Stress distribution and fracture resistance of green reprocessed polyetheretherketone (PEEK) single implant crown restorations compared to unreprocessed PEEK and Zirconia: an in-vitro study.

BACKGROUND: It is unclear which crown materials are optimum to disperse the generated stresses around dental implants. The objective of this study is to assess stress distribution and fracture resistance of green reprocessed Polyetheretherketone (PEEK) in comparison to un-reprocessed PEEK and zirconia single implant crown restorations. METHODS: Twenty crowns (n = 20) were obtained, five from zirconia and fifteen from pressed PEEK that were subdivided into 3 groups of five specimens each (n = 5) according to weight% of reprocessed material used. A 100% new PEEK was used for the first group, 50% new and 50% reprocessed PEEK were used for the second group, and a 100% reprocessed PEEK was used for the third group. Epoxy resin model with dental implant in the second mandibular premolar was constructed with strain gauges located mesially and distally to the implant to record strain while a load of 100 N was applied with 0.5 mm/min then specimens of all groups were vertically loaded till failure in a universal testing machine at cross head speed 1 mm/min. Data was statistically analyzed by using One-way Analysis of Variance (ANOVA) followed by Post-hoc test when ANOVA test is significant. RESULTS: No significant difference between strain values of tested groups (p = 0.174) was noticed. However, a significant difference between fracture resistance values was noticed where the zirconia group recorded a significantly higher value (p < 0.001). CONCLUSIONS: Implant restorative materials with different moduli of elasticity have similar effects regarding stresses distributed through dental implant and their surrounding bone. Reprocessed PEEK implant restorations transmit similar stresses to dental implant and surrounding bone as non-reprocessed PEEK and zirconia restorations. Zirconia failed at higher load values than all tested PEEK restorations but all can be safely used in the posterior area as crown restorations for single implants. CLINICAL RELEVANCE: Applying "green dentistry" principles may extend to include reprocessing of pressed PEEK restorative materials without affecting the material's shock absorption properties.

The effect of mechanical and chemo-mechanical temporary cement cleaning methods on shear bond strength with self-adhesive resin cement (an in-vitro study).

BACKGROUND: Adhesive tooth-colored restorations are strongly dependent on the substrate surface cleanliness to allow intimate contact between resin cement and dentin surface, so several methods were adopted for the total cleaning of temporary cement residues. This study aimed to assess the effect of mechanical and chemo-mechanical cleaning methods of temporary cement on the immediate shear bond strength of self-adhesive resin cement to dentin surface. METHODS: Forty freshly extracted lower first premolars were cut to expose a flat dentin surface. Discs of temporary crown composite resin material were constructed and cemented to the flat dentin surface using resin-based and non-eugenol temporary cement then stored at room temperature in distilled water. Dividing of samples into two groups according to the method of temporary cement cleaning. Group I (n = 20) mechanical cleaning using the rotary instrument, and group II (n = 20) chemo-mechanical cleaning using chlorhexidine-containing scrub. CAD/CAM reinforced Composite discs were bonded to the dentin surface using self-adhesive composite resin cement, then measurement of shear bond strength was done using a universal testing machine. Further analysis of failure mode after debonding was performed by Scanning electron microscope. RESULTS: No statistically significant difference was found between the mean shear bond strength of the two cleaning methods (P-value = 0.636). Regardless of the cleaning method, the group cemented with resin-based temporary cement showed statistically significantly higher mean shear bond strength than non-eugenol temporary cement (P-value = 0.048). CONCLUSION: Both cleaning methods (mechanical and chemo-mechanical) applied in this study were effective in cleaning temporary cement remnants from the dentin substrate surface with statistically significant differences between results of shear bond strength with significantly higher values recorded with resin-based temporary cement.

Evaluation of fracture resistance of zirconia monolithic restorations: an in vitro study / Avaliação da resistência à fratura de restaurações monolíticas de zircônia: um estudo in vitro

Objective: was to evaluate fracture resistance of zirconia monolithic restorations after aging procedures. Material and methods: Monolithic translucent zirconia 3-unit FPDs were fabricated using Cerec inLab CAD/CAM system on 2 stainless steel dies with a uniform 120 degrees circumferential deep chamfer finish line of 1 mm width. FPDs were divided into 2 groups, first group (Group A) was subjected to aging procedures in an autoclave at hydrothermal conditions 134 oC /2 bars for 5 hours. Second group (Group B) was not subjected to any aging procedures (control group). All specimens of each group were loaded compressively in a universal testing machine at cross head speed 0.5 mm/min until fracture occurred. The percentage of monoclinic (m) phase was detected by XRD device. Scanning electron microscope (SEM) was used to examine the fractured surfaces for Aged TZI (Group A) and Non-aged TZI (Group B). Student's t-test was used to compare between fracture resistances of both groups. The significance level was set at P ≤ 0.05. Results: The fracture resistance mean (SD) values of non-aged TZI (Group B) was 2406.9 ± 306.8 N which showed statistically significantly higher than that of aged group (Group A) which was 1964.5 ± 234.5 N. The percentage of monoclinic (m) phase detected by XRD device software in non-aged TZI (Group B) was nearly 0 weight % and in aged TZI (Group A) was about 42 weight %. Conclusions:Accelerated artificial aging decreases the fracture resistance of monolithic TZI FPDs. (AU)

Objetivo: Foi avaliar a resistencia à fratura de restaurações de zircônia monolítica após procedimentos de envelhecimento.Material e Métodos: 3 unidades de FPDs de zircônia monolítica translucida foram fabricadas utilizando o sistema Cerec inLab CAD/CAM com 2 matrizes de aço inoxidável com uma linha de acabamento de chanfro profundo circunferencial de 120 graus de largura de 1 mm. As FPDs foram divididos em dois grupos, primeiro grupo (Grupo A) foi submetido a procedimentos de envelhecimento em autoclave em condições hidrotérmicas de 134 °C /2 bars por 5 horas. O segundo grupo (Grupo B) não foi submetido a nenhum processo de envelhecimento (grupo controle). Todos os espécimes de cada grupo foram carregados compressivamente em uma maquina de teste universal na velocidade de 0.5 mm/min até a fratura ocorrer. A porcentagem da fase monoclínica (m) foi detectada pelo dispositivo XRD. O microscópio eletrônico de varredura (MEV) foi utilizado para examinar as superfícies fraturadas para TZI envelhecido (Grupo A) e TZI não envelhecido (Grupo B). O teste t de estudantes foi usado para comparar as resistências à fraturas de ambos os grupos. O nível de significância foi estabelecido em P ≤ 0.05. Resultados: Os valores médios de resistência à fratura (SD) do TZI não envelhecido (Grupo B) foi 2406.9±306.8 N, o qual se mostrou estatisticamente significativamente maior do que o grupo envelhecido (Grupo A), que foi 1964.5±234.5 N. A porcentagem da fase monoclínica (m) detectada pelo software do dispositivo XRD em TZI não envelhecido (Grupo B) foi próximo de 0% em peso e em TZI envelhecido (Grupo A) foi cerca de 42% em peso. Conclusão: O envelhecimento artificial acelerado diminui a resistência à fratura de FPDs TZI monolítico (AU)