title: The peri-implant hard and soft tissues at different implant systems. A comparative study in the dog. Astra Tech and Brånemark system implants: a 5-year prospective study of marginal bone reactions. Evidence-based dentistry: Part IV. Research design and levels of evidence. Ligature-induced marginal inflammation around osseointegrated implants and ankylosed teeth. Soft tissue response to plaque formation at different implant systems. A comparative study in the dog. Histo-pathologic characteristics of peri-implant soft tissues in Brånemark implants with 2 distinct clinical and radiological patterns. Comparative study between the effects of photodynamic therapy and conventional therapy on microbial reduction in ligature-induced peri-implantitis in dogs. Osseointegrated implants for single-tooth replacement: progress report from a multicenter prospective study after 3 years. Crestal bone changes around titanium implants. A histometric evaluation of unloaded non-submerged and submerged implants in the canine mandible. Influence of the size of the microgap on crestal bone changes around titanium implants. A histometric evaluation of unloaded non-submerged implants in the canine mandible. Methods for comparing the results of different studies. Crestal Bone Loss Around Submerged and Exposed Unloaded Dental Implants: A Radiographic and Microbiological Descriptive Study A bone quality-based implant system: first year of prosthetic loading. Implant-supported mandibular overdentures retained with ball or bar attachments: a randomized prospective 5-year study. Periimplant soft tissue barrier at experimental one-piece mini-implants with different surface topography in humans: A light-microscopic overview and histometric analysis. The effect of subcrestal placement of the polished surface of ITI implants on marginal soft and hard tissues. Do healing abutments influence the outcome of implant treatment? A three-year multicenter study.
abstract: The aim of this study of the present experiment was to study the marginal periimplant tissues at intentionally non-submerged ( 1-stage implants ) and initially submerged and subsequently exposed implants ( 2-stage implants ) . 5 beagle dogs , about 1-year-old , were used , 3 months after the extraction of the m and ibular premolars , fixtures of the Astra Tech Implants Dental System , the Brånemark System and the Bonefit -- ITI system were installed . In each m and ibular quadrant , 1 fixture of each implant system was installed in a r and omised order . The installation procedure followed the recommendations given in the manuals for each system . Thus , following installation , the bone crest coincided with the fixture margin of the Astra Tech Implants Dental System and the Brånemark System , whereas the border between the plasma sprayed and the machined surface of the Bonefit-ITI implant system was positioned at the level of the bone crest . Following a healing period of 3 months , abutment connection was carried out in the 2-stage systems ( the Astra Tech Implants Dental System and the Brånemark system ) . A 6-month period of plaque control was initiated . The animals were sacrificed and biopsies representing each important region dissected . The tissue sample s were prepared for light microscopy and exposed to histometric and morphometric measurements . The mucosal barrier which formed to the titanium surface following 1-stage and 2-stage implant installations comprised an epithelial and a connective tissue component , which for that 3 systems studied , had similar dimensions and composition . The amount of lamellar bone contained in the periimplant region close to the fixture part of the 3-implant systems was almost identical . It is suggested that correctly performed implant installation may ensure proper conditions for both and hard tissue healing , and that the geometry of the titanium implant seems to be of limited importance This paper describes the 5-year results of a comparative study between Astra Tech and Brånemark system implants . The aim was to compare the systems primarily with regard to bone level changes , and also with regard to other variables of interest . Sixty-six patients with edentulous jaws were included in the study . R and omisation schedules were used to allocate the patients to the two implant systems . 184 Astra Tech implants with a titanium-blasted surface and 187 Brånemark implants with a turned surface were used . The implants were inserted with a two-stage technique and the insertion followed the routines for the respective implant system . All patients were provided with full-arch fixed bridges . All patients were followed up with clinical and radiographic examinations from fixture insertion to the 5-year follow-up . The total mean bone level change in the upper jaw between fixture insertion and the 5-year examination was -1.74+/-0.45 mm at the Astra implants and -1.98+/-0.21 at the Brånemark implants . The corresponding values for the lower jaw were -1.06+/-0.19 for Astra and -1.38+/-0.17 for Brånemark . The major postoperative changes of the marginal bone level took place between fixture insertion and baseline . During this period , there was also a different pattern of bone remodelling between the implant systems . Between baseline ( prosthesis connection ) and the 5-year examination , the marginal bone level changes were small , with no difference between the implant systems . The implant stability was examined with the supraconstructions removed . At the 5-year examination , the survival rate for Astra Tech implants was 98.4 % and for the Brånemark implants it was 94.6 % . The difference was not statistically significant Previous papers in this series on evidence -based dentistry have discussed the first 2 steps in seeking answers to clinical problems formulating a clear question and strategically search ing for evidence . The next step , critical appraisal of the evidence , is made easier if one underst and s the basic concepts of clinical research design . The strongest design , especially for questions related to therapeutic or preventive interventions , is the r and omized , controlled trial . Questions relating to diagnosis , prognosis and causation are often studied with observational , rather than experimental , research design s. The strongest study design should be used whenever possible . Rules have been established to grade research evidence . This paper , the fourth in the series , presents an overview of research methodology most commonly used in the dental literature The purpose of the investigation was to gain more underst and ing of marginal inflammatory reactions around osseointegrated implants . The significance of the lacking periodontal ligament of implants was examined in the initial breakdown phase of supporting tissues by comparing clinical and radiographic manifestations of ligature-induced marginal inflammation related to osseointegrated implants with those around ankylosed and normal control teeth in 8 cynomolgus monkeys ( Macaca fascicularis ) . Bilateral extraction of the first and second m and ibular molars was carried out initially , and 12 weeks later 2 implants were placed in each side . Ankylosis of the second maxillary molars was established by extracting and replanting the teeth after a drying period . When ankylosis and osseointegration were established , ligature-induced marginal inflammation was induced in the right or left side at r and om around implants , ankylosed teeth and normal control teeth ( second maxillary premolar ) for 7 weeks . Although the clinical manifestations as expressed by plaque score , gingival score , probing depth and attachment loss were quite similar , the radiographic features differed . Significant loss of bone height was limited to implants and ankylosed teeth and did not occur in relation to normal control teeth . Furthermore , the bone loss around implants was significantly greater than the loss around ankylosed teeth . Bone loss was limited to implants and ankylosed teeth ; the study therefore suggests that the presence of marginal inflammation around implants and ankylosed teeth may have more serious implication s than does marginal inflammation around teeth with a periodontal ligament . However , variations in microbiota and susceptibility of different jaw positions to periodontal breakdown may influence the results of this study The aim of the present experiment was to study the location and composition of plaque associated lesions in the mucosa adjacent to implant systems that differed with respect to both geometry and dimension . At day 0 extraction of the m and ibular premolars were performed . After a healing period of 3 months , fixtures of the Astra Tech Implants , Dental System , the Brånemark System and the ITI Dental Implant System were installed . In each m and ibular quadrant 1 fixture of each implant system was installed in a r and omized order . A period of plaque control was initiated . Following another 3 months of healing , abutment connection was performed in the 2-stage systems ( the Astra Tech Implants , Dental System and the Brånemark System ) . After 1 month , the plaque control measures were ab and oned and plaque formation was allowed for 5 months . The animals were killed and biopsies representing each implant region obtained . The tissue sample s were prepared for light microscopy and exposed to histometric and morphometric measurements . The present study demonstrated that plaque formation result ed in the establishment of an ICT lateral to a pocket epithelium . The lesion was found to be similar regarding extension and composition in the peri-implant mucosa of the 3 implant systems tested . The vertical extension of the ICT was in all systems within 91 - 99 % of the vertical dimension of the junctional epithelium . The marginal bone level , measured from the abutment/fixture ( PS ) border , did not differ between the three systems This investigation is the result of a multicenter research project between the Catholic University of Leuven and the University of Madrid with the purpose of study ing histometrically and ultrastructurally periimplant marginal tissue reactions in mendium-term Brånemark implants . 12 patients were selected and distributed according to predefined clinical and radiological parameters into a periimplant infection group ( A ) and a non-periimplant infection group ( B ) . Biopsies were taken from these patients and analyzed by means of microscopy ( LM ) , histometry ( HM ) and transmission electron microscopy ( TEM ) . With LM group A showed pathological features consistent with an advanced gingivitis lesion , while group B showed signs of healthy gingiva in the connective tissue and vauolae formation in the epithelium . With HM , group A showed significantly higher transmigration of inflammatory cells in the epithelium than group B. In the connective tissue , group A showed a higher % of inflammatory infiltrate with significantly higher numbers of plasma cells and mononuclear cells than group B. With TEM , group A showed an ultrastructural picture consistent with plaque-induced periodontitis , while group B showed a rather healthy connective tissue and vacuolae formation in the epithelium . These results suggest that supracrestal marginal tissues around osseointegrated implants react to plaque bacteria similarly to periodontal tissues around teeth by chronic inflammation BACKGROUND Progressive peri-implant bone losses , which are accompanied by inflammatory lesions in the soft tissues , are referred to as peri-implantitis . The aim of this study was to compare the effects of photodynamic therapy ( PDT ) and conventional technique on microbial reduction in ligature-induced peri-implantitis in dogs . METHODS Eighteen third premolars from nine Labrador retriever dogs were extracted and the implants were submerged . After osseointegration , peri-implantitis was induced . After 4 months , ligature was removed and natural bacterial plaque was allowed to form for another 4 months . The animals were then r and omly divided into two groups . In the conventional group , they were treated using mucoperiosteal flaps for scaling the implant surface and chlorexidine ( conventional ) irrigation . In the PDT group , only mucoperiosteal scaling was carried out before photodynamic therapy . Inside the peri-implant pocket , a paste-based azulene photosensitizer was placed and then a GaAlAs low-power laser ( lambda=660 nm , P=40 mW , E=7.2 J for 3 minutes ) was used . Microbiological sample s were obtained before and immediately after treatment . Before treatment , one implant was removed and analyzed by scanning electron microscopy to vali date the contamination . RESULTS The results of this study showed that Prevotella sp. , Fusobacterium sp. , and S. Beta-haemolyticus were significantly reduced for both groups . After treatment , no significant differences were observed between the groups . CONCLUSION These findings suggest that photodynamic therapy is a non-invasive method that could be used to reduce microorganisms in peri-implantitis After 3 years , 82 of the original 92 patients remain in this prospect i ve multicenter study of single-tooth restorations supported by Brånemark implants . Since the 1-year follow-up , 6 more patients have been lost , but no additional implants have failed in those patients examined at the 3-year follow-up visit . After 1 year of function , 97.2 % of the implants survived in 88 patients , and between the 1- and 3-year follow-up , 100 % survived in 82 patients , giving a 3-year cumulative success rate of 97.2 % . No changes were observed in the status of gingivitis , pocket depth , periodontal pocket bleeding index , and tooth and implant mobility from those reported after 1 year . Marginal bone resorption remained at a low level -- less than 0.1 mm annually during the second and third years . Abutment screw loosening continued , but at a significantly reduced rate from that reported after 1 year . When used , gold rather than titanium abutment screws remained secure BACKGROUND Today , implants are placed using both non-submerged and submerged approaches , and in 1- and 2-piece configurations . Previous work has demonstrated that peri-implant crestal bone reactions differ radiographically under such conditions and are dependent on a rough/smooth implant border in 1-piece implants and on the location of the interface ( microgap ) between the implant and abutment/restoration in 2-piece configurations . The purpose of this investigation was to examine histometrically crestal bone changes around unloaded non-submerged and submerged 1- and 2-piece titanium implants in a side-by-side comparison . METHODS A total of 59 titanium implants were r and omly placed in edentulous m and ibular areas of 5 foxhounds , forming 6 different implant subgroups ( types A-F ) . In general , all implants had a relatively smooth , machined coronal portion as well as a rough , s and blasted and acid-etched ( SLA ) apical portion . Implant types A-C were placed in a non-submerged approach , while types D-F were inserted in a submerged fashion . Type A and B implants were 1-piece implants with the rough/smooth border ( r/s ) at the alveolar crest ( type A ) or 1.0 mm below ( type B ) . Type C implants had an abutment placed at the time of surgery with the interface located at the bone crest level . In the submerged group , types D-F , the interface was located either at the bone crest level ( type D ) , 1 mm above ( type E ) , or 1 mm below ( type F ) . Three months after implant placement , abutment connection was performed in the submerged implant groups . At 6 months , all animals were sacrificed . Non-decalcified histology was analyzed by evaluating peri-implant crestal bone levels . RESULTS For types A and B , mean crestal bone levels were located adjacent ( within 0.20 mm ) to the rough/smooth border ( r/s ) . For type C implants , the mean distance ( + /- st and ard deviation ) between the interface and the crestal bone level was 1.68 mm ( + /- 0.19 mm ) with an r/s border to first bone-to-implant contact ( fBIC ) of 0.39 mm ( + /- 0.23 mm ) ; for type D , 1.57 mm ( + /- 0.22 mm ) with an r/s border to fBIC of 0.28 mm ( + /- 0.21 mm ) ; for type E , 2.64 mm ( + /- 0.24 mm ) with an r/s border to fBIC of 0.06 mm ( + /- 0.27 mm ) ; and for type F , 1.25 mm ( + /- 0.40 mm ) with an r/s border to fBIC of 0.89 mm ( + /- 0.41 mm ) . CONCLUSIONS The location of a rough/smooth border on the surface of non-submerged  1-piece implants  placed at the bone crest level or 1 mm below , respectively , determines the level of the fBIC . In all 2-piece implants , however , the location of the interface ( microgap ) , when located at or below the alveolar crest , determines the amount of crestal bone resorption . If the same interface is located 1 mm coronal to the alveolar crest , the fBIC is located at the r/s border . These findings , as evaluated by non-decalcified histology under unloaded conditions , demonstrate that crestal bone changes occur during the early phase of healing after implant placement . Furthermore , these changes are dependent on the surface characteristics of the implant and the presence/absence as well as the location of an interface ( microgap ) . Crestal bone changes were not dependent on the surgical technique ( submerged or non-submerged ) BACKGROUND Endosseous implants can be placed according to a non-submerged or submerged approach and in 1- or 2-piece configurations . Recently , it was shown that peri-implant crestal bone changes differ significantly under such conditions and are dependent on a rough/smooth implant border in 1-piece implants and on the location of an interface ( microgap ) between the implant and abutment/restoration in 2-piece configurations . Several factors may influence the result ant level of the crestal bone under these conditions , including movements between implant components and the size of the microgap ( interface ) between the implant and abutment . However , no data are available on the impact of possible movements between these components or the impact of the size of the microgap ( interface ) . The purpose of this study was to histometrically evaluate crestal bone changes around unloaded , 2-piece non-submerged titanium implants  with 3 different microgap ( interface ) dimensions and between implants with components welded together or held together by a transocclusal screw . METHODS A total of 60 titanium implants were r and omly placed in edentulous m and ibular areas of 5 hounds forming 6 different implant subgroups ( A through F ) . In general , all implants had a relatively smooth , machined suprabony portion 1 mm long , as well as a rough , s and blasted , and acid-etched ( SLA ) endosseous portion , all placed with their interface ( microgap ) 1 mm above the bone crest level and having abutments connected at the time of first-stage surgery . Implant types A , B , and C had a microgap of < 10 microns , approximately 50 microns , or approximately 100 microns between implant components as did types D , E , and F , respectively . As a major difference , however , abutments and implants of types A , B , and C were laser-welded together , not allowing for any movements between components , as opposed to types D , E , and F , where abutments and implants were held together by abutment screws . Three months after implant placement , all animals were sacrificed . Non-decalcified histology was analyzed histometrically by evaluating peri-implant crestal bone changes . RESULTS For implants in the laser-welded group ( A , B , and C ) , mean crestal bone levels were located at a distance from the interface ( IF ; microgap ) to the first bone-to-implant contact ( fBIC ) of 1.06 + /- 0.46 mm ( st and ard deviation ) for type A , 1.28 + /- 0.47 mm for type B , and 1.17 + /- 0.51 mm for type C. All implants of the non-welded group ( D , E , and F ) had significantly increased amounts of crestal bone loss , with 1.72 + /- 0.49 mm for type D ( P < 0.01 compared to type A ) , 1.71 + /- 0.43 mm for type E ( P < 0.02 compared to type B ) , and 1.65 + /- 0.37 mm for type F ( P < 0.01 compared to type C ) . CONCLUSIONS These findings demonstrate , as evaluated by non-decalcified histology under unloaded conditions in the canine m and ible , that crestal bone changes around 2-piece , non-submerged titanium implants are significantly influenced by possible movements between implants and abutments , but not by the size of the microgap ( interface ) . Thus , significant crestal bone loss occurs in 2-piece implant configurations even with the smallest-sized microgaps ( < 10 microns ) in combination with possible movements between implant components The reader of oral and maxillofacial implant literature is challenged to be cognizant of the quality of clinical research data . The large variety of possible study design s utilized by clinical research ers requires the reader to have a fundamental awareness of the advantages , disadvantages , and limitations of commonly utilized study design s. This article aims to provide the reader with information to make an informed decision regarding the quality of a clinical research paper , so that he or she can judge whether the information presented in any given manuscript was obtained in a manner that truly minimizes bias , in the form of systematic or r and om errors , and whether it warrants serious consideration for clinical decision making . Special consideration is given to scientific literature pertaining to the use of oral and maxillofacial implants . In addition , the reader is presented with a method for placing any single manuscript within a " hierarchy of evidence " enabling an " estimate of confidence " in a particular therapy . By utilizing such methods to appraise the quality of research data , clinicians and patients will be better informed when making treatment-planning decisions The successful maintenance of crestal bone surrounding dental implants is imperative for long-term implant success . Crestal bone loss is reportedly related to stress . However , early perforation and partial exposure of the implant ’s covering device are a focus for plaque accumulation , which , if left untreated , may result in inflammation . The objective of this study was to evaluate the crestal bone levels adjacent to submerged and exposed unloaded dental implants during the initial healing phase . In addition , the microbiota around exposed implants were studied . Bilateral implants were placed in the m and ible of 10 patients . In one quadrant , the implants were covered by the flap . In the other quadrant , the flap was sutured , leaving the cover screws completely exposed . St and ardized periapical radiographs were obtained at implant placement and 4 months later . Radiographs were digitalized , aligned , and analyzed with a computer-assisted method . Cultures were obtained from exposed implant sites . All patients showed more crestal bone loss around exposed dental implants compared to submerged implants . Prevotella sp. , Streptococcus beta-hemoliticus , and Fusobacterium sp. were the microorganisms identified in most of the sites . The exposure of the implant covering device created foci for bacterial plaque accumulation , which may have facilitated periimplant crestal bone loss . The initial healing phase follow-up may be critical for implant success This interim report presents the data from a prospect i ve study of BioHorizons , a bone quality -based implant system , with four implant design s. The surgical survival of 975 implants was 99.4 % , with the survival 100 % for D4 bone . Three critical phases of crestal bone loss have been identified : bone remodeling from stage I to stage II surgery ; stage II uncovery to prosthesis delivery ( transition period ) ; and prosthesis delivery up to the first year of loading ( early loading bone loss ) . The stage I to stage II uncovery crestal bone remodeling result ed in a mean vertical bone loss of 0.21 mm to 0.36 mm ( SD = 0.90 mm ) , dependent on whether the implant became exposed in the oral cavity during osseous healing . No statistically significant difference was found among the four implant design s , diameter , bone density , or location . The stage II to prosthesis delivery mean vertical bone loss ranged from 0.12 mm to 0.20 mm . One hundred three consecutive patients ( partially and totally edentulous ) were restored , with 360 implants and 105 prostheses in function for a period of 12 to 26 months . No early loading implant failure occurred , and all patients with implants are in satisfactory to optimum health according to the Misch Implant Quality Scale . The mean early loading bone loss was 0.29 mm ( SD = 0.99 mm ) . Past clinical reports in the literature indicate most failures or crestal bone loss occur by the first year of loading . This study suggests the bone quality based dental implant design minimizes overall implant failure and crestal bone loss , regardless of bone density PURPOSE The aim of the present study was to evaluate the periimplant conditions and the maintenance requirements for implant-supported overdentures in the m and ible retained with ball or bar  attachments during a 5-year period . MATERIAL S AND METHODS Twenty-six completely edentulous patients had two Astra Tech dental implants placed in the anterior part of the m and ible . The denture attachment system for the patients was chosen r and omly by drawing lots . Eleven patients drew the bar attachment system and fifteen patients drew the ball attachment system .  Plaque Index , Gingival Index , and probing pocket depth were assessed around each implant . Periotest values were recorded , and periodically identical intraoral radiographs were obtained with a specially design ed film-holding device . RESULTS No implants were lost from baseline to the 5-year registration . The periimplant conditions were very healthy after 5 years . No significant differences of the periimplant variables were recorded between the bar and the ball groups . During the first year of function , significantly more complications/repairs were registered in the bar group than in the ball group . In the following years , no significant differences were registered . The mean frequency of complications/repairs per patient per year was 1.0 in the bar group and 0.6 in the ball group during the 5-year observation period . CONCLUSION Two implants with ball or bar attachment supported an overdenture in the m and ible for 5 years with a 100 % survival rate . No differences in marginal bone loss or health of the periimplant mucosa were observed between bar and ball attachment , but the frequency of technical complications/repairs per patient was higher around bar than ball attachments BACKGROUND Following connection to the oral cavity , osseointegrated dental implants and surrounding tissues are exposed to microbiologic and biomechanical challenges . The establishment of a firm functional periimplant soft tissue barrier ( PSTB ) is considered to be important to protect the implant 's interface from invasion of bacteria . The current knowledge on the histologic architecture of the PSTB is mainly based on animal experiments . PURPOSE The aim of this study was to histologically characterize the PSTB formed in humans around experimental one-piece mini-implants with different surface topography . MATERIAL S AND METHODS Five patients received a total of 12 experimental titanium , one-piece mini-implants with an oxidized ( n = 4 ) , an acid-etched ( n = 4 ) , or a machined ( n = 4 ) surface distal to therapeutic implants . Following transmucosal healing of 8 weeks and at abutment connection of the regular implants , the mini-implants were harvested with a layer of surrounding hard and soft tissue . The specimens were fixed and processed for histologic sectioning according to st and ard procedures . The most central bucco-oral section cut in the long axis was used for morphologic analyses of the PSTB . The vertical soft tissue morphology was quantified using histometric measurements . RESULTS The overall height of the soft tissue , that is , the biologic width , was around 4 to 4.5 mm and consisted of an epithelial and a supracrestal connective tissue barrier . The junctional epithelium established the attachment to the implant surface , whereas the collagen fibers and fibroblasts of the connective tissue seal were oriented parallel to the implant . The epithelial attachment was shorter at the oxidized and acid-etched surfaces compared with the machined surfaces . Accordingly , the oxidized and acid-etched mini-implants exhibited a longer zone of connective tissue seal . CONCLUSION The periimplant soft tissue formed at the experimental one-piece mini-implants in humans was of a character similar to that described in animal studies . The oxidized and acid-etched implants revealed less epithelial downgrowth and longer connective tissue seal than machined implants In order to achieve esthetically more satisfying results , it has been proposed to place ITI implants with their border between the rough and smooth surfaces below the level of the alveolar crest , thereby obtaining a submucosally located implant shoulder following healing . The aim of the present experimental study was to clinical ly and radiographically evaluate the tissue response to the placement of one-stage transmucosal implants with the border between the rough and the smooth surfaces sunk by 1 mm into a subcrestal location . 11 patients underwent comprehensive dental care including the placement of 2 implants of the ITI Dental Implant System  in the same quadrant ( test and control ) . R and omly assigned control implants were placed according to the manufacturer 's instructions , i.e. the border between the rough titanium plasma-sprayed and the smooth polished surfaces precisely at the alveolar crest . At the test implant the apical border of the polished surface was placed approximately 1 mm below the alveolar crest . Probing bone levels were assessed at implant placement ( baseline ) , 4 and 12 months later . Modified plaque and modified gingival indices were recorded at 1 , 2 , 3 , 4 and 12 months . Clinical probing depth and " attachment " levels were measured at 4 and 12 months . All parameters were assessed at 6 sites around each implant . The mean for each implant was calculated and used for analysis . The Wilcoxon matched pairs signed rank test and the Student t-test were applied to detect differences over time and between the test and control implants . At baseline , a mean difference in probing bone level of -0.86 mm ( SD 0.43 mm , p < 0.05 ) was found between test and control implants with the test implants being placed more deeply . Both test and control implants lost a significant amount of clinical bone height during the first 4 months ( test 1.16 mm , p < 0.05 ; control 0.58 mm , p < 0.05 ) . However , only the test implants significantly lost clinical bone height from 4 - 12 months ( test 1.04 mm , p < 0.05 ; control 0.45 mm , p = 0.08 ) . Overall , the test implants lost 2.26 mm and the control implants 1.02 mm of bone height during the first year of service . On the average , the test implants demonstrated a bone level of 0.38 mm lower than the controls at 12 months . Except for the modified gingival index at 4 months ( mean difference 0.21 , SD 0.19 , p < 0.05 ) , no clinical parameters yielded significant differences between test and control implants at any time . It is concluded that in addition to the crestal bone resorption occurring at implants placed under st and ard conditions , the bone adjacent to the polished surface of more deeply placed ITI implants is also lost over time . From a biological point of view , the placement of the border between the rough and the smooth surfaces into a subcrestal location should not be recommended STATEMENT OF THE PROBLEM It is not known if healing abutments replaced subsequently with permanent abutments adversely affect the soft tissues and marginal bone levels around dental implants . PURPOSE This study evaluated the mucosal condition and marginal bone levels 3 years after placement of healing abutments in patients provided with fixed prostheses supported by Brånemark implants .  MATERIAL AND METHODS Data were analyzed retrospectively from 117 patients treated at five centers in which 318 healing abutments were placed on maxillary and 112 on m and ibular implants .  A prospect i ve 3-year appraisal with a specific protocol assessed the response of mucosal cuffs and marginal bone levels surrounding surviving implants . RESULTS Exchange of abutments did not affect expected survival rates of implants  ( 94 % maxilla , 99 % m and ible ) or produce mean levels of marginal bone loss greater than anticipated for the system . Mean marginal bone levels correlated significantly with the jaw . Most patients achieved good oral hygiene and favorable peri-implant soft tissue health . CONCLUSION No evidence was found to suggest abutment exchange adversely affects outcome of implant treatment
target: Evidence analysis shows that the present knowledge about biologic width around implants is mainly derived from animal studies and that clinical controlled human studies are insufficient
background: PURPOSE The concept of biologic width forms a basis for successful peri-implant soft tissue integration around titanium implants .
  Therefore , the objectives of this review are to determine and critically evaluate the present knowledge about biologic width around implants and to establish future research trends .