The purpose of this section is to summarize the shape of the external root surface and the internal pulp shape at the level of the cementoenamel junction and halfway down the root toward the apex. The following tooth drawings are labeled with M for mesial, D for distal, F for facial, and L for lingual.

A. MAXILLARY CENTRAL INCISORS

• The cross section of the root at the cervix is somewhat triangular with the mesial side longer than the distal side, consistent with the slight distal placement of the cingulum.
• There are no root grooves (depressions) on this incisor, though the mesial surface may be flattened or have a slight longitudinal depression. The distal root surface is convex.
• The cross section of the root at the cervix is “egg shaped” or ovoid, with the widest mesiodistal portion on the labial.
• A shallow longitudinal root depression is sometimes found on the middle of the mesial root surface extending about half of the root length but not on the distal surface.
• There is one root canal close to 100% of the time.

B. MANDIBULAR LATERAL INCISORS

• The cross section of the root at the cervix is “egg shaped” or ovoid, with the widest mesiodistal portion on the labial.
• A shallow longitudinal root depression is sometimes found on the middle of the mesial root surface extending about half of the root length but not on the distal surface.
• There is one root canal close to 100% of the time.

C. MANDIBULAR CENTRAL AND LATERAL INCISORS

• In cross section, the cervical portion of the root is ovoid, considerably broader labiolingually than mesiodistally.
• Longitudinal root depressions are present on both proximal sides with the distal depression more distinct than the mesial.
• Most often, there is one root canal.^M

D. MAXILLARY CANINES

• The cervical cross section is broad labiolingually and appears ovoid.
• Developmental grooves (depressions) are present on both sides, often deeper on the distal.
• As in other maxillary anterior teeth, there is one root canal almost 100% of the time.

E. MANDIBULAR CANINES

• Roots are wide labiolingually in the cervical half.
• Roots have prominent longitudinal root depressions on both sides, often deeper on the distal, or sometimes clearly separated roots (one labial and one lingual).
• There is most often one root canal.^N

!F. MAXILLARY FIRST PREMOLARS

• There are most often two canals.^O
• Most maxillary first premolars have two roots (one buccal and one lingual) and two canals, and even when only one root is present, two pulp canals are usually found.
• Mesial and distal root depressions occur on both one- and two-rooted first premolars (between the buccal and lingual roots or between the buccal and lingual halves of the single root).
• The prominent mesial depression of the crown continues across the cervical line to join the deep mesial root depression.
• When considering all premolars, the maxillary first premolar is UNIQUE since it has the only root where the mesial root depression is deeper than the distal root depression.
• When two roots are present, the bifurcation occurs in the apical third to half of the root.

!G. MAXILLARY SECOND PREMOLARS

• Although there is normally only one root, there may be two roots as well.^P
• There may be a shallow depression (sometimes called a developmental groove) on the mesial side of the root, but it does not extend onto the crown, as was seen on the maxillary first premolar. A root depression can usually be found on the distal side, often deeper than on the mesial.
• There is most often one root canal.^Q

!H. MANDIBULAR FIRST PREMOLARS

• In cross section, the cervical portion of the root is ovoid and is widest buccolingually.
• Longitudinal depressions are often present on both sides, deeper on the distal. Sometimes these depressions may be quite deep and end in a buccolingual apical bifurcation.
• There is usually one root canal.^R

!I. MANDIBULAR SECOND PREMOLARS

• The cross section of the cervical portion of the root is ovoid buccolingually.
• Longitudinal depressions are not common on the mesial root surface but are frequent on the distal surface in the middle third.
• The cervical cross section of the root of the three-cusp premolars is particularly wide on the lingual, more so than on two-cusp types.
• The root is rarely bifurcated and almost always has one root canal.^S

!J. MANDIBULAR FIRST AND SECOND MOLARS

• Mandibular molars normally have two roots: mesial (broader and longer) and distal. Both roots are broad buccolingually.
• Mandibular first and second molars normally have three root canals, two in the mesial root and one in the distal root.
• The mesial root of both molars commonly has prominent root depressions on the mesial and distal surfaces, and there are usually two root canals nearly 100% of the time. This root may even be divided into a buccal and lingual part. The distal root surface contours are more variable.
• The distal roots in the mandibular first and second molars most often have one canal.^T
• Access to the root bifurcations in the mouth is located near the midbuccal and midlingual root surfaces.
• The root trunk is shorter on first molars than on second molars; the furcation is nearest to the cervical line on the buccal of first molars. The cervical line is more occlusal on the lingual of first molars. Buccal and lingual depressions are seen on the relatively short root trunk, extending from the cervical lines to buccal and lingual furcations. (Recall that enamel at the buccal and lingual cementoenamel junction may extend into the bifurcation.)
• First molar roots are broader and more widely separated than second molar roots, which may exhibit a distal inclination.

!K. MAXILLARY FIRST AND SECOND MOLARS

• There are normally three roots: mesiobuccal, distobuccal (shortest), and lingual (longest).
• Maxillary first and second molars usually have four root canals: two in the wide mesiobuccal root and one each in the distobuccal and lingual roots.
• The mesiobuccal root has mesial and distal side root depressions (and usually has two root canals).
• The distal contour of the distobuccal root varies but is normally convex (and normally has one canal).
• There is usually a slight longitudinal depression on the lingual side on the lingual root of the maxillary first molar. The lingual root has one canal.
• Access to furcations between the roots is located in the cervical third of the root: on the buccal surface, near the center mesiodistally, and on the mesial and distal surfaces, located slightly lingual to the center buccolingually.
• Often, a depression extends from the trifurcation to the cervical line and sometimes into the enamel of the crown on first molars. A distal crown depression is often noted on the distal surfaces of maxillary first molars.
• Separation between roots is more pronounced on first molars than on second molars; on second molars, the buccal roots are more nearly parallel and inclined distally in their apical third.
• The root trunk is broader (longer) than on mandibular molars, so the furcation between the mesiobuccal and distobuccal root may be at the junction of the cervical and middle thirds of the mesiobuccal root, especially on second molars.

A summary of the presence and relative depth of longitudinal root depressions is presented in Table 8-3.

TABLE 8-3

Summary: Presence and Relative Depth of Longitudinal Root Depressions (“Root Grooves”)

General learning guidelines:

1. Maxillary incisors are less likely to have root depressions.

2. All canines and premolars (EXCEPT maxillary first premolars) and mandibular incisors are likely to have deeper distal surface root depressions.

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