Introduction

Panoramic radiography is a simple extra oral radio­graphic technique that allows visualization of all maxillary and mandibular areas on one radiographic film, which is a valuable adjunct to routine diagnostic procedures. (1) It is also one of the most common radiographic techniques in dentistry and it has achieved a special position as a diagnostic tool since its introduction in the early 1960s,. This type of radiography is a popular diagnostic method and is used alone or with other radiographic techniques. (2)

Panoramic radiographs are clinically useful for diagnosing the conditions that require a wide coverage of the jaws, including traumas, position of the third molars, extensive disease entities, identification of suspected large lesions, tooth development (especially in the mixed dentition period), residual teeth or roots (in edentulous patients), and congenital/developmental anomalies. Such cases do not require the high resolution and great detail observed on intraoral images. (1)

Radiographic images of the entire maxillofacial structure can provide good quality with low radiation doses. Patient comfort and usability, even in patients with limited mouth opening, is another benefit.¹ If low quality images are produced, there may be a reduction in diagnostic value, which could lead to inappropriate treatments. The low quality observed in some images is not due to the inherent limitations of these techniques, but are a result of operator or patient errors during the radiography procedures. Panoramic radiography images may contain opaque and lucent areas from the reflection of soft tissue structures in the study area, as well as air paths that affect the actual structures. In cases in which the diagnostic quality is unsatisfactory, the value of the radiographic images decreases and they should be repeated, which results in increased radiation exposure, higher costs and wasted time. (3) This emphasizes the importance of accuracy in the preparation process of radiography film. Preparing and placing the patient in the perfect position is necessary for a readable, accurate and errorless radiographic image. (4)

The aim of this study was to evaluate the quality of panoramic radiographic images and to find common errors that can be avoided.

Materials and methods

This study was approved by the Ethics Committee of Mashhad University of Medical Sciences (The code IR.MUMS.REC.1393.247). In this study, we used simple random sampling to select and evaluate 1,990 digital panoramic radiographs of our archival images that were obtained over a 2-year period (December 2010–December 2012) with a Planmeca Promax (Planmeca Oy, Helsinki, Finland) panoramic radiography unit. All radiographs were prepared in the Radiology Department of Mashhad Dental School by an experienced oral and maxillofacial radiologist [A.B.]. The minimum and maximum ages of patients in this study were 5 and 88, respectively. The persons who were under 12 years old and had both deciduous and permanent teeth in oral cavity together were considered as mixed dentition group. The cases included 678 men and 1,312 women. Radiographs were evaluated according to the inclusion and exclusion criteria outlined below.

Inclusion criterion was patients with permanent or mixed dentition. Exclusion criterion was patients with severe skeletal deformities or considerable asymmetry based on their records, those without teeth and any extensive bone pathology that prevented proper adjustment of the patient's head.

All radiographs were evaluated by one radiologist [A.B.]. Examined errors consisted of patient with a head forward or backward positioning, head turning or tilting, a chin low or high positioning, bending the neck, not positioning the chin in the chin rest, the distance between the tongue and palate, an open mouth and movement of the patient's head. The intra‑observer error was measured by reviewing random samples of 100 (≈5%) panoramic images after a 2-week interval. A paired t-test was applied for the analysis of both readings. All TIFF format panoramic files were examined on a laptop (HP 255 G5 Notebook, 15.6" diagonal HD SVA anti-glare slim LED-backlit [1366 x 768]) in a semi-darkened room. The intra‑observer error was measured by reviewing random samples of 100 (≈5%) panoramic images after a 2-week interval. A paired t-test was applied for the analysis of both readings. The errors examined per patient were put in a pre-designed Excel file. Then, the Excel data were moved to the PASW 18 program. Tables and graphs appropriate to the PASW 18 were then drawn. For data analysis, the χ² test was used. A p < 0.05 was considered statistically significant.

Results

In this study, 1,990 patients (612 males and 1312 females) who were referred for panoramic radiography in Mashhad Dental School were selected. Patients ranged from 5 to 88 years with the mean age of 33.55 ± 15.26 years for the study population. The mean and standard deviation of age were 34.41 ± 15.80 and 33.10 ± 14.95 for males and females, respectively.

Re-examining 100 panoramic radiographs enabled the measurement of the intra-observer reproducibility. The difference between the number of positioning errors on the first and second readings was not significant (p = 0.19).

Given that the clients for dental services were mostly women, the women’s group had the number of participation two times more than the men’s group. For comparison of the average ages of the two studied sex groups, the ages for both sexes, in terms of a normal distribution, were evaluated. A one-sample Kolmogorov-Smirnov test showed that the ages of the two sexes were not distributed normally (p < 0.001). Due to the non-normal distribution of ages in both sexes, a Mann-Whitney test was used to compare the mean rank of ages in both sexes. The results showed that the ages of the two sex groups had no significant differences (p = 0.089).

Comparing positioning errors between the mixed and permanent dentition groups

Due to the smaller anatomical structures in children than in adults, and regarding the fact that they were less cooperative, a comparison between the errors in the permanent and mixed dentition groups was carried out. Table 1 provides the number and percentage of errors observed in the two groups. As shown in the table, most errors can be attributed to the distance between the tongue and palate, followed by errors related to the high positioning of the chin. Patients were evaluated for the possibility of various errors, and patients with no errors were considered as error free. Findings showed that only 63 (2.3%) of the 1,990 patients had no positioning errors.

According to the previously mentioned data, the frequency of a head forward or backward position, turning or tilting of the head to one side, not positioning the chin on the chin rest, and movement or reclining of the patient were the most common errors in patients with permanent teeth. In patients with mixed dentition, the most common errors were excessive low or high chin positioning and distance between tongue and palate. (Fig. 1-3)

Figure 1. "Too far forward" positioning error was detected in this panoramic radiography.

Figure 2. There are two errors in this panoramic image: the head "too far backward" and the "chin high positioning" errors.

Figure 3.  The errors that are seen in this panoramic radiography are "the distance between tongue and palate" and "turning the head to the right side

Presence or absence of errors in the permanent and mixed dentition groups

As shown in Table 2, patients with mixed dentition were more susceptible to errors than those with permanent teeth.

Comparison of patient positioning errors in both sexes

In Table 3, the number and percentage of each error in the two sex groups is shown. According to the table, the maximum errors were the distance between the tongue and palate followed by a high chin position. An open lips error was not observed in any patients.

The frequency of a patient's head forward or backward positioning, turning or tilting of the head to one side, distance between tongue and palate, and movement or reclining of the patient were more common in males. In women, not positioning the chin on the chin rest and having the patient's head in a forward position were more common than in men. This Table shows that no distance between tongue and palate was the most common error observed in patients. After that, a high chin position had the most prevalence. Also, none of the patients had their lips opened.

Presence or absence and total frequency of errors in both sexes

Table 4 shows that the risk of presence of error in men was slightly higher than in women. This table shows that radiographs with only one error had the highest frequency while radiographs with five errors had the lowest frequency among all samples.

Different positioning errors accompanied each other

Because the distance between tongue and palate had the maximum number of errors in this study, its accompaniment with other errors was measured. The χ² test showed that the distance between tongue and palate error was accompanied with the head turning to the right error (χ² = 5.44, p = 0.01). (Table 5)

Table 1. Frequency of errors in each of studied groups

Table 3. Frequency of errors in both sexes

Table 4. Number of errors in studied population according to sex