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Biomedical subjects

P Passi

Publications and source records attributed to P Passi.

At least 19 recordsLinked to original sources
PubMed2004

Polyamines in nickel-titanium archwire-induced gingivitis in adolescents.

BACKGROUND: Polyamines spermine, spermidine, and putrescine are involved in a number of inflammatory diseases, but their role in the development of gingivitis and periodontitis has not been fully investigated. The goal of this investigation was to study the levels and the variations of these amines, and the main enzymes related to their metabolism, during archwire orthodontic treatment, a condition which may induce gingivitis. METHODS: Sixty patients (age range: 11 to 27 years) were examined for gingivitis occurring during nickel-titanium (Ni-Ti) archwire orthodontic treatment. Plaque and gingival indexes (PI, GI) as well as salivary polyamine metabolism before the archwire insertion (T0) and at 3 (T1), 6 (T2), and 12 (T3) months of treatment were measured. RESULTS: In patients in the age range of 14 to 17 years, spermine and spermidine, but not putrescine contents, as well as ornithine-decarboxylase (ODC) and S-adenosylmethionine-decarboxylase (SAMDC) activities, significantly rose at 3 months after insertion, without any change in periodontal parameters, and further increased at 6 months reaching the maximum at 12 months. GI increased later, from 6 to 12 months, while PI did not significantly change. Spermidine/spermine-N1-acetyltransferase (SSAT) activity remained unchanged from T0 to T3. On the contrary, in patients whose age was 11 to 13 or over 18 years, no significant variations in polyamine metabolism and periododontal parameters were observed at any examination time. CONCLUSION: These data support the hypothesis that salivary polyamines might be earlier indicators of gingivitis than the gingival index score in adolescents wearing archwire appliances.

Acetyltransferases↗
PubMed2004

In vitro buffering properties of 3 composite resins.

AIM: A dental composite resin, Ariston pHc, has been described as having a cariostatic effect by buffering acid saliva and preventing decalcification and infiltration of restorations. The buffering effect has been reported due to the release of OH- originated from the alkaline glass embedded in the resin. The release would occur only in the presence of low salivary pH values. The aim of this in vitro investigation was to evaluate pH variations induced by Ariston pHc and 2 other composite resins (P60 and Z100). METHODS: Eighteen samples were prepared for each composite and 5 specimens of each brand were embedded in artificial saliva according to Brugirar and Mazille, at 3 different pH values. A 1(st) group of 5 specimens of each tested resin was immersed in neutral artificial saliva at pH 7.7, a 2(nd) group in acidified artificial saliva at pH 5.45 and a 3(rd) group in alkalised saliva at pH 9.25. Three other samples of each resin were immersed in tubes containing distilled water at pH 7.23 and served as controls. Twelve tubes were filled only with neutral, alkalised and acidified artificial saliva and distilled water at the above mentioned pH values. Measurements of pH modifications were taken after 1, 3, 9, 14, 31 days. RESULTS. Ariston pHc raised the pH of distilled water up to 9.59 after 1 day, and to 8.42 after 31 days. This pH modification shown by Ariston pHc in distilled water, compared to those of the other 2 composites were statistically highly significant, with p<0.001, while the pH variations of saliva containing the 3 resins were negligible, except for acidified saliva with Ariston pHc, where a slight pH enhancement with some statistical significance (p=0.04) was found. However, acidified saliva without any resin embedded was found to shift to neutrality as well. CONCLUSION: These results strongly suggest that none of the 3 tested materials can achieve an effective buffering action in vitro on low salivary pH values. However, the ability of Ariston pHc to raise the pH in distilled water, and to a lesser degree in acidified saliva, suggests that an in vivo buffering effect cannot be excluded.

Buffers↗
PubMed2002

PIXE micro-beam mapping of metals in human peri-implant tissues.

Previous investigations did not agree about the possible presence of titanium and other metals in the tissues around endosteal dental implants and joint prostheses. Indeed, while some authors reported diffusion of metals into the tissues, some others did not find evidence of this phenomenon. In the present study, four dental titanium implants, removed with the surrounding tissues from patients at various time intervals after the insertion, were studied by means of the micro-beam proton-induced X-ray emission (PIXE micro-beam) technique, which draws maps showing the tissue distribution of elements with a detection limit of about 1 ppm. One implant was built in commercially pure titanium, two others in titanium coated with titanium plasma spray, and the fourth in Ti-Al-V alloy. Their composition was confirmed by the PIXE micro-beam analyses. The removed samples were embedded in epoxy and processed with a cutting-grinding appliance, mounted on plastic holders, and ground up to a thickness of about 35 microm. Optical microscope examinations were also carried out, to compare the optical findings with the elemental maps obtained with the PIXE micro-beam. One implant, removed after 70 days because the patient had developed peri-implantitis, had some inflammatory soft tissue attached, with no evidence of metal leakage. The other three implants had been removed after 6, 7 and 9 years of valid clinical service, because of the fracture of the prosthetic abutment or the implant stem. At the optical microscope, all these fixtures were embedded in mature bone. The elemental maps indicated small titanium deposits in about 5% of the bone bordering the implants, while aluminum, when present in the fixture, leaked diffusely into the surrounding bone and vanadium was not found in the tissues. These results suggest that titanium may be found occasionally in peri-implantar tissues, but has very little tendency to spread, while the presence of aluminum in the implant alloy may cause an important leakage of this metal.

Journal Article↗
PubMed2000

Plain and drug loaded polyphosphazene membranes and microspheres in the treatment of rabbit bone defects.

The healing of periodontal surgical defects was studied in rabbits, using polyphosphazenes (POP) membranes and microspheres, both plain or drug-enriched. POP polymers having amino acid ester as backbone substituents, are used since they resorb and undergo hydrolytic degradation to ammonia, phosphate and amino acids. Fourteen animal were operated in tibia, and other fourteen at angle of the mandible, that was reached by extraoral access. Bone defects were performed in tibiae, and covered either with POP or with poly-tetrafluoroethylene (PTFE) membranes, while other rabbits served as controls. The animals were sacrificed after one and two months, and the tibiae taken and processed for optical microscopy. Similar surgical defects were made in mandible, and POP membranes were placed over the breaches, some of which were filled with POP microspheres, both alone or mixed with granular hydroxyapatite. For comparison, two rabbits were treated with PTFE membranes, while other two served as controls. The animals operated at the mandible were all sacrificed after one month, and the operated bones taken and processed for histology. It was found that POP membranes were very effective in promoting the healing in tibiae, while less satisfactory results were found in the animals treated with PTFE membranes and in controls. In mandible, the healing occurred without a clear relationship with the grafted microgranular material or the membrane, since repairing bone was found also in controls. In any case, both POP membranes and microspheres showed excellent biocompatibility, as no inflammatory cells or macrophages were found in the surrounding tissue. This property was completely independent from the presence of drug, since the matrix-entrapped drugs, released in the tissue, did not hamper the bone healing. It was also found that POP, by itself, has a positive effect in stimulating the bone repair.

Journal Article↗
PubMed1999

Polyphosphazene membranes and microspheres in periodontal diseases and implant surgery.

Membranes or microcapsules made from polyphosphazenes bearing amino acid side groups are proposed for the treatment of periodontal diseases. Polyphosphazene membranes, prepared with alanine ethyl ester and imidazole in the molar ratio of 80:20 as phosphorus substituents, gave a degradation rate that corresponded to the healing of the bone defect. These membranes were much more successful in promoting healing of rabbit tibia defects than polytetrafluoroethylene membranes. Antibacterial or anti-inflammatory drugs, useful in periodontal tissue regeneration, could be entrapped in the polyphosphazene membranes and released both in vitro and in vivo at a rate that ensured therapeutic concentrations in the surrounding tissue. Polyphosphazene microspheres, prepared with phenylalanine ethyl ester as a phosphorus substituent and loaded with succinylsulphathiazole or naproxen, were also obtained. The kinetics of release from these matrices were very convenient in yielding local concentrations of the two drugs that are useful per se or when mixed with hydroxyapatite for better bone formation.

Animals↗
PubMed1994

Histochemical and confocal laser scanning microscopy study of the bone-titanium interface: an experimental study in rabbits.

The aim of our study was an analysis of the presence of an unmineralized bone matrix between mineralized bone and titanium screws in rabbit tibiae. A microscopical analysis, using a histochemical technique, was performed on the titanium-bone interface of commercially pure titanium implants placed in rabbit tibiae and harvested after 2 months. Thin ground sections of the specimens were prepared by the cutting-grinding system and stained using the von Kossa method for calcium salts and basic fuchsin for osteoid. The microscopical and morphometrical evaluation showed that bone covered about 40% (+/- 7.5%) of all implants. Mineralized bone was, however, in direct contact with the titanium surface on only about 10% of the implant, while in the remaining 30% the mineralized bone was separated from the implant by an unmineralized tissue. This basophilic, probably osteoid matrix, could represent the medium that allows the biochemical exchanges between bone and cells under the influence of the implant. A small, optically translucent gap (1-5 microns), probably an artifact, was present in some areas between titanium and bone. Confocal laser scanning microscopy (CLSM) in a fluorescent mode showed the presence at the interface of a fluorescent material. Results from our study showed that light microscopy of thin ground sections allowed a good analysis of the real nature of the titanium-bone interface. Moreover, this double staining technique showed the presence of an unmineralized bone matrix at most of the bone-titanium interface.

Animals↗
PubMed1993

Light and confocal laser scanning microscopic evaluation of hydroxyapatite resorption patterns in medullary and cortical bone.

An animal study was conducted with unloaded blocks and hydroxyapatite (HA)-coated titanium implants. Four HA blocks were positioned in rabbit tibiae and four HA-coated titanium implants were positioned in pig tibiae. Implants were positioned so that half was placed in cortical bone and half in medullary space. Biopsy specimens were taken 4 months after implant placement for histologic evaluation. Light microscopy and confocal laser scanning microscopy demonstrated that the HA resorption rate was higher in the medullary spaces, whereas resorption was almost absent in the areas embedded in cortical bone.

Animals↗
PubMed1992

Resistance to fracture of ceramic jacket crowns.

The resistance to fracture of jacket crowns, fabricated of cast glass-ceramic and five traditional ceramics, was evaluated. Four identical jacket crowns of each type were constructed on absolutely equal dental abutments in epoxy resin, obtained from a primary mandibular molar. An increasing load was then applied to the mesiobuccal cusp of each of the 24 crowns. Although the glass-ceramic proved to have the highest fracture resistance, it was not significantly stronger than three other traditional ceramics; neither did it seem to be suitable for constructing jacket crowns on posterior teeth.

Ceramics↗
PubMed1992

The influence of environmental pressure on retentiveness of prosthetic crowns: an experimental study.

To determine the effect of pressure variations on the retention of prosthetic crowns, 36 identical, cast metal crowns were fixed to simulated, epoxy resin crown preparations with zinc oxyphosphate cement. Eighteen specimens were placed in a hyperbaric chamber and subjected to 15 cycles of simulated immersion at 30 m and decompression, as usually carried out by scuba divers. The untreated specimens served as controls. When the force required to dislodge the crowns was measured, the treated crowns were dislodged at about one third the load that was required to dislodge the control group, indicating that a statistically significant decrease in cement strength follows pressure variations.

Atmospheric Pressure↗
PubMed1991

Ultrastructural findings on the interface between hydroxylapatite and oral tissues.

Two patients were treated with surgical implantation of synthetic, granular, nonporous hydroxylapatite to correct bone defects around dental implants. Ultrastructural examination of biopsy specimens taken several months later showed that the hydroxylapatite material was encapsulated mostly by fibrous connective tissue, without any signs of active inflammation. Osteoid and mature bone were also present in many areas. Under the electron microscope, an electron-dense delimiting band was detected at the interface of the tissue and the material. A polygonal, networklike structure, originating from the electron-dense layer and penetrating into the periphery of the hydroxylapatite granules, was also observed. These findings confirm the results of previous studies, in which it was hypothesized that the electron-dense structures were of a mucopolysaccharide nature and might prove the close bond between the hydroxylapatite and the tissues.

Alveolar Process↗
PubMed1989

[Water absorption and resistance to wear of 2 newly invented composite resins].

Two recently built composites, one for posterior teeth, and the other for general employ, were evaluated in relation to their water absorption and resistance to wear by means of the "scratch test". Critical loads and attrition of the two materials were also evaluated, with statistical analysis. The results supported the good qualities of the two composites, which are to be considered very advanced in the field of esthetic reconstruction materials.

Absorption↗