Fibrous Tissue Interposition Research Articles

Short Dental Implants: State of the Art and Systematic Review


 Introduction: The success of dental implants is due to their ability to osseointegrate, with direct contact of the implant surface with the bone, without the interposition of fibrous tissue. Because many patients do not receive implant treatments because they do not have adequate or sufficient bone height, the development of shorter implants could meet the needs of these patients. Objective: To carry out a brief systematic review to present the state of the art of using short implants. Methods: The present study followed a concise systematic review model. The search was carried out in the PubMed, Embase, Ovid, Cochrane Library, Web Of Science, and Scopus databases. The quality of the studies was based on the GRADE instrument and the risk of bias was analyzed according to the Cochrane instrument. Results: Short implants are an increasingly common alternative to other surgical techniques in areas where bone availability is reduced. Despite the advantages they offer, a variety of biological repercussions have been described in the literature that can even lead to their loss. Conclusion: The studies analyzed showed that short implants are a reliable, safe, and practical alternative to be used in situations with reduced bone height. They do not present bone loss or resorption over the years, nor the risk of fracture or any damage to patients, as long as they have an adequate design, correct technique, and meticulous planning.

Osteoconductivity of bioactive Ti-6Al-4V implants with lattice-shaped interconnected large pores fabricated by electron beam melting.

Additive manufacturing has facilitated the fabrication of orthopedic metal implants with interconnected pores. Recent reports have indicated that a pore size of 600 μm is beneficial for material-induced osteogenesis. However, the complete removal of the metal powder from such small pores of implants is extremely difficult especially in electron beam melting (EBM). We therefore developed a new type of Ti-6Al-4V implant with lattice-shaped interconnected pores measuring 880-1400 μm, which allowed for the easy removal of metal powder. This implant was fabricated by EBM and treated with NaOH, CaCl2, heat, and water (ACaHW treatment) to render the metal surface bioactivity. In the present study, the mechanical and chemical property of the implants and the biocompatibility were evaluated. The SEM and micro-CT images demonstrated the 3D interconnectivity of the porous structures. The average porosity of the porous titanium implant was 57.5%. The implant showed maximum compressive load of 78.9 MPa and Young's modulus of 3.57 GPa which matches that of human cortical bone. ACaHW treatment of the porous Ti-6Al-4V implants induced apatite formation in simulated body fluid in vitro. The ACaHW-treated porous implants harvested from rabbit femoral bone showed direct bonding of bone to the metal surface without interposition of fibrous tissue. The porous ACaHW-treated implant had a higher affinity to the bone than the untreated one. The mechanical strength of implant fixation assessed using the push-out test was significantly higher in the ACaHW-treated implant than in untreated one. FE-SEM analysis and EDX mapping after push-out test of solid implants showed a lot of bone tissue patches on the surface of the ACaHW-treated implant. These results suggest that the new ACaHW-treated Ti-6Al-4V implant with lattice-shaped interconnected pores is a superior alternative to conventional materials for medical application.

Effect of interposed tissue and contamination on the initial stability of a highly porous press-fit acetabular cup.

For biologic fixation, press-fit acetabular cups should have initial stability with minimal micromotion and osteoconductive surfaces in contact with bone. Inadequate exposure potentially influences initial stability by increasing the possibility of soft tissue interposition and contamination at the implant-tissue interface. A sawbone model was used to examine how interposed tissue and contamination influence initial cup stability. Seven groups (n = 4) were tested with varying levels of interposed fatty and fibrous tissue placed around the rim of the cup. 54 millimeter in diameter highly porous hemispherical acetabular cups (Stryker, Mahwah NJ) and 54 mm reamed cavities in sawbone blocks were used. Shells were seated and maximum lever out force was recorded for each sample. Cups with fibrous tissue spaced evenly along the rim had a lever out force that was 150% of the control (107 ± 6 vs. 150 ± 12N, p = 0.005), and fatty tissue contamination had a lever out force that was 140% of the control (143 ± 18 vs. 107 ± 6N, p = 0.04). Cups with fibrous tissue placed eccentrically along the rim had a lever out force that was double the control 107 ± 6 N vs. 200 ± 15 N (p = 0.001). Surprisingly, fatty tissue contamination and fibrous tissue interposition at the rim increased initial stability. The eccentrically interposed tissue forced the opposite pole of the cup into the bone, resulting in a more secure press-fit. However, soft tissue interposition decreases implant/bone apposition, and the effect on long term fixation is unknown. Statement of Clinical Significance: Soft tissue interposition between the bone and cup may provide higher initial stability, but its long-term effects are unknown. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

The Selective Serotonin Reuptake Inhibitor Fluoxetine Directly Inhibits Osteoblast Differentiation and Mineralization During Fracture Healing in Mice.

Chronic use of selective serotonin reuptake inhibitors (SSRIs) for the treatment of depression has been linked to osteoporosis. In this study, we investigated the effect of chronic SSRI use on fracture healing in two murine models of bone regeneration. First, we performed a comprehensive analysis of endochondral bone healing in a femur fracture model. C57/BL6 mice treated with fluoxetine, the most commonly prescribed SSRI, developed a normal cartilaginous soft-callus at 14 days after fracture and demonstrated a significantly smaller and biomechanically weaker bony hard-callus at 28 days. In order to further dissect the mechanism that resulted in a smaller bony regenerate, we used an intramembranous model of bone healing and revealed that fluoxetine treatment resulted in a significantly smaller bony callus at 7 and 14 days postinjury. In order to test whether the smaller bony regenerate following fluoxetine treatment was caused by an inhibition of osteogenic differentiation and/or mineralization, we employed in vitro experiments, which established that fluoxetine treatment decreases osteogenic differentiation and mineralization and that this effect is serotonin-independent. Finally, in a translational approach, we tested whether cessation of the medication would result in restoration of the regenerative potential. However, histologic and μCT analysis revealed non-union formation in these animals with fibrous tissue interposition within the callus. In conclusion, fluoxetine exerts a direct, inhibitory effect on osteoblast differentiation and mineralization, shown in two disparate murine models of bone repair. Discontinuation of the drug did not result in restoration of the healing potential, but rather led to complete arrest of the repair process. Besides the well-established effect of SSRIs on bone homeostasis, our study provides strong evidence that fluoxetine use negatively impacts fracture healing. © 2017 American Society for Bone and Mineral Research.

Novel Resorbable and Osteoconductive Calcium Silicophosphate Scaffold Induced Bone Formation.

This aim of this research was to develop a novel ceramic scaffold to evaluate the response of bone after ceramic implantation in New Zealand (NZ) rabbits. Ceramics were prepared by the polymer replication method and inserted into NZ rabbits. Macroporous scaffolds with interconnected round-shaped pores (0.5–1.5 mm = were prepared). The scaffold acted as a physical support where cells with osteoblastic capability were found to migrate, develop processes, and newly immature and mature bone tissue colonized on the surface (initially) and in the material’s interior. The new ceramic induced about 62.18% ± 2.28% of new bone and almost complete degradation after six healing months. An elemental analysis showed that the gradual diffusion of Ca and Si ions from scaffolds into newly formed bone formed part of the biomaterial’s resorption process. Histological and radiological studies demonstrated that this porous ceramic scaffold showed biocompatibility and excellent osteointegration and osteoinductive capacity, with no interposition of fibrous tissue between the implanted material and the hematopoietic bone marrow interphase, nor any immune response after six months of implantation. No histological changes were observed in the various organs studied (para-aortic lymph nodes, liver, kidney and lung) as a result of degradation products being released.

Healing responses following transverse root fracture: a historical review and case reports showing healing with (a) calcified tissue and (b) dense fibrous connective tissue

The understanding and management of transverse intra-alveolar root fractures has evolved to its current high level of sophistication and clinical success from foundations laid down by histological studies as early as the mid-nineteenth century. The aim of the review was to highlight those earlier histological reports and studies that have contributed to the current understanding of the biological processes involved in the healing of transverse root fractures. Healing of a transverse root fracture by calcified tissue was demonstrated histologically by Howe in 1926, while Boulger in 1928 showed the two other patterns of root fracture healing, namely the interposition of fibrous connective tissue and the interposition of bone and periodontal ligament around both fractured segments. Other major histological reports around that time came from members of the so-called 'The Vienna group of Illinois', who had a significant influence in the development of oral biology worldwide. Other important reports and an experimental study emanated from Germany and Switzerland in the late 30s and early 40s, followed in the 1950s and early 1960s by histological material principally from Sweden, Denmark, France, the USA and Britain. Jens Andreasen and Erik Hjörting-Hansen's landmark paper in 1967 included new histological reports and a classification of healing responses following transverse root fractures. The expansion of knowledge related to root fractures since that time has been exponential, with major contributions from Scandinavia and several other countries. Accompanying the historical review are two case reports with histology of root fracture healing by (a) calcified tissue and (b) dense fibrous connective tissue. The role of the pulp and the periodontal ligament in the repair process is described and the clinical significance discussed with particular emphasis to diagnosis and orthodontic management.

In‐vivo behavior of Si‐hydroxyapatite/polycaprolactone/DMB scaffolds fabricated by 3D printing

Scaffolds made of polycaprolactone and nanocrystalline silicon-substituted hydroxyapatite have been fabricated by 3D printing rapid prototyping technique. To asses that the scaffolds fulfill the requirements to be considered for bone grafting applications, they were implanted in New Zealand rabbits. Histological and radiological studies have demonstrated that the scaffolds implanted in bone exhibited an excellent osteointegration without the interposition of fibrous tissue between bone and implants and without immune response after 4 months of implantation. In addition, we have evaluated the possibility of improving the scaffolds efficiency by incorporating demineralized bone matrix during the preparation by 3D printing. When demineralized bone matrix (DBM) is incorporated, the efficacy of the scaffolds is enhanced, as new bone formation occurs not only in the peripheral portions of the scaffolds but also within its pores after 4 months of implantation. This enhanced performance can be explained in terms of the osteoinductive properties of the DBM in the scaffolds, which have been assessed through the new bone tissue formation when the scaffolds are ectopically implanted.

Poster 156: A Histological Study on Several Implants for Augmentation Rhinoplasty in Mouse Calvaria

This study aimed at histologically evaluating Silicone, Gore-tex, AlloDerm and Medpor implants for augmentation rhinoplasty after grafting in the subperiosteal pocket of mouse calvarium. Twenty four male ICR mice were used. Silicone, Gore-tex, AlloDerm and Medpor were grafted respectively into the subperiosteal pocket of the frontal bone. The animals were sacrificed at 1, 4 and 8 weeks after operation. Histological analysis was performed using a light microscope after H-E staining. n/a In the silicone group, the silicone was well enclosed by thin fibrous tissue at 1 week, and this became thicker and stable at 4 weeks and 8 weeks without any destruction or resorption. In the Gore-tex group, the Gore-tex was surrounded by thin fibrous tissue without any destruction and resorption. Some cells were observed in the Gore-tex at 1, 4 and 8 weeks. In the AlloDerm group, AlloDerm was enclosed by fibrous tissue, and cell infiltration was observed at 1, 4 and 8 weeks. In the Medpor group, there was no inflammation, destruction or resorption of Medpor and it contacted directly to the bone without interposition of fibrous tissue. The porous area was filled by bone or soft tissue at 4 and 8 weeks. These results suggest that Gore-tex, AlloDerm and Medpor grafts are more stable than Silicone after grafting.

Amphiphilic bonder improves adhesion at the acrylic bone cement–bone interface of cemented acetabular components in total hip arthroplasty: in vivo tests in an ovine model

Even following the introduction of the "third generation" cementing technique, an improvement of the fixation of the acetabular component similar to that of the femoral has not been shown in clinical studies. The goal of the present study was to achieve a better stability with the use of an amphiphilic bonder while preserving the mechanically important subchondral sclerosis. In a total of 20 sheep, a cemented total hip replacement was implanted. In the treatment group (n = 10), the implantation was carried out following surface conditioning of the acetabular bed with an amphiphilic bonder. All the sheep were followed for 9 months. To assess the biocompatibility, the osseous ingrowth at the cement-bone interface was depicted with the help of an in vivo fluorescent marking of the osteoblasts. Additionally, conventional radiographs were obtained over the course of treatment. Finally, the ovine pelvic regions were split following a standardized technique allowing for histological evaluation of the cement-bone interfaces. The acetabular components of the treatment group revealed a stable cement-bone compound. In the control group, the implants were easily dislodged from their beds. This finding was consistent with the radiological and histological results, which had revealed increased, progressive lytic radiolucent lines and the interposition of fibrous tissue at the cement-bone interface in the control group compared to the treatment group. The bonder was biocompatible. Following the application of the bonder, the cemented acetabular components revealed an improved stability without signs of inflammation or neoplasia in a viable acetabular osseous bed. With the help of this technique, the in vivo longevities of cemented acetabular components can be increased in the clinical setting without sacrificing the biomechanical relevant subchondral sclerosis.

Bone welding – A histological evaluation in the jaw

The expansion of biodegradable osteosynthesis systems in clinical application correlates well to the progress in development of new materials as to the improvement of application methods. One of those new application methods is the ultrasound-aided insertion of Resorb-X pins. The aim of this study was the histological evaluation of possible thermal damage to bone due to the ultrasound insertion. For this purpose, condylar neck fractures in 12 sheep were produced, repositioned and fixed by Resorb-X plates and pins. The animals were sacrificed in two groups, one after 2 weeks and one after 9 weeks. The bone-pin interlinkage and the structure of the bone were histologically evaluated. After 2 weeks a tight bone-polymer interlinkage was seen. Neither a pronounced foreign body reaction nor an interposition of fibrous tissue at the interface or a thermally induced necrosis was observed. The late phase of wound healing after 9 weeks showed pathomorphological characteristics within the normal range of bone healing. The bone seemed to be free of any alteration caused by process engineering. We conclude that thermal stress caused by ultrasound-aided pin insertion does not lead to cellular reaction in the bone. The fast and easy application of this improved biodegradable osteosynthesis system will bring a clear advantage in clinical use.

Immediate Loading of Dental Implants: Overview and Rationale

Brånemark established the concept of osseointegrated dental implants as a predictable modality for treatment of edentulous patients. He defined osseointegration as bone-to-implant contact at the microscopic level. Osseointegration was a revolutionary concept in implant dentistry. While earlier pioneers never considered direct bone anchoring of the implant, and even established interposition of fibrous tissue between implant and bone as desirable to mimic periodontal ligament function, Brånemark et al. demonstrated that direct bone apposition at the implant surface was not only possible, but long lasting.

Étude de deux types d’implants dentaires pour la mise en charge immédiate (implants à expansion et à clavettes) chez le chien beagle

Titanium implants have become a treatment of choice for total or partially edentulous patients. The method, however, requires a double surgical time and the placement of the dental prosthesis after a healing phase of 3 to 6 months during which the patients have a toothless mandible with the top of the implants emerging at the gengiva. Immediate loading of standard implants is responsible for micromotions which induce implant failure. New designs of implants would allow an immediate anchoring in the bone, would prevent the shearing forces and would precociously authorize the setting of the prosthesis. We made an experimental study in the Beagle dog. After partial tooth removal, two types of implants were placed (expansion implants and locking pin implants). After 2 weeks, the implants were covered with a gold-palladium prosthesis and left in place during 12 weeks. After sacrifice, a study by resonance frequency (ISQ) and histomorphometry was done. The two types of implants were covered by the same quantity with bone (volume and interface) without interposition of fibrous tissue. The locking pin implants were associated with an increase in the ISQ parameter of stability, higher than that of the expansion implants. The locking pin implant, tested in the dog which has a chewing function close to man, appears interesting for the immediate loading with dental prosthesis.

Bilayered calcium phosphate coating to promote osseointegration of a femoral stem prosthesis.

A bilayered bioactive-gradient coating, consisting of a superficial layer of biphasic calcium phosphate (BCP) and a deep layer of hydroxyapatite (HA), promotes faster osseointegration and higher shear strength in non-loading conditions than do monolayer BCP or HA coatings. This study evaluated the biofunctionality of this coating in weight-bearing conditions at 6 and 12 months. The coating was plasma-sprayed on the metaphyseal portion of a sandblasted Ti6Al4V canine femoral prosthesis implanted using the surgical press-fit technique. An identical uncoated stem served as the control. Metaphyseal bone-to-implant apposition was increased for coated ( approximately 90% and 80% respectively at 6 and 12 months) as compared to uncoated implant ( approximately 7% at 6 and 12 months). Limited bone apposition was observed at the diaphyseal level. After 12 months, the uncoated implant interface consisted of well-organized, active fibrous tissue, whereas only inactive fibrous tissue interposition was observed at diaphyseal levels of the coated implant. At 6 months, the mineralization apposition rate (MAR) was similar, regardless of implant or bone structures. At 12 months, a significant decrease of MAR was observed around the uncoated implant. Transmission electron microscopy studies of the interface showed precipitation of biological apatite crystals in close association with mineralized collagenous bone matrix. Our results suggest a direct relationship between bioactivity and enhanced bone formation. The sandwich coating used is effective in promoting massive metaphyseal osseointegration, which ensures mechanical stability for early weight-bearing and should prevent long-term complications.

Bone growth response with porous hydroxyapatite granules in a critical sized lapine tibial-defect model

This study evaluated the tissue reaction to porous hydroxyapatite (HA) granules in a critical sized tibial-defect of New Zealand white rabbits for a period of 2, 6, 12 and 24 weeks. Physicochemical characterizations of the granules were done using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and fourier transform infrared spectroscopy to analyse the microstructure, composition, phase purity crystallinity and functional groups of HA. Prior toin vivotesting, the HA granules had proved to be biocompatible and cytocompatibleen route in vitrostudies using L929 mouse fibroblast cells. In the histologic evaluation, as early as 2 weeks, bone ingrowth was observed in the pores and interstices of the granules forming a network of bony trabeculae and over 6, 12 and 24 weeks, it was seen that the granules assisted in bone formation. Fluorochrome multilabels of yellow, red and orange lines showed active sites of bone mineralization in progress in the pores and periphery of the granules. Good osteointegration of the granules with the host bone was observed. There was neither inflammation nor fibrous tissue interposition while resorption of the material was in effect a slow process, since the HA granules still persisted after 24 weeks.

The effect of pulsed electromagnetic fields on the quality of cage-instrumented lumbar vertebral fusion in the ovine model

Alex Ghanayem, MD, Maywood, IL, USA; Mike Larson, DVM, Logan, UT, USAIntroduction: Threaded interbody cages have come into widespread use. Fusion rates are high but not perfect. Problems noted on postoperative radiographs after cage insertion include radiolucency around the cage, indicating a fibrous tissue at the bone–cage interface. Other problems include normal-appearing postoperative radiographs but failure of bony consolidation. Intrinsic and extrinsic factors have been modified in search of increasing fusion rates in cage constructs, including the use of bone graft substitutes and implantable direct current stimulation in a sheep model. External pulsed electromagnetic fields (PEMF) is another way to provide electrical stimulation to improve the fusion/bone graft incorporation process and may enhance the cage fusion rate. This study examines the efficacy of using an externally applied PEMF in promoting bone growth through and around an anterior lumbar cage construct in the ovine model.Methods: Twelve sheep underwent an anterior cage fusion procedure at the L4–5 level using a left retroperitoneal surgical approach. The interspace was distracted and a single working tube placed on the left lateral surface of the disc space. The interspace was then reamed and tapped. A threaded titanium fusion cage (Interfix; Medtronic-Sofamor Danek, Memphis, TN) was then placed transversely across the disc space. Cages were packed with morsilized autogenous ICBG. Six animals were randomly selected and fitted with a customized external PEMF device (Spinal Stim; Orthofix) that provided 4 hours of stimulation every 24-hour cycle. The other six animals did not receive stimulation and served as a control group. At 16 weeks after surgery, animals were euthanized. Specimens were removed en bloc from T12 to S1 and radiographed in the arteroposterior and lateral projections. Lateral flexion and extension radiographs were also obtained. The radiographs were blindly evaluated for the following characteristics: obvious lucency at the cage–vertebral end plate junctions, sclerosis or reactive bone at the cage–vertebral end plate junctions, no lucency or reactive bone at the cage–vertebral end plate junctions, definite bridging bone across the interspace and the absence or presence or motion, or the appearance of lucencies at the cage–vertebral end plate junctions on flexion-extension radiographs. Specimens were prepared for histologic evaluation and surface-stained with hemotoxylin and eoson. Histologic analysis was completed blindly using the following criteria: the presence or absence of a tight interface between the cage and the surrounding bone without fibrous tissue interposition, the presence or absence of bridging bone from one vertebral body, through the cage, to the other body and the presence or absence of bridging bone from one vertebral body, through the cage or around a portion of the cage, that extended to the other body. Criteria for a successful fusion included no lucency or motion on plain radiographs, the presence of tight cage–bone interfaces without fibrous tissue interposition and bridging bone through the cage on histologic evaluation. The lack of lucencies and motion on plain radiographs would not qualify as a successful fusion unless there were confirmation of fusion on the histologic analysis. Lucencies around the cages, motion on flexion-extension radiographs, fibrous tissue interposition at the cage–vertebral body interface and lack of bridging bone on histology would be classified as not fused.Results: All 12 sheep completed the protocol. One animal experienced transient weakness in the hind limb opposite to the side of cage insertion, which resolved spontaneously over the course of 3 days. Radiographs with lucencies always correlated with fibrous tissue at the cage–vertebral body interface on histologic evaluation. The absence of lucencies, however, did not always predict histologic fusion. Four of the six animals in the PEMF group were judged to have a successful fusion. In the control group, one animal was judged to be successfully fused and one was thought to have a partial fusion. If this control animal is considered a success, then the fusion rates was two of six in the control group.Discussion: Previous studies in sheep have shown recombinant human bone morphogenetic protein or internal direct current stimulation of an anterior cage construct can increase the fusion rate. It should be noted that radiographs without evidence of lucencies or motion did not always predict a successful fusion histologically, thus reaffirming a shortcoming of plain radiographs in assessing the success of a cage fusion. Radiographic bridging bone, however, was predictive of a successful fusion. This study has shown that the use of a nonimplantable PEMF device, with 4 hours of stimulation per day, also yields a significant increase in the fusion rate of an anterior cage–autogenous graft fusion construct.

Testing bone substitutes in a small animal model of revision arthroplasty.

This study evaluated a modification of the rat-pin model to enable testing of bone substitute materials. The model was characterized using the ceramic, beta-tricalcium phosphate (betaTCP) as a filler. A 1 mm wide, 3.6 mm deep defect was created around a stainless steel (SS) implant in the proximal tibia of a rat. This defect was filled with a ceramic powder. Large particles (90-312microm) of betaTCP were mixed with Gelfoam to form a paste which was then molded around the proximal end of either an uncoated SS pin or a pin coated with hydroxyapatite (HA). The pin with its ceramic collar was then implanted into the proximal tibia of 16 male Sprague Dawley rats. Two animals with coated implants and two with uncoated implants were sacrificed at 3, 6, 14 and 26 weeks. Longitudinal sections of each tibia were stained with toluidine blue and labeled for tartrate resistant acid phosphatase (TRAP). There was initial fibrous tissue interposition around the implants which was completely remodeled around the HA coated pins but which persisted in apposition to the SS pins. The remodeling process peaked at 3 weeks around the HA coated pins and at 6 weeks around the uncoated implants. There was little remodeling around either implant by 26 weeks. There was considerable residual betaTCP present which was well tolerated as the particles were often encased in bone. The model has several characteristics of revision arthroplasty and the results demonstrate the suitability of this model for testing bone substitutes.

Considerations preliminary to the application of early and immediate loading protocols in dental implantology.

In oral implantology, a 3-6 month stress-free healing period is presently accepted as a prerequisite to achieve bone apposition without interposition of a fibrous scar tissue. This protocol was introduced by Brånemark and co-workers in 1977. The aim of the present paper is to review the reasons that led Brånemark and collaborators to require long delayed loading periods. It is shown that the requirement for long delayed loading periods was drawn from the initiation and development periods of their original clinical trial. Demanding conditions were met involving simultaneously: 1) patients with poor bone quality and quantity, 2) non-optimized implant design, 3) short implants, 4) non-optimized surgical placement, 5) non-optimized surgical protocol and 6) biomechanically non-optimized prosthesis. Extrapolation of the requirement for long healing periods from these particular conditions to more standard situations involving refined surgical protocols and careful patient selection might be questioned. Albeit premature loading has been interpreted as inducing fibrous tissue interposition, immediate loading per se is not responsible for fibrous encapsulation. It is the excess of micromotion during the healing phase that interferes with bone repair. A threshold of tolerated micromotion exists, that is somewhere between 50 microns and 150 microns. It is suggested that loading protocols might be shortened through 2 different approaches. The first way would be to decrease stepwise the delayed loading period for free-standing implants below the presently accepted 3-6 months of healing. The second way would be to identify immediate loading protocols that are capable of keeping the amount of micromotion beneath the threshold of deleterious micromotion. Immediate loading protocols for implants-retained overdentures and fixed bridges are reviewed. It is shown that successful premature loading protocols require a careful and strict patient selection aimed to achieve the best primary stability. These various protocols need to be further documented in order to assess their predictability.

Effect of particles and interface conditions on fibrous tissue interposition between bone and implant. A particle challenge model in rabbit.

Interposed fibrous tissue at bone-implant interfaces was quantitatively measured in the presence or absence of polyethylene (PE) or alumina particles. Three different conditions of the interface were designed by implanting a pre-polymerized polymethylmethacrylate (PMMA) plug (plug group), a doughy PMMA (injection group) and a hydroxyapatite (HA) plug (HA group) in the hole drilled at the intercondylar notch of rabbit knees. PE (170+/-18 microm) or alumina particles (88+/-26 microm) were repeatedly administered into the knee joints at one month intervals (six times). All animals were sacrificed seven months after the implantation. The bone-implant interface was histomorphometrically examined using undecalcified ground sections. In the plug group, the PE particles significantly increased the extent of the interposed fibrous tissue (p < 0.05), while the alumina particles showed no effect. In contrast, both particles showed no significant effects in the injection and the HA groups. These results indicate that both particle characteristics and conditions of the bone-implant interface affected particle-induced fibrous tissue interposition. The loose PMMA plug with PE particles induced the greatest amount of fibrous tissue interposition.

Healing of large (2 mm) gaps around calcium phosphate-coated bone implants: a study in goats with a follow-up of 6 months.

Plasma-sprayed hydroxylapatite (HA) coatings are known for their ability to demonstrate osseointegration with bone. Recently it was found that the amount of bone apposition was strongly reduced 6 weeks after implantation in a goat model if gaps of two millimeters between bone and apatite coating existed. Stability of the apatite coatings examined did not influence the gap-healing ability. This study investigated whether a longer follow-up period of 24 weeks would be sufficient for the restoration of bone apposition on apatite coatings in an identical surgical model with 2 mm gaps, and whether bone apposition on the apatite coatings is influenced by the coating stability. Three coatings were investigated: 25-30% crystalline HA (aHA), 60-63% crystalline HA (cHA), and 85-90% crystalline fluorapatite (FA). Uncoated Ti-6A1-4V implants were used as controls. Implants were inserted in the femoral condyles of both femora of eight goats. Each goat received four implants. Histology revealed that bone formation on each of the apatite coatings remained low and did not increase with an extended follow-up period of 24 weeks. The coatings showed significantly (P < 0.01) more bone contact than the uncoated control implants. The three different coatings did not show significant differences in bone apposition. The aHA coating in most cases had disappeared completely after 24 weeks. Despite the disappearance of the aHA coating, bone contact was seen on the substrate surface without fibrous tissue interposition. The cHA coating showed minor signs of degradation while the FA coatings showed no visible degradation. It is concluded that non-press-fit implantation of apatite-coated implants leads to more bone apposition as compared to uncoated Ti-6A1-4V implants. However, it is suggested by these results that the upper limit of gaps around apatite implants is 2 millimeters in a non-weight-bearing model in goats. Bone apposition will not increase by extending the follow-up period more than six weeks, nor will it be altering the stability of the apatite coatings used.

Regeneration of Diaphyseal Bone Defects Using Resorbable Poly(L/DL-Lactide) and Poly(D-Lactide) Membranes in the Yucatan Pig Model

To determine the effects of tubular resorbable polymer membranes on the healing of a segmental diaphyseal bone defect. A randomized prospective study using the minipig model. Animals were evaluated with in vivo roentgenograms on a biweekly basis until explanted at twelve weeks. After surgery, animals were allowed unrestricted activity and weight bearing between twenty-four and forty-eight hours. Fifteen yearling Yucatan minipigs. A 2.5- to 3.0-centimeter mid-diaphyseal defect was created in the middle third of the radius. Animals were assigned in groups of three to receive the following implants: (a) poly(L/DL-lactide), (b) poly(L/DL-lactide)-CaCO3, (c) poly(D-lactide), (d) poly(D-lactide)-CaCO3, and (e) an untreated defect. No adjunctive internal or external fixation was used as the ulna was left intact. The limbs were studied with in vivo anterior-posterior and lateral radiographs at biweekly intervals for the presence and pattern of bone formation. All limbs were explanted at twelve weeks postimplantation for methyl-methacrylate embedding and histologic and microradiographic study. The bone defects covered with membranes were completely reconstituted by six to eight weeks. Untreated defects healed with less bone formation and in a more disorganized pattern. Histologic evaluation of the implants demonstrated that the entire lumen of the implant was filled with bone, with some periosteal bone formation occurring on the outer surface of the membrane. There was direct apposition of bone onto the membrane surface or minimal fibrous tissue interposition between membrane and new bone. There was no foreign body or adverse reaction to the membrane. Untreated defects showed woven bone formation with clefts and irregularly shaped margins occupied by fibrous tissues or surrounding muscle tissues. This study supports the concept that a membrane enhances bone defect healing by excluding nonosseous tissues from a defect and providing structural scaffolding for periosteal and endosteal bone regeneration.