A comparative scanning electron microscopic study of the effect of three different rotary instruments on smear layer formation.

The aim of this study was to evaluate the effect of RaCe, FlexMaster and ProFile rotary instruments on smear layer formation by scanning electron microscopy. Eighty-four caries-free freshly extracted human single-rooted teeth were selected and divided into three groups, each containing 28 teeth. The teeth were instrumented with rotary instruments sequentially: Group A: ProFile Rotary Instruments; Group B: FlexMaster Rotary Instruments; and Group C: RaCe Rotary Instruments. Instrumentation was performed by the crown-down method and according to the manufacturer's instructions. The specimens were then examined with SEM according to Hülsmann's classification. One-way ANOVA and a post hoc Tukey test were used for statistical analysis. The results showed that there were no statistically significant differences among the three groups in the coronal third (P = 0.39), but at the apical and middle thirds there were statistically significant differences between the RaCe group and the other groups (P < 0.05). Smear layer in the RaCe group was less than that in the ProFile and FlexMaster groups, but the difference between the ProFile group and FlexMaster group was not statistically significant (P > 0.05). It was concluded that RaCe Rotary Instruments produce less smear layer than FlexMaster and ProFile Rotary Instruments.

In vitro comparison of three different lengths of remaining gutta-percha for establishment of apical seal after post-space preparation.

The quality of apical seal with regard to the length of remaining gutta-percha following post-space preparation is still controversial. The purpose of this in vitro study was to compare three different lengths of remaining gutta-percha for apical seal after post-space preparation. A total of 126 single-rooted extracted maxillary human anterior teeth with intact apices, straight roots, and without resorption were used in this study. The root canals were prepared and filled with gutta-percha and AH26 sealer. The post-space preparation was accomplished. Ninety-six teeth were randomly divided into three groups (4, 5 and 6 mm of gutta-percha was retained in group 1, 2 and 3, respectively).Thirty teeth were considered for the control groups in which 5 teeth served as positive and 5 teeth served as negative controls. The specimens were placed in India ink for 48 hours and then divided into two halves. The amount of leakage was observed and measured with a stereomicroscope at x 16 magnification and 0.1 mm accuracy. The results showed that there were significant differences among the three experimental groups (P < 0.05). The best apical seal after post-space preparation was associated with the maximum length of remaining gutta-percha in the apical portion of the treated teeth.

Comparison of the effect of Er, Cr-YSGG laser and ultrasonic retrograde root-end cavity preparation on the integrity of root apices.

The aim of this study was to compare the effect of Waterlase laser and ultrasonic root end cavity preparation on the integrity of root end in extracted human teeth. The canals of 60 extracted maxillary central incisors were cleaned, shaped, obturated and 3 mm of the root end was resected and examined for the presence of any cracks. Class I root-end cavities were then prepared using an ultrasonic unit or Waterlase laser. In the ultrasonic group, KIS 2D tip and medium intensity and in the laser group, 600 mum laser tips and an output power setting of 4 W with 55% water and 65% air were used to prepare the cavity which was studied for the presence of any cracks or chippings. One crack was found in the ultrasonic group, while no cracks were observed in the laser group. There was no significant difference between the two groups (P > 0.05). As for the chipping effect, seven cases (23%) had chipping after cavity preparation in the ultrasonic group but no chipping was found in the specimens of the laser group and the difference was statistically significant (P < 0.05). According to the results of this in vitro study, laser preserves the integrity of root-end cavities better than ultrasonic devices from the standpoint of producing chipping.

A stereomicroscopy study of root apices of human maxillary central incisors and mandibular second premolars in an Iranian population.

Mandibular second premolars and maxillary central incisors usually have one root, one canal, and one apical foramen. However, some studies have revealed anatomic variations in these teeth. The aim of the present study was to investigate such variations in canal configuration, foramina, lateral and accessory canals and apical deltas in the root apex of human maxillary central incisors and mandibular second premolars, using a clearing technique and stereomicroscopy. One hundred maxillary central incisors and 137 mandibular second premolars were collected, and India ink was injected into their canals. The teeth were then demineralized with 0.5 N nitric acid, cleared with methyl salicylate, and studied at x 5 and x 16 magnification. The incidence of one canal and one apical foramen was 100% for maxillary central incisors and 94.16% for mandibular second premolars. The main apical foramen was located in the center of the root apex in 21.89% and 17% of mandibular second premolars and maxillary central incisors, respectively. Lateral and accessory canals were found in 84.50% and 77.15% of maxillary central incisors and mandibular second premolars, respectively. Several foramina were found in 11% of maxillary central incisors and 24.08% of mandibular second premolars. Apical deltas were seen in 4.38% and 2% of mandibular second premolars and maxillary central incisors, respectively. The rate of anatomic variations in the apical part of the tooth, especially in posterior teeth, is thus considered to be high.