A Survey of Radiographic Measurement Estimation in Assessment of Dental Implant Length

Osseointegrated implants are indicated in the rehabilitation of edentulous jaws. Long-term clinical success is based on careful diagnosis and treatment planning.1,^–3 Preoperative planning for implant surgery includes the radiographic examination that provides information related to the localization of anatomical landmarks and the quality and quantity of bone available for implant placement in the potential areas.4,^–5 

Presurgical radiographic examination in dental implants is an important aspect when selecting sites for an ideal number, an optimal size, and a correct position of implants.6 The American Academy of Oral and Maxillofacial Radiology (AAOMR)7 recommends the use of cross-sectional images for the implant site evaluation, such as conventional tomography (T) or computerized tomography (CT). Cross-sectional images have been reported in several studies6^,8,^–11 to be more accurate about bone height dimension than panoramic radiography. The main advantages of the T and CT are uniform magnification, the possibility of having a reproducible image, and images that are free from the superimposition of other bone structures.6,^–11 In addition, studies have shown higher accuracy and precision of CT imaging in implant planning6^,8 and in vertical linear measurements.9,^–11 

In relation to panoramic radiography, over-6 or underestimation8 of vertical linear measurements can be found. These can be explained by imaging magnification in the horizontal and vertical planes. Also, errors in patient positioning during the radiographic examination can contribute to distortion and magnification leading to incorrect measurements. The other disadvantage in panoramic radiography is the lack of cross-sectional information. This explains the difficulty in the evaluation of thickness and contour of the bone in the recipient site.4,^–8 Although panoramic imaging limitations are present, this radiographic modality is considered the standard in the initial presurgical radiographic evaluation because is easily available and provides a view of many structures of maxilla and mandible at a low cost.12 Thus, panoramic or periapical radiographs are also indicated in association with cross-sectional images.

The aim of this study was to survey the radiographic measurement estimation in assessment of dental implant length according to dentists' confidence.

At a dental implant meeting, a total of 69 dentists were interviewed by two graduate students (CES and JANDM) previously trained and calibrated in the use of the questionnaire. All the interviewed dentists are familiar with surgical planning for implant treatment.

A 19-point closed-ended questionnaire with single answers was prepared to collect data regarding dentists' opinions about radiographic prescriptions in dental implant assessment.12 Twelve questions related to over- and underestimated measurements in three radiographic modalities: panoramic radiography (P), T, and CT (Table 1). To be sure that the questions were suitable before the interview began, a pilot study of the questionnaire was performed with a group of dentists that prescribe radiographic examinations for implant site assessment. The database was analyzed by Epi - Info 6.04 software, and the values from two radiographic modalities P and T were compared using a χ2 test.

The answers to questions 4, 6, 10, 12, 16, and 18 were classified in a dichotomous way with only values “yes” or “no.” When the answers were high and medium, the classification was “yes” and for the low and minimal the classification was “no.”

The Figure shows the distribution of measurement estimations when different procedures in imaging are used. The use of CT promotes high precision, and we have verified only 1.92% of underestimation in measurements related to its application. Table 2 shows the comparison between the two types of radiographs (P, T) with high occurrence of over- and underestimation. The association between two radiographic modalities (P and T) and over, under, and exact measurement estimations was statistically significant (χ² = 6.32; P = .0425).

The aim of this study was to survey dentists' confidence related to over- and underestimated measurements in three radiographic modalities concerning dental implant treatment planning.

Functional and aesthetic restoration is the main objective of rehabilitation using dental implants.1,^–3 Thus, the imaging of potential recipient sites should provide accurate information for precise placement of implants in correct three-dimensional position.7 Our study showed that CT is the most precise imaging examination reported by the interviewed dentists. Only one dentist answered about the occurrence of underestimated measurements. This result is in accordance with several studies6^,8,^–11 that showed the high precision of measurements in preoperative assessment using CT images because cross-sectional images exhibit uniform magnification.7 

However, the frequency of cross-sectional imaging prescription related by interviewed dentists is low. Sakakura et al (2003)12 showed that the majority of the dentists prescribed panoramic radiographs alone (63.8%) or associated with other radiographic methods (28.9%). Beason and Brooks13 also found similar results—more than 95% of the dentists took panoramic radiographs on at least 80% of their patients.

In relation to T examination, the occurrence of over- and underestimation measurements was higher than CT in preoperative assessment. Factors related to the acquisition of images, such as blurring of the image or movement of the patient during the examination and the difficulty of the dentists' radiographic interpretation, can explain the occurrence of over- and underestimated measurements.7^,11 The comparison between the frequency of over- and underestimated measurements in T was lower than in P. That phenomenon can be explained by the presence of cross-sectional imaging in T. However, our results showed that interviewed dentists have prescribed less conventional tomography than P, probably because they are unfamiliar with this radiographic modality in dental implant assessment (Table 2).

Panoramic radiographs presented the highest frequencies of over- and underestimation, 38.24% and 47.06%, respectively, in the preoperative radiography examination reported by the interviewed dentists. This fact can be explained by the presence of different levels of magnification and distortion related to anatomical regions and lack of cross-sectional images.6,^–8^,10 Also, panoramic radiography presents a bidimensional image with no other information about buccal-lingual thickness. In this case, the installation of the implant with planned size cannot be possible.1 The image magnification and the low reproducibility of alveolar canal diagnosis can increase the risks of anatomical structure damage to the inferior alveolar nerve.4,^–8^,14 

On the basis of our implant surgery experience, we speculate that dentists correct the P image magnification in 25% by using the template made by the implant manufacturer in the dental implant treatment planning. On the other hand, shorter length implants have been installed in some edentulous jaws because the magnification is not the same as other areas of the jaw. This statement is in agreement with Schropp, Wenzel, and Kostopoulos (2001),15 which results show that in 67% of implant planned size cases in panoramic plus periapical radiographs were modified at surgery. The direction of the changes after the use of tomography was related to length (longer or shorter) and width (wider or narrower) of the implants.

The results of this study showed that the dentists' knowledge about radiographic measurement estimation in dental implant assessment is in according with published papers related to in vitro and clinical studies about over- and underestimated radiographic measurements.

In conclusion, this study has shown that the CT, based on the answers of the interviewed dentists, is the best radiographic modality when considering the measurement estimation in preoperative implant assessment.

The authors greatly appreciate the assistance of Mrs. Kim Kubitza in the editing of the English version.