Tolerance of vertical angle alteration is an important aspect to minimize vertical distortion on lower molars radiographs. To analyze the tolerance of vertical angle alteration on periapical radiograph of lower molars, measurement of clinical tooth length was performed for 30 lower molars, which were then planted in models. Radiographic examination using periapical radiography was performed seven times for each tooth with vertical angles 0°, +5°, +10°, +15°, -5°, -10°, and -15°. Tooth length and buccal and lingual cusp height differences on radiograph were measured. The result showed that a positive vertical angle alteration of 15° during periapical radiographs of lower molars to view tooth length is tolerated. © Published under licence by IOP Publishing Ltd.