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. 2023 Jul 7;102(27):e34203. doi: 10.1097/MD.0000000000034203

A novel method of assessment of BMD using CBCT for implant placement: A retrospective study

Saad Mohammed AlQahtani a,*
PMCID: PMC10328703  PMID: 37417616

Abstract

Nowadays, dental implant evolves as an alternative treatment modality for oral rehabilitation. The success of dental implants is largely dependent on bone density; Cone-beam computed tomography (CBCT) is a well-known modus operandi for the volumetric measurement of bone mineral density (BMD), which measures Grayscale values on 3-D images. This study was conducted with the aim to analyze bone density with CBCT and also test its reliability and reproducibility using Galileos Sirona CBCT Viewer Software and Philips digital imaging and communications in medicine (DICOM) Viewer. A total of 75, CBCT images were obtained from the Department of Oral Radiology, retrospectively, and, BMD in Hounsfield units (HUs) was evaluated in a standardized implant area superimposed on the images. Bone density was also calculated by 2 different independent observers. The estimation of sample size was achieved to attain a power of 90% with 0.5 alpha error and 0.2 effect size as per a previous study. Statistical analysis was performed by statistical package for the social sciences version 22.0; data were presented as mean and standard deviation and Kappa correlation test was applied to check the reproducibility of values. The mean and standard deviation of grayscale values and HUs attained from the interdental area of front teeth were 1837 (288.76) and 270 (125.4), respectively, with a conversion factor of 6.8. Whereas the mean and standard deviation of grayscale values and HUs acquired from posterior interdental spaces were 2880 (489.99) and 640 (204.6), respectively, with a conversion factor of 4.5. To verify the reproducibility Kappa correlation test was applied, which showed correlation values of 0.68 and 0.79. The conversion or exchange factors for grayscale values to HUs determined at the frontal, posterior interdental space area and from the highly radio-opaque area were exceedingly reproducible and consistent. Hence, CBCT can be used as one of the valuable techniques in the estimation of bone density.

Keywords: bone mineral density, CBCT, CT

1. Introduction

The dental implant, over the years, has evolved into a remarkable treatment modality where the primary objective pertains to the replacement of missing teeth in order to restore suitable function and aesthetics with lessening the impact on the nearest hard and soft tissue components. Because using the dental implant as an alternative treatment modality showed favorable outcomes for oral rehabilitation.[1–3] As the success of a dental implant is largely dependent on the volume and quality of the surrounding bone, therefore the level of osseointegration becomes quite a key predictor of initial implant stability. Also, osseointegration plays a significant role in implant anchoring, primarily because the process becomes complicated to achieve in its absence.[4]

Bone quality is a broad terminology that denotes a myriad of crucial factors that influence bone strength. Bone mineral density (BMD) is an objective measure used by many clinicians to distinguish between different types of bone.[5] According to the World Health Organization in 1994, DXA diagnostic criteria of bone marrow density measured through t score, the interpretations are: T score, −1 to + 1 = Normal bone density, T score <−1 to >−2.5 = Low bone mass (Osteopenia), T score ≤−2.5 = Osteoporosis, T score ≤−2.5 + prevalent fragility fracture = Severe (established) Osteoporosis.[6]

Quantitative computed tomography (QCT) is a well-known technique which is utilized for the volumetric measurement of BMD, which also provides 3-dimensional images.[7] Computed tomography (CT) measures beam attenuation, in Hounsfield Units (HU), HU is used to depict and classify bone density.[8] The interpretation of BMD in HU gives rise to 5 different categories of bone density parameters (D1–D5) which are as follows-D1: with HU > 1250 implies very good bone density; D2: with HU varying from 850 to 1250 refers to good bone density; D3: with HU varying from 350 to 850 points towards fair/optimal bone density; D4: with HU 150 to 350 indicates poor bone density; and D5: with HU < 150 infers bad/below average levels of bone density. D1 was revealed to be leading in the anterior mandible, whereas D2 and D3 in the posterior mandible and anterior maxilla, and D4 in the following posterior maxilla.[9–11] Currently, cone-beam computed tomography (CBCT) is extensively used in dental implant surgeries; CBCT endows with 3-dimensional diagnostic images, for treatment planning and prognostic evaluation.[12] CBCT grayscale values are considered approximate values and their measurement allows differentiation of soft tissue and fluid with that of hard tissue because hard tissues soak up larger amounts of X-ray energy in contrast with soft tissues creating diverse shades of gray. Therefore, CBCT uses diverse grayscale values to identify and assess bone density.[13,14] CBCT scans estimated bone density by using grayscale levels, which is dissimilar from conformist HUs. In both units beam attenuation levels are employed to assess bone density, but, the accurateness of grayscale values to HUs is dubious.[15] CBCT, at times though, is unable to provide a consistent BMD reading due to imperfections in correcting local as well as adaptation errors during obtaining grayscale values.[16] On the other hand, CT scans are unrelenting and tend to be riddled with issues pertaining to harmful levels of exposure to radiation that could produce stochastic effects also, QCT is costly and entails exceptional facilities; consequently, the dentist usually avoids using QCT scans for the assessment of BMD levels during implant surgery.[7,17] Therefore, this study was conducted with the aim to analyze bone density with CBCT and also test its reliability and reproducibility using Galileos Sirona CBCT Viewer Software and Philips digital imaging and communications in medicine (DICOM) Viewer. By the means of this investigation, we would be able to ascertain the grayscale values’ accuracy to HUs as it is questionable many times and the importance of CBCT can be emphasized over the CT in determining BMD.

2. Methods

The present study was conducted on both male and female patients with a minimum of 20 years and above age in King Khalid University, Abha, Saudi Arabia. The data collection for CBCT images was performed through retrospective clinical hospital records with the patient informed consent. This study was performed under the authorization of the Institutional Review Board of King Khalid University, Abha, Saudi Arabia (Ethical clearance number SRC/ETH/2019-19/105).

2.1. Inclusion criteria

Only high-quality images that had optimal resolution were selected for the study. Moreover, the included images had to be devoid of any type of radiolucent/radiopaque lesions.

2.2. Exclusion criteria

The following types of images were excluded from the scope of our study- images that had evidential proof of fracture or possessed impacted/supernumerary teeth, images with positioning errors, and images of patients with a history of radiosensitivity, pregnancy & heavy radiation exposure and soft tissue pathology.

2.3. Sample size & sampling method

A total of 75 CBCT images were obtained from the Department of Oral Radiology, and BMD in HUs was calculated in a standardized implant area superimposed on the images. Bone density was also subjectively calculated by 2 independent observers. The calculation of sample size was done to obtain a power of 90% with 0.5 alpha error and 0.2 effect size, as per a previous study.[1]

2.4. Assessment of CBCT images

The current study included data from about 75 CBCT scans. The Vatech A9 CBCT (Vatech America) device was used to take the CBCT scans at the dentistry college, with the following settings: 120 kV, 6 mA, 18,817 mS, 80 mm FOV, and 0.1 mm slice thickness. For the evaluation of CBCTs, Dentsply Sirona Galileos Software was used. Because Philips has software that enables the recalibration of grayscale values, its DICOM CT viewer software operates on a premise that makes it possible to examine the quality of the bone in HUs. Galileos Software was used to acquire the grayscale values for the CBCT, and the Philips DICOM CT viewer software was used to acquire the HUs (Fig. 1). The Philips DICOM viewer contains a unique grid that was used for location standardization and makes it simpler to reconstruct the pictures (Fig. 2). The front, posterior, and high radio-opaque zones, including the area beneath the zygomatic crest and bone thickness, were evaluated at every site. The area between the central, laterals, canines, and first premolars is referred to as the frontal area, whereas the portions between the first and second premolars, second premolar and first molar, and first and second molars are referred to as the posterior areas. With the help of CIRS Model 062M, Electron Density Phantom, Virginia, USA (Fig. 3), the histograms of pixel values for each slice of the Vatech A9 CBCT and the 75 CBCT images were acquired. The shapes of the histograms for each slice of the CBCT images were closed to the shapes of the histograms of the images using the linear scaling technique with a minimum sum of squared differences for the regions of soft tissue and bone in order to perform pixel value correction, thus, enabling us to determine pixel values for the CBCT images in HUs. To obtain a conversion factor (i.e., the ratio of the luminance of the output screen to the input exposure rate of the applied roentgen radiation for a CBCT machine), all Grayscale values obtained from anterior, posterior sites, and radio-opaque areas in the Galileos CBCT viewer were divided by the corresponding HUs values in the Philips DICOM viewer. The values’ consistency and reproducibility were also evaluated using Kappa correlation.

Figure 1.

Figure 1.

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Assessing bone mineral density in the anterior region using Dentsply Sirona Galileos Software.

Figure 2.

Figure 2.

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Assessing bone mineral density in the posterior region.

Figure 3.

Figure 3.

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CIRS Model 062M (for conversion of CBCT values into HU units). CBCT = cone-beam computed tomography, HU = Hounsfield unit.

2.5. Statistical analysis

Statistical package for the social sciences was used for data analysis (Statistical Package for the Social Sciences, version 22.0, statistical package for the social sciences Incorporated, Chicago, IL). The essential information was displayed as mean and SD using one-way analysis of variance test, and the data were represented as mean and standard deviation. After running a kappa statistics test for repeated comparisons of the various sites in the maxilla and mandible, a separate t test was utilized to compare the locations.

3. Results

With a conversion factor of 6.8, the mean and standard deviation of the grayscale values and HUs obtained from the interdental region of the front teeth were 1837 (288.76) and 270 (125.4), respectively. The mean and standard deviation of grayscale values and HUs obtained from posterior interdental spaces, with a conversion factor of 4.5, were 2880 (489.99) and 640 (204.6), respectively. As shown in Tables 1 and 2, the mean and standard deviation of grayscale values and HUs obtained from highly radio-opaque areas were 1789 (367.03) and 1180 (316.11), respectively, with a conversion factor of 1.5 (Fig. 4).

Table 1.

Comparison of mean and standard deviation of grayscale value with Hounsfield units at the anterior and posterior region.

E Mean SD (gray scale values) Mean SD (Hounsfield Units) Conversion factors
Interdental
regions of anterior teeth		 1837 (288.76) 270 (125.4) 6.8
Interdental
region of posterior teeth		 2880 (489.99) 640 (204.6) 4.5
Highly radio opaque regions 1789 (367.03) 1180 (316.11) 1.5
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Table 2.

Comparison of mean and standard deviation of grayscale values with Hounsfield units at the high radio opaque regions of mandible (infra zygomatic crest region, bone thickness).

Mean SD (gray scale values) Mean SD (Hounsfield units) Conversion factors
Highly radio opaque regions 1789 (367.03) 1180 (316.11) 1.5
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Figure 4.

Figure 4.

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Comparison of mean and standard deviation of grayscale values with Hounsfield units at the high radio-opaque regions of the mandible.

The Kappa correlation test was used to confirm the repeatability, and the results showed that the pre-and post-mean grayscale values in the anterior interdental area were 1837 (268.76) and 1553 (205.76), respectively (Fig. 5). While pre- and post-observation mean grayscale values in the posterior interdental area were 2880 (373.99) and 2544 (310.78), respectively. As shown in Table 3, it was determined that acceptable repeatability in both the frontal and posterior interdental areas was discovered with correlation values of 0.68 and 0.79.

Figure 5.

Figure 5.

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Kappa intraclass correlation coefficient to check the reproducibility of values.

Table 3.

Kappa intraclass correlation coefficient to check the reproducibility of values.

Site assessed Gray scale values Correlation
Mean SD (PRE) Mean SD (POST)
Interdental
regions of anterior teeth		 1837 (268.76) 1553 (205.76) 0.68
Interdental
region of posterior teeth		 2880 (373.99) 2544 (310.78) 0.79
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4. Discussion

For planning and success of the dental implant, evaluation of the bone density of the surrounding area of the dental implant is of utmost importance. To properly assess bone density levels, an accurate as well as detailed radiographic examination is of the utmost importance to obtain vital information. Various studies have also revealed that high bone density is directly associated with a high rate of success with implants.[18–22] The primary stability and retention of dental implant is also positively correlated with high bone density.[23,24] Since the precision of grayscale values to HUs is certainly questionable and CBCT possesses a significant number of advantages over CT, therefore the present study was undertaken for the of assessment bone density with CBCT and also to test its reliability and reproducibility using Galileos Sirona CBCT Viewer Software and Philips DICOM Viewer.

According to the present study, optimal conversion factor values were assessed and correlated between grayscale values and HUs in Galileos Software. Similar results were established by Prasanna Arvind TR et al.[18] According to Valiyaparambil et al a strong linear correlation was instituted between HU and grayscale levels.[25] Katsumata A et al, also established that the grayscale values attained from the CBCT imaging can be easily applied as an analogue way of HU values for the assessment of mineral density,[26] since it illustrates a linear association with the attenuation coefficients of the materials.[14,17] In contrast to these findings, Silva et al concluded that the bone density acquired via CBCT in HUs using the device was found unreliable.[27] Similarly to Silva et al, findings, another study concluded that the CBCT cannot be reflected as a suitable choice for the examination of the assessment of credentials of the BMD of osseous areas, particularly when attained values and prearranged customary values are compared.[12]

In this study the mean grayscale value and Hus values from the highly opaque area were 1789 (367.03) and 1180 (316.11) with a 1.5 conversion factor, almost similar to results found by Prasanna Arvind TR et al 18; they found a conversion factor of 1.4 with mean gray and HUs value 1962 (387.8) and 1387 (319.6) correspondently.

According to Nackaerts et al, numerous features like the distinction in the setting of devices image-attainment, an association of the entity to be assessed and field of view, and the location detained by the region of interest all are associated with images attained from CBCT.[28] However; according to Pauwels et al, a few CBCT machines work on a precise set of rules and can produce steady grayscale values which can be easily relatable with HUs in bone density estimation.[29] In the current study, the grayscale values obtained were satisfactorily reliable and reproducible with kappa values of 0.68 and 0.79 in the anterior and posterior regions correspondently. Almost similar results were achieved by Prasanna Arvind TR et al (R = 0.786 and 0.814, respectively).[18]

As in medical CT, the assessment of bone density is always allied with a higher degree of radiation exposure to patients during image acquisition.[30,31] On the other hand CBCT happens to be a relatively simpler-to-use, cost-beneficial device that diminishes the radiation exposure[31,32] and is easily used for 3-D image attainment of the maxillofacial area.[33,34] Several advancements have been reported in CBCT imaging related to the usage of grayscale values correction techniques, which may enhance the approaching and applicability of CBCT-derived grayscale values as CT-derived HUs. Although, clinical validation of all parameters is equally essential for the estimation of bone configuration, to predict bone density during implant surgery and its further outcomes, apart from density alone.[35,36] Consequently, nowadays CBCT has been entitled as one of the keen investigative techniques for the appraisal of BMD.[30,35–38]

4.1. Relevance

The therapeutic significance of this investigation lies in the fact that it demonstrates to clinicians a future manual for evaluating bone density at surgical sites, assisting them in radiologically evaluating the osteotomy sites prior to treatment. Consequently, the CBCT-derived bone density results can be examined in terms of bone quality. Additionally, investigations like ours shed light on the advantages related to the utilization of CBCT, since it can provide more accurate and detailed information about bone density compared to traditional 2D radiographs, and could be useful in identifying patients who may require additional bone grafting procedures before implant placement, leading to improvement in the quality of care for patients undergoing dental implant placement.

4.2. Limitations

The lack of a substantial sample size can be attributed to being one of the most significant limitations of our study since the results obtained may not be representative of the wider population or may lack statistical power. It can also be argued that patients who are included in the study may not be representative of the general population seeking dental implant placement, or that findings from a single-center study may not be generalizable to other settings or populations, both of the factors leading to selection bias. Moreover, a study such as ours that only evaluates short-term outcomes may not be able to capture the long-term success rates of dental implant placement. Hence, we warrant that more studies in this regard, with longer follow-up periods be performed to validate the application of CBCT as a reliable diagnostic tool.

4.3. Recommendations

A central issue associated with major CBCT devices is the uniformity of grayscale values. CBCT devices differ in their exposure restrictions, field of vision, and location of interest. Although CBCT-derived grayscale values can be used as HUs of CT due to significant developments in this technology, however, during implant surgery, the clinician should also pay attention to clinical characteristics related to connected structures.

5. Conclusion

According to the current study findings, the conversion or exchange factors for grayscale values to HUs found at the frontal, posterior interdental space area, and from highly radio-opaque areas were remarkably consistent, repeatable, and reproducible. CBCT can be used as one of the useful methods in the assessment of bone density since it is an easy-to-use, cost-effective equipment that reduces radiation exposure and provides 3-D pictures of the maxillofacial region quickly.

Author contributions

Conceptualization: Saad Mohammed AlQahtani.

Data curation: Saad Mohammed AlQahtani.

Formal analysis: Saad Mohammed AlQahtani.

Funding acquisition: Saad Mohammed AlQahtani.

Investigation: Saad Mohammed AlQahtani.

Methodology: Saad Mohammed AlQahtani.

Project administration: Saad Mohammed AlQahtani.

Resources: Saad Mohammed AlQahtani.

Software: Saad Mohammed AlQahtani.

Supervision: Saad Mohammed AlQahtani.

Validation: Saad Mohammed AlQahtani.

Visualization: Saad Mohammed AlQahtani.

Writing – original draft: Saad Mohammed AlQahtani.

Writing – review & editing: Saad Mohammed AlQahtani.

Abbreviations:

BMD
bone mineral density
CBCT
cone-beam computed tomography
CT
computerized tomography
DICOM
digital imaging and communications in medicine
HU
hounsfield unit
QCT
quantitative computed tomography

Supplementary Materials: NIL.

Institutional Review Board Statement: The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of the Institute at College of Dentistry, King Khalid University, Abha, under # Ethical clearance number SRC/ETH/2018-19/105.

Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

The authors have no funding and conflicts of interest to disclose.

How to cite this article: AlQahtani SM. A novel method of assessment of BMD using CBCT for implant placement: A retrospective study. Medicine 2023;102:27(e34203).

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