The Effects Of Foreign Body Reaction On Crestal Bone Loss Around Dental Implant And Related Mechanism

Long-term maintenance and stability of peri-implant bone level has been identified as the key success criteria of dental implant treatment.However,peri-implantitis characterized as progressive peri-implant bone loss may have negative effect on the long-term survival rate of dental implant,eventually lead to implant failure if left untreated.It is of great significance to prevent the occurrence of peri-implantitis by investigating the mechanism of peri-implant bone loss.Although the theory of bacterial infection prevailed the literatures,nonbacterial factors could not be overlooked.The debate focused on whether bacterial infection initiated marginal bone loss around dental implant in analogy with natural tooth.Multiple factors associated with a combination of implant-,clinician-,and patient-related factors as well as foreign body reactions resulted in crestal bone loss around implant is difficult to be explained by the infectious hypothesis.Emerging studies have concerned on the relationship between foreign body reaction and the health of peri-implant tissue,owing to excess cements and titanium corrosion byproducts have been described to be one of the contributable factors to peri-implant bone loss.Nevertheless,the definite role still remains undetermined.Based on the multi-factors background of peri-implant bone loss,we analyzed the effect of bacterial factors on the peri-implant bone level clinically by comparing the alterations of crestal bone level of implants and natural teeth in uncontrolled periodontitis over a long period of time,and the differences of inflammatory features between the peri-implantitis and chronic periodontitis;Furthermore,we investigate the impacts of foreign body reaction characterized as macrophage activation on the bone metabolism around implants through animal experiments to explore the factors initiating peri-implant bone loss and corresponding mechanism from different aspects.Part 1.Effects of uncontrolled periodontitis on marginal bone alterations around implants: a case-control study Purpose: The aim of this retrospective study was to investigate the effects of uncontrolled periodontitis on marginal bone alterations around implants compared with the periodontal health group at a mean follow-up of at least 6 years.Materials and Methods: Thirty consecutive uncontrolled periodontally compromised patients(PCP)and 30 periodontally healthy patients(PHP),with a total of 96 Straumann implants(PCP=55,PHP=41)were matched for age,gender,smoking and implant characteristics.The inclusion criteria for PCPs were continuing tooth loss due to uncontrolled periodontal disease and no supportive periodontal maintenance after implant therapy.Peri-implant conditions were examined and the number of teeth lost during the follow-up periods was recorded in both groups.Radiographic marginal bone loss of implants and adjacent teeth was calculated having the restoration time point as baseline.Results: No implant loss occurred in both groups.The mean number of teeth lost during the follow-up periods was 0.67±0.80 in the PHP group,3.93±2.36 in the PCP group with statistical significance.The average overall bone loss was significantly greater at teeth than that around implants in the PCP group(0.54±0.27 vs.0.22±0.25 mm,P<0.001),while no statistically significant differences were observed in the PHP group(0.18±0.08 vs.0.22±0.18 mm,P=0.317).No statistically significant differences were observed between PC and PH patients when comparing the peri-implant marginal bone loss.No significant correlations were found between teeth loss and crestal bone loss at implants sites in both groups.Conclusions: This study indicated that the marginal bone level around implants seemed more stable in comparison to that around the natural teeth when exposed to uncontrolled periodontal disease.Part 2: Comparison of histopathological characteristics of inflammatory lesions at implants and natural teeth Objectives: The aim of the present study was to compare the differences of inflammatory features between the peri-implantitis and chronic periodontitis,and to analyze the source of foreign body in the peri-implant retrieved specimens.Materials and Methods: A total of 5 consecutive patients diagnosed with late peri-implantitis requiring surgical treatment or removal were recruited in this study,while the patients with chronic periodontitis were matched by sex,age and tooth position as the control group.The site was anaesthetized and a soft tissue biopsy was collected.All specimens were prepared for histometric and immunohistochemical analysis regarding the proportions of cells positive for the CD138,CD3,CD20,MPO,CD68 markers.The biopsies samples were furtherly analyzed by scanning electron microscopy and the composition of foreign body materials found in the tissues was evaluated by an energy dispersive x-ray spectrometer.Results: At the light microscopy level,the inflammatory lesion of peri-implantitis and chronic periodontitis was a mixture of nonspecific subacute and chronic inflammation.Peri-implantitis lesions contained significantly larger area proportions of CD138-positive cells than periodontitis.The proportion of CD138-positive cells accounted for 35.30±8.62%,which was significantly higher than that of other types of inflammatory cells in peri-implantitis.When compared the distribution and proportion of inflammatory cells,the proportion of CD3-and CD20-positive cells has no significant difference but CD68-and MPO-positive cells increased with statistically significant difference in peri-implantitis and chronic periodontitis.Foreign body giant cells were found in 3/5 of peri-implantitis biopsies.Foreign body particles were found in 4 cases by SEM and EDS analysis showed that the composition of foreign body was titanium particles and dental cement remnants.Conclusions: It is suggested that peri-implantitis lesions exhibit properties that are different from chronic periodontitis lesions.Titanium particles and residual dental cement induced foreign body reaction was found in some cases suffered from peri-implantitis.Part 3: The role of macrophages in the osseointegration of detal implants : Experimental study in vivo.Objectives: The purpose of this study was to determine the changes of macrophages temporally and whether macrophage depletion using clodronate liposomes have negative effects on the process of osseointegration of dental implants in a murine model.Materials and methods: Bilateral maxillary first molars were extracted from 36 SD rats,and implant surgery was performed after four weeks spontaneously healing.All animals were randomly divided into three groups.Macrophages were depleted by the tail vein injection of clodronate liposome(20mg/kg)3 days before implantation and re-injection every 3 days until the sacrifice of the rats(10mg/kg).Animals treated with empty liposome or PBS alone were included in this study as controls.Samples contained implants were retrieved after 3,7,14 and 28 days and evaluated the alerations of macrophages(CD68)and osteoblasts(osterix)using histology and immunohistochemistry technique.Results: Histological analysis showed that the osseointegration of implant has accomplished characterized as formation of mature and mineralized bone tissue in the implant-bone interface within 4w in the group injected with PBS and blank liposome,whreaes the bone healing process were delayed in spite of a large number of newly formed peri-implant bone in the clodronate liposome group.The bone-to-implant contact in the clodronate liposome group was significantly lower than that in the PBS and blank liposome group injection groupd at the time point of 2w,however,there was no significant difference among the three groups at the point of 4w.In the clodronate liposome group,the macrophage density was always at a low level accounting for 6-8%,and the density of Osterix-positive cells was 24.36% at the first week and then gradually increased.In the blank liposome and PBS group,the macrophage density were 26% and 24% at the first week,then slightly decreased to about 17%.The density of Osterix positive cells was about 50% in the 2w,and decreased to about 25% four weeks laterin the blank liposomes and PBS group,compared with 24.36% in the 1w and then went up gradually in the clodronate liposome group.Conclusions: In the process of implant osseointegration,macrophage density increased swiftly and then decreased gradually to normal level during the first two weeks.Depletion of macrophages by clodronate liposome reduce osteoblast amounts and newly bone formation around implants at early after implantation.Part 4: A murine model of marginal bone resorption around dental implant induced by foreign body reaction Objectives: The aim of this study was to investigate the crestal bone alteration induced by local aseptic inflammation triggered by exogenous titanium particles injection around submerged implant.Materials and methods: Bilateral maxillary first molars were extracted in 12 male SD rats(8-week-old).Four weeks after exaction,custom made screw-type pure titanium implants with machined surface were implanted into the extracted sites.A second surgery were performed to examine the crestal bone level around implant 4 weeks later.Eight rats with 16 implants without obvious bone defect around implant neck were selecte.Tweny milligram titanium particles suspended in 50 microliters of PBS were randomly injected into the soft tissue around the implant coronal tip by micropipette at one side of every rat and the other side as self control.The commercial particle size distribution of titanium is 3.32 ±2.39 microns and 93% were less than 3.6 microns in size.The other side of in the maxilla as control was undergone the same surgery without injection.Animals were sacrificed at 8 weeks after injection with titanium particles.Samples were analyzed radiologically to and histologically measure bone level change.Results: No undesirable events were observed and all implant were survival after titanium particles injection.In the group of titanium particles injection,extensive marginal bone resorption was observed by micro-CT and bone histomorphometry analysis with an average of 0.44 ± 0.14 mm around the implants,yet the bone-to-implant interface maintained well apically.In contrast,there was significantly less bone loss(0.13±0.03mm)in the control group than titanium particles injection group.Histologically,titanium particles induced a typical foreign body reaction with features of titanium particles mostly surrounding chronic inflammatory infiltrate or a mixture of subacute and chronic inflammation.But the density of vessels within the inflammatory aera varied slightly.Conclusion: The foreign body reaction initiated by titanium particles in the soft tissue around submerged implant induced an obvious peri-implant bone loss.Part 5: The role of macrophages in bone resorption induced by foreign body reaction Objective: The purpose of this study was to investigate the effects of macrophage on aseptic peri-implant bone resorption induced by foreign body reaction using clodronate liposomes to deplete macrophages? Materials and methods: 16 SD rats with custom made titanium screw implanted in bilateral maxillary first molar area for 4w to achieve osseointergration,were randomly divided into 4 groups.20 mg titanium particles were introduced into the peri-implant tissue to induce aseptic foreign body reaction,and macrophages were depleted by the loacl injection of clodronate liposome 100?l immediately and re-injection every 3 days until the sacrifice of the rats(Ti+LipClod group).Rats without clodronate liposome therapy(Ti+PBS)or treated with empty liposome(Ti+Lip)as well as rats injected with PBS alone(PBS)were included in this study as controls.Eight weeks later,animals were sacrificed and sample contained implants were collected.Half of the samples were analyzed radiologically and histologically to measure bone level change,macrophage number,density,and phenotype distribution.The rest of the samples were used to determine the relative mRNA expression levels of TNF-?,IL-1?,IL-6 and RANKL with qRT-PCR analysis.Results: No obvious infection was found in all surgical areas,and the implant survival rate was 100% with no implant falling off.Compared with Ti+PBS and Ti+Lip group,macrophage density(1.64±0.86%)infiltrated into peri-implant tissue and bone loss(0.17±0.03mm)around implant decreased significantly in the Ti+LipClod group.Immunofluorescence analysis showed more macrophage infiltrated into peri-implant tissue in the Ti+PBS and Ti+Lip group,predominantly M1 macrophages.In contrast,the macrophage density was lower and M2 phenotype was dominant in the PBS group,while macrophages density was significantly reduced and the M1 type macrophages were slightly more than M2 type in the LipClod group.Accordingly,TNF-?,IL-1?,IL6,and RANKL mRNA expression increased significantly in the Ti+PBS and Ti+Lip group compared with PBS and Ti+LipClod group.Conclusions: Titanium particles can form a local inflammatory microenvironment leading to aseptic peri-implant bone loss by recruiting and activating macrophages,which switched to M1 phenotype and promoted the secretion of local inflammatory cytokines.Macrophage depletion using clodronate-liposome reduces titanium particle-induced inflammatory osteolysis and cytokines production.