Friday, April 17, 2009

Cracking the Root of Tooth Strength

Human enamel is brittle. Like glass, it cracks easily; but unlike glass, enamel is able to contain cracks and remain intact for most individuals’ lifetimes. The research team discovered that the major reason why teeth do not break apart is due to the presence of tufts—small, crack-like defects found deep in the enamel. Tufts arise during tooth development, and all human teeth contain multiple tufts before the tooth has even erupted into the mouth. Many cracks in teeth do not start at the outer surface of the tooth, as has always been assumed. Instead cracks arise from tufts located deep inside the enamel. From here, cracks can grow towards the outer tooth surface. Once reaching the surface, these cracks can potentially act as sites for dental decay. Acting together like a forest of small flaws, tufts suppress the growth of these cracks by distributing the stress amongst themselves.

“This is the first time that enigmatic developmental features, such as enamel tufts, have been shown to have any significance in tooth function” said GW researcher Paul Constantino. “Crack growth is also hampered by the “basket weave” microstructure of enamel, and by a ‘self-healing’ process whereby organic material fills cracks extended from the tufts, which themselves also become closed by organic matter. This type of infilling bonds the opposing crack walls, which increases the amount of force required to extend the crack later on.”

This research evolved as part of an interdisciplinary collaboration between anthropologists from The George Washington University and physical scientists from the National Institute of Standards and Technology in Gaithersburg, Md. The team studied tooth enamel in humans and also sea otters, mammals with teeth showing remarkable resemblances to those of humans.

The article, "Remarkable resilience of teeth" appears in the April 2009 edition of Proceedings of the National Academy of Sciences.

Thursday, April 16, 2009

Baby canine teeth: No evidence to support extraction

The practice of extracting baby canine teeth to make way for adult canines that are erupting in the wrong place has no evidential basis, according to a new study by Cochrane Researchers. In a systematic review, the researchers were unable to identify a single high quality study to support the practice.

"The recommendation of extracting the baby canine is in fact based on one uncontrolled study that was carried out over twenty years ago," says lead author of the study Nicola Parkin of the Department of Oral Health and Development at the University of Sheffield.

It is common for adult upper canines to grow in the wrong place. Normally adult canine teeth erupt in the mouth around the age of 12 years and, in approximately 2-3% of the population of 12 year old children, these teeth become displaced in the roof of the mouth. Displaced canines can cause damage to neighbouring teeth as well as unfavourable movement of other teeth and, more rarely, cysts. One suggested way of avoiding canine displacement and encouraging the eruption of the adult canine is to remove a child's baby canine tooth at around 10 to 13 years, under local anaesthetic.

According to the researchers, however, the most commonly cited evidence for this practice comes from one trial, carried out in 1988, in which a group of children with canine displacement had their baby canines extracted. A major flaw of this study was the absence of a control group. Two other studies considered for the review did have an untreated control group, but had to be excluded because of inadequacies in reporting.

"Extracting the primary canine may help the secondary tooth to emerge correctly, but at this time we can't provide any hard evidence," says Dr Parkin. "Greater attention to the design and reporting of studies is needed to improve the quality of clinical trials on this topic."

HOME TOOTH BLEACHING REDUCES ENAMEL STRENGTH

HOME TOOTH BLEACHING SLIGHTLY REDUCES ENAMEL STRENGTH

New research shows that human teeth lost some enamel hardness after the application of several different products used in the home to whiten teeth. The study suggests that future generations of such products might be reformulated in an effort to reduce these side effects.

The researchers noted that teeth typically can restore their previous hardness after losing small amounts of enamel calcification. But this is the first study to show at a nanometer scale – measuring in billionths of a meter – how human teeth are affected by the popular home whiteners.“There is some significant reduction in nano-hardness of enamel, but we are talking on a very minute scale. So even though it may not be visible to the human eye, it’s important for research because that’s how we improve products,” said Shereen Azer, assistant professor of restorative and prosthetic dentistry at Ohio State University and lead author of the study.

Azer and colleagues applied the recommended treatments of five name-brand home whiteners to samples of human teeth and compared the effects to tooth samples that received no treatment. In all cases, the products reduced the hardness of the enamel as well as what is called the elastic modulus or stiffness, a measure of the ability of the tooth surface to bounce back in response to applied force.

Many studies have sought to determine how tooth whitening affects tooth enamel hardness, but results have been inconclusive. Azer said that previous studies measured the loss of enamel hardness in microns, or millionths of a meter, rather than on the nanometer scale used in his study.

“So this just gives us a better understanding of precisely how these products affect human teeth,” he said.

The research is published in a recent issue of the Journal of Dentistry.

Tooth bleaching products contain solutions of various strengths of either hydrogen peroxide or carbamide peroxide, which provide the whitening effect. They bleach teeth by producing unstable free radicals that attack pigment molecules in the organic parts of enamel. The reduction in pigment means the molecules no longer reflect light, so the teeth appear whiter.

Enamel, which is almost entirely inorganic and translucent, appears yellow in most teeth because it reflects the color of the dentin underneath, which is naturally yellow.

“Especially nowadays, people tend to see beauty in white teeth,” Azer said. “And bleaching does have a beautiful effect, but not without side effects.”

The study did not test for two other common side effects of tooth whitening, gum irritation and tooth sensitivity. Azer said these side effects have been addressed by other products, such as toothpastes and treatment gels designed to lessen sensitivity and irritation.

He and colleagues used extracted molars to assemble 65 human tooth samples measuring 4 millimeters square and 2 millimeters deep for the study. Ten samples were used in a pilot study that determined they could achieve accurate results for the research under dry conditions rather than wet conditions simulating the presence of saliva.

Of the remaining samples, five were left untreated, and 50 were divided into five groups of 10 each to undergo treatment.

The researchers used whitening strips on two groups of samples and trays filled with whitening gel on three groups. The treatment times included up to 60 minutes once per day or 60 minutes twice per day according to manufacturer recommendations. All treatments lasted for three weeks except for one tray method, which lasted 10 days.

The treatments included both over-the-counter and professionally provided products to be used in the home.

The scientists used a specialized tool to apply force to test the enamel hardness and stiffness (the surface ability to bounce back), and an atomic force microscope to observe the tiny nanometer-scale effects on the teeth.

The average loss of enamel ranged from 1.2 to 2 nanometers on the treated teeth. The control teeth, on average, actually gained 0.4 nanometers of hardness in comparison over the treatment time frame. The surface ability to bounce back from applied force was reduced by an average of between 6 percent and 18.8 percent among the treated teeth, depending on the type of treatment.

Among the different products, most of the reductions in hardness and elastic modulus were similar. However, there was a significant difference between one strip treatment method and one tray method, with the tray method reducing enamel hardness more dramatically than the strip treatment.

Enamel is the hardest structure in the human body. It protects teeth and maintains the integrity of the bite. But enamel is subject to abrasion by certain products and even too-vigorous brushing, which is why it is important to figure out ways to reduce damage to this part of the tooth, Azer said.

“In the case of these products, manufacturers might be able to alter the concentrations of the materials and the vehicles used to apply the bleach,” he said.

The study did not address how to restore hardness to bleached teeth, but Azer noted that extensive research has indicated that fluoride treatments, including the use of fluoride toothpaste, can promote enamel remineralization.

The products used in the study were Crest Whitestrips Premium Plus, Crest Whitestrips Supreme, Nite White ACP, Oral B Rembrandt and Treswhite Opalescence. The final three are tray treatments.

Azer conducted the research with Camilo Machado and Robert Rashid of the Division of Restorative and Prosthetic Dentistry and Eliana Sanchez of the Division of Primary Care, all in Ohio State’s College of Dentistry.

Wednesday, April 15, 2009

Some orthodontic appliances prone to bacteria

Researchers at the Oregon Health & Science University School of Dentistry (www.ohsu.edu/sod) have found the majority of patients with self-ligating orthodontic brackets retain fewer bacteria in plaque than patients with elastomeric orthodontic brackets. The OHSU team also found that a biochemical technique measuring ATP- (adenosine triphosphate-) driven bioluminescence could be a useful chair-side tool in the rapid quantification of oral bacteria and in the assessment of oral hygiene during orthodontic treatment.

The findings are published in the April 2009 issue of the American Journal of Orthodontics and Dentofacial Orthopedics, one of the leading peer-reviewed orthodontia journals.

Acid-producing bacteria that surround orthodontic appliances are a common orthodontic problem. Such bacteria can lead to tooth enamel breakdown and potential discoloration of the tooth surface, and these aesthetic changes can persist for many years after orthodontic treatment. While the newer bonded orthodontic brackets have many advantages over the old metal bands that were fitted around each tooth, they do impede good oral hygiene, resulting in plaque accumulation and increased tooth enamel breakdown.

While several studies have investigated the effects of fixed orthodontic appliances on bacterial flora, few studies have compared the effects of bracket architecture – specifically the archwire ligation method – or have evaluated the accumulation of bacteria that occurs with the bonding of fixed appliances. The OHSU study also was different from other studies in that it was a randomized clinical study, comparing the numbers of oral bacteria in plaque surrounding two distinct orthodontic appliances, self-ligating versus elastomeric ligating, using a split-mouth design.

The OHSU study examined 14 patients aged 11 to 17, each patient containing both self-ligating and elastomeric orthodontic brackets on opposing sides of the mouth, at both one week and five weeks after bonding. The numbers of oral bacteria in plaque surrounding the brackets were evaluated at both appointments, in addition to a pre-bonding appointment, using both conventional plating techniques enumerating bacterial colony number and the ATP-driven bioluminescence technique.

More bacteria, including oral streptococci, were retained at tooth surfaces in plaque in patients with elastomeric orthodontic brackets at both the one- and five-week post-bonding appointments, and bacterial levels were particularly high at the one-week visit. Higher ATP-driven bioluminescence levels were also observed in plaque surrounding the elastomeric orthodontic appliances.

"We were surprised that the manner of ligation promoted differences in the levels of plaque bacteria surrounding the bonded tooth surfaces," noted Curt Machida, Ph.D., OHSU professor of integrative biosciences and principal investigator, whose lab was host for the study. "Our results suggest that the use of the self-ligating appliances promote reduced retention of plaque bacteria on tooth surfaces surrounding the appliances.

"Our study also provided validation that ATP-driven bioluminescence can be used as a way to quantify bacteria rapidly and reliably at the dental chair-side," he said.

Friday, April 3, 2009

Periodontal disease = risk factor for HIV-1

Can periodontal disease act as a risk factor for HIV-1?

Today, during the 87th General Session of the International Association for Dental Research, convening at the Miami Beach Convention Center, a group of scientists from Nihon University (Tokyo, Japan) will present findings suggesting that periodontal disease could act as a risk factor for reactivating latent HIV-1 in affected individuals.

Latently infected cells harbor HIV-1 proviral DNA genomes integrated with heterochromatins, allowing for the persistence of transcriptionally silent proviruses. Hypoacetylation of histone proteins by histone deacetylases (HDACs) is primarily involved in the maintenance of HIV-1 latency by repressing transcription from HIV-1 provirus. On the other hand, periodontal diseases, caused by infection with the bacterium Porphyromonas gingivalis (P. gingivalis), are found worldwide and are among the most prevalent microbial diseases of mankind.

The investigators demonstrated the effects of such periodontopathic bacteria on HIV-1 replication. They found that P. gingivalis could strongly facilitate HIV-1 reactivation via chromatin modification. The bacteria produced high concentrations of butyric acid, a potent inhibitor of HDACs, and induced acetylation of histones, leading to reactivation of HIV-1 in latently infected cells. These results suggest that periodontal disease could act as a risk-factor for HIV-1 reactivation in latently infected individuals, and might contribute to the systemic dissemination of the virus causing clinical progression of acquired immunodeficiency syndrome (AIDS). The findings emphasize the essential role of maintaining oral hygiene and controlling oral diseases for the prevention of AIDS.

Sports drink consumption can cause tooth erosion

While sipping on sports drinks all day may provide an energy boost, this popular practice is also exposing people to levels of acid that can cause tooth erosion and hypersensitivity, NYU dental researchers have found.

In a recent study, the researchers found that prolonged consumption of sports drinks may be linked to a condition known as erosive tooth wear, in which acids eat away the tooth's smooth hard enamel coating and trickle into the bonelike material underneath, causing the tooth to soften and weaken. The condition affects one in 15 Americans and can result in severe tooth damage and even tooth loss if left untreated.

"This is the first time that the citric acid in sports drinks has been linked to erosive tooth wear," said Dr. Mark Wolff, Professor and Chairman of the Department of Cariology & Comprehensive Care at New York University College of Dentistry, who led the study. The findings were presented today at the annual meeting of the International Association for Dental Research in Miami.

Dr. Wolff's research team cut in half cow teeth, which were used for the study because of their close resemblance to human teeth. They immersed one half of the specimens in a sports drink, the other half in water, then compared the two halves and discovered that the one exposed to the sports drink displayed a significant amount of erosion and softening.

"Five teeth were immersed in each drink for 75 to 90 minutes to simulate the effects of sipping on sports drinks over the course of the day," Dr. Wolff said. The researchers evaluated the effects of a range of top-selling sports drinks on the cow teeth.

According to Dr. Wolff, brushing teeth immediately after consuming a sports drink can compound the problem of tooth erosion, because softened enamel is very susceptible to the abrasive properties of toothpaste.

"To prevent tooth erosion, consume sports drinks in moderation, and wait at least 30 minutes before brushing your teeth, to allow softened enamel to re-harden," Dr. Wolff advised. "If you frequently consume sports drinks, ask your dentist if you should use an acid-neutralizing remineralizing toothpaste to help re-harden soft enamel."

Thursday, April 2, 2009

Salivary diagnostics comes of age

Salivary diagnostics has come of age. In a mere six years, research supported by the National Institute of Dental and Craniofacial Research (NIDCR) has sprung to the forefront of basic, translational, and clinical research. In a scientific session on "Oral Fluid Diagnostics", to be held during the 87th General Session of the International Association for Dental Research, convening today at the Miami Beach Convention Center, researchers will showcase a remarkable spectrum of research outcomes that expands the clinical applications of saliva based on 'diagnostic toolboxes', as well as establishing foundational mechanistic insights into salivary diagnostics.

Three papers will highlight the scientific and translational values of three diagnostic toolboxes (proteins, DNA, and RNA) in saliva. One research team identified 36 novel phosphoproteins in parotid saliva. This elegantly established the systemic phosphoproteome documentation technology, providing a powerful tool to evaluate health vs. disease states of oral and systemic disease. Another group explores the methylation status of genomic DNA contents of 807 cancer-associated genes in the saliva of oral cancer patients. Subpanels of these differentially methylated genes were able to discriminate oral cancer subjects with a specificity of 83-100% and a sensitivity of 62-77%, providing proof-of-concept data that differential methylation analysis of specific cellular genes in saliva can be used to detect oral cancer. A third diagnostic alphabet, the salivary transcriptome, was discovered to exist in saliva encapsulated in a lipid bilayer entity known as the exosome. This is a significant finding, since it provides the long-missing scientific rationale as to why endogenous salivary mRNA is unusually stable, firmly providing the scientific rationale for the translational utilization of the salivary transcriptome for biomarker studies.

This session will also feature a paper that highlights a translational and clinical application of salivary biomarkers for detecting patients with acute coronary syndrome (ACS). Of interest is that discriminatory salivary biomarkers for ACS are gender- and fluid-specific (stimulated vs. unstimulated). The potential use of saliva, rather than blood, for ACS detection presents clear clinical advantages.

Last, there will be a paper demonstrating the mechanistic insights into the value of salivary diagnostics for systemic disease detection. In rodent tumor transplantation models of melanoma and lung cancer, tumor-associative saliva biomarker profiles were observed. A systemic disease-induced salivary biomarker fingerprint is therefore validated. The working model proposed is that tumors, like endocrine organs, produce hormones, lymphokines, and cytokines, which will traverse through the vasculature and reach a distal organ to exert biological actions. When reaching the salivary glands, these hormones/lymphokines/cytokines will lead to transcriptional profile changes and ectopic protein translation, which will be secreted into saliva as tumor-associated surrogate biomarkers. This is the first mechanistic demonstration of a profile connection between systemic disease and salivary biomarkers.

Amalgam fillings are safe, but controversial

Amalgam fillings are safe, but skeptics still claim controversy, researcher says

Dental amalgam has been proven safe and effective for years, yet unfounded controversy still surrounds it, a Medical College of Georgia researcher says.

Dentists have used amalgam, an alloy of mercury with at least one other metal, in fillings for over 200 years. Amalgam fillings don’t contain enough mercury to cause potential health problems associated with larger doses, says Dr. Rod Mackert, professor of dental materials in the MCG School of Dentistry Department of Oral Rehabilitation.

"The dose makes the poison,” he says, quoting 16th century Swiss physician Paracelsus. A person would need between 265 and 310 amalgam fillings before even slight symptoms of mercury toxicity could be felt. A person with seven fillings, which is average, absorbs only about one microgram of mercury daily. About six micrograms are absorbed daily from food, water and air, according to the Environmental Protection Agency.

To create a dental filling, liquid mercury dissolves and reacts with a powder of silver, tin and copper, forming a compound that contains no free mercury. "Anti-amalgam activists say mercury is soaked into metal powder, like water into a sponge, and can come back out of the fillings, but that's not at all true," Dr. Mackert says. In fact, the evaporation rate of mercury from amalgam is a million times lower than from pure mercury.

Anti-amalgam activists also say dental mercury pollutes the environment. However, dental mercury accounts for less than a quarter of a percent of mercury re-entering the environment.

Dr. Mackert presented an overview of amalgam, its controversy and its alternatives today at the 87th General Session of the International Association for Dental Research in Miami.

The amalgam controversy began in the 1970s. Awareness that dental fillings contained mercury was heightened and people were concerned by a couple of mercury-related health scares. In Japan, the release of methyl mercury into industrial wastewater caused a mercury buildup in shellfish and fish, leading to severe mercury poisoning and Minamata disease. Also, a grain covered in mercury fungicide was baked into bread and consumed in Iraq, killing hundreds. "Mercury poisoning was on people's minds and in the press," he says.

Urban legends abounded, including erroneous reports linking vapors from amalgam fillings to kidney damage and degenerative diseases such as Alzheimer's disease, multiple sclerosis and Parkinson's disease. The only documented health effects of amalgam fillings are rare allergic reactions, Dr. Mackert says, but the controversy led many people to have their fillings removed in the misguided hope of curing neurological diseases.

That controversy continues today. "It's mystifying that people persist in saying there is cause for concern with amalgam fillings when there's no evidence that they cause adverse health effects," Dr. Mackert says.

He also disputes claims that ulterior motives have influenced the American Dental Association position attesting to the safety and effectiveness of amalgam fillings. Anti-amalgam activists link the position to patent interests, but the association had only two amalgam patents, now expired, and neither was licensed, according to the U.S. Patent and Trademark Office. Most of the association’s 78 patents are for white filling materials, including composite resin, an alternative to amalgam.

But composite fillings have their own problems. They cost more than amalgam and often are not covered by insurance. Numerous studies have shown that amalgam significantly outlasts composite, while composite causes more secondary cavities and may contribute to plaque formation, Dr. Mackert says.

"The bottom line is people don't need to be concerned with adverse health effects from any type of fillings – amalgam or composites," Dr. Mackert says. Since beginning his studies of amalgam in the early 1980s, his position has never changed. In fact, he has amalgam fillings himself.

Wednesday, April 1, 2009

White wine can make tooth stains darker

NYU College of Dentistry researchers found that drinking white wine can also increase the potential for teeth to take on dark stains

It has long been known that red wine causes teeth to stain. But white wine? A recent study by NYU dental researchers found that drinking white wine can also increase the potential for teeth to take on dark stains.

The researchers compared two sets of six cow teeth, whose surface closely resembles that of human teeth, and used a spectrophotometer, an instrument that measures color intensities, to evaluate staining levels.

They found that teeth soaked for one hour in white wine before being immersed in black tea had significantly darker stains than teeth immersed for one hour in water before exposure to the tea.

"Dipping teeth in white wine for one hour is similar to the effect of sipping the wine with dinner," said Dr. Mark Wolff, Professor and Chairman of the Department of Cariology & Comprehensive Care at New York University College of Dentistry, who oversaw the study, which was led by Ms. Cristina M. Dobrescu, a third-year student at New York University College of Dentistry. The findings were presented today at the annual meeting of the International Association for Dental Research in Miami.

"The acids in wine create rough spots and grooves that enable chemicals in other beverages that cause staining, such as coffee and tea, to penetrate deeper into the tooth," Dr. Wolff explained.

Still, red wine continues to beat out white wine when it comes to staining teeth. When the researchers repeated the experiment with red wine, the resulting stains were significantly darker than those in the white wine group. "Red wine, unlike white, contains a highly-pigmented substance known as chromogen," explained Dr. Wolff.

But he added that connoisseurs concerned about staining need not cut back on their consumption. "The best way to prevent staining caused by wine, as well as other beverages, is to use a toothpaste containing a whitening agent," advised Dr. Wolff.

More Oral Bacteria = Higher Risk of Heart Attack

Several studies have suggested there is a connection between organisms that cause gum disease, known scientifically as periodontal disease, and the development of heart disease, but few studies have tested this theory.

A study conducted at the University at Buffalo, where the gum disease/heart disease connection was uncovered, now has shown that two oral pathogens in the mouth were associated with an increased risk of having a heart attack, but that the total number of germs, regardless of type, was more important to heart health.

Results of the study will be presented during a poster session at the International Association of Dental Research (IADR) General Session being held in Miami, Fla., from April 1-4.

Oelisoa M. Andriankaja, D.D.S., Ph.D., conducted the study in UB's Department of Oral Biology in the School of Dental Medicine, as a postdoctoral researcher. She currently is an adjunct professor at the University of Puerto Rico's School of Dental Medicine.

"The message here," said Andriankaja, "is that even though some specific periodontal pathogens have been found to be associated with an increased risk of coronary heart disease, the total bacterial pathogenic burden is more important than the type of bacteria.

"In other words, the total number of 'bugs' is more important than one single organism," she said.

The study involved 386 men and women between the ages of 35 and 69 who had suffered a heart attack and 840 people free of heart trouble who served as controls. Samples of dental plaque, where germs adhere, were collected from 12 sites in the gums of all participants.

The samples were analyzed for the presence of the six common types of periodontal bacteria, as well as the total number of bacteria.

The patients harbored more of each type of bacteria than the controls, the analysis showed. However, only two species, known as Tannerella Forsynthesis and Preventella Intermedia, had a statistically significant association with an increased risk of heart attack.

An increase in the number of different periodontal bacteria also increased the odds of having a heart attack, results showed.

Prospective studies -- those that measure oral bacteria in participants who have had no heart problems when they enter the study, and again when a heart attack occurs in a participant -- are needed to better assess this potential association, noted Andriankaja.