Motofumi Sogo

Relationship between the bone density estimated by cone‐beam computed tomography and the primary stability of dental implants

OBJECTIVES The aims of this study were to objectively assess bone quality with density values obtained by cone-beam computed tomography (CBCT) and to determine the correlations between bone density and primary stability of dental implants. MATERIAL AND METHODS Eighteen Straumann implants were inserted into 18 fresh femoral heads of swine. The bone densities of implant recipient sites were preoperatively determined by the density value using CBCT. The maximum insertion torque value of each implant was recorded using a digital torque meter. Resonance frequency, which represented a quantitative unit called the implant stability quotient (ISQ), was measured using an Osstell Mentor immediately after the implant placement. Spearmans correlation coefficient was calculated to evaluate the correlations among density values, insertion torques, and ISQs at implant placement. RESULTS The density values ranged from 98 to 902. The mean density value, insertion torque, and ISQ were 591 ± 226, 13.4 ± 5.2 Ncm, and 67.1 ± 8.1, respectively. Statistically significant correlations were found between the density values and insertion torque (r(s) =0.796, P<0.001), density values and ISQ (r(s) =0.529, P=0.024), and insertion torque and ISQ (r(s) =0.758, P<0.001). CONCLUSIONS The bone quality evaluated by specific CBCT showed a high correlation with the primary stability of the implants. Hence, preoperative density value estimations by CBCT may allow clinicians to predict implant stability. Whether the density values obtained by the CBCT device used in the present study could be applied to other devices requires further elucidation.

Assessment of bone density in the posterior maxilla based on Hounsfield units to enhance the initial stability of implants.

PURPOSE The poor bone quality that exists in the posterior maxilla is associated with lower initial stability and higher failure rates in implants. This study examined the bone densities of edentulous posterior maxillae by computed tomography (CT). MATERIALS AND METHODS Based on CT images, the voxel values representing implant replacement in the posterior maxillary regions of 30 patients were calculated in the range from 150 to 2,000 Hounsfield units (HU). The bone densities of these regions were categorized according to Mischs classification and compared among individuals and between sexes. RESULTS The average of the median individual CT values was 495 HU (95% confidence interval: 442-547 HU) and was significantly higher in males than in females. Most of the bone in the posterior maxillae was classified as D3 (350-850 HU) or D4 (150-350 HU) according to Mischs classification, comprising 50% and 32% of the entire regions, respectively. CONCLUSIONS More than 80% of the edentulous posterior maxillae consisted of porous cortical crest or no cortical bone according to CT, although the bone densities varied markedly among individuals. More detailed assessments of bone density may be useful to enhance initial stability of implants in the posterior maxilla.

Relationship between the CT Value and Cortical Bone Thickness at Implant Recipient Sites and Primary Implant Stability with Comparison of Different Implant Types.

BACKGROUND Studies have shown that bone quality at the implant recipient site can influence primary stability. PURPOSE The aims of this study were to explore the quantitative estimation of the primary stability of implants preoperatively using CT values and to examine the effect of different implant designs with recommended socket preparation on primary stability. MATERIALS AND METHODS Forty-four fresh porcine femoral heads were prepared. The bone surrounding implant sockets was preoperatively evaluated by helical CT. Forty-four implants (φ 4.3 × 10 mm), 22 straight and 22 tapered, were placed according to the manufacturers instructions. The insertion torque value (ITV), implant stability quotient (ISQ), and removal torque value (RTV) were recorded as indicators of primary implant stability. RESULTS Significant correlations and linear relationships were found between the CT value and ITV, ISQ, and RTV for both straight and tapered implants (Spearmans correlation coefficient, p < .001; linear regression analysis, p < .01). Tapered implants had a significantly higher ITV than straight implants (analysis of covariance, p < .01). CONCLUSIONS Obtained results suggest that the primary stability of implants could be quantitatively estimated using the CT value preoperatively, indicating the CT value of bone surrounding an implant can contribute considerably to implant planning and design choice in clinical situations.

Can we predict the insertion torque using the bone density around the implant

The purpose of this study was to examine the correlation between initial stability and bone density in patients undergoing implant treatment. Twenty-five screw-type dental implants were inserted in 12 patients. All patients underwent multi-detector computed tomography (CT) examination prior to implant insertion. The implant sockets were prepared according to the drilling protocol, and peak insertion torque values were measured. CT values around the implants were measured using preoperatively scanned CT data, which were combined with actual implant positions. Spearmans rank correlation coefficient was used to investigate the correlation between insertion torque values and CT values (in Hounsfield units, HU). Twenty-three implants (8 or 10 mm in length) were inserted in the mandibular molar region and two (10mm length) in the maxillary molar region. The mean CT value of the 8-mm implants was 508.6 ± 187.0 HU and mean insertion torque was 27.2 ± 12.1 N·cm; for the 10-mm implants, these values were 579.6 ± 224.3 HU and 28.1 ± 14.6 N·cm, respectively. Statistical analysis revealed a strong positive correlation between the insertion torque and mean CT values (r=0.699, 8 mm; r=0.771, 10 mm). The results revealed that bone density around the implant is a useful index. This study indicates that preoperative CT may enable the prediction of initial implant stability.

The Evaluation of the Heat Generated by the Implant Osteotomy Preparation Using a Modified Method of the Measuring Temperature.

PURPOSE To establish a method for measuring the heat generated when preparing an osteotomy site, and to assess for correlations of rotational speed, proceeding speed, loading value of the drill (contact pressure), motion pattern, and bone density with temperature increases. MATERIALS AND METHODS A thermocouple was placed in the internal irrigation hole of a 2.0-mm-diameter twist drill used for measuring osteotomy site temperature. In the artificial blocks, two different densities were used to drill under varying conditions including drill proceeding, rotating speed, and motion pattern. The drilling procedure was repeated five times for each combination, and the data collected were statistically analyzed using multiple regression analysis. RESULTS Strong positive correlations were found among bone density, drill motion pattern, and maximum temperature, and a positive correlation was found in proceeding speed (P < .001). Rotation speed and maximum temperature were not correlated (P < .001). Conversely, loading values of the drill increased with the lower rotation speed and higher proceeding speed, which were effective in controlling the temperature rise. CONCLUSION When preparing a simulated bone for an osteotomy with a thermocouple inserted into a twist drill with internal irrigation, the drilling motion pattern, bone density, drill speed, and proceeding rate affected bone temperature, in descending order. It was also observed that bone temperature correlated positively with speed and negatively with proceeding speed, independent of density. This indicates that lower drill speed and higher proceeding speed without excessive loading values minimize the bone temperature heat.

Biomechanical Simulation of the Osteoporotic Trabecular Pattern Around a Tooth

The purpose of this study was to elucidate the biomechanical mechanisms controlling the relationship between the mechanical loading environment on a tooth and its internal architecture, or so-called trabecular pattern, in the mandible. A computer-assisted simulation of the biomechanical rearrangement process of trabeculae around a tooth in the mandible was developed using the two-dimensional finite element method. This simulation predicted the stable trabecular pattern around a tooth, which was then compared with a human physiological pattern. The principal stress distribution of the simulated configuration showed a close similarity to the real trabecular pattern. In addition, the simulation procedure was used to model the trabecular pattern in the osteoporotic situation. The resulting patterns contained a pattern of compressive trabeculae that were thick and tensile trabeculae that were thin. Further, the resulting trabeculae had a high level of stress. The results suggest a high clinical risk of microfracture in an osteoporotic mandible.