Effect of the number of abutments on biomechanics of Branemark prosthesis with straight and tilted distal implants

Abstract

Objective: This study aimed to evaluate the bending moments, and compressive and tensile forces in implant-supported prostheses with three, four or five abutments.

Material and methods: Ten Pd-Ag frameworks were tested over two master models with: 1) parallel vertical implants, and 2) tilted distal implants. Strain gauges were fixed on the abutments of each master model to measure the deformation when a static load of 50 N was applied on the cantilever (15 mm). The deformation values were measured when the metallic frameworks were tested over three, four or five abutments, and transformed into force and bending moment values. Data were analyzed by ANOVA and Tukey's test for multiple comparisons at 5% level of significance.

Results: Abutment #1 (adjacent to the cantilever) had the highest values of force and sagittal bending moment for all tests with three, four or five abutments. Independently from the number of abutments, axial force in abutment #1 was higher in the vertical model than in the tilted model. Total moment was higher with three abutments than with four or five abutments. Independently from the inclination of implants, the mean force with four or five abutments was lower than that with three abutments.

Conclusion: The results suggest that in the set-ups with four or five abutments tilted distal implants reduced axial force and did not increase bending moments.

Figure 1

Scheme of the lateral view of the assembly with vertical implants (A) and with tilted distal implants (B). For both models, the sagittal distance between the most anterior and posterior points of the implant platform was 15 mm. The loading site on the cantilever was 15 mm from the emergency of the distal implant

Figure 2

Measuring set-up for the three-implant configuration with the model with vertical implants. Abutments #2 and #4 were removed to perform the loading test of the framework supported by three abutments. Each abutment had three strain gauges attached 120º apart

Figure 3

Axial force (A), sagittal bending moment (B), and lateral bending moment (C) in each abutment for the model with three abutments (#1, #3, and #5). Error bars are standard error of the mean. Distinct letters (uppercase letters for the factor “Model” and lowercase letters for the factor “Abutment”) indicate that the means are significantly different (α=0.05). For axial force no significant interaction was found between Model and Abutment (P=0.070) but both main effects were significant (Model: P=0.006; Abutment: P<0.001). For sagittal bending moment, only the factor Abutment was significant (P<0.001). For lateral bending moment, there was significant interaction between Model and Abutment (P<0.001)

Figure 4

Axial force (A), sagittal bending moment (B), and lateral bending moment (C) in each abutment for the model with four abutments (#1, #2, #4, and #5). Error bars are standard error of the mean. Distinct letters (uppercase letters for the factor “Model” and lowercase letters for the factor “Abutment”) indicate that the means are significantly different (α=0.05). For axial force, there was significant interaction between Model and Abutment (P=0.029). For sagittal bending moment, there was no interaction between Model and Abutment (P=0.052) but both main effects were significant (Model: P=0.018; Abutment: P<0.001). Regarding lateral bending moment, there was a significant interaction between Model and Abutment (P=0.018)

Figure 5

Axial force (A), sagittal bending moment (B), and lateral bending moment (C) in each abutment for the model with five abutments (#1, #2, #3, #4, and #5). Error bars are standard error of the mean. Distinct letters (uppercase letters for the factor “Model” and lowercase letters for the factor “Abutment”) indicate that the means are significantly different (α=0.05). For axial force there was significant interaction between Model and Abutment (P<0.001). For sagittal and lateral bending moments, only the factor Abutment was significant (P<0.001)

Figure 6

Axial force (A), sagittal bending moment (B), and lateral bending moment (C) in the abutment adjacent to the cantilever under loading (abutment #1). Error bars are standard error of the mean. For force values, a positive signal means compressive force and a negative signal means tensile force. Distinct letters above the bars of axial force means indicate that the means are significantly different (α=0.05). Sagittal and lateral bending moment means were not statistically different