Load bearing capacity of 3-unit screw-retained implant-supported fixed dental prostheses with a mesial and distal cantilever on a single implant: A comparative in vitro study

OBJECTIVES

To assess the mechanical durability of monolithic zirconia implant-supported fixed dental prostheses (iFDP) design on one implant, with a distal and a mesial extension cantilever bonded to a titanium base compared to established designs on two implants.

MATERIALS AND METHODS

Roxolid Tissue level (TL), and tissue level x (TLX) implants were used to manufacture screw-retained 3-unit iFDPs (n = 60, n = 10 per group), with following configurations (X: Cantilever; I: Implant, T: Test group, C: Control group): T1: X-I-X (TL); T2: X-I-X (TLX); T3: I-I-X (TL); T4: I-I-X (TLX); C1: I-X-I (TL); C2: I-X-I (TLX). The iFDPs were thermomechanically aged and subsequently loaded until fracture using a universal testing machine. The failure load at first crack (Finitial) and at catastrophic fracture (Fmax) were measured and statistical evaluation was performed using two-way ANOVA and Tukey's post-hoc tests.

RESULTS

The mean values ranged between 190 ± 73 and 510 ± 459 N for Finitial groups, and between 468 ± 76 and 1579 ± 249 N for Fmax, respectively. Regarding Finitial, neither the implant type, nor the iFDP configuration significantly influenced measured failure loads (all p > 0.05). The choice of implant type did not show any significant effect (p > 0.05), while reconstruction design significantly affected Fmax data (I-I-Xa < X-I-Xb < I-X-Ic) (p < 0.05). The mesial and distal extension groups (X-I-X) showed fractures only at the cantilever extension site, while the distal extension group (I-I-X) showed one abutment and one connector fracture at the implant/reconstruction interface.

CONCLUSION

Results suggest that iFDPs with I-X-I design can be recommended regardless of tested implant type followed by the mesial and distal extension design on one implant abutment (X-I-X).

Digital technique to analyze the wear of screw-retained implant supported metal-ceramic dental prostheses and natural tooth as antagonist: a pilot study

The aim of this study was to describe a novel digital technique to analyze the wear of screw-retained implant-supported metal-ceramic dental prostheses and natural tooth as antagonist.Materials and methods Ten patients were consecutively included to rehabilitate partial edentulism by dental implants. Both the screw-retained implant-supported metal-ceramic dental prostheses and the natural tooth as antagonist were submitted to a digital impression through an intraoral scan to generate a Standard Tessellation Language digital file preoperatively (STL1), at 3 months (STL2), and 6 months (STL3) follow-up. Afterwards, an alignment procedure of the digital files (STL1-STL3) was performed on a reverse engineering morphometric software (3D Geomagic Capture Wrap) and volume changes at the screw-retained implant-supported metal-ceramic dental prostheses and the natural tooth as antagonist were analyzed using Student's t-test. Moreover, Gage R&R statistical analysis was conducted to analyze the repeatability and reproducibility of the digital technique.Results Gage R&R showed a variability attributable to the digital technique of 3.8% (among the measures of each operator) and 4.5% (among operators) of the total variability; resulting repeatable and reproducible, since the variabilities were under 10%. In addition, statistically significant differences were shown at the wear volume (μm3) of both the natural tooth as antagonist (p < 0.0001) and the screw-retained implant-supported metal-ceramic dental prostheses between 3- and 6-months follow-up (p = 0.0002).Conclusion The novel digital measurement technique results repeatable and reproducible to analyze the wear of screw-retained implant-supported metal-ceramic dental prostheses and natural tooth as antagonist.

Fracture loads of screw-retained implant-supported zirconia prostheses after thermal and mechanical stress

PURPOSE

The objective of the present study was to evaluate fracture loads of screw-retained implant-supported zirconia prostheses after artificial aging.

METHODS

Four types of screw-retained implant-supported prostheses were fabricated (n=11 each); porcelain-veneered zirconia prosthesis (PVZ), indirect composite-veneered zirconia prosthesis (IVZ), porcelain-fused-to-metal prosthesis (PFM), and monolithic zirconia prosthesis (ML). The specimens were subjected to 10,000 thermocycles and cyclic loading for 1.2 million cycles. Fracture loads were measured, and the data were analyzed with the Kruskal-Wallis and Steel-Dwass tests (α=0.05).

RESULTS

All specimens survived the artificial aging procedures. The fracture loads for the PVZ (1.52kN), IVZ (1.62kN), and PFM groups (1.53kN) did not significantly differ; however, the fracture load for the ML group (6.61kN) was significantly higher than those for the other groups. The fracture load for the IVZ group was comparable to those for the PVZ and PFM groups.

CONCLUSIONS

The monolithic zirconia prostheses exhibited significantly higher fracture loads than the bilayered prostheses. All the investigated types of screw-retained implant-supported zirconia prostheses appear sufficient to resist posterior masticatory forces during long-term clinical use.

Comparison of access-hole filling materials for screw retained implant prostheses: 12-month in vivo study

BACKGROUND

Screw retained implant prostheses seem to be an efficient restorative method to prevent peri-implantitis caused by cement excess around the abutment. The drawback of the screw-retained prostheses is the difficulty to realize an efficient access-hole filling functionally and aesthetically. Up to now, few in vitro and in vivo studies were reported in the literature. The aim of this study was to evaluate clinical performances of two direct filling materials through a period of 12 months.

METHODS

To pursue a previous in vitro evaluation, this in vivo 12 months prospective study followed up and compared the access-hole filling integrity of a modified 4-META (4-methacryloxyethyl trimellitate anhydride)/MMA-TBB (methyl methacrylate-tri-n-butyl borane) - based resin (M4M) and a photo-polymerizing nano-hybrid composite resin (CR). Twenty-eight access-holes were filled with both materials respectively, then impressions and intra-oral photographs were taken at T = 0, T = 1 M (month), 3, 6, and 12 M. The access-hole surface measurement and the margin analysis (depth and angle) were carried out. The VAS (visual analogue scale) value on marginal discoloration and integrity at the baseline T = 0 and T = 12 M was recorded.

RESULTS

The mean values of the surface areas changes from T = 1 to T = 12 M were 83.3 ± 11.5% for group CR and 77.1 ± 13.1% for group M4M, respectively. (Mann-Whitney test p < 0.05, p = 0.046). The mean marginal depth at T = 12 M for group CR were 141.2 ± 125.5 μm and 132.1 ± 107.8 μm for the group M4M, respectively. (Mann-Whitney test p > 0.05, p = 0.58). The mean values of the angle formed at the margin (T = 12 M) were for group CR 39.5 ± 19.4° and 28.2 ± 17.2° for group M4M, respectively (Mann-Whitney test p < 0.0001). The photographical analysis by VAS values showed no significant difference between CR and M4M groups (Mann-Whitney test p > 0.05, p = 0.848).

CONCLUSIONS

Based on intra- and extra-oral evaluations with the limitation, both CR and M4M combined with a ceramic primer are indicated as promising materials to fill the access-hole. Further long-term investigation is necessary to confirm this finding.