Howe and Poyton (1960) found that darkening of the root was the most reliable sign indicating the true relationship of the third molar with the inferior alveolar canal on the X-ray. They reported that 93.1% of the teeth in true relationship to the canal showed this sign whereas, 33.7% of teeth were in true relationship with the canal when narrowing of the Inferior Alveolar canal was seen on the radiograph.