Wear and corrosion interactions on titanium in oral environment : literature review

The oral cavity is a complex environment where corrosive substances from dietary, human saliva, and oral biofilms may accumulate in retentive areas of dental implant systems and prostheses promoting corrosion at their surfaces. Additionally, during mastication, micromovements may occur between prosthetic joints causing a relative motion between contacting surfaces, leading to wear. Both processes (wear and corrosion) result in a bio-tribocorrosion system once that occurs in contact with biological tissues and fluids. This review paper is focused on the aspects related to the corrosion and wear behavior of titanium-based structures in the oral environment. Furthermore, the clinical relevance of the oral environment is focused on the harmful effect that acidic substances and biofilms, formed in human saliva, may have on titanium surfaces. In fact, a progressive degradation of titanium by wear and corrosion (tribocorrosion) mechanisms can take place affecting the performance of titanium-based implant and prostheses. Also, the formation of wear debris and metallic ions due to the tribocorrosion phenomena can become toxic for human tissues. This review gathers knowledge from areas like materials sciences, microbiology, and dentistry contributing to a better understanding of bio-tribocorrosion processes in the oral environment.(undefined

Bond strength of different endodontic sealers to dentin: push-out test

OBJECTIVE: The aim of this in vitro study was to evaluate the bond strength of different root canal sealers to dentin. MATERIAL AND METHODS: Forty extracted single-rooted human teeth were examined and the coronal and middle thirds of the canals were prepared with a 1.50 mm post drill (FibreKor Post System, Pentron). The teeth were allocated in two experimental groups, irrigated with 2.5% NaOCl+17% EDTA or saline solution (control group) and instrumented using Race rotary files (FKG) to a size #40 at the working length. Then, the groups were divided into four subgroups and filled with Epiphany sealer (Group 1), EndoREZ (Group 2), AH26 (Group 3) and Grossman's Sealer (Group 4). After 2 weeks of storage in 100% humidity at 37ºC, all teeth were sectioned transversally into 2-mm-thick discs. Push-out tests were performed at a cross-head speed of 1 mm/min using a universal testing machine. The maximum load at failure was recorded and expressed in MPa. RESULTS: Means (±SD) in root canals irrigated with 2.5% NaOCl and 17% EDTA were: G1 (21.6±6.0), G2 (15.2±3.7), G3 (14.6±4.5) and G4 (11.7±4.1).Two-way ANOVA and Tukey's test showed the highest bond strength for the Epiphany's group (p< 0.01) when compared to the other tested sealers. Saline solution decreased the values of bond-strength (p<0.05) for all sealers. CONCLUSION: Epiphany sealer presented higher bond strength values to dentin in both irrigating protocols, and the use of 2.5% NaOCl and 17% EDTA increased the bond strength values for all sealers

Fracture Resistance of Teeth Restored With All-ceramic Inlays and On lays: An In Vitro Study

Fracture resistance of inlays and onlays may be influenced by the quantity of the dental structure removed and the restorative materials used. The purpose of this in vitro study was to evaluate the effects of two different cavity preparation designs and all-ceramic restorative materials on the fracture resistance of the tooth-restoration complex. Fifty mandibular third molar teeth were randomly divided into the following five groups: group 1: intact teeth (control); group 2: inlay preparations, lithium-disilicate glass-ceramic (IPS e.max Press, Ivoclar Vivadent AG, Schaan, Liechtenstein); group 3: inlay preparations, zirconia ceramic (ICE Zirkon, Zirkonzahn SRL, Gais, Italy); group 4: onlay preparations, lithium-disilicate glass-ceramic (IPS e.max Press); and group 5: onlay preparations, zirconia ceramic (ICE Zirkon). The inlay and onlay restorations were adhesively cemented with dual polymerizing resin cement (Variolink II, Ivoclar Vivadent AG). After thermal cycling (5 degrees to 55 degrees C x 5000 cycles), specimens were subjected to a compressive load until fracture at a crosshead speed of 0.5 mm/min. Statistical analyses were performed using one-way analysis of variance and Tukey HSD tests. The fracture strength values were significantly higher in the inlay group (2646.7 +/- 360.4) restored with lithium-disilicate glass-ceramic than those of the onlay group (1673.6 +/- 677) restored with lithium-disilicate glass-ceramic. The fracture strength values of teeth restored with inlays using zirconia ceramic (2849 +/- 328) and onlays with zirconia ceramic (2796.3 +/- 337.3) were similar to those of the intact teeth (2905.3 +/- 398.8). In the IPS e.max Press groups, as the preparation amount was increased (from inlay to onlay preparation), the fracture resistance was decreased. In the ICE Zirkon ceramic groups, the preparation type did not affect the fracture resistance results

ADVENTITIOUS SHOOT REGENERATION FROM DIFFERENT EXPLANTS OF WILD LENTIL (LENS CULINARIS SUBSP. ORIENTALIS)

ABSTRAC

The influence of occlusal loading location on stresses transferred to implant-supported prostheses and supporting bone: A three-dimensional finite element study

Statement of problem. Information about the influence of occlusal loading by location on the stress distribution in an implant-supported fixed partial denture and supporting bone tissue is limited. Purpose. The purpose of this study was to investigate the effect of loading at I to 3 different locations on the occlusal surface of a tooth on the stress distributions in an implant-supported mandibular fixed partial denture (FPD) and surrounding bone, using 3-dimcnsional finite element analysis. Material and methods. A 3-dimensional finite element model of a mandibular section of bone (Type 2) with missing second premolar and its superstructures were used in this study. A 1-piece 4.1 X 10-mm screw-shape ITI dental implant system (solid implant) was modeled for this study. Cobalt-Chromium (Wiron 99) was used as the crown framework material and porcelain was used for occlusal surface. The implant and its superstructure were simulated in a Pro/Engineer 2000i program. Total loads at 300 N were applied at the following locations: 1) tip of buccal cusp (300 N); 2) tip of buccal cusp (150 N) and distal fossa (150 N); or 3) tip of buccal cusp (100 N), distal fossa (100 N), and mesial fossa (100 N). Results. The results demonstrated that vertical loading at I location resulted in high stress values within the bone and implant. Close stress levels were observed within the bone for loading at 2 locations and 3 locations; the former created the most extreme stresses and the latter the most even stresses within the bone. With loading at 2 or 3 locations, stresses were concentrated on the framework and occlusal surface of the FPD, and low stresses were distributed to the bone. Conclusion. For the loading conditions investigated, the optimal combination of vertical loading was found to be loading at 2 or 3 locations which decreased the stresses within the bone. In this situation, von Mises stresses were concentrated on the framework and occlusal surface of the FPD

Effect of three different acidic beverages on surface characteristics of composite resin restorative materials

The purpose of this study was to compare the effects of different beverages upon the surface hardness, roughness and micromorphology of light cured composite resins. One microhybrid (Artemis), one nanohybrid (Grandio), one microfil (Tescera) and Filtek Silorane composite resin materials were selected for this study. Sixty-four disc shaped specimens (8 x 2 mm) of each resin composite were prepared according to manufacturers' instructions. After light curing, the specimens were polished with flexible aluminium oxide discs (Sof-Lex; 3M ESPE) under water spray and immersed in 37 degrees C distilled water for 24 h. Sixteen specimens (half for hardness and half for roughness) were set aside to measure the initial hardness and roughness of four different composites. Baseline surface roughness R-a (in mm) measurements were taken by a surface profilometer (Mitutoyo Surfcorder/SE-40D; Kosaka Laboratory Ltd, Japan) on the top of the specimens. Baseline Vickers hardness measurements were made on the surface of eight specimens for each composite group with a Vickers hardness testing machine (Buehler OmniMet MHT1600-4980T). The remaining specimens were exposed to a dynamic pH cyclus in three different beverages (orange juice, spring water and Coca Cola) over 7 days. After a 7-day storage, samples were taken from the beverages. Specimens were subjected to post-immersion surface roughness and microhardness testing. Samples of SEM images were recorded before and after storage. Data were analysed using two-way ANOVA and Duncan's test at a significance level of 0.05. The results of this study showed that acidic drinks did not reduce the surface hardness of composite restoratives. However, for all resin composites, surface roughness measurements showed a statistically significant increase (p < 0.05) after the seven days' storage. Micromorphological changes were noticed in a situation of acid challenge. This study evaluated the effect of three acidic beverages under ph cycling conditions on four composite resins after seven days' storage protocol. Microhardness and surface roughness were measured to evaluate mechanical surface properties. Surface degradation and changes were evaluated using SEM. The one-week period of storage in different beverages presented no significant deleterious alteration or softening effect on the surface of the composites, although it did have a significant effect on the surface roughness of composites. Surface degradation was observed in specimens immersed in different beverages