Application of Tribology Concept in Dental Composites Field: A Scoping Review

Tribology is the discipline concerning the application of friction, lubrication, and wear concepts of interacting surfaces in relative motion. A growing interest has developed in tribology application in medical biomaterials, such as resin composites used in restorative dentistry. Yet, the keywords “tribology” and “biotribology” are little applied in the pertinent publications. The aim of this scoping review was to offer an overview of tribology application in dental composites research and to identify knowledge gaps and address future research. A literature search was conducted on Pubmed and Scopus databases and the studies investigating the tribological behavior of resin composites were included for qualitative synthesis. The majority of studies on dental tribology were published in the research areas of mechanical engineering/nanotechnology and differed in several methodological aspects. The preponderant engineering approach and the lack of standardized testing make the laboratory findings poorly informative for clinicians. Future research should focus on the tribological behavior of dental materials composites by means of an integrated approach, i.e., engineering and clinical, for improving development and advancement in this field of research

Influence of NiTi wire diameter on cyclic and torsional fatigue resistance of different heat-treated endodontic instruments

We compared the mechanical properties of 2Shape mini TS2 (Micro-Mega, Besançon, France) obtained from 1.0 diameter nickel-titanium (NiTi) wires and 2Shape TS2 from 1.2 diameter nickel-titanium (NiTi) wires differently thermally treated at room and body temperature. We used 120 NiTi TS2 1.0 and TS2 1.2 files made from controlled memory (CM) wire and T-wire (n = 10). Cyclic fatigue resistance was tested by recording the number of cycles to fracture (NCF) at room and body temperatures using a customized testing device. Maximum torque and angle of rotation at failure were recorded, according to ISO 3630-1. Data were analyzed by a two-way ANOVA (p < 0.05). The CM-wire files had significantly higher NCFs at both temperatures, independent of wire dimensions. Testing at body temperature negatively affected cyclic fatigue of all files. The 1.0-mm diameter T-wire instruments showed higher NCF than the 1.2-mm diameter, whereas no significant differences emerged between the two CM wires at either temperature. The maximum torque was not significantly different across files. The TS2 CM-wire files showed significantly higher angular rotation to fracture than T-wire files. The TS2 CM-wire prototypes showed higher cyclic fatigue resistance than T-wire prototypes, regardless of wire size, exhibiting suitable torsional properties. Torsional behavior appears to not be affected by NiTi wire size

Cyclic fatigue resistance of nickel-titanium rotary instruments according to the angle of file access and radius of root canal.

INTRODUCTION: The aim of this study was to compare the influences from different access angles and curvature radii on cyclic fatigue resistance of nickel-titanium rotary files. METHODS: Two file systems (2Shape [TS; MicroMega, Besançon, France] and HyFlex CM [HCM; Coltène/Whaledent, Allstätten, Switzerland]) were used. A total of 192 instruments of TS #25/.04 (TS1), TS #25/.06 (TS2), HCM #25/.04, and HCM #25/.06 were evaluated at 3 insertion angles (0°, 10°, and 20°) and 2 radii (5 mm and 3 mm) in 16-mm stainless steel artificial canals with a 60° curvature. Cyclic fatigue resistance was determined by the number of cycles to failure (NCF) using a customized testing device. Data were analyzed statistically with the significance level established at 95%. RESULTS: In the 3-mm radius canal, the instruments showed lower cyclic fatigue resistance than in the 5-mm radius canal (P < .05). HCM #25/.06 and all .04 taper instruments had a significant NCF reduction at 20° and 10° in the 3-mm radius canal (P < .05), whereas TS2 showed no significant differences. In the 5-mm radius of curvature, although .06 taper instruments had no significant NCF reduction for each angle tested, .04 taper files exhibited significant NCF reduction when tested at 20° (P < .05). Comparing the same size instruments, HCM had higher NCF than TS (P < .05). Instruments with a .04 taper exhibited higher NCF than the .06 ones with the same heat treatment (P < .05). CONCLUSIONS: An inclined insertion into the canals decreased cyclic fatigue resistance of thermal-treated instruments with a .04 taper at all radii of curvature tested. The synergistic effect of a small radius of curvature and access angulation of heat-treated instruments decreases their fatigue resistance

Influence of different angles of file access on cyclic fatigue resistance of 2shape rotary instruments in different artificial canals

Aim: Several parameters including extent of the curvature and angulated insertion of file into the canal could influence cyclic fatigue of nickel-titanium files. The purpose of this study was to compare the influence of different access angles associated to different curvature radii on cyclic fatigue resistance of 2Shape (TS; Micro-Mega, Besancon, France) rotary instruments. Methods: 60 instruments were tested in two 16mm- stainless steel artificial canals with angle of curvature of 60° and 5mm or 3mm radius of curvature respectively. 2Shape TS2 #25.06 and 2Shape TS1 #25.04 were evaluated at 0°, 10° and 20° insertion angles (n=10 for each angle of access). Cyclic fatigue resistance was determined by Number of Cycles to Failure (NCF) using a new testing device machine. This device consists of a platform composed of a block containing the electric handpiece and a mobile support on rails for insertion/disconnection of the file. Moreover, a metal mobile platform is connected to the mobile support. This second platform with the artificial canal produces the different inclination of insertion of tested file maintaining the entrance of instrument perpendicular to the canal. Each instrument was tested in continuous rotation (300 rpm) following the manufacturer’s instructions. Fracture surface was examined with a scanning electron microscope. Data were statistically analyzed using 2-way analysis of variance and the Bonferroni multiple comparison post-hoc test (Prism 7.0; GraphPad Software, Inc, La Jolla, CA) with a significance level of P<0.05. Results: TS1 (#25.04) exhibited higher cyclic fatigue resistance than TS2 (#25.06) for each angle and radius tested (P<0.05). When files were tested inside 3mm- radius canal, independently from taper, they recorded lower cyclic fatigue resistance than in 5mm-radius one (P<0.05). Considering canal with 5mm-radius of curvature, no significant cyclic fatigue resistance reduction was observed for .06 taper-instruments for each angle tested (P>0.05), while files with .04 taper exhibited significant lower NCF when tested at 20° (P<0.05). In canals with 3mm radius of curvature, TS2 (#25.06) showed no significant differences for each angle tested (P>0.05). TS1 (#25.04) exhibited significant resistance reduction between 0° and 10° as well as between 0° and 20° (P<0.05), with no difference between 10° and 20° (P>0.05). Conclusion: Inclined angle of file access into the canals decreased cyclic fatigue resistance of #25.04 files especially when the radius of curvature is reduced. Cyclic fatigue resistance of #25.04 instruments was higher than #25.06 files made with the same thermal treatment. Independently from taper, each file tested in 3mm-radius canal showed lower cyclic fatigue resistance than instruments tested in 5mm-radius canal

A micro-computed tomographic analysis of obturation quality and retreatability of an epoxy resin-based sealer

BacKGrOUND: to evaluate the voids percentage and the retreatability by different supplementary irrigation tech- niques of a matched-taper single cone and epoxy resin-based sealer. METHODS: A total of 72 single-rooted premolars were prepared and filled with gutta-percha and MM-Seal. The per- centage of voids in the whole root canal and each anatomical part were evaluated by Micro-CT scans. After root filling removal, the teeth were randomly allocated (N.=24) to group a, syringe irrigation; group B, tornado Brush, and group C, ultrasonically activated irrigation and re-scanned to establish the volume of remnant root filling material. The data relative to voids and retreatment techniques were established by the Kruskal-Wallis test. Differences in retreatment time were examined using one-way aNOVa and tukey’s test (P<0.05). RESULTS: No significant difference was found in the voids percentage between the different root-thirds and between the supplementary irrigation groups in the MM-Seal remnants for the whole root canal and each section. in all groups, the coronal region exhibited more remaining material than other sections. CONCLUSIONS: MM-Seal showed low voids percentage and its removal was not significantly improved by supplemen- tary irrigation techniques

Influence of kinematics and incidence angles on the cutting efficiency of two single-file nickel-titanium rotary instruments

To compare the cutting efficiency of F6 Sky Taper (F6ST) and One Curve (OC) with different kinematics and cutting inclinations. Cutting efficiency of 80 new F6ST and OC was tested at 90° and 70° inclination in relation to the sample, in continuous rotation and reciprocation, against standardised gypsum samples for 120 seconds using a customised device. Data expressed as weight loss and length of the sample cut were analysed using two-way analysis of variance and Tukey t-test (P<.05). F6ST showed significantly higher cutting efficiency in reciprocation, while OC in continuous rotation. Regardless of inclination, F6ST showed statistically higher values than OC in reciprocation, while OC exhibited higher cutting ability in continuous rotation. The 70° inclination significantly improved the cutting efficiency of both files. Reciprocation improved the cutting efficiency of F6ST while continuous rotation enhanced cutting ability of OC. An inclined insertion improved the cutting ability, independently from the movement