Tobacco Heating System (THS) aerosol stains teeth less than cigarette smoke
Smoking cigarettes causes serious diseases and adversely affects our health, including oral health. Smoking discolors teeth, and it can lead to gum disease, tooth loss, and can even cause mouth cancer in severe cases.
A smoker’s teeth are exposed to the thousands of chemicals found in cigarette smoke. This includes colored compounds in the smoke that can end up on the surface of the teeth or penetrate the hard dental tissues, causing discoloration. A recent survey in the United Kingdom indicated that the risk of severe tooth discoloration in smokers was 2.4 times higher than in non-smokers, though other things can also stain teeth, such as coffee, red wine, or soy sauce.
The tooth’s structure. The inner pulp of the tooth, containing the soft connective tissue, is covered by naturally yellow dentin. Dentin is naturally softer than enamel, which is the hard, outer layer of the tooth. The natural color of dentin ranges from light yellow to grayish white.
The process of combustion is eliminated in THS. Not only does this cause the product to produce levels of harmful chemicals that are on average 90-95% lower than those measured in cigarette smoke (3R4F), but we also expect to see significantly reduced tooth discoloration compared to that caused by cigarette smoke.
Exposing teeth to aerosol and smoke
The goal of our study comparing the effects of cigarette smoke and heated tobacco aerosol on teeth was to compare the level of discoloration, if any, caused by THS with that caused by cigarette smoke and to examine whether product use would lead to any color mismatches between dental resins and teeth.
Our researchers* collected premolars that were extracted for orthodontic reasons, collected fresh from oral surgery, and sterilized them with ethylene oxide overnight before use. Next, cavities were created in 22 teeth, and dental resins were applied to restore them. The teeth were then evenly separated into two groups. One group was exposed to THS aerosol, and the other was exposed to cigarette smoke.
The color of the human premolar teeth and composite resin restorations were assessed in the CIE Lab space to establish baseline values. Each week after exposure to THS aerosol or cigarette smoke, the teeth were brushed with a toothbrush and toothpaste and assessed for color. When the teeth were not exposed to aerosol or being assessed, they were incubated in artificial saliva. In this graphic, "Platform 1" refers to THS.
Both groups of teeth were exposed to smoke (equivalent to 10 cigarettes) or aerosol (equivalent to 10 THS tobacco sticks) for 28 minutes. These exposure sessions occurred twice a day, four days a week, for three weeks – a total of 24 exposure sessions for each tooth. The teeth were kept in artificial saliva between sessions.
Assessing tooth color using CIE Lab
At baseline and each week after exposure, the teeth were brushed following a strict protocol. Then, the color of the teeth was assessed in the Commission internationale de l'éclairage L*a*b (CIE Lab) color space. This color space defines color values on three coordinates: L* (dark to light scale), a* (red to green scale), and b* (yellow to blue scale).
At the end of the three weeks, cigarette smoke caused an overall larger color change compared with THS, showing decreased lightness and increased redness of the enamel, dentin, and composite resin restorations. THS aerosol caused similar trends in color change, but to a much lesser extent. It also caused no measurable mismatch between the tooth and the dental resin, unlike cigarette smoke. Artificially aging the restorations had no effect on the discoloration.
Comparison of the color change caused by THS (top) and cigarette smoke (bottom). After three weeks, THS aerosol caused no obvious discoloration to the teeth and no color mismatch between the teeth and dental resins, unlike cigarette smoke. In this graphic, "Platform 1" refers to THS.
Lack of combustion is a major factor
Still, quitting smoking and other nicotine-containing products is the best choice smokers can make, including for oral health and teeth discoloration. Although the color changes caused by THS during this study could not be noticed by the naked eye, THS aerosol and cigarette smoke both increased the level of yellow color in the teeth. It's possible that this is a result of nicotine exposure. While nicotine in its original state is not colored, it becomes yellow when oxidized, which may be responsible for the slight yellow color change.
Considering that the lack of combustion is an important factor in the reduced impact of THS on tooth color, we would also expect that e-cigarettes and other smoke-free products should have similar outcomes. In fact, we’re in the process of exploring the effects of e-cigarettes on tooth color, including both composite resin and dental hard tissue. We’ve presented our work in progress at the 97th General Session of the International Association for Dental Research.
* This study was conducted by PMI researchers Dr. Filippo Zanetti, Prof. Manuel C. Peitsch, and Dr. Julia Hoeng, in collaboration with others working with Prof. Yangfang Ren of the University of Rochester.
