Additional Diagnostic Value of Digital Bitewing Radiographs in Detecting Proximal Caries in Primary Molars

Gunashekhar Madiraju, BDS, MDS

Making a diagnosis of proximal carious lesions in primary teeth is difficult due to their unique morphologic characteristics, resulting in a rapid rate of caries progression.^1-3 Furthermore, broad contact areas of primary molars4 encourage accumulation of cariogenic microorganisms, leading to initiation and progression of the disease.

Bitewing radiographs are routinely used in clinical dentistry in the diagnosis of proximal carious lesions.^4,5 Kidd and Pitts⁶ in a review study reported that the use of bitewing radiographs as an aid to making a clinical diagnosis is essential for detection of approximal caries. Studies have shown that the use of clinical examination as a sole diagnostic method for caries detection results in underestimation of carious lesions.^7-9 However, the value of bitewing radiographs in detecting proximal caries in epidemiologic studies remains controversial. Most studies have been either in vitro or in adult populations. Studies on primary teeth regarding this issue are scarce in the literature. Consequently, the present study was conducted to determine the additional benefit of bitewing radiographs compared to clinical examination in the estimation of proximal caries in primary molars.

Materials and Methods

The study sample consisted of 238 (126 males and 112 females) 5- to 6-year-old healthy children (mean age 6.1 years) who participated in a clinical epidemiologic survey conducted in two urban areas of West Godavari district, AP, India. The study was reviewed and approved by the local Human Research Ethics Committee.

Procedure

Clinical data were collected from clinical oral examinations in outpatient clinics under aseptic conditions. Children were examined clinically for proximal caries using a mouth mirror and probe under artificial illumination. Teeth were dried with a triplex syringe prior to the examination. Clinical criteria (visual-tactile) included:

• C1: sound surface (Figure 1)
• C2: discolored surface that the sickle explorer could not enter (Figure 2)
• C3: decayed surface that the sickle explorer withdrew with some resistance (Figure 3)
• C4: decayed lesion, not involving pulp, in which the sickle explorer moved freely (Figure 4)
• C5: a lesion involving the pulp

An approximal tooth surface was recorded as decayed when a lesion was present as a clearly undermined marginal crista or as a discontinuity of enamel (score 1). At the end of the clinical examination, bitewing radiographs were taken after an informed written consent was obtained from the parent or legal guardian. Because of the concern regarding exposure to ionizing radiation, digital radiography was used in this study.

For each patient, two standard radiographs, ie, two bitewing radiographs (right and left), were taken. In each individual, eight surfaces between teeth, primary first molar, and primary second molar in all the four quadrants were studied. Although digital radiography provided less radiation, radiographs were taken with the child wearing a thyroid collar and a lead apron. Digital bitewing images were taken at 70 Kvp, 4 mA to 10 mA for 12 seconds according to patient size in order to maintain consistent radiographic density from the unit. The digital images were taken at 12-bit gray-scale levels and saved as TIFF (tagged image file format) files. Images were obtained by one trained investigator to order to provide consistency in the radiographic techniques.

The digital bitewing images were displayed on a 17-inch super VGA monitor with a screen resolution of 1,024 x 768 pixels. The contrast and brightness were set to 100 and 0, respectively. The operating system was Microsoft Windows XP, and the digital imaging software used was VixWinpro version 5 (Gendex, www.gendex.com). All images were evaluated under subdued lighting conditions, and the viewing distance was kept at approximately 70 cm.

The number of proximal spaces for each subject and number of surfaces were calculated. Data regarding proximal caries affecting the particular spaces were recorded in a specially designed sheet. Only one trained examiner recorded the data to avoid inter-examiner variability. The clinician assessed the distal surface of the first primary molar and the mesial surface of the second primary molar in the bitewing radiographs, using the following criteria:

• Score 0: no radiolucency visible in enamel and/or in dentin (Figure 5)
• Score 1: a circumscribed radiolucency visible in dentin (Figure 6)
• Score 2: no judgment can be made (due to overlap, or dislocated film position) (Figure 5)

An extensive description of the protocol including these criteria has been given by Poorterman.¹⁰ Data were analyzed using Chi-square tests, and intra-examiner reliability was tested using kappa statistics.

Results

Kappa values for intra-examiner agreement were 0.91 and 0.89 for clinical and radiographic examinations, respectively. Gender distribution according to number of decayed proximal surfaces after clinical examination is presented in Table 1. In each participant, eight surfaces were clinically examined, ie, 1,008 surfaces in 126 males and 896 in 112 females, respectively. Based on clinical judgment alone, the number of carious proximal surfaces was 62.7% (632 surfaces) in males and 58.9% (528 surfaces) in females. Chi-square analysis revealed no significant differences between the genders regarding detection of proximal lesions clinically (χ2 = 2.87, df = 1, p > .05).

Gender distribution according to number of decayed proximal surfaces after bitewing radiographic examination is shown in Table 2. When bitewing radiographic judgment was included, the number increased to 80.6% (812 surfaces) in males and 71.9% (644 surfaces) in females. Chi-square analysis revealed a significant difference between the genders regarding detection of proximal lesions using bite-wing radiographs (χ2 = 19.8, df = 1, p < .05). The additional diagnostic yield of the digital bitewing radiographs was calculated as the number of additionally detected proximal lesions in radiographs, which amounted to18% in males and 13% in females.

Discussion

Clinical examinations involving visual inspection and tactile examination by probing, and bitewing radiographs either in combination or alone are used to diagnose proximal carious lesions in primary dentition. The present study aimed at determining the additional yield of bitewing radiographs compared to clinical examination (visual and tactile) in the estimation of proximal caries in primary molars.

The present data revealed that the visual tactile technique detected 60.9% of proximal caries compared to 76.5% for bitewing radiography, which resulted in an overall underestimation of proximal caries prevalent in primary molars by 15.6% in the absence of bitewing radiography. Hopcraft and Morgan⁵ reported that a clinical examination detected only 60% of all occlusal and proximal dentin caries on posterior teeth of young adults. They suggested that underestimation of caries prevalence by about 10% occurs in epidemiologic surveys that did not use bitewing radiographs. Pooterman et al⁸ reported an underestimation between 1% and 12% in the absence of bitewing radiography. Newman et al⁹ found that the visual tactile technique could detect only 43% of caries compared to 91% for bitewing radiography. The difference in their study could be related to the inclusion of occlusal caries in addition to proximal caries. In the present study, the additional benefit of bitewing radiographs compared to clinical examination in detection of proximal carious lesions was 18% in males and 13% in females.

As radiographic techniques are widely used for detecting carious proximal lesions and with rapid development in digitization of radiographic images, the present study used the digital bitewing radiography in the diagnosis of proximal caries. Digitized radiographs have some advantages such as image enhancement compared to conventional film-based radiographs, which may improve the diagnostic value.^11,12 Another benefit of using digital radiography in the present study was the reduced exposure to radiation in young children. The ethical dilemma concerning unnecessary exposure of patients to radiographs was overcome in the present study by using digital radiography with radiation protection and informed written parental consent.

Poorterman⁷ suggested that bitewing radiography does not truly correspond to the actual state of the disease because some lesions may be false negative (not detected) and a number of sound surfaces may be diagnosed as false positive (carious). Moreover, as false-positive and false-negative diagnoses largely influence individual treatment decisions, further research should be aimed at obtaining more information about the accurate extent of undiagnosed proximal caries.

The present data support the recommendations that bitewing radiography be considered part of the routine initial dental examination in cooperative older children with proximal surfaces that cannot be visualized.^9,13 The study also serves as a wake-up call for epidemiologists and general dental practitioners, with respect to the outcome of clinical caries diagnosis.

Conclusions

The additional yield of bite-wing radiographs in the detection of proximal caries in the present study was 18% and 13% in males and females, respectively. The benefits of digital bitewing are that radiographs can be used in epidemiologic studies and clinical practice to avoid underestimation of proximal caries.

References

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13. American Academy of Pediatric Dentistry reference manual 2007-2008. Pediatr Dent. 2007-2008;29(7 suppl):222.

About the Author

Gunashekhar Madiraju, BDS, MDS
Associate Professor
Pediatric Dentistry
NTRUHS, AP, India