|SECTION III||ETHNIC VARIATIONS IN PULP AND ROOT CANAL MORPHOLOGY|
Research on root canal and pulp morphology has shown that ethnic variations exist. Root canal variations are more prevalent in maxillary and mandibular premolars and molars, especially in Asian, Pacific, sub-Saharan, Australian, Middle Eastern, and subpopulations within these larger ethnic groups. One of the most frequent variations reported is the incidence of C-shaped root canals in the maxillary and mandibular molars and mandibular premolars in the Asian population.4 A C-shaped canal is named for the ribbon-shaped, 180-degree arc morphology viewed in the cross section of a root that replaces the discrete, separate canal openings normally seen.
Another common variation is the incidence of bifurcated root canal systems in mandibular first premolars. A review of the literature shows a higher incidence of bifurcated root canals in African Americans (16% to 33%), Turkish populations (36% to 40%), Kuwaiti populations (40%), and Chinese populations (22% to 36%) as compared to Caucasians (6% to 14%).5 These variations need to be identified (usually using radiographs) prior to endodontic therapy so that appropriate adjustments to the access opening can be made, and thorough debridement of the root canals can be accomplished.
Each of the following questions may have more than one correct answer.
- Which teeth are NOT likely to have root depressions on both the mesial and distal surfaces of the root?
- Maxillary central and lateral incisor
- Maxillary canine
- Maxillary second premolar
- Mandibular second premolar
- Maxillary anterior teeth are most likely to have how many root canals?
- One or two
- Maxillary first molars are most likely to have _____ roots and _____ root canals.
- Two, two
- Two, three
- Two, four
- Three, three
- Three, four
- The one premolar most likely to have two roots (and two root canals) is the
- Maxillary first premolar.
- Maxillary second premolar.
- Mandibular first premolar.
- Mandibular second premolar.
- The two roots of a maxillary first premolar are called
- Mesial and lingual.
- Mesial and distal.
- Buccal and mesial.
- Buccal and lingual.
- Mesiobuccal and distobuccal.
- On a tooth with severe bone loss due to periodontal disease, a probe can access the root furcation of a maxillary first molar on which of the following surfaces?
- Buccal surface
- Lingual surface
- Mesial surface
- Distal surface
ANSWERS: 1–a, d; 2–a; 3–e; 4–a; 5–d; 6–a, c, d
1. Jeremiah Smith requires endodontic therapy on a maxillary first molar. How can the dentist determine how many canals this tooth has that require filling? Optional for a take home assignment: the student may ask a dentist for advice.
2. Search on the computer for images of “radiographs of molar root canals,” and see how many maxillary molars appear to have three canals and how many appear to have four. Be aware that sometimes the root canal fillings can be superimposed over one another, so the count may not be accurate. Then look at mandibular molars to see how many appear to have two canals as opposed to three. You may even find more canals than you expect.
OTHER GENERAL REFERENCES
Estrela C, Pereira HL, Pecora JD. Radicular grooves in maxillary lateral incisor: case report. Braz Dent J 1995;6(2): 143–146.
Pecora JD, Saquy PC, Sousa Neto MD, et al. Root form and canal anatomy of maxillary first premolars. Braz Dent J 1991;2(2): 87–94.
Pecora JD, Sousa Neto MD, Saquy PC, et al. In vitro study of root canal anatomy of maxillary second premolars. Braz Dent J 1992;3(2):81–85.
Pecora JD, Woelfel JB, Sousa Neto MD. Morphologic study of the maxillary molars. Part I: external anatomy. Braz Dent J 1991; 2(1):45–50.
Pecora JD, Woelfel JB, Sousa Neto MD, et al. Morphologic study of the maxillary molars. Part II: internal anatomy. Braz Dent J 1992;3(1):53–57.
Walton RE, Torabinejad M. Principles and practice of endodontics. 3rd ed. Philadelphia, PA: W.B. Saunders Company, 2002.
Web site: www.aae.org/media/index.html—American Association of Endodontists (with information for the professional and for media/public).
DR. WOELFEL’S ORIGINAL RESEARCH DATA
Specific facts are referenced throughout this chapter by using superscript letters like this (dataA). The referenced facts are listed here after each letter.
B. Mandibular central and lateral incisors have one root canal 60% of the time. Mandibular central incisors may have two canals with two separate apical foramina (type III) 3% of the time and two canals converging to one foramen (type II) from 17% to 43% of the time. Mandibular lateral incisors may have two canals from 20% to 45% of the time (usually type II with one foramen or type III with two separate foramina about 3% of the time). Mandibular canines may have two canals from 4% to 22% of the time. When two canals are present, one is facial and one is lingual, often with type IV formation.
C. Approximately 57% of maxillary first premolars have two roots, but only 39% have one root. When two roots are present, the canals in both roots exhibit a type I configuration, and, when one root is present, the canal configuration is either a type II or type III.7
F. Mandibular first premolars have one root and one canal (type I) 70% of the time (Fig. 9-10A) and 98% of the time in second premolars. Mandibular first premolars may have two canals (type IV) 24% of the time (Fig. 9-10B), but mandibular second premolars have two canals only 2.5% of the time.9
G. The mesiobuccal root of the maxillary first molar has two canals 90% of the time, one located more buccally within this root called mesiobuccal canal and one located more lingually within this root called the mesiolingual canal. Type III canal systems have been reported to occur 33% to 60% of the time.10 Opening into the palatal root canal, the palatal orifice on the floor of the pulp chamber is located beneath the mesiolingual cusp (Fig. 8-9). Opening into the mesiobuccal root, the mesiobuccal orifice is located slightly mesial to and beneath the mesiobuccal cusp tip. The mesiolingual orifice is located slightly to the palatal aspect of the mesiobuccal orifice. Usually, this orifice is difficult to locate because of an overhanging dentin shelf. Opening into the distobuccal root, the distobuccal canal orifice is located on a line between the palatal orifice and the buccal developmental groove at a point just short of the angle formed by the buccal and distal walls of the pulp chamber.
I. The mesial roots of mandibular first molars have two canals virtually all of the time: a type III canal system is present 60% of the time, and a type II canal system is present 40% of the time.11 The mesial roots of mandibular second molars have two canals 64% of the time: a type II canal system 38% of the time and a type III canal system 26% of the time, but one canal 27% of the time.9
J. In the distal roots of mandibular first molars, there are two canals approximately 35% of the time, usually type II configuration,12 whereas the distal roots of mandibular second molars have one canal 92% of the time.9
K. In both mandibular first and second molars, the mesiobuccal canal orifice on the chamber floor is located slightly mesial but close to the mesiobuccal cusp tip (Fig. 8-9). The mesiolingual canal orifice is just lingual to the mesial developmental groove of the mesial marginal ridge. It is not under the mesiolingual cusp tip but is in a more central location. If the distal root has one canal, the distal canal orifice is large and located just distal to the center of the crown. When two canals are present, the distolingual orifice is small and is located centrally just lingual to the central fossa. Careful inspection of the chamber floor toward the buccal will successfully locate the distobuccal orifice.
L. In a radiographic study of 259 children in England, from their 11th to 14th birthdays, the mesiodistal and roof-to-floor pulp dimensions were recorded with a Lysta-Dent Digitizer. Mesiodistal reduction in size in mandibular first molars over 3 years was minimal (1% to 3.5%) compared to a considerable height reduction (15%) of the pulp chambers. This was mostly the result of secondary dentin deposition on the floor, not the roof, of the chamber.13