cleaning of root canal system during biomechanical preparation aims to eliminate irritating agents , such as bacteria and their byproducts , degenerated pulp tissue and contaminated dentin22 .
this process occurs by the mechanical action the endodontic instruments on the root canal walls associated with the chemical properties of irrigating solutions and physical action of the flushing / aspirating process .
the smear layer , composed of dentin chips , remnants of pulp tissue , odontoblastic processes , and sometimes microorganisms , is formed on the root canal walls as a result of chemomechanical instrumentation and is deposited mainly at the apical third17 . over the years
, the development of several types of instruments and irrigating solutions have optimized the cleaning and shaping of root canals , thus increasing the safety and decreasing the duration of endodontic therapy . among the currently available irrigating solutions , sodium hypochlorite ( naocl ) at different concentrations is the most commonly used and accepted worldwide due to its properties of clarification , organic tissue dissolution , saponification , transformation of amines into chloramines , deodorizing and antimicrobial effects2,22,23 .
although sodium hypochlorite is still the most used root canal irrigant , studies have searched for alternative solutions and therapeutic resources that may improve the success rate of endodontic treatment .
the development of polyurethane resins derived from castor oil ( obtained from the bean produced by ricinus communis ) widened the scopes in different fields of medical and dental research , as they were shown to have biocompatibility and potential applicability in several areas5,18 . the castor plant ( ricinus communis ; division magnoliophyta , class magnoliopside , sub - class rosidae , order euforbiales , family euforbiaceae ) is a vegetal typically found in tropical climate areas .
although originally native to northeastern africa and the middle east , it has become naturalized in several tropical and warm temperate regions throughout the world , including brazil .
because of its climatic characteristics , natural resources and territorial extension of continental dimensions , brazil has one of the largest areas cultivated with castor bean plant in the world .
the ricinus communis has great oil - chemical potential that may guarantee the supply of prepolymers and polyols derived from fatty acid in large scale .
because of its composition , 81 - 96% of triglyceride of the ricinoleic acid , the castor bean oil is considered a natural polyol , since it has three hydroxyl radicals that are liable to be utilized in the synthesis of polyurethanes based on the outcomes of biocompatibility studies in orthopedics4,15 , dental researchers have reported the viability of using materials derived from ricinus communis for bone reconstruction and repair of intrabony defects , maxillary sinus floor elevation and filling of dental alveolus , in such a way to provide viable sites for placement of implants and metallic pins and frameworks5,6 . in endodontics , a detergent derived from the castor bean oil
this ricinus communis detergent has similar antimicrobial activity as 0.5% sodium hypochlorite when used for irrigation of necrotic root canals11,12 , is biocompatible with the periapical tissues6 , increases dentinal permeability19 and has similar ability to remove smear layer from the root canals as 17% edta24 .
therefore , the purpose of this study was to investigate , by morphologic and morphometric analyses , the cleaning of root canals instrumented with nickel - titanium rotary system using 3.3% ricinus communis detergent and 1% sodium hypochlorite as irrigating solutions .
twenty - seven human single - rooted mandibular premolars , with straight roots and no flattening ( either in mesio - distal or bucco - lingual direction ) were selected for this study .
the teeth were washed in running water for 24 h and stored in distilled water until use .
pulp chamber access was performed according to the guidelines recommended by de deus7 ( 1992 ) under irrigation with distilled water to avoid that dentin chips and other debris were taken into the root canal inadvertently .
the root canal was explored with a size 10 k - file ( dentsply / maillefer , ballaigues , switzerland ) until the tip of the instrument penetrated and engaged the apical foramen .
the teeth were randomly divided into 3 groups ( n=9 ) according to the irrigating solution used : group i : distilled and deionized water ( 2 ml at each file change ; 20 ml total ) ; group ii : 1% naocl ( 2 ml at each file change ; 20 ml total ) and group iii : 3.3% ricinus communis detergent ( 2 ml at each file change ; 20 ml total ) .
biomechanical preparation was performed with nickel - titanium rotary instruments activated by endo plus electric engine ( vk driller equipamentos eltricos ltda , so paulo , brazil ) adjusted to 250 rpm .
the canal entrance was prepared with a 25/02 endo - flare instrument ( micromega , besanon , france ) , whereas the cervical and middle thirds were prepared with protaper ( dentsply / maillefer , ballaigues , switzerland ) s1 , sx and s2 shaping files .
instrumentation was continued using the hero 642 system ( micromega , besancon , france ) in the following sequence : 25/02 ( apical ) , 25/04 ( apical ) , 25/06 ( middle ) , 30/02 ( apical ) , 30/04 ( apical ) and 35/02 ( apical ) .
the size of the instrument was recorded and standardized for all specimens . in all groups , at every change of instrument , the root canals were flushed with 2 ml of the respective irrigating solution using the ultradent syringe ( ultradent , endodontics products , texas , usa ) . after biomechanical preparation , the organic debris remaining in the root canals were fixated by 12-hour immersion of specimens in 10% buffered formalin .
transverse 6-m - thick semi - serial sections were obtained and stained with hematoxylin - eosin for morphometric analysis .
the cross - sections were examined with an optical microscope ( eclipse e 600 ; nikon , shinagawa - ku , tokyo , japan ) at x40 magnification connected to a computer .
the images were captured using adobe premier 5.1 software and analyzed using corel photo paint 10 software .
a grid was placed over these images to evaluate the total area of the canal and the area containing debris ( figure 1 ) .
after the count of the points in the clean area and the debris area , the percentage of debris in the root canal at the apical third was calculated .
these data were submitted to statistical analysis with anova and the tukey test ( p<0.01 ) .
the percentages ( means and standard deviation ) of debris remaining in the apical thirds of the root canals in each group are shown in table 1 . tukey test ( p<0.01 ) : critical value = 0.33 .
different letters indicate statistically significant difference the tukey test was applied and the results showed no statistically significant difference ( p>0.01 ) between the groups irrigated with 1% naocl and 3.3% ricinus communis detergent , which had the lowest amount of debris at the apical third ( table 1 ; different letters indicate statistically significant differences ) and the group irrigated with distilled and deionized water presented the greatest percentage of debris ( 15.58% ) and was statistically different from the other groups ( p<0.01 ) .
despite the noticeable technical and scientific advances recently experienced in endodontics , which led to the development of a wide variety of instruments , equipments and materials , research has demonstrated that biomechanical preparation does not yield complete removal of organic and inorganic debris from instrumented root canals1,10 .
biomechanical preparation of the root canal system with ni - ti rotary instruments driven by electric and pneumatic engines is a worldwide spread reality that has brought several conceptual changes and remarkably improved the effectiveness and rapidness of endodontic therapy .
nevertheless , while investigating the cleaning capacity of manual and rotary instrumentation techniques in mesio - distal flattened canals by morphometric analysis , barbizam , et al.3 ( 2002 ) found that rotary instrumentation with ni - ti files acts within a well - delimited area , leaving non - instrumented polar regions , in which the arrangement of dentinal tubules facilitates the entrapment and maintenance of viable microorganisms .
it has also been pointed out that , even in canals with circular internal anatomy , the capacity of thoroughly cleaning the endodontic space does not depend exclusively on instrumentation10 .
these findings emphasize the need to use an effective irrigating solution that has specific chemical properties , among which organic tissue dissolution2,16 .
this study evaluated , by morphologic and morphometric analyses , the cleanliness of the apical third of root canals after niti rotary instrumentation associated with the use of either 3.3% ricinus communis detergent or 1% naocl , as irrigating solutions .
the percentage of debris at the apical third of root canals after chemo - mechanical preparation was assessed morphometrically , as described in previous studies1,3,10,21 .
the findings of the present study revealed that there was no statistically significant difference ( p>0.01 ) between groups irrigated with 1% naocl and 3.3% ricinus communis detergent , which had the lowest amount of debris at the apical third .
these groups , in turn , were statistically different ( p<0.01 ) from the control group irrigated with distilled and deionized water .
the results obtained for specimens irrigated with 1% naocl are probably derived from the sodium hypochlorite capacity to dissolve organic tissue remnants2,9,13,23 .
estrela , et al.8 ( 2002 ) , while discussing the mechanism of action of sodium hypochlorite , reported that this chemical agent is able to produce alterations in cellular biosynthesis and changes in cellular metabolism and phospholipid degradation , by formation of chloramines that interfere with cellular metabolism , oxidation action that promotes irreversible bacterial enzymatic inhibition , and degradation of fatty acids and lipids .
the group irrigated with 3.3% ricinus communis detergent during rotary instrumentation had similar results as those of the group irrigated with 1% naocl , regarding the removal of smear layer from root canals .
it is worthy mentioning that the use of a ricinus communis - based detergent as an endodontic irrigant is in compliance with the recommendations of the world health organization , which has encouraged the search for substances and products derived from animal , vegetal and mineral sources .
the results obtained in the group irrigated with the ricinus communis detergent may be ascribed to its low surface tension and consequent moisturizing capacity , which allow for an intimate contact of the solution with the entire surface of root canal walls .
after humectation , the adsorption phenomenon takes place , i.e. , the hydrophobic portion ( which is also lipophilic ) binds to the fatty matter , and the hydrophilic portion binds to water .
therefore , the hydrocarbonated chain works as a structure that has fat bound to one end and water bound to the other .
this configuration leaves the surface free from fatty ( oil ) contamination , protected by the detergent molecules attached to it19 . as a result
, the mechanical action of endodontic files during instrumentation increases the contact surface between the detergent and root canal walls , thus facilitating the removal of debris .
studies have shown that , in addition to its ability of removing root canal debris , the 3.3% ricinus communis detergent has antimicrobial activity11,12 and smear layer removal capacity24 , increases dentinal permeability20 and presents biocompatibility with the periapical tissues5,6 .
because of the aforementioned properties and based on the outcomes of this study and previous investigations11,12,20,24 , it seems feasible to suggest that this intracanal irrigating solution derived from ricinus communis may be a viable alternative for patients that have hypersensitivity to sodium hypochlorite . in view of the issues discussed throughout this paper , and considering that the currently available endodontic irrigants do not have anti - inflammatory activity and biocompatibility , the authors ' expectation with this study was to offer new perspectives and research - based information that might be helpful in evaluating whether the 3.3% ricinus communis detergent , a natural product derived from a vegetal source , may be used as an irrigating solution during biomechanical preparation of root canals .
according to the methodology proposed and based on the results of this study , the following conclusions may be drawn : 
 none of the tested solutions yielded complete removal of debris from the apical third of root canals;3.3% ricinus communis detergent and 1% naocl presented similar cleaning effectiveness on elimination of debris from the apical third of root canals . 
 
none of the tested solutions yielded complete removal of debris from the apical third of root canals ; 3.3% ricinus communis detergent and 1% naocl presented similar cleaning effectiveness on elimination of debris from the apical third of root canals .
 this study evaluated , by morphologic and morphometric analyses , the cleaning of apical third of root canals instrumented with nickel - titanium rotary files using different irrigating solutions . 
 twenty - seven single - rooted mandibular premolars were assigned to three groups ( n=9 ) , according to the irrigating solution used : group i , distilled and deionized water ; group ii , 1% naocl ; and group iii , 3.3% ricinus communis detergent . 
 biomechanical preparation was performed with protaper plus nickel - titanium files as follows : s1 , sx and s2 at the cervical and middle thirds , and 25/02 , 25/04 , 25/06 , 30/02 , 30/04 and 30/06 to complete the instrumentation , operating at 1 mm from the root apex . 
 irrigation was done at each file change with 2 ml of irrigating solution , totalizing 20 ml for each tooth . 
 after biomechanical preparation , the apical thirds were serially sectioned and histologically processed . 
 the cross - sections were examined by an optical microscope ( x40 ) connected to a computer . 
 the images were captured and analyzed using a computer software and submitted to morphometric analysis with aid of a grid . 
 the percentage of debris remaining at the apical third was calculated . 
 data were submitted to statistical analysis by anova and tukey test . 
 the results showed no statistically significant difference ( p>0.01 ) between the groups irrigated with 1% naocl and 3.3% ricinus communis detergent , which presented the lowest percentage of debris at the apical third , 8.49% and 10.11% , respectively . 
 the group irrigated with distilled and deionized water had the highest percentage of debris ( 15.58% ) and was statistically different from the other groups ( p<0.01 ) . 
 it may be concluded that 3.3% ricinus communis detergent and 1% naocl had similar cleaning effectiveness on removal of debris from root canals . 
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS