Shining a Light on Cavities

Oct. 3, 2014

By Medical Discovery News

For all those who cringe at the thought of going to the dentist or hearing the word cavity, there is hope. Apparently, when low-power laser light is focused onto damaged teeth, it stimulates the regrowth of dentin to correct the damage. The laser light stimulates the stem cells that are already in teeth to differentiate and repair damage from within, so that someday dentists can repair or even regrow teeth without fillings.

Teeth consist of four different tissues, three of which are harder than bone (enamel, dentin, and cementum) while one (dental pulp) is soft. Enamel, the hardest material in the body, is the outer surface of the crown of a tooth. Once enamel has completely formed it cannot be repaired, but it can remineralize. It allows teeth to withstand large amounts of stress, pressure, and temperature differences.

Dentin lies beneath enamel and forms the main portion of a tooth through numerous microscopic channels called dentin tubules. These tubules house dentinal fibers, which are the trouble-makers responsible for transmitting pain stimuli. Cementum is a thin layer of tissue surrounding the root of a tooth. Within the center of the tooth is the pulp, which provides nutrition to the tooth and mediates dentin repair. The pulp contains nerves, blood vessels, lymph vessels, connective tissue, cells that produce dentin, and stem cells.

By adding specific molecules, stem cells are coaxed into regenerating or repairing tissues. Growth factors or chemicals, among others, stimulate them to differentiate into the types of cells that make up tissues. It is a challenge to stimulate stem cells in the body without them growing uncontrollably. As a result, most approaches to stem cells involve removing them from the body, manipulating them in the lab, and then returning them. However, scientists have found that lasers promote regeneration in the heart, skin, lung, and nervous tissues. The idea was that since teeth contain stem cells, laser light might be able to stimulate them to regenerate tooth tissue and repair damaged teeth.

To test this theory, scientists drilled holes in the dentin in the teeth of rats and then shined a non-ionizing, low-power laser on the damaged area and the pulp just above the stem cells. They then capped the damaged teeth to keep the animals comfortable and healthy. With just a single five-minute treatment, new dentin formed in the damaged area in 12 weeks. The laser seems to create micro-injuries and induce highly reactive oxygen species, which indirectly activate stem cells.

They also proved that dentin production could be stimulated with lasers in cultured human dental stem cells. However, this treatment still needs some work before it could benefit people, since the stem cells that produce enamel are not present in mature teeth. And dentists would still play a role in repairing damaged teeth.

Before this experiment, results of laser treatments have generally been inconsistent, making these results that much more significant. It is the first time scientists have been able to determine how low-power laser treatment works on the molecular level. Scientists aim to advance this study into human clinical trials and even use this approach to regenerate other tissues.

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Rise of Cavities

August 9, 2013

By Medical Discovery News

By 65, 92 percent of Americans have cavities in their permanent teeth, and an average of 3.28 teeth missing or decayed. The answer to why this is may not concern toothpaste ingredients or brushing time, but the lifestyles of ancient humans, as two new studies have discovered.

Humans used to live as hunter-gatherers, meaning they hunted for game and foraged for plants to eat. They were mainly nomadic, following herds to keep their food source. That changed about 10,000 years ago when agriculture was invented. They began to settle down in one place, raising livestock and growing crops for food. The human diet changed as it now included more starch from the grains they harvested.

The breakdown of starch begins with enzymes in the mouth that split the starch into shorter chains of sugars. The process continues in the stomach and the small intestine until the sugar chains are broken down into individual sugar molecules. This leaves a residue of sugar in a film on and between teeth, creating an ideal environment for the growth of bacteria. Two recent studies have documented how this change in diet caused bacteria associated with cavities and periodontal disease to emerge and eventually become widespread.

One group analyzed the bacterial DNA in samples of tarter from ancient teeth to monitor the changes in the types of bacteria that were present. What they found was a record of how humans have wrecked the bacterial ecosystem in their mouths. The increase in starchy foods caused sugar-loving bacteria to flourish.

With new DNA sequencing technologies, scientists isolated bacterial DNA from 34 teeth of Northern Europeans that are 7,000 to 400 years old, including the last hunter-gatherers from Poland and early farmers from Germany. Hunter-gatherers’ teeth harbored fewer types of cavity-causing bacteria, while early farmers’ teeth revealed a sharp increase in bacteria that cause tooth decay and periodontal disease. 

One bacterium, called Streptococcus mutans, contributes to cavities, diabetes, and cardiovascular diseases. In the mid-1800s, Strep mutans became even more dominant in the oral microbiome. This change correlates with the Industrial Revolution, which introduced refined grains and sugars. The simple sugars from these processed foods are the basis for microbial fermentation, which lowers the pH of the mouth and causes damage to tooth enamel.

The second study focused on changes in the DNA of Strep mutans alone from the present then going back in time. They sequenced the genomes of the bacterium from 57 people worldwide, then used some clever genetics modeling to calculate when the Strep mutans started expanding and diversifying. They think that occurred about 10,000 years ago, which correlates to the start of agriculture. 

Both studies show that the oral microbiome changed with the development of agriculture. What neither group has dealt with are the influences of modern behaviors like using toothpaste, adding chlorine and fluoride to drinking water, and more changes to the human diet, particularly the shift to fast food.

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