A comparison of two techniques for the removal of calcium hydroxide from root canals.

AIM: To compare the ability of two irrigant regimens to remove calcium hydroxide (CH) mixed with different vehicles from root canal walls. METHODOLOGY: The root canals of 92 freshly extracted bovine incisor teeth were prepared with a step-back technique and randomly assigned into two experimental groups (n = 40), whilst the remaining teeth (n = 12) served as positive and negative controls. In each experimental group, ten teeth were assigned to each CH preparation: G1 - CH powder; G2 - CH + saline solution; G3 - CH + polyethylene glycol (PEG); G4 - CH + PEG + camphorated paramonochlorophenol (CPMC). The negative control did not receive CH placement, and the positive control received the intracanal dressing, but no subsequent removal. After 7 days, the CH was retrieved using manual or passive ultrasonic irrigation (PUI). The roots were grooved longitudinally and split into halves. Images of each half of the canal were acquired by a digital camera, and the percentage of CH coated surface area in relation to the surface area of each third of the canal was calculated. The results were statistically analysed with anova with post hoc Tukey test with the null hypothesis set as 5%. RESULTS: Remnants of medicament were found in all experimental groups. The positive control group had complete coverage of the canal walls with CH in contrast to the negative control (P < 0.001). Considering the cervical and middle thirds, the percentage of CH retention in G1 was significantly lower using PUI (26.6% and 32.2%, respectively) than the manual (38.7% and 46.1%, respectively) technique (P < 0.05). No significant differences were observed between G2, G3 and G4 in all thirds and the experimental groups at the apical third (P > 0.05). CONCLUSIONS: Neither syringe injection nor PUI methods were efficient in removing the inter-appointment root canal medicaments. Remnants of medicament were found in all experimental groups regardless of the vehicle used.

Influence of the shape core on custom cast dowel and core removal by ultrasonic energy.

The aim of this study was to assess the influence of the shape of custom cast dowel and cores on their removal by the use of ultrasound technique. Twenty-four single-rooted bovine teeth were prepared and had cast dowel fixed with zinc phosphate cement. The teeth were randomly divided into two groups: group I- received custom cast dowel and cores made without the coronal portion anatomy, simulating removal this portion with a bur, and group II- received cores that reproduced the coronal anatomy. Both were treated with an ultrasound device in two three-minute cycles (US). The force necessary for dowel removal was determined using a mechanical test machine. In the second stage of the study, the custom cast dowel and cores were again cemented and no ultrasound vibration was used on them (C). Data were submitted to the two-way anova (2 x 2) and Tukey test (P < 0.05), resulting in decreased tensile strength values (Kgf): GIC (49.85 +/- 11.10); GIIC (48.22 +/- 11.09); GIIUS (32.36 +/- 6.21) and GIUS (8.0 +/- 7.52). It was concluded that the shape of the core without the anatomic coronal portion facilitated removal of intra-radicular retention only when associated with the use of ultrasound.

A comparative histological evaluation of the biocompatibility of materials used in apical surgery.

AIM: To evaluate the biological properties of a variety of materials that could be used in apical surgery. METHODOLOGY: The intraosseous implant technique recommended by the FDI (1980) and ADA (1982) was used to test the following materials: zinc oxide-eugenol (ZOE), mineral trioxide aggregate (MTA), and Z-100 light-cured composite resin. Thirty guinea-pigs, 10 for each material, divided into experimental periods of 4 and 12 weeks, received one implant on each side of the lower jaw symphysis. The connective tissue response alongside the lateral wall outside the cup served as a negative control for the technique. At the end of the observation periods, the animals were killed and the specimens prepared for routine histological examination to evaluate their biocompatibility. RESULTS: The reaction of the tissue to the materials diminished with time. The ZOE cement was highly toxic during the 4-week experimental period, but this profile changed significantly after 12 weeks, when it showed biocompatible characteristics. MTA and Z-100 showed biocompatibility in this test model at both time periods. CONCLUSIONS: MTA and Z-100 composite were biocompatible at 4 and 12 weeks in this experimental model.