Abstract
This study evaluated the increase of the instrumented area and dentin thickness in the mesial and distal aspects of mesial canals of mandibular molars after the use of Gates Glidden (GG), LA Axxess (LA) and Orifice Shaper (OS) instruments. A total of 53 canals from 27 mandibular molars were embedded in resin and divided into 3 groups. The roots were sectioned 3 mm below the cementoenamel junction and the images were captured before and after instrumentation. The increase of the instrumented area in terms of percentages and the remaining dentin thickness, in mm, at the mesial and furcal aspects were calculated using the Image tools software. Data were analyzed using the Kruskal-Wallis and Dunn's test. The significance level was set at 5%. All instruments promoted cervical flaring with different amounts of dentin removal at the mesial and distal aspects of the root canals. Statistically significant difference (p<0.05) was found between LA and all other instruments after using the first instrument. Regarding dentin thickness, no significant difference (p>0.05) was found between the mesial and distal walls in all groups. It may be concluded that LA 35.06 and GG 3 burs produced the thinnest dentin walls, and thus their use in mesial canals of mandibular molars should be done with caution.
Highlights
The crown-down technique using rotary instruments is commonly used during the cleaning and shaping procedures of root canal treatment
The first rotary instruments used for cervical preflaring were Gates Glidden burs [7], which are still commonly used during endodontic procedures
Perforation occurred in only one root canal in the Gates-Glidden group
Summary
The crown-down technique using rotary instruments is commonly used during the cleaning and shaping procedures of root canal treatment. This step minimizes cervical interferences and allows instruments to move freely inside the root canal during apical instrumentation by reducing the torque on canal walls and minimizing tensions on the file at the apical region [1]. The diameter of the Gates Glidden bur #2 (0.70 mm) is generally considered safe for the cervical preflaring of mesial canals of mandibular molars [8], but it cannot completely remov cervical interferences, below the cementoenamel junction [9]. Isom et al [10] studied the anti-curvature motion using Gates Glidden burs #2 and #3 and found significant dentin removal at the furcal aspect of the root canal (danger zone)
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