this study was approved by the institutional review board of loma linda university and was conducted in the center for implant dentistry , loma linda university school of dentistry . to be included in this study , the patients must : ( i ) be at least 18 years of age with good oral hygiene , ( ii ) possess one or more missing teeth in the maxillary or mandibular posterior region ( excluding third molars ) , ( iii ) have adequate bone thickness to accommodate a 4.5  mm diameter implant , ( iv ) have the presence of opposing dentition . those patients with : ( i ) implant insertion torque value of < 35  ncm , ( ii ) a history of alcohol or drug dependency , or any medical , physical , or psychological factor that might affect the surgical or prosthodontic treatment and required follow - up examinations , ( iii ) history of bruxism , ( iv ) history of smoking , and/or ( v ) head and neck radiation treatment were excluded . a coin toss was utilized to randomize the abutment ( ps or nps ) placed in the patient . if patients were receiving more than one implant , the randomization was performed in such a way that the difference in the number of abutments of each group in the patient was not more than one . for example , if a patient was receiving 5 implants , 2 abutments would belong to one group and 3 abutments would belong to another group . following the administration of local anesthetic ( 2% lidocaine with 1  :  100,000 epinephrine [ dentsply , york , pa , usa ] ) , a full - thickness flap was reflected , and alveoloplasty was performed to level the alveolar crest prior to implant placement . the implants used in this study were 4.5  mm in diameter , threaded with sla surface , and an internal conical connection ( superline , dentiumusa , cypress , ca , usa ) ( fig.1 ) . the implants were placed 0.5  mm subcrestally with a minimum insertion torque of 35  ncm ( fig.2 ) . resonance frequency analysis ( rfa ) multiple unit abutments ( either ps or nps ) were randomly selected and placed at time of surgery . , gangnam - gu , seoul , korea ) with a horizontal mismatch of 0.6  mm was used as the control group ( fig.1 ) , while the nps multiple unit abutment ( dentium co. , ltd . ) the abutments were torqued to 25 ncm ( fig.3 ) and plastic healing covers ( comfort cap , dentium co. , ltd . ) placed . flaps were approximated to allow for non - submerged healing using an absorbable polyglactin sutures ( 5 - 0 vicryl plus antibacterial suture [ ethicon ; johnson & johnson , somerville , nj , usa ] ) . the distance between the iaj and the rl was 0.4  mm for the ps multiple unit abutment ( a ) and 0.1  mm for the nps multiple unit abutment ( b and c ) . antibiotics ( amoxicillin 500  mg [ ranbaxy laboratories ltd . , new delhi , india ] ) and analgesics ( ibuprofen 800  mg [ basf corporation , shreveport , la , usa ] ) were prescribed post - operatively . the patients were instructed to rinse with a 0.12% chlorhexidine gluconate solution ( peridex , zila pharmaceuticals , inc . , phoenix , az , usa ) twice daily and refrain from functioning over the surgical site for the initial 3  weeks . a soft diet was recommended throughout the remaining healing period ( 3  months ) . at 2 months , a definitive abutment level impression was made ( aquasil monophase ; dentsply , milford , de , usa ) . at 3 months , definitive screw - retained all ceramic crown ( dentium co. , ltd . ) was connected to the multiple unit abutment with a torque of 10  ncm ( manufacturer 's recommendation ) ( fig.4 ) . evaluations were made at the time of implant surgery ( 0 ) and at 3 , 6 , and 12  months following implant placement . the following parameters were evaluated at each follow - up appointment when applicable : implant success ( smith & zarb 1989 ) , marginal bone level ( mbl ) and marginal bone level change ( mblc ) , rfa ( sennerby & meredith 2008 ; zix et  al . the implant success rates were evaluated according to the criteria proposed by smith and zarb ( 1989 ) where applicable . the mbls were measured on the mesial and distal aspects of each implant using sequential standardized periapical radiographs and the long - cone paralleling technique ( strid 1985 ) . a customized occlusal jig was made using a polyvinyl siloxane bite registration material ( exabite ; gc america inc , alsip , il , usa ) to standardize the angulation and position of the film . the junction between the micro - roughened surface and the machined surface was used as the reference line ( rl ) ( fig.5 ) . the distance between the rl and the most coronal bone  implant contact was measured . the value zero was designated when the mbl was at the same level or coronal to the rl and negative when the bone  implant contact was apical to the rl . the average value of the mesial and distal measurements was used to represent the mbl for each implant . the mbls were measured at 0 , 3 , 6 and 12  months after implant placement ( figs6 and 7 ) . the mbls and mblcs were calculated and compared within group and between groups at designated time intervals . the intraexaminer reliability of the measurements was determined by using double assessments of mbl taken 2  months apart by one examiner and expressed as the intraclass correlation coefficient ( icc ) . reference line ( rl ) used to determine marginal bone level for the ps group ( a ) and the nps group ( b ) . radiographs taken at the day of implant placement ( 0 ) ( a ) , 3 months ( b ) , 6 months ( c ) , and 12 months ( d ) for the ps group . radiographs taken at the day of implant placement ( 0 ) ( a ) , 3 months ( b ) , 6 months ( c ) , and 12 months ( d ) for the nps group . the rfa instrument ( osstell isq , gothenburg , sweden ) was used to evaluate implant stability immediately after implant placement ( sennerby & meredith 2008 ; zix et  al . 2008 ) . presence or absence of plaque was assessed at 6 sites ( mesiolabial , labial , distolabial , mesiolingual , lingual , and distolingual ) around the abutment or the definitive restoration ( mombelli et  al . surgical complications were recorded and included but not limited to soft tissue problems , infection , or modifications of manufacturer 's recommendations for implant placement . prosthetic complications were documented , but were not limited to screw loosening , and/or repair of definitive restoration . the friedman test with post hoc pairwise comparisons was used to compare the mbls and mblcs within group , while the mann  whitney u - test was used to assess the mbls and mblcs between groups . pearson chi - square test was performed to evaluate the intragroup and intergroup differences in mpi . this study was approved by the institutional review board of loma linda university and was conducted in the center for implant dentistry , loma linda university school of dentistry . to be included in this study , the patients must : ( i ) be at least 18 years of age with good oral hygiene , ( ii ) possess one or more missing teeth in the maxillary or mandibular posterior region ( excluding third molars ) , ( iii ) have adequate bone thickness to accommodate a 4.5  mm diameter implant , ( iv ) have the presence of opposing dentition . those patients with : ( i ) implant insertion torque value of < 35  ncm , ( ii ) a history of alcohol or drug dependency , or any medical , physical , or psychological factor that might affect the surgical or prosthodontic treatment and required follow - up examinations , ( iii ) history of bruxism , ( iv ) history of smoking , and/or ( v ) head and neck radiation treatment were excluded . a coin toss was utilized to randomize the abutment ( ps or nps ) placed in the patient . if patients were receiving more than one implant , the randomization was performed in such a way that the difference in the number of abutments of each group in the patient was not more than one . for example , if a patient was receiving 5 implants , 2 abutments would belong to one group and 3 abutments would belong to another group . following the administration of local anesthetic ( 2% lidocaine with 1  :  100,000 epinephrine [ dentsply , york , pa , usa ] ) , a full - thickness flap was reflected , and alveoloplasty was performed to level the alveolar crest prior to implant placement . the implants used in this study were 4.5  mm in diameter , threaded with sla surface , and an internal conical connection ( superline , dentiumusa , cypress , ca , usa ) ( fig.1 ) . the implants were placed 0.5  mm subcrestally with a minimum insertion torque of 35  ncm ( fig.2 ) . resonance frequency analysis ( rfa ) multiple unit abutments ( either ps or nps ) were randomly selected and placed at time of surgery . , gangnam - gu , seoul , korea ) with a horizontal mismatch of 0.6  mm was used as the control group ( fig.1 ) , while the nps multiple unit abutment ( dentium co. , ltd . ) the abutments were torqued to 25 ncm ( fig.3 ) and plastic healing covers ( comfort cap , dentium co. , ltd . ) placed . flaps were approximated to allow for non - submerged healing using an absorbable polyglactin sutures ( 5 - 0 vicryl plus antibacterial suture [ ethicon ; johnson & johnson , somerville , nj , usa ] ) . the distance between the iaj and the rl was 0.4  mm for the ps multiple unit abutment ( a ) and 0.1  mm for the nps multiple unit abutment ( b and c ) . antibiotics ( amoxicillin 500  mg [ ranbaxy laboratories ltd . , new delhi , india ] ) and analgesics ( ibuprofen 800  mg [ basf corporation , shreveport , la , usa ] ) were prescribed post - operatively . the patients were instructed to rinse with a 0.12% chlorhexidine gluconate solution ( peridex , zila pharmaceuticals , inc . , phoenix , az , usa ) twice daily and refrain from functioning over the surgical site for the initial 3  weeks . a soft diet was recommended throughout the remaining healing period ( 3  months ) . at 2 months , a definitive abutment level impression was made ( aquasil monophase ; dentsply , milford , de , usa ) . at 3 months , definitive screw - retained all ceramic crown ( dentium co. , ltd . ) was connected to the multiple unit abutment with a torque of 10  ncm ( manufacturer 's recommendation ) ( fig.4 ) . evaluations were made at the time of implant surgery ( 0 ) and at 3 , 6 , and 12  months following implant placement . the following parameters were evaluated at each follow - up appointment when applicable : implant success ( smith & zarb 1989 ) , marginal bone level ( mbl ) and marginal bone level change ( mblc ) , rfa ( sennerby & meredith 2008 ; zix et  al . the implant success rates were evaluated according to the criteria proposed by smith and zarb ( 1989 ) where applicable . the mbls were measured on the mesial and distal aspects of each implant using sequential standardized periapical radiographs and the long - cone paralleling technique ( strid 1985 ) . a customized occlusal jig was made using a polyvinyl siloxane bite registration material ( exabite ; gc america inc , alsip , il , usa ) to standardize the angulation and position of the film . the junction between the micro - roughened surface and the machined surface was used as the reference line ( rl ) ( fig.5 ) . the distance between the rl and the most coronal bone  implant contact was measured . the value zero was designated when the mbl was at the same level or coronal to the rl and negative when the bone  implant contact was apical to the rl . the average value of the mesial and distal measurements was used to represent the mbl for each implant . the mbls were measured at 0 , 3 , 6 and 12  months after implant placement ( figs6 and 7 ) . the mbls and mblcs were calculated and compared within group and between groups at designated time intervals . the intraexaminer reliability of the measurements was determined by using double assessments of mbl taken 2  months apart by one examiner and expressed as the intraclass correlation coefficient ( icc ) . reference line ( rl ) used to determine marginal bone level for the ps group ( a ) and the nps group ( b ) . radiographs taken at the day of implant placement ( 0 ) ( a ) , 3 months ( b ) , 6 months ( c ) , and 12 months ( d ) for the ps group . radiographs taken at the day of implant placement ( 0 ) ( a ) , 3 months ( b ) , 6 months ( c ) , and 12 months ( d ) for the nps group . the rfa instrument ( osstell isq , gothenburg , sweden ) was used to evaluate implant stability immediately after implant placement ( sennerby & meredith 2008 ; zix et  al . 2008 ) . presence or absence of plaque was assessed at 6 sites ( mesiolabial , labial , distolabial , mesiolingual , lingual , and distolingual ) around the abutment or the definitive restoration ( mombelli et  al . surgical complications were recorded and included but not limited to soft tissue problems , infection , or modifications of manufacturer 's recommendations for implant placement . prosthetic complications were documented , but were not limited to screw loosening , and/or repair of definitive restoration . the implant success rates were evaluated according to the criteria proposed by smith and zarb ( 1989 ) where applicable . the mbls were measured on the mesial and distal aspects of each implant using sequential standardized periapical radiographs and the long - cone paralleling technique ( strid 1985 ) . a customized occlusal jig was made using a polyvinyl siloxane bite registration material ( exabite ; gc america inc , alsip , il , usa ) to standardize the angulation and position of the film . the junction between the micro - roughened surface and the machined surface was used as the reference line ( rl ) ( fig.5 ) . the distance between the rl and the most coronal bone  implant contact was measured . the value zero was designated when the mbl was at the same level or coronal to the rl and negative when the bone  implant contact was apical to the rl . the average value of the mesial and distal measurements was used to represent the mbl for each implant . the mbls were measured at 0 , 3 , 6 and 12  months after implant placement ( figs6 and 7 ) . the mbls and mblcs were calculated and compared within group and between groups at designated time intervals . the intraexaminer reliability of the measurements was determined by using double assessments of mbl taken 2  months apart by one examiner and expressed as the intraclass correlation coefficient ( icc ) . reference line ( rl ) used to determine marginal bone level for the ps group ( a ) and the nps group ( b ) . radiographs taken at the day of implant placement ( 0 ) ( a ) , 3 months ( b ) , 6 months ( c ) , and 12 months ( d ) for the ps group . radiographs taken at the day of implant placement ( 0 ) ( a ) , 3 months ( b ) , 6 months ( c ) , and 12 months ( d ) for the nps group . the rfa instrument ( osstell isq , gothenburg , sweden ) was used to evaluate implant stability immediately after implant placement ( sennerby & meredith 2008 ; zix et  al . presence or absence of plaque was assessed at 6 sites ( mesiolabial , labial , distolabial , mesiolingual , lingual , and distolingual ) around the abutment or the definitive restoration ( mombelli et  al . surgical complications were recorded and included but not limited to soft tissue problems , infection , or modifications of manufacturer 's recommendations for implant placement . prosthetic complications were documented , but were not limited to screw loosening , and/or repair of definitive restoration . the friedman test with post hoc pairwise comparisons was used to compare the mbls and mblcs within group , while the mann  whitney u - test was used to assess the mbls and mblcs between groups . pearson chi - square test was performed to evaluate the intragroup and intergroup differences in mpi . a total of 30 implants ( 15 with ps abutments and 15 with nps abutments ) randomly assigned to nine male and 10 female patients between ages of 23 and 76 ( mean age 55.4  years ) were included in this study ( table  1 ) . all implants possessed a diameter of 4.5 mm , with varied length ( 8 , 10 and 12  mm ) . for the ps group , 5 implants were placed in the posterior maxilla and 10 implants in the posterior mandible , while for the nps group , 3 implants were placed in the posterior maxilla and 12 implants in the posterior mandible . after one year , all implants ( 30/30 ) were stable and none had lost osseointegration , which corresponded to an overall implant success rate of 100% . patient distribution , locations , and implant dimensions the icc for marginal bone level measurements was 0.99 , indicating that the measurements were reliable and reproducible . at baseline , the mbls were at or coronal to the rl for all mesial and distal sites for the ps ( 30/30 ) and nps ( 30/30 ) group , while at 12-months , the mbls of only 20/30 for the ps group and 15/30 for the nps group were still found at or coronal to the rl . for statistical analysis , one implant per patient was randomly selected accounting for eight independent implants in the ps group and 11 independent implants in the nps group ( tables  25 ) . the overall mbls at different time intervals and corresponding mblcs for the two groups are listed in tables  24 . for the ps group , changes in mbls were not statistically significant between all time periods ( p  >  0.05 ; table  2 ) . for the nps group , significant differences were noted between all time points ( p  <  0.05 ) except between 0 and 3  months ( p  =  0.066 ) , and 6 and 12  months ( p  =  0.483 ) ( table  3 ) . when comparing mblc between ps and nps groups , statistically significant differences were noted at 012  months ( p  =  0.041 ) and 312  months ( p  =  0.026 ) ( table  4 ) . comparison of the overall marginal bone level ( mbl ) and marginal bone level change ( mblc ) at different time intervals for the ps group using friedman test with post hoc pairwise comparisons at   =  0.05 [ ] denotes mean    sd of marginal bone level changes between the time intervals . comparison of the overall marginal bone level ( mbl ) and marginal bone level change ( mblc ) at different time intervals for the nps group using friedman test with post hoc pairwise comparisons at   =  0.05 statistically significant difference . [ ] denotes mean    sd of marginal bone level changes between the time intervals . comparison of marginal bone level changes ( mblcs ) at different time intervals between the ps and the nps groups ( 03 , 06 , 012 , 36 , 312 , 612  months ) using mann distribution and comparison of mpi scores at different time intervals using pearson chi - square test at   =  0.05 p , comparison between groups ; p , comparison within group . the mean isq value at the time of implant placement was 70 ( range = 5782 ) . the mpi scores of 0 and 1 were consistently observed throughout the study ( table  5 ) . no statistically significant difference was found within the group or between the two groups at the three time intervals ( p  >  0.05 ; table  5 ) . insertion torque of < 35  ncm was observed with 4 implants during placement , and they were not included in the study . prosthetic screw loosening was observed on 2 implants in two patients at 6-month follow - up and on 7 implants in four patients at 12-month follow - up . each incidence of screw loosening was associated with a different implant for a total of 9 implants . no recurrence of prosthetic screw loosening on the same implant was noted in this study . higher incidence of screw loosening was noted in the molar area ( 78% [ 7/9 ] ) than the premolar area ( 22% [ 2/9 ] ) . all loose prosthetic screws were replaced and torqued to 10  ncm ( manufacturer 's recommendation ) . in this study , all implants remained osseointegration at 1 year , corresponding to a 100% ( 30/30 ) implant success rate . these findings are comparable to studies with various implant systems placed at healed sites with either ps ( norton 2001 ; nentwig 2004 ; mangano et  al . 2011 ) [ 95.6100% ] or nps ( naert et  al . 2000 ; polizzi et  al . the success rate of implants with sla surface used in this study is also comparable to that reported for implants with similar surface ( 98.8100% ) ( bornstein et  al . 2011 ) . in this study , although the difference in mblc at 12 months between the ps group ( 0.04  mm ) and the nps group ( 0.19  mm ) was statistically significant ( p  =  0.041 ; table  4 ) , it was not clinically significant . it is interesting to note that the mblc reported in studies using implants with ps connection ( ranged from 0.11 to 1.1  mm ) ( mangano et  al . 2011a , b ; norton 2006 ; donovan et  al . 2010 ; canullo et  al . 2012 ) was much less than those reported in studies using implants with the nps connection ( ranged from 0.7 to 1.5  mm ) ( polizzi et  al . studies investigating the ps implant  abutment interface have demonstrated that the greater the horizontal mismatch , the less marginal bone level changes were observed ( baffone et  al . . however , in this study , the similar mblcs observed in the two groups may be in part attributed to the conical connection being used for both the ps and the nps groups . microbial leakage between implants and abutments has been identified as a causative factor for chronic inflammatory infiltration of the peri - implant tissues and subsequent bone loss ( quirynen et  al . although microgaps have been noted at the implant prosthetic platform ( jansen et  al . 2008 ) , implants with an internal conical connections may provide a more superior seal ( jansen et  al . 2000 ; norton 2000 ; hansson 2003 ) , allowing less bacterial leakage ( tesmer et  al . 2009 ; assenza et  al . the greatest amount of mblc observed in this study was during the first 6 months for both ps and nps groups ( tables2 and 3 ) . this is in accordance with studies that have shown most of the mblcs tend to occur within 36  months following one - stage implant procedures ( cochran et  al . 2010 ) , and it had been suggested to be related to the establishment of proper physiological  biological dimension ( hartman & cochran 2004 ) . in fact , during 612  months , the ps groups in this study showed bone gain ( table  2 ) . this can be attributed to one implant , which originally presented with distinct bone loss at 3 months , and resulted in some bone filled at 12 months . few authors have related the peri - implant bone gain to the stimulating capacity of loaded implants in bone remodeling ( brunski 1999 ) and to the implant surface ( urdaneta et  al . the rfa has been shown to be effective in evaluating implant stability ( bischof et  al . study has shown that the rfa can reliably determine the implant stability with an isq  47 ( nedir et  al . 2004 ) . as for predicting future osseointegration , it has been noted that implants with an isq    49 at placement , and loaded after 3  months , showed osseointegration after 1 year of function ( nedir et  al . others have observed similar finding for successfully osseointegrated implants which had an isq of 4182 at placement using one - stage technique ( guler et  al . 2011 ) . in this study , the isq of 5782 recorded during surgery was within the range of aforementioned studies , and all the 30 implants maintained osseointegration after 1  year , suggesting primary stability had been achieved at the time of implant placement . the relationship between oral hygiene and implant failure has been controversial ( berglundh et  al . 1993 ) ; however , it is generally agreed upon that plaque accumulation can cause an inflammatory response resulting in peri - implant bone changes ( lindquist et  al . the mpi scores observed throughout the course of this study were either 0 or 1 without significant differences noted between groups , implying that the patients were able to maintain a good level of oral hygiene . therefore , the negative effect of plaque on the marginal bone levels for this study can be considered negligible . in this study , this may be partially attributed to the small prosthetic screw with a limitation of 10  ncm maximum torque used to connect the definitive crown to the prefabricated multiple unit abutments . with a similar prosthetic design , levine et  al . ( 1999 ) also found high incidences of prosthetic screw loosening ( 22.2% ) for single - tooth replacement . as all of the definitive crowns in this study were screw - retained , the screw loosening complications were easily resolved . platform switching and conical implant - abutment connections have both been contributory to the maintenance of the peri - implant bone . within the limits of this 1-year prospective clinical study , mean marginal bone level change at 12 months was similar for the ps ( 0.04    0.08  mm ) and nps ( 0.19    0.16  mm ) groups . evidence from this study suggests that peri - implant marginal bone level change may not be related to the platform switch feature as much as the seal at the implant  abutment interface . nevertheless , due to the small sample size , the results should be interpreted with cautions , and long - term study with larger sample size is warranted . additional supporting information may be found in the online version of this article : consort 2010 checklist of information to include when reporting a randomized trial .
objectivesthis 1-year prospective study evaluated the implant success rate and marginal bone response of non - submerged implants with platform and non - platform switching abutments in posterior healed sites.material and methodsnineteen patients ( 9 male , 10 female ) with posterior partially edentulous spaces , between the ages of 23 and 76 ( mean = 55.4  years ) , were included in this study . 
 a total of 30 implants ( 15 implants restored with platform switching [ ps ] abutments [ control ] and 15 implants restored with non - platform switching [ nps ] abutments [ test ] ) were assigned between two groups using a randomization procedure . 
 the definitive abutments with conical connections were placed at the time of surgery , and the definitive restorations were placed at 3 months . 
 all patients were evaluated clinically and radiographically using standardized radiographs at time of implant placement ( 0 ) , 3 , 6 and 12 months after implant placement . 
 data were analyzed using friedman test with post hoc pairwise comparisons , mann 
 whitney u - test , and pearson 's chi - square test at the significance level of   =  0.05.resultsat 12  months , all 30 implants remained osseointegrated corresponding to a 100% success rate . 
 the overall mean marginal bone level change at 12  months was 0.04    0.08  mm for ps group and 0.19    0.16  mm for nps group . 
 statistically significant difference in the marginal bone level change was observed between groups at 0 to 12  months and 3 to 12  months ( p  <  0.05).conclusionsthis 1-year randomized control study suggests that when a conical implant  abutment connection is present , similar peri - implant tissue responses can be achieved with platform switching and non - platform switching abutments .