2.2 Preparation of Specimens
The mandibles, labial papules and mandibular papules prepared as above were cleaned three times in an ultrasonic bath JP-010T (Skymen Cleaning Equipment CO., Ltd., Shenzhen, China) at 250 W for 350 s each time. The mandibles, labial papules and mandibular papules were fixed with 3% glutaraldehyde at 5℃ for 15 h, and dehydrated with 60%, 70%, 80%, 90%, and 100% liters of ethanol, with an interval of 8 min. The prepared mandibles, labial papules and mandibular papules were stored in glass containers which was already cleared and dried for 36 h. After drying, the specimens were mounted on a holder using double-sided sticky tape (dorsal, ventral), sputter coated with gold-palladium. Subsequently, the prepared were scanned by using an electron microscope (model S-3400N, Hitachi, Ibaraki, Japan) at an accelerating voltage of 3-10 kV. The images were named separately and stored on a computer.