Abstract
AimTo precisely quantify the circumferential strains created along the radicular dentin of maxillary incisors during a simulated clinical procedure of lateral compaction.MethodsSix miniature strain gauges were bonded on the roots of fourteen recently extracted maxillary central incisors that were subjected to root canal instrumentation. The strain gauges were bonded at three levels (apical, middle, and coronal) and four aspects (buccal, lingual, mesial, and distal) of the roots. Each tooth was embedded in a PVC cylinder containing polyvinyl-siloxane impression material. Root filling was then performed by simulating the clinical procedure of lateral compaction using nickel-titanium finger spreaders. The force applied to the spreader and the strains developing in the surface root dentin were continuously recorded at a frequency of 10 Hz.ResultsThe highest strains that developed during lateral compaction were in the mesial and distal aspects at the apical level of the root. The magnitudes of the maximal mesial/distal strains at the apical as well as the mid-root levels were approximately 2.5–3 times higher than those at the buccal/lingual aspects (p = 0.041). The strains decreased significantly (p<0.04) from the apical through the mid-root levels to the coronal level, yielding gradients of 2.5- and 6-fold, respectively. The mesial and distal strains were consistently tensile and did not differ significantly; however, the buccal strains were generally 35–65% higher than the lingual strains (p = 0.078). Lateral compaction resulted in the gradual build-up of residual strains, resulting in generation of a 'stair-step' curve. These strains declined gradually and almost completely disappeared after 1000 sec.ConclusionsWith proper mounting of several miniature strain gauges at various levels and aspects of the root, significant circumferential strains can be monitored under clinically relevant compaction forces. The residual strains at the end of lateral compaction are not stored in the dentin but decrease gradually to negligible levels.
Highlights
Lateral compaction, frequently cited as the 'gold standard' technique for root canal filling, is one of the most commonly used methods and is utilized by more than half of all practitioners worldwide [1,2,3]
The highest strains that developed during lateral compaction were in the mesial and distal aspects at the apical level of the root
Lateral compaction resulted in the gradual build-up of residual strains, resulting in generation of a 'stair-step' curve
Summary
Frequently cited as the 'gold standard' technique for root canal filling, is one of the most commonly used methods and is utilized by more than half of all practitioners worldwide [1,2,3]. The apical force applied through finger spreaders during compaction of gutta-percha, which is currently the most commonly used root filling material, exerts pressure on the material, resulting in circumferential tensile stresses on the canal surface [11]. Such stresses are a concern, especially when preexisting micro-cracks are present in the dentin, with potential propagation from a subcritical to a critical length [12]. Such micro-cracks in radicular dentin might be created by rotary NiTi instruments through the process of canal instrumentation [13, 14]
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