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Effect of Ultrasound on Cleaning with Citric Acid from the Radicular Duct System. An Analysis of Variable Qualitative Response in R Language

Manlla AM, Oliva MA, Lopez GL and Lopez ME

Citric acid is an irrigation solution used in endodontic as a sodium hypochlorite adjuvant since it has a demineralizing action, which facilitates instrumentation in narrow or calcified canals and contributes to the elimination of dentine clay. In a statistical analysis, the response variables are those that best express the effect of the experimental factors on the observation units and can be qualitative or quantitative. The objective of this paper is to present a routine to analyze qualitative variables in R language, from data related to the cleaning of the root canal system with ultrasound and citric acid as an endodontic irrigator. The contingency table was organized with the records of the response variable "Cleaning with citric acid from the root canal system" based on the experimental factor "Exposure to ultrasound". With the frequencies of occurrence of the different categories of the response variable (TA-0: "all open tubules, no mud in the dentin wall", TA-1: "more than 50% of the open tubules", TA-2 : "Less than 50% of open tubules" and TO-3: "all obliterated tubules") registered in both levels of the experimental factor (CU: "with ultrasound" and SU: "without ultrasound"), without discriminating by third observed (AP: "apical", CE: "cervical" and ME: "medium"), proportions were determined as frequencies relative to the general total (all values are comparable) and represented in bar graphs to facilitate the identification of models of cleanliness behaviors in samples exposed and not exposed to ultrasound. Subsequently, hypotheses were formulated regarding the association between the response variable and the experimental factor (level of cleanliness and exposure to ultrasound) and the difference between pairs of proportions (of the samples exposed and not exposed to the experimental factor in the different levels of the variable answer), to be contrasted with the Chi Square or Exact Fisher test and Z for proportions. Finally, the association measures between qualitative variables were calculated, based on the test statistic of the first test. The results of the Fisher Exact test (on the original contingency table) and Chi square (on the modified contingency table so that the categories do not have frequencies less than 5) indicate that the association (p>0.05) between "Cleaning with citric acid" and "Exposure to ultrasound". That is, the differences between the proportions of the samples with and without ultrasound at the different cleaning levels are not significant. This was confirmed with the results of the Z test for proportions since no significant differences were detected in the comparisons made) and with the calculated association measures (the highest value corresponded to the corrected contingency coefficient K=0.153962, which due to its proximity to zero induces to estimate a weak association between the response variable and the experimental factor). Citric acid achieved the level of cleanliness TA-0 in the sample with ultrasound, contrary to another irrigant that achieved the aforementioned cleaning level in the sample without ultrasound.