineering said: "The impact of the results is significant. For example, the risk categorisation for dental procedures included in the FGDP (UK) document was certainly influenced by our work."

The team's research is ongoing. They are currently better assessing the risk of infection by quantifying the amount of saliva mixed into the generated aerosols by dental instruments.

Alterations to oral microbiota reduce the cardiovascular benefits of sport

Research by the University of Plymouth in conjunction with the UOC assesses the factors that determine the composition of buccal bacteria

UNIVERSITAT OBERTA DE CATALUNYA (UOC)

Research News

    SHARE

 PRINT  E-MAIL

IMAGE: SPORTSMEN CONSUME A LOT OF DRINKS CONTAINING SUGAR AND ACID THAT CAN AFFECT ORAL HEALTH AND THE ABUNDANCE OF BACTERIAview more 

CREDIT: PHOTO: NIGEL MSIPA/UNSPLASH

Exercise plays a key role in maintaining good physical and mental health throughout life. There is an increasing amount of scientific evidence that some of the immune system and metabolism benefits provided by sport are related to the thousands of millions of bacteria that colonize the digestive tract, from the mouth to the intestines, known as microbiota. Although most studies in this field have traditionally focused on the microorganisms present in the intestine, in recent years it has been found that the bacteria in the mouth, the second most complex microbiome in the body, after the intestine, also play an important role.

Researchers from the University of Plymouth (United Kingdom) and the Universitat Oberta de Catalunya (UOC) have carried out research and assessed the scientific evidence available regarding the impact of physical exercise on the oral cavity, especially on saliva buccal microbiota, and they have published part of the results in the journal PharmaNutrition.

"The majority of bacteria in the mouth are essential for us to be healthy. Only a minority produce illnesses such as caries or periodontitis," the researchers point out in the study. "In fact, previous studies have shown that if you inhibit the activity of the bacteria in the mouth, the cardiovascular benefits of sport are reduced," said Raúl Bescós, professor of Physiology at the University of Plymouth and first author of the study.

"There were indications of the connection between sport and oral microbiota, but also a lot of gaps, which is why we wanted to review what impacted on oral microbiota and how that could affect the benefits of sport," he added.

Diet, a key factor

Recent studies have verified the relationship between the consumption of nitrates - present in leafy green vegetables such as rocket, broccoli and spinach, and also in beetroot - and sporting performance and cardiovascular health.

The study led by Bescós with the assistance of Patrícia Casas-Agustench, professor at the UOC Faculty of Health Sciences and associate researcher at the University of Plymouth, indicates that the nitrate is a molecule that we either consume in food or produce endogenously during physical activity. It acts as a nutrient for the bacteria in the mouth, which then convert it into nitrite. This nitrite can be used in the stomach and blood vessels, increasing the flow of blood to the muscles and reducing blood pressure.

This is why leading sports clubs such as FC Barcelona ensure that the diets of their players include foods rich in nitrates. Paradoxically observational studies suggested that the prevalence of oral disorders, including dental erosion, caries and periodontitis, among elite athletes is similar to or greater than it is among the general population. And it was felt that the reason could be related to diet and hydration.

"Sportsmen consume a lot of drinks containing sugar and acid that can affect oral health and the abundance of bacteria. They also consume a lot of carbohydrates, including products with a lot of sugar like energy bars and gel, that can alter the microbiota in the mouth," said Casas-Agustench, co-author of the study. The most notable results of these studies were presented during the #SportsTomorrow conferences organized by Barça Innovation Hub.

As well as diet, other factors must be taken into account, such as dehydration or dryness of the mouth, occurring when athletes run or cycle, that can affect the diversity and abundance of oral microbiota and reduce protection for the teeth. "Some athletes often vomit as a result of the anxiety they feel before competing or during competitions because of the effort they are making, and that leads to alterations to the pH level in their mouths, erodes the enamel and alters the composition of the bacteria," she added.

Antibacterial mouthwash, only with a doctor's prescription

Another factor that has also been seen to have a negative effect on the composition and balance of oral microbiota is the use of antibacterial mouthwashes, like those containing chlorhexidine, when not prescribed by a doctor. "They inhibit the bacteria in the mouth and it has been observed that when chlorhexidine is used, the positive effects of exercise on blood pressure are drastically reduced," said Bescós, who reminded us that "oral microbiota is essential in the cardiovascular response to physical exercise. If the mouth is healthy, the bacteria help to break the nitrates down into nitrites. Otherwise, we lose much of the benefit of exercise".

The researchers also point out that there is a close relationship between oral and intestinal microbiomes, as detailed in various recent studies. We swallow nearly a litre of saliva every day and this contains a large amount of oral bacteria. Many are destroyed by the acids in the stomach but some can resist and reproduce there, a case in point being Helicobacter pylori, which causes stomach ulcers. Others can reach the colon, which they can colonize and where they will reproduce. As a result, according to Bescós and Casas-Agustench, oral health can affect intestinal health and vice versa.

The importance of chewing

"The best way to look after oral microbiota and improve sporting performance and cardiovascular health is to eat more vegetables that are rich in nitrates, but also to chew more. It helps you to salivate, and saliva is essential for regulating the pH in the mouth, and the composition and activity of bacteria in the mouth. So, products rich in fibre, like fruit, vegetables and nuts should be included in your diet," Bescós and Casas-Agustench advised.

How poor oral hygiene may result in metabolic syndrome

 

TOKYO MEDICAL AND DENTAL UNIVERSITY

Research News

    SHARE

 PRINT  E-MAIL

IMAGE: ANTI-PORPHYROMONAS GINGIVALIS ANTIBODY TITERS POSITIVELY CORRELATED WITH INTRAMUSCULAR ADIPOSE TISSUE CONTENT IN METABOLIC SYNDROME PATIENTS. ADMINISTRATION OF P. GINGIVALIS IMPAIRED GLUCOSE TOLERANCE AND INSULIN RESISTANCE, ALTERED THE GUT MICROBIOME. SKELETAL... view more 

CREDIT: DEPARTMENT OF PERIODONTOLOGY,TMDU

Researchers from Tokyo Medical and Dental University (TMDU) identify a novel mechanism by which periodontal disease may cause diabetes

Tokyo, Japan - Periodontal or gum disease is known to be a significant risk factor of metabolic syndrome, a group of conditions increasing the risk for heart disease and diabetes. In a new study, researchers from Tokyo Medical and Dental University (TMDU) discovered that infection with Porphyromonas gingivalis, the bacterium causing periodontal disease, causes skeletal muscle metabolic dysfunction, the precursor to metabolic syndrome, by altering the composition of the gut microbiome.

Periodontal bacteria have long been known to cause inflammation within the oral cavity, but also systemically increase inflammatory mediators. As a result, sustained infection with periodontal bacteria can lead to increases in body weight and lead to increased insulin resistance, a hallmark of type 2 diabetes. The function of insulin is to help shuttle glucose from the blood into tissues, most importantly to skeletal muscle, where one quarter of all glucose in stored. Unsurprisingly, insulin resistance plays a key role in the development of metabolic syndrome, a group of conditions including obesity, altered lipid metabolism, high blood pressure, high blood glucose levels, and systemic inflammation. Although skeletal muscle plays a key role in decreasing blood glucose levels, a direct connection between periodontal bacterial infection and the metabolic function of skeletal muscle has not been established yet.

"Metabolic syndrome has become a widespread health problem in the developed world," says first author of the study Kazuki Watanabe. "The goal of our study was to investigate how periodontal bacterial infection might lead to metabolic alterations in skeletal muscle and thus to the development of metabolic syndrome."

To achieve their goal, the researchers first investigated antibody titers to Porphyromonas gingivalis in the blood of patients with metabolic syndrome and found a positive correlation between antibody titers and increased insulin resistance. These results showed that patients with metabolic syndrome were likely to have undergone infection with Porphyromonas gingivalis and thus have mounted an immune response yielding antibodies against the germ. To understand the mechanism behind the clinical observation, the researchers then turned to an animal model. When they gave mice that were fed a high-fat diet (a pre-requisite to developing metabolic syndrome) Porphyromonas gingivalis by mouth, the mice developed increased insulin resistance, and fat infiltration and lower glucose uptake in the skeletal muscle compared with mice that did not receive the bacteria.

But how was this bacterium capable of causing systemic inflammation and metabolic syndrome? To answer this question, the researchers focused on the gut microbiome, the network of bacteria present in the gut and with which the organism co-exists symbiotically. Intriguingly, the researchers found that in mice administered with Porphyromonas gingivalis the gut microbiome was significantly altered, which might decrease insulin sensitivity.

"These are striking results that provide a mechanism underlying the relationship between infection with the periodontal bacterium Porphyromonas gingivalis and the development of metabolic syndrome and metabolic dysfunction in skeletal muscle," says corresponding author of the study Professor Sayaka Katagiri.

Reversible stickiness is something to smile about

    SHARE

 PRINT  E-MAIL

IMAGE: TO FACILITATE THE DEBONDING OF DENTAL RESTORATIVE MATERIALS ADHERED ON TOOTH SURFACES, UV LIGHT-EMBRITTLED DENTAL RESIN CEMENT CONTAINING PHOTODEGRADABLE POLYROTACANE (PRX) CROSS-LINKERS WAS DEVELOPED. PRX IS A SUPRAMOLECULAR INTERLOCKED POLYMER... view more 

CREDIT: DEPARTMENT OF ORGANIC BIOMATERIALS,TMDU

Tokyo Medical and Dental University (TMDU) researchers report a cross-linker for dental cement that breaks down under UV light, making treatments easier to reverse.

Tokyo - Everyone who has had tooth cavities filled knows that the best dental materials stay where the dentist puts them. The adhesion of currently available dental materials to tooth surfaces continues to improve, but what about short-term treatments that are not supposed to adhere indefinitely? TMDU researchers have developed a method of making dental materials easier to remove; their findings are published in ACS Applied Polymer Materials.

The continual improvement of long-lasting caries treatments can be regarded a triumph of dental material research. However, there are dental procedures that require non-permanent adhesion to the tooth surface, such as the fixing of orthodontic brackets. Removing adhered materials after such procedures generally requires mechanical detachment that can damage tooth enamel.

Efforts to improve removal processes have produced materials that are weakened by triggers, such as heat or electric currents. However, approved sources of these stimuli are not readily available in standard dental clinics. The researchers therefore focused on UV light-responsive materials that can be triggered by the UV sources widely used by dentists to cure resin cements and composites.

The toughness of many dental cements is a result of mixing them with a cross-linker that locks the cement molecules to each other to form a stable network. The researchers have introduced a chemical 'switch' into a new cross-linker that opens when UV light is shined on it.

"The cross-linker structure resembles rings threaded onto a piece of string with bulky stoppers at each end," study lead author Atsushi Tamura explains. "We have added a section to the string--an o-nitrobenzyl ester group--that breaks under UV light causing the rings to slide off. This has a significant effect on the stability of the cement material the cross-linker is holding in place."

The researchers used their cross-linker to stabilize a commercially available resin cement that was used to stick two polymer blocks together, or to attach a polymer block to a bovine tooth. After shining UV light on the cross-linked cement for just 2 minutes, the cement showed a significant reduction in adhesion strength in both tests, meaning separation of the bonded materials was easier following UV treatment.

"We are very encouraged by the initial findings using our cross-linker," study corresponding author Nobuhiko Yui explains. "Although the UV wavelength used to disrupt the material was not clinically appropriate in this case, we intend to develop the chemistry of our internal switch so that it can provide a facile and readily accessible method of removing adhesives in the clinic."

The article, "Light-Embrittled Dental Resin Cements Containing Photodegradable Polyrotaxane Cross-Linkers for Attenuating Debonding Strength", was published in ACS Applied Polymer Materials (DOI: https://doi.org/10.1021/acsapm.0c01024).

At the same time, the article was selected to be featured as ACS (American Chemical Society) Editors' Choice (on 25th November, 2020) based on recommendations by ca. 70 ACS journals' editors due to its potential for broad public interest, an honor given to only one article from the entire ACS portfolio each day of the year.