Mechanical resistance of zirconium implant abutments: a review of the literature

Implant angulation and fracture resistance of one-piece screw-retained hybrid monolithic zirconia ceramic restorations

OBJECTIVE

This study aimed to investigate the fracture resistance of one-piece screw-retained hybrid monolithic zirconia ceramic restorations in different implant angulations.

MATERIALS AND METHODS

Three implant fixtures were embedded in acrylic resin blocks with 0°, 15°, and 25° angulations. For each group of implant angulations, 11 screw-retained one-piece monolithic zirconia restorations were made and bonded to the titanium inserts with a dual-cure self-adhesive resin. The complexes were screwed to the implant fixtures with titanium screws. The samples were thermocycled, subjected to compressive load, and fracture modes were recorded. One-way ANOVA and post hoc Tukey's test were used for statistical analyses (α = 0.05).

RESULTS

One-way ANOVA showed the fracture resistance to be significanltly different among the study groups (P = 0.036). The 15° group was significantly more resistant than 0° (P = 0.031). However, the 25° group was not significantly different from the 15° (P = 0.203) and 0° groups (P = 0.624). Fractures occurred only on the restorations, not at the screw levels.

CONCLUSIONS

Tilting the implant up to 15° improves the fracture resistance of one-piece screw-retained hybrid monolithic zirconia restorations; however, increasing the tilt to 25° would not yield restorations with significantly better fracture strength than the straight implants. Accordingly, when angulated implants are indicated in the esthetic zones, one-piece screw-retained hybrid monolithic zirconia ceramic restorations can be used with acceptable fracture strength.

Influence of Screw Channel Angulation on the Fracture Resistance of Zirconia Abutments: An In Vitro Study

PURPOSE

The aim of this study was to investigate the effect of implant screw channel angulation on the fracture resistance of zirconia abutments without artificial aging.

MATERIALS AND METHODS

Ten implant replicas were embedded in a jig of autopolymerizing acrylic resin. Using a surveyor and a metallic platform, the implant replicas were mounted centrally and with an angulation of 30°. A maxillary left central incisor crown was fabricated from pattern resin and scanned. The digital design of a monolithic zirconia implant abutment-crown was completed using a 3D imaging software. For all specimens of this group (ASC₂₅ ), the screw channel was positioned at 25° to the lingual. Following fabrication, the samples were attached onto the embedded implant replicas and manually torqued to 35 Ncm as recommended by the manufacturer. The monolithic zirconia implant abutment-crowns were mounted in a metallic platform, positioned perpendicular to the indenter, and subjected to loading until failure. Crosshead speed was set at 0.5 mm/min for the universal testing machine. Data from a similar in vitro study where straight zirconia custom abutments (ASC₀ ) were subjected to static load until failure was used as a control group. An unpaired Student's t-test was used to determine if fracture resistance based on load at failure and maximum load in each group were significantly different from each other (ASC₂₅ vs ASC₀ ). Statistical significance level was inferred at p ≤ 0.05 RESULTS: Group ASC₂₅ fractured at a mean (SD) load of 215.49 (47.10) N and a mean (SD) maximum load of 420.50 (17.18) N. Group ASC₀ fractured at a mean (SD) load of 534.04 (133.77) N and a mean (SD) maximum load of 762.69 (109.59) N. The difference was statistically significant for both mean load and mean maximum load at failure (p ≤ 0.05). The survival rate of 0° zirconia abutments was significantly higher than that of 25° ASC zirconia abutments.

CONCLUSIONS

Within the limitations of this in vitro study the mean fracture load was significantly higher in the group with a straight channel angulation.

Mechanical behavior of single-layer ceramized zirconia abutments for dental implant prosthetic rehabilitation

Objectives: This study was undertaken to characterize the mechanical response of bare (as-received) and single-layer ceramized zirconia abutments with both internal and external connections that have been developed to enhanced aesthetic restorations. Material and Methods: Sixteen zirconia implant abutments (ZiReal Post®, Biomet 3i, USA) with internal and external connections have been analyzed. Half of the specimens were coated with a 0.5mm-thick layer of a low-fusing fluroapatite ceramic. Mechanical tests were carried out under static (constant cross-head speed of 1mm/min until fracture) and dynamic (between 100 and 400N at a frequency of 1Hz) loading conditions. The failure location was identified by electron microscopy. The removal torque of the retaining screws after testing was also evaluated. Results: The average fracture strength was above 300N for all the abutments, regardless of connection geometry and coating. In most of the cases (94%), failure occurred by abutment fracture. No significant differences were observed either in fatigue behavior and removal torque between the different abutment groups. Conclusions: Mechanical behavior of Zireal zirconia abutments is independent of the type of internal/external connection and the presence/absence of ceramic coating. This may be clinically valuable in dental rehabilitation to improve the aesthetic outcome of zirconia-based dental implant systems.

Key words:Dental implant, zirconia, ceramic structure, mechanical properties.

Formation of white oxide layer on Zr-14Nb alloy using thermal treatment

This study aimed to develop a novel abutment material with good esthetic and mechanical properties by producing a white oxide layer on a zirconium-14 mass% niobium (Zr-14Nb) alloy substrate using a thermal oxidation process. Oxidation temperatures ranged 700-1000°C and oxidation time ranged 30-180 min. The color of the oxide layer varied depending on temperature and time. A white oxide layer was obtained under appropriate conditions. The oxide layer thickness increased with increased temperature and time, as revealed by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Moreover, X-ray diffraction and X-ray photoelectron spectroscopy revealed that the oxide layer was predominantly monoclinic ZrO2, tetragonal ZrO2, and Nb2O5. The oxide layer revealed good abrasion resistance and high adhesion to the substrate. This novel process for producing white materials with good mechanical properties will be useful for abutments and prostheses in dental implant treatment.

Multiple teeth replacement with endosseous one-piece yttrium-stabilized zirconia dental implants

Objectives: The purpose of this study is to clinically and radiographically evaluate survival and success rate of multiple zirconia dental implants positioned in each patient during a follow-up period of at least 12 months up to 48 months. Study Design: Eight patients were treated for multiple edentulism with 29 zirconia dental implants. All implants received immediate temporary restorations and 6 months after surgery were definitively restored. 6 months to 4 years after implant insertion, a clinical-radiographic evaluation was performed in order to estimate peri-implant tissues health and peri-implant marginal bone loss. Results: Survival rate within follow-up period was therefore 100%. The average marginal bone loss (MBL) from baseline to 6 months was +1.375±0.388 mm; from 6 months to 1 year was +0.22±0.598 mm; from 1 year to 2 years was -0.368±0.387 mm; from 2 years to 3 years was -0.0669±0.425 mm; from 3 years to 4 years +0.048±0.262 mm. The mean marginal bone loss at 4 years from the implants insertion was +1.208 mm. Conclusions: According to several studies, when using a radiographic criterion for implant success, marginal bone loss below 0.9-1.6 mm during the first year in function can be considered acceptable. In our work, radiographic measurements of MBL showed values not exceeding 1.6 mm during the first year of loading and also 1 year up to 4 years after surgery further marginal bone loss was minimal and not significant. This peri-implant bone preservation may be associated to the absence of micro-gap between fixture and abutment since zirconia dental implants are one-piece implant. Moreover, zirconia is characterized by high biocompatibility and it accumulates significantly fewer bacteria than titanium.

Key words:Zirconia dental implants, multiple implants, radiographic evaluation, marginal bone loss (MBL).