Fracture analysis of one/two-piece clinically failed zirconia dental implants.

OBJECTIVES: Analyzing factors that may have led to fracture of zirconia implants by macro/micro-fractography. METHODS: Six one-piece and ten two-piece full-ceramic zirconia implants from two manufacturers, Z-Systems and CeraRoot, were retrieved after clinical failure. The time-to-failure ranged from 3 to 49 months. Optical and scanning electron microscopy (SEM) were used to analyze the fracture planes at the macro- and microscopic level. Treatment planning, surgical protocol, fracture-origin location and characteristic fracture features were assessed. RESULTS: The fracture of all implants seemed to have been primarily due to overload in bending mode, while the fracture-initiation sites varied for the one- and two-piece implants. The fracture of all one-piece implants originated in the constriction region between two threads in the endosseous implant part. For two-piece implants, the abutment neck, internal abutment-implant connections and inner threads were found to be the main fracture-initiation sites. Surface defects at the root area for one-piece implants and damages at the abutment surface for two-piece implants were connected to the fracture origins. Importantly, the clinical failures of implants were often found to result from combined effects related to patient aspects, treatment planning/protocols, a high bending moment at the weakest link, implant-surface conditions and specific implant designs. SIGNIFICANCE: This study provided information to be considered for future optimization of treatment planning and the surgical protocol for zirconia implants. Optimization of the surface conditions and the zirconia-starting powder were also suggested.

Influence of artificial aging on mechanical properties of commercially and non-commercially available zirconia dental implants.

OBJECTIVE: To evaluate the effect of artificial aging on the mechanical resistance and micromechanical properties of commercially and noncommercially available zirconia dental implants. METHODS: Scanning electron microscopy (SEM) and X-ray computed tomography (X-CT) were performed on implant systems including: Z-systems®, Straumann®, Zibone® and commercially and non-commercially available TAV dental® with varying grain sizes. Accelerated aging was performed at 134 °C and 2-bar pressure for 30 hours. Before and after aging, the mechanical load to failure was investigated and the bending moments were calculated. Nanoindentation responses of the representative Zibone implant before and after aging were performed to evaluate the effects of aging on hardness (H) and Young's modulus (E). A two-sample t-test statistical analysis was used to determine significant differences of bending moments within groups. RESULTS: All implants presented with compact and homogenous core structures without porosities. The bending moment was significantly increased after aging for all groups (P ≤ 0.05) except for Z-systems (significant decrease (P = 0.022)) and TAV group 3 (no significant increase (P = 0.181)). The increase in bending moment was less pronounced with increasing grain size in TAV groups (group 1: P = 0.036, group 2: P = 0.05, group 3: P = 0.18). E and H were reduced approximately 32% and 18% respectively following aging within the transformed, microcracked zone of the presentative Zibone implant. CONCLUSIONS: Aging led to both increase and decrease of the mechanical properties of the implant systems analyzed. The apparent contrast amongst groups can be explained based on differences in grain sizes and surface features. Aging decreased micromechanical properties of one implant system which warrants further investigation.

Zirconia dental implants: A clinical and radiographic evaluation.

OBJECTIVE: Limited clinical evidence has been reported in dental literature regarding zirconia dental implants. The aim of the present retrospective consecutive case series was to evaluate the clinical outcome of zirconia dental implants with 1 to 5 years of follow-up. CLINICAL CONSIDERATIONS: The clinical outcome of 24 implants in 12 consecutive patients (male 5, female 7) with a mean age of 55 years (range 27-86) is reported. Radiographic crestal bone level was assessed by the use of "ImageJ" software program. Gingival and plaque indices were recorded at baseline and latest follow-up. CONCLUSION: The overall success rate of zirconia implants was 92%. Within the limitations of the present clinical evaluation, zirconia implants provided excellent clinical results and esthetic outcomes. A mean periimplant bone loss of 0.3 mm was measured in 33.3% of the implants and 66.7% were not affected by radiographic detectable periimplant bone loss. Two implants in two patients failed. Low gingival and plaque indices were predominant values for both interim and final restorations. The apparent less affinity to plaque accumulation may favor soft tissue health around zirconia dental implants and decrease the risk of inflammation or infection. Zirconia dental implant merits further investigation. CLINICAL SIGNIFICANCE: Zirconia dental implants are emerging as an option in clinical practice of implant dentistry providing stable clinical results and esthetic outcomes.

The Impact of In Vitro Accelerated Aging, Approximating 30 and 60 Years In Vivo, on Commercially Available Zirconia Dental Implants.

BACKGROUND: Despite increased popularity of Zirconia dental implants, concerns have been raised regarding low temperature degradation (LTD) and its effect on micro-structural integrity. PURPOSE: This study evaluated the effect of LTD on four types of Zirconia dental implants at 0, 30, and 60 years of artificial aging. The impact of aging on t-m transformation and micro crack formation was measured. MATERIALS AND METHODS: Accelerated aging at 15 and 30 hours, approximating 30 and 60 years in vivo, aged 36 Zirconia dental implants: Z systems® (A), Straumann® (B), Ceraroot® (C), and Zeramex® (D). Focused ion beam-scanning electron microscopic analysis determined the micro structural features, phase transformation, and the formation of micro cracks. RESULTS: At 15 hours, type A implant presented with micro cracks and t-m transformation of 0.9 µm and 3.1 µm, respectively. At 30 hours, micro cracks remained shallow (1 µm). At 15 hours, type B implant presented micro cracks (0.7 µm) and grain transformation (1.2 µm). At 30 hours, these features remained superficial at 0.6 and 1.5 µm, respectively. Type C implant presented surface micro cracks of 0.3 µm at 15 hours. The depth of t-m transformation slightly increased to 1.4 µm. At 30 hours, number of micro cracks increased at the surface to an average depth of 1.5 µm. Depth of t-m transformation increased to an average of 2.5 µm. At 15 hours, micro cracks remained superficial (0.8 µm) for type D implant and depth of t-m transformation increased to 2.3 µm. At 30 hours, the depth of micro cracks increased to an average of 1.3 µm followed by increased t-m transformation to a depth of 4.1 µm. CONCLUSION: Depth of grain transformation remained within 1-4 µm from the surface. The effect of aging was minimal for all Zirconia implants.