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.

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 resultant 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 randomly placed in edentulous mandibular 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, sandblasted, 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 (standard 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 mandible, 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.     

Crestal bone changes around titanium implants: a methodologic study comparing linear radiographic with histometric measurements

Generally, endosseous implants can be placed according to a nonsubmerged or a submerged technique and in 1-piece or 2-piece configurations. Recently, it has been shown that peri-implant crestal bone reactions differ significantly radiographically as well as histometrically under such conditions and are dependent on a rough/smooth implant border in 1-piece implants and on the location of a microgap (interface) between the implant and the abutment/restoration in 2-piece configurations. The purpose of this study was to evaluate whether standardized radiography as a noninvasive clinical diagnostic method correlates with peri-implant crestal bone levels as determined by histometric analysis. Fifty-nine implants were placed in edentulous mandibular areas of 5 foxhounds in a side-by-side comparison in both submerged and nonsubmerged techniques. Three months after implant placement, abutment connection was performed in the submerged implant sites. At 6 months, all animals were sacrificed, and evaluations of the first bone-to-implant contact (fBIC), determined on standardized periapical radiographs, were compared to similar analyses made from nondecalcified histology. It was shown that both techniques provide the same information (Pearson correlation coefficient = 0.993; P < .001). The precision of the radiographs was within 0.1 mm of the histometry in 73.4% of the evaluations, while the level of agreement fell to between 0.1 and 0.2 mm in 15.9% of the cases. These data demonstrate in an experimental study that standardized periapical radiography can evaluate crestal bone levels around implants clinically accurately (within 0.2 mm) in a high percentage (89%) of cases. These findings are significant because crestal bone levels can be determined using a noninvasive technique, and block sectioning or sacrifice of the animal subject is not required. In addition, longitudinal evaluations can be made accurately such that bone changes over various time periods can be assessed. Such analyses may prove beneficial when trying to distinguish physiologic changes from pathologic changes or when trying to determine causes and effects of bone changes around dental implants.     

Influence of a machined collar on crestal bone changes around titanium implants: a histometric study in the canine mandible

Background: It has been shown that peri‐implant crestal bone reactions are influenced by both a rough–smooth implant border in one‐piece, non‐submerged, as well as an interface (microgap [MG] between implant/abutment) in two‐piece butt‐joint, submerged and non‐submerged implants being placed at different levels in relation to the crest of the bone. According to standard surgical procedures, the rough–smooth implant border for implants with a smooth collar should be aligned with the crest of the bone exhibiting a smooth collar adjacent to peri‐implant soft tissues. No data, however, are available for implants exhibiting a sandblasted, large‐grit and acid‐etched (SLA) surface all the way to the top of a non‐submerged implant. Thus, the purpose of this study is to histometrically examine crestal bone changes around machined versus SLA‐surfaced implant collars in a side‐by‐side comparison. Methods: A total of 60 titanium implants (30 machined collars and 30 SLA collars) were randomly placed in edentulous mandibular areas of five foxhounds forming six different subgroups (implant subgroups A to F). The implants in subgroups A to C had a machined collar (control), whereas the implants in subgroups D to F were SLA‐treated all the way to the top (MG level; test). Furthermore, the MGs of the implants were placed at different levels in relation to the crest of the bone: the implants in subgroups A and E were 2 mm above the crest, in subgroups C and D 1 mm above, in subgroup B 3 mm above, and in subgroup F at the bone crest level. For all implants, abutment healing screws were connected the day of surgery. These caps were loosened and immediately retightened monthly. At 6 months, animals were sacrificed and non‐decalcified histology was analyzed by evaluating peri‐implant crestal bone levels. Results: For implants in subgroup A, the estimated mean crestal bone loss (± SD) was ?0.52 ± 0.40 mm; in subgroup B, +0.16 ± 0.40 mm (bone gain); in subgroup C, ?1.28 ± 0.21 mm; in subgroup D, ?0.43 ± 0.43 mm; in subgroup E, ?0.03 ± 0.48 mm; and in subgroup F, ?1.11 ± 0.27 mm. Mean bone loss for subgroup A was significantly greater than for subgroup E (P = 0.034) and bone loss for subgroup C was significantly greater than for subgroup D (P <0.001). Conclusions: Choosing a completely SLA‐surfaced non‐submerged implant can reduce the amount of peri‐implant crestal bone loss and reduce the distance from the MG to the first bone–implant contact around unloaded implants compared to implants with a machined collar. Furthermore, a slightly exposed SLA surface during implant placement does not seem to compromise the overall hard and soft tissue integration and, in some cases, results in coronal bone formation in this canine model.     

Crestal bone changes around titanium implants. Part I: A retrospective radiographic evaluation in humans comparing two non-submerged implant designs with different machined collar lengths

BACKGROUND: Experimental studies demonstrated that peri-implant crestal hard and soft tissues are significantly influenced in their apico-coronal position by the rough/smooth implant border as well as the microgap/ interface between implant and abutment/restoration. The aim of this study was to evaluate radiographically the crestal bone level changes around two types of implants, one with a 2.8 mm smooth machined coronal length and the other with 1.8 mm collar. METHODS: In 68 patients, a total of 201 non-submerged titanium implants (101 with a 1.8 mm, 100 with a 2.8 mm long smooth coronal collar) were placed with their rough/smooth implant border at the bone crest level. From the day of surgery up until 3 years after implant placement crestal bone levels were analyzed digitally using standardized radiographs. RESULTS: Bone remodeling was most pronounced during the unloaded, initial healing phase and did not significantly differ between the two types of implants over the entire observation period (P >0.20). Crestal bone loss for implants placed in patients with poor oral hygiene was significantly higher than in patients with adequate or good plaque control (P <0.005). Furthermore, a tendency for additional crestal bone loss was detected in the group of patients who had been diagnosed with aggressive periodontitis prior to implant placement (P = 0.058). In both types of implants, sand-blasted, large grit, acid-etched (SLA) surfaced implants tended to have slightly less crestal bone loss compared to titanium plasma-sprayed (TPS) surfaced implants, but the difference was not significant (P >0.30). CONCLUSION: The implant design with the shorter smooth coronal collar had no additional bone loss and may help to reduce the risk of an exposed metal implant margin in areas of esthetic concern.     

Crestal bone loss around submerged and exposed unloaded dental implants: a radiographic and microbiological descriptive study

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 mandible 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. Standardized 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.     

A radiographic evaluation of bone healing around submerged and non-submerged dental implants in beagle dogs

BACKGROUND: The rehabilitation of the oral cavity with dental implants has become a predictable treatment modality. However, there have been only a few direct comparisons evaluating the submerged and nonsubmerged placement techniques. The purpose of this study was to characterize radiographic peri-implant bone changes following the insertion of submerged and nonsubmerged implants in the beagle dog. METHODS: At the end of the extraction healing phase, 19 submerged and 19 nonsubmerged implants were randomly placed in a split-mouth study design and observed over an 18-week period. For submerged implants, a second stage surgery and transmucosal abutment attachment was performed at week 12. Standardized dental radiographs taken at baseline, week 12, and week 18 were used to measure peri-implant bone changes. The radiographs were analyzed with a simple computer assisted method. RESULTS: A total of 43 standardized radiographs were exposed to evaluate the 38 implants. During the study period, all submerged and nonsubmerged implants demonstrated peri-implant bone loss. At baseline, both submerged and nonsubmerged implants had similar bone levels (P > or = 0.05). When the mean peri-implant bone levels for submerged and nonsubmerged implants were compared from baseline to week 12, nonsubmerged implants had a significantly greater amount and rate of bone resorption than submerged implants (P < or = 0.05). Following week 12, the initially submerged implant had a significantly higher rate and amount of peri-implant bone loss than the nonsubmerged implants (P < or = 0.05). However, by the end of the study period, week 18, both submerged and nonsubmerged implants had comparable bone levels (P > or = 0.05). CONCLUSIONS: The study indicates that, although the temporal patterns of peri-implant bone resorption differed, there were no differences between submerged and nonsubmerged implants in the overall amount and rate of peri-implant bone loss.     

Biologic width changes around loaded implants inserted in different levels in relation to crestal bone: histometric evaluation in canine mandible

Objectives: The aim of the present study was to evaluate histometric changes around dental implants inserted at different levels in relation to the crestal bone, under different loading conditions. Material and methods: Thirty‐six implants were inserted in the edentulous mandible of six mongrel dogs. Each implant was assigned to an experimental group according to the distance from the top of the implant to the crestal bone: Bone Level (at the crestal bone level), Minus 1 (1 mm below the crestal bone) or Minus 2 group (2 mm below the crestal bone). Each hemimandible was submitted to a loading protocol: conventional or immediate restoration. After 90 days, the animals were killed. Specimens were processed, and measurements were performed concerning the length of soft and hard peri‐implant tissues. Data were analyzed using ANOVA and Student's t test (α=5%). Results: Among conventionally restored sites, the distance from the most coronal position of soft tissue margin (PSTM) and first bone–implant contact (fBIC) was greater for Minus 2 than for Bone Level and Minus 1 sites (P=0.03), but significant differences were not observed among immediately restored sites. Differences among groups were not observed concerning the PSTM, and the distance from the implant–abutment junction to fBIC. Greater amounts of lateral bone loss were observed for conventionally than for immediately restored sites (P=0.006). Conclusions: These findings suggest that the apical positioning of the top of the implant may not jeopardize the position of soft peri‐implant tissues, and that immediate restoration can be beneficial to minimize lateral bone loss. Further studies are suggested to evaluate the clinical significance of these results in longer healing periods.     

Comparison of healed tissues adjacent to submerged and non‐submerged unloaded titanium dental implants. A histometric study in beagle dogs.

This study involved histometry of the healed tissues around submerged and nonsubmerged dental implants in beagle dogs. In a split‐mouth design, 19 submerged and 19 nonsubmerged commercially pure titanium implants, titanium plasma‐sprayed in the bone anchoring part and smooth in the transmucosal portion were placed in the mandibles of 6 dogs. Oral hygiene was performed 3 times weekly. After 3 months of healing, transmucosal abutments were inserted in the submerged implants. Six weeks after second stage surgery, the dogs were sacrificed and specimens obtained and processed for histology and histometry. Using a light microscope and a digitizing pad, the distance from implant top to mucosa border (DIM), the extent of epithelial downgrowth (ED), the attachment level (AL). the length of connective tissue contact (CTC) and the distance of the first coronal alveolar bone contact from the implant top (DIB) were measured at the mesial and distal aspects. Means+standard deviations for submerged and nonsubmerged implants were calculated, with the dog being the unit of measure. No statistically significant differences between submerged and nonsubmerged implants here found for DIM, CTC and DIB. However, significant differences were observed for ED and AL. This study in beagle dogs indicates that the apical extension of the peri‐implant epithelium is significantly greater and the attachment level significantly lower adjacent to submerged implants with second‐stage transmucosal abutments than in nonsubmerged, one‐stage implants.     

Peri-implant tissues at submerged and non-submerged titanium implants

The present experiment was performed to study the peri-implant tissue response to non-submerged (1-stage) and initially submerged (2-stage) implant installation procedures. 6 beagle dogs were used. All mandibular premolars and the 1st, 2nd and 3rd maxillary premolars were extracted. After 3 months of healing, 3 fixtures of the Astra Tech System were installed and submerged in the right (or the left) edentulous, premolar region in each of the 6 dogs. Radiographs were obtained immediately after fixture installation. In the radiographs, the distance between the abutment-fixture junction and the most "coronal" bone in contact with the implant surface was determined. 3 months later, abutments were connected to the initially submerged fixtures and another 3 fixtures of the same system were installed in the contralateral, edentulous premolar region. Abutments were, however, immediately connected to the newly-installed fixtures (non-submerged side; test side). The mucosal flaps were replaced, adjusted and sutured in such a way that the coronal portion of the abutments remained exposed in the oral cavity. A new set of radiographs were obtained from all 6 implant sites in each animal. A period of plaque control was initiated. Clinical examinations were performed and radiographs obtained from all implant sites after another 3 months and at the termination of the experiment. 9 months after the 1st fixture installation procedure, the animals were sacrificed, the mandibles were removed, and each implant region dissected. The most mesially-located implant sites were processed for ground sectioning. The remaining biopsies were processed and embedded in EPON. The histometric analysis included assessment of the vertical dimension of the marginal soft and mineralized peri-implant tissues. The ground sections were used for measurements describing (i) "bone to implant contact" and (ii) "bone density". It was observed that the mucosa and bone tissue that formed at implants placed in a non-submerged or a submerged procedure had many features in common. Thus, figures describing (i) the height of the mucosa, (ii) the length of the junctional epithelium and the height and quality of the zone of "connective tissue integration", (iii) the % of bone to implant contact as well as (iv) the density of the peri-implant bone, were similar in the submerged and the non-submerged groups. It is therefore suggested that a non-submerged (1-stage) installation technique may provide conditions for tissue integration that are similar to those obtained using a submerged (2-stage) approach.     

Comparative evaluation of the peri-implant bone tissue mineral density around unloaded titanium dental implants

OBJECTIVE: The mechanical properties of bone are greatly influenced by the percentages of organic and mineral constituents. Nevertheless, the information about the mineral content on a microscopic scale in peri-implant bone is scarce. The aim of this work was to analyze the bone mineral density of peri-implant bone under different techniques. DESIGN: Five unloaded titanium dental implants with a micro-structured surface (three XiVE plus and two Frialit 2, DENTSPLY-Friadent, Mannheim, Germany) were retrieved from the mandible of five patients after a 6-month period. scanning electron microscopy with backscattered electron signal (BSE), light microscopy (LM) with a double staining technique, fluorescence microscopy and confocal laser microscopy were used for measuring microscopic mineral content variations in peri-implant bone. Histomorphometry and image intensity (grey level) were evaluated using a software package for image analysis. RESULTS: The low mineral density index (LMDI) for LM was of 29.2+/-3.1 (mean+/-S.D.), while the high mineral density index (HMDI) was of 88.2+/-3.6 (mean+/-S.D.). The one-way ANOVA analysis showed a significant difference (P<0.001) among the groups. The pairwise Holm-Sidak test identified the differences among HMDI indexes for both LM and SEM values and also for cross-evaluation of the LMDI and HMDI values. The comparison between LMDI indexes for both SEM and LM did not show any significance. The fluorescence microscopy analysis showed clearly the difference between old (high mineralized) and new (low mineralized) bone tissue near the implant surface. Under confocal laser microscopy the same sections showed the area of bone modelling closest to implant surface. CONCLUSION: In this study it was found that bone around unloaded implants showed a low mineral density index under all the investigation methods used. It was also found that the conventional LM technique with the double staining method was able to intensely stain the bone area with a low mineral content.     

Soft tissue reactions to non-submerged unloaded titanium implants in beagle dogs.

The soft tissue reactions to non-submerged unloaded titanium implants were examined. A total of 24 implants were placed in 6 beagle dogs. The implants differed in their crestal area by having either a rough sandblasted, a fine sandblasted, or a polished surface. After 3 months, all implants were firmly anchored in the bone and had no clinical signs of peri-implant inflammation. Undecalcified histologic sections demonstrated that all implants achieved osseointegration with direct bone contact. The epithelial structures showed a peri-implant sulcus with a non-keratinized sulcular epithelium and a junctional epithelium. None of the sections exhibited epithelial downgrowth to the alveolar crest. In the supracrestal area, a direct connective tissue contact to the implant post was observed. An approximately 50 to 100 microns wide zone of dense circular fibers was found close to the implant surface. It was free of blood vessels and resembled closely an inflammation-free scar tissue formation. This zone was surrounded by a looser connective tissue with a 3-dimensional network of collagen fibers running in different directions. No significant differences concerning soft tissue reactions were found between the 3 implant surfaces. In particular, the length of direct connective tissue contact was similar. Concerning bone reactions, a significantly shorter distance from the top of the implant to the most coronal bone-implant contact was observed for rough surfaces. It is concluded that non-submerged unloaded titanium implants achieved a complication-free tissue integration with a dense connective tissue in direct contact to the implant surface in the supracrestal area, and epithelial structures similar to those around natural teeth. The different surface textures did not influence the healing pattern of the soft tissues, but had an influence on the location of the most coronal bone-implant contact.     

Nicotine and bone density around titanium implants: a histometric study in rabbits

This study investigated the influence of nicotine on bone density around titanium implants inserted in rabbits. Thirty-two New Zealand rabbits were included. After anesthesia, the tibiae surfaces were exposed and two screw-shaped, commercially available, pure titanium implants of 7.0 mm in length and 3.75 mm in diameter were placed bilaterally. A total of 128 implants were inserted: 64 blasted with Al2O3 particles (group 1) and 64 with a machined surface finish (group 2). The animals were randomly assigned to one of four treatment subgroups, and daily subcutaneous injections of nicotine were administered. After 42 days, the animals were killed and undecalcified sections were prepared. The bone density was measured in the cortical passage of the implant. Statistical analysis (two-way analysis of variance) revealed no significant difference neither regarding the effect of nicotine nor the effect of surface design on bone density around the implants (P > 0.05). Within the limits of the present study, it can be assumed that daily nicotine administration may not statistically influence bone density around titanium implants.     

非埋植型与埋植型牙种植体骨界面改建的X线观察

目的 比较非埋植型与埋植型两种不同种植方式种植体－骨界面组织变化的异同。方法 选用成年杂种犬8只，在其下颌分别植入埋植型与非埋植型种植体，分不同时期处死动物，采用X线对非埋植型与埋植型种植体－骨界面愈合过程进行动态观察，比较两者者界面改建的异同。结果 X线观察1、2、4周非埋植型和埋植型种植体－骨界面新骨形成的速度与骨性结合的程度均无明显差异。12周时，非埋植型和埋植型种植体与骨组织均紧密接触，但非埋植型种植体颈部观察到牙槽骨轻微吸收现象。结论 非埋植型种植体尽管植入后基桩在整个愈合过程中承受了一定的咬合力，但它能与埋植型种植体一样获得良好的骨结合。     

Estrogen deficiency affects bone healing around titanium implants: a histometric study in rats

The purpose of this study was to evaluate the influence of an estrogen-deficient state on bone around titanium implants placed in rats. Thirty female Wistar rats were divided into 2 groups: test (n = 15), ovariectomized rats (OVX); and control (n = 15), sham-operated rats. Screw-type titanium implants were placed bilaterally in rats 21 days after ovariectomy or sham surgery. After 60 days, the animals were killed and undecalcified sections obtained. Blood samples were collected to obtain serum levels of alkaline phosphatase at the time of killing. Bone-to-implant contact (BIC), bone area (BA) around the implants, and bone density (BD) in a 500 microns-wide zone lateral to the implant were obtained and arranged separately for the cortical (zone A) and cancellous (zone B) regions. In zone A, there was no significant difference between test and control groups regarding BIC and BD (P > 0.05). A lower BA was observed in the estrogen-deficient animals (P < 0.05). In zone B, data analysis showed that estrogen deficiency could result in a lower percentage of BIC, BA, and BD (P < 0.05). In addition, a higher concentration of alkaline phosphatase was observed for the test group. An estrogen-deficient state could affect bone healing and bone density around titanium implants placed in rats, especially in the cancellous bone area.     

Collagen fiber orientation in human peri-implant bone around immediately loaded and unloaded titanium dental implants

BACKGROUND: The main factor in determining the mechanical properties of bone is the collagen configuration. METHODS: This study investigated the birefringence in human bone around loaded and unloaded titanium dental implants to evaluate the collagen fiber orientation using circularly polarized light (CPL) and scanning electron microscopy (SEM). A total of 10 titanium dental implants, five immediately loaded and five unloaded, were used. The birefringence measurements were performed on digitized images of both loaded and unloaded implants. All images detected at 50x were measured using a software image analysis. RESULTS: In the bone around loaded implants, the transverse collagen fiber area was 45,481+/-3,037 pixel2 (mean+/-SD), while the area of longitudinal collagen fibers was 13,676+/-2,232 pixel2 (mean+/-SD). In the unloaded implants, the transverse collagen fiber area was 32,174+/-2,554 pixel2 (mean+/-SD), while the area of longitudinal collagen fibers was 89,073+/-1,960 pixel2 (mean+/-SD). The CPL measurements of the birefringence for transverse collagen fibers of loaded versus unloaded implants indicated that the differences were statistically significant (P <0.05). The results for the longitudinal collagen fibers of loaded versus unloaded implants were also statistically significant (P <0.05). CONCLUSIONS: In the bone around loaded dental implants, transverse collagen fibers were more abundant, while in the unloaded implants, collagen fibers run more longitudinally. The load seemed to determine the collagen fiber orientation.     

Crestal bone remodeling in loaded and unloaded implants and the microgap: a histologic study

PURPOSE: The aim of this study was to histologically evaluate the crestal bone response to loaded and unloaded implants in beagle dogs. MATERIALS AND METHODS: Sand-blasted and acid-etched implants (Bone System, Milano, Italy) were placed in the mandible of six beagle dogs. The two premolars and the first molars had been extracted 3 months previously. Each dog received 12 implants in the mandible, and a total of 72 implants were used in this study. Three months after implantation, second-stage surgeries were performed for placement of abutments or healing screws. Three dogs were killed after 6 months, and three dogs were killed after 12 months. All 72 implants were retrieved. RESULTS: No statistically significant differences were found in the amount of bone loss between test and control implants, both at 6 and 12 months. Statistically significant differences were found, in both groups, between the bone loss observed at 6 months and that found at 12 months. CONCLUSION: Loading does not seem to be a relevant factor in the peri-implant bone resorption observed during the first year of function. Our results support previous findings that bone crest level changes could depend on the location of the microgap.     

The effect of an immunosuppressive therapy and its withdrawal on bone healing around titanium implants. A histometric study in rabbits.

BACKGROUND: Immunosuppressive agents have been recognized as a factor affecting bone metabolism. We investigated the consequences of the administration and withdrawal of cyclosporin A/nifedipine on bone around titanium implants to observe whether these changes occur and if they are reversible. METHODS: Twenty-eight New Zealand rabbits were included in the study. Following anesthesia, the tibiae surface was exposed, and 2 screw-shaped implants 7.0 mm in length and 3.75 mm in diameter were placed bilaterally. The animals were randomly assigned to 1 of 4 experimental groups and received daily subcutaneous injections for 14 days: groups A and C were injected with vehicle while groups B and D received cyclosporin A (10 mg/kg) plus nifedipine (0.5 mg/kg). Groups A and B were sacrificed 14 days and groups C and D 42 days postoperatively. The degree of bone contact with the implant surface and the bone area within the limits of the threads of the implant were measured. RESULTS: Intergroup analysis revealed no significant difference (P > 0.05) in the degree of bone contact with the implant surface between the control and test groups on days 14 and 42. In contrast, the treated animals demonstrated a significant (P < 0.05) decrease in the bone area within the limits of the threads of the implant in both periods. CONCLUSIONS: The data of the present study suggest that the use of cyclosporin A/nifedipine may influence bone healing around titanium implants. This observation may have important clinical implications.     

Early cellular responses in cortical bone healing around unloaded titanium implants: an animal study

BACKGROUND: A clear understanding of the early cellular events leading to osseointegration of implants is currently lacking. To gain better insight, titanium implants were inserted in a rabbit model and histologic and histomorphometric analyses were performed at early time points after insertion. METHODS: Thirty-six cylindrical implants were inserted in the tibial diaphysis of six rabbits and left to heal for 1 to 42 days. Samples were processed into paraffin or methylmethacrylate sections, on which the surface of new bone, region of altered nuclear morphology, relative surface of basic multicellular units (BMUs) and blood vessels, and bone-to-implant contact were measured. RESULTS: After coagulum formation, osteoclasts and osteoblasts were observed at the bone surface 1 week after healing. In the preexisting bone, osteocytic lacunae appeared to be devoid of cells. This region of altered nuclear morphology continued to extend for 28 days (P <0.05) after implant insertion. This expansion was accompanied by an invasion of the damaged bone by BMUs that initiated intensive bone remodeling, which reached its maximum after 4 weeks (P <0.05) but was ongoing after 6 weeks of implant insertion. CONCLUSIONS: This study evaluated the early cellular events in cortical bone surrounding titanium implants. The insertion of an implant into bone initiates a series of biologic processes, including the formation of a hematoma, altered nuclear morphology of the osteocytes surrounding the implantation site, intensive bone remodeling, and the formation of new bone, eventually leading to the osseointegration of the implant.     

Influence of cyclosporin A therapy on bone healing around titanium implants: a histometric and biomechanic study in rabbits

BACKGROUND: Immunosuppressive agents may induce severe changes on bone metabolism. The purpose of the present study was to evaluate the influence of the administration of cyclosporin A (CsA) on the bone tissue around titanium implants. METHODS: Eighteen New Zealand rabbits were randomly divided into 2 groups of 9 each. The test group (CsA) received daily subcutaneous injection of CsA (10 mg/kg body weight) and the control group (CTL) received saline solution by the same administration route. Three days after therapy began, 2 implants (7.0 mm long and 3.75 mm in diameter) were inserted bilaterally at the region of the tibial methaphysis. After 4, 8, and 12 weeks the animals were sacrificed and biomechanical tests and histometrical procedures, consisting of the determination of the percentages of bone-implant contact and bone area within the limits of the implant threads, were performed. RESULTS: Intergroup analysis showed that the removal torque and the percentage of bone contact with the implant surface for CsA group were significantly lower than those of the CTL group at 12 weeks (28.5 and 39.2 N cm, P = 0.01; 7.76% and 18.52%, P = 0.02, respectively). CONCLUSION: The data from the present study suggest that long-term administration of cyclosporin A may negatively influence bone healing around dental implants.     

Thyroid hormones may influence cortical bone healing around titanium implants: a histometric study in rats

BACKGROUND: The aim of the present study was to evaluate, by histometric analysis, the influence of the thyroid hormones, triiodothyronine (T(3)) and thyroxine (T(4)), on bone healing around titanium implants inserted in rat tibiae. METHODS: Forty-two male Wistar rats were randomly assigned to the experimental groups: G1 = healthy animals (control; N = 15); G2 = hypothyroidism (N = 13); and G3 = hyperthyroidism (N = 14). Once alterations were confirmed by total serum levels of T(3) and T(4), one screw-shaped titanium implant was placed in the rat tibiae. Sixty days later, the animals were sacrificed, and undecalcified sections were obtained. Bone-to-implant contact (BIC), bone area within the limits of the implant threads, and bone density in a 500-microm-wide zone lateral to the implant were obtained separately for the cortical (zone A) and cancellous (zone B) bone regions. RESULTS: Intergroup analysis demonstrated that thyroid hormones may significantly affect cortical bone healing around titanium implants. Hyperthyroidism significantly increased the area of newly formed bone in zone A (P <0.05), whereas hypothyroidism significantly decreased the area of newly formed bone and bone density around the implant in zone A (P <0.05) compared to the healthy group. In addition, hyperthyroidism significantly increased BIC extension in zone A compared to hypothyroidism (P <0.05). CONCLUSION: Thyroid hormones may influence the healing process in the cortical bone around titanium implants placed in rats, whereas cancellous bone seems to be less sensitive to changes in T(3) and T(4) serum levels.