PubMed · 4392512
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M Tulio Mérida. 1968. [Microbiologic control in root canals].. https://pubmed.ncbi.nlm.nih.gov/4392512/
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AIM: To describe the preparation of Large Root canals with small apical diameters by the GT file technique. SUMMARY: Large Root canals with small apical diameters can usually be prepared with one to three GT files; one to nine clinical steps, and one to five minutes of clinical time. Following proper access, pulp tissue should be removed, and lubricant applied to prevent pulp compaction and blockage. Initial crown-down enlargement is accomplished with up to three standard GT rotary files 0.10, 0.08 and 0.06 taper, running at 300 r.p.m., and with light touch. Care should be taken not to overload instruments, and they should be withdrawn, cleaned and inspected whenever they bind. Sometimes, the shaping objective is achieved with a single instrument; often waves of instrumentation are required before the shaping objective file cuts to length. Prior to cone-fit, the apical resistance form is confirmed with conventional files, employed as feeler gauges of the tapering form created at the canal terminus. Regardless of the shaping time, canals should be soaked with sodium hypochlorite solution for at least 30 min for effective cleaning. KEY LEARNING POINTS: Large Root canals with small apical diameters should be prepared to shaping objectives 0.08 or 0.10 taper. Compacted pulp tissue causes many canal blockages. It should be removed early, and canals should be well lubricated. Large Root canals with small apical diameters should be prepared in crown-down sequence, with recapitulation of steps until the shaping objective is achieved. Apical resistance form should always be confirmed before cone-fit. Canals should be exposed to sodium hypochlorite for at least 30 min for effective cleaning.
Two groups of 30 mature molars each (S and F) were instrumented with Profile .04 taper Series 29 rotary instruments. Group S molars were instrumented at 150 rpm and group F at 350 rpm. The number of fractures, deformed files, and instrumentation time were recorded for each tooth. No instrument fractures occurred in either group. In group S the mean deformation rate and instrumentation time were 1.1 deformed files and 8.0 min per molar. In group F they were 0.57 deformed files and 4.6 min per molar. Both differences were significant (p < 0.05). The results indicate that Profile .04 taper Series 29 rotary instruments should be used at 350 rpm to nearly double efficiency and halve the deformation rate, compared with 150 rpm. Because no instrument fractures occurred while instrumenting 60 mature molars, both speeds should be considered safe.
An extensively redesigned muffle system is presented incorporating improved design features, such as rigid external fixation and machined internal indexing to enable a more accurate, clinically relevant, and reproducible evaluation of root canal anatomy before and after preparation. Given the ability to directly observe and quantify changes in the root canal system, the information obtained using this design is comprehensive. In each tooth pretreatment evaluation provides the ideal control, reinforcing the suitability of this technique.