Guidelines for analysis and redesign of dental implants.

This article describes the simulation of the mechanical behavior of two types of endosseous-threaded dental implants and the development of design guidelines for such implants. Two- and three-dimensional representations, static and dynamic cyclic loads, different material models, axial loads, and loads directed at the occlusal angle are all used. A novel model of trabecular bone is used to incorporate fatigue effects. Directional material behavior, progressive bone loss, and partial osseointegration are also modeled. Bone support using muscle attachment is modeled using spring constraints as opposed to fixed constraints used in previous studies. The tapered thread design from Brånemark Inc. exhibited higher stress levels in bone than those observed in the parallel profile thread from BUD Medical Devices, Inc. The BUD implant distributes stresses more evenly. Studies examining 25%, 75%, and 100% osseointegration showed cortical bone carried most of the load with resulting overload leading to crestal bone loss. Plots of stress showed that with increasing crestal bone loss, the majority of the load was transferred directly to the weaker trabecular bone tissue. Finally, it was shown that with proper implant redesign, loads can be transferred more evenly to the implant. This also improves fatigue life of the bone.

Stimulation of in vivo calcification using collagen membranes cultured with osteoblastic cells in vitro: a preliminary report.

Guided tissue regeneration (GTR) is a useful modality in the management of periodontal disease and for bone augmentation around osseointegrated implants. This study evaluated the in vivo use of atelocollagen membrane (AC) on which osteoblastic cells (OBCs) were cultured in vitro, for application as a GTR membranous material. Osteoblastic cells isolated in our laboratory from mouse calvaria formed a thin film on the AC in vitro which was easily manipulated after 21 days in culture. The AC and OBCs complex material (ACOB) was subjected to freezing and thawing and implanted in mouse subcutaneous tissue for the study of histologic events surrounding the implanted ACOB. Histologic findings in the subcutaneous tissue showed calcification on the ACOB at 28 days postimplantation, while no such finding was evident at the control site, where only AC without OBCs were grafted. The present study suggests the possibility of membrane calcification for GTR through ACOB produced by OBCs on an AC in vitro.

An in vivo evaluation of an osteoinductive implantable material produced by osteoblastic cells in vitro.

Osteoinductive implantable materials have been a subject of basic science research in clinical implantology. This study examined the osteoinductive effect of an implantable material produced by osteoblastic cells that were isolated in the laboratory from mouse calvaria. After 21 days in culture, osteoblastic cells formed a thin film that could be easily manipulated. This thin film was subjected to freezing and thawing and was implanted in mouse muscle tissue. Osteoblastic cells were strongly positive for alkaline phosphatase reactivity and Von Kossa stain in vitro. Collagen type I, osteocalcin (BGP), and alkaline phosphatase were identified at the immunohistochemical electron microscopic level. Histologic findings showed an osteoinductive effect of the implanted material. The results strongly suggest the possibility of producing an osteoinductive implantable material by culturing osteoblastic cells in vitro.

Osteogenesis of hydroxyapatite and tricalcium phosphate used as a bone substitute.

Hydroxyapatite (HA) and tricalcium phosphate (TCP) are useful for grafting and augmentation of bone tissue. In this study, conventional and histochemical transmission electron microscopy were used to study osteogenic events at the interface between the implanted materials and adjacent tissue from 1 to 4 weeks postoperatively. The microscopic results indicated that TCP was resorbed more rapidly than HA after implantation, with a notable breakdown of material and replacement by mesenchymal cells with ultrastructural features resembling osteoprogenitor cells and collagen up to 4 weeks postoperatively. Alkaline phosphatase and acid phosphatase reactivity in the tissues helped to identify and differentiate the histologic differences observed between HA and TCP.

Visualization and initial characterization of the titanium boundary of the bone-implant interface of osseointegrated implants.

A simple procedure has allowed consistent visualization of the titanium boundary of the bone-implant interface of osseointegrated titanium implants at the electron microscope level. This was accomplished by embedding the intact bone-implant specimen block with low-viscosity resin prior to removal of the device in preparation for sectioning. The titanium boundary consisted of either a thin, compact amorphous electron dense layer, a broad layer of dense amorphous granules, or both. This material was removed by decalcification in formic acid (prior to embedding) and did not diffract electrons (ie, was noncrystalline). Scanning-transmission electron microscopy-EDX analysis indicated the presence of titanium, calcium, and phosphorus in the electron dense material. Field emission scanning electron microscopy-EDX dot-mapping analysis confirmed the presence of these elements and mapped them to the same locations at the implant-interface boundary.

Microscopic observations of the bone/implant interface of surface-treated titanium implants.

Light microscopy, and transmission and scanning electron microscopy were used to evaluate osseointegration of extraoral titanium implant surfaces treated by either autoclaving, exposure to ultraviolet light (UV), or radiofrequency glow discharge (RFGD). Ultraviolet and RFGD-treated implants showed faster healing in the initial 5-week to 3-month period. By 6 months of healing, no structural differences were found at the bone/implant interface among the different treatments. It was concluded that UV or RFGD surface treatment of titanium implants may shorten the time interval between placement and loading.

Histopathology of veins and venous valves of patients with venous insufficiency syndrome: ultrastructure.

Vein and vein valve biopsies were obtained from venous insufficiency syndrome (VIS) patients undergoing venous valve transplants. Normal control biopsies were obtained from other non-VIS procedures. The specimens were examined using light and transmission electron microscopy (TEM). Biopsies from VIS patients showed a variety of changes from what was considered normal structure. Most histopathologic changes were noted in the endothelium and subendothelial layer of the vein valve and wall, and in the media of the vein wall. These changes included 1) erosion of the endothelium with consequent adherence of blood elements, 2) intact endothelium with a thickened subendothelial zone which was populated with migrated smooth muscle and perhaps other cell types, 3) occurrence of abnormal or over-abundant collagen, and 4) thickening of the media with changes in the smooth muscle population therein.

On the presence and localization of epidermal and nerve growth factors in human whole saliva.

Using antibodies to mouse submandibular epidermal growth factor (EFG) and nerve growth factor (NGF), immunohistochemical studies were performed on sections of flash-frozen human whole saliva in both light and transmission electron microscopy. Light microscopy showed the presence of overall network-like immunoreactions in both the EGF and NGF antibody-treated sections. Electron microscopy showed clearly detectable ultrastructural reaction patterns for both growth factor antibodies. The individual structural elements were more distinct for the EGF antibody-treated sections, in which the reaction elements had approximate diameters of 0.05 micron. In the NGF antibody-treated sections the corresponding approximate diameters were 0.02 micron. In both the EGF and NGF antibody-treated sections heavily stained bacteria-like particles were also frequently observed.

Coexpression of keratin and vimentin in salivary pleomorphic adenomas.

The coexpression of keratin and vimentin is described in 45 pleomorphic adenomas using an immunoperoxidase MAb method. Histopathologically, the outer layer of tubuloductal structures and peripheral tumor cells in solid masses, including modified or neoplastic myoepithelial cells, showed positive staining with monoclonal keratin antibody K8.12 and vimentin. This staining was found in the ratio of 10/26 (38.5%) in tubuloductal structures, 2/7 (28.6%) in peripheral tumor cells and 8/12 (66.7%) in modified myoepithelial cells. Concomitant staining of other keratin antibodies (PKK1, KL1) and vimentin did not exist. In addition, the ductal basal cells of normal salivary glands showed positive K8.12 labelling. The histogenesis of pleomorphic adenoma is discussed in relation to the differentiation of either ductal basal cells or ductal luminal cells from a single stem cell origin or the direct transformation of ductal basal cells to outer tumor cells and/or modified myoepithelial cells, both coexpressing K8.12 and vimentin.

Effects of pretreatment sterilization and cleaning methods on materials properties and osseoinductivity of a threaded implant.

A new endosseous titanium implant has been designed to replace skin adhesives as a method of retention of maxillofacial prostheses. The effects of various methods of preimplantation preparation on surface characteristics of the implant were analyzed with electron spectroscopy for chemical analysis. Having undergone one of several pretreatment protocols, fixtures were implanted in the crania of Yucatan miniature hairless swine. Both argon radiofrequency glow discharge and ultraviolet chamber treated implants were associated with the rapid ingrowth and maturation of new bone around the fixture. Conventional steam sterilization was associated with a paucity of neo-osteogenesis accompanied by the production of thick collagen slings at the interface. Apparently, the bulk material, fixture design, and method of surface preparation all contribute to the ultimate clinical fate of an implant.

Investigation of tissue/implant interactions during the first two hours of implantation.

The objective of this study was to determine whether detectable differences exist in the initial process of tissue incorporation of implant materials of different original surface energies. Our earlier work focused on materials implanted for days to months; the experiments reported here addressed the initial 2 hours of implantation. Surface-treated metal implants were placed in the fascial plane in the back of New Zealand white rabbits for 5 minutes to 2 hours. Prior to implantation, the metal plates were characterized by infrared spectroscopy, ellipsometry, and contact potential methods; the same analytical techniques, as well as scanning electron microscopy and contact angle measurements were applied to the explanted samples. No significant cellular adhesion was observed within the first 2 hours of implantation. Films rich in lipids and proteins were detected on the implants, however, within 5 minutes. There is good evidence for specific film differentiation as a function of differing initial substratum surface energies.

Identification of the interleukin-2 receptor (IL-2R) on human leukemic T cells using colloidal gold and scanning electron microscopy.

Results of studies demonstrating the identification of the interleukin-2 receptor (IL-2R; i.e., anti-Tac) on the membrane ultra-structure of human leukemic T cells with an antibody carrying an electron dense colloidal gold microsphere (e.g., immunogold) that was visualized using a scanning electron microscope (SEM) are reported. Our IL-2R model system employed HTLV-1 retrovirus-infected lymphoblastoid cells of the long-term human leukemic T cell line HUT-102B2. The presence of the IL-2R on these cells was defined using a double antibody procedure that employed as the primary antibody a purified mouse monoclonal anti-Leu-IL-2R antibody (mIgGlk, anti-Tac, CD25), and used as the secondary antibody a goat anti-mouse IgG (gamma-chain specific) antibody that had been covalently bonded to a 40 nm colloidal gold particle. More than 95% of the HUT-102B2 were IL-2R+, and there was a uniform distribution of the IL-2R over the surface of the cells. Corresponding controls were employed in all examinations and included IL-2R- Jurkat human leukemic T cells and isotype identical immunoglobulins. The primary and secondary antibody reagents contained whole human serum and bovine serum albumin, and there was no evidence of the non-specific binding of these antibodies. These studies are the first to demonstrate the presence of a lymphokine receptor on the surface architecture of a cell. We anticipate no difficulty in applying the immunogold/SEM technology to define both normal and malignant cell membrane receptors for other cytokines.

The use of elemental microanalysis in verification of the composition of presumptive amalgam tattoo.

Routine histochemistry, special stains, and energy dispersive x-ray microanalysis (EDX) were used to analyze 15 cases of presumptive amalgam tattoo. Histologically, the fine, spherical, golden brown granules of amalgam were remarkably similar to hemosiderin and melanin granules, and routine and special stains were not always reliable in differentiating one from the others. EDX provided a simple, fast, inexpensive, and reliable method for identifying the precise elemental composition of the pigmented material.

Immunohistochemical study of carbonic anhydrase in mixed tumours from major salivary glands and skin.

Immunohistochemical distribution of carbonic anhydrase isoenzyme I and II was studied in mixed tumours of major salivary glands and skin. The normal salivary glands displayed strong carbonic anhydrase activity in both ductal epithelium and serous acinar cells and the serous demilune cells in the submandibular glands, including the eccrine ducts. Pleomorphic adenoma salivary gland origin exhibited positive staining in the inner-layer of epithelial cells of tubular, duct-like and glandular structures. No enzymatic staining was noted in the outer layer of tumour cells in these structures. Spindle tumour cells or the fibroblast-like cells with long cytoplasmic processes identified in the adjacent hyalin and myxomatous stroma were rarely positive, while chondroidal and osteo-chondroidal cells were highly reactive. Mixed tumours of eccrine gland origin showed the most reactive staining cells scattered throughout neoplastic epithelium in all tissues examined. Immunohistochemical stainability was usually higher for carbonic anhydrase II than I for both normal and tumour tissues. The biological roles of the distribution profiles of carbonic anhydrase are discussed.

Immunohistochemical localization of carbonic anhydrase in submandibular salivary glands of mice and hamsters treated with phenylephrine, testosterone or duct-ligation.

Using the peroxidase antiperoxidase (PAP) technique, the submandibular glands (SMG) from normal mice showed positive carbonic anhydrase (CA) staining in both striated duct (SD) and granular convoluted tubule (GCT) cells, which varied from moderate to strong. In normal hamsters, the GCT showed strong focal staining. Phenylephrine in mice and hamsters resulted in a decrease in CA in GCT cells; staining was much reduced in the GCT segments of the mouse. One hour after a phenylephrine injection into testosterone-treated mice, there was no change in the staining intensity of GCT cells but an increase in cell size. Only a slight decrease in immunostaining occurred in mouse and hamster SD cells. CA staining in duct-ligated glands of mice decreased within 3 days but regenerated duct-like structures at later stages showed moderate staining.

Vein valve transplant. Indications and results.

The vein valve transplant has, in our experience, subjectively relieved symptoms in the majority of patients. More importantly, elevated venous pressure has been decreased in most patients. Thus, patients exhibiting signs of venous insufficiency syndrome as well as elevated venous pressure and proven valvular incompetence should be considered candidates for vein valve transplants after an unsuccessful trial of medical management.

Vein valve transplantation.

The vein valve transplantation has, in our experience, subjectively relieved symptoms in the majority of patients. More importantly, elevated venous pressure has been decreased in most patients. Thus, patients exhibiting signs of venous insufficiency syndrome as well as elevated venous pressure and proved valvular incompetence should be considered candidates for vein valve transplantation after an unsuccessful trial of medical management.

Heterotopic gastric mucosa: a case report.

A case of heterotopic gastric mucosa in discrete nodules of the duodenum is presented. Its radiographic and endoscopic appearance is described. The light and electron microscopic features are analyzed. Ultrastructural examination of its organization, cellular and subcellular components revealed similarities to normal fundic gastric mucosa. The histological and clinical differences between heterotopic gastric mucosa and duodenal metaplastic change are discussed.