Static and Fatigue Loading of Veneered Implant-Supported Fixed Dental Prostheses

Marginal fit and fracture resistance of polyetheretherketone, zirconia, and titanium implant-supported prosthesis frameworks for a partially edentulous arch after thermomechanical aging

STATEMENT OF PROBLEM

Although polyetheretherketone (PEEK) and zirconia (Zir) have been used as implant-supported prosthesis (ISP) frameworks, the long-term effects of thermomechanical aging on the marginal fit and fracture resistance of PEEK and Zir ISP frameworks with titanium (Ti) bases for patients with a partially edentulous arch are not clear.

PURPOSE

The purpose of this in vitro study was to determine the marginal fit and fracture resistance of PEEK and Zir ISP frameworks with Ti bases and Ti ISP frameworks for partially edentulous arches after aging.

MATERIAL AND METHODS

A total of 30 ISP epoxy resin casts were obtained from a typodont with 1 straight implant (Nobel Biocare) in the mandibular right canine region and 1 implant with a 30-degree distal tilt in the mandibular right first molar region. All frameworks (n=10) were fabricated on their own epoxy resin cast with multiunit abutment replicas by using a computer-aided design and computer-aided manufacturing system (exocad-Yenadent). The PEEK and Zir frameworks were fabricated with Ti-bases. Primer (MKZ) and resin cement (DTK adhesive) were used to cement the frameworks to the Ti-bases under a static load of 10 N. After thermomechanical aging (1.2×106 cycles, 120 N, 5 °C-55 °C), marginal gaps between the Ti-bases and cemented frameworks and vertical and passive fits between the Ti-bases and framework and multi-unit abutments were measured by using a stereomicroscope (Euromex) at ×100 magnification. Fracture resistances and types were then determined by using a universal test machine and a stereomicroscope at ×40 magnification. Data were analyzed by using 1-way analysis of variance (ANOVA) and the Tukey HSD and Fisher-Freeman-Halton tests (α=.05).

RESULTS

The marginal gaps of the PEEK and Zir frameworks were respectively 83.5 ±27.1 and 81.8 ±17.8 µm. PEEK (23.7 ±4.6) and Zir (32.9 ±8.7) had a better vertical fit (µm) than Ti (52.5 ±10.6) (P<.001). Zir (49.3 ±16.2) (P<.001) and PEEK (70.9 ±19.6) (P>.05) frameworks had better passive fit (µm) than Ti (91.3 ±24.2). Ti had the highest mean fracture resistance (N) (14800.2 ±3442.3) followed by Zir (7318.7 ±1385.1) and PEEK (3448.9 ±486.6) (P<.001). Fracture types were different in different groups (P<.001).

CONCLUSIONS

The PEEK and Zir frameworks with Ti bases had better vertical and passive fit than the Ti frameworks. All ISP frameworks represented mean marginal fit below 92 µm and withstood physiologic occlusal forces after thermomechanical aging.

Effect of Cement Type on Fracture Resistance and Mode of Failure of Monolith vs Bilayered Zirconia Single Crowns

AIM

To compare the fracture resistance and the mode of failure between monolith second-generation zirconia and bilayered first-generation zirconia single crowns cemented by resin cement and glass ionomer cement (GIC).

MATERIALS AND METHODS

A total of 36 maxillary first premolar crowns (5 mm in length × 4 mm in cervical diameter, with a base of 6 mm) were computer-aided design-computer-aided manufacturing (CAD-CAM) milled. They were divided into the following two groups (n = 18) according to the fabrication techniques: Group M - monolith zirconia crown (1-mm axial thickness and 2-mm occlusal thickness) and group B - bilayer zirconia crown (0.5-mm axial thickness and 1-mm occlusal thickness). Each group was further subdivided into the following two subgroups (n = 9) according to the cement used: Subgroup G - cemented using GIC; subgroup R - cemented using resin cement. All crowns were cemented to their corresponding resin dies and stored in distilled water for 72 hours. Each specimen was mounted to the lower member of the universal testing machine with a load cell of 5 kN and a crosshead speed of 0.5 mm/minute. Failure modes were analyzed for fractured parts using scanning electron microscopy (SEM).

RESULTS

Subgroup MR recorded the highest fracture resistance mean value (3616 ± 347.2 N) while the BG subgroup recorded the statistically significant lowest fracture resistance mean value (1728.7 ± 115.3 N). One-way analysis of variance (ANOVA) followed by pairwise Tukey's post hoc tests revealed a statistically significant difference (p = 0.0001) between groups M and B. One-way ANOVA followed by pairwise Tukey's post hoc tests also showed a statistically significant difference (p = 0.0297) between the types of cement used (subgroups G and R).

CONCLUSION

Monolith zirconia crowns had better mean fracture resistance than bilayered zirconia crowns. Resin cement improved the fracture resistance compared to GIC. Monolith zirconia crowns showed bulk fracture while bilayered zirconia crowns showed chipping fracture.

CLINICAL SIGNIFICANCE

Monolith zirconia crowns present a good prosthetic alternative overcoming the veneer chipping drawback of bilayered zirconia crowns. In addition, resin cement could increase the fracture resistance of zirconia crowns.

'Thermo-mechanical behavior of alternative material combinations for full-arch implant-supported hybrid prostheses with short cantilevers'

OBJECTIVES

To compare the fracture resistance (FR) of three combinations of materials for full-arch maxillary implant-supported hybrid prostheses (HPs) with short cantilevers (≤ 10 mm).

METHODS

Maxillary HPs were fabricated and classified as follows (n = 5 each): Group-1 (CC-A, control): acrylic-resin-veneered Co-Cr frameworks; Group-2 (CF-A): acrylic-resin-veneered carbon-fiber mesostructures; and Group-3 (CF-R): composite-resin-veneered carbon-fiber frames. Specimens were thermal-cycled (5,000 cycles; 5 °C-55 °C; dwell time: 30 s). Vertical loads were applied until failure, first at the 10-mm-long cantilever (LC), and, afterwards, at the anterior region (AR), using a universal testing machine (crosshead speed: 0.05 mm/s). The fracture pattern was assessed by stereomicroscope and SEM. The one-way ANOVA, the Bonferroni, and the independent samples t tests, were run (α= 0.05).

RESULTS

At LC, CF-A, and CC-A samples exhibited the highest FR values (p< 0.001), showing no differences to each other. At AR, CC-A specimens recorded the highest FR, followed by CF-A samples (p< 0.001). CF-R HPs displayed the lowest FR at both locations (p< 0.001). The only group with differences between the tested sites was the CC-A, the AR being more resistant (p< 0.001). Most CC-A and CF-A HPs failed cohesively. CF-R prostheses mainly failed adhesively.

CONCLUSIONS

Maxillary HPs with short cantilevers (≤ 10 mm) made of Co-Cr or carbon-fiber veneered with acrylic resin demonstrated an adequate mechanical resistance (> 900 N).

CLINICAL SIGNIFICANCE

For maxillary HPs with cantilevers up to 10 mm, acrylic-veneered carbon- fiber mesostructures may be recommended, whereas coating carbon-fiber frames with composite resin seems not suitable.

Failure Load and Fatigue Behavior of Monolithic and Bi-Layer Zirconia Fixed Dental Prostheses Bonded to One-Piece Zirconia Implants

No evidence-based prosthetic treatment concept for 3-unit fixed-dental-prostheses (FDPs) on ceramic implants is currently available. Therefore, the aim of this in vitro study was to investigate the failure load and fatigue behavior of monolithic and bi-layer zirconia FDPs supported by one-piece ceramic implants. Eighty 3-unit FDPs supported by 160 zirconia-implants (ceramic.implant; vitaclinical) were divided into 4 groups (n = 20 each): Group Z-HT: 3Y-TZP monolithic-zirconia (Vita-YZ-HT); Group Z-ST: 4Y-TZP monolithic-zirconia (Vita-YZ-ST); Group FL: 3Y-TZP zirconia (Vita-YZ-HT) with facial-veneer (Vita-VM9); Group RL (Rapid-layer): PICN “table-top” (Vita-Enamic), 3Y-TZP-framework (Vita-YZ-HT). Half of the test samples (n = 10/group) were fatigued in a mouth-motion chewing-simulator (F = 98 N, 1.2 million-cycles) with simultaneous thermocycling (5−55 °C). All specimens (fatigued and non-fatigued) were afterwards exposed to single-load-to-failure-testing (Z010, Zwick). Statistical analysis was performed using ANOVA, Tukey’s post-hoc tests and two-sample t-tests (p < 0.05, Bonferroni-corrected where appropriate). All specimens withstood fatigue application. While the effect of fatigue was not significant in any group (p = 0.714), the choice of material had a significant effect (p < 0.001). Material FL recorded the highest failure loads, followed by Z-ST, Z-HT and RL, both with and without fatigue application. Taken together, all tested FDP material combinations survived chewing forces that exceeded physiological levels. Bi-Layer FL and monolithic Z-ST showed the highest resilience and might serve as reliable prosthetic reconstruction concepts for 3-unit FDPs on ceramic implants.

Thermal Load and Heat Transfer in Dental Titanium Implants: An Ex Vivo-Based Exact Analytical/Numerical Solution to the ‘Heat Equation’

Introduction: Heat is a kinetic process whereby energy flows from between two systems, hot-to-cold objects. In oro-dental implantology, conductive heat transfer/(or thermal stress) is a complex physical phenomenon to analyze and consider in treatment planning. Hence, ample research has attempted to measure heat-production to avoid over-heating during bone-cutting and drilling for titanium (Ti) implant-site preparation and insertion, thereby preventing/minimizing early (as well as delayed) implant-related complications and failure. Objective: Given the low bone–thermal conductivity whereby heat generated by osteotomies is not effectively dissipated and tends to remain within the surrounding tissue (peri-implant), increasing the possibility of thermal-injury, this work attempts to obtain an exact analytical solution of the heat equation under exponential thermal-stress, modeling transient heat transfer and temperature changes in Ti implants (fixtures) upon hot-liquid oral intake. Materials and Methods: We, via an ex vivo-based model, investigated the impact of the (a) material, (b) location point along implant length, and (c) exposure time of the thermal load on localized temperature changes. Results: Despite its simplicity, the presented solution contains all the physics and reproduces the key features obtained in previous numerical analyses studies. To the best of our knowledge, this is the first introduction of the intrinsic time, a “proper” time that characterizes the geometry of the dental implant fixture, where we show, mathematically and graphically, how the interplay between “proper” time and exposure time influences temperature changes in Ti implants, under the suitable initial and boundary conditions. This fills the current gap in the literature by obtaining a simplified yet exact analytical solution, assuming an exponential thermal load model relevant to cold/hot beverage or food intake. Conclusions: This work aspires to accurately complement the overall clinical diagnostic and treatment plan for enhanced bone–implant interface, implant stability, and success rates, whether for immediate or delayed loading strategies.

New generation CAD-CAM materials for implant-supported definitive frameworks fabricated by using subtractive technologies

Innovations in digital manufacturing enabled the fabrication of implant-supported fixed dental prostheses (ISFDPs) in a wide variety of recently introduced materials. Computer-aided design and computer-aided manufacturing (CAD-CAM) milling allows the fabrication of ISFDPs with high accuracy by reducing the fabrication steps of large-span frameworks. The longevity of ISFDPs depends on the overall mechanical properties of the framework material including its fit, and the physical properties of the veneering material and its bond with the framework. This comprehensive review summarizes the recent information on millable CAD-CAM framework materials such as pre-sintered soft alloys, fiber-reinforced composite resins, PEEK, and PEKK in high-performance polymer family, and 4Y-TZP. Even though promising results have been obtained with the use of new generation millable CAD-CAM materials for ISFDPs, clinical studies are lacking and future research should focus on the overall performance of these millable materials in both static and dynamic conditions.

Evaluation of the Fatigue Strength of a CAD-CAM Nanoceramic Resin Crown on Titanium and Zirconia-Titanium Abutments

A computer-aided design/computer-aided manufacturing (CAD/CAM) resin block material for restoration of single-implant abutments can be milled and cemented on an optimized standard titanium abutment as a cheaper solution or, alternatively, individualization of the crown–abutment connection is required to fulfill the same mechanical requirements. The aim of this study was to evaluate how different structural and geometric configurations of the abutment influence the resistance of a nano ceramic resin crown (NCRC). During the test, 30 implants with an internal conical tapered configuration were considered. Each implant received a standard titanium abutment: in group 1, NCRCs were directly bonded to the titanium abutments; in group 2, NCRCs were cemented on a customized zirconia framework and then cemented on a standardized titanium abutment. Three crowns of each group were submitted to a static load test until failure. The remaining crowns were submitted to a fatigue test protocol with a dynamic load. The static and dynamic test showed earlier failure for group 1. In group 1, complete breaking of NCRCs was observed for all samples, with an almost total titanium abutment exposition. In the static tests, group 2 showed a mode of failure that involved only the crown, which partially debonded from the zirconia abutment. Within the limitations of the present preliminary study, it was possible to conclude that the shape of the abutment mainly influences the fatigue strength compared to the static tensile strength. The results of the performed test show that NCRC bonded to the customized zirconia abutments, and presented a 75% survival rate when compared to the same material bonded directly to a standard titanium abutment.