Bone Response to Implant-Supported Frameworks with Differing Degrees of Misfit Preload: In Vivo Study in Rabbits

PURPOSE

To study the bone response around implants placed in tibia of rabbits that supported misfitting superstructures secured with different degrees of preload.

MATERIALS AND METHODS

Twelve rabbits were provided with two terminal 10-mm and one intermediate 7-mm-long implant in each tibia. After an integration time of about 9 weeks, nine of the animals received one control framework each (n = 9), designed with good fit to all three implants. In the other tibia of these animals, and in both tibias in the remaining three rabbits, test frameworks (n = 15) were connected with a vertical misfit of about 1 mm to the intermediate implant. The intermediate set screws were tightened with a torque ranging from 15 Ncm to 26 Ncm in the different test frameworks. The fascia and skin was then sutured back over the implants. After a loading period of 2 to 3 weeks, the animals were sacrificed, and histomorphometric measurements were made and correlated to the different levels of preload of the central implant.

RESULTS

The mean bone-to-metal contact for the three best consecutive threads of the central implant was 40% for both test and control sites (p > .05). Compared to the other regions of the implant thread, less bone-to-metal contact was found at the tip of the test implant threads in the low preload group (p < .05). However, the same relation was not observed in the high preload group. A significant correlation was observed between increasing degree of preload in the central screw joint and increasing bone-to-metal contact, most obviously noticed at the tip of the implant thread (p < .01).

CONCLUSIONS

Misfit stress levels of clinical magnitudes do not seem to jeopardize osseointegration per se. On the contrary, clinical levels of preload stress seem to significantly promote bone remodeling at the tip of the implant thread.

Histological and histomorphometrical analyses of biopsies harvested 11 years after maxillary sinus floor augmentation with deproteinized bovine and autogenous bone

OBJECTIVE

The purpose of the present study was to histologically and histomorphometrically evaluate the long-term tissue response to deproteinized bovine bone (DPBB) particles used in association with autogenous bone and to compare particle size after 6 months and 11 years, in the same patients, in order to determine possible resorption.

MATERIAL AND METHODS

Twenty consecutive patients (14 women and six men) with a mean age of 62 years (range 48-69 years) with severe atrophy of the posterior maxilla were included in this study. Thirty maxillary sinuses with <5 mm subantral alveolar bone were augmented with a mixture of 80% DPBB and 20% autogenous bone. Eleven years (mean 11.5 years) after augmentation, biopsies were taken from the grafted areas of the 11 patients who volunteered to participate in this new surgical intervention. The following histomorphometrical measurements were performed in these specimens: total bone area in percentage, total area of the DPBB, total area of marrow space, the degree of DPBB-bone contact (percentage of the total surface length for each particle), the length of all DPBB particles and the area of all DPBB particles. The length and the area of the particles were compared with samples harvested from the same patients at 6 months (nine samples) and pristine particles from the manufacturer.

RESULTS

The biopsies consisted of 44.7+/-16.9% lamellar bone, 38+/-16.9% marrow space and 17.3+/-13.2% DPBB. The degree of DPBB to bone contact was 61.5+/-34%. There were no statistically significant differences between the length and area of the particles after 11 years compared with those measured after 6 months in the same patients or to pristine particles from the manufacturer.

CONCLUSION

DPBB particles were found to be well integrated in lamellar bone, after sinus floor augmentation in humans, showing no significant changes in particle size after 11 years. To cite this article: Mordenfeld A, Hallman M, Johansson CB, Albrektsson T. Histological and histomorphometrical analyses of biopsies harvested 11 years after maxillary sinus floor augmentation with deproteinized bovine and autogenous bone.

Short- and long-term animal studies with a plasma-sprayed calcium phosphate-coated implant

A commercially available hydroxyapatite (HA)-coating was investigated in a 4- and 24-week animal study. HA-coated and uncoated commercially pure (c.p.) titanium threaded implants were inserted in rabbit tibia and femur. Qualitative histology showed giant cells and macrophages around both types of implants. Histomorphometry demonstrated significantly more bone in contact to the HA-coated specimens at both follow-up periods. In contrast, bone area measurements (the amount of bone inside and/or outside the threads) revealed significantly higher percentages of bone around the uncoated c.p. titanium controls after 6 months of follow-up. The inferior amount of bone around the HA-coated implants in the longer-term perspective may relate to macrophage-induced resorption.

Bone tissue reactions to an electrophoretically applied calcium phosphate coating

Oral implants of a threaded design, calcium phosphate (CaP)-coated using an electrophoretic deposition technique, were compared to uncoated commercially pure (c.p.) titanium control in an animal study with 4 weeks and 6 months of follow-up, respectively. The 3D surface roughness of a CaP-coated implant was about three times greater than that of an uncoated control. Histomorphometric analyses of the direct bone-implant contact demonstrated a short-term advantage to the CaP-coated implants, whereas no significant difference to the uncoated titanium was found after 6 months. Comparison of the amount of bone inside or outside the threads showed similar values for test and control after 4 weeks. Significantly higher amounts of bone outside the uncoated c.p. titanium implants were measured after the long-term follow-up.

Diterpenes from the berries of Juniperus excelsa

From the hexane extract of berries of Juniperus excelsa, one new and four known diterpenes were isolated besides a known sesquiterpene. The structures of the known diterpenes were identified as isopimaric, isocommunic, (-)ent-trans communic and sandracopimaric acids, along with the sesquiterpene 4a-hydroxycedrol and the new compound which was elucidated as 3 alpha-acetoxylabda-8(17),13(16),14-trien-19-oic acid (juniperexcelsic acid). Cytotoxic activity of the hexane extract was investigated against a panel of cell line and found highly active against LNCaP, KB-V (+VLB) and KB-V (-VLB) cell lines. Furthermore, the hexane and methanol extracts, and the new compound were found to be moderately active against Mycobacterium tuberculosis.

The effect of static bone strain on implant stability and bone remodeling

Bone remodeling is a process involving both dynamic and static bone strain. Although there exist numerous studies on the effect of dynamic strain on implant stability and bone remodeling, the effect of static strain has yet to be clarified. Hence, for this purpose, the effect of static bone strain on implant stability and bone remodeling was investigated in rabbits. Based on Finite Element (FE) simulation two different test implants, with a diametrical increase of 0.15 mm (group A) and 0.05 mm (group B) creating static strains in the bone of 0.045 and 0.015 respectively, were inserted in the femur (group A) and the proximal tibia metaphysis (groups A and B respectively) of 14 rabbits to observe the biological response. Both groups were compared to control implants, with no diametrical increase (group C), which were placed in the opposite leg. At the time of surgery, the insertion torque (ITQ) was measured to represent the initial stability. The rabbits were euthanized after 24 days and the removal torque (RTQ) was measured to analyze the effect on implant stability and bone remodeling. The mean ITQ value was significantly higher for both groups A and B compared to group C regardless of the bone type. The RTQ value was significantly higher in tibia for groups A and B compared to group C while group A placed in femur presented no significant difference compared to group C. The results suggest that increased static strain in the bone not only creates higher implant stability at the time of insertion, but also generates increased implant stability throughout the observation period.

Healing of implant dehiscence defects with and without expanded polytetrafluoroethylene membranes: a controlled clinical and histological study

Bone augmentation around implant fixtures using the technique of guided tissue regeneration has been described in a number of reports. The aim of this study was to evaluate bone fill around dehiscence defects at matched defects randomly allocated to test (expanded polytetrafluoroethylene; Gore-Tex) or control treatments within the same patient. Six edentulous subjects were treated with overdentures supported by 2 fixtures ad modum Bränemark. In addition, 2 experimental 7-mm fixtures with nearly identical dehiscence defects on the labial aspect were placed in the anterior part of the mandible. Baseline defect heights ranged from 2.5 to 4.0 mm with 2 to 4 threads exposed. The test fixture dehiscence was covered with a Gore-Tex membrane secured with a cover screw. The experimental fixtures were exposed after 5 months at stage 2 surgery and measurements and photographs repeated. The fixtures were then removed with a trephine and processed for histological evaluation. Regeneration of a hard tissue resembling bone was observed in 4 of 6 cases treated with Gore-Tex, amounting to between 95 and 100% elimination of the dehiscence and total coverage of the threads. However, in one of these cases, histological evaluation showed that it was soft tissue and not bone, and in a further case soft tissue regeneration was apparent both clinically and histologically. In another case there was no significant regeneration at either test or control defects. Although there was a trend for the Gore-Tex-treated dehiscences to respond more favourably, the differences in clinical and histological measurements between test and control failed to reach statistical significance.

Protein adsorption to surface chemistry and crystal structure modification of titanium surfaces

Objectives

To observe the early adsorption of extracellular matrix and blood plasma proteins to magnesium-incorporated titanium oxide surfaces, which has shown superior bone response in animal models.

Material and Methods

Commercially pure titanium discs were blasted with titanium dioxide (TiO₂) particles (control), and for the test group, TiO₂ blasted discs were further processed with a micro-arc oxidation method (test). Surface morphology was investigated by scanning electron microscopy, surface topography by optic interferometry, characterization by X-ray photoelectron spectroscopy (XPS), and by X-ray diffraction (XRD) analysis. The adsorption of 3 different proteins (fibronectin, albumin, and collagen type I) was investigated by an immunoblotting technique.

Results

The test surface showed a porous structure, whereas the control surface showed a typical TiO₂ blasted structure. XPS data revealed magnesium-incorporation to the anodic oxide film of the surface. There was no difference in surface roughness between the control and test surfaces. For the protein adsorption test, the amount of albumin was significantly higher on the control surface whereas the amount of fibronectin was significantly higher on the test surface. Although there was no significant difference, the test surface had a tendency to adsorb more collagen type I.

Conclusions

The magnesium-incorporated anodized surface showed significantly higher fibronectin adsorption and lower albumin adsorption than the blasted surface. These results may be one of the reasons for the excellent bone response previously observed in animal studies.

Enhanced bone healing around nanohydroxyapatite-coated polyetheretherketone implants: An experimental study in rabbit bone

Objective

To investigate the bone response to threaded polyetheretherketone (PEEK) implants coated with nanohydroxyapatite.

Materials and methods

A total of 39 PEEK implants were coated with nanocrystalline hydroxyapatite and 39 uncoated implants were used as controls. The implant surface was characterized by optical interferometry and scanning electron microscope. The implants were inserted in the tibia and femur of 13 rabbits. After 6 weeks of healing, quantitative and qualitative analyses were performed.

Results

The test implants showed significantly higher removal torque test values compared with the control group. Histomorphometric evaluation demonstrated higher bone-to-implant contact for the test implants; however, there were no differences in bone area between the groups. Qualitative histological analyses demonstrated inflammatory cellular reactions in close vicinity of both implant surfaces. A two-cell layer of foreign body giant cells was observed irrespective of sample type.

Conclusion

Our findings demonstrate that implants with a threaded design render good stability to PEEK in both coated and uncoated implants. Nanohydroxyapatite-coated PEEK implants demonstrated improved bone formation compared with uncoated controls.

Enamel matrix derivative and titanium implants

AIM

The aim of present study was to evaluate if an enamel matrix derivative (Emdogain) may enhance bone formation and osseointegration of titanium implants, using a well-documented rabbit model.

MATERIAL AND METHODS

Thirty-six threaded commercially pure titanium (cp.ti.) implants were inserted in six New Zealand white rabbits. One implant was placed in each femur and two in each tibia. Prior to implant insertion approximately 0.5 mL of Emdogain (EMD) (test) or the vehicle gel (PGA: propylene glycol alginate) (control) was injected into the surgically prepared implant site. The follow-up time was 6 weeks. Biomechanical evaluations by resonance frequency analysis (RFA) and removal torque measurements (RTQ) were performed. Histomorphometrical quantifications were made on ground sections by measurements of the percentage of bone-to-metal contact, bone area inside the threads as well as outside the threads (mirror image). Bone lengths along the implant surface were also measured and used for shear strength calculations.

RESULTS

The results demonstrated no beneficial effects from the EMD treatment on bone formation around titanium implants in any of the tested parameters. Significant differences were demonstrated with removal torque test and shear force calculations for the control implants. No other parameter demonstrated a statistically significant difference.

CONCLUSION

The results of the present study may indicate that EMD does not contribute to bone formation around titanium implants. This observation may indicate that the bone formation that occurs after EMD treatment in periodontal defects is the result of functional adaptation. However, further research is required to evaluate the effect of EMD treatment on bone formation.

Application of oxygen ion implantation to titanium surfaces: effects on surface characteristics, corrosion resistance, and bone response

BACKGROUND

The surface oxide layer of titanium plays a decisive role in determining biocompatibility. However, there are some reports demonstrating that the natural oxide film may not be sufficiently protective in the aggressive biologic environment.

PURPOSE

The goal of this study was to examine the effectiveness of a thick oxide layer on corrosion resistance in vitro and the bone formation around titanium implants in vivo.

MATERIALS AND METHODS

A plasma source ion implantation (PSII) method was used to increase the thickness of the surface oxide layer. Several instruments were employed to confirm the surface properties before and after the surface modification. Potentiodynamic polarization measurements in a phosphate-buffered saline (PBS) solution were carried out to investigate corrosion resistance in vitro. Bone formation around this surface-modified specimen was examined in a rabbit model and assessed in histomorphometry.

RESULTS

Improved corrosion resistance was demonstrated by the potentiodynamic polarization measurements. Light microscopic histomorphometry showed that all implants were in contact with bone and had some proportion of bone within the threads at 4 weeks; however, there were no significant differences compared with as-machined controls.

CONCLUSIONS

The results indicate that in spite of improved corrosion resistance in vitro, a thick oxide layer fabricated with the PSII method does not influence early bone formation around titanium implants in vivo.

Improved bone ingrowth and fixation with a thin calcium phosphate coating intended for complete resorption

Bonit is claimed to be a resorbable electrochemically deposited calcium phosphate coating consisting mainly of brushite, which is a hydroxyapatite precursor. This study involved a comparison of Ti6Al4V screw-shaped implants with and without a 15 +/- 5 microm Bonit coating in rabbit tibia and femur, after 6 and 12 weeks of insertion. The biomechanical removal torque test showed significantly increased values for the coated implants after 12 weeks (p < 0.05) but not after 6 weeks of integration. Higher bone-implant contact was found for the coated implants in the tibia after 6 weeks and for both tibial and femoral screws after 12 weeks (p < 0.05). There was no difference in the inflammatory reaction around the implants, and possible grains of the coating could be detected after 6 weeks, but not after 12 weeks of follow-up. This unloaded short-term study has shown promising results for the easily applicable and resorbable coat (Bonit) compared to uncoated titanium-alloy implants.

A new approach to demonstrate cellular activity in bone formation adjacent to implants

Bone tissue repeatedly formed in titanium 6-aluminum 4-vanadium rabbit bone harvest implants was collected in vivo at various times between 12 days and 5 weeks. Qualitative and quantitative examinations on undecalcified thin sections were performed in the light microscope. The amount of bone tissue was calculated on routinely stained sections. Alkaline (ALP) and acid phosphatase (ACP) enzyme activities were investigated. We also performed immunohistological detection of bone matrix proteins. Increasing bone density as well as an increasing mineralization of the tissue was observed in the biopsies with increasing time. The ALP and ACP activities were similar at short times (12 days and 2 weeks). With increasing time the ALP activity was stronger than that of ACP. The results from the immunohistochemical detection of osteonectin, osteopontin, bone sialoprotein, and collagen I and II demonstrated changes in the tissue differentiation with time. The tissue formation in the canal became more mature with time of ingrowth, as observed with the various techniques used in this study. Owing to these methodical developments, undecalcified ground sections may be used for detailed analysis of various phases of tissue formation in close proximity to implants.

Effect of submicron polyethylene particles on an osseointegrated implant: an experimental study with a rabbit patello-femoral prosthesis

In a rabbit model of a weight bearing, articulating prosthetic joint we repeatedly injected submicron particles of Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) produced in a hip simulator. The contralateral knee with the same prosthesis was injected with carrier (NaCl) without UHMWPE. Histomorphometrical studies on undecalcified cut and ground sections at 26 and 42 weeks involved quantifications of the entire bone to metal contact and the bone area around each implant. We found no statistically significant differences between test and control groups, and the UHMWPE debris did not induce any significant osteolysis, indicating that an osseointegrated implant with a sealed interface may not be affected by UHMWPE debris or progress to aseptic loosening.

Biofilm formation on polyetheretherketone and titanium surfaces

Objective

Polyetheretherketone (PEEK) is a polymer used in devices in orthopedic and dental rehabilitation. The aim of this in vitro study was to compare biofilm formation by a range of important oral bacterial species on PEEK, blasted PEEK, commercially pure titanium (cp-Ti), and titanium-6 aluminium-4 vanadium (Ti6Al4V).

Material and methods

Coin-shaped samples were manufactured, and the surfaces were characterized using optical interferometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and contact angle measurements. Bacterial species of Streptococcus sanguinis, Streptococcus oralis, Enterococcus faecalis, and Streptococcus gordonii were cultured on the four material surfaces for varying amounts of time. Biofilms were quantified following staining with crystal violet.

Results

Roughness and contact angle results showed blasted PEEK > PEEK > cp-Ti = Ti6Al4V. There was increased biofilm formation on blasted PEEK by S. sanguinis, S. oralis, and S. gordonii, whereas the bacterial adhesion was similar on PEEK, cp-Ti, and Ti6Al4V. The bacterial growth of E. faecalis was significantly higher on cp-Ti compared with the other three groups.

Conclusion

The results, taking into consideration the biofilm formation, suggest that PEEK should perform as well as cp-Ti or TiAl6V4 when used as a dental restorative material.

Tissue reactions adjacent to well-fixed hydroxyapatite-coated acetabular cups. Histopathology of ten specimens retrieved at reoperation after 0.3 to 5.8 years

Ten acetabular cups coated with hydroxyapatite (HA) had originally been inserted in five primary and five revision total hip replacements. The thickness of the HA was 155 +/- 35 microm. The cups, which were well-fixed, were retrieved, with their adherent tissue, at reoperation after 0.3 to 5.8 years because of infection (five hips), wear of polyethylene (three hips), and instability (two hips). Undecalcified sections showed a direct contact between bone and osteoid-like tissue which had formed directly onto the HA coating. The area within the threads and their mirror images, as well as the implant-tissue interfaces consisted of similar amounts of bone and soft tissue. Degradation of HA was seen in all hips. The mean thickness of the remaining HA coating was 97 microm (95% CI 94 to 101). The metal interface comprised 66% HA. The HA-tissue interface contained more bone than soft tissue (p = 0.001), whereas the metal-tissue interface included more soft tissue than bone (p = 0.019). Soft tissue at the implant interface and poor replacement of HA by bone may interfere with long-term fixation.

Inaccuracy of acetabular reaming under surgical conditions

Press-fit uncemented acetabular components require accurate implant-bone cavity fit. Ten cavities produced during actual hip arthroplasty using debris-retaining reamers were replicated in dental alginate. An experimental reamer with better cutting prepared 12 acetabulae in mortuo under similar conditions. Positives in dental stone were measured on a coordinate measuring center. Spheres of best-fit and variation of each point from these spheres were calculated. Control cavities in polyurethane foam were measured to estimate casting errors. Diametral errors of conventionally reamed cavities averaged 2.1%, whereas experimental reamers' cavities varied by 0.5% (P < .005). Overall surface variation from hemispheric form in conventionally reamed cavities exceeded the experimental reamer's results (P < .005). Conventional acetabular reamers cut bone inaccurately. Reamers designed for improved bone cutting reduce cavity errors.

Extracting 3D information on bone remodeling in the proximity of titanium implants in SRμCT image volumes

Bone-implant integration is measured in several ways. Traditionally and routinely, 2D histological sections of samples, containing bone and the biomaterial, are stained and analyzed using a light microscope. Such histological section provides detailed cellular information about the bone regeneration in the proximity of the implant. However, this information reflects the integration in only a very small fraction, a 10 μm thick slice, of the sample. In this study, we show that feature values quantified on 2D sections are highly dependent on the orientation and the placement of the section, suggesting that a 3D analysis of the whole sample is of importance for a more complete judgment of the bone structure in the proximity of the implant. We propose features describing the 3D data by extending the features traditionally used for 2D-analysis. We present a method for extracting these features from 3D image data and we measure them on five 3D SRμCT image volumes. We also simulate cuts through the image volume positioned at all possible section positions. These simulations show that the measurement variations due to the orientation of the section around the center line of the implant are about 30%.

Cutting directions of bone with biomaterials in situ does influence the outcome of histomorphometrical quantifications

Ten commercially pure titanium implants were inserted in the tibia of ten mature New Zealand white rabbits for a healing period of 3 months. Cut and ground sections were performed on transversely and longitudinally cut tibia bone with implants in situ. Each implant with surrounding bone was processed by (a) dividing it into two parts by cutting transversely through the tibia and then (b) cutting one of the implant halves longitudinally through the tibia. In both cases 10 microns sections were made. Computerized histomorphometrical calculations of the bone-to-metal contact and the bone area in the threads were performed and comparisons of the differently cut sections were made for the same implant. Larger amounts of bone-to-metal contact and bone area in the threads were observed in the longitudinally cut samples in comparison to transversely cut ones. A strong statistically significant difference was obtained when comparing the transversely with the longitudinally cut samples with respect to bony contacts in the cortical region, demonstrating 25% more bone-to-metal contact lengths in the longitudinal cutting direction of the tibia. Quantitative histomorphometrical comparisons should, therefore, be performed on samples that are cut in the same direction.

Bone-Tissue Formation and Integration of Titanium Implants: An Evaluation with Newly Developed Enzyme and Immunohistochemical Techniques

BACKGROUND

Examination of the tissue surrounding retrieved implants involve routine investigations on cut and ground sections. Undecalcified sections with implants in situ are histologically stained followed by qualitative and quantitative observations of the tissue response to the implants by light microscopy.

PURPOSE

A novel technique that allows for the accurate definition and quantification of enzymes involved in bone formation (alkaline phosphatase) and resorption (acid phosphatase) in the tissue is presented.

MATERIALS AND METHODS

Commercially pure titanium and titanium alloy (Ti6Al4V) implants were retrieved after 6 and 12 weeks of healing in rabbit bone. In addition, 4-week specimens from commercially pure titanium bone harvest chambers placed in rabbit bone were used. Undecalcified cut and ground sections were produced and evaluated with enzyme and immunohistochemical staining techniques.

RESULTS

The titanium implants retrieved after 6 weeks of insertion in rabbit bone revealed a higher activity of both alkaline phosphatase and acid phosphatase activity compared to the implants followed for 12 months. The former samples revealed ongoing bone-tissue remodeling in the interface, whereas the latter ones showed steady-state bone conditions. Applying the new technique allowed for investigation of various bone proteins present in the tissue that had formed inside titanium canals of harvest chambers at various times of follow-up.

CONCLUSIONS

The combination of routine histologic stainings with enzyme and immunohistochemical technique of cut and ground specimens is a valuable tool in the investigations of retrieved implants from humans and animals. This novel technique now may be used to describe the state of bone regeneration in the interface zone associated with implant research.