Radiographic anatomy of pulpal chambers of primary molars.

The radiographic anatomy of the superior borders of pulpal chambers of primary molars was studied to clarify interpretation of superimposing cuspal images. First and second maxillary and mandibular molars were sectioned transaxially in the cervical region. The pulpal tissue was replaced by radiopaque resin before embedding the crowns in clear plastic blocks and obtaining buccolingual radiographs. The embedded crowns were then sectioned mesiodistally and radiographed buccolingually. The postsectional radiographic outlines of the pulpal chambers then were compared to presectional radiographs. An average radiographic image for each tooth type was constructed from a median of the aggregate tracings of the particular tooth. The radiographic appearance of each primary molar presented two to five overlapping pulpal horns, corresponding to their morphological anatomies. On dental radiographs, the lingual pulpal outline is sharper and more radiopaque than the buccal pulpal outline. JL he majority of studies of pulp cavity morphology during the last 70 years have concentrated on the permanent teeth—only a few have described primary teeth. A literature review revealed a lack of studies of the radiographic anatomy of pulpal cavities of primary teeth. Many investigators' illustrated the relationship of the pulp cavity to the whole tooth using a variety of injected materials. Their findings were found, in general, to be similar and accurate. Barker et al.'" developed two techniques for injecting pulpal chambers and root canals. The first method used papain hydrochloride solution to macerate the pulp tissue, injection of a silicone elastomer, and then radiographic examination. The second method consisted of filling the pulpal chamber and root canals with red epoxy resin. While these two approaches illustrated the complexities of pulpal chamber and root canal anatomy of primary and permanent teeth, attention was not directed specifically toward the cuspal outlines of the pulpal chambers. The purpose of this study, therefore, was to determine the radiographic anatomy of the occlusal border of pulpal chambers of primary molars in order to clarify interpretation of superimposing cuspal images, as well as to obtain an average radiographic image of each primary molar (Figure 1). Methods and Materials Twenty human primary teeth of children between the ages of 6 and 12 years (x = 8.5) were selected for this study. These teeth were extracted for orthodontic purposes. When compared to average measurements, they were found to have at least one-third of the root structure intact. Inspection and radiographs revealed that they were either caries-free (75%) or had only incipient carious lesions (25%). On the basis of the above factors, four study groups were formed (Table 1). Following storage in 50% glycerine in ethyl alcohol solution, each tooth was divided at the cervical region into apical and coronal portions. The crowns were then hydrolyzed in 1% papain hydrochloride solution at Figure 1. Radiograph of the occlusal borders of pulpal chambers of primary molars shows superimposing cuspal images. Clarification of these overlapping images would aid radiographic interpretation and planning of treatment. PEDIATRIC DENTISTRY: Volume 5, Number 1 25 Table 1. Type and Condition of Tooth Specimens Study Carious Group N Type of Specimen N Lesions I 7 Right second primary molars 3 0 (Mandibular) Left second primary molars 4 II 5 Left first primary molars 2 (Mandibular) Right first primary molars 3 4 III 5 Right second primary molars 2 (Maxillary) Left second primary molars 3 0 IV 3 Right first primary molars 1 (Maxillary) Left first primary molars 2 37°C for 48-72 hours 1~ to macerate the remaining pulpal tissue. Following washing in running water and dehydration in absolute alcohol, the crowns were warmed to remove any liquid residue. A radiopaque material consisting of equal portions of lead dioxide a and plymethyl methacrylate resin b was placed into each crown through the cervical opening and centrifuged to thoroughly fill the pulpal chamber. The filled crowns then were embedded in clear plastic resin c rectangular blocks with sides parallel to the surfaces of the tooth crown. The cervical portions of the blocks and teeth were notched in a buccolingual direction so that the notches would lie close to the mesial and distal surfaces. These notches served as guides for aligning the tooth sections in the radiographic films. Radiographs were taken in a buccolingual direction using a "film-tooth" holding device which positioned a long-cone tube in a consistent relationship to the tooth and film (Figure 2). The embedded crowns then were sectioned mesiodistally through the central fissure to produce a buccal and a lingual segment. Radiographs were obtained, as described above, for each segment of the crown. In all instances, the x rays were directed at the buccal aspects of the intact teeth and sections. The radiographs of the crowns and crown sections were projected onto a screen at a constant distance and magnification. Outlines of the crowns and pulpal chambers were drawn on paper and cut. The ensuing tracings, oriented on the mesial and distal identification notches, were assembled on plastic posts mounted on a rigid base. This assembly method allowed the position differences between the radiographs of the buccal and lingual portions to be compared to the presectioned radiographic image (Figure 3). An average radiographic image (ARI) of each primary molar was obtained by drawing a line approximately horizontal to the occlusal surface in the cervical area of each tracing and drawing vertical lines to the greatest convexity and the greatest concavity of the pulp chamber outline (Figure 4). An ’R’ (registration) point was created Certified A.C.S. Lead dioxide powder, Fisher Scientific Co., Fair Lawn, N.J. Raypaque, COE Laboratories, Chicago, Ill. Ward’s Bioplastic, Ward’s Natural Science Establishment, Rochester, N.Y. LONG CONE X-RAY TUBE