***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: This study presents the outcome of  single-tooth restorations supported by Astra Tech single-tooth implants  followed for 2 years . Forty-seven implants were placed in the same number of patients . Forty-three patients attended the second recall visit , and none of the evaluated implants have been removed . The mean marginal bone loss after 2 years of service was 0.31 ( SD = 0.48 ) mm . Overall , few complications were recorded during the 2-year period , the most frequent of which were loose crowns ( 7 ) PURPOSE The purpose of this study was to record the effectiveness of Gold-Tite square abutment screws , tightened to 35 Ncm with a torque indicator , in maintaining a clinical ly stable implant/abutment connection . MATERIAL S AND METHODS The study consisted of 73 patients who were treated with 110 Osseotite implants . All patients were restored with either pre-machined titanium or customized UCLA hexed abutments . All abutments were fabricated per the Gold St and ard ZR abutment design of Implant Innovations . All of the abutment screws were Gold-Tite square abutment screws . They were torqued to 35 Ncm with a torque indicator at the time of abutment connection . All crown restorations were cemented to the abutments . Patients were followed for at least 1 year post-occlusal loading . RESULTS Four patients with 6 implants were lost  between the 6- and 12-month recall appointments . Clinical assessment s of implant/restoration mobility were made by the author . One abutment screw was found to be loose at the 12-month recall appointment , representing a 99 % survival rate . DISCUSSION These results add to the growing evidence that abutment screws with enhanced surfaces may provide increased screw/implant contact , higher rotational values , and calculated preload values . CONCLUSION The use of the Gold-Tite square abutment screws , torqued to 35 Ncm , maintained a stable implant/abutment connection that was successful in clinical practice for this minimal evaluation period Screw loosening is considered to be a common problem with both screw - retained and cemented implant restorations . A wider abutment platform , as well as using a torque driver to tighten specifically design ed screws may help prevent this loosening . However , there has been no clinical study evaluating either of these . To longitudinally compare the frequency of screw loosening in st and ard diameter , ( 3.75 and 4.0 mm ) implant supported prostheses to that of wide diameter , ( 5.0 and 6.0 mm ) implant supported prostheses that were h and tightened , and to evaluate whether using a torque driver would minimize or prevent this problem , if screw loosening occurred . A total of 213 dental implants in 106 patients were included in this prospect i ve longitudinal study . Of the implants 68 were wide diameter and 145 were st and ard diameter implants . Wide diameter implants showed 5.8 % screw loosening , while st and ard diameter implants showed 14.5 % screw loosening after insertion with only h and torquing . When these loose screws were tightened with a torque driver , there was no more loosening of screws . Within the limitations of this study , the wide diameter implants tested showed less screw loosening than the st and ard diameter implants when h and torqued . Additionally , within the scope of our study , using a torque driver to tighten the screws with the recommended force prevented this loosening from reoccurring in all cases STATEMENT OF PROBLEM Chronic implant screw loosening remains a problem in restorative practice s. Some implant manufacturers have introduced abutment screws with treated surfaces in an effort to increase preload and reduce potential loosening . Purpose . This study evaluated the material s and surfaces of 4 commercially available abutment screws  on preload generation . MATERIAL AND METHODS Twenty of each of the following abutment screws-Gold-Tite ( Gt ) , TorqTite ( Tt ) , gold alloy ( Ga ) , and titanium alloy (Ta)-were divided into 2 groups . Measurements were recorded for each abutment screw on a mounted 3.75 x 18 mm external hex implant with a titanium abutment .  Rotational angle measurements were conducted on the 4 abutment screws at 20 and 32 Ncm . Removal torque values were recorded and used to indirectly generate preload values . R and om implant block specimens were sectioned and qualitatively evaluated with an SEM . RESULTS At 20 and 32 Ncm , the largest rotational angles were recorded for the Tt groups : 21.2 + /- 3.1 degrees and 38.1 + /- 8.7 degrees , respectively . The greatest preload values at 20 and 32 Ncm were calculated for the Gt groups : 596.8 + /- 101.2 N and 1015.3 + /- 191.2 N , respectively . SEM analysis of the 4 implant block specimens revealed mating thread contacts located in the middle portion of the superior surface of the abutment screw thread . The greatest number of mating thread contacts were seen in the Gt implant block specimen ( 14 of 20 possible thread contacts ) . CONCLUSION The Gt and Tt abutment screws with enhanced surfaces that help reduce the coefficient of friction produced greater rotational angles and preload values than the conventional gold alloy and titanium alloy screws One hundred seven Brånemark implants were placed in 92 patients participating in an international multicenter trial on single-implant restorations at seven centers . The patients were followed for 5 years in a prospect i ve study focusing on implant success and crown function . Plaque and gingival indexes , as well as probing depths , were recorded around teeth and implants . The marginal bone level at implants was determined from intraoral radiographs . Only three implants ( 2.8 % ) had been lost at the final annual checkup . During the follow-up period , a total of 17 patients dropped out or were excluded because of nonconformity with the protocol . Based on the remaining patients , a total of 86 implants were clinical ly and radiographically evaluated at the 5-year follow-up period , result ing in a cumulative success rate of 96.6 % ( 71 implants ) in the maxillae and 100 % ( 15 implants ) in the m and ibles . Plaque and gingival indexes showed a similar pattern of good health around both natural teeth and titanium abutments . The marginal bone loss during the 5-year period did not exceed 1 mm as a mean for all implants analyzed . The most frequent complication recorded during the follow-up was loosening of the abutment fixation screw . The outcome of this study indicated that safe and highly predictable results can be obtained for 5 years when Brånemark implants are used to support single-tooth restorations This article presents prospect i ve four-year prosthetic results of the placement of 432 posterior freest and ing , conventionally cemented prosthetic tooth implants in posterior edentulous spaces using the Bicon Dental Implants system ( Bicon Dental Implants ) . Over four years , 0.74 percent of the abutments loosened , 0.5 percent of the abutments fractured , and 2.47 percent of the crowns experienced porcelain fracture , ( all porcelain fractures occurred at time of placement ) . This low rate of problems appears to make free-st and ing single-tooth implant restorations a reliable solution to treating posterior edentulism OBJECTIVE Because osseointegration has been successful in the management of completely edentulous patients , it is tempting to extrapolate these results and infer the success of single-tooth replacement . Yet there are major clinical differences between edentulous and partially edentulous patients . This prospect i ve study is a follow-up to one started at the University of Toronto in 1986 . The purpose of this study was to continue longitudinal assessment of implant-supported single-tooth replacements . METHODS The original study comprised 42 consecutively treated patients with a total of 49 implants . The patient group consisted of all University of Toronto patients treated with single Br nemark implants whose treatment had been completed more than 5 years previously ( i.e. , before 1994 ) . No exclusion criteria applied . One implant was not osseointegrated at the time of stage 2 surgery , and 6 patients with reportedly successful osseointegrated implants were not available for recall . For the preparation of this report , 30 of the remaining 42 implants were assessed during recall examinations . Assessment of success was based on published criteria . In addition , soft-tissue appearance , implant immobility , occlusal contacts in centric occlusion and excursions , proximal contacts , tightness of crown and abutment screws , and patients ' responses on satisfaction question naires were evaluated . RESULTS The criteria defining success of treatment in implant prosthodontics were met by all 30 of the single-tooth implants , which had been in place for 5 or more years . Each implant was immobile , and each had a mean vertical bone reduction of less than 0.2 mm annually . CONCLUSION Stable long-term results can be achieved with single Brånemark implant-supported crowns In this multicenter prospect i ve study , the results achieved with the use of Brånemark implants for single tooth replacement were evaluated . The overall cumulative success rate was 95.9 % for implants and 91.1 % for crowns . Two of the 99 implants placed had to be removed before the prosthodontic stage of treatment ; thus , 97 were restored with CeraOne crowns . Seventy-seven implants were evaluated radiographically at the 1-year follow-up , 57 at 3 years , and 47 at 5 years . Mean marginal bone resorption was well within the limits set by Albrektsson et al in 1986 . The status of the soft tissue around crowns and adjacent teeth remained stable over the evaluation period . The gold abutment screw in the CeraOne system seems to have eliminated the problem of loosening abutment screws in single tooth replacements . The results suggest that the Brånemark system can be safely used for tissue-integrated replacement of single teeth The purpose of this study was to determine implant survival rates by means of life table analyses for a cohort of patients not part of a prospect i ve efficacy trial and treated by practitioners at varying experience levels . Prognostic variables associated with implant failure were identified by means of proportional hazards models and advanced statistical methods that account for patient effects . Ninety-nine consecutive patients treated from 1987 to 1991 with follow-up to 1994 were included in this retrospective study . A total of 384 dental implants ( 79.7 % Brånemark , 19.3 % IMZ plasma-sprayed , 1 % IMZ hydroxyapatite-coated )  were placed and subsequently supported 108 prostheses . Survival and proportional hazards modeling were used to generate Kaplan-Meier survival curves and to identify variables associated with implant failure . Survey data analysis was used to adjust for any patient effects for variables identified as significant through the proportional hazards models . Thirty-four implants failed over the follow-up period ( median follow-up time 3.6 years ) , result ing in an overall failure rate of 8.9 % . Seventeen of 99 patients experienced an implant failure . When prosthesis type was excluded from the modeling process , survey data analysis identified posterior location and an implant width of less than 4.0 mm as being associated with implant failure ( all P < .05 ) The time-intensive , multi-step process of dental implant therapy limits patient acceptance . This 3-year prospect i ve multicenter study sought to determine the safety of an expedited therapy that consisted of loading unsplinted maxillary anterior single-tooth implants 3 weeks after 1-stage surgical placement , and determination of the peri-implant cortical bone and mucosal responses to the expedited procedure . Fifty-two patients missing 1 or 2 maxilliary anterior teeth were enrolled in a study approved by the Institutional Committee on Human Subjects Research and based on strict inclusion and exclusion criteria .  Astra Tech ST implants placed in a 1-stage procedure were restored 3 weeks later with ST abutments and a provisional crown ( baseline ) ; 7 to 9 weeks later , a porcelain-fused-to-metal or all-ceramic crown was cemented .  Radiographic and clinical examinations were made at baseline and at 6 and 12 months . Implant survival was recorded . Cortical bone responses and peri-implant mucosal responses were evaluated . Fifty-eight implants were placed . During the 3-week period after implant placement , 4 patients were dismissed because of smoking cigarettes ( a protocol deviation ) , and 1 patient was excluded because of deviation in loading time . Of the remaining 53 implants , 2 failed before definitive crown cementation . The result ant 96.2 % survival rate was independent of implant length , tooth position , and bone quality /quantity . The mean change in marginal bone level was 0.4 mm at 12 months . The number of surfaces with plaque decreased from 3.4 % at baseline to 0.5 % at 12 months . The surfaces with inflammation also decreased . A mean gain in papilla length of 0.61 mm occurred , and a gain in buccal gingiva ( x = 0.34 mm ) was observed . A high success rate with positive tissue responses was achieved for maxillary anterior unsplinted single-tooth implants placed in a 1-stage surgery and restored at 3 weeks . This 2-component system is suited to a single-stage , rapid loading protocol for esthetic single-tooth replacement PURPOSE The aim of this study was to evaluate the clinical and radiographic performance of patients who received implants and fixed prostheses with laser-welded tit 
    Output:
    
The results show that abutment screw loosening is a rare event in single-implant restorations regardless of the geometry of implant-abutment connection , provided that proper antirotational features and torque are employed