Maxillary First Molar

The maxillary 1st molar always has 3 separate roots, 2 buccal and 1 palatal. The disto-buccal and palatal roots always have one canal each, but the mesio-buccal may have a configuration of Type I, II or III.

A mesio-distal section through the buccal roots shows that the buccal canals are thin and well centered in their respective roots but with both orifices on the mesial three-fifths of the crown. The bucco-lingual section shows the palatal canal to be much wider than either of the buccal canals, with a buccal curve occurring near the apex in most teeth.

The orifice of the palatal root is more prominent than either buccal orifice and is located beneath the mesio-palatal cusp. The orifice of the mesio-buccal canal is located beneath the mesio-buccal cusp, but the orifice of the disto-buccal canal has no direct relation to its cusp. The disto-buccal orifice is usually located by means of its relation to the mesio-buccal orifice. The disto-buccal orifice is found approximately 2-3 mm to the distal and slightly to the palatal aspect of the mesiobuccal orifice.

In a tooth considerable dentinal sclerosis, the distance between the 2 buccal orifices will be greater. Since the buccal roots diverge as they leave the crown, the canals form a ‘V’ shape and approach each other near the floor of the chamber. In dentinal sclerosis, as the reparative dentin fills the chamber and the canal diameter reduces, the orifices are found farther apart. You must keep this in mind when preparing access cavity for a tooth with heavy dentinal sclerosis.

A cross section through the cervical area shows that the pulp chamber floor has the shape of a quadrilateral, with four unequal sides. For maxillary molars the access preparation is quadrilateral with rounded corners. The shortest side is the palatal, parallel to the central groove. The next shorter side is the buccal and has a slope toward the disto-palatal aspect because the position of the distobuccal orifice is farther towards the palatal than the mesio-buccal orifice. The longest side is the mesial, with the opposite side towards the distal slightly shorter.

It is because of the quadrilateral shape that the mesial side does not make a sharp angle towards the palatal, and more room is available to locate the frequently found second mesio-buccal canal. Since all the orifices of this tooth lie on the mesial three-fifths of the crown, there is no need to violate the oblique ridge in preparing the access cavity.

The access cavity preparation is begun using a tapered fissure bur to penetrate the enamel in the centre of the central groove, and the access is increased in depth towards the mesio-palatal cusp. Since the palatal canal is the largest and easiest to find, it is best to locate that canal first. Once the roof of the chamber has been penetrated, a safe tipped bur is used to complete the palatal extension of the access near the mesio-palatal cusp. You can use the endodontic explorer to locate the orifice of the palatal canal. Its position will aid in the uncovering of the smaller and more difficult to locate buccal canals. The safe tipped bur is kept in contact with the floor of the pulp chamber and moved buccally to uncover the entire chamber.

Once the mesio-buccal orifice is located beneath its cusp, the disto-buccal canal will be uncovered by moving the bur distally and slightly towards the palatal surface. The second mesio-buccal canal either occurs as a separate canal or merges with the main canal in approximately 50 per cent of all maxillary first molars. To uncover this fourth canal the bur is moved from the mesio-buccal orifice towards the palatal canal at a distance of 2-3 mm.