This study used 150 periapical radiographs of primary mandibular molars along with an aluminum stepwedge consisting of 5 steps from 2 to 10 mm which were exposed and developed under standard conditions. A Mustek (Taiwan, R.O.C.) flatbed scanner with transparency adapter was used to digitize the radiographs. A 600 dpi, 10 bit gray level scanning and transparency scanning mode were used. The thickness of the lamina dura was measured with the electronic ruler whereas density of dentin was calculated using the density function of a software program (Image Tool 2.0). Dentin density of the bifurcation area was calculated as 7.42 +/- 1.37 mm = A1 in primary second molars and 11.02 +/- 1.37 mm = A1 for permanent first molar teeth. Differences in the thickness of the lamina dura in primary posterior teeth ranged from 0.23 +/- 0.01 mm to 0.42 +/- 0.01 mm.