Effect of Loading Angles and Implant Lengths on the Static and Fatigue Fractures of Dental Implants

Material properties and finite element analysis of adhesive cements used for zirconia crowns on dental implants

This study aimed to evaluate the material properties of four dental cements, analyze the stress distribution on the cement layer under various loading conditions, and perform failure analysis on the fractured specimens retrieved from mechanical tests. Microhardness indentation testing is used to measure material hardness microscopically with a diamond indenter. The hardness and elastic moduli of three self-adhesive resin cements (SARC), namely, DEN CEM (DENTEX, Changchun, China), Denali (Glidewell Laboratories, CA, USA), and Glidewell Experimental SARC (GES-Glidewell Laboratories, CA, USA), and a resin-modified glass ionomer (RMGI-Glidewell Laboratories, CA, USA) cement, were measured using microhardness indentation. These values were used in the subsequent Finite Element Analysis (FEA) to analyze the von Mises stress distribution on the cement layer of a 3D implant model constructed in SOLIDWORKS under different mechanical forces. Failure analysis was performed on the fractured specimens retrieved from prior mechanical tests. All the cements, except Denali, had elastic moduli comparable to dentin (8-15 GPa). RMGI with primer and GES cements exhibited the lowest von Mises stresses under tensile and compressive loads. Stress distribution under tensile and compressive loads correlated well with experimental tests, unlike oblique loads. Failure analysis revealed that damages on the abutment and screw vary significantly with loading direction. GES and RMGI cement with primer (Glidewell Laboratories, CA, USA) may be suitable options for cement-retained zirconia crowns on titanium abutments. Adding fillets to the screw thread crests can potentially reduce the extent of the damage under load.

An In Vitro Investigation of the Role of Implant Abutment Materials on the Fracture Resistance and Failure Mode of Implant-Supported Restorations

BACKGROUND

Implant-supported restorations have gained popularity in modern dentistry, and the choice of abutment material is crucial for their long-term success. This in vitro study aimed to evaluate the fracture resistance and failure mode of implant-supported restorations using different abutment materials.

METHODS

Ninety standardized implant-supported restorations were included in the study. Abutments made of titanium, zirconia, and a hybrid material (titanium base with a zirconia veneer) were evaluated. Standardized abutments were fabricated, and screw-retained restorations were fabricated using a resin-based composite material. Cyclic loading was applied using a universal testing machine to simulate masticatory forces. Fracture resistance was measured in terms of the number of cycles to failure (NCF), and failure modes were analyzed.

RESULTS

The findings indicate that zirconia abutments exhibited higher fracture resistance compared to titanium and hybrid abutments. Longer implants demonstrated higher fracture resistance, suggesting improved stability and resistance to mechanical forces. Increased loading angles resulted in decreased fracture resistance of implant-supported restorations, emphasizing the need for proper occlusal adjustment. Central loading showed higher fracture resistance than lateral and posterior loading locations. The distribution of failure modes varied among the abutment materials, with bulk prosthesis fracture being the most common in the titanium group, while abutment fracture was predominant in the zirconia and hybrid groups.

CONCLUSION

This in vitro study demonstrated that the choice of abutment material significantly influenced the fracture resistance and failure mode of implant-supported restorations. Zirconia abutments exhibited the highest fracture resistance, followed by hybrid and titanium abutments. The failure mode analysis revealed different patterns of failure for each abutment material.

Mechanical and Biological Properties of Titanium and Its Alloys for Oral Implant with Preparation Techniques: A Review

Dental implants have revolutionised restorative dentistry, offering patients a natural-looking and durable solution to replace missing or severely damaged teeth. Titanium and its alloys have emerged as the gold standard among the various materials available due to their exceptional properties. One of the critical advantages of titanium and its alloys is their remarkable biocompatibility which ensures minimal adverse reactions within the human body. Furthermore, they exhibit outstanding corrosion resistance ensuring the longevity of the implant. Their mechanical properties, including hardness, tensile strength, yield strength, and fatigue strength, align perfectly with the demanding requirements of dental implants, guaranteeing the restoration's functionality and durability. This narrative review aims to provide a comprehensive understanding of the manufacturing techniques employed for titanium and its alloy dental implants while shedding light on their intrinsic properties. It also presents crucial proof-of-concept examples, offering tangible evidence of these materials' effectiveness in clinical applications. However, despite their numerous advantages, certain limitations still exist necessitating ongoing research and development efforts. This review will briefly touch upon these restrictions and explore the evolving trends likely to shape the future of titanium and its alloy dental implants.

Stress-strain and fatigue life numerical evaluation of two different dental implants considering isotropic and anisotropic human jaw

Dental prostheses are currently a valid solution for replacing potential missing tooth or edentulism clinical condition. Nevertheless, the oral cavity is a dynamic and complex system: occlusal loads, external agents, or other unpleasant events can impact on implants functionality and stability causing a future revision surgery. One of the failure origins is certainly the dynamic loading originated from daily oral activities like eating, chewing, and so on. The aim of this paper was to evaluate, by a numerical analysis based on Finite Elements Method (FEM), and to discuss in a comparative way, firstly, the stress-strain of two different adopted dental implants and, subsequently, their fatigue life according to common standard of calculations. For this investigation, the jawbone was modeled accounting for either isotropic or anisotropic behavior. It was composed of cortical and cancellous regions, considering it completely osseointegrated with the implants. The impact of implants' fixture design, loading conditions, and their effect on the mandible bone was finally investigated, on the basis of the achieved numerical results. Lastly, the life cycle of the investigated implants was estimated according to the well-established theories of Goodman, Soderberg, and Gerber by exploiting the outcomes obtained by the numerical simulations, providing interesting conclusions useful in the dental practice.

Does the Length of Mini Dental Implants Affect Their Resistance to Failure by Overloading?

Objective: We aimed to evaluate the failure resistance of different lengths of mini dental implants from the same manufacturer, and to assess their failure following overloading. Materials and Methods: According to the ISO 14801, 15 mini dental implants 2.4 mm in diameter, with lengths of 8.5 mm, 10 mm, or 13 mm, were subjected to compression loading until failure using a universal testing machine. The mean load-to-failure values for each length of the mini dental implants were calculated and analysed using SPSS®, via one-way ANOVA (p < 0.05). Results: The mean load to failure for mini dental implants was 329 N (SD 6.23), 326 N (SD 5.95), and 325 N (SD 6.99) for the 13 mm, 10 mm, and 8.5 mm implants, respectively. A comparison of means showed no significant difference between the groups (p = 0.70). The tested mini dental implants exhibited bending failure modes below the first thread. Conclusion: Under high compressive loading testing, there was no effect of the length on the failure of the mini dental implants following overloading. Moreover, all tested mini dental implants with different lengths showed the same failure mode and distortion location.

Analysis of microstructure and fatigue of cast versus selective laser-melted dental Co-Cr alloy

STATEMENT OF PROBLEM

The forces exerted on teeth and prostheses during mastication are repeated and dynamic, resulting in fatigue damage to dental prostheses. Most fractures of dental restorations are fatigue failure. The 4-point bend fatigue behavior of Co-Cr-Mo-W alloys manufactured by investment casting (CAST) and selective laser melting (SLM) has received little attention.

PURPOSE

The purpose of this in vitro study was to evaluate the 4-point bend fatigue property of dental Co-Cr alloys and determine the relationship between microstructure and the 4-point bend fatigue property of Co-Cr alloys created by traditional casting and SLM. These can guide the use of Co-Cr alloy in dentistry.

MATERIAL AND METHODS

Co-Cr-Mo-W alloys were fabricated with a dimension of 45×2×2 mm by investment casting and SLM. The 3-point bend test measured the ultimate bend strength with 3 specimens in each group. The 4-point bend fatigue test evaluated the fatigue life under various stresses, with 6 specimens in each group. The specimens were mechanically ground, polished, and electrochemically etched. Scanning electron microscopy was used to identify the microstructures of both etched specimens and fracture surfaces. X-ray diffraction investigations were used to determine the phases. Significant differences in the bend strength were analyzed by using the independent samples t test (α=.05), and the fatigue test was analyzed with ANCOVA (α=.05).

RESULTS

The mean ±standard deviation bend strength of SLM specimens was 1837 ±3 MPa, higher than the 1200 ±6 MPa for CAST specimens (P<.05). The maximum bend stress of the SLM specimens without fatigue failure was 735 MPa, which was statistically higher than the 394 MPa for CAST specimens (P<.05). The microstructure characteristics of the SLM alloy contributed to its excellent fatigue performance. In SLM alloy, the γ phase constituted the majority with some ε and Laves phases, while the cast alloy possessed higher ε and Laves phases. The grains of SLM alloy were equiaxed and fine, and the second phases were fine and dispersive. In contrast, the cast alloy possessed clear dendrites, and the second phases were sizable.

CONCLUSIONS

The SLM dental Co-Cr-Mo-W alloy had statistically better 4-point bend fatigue properties than cast alloy, which was associated with an improved microstructure.

Effects of abutment screw preload and preload simulation techniques on dental implant lifetime

Background

This study aimed to investigate how the predicted implant fatigue lifetime is affected by the loss of connector screw preload and the finite element analysis method used to simulate preload.

Methods

A dental implant assembly (DI1, Biomet-3i external hex; Zimmer Biomet) was scanned using microcomputed tomography and measured using Mimics software (Materialise) and an optical microscope. Digital replicas were constructed using SolidWorks software (Dassault Systèmes). The material properties were assigned in Abaqus (Dassault Systèmes). An external load was applied at 30° off-axial loading. Eight levels of connector screw preload (range, 0-32 Ncm) were simulated for DI1. This assembly and an additional model (DI2) having a longer and narrower screw were compared regarding their fatigue limits (using fe-safe software [Dassault Systèmes]) for 2 preloading methods: (1) adding preload torque or (2) adding bolt axial tension.

Results

The maximum von Mises stresses of DI1 (on the connector screw threads) with and without preload were 439.90 MPa and 587.90 MPa. The predicted fatigue limit was the same for preloads from 100% through 80% of the manufacturer^'s recommendation and dropped precipitously between 80% and 70% preload. Adding a preload torque on the screw resulted in a more uniform stress distribution on the screw compared with bolt axial tension, especially for DI2, which had a longer and narrower screw than DI1.

Conclusions

A substantial loss of preload can be accommodated without compromising the fatigue resistance of this dental implant. Computer models should be constructed using torque instead of a bolt axial tension.