Journal of Dental Implants

: 2014  |  Volume : 4  |  Issue : 1  |  Page : 11--15

Comparative evaluation of peri-implant bone height in digital conventional radiographs and digital subtraction images

Mozhdeh Mehdizadeh1, Moeen Hosseini Shirazi2, Foroozan Farahbod2, Kousha Gholamrezaei3,  
1 Department of Oral Radiology, School of Dentistry, Torabinejad, Dental Research Center, Isfahan, Iran
2 Dentist, Doctor of Dental Surgery, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran
3 Dentist, Doctor of Dental Surgery, Private Practice, Isfahan, Iran

Correspondence Address:
Mozhdeh Mehdizadeh
Department of Oral Radiology, School of Dentistry, Torabinejad Dental Research Center, Isfahan University of Medical Sciences, Isfahan


Introduction: Long-term clinical evaluation of dental implants and their surrounding structures is necessary to acquire more knowledge about the reasons for success and failure of implants. However, accurate and reproducible results are difficult to obtain. The aim of this study was to evaluate bone height around endosseous implants using digital conventional radiographs (DCR) and direct digital subtraction images (DSI) prior to loading. Materials and Methods: In this study, 10 dental implants from 6 patients were studied. Standardized digital radiographs were obtained one week and 3 months postoperatively and subtracted by means of EMAGO software. Then two radiologists evaluated bone height on digital conventional radiographs and digital subtraction images . Data was analyzed with paired t-test using the MINITAB 1.4 software program. Results: Comparative evaluation of bone height indicated significantly higher values on DCR than on DSI (p value = 0.002). The observers also had statistically significant variability in this assessment (p value = 0.00003). Conclusion: The problem in evaluating bone height was the inevitable effect of the operator which should be taken into consideration in follow ups. Additionally, DSI technique can be effective in predicting the dental implant success because it can show lower amounts and less differences in evaluation of bone height reported by different operators.

How to cite this article:
Mehdizadeh M, Shirazi MH, Farahbod F, Gholamrezaei K. Comparative evaluation of peri-implant bone height in digital conventional radiographs and digital subtraction images.J Dent Implant 2014;4:11-15

How to cite this URL:
Mehdizadeh M, Shirazi MH, Farahbod F, Gholamrezaei K. Comparative evaluation of peri-implant bone height in digital conventional radiographs and digital subtraction images. J Dent Implant [serial online] 2014 [cited 2022 Oct 6 ];4:11-15
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Long-term clinical evaluation of dental implants and their surrounding structures is necessary to acquire more knowledge about the reasons for success and failure of implants. [1] The marginal bone level around the implant is one of the most important factors that should be examined because a reduction in bone height represents the loss of the implant-bone fit. [1]

Bone attachment loss might progress from crestal bone to severe bone loss and complete failure in dental implants. [2] According to Adell et al., the pre-implant crestal bone loss in the 1 st year is 1.2 mm. [3] According to Smith (1989) after the 1 st year, <0.2 mm bone loss annually is normal in dental treatments. [4] These minor changes in the surrounding structures make it necessary to use a precise and reproducible technique to evaluate dental implants and their surrounding structures. Usually the evaluation of the quality and quantity of bone during the restorative phase of implants is carried out via serial radiographs. Conventional techniques for assessment of bone height cannot show minor changes in bone loss or regeneration. [5] Digital subtraction image (DSI) technique, which has been used since 1980, is a useful technique for detecting minor changes in serial radiographs. This technique is a powerful tool for detecting small lesions and assessment of changes in bone height. [6]

Approximately 30-60% of change is necessary in bone mineralization for the lesion to be visible on conventional radiographs by an expert radiologist. However, changes of up to 1-5% in bone mineralization are easily detectable by digital subtraction technique. [7] In this technique unchanged background images are omitted, reducing the background noise and changes can be readily detected by different superimposed images. [7]

Janssen et al. emphasized that in their in vitro study on the evaluation of different artificially-produced periodontal lesions, the DSI technique proved very accurate. However, DSI might be less accurate during in vivo studies due to difficulties in standardization of images and differences in exposure parameters during follow-ups. [8]

Wander and Weber carried out a research study on digital radiography and reported that it is potentially a start to major developments in dental diagnosis and treatment planning. They reported less patient exposure and complete omission of film chemical processing as the most important advantages of digital radiography. [9] They specifically worked on the digital subtraction radiography (DSR) and added that dentists can easily detect and report the progression of gingival diseases and dental caries with the help of this technique. [9]

Assessment of healing of periapical lesions with the use of DSR is another related study carried out by Yoshika in 2002. It was concluded that with the use of DSR the difficulties of chemical film processing can be resolved and also the initial minor changes in surrounding tissues can be clearly detected. It was reported that with the use of this system it is possible to detect small changes which immediately appear after treatment and finally DSI can be very useful during follow-ups. [10]

Cury et al. carried out a long-term comparison between digital radiography and subtraction radiography in the evaluation of periodontal treatment success. The results showed that the conventional interpretation system is more reliable in detecting periodontal bone changes in mandibular molars compared to subtraction technique. [11]

Mikrogeorgis et al. evaluated the DSR technique in the assessment of the progression of chronic periapical periodontitis. They reported that minor changes in the progression of chronic apical periodontitis are more clearly detectable in a short period of time; therefore, they concluded that in short periods of time, DSR is more useful compared with other techniques. [12]

Lee and Huh worked on assessment and improvement of DSR software programs. [6] They compared a new software program called EMAGO with a software program on the market. The comparison showed significant differences between the two software programs by different users and in different intraoral regions. [13]

In 2006, Bittar-Cortez et al. evaluated the pre-implant hard tissue changes using digitalized conventional radiography and subtraction images and concluded that there are no significant differences between these techniques. [5]

The aim of this study was to evaluate bone height around endosseous implants using digital conventional radiographs (DCR) and direct DSI prior to loading.

 Materials and Methods

In this study, 10 dental implants from 6 patients referring to Isfahan University of Medical Sciences Faculty of Dentistry in 2010 were studied. All the implants were submerged BioHorizon with a length of 12 mm. The procedure was fully described to the patients and written consent forms were obtained from all of them. At 1 week and 3 months after the surgery, each patient was recalled for a follow-up visit. Radiographs were taken from marked places around the dental implants using the parallel technique with a digital system-ray machine (Planmeca, Helsinki, Finland) under 0.03 s, 63 kVp and 10 mA exposure conditions [Figure 1]. Before taking the radiographs, the exact locations of the sensor and film holder in the patients' mouths were examined to ensure that the sensor was parallel to the long axis of the adjacent teeth and was in the nearest location to the dental implant. After securing the sensor's location in the patient's mouth, by using the molding silicon putty material which was located between the dental implant area and the film holder, the patient's occlusion was recorded. After the setting time of the molding material, the primary radiograph was taken. Exposure conditions were similar all the time at 0.03 s, 10 mA, 63 kVp. Then the molding material was separated from the film holder and after disinfection with Deconex, they were stored in a sealed box until the next follow-up session. The next follow-up radiograph was taken 3 months after the surgery by placing the molding material in the similar position with the use of the patients' recorded occlusion. In the subtraction stage, the images were subtracted using the EMAGO/advanced 3.43 software program [Figure 1].

The first step in subtraction with the computer was matching all the gray pixels on the first and second radiographs using the "gamma correction" option. Then the images were coordinated for correction of tiny geometric differences using the "reconstruction" option. Four reference points around each dental implant were considered on the first and second radiographs for matching. Then by reducing the gray level of both radiographs subtraction was carried out, which resulted in a high-quality image showing the major differences on both radiographs.{Figure 1}

After obtaining DSIs, both images (linear DSI and DRs) were interpreted by two experienced radiologists. The bone height around the implants was measured using the "measuring device" in EMAGO. Both interpreters drew a line from the end of the implant to the marginal bone in the mesial and distal aspects of the implant using the software mentioned [Figure 2]. The mean length was reported as the bone height.{Figure 2}

The bone height which was in pixels was converted to millimeters before carrying out any statistical analysis. Data was analyzed with paired t-test using the Minitab Release 14, Minitab Inc., Philadelphia software program.


Bone height mean around dental implants in the DSI technique was 8.99 mm with a standard deviation of 0.38 and the mean bone height around the dental implants in the DCR technique was 9.8 mm with a standard deviation of 0.5 [Table 1]. Based on paired t-test there was a significant difference between the results in DSI and DCR (P = 0.002).{Table 1}

Paired t-test also showed that the measurements by two interpreters were significantly different, which shows the effect of different interpreters in bone height evaluation regardless of the technique used Diagrams 1 and 2. [SUPPORTING:1] [SUPPORTING:2]


It is clear that using precise methods of radiography is very important in the exact assessment of bone height around dental implants. Using DSI technique is one of the newest methods.

Smith and Zarb concluded that evaluating bone height in the long-term requires precise methods. This measurement should be the same when carried out by different operators or one operator at different times. However, there are some discrepancies in these measurements. [13] in this study, there was a statistically significant difference between the reports of the two operators (P = 0.0002), demonstrating the effect of operator on the assessment of bone height, regardless of the method used. According to recent studies different factors can cause such differences, including the density of the radiograph, projection geometry, time after loading the fixtures and bone loss grades. [13] According to Grondahl et al., the density of radiograph and bone loss grade have the greatest effect on discrepancies of evaluations by operators. [14]

In a study by Weber et al. for the evaluation of marginal bone height, they used the digitized conventional radiography and they used film holders with bite impression for standardization of the images and repeating the radiography in the previous location. [15] In the present study, the same method was employed by using a condensation silicon bite impression from the implant and adjacent teeth and a film holder with a sensor inserted in it. With this method it was possible to repeat the tube position for the follow-ups. Therefore, the effect of geometric projection was avoided because it can result in discrepancies in interpreting the images. The technology used in the present study was more precise and modern compared with previous studies due to digital images were used and the digitization process of conventional images was eliminated.

In this study, the differences between the two operator reports were 0.24 mm in DSI and 0.42 mm in DCR, which is important in the success rate of implants because studies have shown that success is achieved when implant bone loss is <0.02 mm after the 1 st year. [15] In the present study, although the differences between the operators in DSI were less than those in DCR, the difference was more than that, which should be used in the evaluation of the implant after the 1 st year of loading.

In the present study, the diagnostic precision of the methods used was not tested because it was not possible to determine the real bone height. However, comparison between this study and previous ones leads to the same conclusions. In a study in which the interproximal bone recession was directly measured after the periodontal surgery and compared to the measurements from the radiographs, it was concluded that radiographic techniques significantly show the interproximal bone recession approximately 1.4 mm shorter than the real height. [16]

However, in previous studies carried out by Sewerin and Schliephake et al., it was emphasized that in the conventional radiographic images there is a distortion in the buccal and lingual bone around the implant and radiographic techniques show the height of the bone around the implant higher than the real situation, which is attributed to the fact that parallelizing the film with the implant long axis is usually impossible. [15],[17] In DSI with omission of noise and also elimination of unchanged anatomical structures the position of the marginal bone might be more precisely detected.

Considering the results of studies mentioned above and given the fact that radiographs show recession of the marginal bone less than the real amount, in the present study the reported measurements of bone height around the implant were more than the real bone height and considering the fact that DSI showed bone height significantly less than that shown by DCR it can be concluded that DSI has less image magnification. In addition, Bittar et al. reported significant differences between DSI and digitized conventional radiography in bone height measurements around implants. In their study DSI showed significantly less bone height compared with conventional radiography, [1] consistent with the results of the present study. They used conventional radiography but in the present study direct digital radiographs were taken instead and interpretation techniques were different. In DSI any change in bone density is considered recession but in DCR wherever there is opacity it is considered marginal bone, irrespective of the density of that area.

The problem in evaluating bone height was the inevitable effect of the operator, which was clearly shown in this study; therefore, during evaluation of the success of a dental implant this fact should be taken into consideration. Additionally, DSI technique can be effective in predicting the dental implant success because it can show lower amounts and fewer differences in evaluation of bone height reported by different operators. However, difficulties in using subtraction techniques which include the cost and time-consuming nature of the technique restrict their use by clinicians.


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