Japan's dental arts technology can be traced all the way back to the Yayoi Period (ca. 300 BC–300 AD), when artisans sculpted artificial teeth from pagodite stone. In the Heian Period (794–1185 AD), Buddhist figurine sculptors masterfully carved dentures from boxwood. These dentures, once considered luxury items, became more widely available to the general public during the Edo Period (1603–1867 AD). In the Meiji Period (1868–1912 AD), Western dental technology and techniques were introduced to Japan. Today in Japan, crowns and dentures are classified as artificial organs. Only licensed dentists and certified dental technicians are authorized to perform dental work. To become a dental technician, one must study for at least two years at a government-certified institute and pass a rigorous national examination. The curriculum and exam cover a wide range of subjects, including Dental Anatomy, Denture Technology, Restoration Technology, Orthodontics, Pediatric Dentistry, the Jaw and Oral Cavity System, Dental Science and Engineering, and Dental Practice Law.