Finite element analysis of implant-supported prosthesis with pontic and cantilever in the posterior maxilla

Biomechanical Evaluation of Cantilevered 2-Unit Implant-Supported Prostheses: A 3D Finite Element Study

OBJECTIVE

To assess the biomechanical performance of cantilevered 2-unit implant-supported prostheses with zirconia and polyetherketoneketone (PEKK) under 3 loading conditions.

METHOD

A cone beam computer tomography (CBCT) scan of an edentulous mandible was segmented using Mimics software and refined in 3-Matic software to create trabecular and cortical bone structures. Implant CAD files were integrated using SolidWorks software, generating 4 models with varying implant positions: M1 (first premolar implant supporting a second premolar), M2 (second premolar implant supporting a first premolar), M3 (second premolar implant supporting a first molar), and M4 (first molar implant supporting a second premolar). Prostheses were constructed from zirconia or PEKK. Finite element analysis (FEA) in ANSYS software simulated static loading: vertical (100 N) and oblique (30° and 45°, 50 N). von Mises stress and total deformation were analyzed.

RESULTS

Vertical loading showed the highest von Mises stress at cantilever connectors, with M3 displaying the highest cortical bone stress (117 MPa). Zirconia models had slightly higher prosthetic stress, while PEKK models exhibited greater implant and cortical bone stress. Oblique loading caused higher stress in implants and prostheses but remained below yield limits. Maximum deformation was under 25 micrometers for the implant and bone, and 65 micrometers for the prosthesis.

CONCLUSION

Single implants can support 2-unit cantilevered prostheses when additional implants are unfeasible. The location of the cantilever has minimal impact compared to its size, as a larger cantilevered part increases stress. Zirconia better resists bending forces and reduces implant stress compared to PEKK.

CLINICAL SIGNIFICANCE

This study guides prosthodontists in designing 2-unit implant-supported prostheses, emphasizing that multiple implants optimize stress distribution, and that zirconia is preferable for cantilevered designs.

Comparison of fracture resistance of implant-supported fixed prothesis substructure materials with different cross-sectional geometry

BACKGROUND

The aim of this study was to compare fracture resistance after thermomechanical ageing of prosthetic substructure materials with different connector designs.

METHODS

Three different prosthetic substructure materials were used in this study: (1) GroupZir: (Zirconia, Fusion ceram, Turkey), (2)GroupPEEK (PEEK, Whitepeaks, CopraPeek, Essen, Germany), (3)GroupFRC (Fibre-reinforced composite, Trinia, Bicon Implant, Rep. of Ireland). A total of 72 implant-supported prosthesis triangular, square, and oval connector designs were created between 2nd premolar and mandibular 2nd molar teeth. After adhesion to the implant abutments with resin cement (Pentron breeze, Kerr), the samples were applied with dynamic loading and thermomechanical ageing (120,000 cycles,120 N,5-55 °C). Fracture resistance values were obtained with a universal test device and SEM images were analysed. The analyses were performed with Two-Way ANOVA and the Tukey test (SPSS 23.00).

RESULTS

Both the material and the connector type were found to affect the fracture resistance (F = 8.354, p < 0.05). The highest fracture resistance value was obtained from the triangular shape in GroupZir(3200 ± 91.05) and the lowest from the oval connector design of GroupPEEK material (2410 ± 157.23). Statistically significant differences were determined in the different connector designs of GroupZir(p < 0.05). In the comparisons made according to connector design, a significant difference was obtained between GroupZir and GroupPEEK and between GroupZir and GroupFRC. Deformations were observed in the fracture pattern of the Group Zir samples and deformations in the form of rupture were seen in the GroupPEEK and GroupFRC material samples.

CONCLUSIONS

The study results demonstrated that the fracture resistance of zirconia, PEEK, and FRC restorations over 3-unit implants with different connectors is affected by connector design. All the materials were seen to be comparable in respect of the forces formed in chewing dynamics.

Biomechanical behavior of cantilevered 3-unit implant-supported prostheses made of PEKK and monolithic zirconia: A finite element study

OBJECTIVE

To evaluate the biomechanical performance of various designs of cantilevered three-unit implant-supported prostheses, using two distinct prosthetic materials and under different loading conditions.

METHOD

Three mandibular models were created with varying implant positions to support a 3-unit prosthesis using two materials (Zirconia and PEKK), resulting in three different designs: distal cantilever (M1), fixed-fixed (M2), and mesial cantilever (M3). The geometric model was created by segmenting a CBCT scan of an edentulous mandible using Mimics software, followed by refinement in 3-Matic to generate a trabecular bone core encased by a 2 mm-thick cortical shell and a 1 mm-thick mucosal layer. Implant CAD files were integrated, and the models were processed in SolidWorks to finalize solid geometries. These were then imported into ANSYS for mesh generation and finite element analysis, with materials assumed to be isotropic and elastic. Models underwent 3 different static loading protocols (Vertical 100 N, 30° Oblique 50 N, 45° Oblique 50 N). Von Mises stress and total deformation were calculated.

RESULTS

Model 2 demonstrated the best performance. Under vertical loading, PEKK prostheses showed lower stress than zirconia in the prosthetic body (10-45 %) and the cortical bone (3-40 %), but higher stresses in the implant (4-10 %). Compared to vertical loading, oblique loading generated higher stress but remained within a safe range without compromising function.

CONCLUSION

The fixed-fixed design showed optimal biomechanical performance. The mesial cantilever was more favorable than the distal for stress distribution. Zirconia provided superior stress dissipation, while PEKK showed reduced stress in the prosthetic body but increased stress I the implant and bone.

CLINICAL SIGNIFICANCE

The study provides prosthodontists with evidence recommending design and materials for 3-unit implant-supported prostheses. Zirconia is ideal for cantilevered designs, resisting high bending forces and minimizing implant stress, while PEKK is more suitable for fixed-fixed designs with lower stress levels.

Occlusion and Biomechanical Risk Factors in Implant-Supported Full-Arch Fixed Dental Prostheses-Narrative Review

The biophysiological differences between teeth and dental implants and the issue of occlusal overload, although controversial, form the basis for the management of occlusion in implant-supported full-arch fixed dental prostheses (ISFAFDPs). Although there is currently a lack of scientific evidence on occlusal management, it is clear that the favorable prognosis of ISFAFDPs is linked to a correct understanding of the biomechanical principles involved. In the design of ISFAFDPs, the lack of proprioceptive feedback requires special attention to biomechanical factors: minimizing overloading complications and providing biomechanical stability are among the main goals of the occlusion. In ISFAFDPs, the occlusion must be decided on the basis of several factors that influence the loads on prosthesis and implants: each case must be evaluated individually and requires a personalized occlusion. The main aim of this narrative review is to provide an overview of the occlusal principles and materials that can be used in ISFAFDPs based on the data currently available in the literature. Practical clinical recommendations for the occlusion management of ISFAFDPs and a biomechanical risk score index to personalize implant-prosthetic treatment are proposed.

Implant-supported fixed prostheses with cantilever: a systematic review and meta-analysis

PURPOSE

This systematic review (SR) aimed to investigate whether the presence of a cantilever affects the results of implant treatment for partial edentulism, including an analysis of the anterior and posterior regions of the dental arches.

METHODS

An electronic search was performed, and original articles published between 1995 and November 2023 were included. The outcomes were the implant survival rate, patient satisfaction, occurrence of mechanical complications, and marginal bone loss around the implants. Two SR members independently examined the validity of the studies, extracted evidence from the included studies, and performed risk of bias assessment, comprehensive evidence evaluation, and meta-analysis.

RESULTS

Nine studies met our inclusion criteria. Implant survival rate tended to be lower in the cantilever group, and marginal bone loss tended to be higher in the cantilever group; however, there was no significant difference. There was no significant difference in patient satisfaction based on the presence or absence of a cantilever. Moreover, the incidence of mechanical complications was significantly higher in the cantilever group. According to the analysis of anterior and posterior regions, implant survival rate tended to be lower in the cantilever group of the posterior region, and marginal bone loss around the implants tended to be higher in the cantilever group of the anterior region.

CONCLUSION

Implant-supported fixed prostheses with cantilevers did not negatively affect implant survival rate, marginal bone loss, or patient satisfaction. However, the incidence of mechanical complications significantly increased in the cantilever group.

Single missing molar with wide mesiodistal length restored using a single or double implant-supported crown: A self-controlled case report and 3D finite element analysis

PURPOSE

Based on a self-controlled case, this study evaluated the finite element analysis (FEA) results of a single missing molar with wide mesiodistal length (MDL) restored by a single or double implant-supported crown.

METHODS

A case of a missing bilateral mandibular first molar with wide MDL was restored using a single or double implant-supported crown. The implant survival and peri-implant bone were compared. FEA was conducted in coordination with the case using eight models with different MDLs (12, 13, 14, and 15 mm). Von Mises stress was calculated in the FEA to evaluate the biomechanical responses of the implants under increasing vertical and lateral loading, including the stress values of the implant, abutment, screw, crown, and cortical bone.

RESULTS

The restorations on the left and right sides supported by double implants have been used for 6 and 12 years, respectively, and so far have shown excellent osseointegration radiographically.The von Mises stress calculated in the FEA showed that when the MDL was >14 mm, both the bone and prosthetic components bore more stress in the single implant-supported strategy. The strength was 188.62-201.37 MPa and 201.85-215.9 MPa when the MDL was 14 mm and 15 mm, respectively, which significantly exceeded the allowable yield stress (180 MPa).

CONCLUSIONS

Compared with the single implant-supported crown, the double implant-supported crown reduced peri-implant bone stress and produced a more appropriate stress transfer model at the implant-bone interface when the MDL of the single missing molar was ≥14 mm.

Influence of a mesial cantilever on stress, strain, and axial force in fixed partial dentures with a distally tilted implant in the atrophic posterior maxilla

PURPOSE

This study aimed to investigate whether the presence of a mesial cantilever influences the biomechanical behavior and screw loosening in fixed partial dentures (FPDs) with a distally tilted implant in the atrophic posterior maxilla and where to best place the distal implant.

METHODS

Two configurations of implant-supported four-unit FPDs were modelled using finite element analysis. Five interabutment distances were considered. The stress and strain distributions in the implants, abutments, and prosthetic screws were verified under occlusal loading. The development of the axial force on the abutments and screws was also examined. Two-sample t-tests were used to identify differences (P < 0.05).

RESULTS

The von Mises stress distributions of the components in the two configurations were similar, as were the maximum plastic strains of the distal prosthetic screws, distal implants, and 30° abutments. The difference in the maximum plastic strains of the straight abutments was statistically significant. The preload of the 30° abutment screws was significantly reduced after the initial loading. In the absence of a mesial cantilever, the axial force on the straight abutments increased. However, when a mesial cantilever was used, the preload of the straight abutments was maintained, and the axial force on the prosthetic screws fluctuated less. The axial force fluctuation of the abutments gradually decreased as the interabutment distance increased.

CONCLUSIONS

Mesial cantilever usage had minimal effect on stress or strain distribution in FPD implants, abutments, or prostheses. However, it helped resist screw loosening. The distal screw access hole was preferably positioned close to the prosthetic end.

Impact of type and position of abutment connection on microstrain distribution: an in vitro study

PURPOSE

The aim of this study was to investigate microstrains around two non-parallel implant-supported prostheses and different abutment connections and positions under vertical static load using strain gauges.

MATERIALS AND METHODS

4 models simulating the mandibular unilateral free-end were fabricated. 8 implants (4.0 × 10 mm and 5.0 × 10 mm) were inserted in the second premolar, perpendicular to the occlusal plane, and the second molar, tilted at 15°. Four groups were analyzed: engaging and angled abutments (control group), both non-engaging abutments, both screw-and cement-retained prosthesis (SCRP) abutments, and engaging and non-engaging abutments. Strain gauges were placed buccally, lingually, mesially, and distally adjacent to each implant. The restoration was cement-retained in the control group and screw and cement-retained in the rest. Zirconia bridges were fixed on the abutment with NX3, and a 300 N vertical static load was applied. Microstrains were recorded and analyzed.

RESULTS

Both non-engaging abutments showed the highest compressive microstrains (-52.975), followed by engaging, angled abutment (-25.239). SCRP-SCRP abutments had the lowest compressive microstrains (-14.505), while the engaging, non-engaging abutments showed tensile microstrains (0.418). Microstrains in SCRP-SCRP and engaging, non-engaging groups were significantly lower than in the control group (α = .05). Premolar areas showed compressive microstrains (-47.06), while molar sites had tensile microstrains (+0.91), with microstrains in premolars being significantly higher than in molar area (α = .05).

CONCLUSION

The types of abutment connections and positions may have a potential effect on microstrains at the implant-bone interface. SCRP-SCRP abutments could be an alternative to use in non-parallel implant-supported prostheses when two implants make an angle of no more than 20 degrees.

Clinical and radiographic outcomes of implant-supported fixed prostheses with cantilever extension in anterior mandible: A retrospective study

OBJECTIVES

The objective of this study is to analyze the clinical and radiographic outcomes of implant-supported fixed protheses with cantilever extensions (ISFPCs) in the partially edentulous anterior mandible.

MATERIALS AND METHODS

Patients who received anterior mandible implant restoration between January 2016 and December 2021 were included. Patients with two, three, or four continuous missing teeth receiving adjacent implant supported single-unit crowns (ISSCs), ISFPCs, implant-supported fixed protheses without cantilever extensions (ISFPNs) were divided into groups: ISSC+ISSC, ISFPC, ISSC+ISFPC, three-unit ISFPN, ISFPC+ISFPC, or four-unit ISFPN, respectively. We recorded and evaluated survival rates, mechanical and biological complications, peri-implant marginal bone loss (MBL), esthetic outcomes, and patient perceptions. Statistical analysis was performed using linear mixed models (LMM).

RESULTS

The study included 87 patients and 152 implants. No implant loss occurred during an average follow-up of 3.48 ± 1.85 years (range: 1-7 years). According to LMM models, prosthetic type had a statistically significant impact on MBL during follow-up periods, in favor of the ISFPC and ISFPC+ISFPC groups (0.16 ± 0.48 mm vs. 0.51 ± 0.49 mm, p = .034; 0.22 ± 0.49 mm vs. 0.60 ± 0.62 mm, p = .043, respectively). Mechanical and biological complications were relatively low and comparable. The four-unit ISFPC group had higher subjective esthetic scores compared with the ISSC+ISSC group (98.6 vs. 83.8, p < .05), and patients in the ISFPC+ISFPC group expressed greater satisfaction with cleanability than the ISFPN group (98.8 vs. 80.6).

CONCLUSION

ISFPCs offer a highly predictable treatment option in the anterior mandible, characterized by high survival rates, and comparable complication rates, peri-implant bone stability and esthetics to adjacent ISSCs or ISFPNs.

Material and abutment selection for CAD/CAM implant-supported fixed dental prostheses in partially edentulous patients - A narrative review

Restorative material selection has become increasingly challenging due to the speed of new developments in the field of dental material science. The present narrative review gives an overview of the current indications for implant abutments and restoration materials for provisional and definitive implant-supported fixed dental prostheses in partially edentulous patients. For single implant restorations, titanium base abutments for crowns are suggested as an alternative to the conventional stock- and customized abutments made out of metal or zirconia. They combine the mechanical stability of a metallic connection with the esthetic potential of ceramics. For multiple-unit restorations, conical titanium bases especially designed for bridges are recommended, to compensate for deviating implant insertion axes and angulations. Even though titanium base abutments with different geometries and heights are available, certain clinical scenarios still benefit from customized titanium abutments. Indications for the definitive material in fixed implant restorations depend on the region of tooth replacement. In the posterior (not esthetically critical) zone, ceramics such as zirconia (3-5-Ymol%) and lithium-disilicate are recommended to be used in a monolithic fashion. In the anterior sector, ceramic restorations may be buccally micro-veneered for an optimal esthetic appearance. Lithium-disilicate is only recommended for single-crowns, while zirconia (3-5-Ymol%) is also recommended for multiple-unit and cantilever restorations. Attention must be given to the specific mechanical properties of different types of zirconia, as some feature reduced mechanical strengths and are therefore not indicated for all regions and restoration span lengths. Metal-ceramics remain an option, especially for cantilever restorations.

Mechanical and modal analysis of different implant strategies for loss of three teeth with bone atrophy in the maxillary posterior region

PURPOSE

This study aimed to evaluate the stress distribution and secondary stability involved in five implant strategies, including implant-supported prostheses (ISP) and tooth-implant-supported prostheses (TISP), used for bone atrophy in the maxillary posterior region with teeth loss using finite element analysis, and to explore the more desirable implant methods.

METHODS

Five implant strategies were made to analyze and compare: M1, implant-supported prosthesis consisting of a short implant with a regular implant; M2, implant-supported prosthesis consisting of a tilted implant with a regular implant; M3, cantilever structure; M4, tooth-implant-supported prosthesis consisting of a short implant with a regular implant; M5, tooth-implant-supported prosthesis consisting of a regular implant, and M6, with only the natural teeth as a control group. Dynamic loading of the above models was performed in finite element analysis software to assess the stress distribution of the bone tissue and implants using the von Mise criterion. Finally, the secondary stability of different models was evaluated by modal analysis.

RESULTS

The maximum stress distribution in the cortical bone in M1(60 MPa) was smaller than that in M2(97 MPa) and M3(101 MPa), The first principal strain minimum was obtained in M2 (2271μ ε ). M4 (33 MPa, 10085 Hz) with the best mechanical properties and highest resonance frequency. But increased the loading on the natural teeth.

CONCLUSIONS

Short implants and tilted implants are both preferred implant strategies, if cantilever construction is necessary, a tooth-implant-supported prosthesis consisting of a short implant and a regular implant is recommended.

Biomechanical behavior of implant retained prostheses in the posterior maxilla using different materials: a finite element study

BACKGROUND

The aim of this study is to evaluate the biomechanical behavior of the mesial and distal off-axial extensions of implant-retained prostheses in the posterior maxilla with different prosthetic materials using finite element analysis (FEA).

METHODS

Three dimensional (3D) finite element models with three implant configurations and prosthetic designs (fixed-fixed, mesial cantilever, and distal cantilever) were designed and modelled depending upon cone beam computed tomography (CBCT) images of an intact maxilla of an anonymous patient. Implant prostheses with two materials; Monolithic zirconia (Zr) and polyetherketoneketone (PEKK) were also modeled .The 3D modeling software Mimics Innovation Suite (Mimics 14.0 / 3-matic 7.01; Materialise, Leuven, Belgium) was used. All the models were imported into the FE package Marc/Mentat (ver. 2015; MSC Software, Los Angeles, Calif). Then, individual models were subjected to separate axial loads of 300 N. Von mises stress values were computed for the prostheses, implants, and bone under axial loading.

RESULTS

The highest von Mises stresses in implant (111.6 MPa) and bone (100.0 MPa) were recorded in distal cantilever model with PEKK material, while the lowest values in implant (48.9 MPa) and bone (19.6 MPa) were displayed in fixed fixed model with zirconia material. The distal cantilever model with zirconia material yielded the most elevated levels of von Mises stresses within the prosthesis (105 MPa), while the least stresses in prosthesis (35.4 MPa) were recorded in fixed fixed models with PEKK material.

CONCLUSIONS

In the light of this study, the combination of fixed fixed implant prosthesis without cantilever using a rigid zirconia material exhibits better biomechanical behavior and stress distribution around bone and implants. As a prosthetic material, low elastic modulus PEKK transmitted more stress to implants and surrounding bone especially with distal cantilever.

Splinting or non-splinting of fixed prostheses on adjacent implants: A critical review

PURPOSE

The present study aimed to identify, through a critical review of the literature, the success factors associated with the splinting of fixed prostheses on adjacent implants of the posterior sectors in partially edentulous patients compared with those not splinted.

STUDY SELECTION

A MEDLINE strategy was implemented based on a research question to systematically search and extract information from databases (PubMed and Scopus) using MeSH terms/keywords identified for each domain. Systematic reviews, clinical and in vitro studies were selected and classified according to eligibility criteria based on the research question and level of evidence using the PRISMA flowchart.

RESULTS

A total of 32 studies were selected for data extraction and analysis according to study design (three systematic reviews, 14 clinical studies, and 15 in vitro studies). Overall, the studies found no significant difference in the association between the survival rate and prosthesis type. In clinical studies, there have been no differences in marginal bone loss between splinted and non-splinted prostheses, and the influence of peri-implant status and restorative materials has been poorly evaluated. The distribution of stress and loads determined in the in vitro studies showed results that could favor splinted prostheses; however, are generally associated with implant design.

CONCLUSIONS

The need for splinted or non-splinted adjacent implant-supported prostheses remains controversial. The reviewed evidence indicates that factors such as implant size and its relationship with coronal height could be important in decision-making.

Effect of implant type on the stability of cantilever fixed dental prostheses: An in vitro study

OBJECTIVES

To simulate the replacement of a premolar with an implant-supported cantilever fixed dental prosthesis (ICFDP) and how the fracture load is affected by implant type, positioning within the zirconia blank, and aging protocol.

MATERIALS AND METHODS

Seventy-two ICFDPs were designed either within the enamel- or dentin layer of a 4Y-PSZ blank for bone-level and tissue-level titanium-zirconium implants. Fracture load was obtained on the cantilever at baseline (no aging) or after aging in a chewing simulator with the load applied within the implant axis (axial aging) or on the cantilever (12 groups with n = 6). A three-way ANOVA was applied (α = .05).

RESULTS

A three-way ANOVA revealed a significant effect on fracture load values of implant type (p = .006) and aging (p < .001) but not for the position within the zirconia blank (p = .847). Fracture load values significantly increased from baseline bone level (608 ± 118 N) and tissue level (880 ± 293 N) when the implants were aged axially, with higher values for tissue level (1065 ± 182 N) than bone level (797 ± 113 N) (p < .001). However, when the force was applied to the cantilever, fracture load values decreased significantly for tissue-level (493 ± 70 N), while values for bone-level implants remained stable (690 ± 135 N).

CONCLUSIONS

For ICFDPs, the use of bone-level implants is reasonable as catastrophic failures are likely to be restricted to the restoration, whereas with tissue-level implants, the transmucosal portion of the implant is susceptible to deformation, making repair more difficult.

Anterior provisional fixed partial dentures: A finite element analysis

PURPOSE

The aim of this study was to analyze the stress distribution of fiber-reinforced composite provisional fixed partial denture utilizing a finite element analysis model.

MATERIAL AND METHODS

Three anterior teeth were collected: upper right central, left central, and right lateral incisors. A fiber-reinforced composite strip was applied to the palatal surfaces of the teeth. Micro-computed tomographic scans were acquired of the models in order to generate three-dimensional geometrical replicas. Finite element analysis was used to assess the stress distribution of fiber-reinforced composite provisional fixed partial denture using different pontic types under static applied forces that were 100, 30, and 0 N.

RESULTS

The maximum stress values were found on the unprepared natural pontic. Stress values ranged from 92.2 to 909.8, 116.4 to 646.7, and 93.8 to 393.5 MPa for composite, naturally prepared, and natural unprepared pontic, respectively.

CONCLUSIONS

Using unprepared natural tooth pontic in anterior provisional fixed partial denture to replace missing central incisors is considered superior to other types in terms of stress distribution.

Biomechanical effects of inclined implant shoulder design in all-on-four treatment concept: a three-dimensional finite element analysis

OBJECTIVES

The aim of the present study was to assess the biomechanical behaviour of using a posterior implant design with inclined shoulder designs in all-on-four treatment via three-dimensional finite element analysis.

METHODS

Implants with standard and inclined shoulder designs were modelled for posterior implants. Implants were positioned into the maxilla and mandible models according to the all-on-four concept. Compressive stresses in the peri-implant bone, the von Mises stresses in the different components of the prosthetic restoration, and movement of the prosthesis were obtained.

RESULTS

The compressive stresses of the models with inclined shoulder design resulted in 15-58 % decrease compared with standard shoulder design. The von Mises stresses in the posterior implants reduced 18-47 %, stresses in the implant body increased 38-78 %, stresses in the abutment screw reduced 20-65 %, stresses in the framework of prosthesis reduced 1-18 % and deformation of the prosthesis was reduced 6-37 % in the models of inclined shoulder design compared with models of standard shoulder design. The compressive and von Mises stresses were generally higher in the mandible models than in the maxilla models for standard and inclined shoulder designs.

CONCLUSIONS

All evaluated components of the simulated treatment except for posterior abutment bodies showed better biomechanical behaviour with inclined shoulder design. The clinical success of all-on-four treatment maybe enhanced by using posterior implants with an inclined shoulder design.

Implant survival rate and marginal bone loss with the all-on-4 immediate-loading strategy: A clinical retrospective study with 1 to 4 years of follow-up

STATEMENT OF PROBLEM

Assessing peri-implant marginal bone loss (MBL) and its risk factors with cone beam computed tomography (CBCT) may clarify the risk factors for the all-on-4 (5 or 6) strategy and further improve its survival rate.

PURPOSE

The purpose of this retrospective clinical study was to evaluate the implant survival rate, MBL, and associated risk factors of all-on-4 (5 or 6) prostheses after 1 to 4 years of follow-up with CBCT.

MATERIAL AND METHODS

A total of 56 participants rehabilitated with 325 implants by using the all-on-4 (5 or 6) concept between October 2015 and December 2019 were included. Outcome measures were cumulative implant survival (life-table analysis) and MBL. Four CBCT scans, a scan immediately after surgery (T0), a scan 1 year after surgery (T1), a scan 2 years after surgery (T2), and a scan 3 to 4 years after treatment (T3), were obtained to evaluate the MBL. The Pearson correlation coefficient analysis and linear mixed models were performed to assess the potential risk factors for MBL (α=.05).

RESULTS

The implant survival rate was 99.38%, and the prosthesis survival rate was 100%. The reductions in the vertical buccal bone height (△VBBH) were 0.74 ±0.10 mm (T0-T1), 0.37 ±0.12 mm (T1-T2), and 0.15 ±0.14 mm (T2-T3). Except for T2-T3, the △VBBH showed a significant difference at T0-T1 and T1-T2 (P≤.05). The alterations in vertical mesial bone height (VMBH), vertical distal bone height (VDBH), and vertical lingual bone height (VLBH) were similar to the trend observed in VBBH. The △VBBH (T0-T3) was negatively correlated with the horizontal buccal bone thickness (HBBT) (T0) (r=-.394, P<.001). Linear mixed models revealed that factors such as smoking (P=.001), mandible implant site (P<.001), immediate implant (P=.026), tilted implant (P<.001), female sex (P=.003), systemic disease (P=.025), and bruxism (P=.022) negatively affected MBL. The cantilever length (CL) also had a negative effect on MBL around the implants at the distal extension (P<.001).

CONCLUSIONS

The high implant and prosthesis survival rates and low MBL confirmed the predictability of the all-on-4 (5 or 6) concept. Smoking, mandible implant site, systemic disease, bruxism, female sex, immediate implant, tilted implant, and CL were identified as potential risk factors for MBL.

Effect of different implant angulations on the biomechanical performance of prosthetic screws in two implant-supported, screw-retained prostheses: A numerical and experimental study

STATEMENT OF PROBLEM: A mesiodistal angle frequently forms between 2 splinted implant-supported, screw-retained fixed dental prostheses (TIS-FDPs). Mechanical complications commonly occur in prosthetic screws. Studies regarding the effect of the degree of implant angulation on the biomechanical performance of prosthetic screws in TIS-FDPs are sparse.

PURPOSE

The purpose of this numerical and experimental study was to investigate the effects of different implant angulations on the biomechanical performance, including stress distribution, stability of the screw joint, and surface morphology change of the prosthetic screws in TIS-FDPs.

MATERIAL AND METHODS

TIS-FDPs were classified into 4 groups: 0, 10, 20, and 30 degrees based on the degree of mesiodistal angle between the long axes of the 2 implants. In the finite element analysis (FEA), 4 series of 3D models were constructed and loaded with simulated occlusal forces. The von Mises stresses and rotational angles of the prosthetic screws were then calculated. In the mechanical test, each group of 5 TIS-FDPs with 10 prosthetic screws was tested under 1 million loading cycles by using a universal testing machine. The removal torque values (RTVs) and the surface roughness of the prosthetic screws were measured after cyclic loading. The normality of the outcome variables was assessed by the Shapiro-Wilk test. Analysis of variance and the Kruskal-Wallis test were used for further analysis (α=.05).

RESULTS

The FEA results showed that the von Mises stresses of the prosthetic screws were concentrated in the first screw thread crest engaged with the abutment, and the maximum values of the threads and the rotation angles of the prosthetic screws increased in the 2-implant mesiodistal angulation from 0 to 30 degrees. The mechanical tests showed that the RTVs of the prosthetic screws in each group were not significantly different after 1 million loading cycles (P=.107). The surface roughness of the crest of the first 2 threads of the prosthetic screws in the 30-degree group changed significantly compared with those in the other groups.

CONCLUSIONS

When TIS-FDPs were delivered, larger angulations of the 2 splinted implants seemed to increase the stress concentrated on the crest of the first engaged thread and the rotation angles of the prosthetic screws. After 1 million loading cycles, significant surface adhesive wear was identified on the crest of the first 2 threads of the prosthetic screws in the 30-degree group compared with groups with a smaller angulation.

Implant-supported zirconia fixed partial dentures cantilevered in the lateral-posterior area: A 4-year clinical results

Background

Implant-supported cantilever prostheses enable a more straightforward rehabilitation and may be a therapeutic option to reduce treatment morbidity, costs, and time. This study evaluated the clinical outcomes of fixed implant-supported partial dentures made of monolithic zirconia with a cantilever design to replace missing posterior teeth.

Methods

Fifteen partially edentulous patients received 34 implants and were provided with 16 zirconia fixed partial prostheses (FPPs) with one cantilever extension replacing mandibular or maxillary missing posterior and lateral teeth. Patients were re-examined for up to 4 years. Patient ages ranged from 41 to 65 years, with a mean age of 53±12 years; 47% were female, and 53% were male. The patients were observed for a mean period of 42±6 months with a minimum of 3 years and a maximum of 4 years.

Results

Peri-implantitis was observed in two cases. No chipping or fracture of any FPP was detected. Loosening of the abutment screw was a technical complication in one case. The rehabilitation survival rate was 100%. Implant-supported zirconia FPP with one mesial cantilever extension provides an aesthetic, functional treatment alternative to replace missing molars, premolars, and canines. These excellent clinical outcomes occurred over a mean observation time of 42±6 months.

Conclusion

Using monolithic zirconia milled with CAD-CAM technology might be an alternative to the metal-ceramic restoration in implant-supported FPP with one cantilever.

Does implant location influence the risk of peri-implantitis?

Peri-implantitis is characterized by nonreversible and progressive loss of supporting bone and is associated with bleeding and/or suppuration on probing. Peri-implant disease is considered as the main etiologic factor related to implant failure. Peri-implant disease has a pathogenesis similar to that of periodontal disease, both being triggered by an inflammatory response to the biofilm accumulation. Although the prevalence of peri-implantitis has been evaluated by several clinical studies with different follow-ups, there are currently little data on the impact of implant location and the prevalence of peri-implantitis. The aim of this review, therefore, was to summarize the evidence concerning the prevalence of peri-implantitis in relation to implant location and associated risk predictors. Even though most studies evaluating the prevalence of peri-implantitis in relation to implant location are cross-sectional or retrospective, they suggest that the occurrence of peri-implantitis is most prevalent in the anterior regions of the maxilla and mandible. Moreover, it seems that there is a higher prevalence of peri-implantitis in the maxilla than in the mandible.

Stability of Cantilever Fixed Dental Prostheses on Zirconia Implants

Background: The objective was to determine the optimal connector size and position within zirconia disks for implant-supported cantilever fixed dental prostheses (ICFDP). Methods: Two-unit ICFDPs (n = 60) were designed for the premolar region with connector sizes of either 9 or 12 mm² and positioned in the enamel or dentin layer of two different types of zirconia disks. The restorations were milled and cemented onto zirconia implants. After simulated chewing for 1.2 Mio cycles, the fracture load was measured and fractures were analyzed. Results: No fractures of ICFDPs or along the implants were detected after simulated aging. The mean fracture load values were significantly higher for a connector size of 9 mm² (951 N) compared with 12 mm² (638 N). For the zirconia material with a higher biaxial flexural strength, the fracture load values were increased from 751 to 838 N, but more implant fractures occurred. The position within the zirconia disk did not influence the fracture load. Conclusions: A connector size of 9 mm² and a zirconia material with a lower strength should be considered when designing ICFDPS on zirconia implants to reduce the risk of fractures along the intraosseous implant portion.

Two short implants versus one short implant with a cantilever: 5-Year results of a randomized clinical trial

Aim

To test whether or not the use of a short implant with a cantilever results in similar clinical and radiographic outcomes compared to two adjacent short implants with single tooth reconstructions.

Materials and methods

Thirty‐six patients with two adjacent missing teeth in the posterior region were randomly assigned to receive either a single 6‐mm implant with a cantilever (ONE‐C) or two 6‐mm implants (TWO). Fixed reconstructions were inserted 3–6 months after implant placement and patients were re‐examined up to 5 years (FU‐5).

Results

A total of 26 patients were available for re‐examination at FU‐5. The survival rate amounted to 84.2% in ONE‐C and to 80.4% in TWO (inter‐group: p = .894). Technical complication rates amounted to 64.2% (ONE‐C) and to 54.4% (TWO) (inter‐group: p = 1.000). From baseline to FU‐5, the median changes of the marginal bone levels were 0.13 mm in ONE‐C and 0.05 mm in TWO (inter‐group: p = .775). Probing depth, bleeding on probing, and plaque control record values showed no significant differences between the two treatment modalities (p > .05).

Conclusions

Short implants with a cantilever render similar clinical and radiographic outcomes compared to two adjacent short implants at 5 years, however, they tend to fail at earlier time points suggesting an overload of the implants. Considering the modest survival rates, the clinical indication of either treatment option needs to be carefully evaluated. ClinicalTrials.gov (NCT01649531).

Biomechanical effect of an occlusal device for patients with an implant-supported fixed dental prosthesis under parafunctional loading: A 3D finite element analysis

STATEMENT OF PROBLEM

Whether providing an occlusal device for a patient with bruxism and an implant-supported fixed dental prosthesis leads to improved biomechanics is unclear.

PURPOSE

The purpose of this 3D finite element analysis (FEA) study was to evaluate the biomechanical behavior of 3-unit implant-supported prostheses under parafunctional forces with and without an occlusal device.

MATERIALS AND METHODS

Eight 3D models consisting of a posterior (type IV) maxillary bone block with 3 external hexagon implants (Ø4.0×7.0 mm) and 3-unit implant-supported prostheses with different crown connections (splinted or unsplinted) and an occlusal device under functional and parafunctional loading were simulated. The abutment screws were evaluated by von Mises stress maps, and the bone tissue by maximum principal stress and microstrain maps by using a finite element software program.

RESULTS

An occlusal device improved the biomechanical behavior of the prostheses by reducing stress in the abutment screws and stress and strain in the bone tissue. However, the use of an occlusal device was not sufficiently effective to negate the biomechanical benefit of splinting.

CONCLUSIONS

The use of splinted crowns in the posterior maxillary region with an occlusal device was the most effective method of reducing stress in the abutment screws and stress and strain in the bone tissue when parafunction was modeled.

The prosthetic screw loosening of two-implant supported screw-retained fixed dental prostheses in the posterior region: A retrospective evaluation and finite element analysis

The study was aimed to investigate the prosthetic screw loosening of two splinted implants-supported, screw-retained (2-4-unit) fixed dental prostheses (TIS-FDPs) in posterior region and to explore the underlying mechanism. In the retrospective study, a study group of TIS-FDPs (n = 23) presenting prosthetic screw loosening and a control group of TIS-FDPs (n = 32) absent of prosthetic screw loosening during observation period were included. The prosthesis height (PH), inter-implant distance (ID) and cantilever distance (CD) of TIS-FDPs were measured and compared within two groups. In the finite element analysis (FEA) part, three serials of models presenting different clinical scenarios were constructed based on the abovementioned PH, ID and CD values respectively. In the clinical evaluation, the values of pH and CD in study group were statistically higher than those in control group, whereas the values of ID had no significant difference. In the FEA, the results indicated that there was no linear correlation between the increased ID values and the maximum von Mises stresses and the rotation angles. On the other hand, the increased PH and CD values would result in a strong linear growth of the maximum von Mises stresses and the rotation angles. Besides, it was found that the regression coefficients in PH model were all higher than those in ID and CD models. When TIS-FDPs were delivered in posterior region, the PH and the CD, rather than the ID, seemed to have a significant impact on the stress concentration of the prosthetic screws and the incident of prosthetic screws loosening.

Finite Element Method and Von Mises Investigation on Bone Response to Dynamic Stress with a Novel Conical Dental Implant Connection

The bioengineering and medical and biomedical fields are ever closer, and they manage to obtain surprising results for the development of new devices. The field of simulations and studies in silica has undergone considerable development in recent years, favoring the advancement of medicine. In this manuscript, a study was carried out to evaluate the force distribution on the implant components (In-Kone® Universal) and on the peri-implant tissues subjected to loading. With the finite element analysis and the Von Mises method, it was possible to evaluate this distribution of forces both at 0 degrees (occlusal force) and at 30 degrees; the applied force was 800 N. The obtained results on this new type of connection and on all the implant components are satisfactory; the distribution of forces appears optimal even on the peri-implant tissues. Surely, studies like this help to obtain ever more performing devices, improving both the clinic and the predictability of rehabilitations.

Biomechanical performance design of joint prosthesis for medical rehabilitation via generative structure optimization

This paper proposes a biomechanical performance design method of joint prosthesis for medical rehabilitation via Generative Structure Optimization (GSO). Firstly, the 3D reconstruction of manifold structure involving hard bone and cartilage is sequentially and progressively implemented from heterogeneous medical images such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) via iteration. On the basis of reconstructed mesh structure, the finite element method (FEM) is hereby employed to verify the structure by evaluating the mechanical force distribution. The biomechanical performance design model for 3 D printing (3DP) is then built using multi-objective optimization (MOO) by considering adaptive layer thickness, infill patterns and infill trajectories, etc. The GSO outlets a generative data-driven system which covers various stages such as personalized CT, subsequent 3 D reconstruction, further finite element analysis (FEA) and even structural parameter optimization. The physical experiment of Additive manufacturing (AM) proves that, the relative density, surface topography and wear-resisting performance of joint prosthesis can be improved by GSO which helps to improve biomechanical performance, including kinematics and dynamics. The proposed method may arouse the huge attention in the prosthesis applications to promote patients' high-end customization well-being.

Principles of biomechanics in oral implantology

Background and aims

The principles of biomechanics comprise all the interactions between the body (tissues) and the forces acting upon it (directly or via different medical devices). Besides the mechanical aspects, the tissues response is also studied. Understanding and applying these principles is vital for the researchers in the field of oral implantology, but they must be equally known by the practitioners. From the planning stages to the final prosthetic restoration, they are involved in each and every aspect. Ignoring them inevitably leads to failure.

Methods

The first part of this paper includes a review of our current research in oral implantology (mechanical, digital and biological testing), while the second part includes a review of the available literature on certain biomechanical aspects and their implications in everyday practice.

Results

Our research opens new study directions and provides increased chances of success for dental implant therapy. The practical aspects of our findings, combined with the available literature (from the basic principles described more than 40 years ago to the most recent studies and technologies) can serve as a guide to practitioners for increasing their success rate.

Conclusion

While no therapy is without failure risk, a good understanding of the biomechanics involved in oral implantology can lead to higher success rates in implant supported prosthetic restorations.

The Effect of the Length and Distribution of Implants for Fixed Prosthetic Reconstructions in the Atrophic Posterior Maxilla: A Finite Element Analysis

In this study, different prosthetic designs that could be applied instead of advanced surgical techniques in atrophic maxilla were evaluated with finite element analysis. Atrophic posterior maxilla was modeled using computer tomography images and four models were prepared as follows: Model 1 (M1), two implants supporting a three-unit distal cantilever prosthesis; Model 2 (M2), two implants supporting a three-unit conventional fixed partial denture; Model 3 (M3), three implants supporting three connected crowns; and Model 4 (M4), two implants supporting two connected crowns. Implants 4 mm in width and 8 mm or 13 mm in length were used. A linear three-dimensional finite element programme was used for analysis. The maximum principle stress (tensile) and minimum principle stress (compressive) were used to display stress in cortical and cancellous bones. The von Mises criteria were used to evaluate the stress on the implants. M1 was found to be the most risky model. The short dental arch case (M4) revealed the lowest stresses among the models but is not recommended when one more implant can be placed because of the bending forces that could occur at the mesial implant. In M2 and M3, the distal implants were placed bicortically between the crestal and sinus cortical plates, causing a fall of the stresses because of the bicortical stability of these implants.

Biomechanical comparison of implant inclinations and load times with the all-on-4 treatment concept: a three-dimensional finite element analysis

The purpose of this study was to compare the effects of implant inclinations and load times on stress distributions in the peri-implant bone based on immediate- and delayed-loading models. Four 3D FEA models with different inclination angle of the posterior implants (0°, 15°, 30°, 45°) were constructed. A static load of 150 N in the multivectoral direction was applied unilaterally to the cantilever region. The stress distributions in the peri-implant bone were evaluated before and after osseointegration. The principal tensile stress (σ_max), mean principal tensile stress (σ_max), principal compressive stress (σ_min) and mean principal compressive stress (σ_min) of the bone and micromotion at the contact interface between the bone and implants were calculated. In all the models, peak principal stresses occurred in the bone surrounding the left tilted implant. The highest σ_max and σ_min were all observed in the 0° model for both immediate- and delayed-loading models. And the 0° and 15° models showed higher σ_max and σ_min values. The 0°models showed the largest micromotion. The observed stress distribution was better in the 30° and 45° models than in the 0° and 15° models.

Evaluation of the Cortical Deformation Induced by Distal Cantilevers Supported by Extra-Short Implants: A Finite Elements Analysis Study

Background: The aim of the study was to analyze the distribution of stresses caused by an axial force in a three-dimensional model with the finite element method in the implant-supported fixed partial denture with distal overhang (PPFIVD) on short dental implants in the posterior edentulous maxilla. Methods: geometrical models of the maxilla with a bone remnant of 9 and 5 mm were created. Straumann SP® (Base, Switzerland) implants were placed in the premolar area. Two groups with subgroups were designed. Group A (GA): PPFIVD on two implants (GA1: 4.1 × 8 mm and GA2: 4.1 × 4 mm); Group B (GB): PPFIVD on the single implant (GB1: 4.1 × 8 mm and GB2: 4.1 × 4 mm). It was applied to a static force of 100 N to 30°. Results: PPFIVD on two implants reached the maximum tension in GA2 with respect to GA1; the difference was not significant in implants. In the maxilla GA2 was lower in relation to GA1; the difference was not significant. In PPFIVD over an implant, the stress was greater in GB2 with respect to GB1; the difference was significant in maxilla and implants. Peri-implant bone micro deformations and prosthesis-implant displacements were observed. Conclusions: PPFIVD over short splinted implants could be viable in the maxilla with reduced bone height, being an option when lifting the floor of the maxillary sinus. The rehabilitation with unitary implant (4 mm) did not provide adequate results. The dominant tensions evidenced bone micro-distortions with a displacement of the prosthesis-implant set. The real statement of this paper was to define that short splinted implants can be used in soft bone with high success rate in reducing bending forces.