Non-axial Loading Research Articles

Factors associated with abutment screw loosening in single implant supported crowns: A cross-sectional study

BackgroundImplant restorations are considered an ideal treatment option for replacement of missing teeth in partially edentulous patients. Abutment screw loosening is one of the frequently observed technical complications of implant-supported prosthesis. This study aimed to determine the prevalence and factors associated with the abutment screw loosening in cement-retained single-implant crowns. MethodsEnrolment criteria included partially edentulous patients who have been rehabilitated with one or more cement-retained single-implant crowns with minimum postcementation period of 1 year. They were recalled and evaluated for the presence or absence of screw loosening both clinically and radiographically. They were further evaluated for the presence or absence of factors associated with screw loosening such as parafunctional habits, wider occlusal table, steep cuspal inclines, non-axial loading and cantilevering of the pontic. ResultsTwenty-six cement-retained single-implant crowns out of 280 showed screw loosening, making the overall prevalence rate of 10.77%. Among the factors evaluated, parafunctional habits were associated with three cases, wider occlusal table in four, steep cuspal inclines in three, non-axial loading in nine and cantilevering of the pontic in three cases. Exact reasons could not be ascertained in four cases. ConclusionAbutment screw loosening seems to be a significant prosthetic complication of cement-retained single-implant crowns. Factors evaluated significantly affect the functional durability of the prosthesis. These factors should be considered while restoring to enhance the longevity of such restorations.

Effect of rod-to-grain angle on capacity and stiffness of axially and laterally loaded long threaded rods in timber joints

Long threaded rods have recently been widely used as a reinforcement of glued laminated timber in perpendicular to the grain direction. The recent research has thus focused mainly on the withdrawal properties of the threaded rods in the axial direction. Utilizing their large withdrawal stiffness and strength, the threaded rods can also effectively be used as connectors in moment resisting timber joints. Yet, in joints, the threaded rods are often imposed to a non-axial loading, due to inclination of the rod axis to the grain as well as loading direction different from the rod axis. No design models are currently available for the combined axial and lateral loading of the threaded rods. In the present work, the effects of the rod-to-grain and load-to-rod angles on capacity and stiffness of the threaded rods are investigated by use of experiments and finite element models. Based on those, analytical expressions for determining stiffness and capacity of axially and laterally loaded threaded rods are proposed, intended as a basis for practical joint design. Furthermore, effect of various boundary conditions applied at the rod-ends is studied.

Retention force of removable partial dentures with different double crowns.

The aim of the study was to compare the retentive behaviors of double crowns with different designs and material compositions before and after artificial aging. Six pairs of double crowns were fabricated: telescopic crowns 0° made of high-noble metal (group A) or non-precious metal (group B), telescopic zirconia copings with secondary crowns made of electroplated gold 2° (group C), crowns with friction pins 2° made of non-precious metal (group D) or zirconia (group E), and conical crowns 6° made of high-noble metal (group F). Retention forces were assessed before and after artificial aging, and after axial and non-axial loading. Initially, specimens in group D (13.9N), B (12.5N), and E (12.2N) exhibited the highest retention forces. Retention forces in groups A (9.6N), C (7.4N), and F (6.0N) were statistically significantly lower than those of the other groups (p<0.05). After artificial aging, double crowns with additional retention elements exhibited the highest retention forces. The largest retention force losses were evident in groups A (70%), B (64%), C (39%), and F (47%). Double crowns with different designs and made of different materials exhibited different retention forces and different long-term retentive behavior. The highest retention force losses were evident in double crowns with more extended surface contact, such as telescopic crowns. Telescopic crowns with additional retention elements were more resistant to wearing than double crowns without additional retention elements. An additional clinical benefit might be the quick and easy possibility of enhancing retention.

Stress distribution pattern of screw-retained restorations with segmented vs. non-segmented abutments: A finite element analysis.

Background. Screw-retained restorations are favored in some clinical situations such as limited inter-occlusal spaces. This study was designed to compare stresses developed in the peri-implant bone in two different types of screw-retained restorations (segmented vs. non-segmented abutment) using a finite element model. Methods. An implant, 4.1 mm in diameter and 10 mm in length, was placed in the first molar site of a mandibular model with 1 mm of cortical bone on the buccal and lingual sides. Segmented and non-segmented screw abutments with their crowns were placed on the simulated implant in each model. After loading (100 N, axial and 45° non-axial), von Mises stress was recorded using ANSYS software, version 12.0.1. Results. The maximum stresses in the non-segmented abutment screw were less than those of segmented abutment (87 vs. 100, and 375 vs. 430 MPa under axial and non-axial loading, respectively). The maximum stresses in the peri-implant bone for the model with segmented abutment were less than those of non-segmented ones (21 vs. 24 MPa, and 31 vs. 126 MPa under vertical and angular loading, respectively). In addition, the micro-strain of peri-implant bone for the segmented abutment restoration was less than that of non-segmented abutment. Conclusion. Under axial and non-axial loadings, non-segmented abutment showed less stress concentration in the screw, while there was less stress and strain in the peri-implant bone in the segmented abutment.

A Three-dimensional Finite Element Analysis of Stress Distribution in the Cortical Bone in Single Tooth Implant and Post Core-treated Tooth subjected to variable Loads

ABSTRACT Purpose In spite of many advances in the field of prosthetic dentistry, the choice of whether to treat and retain a grossly compromised tooth or to extract and replace with an implant is debatable. Alveolar bone preservation is one of the main criteria to select the treatment option. This is directly affected by the stress generated in the cortical bone under variable loads and is therefore, relevant. Materials and methods Two three-dimensional finite element models were generated in relation to maxillary second premolar using ANSYS software. Model-I was parallel-tapered titanium implant with screw-retained titanium abutment and porcelain fused to metal (PFM) crown. Model-P was fiber post and com- posite resin core with PFM crown. Luting cement was resin cement. Both the models were surrounded by homogeneous and isotropic cortical and cancellous bone, and were subjected to variable loads of 300, 400, and 500 N in axial (0°) and nonaxial (15°, 45°) directions. Results Stress in the cortical bone in megapascal (MPa) in Model-I/Model-P when subjected to variable loads in newtons(N) in axial direction was 300 N - 37.6 MPa/47.3 MPa; 400 N - 50.2 MPa/63.0 MPa; 500 N - 62.7 MPa/63.0 MPa. 15°- 300 N - 68.5 MPa/65.9 MPa; 400 N - 91.3 MPa/87.9 MPa; 500 N - 114.2 MPa/87.9 MPa. 45° - 300 N - 136.3 MPa/88.9 MPa; 400 N - 181.8 MPa/118.5 MPa; 500 N - 227.2 MPa/118.5 MPa. Conclusion Within the limitation of this study, it was concluded that on axial loading, both the treatment modalities showed no significant difference, but on nonaxial loading, the cortical bone in the implant model showed to have considerably higher stress than post core-treated tooth model. Hence, given a choice, this study favors retaining and restoring a compromised tooth with post core and crown rather than extracting and replacing with an implant. How to cite this article Rao S, Arora H, Hameed S. A Three- dimensional Finite Element Analysis of Stress Distribution in the Cortical Bone in Single Tooth Implant and Post Core-treated Tooth subjected to variable Loads. Int J Prosthodont Restor Dent 2017;7(1):8-16.

Pedicle Screw Fixation Under Nonaxial Loads: A Cadaveric Study.

An experimental study of pedicle screw fixation in human cadaveric vertebrae. The aim of this study was to experimentally characterize pedicle screw fixation under nonaxial loading and to analyze the effect of the surgeons' screw and placement choices on the fixation risk of failure. Pedicle screw fixation performance is traditionally characterized with axial pullout tests, which do not fully represent the various tridimensional loads sustained by the screws during correction maneuvers of severe spinal deformities. Previous studies have analyzed the biomechanics of nonaxial loads on pedicle screws, but their effects on the screw loosening mechanisms are still not well understood. A design of experiment (DOE) approach was used to evaluate 2 screw thread designs (single-lead and dual-lead threads), 2 insertion trajectories in the transverse and sagittal planes, and 2 loading directions (lateral and cranial). Pedicle screws were inserted in both pedicles of 12 cadaveric lumbar vertebrae for a total of 24 tests. Four sinewave loading cycles (0-400 N) were applied, orthogonally to the screw axis, at the screw head. The resulting forces, displacements, and rotations of the screws were recorded. In comparison to the other cycles, the first loading cycle revealed important permanent deformation of the bone (mean permanent displacement of the screw head of 0.79 mm), which gradually accumulated over the following cycles to 1.75 mm on average (plowing effect). The cranial loading direction caused significantly lower (P < 0.05) bone deformation than lateral loading. The dual-lead screw had a significantly higher (P < 0.05) initial stiffness than the single-lead thread screw. Nonaxial loads induce screw plowing that lead to bone compacting and subsequent screw loosening or even bone failure, thus reducing the pedicle screw fixation strength. Lateral loads induce greater bone deformation and risks of failure than cranial loads. N/A.

A methodology to assess non-axial loading on the distal radius

Osteoporosis is a worldwide health problem related to bone fragility. Micro-finite element analysis (μFEA) based on high-resolution peripheral quantitative computed tomography (HR-pQCT, Scanco) ima...

The effects of off-axial loading on periimplant marginal bone loss in a single implant

A discrepancy between crown width and implant width may contribute to potential bending overload. The purpose of this study was to evaluate the influence of the crown width-fixture width ratio on crestal bone loss around single dental implants placed in the first molar area. Seventy-six participants (37 men and 39 women; age range, 25-83 years; mean age [standard deviation], 56.3 ±10.6 years) were selected from individuals who were treated with single tooth implants between May 2004 and December 2009 at the Department of Periodontology, Gangnam Severance Dental Hospital. The marginal bone-level change and gingival parameters (modified plaque index and modified sulcus bleeding index) of the periimplant soft tissue were assessed 1 year after functional loading. The perpendicular distances from the vertical axis of each fixture to the most distal aspect of the crown and most mesial aspect of the crown were measured in the periapical radiographic view. No statistically significant relationship was found between crown width-fixture width ratio and the 1-year bone-level change (Pearson correlation, P=.06; Spearman rank test, P=.14). No statistically significant differences in marginal bone-level change were found between axial and nonaxial loading implants (2 independent samples t test; P=.19). The bone-level change for the surface adjacent and distant to the cantilever was not statistically significant (paired t test; P=.10). From this study, it may be concluded that off-axial loading that results from a high crown width-fixture width ratio does not increase the risk for periimplant marginal bone loss after 1-year functional loading.

Complications, Risk Factors, and Failures of Immediate Functional Loading of Implants Placed in the Completely Edentulous Maxillae

The aim of this article was to document the failure of immediate functional loading of implants placed in 3 consecutive completely edentulous maxillae to analyze the possible causes, risk factors, and how to avoid the complications that occur due to this procedure. Six implants with standardized length and diameter were placed in 3 consecutive patients with completely edentulous maxillae in the canine, premolar, and molar region bilaterally and flaplessly using computer-guided surgical guides. Screw-retained conversion maxillary prostheses were delivered immediately after the surgery. Patients complained from severe to moderate pain. For the first and second patients (P1 and P2), 4 implants per patient were lost during the second week after implant surgery, whereas 5 implants were lost during the third week after implant surgery for the third patient (P3). This high failure rate presented in this report may be explained by 1 or more of the following reasons: poor maxillary bone quality, nonaxial loading of the implants, nonrigid splinting material, high forces delivered from the opposing dentition, and/or patients with para-functional habits.

Photoelastic analysis of fixed partial prosthesis crown height and implant length on distribution of stress in two dental implant systems.

The aim of this study was to evaluate by photoelastic analysis stress distribution on short and long implants of two dental implant systems with 2-unit implant-supported fixed partial prostheses of 8 mm and 13 mm heights. Sixteen photoelastic models were divided into 4 groups: I: long implant (5 × 11 mm) (Neodent), II: long implant (5 × 11 mm) (Bicon), III: short implant (5 × 6 mm) (Neodent), and IV: short implants (5 × 6 mm) (Bicon). The models were positioned in a circular polariscope associated with a cell load and static axial (0.5 Kgf) and nonaxial load (15°, 0.5 Kgf) were applied to each group for both prosthetic crown heights. Three-way ANOVA was used to compare the factors implant length, crown height, and implant system (α = 0.05). The results showed that implant length was a statistically significant factor for both axial and nonaxial loading. The 13 mm prosthetic crown did not result in statistically significant differences in stress distribution between the implant systems and implant lengths studied, regardless of load type (P > 0.05). It can be concluded that short implants showed higher stress levels than long implants. Implant system and length was not relevant factors when prosthetic crown height were increased.

Influence of implant with different dimensions and designs in ideal stress distribution in bone for application in compromised situations: Analysis by three-dimensional finite element method

Background : To determine the value and direction of the stress and strain across the different implants placed in the bone when loaded with normal or heavy forces; with either a healthy or compromised anatomical condition is always a controversial topic with quite a bit of ambiguity. Studies suggest more favorable stress distribution in bone with a wider diameter implant and by selecting threaded implant. Ideally 12 mm implant length needs to be maintained in favorable condition but the same rule cannot be applied in compromised anatomical conditions. There is a need for a study to evaluate the favorable stress distribution in bone using different implant dimensions and designs both threaded and nonthreaded, to achieve a better control over loading and stress release. Objectives: A finite element analysis (FEA) study was designed to study ideal stress distribution in cancellous and cortical bone under axial and nonaxial loading using, (1) different implant dimensions and (2) designs. Materials and Methods: A finite element models of eight dental implants with crowns were modeled using Catia, a modeling software with material properties as limitation (FEA elements = 113,388, FEA nodes = 173,212). Results: Magnitude of stresses along the implants and surrounding bone did not increase appreciably when the implant length was changed from 10 to 14 mm. With the increase in implant diameter, the stress levels within the bone reduced in threaded implant and in nonthreaded implant the stress levels increased.Conclusion: The results indicate that, for implants with a wider diameter and in threaded implant with a shorter length, there was favorable distribution of stress and strain pattern during axial and nonaxial loading.

Microstrain Around Dental Implants Supporting Fixed Partial Prostheses Under Axial and Non–Axial Loading Conditions, In Vitro Strain Gauge Analysis

The current study used strain gauge analysis to perform an in vitro evaluation of the effect of axial and non-axial loading on implant-supported fixed partial prostheses, varying the implant placement configurations and the loading points. Three internal hexagon implants were embedded in the center of each polyurethane block with in-line and offset placements. Microunit abutments were connected to the implants using a torque of 20 N · cm, and plastic prosthetic cylinders were screwed onto the abutments, which received standard patterns cast in Co-Cr alloy (n = 10). Four strain gauges (SGs) were bonded onto the surfaces of the blocks, tangentially to the implants: SG 01 mesially to implant 1, SG 02 and SG 03 mesially and distally to implant 2, respectively, and SG 04 distally to implant 3. Each metallic structure was screwed onto the abutments using a 10-N·cm torque, and axial and non-axial loads of 30 kg were applied at 5 predetermined points. The data obtained from the strain gauge analyses were analyzed statistically through the repeated measures analysis of variance and the Tukey test, with a conventional level of significance of P < 0.05. The results showed a statistically significant difference for the loading point (P = 0.0001), with point E (nonaxial) generating the highest microstrain (327.67 μ[Latin Small Letter Open E]) and point A (axial) generating the smallest microstrain (208.93 μ[Latin Small Letter Open E]). No statistically significant difference was found for implant placement configuration (P = 0.856). It was concluded that the offset implant placement did not reduce the magnitude of microstrain around the implants under axial and non-axial loading conditions, although loading location did influence this magnitude.

Predicting Peri-implant Stresses Around Titanium and Zirconium Dental Implants—A Finite Element Analysis

Due to anatomical and surgical constrains the implant placement may not be parallel to each other always. Non-parallel implants are subjected to detrimental stresses at implant bone interface. Also depending on type of implant material i.e. titanium or zirconium, stresses tend to vary due to change in physical and mechanical properties. Hence stress analysis at implant bone interface between different parallel and non-parallel implants becomes significant. Evaluation and comparison of stress distribution in the bone around two parallel and non-parallel titanium and zirconium dental implants on axial and non-axial loading supporting three unit fixed prosthesis. Three dimensional finite element models (M1, M2, M3) were made of three differently angulated implants in ANSYS (11.0 Version) software and P4 processor with a speed of 3GHz and 3Gb RAM hardware, common for titanium and zirconium implants. Stress around the implants was analyzed on an axial load of 200N and a non-axial load of 50N. In both titanium and zirconium implants on axial loading in cortical bone, higher stresses were observed in M3 followed by M2 and M1. On non-axial loading higher stresses were observed in M2, followed by M3 and M1. In both titanium and zirconium implants on axial and non-axial loading in cancellous bone stresses were higher in M3 followed by M2 and M1. Zirconium implants showed lower stresses in cortical bone and higher stresses in cancellous bone compared to titanium implants. Over all Stresses in the bone were more due to titanium implants than zirconium implants. Zirconium implants led to lower peri-implant stresses than titanium implants.

An organized start to implant-supported prosthesis

Various treatment options are available for rehabilitating the complete edentulous patients with implants. However, due consideration for the prosthesis is not given prior to implant surgery. This can result in implant being placed in locations that do not provide the best esthetic and functional result. Incorrect implant localization and angle are the primary cause of non-axial loading and may contribute to loss of Osseo-integration. For predictable outcome, the treatment should begin with visualizing the end result. A step-wise pre-implant surgery evaluation is necessary to achieve the objectives. This is a case report of a completely edentulous patient who was treated with fixed implant prosthesis following various steps in the pre-implant surgery evaluation.

Straight and Offset Implant Placement under Axial and Nonaxial Loads in Implant‐Supported Prostheses: Strain Gauge Analysis

The aim of this in vitro study was to quantify strain development during axial and nonaxial loading using strain gauge analysis for three-element implant-supported FPDs, varying the arrangement of implants: straight line (L) and offset (O). Three Morse taper implants arranged in a straight line and three implants arranged in an offset configuration were inserted into two polyurethane blocks. Microunit abutments were screwed onto the implants, applying a 20 Ncm torque. Plastic copings were screwed onto the abutments, which received standard wax patterns cast in Co-Cr alloy (n = 10). Four strain gauges were bonded onto the surface of each block tangential to the implants. The occlusal screws of the superstructure were tightened onto microunit abutments using 10 Ncm and then axial and nonaxial loading of 30 Kg was applied for 10 seconds on the center of each implant and at 1 and 2 mm from the implants, totaling nine load application points. The microdeformations determined at the nine points were recorded by four strain gauges, and the same procedure was performed for all of the frameworks. Three loadings were made per load application point. The magnitude of microstrain on each strain gauge was recorded in units of microstrain (με). The data were analyzed statistically by two-way ANOVA and Tukey's test (p < 0.05). The configuration factor was statistically significant (p= 0.0004), but the load factor (p= 0.2420) and the interaction between the two factors were not significant (p= 0.5494). Tukey's test revealed differences between axial offset (με) (183.2 ± 93.64) and axial straight line (285.3 ± 61.04) and differences between nonaxial 1 mm offset (201.0 ± 50.24) and nonaxial 1 mm straight line (315.8 ± 59.28). There was evidence that offset placement is capable of reducing the strain around an implant. In addition, the type of loading, axial force or nonaxial, did not have an influence until 2 mm.

Peri-Implant Biomechanical Responses to Standard, Short-Wide, and Mini Implants Supporting Single Crowns Under Axial and Off-Axial Loading (an In Vitro Study)

This study compared the biomechanical responses of 3 single crowns supported by 3 different implants under axial and off-axial loading. A standard implant (3.75 mm diameter, 13 mm length), a mini implant (3 mm diameter, 13 mm length), and a short-wide implant (5.7 mm diameter, 8 mm length) were embedded in epoxy resin by the aid of a surveyor to ensure their parallelism. Each implant supported a full metal crown made of Ni-Cr alloy with standardized dimensions. Strain gauges and finite element analysis (FEA) were used to measure the strain induced under axial and off-axial functional loads of 300 N. Results showed that mini implants recorded the highest microstrains, under both axial and off-axial loading. All implants showed a considerable increase in strain values under off-axial loading. Standard and short-wide implants proved to be preferable in supporting crowns, as the standard implant showed the lowest strains under axial and off-axial loading using FEA simulation, while the short-wide implant showed the lowest strains under nonaxial loading using strain gauge analysis.

Influence of Implant Surface Topography and Loading Condition on Stress Distribution in Bone Around Implants: A Comparative 3D FEA

A three-dimensional Finite Element Method was used to study the influence of porous coated surface topography of an implant on stress and strain distribution pattern in the cortical and cancellous bone during axial and non-axial loading. Two implants, one with porous surface topography and one with smooth surface were embedded in separate geometric models of posterior mandibular region which was generated using a CT scan data. Material properties and boundary conditions were applied. Load of 100 and 50N were applied on to the abutment from axial and non-axial directions respectively. Porous surface topography appeared to distribute stress in a more uniform pattern around the implant with near absence of stress in the apical region of implant. Smooth surfaced implant showed high punching stress at the apex of the implant. The porous coated interface was considered to simulate the shock absorbing behavior of periodontal ligament of natural dentition. Maximum amount of stress concentration was observed in the cortical bone which plays a major role in the dissipation of the stress.

Study of Biomechanics of Porous Coated Root Form Implant Using Overdenture Attachment: A 3D FEA

The purpose of this article is to do a three-dimensional finite element stress analysis, in relation to root form implant supported by overdenture attachment, during axial and non-axial loading. Two porous coated Titanium-aluminum-vanadium (Ti-6Al-4V) implants with overdenture abutment were embedded in both simple and 3D model of interforaminal region of mandible. The material properties of tissue ingrowth bonded interface were calculated considering Iso-Strain condition. The masticatory forces: axial load of 35N, a horizontal load of 10N, and an oblique load of 120N, was applied for the two qualities of cancellous bone. It implied that porous topography of the implant led to optimal stress transfer at the tissue ingrowth bonded interface and insignificant punching stress at the apex than a smooth surface implant. The inferior bone quality was deformed even under physiologic loads and showed wider stress pattern. Simulated implant abutment to implant bone interface stress may be significantly affected by the quality of the bone and the surface topography of the implant. The interface is affected to a lesser extent by the prosthetic material properties. Threedimensional anatomical model was more close to reality than the geometry of much simpler altered models.

Study on the In Situ SEM Tension Observation of E-A356 Alloys

The fracture mechanisms of E-A356 alloys (T5 treatment) have been investigated by means of in situ SEM under nonaxial tension loading. It is found that the crack initiated at the casting defects, such as at the gas or the shrinkage pores, because of the debonding of the silicon particles from the Al matrix. The crack propagation was mainly in the Al matrix and along the matrix/particle interface secondarily. The crack growth could be influenced by the eutectic silicon particles, when it encountered the Si particles, the growth direction would be changed and turned toward the weaker areas. The fracture resistance or the mechanical properties of the E-A356 alloys will be improved by means of reducing, eliminating gas or shrinkage pores and increasing the interface bound strength of the eutectic silicon particles with the Al matrix.

Radiographic and surgical guide for placement of multiple implants

It is the responsibility of the restorative dentist to fabricate a surgical guide that dictates to the surgeon exact placement of each implant.1 Misaligned implants complicate the clinical and laboratory procedures in the fabrication of definitive restorations.2 The nonparallel placement of implants, especially when multiple implants are placed, can cause nonaxial loading during function, which may compromise the long-term success of the implants.3,4