***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 aim of this study was to test the null hypothesis that sodium hypochlorite irrigation of root canals does not alter the properties of dentine and contribute to the weakening of root-treated teeth .  METHODOLOGY The effect of two concentrations ( 0.5 % , 5.25 % ) of sodium hypochlorite ( NaOCl ) and saline on ( i ) the elastic modulus and flexural strength of machined dentine bars , and ( ii ) changes in strain of ' whole ' extracted human teeth were evaluated . One hundred st and ardized plano-parallel dentine bars ( > 11.7 x 0.8 x 0.8 mm ) were r and omly divided into the three groups , immersed for 2 h in the respective solutions and then subjected to a three-point bend test . Changes in strain of each of 10 teeth on cyclical nondestructive occlusal loading were measured using electrical resistance strain gauges bonded to the cervical aspects . Each tooth had its crown and enamel reduced and root canal prepared . These were irrigated sequentially in a series of four separate , 30-minute regimes ; initial-saline , 0.5 % NaOCl , 5.25 % NaOCl and final-saline . The changes in strains after each irrigation regime were compared . RESULTS There was a significant decrease in elastic modulus of the dentine bars immersed in 5.25 % NaOCl compared with the saline group ( P < 0.01 ) . There was also a significant decrease in flexural strength of the dentine bars in the 5.25 % NaOCl group compared to both the saline and 0.5 % NaOCl groups ( P < 0.01 ) . The strain data from the nondestructive tooth loading tests revealed significant increases in tensile strain between the initial-saline and the final-saline stages ( P < 0.01 ) . Significant increases in compressive strains were also found between initial-saline and 5.25 % NaOCl ; and between 0.5 % NaOCl and 5.25 % NaOCl stages ( P < 0.01 ) . CONCLUSIONS The null hypothesis was rejected , 5.25 % NaOCl reduced the elastic modulus and flexural strength of dentine . Irrigation of root canals of single , mature rooted premolars with 5.25 % NaOCl affected their properties sufficiently to alter their strain characteristics when no enamel was present AIMS AND METHODS The purpose of this retrospective , non-r and omised cohort study was to evaluate the success rate of 775 endodontically treated teeth depending on the restoration type . A total of 508 patients with 775 endodontically treated teeth were examined during at least 12 months . The radiographic controls , time span between root canal filling and definitive restoration , restoration material type , inserted post system type and the occurrence of possible endodontically as well as restorative post-operative complications were recorded . RESULTS 18.3 % of the 775 investigated teeth were incisors and canines , 33.5 % were premolars and 48.2 % molars . Pre-fabricated and casted metal post systems were used only in 15.6 % of the endodontically treated teeth ( 18.4 % incisors and canines , 44.8 % premolars , 36.8 % molars ) . 6.6 % of the teeth had endodontically related symptoms or severe complications , whereas in 13.2 % of the teeth restored with metal posts showed complications , such as root or crown fractures . The Cox-Regression analysis showed that teeth restored with a post system had a statistically significant higher failure rate ( p = 0.044 ) than those which had been restored without posts . CONCLUSIONS The results showed a high success rate for endodontically treated teeth when the final restoration was placed within a short period of time ( two weeks ) . A higher tooth loss was observed when metal post systems were employed suggesting that pre caution is recommended when these types of posts are inserted STATEMENT OF PROBLEM Crowns have been considered the restoration of choice for endodontically treated teeth , but their selection has been based primarily on anecdotal evidence . PURPOSE This study tested the hypothesis that crown placement ( coronal coverage ) is associated with improved survival of endodontically treated teeth when preaccess , endodontic , and restorative factors are controlled . MATERIAL AND METHODS A University of Iowa College of Dentistry treatment data base was used to identify permanent teeth that had undergone initial obturation between July 1 , 1985 , and December 31 , 1987 . Study patients were restricted to persons with at least 1 dental visit in each 2-year interval from 1985 to 1996 ; a simple r and om sample of 280 patients ( n = 400 teeth ) was selected . Dental charts , radiographs , and computerized data bases were examined to ascertain variables of interest and to verify study inclusion criteria . Kaplan-Meier survival estimates were generated for the 203 teeth that satisfied study inclusion criteria . Multivariate Cox proportional hazards regression models were developed , with st and ard errors adjusted to account for clustering of teeth within patients . RESULTS When tooth type and radiographic evidence of caries at access were controlled , the final Cox model showed that endodontically treated teeth not crowned after obturation were lost at a 6.0 times greater rate than teeth crowned after obturation ( 95 % confidence interval : 3.2 to 11.3 ) . CONCLUSION Within the limitations of this study , a strong association between crown placement and the survival of endodontically treated teeth was observed . These results may impact treatment planning if long-term tooth retention is the primary goal AIM To consider the survival of  root canal treatment provided within the General Dental Services in Engl and and Wales , with failure being defined as re-treating of a root canal , apical surgery or extraction . METHODS A data set was established consisting of patients , 18 years or older , whose birthdays were included within a set of r and omly selected date s and whose restoration records contained the placement of one or more direct restorations or crowns in courses of treatment between September 1990 and January 2002 . The history of each root canal-treated tooth was consulted , and the next date for an intervention on the root canal of the tooth , defined as a re-treatment , apical surgery or extraction , was obtained . Thus , a data set was created of root canal-treated teeth , with the date s of root canal filling placement and the date s , if any , of re-intervention . RESULTS Data for over 80,000 different adult patients were analysed , and a total of 30,843 root canal-treated teeth identified from the data over a period of 11 years . The proportion surviving without further treatment of the root canal was estimated at 74 % within an observation time of up to 10 years , with survival being strongly correlated with the characteristics of the patient , including age and treatment history , with older patients having root canal treatment with earlier re-intervention than those of younger patients . CONCLUSION Within the data set analysed , an estimated 74 % of root canal-treated teeth pass through 10 years without re-treatment , apical surgery or extraction AIM To assess survival rates and complications of  root-filled teeth restored with or without post- and -core systems  over a mean observation period of > or=4 years . METHODOLOGY A total of 325 single- and multirooted teeth in 183 subjects treated in a private practice were root filled and restored with either a cast post- and -core or with a prefabricated titanium post and composite core . Root-filled teeth without post-retained restorations served as controls . The restored teeth served as abutments for single unit metal-ceramic or composite crowns or fixed bridges . Teeth supporting cantilever bridges , overdentures or telescopic crowns were excluded . RESULTS Seventeen teeth in 17 subjects were lost to follow-up ( 17/325 : 5.2 % ) . The mean observation period was 5.2 + /- 1.8 ( SD ) years for restorations with titanium posts , 6.2 + /- 2.0 ( SD ) years for cast post- and -cores and 4.4 + /- 1.7 ( SD ) years for teeth without posts . Overall , 54 % of build-ups included the incorporation of a titanium post and 26.5 % the cementation of a cast post- and -core . The remaining 19.5 % of the teeth were restored without intraradicular retention . The adjusted 5-year tooth survival rate amounted to 92.5 % for teeth restored with titanium posts , to 97.1 % for teeth restored with cast post- and -cores and to 94.3 % for teeth without post restorations , respectively . The most frequent complications included root fracture ( 6.2 % ) , recurrent caries ( 1.9 % ) , post-treatment periradicular disease ( 1.6 % ) and loss of retention ( 1.3 % ) . CONCLUSION Provided that high- quality root canal treatment and restorative protocol s are implemented , high survival and low complication rates of single- and multirooted root-filled teeth used as abutments for fixed restorations can be expected after a mean observation period of > or=4 years BACKGROUND A prospect i ve study was started in 1995 to evaluate the success of carbon fibre reinforced epoxy resin ( CFRR ) posts used to restore endodontically treated teeth . All the teeth in the study had lost more than 50 % of their coronal structure . METHODS Fifty-nine carbon fibre Composiposts cemented with Metabond and built up with Core Paste cores were placed into the teeth of 47 patients . Each tooth received a full-coverage restoration ( porcelain fused to metal crown ) and was followed for 6.7 - 45.4 months ( average = 28.0 months , st and ard deviation = 10.7 ) . RESULTS Results for 52 teeth in 42 patients were analyzed . There were no fractures . The overall failure rate was 7.7 % and the cumulative survival rate was 89.6 % at the end of the follow-up period . The only statistically significant finding ( p = 0.04 ) was that posts in lower premolars were at higher risk of failure . CONCLUSION CFRR posts are among the most predictable systems available today . CFRR posts in the upper anterior teeth are associated with a higher success rate and longer life than those placed in premolars , especially lower premolars . This study contributes to the growing body of evidence that supports the use of CFRR posts in the restoration of endodontically treated teeth AIM The present study tested the hypothesis that having two proximal contacts ( PCs ) at access is associated with improved survival of root canal treated ( RCT ) teeth  , controlling for important presenting conditions , endodontic variables and restorative factors . METHODOLOGY A treatment data base at the University of Iowa College of Dentistry was used to identify permanent teeth undergoing obturation between 1 July 1985 and 31 December 1987 . The list was restricted to teeth of patients with at least one dental visit in each two-year interval from 1985 to 1996 , and a simple r and om sample of 280 patients ( n = 400 teeth ) was selected . Dental charts , radiographs , and computerized data bases were examined to ascertain variables of interest and to verify study inclusion criteria . Kaplan-Meier survival estimates were generated for the 221 teeth satisfying study inclusion criteria . Multivariate Cox models were developed , with st and ard errors adjusted to account for clustering of teeth within patients . RESULTS The final Cox model showed that teeth with < or = 1 PC at access were lost at a rate three times that of teeth with 2 PCs ( hazard ratio = 3.1 ; 95 % confidence interval = 1.9 - 5.1 ) , controlling for tooth type , presence of radiographic caries at access , and presence of a crown before or after obturation . CONCLUSIONS Because RCT teeth with two PCs at access experienced substantially better survival than teeth with fewer than two PCs , the influence of PCs on prognosis should be recognized during treatment planning . Future research should employ prospect i ve study design s , capture additional variables , and provide data to support endodontic treatment decisions AIM To evaluate the effect of irrigation regimens on tooth surface strain using saline , sodium hypochlorite ( 3 % and 5 % NaOCl ) and ethylenediaminetetraacetic acid ( 17 % EDTA ) , individually and in alternating combinations . METHODOLOGY Single-rooted premolar teeth with single canals prepared to st and ardized dimensions were grouped by anatomical features and r and omly distributed amongst six experimental groups ( n = 12 each ) . The six groups were : ( 1 ) saline ; ( 2 ) 5 % NaOCl ; ( 3 ) 3 % NaOCl ; ( 4 ) 17 % EDTA ; ( 5 ) 3 % NaOCl and 17 % EDTA ; ( 6 ) 5 % NaOCl and 17 % EDTA . All groups underwent four ( group 1 ) or five ( groups 2 , 3 , 4 , 5 , 6 ) sequential 30-min irrigation periods following each of which the tooth was subjected to a st and ard regime of cyclic , nondestructive , occlusal loading . Tooth surface strain was measured during each loading cycle using electrical strain gauges mounted cervico-proximally . The data were analysed by Hierarchical anova and post hoc multiple comparisons . RESULTS Irrigation with 5 % NaOCl alone or alternating with 17 % EDTA significantly ( P < 0.001 ) increased the peak strain values for each of the irrigation periods compared with that of saline ( group 1 ) . The data for the other groups revealed no significant differences compared with those of saline . The strain increase after the fourth irrigation cycle was significantly higher for group 6 than for group 2 . The measured canal morphology and dentine 
    Output:
    
Based on the data available for meta-analyses , four conditions were found to significantly improve tooth survival .