Inorganic mercury is from dental fillings is very damaging to key cell processes

University of Georgia research has found that inorganic mercury, which was previously thought to be a less harmful form of the toxic metal, is very damaging to key cell processes.

This study is the first to compare the effects of inorganic and organic mercury compounds at the biochemical, physiological and proteomic levels in any model organism, according to the study's lead author Stephen LaVoie, a microbiology doctoral student. Published in December in the Journal of Biological Inorganic Chemistry, the research looked at how inorganic and organic mercury affected specific molecular processes.

Inorganic mercury from the ore cinnabar was used for centuries against infections; in modern times, humans synthesized organic mercurials as antimicrobials, such as merthiolate.

"Today, most human exposure to inorganic mercury is from dental fillings, and organic mercury exposure is from methylmercury in fish," said study co-author Anne Summers, a microbiology professor in the Franklin College of Arts and Sciences.

Organic mercury exposure is associated with neurological disease, LaVoie explained, whereas inorganic mercury is known to cause neurological, kidney and autoimmune diseases. However, the molecular basis for their distinct toxicity profiles was not understood.

Owing to concern about fish consumption, most research has emphasized organic mercury, assuming it was more toxic, LaVoie said. But comparing them on key cellular processes, he found that inorganic mercury "caused more damage at lower concentrations than organic mercury."

For his study, LaVoie used a common lab strain of E. coli bacteria as a model cellular system. He exposed growing cells to mercury compounds and measured their reactive sulfur called thiols -- essential metals and proteins that naturally bind essential metals via amino acid thiols.

"We used a fluorescent probe to detect thiols," LaVoie said. After mercury exposure the thiols decreased more with inorganic than organic mercury. Inorganic mercury was much more efficient at removing iron from iron-dependent proteins than the best organic mercury compound tested.

"As fellow oxygen-breathing creatures, it's important to know that inorganic mercury is more potent than organic mercury in disrupting protein-iron centers such as those we have in our own cells, " Summers said.

"More is being learned about the bacteria in and on our bodies," LaVoie said. "What we ingest affects them, too, and their health affects our health."

Future work will examine the mercury resistance genes that many bacteria have and how these genes help spread antibiotic resistance genes.

Dental implant complications and peri-implantitis

The International and American Associations for Dental Research (IADR/AADR) have published in the January issue of the Journal of Dental Research articles that explore new evidence on the biological complications of dental implants and the great challenges associated with predictable implant therapy.

Dental implants have become an important treatment for the replacement of teeth lost due to disease, injury or congenital tooth agenesis. Over the past 30 years, the incorporation of dental implants into everyday clinical dental practice has resulted in major improvements in oral health of patients through enhancements in function, esthetics and phonetics.

"While dental implant therapy remains an important treatment modality to replace missing teeth, these studies also underscore the importance of tooth preservation in patients susceptible to gum infections such as periodontitis. The caution is that careful assessments and treatment planning amongst dental generalists and specialists should be performed to optimize the clinical decision-making for patients receiving advanced reconstructive implant or periodontal therapy," said JDR Editor William Giannobile. "We believe the outcomes of these studies will be beneficial to patient care and oral health."

The erroneous belief of implants yielding a better long-term prognosis than teeth has now clearly been rejected in several comparative studies and systematic reviews. Teeth even compromised because of periodontal disease or endodontic problems may have a longevity that surpasses that of the average implant in many cases.

Some of the articles in the January issue that elaborate on the prevalence of peri-implantitis and risk of dental implant loss include an editorial from Dennis Tarnow on 'Increasing Prevalence of Peri-implantitis-How Will We Manage?'; and another editorial 'Are Dental Implants a Panacea or Should We Better Strive to Save Teeth?', authored by William Giannobile and Klaus Lang; 'Surgical Treatment of Peri-implantitis. A Randomized Controlled Clinical Trial' by Olivier Carcuac et al; 'Prevalence of Peri-implantitis' by Jan Derks et al among other papers in this issue.

This issue also includes a freely accessible podcast to the JDR article titled 'Prevalence of Peri-implantitis' of an interview with leading experts in implant therapy by Tord Berglundh of the Sahlgrenska Academy, Department of Periodontology at Gothenburg University, Sweden and Dennis Tarnow of Columbia University in New York, USA. Please visit the JDR website at jdr.sagepub.com/site//misc/Index/Podcasts.xhtml to access the podcast.

Tooth fillings of the future may incorporate bioactive glass

A few years from now millions of people around the world might be walking around with an unusual kind of glass in their mouth, and using it every time they eat.

Engineers at Oregon State University have made some promising findings about the ability of "bioactive" glass to help reduce the ability of bacteria to attack composite tooth fillings - and perhaps even provide some of the minerals needed to replace those lost to tooth decay.

Prolonging the life of composite tooth fillings could be an important step forward for dental treatment, the researchers say, since more than 122 million composite tooth restorations are made in the United States every year. An average person uses their teeth for more than 600,000 "chews" a year, and some studies suggest the average lifetime of a posterior dental composite is only six years.

The new research was just published in the journal Dental Materials, in work supported by the National Institutes of Health.

"Bioactive glass, which is a type of crushed glass that is able to interact with the body, has been used in some types of bone healing for decades," said Jamie Kruzic, a professor and expert in advanced structural and biomaterials in the OSU College of Engineering.

"This type of glass is only beginning to see use in dentistry, and our research shows it may be very promising for tooth fillings," he said. "The bacteria in the mouth that help cause cavities don't seem to like this type of glass and are less likely to colonize on fillings that incorporate it. This could have a significant impact on the future of dentistry."

Bioactive glass is made with compounds such as silicon oxide, calcium oxide and phosphorus oxide, and looks like powdered glass. It's called "bioactive" because the body notices it is there and can react to it, as opposed to other biomedical products that are inert. Bioactive glass is very hard and stiff, and it can replace some of the inert glass fillers that are currently mixed with polymers to make modern composite tooth fillings.

"Almost all fillings will eventually fail," Kruzic said. "New tooth decay often begins at the interface of a filling and the tooth, and is called secondary tooth decay. The tooth is literally being eroded and demineralized at that interface."

Bioactive glass may help prolong the life of fillings, researchers say, because the new study showed that the depth of bacterial penetration into the interface with bioactive glass-containing fillings was significantly smaller than for composites lacking the glass.

Fillings made with bioactive glass should slow secondary tooth decay, and also provide some minerals that could help replace those being lost, researchers say. The combination of these two forces should result in a tooth filling that works just as well, but lasts longer.

Recently extracted human molars were used in this research to produce simulated tooth restoration samples for laboratory experiments. OSU has developed a laboratory that's one of the first in the world to test simulated tooth fillings in conditions that mimic the mouth.

If this laboratory result is confirmed by clinical research, it should be very easy to incorporate bioactive glass into existing formulations for composite tooth fillings, Kruzic said.

The antimicrobial effect of bioactive glass is attributed, in part, to the release of ions such as those from calcium and phosphate that have a toxic effect on oral bacteria and tend to neutralize the local acidic environment.

"My collaborators and I have already shown in previous studies that composites containing up to 15 percent bioactive glass, by weight, can have mechanical properties comparable, or superior to commercial composites now being used," Kruzic said.

Periodontal disease associated with increased breast cancer risk in postmenopausal women

Bottom Line: Postmenopausal women with periodontal disease were more likely to develop breast cancer than women who did not have the chronic inflammatory disease. A history of smoking significantly affected the women's risk. 

Journal in Which the Study was Published: Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research

Author: Jo L. Freudenheim, PhD, distinguished professor in the Department of Epidemiology and Environmental Health in the University at Buffalo's School of Public Health and Health Professions.

Background: Periodontal disease is a common condition that has been associated with heart disease, stroke, and diabetes. Previous research has found links between periodontal disease and oral, esophageal, head and neck, pancreatic, and lung cancers, so the researchers wanted to see if there was any relationship with breast cancer.

How the Study Was Conducted: Freudenheim and colleagues monitored 73,737 postmenopausal women enrolled in the Women's Health Initiative Observational Study, none of whom had previous breast cancer. Periodontal disease was reported in 26.1 percent of the women. Because prior studies have shown that the effects of periodontal disease vary depending on whether a person smokes, researchers examined the associations stratified by smoking status. 

Results: After a mean follow-up time of 6.7 years, 2,124 women were diagnosed with breast cancer. The researchers found that among all women, the risk of breast cancer was 14 percent higher in women who had periodontal disease. 

Among women who had quit smoking within the past 20 years, those with periodontal disease had a 36 percent higher risk of breast cancer. Women who were smoking at the time of this study had a 32 percent higher risk if they had periodontal disease, but the association was not statistically significant. Those who had never smoked and had quit more than 20 years ago had a 6 percent and 8 percent increased risk, respectively, if they had periodontal disease.

Author Comment: "We know that the bacteria in the mouths of current and former smokers who quit recently are different from those in the mouths of non-smokers," Freudenheim explained. One possible explanation for the link between periodontal disease and breast cancer is that those bacteria enter the body's circulation and ultimately affect breast tissue. However, further studies are needed to establish a causal link, Freudenheim said.

Study Limitations: Women self-reported their periodontal disease status, after being asked whether a dentist had ever told them they had it. Also, since the study focused on women who were already enrolled in a long-term national health study, they were more likely than the general population to be receiving regular medical and dental care, and were likely more health-conscious than the general population.

Build a better toothbrush: Aural feedback for oral hygiene

Researchers in Japan have discovered that how effectively we clean our teeth and how satisfied we are with the brushing job we do depends a lot on the sound of the bristles scrubbing against the enamel. In trials with volunteer teeth cleaners, the team has used a tiny microphone in a modified toothbrush to 'sample' the sound being made in the mouth during brushing and to modulate it and then feed that sound back to the volunteer via headphones to see what effect it would have on cleaning efficacy and satisfaction. They describe details in the International Journal of Arts and Technology.

Taku Hachisu and Hiroyuki Kajimoto of The University of Electro-Communications, in Chofu, Japan explain how modulating the brush sound affects brushing efficacy and satisfaction. The team found that if they manipulated the pitch, or frequency and loudness, of the brushing sound they could alter the volunteers' perception of comfort and accomplishment. They also showed that if they gradually increased the frequency as teeth cleaning progressed, the volunteers felt like the process was more comfortable and that their teeth were cleaner at the end of the process.

"Tooth brushing provides a 'negative reward' for users as they brush their teeth to avoid developing caries," the team explains. Many people find the task boring. "Subsequently, users do not consider the impact of omitting the action until suffering from caries or other dental diseases," the team adds. Their results show that it is possible to motivate users by interactively manipulating the frequency of brushing sounds, so that the task becomes more satisfying. Importantly, the system can tell, through a built-in force sensor, whether a person is brushing too hard, which can damage the gum line, and so give them aural feedback to encourage them to clean their teeth more gently.

The prototype system requires the teeth cleaner to wear headphones, which is impractical in real life. However, there are bone conduction speaker systems that might be incorporated into the smart toothbrush so that the amplified feedback loop is created in one's mouth. The team will next recruit volunteers to test the system in their comfort of their own bathrooms.

'No-drill' dentistry stops tooth decay

 

The white patches are signs of early decay that can be stopped and reversed before they become cavities (brown patch on tooth on the right).

Credit: University of Sydney

 

A University of Sydney study has revealed that tooth decay (dental caries) can be stopped, reversed, and prevented without the need for the traditional 'fill and drill' approach that has dominated dental care for decades.

The results of the seven year study, published today in Community Dentistry and Oral Epidemiology, found that the need for fillings was reduced by 30 to 50 per cent through preventative oral care.

"It's unnecessary for patients to have fillings because they're not required in many cases of dental decay," said the study's lead author, Associate Professor Wendell Evans of the University of Sydney.
"This research signals the need for a major shift in the way tooth decay is managed by dentists -- dental practice in Australia needs to change. Our study shows that a preventative approach has major benefits compared to current practice.

"For a long time it was believed that tooth decay was a rapidly progressive phenomenon and the best way to manage it was to identify early decay and remove it immediately in order to prevent a tooth surface from breaking up into cavities. After removing the decay, the affected tooth is then restored with a filling material -- this process is sometimes referred to as 'drilling and filling'.

"However, 50 years of research studies have shown that decay is not always progressive and develops more slowly than was previously believed. For example, it takes an average of four to eight years for decay to progress from the tooth's outer layer (enamel) to the inner layer (dentine).

"That is plenty of time for the decay to be detected and treated before it becomes a cavity and requires a filling."

Professor Wendell Evans and his team developed the Caries Management System (CMS) -- a set of protocols which cover the assessment of decay risk, the interpretation of dental X-rays, and specific treatment of early decay (decay that is not yet a cavity).

The CMS treatment 'no-drill' involves four aspects:
1. Application of high concentration fluoride varnish by dentists to the sites of early decay
2. Attention to home tooth brushing skills
3. Restriction of between-meal snacks and beverages containing added sugar
4. Risk-specific monitoring.M/ul>
"The CMS was first tested on high risk patients at Westmead Hospital with great success," said Professor Evans.
"It showed that early decay could be stopped and reversed and that the need for drilling and filling was reduced dramatically.
"A tooth should be only be drilled and filled where an actual hole-in-the-tooth (cavity) is already evident," he said.
The CMS treatment was then tested in general dental practices in New South Wales and Australian Capital Territory. The Monitor Practice Program (MPP), funded by the National Health and Medical Research Council of Australia (NHMRC), confirmed that after seven years, decay risk was substantially reduced among the CMS patients and their need for fillings was reduced by 30 to 50 per cent compared to the control group.
"The reduced decay risk and reduced need for fillings was understandably welcomed by patients," Professor Evans said. "However, patients play an important role in their treatment. This treatment will need a partnership between dentists and patients to be most successful."

Graphene oxide could make stronger dental fillings

Graphene oxide could be used to make super strong dental fillings that don't corrode, according to a new study published in Colloids and Surfaces B: Biointerfaces.

Research suggests we chew around 800 times in an average meal; that's almost a million times a year. We put our teeth under huge strain, and often require fillings to repair them. Fillings are typically made of a mixture of metals, such as copper, mercury, silver and tin, or composites of powdered glass and ceramic.

Typical metal fillings can corrode and composite fillings are not very strong; Graphene on the other hand is 200 times stronger than steel and doesn't corrode, making it a prime new candidate for dental fillings.

In the study, researchers from Iuliu Hatieganu University of Medicine and Pharmacy, the National Institute for Research and Development of Isotopic and Molecular Technologies, and the University of Agricultural Sciences and Veterinary Medicine in Romania, and Ross University School of Veterinary Medicine Basseterre in the West Indies investigated whether different forms of graphene are toxic to teeth.

"The idea of the project was to add graphene into dental materials, in order to increase their resistance to corrosion as well as to improve their mechanical properties," explained Dr. Stela Pruneanu, one of the authors of the study from the National Institute for Research and Development of Isotopic and Molecular Technologies in Romania. "There is contradictory information regarding the cytotoxicity of graphene, so we first wanted to determine how toxic it is for teeth."

Graphene comes in different forms, including graphene oxide, nitrogen-doped graphene and thermally reduced graphene oxide. The researchers tested how toxic these different types of graphene are in vitro for stem cells found in teeth.

Thermally reduced graphene oxide was highly toxic, making it inappropriate as a dental filling material. Nitrogen-doped graphene caused membrane damage at high doses (20 and 40 micrograms per milliliter). However, it was shown to have antioxidant properties, so it could be useful if covered in a protective layer. Graphene oxide was least toxic to cells, making it an ideal candidate.

"The results were very interesting and proved that graphene is appropriate for use in dental materials," said Dr. Gabriela Adriana Filip, one of the authors of the study and Associate Professor at Iuliu Hatieganu University of Medicine and Pharmacy Cluj-Napoca in Romania. "We believe that this research will bring new knowledge about the cytotoxic properties of graphene-based materials and their potential applications in dental materials."


The next step for this research is for the team to make dental materials with graphene oxide and test how compatible they are with teeth, and how toxic they are to cells. The results are due to be published soon.