***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: AIM The purpose of the present study is to evaluate the healing of periapical lesions of teeth with positive and negative canal cultures at the time of obturation , and to evaluate the periapical healing of teeth treated in one visit ( without ) or in two visits with an interappointment dressing of calcium hydroxide . METHODOLOGY Thirty-nine patients received root-canal treatment .  In the first visit , teeth were instrumented , and 18 of these teeth were filled ( after microbiological sampling ) with calcium hydroxide in sterile saline . The other 21 teeth were obturated with gutta-percha and AH-26 sealer after microbiological sampling . Four weeks later , the teeth with calcium hydroxide were accessed again and after microbiological sampling they were obturated with gutta-percha and AH-26 sealer .  Healing of periapical radiolucency was recorded over a period up to 4.5 years . RESULTS In both the treatment groups , the size of the periapical lesions reduced significantly during the follow-up period . Complete radiographic healing was observed in 81 % of the cases in the one-visit group , and in 71 % of the cases in the two-visit group . The probability of success increased continuously over time for both treatment groups . Seven out of eight cases ( 87.5 % ) that showed a positive root-canal culture at the time of obturation healed . The number of colony forming units ( CFU ) in six out of eight positive canals was < 10(2 ) CFU mL(-1 ) . CONCLUSIONS Within the limitations of this study , no significant differences in healing of periapical radiolucency was observed between teeth that were treated in one visit ( without ) and two visits with inclusion of calcium hydroxide for 4 weeks . The presence of a positive bacterial culture ( CFU<10(2 ) ) at the time of filling did not influence the outcome of treatment OBJECTIVES This prospect i ve study was conducted to determine whether there is any significant difference in the incidence of postobturation pain after single- and multiple-visit root canal treatment ( RCT ) . METHODS The frequency of postobturation pain was recorded and evaluated over an observation period of 30 days in 291 of 300 consecutive patients receiving RCT .  The patients were assigned r and omly and consecutively into either single- or multiple-visit groups . The canals of all teeth were prepared and filled by a single operator using the step-back and lateral condensation techniques . The data were analysed statistically to determine the relationship , if any , between the pain experienced and pulpal vitality , tooth type , pre-operative pain , and the sex and age of the patient . RESULTS Nine of the 300 patients were excluded from the analysis as they failed to attend for postoperative review s. A significantly higher incidence ( P < 0.01 ) of postobturation pain was found in the multiple-visit group ( 38 % ) than in the single-visit group ( 27 % ) within 24 h of obturation . The incidence of pain decreased thereafter , with all patients being sysmptom free at the end of the observation period . No significant correlation was found between postobturation pain and any other factor , with the exception that teeth which had nonvital pulp prior to treatment were associated with a significantly greater ( P < 0.005 ) incidence of postobutration pain . CONCLUSIONS Pain was significantly higher in the multiple-visit RCT group and significantly associated with the treatment of the nonvital pulp OBJECTIVES This prospect i ve study evaluated the frequency and intensity of postobturation pain and associated factors in adolescents undergoing one- and two-visit root canal treatment .  METHODS 121 patients aged 11 - 18 years presenting with molars with pulp necrosis were assigned r and omly into two treatment groups : one- and two-visit ( including interappointment dressing with calcium hydroxide paste ) . The canals of all teeth were prepared using a preflaring ( 2/3 middle-cervical ) and step-back ( 1/3 apical ) preparation techniques and filled with laterally compacted gutta-percha and sealer .  Postobturation pain was recorded on a visual analogue scale ( VAS ) of 0 - 5 . Data were statistically analyzed using multivariate logistic regression . RESULTS The frequencies of postobturation pain were 10.5 % ( 6/57 ) in the one-visit group and 23.0 % ( 14/61 ) in the two-visit group . There were no statistically significant differences between the groups ( p=0.07 ) . The intensity of the pain was similar in both groups , particularly flare-ups , with a prevalence of 1.75 % in the one-visit group and 1.65 % in the two-visit group . Postobturation pain was significantly associated with the presence of preoperative pain ( p=0.04 ; OR=3.54 ; CI 95%=1.02 - 12.30 ) and a positive culture at the time of obturation ( p=0.00 ; OR=9.43 ; CI 95%=2.93 - 30.35 ) . CONCLUSIONS Postobturation pain was more present in the two-visit group , but was not statistically significant . The intensity of postobturation pain was similar . Effective microbiological control and the presence of preoperative pain may influence the postobturation pain in adolescents Acute pain and swelling following endodontic treatment are a challenge for both the patient and the dentist . According to previous studies , the incidence of flare-ups increases after endodontic treatment of teeth with necrotic pulps . Calcium hydroxide is currently used as a multi- purpose drug in root canal therapy . The aim of this study was to evaluate the incidence and severity of flare-ups after treatment of pulpless teeth using calcium hydroxide as an intracanal dressing .  Sixty patients with single-root necrotic teeth participated in this study . These patients were r and omly divided into three groups of 20 . The patients were treated in Group A in a single-visit approach , in group B with a two-visit approach without any intracanal dressing and group C with a two-visit approach using calcium hydroxide as an intracanal dressing for one week . All of the patients were followed for 72 hours after each treatment session . The information about the incidence and severity of pain and swelling was recorded in tables , using a modified Visual Analogue Scale for pain severity measurement and a scale with four degrees for measuring the severity of swelling . The data were analyzed by chi-square test and GENMODE procedure The choice of one-visit versus two-visit root canal therapy for necrotic teeth with apical periodontitis is a source of current debate . The primary objective of this r and omized controlled clinical trial was to compare radiographic evidence of periapical healing after root canal therapy completed in one visit or two visits with an interim calcium hydroxide/chlorhexidine paste dressing .  Ninety-seven patients met the inclusion criteria and consented to participate in this study . Patients were r and omly assigned to either the one-visit or two-visit group , and root canal therapy was performed with a st and ardized protocol . Patients in the two-visit group received an intracanal dressing of calcium hydroxide/chlorhexidine paste . Sixty-three patients , 33 in the one-visit group and 30 in the two-visit group , were evaluated at 12 months . The primary outcome measure was change in apical bone density by using the periapical index ( PAI ) . Secondary outcome measures were proportion of teeth healed or improved in each group . Both groups exhibited equally favorable periapical healing at 12 months , with no statistically significant differences between groups The purpose of this study was to compare intracanal bacterial reduction on teeth instrumented with 0.04 tapered nickel-titanium ( NiTi ) rotary instrumentation to bacterial reduction when using a stainless-steel K-file step-back technique using sterile saline irrigation .  Forty-eight patients with apical periodontitis were r and omly assigned treatment type . The canals were sample d before , during , and after instrumentation . The sample s were incubated anaerobically for 7 days at 37 degrees C , colony-forming unit numbers calculated , and a log transformation performed to normalize the counts . Teeth exhibiting apical periodontitis were uniformly infected , whereas vital control teeth were not . A similar and uniform reduction occurred with progressive filing , regardless of technique ( p < 0.0001 ) . There was no detectable difference in colony-forming unit count after NiTi rotary or stainless-steel h and instrumentation ( p = 0.42 ) . Neither technique could predictably render canals free of bacteria . The results of this study indicate NiTi rotary and stainless-steel h and K-file step-back instrumentation techniques were not significantly different in their ability to reduce intracanal bacteria The objective was to evaluate the clinical efficacy of chemomechanical preparation of the root canals with sodium hypochlorite and interappointment medication with calcium hydroxide in the control of root canal infection and healing of periapical lesions .  Fifty teeth diagnosed with chronic apical periodontitis were r and omly allocated to one of three treatments : Single visit ( SV group , n = 20 ) , calcium hydroxide for one week ( CH group n = 18 ) , or leaving the canal empty but sealed for one week ( EC group , n = 12 ) . Microbiological sample s were taken to monitor the infection during treatment . Periapical healing was controlled radiographically following the change in the periapical index at 52 wk and analyzed using one-way ANOVA . All cases showed microbiological growth in the beginning of the treatment . After mechanical preparation and irrigation with sodium hypochlorite in the first appointment , 20 to 33 % of the cases showed growth . At the second appointment 33 % of the cases in the CH group revealed bacteria , whereas the EC group showed remarkably more culture positive cases ( 67 % ) .  Sodium hypochlorite  was effective also at the second appointment and only two teeth remained culture positive . Only minor differences in periapical healing were observed between the treatment groups . However , bacterial growth at the second appointment had a significant negative impact on healing of the periapical lesion ( p < 0.01 ) . The present study indicates good clinical efficacy of sodium hypochlorite irrigation in the control of root canal infection . Calcium hydroxide dressing between the appointments did not show the expected effect in disinfection the root canal system and treatment outcome , indicating the need to develop more efficient inter-appointment dressings The antimicrobial efficacy of endodontic procedures performed in one-visit ( including a 10-min intraappointment dressing with 5 % iodine-potassium-iodide ) was compared with a two-visit procedure ( including an interappointment dressing with calcium-hydroxide paste ) . Teeth with apical periodontitis ( n = 96 ) were r and omly assigned to either group .  Root canal sampling and culturing  were performed before and immediately after instrumentation , and after medication . Initial sampling demonstrated the presence of microorganisms in 98 % of the teeth . Postinstrumentation sampling showed reduction of cultivable microbiota . Antibacterial dressing further reduced the number of teeth with surviving microbes . In the postmedication sample s , residual microorganisms were recovered in 29 % of the one-visit teeth and in 36 % of the two-visit treated teeth . No statistically significant differences between the groups were discerned . It was concluded that from a microbiological point of view , treatment of teeth with apical periodontitis performed in two appointments was not more effective than the investigated one-visit procedure AIM This prospect i ve clinical study explored the influence of calcium hydroxide as an interappointment dressing on the healing of periapical lesions associated with pulpless teeth that had not been endodontically treated previously . This was achieved by comparing the prognosis after a two-visit root canal treatment with that following a one-visit treatment . METHODOLOGY Seventy-three patients were recruited having one tooth with an endodontically induced lesion . Of these patients , 67 could be re-examined .  Calcium hydroxide was placed in the instrumented root canals of 31 teeth for at least one week and the treatment finished at the second visit . Thirty-six teeth were root canal treated at one visit . The criteria for success were the absence of signs and symptoms indicating an acute phase of periapical periodontitis and radiographically a periodontal ligament space of normal width . Methods for event time analysis were used to evaluate and compare the prognosis of both treatment approaches . RESULTS The probability that complete periapical healing will take place increased continuously with the length of the observation period . In both treatment groups the likelihood that the root canal treatment yields a success within an observation time of five years exceeded 90 % . A statistically significant difference between the two treatment groups could not be detected . CONCLUSIONS From a microbiological perspective , one-visit root canal treatment created favourable environmental conditions for periapical repair similar to the two-visit therapy when calcium hydroxide was used as antimicrobial dressing . One-visit root canal treatment is an acceptable alternative to two-visit treatment for pulpless teeth associated with an endodontically induced lesion OBJECTIVE The purpose of this clinical study was to determine the effect of 1- or 2-visit root canal treatment on the postoperative pain in the retreatment cases . STUDY DESIGN Two hundred eighteen cases that required retreatment were included in the study . Obturated and unfilled canal space and the status of periapical tissues were evaluated according to the PAI index . The patients were subcategorized in regard to the presence or the absence of preoperative pain . Approximately half of each category was treated in 1 appointment . After removing the previous root canal obturation material s and biomechanic preparation of root canals , the teeth in the 1-visit group were obturated at the first appointment by using AH 26 sealer and laterally compacted gutta-percha 
    Output:
    
No significant difference was observed in the healing rate between single- versus multiple-visit root canal treatment , as well as the incidence of medium-term post-obturation pain .
On the basis of current studies , the healing rate of single- and multiple-visit root canal treatment is similar for infected teeth .
Patients experience less frequency of short-term post-obturation pain after single-visit than those having multiple-visit root canal treatment