María B. Guglielmotti

Biological performance of boron-modified bioactive glass particles implanted in rat tibia bone marrow.

The aim of the present study was to characterize the neoformed bone tissue around boron-modified bioactive glass particles implanted in rat tibia bone marrow by histologic, histomorphometric and microchemical evaluation. Melt-derived glasses were prepared from a base 45S5 bioactive glass of nominal composition (45% SiO(2), 24.5% CaO, 24.5% Na(2)O and 6% P(2)O(5) in wt%). The glass composition was modified by adding 2% wt of boron oxide (45S5.2B). Histological and histomorphometric analyses using undecalcified sections showed that at 15 days post-implantation the area of neoformed bone tissue around the 45S5.2B particles was significantly higher than control 45S5 glass. No statistically significant differences were observed at 30 days post-implantation. The thickness of osseointegrated tissue on 45S5.2B BG particles was significantly greater than on the control at all experimental time-points evaluated. A statistically significant increase in the Ca:P ratio was observed in the neoformed bone around 45S5.2B particles 15 days post-implantation. The results of the present study provide evidence that particles of boron-modified 45S5 BG (45S5.2B) enhance bone formation more than 45S5 glass when implanted into the intramedullary canal of rat tibiae.

An experimental study of the dissemination of Titanium and Zirconium in the body.

Metallic implants can generate and release titanium oxide (TiO2) and zirconium oxide (ZrO2) to the tissues. These products can accumulate locally or disseminate systemically. The aim of the present study was to assess the distribution of TiO2 and ZrO2 administered intraperitoneally to rats. We used male Wistar rats of approximately 100 g body weight throughout the study. An intraperitoneal injection of a suspension of TiO2 or ZrO2 (16, 1600 and 16×103 mg/kg body weight) was administered. The animals were killed at 5–10 months post-administration by ether overdose. Samples of peritoneum, liver, kidney, lung and spleen were taken, fixed in formalin and routine processed for embedding in paraffin. One set of sections was stained with hematoxylin and eosin and another set was prepared unstained. The presence of titanium in the tissues was detected by X-ray diffraction crystallography. The histological analysis revealed the presence of abundant intracellular aggregates of metallic particles of Ti and Zr in peritoneum, liver, lung and spleen. The crystallographic study revealed the presence of anatasa. The dissemination of metallic particles from orthopedic or odontological implants would not be restricted to a local phenomenon. The particles also target vital organs. The distribution of these deposits over lengthy periods deserves meticulous attention given the clinical relevance of this phenomenon.

Biocompatibility of Two Calcium Hydroxide-based Endodontic Sealers: A Quantitative Study in the Subcutaneous Connective Tissue of the Rat

In this study, the biocompatibility of two calcium hydroxide-based endodontic sealers was investigated. Silicone tubes containing freshly mixed Sealapex or CRCS were implanted in the dorsal subcutaneous connective tissue of the rat. Equal size solid silicone rods were also implanted and used as controls. The tissue reaction to test and control materials was histometrically and quantitatively analyzed under light microscopy. After 7, 30, and 90 days of implantation, different grades of tissue reaction to the tested materials were recorded at the end of the tubes. A granulomatous tissue containing foreign body giant cells and macrophages with engulfed material in their cytoplasm as well as many fibroblasts and vessels was initially observed in contact with Sealapex. This reaction increased progressively at the 30- and 90-day observation period. An acute inflammation was detected in tissues in contact with CRCS. However, the severity of this reaction decreased with time and it seemed to be resolved at the 90-day observation period. Taking into account the limitations of the experimental model used in this study, we consider that more extensive experiences will be necessary prior to extrapolating these findings to the actual clinical situation.

Histomorphometric Study of Alveolar Bone Healing in Rats Fed a Boron-Deficient Diet

Bone healing after tooth extraction in rats is a suitable experimental model to study bone formation. Thus, we performed a study to determine the effects of boron (B) deficiency on bone healing by using this model. The first lower right molar of weanling Wistar rats was extracted under anesthesia. The animals were divided into two groups: +B (adequate; 3 mg B/kg diet), and −B (boron‐deficient; 0.07 mg/kg diet). The animals in both groups were killed in groups of 10 at 7 and 14 days after surgery. The guidelines of the NIH for the care and use of laboratory animals were observed. The mandibles were resected, fixed, decalcified, and embedded in paraffin. Buccolingually oriented sections were obtained at the level of the mesial alveolus and used for histometric evaluations. Total alveolar volume (TAV) and trabecular bone volume per total volume (BV/TV) in the apical third of the alveolus were determined. Percentages of osteoblast surface (ObS), eroded surface (ES), and quiescent surface (QS) were determined. No statistical significant differences in food intake and body weight were observed. Histomorphometric evaluation found −B rats had 36% and 63% reductions in BV/TV at 7 and 14 days, respectively. When compared with +B rats, −B rats had significant reductions (57% and 87%) in ObS concomitantly with increases (120% and 126%) in QS at 7 and 14 days, respectively. The findings show that boron deficiency results in altered bone healing because of a marked reduction in osteogenesis. Anat Rec, 291:441–447, 2008.

A histomorphometric study of alveolar bone modelling and remodelling in mice fed a boron-deficient diet

OBJECTIVE Emerging evidence indicates that boron (B) plays a role in bone formation and maintenance. Thus, a study was performed to determine whether dietary B-deficiency affects periodontal alveolar bone modelling and remodelling. DESIGN Weanling Swiss mice (n=30) were divided into three groups: control diet (GI, 3mg B/kg); B-deficient diet (GII, 0.07 mg B/kg); and pair-fed with GII (GIII). The animals were maintained on their respective diets for 9 weeks and then sacrificed. The guidelines of the NIH for the care and use of laboratory animals were observed. The mandibles were resected, fixed, decalcified in 10% EDTA and embedded in paraffin. Buccolingually oriented sections were obtained at the level of the mesial root of the first lower molar and stained with H-E. Histomorphometric studies were performed separately on the buccal and lingual sides of the periodontal alveolar bone. Percentages of osteoblast surfaces (ObSs), eroded surfaces (ESs), and quiescent surfaces (QSs) were determined. RESULTS No statistically significant differences in food intake and body weight were observed between the groups. When compared with GI and GIII mice, GII mice (B-deficient) had 63% and 48% reductions in ObS and 58% and 73% increases in QS in buccal and lingual plates, respectively. ES were not affected by B nutriture. CONCLUSION The results are evidence that dietary boron deprivation in mice alters periodontal alveolar bone modelling and remodelling by inhibiting bone formation.

Histomorphometric study of bone healing around laminar implants in experimental diabetes.

The aim of this study was to evaluate the effects of experimental diabetes on the healing period leading to osseointegration. Wistar rats were injected with a single dose of streptozotocin (STZ); body weight and food intake were assessed every 48 hours. On days 2, 12, 26, and 42 post-STZ, glucemia, plasma hemoglobin, and urea were determined. Twelve days post-STZ, a titanium laminar implant was placed in the right tibia of each rat. Two groups of 20 rats each were killed on days 14 and 30 postimplantation, respectively. Results (ANOVA test) showed STZ-treated rats to have 1) a significant decrease in body weight; 2) an increase in food intake; 3) normal hemoglobin and plasma urea values; 4) a significant increase in glucemia; and 5) a decrease in tibiae length. Microscopic evaluation 14 days postimplantation revealed the presence of woven bone, and, at 30 days, laminar bone was in contact with the implant. Our findings show that, in this model of periimplant bone repair and under the experimental conditions stated herein, STZ-induced diabetes retards periimplant bone healing.

Local effect of titanium implant corrosion: an experimental study in rats.

The aim of this study was to evaluate histologically the biological effect of pitting corrosion and to contribute clinically relevant data on the permanence of titanium metal structures used in osteosynthesis in the body. Commercially pure titanium laminar implants (control) and commercially pure titanium laminar implants with pitting corrosion (experimental) were implanted in the tibiae of rats. At 14 days post-implantation the animals were killed. The tibiae were resected, fixed, radiographed and processed for embedding in methyl methacrylate. Percentage of bone-implant contact and peri-implant bone volume were evaluated. The histological study of the titanium implants submitted to pitting corrosion showed scarce bone-implant contact, it was only present in the areas with no pitting and/or surface alterations. There was a statistically significant lower percentage of bone-implant contact in the experimental group (6%+/-4) than in the control group (26%+/-6) (p<0.001). Products of corrosion in the peri-implant bed, especially around the blood vessels and areas of bone marrow in the metal-tissue interface, were observed. The microchemical analysis of corrosion products revealed the presence of titanium. The adverse local effects caused by pitting corrosion suggest that titanium plates and grids should be used with caution as permanent fixation structures.

Oral Mucosa Tissue Response to Titanium Cover Screws

BACKGROUND Titanium is the most widely used metal in dental implantology. The release of particles from metal structures into the biologic milieu may be the result of electrochemical processes (corrosion) and/or mechanical disruption during insertion, abutment connection, or removal of failing implants. The aim of the present study is to evaluate tissue response of human oral mucosa adjacent to titanium cover screws. METHODS One hundred fifty-three biopsies of the supra-implant oral mucosa adjacent to the cover screw of submerged dental implants were analyzed. Histologic studies were performed to analyze epithelial and connective tissue as well as the presence of metal particles, which were identified using microchemical analysis. Langerhans cells, macrophages, and T lymphocytes were studied using immunohistochemical techniques. The surface of the cover screws was evaluated by scanning electron microscopy (SEM). RESULTS Forty-one percent of mucosa biopsies exhibited metal particles in different layers of the section thickness. Particle number and size varied greatly among specimens. Immunohistochemical study confirmed the presence of macrophages and T lymphocytes associated with the metal particles. Microchemical analysis revealed the presence of titanium in the particles. On SEM analysis, the surface of the screws exhibited depressions and irregularities. CONCLUSIONS The biologic effects seen in the mucosa in contact with the cover screws might be associated with the presence of titanium or other elements, such as aluminum or vanadium. The potential long-term biologic effects of particles on soft tissues adjacent to metallic devices should be further investigated because these effects might affect the clinical outcome of the implant.

Titanium transport through the blood stream. An experimental study on rats.

Different metals are increasingly being used to manufacture implants, especially in the fields of dentistry and orthopedics. No metal or alloy is completely inert in vivo. The metal and the organic fluids interact releasing, for example, metallic products. Several hypotheses regarding the probable dissemination routes of titanium have been postulated, but its valence, the organic nature of its ligands and its potential toxicity have yet to be established. In a previous experimental study we demonstrated that i.p. injected titanium and zirconium oxides disseminate and deposit in organs such as liver and lung. The aim of this work was to study the eventual participation of blood cells in the transport mechanism of titanium employing the intraperitoneal injection of titanium oxide in rats as the experimental model. Twenty male Wistar rats, x: 100 g body weight, were intraperitoneally injected with 16×103 mg/kg b.w. of TiO2 in saline solution. Blood samples were taken by heart puncture at 3 and 6 months; blood smears were performed and stained with safranin evidencing monocytes containing titanium particles. The results obtained in this study would indicate that one of the ways in which titanium is disseminated is through the blood stream, via blood cells.

Histomorphometry of initial bone healing around zirconium implants in rats.

Histometric evaluations as a function of time were performed with zirconium implants during the healing period in 10 Wistar rats. The implants (7 mm × 1 mm × 0.1 mm) were placed in the right tibia of the animals. Five rats were killed after 14 days and the remainder were sacrificed 30 days after implantation. The tibiae were resected, radiographed, and embedded in poly(methyl methacrylate). Three cross-sections were obtained transverse to the major axis of each tibia. Osseointegrated tissue thickness, percentage of direct bone-to-implant contact, and osseointegrated tissue volume were evaluated for each specimen. Bone formation was observed on the surface of the implanted strip that was in contact with tibia marrow. This method is proposed for the evaluation of the first stage of healing of bone in contact with different implant materials subjected to various surface treatments. (Implant Dent 1993;2:264–267)