1. Department of Conservative Dentistry, Faculty of Dentistry, Universitas Sumatera Utara, Medan, Sumatera Utara, Indonesia.
2. Department of Chemistry, Faculty of Natural and Mathematical Sciences, Universitas Sumatera Utara, Medan, Sumatera Utara, Indonesia.
3. Department of Oral Biology, Faculty of Dentistry, Universitas Syiah Kuala, Darussalam, Banda Aceh, Aceh, Indonesia.