Effect of Calcium Hydroxide and Antioxidant Agents Filling the Pulp Chamber after Internal Bleaching.

To evaluate the effect of calcium hydroxide (CH), sodium ascorbate (SA) and sodium thiosulfate (ST) filling the pulp chamber on color stability and longevity of teeth after internal bleaching. Crowns of bovine incisors were submitted to internal bleaching and divided into groups according the material used in the pulp chamber: Control, CH, SA, ST. Each group was divided into two subgroups according to the time to perform restorative procedures (7 or 15 days). Color measurement was performed with a spectrophotometer at nine periods. The darkening (ΔE) values were calculated. The Mann-Whitney test was used to statistically analyze the data (p ⟨ 0.05). After bleaching, ΔE values were higher than 3.5, showing that the procedure was effective. After 24 hours, no difference was observed between groups. After 7 days, SA showed higher ΔE than the control group (p ⟨ 0.05). CH and TS did not differ from the control group. In restorations performed after 7/15 days, SA group showed higher values of darkening after 1 and 4 months than the control group (p ⟨ 0.05). SA induced perceptible darkening after bleaching and should not be used to fill the pulp chamber. ST and CH show color stability and longevity after 12 months.

Influence of minimally invasive endodontic access cavities on root canal shaping and filling ability, pulp chamber cleaning and fracture resistance of extracted human mandibular incisors.

AIM: To evaluate the influence of the location and design of endodontic access cavities on root canal shaping and filling ability, pulp chamber cleaning and fracture resistance of extracted human mandibular incisors. METHODOLOGY: After pre-selection using periapical radiographs, forty extracted intact human mandibular incisors were scanned in a micro-computed tomographic device. The teeth were matched based on similar anatomical features of the canals and assigned to four experimental groups (n = 10) according to the endodontic access cavity and root canal preparation protocol: traditional/TRUShape (T/TRU); traditional/MTwo (T/MT); minimally invasive/TRUShape (MI/TRU); and minimally invasive/MTwo (MI/MT). The samples were scanned after root canal instrumentation and filling procedures. The parameters evaluated were as follows: volume and area of the root canal, noninstrumented canal areas, canal transportation and centring ratio, accumulated hard tissue debris, voids in root canal fillings and remnants of root canal filling materials in the pulp chamber. After root canal filling and cavity restoration procedures, the samples were submitted to a fracture resistance test. Data were statistically analysed using Shapiro-Wilk, one-way anova and Bonferroni tests with a significance level of 5% (α = 0.05). RESULTS: There was no difference regarding all parameters evaluated before and after root canal preparation (volume and area of the root canal, noninstrumented canal areas, canal transportation and centring ratio, and accumulated hard tissue debris) amongst the groups (P > 0.05). MI/TRU and MI/MT groups were associated with significantly more voids in root canal fillings when compared to the T/TRU and T/MT groups (P < 0.05). Percentage of root canal filling material remnants in the pulp chamber after cleaning procedures and mean fracture resistance values were not significantly different amongst the four experimental groups (P > 0.05). CONCLUSIONS: The location and design of the endodontic access cavity did not impact on root canal preparation nor resistance to fracture of extracted mandibular incisors, regardless of the instrument used. Minimally invasive access cavities were associated with significantly more voids in root canal fillings.

Influence of heat treatment on torsional resistance and surface roughness of nickel-titanium instruments.

AIM: To evaluate the influence of controlled memory (CM) thermal treatment on the torsional resistance and surface roughness of nickel-titanium instruments with identical geometric and dimensional characteristics. The influence of environmental temperature on torsional resistance was also evaluated. METHODOLOGY: A sample of 25 conventional NiTi alloy and 25 CM thermal-treated NiTi instruments, with an identical geometric design and a nominal size of 0.25 mm at D0 and a nominal taper of .06 mm mm-1 were selected. The torsional strength and the angle of rotation of the instruments were tested following ISO 3630-1 at two temperatures: 21 and 35 °C. The fracture surfaces of all tested instruments were verified with a scanning electron microscope. The surface roughness of the blades of conventional NiTi alloy and CM wire files was evaluated by using a New View 7100 Profilometer. Statistical analysis was performed using Student's t-test and paired t-test to analyse the torsional resistance and surface roughness at a significance level of P < 0.05. RESULTS: The torsional strength of thermally-treated instruments was significantly lower than nontreated instruments (P < 0.05). However, thermally-treated instruments had significantly greater angular rotation to fracture than nontreated instruments (P < 0.05). Temperature did not influence the torsional strength (P > 0.05) and the angular rotation (P > 0.05) of the instruments. Regarding the roughness measurements, groove depth was lower at the surface of thermally-treated instruments when compared to nontreated instruments (P < 0.05). CONCLUSION: Thermal treatment influenced the torsional resistance and surface roughness of NiTi instruments with identical geometric and dimensional characteristics. Temperature did not affect torsional behaviour.

Resistance to vertical root fracture of root filled teeth using different conceptual approaches to canal preparation.

AIM: To evaluate the resistance to vertical root fracture of root filled teeth using different root canal preparation concepts: apical stop and continuously tapering preparation, with different foraminal enlargement. In addition, the effect of filling associated with these different concepts was assessed. METHODOLOGY: Ninety single-rooted premolars were used. The crowns were removed to standardize the root length at 11 mm. Ten roots were not instrumented and not filled (control group). The other roots were divided into four groups (n = 20): apical stop to finishing file size 25, 0.08 taper; apical stop to finishing file size 45, 0.02 taper; continuously tapering preparation to finishing file size 25, 0.08 taper; and continuously tapering preparation to finishing file size 45, 0.02 taper. Afterwards, 10 roots of each group were root filled using Gutta-percha and AH Plus. A continuous wave of condensation was used as the filling technique. The roots were evaluated as regards resistance to vertical fracture using a universal testing machine. The data were evaluated using the Kruskal-Wallis and Mann-Whitney tests. RESULTS: No significant difference in performance was observed between continuously tapering preparation size 25, 0.08 taper and apical stop size 45, 0.02 taper groups. Lower resistance values were found in continuously tapering preparation size 45, 0.02 taper group and the highest in apical stop size 25, 0.08 taper group. After filling, a significant increase in resistance values was observed in all groups. In addition, the continuously tapering preparation size 45, 0.02 taper group had values comparable with those of the control. CONCLUSION: The different canal preparation techniques reduced resistance to fracture when compared with the control group; however, after root filling, there was a significant increase in resistance.