Erratum
After publication of [1] the authors realised that the original publication had two descriptive errors when referring to diseases. “periodontal” was written rather than “mucous membrane” in the article on page 1, lines 12 and 25. “periodontal disease” was written rather than “mucous membrane hyperkeratosis” in the article on page 2, lines 72 and 73. The correct spelling of these is included in this erratum.
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