osseointegration is the most important factor in successful implant treatment . in the early stage , machined surface implants using pure titanium were reported to have achieved successful osseointegration , but there were limitations in case of low volume and quality of bony tissue1 . in addressing these issues , various surface - treated implants were developed and sold to facilitate osseointegration and promote initial healing . among them , hydroxyapatite ( ha)-coated implants made by applying ha on the surface using plasma spray to generate depression , undercut , and porosity were introduced in the mid-1980s to increase osteogenesis and facilitate osseointegration2 ; they were actively used in the 1990s . note , however , that most products were terminated because many researchers reported high failure rates . some researchers claimed that , from the long - term perspective , ha - coated implants can lose osseointegration because , if the coated surface is detached from the fixture or resorbed , the implant and bone are separated ; thus becoming dynamically unstable . even with satisfactory early osseointegration , the ha - coating is easily contaminated , and this results in its resorption and subsequent failure of the implant3 . nonetheless , some researchers report that advancements in ha - coating technology have resolved these problems and produced long - term stable clinical results . insufficient stability resulting from ha - coating desquamation and irregular coating thickness has been addressed with technological advancements such as ion plating4 and ion sputtering5 , thermal decomposition method6 , and biomimetic process . another viable option is the more recently developed thermally induced liquid - phase deposition method 7 . currently , it is regarded as principle wherein a certain healing period is assigned without loading . according to brnemark et al.8 , premature loading after implant placement can generate fibrous tissue on the bone - implant interface rather than bone deposition ; thus , insufficient healing period increases the possibility of early or delayed mobility of the implant . the minimum healing period suggested by brnemark in 1977 , based on 10 years ' clinical experience , was 3 months for the mandibular implant and 5 - 6 months for the maxillary one8 . excessive loading during this period can damage the balance between bone generation and bone resorption and result in fibrous connective tissue that interferes with osseointegration . note , however , that the traditional healing period suggested by brnemark may not be suitable today because the brnemark research was based only on machined surface implant ; it did not consider the implant design , surface treatment , surgical method , and biomechanical prosthesis10 . recent research on the stability of immediate and early loading reported success rates of 88 - 10% , suggesting that the healing period after treatment will continue to decrease1,11,12 . marginal bone height is an important factor in the implant 's functional and aesthetic success , and maintaining the proper height of marginal bone is a precondition for the implant 's long - term , satisfactory use . marginal bone resorption in the bone - implant interface interferes with the stability of surrounding tissues and causes periimplantitis or mobility of the implant . vercruyssen and quirynen13 reported that , in their long - term research , smoking , guided bone regeneration , dehiscence defect , and bony tissue are closely related to the height of marginal bone around the implant . based on the researchers ' reports , i.e. , failure of a loading implant most frequently occurs within one year of functioning14 , this study measured the amount of resorption after one year of loading . to compare the stability of ha - coated implants with different loading initiation times , two different implants that secured thinner and more even thickness of ha coating and increased crystallization rate were placed on patients : osstem ts iii ha ( osstem implant co. , busan , korea ) and zimmer tsv - ha ( zimmer dental , carlsbad , ca , usa ) . after applying immediate and delayed loading based on the definition of cochran et al.15 , implant survival rate was measured according to criteria established by buser et al.16 and cochran et al.17 after one year of loading , the resorption amount of crestal bone was evaluated retrospectively . this study was conducted by the section of dentistry at seoul national university bundang hospital , following approval by the institutional review board ( approval no . the 1-year retrospective study involved a total of 41 patients ( 74 implants , 22 males and 19 females with mean age of 53.110.70 ) who had 1 or 2 implants placed consecutively in their posterior maxilla or mandible and immediate or delayed loading between september 2010 and april 2011 . osstem ts iii ha was implanted in 17 patients ( 33 implants ) , and zimmer tsv - ha ( 41 implants ) , in 24 patients.(table 1 ) patient selection criteria for implant placement were as follows : 1 ) patients older than 18 years whose jaw growth was finished ; 2 ) patients with posterior teeth loss and available alveolar bone height of more than 6 mm ; 3 ) patients with adequate mesio - distal and horizontal available bones ; and 4 ) patients with antagonistic tooth of placed implant . the following were the criteria for exclusion : 1 ) pregnant women ; 2 ) patients who had a heart attack only recently ; 3 ) patients with uncontrollable systemic disease ; 4 ) patients with hemorrhagic disease or disease requiring the administration of anticoagulant ; 5 ) patients with , or suspected of having , a psychological disease ; 6 ) patients who were scheduled to undergo tooth extraction within 2 months in the placement area and patients with severe periodontal disease in the surrounding teeth ; 7 ) patients with grade d4 bony tissue ; 8) patients who need extensive bone graft ; and 9 ) patients for which placing an implant is difficult ( patients with severe oral habit such as bruxism ) . in this study , all surgeries and prosthesis treatments were performed by 1 surgeon and 1 prosthodontist . implants were placed according to each manufacturer 's guidelines , and bone graft was performed when a small defect around the implant was noted . if the residual bone in the maxillary posterior teeth was 6 - 10 mm , sinus membrane elevation and bone graft were performed using a crestal approach , and implantation was done at the same time . based on the period from implant placement to loading by prosthesis , 42 implants were categorized as immediate loading ( il ) group , and 32 implants , as delayed loading ( dl ) group . the il group was then subdivided into 18 osstem ts iii ha implants and 24 zimmer tsv - ha implants based on the implant system . the dl group was also subdivided into 15 osstem ts iii ha implants and 17 zimmer tsv - ha implants.(table 2 ) based on the definition of ioannidou and doufexi12 , the il group had a temporary crown restored within 48 hours as well as occlusion with the opposite tooth ( after 1.810.40 days on the average ) ; final restoration was done 3 - 6 months after placement ( 6 months for the maxilla and 3 months for the mandible ) after confirming osseointegration . the dl group had healing period of 2.8 - 7.9 months ( 5.5 months for the maxilla and 3.0 months for the mandible on the average ) after placement , with final restoration and occlusion with the opposite tooth . for the temporary crown restoration of the il group , occlusion space as wide as 1 accufilm ( parkell , farmingdale , ny , usa ) was applied when biting slightly ; occlusal contact was unavailable for lateral movement . in the final restoration of the successful il group and dl group , occlusion space as wide as 1 shimstock ( kocodental , bucheon , korea ) was created when biting slightly . both the il group and dl group visited our hospital on the initial day of loading and 1 year later for periapical radiography and to evaluate the clinical symptoms , mobility of implant , radiolucency around the implant , and status of soft tissue to determine the implants ' survival rate . using the criteria suggested by buser et al.16 and cochran et al.17 , the implant survival rate was evaluated : a. no clinical implant mobility ; b. no pain or neural problem ; c. either infection around the implant is not consistent , or it has not recurred ; d. neither radiolucency around the implant nor rapid bone loss . to measure and compare marginal bone resorption around the implant , digital periapical radiography was taken vertically from the longitudinal axis using the parallel cone technique . marginal bone level was measured on the mesial and distal sides of the implant , with the mean of two values regarded as representative value . considering the fact that the distance between the threads of fixture ( thread pitch ) was 0.8 mm ( 4.5 mm in diameter ) or 0.9 mm ( 5 mm in diameter ) for ts iii ha and 0.6 mm for tsv , the distance from the implant platform to the first bone - implant contact ( bic ) in radiographs was measured and calculated by enlargement ratio . marginal bone loss was calculated as the difference between the values taken on the initial day of loading and values taken at 1-year prosthetic loading . because of the submerged machined collar ( 1 mm band ) of tsv , the placement depth of machined - to - resorbable blast media junction during surgery had to be compensated when bone loss was measured at 1-year follow - up . this depth was subtracted from the measurement to adjust the actual bone loss of the textured surface . the difference was measured by setting 2 dots on the radiograph using impax ( agfa corp . measurement was conducted by one dentist who did not participate in the implant treatment . after placing the ha - coated implants , data was examined to determine whether there is significant relationship between initial loading time , initial loading time by implant system , initial loading time by maxilla and mandible , and change of crestal bone 's height after 1 year of loading using mann - whitney ( =0.05 ) of ibm spss statistics ver . this study was conducted by the section of dentistry at seoul national university bundang hospital , following approval by the institutional review board ( approval no . the 1-year retrospective study involved a total of 41 patients ( 74 implants , 22 males and 19 females with mean age of 53.110.70 ) who had 1 or 2 implants placed consecutively in their posterior maxilla or mandible and immediate or delayed loading between september 2010 and april 2011 . osstem ts iii ha was implanted in 17 patients ( 33 implants ) , and zimmer tsv - ha ( 41 implants ) , in 24 patients.(table 1 ) patient selection criteria for implant placement were as follows : 1 ) patients older than 18 years whose jaw growth was finished ; 2 ) patients with posterior teeth loss and available alveolar bone height of more than 6 mm ; 3 ) patients with adequate mesio - distal and horizontal available bones ; and 4 ) patients with antagonistic tooth of placed implant . the following were the criteria for exclusion : 1 ) pregnant women ; 2 ) patients who had a heart attack only recently ; 3 ) patients with uncontrollable systemic disease ; 4 ) patients with hemorrhagic disease or disease requiring the administration of anticoagulant ; 5 ) patients with , or suspected of having , a psychological disease ; 6 ) patients who were scheduled to undergo tooth extraction within 2 months in the placement area and patients with severe periodontal disease in the surrounding teeth ; 7 ) patients with grade d4 bony tissue ; 8) patients who need extensive bone graft ; and 9 ) patients for which placing an implant is difficult ( patients with severe oral habit such as bruxism ) . in this study , all surgeries and prosthesis treatments were performed by 1 surgeon and 1 prosthodontist . implants were placed according to each manufacturer 's guidelines , and bone graft was performed when a small defect around the implant was noted . if the residual bone in the maxillary posterior teeth was 6 - 10 mm , sinus membrane elevation and bone graft were performed using a crestal approach , and implantation was done at the same time . based on the period from implant placement to loading by prosthesis , 42 implants were categorized as immediate loading ( il ) group , and 32 implants , as delayed loading ( dl ) group . the il group was then subdivided into 18 osstem ts iii ha implants and 24 zimmer tsv - ha implants based on the implant system . the dl group was also subdivided into 15 osstem ts iii ha implants and 17 zimmer tsv - ha implants.(table 2 ) based on the definition of ioannidou and doufexi12 , the il group had a temporary crown restored within 48 hours as well as occlusion with the opposite tooth ( after 1.810.40 days on the average ) ; final restoration was done 3 - 6 months after placement ( 6 months for the maxilla and 3 months for the mandible ) after confirming osseointegration . the dl group had healing period of 2.8 - 7.9 months ( 5.5 months for the maxilla and 3.0 months for the mandible on the average ) after placement , with final restoration and occlusion with the opposite tooth . for the temporary crown restoration of the il group , occlusion space as wide as 1 accufilm ( parkell , farmingdale , ny , usa ) was applied when biting slightly ; occlusal contact was unavailable for lateral movement . in the final restoration of the successful il group and dl group , occlusion space as wide as 1 shimstock ( kocodental , bucheon , korea ) was created when biting slightly . both the il group and dl group visited our hospital on the initial day of loading and 1 year later for periapical radiography and to evaluate the clinical symptoms , mobility of implant , radiolucency around the implant , and status of soft tissue to determine the implants ' survival rate . using the criteria suggested by buser et al.16 and cochran et al.17 , the implant survival rate was evaluated : a. no clinical implant mobility ; b. no pain or neural problem ; c. either infection around the implant is not consistent , or it has not recurred ; d. neither radiolucency around the implant nor rapid bone loss . to measure and compare marginal bone resorption around the implant , digital periapical radiography was taken vertically from the longitudinal axis using the parallel cone technique . marginal bone level was measured on the mesial and distal sides of the implant , with the mean of two values regarded as representative value . considering the fact that the distance between the threads of fixture ( thread pitch ) was 0.8 mm ( 4.5 mm in diameter ) or 0.9 mm ( 5 mm in diameter ) for ts iii ha and 0.6 mm for tsv , the distance from the implant platform to the first bone - implant contact ( bic ) in radiographs was measured and calculated by enlargement ratio . marginal bone loss was calculated as the difference between the values taken on the initial day of loading and values taken at 1-year prosthetic loading . because of the submerged machined collar ( 1 mm band ) of tsv , the placement depth of machined - to - resorbable blast media junction during surgery had to be compensated when bone loss was measured at 1-year follow - up . this depth was subtracted from the measurement to adjust the actual bone loss of the textured surface . the difference was measured by setting 2 dots on the radiograph using impax ( agfa corp . , after placing the ha - coated implants , data was examined to determine whether there is significant relationship between initial loading time , initial loading time by implant system , initial loading time by maxilla and mandible , and change of crestal bone 's height after 1 year of loading using mann - whitney ( =0.05 ) of ibm spss statistics ver . implant survival rate after 1 year of loading was 100% , and mean bone loss of all test groups was 0.260.59 mm . for the comparison based on loading time , mean bone loss of the il group was 0.320.69 mm , and that of the dl group was 0.160.42 mm , but the difference was not statistically significant ( p=0.260).(table 3 ) regarding bone loss of the il group and delayed group receiving the osstem ts iii ha , bone loss was 0.521.00 mm and 0.110.20 mm , respectively , but the difference was not statistically significant ( p=0.556).(table 4 ) for patients receiving the zimmer tsv - ha , bone loss of the il group and dl group was 0.170.21 mm and 0.170.21 mm , respectively , but the difference was not statistically significant ( p=0.338).(table 5 ) in comparing the bone loss of il group and dl group in the maxilla and the mandible , bone loss in the maxilla was 0.410.82 mm and 0.100.16 mm in the il group and dl group , respectively , but the difference was not statistically significant ( p=0.526).(table 6 ) likewise , in the mandible , bone loss of the il group was 0.270.61 mm , and that of the dl group was 0.390.84 mm ; the difference was not statistically significant ( p=0.620).(table 7 ) ha - coated implants were introduced in the 1990s and were found to facilitate the adhesion and proliferation of osteoblasts with good coherence of serum protein and growth factors , perform well on poor - quality bony tissue by significantly increasing osseointegration between implant and bony tissue , and allow performing early loading by shortening the osseointegration period18 - 20 . note , however , that the coating quality and thickness varied by manufacturer , and the coating was occasionally removed during implantation . thus , a divided ha was found to have risk of impairing osseointegration and initiating an inflammatory response3,21 . after the introduction of ion plating and ion sputtering , these problems were resolved , and the success rate has steadily increased along with advancements in ha - coated technology7 . in 2005 , trisi et al.18 collected samples from the clinical specimen of 10-year - old ha - coated implants and , after histological analysis , reported loss of less than 25% for the ha - coating surface and bic rate of 78.48% . in other words , for patients receiving proper prosthetic treatment and adequate maintenance , persistent ha coating and long - term survival were possible . many other studies also noted progress in ha - coated implants and good clinical results18 - 20 . haptite ( dentis co. , ltd . , daegu , korea ) claimed to have resolved uneven coating and desquamation problems by reducing coating thickness to 2 m using an ultra - thin coating technique applied in vacuum at room temperature22 . the zimmer tsv - ha used in this study recorded a 97% success rate because it increased the ha crystallization rate to 97% with the application of plasma coating over ha and special mp-1 process using compressed hydration heat treatment23 . crystallization rate is an important factor in ha - coated implants because a non - crystallized ha - coated surface may melt , break , or disintegrate and cause the implant to fail . in this study , the coating thickness of osstem ts iii ha was 20 - 70 m , and that of zimmer tsv - ha was 20 - 150 m . in both products , ( xrd ) and energy dispersive spectrometer ( eds ) analysis , the ca / p ratio of osstem ts iii ha was 1.69 , and that of zimmer tsv - ha was 1.65 . the crystallization level of osstem ts iii ha was 98% , and that of zimmer tsv - ha was 96.30.6 . in iso / tc106 , ha implants must have crystallization rate of more than 62% . considering the fact that the crystallization rate of the steri - oss implant ( nobel biocare ab , gteborg , sweden ) is 73.3% , both products used in this study have high crystallization rates . for successful osseointegration under immediate loading following implantation , various tests and research have been conducted , and their results have been reported . in an animal test that compared a function group and a non - function group by applying a crown immediately after implantation , the microscopic examination revealed a higher rate of osseointegration in the function group . in addition , some studies found that successful osseointegration relies on loading , dental hygiene , condition of bony tissue , surgical technique , and prosthesis ; thus , if the bony tissue at the implant site is healthy , tissues are subjected to minimal damage during the surgical process , and prosthesis restoration is performed carefully , osseointegration within 2 weeks is possible with early functional loading24 . according to some studies , the success rate and survival rate under protocols calling for early loading and delayed loading following normal healing period do not differ greatly , but implant failure is greatly affected by the patient 's overall physical condition , local factors such as poor oral hygiene , and unsuitable bony tissue at the implantation site25,26 . based on this study 's results , even when applying immediate loading to ha - coated implants , the survival and bone resorption rates are not significantly different when applying delayed loading after a normal healing period . loading was reported not to cause independently the generation of fibrous tissue membrane , but the amount of micromotion at the bone - implant interface was more relevant . calandriello and tomatis27 reported that micromotion of more than 100 m retards healing at the bone - implant surface , whereas szmukler - moncler et al.10 claimed that micromotion of more than 150 m causes the generation of fibrous tissue membrane rather than bone deposition . therefore , reducing micromotion and increasing the success rate with immediate loading require using an implant that has been designed for easy placement and less mobility to secure primary stability10,27 . in both groups , average alveolar bone resorption rates under different loading times were within 0.240.59 mm ; this was lower than the results of previously published research . according to schincaglia et al.28 , the average bone resorption rate after 1 year of loading in mandibular single implant restoration was 1.200.55 mm in the il group and 0.770.38 mm in the dl group . recently , elsyad et al.29 reported a rate of 0.910.63 mm in the il group and 0.510.39 in the dl group . for a two - piece implant , bone resorption rate of 1.5 - 2.0 mm from the 2nd surgery to 1 year of loading is regarded as normal30,31 . in 1994 , albrektsson and colleagues32,33 stressed that a successful implant should have less than 1.5 mm bone resorption during the first year of prosthetic treatment and subsequent annual bone resorption rate of less than 0.2 mm . therefore , the bone resorption rate of both groups in this study is believed to be low due to the successful early stability of the ha - coated implant , skilled surgical technique , and highly motivated patients . this research is limited because it is neither a retrospective study nor based on a selected test group and a control group . initial stability following implantation was not measured in all cases using ostell mentor ( integration diagnostics ab , gteborg , sweden ) or others ; neither were bone resorption rates by type of prosthesis compared because we reviewed medical records and radiographs of patients who had previously received implant treatment . another limitation of this study was its insufficient control of statistical data because each patient received a different number of implants ; the location of implant placement and its length and diameter also differed . the results of this study demonstrated no significant difference , but this may be due to a number of factors in this study design . for one , the use of two different implant brands increases the difficulties in interpreting the results properly . the different implants not only had different coating properties but also different thread design and different diameters , which may influence implant stability during the healing period . long - term follow up after 1 year of observation is necessary , and future research with prospective study should be undertaken with only 1 implant system by strictly controlling patient age , location and number of implant placements , initial stability of implant , and follow - up surgical treatment . in this retrospective research , ha - coated implant placed in the maxillary and mandibular posterior areas recorded short - term clinical success regardless of the loading time ; the amount of marginal bone resorption also met the criteria for successful implantation . mean bone loss after 1 year of loading was not significantly different between the il group and the dl group ; neither was the difference in bone resorption rates statistically significant between the two groups by type of implant system and by dental location . the limitations of this study include not only the study period but also other variables such as surgeon 's bias , different brands of implant , etc . even with the limited study period of one year , however , this study suggests that ha - coated implants can secure a high success rate under immediate loading .