A finite element analysis to study the stress distribution on distal implants in an all-on-four situation in atrophic maxilla as affected by the tilt of the implants and varying cantilever lengths

Stress distribution pattern in all-on-four maxillary restorations supported by porous tantalum and solid titanium implants using three-dimensional finite element analysis

Success/failure of dental implants depends on stress transfer and distribution at the bone-implant interface. This study aimed to assess the stress distribution pattern in all-on-four maxillary restorations supported by porous tantalum and solid titanium implants using three-dimensional (3D) finite element analysis (FEA). In this FEA, a geometric model of an edentulous maxilla, Zimmer screw-vent tantalum and solid titanium implants were modelled. Four models with the all-on-four concept were designed. The fifth model had 6 vertical implants (all-on-six). Two different implant types (porous tantalum and solid titanium) were modelled to yield a total of 10 models, and subjected to 200 N bilateral vertical load. Pattern of stress distribution and maximum von Mises stress values in cancellous and cortical bones around implants were analysed. In tantalum models, the effect of increasing the distal tilting of posterior implants was comparable to the effect of increasing the number of implants to 6 on von Mises stress values in cortical bone. However, in cancellous bone, the effect of increasing the tilting of posterior implants on stress was slightly greater than the effect of increasing the number of implants to 6. In solid titanium models, the effect of both of the abovementioned parameters was comparable on stress in cancellous bone; but in cortical bone, the effect of increasing the implant number was slightly greater on stress reduction. Despite similar pattern of stress distribution in bone around implants, higher maximum von Mises stress values around tantalum implants indicate higher stress transfer capacity of this type of implant to the adjacent bone, compared with solid titanium implants.

Difference in marginal bone loss around implants between short implant-supported partial fixed prostheses with and without cantilever: a retrospective clinical study

PURPOSE

To investigate the influence of cantilever prosthetic arm on the marginal bone loss (MBL) over time around dental implants supporting short fixed partial dentures (FPDs), in a record-based retrospective study.

METHODS

All cases of 3-unit implant-supported FPDs, supported by 2-3 implants, from the database of cases treated at one specialist clinic were considered for inclusion. Only implants with a minimum of 36 months of radiological follow-up were considered. Univariate linear regression models were used to compare MBL over time between 12 clinical covariates, after which a linear mixed-effects model was built.

RESULTS

One-hundred-thirty-nine patients (64 men, 75 women) with 164 3-unit implant-supported FPDs (333 implants supporting non-cantilevered FPDs, 94 supporting cantilevered FPDs) were included in the study. The patients were followed up clinically and radiographically for a mean of 154.1 ± 78.0 (min-max, 37.3-364.6) and 132.9 ± 77.3 months (min-max, 36.8-329.9), respectively. The total number of marginal bone level double measurements (mesial and distal sides of each implant) was 2909. FPDs with cantilever presented an estimated greater MBL over time compared to FPDs without cantilever. Bruxism, sex (women), implant (modified) surface, and (poor) bone quality were also associated with higher MBL over time.

CONCLUSIONS

The use of a cantilever extension is suggested to negatively affect the bone marginal level over time around implants supporting 3-unit FPDs. Due to the small difference of the estimated MBL over long periods of follow-up between the groups, it is a matter of debate if the observed negative effect may be of clinical significance.

Biomechanical Comparison of Asymmetric Implant Configurations for All-on-Four Treatment Using Three-Dimensional Finite Element Analysis

The aim of this study is to examine the effect of unilaterally more posterior placement of implants (Straumann BLT 4.1 mm in diameter and 12 mm long) applied according to the all-on-four concept on the stress distribution on bone, implants, and other prosthetic components, using the finite element analysis method. Three scenarios were modelled: For Model 1 (M1), anterior implants were placed symmetrically perpendicular to the bone in the right and left lateral incisor region, while the necks of the posterior implants placed symmetrically in the second premolar region were angled at 30 degrees. For Model 2 (M2) the implant in the left second premolar region was placed to the first molar region unilaterally. For Model 3 (M3) the implant in the left lateral incisor region was placed to the canine region unilaterally. Vertical and oblique forces (100 N) were applied in the right first molar region. The von Mises and maximum (Pmax) and minimum (Pmin) principal stresses were obtained. The highest stress concentration on the cortical bone was observed in the second premolar region in all models when oblique forces were applied. M1 was highest (8.992 MPa) followed closely by M3 (8.780 MPa) and M2 was lowest (3.692 MPa). The highest stress concentration on the prosthetic parts was observed in this framework when oblique forces were applied. M2 was highest (621.43 MPa) followed by M3 (409.16 MPa) and the lowest was M1 (309.43 MPa). It is thought that placing the implant further posterior to first molar region may prevent the bone resorption that occurs with high stress around the crestal bone. However, increased stress on the implants and prosthetic parts may lead to failures.

Biomechanical analysis of stress around the tilted implants with different cantilever lengths in all-on-4 concept

Background

Many clinical studies have reported the high success rate of the All-on-4 concept. In the present study, we aimed to compare the stress distribution with different tilted distal implants and cantilever lengths in an All-on-4 system using the two-dimensional photoelastic method and to establish the All-on-4 implant photoelastic model by computer-aided design (CAD) and rapid prototyping (RP). 

Methods

The data of the human edentulous mandible were acquired by computed tomography (CT). Three human edentulous mandible All-on-4 implant models with different distally inclined implant holes were fabricated using Mimic, Geomagic Studio software, and a light solidifying fast shaping machine. Then the final photoelastic models were established through the traditional method. Each of the three models had four NobelSpeedy Replace implants between the interforaminal regions. The two posterior implants were placed 0, 15, and 45 degrees distally before the mental foramen. The four implants were splinted by wrought cobalt-chromium alloy frameworks. Each of the three photoelastic models was submitted to a 150 N vertical load at five points on the framework: the central fossa of the mandibular first molar, and 0 mm, 5 mm, 10 mm, and 15 mm of the cantilever length. The stress produced in the models was photographed with a digital camera, and the highest value of the stressed fringe pattern was recorded.

Results

The All-on-4 implant photoelastic model established by CAD and RP was highly controllable and easy to modify. The position and inclination of implants were accurate, and the frameworks could be passively emplaced. The stress values were higher around a single tilted implant compared with the distal implant in All-on-4 with the same inclination. The 0-degree distal implant and 45-degree distal implant demonstrated the highest and lowest stress when loading at the central fossa of the mandibular first molar, respectively. With the same inclination of distal implant, the peri-implant bone stress increased as the length of cantilever increased.

Conclusion

The method of establishing the All-on-4 implant photoelastic model by CAD and RP was highly controllable, convenient, fast, and accurate. The tilted implants splinted in the fully fixed prosthesis with reduced cantilever lengths did not increase the stress level compared with the vertical distal implants.And this illustrated that the influence of cantilever on stress distribution was greater than the influence of implant inlination.

A comparative evaluation of stress distribution between an All-on-Four implant-supported prosthesis and the Trefoil implant-supported prosthesis: A three-dimensional finite element analysis study

Aim

The primary aim of this study is to analyse the stress distribution between an ALL ON FOUR implant supported prosthesis and the TREFOIL implant supported prosthesis with 3D finite element models.

Settings and Design

An in vitro perspective.

Materials and Methods

Two mandibular three-dimensional Finite Element Models were constructed by the CREO version 5 software, in which Model A depicts a mandible with ALL ON FOUR implant supported prost hesis and Model B will depict TREFOIL implant supported prosthesis. Model A contains four implants, two anterior straight and posterior tilted implants (30°), a bar and denture containing acrylic teeth. In Model B, it contains three straight implants and a prefabricated compensatory bar with standardised dimensions. To evaluate and compare the stress distribution between the bone and implant interface, one deleterious cantilever load of upto 300 N is applied on the second molar bilaterally and simultaneously. Another full bite biting load of 150 N is given bilaterally and simultaneously on the central groove of premolars and molars.

Statistical Analysis Used

The results of the simulations obtained were analysed in terms of Von Mises equivalent stress levels at the bone -implant interface.

Results

The results of loading 1 showed that the maximum Von Mises stress was recorded in the anterior implant region of the Trefoil system (Model B) when compared to All on four concept. The results of loading 2 showed that the maximum Von Mises stress were recorded in the anterior implant region Trefoil system (Model B) when compared to All on four concept.

Conclusion

This invitro study concludes that All on Four implant supported prosthesis showed better stress distribution when compared to the Trefoil concept.

Clinical success between tilted and axial implants in edentulous maxilla: A systematic review and meta-analysis

Aim:

This systematic review and meta-analysis evaluated the clinical survival of axial and tilted implants in atrophic edentulous maxilla after three years of immediate loading and also the corresponding marginal bone loss.

Setting and Design:

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines (PRISMA).

Materials and Methods:

The relevant studies were retrieved from MEDLINE(PubMed), the Cochrane Central Register of Controlled Trials (CENTRAL), Science Direct, Google Scholar databases. The search was limited to studies published in the English language with no date restrictions. A further hand search was conducted on individual journals and reference lists of studies. The risk of bias in included studies was assessed by using the Evidence Project risk of bias tool.

Statistical Analysis Used:

Statistical meta-analysis was conducted using RevMan 5.4 software. The assessment for the level of evidence was done using GRADEpro software.

Results:

Eleven studies were finalised. All were included in the meta-analysis for implant survival, while only seven studies were included in the meta-analysis of marginal bone loss. After three years, the meta-analysis results for implant survival showed no statistical difference between axial and tilted implants, with the forest plot neither favouring axial nor tilted implants (RR = 1.00 (95% CI: 0.98-1.01); P-value = 0.59). After three years, the meta-analysis results for marginal bone showed no statistical difference between axial and tilted implants, with the forest plot neither favouring axial nor tilted implants (MD = -0.02; 95% CI; -0.09-0.06; P-value = 0.69).

Conclusion:

In the immediately loaded rehabilitation of completely edentulous atrophic maxillae, tilting of implants did not induce any significant alteration in their survival and their corresponding marginal bone loss levels compared to conventionally placed axial implants even after three years of function.

Tilted implantation technique for edentulous patients

The tilted implantation technique is characterized by placing the implant at an angle of more than 15° and less than 45° from the horizontal plane. This technique can avoid damaging the maxillary sinus, inferior alveolar nerve, nasal base, and other anatomical structures when the height of the upper and lower jaw available bone is insufficient, to maximize the use of available bone and avoid a large range of bone increment. The tilted implantation technique can reduce the trauma of the surgery, increase the possibility of immediate restoration and shorten the treatment cycle, which has been widely used clinically. In this review, the scope of application, design elements, design scheme and complications of the tilted implantation technique for edentulous patients will be described.