Probabilistic analysis of peri-implant strain predictions as influenced by uncertainties in bone properties and occlusal forces

Evaluating the Feasibility of Short Dental Implants as Alternatives to Long Dental Implants in Mandibular Bone: A Finite Element Study

This study uses finite element analysis to investigate the potential application of shorter dental implants as a substitute for longer implants in the lower jaw (mandible). FEA allows the evaluation of the stress patterns around the implant-bone interface, a critical factor for successful osseointegration. Ten models were generated, encompassing five long (L1-L5) and five short implant models (S1-S5) with variations in diameter and length. Hypermesh software was utilized to meticulously prepare the FEA models, ensuring accurate mesh generation. The FEA simulations were conducted under four distinct loading scenarios (100 N occlusal load, 40 N lateral load, 100 N oblique at 30°, and 100 N oblique at 45°) to realistically mimic the forces exerted during biting, using an ABAQUS CAE solver. The results revealed that the von Mises stress generated within the short implant models was demonstrably lower compared to their long implants. Additionally, a significant drop in stress was observed with increasing the diameter of the short implants, to a certain diameter range. These findings suggest the potential for successful substitution of long implant model L4 with short implant model S4 due to the demonstrably lower stress values achieved. Furthermore, the data indicates the possibility of utilizing short implant models S3 and S5 as alternatives to long implant models L3 and L5, respectively. These observations hold significant promise for evaluating the feasibility of replacing long implants with shorter variants, potentially leading to a reduction in implant-related failures.

Fatigue life estimation of dental implants using a combination of the finite element method and traditional fatigue criteria

Failure by fatigue can be sudden and catastrophic. Therefore, ensuring that dental implants, which are under constant cyclic loading, do not fail to fatigue is imperative. The majority of the studies about the topic only performed in vitro tests, which are expensive and time-consuming. The Finite Element (FE) method is less costly and it allows the simulation of several different loading scenarios. Nonetheless, there are only a few studies analysing fatigue in dental prostheses using FE models, and the few available did not include all the relevant parameters, such as geometry effect, surface finishing, etc. Therefore, this study aimed to analyse the fatigue behaviour of a single-unit dental implant with two screws using a combination of the numerical results and the traditional fatigue criteria - a combination that was not yet fully and correctly explored. A finite element model comprising a single implant, one abutment, one abutment screw, one fixation screw and one prosthetic crown was developed. Material properties were assigned based on literature data. A 100 N load was applied to mimic the mastication forces and fatigue analysis was conducted using the Gerber, Goodman and Soderberg fatigue criteria. The fatigue analysis demonstrated that the abutment screw could fail in less than 1 year, depending on the criteria, while the fixation screw exhibits an infinite life. The results illustrated the importance of analysing the fatigue behaviour of dental implants and highlighted the potential of finite element models to simulate the biomechanical behaviour of dental implants.

Mandibular reconstruction system reliability analysis using probabilistic finite element method

The aim of this study was to design for mandibular reconstruction of large lateral defect with minimum target reliability with designated confidence interval under bite force range of 300 ± 102 N. The performance of the models has been evaluated by numerical analysis considering the uncertainty of input parameters. Computer-Aided design was used to develop the models of three designs according to the patient's anatomy and to achieve to near symmetry of the mandible. Stress-strength modeling was utilized for the probabilistic physics of failure analysis under assumption of a quasi-static load. Monte-Carlo simulation was also applied for probabilistic finite element analysis and reliability assessment. The sensitivity analysis of the models was developed to reflect the significance of the variables in the models. The deterministic stress analysis shows that the highest stress and the second maximum stress are 110 MPa and 85 MPa for cortical bone around the screws, respectively. Also, it is determined that the maximum plate stress of the titanium conventional plate model is 580 MPa. The reconstruction system success rate was improved in all models by observing the anatomy of the patient's mandible in the plate designs by computer-aided design and additive manufacturing techniques. Based on the results, the reliability of plate strength and pull-out screws strength are 99.99% and 96.71% for the fibula free flap model, respectively, and 99.99% and 94.17%, respectively, for the customized prosthesis model. Probability sensitivity factors showed that uncertainty in the elastic modulus of the cortical bone has the greatest effect on the probability of screws loosening.

Effect of specific retention biomaterials for ball attachment on the biomechanical response of single implant-supported overdenture: A finite element analysis

PURPOSE

The purpose of this finite element analysis (FEA) was to evaluate the effect of specific retention biomaterials with different elastic modulus on the biomechanical response to the axial and off-axial biting loads of a mandibular midline single implant-supported overdenture (SIO) model.

METHODS

Five 3-dimensional (3D) finite element models of an edentulous mandible with SIO were designed as follows: model M with a titanium retentive element for ball attachment, model P with a PEEK retentive element, model S with a silicone resilient liner retentive element, model T with a thermoplastic acrylic resin retentive element made from a CAD-CAM material, and model A with a polyacetal resin retentive element. Posterior bilateral vertical load (PV) at the 1st molar areas and anterior oblique load (AO) at the incisal edge of the mandibular central incisors at a 30-degree angle of 100 N were applied. Stress values were recorded.

RESULTS

Stress values were higher for all models under (AO) loading than under (PV) loading. Model M recorded the highest stress values on the implant, its components, cortical, and cancellous bone under both loading conditions. Under (AO) loading condition, the ball abutment von Mises stress value in model S was almost 7 times lower than that of model M (19 and 130 MPa respectively) and the other 3 models (P, T, and A) (119, 121, and 120 MPa respectively). However, model S recorded the highest value of denture base stress at the attachment area.

CONCLUSIONS

The elastic modulus of retention materials can affect stresses generated on the implant overdenture components and supporting structures.

The effects of bone density and crestal cortical bone thickness on micromotion and peri-implant bone strain distribution in an immediately loaded implant: a nonlinear finite element analysis

Purpose

This study investigated the effects of bone density and crestal cortical bone thickness at the implant-placement site on micromotion (relative displacement between the implant and bone) and the peri-implant bone strain distribution under immediate-loading conditions.

Methods

A three-dimensional finite element model of the posterior mandible with an implant was constructed. Various bone parameters were simulated, including low or high cancellous bone density, low or high crestal cortical bone density, and crestal cortical bone thicknesses ranging from 0.5 to 2.5 mm. Delayed- and immediate-loading conditions were simulated. A buccolingual oblique load of 200 N was applied to the top of the abutment.

Results

The maximum extent of micromotion was approximately 100 μm in the low-density cancellous bone models, whereas it was under 30 μm in the high-density cancellous bone models. Crestal cortical bone thickness significantly affected the maximum micromotion in the low-density cancellous bone models. The minimum principal strain in the peri-implant cortical bone was affected by the density of the crestal cortical bone and cancellous bone to the same degree for both delayed and immediate loading. In the low-density cancellous bone models under immediate loading, the minimum principal strain in the peri-implant cortical bone decreased with an increase in crestal cortical bone thickness.

Conclusions

Cancellous bone density may be a critical factor for avoiding excessive micromotion in immediately loaded implants. Crestal cortical bone thickness significantly affected the maximum extent of micromotion and peri-implant bone strain in simulations of low-density cancellous bone under immediate loading.

Influence of bone parameters on peri-implant bone strain distribution in the posterior mandible

OBJECTIVES

The success rate of dental implants depends on the type of bone at the implant site. The purpose of the present study was to investigate the effects of the bone parameters at the implant-placement site on peri-implant bone strain distributions.

STUDY DESIGN

The morphologies and bone densities of seventy-five potential implant sites in the posterior mandible were measured using computed tomography (CT). Based on the CT data, we defined bone parameters (low and high in terms of cancellous-bone density and crestal-cortical bone density, and thin and thick in terms of crestal-cortical bone thickness), and we constructed finite-element models simulating the various bone types. A buccolingual oblique load of 200 N was applied to the top of the abutment. The von Mises equivalent (EQV) strains in the crestal-cortical bone and in the cancellous bone around the implant were calculated.

RESULTS

Cancellous-bone density greatly affected the maximum EQV strain regardless of the density and thickness of the crestal cortical-bone. The maximum EQV strains in the crestal cortical-bone and the cancellous bone in the low-density cancellous-bone models (of 150 Hounsfield units (HU)) were 1.56 to 2.62-fold and 3.49 to 5.31-fold higher than those in the high-density cancellous-bone models (of 850 HU), respectively. The crestal cortical-bone density affected the maximum EQV strains in the crestal cortical-bone and in the cancellous bone in the low-density cancellous-bone models. The crestal cortical-bone thickness affected the maximum EQV strains in the cancellous bone and in the crestal cortical-bone in the low-density cancellous-bone models.

CONCLUSIONS

Our results confirm the importance of bone types for the peri-implant bone strain distribution. Cancellous-bone density may be a critical factor for peri-implant bone strain.

Influence of Different Soft Liners on Stress Distribution in Peri-Implant Bone Tissue During Healing Period. A 3D Finite Element Analysis

The aim of this study was to evaluate the stress distribution in the bone adjacent to submerged implants during masticatory function in conventional complete dentures with different soft liners through finite element analysis. Three-dimensional models of a severely resorbed mandible with 2 and 4 submerged implants in the anterior region were created and divided into the following situations: (1) conventional complete dentures (control group); and conventional complete dentures with different soft liner materials, (2) Coe-Comfort, (3) Softliner, and (4) Molteno Hard. The models were exported to mechanical simulation software and 2 simulations were done with the load in the inferior right canine (35 N) and the inferior right first molar (50 N). The data were qualitatively evaluated using the maximum principal stress and microstrain values given by the software. The use of soft liners provides decreased levels of stress and microstrains in peri-implant bone when the load was applied to canine teeth. Considering all of the values obtained in this study, the use of softer materials is the most suitable for use during the period of osseointegration.

Life prediction of different commercial dental implants as influence by uncertainties in their fatigue material properties and loading conditions

Probabilistic analyses allow the effect of uncertainty in system parameters to be determined. In the literature, many researchers have investigated static loading effects on dental implants. However, the intrinsic variability and uncertainty of most of the main problem parameters are not accounted for. The objective of this research was to apply a probabilistic computational approach to predict the fatigue life of three different commercial dental implants considering the variability and uncertainty in their fatigue material properties and loading conditions. For one of the commercial dental implants, the influence of its diameter in the fatigue life performance was also studied. This stochastic technique was based on the combination of a probabilistic finite element method (PFEM) and a cumulative damage approach known as B-model. After 6 million of loading cycles, local failure probabilities of 0.3, 0.4 and 0.91 were predicted for the Lifecore, Avinent and GMI implants, respectively (diameter of 3.75mm). The influence of the diameter for the GMI implant was studied and the results predicted a local failure probability of 0.91 and 0.1 for the 3.75mm and 5mm, respectively. In all cases the highest failure probability was located at the upper screw-threads. Therefore, the probabilistic methodology proposed herein may be a useful tool for performing a qualitative comparison between different commercial dental implants.

Effects of magnesium intake deficiency on bone metabolism and bone tissue around osseointegrated implants

OBJECTIVES

This study evaluated the effect of magnesium dietary deficiency on bone metabolism and bone tissue around implants with established osseointegration.

MATERIALS AND METHODS

For this, 30 rats received an implant in the right tibial metaphysis. After 60 days for healing of the implants, the animals were divided into groups according to the diet received. Control group (CTL) received a standard diet with adequate magnesium content, while test group (Mg) received the same diet except for a 90% reduction of magnesium. The animals were sacrificed after 90 days for evaluation of calcium, magnesium, osteocalcin and parathyroid hormone (PTH) serum levels and the deoxypyridinoline (DPD) level in the urine. The effect of magnesium deficiency on skeletal bone tissue was evaluated by densitometry of the lumbar vertebrae, while the effect of bone tissue around titanium implants was evaluated by radiographic measurement of cortical bone thickness and bone density. The effect on biomechanical characteristics was verified by implant removal torque testing.

RESULTS

Magnesium dietary deficiency resulted in a decrease of the magnesium serum level and an increase of PTH and DPD levels (P ≤ 0.05). The Mg group also presented a loss of systemic bone mass, decreased cortical bone thickness and lower values of removal torque of the implants (P ≤ 0.01).

CONCLUSIONS

The present study concluded that magnesium-deficient diet had a negative influence on bone metabolism as well as on the bone tissue around the implants.

Evaluation of functional dynamics during osseointegration and regeneration associated with oral implants

OBJECTIVES

The aim of this paper is to review current investigations on functional assessments of osseointegration and assess correlations to the peri-implant structure.

MATERIAL AND METHODS

The literature was electronically searched for studies of promoting dental implant osseointegration, functional assessments of implant stability, and finite element (FE) analyses in the field of implant dentistry, and any references regarding biological events during osseointegration were also cited as background information.

RESULTS

Osseointegration involves a cascade of protein and cell apposition, vascular invasion, de novo bone formation and maturation to achieve the primary and secondary dental implant stability. This process may be accelerated by alteration of the implant surface roughness, developing a biomimetric interface, or local delivery of growth-promoting factors. The current available pre-clinical and clinical biomechanical assessments demonstrated a variety of correlations to the peri-implant structural parameters, and functionally integrated peri-implant structure through FE optimization can offer strong correlation to the interfacial biomechanics.

CONCLUSIONS

The progression of osseointegration may be accelerated by alteration of the implant interface as well as growth factor applications, and functional integration of peri-implant structure may be feasible to predict the implant function during osseointegration. More research in this field is still needed.