Evaluation of Tooth Anatomy: Problem Prevention

The process of radiographic interpretation should begin with examination of the teeth. Assessment is limited in all areas of dentistry by the fact that the intraoral radiograph is a two-dimensional representation of three-dimensional objects. For example, even with well-made digital or film images, it is rarely possible to confirm or rule out the presence of a second canal in the mesial buccal root of a maxillary molar. Three-dimensional radiography is available in dentistry in the form of cone-beam computed tomography (CBCT),^10,24,30 which is developing but not yet sufficiently refined to routinely produce the detailed images required for endodontic diagnosis and treatment.^6,10,24 When combined with digital radiography, however, CBCT can significantly enhance endodontic care.

Once a quality radiographic film is obtained, knowledge of dental anatomy is crucial for extrapolating two-dimensional representations into three-dimensional mental images. For example, anatomic examination of mandibular molar roots teaches that these roots are narrow in the mesial-distal dimension and very wide in the buccal-lingual dimension. A very wide root buccal-lingually will appear narrow on an optimal clinical radiograph. If the radiograph is made using variable angulations of the radiation beam (from the mesial or distal), the root will appear wider.³¹ More than one periodontal ligament space may be observed, and the image may be more difficult to interpret if roots of adjacent teeth are overlapped.

One objective of tooth evaluation will be to confirm anatomic form and any variations: it is sometimes possible to see two roots on a mandibular canine (Fig. 3-1, A), but it is equally important to know that a mandibular canine can have two roots, and many such cases will not be discoverable on radiographs.¹³ Additional roots and canals must be found by internal exploration during treatment, and CBCT images can assist in this anatomic assessment (see Fig. 3-1, B and C).

FIGURE 3-1 A, Mandibular canine with a bifurcated root. B, Another case of a mandibular canine investigated using cone-beam computed tomography (CBCT); occlusal view (arrow indicates tooth being evaluated). C, Proximal view of the two-rooted canine tooth using CBCT. Note sections 94 to 97; not only do they provide a good view of the two roots and two canals, but they also provide valuable information as to the location of the lingual canal and the challenges faced in access opening and orifice location.

Teeth that may be indicated for root canal treatment should be examined for relative length, the number of roots, calcification of canals, and general morphology. Once assessment has been completed, anatomy confirmed, and treatment initiated, canal morphology should be clearly visualized in the mind of the clinician and retained throughout treatment. Variations in the anatomy of posterior teeth such as the mandibular first molar are seen routinely (Fig. 3-2). Fig. 3-2, A shows a molar with two divergent mesial roots; Fig. 3-2, B shows a molar tooth with two divergent distal roots. Even more variations may exist in various ethnic populations.

FIGURE 3-2 A, Mandibular molar with two mesial roots. B, Mandibular molar with two distal roots.

The number of roots treated should be noted in each case of a previously treated tooth, as well as the quality of treatment (length of fill, density of fill, shape of canal, etc.). Although no abnormal changes may be found radiographically, the tissue remaining in uncleaned canals can give rise to symptoms of thermal sensitivity, percussion sensitivity, and spontaneous pain. Any teeth found to have poor or questionable root canal treatment could be possible sources of symptoms and potential candidates for treatment revision. Further clinical examination of these teeth would be indicated.

CLINICAL PROBLEM

Problem

A 53-year-old male with a current history of acute pain to heat stimulation in the maxillary right posterior area was evaluated for treatment. The periapical film indicated that the second molar had past root canal treatment, but no carious lesions were seen radiographically or upon clinical exam. There was no evidence of periapical pathosis (Fig. 3-3, A).

FIGURE 3-3 A, Maxillary second molar with confirmed heat sensitivity. B, Posttreatment image indicating previously untreated distal canal.

Solution

Routine sensibility tests were performed. The maxillary right first molar and two premolars responded normally to cold but did not respond to heat. The second molar responded abnormally to heat, with lingering pain. The patient stated this was the pain he had been experiencing. Examination of the radiograph revealed that the treated canals appeared asymmetrically located to the mesial of the root with respect to the overall morphology of the root anatomy. An untreated canal was suspected in the distal buccal root. Following access opening, the canal was identified, cleaned, shaped, disinfected, and obturated (see Fig. 3-3, B). The patient reported that once anesthesia was gone, the previous discomfort to heat was absent.

A similar case is seen in Fig. 3-4, A to C. The patient was referred for root canal treatment on the maxillary left second molar. She had been experiencing intermittent episodes of a dull ache in the maxillary premolar area for 1 year. At examination, the patient pointed to the pontic area as the felt location of the pain. Root canal treatment had been completed on the left first premolar 8 years previously. Sensibility testing with heat clearly identified the premolar as the source of pain. Preoperative radiographs were made at different angles (see Fig. 3-4, A and B). Careful analysis of the radiograph (see Fig. 3-4, B) suggested that filling material might have been compacted into the orifice of an untreated canal. An occlusal access opening was made, but locating the orifice of the third canal was a challenge. Once the untreated canal was located, the pulp was found to be vital. Following successful treatment of this root canal, the symptoms resolved (see Fig. 3-4, C).

FIGURE 3-4 A, Initial radiograph of the maxillary left first premolar with heat sensitivity. B, Second view angulated slightly from the distal. Note the small bulge in the gutta percha extending mesially in the coronal third. C, Posttreatment image indicating a previously untreated canal.

(Courtesy Dr. Ryan Wynne.)

Radiographic Changes Associated With Dental Caries

The radiographic appearance of dental caries is basic to all dental education, and ample resources exist in the dental literature for further reading on detecting dental caries on routine radiographic surveys.²³ For endodontic diagnostic purposes, the depth of caries past or present is an important radiographic indicator of teeth with pulpal pathosis. While carious exposures of the pulp cannot be seen radiographically, gross caries that approximates the radiographic outline of the pulp chamber is frequently evident even in the absence of symptoms (Fig. 3-5, A). Pulp exposure would be a logical expectation following excavation of such lesions, and root canal treatment of this tooth would be a necessary part of the treatment plan. Bitewing radiographs greatly assist identification of caries and its proximity to the dental pulp; they can be taken with traditional film or as digital images (Fig. 3-5, B)

FIGURE 3-5 A, Carious exposure of mesiobuccal pulp horn in a maxillary second molar. B, Bitewing digital radiograph showing the location and extent of dental caries.

Carious lesions that appear near pulp horns also are likely to be carious exposures upon excavation. Demineralization of dentin that occurs in the process of caries is progressive and lacks a clear clinical or radiographic border. Most carious lesions extend deeper into the dentin than what can be ascertained radiographically. Fig. 3-6, A represents a symptomatic tooth with a carious lesion in close proximity to the mesial pulp horn. Excavation revealed a gross carious exposure and necrotic pulp. Root canal treatment was indicated (see Fig. 3-6, B).

FIGURE 3-6 A, Caries near mesiobuccal pulp horn. B, Excavation revealed carious exposure and necrotic pulp. Root canal treatment was indicated.

For many teeth with large carious lesions, there may be no history of symptoms, and sensibility tests may provide normal responses (Fig. 3-7). The most reasonable approach to treatment is to advise the patient that the caries should be excavated, and the decision to treat endodontically or with vital pulp therapy will depend on the remaining dentin thickness (RDT).^5,21,22 Although dentistry has no instrument to measure this dimension, there is a good clinical indicator: if the RDT is 0.5 mm or less, the proximity of the pulp will make the dentinal wall appear pink. Studies show that with an RDT of less than 0.5 mm, the prognosis for pulp survival is doubtful.^21,22 The majority of teeth in this situation will develop symptoms of acute irreversible pulpitis after restoration, and root canal treatment will be necessary. On the other hand, vital pulp therapy has a good chance of success regardless of dentinal thickness, if the patient is young (Fig. 3-8). (Chapter 7 will address vital pulp therapy in detail.)

FIGURE 3-7 Large occlusal carious lesion. The tooth responds normally to sensibility tests.

FIGURE 3-8 A, Large occlusal carious lesion in a 10-year-old patient. B, 12 month re-evaluation after vital pulp therapy using mineral trioxide aggregate (MTA) for a direct pulp cap. The patient was asymptomatic and the tooth responded normally to sensibility tests.

(Courtesy Dra. Silvina Díaz.)

The decision to treat a tooth endodontically can sometimes be influenced by the economic situation of the patient; successful vital pulp therapy could avoid additional expense. If it fails, the patient will still be able to receive root canal treatment (Fig. 3-9).

FIGURE 3-9 Pulpal necrosis and periapical pathosis following vital pulp therapy. Endodontic treatment was then indicated.

The radiographic appearance of recurrent decay is most often obvious at the margins of existing restorations. Caries beginning at the depth of a previous caries excavation will almost invariably involve the pulp (Fig. 3-10). Caries under existing crowns appears along the margin but may extend extensively under the clinical crown (Fig. 3-11). Bridge abutments are occasionally completely undermined and have no retention.

FIGURE 3-10 Recurrent caries is deeper than original carious lesion. A carious exposure is likely.

FIGURE 3-11 A, Recurrent caries under the buccal (or lingual) margin of crown. B, Clinical view of excavated caries shown in A.

CLINICAL PROBLEM

Problem

A 57-year-old male patient was examined for the chief complaint of recurrent spontaneous pain in the mandibular right teeth (Fig. 3-12, A). Sensibility tests indicated normal responses from the central incisors through the second premolar, but there was no response to testing on the second molar. Radiographs showed no periapical pathosis, but recurrent caries was noted around the margins of the second molar bridge abutment. No other signs of pathosis or abnormalities were noted. The patient had a full maxillary denture.

FIGURE 3-12 A, Radiograph of the abutment teeth of a mandibular right posterior bridge. Note the caries at margins of the crown on second molar. B, Following bridge removal, gross caries was found to involve the entire clinical crown on the molar abutment. C, Gross caries excavated. There is no clinical crown remaining.

Solution

The diagnosis centered on the mandibular second molar, since all other teeth were ruled out as having normal pulps. A shepherd’s hook explorer (No. 23) was placed under the solder joint immediately anterior to the crown of the second molar. Lifting the bridge with the explorer confirmed that the bridge was loose on this tooth but well retained on the second premolar. Not only was vertical mobility observed, but bubbles appeared in the saliva along the margins of the crown as the bridge was elevated and reseated. The decision was made to cut the bridge distal to the second premolar. Gross caries was found to have undermined the entire clinical crown of the second molar (see Fig. 3-12, B). Following excavation, there was no remaining clinical crown (see Fig. 3-12, C), and the pulp was nonvital. The tooth was eventually retained and restored with a new bridge following a crown-lengthening procedure (see Chapter 17).

Radiographic Changes Associated With Tooth Fractures

Coronal Fractures

Radiographically, the most commonly observed fracture is the posttraumatic image of an anterior tooth with coronal tooth loss (Fig. 3-13, A). Generally, the diagnosis does not depend on radiographic findings, but it is wise to make a radiograph to rule out additional fractures below the level of the crestal bone. Complete coronal fractures often occur in older individuals owing to combined factors of heavy occlusal contacts, full crown preparations and calcification. While these patients are frequently asymptomatic, the teeth are functional and exhibit no periapical pathosis. The diagnostic radiograph is important to assess the degree of canal calcification and the overall root morphology (Fig. 3-13, B). Short roots with severely calcified canals might be treatment planned for extraction.

FIGURE 3-13 A, Typical traumatic coronal fracture of maxillary incisor in a young person. Note open apex. B, An anterior crown fracture in an elderly patient. Note calcification of canal.

Coronal fractures in posterior teeth generally occur in a mesial–distal orientation (Fig. 3-14, A), consequently, radiographic evidence of the fracture is seldom visible in the tooth structure (Fig. 3-14, B). The most typical radiographic signs of coronal fracture are changes in the coronal alveolar bone mesially, distally and in the furcation extending apically as far as the midroot level (Fig. 3-14, C) also review Fig. 1-3.

FIGURE 3-14 A, Coronal fractures in posterior teeth tend to be mesial-distal in direction. B, Unusual buccolingual fracture in maxillary molar crown is visible on radiograph. C, Mandibular molar with coronal fracture extending to a level below the furcation; note bone loss. The patient did not have evidence of periodontal disease in other areas of the dentition.

Midroot Fractures

Trauma can also result in midroot fractures. If the fracture occurs just submarginally, the crown will be extremely mobile (Fig. 3-15, A). Radiographically the root is not connected to the crown. If the fracture is more apical, the coronal segment may not be mobile, and the radiograph will be essential in making an assessment and determining the level and extent of the fracture. Midroot fractures will usually not be evident on clinical examination (Fig. 3-15, B). Chapter 19 offers in-depth discussion on treating these teeth.

FIGURE 3-15 A, Root fracture near crestal bone level. B, Midroot fracture. Note ovoid appearance of the fracture line.

Vertical Root Fractures

Vertical root fractures are a frequent cause of tooth loss almost unique to root-treated teeth. A second unique feature of this problem is the consistent location of the crack lines on the midfacial/buccal or 180 degrees on the midlingual/palatal regions of most roots. Occasionally a root is found with fractures in both positions. Lack of separation of the fractured segments of the root makes vertical root fractures seldom visible radiographically. The characteristic radiographic change is in the adjacent bone, which is the result of bone resorption along the fracture line. Early changes are typified by lateral widening of the periodontal ligament space. Often there is no apical involvement. As bone resorption continues, a distinct lateral radiolucency develops parallel to the root surface (Fig. 3-16).

FIGURE 3-16 A, A vertical root fracture is not usually visible on a radiograph. B, Lateral bone loss associated with a vertical root fracture.

When a fracture is visible and significant separation of the fractured segments of the root has occurred, the fracture has probably been present for a long time (Fig. 3-17). A number of causes of root fractures have been suggested by many authors. The etiology is said to involve anatomic, restorative, periodontal, or endodontic factors.²⁷ No doubt this is probably a multifactorial problem. Endodontically, excessive removal of root structure during cleaning and shaping can weaken a root. During obturation, using excessive lateral compaction pressure in the presence of an improperly shaped canal and using a spreader that is too large for the shape of the canal can cause a fracture (Fig. 3-18).²⁷ (See Chapter 12.)

FIGURE 3-17 Wide separation of root segments after vertical root fracture. Clinically, deep narrow periodontal defects are found on both buccal and facial surfaces in cases of complete root fracture.

FIGURE 3-18 Vertical root fracture in a second premolar caused by excessive condensation pressure during obturation. Note the widened periodontal ligament space on the distal from crestal bone to the apex. Lateral and longitudinal extrusion of filling materials is a possible sign that fracture occurred during the procedure.

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