Evaluation of a combined thiourea and hydrogen peroxide regimen to bleach bloodstained teeth.

BACKGROUND: Current techniques for intra-coronal bleaching of stained root-filled teeth employ oxidative bleaching with hydrogen peroxide. However, concern over the potential for invasive cervical resorption following the use of hydrogen peroxide has been expressed by many researchers, and recommendations have been made to limit the use of this agent. A reductive-oxidative bleaching process using a thiourea and hydrogen peroxide regimen is proposed as an effective and safer bleaching combination. The efficacy of this novel bleaching regimen is evaluated in this study. METHODS: The study involved a quantitative and qualitative spectrophotometric assessment of the ability of two amine (bleaching) agents, aqueous thiourea and acidified thiourea, to alter the absorption spectra of haemoglobin and methaemoglobin compared to hydrogen peroxide. In addition, extracted premolar teeth discoloured by blood were subjected to different bleaching regimens using amine reducing agents and hydrogen peroxide. The change in the colour of the bloodstained dentine samples was measured at each stage of the bleaching process with a Photometer and Reflectance Densitometer. Comparisons of different treatments were made using a method of least significant difference and/or analysis of variance. RESULTS: Spectrophotometric studies showed that acidified thiourea solution greatly reduced the colour of the haemoglobin and methaemoglobin in the visible range (330-760 nm). Aqueous thiourea had no effect on the presence of haemoglobin and methaemoglobin. Reflection Densitometer and Photometer scores indicate that the greatest bleaching effect was achieved by the combined acidified thiourea and hydrogen peroxide regimen. CONCLUSION: The recognition that bleaching discoloured teeth is a chemical process, which can be achieved by both reducing and oxidizing agents, offers the possibility of developing new and safer clinical bleaching protocols. It is concluded that the bleaching regimen which employs the sequential use of 0.1 M acidified thiourea and 30% w/v hydrogen peroxide is as effective at bleaching bloodstained dentine as 30% w/v hydrogen peroxide alone. However, the addition of thiourea to the bleaching regimen has the potential benefit of reducing the level of damaging hydroxyl radicals and achieving a safer bleaching process.

A quantitative comparison of traditional and non-peroxide bleaching agents.

Single-rooted premolar teeth, stained with blood utilizing the technique devised by Freccia & Peters (1981), were subjected to traditional and non-peroxide bleaching agents. Colour changes were recorded over a period of 7 days using a Speedmaster R75-CP Reflection Densitometer. The most efficient removal of staining occurred after the application of 30% hydrogen peroxide, with sodium perborate being 75% as effective. All bleaching agents realized their optimum efficacy within the first 3 days. A combination of three enzymes (amylase, lipase and trypsin) with disodium edetate was not as effective as the routine bleaching agents; however, the combination did have a modifying effect on the blood stains. It is suggested that other non-peroxide agents should be investigated to determine their efficacy in removing staining from experimentally induced blood-stained teeth.

Hydroxyl radical activity in thermo-catalytically bleached root-filled teeth.

Intra-coronal bleaching of root-filled teeth has been associated with invasive cervical root resorption. It is considered that during bleaching hydrogen peroxide diffuses through the tooth structure into the cervical periodontium, resulting in periodontal tissue destruction and initiating a resorptive process. Hydrogen peroxide is capable of generating hydroxyl radical, an oxygen-derived free radical, in the presence of ferrous salts. Hydroxyl radicals are extremely reactive and have been shown to degrade components of connective tissue, particularly collagen and hyaluronic acid. The aim of the present study was to determine whether hydroxyl radicals are generated during the bleaching of root-filled teeth which have been discoloured by blood. Forty extracted human premolar teeth were root-filled with gutta-percha and AH26 sealer cement. Twenty of the teeth were experimentally discoloured by blood. All teeth were then thermo-catalytically bleached using 30% hydrogen peroxide while tooth roots were seated in a test solution of sodium salicylate. Hydroxyl radical generation was determined by the detection of reaction products of this radical with salicylate using high performance liquid chromatography with electrochemical detection (HPLC-ECD). The presence of hydroxyl radicals was detected in twenty-five of the teeth. There was a significant association between the production of hydroxyl radicals and the presence of tooth discolouration caused by blood components. Greatest yields of hydroxyl radicals occurred in teeth in which EDTA had been used to clean the pulp chamber prior to bleaching. It was concluded that hydroxyl radicals are generated during the thermo-catalytic bleaching of root-filled teeth. Generation of this toxic chemical species may be one mechanism underlying periodontal tissue destruction and root resorption after intra-coronal bleaching.

Forensic implications of the variation in morphology of marginal serrations on the teeth of the great white shark.

The teeth of the Great White Shark have been examined to ascertain whether there is any commonality in the arrangement or number of the marginal serrations (peaks) or, indeed, whether individual sharks have a unique pattern of shapes or size of the peaks. The teeth of the White Shark are characteristic in size and shape with serrations along almost the entire mesial and distal margins. This study has revealed no consistent pattern of size or arrangement of the marginal serrations that was sufficiently characteristic within an individual shark to serve as a reliable index of identification of a tooth as originating from that particular shark. Nonetheless, the serrations are sufficiently distinctive to enable the potential identification of an individual tooth as having been the cause of a particular bitemark.

Quantitative forensic evaluation of bite marks with the aid of a shape analysis computer program: Part 1; The development of "SCIP" and the similarity index.

Bite marks left on human tissue and bitten material have become an important aspect of scientific evidence used for the conviction or acquittal of a suspect. Expert opinion has often been based on subjective comparisons rather than any objective metrical analysis and many experts will agree that there is a need to employ additional comparative tests to achieve unbiased objectivity in their investigation. In this study, an interactive shape analysis computer program ("SCIP"-Shape Comparison Interactive Program) has been employed in an attempt to derive experimentally a quantitative comparison, in the form of a Similarity Index (S.I.), between the "offender's" teeth and the bite marks produced on a standard flat wax form. The S.I. values obtained using "SCIP" were evaluated in a variety of experimental bite mark situations. It was found that in no case could the S.I. values produced by comparison of the bite mark with the dental casts from non-perpetrators be confused with the much lower S.I. from comparison of the bite mark with the dental cast of the perpetrator. The use of the Similarity Index derived using the "SCIP" program is recommended as a simple, accurate and objective means of comparing bite marks in suitable forensic cases.

Quantitative forensic evaluation of bite marks with the aid of a shape analysis computer program: Part 2; "SCIP" and bite marks in skin and foodstuffs.

In a previous paper 1, we have shown that the use of an interactive shape analysis computer program ("SCIP") and the derivation of a quantitative Similarity Index 1 greatly facilitated the comparison of experimental flat wax bite marks with the dentition of various 'suspects' and the identification of the agent producing the bite. In this study, "SCIP" was employed in an attempt to quantify the comparison, in the form of the Similarity Index (S.I.), between the "offender's" teeth and the bite marks produced on foodstuffs and on human skin, under experimental conditions. The use of "SCIP" and the S.I. is recommended as a routine means of eliminating suspects in bite mark cases. If a reasonable number of reference points have been registered in the bitten material and particularly if the perpetrator has any unusual features in the anterior dentition, the matching of the bite mark with the actual offender is a possibility with this method.

Allometric relationships of the dentition of the great White Shark, Carcharodon carcharias, in forensic investigations of shark attacks.

As a result of a systematic morphometric study of shark dentitions, a system of notation for describing the location of shark teeth has been developed and is proposed as a standard to be adopted for use in similar studies in the future. The macroscopic morphology of White Shark teeth has been characterised in order to gain quantitative data which might assist in identification of these sharks from bite marks on victims or objects or from shark carcasses. Using these data, a nomogram has been developed which can be used to estimate the body length of a White Shark from measurements of tooth or bite mark morphology. An example of the forensic application of such allometric data is provided as it applied to a recent fatal attack on a diver by a White Shark.

A rapid and sensitive method for the identification and quantitation of sub-picomolar amounts of neurohypophysial peptides.

A simple, rapid and sensitive method, using isocratic reversed-phase HPLC, is described for the concomitant identification and quantitation of low levels of the various neurohypophysial peptides in biological tissues and fluids. The method requires little or no sample preparation and utilises UV peak detection at 215 nm with a serial signal amplification system to achieve a usable maximum sensitivity of less than 200 fmol of peptide.

Perfusion of the septum of the rabbit with vasopressin antiserum enhances endotoxin fever.

The septal region of the brains of conscious, adult, male New Zealand White rabbits were perfused by means of a push-pull system before and after an intravenous administration of bacterial pyrogen extracted from Salmonella abortus equi. Perfusion of the septal area with sucrose solution (260 mM) had no significant effect on the resulting fever (1.13 +/- 0.09 degrees C) when compared to a control fever without the push-pull perfusion (1.06 +/- 0.12 degrees C). Arginine vasopressin (AVP) added to the perfusing solution (20 micrograms/ml) caused a significant attenuation of the fever (0.81 +/- 0.20 degrees C). An antiserum specific to AVP when added to the perfusing solution resulted in a fever which was significantly greater (2.38 +/- 0.13 degrees C) than the control. Radioimmunoassay of perfusates collected from the control perfusions before and during fever showed that, as the body temperature rose in response to the pyrogen, the level of AVP in the perfusate collected from the septal area decreased. These results provide further evidence that AVP may act in the septal area of the brain to modulate the febrile response.

The hypothalamo-neurohypophysial system of native Australian desert rodents. The vasopressin and oxytocin contents of hypothalamus and posterior pituitary of Notomys alexis and Pseudomys australis compared with those of the laboratory rat and mouse in different states of water balance.

The neurohypophysial hormones vasopressin (the antidiuretic hormone) and oxytocin have been quantified in xerophilic and mesophilic rodents under normal and dehydrated conditions in order to study the relative contribution of these hormones to survival under drought conditions. The ability to cope adequately with water deprivation or saline ingestion was found to be closely related to the magnitude (relative to body size) of pre-existing hormone stores in the neural lobe and to the subsequent ability to enhance hypothalamic biosynthesis of vasopressin and oxytocin sufficiently to maintain those stores at near-normal levels despite a continuing high level of demand for vasopressin and, apparently, also oxytocin. The possible role(s) of the release of oxytocin in these conditions is discussed. Attempts have been made to explain differences observed between laboratory-bred Notomys and those taken from the wild in their relative abilities to withstand water deprivation, the former seeming to be more dependent upon acutely accelerated hormone biosynthesis than on previous adaptation via renal medullary 'work-load' hypertrophy.

The hypothalamo-neurohypophysial system of native Australian desert rodents. The catecholamine contents of the hypothalamus and posterior pituitary of Notomys alexis, Pseudomys australis and the laboratory rat.

The putative central catecholamine neurotransmitters, adrenaline, noradrenaline and dopamine, have been quantified by enzyme radiochemical methods in the hypothalamo-neurohypophysial system (HNS) of the xeric rodents, Notomys alexis and Pseudomys australis, using the laboratory rat for comparison. All three catecholamines were found (noradrenaline greater than dopamine greater than adrenaline) in the hypothalami of the three species. The hypothalami of the two xeric rodents contained some 5-10 times as much of each of the catecholamines (when expressed as ng per body weight) as the rat. The ratio of noradrenaline to dopamine was constant (3 X 8-4 X 2) between species. Posterior pituitary contents of the catecholamines were generally inconsistent within and between species, with only dopamine being invariably and consistently present. It was also found that, like the antidiuretic hormone content, the dopamine content of the neural lobe was significantly correlated with the body surface area of the animal. Withdrawal of drinking water or its replacement with 2 X 5% saline increased hypothalamic noradrenaline synthesis and dopamine utilisation. In the neural lobe, saline ingestion produced a significant increase in all three catecholamines, but with water deprivation only dopamine was increased (relative to body weight). The results of these studies are interpreted as indicating a possible role for catecholamine neurotransmitters, particularly dopamine, in the control of neurohypophysial hormone release in the HNS.

The effect of dopamine on neurohypophysial hormone release in vivo and from the rat neural lobe and hypothalamus in vitro.

1. The rat hypothalamus (containing the supra-optic nuclei, paraventricular nuclei, median eminence and proximal pituitary stalk) has been incubated in vitro and shown to be capable of releasing the neurohypophysial hormones, oxytocin and arginine vasopressin, at a steady basal rate about one twentieth that of the rat neural lobe superfused in vitro. 2. The hypothalamus and neural lobe in vitro released both hormones in a similar arginine vasopressin/oxytocin ratio of about 1-2:1. However, when release was expressed relative to tissue hormone content, the hypothalamus was shown to release about three times as much arginine vasopressin and six times as much oxytocin as the neural lobe. 3. Dopamine in a concentration range of 10(-3)-10(-9)M caused graded increases in hormone release from the hypothalamus in vitro to a maximum fivefold increase over preceding basal levels. The demonstration that apomorphine also stimulated hormone release whereas noradrenaline was relatively ineffective suggested that a specific dopamine receptor was involved. A separate cholinergic component in the release process was indicated by the finding that acetylcholine stimulated release to a maximum fivefold increase in concentrations of 10(-3)-10(-9)M. 4. The fact that the isolated hypothalamus can be stimulated by dopamine and acetylcholine to release increased amount of oxytocin and arginine vasopressin raises the question of the origin and fate of the hormones released in this way. The possibility that they could be released into the hypophysial portal circulation from median eminence to affect the anterior lobe of the pituitary is discussed. 5. In similar doses, both dopamine and noradrenaline injected into the lateral cerebral ventricles of the brain of the anaesthetized, hydrated, lactating rat caused the release of arginine vasopressin and oxytocin. Apomorphine release both hormones but at a higher dose level and to less effect than the catecholamines. 6. The hormone release induced in vivo by dopamine could be prevented by the prior administration of haloperidol or phentolamine and these antagonists were equally effective in blocking the hormone release due to noradrenaline. The involvement of a specific dopamine receptor was more clearly implicated by the use of pimozide which completely inhibited the hormone release due to dopamine and apomorphine but not that due to noradrenaline. 7. It is suggested that the release of neurohypophysial hormones can be stimulated via a dopaminergic nervous pathway in addition to a cholinergic one. The possibility that the osmoreceptor mechanism for the release of antidiuretic hormone from the neural lobe of the pituitary may involve such a dopaminergic pathway is discussed.