Body temperature fatigue behaviour of reciprocating and rotary glide path instruments in sodium hypochlorite solutions alone or combined with etidronate

The aim of the study was to compare cyclic fatigue (CF) resistance of reciprocating and rotary glide path instruments in the presence of irrigation solutions at body temperature. CF resistance of 100 instruments (50 ProGlider and 50 WaveOne Gold Glider) was tested in sodium hypochlorite solutions alone (NaOCl) or in combination with etidronate (NaOCl/HEBP). The CF platform with a simulated canal (curvature = 60°/radius = 3 mm) was submerged in a temperature-controlled bath with the solutions kept at 37 ± 1°C controlled by a precision mercury glass thermometer. Instruments were actioned following manufacturer guidelines, and time to failure was recorded and compared among groups with Weibull analysis. Reciprocating glide path preparation instruments were more resistant to CF than rotary instruments in both irrigation solutions. The irrigation solution did not affect the mean life of ProGlider, but reciprocating instruments lasted significantly longer used in presence of NaOCl compared to NaOCl/HEBP.

Effect of gamma-ray sterilization on phase transformation behavior and fatigue resistance of contemporary nickel-titanium instruments

OBJECTIVES

The aim of this study was to compare body temperature cyclic fatigue resistance (CF) of heat-treated NiTi rotary instruments submitted to gamma-irradiation or autoclave sterilization.

MATERIALS AND METHODS

A total of 176 instruments (88 Hyflex EDM (HEDM) and 88 TRUShape (TS)) were used. Forty-four of each were submitted to gamma-irradiation. Twenty-two in each group were further autoclaved, resulting in a total of eight groups (n = 22 each): TS-γ and HEDM-γ (gamma-irradiated)/TS-γ-ac and HEDM-γ-ac (gamma-irradiated and autoclaved)/TS-non-γ and HEDM-non-γ (non-sterilized controls, non-gamma-irradiated/non-autoclaved)/TS-non-γ-ac and HEDM-non-γ-ac (non-gamma-irradiated and autoclaved). Twenty in each were tested for CF. Weibull parameters were calculated and compared. The remainder was used for differential scanning calorimetry analysis.

RESULTS

TS instruments lasted significantly longer if not submitted to gamma-irradiation (TS-non-γ mean-life = 101.5 s, 95 CI% 91.7-112.3; TS-γ mean-life = 83.2 s, 95 CI% 76-91.1); further autoclaving did not significantly affect CF. Gamma-irradiation did not affect HEDM (HEDM-γ mean-life = 717.9 s, 95 CI% 636.8-809.3; HEDM-non-γ: mean-life = 678.8 s, 95 CI% 595.1-744.2); further sterilization significantly decreased fatigue resistance (HEDM-γ-ac mean-life = 524.1 s, 95 CI% 476.1-576.8; HEDM-non-γ-ac mean-life = 570.6, 95 CI% 512.3-635.5). Gamma irradiation benefited HEDM conversion to martensite state and its maintenance, while further autoclave sterilization reverted the benefit.

CONCLUSIONS

Gamma-irradiation and autoclaving differentially affected fatigue life span and transformation temperatures of contemporary martensitic rotary instruments manufactured with different methods.

CLINICAL RELEVANCE

Gamma-ray processing is increasingly utilized by manufacturers for clinician to use fully sterile packaged instruments; however, the sterilization method of choice should vary depending on the effects on the behavior of contemporary martensitic rotary instruments manufactured with different methods.

Microtensile bond strength distributions of three composite materials with different polymerization shrinkages bonded to dentin

PURPOSE

To assess the detrimental effects that polymerization contraction causes on the interfacial microtensile bond strength (μTBS) to dentin of three light-curing resin composites: two conventional bis-GMA-based composite resins (Filtek Z250, TPH Spectrum) and a low shrinkage material (Filtek Silorane [SIL]).

MATERIALS AND METHODS

Flat surfaces of labial dentin were made in 46 bovine teeth and restored in single (group A) or in three separate (group B) one-increment visible-light cured resin composite blocks, with similar locations among teeth. After 24 h, restored teeth were sectioned perpendicular to interfaces, producing rectangular compound specimens (385 specimens were produced in group A, and 132 in group B), and submitted to tension (crosshead speed 1mm/min) until failure. μTBS results were adjusted to bonded area and transformed to percentages of maximum values within each tooth (PTens). In A groups, distances of specimens to the gingival ends of each restoration were transformed to PDistances: the percentage of that distance within its specimen.

RESULTS

Spearman's nonparametric correlation test showed that for Z250, TPH and SIL, in A groups, a material's correlation coefficient was positive for the first half of restorations (0% to 50% PDistances) and negative for the second (50% to 100%). For all materials, PTens values in extremes of restorations (pooled 0 and 100% PDistances) in A groups were smaller than corresponding values in B groups. These differences were statistically significantly (Student's t-test) only for Z250 and TPH.

CONCLUSION

Even in cases of favorable configuration factor, polymerization shrinkage in large restorations can reduce interface mechanical characteristics. The relevance of this decrease has still to be established.

[Dens in dente. Histological characteristics of an unusual case of dens in dente]

We describe a rare case of "dens in dente" in an accessory germ in central location of an anencephalic phoetus. Its characteristics of having enamel surrounding normal dentin and normal pulpar cavity, all of them surrounded by the unaffected accessory germ leads us to describe the term "dente in dente". Such alteration is not previously described.