In vitro assessment of PEEK and titanium implant abutments: Screw loosening and microleakage evaluations under dynamic mechanical testing.

STATEMENT OF PROBLEM: Polyetheretherketone (PEEK) has been advocated to replace metal components in dentistry. Although PEEK is a high-performance polymer with a white color, adequate biological response, and resistance to fracture, data to support PEEK as an alternative material for implant abutments are lacking. PURPOSE: The purpose of this in vitro study was to assess the mechanical and functional properties of PEEK implant abutments as a nonmetallic alternative to titanium abutments, which presents esthetic limitations and greater difficulty to customize clinically. MATERIAL AND METHODS: Implant abutments manufactured by using PEEK (n=24) or titanium grade 5 (n=24) were attached to MIS Implants type M4 3.75×16 mm with an internal screw tightened to 25 Ncm. Screw loosening and microleakage was assessed by submersion in a 2% methylene blue solution for 48 hours at 37 °C. Both groups were compared with and without applying dynamic loading; fatigue testing was performed following the International Organization for Standardization (ISO) 14801:2016 standard. All specimens were observed under a stereomicroscope at ×8 magnification. Statistically significant differences among the PEEK and titanium implant abutments were tested with 2-factor ANOVA and the chi-square analysis for nonpaired and paired data, respectively (α=.05). RESULTS: The implant abutments made of titanium were better in all mechanical tests. The torque loss of titanium abutments was approximately 10%, while PEEK showed a significantly higher (P<.05) torque loss of up to 50%. Moreover, 91.6% of the titanium abutments did not present microleakage, while there was no specimen of PEEK abutments without microleakage, once subjected to dynamic loading (P<.05). CONCLUSIONS: Titanium implant abutments (Ti6Al4V) were better in all tests performed. However, PEEK abutments may be suitable for long-term interim restorations, especially in the anterior area, in patients without parafunction.

Fracture Resistance of Two Different Composite Resin CAD/CAM Crowns Bonded to Titanium Abutments.

PURPOSE: To determine the influence of thermal and mechanical cycling on fracture load and fracture pattern of resin nanoceramic crowns and polymer-infiltrated ceramic-network (PICN) crowns, both fabricated with CAD/CAM technology. MATERIALS AND METHODS: A total of 90 premolar crowns bonded to titanium abutments were divided into three groups of 30 crowns each: 30 resin nanoceramic crowns (LU); 30 PICN crowns (VE); and 30 metal-ceramic crowns (MC). The 30 specimens of each group were further divided into three subgroups of 10 each that underwent (1) no treatment, (2) thermocycling (2,000 cycles, 5°C to 55°C), and (3) thermocycling with subsequent mechanical cycling (120,000 cycles, 80 N, 2 Hz). The specimens were loaded to failure, and two-way ANOVA and chi-square test were used to determine differences in fracture resistance and pattern. RESULTS: Mechanical and thermal cycling significantly influenced the critical load to failure of the three materials; however, no significant differences were observed between the thermocycled materials and the materials that were thermocycled with subsequent mechanical cycling. The MC specimens experienced significantly higher fracture loads than those of the LU and VE specimens, which showed no differences from each other in fracture resistance. The fracture patterns showed chipping in MC crowns and partial or complete fracture in LU and VE crowns. The fracture pattern depended on the material and was unrelated to the type of treatment it underwent. CONCLUSION: All crowns showed adequate resistance to normal masticatory forces in the premolar area. The cyclic fatigue load negatively influenced all three materials.

Postes intrarradiculares de fibra de vidrio retenidos con cementos resinosos: revisión de la literatura / Glass fiber posts retention to radicular dentin with resin cements: a literature review

Introducción: La descementación del poste es una causa importante del fracaso de los dientes endodonciados reconstruidos con retención intrarradicular, por lo que es un reto restaurativo para el clínico. Aún existe controversia acerca de qué sistema de cementado proporciona mayor retención del poste. El objetivo de esta revisión es hacer un análisis descriptivo de las publicaciones que existen sobre la retención de los postes de fibra de vidrio con los tres tipos de cementos resinosos: grabado y lavado, autograbadores y autoadhesivos. Material y métodos: Búsqueda en la base de datos MEDLINE (Pubmed), limitando la búsqueda a estudios in vitro publicados en revistas indexadas, con máximo 10 años de antigüedad y en idioma inglés. Las palabras clave utilizadas fueron «glass fiber post & resin cements» y «posts retention & resin cements». Resultados: Tras la búsqueda se hallaron 42 artículos, de los cuales solo 20 cumplían los criterios de selección. De los nueve artículos que valoraban la retención con los tres sistemas de cementos resinosos, la mayoría encontró valores superiores de retención para los cementos autoadhesivos. De los siete artículos en que se comparaba la retención de los sistemas de cementos de resina convencional y los autoadhesivos, también la mayoría encontró mayores valores de retención para los cementos autoadhesivos. Conclusiones: La retención de los postes de fibra de vidrio mediante cualquiera de los cementos resinosos es una técnica válida y predecible, existiendo evidencia parcial de que los sistemas autoadhesivos consiguen una mayor retención a la dentina radicular

Introduction: Post debonding is the main cause of failure of endodontically treated teeth and its restoration remains a challenge for clinicians. There is still controversy about which system provides greater post retention. The objective of this review is to make a descriptive analysis of the publications about the retention of glass fiber post using the three resin cement systems: etch and rinse, self-etch and self-adhesive. Material and Methods: Search in MEDLINE databases (Pubmed), limiting the search to «in vitro» studies published in indexed journals within the last ten years. The key words used were: «glass fiber post & resin cements» and «posts retention & resin cements». Results: They were found 42 articles, which only 20 met the selection criteria. Nine studies compared the retention using the three resin cements systems, finding most of them higher retention values for the self-adhesive systems. Amongst the seven studies comparing the retention of conventional resin cements systems with self-adhesive systems, self-adhesive systems showed higher retention. Conclusions: Glass fiber post retention using resin cements seems to be a valid and predictible technique, with partial evidence suggesting that self-adhesive systems achieve a higher retention to radicular dentin

In-vitro development of a temporal abutment screw to protect osseointegration in immediate loaded implants.

PURPOSE: In this study, a temporal abutment fixation screw, designed to fracture in a controlled way upon application of an occlusal force sufficient to produce critical micromotion was developed. The purpose of the screw was to protect the osseointegration of immediate loaded single implants. MATERIALS AND METHODS: Seven different screw prototypes were examined by fixing titanium abutments to 112 Mozo-Grau external hexagon implants (MG Osseous®; Mozo-Grau, S.A., Valladolid, Spain). Fracture strength was tested at 30° in two subgroups per screw: one under dynamic loading and the other without prior dynamic loading. Dynamic loading was performed in a single-axis chewing simulator using 150,000 load cycles at 50 N. After normal distribution of obtained data was verified by Kolmogorov-Smirnov test, fracture resistance between samples submitted and not submitted to dynamic loading was compared by the use of Student's t-test. Comparison of fracture resistance among different screw designs was performed by the use of one-way analysis of variance. Confidence interval was set at 95%. RESULTS: Fractures occurred in all screws, allowing easy retrieval. Screw Prototypes 2, 5 and 6 failed during dynamic loading and exhibited statistically significant differences from the other prototypes. CONCLUSION: Prototypes 2, 5 and 6 may offer a useful protective mechanism during occlusal overload in immediate loaded implants.

Adhesion of dental porcelain to cast, milled, and laser-sintered cobalt-chromium alloys: shear bond strength and sensitivity to thermocycling.

STATEMENT OF PROBLEM: New technologies have led to the introduction of new materials, so an evaluation of the adhesion of ceramics to these materials is needed. PURPOSE: The purpose of this study was to compare the shear bond strength of dental porcelain to cast, milled, and laser-sintered cobalt-chromium alloys, and to investigate the adhesive bond and failure type after thermocycling, 90 metal cylinders (10 mm diameter and 10 mm height) were prepared from cast (30 specimens), milled (30 specimens), and laser-sintered (30 specimens) alloys. MATERIAL AND METHODS: Ceramic cylinders (2.5 mm diameter and 4 mm length) were fused to the alloy cylinders. For each group, 15 specimens were thermocycled 5500 times at temperatures between 4°C and 60°C before testing. After testing, the specimen surfaces were visually examined to determine the failure mode. Differences in adhesion values according to manufacturing method, testing condition (thermocycling or no thermocycling), and interaction between the factors were evaluated with a 2-way ANOVA. The χ(2) test (95% confidence level) was performed to determine whether the failure mode was associated with the testing condition. RESULTS: Adhesion strengths for the nonthermocycled specimens were 42.79 ±14.14 MPa (cast), 37.56 ±9.18 MPa (milled), and 29.09 ±6.95 MPa (laser-sintered), and, for the thermocycled specimens, 16.52 ±8.96 MPa (cast), 22.21 ±13.25 MPa (milled), and 24.28 ±10.13 MPa (laser-sintered). Two-way ANOVA results indicated no statistically significant differences in adhesion among the manufacturing methods (P=.257), but statistically significant differences were observed according to both testing conditions (P<.001) and interaction between the factors (P=.015). The χ(2) test indicated that the failure mode was not associated with the testing condition (thermocycled, P=.280; nonthermocycled, P=.240). CONCLUSIONS: The porcelain adhesion values for all the materials were adequate for clinical applications. No significant adhesion differences were observed between cast, milled, and laser-sintered specimens, or among thermocycled and nonthermocycled laser-sintered specimens. However, significant adhesion differences were observed among the thermocycled and nonthermocycled cast and the milled specimens.

Influence of abutment height and surface roughness on in vitro retention of three luting agents.

PURPOSE: This study evaluated the effects of abutment height, airborne-particle abrasion, and type of cement on the tensile resistance to dislodgement of cement-retained implant restorations. MATERIALS AND METHODS: Three groups of 12 standardized abutments each were prepared with different heights (4 mm, 5 mm, and 6 mm) using a milling machine. Crowns were cast in cobalt-chrome using the lost-wax technique, airborne particle-abraded using 50-Μm aluminum oxide, and cleaned with acetone. Restorations were cemented using a noneugenol acrylic urethane cement, a resin-modified glass ionomer, or a zinc oxide-noneugenol cement. A 5-kg load was applied for 10 minutes. Samples were kept at 37°C and 100% humidity overnight. A tensile force was applied to the crown using a testing machine at a crosshead speed of 5 mm/minute until failure occurred. Next, the abutments were airborne particle-abraded with 50-Μm aluminum oxide, and the cementation and testing procedures were repeated. The effects of cement, abutment height, and surface treatment were evaluated statistically. RESULTS: There were significant differences among the cements. The resin-modified glass ionomer provided the greatest retention in all the tested conditions, while the zinc oxide-noneugenol cement produced the lowest retention values. Significant differences were also detected between 4-mm and 6-mm abutments, with the 6-mm abutments being more retentive. No differences were found between 4-mm and 5-mm abutments or between 5-mm and 6-mm abutments. The effect of airborne-particle abrasion was also found to be significant. A maximum increase of 90 N in retention force was observed after airborne-particle abrasion for the 5-mm abutments cemented with the acrylic urethane cement. CONCLUSIONS: Cement, airborne-particle abrasion, and abutment height can significantly influence retention of implant-supported crowns. Different parameters, including those specific to the patient, should be considered in the selection of a luting agent.

A method for registering the abutment screw position of cement-retained implant restorations.

The primary concern with cement-retained implant restorations is retrievability. A simple method is described that allows identification of the location of the abutment screw in cement-retained implant restorations by superposition of 2 digital photographs of the definitive cast with and without the restoration.