mandibular second premolar is similar to the first premolar, with the following differences: the lingual pulp horn usually is larger; the root and root canal are more often oval than round; the pulp chamber is wider buccolingually; and the separation of the pulp chamber and root canal is normally distinguishable compared with the more regular taper in the first premolar. The canal morphology of the mandibular second premolar is similar to that of the first premolar with its many variations: two, three, and four canals and a lingually tipped crown. Fortunately, these variations are found less often in the second premolar.

The access cavity form for the mandibular second premolar varies in at least two ways in its external anatomy. First, because the crown typically has a smaller lingualIranian population in the North-West of Iran.

Materials and Methods {#s1}
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A total of 163 extracted mandibular first and 103 mandibular second premolars were collected from Tabriz Faculty of Dentistry, dental clinics and private offices of Tabriz, a city in the North-West of Iran. The identification of these teeth as mandibular second premolars was confirmed by two independent observers using accepted criteria of Woelfel (1990).^[@R05]^ Only those teeth on which both investigators agreed were used in this study. The teeth were collected during one year and stored in 10% formalin. Since a large number of these teeth had been extracted because of periodontal problems, they were intact or had small caries or fillings in coronal portions. The selected teeth were cleaned of any adherent soft tissues, bone fragments and calculus