Influence of abutment height and convergence angle on the retrievability of cement-retained implant prostheses with a lingual slot

Design Factors of Ti-Base Abutments Related to the Biomechanics Behavior of Dental Implant Prostheses: Finite Element Analysis and Validation via In Vitro Load Creeping Tests

This study has been carried out to analyze the influence of the design of three geometric elements (wall thickness, platform width, and chamfer) of Ti-base abutments on the distribution of stresses and strains on the implant, the retention screw, the Ti base, and the bone. This study was carried out using FEA, analyzing eight different Ti-base models based on combinations of the geometric factors under study. The model was adapted to the standard Dynamic Loading Test For Endosseous Dental Implants. A force of 360 N with a direction of 30° was simulated and the maximum load values were calculated for each model, which are related to a result higher than the proportional elastic limit of the implant. The transferred stresses according to von Mises and microdeformations were measured for all the alloplastic elements and the simulated support bone, respectively. These results were validated with a static load test using a creep testing machine. The results show that the design factors involved with the most appropriate stress distribution are the chamfer, a thick wall, and a narrow platform. A greater thickness (0.4 mm) is also related to lower stress values according to von Mises at the level of the retaining screws. In general, the distributions of tension at the implants and microdeformation at the level of the cortical and trabecular bone are similar in all study models. The in vitro study on a Ti-base control model determined that the maximum load before the mechanical failure of the implant is 360 N, in accordance with the results obtained for all the Ti-base designs analyzed in the FEA. The results of this FEA study show that modifications to the Ti-base design influence the biomechanical behavior and, ultimately, the way in which tension is transferred to the entire prosthesis-implant-bone system.

Effect of Abutment Geometry and Luting Agents on the Vertical Marginal Discrepancy of Cast Copings on Implant Abutments: An In Vitro Study

Aim

Vertical marginal discrepancy (VMD) influences the success of implant-supported restorations. However, there is little literature that has investigated the influence of geometry and cementing agent on changes in VMD of metal copings on implant abutments. The objective was to evaluate the effect of the geometry of the abutment and cementing agents on VMD.

Methods

Cast copings were cemented on implant abutments customized cylindrical (4, 5.5, and 7 mm) and on hexagonal implant abutments (4 mm) cemented or uncemented molded copings were placed (n = 4, totally 64 samples) with different luting agents. The VMD of the copings were measured in the coping-abutment interface at three reference points using a stereomicroscope. The independent Student's t test was used for comparison between the two different abutment walls. The post hoc statistical analysis was performed by the Tukey test.

Results

There was a significant VMD increase between noncemented and cemented cast copings using different luting agents. Abutment geometry and luting agents significantly influenced the VMD (p ≤ 0.05). Cylindrical abutment at 7 mm in height cemented with different luting agent tested showed significantly higher VMD values than cylindrical abutments of 4 mm (p=0.019). Hexagonal abutments with a 4 mm height showed significantly higher VMD values than cylindrical 4 mm abutments using zinc oxide noneugenol and glass ionomer cements (p=0.032).

Conclusions

Abutment geometry and luting agents influence the VMD of cast copings cemented on implant abutment. The higher the cylindrical abutment, the greater the VMD, and hexagonal wall abutments promote greater marginal gap.

[Analysis of the fit quality of the metal frames on implants depending on the abutment taper]

OBJECTIVE

The objectivewas to study the effect of changing the anglconvergence of the abutment walls, depending on their height, as well as the number of supports, on the accuracy of fitting metal-ceramic prostheses to the abutments.

MATERIAL AND METHODS

It was studied 72 constructions: prostheses on single abutments with abutment heights from 3 mm to 9 mm with an increase in height of 2 mm, an angle of convergence of the abutment walls from 0° to 10° with an increase in convergence of 2° in the amount of 24 prostheses; 24 framework designs supported by two abutments, with the same parameters (height and angle of inclination of the abutment walls) and prostheses supported by three abutments in the amount of 24 designs. The abutments were milled from a titanium alloy Ti-6Al-4V, and the prostheses were cast from a cobalt-chrome alloy. During fabrication of the prostheses, a compensation varnish was applied to the respective abutments to create a gap between the framework and the abutment for a 50 μm thick cement film. The crown prostheses were cemented onto the abutments with GC Fuji + glass-ionomer cement, followed by vertical sawing in the medio-distal direction. After sawing, the gaps between the inner edges of the prostheses walls and the outer edges of the abutment walls were measured using a «Levenhuk DTX 90» digital microscope (Russia) at x100 magnification.

RESULTS

Abatement height 3 mm with any number of supports and 5 mm with up to 3 supports do not need taper for precise fitting. In 5 mm abatements and 3 and more supports minimal required taper is 2°. Seven mm singular abatement requires 4° taper, but the increased number of supports enhances it up to 6°. For 9 mm abatement optimal abatement taper for the best fitting is 8°.

CONCLUSION

The study showed the relationship between the fitting accuracy and the change in the abutment taper, their height, and the number of supports in the structure.

In Vitro Simulation of Dental Implant Bridges Removal: Influence of Luting Agent and Abutments Geometry on Retrievability

Implant fixed dental prostheses are widely used for the treatment of edentulism, often preferred over the screw-retained ones. However, one of the main features of an implant-supported prosthesis is retrievability, which could be necessary in the case of implant complications. In this study, the retrievability of implant-fixed dental prostheses was investigated considering two of the main factors dental practitioners have to deal with: the abutments geometry and the luting agent. Impulsive forces were applied to dental bridge models to simulate crowns’ retrievability in clinical conditions. The number of impulses and the impulsive force delivered during each test were recorded and used as retrievability indexes. One-hundred-and-five tests were conducted on 21 combinations of bridges and luting agents, and a Kruskal-Wallis test was performed on the results. The abutment geometry significantly influenced the number of impulses needed for retrieval (p < 0.05), and a cement-dependent trend was observed as well. On the other hand, the forces measured during tests showed no clear correlation with bridge retrievability. The best retrievability was obtained with long, slightly tapered abutments and a temporary luting agent.