GGTLC1 and periodontitis: The results showed that age‐adjusted regression coefficients of serum aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, gamma‐glutamyl transpeptidase, cholinesterase, high‐density lipoprotein cholesterol, fasting blood glucose, blood cell count, total protein, and urea were significantly associated with the severity of periodontitis.