Bone Loss at Implant with Titanium Abutments Coated by Soda Lime Glass Containing Silver Nanoparticles: A Histological Study in the Dog

The aim of the present study was to evaluate bone loss at implants connected to abutments coated with a soda-lime glass containing silver nanoparticles, subjected to experimental peri-implantitis. Also the aging and erosion of the coating in mouth was studied. Five beagle dogs were used in the experiments. Three implants were placed in each mandible quadrant: in 2 of them, Glass/n-Ag coated abutments were connected to implant platform, 1 was covered with a Ti-mechanized abutment. Experimental peri-implantitis was induced in all implants after the submarginal placement of cotton ligatures, and three months after animals were euthanatized. Thickness and morphology of coating was studied in abutment cross-sections by SEM. Histology and histo-morphometric studies were carried on in undecalfied ground slides. After the induced peri-implantitis: 1.The abutment coating shown losing of thickness and cracking. 2. The histometry showed a significant less bone loss in the implants with glass/n-Ag coated abutments. A more symmetric cone of bone resorption was observed in the coated group. There were no significant differences in the peri-implantitis histological characteristics between both groups of implants. Within the limits of this in-vivo study, it could be affirmed that abutments coated with biocide soda-lime-glass-silver nanoparticles can reduce bone loss in experimental peri-implantitis. This achievement makes this coating a suggestive material to control peri-implantitis development and progression.     

Evaluation in a Dog Model of Three Antimicrobial Glassy Coatings: Prevention of Bone Loss around Implants and Microbial Assessments

ObjectivesThe aim of the present study is to evaluate, in a ligature-induced peri-implantitis model, the efficacy of three antimicrobial glassy coatings in the prevention of biofilm formation, intrasulcular bacterial growth and the resulting peri-implant bone loss.MethodsMandibular premolars were bilaterally extracted from five beagle dogs. Four dental implants were inserted on each hemiarch. Eight weeks after, one control zirconia abutment and three with different bactericidal coatings (G1n-Ag, ZnO35, G3) were connected. After a plaque control period, bacterial accumulation was allowed and biofilm formation on abutments was observed by Scanning Electron Microscopy (SEM). Peri-implantitis was induced by cotton ligatures. Microbial samples and peri-implant crestal bone levels of all implant sites were obtained before, during and after the breakdown period.ResultsDuring experimental induce peri-implantitis: colony forming units counts from intrasulcular microbial samples at implants with G1n-Ag coated abutment remained close to the basal inoculum; G3 and ZnO35 coatings showed similar low counts; and anaerobic bacterias counts at control abutments exhibited a logarithmic increase by more than 2. Bone loss during passive breakdown period was no statistically significant. Additional bone loss occurred during ligature-induce breakdown: 0.71 (SD 0.48) at G3 coating, 0.57 (SD 0.36) at ZnO35 coating, 0.74 (SD 0.47) at G1n-Ag coating, and 1.29 (SD 0.45) at control abutments; and statistically significant differences (p<0.001) were found. The lowest bone loss at the end of the experiment was exhibited by implants dressing G3 coated abutments (mean 2.1; SD 0.42).SignificanceAntimicrobial glassy coatings could be a useful tool to ward off, diminish or delay peri-implantitis progression.     

Finite element investigation of implant-supported fixed partial prosthesis in the premaxilla in immediately loaded and osseointegrated states

The aim of this study was to gain insight into the behaviour of the stresses and strains at the bone–implant interface of an implant-supported fixed partial prosthesis (FPP) in the premaxilla under immediate loading and osseointegrated conditions. Finite element models of a four-unit FPP were generated. An extreme condition was simulated, using only two immediately loaded implants in order to derive recommendations for possible clinical application. Straight and 20°-angled abutments and bonded or sliding contact between the bridge and abutment were simulated. In addition, two models were generated with two completely osseointegrated implants. A 150 N load to the prosthesis at a 45° angle to the long axis of each implant was applied. Minor differences were observed in implant displacements, stress and strain distributions of the two abutment designs. However, bone loading exceeded the physiological limits, including a risk of bone atrophy. A considerable decrease in implant displacements and bone loading was observed in the osseointegrated cases. An FPP supported by only two implants cannot be recommended for immediate loading.     

Genome analysis and clinical implications of the bacterial communities in early biofilm formation on dental implants restored with titanium or zirconia abutments

This cross-sectional study aimed to identify and quantify up to 42 target species colonizing the early biofilm of dental implants restored with titanium or zirconia abutments. A total of 720 samples from 20 healthy individuals were investigated. Biofilm samples were collected from the peri-implant sulci, inner parts of implants, abutment surfaces and prosthetic crowns over a functioning period of 30 days. Checkerboard DNA–DNA hybridization was used for microbial detection and quantitation. Clinical characteristics (probing depth, bleeding on probing, clinical attachment level and marginal bone loss) were also investigated during the monitoring period. Genome counts were low at the implant loading time point for both the abutment materials, and increased over time. Both the titanium and the zirconia groups presented similar microbial counts and diversity over time, and the microbiota was very similar to that colonizing the remaining teeth. Clinical findings were consistent with a healthy condition with no significant difference regarding marginal bone loss between the two materials.     

Evaluation of change in implant abutment after teeth surface modifications

The surface modifications in teeth increase the retentive strength of cemented castings by providing micro as well as macro retentive ridge and groove patterns. Restoring the dental implants with cement-retained prosthesis is well known. Therefore, it is of interest to compare retentive property of implant abutments with and without circumferential grooves. Hence, 20 straight shoulder type titanium abutments were with abutment screws as well as prefabricated plastic copings and corresponding 12 mm-long stainless steel laboratory implant analogs were used. The abutments were divided into two subgroups of 10 abutments each: without grooves and with grooves. After thermocycling and storing the cemented abutments in water at 37°C water for 6 days they were assembled in the Universal testing machine and subjected to a pullout test (retention) at a crosshead speed of 5.0mm/min to record forces in Newton. Data suggest that the addition of grooves increased the retention. The mean retentive forces of standard machined abutments (plain) cemented with Resin modified GIC showed 339.34 N. Retention increased by 667.39N after addition of circumferential grooves. The surface modification of an implant abutment by means of circumferential grooves is an effective method of improving the retention of cast crowns cemented with resin modified GIC especially in short abutments.     

Influence of transmucosal height in abutments of single and multiple implant-supported prostheses: a non-linear three-dimensional finite element analysis

The aim of this study was to analyze the influence of three different transmucosal heights of the abutments in single and multiple implant-supported prostheses through the finite element method. External hexagon implants, MicroUnit, and EsthetiCone abutments were scanned and placed in an edentulous maxillary model obtained from a tomography database. The simulations were divided into two groups: (1) one implant with 3.75 × 10 mm placed in the upper central incisor, simulating a single implant-supported fixed prosthesis with an EsthetiCone abutment; and (2) two implants with 3.75 × 10 mm placed in the upper lateral incisors with MicroUnit abutments, simulating a multiple implant-supported prosthesis. Subsequently, each group was subdivided into three models according to the transmucosal height (1, 2, and 3 mm). A static oblique load at an angle of 45 degrees to the long axis of the implant in palatal-buccal direction of 150 and 75 N was applied for multiple and single implant-supported prosthesis, respectively. The implants and abutments were assessed according to the equivalent Von Mises stress analyses while the bone and ceramics were analyzed through maximum and minimum principal stresses. The total deformation values increased in all models, while the transmucosal height was augmented. The transmucosal height of the abutments influences the stress values at the bone, ceramics, implants, and abutments of both the single and multiple implant-supported prostheses, with the transmucosal height of 1 mm showing the lowest stress values.     

Extent and location of bone loss at dental implants in patients with peri-implantitis

Peri-implantitis is an infectious disease, which leads to loss of supporting bone around dental implants. To evaluate the extent and location of bone loss, 43 patients with peri-implantitis were examined. The bone loss was clinically measured at the time of dental surgery. Data revealed that 25% of subjects had bone loss associated with all their implants although the majority of the subjects had fewer than 50% of their implants affected by bone loss. A total number of 264 implants were examined and 131 of those had peri-implantitis associated bone loss. The pattern of bone loss at implants varied between and within subjects and location in the jaws. The highest proportion of implants with peri-implantitis was found in the upper jaw and within this group, at implants located in the incisor area of the upper jaw; the lowest was the canine area of the lower jaw. The highest proportion of implants that lost ≥ 2/3 of their bone support was found in the incisor area of the maxilla. We concluded that in the presence of peri-implant inflammation, bone quantity and characteristics may influence the progression of peri-implantitis bone loss at dental implants. We hypothesize that the ability of the bone to withstand occlusal forces will be altered as consequence of the loss of bone at the neck of the implants. To achieve an understanding of the local degradation of bone due to peri-implantitis, we need to analyze the microstructure of the bone as well the cellular biology of the peri-implant inflammation.     

氧化锆基台的制作及其与钛基台抗折强度的比较

目的：制作氧化锆基台并将其与钛基台的抗折强度相比较,从而探讨其临床应用的可行性。方法：选用纳米氧化锆粉,采用冷等静压成型和二次烧结工艺制作0sstem USⅡ系统氧化锆基台;选取氧化锆基台和成品钛基台（OSSTEM公司,韩国）各10枚,分别与0sstem USⅡ种植体装配,然后固定于不锈钢夹具中置于万能试验机,将万能试验机压头与种植体长轴成90°角施加压力,记录基台损坏时的加载力值,比较分析两组试件的强度差异。结果：氧化锆基台和钛基台的平均抗折强度分别为（540.5±84.6）N和（753.9±160.8）N,差别有统计学意义（P〈0.05）。氧化锆基台组10枚基台全部颈部折裂;钛基台组2枚种植体损坏,6枚中央固位螺钉损坏,2枚基台颈部折裂。结论：本研究制作的0sstem USⅡ系统的氧化锆基台的抗折强度虽然低于钛基台,但尚能满足临床应用要求。     

A novel nonsurgical therapy for peri-implantitis using focused pulsed electromagnetic field: A pilot randomized double-blind controlled clinical trial

Pulsed electromagnetic field (PEMF) therapy modulates the immune response and is successfully used in orthopedics to treat osteoarthritis and improve bone regeneration. This may suggest that this treatment may consequently reduce peri-implant soft tissue inflammation and marginal bone loss. To compare clinical, radiographic, and immunological results following nonsurgical treatment for peri-implantitis with or without PEMF therapy. Patients with peri-implantitis were included: pocket probing depth (PPD) between 6 and 8 mm with bleeding on probing (BOP); crestal bone loss between 3 and 5 mm. A novel healing abutment that contained active (test) or inactive (control) PEMF was connected. PEMF was administered via the abutment at exposure ratio of 1/500–1/5000, intensity: 0.05–0.5 mT, frequency: 10–50 kHz for 30 days. Nonsurgical mechanical implant surface debridement was performed. Patients were examined at baseline, 1 and 3 months. Clinical assessment included: plaque index, BOP, PPD, recession, and bone crest level which was radiography measured. Samples of peri-implant crevicular fluid were taken to analyze interleukin-1β (IL-1β). Twenty-three patients (34 implants; 19 control, 15 test) were included. At the follow-up, mean crestal bone loss was lower in the test group at 1 and 3 months (2.48 mm vs. 3.73 mm, p < 0.05 and 2.39 vs. 3.37, p < 0.01). IL-1β levels were also lower in the test group at 2 weeks (72.86 pg/mL vs. 111.7, p < 0.05). Within all the limitation of this preliminary study, the test group improved clinical parameters after a short-term period compared to the control group.     

Interruption of Electrical Conductivity of Titanium Dental Implants Suggests a Path Towards Elimination Of Corrosion

Peri-implantitis is an inflammatory disease that results in the destruction of soft tissue and bone around the implant. Titanium implant corrosion has been attributed to the implant failure and cytotoxic effects to the alveolar bone. We have documented the extent of titanium release into surrounding plaque in patients with and without peri-implantitis. An in vitro model was designed to represent the actual environment of an implant in a patient’s mouth. The model uses actual oral microbiota from a volunteer, allows monitoring electrochemical processes generated by biofilms growing on implants and permits control of biocorrosion electrical current. As determined by next generation DNA sequencing, microbial compositions in experiments with the in vitro model were comparable with the compositions found in patients with implants. It was determined that the electrical conductivity of titanium implants was the key factor responsible for the biocorrosion process. The interruption of the biocorrosion current resulted in a 4–5 fold reduction of corrosion. We propose a new design of dental implant that combines titanium in zero oxidation state for osseointegration and strength, interlaid with a nonconductive ceramic. In addition, we propose electrotherapy for manipulation of microbial biofilms and to induce bone healing in peri-implantitis patients.     

The influence of implant number and abutment design on the biomechanical behaviour of bone for an implant-supported fixed prosthesis: a finite element study in the upper anterior region

It is always recommended to use more implants for supporting a prosthesis in the immediate loading condition than in the classical two-stage treatment procedure. By means of the finite element (FE) method, the influence of the number of implants used in immediately loaded fixed partial prosthesis (FPP) on the load distribution was investigated, considering the abutment geometry. Two 3D FE models were studied employing four implants to support a FPP in the premaxilla. One model was designed with straight abutments and the other with 20°-angled abutments. The results concerning implant displacements, stresses and strains were compared with those of two implant-supported FPPs, obtained in a previous study. A noticeable reduction in the determined biomechanical bone loading was observed with the use of more implants in supporting an immediately loaded prosthesis. This study confirms that the use of additional numbers of implants in an immediately loaded prosthesis is highly recommended.     

Influence of Different Abutment Designs on the Biomechanical Behavior of One-Piece Zirconia Dental Implants and Their Surrounding Bone: A 3D-FEA

BackgroundIn a dental implant/bone system, the design factors affect the value and distributions of stress and deformations that plays a pivotal role on the stability, durability and lifespan of the implant/bone system.ObjectiveThe aim of this study was to compare the influence of different abutment designs on the biomechanical behavior of one-piece zirconia dental implants and their surrounding bone tissues using three-dimensional finite element analysis.MethodsA three-dimensional geometrical model of a zirconia dental implant and its surrounding bone tissue were created. The occlusal loading force applied to the prosthetic abutments was a combination of 114.6 N in the axial direction, 17.1 N in the lingual direction and 23.4 N toward the mesial direction where these components represent masticatory force of 118.2 N in the angle of approximately 75° to the occlusal plane.ResultsThe system included implant abutment Model 01 showed a decrease of 9.58%, 9.92% and 3.62% at least in the average value of maximum von Mises stress compared to Model 02, Model 03 and Model 04 respectively. The results also showed that the system included implant abutment Model 01 decreases the average value of maximum deformation of 16.96%, 7.17% and 9.47% at least compared to Model 02, Model 03 and Model 04 respectively.ConclusionThe one-piece zirconia dental implant abutment Model 01 presents a better biomechanical behavior in the peri-implant bone than others. It can efficiently distribute the applied load and present more homogeneous behavior of stress distribution and has less deformation than others, which will enhance the stability of implant/bone system and prolong its lifespan.     

The influence of implant number and abutment design on the biomechanical behaviour of bone for an implant-supported fixed prosthesis: a finite element study in the upper anterior region

It is always recommended to use more implants for supporting a prosthesis in the immediate loading condition than in the classical two-stage treatment procedure. By means of the finite element (FE) method, the influence of the number of implants used in immediately loaded fixed partial prosthesis (FPP) on the load distribution was investigated, considering the abutment geometry. Two 3D FE models were studied employing four implants to support a FPP in the premaxilla. One model was designed with straight abutments and the other with 20°-angled abutments. The results concerning implant displacements, stresses and strains were compared with those of two implant-supported FPPs, obtained in a previous study. A noticeable reduction in the determined biomechanical bone loading was observed with the use of more implants in supporting an immediately loaded prosthesis. This study confirms that the use of additional numbers of implants in an immediately loaded prosthesis is highly recommended.     

Three-dimensional numerical simulation of stress induced by different lengths of osseointegrated implants in the anterior maxilla

Lower survival rates were observed for the implant placed in the anterior maxilla. The purpose of this study was to investigate the influence of different implant lengths on the stress distribution around osseointegrated implants under a static loading condition in the anterior maxilla using a three-dimensional finite element analysis. The diameter of 4.0 mm external type implants of different lengths (8.5 mm, 10.0 mm, 11.5 mm, 13.0 mm, 15.0 mm) was used in this study. The anterior maxilla was assumed to be D3 bone quality. All the material was assumed to be homogenous, isotropic and linearly elastic. The implant–bone interface was constructed using a rigid element for simulating the osseointegrated condition. Then, 176 N of static force was applied on the middle of the palatoincisal line angle of the abutment at a 120°angle to the long axis of abutment. The von Mises stress value was measured with an interval of 0.25 mm along the bone–implant interface. Incremental increase in implant length causes a gradual reduction of maximum and average von Mises stress at the labial portion within the implant. In the bone, higher stress was concentrated within cortical bone area and more distributed at the labial cortex, while cancellous bone showed relatively low stress concentration and even distribution. An increase in implant length reduced stress gradients at the cortical peri-implant region. Implant length affects the mechanisms of load transmission to the osseointegrated implant. On the basis of this study the biomechanical stress-based performance of implants placed in the anterior maxilla improves when using longer implants.     

Marginal bone loss around axial and straight implants supported with prefabricated SFI-Bar with mandibular overdentures

To assess the role of prefabricated SFI-Bar in peri-implant bone loss around immediately axially loaded and straight implants. This study comprised of 40 complete denture wearer patients who received two axially parallel implants connected by SFI-Bars in group I and two 15° mesially tilted implants connected by SFI-Bars in group II. Peri- implant bone loss (PiBL) was measured at 1 year, 2 years and 3 years. The mean PiBL at 1 year in group I was 0.21 mm and I group II was 0.22, at 2 years in group I was 0.26 mm and in group II was 0.23 mm and at 3 years, in group I was 0.29 mm and in group II was 0.34 mm. The difference was significant at 3 years (P< 0.05). The mean mesial PIBL at 1 year in group I was 0.18 mm, in group II was 0.20 mm, at 2 years in group I was 0.19 mm and in group II was 0.07 mm and at 3 years, in group I was 0.25 mm and in group II was 0.29 mm. The difference found to be significant in each time duration in both groups (P< 0.05).The mean distal PIBL at 1 year in group I was 0.23 mm, in group II was 0.22 mm, at 2 years in group I was 0.33 mm and in group II was 0.39 mm and at 3 years, in group I was 0.34 mm and in group II was 0.39 mm. The difference found to be significant at 2 and 3 years in both groups (P< 0.05). Authors found that mandibular overdentures retained with Prefabricated SFI-Bar with axial and straight inserted implants may be useful in patients with reduced bone height.     

Multi-factorial analysis of variables influencing the bone loss of an implant placed in the maxilla: Prediction using FEA and SED bone remodeling algorithm

The aim of this study was to investigate the interactions of implant position, implant–abutment connection and loading condition influencing bone loss of an implant placed in the maxilla using finite element (FE) analysis and mathematical bone remodeling theory. The maxilla section contours were acquired using CT images to construct FE models containing RS (internal retaining-screw) and the TIS (taper integrated screwed-in) implants placed in SC (along the axis of occlusal force) and RA (along the axis of residual ridge) positions. The adaptive strain energy density (SED) algorithm was combined with FE approach to study the preliminary bone remodeling around implant systems under different load conditions. The simulated results showed that the implant position obviously influenced the bone loss. An implant placed in the RA position resulted in substantially increased bone loss. Implant receiving a lateral load slightly increased bone loss compared with an axial load. The implant type did not significantly influence bone loss. It was found that buccal site suffered the most bone loss around the implant, followed by distal, lingual and mesial sites. The implant position primarily influenced bone loss and it was found most obviously at the buccal site. Implant placed along the axial load direction of a proposed prosthesis could obtain less bone loss around the implant. Attaining proper occlusal adjustments to reduce the lateral occlusal force is recommended in implant–bone–prosthesis system. Abutments of internal engagement with or without taper-fit did not affect the bone loss in the surrounding bone.     

Implant Optimisation for Primary Hip Replacement in Patients over 60 Years with Osteoarthritis: A Cohort Study of Clinical Outcomes and Implant Costs Using Data from England and Wales

Background

Hip replacement is one of the most commonly performed surgical procedures worldwide; hundreds of implant configurations provide options for femoral head size, joint surface material and fixation method with dramatically varying costs. Robust comparative evidence to inform the choice of implant is needed. This retrospective cohort study uses linked national databases from England and Wales to determine the optimal type of replacement for patients over 60 years undergoing hip replacement for osteoarthritis.

Methods and Findings

Implants included were the commonest brand from each of the four types of replacement (cemented, cementless, hybrid and resurfacing); the reference prosthesis was the cemented hip procedure. Patient reported outcome scores (PROMs), costs and risk of repeat (revision) surgery were examined. Multivariable analyses included analysis of covariance to assess improvement in PROMs (Oxford hip score, OHS, and EQ5D index) (9159 linked episodes) and competing risks modelling of implant survival (79,775 procedures). Cost of implants and ancillary equipment were obtained from National Health Service procurement data.

Results

EQ5D score improvements (at 6 months) were similar for all hip replacement types. In females, revision risk was significantly higher in cementless hip prostheses (hazard ratio, HR = 2.22, p<0.001), when compared to the reference hip. Although improvement in OHS was statistically higher (22.1 versus 20.5, p<0.001) for cementless implants, this small difference is unlikely to be clinically important. In males, revision risk was significantly higher in cementless (HR = 1.95, p = 0.003) and resurfacing implants, HR = 3.46, p<0.001), with no differences in OHS. Material costs were lowest with the reference implant (cemented, range £1103 to £1524) and highest with cementless implants (£1928 to £4285).Limitations include the design of the study, which is intrinsically vulnerable to omitted variables, a paucity of long-term implant survival data (reflecting the duration of data collection), the possibility of revision under-reporting, response bias within PROMs data, and issues associated with current outcome scoring systems, which may not accurately reflect level of improvement in some patients.

Conclusions

Cement fixation, using a polyethylene cup and a standard sized head offers good outcomes, with the lowest risks and at the lowest costs. The most commonly used cementless and resurfacing implants were associated with higher risk of revision and were more costly, while perceptions of improved function and longevity were unsupported.     

C-Reactive Protein,Erythrocyte Sedimentation Rate and Orthopedic Implant Infection

Background

C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) have been shown to be useful for diagnosis of prosthetic hip and knee infection. Little information is available on CRP and ESR in patients undergoing revision or resection of shoulder arthroplasties or spine implants.

Methods/Results

We analyzed preoperative CRP and ESR in 636 subjects who underwent knee (n = 297), hip (n = 221) or shoulder (n = 64) arthroplasty, or spine implant (n = 54) removal. A standardized definition of orthopedic implant-associated infection was applied. Receiver operating curve analysis was used to determine ideal cutoff values for differentiating infected from non-infected cases. ESR was significantly different in subjects with aseptic failure infection of knee (median 11 and 53.5 mm/h, respectively, p = <0.0001) and hip (median 11 and 30 mm/h, respectively, p = <0.0001) arthroplasties and spine implants (median 10 and 48.5 mm/h, respectively, p = 0.0033), but not shoulder arthroplasties (median 10 and 9 mm/h, respectively, p = 0.9883). Optimized ESR cutoffs for knee, hip and shoulder arthroplasties and spine implants were 19, 13, 26, and 45 mm/h, respectively. Using these cutoffs, sensitivity and specificity to detect infection were 89 and 74% for knee, 82 and 60% for hip, and 32 and 93% for shoulder arthroplasties, and 57 and 90% for spine implants. CRP was significantly different in subjects with aseptic failure and infection of knee (median 4 and 51 mg/l, respectively, p<0.0001), hip (median 3 and 18 mg/l, respectively, p<0.0001), and shoulder (median 3 and 10 mg/l, respectively, p = 0.01) arthroplasties, and spine implants (median 3 and 20 mg/l, respectively, p = 0.0011). Optimized CRP cutoffs for knee, hip, and shoulder arthroplasties, and spine implants were 14.5, 10.3, 7, and 4.6 mg/l, respectively. Using these cutoffs, sensitivity and specificity to detect infection were 79 and 88% for knee, 74 and 79% for hip, and 63 and 73% for shoulder arthroplasties, and 79 and 68% for spine implants.

Conclusion

CRP and ESR have poor sensitivity for the diagnosis of shoulder implant infection. A CRP of 4.6 mg/l had a sensitivity of 79 and a specificity of 68% to detect infection of spine implants.     

Prognosis of implant longevity in terms of annual bone loss: a methodological finite element study

Dental implant failure is mainly the consequence of bone loss at peri-implant area. It usually begins in crestal bone. Due to this gradual loss, implants cannot withstand functional force without bone overload, which promotes complementary loss. As a result, implant lifetime is significantly decreased. To estimate implant success prognosis, taking into account 0.2 mm annual bone loss for successful implantation, ultimate occlusal forces for the range of commercial cylindrical implants were determined and changes of the force value for each implant due to gradual bone loss were studied. For this purpose, finite element method was applied and von Mises stresses in implant–bone interface under 118.2 N functional occlusal load were calculated. Geometrical models of mandible segment, which corresponded to Type II bone (Lekholm & Zarb classification), were generated from computed tomography images. The models were analyzed both for completely and partially osseointegrated implants (bone loss simulation). The ultimate value of occlusal load, which generated 100 MPa von Mises stresses in the critical point of adjacent bone, was calculated for each implant. To estimate longevity of implants, ultimate occlusal loads were correlated with an experimentally measured 275 N occlusal load (Mericske-Stern & Zarb). These findings generally provide prediction of dental implants success.     

种植修复后牙周菌群在不同时期变化的定量研究

目的观察种植修复后牙周菌群在不同时期的变化,比较牙周病人群和健康人群种植术后菌群分布差异。方法选择牙种植患者28例,接受37颗种植修复（无牙周病史19颗,有牙周病史18颗）,采取前后对照设计。采用细菌分离鉴定及菌落形成单位计数的检测方法,以正常同名天然牙为基线对照,追踪观察愈合基台龈袖口、全冠修复后1周、负荷12个月后牙龈沟菌丛变化情况。结果种植体龈沟液内的细菌数量增加构成日趋复杂,在愈合基台期细菌数量最低,冠修复后1年,两组人群的菌群数量和构成差异有显著性（P〈0．05）,而健康人群成功种植体和天然牙有相似的菌群构成;但以往有牙周病史的患者,种植体植入区域内普遍有牙周病原体量的增加。结论随着时间的延长,具有牙周病史的患者的种植体周围炎的风险增加。