Abutment Height Research Articles

Effect of Ti-Base Abutment Gingival Height on Maintenance of Crestal Bone in Thick Biotype Patients: A Randomized Clinical Trial with 1-Year Follow-up.

To determine the effect of 0.7- and 2.4-mm transmucosal abutment height titanium bases on the crestal bone stability and peri-implant soft tissue condition of bone-level implants with platform switching in patients with vertically thick soft tissues. Sixty bone-level platform-switched implants were placed in the molar and premolar regions of both arches in 60 patients. All epicrestally inserted nonsubmerged implants had a 4.1-mm diameter and, after osteointegration, were randomly allocated into two groups: (1) the short group, with a titanium base of 0.7-mm transmucosal abutment height, and (2) the high group with a 2.4-mm height. Monolithic zirconia restorations were fabricated for all implants. Parallel intraoral radiographs were obtained after the delivery of restorations (T1) and after 1 year (T2). Crestal bone levels and peri-implant soft tissue conditions were calculated for each implant. The significance level was set at α = .05. After 1 year, 55 patients were evaluated, with a mean bone loss of 0.6 ± 0.51 mm (median: 0.71, range: 0 to 2.09 mm) in the short group (23 patients) and 0.45 ± 0.59 mm (median: 0.65, range: 0 to 2.12 mm) in the high group (22 patients), showing no significant difference between groups (P = .168). A significant increase in marginal bone height was noted between the T1 and T2 time points in the short and high (P = .029 and .001, respectively) groups. The peri-implant soft tissue health parameters did not show statistically significant differences. Crestal bone stability after 1 year of follow-up around epicrestally placed platform-switched implants is not influenced by transmucosal abutment height, if the vertical soft tissue thickness is ≥ 3 mm.

Impact of cement type and abutment height on pull-off force of zirconia reinforced lithium silicate crowns on titanium implant stock abutments: an in vitro study

BackgroundPull-off forces of cement-retained zirconia reinforced lithium silicate (ZLS) in implant-supported single crowns on stock titanium abutments with respect to abutment height and implant cement were evaluated and compared.MethodsPull-off force of ZLS crowns on stock titanium abutments was evaluated concerning dental cement and abutment height. A total sample size of 64 stock abutments with heights of 3 mm (n = 32) and 5 mm (n = 32) was used. The ZLS crowns were cemented with four different types of cement (one temporary, two semi-permanent, and one permanent). After cementation, water storage, and thermocycling each sample was subjected to a pull-off test using a universal testing machine.ResultsThe temporary cement showed the least pull-off force regardless of abutment height (3/5 mm: means 6 N/23 N), followed by the semi-permanent methacrylate-infiltrated zinc oxide cement (28 N/55 N), the semi-permanent methacrylate-based cement (103 N/163 N), and the permanent resin composite cement (238 N/820 N). Results of all types of cement differed statistically significantly from each other (p ≤ .012). The type of implant cement has an impact on the pull-off force of ZLS crowns and titanium abutments.ConclusionsPermanent cements present higher retention than semi-permanent ones, and temporary cements present the lowest values. The abutment height had a subordinate impact.

Vertical Discrepancy in Height of Morse Cone Abutments Submitted to Different Torque Forces.

The present study aimed to evaluate the influence of manual torque (10 Ncm) versus clinical torque (30 Ncm), which is recommended by the manufacturer, on the total length of morse cone implant abutments. Twenty specimens were prepared and distributed into two groups: group 1 with ten analogs for morse cone type implant, and group 2 with ten morse type implants, size 4.3 × 15 cm. In each group, the distance between the implant platform to the top of the prosthetic abutment (abutment height) was measured and subjected to a torque of 10 Ncm. Then, the 30 Ncm torque was applied to the same abutment, and abutment height was measured. The distance between the top of the abutment and the implant/analog base was measured. In order to verify the clinical reproducibility of the experiment, comparisons between the abutment height of the analog at 10 Ncm and the implant at 30 Ncm were performed, showing a greater discrepancy in torque for the 10 Ncm analog (p < 0.05). In order to verify if the change in the laboratory protocol from 10 to 30 Ncm could minimize the differences in the height of the prosthetic abutments, the abutment height in groups 1 and 2 was compared with 30 Ncm, and no significant difference was observed (p > 0.05). The data indicated that the manual torque and the torque recommended by the manufacturer influence the total length of the prosthetic abutments of morse cone implants.

Bone‐level changes around implants with 1‐ or 3‐mm‐high abutments and their relation to crestal mucosal thickness: A 1‐year randomized clinical trial

To evaluate 1-year bone-level changes around subcrestal platform-switching implants with 1 or 3 mm definitive abutments. The influence of mucosal thickness on bone-level alterations was further analysed. Implants were placed in the posterior sextants and positioned 1.5 mm subcrestally with an abutment of 1 or 3 mm height. Final restorations were delivered after 16 weeks. Radiographic measurements of inter-proximal bone level were the primary outcome and were adjusted by vertical mucosal thickness. Peri-implant clinical conditions and resonance frequency analysis were also compared. A total of 65 subjects with 99 implants were analysed. The overall 1-year implant survival rate between the 1- and 3-mm groups was 96.4% and 94.4%, respectively. Statistically significant lower inter-proximal marginal bone-level changes were observed in the 3-mm group (1 mm: -0.17 ± 0.02 mm at mesial and -0.21 ± 0.02 mm distal; 3 mm: -0.03 ± 0.02 mm at mesial and -0.03 ± 0.02 mm and distal; mesial: p=.001; distal: p < .001). Initial vertical mucosal thickness was not correlated with inter-proximal marginal bone loss. Subcrestal implants with 3-mm abutment were associated with minimal inter-proximal bone loss. Independent of the abutment height, crestal mucosal thickness was not correlated with bone loss.

Fracture strength analysis of titanium insert-reinforced zirconia abutments according to the axial height of the titanium insert with an internal connection.

This study aimed to analyze fracture strength in vitro by varying the axial height of the titanium insert and the labial height of the zirconia abutment in an internal connection implant to identify the titanium insert axial height with optimal mechanical stability. Sixty implants with an internal connection system were used. Two-piece zirconia abutments were used with the titanium inserts. Combinations of different titanium insert axial heights (mm) and zirconia abutment labial heights (mm) constituted five groups: Gr1 (1-3), Gr2 (3-3), Gr3 (3-5), Gr4 (5-3), and Gr5 (5-5). After thermocycling, a fracture load test was performed with a universal testing machine. The initial deformation load and the fracture load were measured and analyzed. The fractured surface and cross-section of the specimens were examined by scanning electron microscopy (SEM). The groups of titanium inserts with axial heights of 3 mm and 5 mm showed significantly greater initial deformation load and fracture load than the group with an axial height of 1 mm (p < 0.05), but there was no significant difference between the two groups with axial heights of 3 mm and 5 mm. The labial height of the zirconia abutment had no significant influence on the initial deformation load and fracture load. In some specimens in Gr4 and Gr5, cracking or bending of the titanium insert and abutment screw was observed on SEM. The axial height of the titanium insert should be designed to not be less than 3 mm to increase the fracture strength and promote the long-term stability of implants.

Factors Affecting Implant Stability Quotients at Immediately and Conventionally Loaded Implants in the Posterior Maxilla: A Split-Mouth Randomized Controlled Trial.

To assess primary and secondary stability of variable-thread tapered implants in the posterior maxilla and analyze the impact of various factors on implant stability quotients (ISQs). Twenty-six subjects received 3-4 adjacent implants in the maxillary premolar-molar sextants to replace bilateral tooth loss. The implants on one side were immediately loaded with a provisional fixed prosthesis regardless of their primary stability. The contralateral control implants were conventionally loaded. Bone quality was subjectively recorded and primary stability was assessed by means of insertion torque values (ITVs) and ISQs in 4 directions. Secondary stability was measured by ISQ at definitive prosthesis delivery (3-3.5 months postoperatively), and 12 months after definitive loading. The impact of measurement direction, loading protocol, time, site-related (bone quality, implant position, crestal buccal bone thickness, apical cortical anchorage), and implant-related (implant dimensions, abutment height) variables on ISQs was assessed. For logistic reasons, ISQs were obtained for only 18 patients with 60 test and 60 control implants. Most of the implants (82%) at baseline had their lowest ISQ on the buccal aspect. There were no significant differences between ISQs measured in the buccal and palatal directions, or between ISQs in the mesial and distal directions. The mean of buccal and palatal ISQs was significantly lower than the mean of the 2 interproximal measurements at all evaluation periods. ISQs were not significantly different between the 2 loading groups at any time point. All implants showed a time-dependent increase in ISQs. Baseline ISQ correlated weakly with bone quality and ITV. None of the variables had a significant impact on baseline ISQs, except for implants in second molar sites which showed poorer primary stability than first premolars. Measurement direction and time are the most significant parameters affecting ISQs of variable-thread tapered implants in the posterior maxilla.

Effect of the Features of Mandibular Implant Overdenture Attachments on the Bending Strain Around Implants

To examine the effect of the attachment features (abutment height, retention, and freedom of rotation) of implant overdentures on the bending strain around implants under an overdenture. Mandibular and maxillary edentulous models were fabricated and covered with silicone rubber. Strain gauges were attached to the four sides of each implant. Two implants (tissue-level implant, 4.1-mm diameter, 10-mm length) were placed bilaterally in the area between the mandibular canines and lateral incisors. A maxillary conventional denture and a mandibular overdenture were made to fit the edentulous models. Three levels of peri-implant bone resorption were created sequentially: no bone resorption, 0.8 mm, and 1.5 mm. Three kinds of attachments (magnetic, stud, and ball attachments) were used. Bending strains generated from a 98-N occlusal load through the maxillary denture were measured using a sensor interface, and the data were analyzed using the Kruskal-Wallis and Bonferroni tests. Multiple regression analysis was used to find the relationship between independent variables (peri-implant bone resorption level, abutment height, retention, and freedom of rotation) and the dependent variable (bending strain). For all attachment types, the bending strains were smallest with no bone resorption and largest with 1.5-mm bone resorption (P < .05). Multiple regression analysis showed that abutment height had the greatest impact on the reduction of bending strain (beta = .413), followed by freedom of rotation (beta = -.349), and retention (beta = .107). Low abutment height, large freedom of rotation, and low retention can minimize bending strain around implants.

Comparison of stress distribution on dental implant with different abutment types

Dental implants have a triumph pace of 90–98%, which in clinical terms is essentially high. Implant failure may occur at earlier or later stage. In assessment of the drawn-out accomplishment of a dental implant, the reliability and the stability of the implant–abutment play a vital role. In general, the achievement of the treatment relies upon numerous factors influencing the implant, implant–abutment and abutment–prosthesis interfaces. Early implant failure occurs due to the improper mechanical stability. This study researches the stress distribution in an implant with different implant abutments with different height and angle in different loading criteria. The abutment heights are 5.50 mm, 3.50 mm and 3.60 mm respectively. The loading conditions are applied in vertical and 30˚ angle with the value of 36 N & 100 N. Cobalt chromium alloy is used which has the superior properties like high stiffness, tightly polished, wear resistant and also it is used to avoid crevice corrosion. Computational models of abutment types with different heights were modeled using CAD software and Analyzed with FEA software for finding out the total deformation, Maximum principle stress, and Maximum shear stress. Based on the structure of a dental implant system, it gives significant performance. The minimum and maximum total deformation, Maximum principle stress, and Maximum shear stress were noted in the Type 3 under 36 N vertical condition and Type 1 under 100 N under 30˚ respectively.

Periimplant bone changes in different abutment heights and insertion timing in posterior mandibular areas: Three-year results from a randomized prospective clinical trial.

To compare the influence of the abutment height and its insertion timing on the marginal bone change (MBC) variation of implants placed at posterior mandibular partial edentulous areas in a medium follow-up period. This randomized clinical trial (RCT) comprised a sample of patients with posterior mandibular edentulous areas, treated with at least two implants and distributed into three groups: implants connected to a 2mm height abutment during the surgical stage (Group A); implants connected to a 1mm height abutment during the surgical stage (Group B); and implants connected to a 2mm height abutment after 2months (Group C). Clinical and radiographic measurements were performed during a 36-month period (T4). The MBC was set as the main variable in study. Statistical significance was set at 0.05. A total of 29 subjects and 59 implants were enrolled in this study. A mean MBC of 0.35±0.46mm, 0.60±0.81mm, and 0.71±0.90mm was computed for groups A, B and C, respectively, at T4. Significant differences were found between groups A and C in terms of MBC variation after 3years of treatment (p=.048). Multiple linear regression analysis showed a significant influence of the first-year MBC and the abutment insertion timing has independent predictor variables for the MBC assessed at T4. The installation of 2-mm prosthetic abutments, at the time of implant placement, in areas with limited keratinized mucosa presents as a favorable treatment option in terms of periimplant marginal bone maintenance.

Estimation Modeling of Abutment Volume with Variations of Bridge Span, Abutment Height, and Seismic Zone

The initial cost estimate for a bridge project using an estimation model can be done based on the dimensions, type, and material of the bridge. Research that has included bridge location as a determinant variable for initial bridge cost estimation has not been carried out much. The different locations of the bridge project will have different seismic accelerations and seismic load analysis. This study aims to create a model used to calculate the quantity needed for the construction of abutment in various locations with a PCI-Girder superstructure. The data used for the quantity estimation model was derived from the abutment design results. The data obtained from the calculation of concrete and reinforcing steel quantities from the abutment design with variations in bridge span i.e. 20 m; 25 m; 30 m; 35 m; and 40 m, abutment height i.e. 4 m; 6 m; and 8 m, and seismic zone 1, 2, 3, and 4. Volume estimation models are obtained by multiple linear regression analysis. The results show a very strong correlation between the span of the bridge and the height of abutment with the dependent variables. While the seismic zone has a strong correlation with the dependent variables. However, the seismic zone in this study did not meet the linear regression assumptions. This study developed 8 models to estimate abutment volumes. The R2 values of these models are 0.983 – 0.997. These showed that the models are properly made to be used to estimate abutment volumes with a PCI-Girder superstructure.

Cementation Protocol for Bonding Zirconia Crowns to Titanium Base CAD/CAM Abutments.

To establish the most effective cementation protocol for bonding zirconia crowns to Ti-Base CAD/CAM abutments in terms of abutment height, cement type, and surface pretreatment. Zirconia crowns were designed to fit abutments of 2.5-mm (short) and 4.0-mm (tall) height. The retention of conventional resin cement with a universal adhesive (RelyX Ultimate, 3M ESPE) was compared to self-adhesive resin cement (RelyX U200, 3M ESPE) following different surface pretreatments (n = 10/group): (1) no treatment (NT); (2) Ti-Base abutment surface blasting with alumina particles (SB); (3) zirconia crown tribochemical surface blasting with silica-coated alumina particles (TBS); and (4) a combination of SB + TBS. Pull-out testing was performed in a universal testing machine. Data were statistically evaluated using a linear mixed model following least significant difference post hoc test. Pull-out data as a function of Ti-Base height demonstrated higher retention for tall compared to short abutments (P < .001). Ultimate outperformed U200 cement (data collapsed over height and pretreatment) (P < .001). Analysis of pretreatment depicted higher retention for SB + TBS, followed by SB, TBS, and NT (P < .04). The interaction between Ti-Base height and cement type highlighted the superior adhesive strength of Ultimate compared to U200 for both heights (P < .001). Irrespective of type of pretreatment, surface pretreatment improved the retention for U200 cement and short Ti-Base (P < .03 compared to NT). In contrast, higher retention was demonstrated for SB + TBS, followed by SB, TBS, and NT, for Ultimate cement combined with tall Ti-Base (P < .02) (data collapsed over height and cement, respectively). There was a direct relationship among Ti-Base height, micromechanical and/or chemical pretreatment, and conventional adhesive bonding in improving the retention of zirconia crowns.

Immediate rehabilitation of the edentulous and potential edentulous jaws with implant-supported full-arch prostheses: a retrospective analysis of 225 cases

Objective: To evaluate the outcomes of immediate rehabilitation of the edentulous and potential edentulous jaws with implant-supported full-arch prostheses and analyse the risk factors of the complications. Methods: This retrospective study included 273 patients treated with immediate rehabilitation of the edentulous and potential edentulous jaws with implant-supported full-arch prostheses from April 2008 to December 2018 in Department of Implantology, Peking University School and Hospital of Stomatology. The patients' sex, age, place of residence, jaw position, opposing dentition, number of implants, diameter and length of implants, abutment height and abutment angle were recorded. The survival rate of implants and marginal bone loss were calculated and analyzed. Cox proportional hazards ratio model was adopted to analyze the potential risk factors of prosthetic complications. Results: A total of 225 patients (288 jaws) and 1 260 implants were included, with 126 males and 99 females, aged (57.3±11.0) years, with a following time of (5.04±3.08) years. The 1-year cumulative survival rate of implants was 98.0% (1 235/1 260). Forty-eight implants were lost during the follow-up, with 39 implants in the maxillae and 9 implants in the mandible. The risk of implant failure of the maxillae ［7.2% （39/541）］ is significantly higher than that of the mandible ［1.3% （9/719）］ (P<0.01). Average marginal bone loss at 1 and 5 years was (0.7±0.2） mm and （1.1±0.3） mm. One hundred and twenty patients experienced prosthetic complications including screw/abutment loosening (44 cases), screw/abutment fracture (2 cases) and artificial tooth/denture base fracture (99 cases). The possibility of immediate prosthesis fracture within 6-8 months was high but declined over the following years with the final prosthesis delivered. Cox regression analysis showed that the use of 17° abutments in the anterior region was significantly related to the prosthetic complications （hazard ratio=1.797, P=0.002）. Conclusions: Immediate rehabilitation of the edentulous jaws with implant-supported full-arch prostheses can be a predictable technique. The immediate prosthetic mechanical complication prevalence was high. The use of 17° abutments in the anterior region may increase the risk of screw/abutment loosening. It is necessary to review in time.

What Are the Effects of Different Abutment Morphologies on Peri-implant Hard and Soft Tissue Behavior? A Systematic Review and Meta-Analysis.

To evaluate the effect of different abutment morphologies on peri-implant hard and soft tissue behavior. The focus question for this literature search was: What are the effects of different abutment morphology (concave vs convex) on peri-implant hard and soft tissue behavior? Randomized clinical trials (RCTs) with a minimum sample size of 20 implants (10 per group) and a follow-up period of at least 3 months after implant loading were considered eligible for this study. This review excluded studies comparing different abutment heights or surfaces and different implant shapes. Two different meta-analyses were performed: one for marginal bone loss (MBL) to evaluate hard tissue changes, and one for Pink Esthetic Score (PES) as an indicator of soft tissue modifications. Four publications from 12 full texts analyzed were included. The meta-analysis (data from 117 patients and 173 abutments) indicated that a statistically significant difference (P < .00001) was detected from the data regarding MBL between the two groups (mean difference = -0.21 [95% CI: -0.25, -0.16]), but not considering the PES (mean difference = -0.69 [95% CI: -2.08, 0.70]) after a minimum period of 3 months after implant loading. All such evidence was confirmed by the trial sequential analysis on both MBL and PES. The results demonstrate that abutment design may have an influence on MBL but no impact on soft tissues. However, the existing evidence is moderate, as few RCTs were conducted and follow-up periods were short.

Cleaning Efficacy of Poly-ether-ether-ketone Tips in Eliminating Cement Remnants Around Implants With Different Abutment Heights.

The excess cement not removed after the cementation of fixed implant-supported restorations may cause loss of peri-implant attachment or adjacent bone. The aims of this study were to evaluate the amount of residual cement at different abutment-crown connection levels and to test the cleaning efficacy of poly-ether-ether-ketone (PEEK) ultrasonic tips after cementation. One implant was placed in an anterior central tooth position 5 mm below the gingival margin in an acrylic model, and 32 stone models were obtained with implant analogs. Abutment heights of 1-2 and 2.5-4 mm were used on the vestibular and lingual sides, respectively. Crowns were cemented and cleaned, and half of the samples were cleaned again using PEEK tips. The abutment-crown suprastructure was then disconnected, and cleaning efficacy was evaluated. Varying amounts of excess cement were found on all specimens except for the PEEK group with abutment-crown connections 1 mm below the gingival margin. An increase of undetected cement remnants was observed when the restoration margins were located deeper subgingivally. Various amounts of excess cement associated with margin location were detected on the abutment-restoration complex despite meticulous cleaning efforts. Ultrasonic PEEK tips were effective at cleaning the cement remnants around implants to a certain depth.

In Vitro Impact Testing to Simulate Implant-Supported Prosthesis Retrievability in Clinical Practice: Influence of Cement and Abutment Geometry.

Cement-retained implant-supported prosthetics are gaining popularity compared to the alternative screw-retained type, a rise that serves to highlight the importance of retrievability. The aim of the present investigation is to determine the influence of luting agent, abutment height and taper angle on the retrievability of abutment–coping cementations. Abutments with different heights and tapers were screwed onto an implant and their cobalt-chrome copings were cemented on the abutments using three different luting agents. The removals were performed by means of Coronaflex®. The number of impulses and the forces were recorded and analyzed with a Kruskal–Wallis test. Harvard cement needed the highest number of impulses for retrieval, followed by Telio CS and Temp Bond. However, abutment height and taper showed a greater influence on the cap’s retrievability (p < 0.05). Long and tapered abutments provided the highest percentage of good retrievability. The influence of the luting agent and the abutment geometry on the cap’s retrieval performed by Coronaflex® reflects data from literature about the influence of the same factor on the maximum force reached during uniaxial tensile tests. The impulse force was slightly affected by the same factors.

Evaluation of Dimensional Accuracy of Three Combinations of Polyvinyl Siloxane Impression Material: An In Vitro Study

The aim of the study was to evaluate the dimensional accuracy of three combinations of polyvinyl siloxane impression material by double-mix single-step impression technique. Metal master model was made according to the ADA specification no. 19; ISO 4823:2000/AMD 2007. Impressions were made using perforated custom-made metallic trays of 2 mm and 4 mm spacing, the impression materials used were putty, heavy body, regular body and light body. A total of 30 impressions were made by single-step technique and poured in die stone to obtain resultant cast. Ten impressions were made of each combination of polyvinyl siloxane (PVS). Three dimensions (interabutment distance, height and diameter) on resultant cast were measured and compared with metal master model. The results were statistically analyzed and tabulated. Diameter of abutment, the height of abutment and interabutment distance in each group were larger in dimensions as compared with metal master model. The dimensional discrepancies of group I, group II and group III casts when compared with the master model were significantly different from each other. The least difference was found in group I. The one-step putty-light body combination (group I) produced the most accurate stone casts compared with one-step heavy body-light body and regular body-light body combinations. In everyday dental practice, impression making is imperative. Hence, by doing this study, we tried to find out which material combination is suitable to give us predictable and accurate results.

Investigation on Flooding‐Resistant Performance of Integral Abutment and Jointless Bridge

Bridge washouts connected to flood events are deemed one of the main reasons for structural collapse. Compared to traditional continuous jointed bridges, integral abutment and jointless bridges (IAJBs) have better lateral stability because there are no expansion devices. The mechanical performance of Shangban IAJ bridge, located in Fujian, China, is thoroughly investigated by Finite Element Analysis (FEA). The numerical model is created and validated based on experimental results obtained from static load tests performed on the bridge. A detailed parametric analysis is carried out to assess the correlation between the flood‐resistant performance and a number of parameters: skew angle, water‐blocking area, span number, pile section geometry, and abutment height. Except for the abutment height, other parameters significantly affect the bridge performance. Furthermore, the change in the span number has a meaningful impact only when fewer than four spans are modeled. Finally, pushover analyses estimate the maximum transverse displacement and the sequence of plastic hinge creation as well as the mechanical behaviour of the structure under lateral flood loads. The analysis results show that IAJBs have better flooding‐resistant performance than conventional jointed bridges.

Mechanical analysis of the effects of implant position and abutment height on implant-assisted removable partial dentures

PurposeAn increasing number of clinical reports describe the use of dental implants as abutments in implant-assisted removable partial dentures (IARPD). We used three-dimensional finite element analysis to evaluate IARPD as a unilateral mandibular distal extension denture. Specifically, the mechanical effects of implant position and abutment height on the abutment tooth, denture, and denture-supporting tissue were assessed. MethodsThe models analyzed were defects of the left mandibular second premolar and first and second molars prosthetically treated with an IARPD using one implant for each tooth position. There were two abutment heights: one equal to that of the mucosa and another that was elevated 2 mm above the mucosa. Six models were constructed. ResultsFor mucosal-level abutments, movement of the abutment tooth was lower for implants positioned distal to the abutment tooth than for those positioned medial to the abutment tooth. For elevated abutments, movement of the abutment tooth was lower for implants positioned medial to the abutment tooth than for those positioned distal to the abutment tooth. ConclusionsThe mechanical effects on abutment teeth at the same implant position differed in relation to implant abutment height.

Multi-criteria shape optimization of open-spandrel concrete arch bridges: Pareto front development and decision-making

PurposeThis paper aims to study the shape of the concrete arched bridge by particle swarm optimization algorithm.Design/methodology/approachFinite element model of open-spandrel concrete arch bridges was constructed using a number of parameters. Design variables of optimization problem include height of skewback abutment, height of arch crown, position of crown with respect to global axes and left and right radius of up and down arches. After parametric modeling of bridge geometry and application of multi-objective particle swarm optimization, the shape optimization of bridge arch was determined. The concrete volume used in bridge substructure construction and maximum principal tensile stress of concrete arch body was adopted as two objective functions in this study. The optimization problem aims to minimize the two objective functions. Geometric and stress constraints are also included in the problem.FindingsBased on the results presented in the paper, the Pareto front is generated which helps the decision-maker or designer to pick the compromise solution from among 20 optimum designs according to their subjective preferences or engineering judgment, respectively. Moreover, to help the decision-maker, the two multiple objective decision-making methods were used for selection of the best solution from among nondominated solutions.Originality/valueThis research aims to solve an interesting optimization problem in structural engineering. Optimization of arch bridges structure was done for reducing construction costs and increasing safety for the first time.

Effect of coded healing abutment height and position on the trueness of digital intraoral implant scans

Statement of problemInformation regarding the effect of the height and position of a coded healing abutment (CHA) on the trueness of intraoral digital scans is lacking. PurposeThe purpose of this in vitro study was to investigate the effect of the height and position of a scannable CHA on the trueness (distance and angular deviations) of intraoral digital scans. Material and methodsScannable CHAs (BellaTek Encode Impression system; Zimmer Biomet Dental) were used in 2 different height pairs (3 mm and 8 mm) on 2 implants at mandibular left second and first molar positions. Each pair was scanned 10 times by using 1 intraoral scanner (TRIOS; 3Shape) by 1 operator to generate a total of 20 intraoral scan files. Master standard tessellation language (STL) files were created for both 3-mm and 8-mm CHA pairs by using a structured blue light scanner (COMET L3D 8M 150 Precision Structured Blue Light Scanner; ZEISS). These master STL files were imported into a software program (PolyWorks Inspector) and were used as the reference for the inspection. Scans obtained by using the intraoral scanner were aligned to the reference scan by using a best-fit alignment to measure the distance and angular deviations. Two-way repeated-measures ANOVA was used to analyze the data, and the Tukey-Kramer test was used to determine significant differences among groups (α=.05). ResultsThe CHA position had a significant effect on distance deviation (P<.001). However, no significant effect of CHA height on distance deviation was found. The interaction between CHA height and position had a significant effect on the angular deviation (P=.041). The 3-mm posterior CHA (P=.026) and 8-mm anterior CHA (P=.039) had significantly lower angular deviations than the 8-mm posterior CHA. ConclusionsThe distance deviation of CHA was significantly influenced by position. CHAs in the anterior had lower distance deviations for both 3 mm and 8 mm. The effect of CHA height on distance deviation was found to be small and was affected by the location of the CHA. Height affected angular deviation depending on the position of the CHA. Both 3-mm posterior and 8-mm anterior CHAs showed lower angular deviations than the 8-mm posterior CHA.