1. National Clinical Research Center for Oral Diseases & State Key Laboratory of Military Stomatology & Shaanxi Key Laboratory of Stomatology, School of Stomatology The Fourth Military Medical University Xi'an Shaanxi 710032 P. R. China
2. Institute of Electronic and Sensor Materials TU Bergakademie Freiberg Freiberg 09599 Germany
3. Center for Advanced Technology Adam Mickiewicz University Poznan 61‐614 Poland
4. Department of Applied Physics Xi'an Jiaotong University Xi'an Shaanxi 710049 P. R. China
5. School of Medicine University of Washington Seattle WA 98195 USA
6. The Dental College of Georgia Augusta University Augusta GA 30912 USA