Oral Health Group

Radiographic Interpretation of Infected Primary Molar Teeth

July 1, 2004
by Oral Health

By Keith Titley BDS, MScD, FRCD(C), Mark Merryfield DMD, Howard Stein BSc, DDS, MEd.

Infected primary molar teeth display radiographic bony changes that are different from those of permanent molars.1 Typically the infection is the result of caries progressing towards the pulp with consequent necrosis and abscess formation. In permanent teeth the infection spreads though the root apex to the periodontal ligament and surrounding bone, causing degeneration of both of these structures. At an early stage when the infection is confined to the periodontal ligament the tooth will be mobile, raised in its socket and tender to percussion.2 If it is not treated promptly and properly the infection may become chronic with the resultant radiographic appearance of a rarefaction at the root apex or apices. Unlike permanent molars, however, chronically infected primary molars show an inter-radicular rarefaction with maximum intensity in the bifurcation area between the roots. It has been postulated that there are several reasons for the inter-radicular positioning of chronic abscesses in primary molar teeth. Among them are accessory canals on the inter-radicular surface of the root and that the infective process increases the porosity of the dentin and cementum of the pulpal floor causing structural alterations in both of these tissues.1,3,4


Periapical radiographs are generally used to detect the effects that necrotic infected pulpal tissue have on the lamina dura and bone surrounding the root apices of permanent teeth and on the furcal area between the roots of primary molar teeth. Although posterior bitewing radiographs are traditionally used for the identification of clinically undetectable interproximal carious lesions they have many other uses. These include evaluation of the depth of caries penetration and its relationship to the pulp; assessment of the boundaries of the pulp chamber and the height of the pulp horns; discovery and location of retained primary tooth roots; assessment of the succadaneous tooth bud and its relation to the primary tooth root; and assessment of the resorptive pattern of primary tooth roots.2 The posterior bitewing radiograph’s greatest ancillary use, however, is in the detection of furcal radiolucencies caused by pulpally infected primary molar teeth. It is particularly useful in viewing the root areas of maxillary primary molars where developing premolars obscure the furca in periapical radiographs.2

Intra-oral radiographs play an essential part in the diagnosis of dental disease because they reveal many conditions that cannot be diagnosed by any other method. Practitioners can generally expect excellent co-operation from pre-school children above the age of three years when taking radiographs provided that the procedure is carefully explained to them. If difficulty is experienced the assistance of the parent can be sought in the holding of the child’s head and radiographic film in the correct position.5 In this instance it is preferable to limit the number of films to those necessary for the assessment of infected teeth or trauma. If the age and behaviour of the child are a negative factor additional films may be obtained at a subsequent time when the child is older and co-operation improves.5

Radiographs should be of acceptable diagnostic quality and should meet particular standards. Posterior bitewing radiographs should include the distal surface of the canine to the mesial surface of the most distal erupted tooth and include an unobstructed view of all contact and furcal areas. All periapical radiographs should include an unobstructed view of the root apices and surrounding periapical bone. In addition none of these radiographs should be cone cut, overlapped, elongated, shortened and should be of proper exposure and correctly developed.6

This paper will present two cases. The first case illustrates the possible problems arising from committing to a treatment decision using a diagnostically unacceptable radiograph. The second case illustrates the need to take further films when posterior bitewings taken during a routine recall appointment raises suspicions that teeth reported to have no history of pain or swelling are, in fact, chronically infected.


A four-and-a-half-year-old male was referred to one of the authors (H.S.) for the extraction of the mandibular first primary molar (tooth 74). The medical history was non-contributory and the patient and parent reported no history of oral pain or discomfort. A periapical radiograph, taken and sent with the patient by the referring practitioner, revealed what appeared to be a large distal carious lesion and radiolucency in the furcation of tooth 74 (Fig. 1). The radiograph, however, was elongated, blurred and poorly exposed and not of good diagnostic quality. The reason for the referral was that the child was uncooperative.

A clinical examination showed that tooth 74 had a large disto-occlusal carious lesion and there was no tenderness to percussion and there was no evidence of redness or swelling in the buccal or lingual mucosa associated with the tooth. Although the child was anxious an explanation of the necessity to take another film and how it would be accomplished gained co-operation and a second film was obtained (Fig. 2). This film showed that the bone and lamina dura in the furcation area showed no evidence of pathology. Tooth 74 was subsequently treated with a vital formocresol pulpotomy and stainless steel crown.


A six-and-a-half-year-old female presented for a recall appointment at a clinic run by the City of Toronto (M.M.). The parent reported that the child had received regular dental care in their country of origin and that they were recent immigrants to Canada. The medical history was non-contributory and the patient and parent reported no history of oral pain or discomfort. Clinical examination revealed the presence of large composite restorations in all four second primary molar teeth and Class II composite restorations in both of the mandibular first primary molars. There was also evidence of recurrent caries in both of the maxillary second primary molars. The buccal and lingual mucosa was within normal limits with no evidence of any redness of swelling. Because of the recurrent caries and the size of the restorations in the second primary molar teeth, right and left posterior bitewing radiographs were taken (Fig. 3).

Careful examination of these radiographs showed clear evidence of the presence of furcal radiolucencies in both of the mandibular and in the maxillary left second primary molar teeth. The appearance of the bone in the furcation of the maxillary right second primary molar appeared to be within normal limits. Accordingly the decision was made to take periapical views of each of the second primary molar teeth (Fig. 4). These confirmed the finding on the bitewings and also revealed that the three infected teeth were undergoing pathologic root resorption. As a result the decision was made to extract these three teeth and to retain the space with space maintainers. It was also noted that the maxillary left periapical radiograph was cone cut in the primary cuspid-first molar area but since the view showed the second primary molar in its entirety it was decided that it was not necessary to take another radiograph.

The right maxillary second primary molar was treatment planned for a possible formocresol pulpotomy and stainless steel crown. Unfortunately the patient missed several subsequent appointments and subsequently presented as an emergency with pain and swelling in her right maxillary quadrant. A periapical radiograph revealed the presence of a radiolucent area in the furcation of the infected tooth so that this tooth also had to be extracted and the appropriate space maintainer fabricated (Fig. 5).


These two cases illustrate the importance of the need to thoroughly evaluate clinically symptomless teeth with large carious lesions or restorations with appropriate radiographs that are of a good diagnostic quality. Case One is an ex
cellent example of the importance of having a diagnostically acceptable radiograph available before making what would have been an irrevocable treatment decision to extract a restorable tooth. Case Two illustrates the importance of taking posterior bitewing radiographs at recall appointments particularly when recurrent caries is clinically seen around large restorations and the patient reports no associated pain or discomfort. The case also illustrates the important ancillary use of the posterior bitewing in the detection of non-vital primary molar teeth. Examination of any posterior bitewing of a carious or restored primary molar tooth must include the furcal areas. Similarly a cone cut does not necessarily entail a re-take of a radiograph provided that the tooth and surrounding structures of interest can be clearly identified.

Dr. Keith Titley is Professor, Department of Paediatric Dentistry, University of Toronto and is Oral Health’s editorial board member for Paediatrics.

Dr. Mark Merryfield is an Associate in Dentistry, University of Toronto and practices in the City of Toronto’s Victoria Street Clinic.

Dr Howard Stein is an Associate in Dentistry, University of Toronto and operates a private Paediatric Dentistry practice.

Oral Health welcomes this original article.


1.Moss SJ, Addelston H, Goldsmith ED. (1965) Histologic study of pulpal floor of deciduous molars. J Am Dent Assn 70:372-379.

2.Braham RL, Morris ME. (1985) Textbook of pediatric dentistry. 2nd Edition. Williams and Wilkins, Baltimore, London, Sydney.

3.Winter GB. (1962) Abcess formation in connexion with deciduous molar teeth. Arch Oral Biol 7:373-379

4.Ringelstein D, Seow WK. (1989) The prevalence of furcation foramina in primary molars. Ped Dent 11:198-201.

5.Titley KC. (1986) Examination, radiographic techniques, and interpretation in children as a guide to treatment planning. 433-442. In: Levine N Ed. Current treatment in dental practice. WB Saunders Co.

6.Mathewson RJ, Primosch RE, Robertson D. (1987) Fundamentals of pediatric dentistry. Quintessence Publishing Co., Inc.

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