If the pulp of the single rooted canal is triangular in cross-section with the base of the triangle located facially and apex located lingually with the mesial arm longer than the distal, the tooth is most likely:
Max. central incisor
Max. lateral incisor
Mand. second premolar
Mand. central incisor
SHAPE OF ACCESS CAVITY:
Maxillary Incisors - Rounded triangle with the apex towards cingulum.
Maxillary Canine - Ovoid labiolingually.
Maxillary Premolar - Ovoid in Buccolingual direction (Slot shaped).
Maxillary Molars - Triangle in the mesial half base towards buccal and apex towards palatal side.
Note if asked in exams:
           - Rhomboidal (1st choice) 
           - Rounded Triangle (2nd choice)
Modified Access Cavity in maxillary molars (to accommodate accessory orifice):
           - Clove leaf.
           - Shamrock preparation.
MANDIBULAR TEETH:
Mandibular Incisors - Narrow rounded triangle or ovoid.
Mandibular Canine - Ovoid / funnel shaped.
Mandibular Premolar - Ovoid buccolingually.
Mandibular Molars - Trapezoidal (1st choice)
                    - Rounded Triangle (2nd choice)