Computer Image Analysis of Minocycline Discoloration of Rodent Teeth

Minocycline discoloration of the natural tooth in adults has been reported to be the product of an oxidation reaction.  Minocycline is believed to bind to iron ions and causes the formation of insoluble salts that stain the enamel extrinsically or incorporated into the secondary dentin.  

Objectives: The purpose of this study was to evaluate the discoloration of minocycline in vivo and to determine subsequent changes with the intervention of antioxidants.

Methods: Four groups of five Male Sprague-Dawley rats (150-200 gm) each were fed Harlan 7013 (negative control), or one containing either Vitamin E, Vitamin C, or Epigallocatechin gallate (EGCG) for 3 months. Four other groups received the same diets, plus minocycline 0.5mg/kg calculated therapeutic dose (positive controls).  The diets and rat droppings were analyzed blindly via HPLC to confirm the presence of minocycline.  Digital images of rat incisors were recorded every 2 weeks for 3 months until the animals were euthanized (Fig 1).  Images were analyzed for color change by RGB values.  The values were changed into the CIEL*a*b* values and DE calculated compared to base line according to the formula: DE*= [(DL*)² + (Da*)² + (Db*)²]^1/2 .

Results: (Table 1) The data were analyzed by the GLM procedure and t Tests (LSD).

Conclusion:  There is a significant association between diet and time period and also diet*time period, but this general association is not hold in some combination of diet and time period.

Funded by a research fellowship grant from the Academy of Operative Dentistry and Washington Dental Service Endowment.