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Biomedical subjects

S Radin

Publications and source records attributed to S Radin.

At least 37 records · Page 2Linked to original sources
PubMed1993

The effect of calcium phosphate ceramic composition and structure on in vitro behavior. I. Dissolution.

Synthetic calcium phosphate ceramic (CPC) surfaces can be transformed to a biological apatite through a sequence of reactions which include dissolution, precipitation, and ion exchange. By virtue of the reactions being material-dependent, it is important to determine parametric rate effects. In this study we focused on the effect of stoichiometry and crystal structure of CPCs on the dissolution kinetics. Monophase, biphase, and multiphase CPCs with a Ca/P ratio equal to or greater than 1.5 were studied. The experiments were performed in a calcium- and phosphate-free Tris buffer solution at pH 7.3. The dissolution behavior of the CPCs studied was found to vary over a wide range. The dissolution rate of the monophase CPCs increased in the order of stoichiometric hydroxyapatite, calcium deficient hydroxyapatite, oxyhydroxyapatite, beta-tricalcium phosphate, alpha-tricalcium phosphate, and tetracalcium phosphate. Dissolution of biphase and multiphase CPCs increased prorated the concentration of more soluble component.

Biocompatible Materials↗
PubMed1991

Clinical evaluations on thermal versus mechanical debonding of ceramic brackets.

Removal of ceramic orthodontic brackets, utilizing orthodontic pliers, has resulted in significant patient discomfort, enamel trauma and bracket shattering. The purpose of this clinical study was to compare the safety and efficacy of standard orthodontic mechanical debonding with a new Dentaurum thermal debonding device. Fifteen healthy patients with maxillary or mandibular premolars scheduled for extraction completed this study. One week after bracket placement, removal was accomplished by mechanical pliers or a thermal debonding device. Both procedures were performed on each patient in random order. Efficacy was monitored using scanning electron microscopy (SEM) on impressions made before and at selected times after debonding. Extracted teeth were subjected to histological evaluation to check potential injury to the pulp. Comfort levels were determined by questionnaires. Data was analyzed by Chi square. No irritation or overt changes were reported or observed. Significant differences (p less than 0.05) favoring the thermal devices were determined from the questionnaire on comfort during the removal process. Evaluation of SEM surfaces found significantly less (p less than 0.05) changes produced with the thermal debonding device, compared to mechanical removal. No histological evidence of pulpal injury related to product treatments were determined. The Dentaurum thermal debonding device was judged less traumatic by patients and produced minimal enamel surface changes compared to a mechanical debonding plier.

Adolescent↗
PubMed1990

Calcium phosphate ceramic coatings on porous titanium: effect of structure and composition on electrophoretic deposition, vacuum sintering and in vitro dissolution.

Bioactive calcium phosphate ceramics (CPC) guide bone formation along their surface. This property is conceptually attractive from the viewpoint of enhancing early bone tissue formation in porous metal coatings. The various studies conducted to exploit this idea, however, reveal a considerable variability of the effect. This suggests material- and processing-induced parametric influences. Thus this study focuses on the formulation of model porous metal-CPC materials for use in one-parametric analyses of material factors. Easily reproducible, porous metals with a uniform porous structure and CPC coating are made with orderly oriented wire mesh (OOWM) porous metal coatings and electrophoretically deposited CPC films. The deposition of the ceramic can be hampered by adsorbed water. Subsequent vacuum sintering leads to several phase transformations: hydroxyapatite is transformed to a mixture of oxyhydroxyapatite and tetracalcium phosphate; the underlying titanium promotes the beta- to alpha-tricalcium phosphate transformation; and Ca-deficient hydroxyapatite is transformed to a mixture containing oxyhydroxyapatite and alpha- and beta-tricalcium phosphate. These phase transformations provoke a considerable increase of in vitro dissolution in 0.05 M tris buffered physiological solution.

Biocompatible Materials↗
PubMed1990

Effect of calcium phosphate coating characteristics on early post-operative bone tissue ingrowth.

The synthesis of model porous metal-CPC materials, and their use in one-parametric studies of bone tissue ingrowth enhancement were considered. By using the same starting calcium-deficient hydroxyapatite powder, three different coatings, CAP1, CAP2 and CAP3, were obtained of thicknesses 50 +/- 5, 75 +/- 5 and 75 +/- 5 microns, respectively. CAP1 and 2 were either the starting powder mixed in a 3:1 ratio CPC: poly(lactic acid) or the powder by itself. The CAP3 coating was the result of a thermal treatment producing a mixture of oxyhydroxyapatite, alpha- and beta-tricalcium phosphate. Orderly oriented wire mesh porous coated specimens were implanted, along with the same specimens lined with CAP 1, 2 or 3. Subsequently, the total of 156 specimens was retrieved at 2, 4 or 6 wk, and tested mechanically and processed for histomorphometry. The data produced considerable evidence for the CPC-dependent enhancement of bone tissue ingrowth in porous metals immediately after implantation. They prove that the materials processing of CPC coatings influences the resulting biological behaviour substantially. Furthermore, they support the hypothesis that ceramic dissolution is a causative factor on the bone tissue growth enhancement mechanisms.

Animals↗
PubMed1989

Pancreaticoduodenal graft in the rat: an original microsurgical technique.

The authors describe an original surgical technique for pancreatic transplantation carried out on an experimental rat model which duplicates as closely as possible the anatomic-functional situation of a pancreatic graft in man (one arterovenous vascular peduncle with one functioning kidney only). The technique entails a microanastomosis between the mesenteric artery and the portal vein of the donor organ with the left renal artery and vein of the recipient. This method appears to be technically encouraging and particularly useful in studying the early phases of ischemic graft injuries, a field in which the authors are particularly interested.

Animals↗
PubMed1989

Studies on the retina of the diabetic db/db mouse. I. Endothelial cell-pericyte ratio.

The genetically diabetic db/db mouse is a model of type-2 diabetes, where nephropathy and neuropathy, but not retinopathy were observed. The authors studied the retinas (trypsin digestion technique) of 16 db/db mice and 16 age-matched litter mates (db/m; controls), divided into five age groups. They noted a marked increase in the ratio of endothelial cells to intramural pericytes in diabetic mice compared to controls. This increase resulted from a selective and highly significant loss of pericytes in db/db mice (p less than 0.05). Some strand-like and relatively acellular capillaries were also observed. The db/db mouse may represent an adequate model for studies on the pathogenesis of retinopathy.

Age Factors↗
PubMed1989

[Biomechanico-clinical interpretation of firearm wounds. General problems (III). A propedeutic ABC on terminal ballistics].

The surgeon should have a comprehensive knowledge of firearms as thermochemico-ballistic machines in order to come to grips in an adequate manner with the wounds they inflict on the human body. The traces left on the body to all intents and purposes embrace a cultural "cul de sac" which risks being defrauded of most of its content by a lack of those propedeutics elements which painstaking reflection is capable of affording us. Only the interpretation of each individual ballistic phase, both as a complete phenomenon in itself and as a component in a single articulated complex, can offer such elements: credit is due at least for a wholehearted commitment in this direction, while never losing sight at any time of the clinical perspective of such wounds.

Forensic Medicine↗
PubMed1988

[Biomechanico-clinical study of gunshot wounds (general problems--II)].

Whenever the surgeon finds himself face to face with a wound (probably this is the only opportunity for a meeting between physician and pathology which seems to be able to leave the "illness" on one side, almost forgotten, as it were), even when immersed in routine, he can hardly help making a number of considerations of a general nature, to which the sentence above in brackets is not entirely extraneous. In practice, we cannot help asking ourselves an apparently simple, almost banal, question: what exactly is trauma? This triggers off a whole series of secondary queries, such as, for instance, what the relationship is between trauma and classical pathology? In the first place, it should be pointed out that "traumatic" pathology is undoubtedly the only instance of pathology in which, as a rule, at least at the outset, one can justifiably talk about the "isolated" role of what can certainly be regarded as an out-of-body factor. If, then, we consider the specifically morphological and pathophysiological aspects of the period subsequent to the traumatic insult, we find ourselves in an even more embarrassing position: we are faced with irreparably devastated organ and body structures, or with a situation which is already on the way to convalescence. One last alternative is that the traumatic insult is merely a memory, a key finding in the case history, a past reality which to all intent and purposes has ceased to exist, and we are faced with extremely complex clinical pictures which we tend to label as complications. A few examples by way of explanation: shock, adult respiratory distress syndrome (ARDS), stress ulcer, acute post-traumatic cholecystitis, haemorrhagic pancreatitis, and problems caused by resolving the hypovolaemia-ischaemia situation and by implementing reperfusion (oxygen radicals). Trauma favours - and surgeons concerned with organ transplants are well aware of this - the only possibility of death which, perhaps with a grain of excessive optimism, we may even accept as fruitful, in that it occurs without all the destructive deterioration involved in the process of dying. The above consideration probably plays a major role in our attitudes of almost fatalistic resignation towards the youthful victims of trauma.(ABSTRACT TRUNCATED AT 400 WORDS)

Physical Phenomena↗
PubMed1988

[Biomechanical and clinical study of gunshot wounds (general problems). I].

Above and beyond their effective epidemiological incidence, which is perhaps somewhat greater than is commonly imagined even outside the war context, gunshot wounds constitute a unique cultural opportunity for the traumatologist and for surgeons in general. The actual morphological and clinical features of such wounds, which bear precise, localized witness to, and reflect in a virtually mathematical manner, a programmed, and thus readily quantifiable, dimension of kinetic energy (rich in experimental implications), stand out against the backcloth of an extremely extensive involvement of the body in which, amongst other things, the intervention of a whole host of mediators may be seen to play a decisive role. Lastly, it should not be forgotten that it is precisely in field hospitals or their equivalents that surgery has found a precious opportunity to escape the environmental or "cultural" conditioning of the moment and play a leading role not only in terms of technological solutions but also in terms of reflection on the main leitmotive of pathophysiology, from shock to ARDS.

Biomechanical Phenomena↗
PubMed1987

[Hypothesis of the pathology of mediation in surgery (2)].

There are clearly numerous examples of mediation pathology in surgery. They go far beyond what may be defined as severe forms, in which the entire body is involved in the precipitating disease process and in which the mediation appears more easily recognizable, in that it evokes a resonance which wipes out all specificity and becomes the true protagonist of the critical situation. Forms which can be traced to a well defined pathogenesis, and others to a more debatable pathogenesis, afford great scope for mediation. May one, for instance, be justified in suggesting a mediation hypothesis for a classic surgical disease such as duodenal ulcer?

Disease↗
PubMed1987

[Hypothesis of the pathology of mediation in surgery (3)].

There are three aspects to mediation: the first of these is purely physiological, or rather is concerned with performance of service functions such as ovulation, sexual activity, sleep, etc.; the second, strictly speaking, may be defined as pathophysiological, as its starting point is considered to be an aggressive event, even when a routine occurrence (in the stomach, for instance, aggression is a constant feature, even when of only slight intensity, as produced by the physical characteristics of the enormous quantities of food transiting the stomach and by particular environmental conditions; the third aspect is distinctly pathological, in that it constitutes the basis for the aggravation of a pathological situation already in progress, sometimes according to the logic of plain addition, but more often according to a more catastrophic process of multiplication (less frequently it takes the form of induction of a prevalent or independent disease condition). This break-down of mediation into distinct types, though necessary from the point of view of academic classification, proves extremely difficult to apply in practice. The validity of this latter consideration obviously depends on the specific area we are tackling. As regards the sex glands and male genital organ, the service role is unquestionable; elsewhere, we can be equally sure that we faced with pathophysiological aspects. In the stomach, for example, the difference between "normality" and "disease" does not lie so much in the absence, as opposed to the presence, of lesions, but rather in their extent and duration. This makes it extremely difficult to draw the line between physiology and pathology, and at the same time suggests that the state of health may be an unstable equilibrium phase somewhere midway between divergent forces belonging to the same mechanism. This latter mechanism may therefore be the key factor both in vital performance and in disease processes, whereas the "classic" aetiological factor may actually be relegated to a secondary role, at least in most cases.

Homeostasis↗
PubMed1987

[Hypothesis of mediation pathology in surgery (4)].

The mediation pathology concept takes account to a large extent, though by no means exhaustively, of that horizontal language between peripheral cells, based on locally produced hormone-like substances and aimed at covering extremely short distances. This brings us well and truly into the paracrine domain of intercellular communication, whereby an exchange of messages takes place between adjacent cells via the interstitial spaces. Alongside this short-range communication network, there also exists a long-range network, involving above all the blood stream both as an intermediary and as mediation terrain. To the mediatory processes partakes the neuro-endocrine system, albeit it is not the predominant one as it was classically thought. There are other actors on the mediation stage: oxygen radical plays an important role.

Cell Communication↗
PubMed1986

[Hypothesis of the pathology of mediation in surgery (1)].

The mediation pathology hypothesis is not new. As early as 1955, Laborit hinted at something of the kind in his phrase "N'est malade que l'organisme qui le vent bien". Today, however, in the light of free oxygen radicals, which together with other mediators may possibly represent only the tip of an enormous iceberg, we may venture a number of admittedly cautious theoretical considerations. This would appear to be particularly relevant today, in that surgery at this precise moment, I would venture to say, is at a turning point. On the one hand, surgery is pushing to extremes its classic restrictive morpho-mechanistic approach to disease, while on the other, together with cardiology, it is quick to perceive new biological horizons, which until very recently were unimaginable and, as such, constitute its elective target of interest. Paradoxically, to all intent and purposes at least, the biological rite appears to have found the most natural place for its celebration precisely on the site where the morpho-mechanistic ritual seems to have reached its zenith and, at the same time, its moment of glory.

Animals↗
PubMed1986

[Biology and surgery: a bound pair or merely a couple of disciplines? (2)].

Carcinoma of the breast, to our way of thinking, appears to be capable of providing what is virtually a master key to the interpretation of surgical oncological pathology. In the wake of the acquisitions made in this field--not always as a result of the initiative of the surgeon - a definite process of revision of the age-old concept of surgical radicality is underway, albeit in a somewhat surreptitious manner. Oncological surgery is clearly passing through a difficult phase, almost a crisis of identity, and, in the authors' opinion, may to some extent come back into its own, albeit only after a great deal of painstaking effort, by adopting a "biological" approach with greater respect for the morpho-functional integrity of the patient, who must no longer be viewed as merely the victim of disease, but rather as the prime mover of the disease itself.

Cocarcinogenesis↗