How dark can it be? So dark that doctors now avoid prescribing this antibiotic to children lest they spend a lifetime afraid to smile. So dark that none of the professional tooth-color reference scales go this far toward blackness.
Yet dentists are gaining ground in the effort to whiten such teeth. So reported the November-December 2006 issue of Operative Dentistry: "Tetracycline-stained teeth can be effectively lightened with the extended use of tooth whiteners."
Not just any whitener, though. As the article points out, carbamide peroxide has emerged as the most promising compound tested for this purpose. While previous studies had drawn the same conclusion, the international team of investigators, from Indiana University in the United States and Wuhan University in China, went further.
First, they created a new color reference by adding three successively darker tabs to the Vitalescence Esthetic Restorative Masters Shade Guide. Having a guide that measured the darker shades was important so the team could more accurately indicate how much lighter the teeth became.
Second, the researchers tested three different concentrations of carbamide peroxide gel -- 10 percent, 15 percent or 20 percent -- to see which was most effective and whether one was more irritating than the other.
The investigators randomly divided 44 subjects into six different groups. Each group was assigned to use one of the three concentrations on the left side and another concentration on the right side. The researchers constructed a custom maxillary arch tray for each patient and instructed them to soak their teeth overnight for six months.
The investigators met with their subjects with decreasing frequency over five years to measure their tooth color. They also asked patients to rate their gingival sensitivity to the carbamide peroxide and prescribed a desensitizing gel to any with more than moderate sensitivity. None withdrew from the study because of sensitivity.
And indeed, their teeth got whiter, with 55 percent of the whitening effect occurring in the first month. After nine months, the teeth gained a mean 15.64 chroma meter values. But after two years, the teeth began to darken again; at four-and-a-half years, the teeth had lost 35 percent of the brightness they'd had at their peak, nine months into the study-- leading investigators to recommend that dentists have their patients with tetracycline stains consider a second bleaching after five years.
As expected, the stronger the concentration of carbamide peroxide, the faster the bleaching. But the difference was only modest, and patients using the different concentrations got virtually the same whitening effect by the end of the five years. Worse, the strongest gel caused significantly more irritation. Two overall caveats from the study: teeth didn't whiten uniformly, and the cervical area was the hardest to lighten.
At the end of three months, 88 percent of the subjects were "pleased" with the results. At the end of five years, only 41 percent felt this way, but 91 percent said they would recommend the bleaching to a friend with similarly stained teeth.
The bottom line, say the researchers? Tetracycline stains can be removed very successfully with this bleaching technique. Although the researchers didn't recommend one concentration over another, patients experiencing sensitivity should switch to a lower concentration.
The investigators also recommended more than six months of bleaching for patients with cervical tetracycline stains. "The categories that were most likely to produce an excellent result were those where tetracycline staining was homogenous, concentrated in the incisal two-thirds of the tooth or where banding was evident," they wrote.
BA Matis et al., "Extended bleaching of tetracycline-stained teeth: a 5-year study."
Operative Dentistry, 31(6):643-51 Nov-Dec 2006
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