Yasuyuki Matsushita

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.

Deformation analysis of the periodontium considering the viscoelasticity of the periodontal ligament

OBJECTIVES The aim of the present work was, by means of a combined experimental and numerical approach, to investigate the full-field distributions of displacement, stress and strain, and their evolution with loading in the entire fresh periodontium under an externally applied force. METHODS In situ intrusion tests were performed to identify the nonlinear, viscoelastic behavior of the periodontal ligament (PDL) of a pig mandible; a digital image correlation method was applied to examine the full-field deformation patterns in the entire periodontium. The finite element (FE) model was created based on the actual anatomic profiles of individual constituents of the tooth structure; the nonlinear and time-dependent viscoelastic properties of the PDL were input into the FE model to fit the numerical computations with the experimental measurements. RESULTS The nonlinear, viscoelastic behavior of the PDL was identified and characterized quantitatively. The simulation results were validated by the experiments. The results showed the tilting of tooth and the movement of cervical bone toward the mid-tooth in the studied periodontium under vertical compressive loading. Major strain was concentrated in the PDL, with the maxima near to the tooth apexes, at the tooth-root bifurcation and also at the sides of the tooth roots, and maintained a slight rise during holding of the applied displacement. High stress in the tooth was located mainly at the sides of tooth roots, in the bone it was concentrated near the apexes and the root bifurcation, and these stresses decreased gradually during the holding period. SIGNIFICANCE The combined approach of experiments that apply the digital image correlation method and FE analyses that take into account the nonlinear and time-dependent viscoelasticity of the PDL enables the acquisition of a full picture of detailed, realistic stress/strain fields and deformation patterns of the entire fresh periodontium, being of essence in orthodontics and dentistry.

Effects of mucosal thickness on the stress distribution and denture stability of mandibular implant-supported overdentures with unsplinted attachments in vitro

The aim of this study was to compare the effects of mucosal thickness on the stress pattern around implants and movement of implant-supported overdentures with ball/female and three different types of magnetic attachments. After insertion of two root-form implants into a mandibular model, the surface of the model was covered with a 1.5- or 3-mm layer of impression material to simulate the oral mucosa, and removable overdentures were fabricated on each model. A 50-N vertical force was applied to the right first molar, and the resultant stress distribution and denture movement were measured. In the 1.5-mm mucosal model, the magnetic attachments showed significantly lower bending moments than did the ball attachment. The denture base displacement was the lowest on a magnetic attachment. In this study, use of magnetic attachments could be advantageous for mandibular implant-supported overdentures based on lower stress and better denture stability especially in the thin mucosal model.

Relationship between magnitude of immediate loading and peri‐implant osteogenesis in dogs

OBJECTIVES The purpose of this study was to investigate the influence of the magnitude of immediate loading on peri-implant bone in an animal model of dental implantation. MATERIAL AND METHODS Eight weeks after the extraction of maxillary and mandibular premolars, three implants were inserted bilaterally in the mandibles of six Beagle dogs. One implant was unloaded (UL) as a control, and two implants were loaded immediately with 10 N (mild loading: ML) or 50 N (excessive loading: EL) laterally using a cyclic loading device twice a week for 3 weeks. Fluorescent bone markers were injected to examine bone formation around the implants. The animals were sacrificed 3 weeks after implantation. Peri-implant osteogenesis was assessed by histomorphometric procedures, i.e., measuring bone-implant contact (BIC) and bone density (BD). RESULTS The UL and ML groups had no peri-implant infection, and newly formed bone was observed over a wide area from the implant neck toward the tip, and in direct contact with the implant surface. In contrast, in the EL group, newly formed bone was rarely observed around the implant neck and there were signs of infection. Both BIC and BD in the ML group were significantly greater than those in the other groups. BIC and BD in the EL group were significantly lower than those in the other groups. CONCLUSION A suitable magnitude of load applied immediately after dental implantation promotes peri-implant osteogenesis.

Maxillary Sinus Augmentation without Grafting Material with Simultaneous Implant Installation: A Three‐Dimensional Finite Element Analysis

PURPOSE The study aims to provide a theoretical guidance of postmaxillary implant in the augmented sinus without grafting materials by establishing a three-dimensional model of this new implant restorative technique, evaluating failure risk of sinus augmentation without grafting materials of different alveolar ridge heights, and analyzing stress distribution of different healing stage. MATERIALS AND METHODS Seventeen three-dimensional finite element models of a posterior maxillary region with sinus mucosa and different elevation heights were constructed according to anatomical data of sinus area, and the standard implant model based on Nobel Biocare implant system were created via computer-aided design software. All materials were assumed to be isotropic and linearly elastic. Axial force of 150 N was applied. The von Mises stress, stress distribution, and implant displacement were calculated with software. RESULTS With the height of the alveolar ridge reducing, the maximum von Mises stress of tissues and the displacement of the implant are on the rise, especially when the height of the bone is less than 7 mm. When the height decreased to 4 mm, the data may be doubled. After the stiff callus stage, the stress and displacement were close to the control model. CONCLUSION For maxillary sinus augmentation without grafting material implant technique, the stress of different tissues and the displacement of the implant were not increased much when the height of alveolar ridge is more than 7 mm. But if the alveolar bone height is less than 4 mm, this implant technique is not suggested. Immediately loading is not suggested and the loading opportunity should be after the stiff callus stage at least to improve the success rate.

Fit of e.max Crowns Fabricated Using Conventional and CAD/CAM Technology: A Comparative Study.

PURPOSE The aim of this study was to examine the fit accuracy of e.max crowns by investigating marginal and internal gaps. MATERIALS AND METHODS In experiment 1, 60 e.max computer-aided design/computer-assisted manufacture (CAD/CAM) crowns were manufactured. The crowns were fabricated using optical scanning of artificial teeth (Op group) or scanning of a plaster model following a silicone impression (M group). Cement space settings of 90, 120, and 150 μm were applied. Marginal and internal crown gaps were compared among six conditions (Op90, Op120, Op150, M90, M120, M150). In experiment 2, e.max CAD crowns from the Op group (CADop group) and the M group (CADm group) were compared with e.max Press crowns (Press group) by measuring marginal and internal gaps of the crowns using Scheffe multiple comparison test. The level of significance was set at .05. RESULTS In experiment 1, the marginal gap of the Op90 group was significantly higher than that of the Op120 and Op150 groups. The marginal gap of the M90 group was significantly higher than those of the M120 and M150 groups, and the internal gap of the M90 group was significantly lower than that of the M150 group. Although there was no statistically significant difference in marginal gap among the three groups, the internal gap of the CADm group was significantly higher than the Press group. CONCLUSION Although the variation in cement space settings and fabrication techniques affected accuracy, e.max CAD crowns fabricated using optical scanning of melamine teeth achieved a clinically acceptable fit.

Additional effects of platelet-rich fibrin on bone regeneration in sinus augmentation with deproteinized bovine bone mineral: Preliminary results

Purpose:Platelet-rich fibrin (PRF) has been reported to contribute to bone regeneration; however, little is known about details with deproteinized bovine bone mineral (DBBM). This study aims to evaluate additional effects of PRF on bone regeneration in sinus augmentation with DBBM. Materials and Methods:Sinus augmentations were made with DBBM/PRF mixture as lateral approach for 4 sinuses from 4 patients. Bone biopsies were obtained from posterior maxilla at the implant placements 7 or 10 months after sinus augmentations. Histological observations and histomorphometric analyses from augmented areas were performed. Results:The new bone formation was found around the DBBMs with very good contact while surfaces of DBBMs were partly resorbed. Osteoclasts recognized the DBBMs for remodeling, followed by new bone running. The histomorphometric analyses revealed that mean percentages of newly formed bone were 31.7 ± 1.2%, 21.0 ± 1.0%, 38.0 ± 0.6%, and 47.0 ± 0.6%, respectively (mean 34.5 ± 5.7%). Conclusions:Additional effects of PRF could be found because of higher percentages of newly bone formation by DBBM/PRF mixture than those by DBBM individual in previous reports.

Immediate loading of complete-arch fixed prostheses for edentulous maxillae after flapless guided implant placement: a 1-year prospective clinical study.

PURPOSE The purpose of this study was to evaluate prospectively the clinical effectiveness of immediate loading of implants with complete-arch fixed prostheses in edentulous maxillae after the implants were placed with flapless guided surgery. MATERIALS AND METHODS Patients with edentulous maxillae who visited a single dental clinic during the recruitment period (April 2011 to May 2012) were selected by consecutive sampling and predetermined selection criteria. Four to six implants were placed in each patient with flapless guided surgery. The outcome measures were insertion torque, surgical time, postoperative pain (100-mm visual analog scale), marginal bone level change, implant survival, and oral health-related quality of life. Patients were followed for up to 1 year. RESULTS Fifty patients received 290 implants. All implants were immediately loaded 2 hours after placement with prefabricated fixed provisional prostheses. Two patients dropped out of the study. Hence, analyses were conducted for 278 implants in 48 patients (26 men, 22 women; mean age 56.0 ± 8.3 years; age range, 34 to 74 years). The average insertion torque was 57.7 ± 16.6 Ncm, the average surgical time was 22.9 ± 4.7 minutes, and the average score for postoperative pain was 14.7 ± 9.3. One year after immediate loading, the implant survival rate was 98.6%. Four implants showed mobility early after implant placement and were lost. Mean marginal bone level changes were -0.32 ± 0.43 mm. Scores on the Oral Health Impact Profile-54 (Japanese version) improved significantly after prosthetic treatment. CONCLUSION The results of this study indicate that this treatment method for edentulous maxillae is predictable, with a high implant survival rate and a clinically reasonable improvement in oral health-related quality of life.

Accuracy of implant surgery with surgical guide by inexperienced clinicians: an in vitro study

Implant surgery with surgical guide has been introduced with a concept of position improvement. The surgery might be considered as easy even for inexperienced clinician because of step simplicity. However, there are residual risks, resulting in postoperative complications. The aim of this study was to assess the accuracy of implant surgery with surgical guide by inexperienced clinicians in in vitro. After preoperative computed tomographies (CTs) of five artificial models of unilateral free‐end edentulism with scan templates, five surgical guides were established from templates. Following virtual planning, 10 implants were placed in the 45 and 47 regions by five residents without any placement experiences. All drillings and placements were performed using surgical guides. After postoperative CTs, inaccurate verifications between virtual and actual positions of implants were carried out, by overlaying of pre/postoperative CT data. The angle displacement of implant axis in the 47 region was significantly larger than that in the 45 region (P = 0.031). The 3D offset of implant base in the 47 region was significantly larger than that in the 45 region (P = 0.002). For distal/apical directions, displacements of base in the 47 region were significantly larger than those in the 45 region (P = 0.004 and P = 0.003, respectively). The 3D offset of implant tip in the 47 region was significantly larger than that in the 45 region (P = 0.003). For distal/apical directions, displacements of tip in the 47 region were significantly larger than those in the 45 region (P = 0.002 and P = 0.003, respectively). Within limitations of this in vitro study, data for accuracy of implant surgery with surgical guide would be informative for further studies, because in vitro studies should be substantially made to avoid unnecessary burden of patients, in advance of retro/prospective studies. A comparison of the accuracy in this in vitro model between by inexperienced and well‐experienced operators should be necessary for clinicians intending to use surgical guide for placement.

The effective design of zirconia coping on titanium base in dental implant superstructure

Zirconia exhibits good tissue compatibility and nontoxicity, making it a widely used esthetic replacement material for implant abutments. To avoid abutment-fracture, the parts composed of zirconia with a bonded metal component connected to the implant can be used. The purpose of this study was to design titanium and zirconia components with high fracture resistance at the zirconia components edge line. Three edge line designs of the titanium base and zirconia sleeve were made: chamfer, shoulder, and back-taper. To assess the strength of the abutment design, static loads were applied vertically and 30 degrees from the vertical axis. A test of tensile strength was also performed after chewing simulation. Conventional zirconia components mounted on a chamfer-type titanium base showed significantly lower fracture resistance than shoulder and back-taper types. This study suggests that to improve the durability of zirconia abutments with a titanium base, a back-tapered edge design is recommended.