Dental implants are among the most viable treatment options to provide the esthetic and function for the missing teeth. ¹ Implant-based dental restorations are among the most successful treatments, and their long-term success is predictable. ² A dental implant is a titanium alloplastic material surgically placed in the jawbone as a prosthetic base. Following the implant placement in the bone, a micromechanical connection is established between the body of the implant and the living bone, which is called osseointegration. ³ The success or failure of dental implants depends on the quality of the bone contact surface and the ability of the implant to transfer forces from the implant to the bone and provides initial stability. ⁴ Once the implant is placed in the bone, its initial stability is defined, which depends on the quality of the bone, the geometry of the implant, and the surgical procedure. If there is no looseness, the implant will have initial stability. ⁵ Therefore, primary implant stability is one of the critical factors for achieving osseointegration, and it is a prerequisite for immediate implant treatments. ⁶ Various methods have been proposed in studies to assess the initial stability of dental implants. Still, the prominent insertion torque (IT) and resonance frequency analysis (RFA) methods are used during implant insertion. ⁷

The IT method examines the extent to which the bone is attached to the implant. One of the disadvantages of this technique is the possibility of being destructive due to the entry of unnecessary forces into the body of the implant being stowed and the lack of grading on the quantity and quality of the staging process. This method is characterized by the presence or absence of osseointegration. ⁸ RFA is a simple and noninvasive method to measure the stability of an implant at different time intervals. However, the IT method can only be used for implant placement during surgery. RFA measures the hardness and flexibility of the bone–implant complex. ⁹ The unit of measurement in this technique is called implant stability quotient (ISQ), which, if the recorded number ranges between 57 and 82 (average 69), it indicates the success of the implant, and a score <50 indicates a high risk for implant failure. ¹⁰

Various studies have examined the relationship between implant density and RFA/IT values and the relationship between IT and RFA. ⁹ , ¹⁰ , ¹¹

After performing clinical examinations for a patient who is a candidate for dental implant treatment, the quantity and the quality of the bone at the implant sites must be assessed by radiographic examinations. Computed tomography (CT) scan is one of the most common radiographic techniques used to evaluate bone quality and quantity before performing surgery. ¹² Determining the bone density or the quality based on the Hounsfield unit is one of the most important advantages of using this technique which is proportional to the degree of X-ray attenuation by the tissue, and it is shown by gray scale (voxel value). However, one of the most important disadvantages of CT scans in assessing those areas requiring an implant is the high dose of radiation imposed on the patient. ¹³ With the advent of cone-beam CT (CBCT), higher quality images with lower radiation doses can be produced. However, due to technical reasons such as calibration problems with various CBCT devices, the final results are not reliable. ¹⁴ This study aimed to investigate the density of jawbones at implant candidate sites using the Ondemand three-dimensional (3D) dental CBCT device and its relationship with the values obtained by the RFA method after inserting the implant in the jaw bone.

In this descriptive-analytic study, 17 implant treatment sites were selected from a total of 3 patients (including one male and two females). The mean age of the patients was 48.6 3 ± 3.45. The inclusion criteria for entering the study included healthy individuals aged between 30 and 50 and those requiring implant treatments in the maxillary and mandibular areas. Conditions including a systemic bone disease such as osteoporosis, osteomalacia, Paget's disease, bone tumors, and systemic diseases that could weaken the immune system such as diabetes, blood diseases, and a history of antibiotic therapy in the last 6 months were determined as exclusion criteria in this study.

All patients were informed of how the study was performed, and they participated in the study after obtaining informed consent. After conducting clinical examinations of qualified patients, an impression was taken to fabricate a surgical guide via a stereolithographic printer as one of the fastest prototyping methods for each patient Figure 1. In the meantime, patients were referred to an oral and maxillofacial radiology center to obtain CBCT images of implant treatment areas. All CBCTs were obtained using Cranex 3D (Soredex/Helsinki/Finland) with a field of view of 8 × 6, high-resolution mode and by using Ondemand 3D Dental Software. Afterward, the information related to each patient's CBCT images and the images related to digital scanning of the casts were uploaded into the Kaveh surgical guide software (Iran). In the next step, by assembling the patient's CBCT images and scanning the patient's cast, 3D models of implant treatment candidate areas were prepared using Kaveh surgical guide software. Figure 1

Surgical guide printed by a stereolithography printer

In three patients, 17 implants were placed Figure 2and Figure 3. In the first patient, all implants were placed in the maxilla, and in the other two patients, the implants were placed in the mandible. The location of each implant in all patients was shown separately in the respective tables. The results showed that the initial stability values of the implant and bone density varied from patient to patient in different implant areas. For example, the initial stability of the implant in the first patient was 70, which was in the right canine area of the maxilla and the bone density was 528.8. The values of the gray scale and ISQ were reported separately for each patient and the implant site in Table 1, Table 2, Table 3. Figure 2

Radiographic view of the areas intended for implant placement and the grayscale value of the bone

Primary successful stability is necessary for optimum osseointegration. Many factors, including bone density, implant geometry, surgical techniques, and the overall health conditions of the patient, can affect the primary stability and survival rates of dental implants. ¹⁵ The present study showed that the two variables, gray scale and ISQ, had a normal distribution and were strongly correlated Figure 4. Formerly, CT scans were used to evaluate preimplant surgery. ¹² This technique had some advantages and disadvantages. The most important advantage of using this technique was determining the density or the quality of the bone based on the gray scale. ¹³ Mikić et al. also showed that the bone density in HU units assessed with CBCT was significantly associated with primary implant stability in ISQ units, consistent with the present study results. ¹⁶ Figure 4

Mean ± standard deviation of gray scale (bone density) and implant stability quotient

The present study results showed that the two variables, gray scale and the initial stability of the implant, had a normal distribution, and there is a significant correlation between these two variables. The correlation coefficient was 0.811, of which 66.3% of the ISQ changes are predictable with grayscale values. Due to the limitations of the present study and the high correlation between the grayscale values measured with ISQ, the Cranex 3D CBCT device could help assess bone density before implant surgery.

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Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.