Fracture strength of anterior cantilever resin-bonded fixed partial dentures fabricated from high translucency zirconia with different intaglio surface treatments

Optimal design of the retainer and connector for a lithium disilicate resin-bonded fixed partial denture: A finite element analysis study

STATEMENT OF PROBLEM

How the connector shape, retainer type, and retainer placement affect the functional stresses in lithium disilicate cantilever resin-bonded fixed partial dentures (RBFPDs) is unclear.

PURPOSE

The purpose of this finite element analysis (FEA) study was to evaluate the effects of the connector shape, retainer type, and retainer placement on the stress distribution and magnitude of stress in RBFPDs.

MATERIAL AND METHODS

Cantilever RBFPDs of the maxillary anterior lateral incisor with a retainer on the canine were modeled to conduct a 3-dimensional FEA. These designs were divided into 2 groups based on connector shape: rectangular and trapezoidal. Each group included 4 different retainer configurations-either labial or palatal veneer RBFPDs (LV-RBFPD or PV-RBFPD) or labial or palatal contact-point RBFPDs (LC-RBFPD or PC-RBFPD). FEA was performed for each RBFPD to evaluate stresses during regional and 3-point loading, including maximal intercuspal, protrusive, and lateral mandibular positions. The results were evaluated via colorimetric stress maps of the equivalent von Mises stress, maximum principal stress, and minimum principal stress in the prosthesis.

RESULTS

The connector shape, retainer type, and placement affected the RBFPD stress, and the lowest stress was observed in the rectangular group. The LC-RBFPD group presented the lowest maximum principal stress (348.2 MPa) and minimum principal stress (49.1 MPa) under regional loading and the lowest equivalent stress (273.4 MPa) and maximum principal stress (356.0 MPa) with the protrusion position. The LV-RBFPD group presented the lowest equivalent stress (52.0 MPa), the lowest maximum principal stress (47.5 MPa), and the minimum principal stress (1.04 MPa) at the maximal intercuspal position, the lowest minimum principal stress (1.04 MPa) at the protrusion position, and the lowest equivalent stress (46.7 MPa) at the lateral position. The PV-RBFPD group presented the lowest equivalent stress (268.5 MPa) under regional loading and the lowest maximum principal stress (37.7 MPa) and minimum principal stress (2.02 MPa) under lateral loading.

CONCLUSIONS

A rectangular cross-sectional connector design for all groups could help disperse occlusal force and improve the resistance of the restoration. Both the veneer and contact-point retainer in the rectangular group were clinically acceptable and could resist fracture.

A dual composite resin injection molding technique with 3D-printed flexible indices for biomimetic replacement of a missing mandibular lateral incisor

PATIENTS

This case report presents a minimally invasive approach to replace a missing mandibular lateral incisor using a dual-injection molding technique with flowable composite resins. Integrated with a comprehensive digital workflow, this method achieves a structurally and esthetically biomimetic, bi-layered prosthetic solution. A 34-year-old woman with congenital absence of a mandibular lateral incisor was successfully rehabilitated using a direct composite resin-bonded fixed partial denture (RBFPD).

DISCUSSION

Two specialized three-dimensional (3D)-printed flexible indices stabilized by a custom-designed 3D-printed rigid holder were employed to ensure the meticulous injection molding of flowable composite resins formulated to emulate the inherent chromatic gradations between dentin and enamel. The inherent flexibility of the indices, combined with the holder, facilitated accurate and seamless adaptation to the complex morphological features of the dental arch, thereby mitigating the challenges commonly associated with rigid 3D-printed resin indices.

CONCLUSIONS

The bilayered direct composite RBFPD using 3D printed flexible indices prepared with a full digital workflow has several advantages over other dental prosthetic solutions, including noninvasiveness, cost-effectiveness, biomimetic esthetics, repairability, and shortened treatment times. Although the initial results are promising, further longitudinal studies with larger patient cohorts are required to confirm the long-term efficacy of this approach.

Shear bond strength between standard or modified zirconia surfaces and two resin cements incorporating or not 10-MDP in their matrix

OBJECTIVE

This study aimed first to compare the shear bond strength between zirconia samples luted to enamel with a 10-MDP- containing resin cement (Panavia F2.0, Kuraray, Japan) and those luted with a resin cement using a separated 10-MDP monomer-containing bottle (Panavia V5, Kuraray, Japan). The second objective was to evaluate the bond stability after 150 days of aging in water, between enamel and zirconia ceramic surface enhanced with a glass-ceramic coating.

MATERIALS AND METHODS

80 specimens composed of ceramic cylinders and enamel disks were obtained, within eight experimental groups (n = 10). 60 zirconia cylinders (Katana STML zirconia, Kuraray, Japan) were assigned to 3 groups according to their surface treatment: milled/sintered surface (ZRCT), tribochemical silica-coating (Cojet™ Sand, 3 M ESPE, Seefeld, Germany) (ZRTC), and glass-ceramic coating (IPS e.max Zirpress) (ZRZP). 20 cylinders of lithium disilicate had a milled surface (IPS e.max CAD, Ivoclar-Vivadent, Schaan, Liechtenstein) (ECAD). The cylinders of each group were further divided into two subgroups according to the resin cement used: Panavia F2.0 (-PF) and Panavia V5 (-PV). All specimens were stored in distilled water for 150 days before shear bond strength (SBS) tests. The fracture mode was analyzed, and data were statistically computed (two-way ANOVA, post hoc Tukey test, p < 0.05, SPSS, IBM, v26).

RESULTS

The ECAD-PF group recorded the highest SBS values (31.75 ± 2.2), and the ZRCT-PF group recorded the lowest values (5.59 ± 1.1). The two-way ANOVA test showed that ceramic surface treatment had a statistically significant effect on SBS (F (3,72) = 38.95, p < 0.001) while the type of ARC did not (F (1,72) = 2.40, p = 0.126). Tukey's post hoc test revealed no statistical difference between the ZRZP and the ZRTC or ECAD groups.

CONCLUSION

Within the limitations of this study, the PV resin achieved similar shear bond strength results between tribocoated zirconia and enamel compared to the one for glass-ceramic and enamel. Furthermore, a long-term durable bond, similar to the glass-ceramic one, was achieved with the heat pressed ceramic coated specimens. Thus, this new surface treatment could be recommended for anterior cantilever bridges for its fracture resistance and bonding ability.