Comparison of 3D accuracy of three different digital intraoral scanners in full-arch implant impressions.

PURPOSE: This in vitro study aimed to evaluate the performance of digital intraoral scanners in a completely edentulous patient with angled and parallel implants. MATERIALS AND METHODS: A total of 6 implants were placed at angulations of 0°, 5°, 0°, 0°, 15°, and 0° in regions #36, #34, #32, #42, #44, and #46, respectively, in a completely edentulous mandibular polyurethane model. Then, the study model created by connecting a scan body on the implants was scanned using a model scanner, and a 3D reference model was obtained. Three different intraoral scanners were used for digital impressions (PS group, TR group, and CS group, n = 10 in each group). The distances and angles between the scan bodies in these measurement groups were measured. RESULTS: While the Primescan (PS) impression group had the highest accuracy with 38 µm, the values of 104 µm and 171 µm were obtained with Trios 4 IOSs (TR) and Carestream 3600 (CS), respectively (P = .001). The CS scanner constituted the impression group with the highest deviation in terms of accuracy. In terms of dimensional differences in the angle parameter, a statistically significant difference was revealed among the mean deviation angle values according to the scanners (P < .001). While the lowest angular deviation was obtained with the PS impression group with 0.185°, the values of 0.499° and 1.250° were obtained with TR and CS, respectively. No statistically significant difference was detected among the impression groups in terms of precision values (P > .05). CONCLUSION: A statistically significant difference was found among the three digital impression groups upon comparing the impression accuracy. Implant angulation affected the impression accuracy of the digital impression groups. The most accurate impressions in terms of both distance and angle deviation were obtained with the PS impression group.

Determination of the Effect of TiN Coating on Self-Fitting Properties of Dental Implants Made of NiTi Alloy.

Design and material research continues to increase dental implants' success rates, which is a widely applied treatment type. The size and morphology of the implant-bone interface are essential for implant stability. Our study produced a dental implant with two artificial tooth roots from NiTi alloy to increase the implant-bone contact surface. The properties of NiTi alloy, such as transformation temperature and composition, were determined by material characterization tests. Using NiTi alloy's shape memory effect, these artificial roots at body temperature were programmed with appropriate heat treatments for the self-fitting feature. Dental-implant-like models are coated with TiN to prevent Ni ion release. The corrosion tests were performed in Ringer's solution to determine the effect of TiN coating on Ni ion release. The nickel ion emission values showed that the TiN coating inhibited the release. In addition, it was determined that the TiN coating increased the shape memory transformation time of the NiTi alloy. In in vitro tests of NiTi and TiN-coated NiTi implants, it was observed that they completed self-fitting by deforming the trabecular bone, but the placement in the cortical bone was not complete. During the use of a shape memory implant, it should complete its transformation without contacting the cortical bone and should not cause a stress concentration.

Investigation of the Type of Angled Abutment for Anterior Maxillary Implants: A Finite Element Analysis.

PURPOSE: The optimal abutment material and design for an angled implant-abutment connection in the esthetic zone is unclear. The purpose of this finite element analysis (FEA) study was to compare different abutment models by evaluating the stress values in the implant components and strain values on the simulated bone around an anterior maxillary implant with different angled abutment models and loading conditions. MATERIALS AND METHODS: One Ø3.5×12-mm implant was placed in 3D FEA models representing the anterior left lateral segment of the maxilla. Three different contemporary implant models were created with 17° or 25° angled abutments (Ti base abutment, zirconia abutment, and titanium abutment) and 3D-modeled. The implant abutment model was an angled Ti base abutment (TIB), an angled zirconia abutment (ZIR), or an angled titanium abutment (TIT). Vertical and oblique loads of 100 N for the central incisors were applied as boundary conditions to the cingulum area and incisal area in a nonlinear FEA. RESULTS: The TIB model resulted in reduced stress conditions. According to the von Mises stresses occurring on the screw, abutment, crown, and implant, especially under oblique loads, the TIB model was exposed to less stress than the ZIR or TIT models. Strain values in simulated cortical and trabecular bones were obtained lower in the TIB model. CONCLUSIONS: When a standard implant was placed in the esthetic zone at an increased angle, the implants, abutments, and screws had more unfavorable stress levels; therefore, using a Ti-base abutment may reduce stress. The amount of contact surface of the implant with the simulated cortical bone is also an important factor affecting stress and strain.

A new porous fixation plate design using the topology optimization.

Fixation plates are used to accelerate the biological healing process in the damaged area by providing mechanical stabilization for fractured bones. However, they may cause mechanical and biological complications such as aseptic loosening, stress shielding effect and necrosis during the treatment process. The aim of this study, therefore, was to reduce mechanical and biological complications observed in conventional plate models. For this purpose, an optimum plate geometry was obtained using the finite element based topology optimization approach. An optimum and functionally graded porous model were obtained for the plates used for transverse fractures of diaphysis in long bones. This model was combined with a functional graded porous cage structure, and thus a new generation porous implant model was proposed for fixation plates. In order to determine the performance of the optimum plate model, it was produced by additive manufacturing. Three models; i.e. conventional, optimum and porous fixation plates were statically tested, and they were compared experimentally and numerically using the finite element analysis (FEA). The porous model can be considered as the most suitable option since it requires less invasive inputs, and might lead minimum necrosis formation due to having lesser contact surface with the bone.

Effect of different design of abutment and implant on stress distribution in 2 implants and peripheral bone: A finite element analysis study.

STATEMENT OF PROBLEM: How adjacent dental implants with different sizes, designs, and abutment connection shapes affect stress on the prosthetic structure is unclear. PURPOSE: The purpose of this finite element analysis (FEA) study was to analyze stress distribution around bone and around 2 implants with different sizes, diameters, shapes, and loading directions placed next to each other in splinted and unsplinted prostheses. MATERIAL AND METHODS: On 3D FEA models representing the posterior right lateral segment of the mandible, 1 implant (Ø3.5×12 mm) and 1 implant (Ø5.5×8 mm) were placed adjacent. Three different contemporary implant models were created with different teeth, pitch, spiral numbers, and self-taping features, and different abutments for them were modeled in 3D. The implant-abutment connection was internal hexagonal (MIH), stepped conical (MSC), and internal conical (MIC). Vertical and oblique loads of 365 N for molar teeth and of 200 N for premolar teeth were applied as boundary conditions to the cusp ridges and grooves in a nonlinear FEA. RESULTS: The MIH implants resulted in improved stress conditions. According to the von Mises stresses occurring on the screw, abutment, and implant, especially under oblique loads, MIH was exposed to less stress than MSC, and MSC was exposed to less stress than MIC. CONCLUSIONS: When a standard implant and a short implant were placed adjacent and splinted by crowns, the implants, abutments, and screws had unfavorable stress levels; therefore, adjacent splinted implants should be of similar size. The form of the implant-abutment junction is also an important factor affecting stress.

Three-Dimensional Accuracy of Conventional Versus Digital Complete Arch Implant Impressions.

PURPOSE: The accuracy of digital impressions is still controversial for complete arch implant cases. The aim of this study is to compare the accuracy of different intraoral scanners with the conventional technique in terms of trueness and precision in a complete arch implant model. MATERIAL AND METHODS: Eight implants were inserted asymmetrically in a polyurethane edentulous mandibular model with different angulations. A 3-dimensional (3D) reference model was obtained by scanning this polyurethane model with an optical scanner. First, digital impressions were made by using 3 different intraoral scanners: Carestream 3500 (DC), Cerec Omnicam (DO) and 3Shape Trios 3 (DT). Subsequently, a nonsplinted open tray impression technique was used for conventional impression group (C) and then the master casts were digitalized with a lab scanner. Each 10 STL files belonging to 4 different impression groups were imported to a reverse engineering program, to measure distance and angle deviations from the reference model. All statistical analyses were performed after taking absolute values of the data. After comparing the impression groups with one-way ANOVA, the trueness and precision values were analyzed by Tukey post hoc test and 0.05 was used as the level of significance. RESULTS: The mean trueness of distance was 123.06 ± 89.83 µm for DC, 229.72 ± 121.34 µm for DO, 209.75 ± 47.07 µm for DT, and 345.32 ± 75.12 µm for C group (p < 0.0001). While DC showed significantly lower deviation compared to DO and C, no significant difference was found between DC and DT. C showed the highest distance deviation significantly in all groups; and no significant difference was found between DO and DT groups. In angle measurements; the trueness was 0.26° ± 0.07° for DC, 0.53° ± 0.42° for DO, 0.33° ± 0.30° for DT, and 0.74° ± 0.65° for C group. There was no significant difference between the groups in terms of angular trueness (p = 0.074). In terms of the precision for distance, the results of DC 80.43 ± 29.69 µm, DO 94.06 ± 69.96 µm, DT 35.55 ± 28.46 µm and C 66.97 ± 36.69 µm were determined (p = 0.036). The significant difference was found only between DT and DO among all groups. Finally, angular precision was determined to be 0.19° ± 0.11° for DC, 0.30° ± 0.28° for DO, 0.22° ± 0.19° for DT, and 0.50° ± 0.38° for Group C. No significant difference was found between the groups, in terms of angular precision (p = 0.053). CONCLUSIONS: All digital impression groups yielded superior data compared to conventional technique in terms of trueness. DC formed the impression group with the highest trueness in both distance and angular measurements. The results of this in vitro study suggest the use of intraoral scanners compared to the conventional impression techniques in complete arch implant cases with high angulations.

An Analysis of Mandibular Symphyseal Graft Sufficiency for Alveolar Cleft Bone Grafting.

The purpose of this study was to evaluate the sufficiency of the mandibular symphysis as a donor site for unilateral and bilateral alveolar grafting, measuring both the alveolar cleft volume and maximum bone graft volume that can be harvested from the mandibular symphysis using 3-dimensional computed tomography (CT) and software in children and adults. Computed tomography data obtained from 20 unilateral and bilateral cleft lip palates patients in the preoperative period were used in this study. The patients were divided into 2 groups: children (female, n = 5; male, n = 5) and adults (female, n = 5; male, n = 5). The required bone graft volume for grafting and the maximum bone graft volume that can be harvested from the mandibular symphysis were measured based on cone beam CT data and software. The average required bone graft volume (cleft volume) for unilateral alveolar grafting was 963.51 ±â€Š172.31 mm in the children and 1001.21 ±â€Š268.16 mm in the adults. The average required bone graft volume for bilateral alveolar grafting was 1457.82 ±â€Š148.18 mm in the children and 2189.59 ±â€Š600.97 mm in the adults. The average the mandibular symphysis bone graft volume was 819.29 ±â€Š330.85 mm in the children and 2164.9 ±â€Š1095.86 mm in the adults. The results demonstrated that the mandibular symphysis region provided an adequate bone volume for alveolar grafting in adults with unilateral alveolar clefts. However, it is difficult to standardize these results, due to cleft volume and graft volume that could be harvested from the mandibular symphysis are highly variable among individuals.

A New Design for Maximum Conformity of Total Knee Prosthesis to Femur and Tibia.

Total knee arthroplasty (TKA) is a common procedure for treating patients with excessively arthritic knees. Nonetheless, early failure of TKA may occur in the first 5 yr, and up to 20% of TKA procedures can fail after 20 yr. In this study, a new anatomic prosthesis was designed to provide maximum conformity to knee bones and produce less stress and strain, in an effort to avoid possible failure of the prosthesis. Anatomical and conventional knee models were compared on the basis of both geometric conformity and stress and strain results obtained from finite element analysis. To compare geometric conformity, anatomic prosthesis components were manufactured by laser melting, and conventional prosthesis components were fixed to sawbone knee models. The anatomical model yielded up to 50% less contact pressure at the insert, which may indicate potential for reduced wear between insert and femur components. This model also resulted in less principal strain value at the tibial component, considered to be an important parameter to indicate loosening. The anatomical model with a new femur component in the anterior cortex design also yielded less stress at the femoral cortex, when compared to the conventional model. The findings in this study suggest that the anatomic prosthesis model may be a better design alternative to conventional knee prostheses in terms of wear, aseptic loosening, and normal joint biomechanics.