Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Fluctuating selection”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,603 records · Page 89Linked to original sources
PubMed2003

Relationship between fluctuating asymmetry and fitness within and between stressed and unstressed populations of the wolf spider Pirata piraticus.

Although developmental instability, measured as fluctuating asymmetry (FA), is expected to be positively related to stress and negatively to fitness, empirical evidence is often lacking or contradictory when patterns are compared at the population level. We demonstrate that two important properties of stressed populations may mask such relationships: (i) a stronger relationship between FA and fitness, resulting in stronger selection against low quality (i.e. developmental unstable) individuals and (ii) the evolution of adaptive responses to environmental stress. In an earlier study, we found female wolf spiders Pirata piraticus from metal exposed populations to be characterized by both reduced clutch masses and increased egg sizes, the latter indicating an adaptive response to stress. By studying the relationship between these two fitness related traits and levels of FA at individual level, we here show a significant negative correlation between FA and clutch mass in metal stressed populations but not in unstressed reference populations. As a result, levels of population FA may be biased downward under stressful conditions because of the selective removal of developmentally unstable (low quality) individuals. We further show that females that produced larger eggs in stressed populations exhibited lower individual FA levels. Such interaction between individual FA and fitness with stress may confound the effect of metal stress on FA, resulting in an absence of relationships between FA, fitness and stress at the population level.

Adaptation, Physiological↗
PubMed1997

In vitro characterization of astaxanthin biosynthetic enzymes.

Escherichia coli strains expressing the marine bacteria (Agrobacterium aurantiacum and Alcaligenes sp. strain PC-1) astaxanthin biosynthetic genes (crtZ and W), Haematococcus pluvialis bkt, and Erwinia uredovora crtZ genes were used for in vitro characterization of the respective enzymes. Specific enzyme assays indicated that all of the enzymes are bifunctional, in that the CrtZ enzymes formed zeaxanthin from beta-carotene via beta-cryptoxanthin, as well as astaxanthin from canthaxanthin via phoenicoxanthin (adonirubin). The BKT/CrtW enzymes synthesized canthaxanthin via echinenone from beta-carotene and 4-ketozeaxanthin (adonixanthin) with trace amounts of astaxanthin from zeaxanthin. Comparison of maximum catalytic activities as well as selectivity experiments carried out in the presence of both utilizable substrates indicated that the CrtZ enzymes from marine bacteria converted canthaxanthin to astaxanthin preferentially, whereas the Erwinia CrtZ possessed a favorability to the formation of zeaxanthin from beta-carotene. The CrtW/BKT enzymes were not so defined in their substrate preference, responding readily to fluctuations in substrate levels. Other properties obtained indicated that the enzymes were strictly oxygen-requiring; and a cofactor mixture of 2-oxoglutarate, ascorbic acid, and Fe2+ was beneficial to activity. Based on enzymological data, a predicted pathway for astaxanthin biosynthesis is described, and it is proposed that CrtZ-like enzymes be termed carotenoid 3, (3')-beta-ionone ring hydroxylase and CrtW/BKT carotenoid 4, (4')-beta-ionone ring oxygenase.

Bacterial Proteins↗
PubMed1988

Natural variability of pulmonary haemodynamics.

In the interpretation of the effect of a drug or intervention in a single patient, it is desirable to know the spontaneous fluctuations of the variable under study. A few studies have determined pulmonary haemodynamic variability in acute and short-term intervals. It seems reasonable to adopt a confidence limit of 6 mmHg or 22% for PPA changes to be significant. The long-term evolution is difficult to determine because of the unavoidable patient selection for repeat examinations several years apart, and because of the necessary treatment. In slight or moderate pulmonary hypertension the changes in PPA with time seem to be of small magnitude: less than 1 mmHg per year.

Exercise↗
PubMed1989

Allozyme-associated heterosis in Drosophila melanogaster.

Two large experiments designed to detect allozyme-associated heterosis for growth rate in Drosophila melanogaster were performed. Heterosis associated with allozyme genotypes may be explained either by functional overdominance at the allozyme loci, or closely linked loci; or by genotypic correlations between allozyme loci and loci at which deleterious recessive alleles segregate. Such genotypic correlations would be favored by consanguineous mating, small effective population size, population mixing and strong natural or artificial selection. D. melanogaster is outbred, has large effective population size and there is little evidence for genotypic disequilibria. Therefore it would be unlikely to show allozyme heterosis due to genotypic correlations. In the first experiment I estimated the genotypic values of 97 replicated genotypes. In the second experiment, 500 individuals were raised in a fluctuating, stressful environment. In neither experiment was there any consistent evidence for allozyme heterosis in size or development rate, fluctuating asymmetry for size or in tendency to deviate from the population mean. In the first experiment, heterosis explained less than 5.6% of the genetic variance in growth characters. In the second, heterosis explained less than 0.1% of the phenotypic variance in growth characters. Outside of the molluscs, species which show allozyme heterosis have population structures or histories which tend to promote genotypic correlations. There is little evidence that functional overdominance is responsible for observations of allozyme-associated heterosis.

Acid Phosphatase↗
PubMed1999

Hormone secretion in the asian elephant (Elephas maximus): characterization of ovulatory and anovulatory luteinizing hormone surges.

In the elephant, two distinct LH surges occur 3 wk apart during the nonluteal phase of the estrous cycle, but only the second surge (ovLH) induces ovulation. The function of the first, anovulatory surge (anLH) is unknown, nor is it clear what regulates the timing of these two surges. To further study this observation in the Asian elephant, serum concentrations of LH, FSH, progesterone, inhibin, estradiol, and prolactin were quantified throughout the estrous cycle to establish temporal hormonal relationships. To examine long-term dynamics of hormone secretion, analyses were conducted in weekly blood samples collected from 3 Asian elephants for up to 3 yr. To determine whether differences existed in secretory patterns between the anLH and ovLH surges, daily blood samples were analyzed from 21 nonluteal-phase periods from 7 Asian elephants. During the nonluteal phase, serum LH was elevated for 1-2 days during anLH and ovLH surges with no differences in peak concentration between the two surges. The anLH surge occurred 19.9+/-1.2 days after the end of the luteal phase and was followed by the ovLH surge 20.8+/-0.5 days later. Serum FSH concentrations were highest at the beginning of the nonluteal phase and gradually declined to nadir concentrations within 4 days of the ovLH surge. FSH remained low until after the ovLH surge and then increased during the luteal phase. Serum inhibin concentrations were negatively correlated with FSH during the nonluteal phase (r = -0.53). Concentrations of estradiol and prolactin fluctuated throughout the estrous cycle with no discernible patterns evident. In sum, there were no clear differences in associated hormone secretory patterns between the anLH and ovLH surge. However, elevated FSH at the beginning of the nonluteal phase may be important for follicle recruitment, with the first anLH surge acting to complete the follicle selection process before ovulation.

Animals↗
PubMed2004

HLA-B and HLA-C alleles and haplotypes in the Dravidian tribal populations of southern India.

The Dravidians are believed to be the earliest inhabitants of India. Their subsequent migration and admixture with invading racial groups has been of scientific interest for population geneticists. In the present study, seven highly endogamous and extremely isolated colonies of Dravidian tribal populations (n = 105) from Kerala in South India were analysed and compared with random non-tribal Dravidian (RND) samples (n = 78) of southern India using the polymerase chain reaction with sequence-specific primer method for HLA-B and HLA-C typing. The tribal group comprises Adiya, Kanikkar, Kattunaikka, Kuruma, Kurichiya, Malapandaram and Paniya, while the RND group includes Malayalam-speaking individuals from various non-tribal castes of Kerala selected randomly. Some of the most frequent HLA-B alleles in the RND population were similar to the North Indian population and included B*07, B*61 (B*40), B*44, B*51, B*35 and B*52. Although B*61 was the most frequent allele in our total study population, the frequency fluctuated in individual populations. HLA-Cw*14 was one of the most frequent alleles while HLA-Cw*17 was totally absent in all populations studied. The haplotype B*61-Cw*14 was present in all the study groups except in Kurichiya, and the haplotype B*51-Cw*14 was only absent in Kattunaikka. Phylogenetic tree and correspondence analysis indicate that all the Dravidian tribal communities group together as a separate cluster, while the RND group of individuals from South India lie close to the North Indian population. This suggests that the RND population of South India might have a crypto-Dravidian origin, while the smaller Dravidian tribal communities have a distinct Dravidian origin.

Alleles↗
PubMed1996

Actions of the digitalis analogue strophanthidin on action potentials and L-type calcium current in single cells isolated from the rabbit atrioventricular node.

1. The atrioventricular node (AVN) of the heart is vital to normal cardiac function and is a major site of antiarrhythmic drug action. This study describes the effects of the cardiac glycoside analogue strophanthidin on spontaneous action potentials and L-type calcium current recorded from single AVN cells isolated from the rabbit heart. 2. With a standard KCl-based internal dialysis solution, exposure to 50 microM strophanthidin produced a progressive depolarization of the maximum diastolic potential and a reduction in action potential amplitude and upstroke velocity. Sustained application resulted in the loss of action potentials and occurrence of spontaneous 'bell-shaped' depolarizations. 3. Cells were whole-cell voltage clamped at -40 mV and depolarizing voltage clamps applied. With a standard KCl-based internal dialysis solution, exposure to 50 microM strophanthidin caused a large reduction of ICa,L at all potentials between -30 and +40 mV (n = 4). At + 10 mV, the mean ICa,L amplitude was reduced from -232 +/- 65 pA to -48 +/- 26 pA (P < 0.05; 1 test; n = 5 cells). 4. To record ICa,L more selectively, cells were dialysed with a Cs-based pipette solution. A short strophanthidin exposure reduced ICa,L amplitude from -250 +/- 31 pA to -88 +/- 19 pA (P < 0.001; n = 8 cells). For both KCl and CsCl-based solutions it was observed that sustained exposure to strophanthidin for several minutes caused spontaneous inward fluctuations in the membrane current record similar to the 'ITI' (arrhythmogenic oscillatory transient inward) current shown for other cardiac cells. 5. When the calcium chelator BAPTA was added to the pipette solution (10 mM), the reduction in ICa,L by strophanthidin was largely eliminated (P > 0.1), and no spontaneous inward current fluctuations were observed after sustained exposure to strophanthidin (n = 8 cells). 6. When external Ca in the perfusate was replaced with Ba, strophanthidin did not significantly reduce the Ba current through L-type calcium channels (n = 5 cells). 7. We conclude that strophanthidin reduces ICa,L by an indirect action, mediated by the rise in intracellular calcium (Cai) which follows inhibition of the Na/K pump caused by cardiac glycosides. The appearance of spontaneous ITI with strophanthidin would also seem to be mediated by a rise in Cai, and may contribute to the spontaneous oscillations in membrane potential observed after prolonged strophanthidin exposure.

Action Potentials↗
PubMed2003

Atmospheric optical communication with a Gaussian Schell beam.

We consider a wireless optical communication link in which the laser source is a Gaussian Schell beam. The effects of atmospheric turbulence strength and degree of source spatial coherence on aperture averaging and average bit error rate are examined. To accomplish this, we have derived analytic expressions for the spatial covariance of irradiance fluctuations and log-intensity variance for a Gaussian beam of any degree of coherence in the weak fluctuation regime. When spatial coherence of the transmitted source beam is reduced, intensity fluctuations (scintillations) decrease, leading to a significant reduction in the bit error rate of the optical communication link. We have also identified an enhanced aperture-averaging effect that occurs in tightly focused coherent Gaussian beams and in collimated and slightly divergent partially coherent beams. The expressions derived provide a useful design tool for selecting the optimal transmitter beam size, receiver aperture size, beam spatial coherence, transmitter focusing, etc., for the anticipated atmospheric channel conditions.

Journal Article↗
PubMed1994

Mechanism of periodic breathing in patients with cardiovascular disease.

Although periodic breathing consisting of alternating hyperpnea and hypopnea has been recognized in heart failure patients, its mechanism has not been clarified. We hypothesized that heart failure patients who have oscillations in ventilation will also be found to have oscillations in pulmonary blood flow, as reflected in left ventricular ejection fraction. To test this hypothesis, we analyzed continuously gas exchange and left ventricular ejection fraction during exercise in cardiac patients who exhibited periodic breathing. Out of 48 consecutive patients with reduced left ventricular function who performed a symptom-limited incremental exercise test using an upright cycle ergometer, we selected 5 patients who exhibited clear ventilatory oscillations during exercise. These patients repeated the same exercise test on another day for measuring gas exchange and left ventricular ejection fraction continuously. Oscillatory changes were noted both in left ventricular ejection fraction and in ventilation in these patients. These observations offer support for the hypothesis that fluctuations in pulmonary blood flow are primarily responsible for the periodic breathing seen in heart failure patients.

Aged↗
PubMed2005

Estimation of direct and maternal genetic and permanent environmental effects for weights from birth to 356 days of age in a herd of Japanese Black cattle using random regression.

A total of 11,815 weight records from 23,94 Japanese Black calves was used to estimate direct, maternal, direct permanent environmental, and maternal permanent environmental effects on growth from birth to 356 d of age. The data were collected from a herd of Japanese Black cattle in Shiroshi city, Miyagi prefecture, Japan. A random regression model, including parity of dam and year-season of calving-sex of calf as fixed effects and animal, dam, animal permanent environmental, and maternal permanent environmental as random effects, was fitted to the data using Legendre polynomials for age of calf. Direct heritability estimates increased from 0.38 at birth to 0.65 at 120 d of age, decreased to 0.38 at 300 d, and then increased again up to 0.47 at 356 d. The ratio of animal permanent environmental variance to phenotypic variance decreased from 0.41 at birth to 0.12 at 90 d, and then increased gradually up to 0.40 at 270 d and oscillated around this value up to the end of the test period. Maternal genetic heritabilities increased from 0.04 at birth to 0.09 at 120 d and then decreased to 0.06 thereafter, whereas the variance ratios due to maternal permanent environment were fairly constant across the age trajectory, fluctuating around the value of 0.03. Direct genetic, phenotypic, maternal genetic, animal permanent environmental, and maternal permanent environmental correlations between different ages were all positive, and they generally decreased as the interval between ages increased. These correlations were lower between weights from nonadjacent ages than those between weights from adjacent ages. Results suggest that selection on preweaning weights would have a positive effect on weights at later ages.

Animals↗
PubMed2002

Lactate, glucose and energy metabolism in the ischemic brain (Review).

For many decades, lactate was considered to be an end product of anaerobic glycolysis in mammalian tissues with no other function in metabolism. As determination of lactate level became a routine in hospital blood work, fluctuations in its levels were associated with situations other than oxygen lack. It was just a matter of time before elevated lactate blood levels emerged as a 'red flag' for potential malaise and frequently was blamed as the of it. Lactate and its accompanying acidosis are still considered today to be major contributors to selective neuronal damage in cerebral ischemia despite the emergence of alternative, more compelling postulates as to the causes of this damage. The attitude, especially among clinicians, has been difficult to change despite recent findings that strongly indicate lactate to be a possible beneficial intermediate in brain energy metabolism. This review revisits briefly the annals that brought about the lingering negative attitude toward lactate and expands on the more recent findings and debates that have illuminated this monocarboxylate in a different, more positive light.

Acidosis, Lactic↗
PubMed2004

High-potency benzodiazepines: recent clinical results.

As high-potency benzodiazepines, essentially alprazolam, clonazepam, and lorazepam, have been used to treat anxiety disorders for almost 2 decades, most efficacy and safety data appeared several years ago. The release of new formulations of 2 of them, clonazepam and alprazolam, invites review of these broadly effective anxiolytics. Clonazepam has recently become available in a lyophilized wafer that disintegrates when exposed to saliva and enhances ease of administration without altering its pharmacology, as shown by bioequivalence studies. Two U.S. multicenter trials carried out in the 1990s, among others, have provided strong confirmatory evidence for the use of clonazepam in panic disorder. Other recently published data on clonazepam pertain to its use as augmentation therapy with selective serotonin reuptake inhibitors and in the prevention of recurrences of major depressive disorder. A new, extended-release formulation of alprazolam now allows for once-daily rather than t.i.d. or q.i.d. dosing. With extended release, the blood drug concentrations of alprazolam remain within the therapeutic window for several hours, which should reduce fluctuation in therapeutic effect and curb the clock-watching phenomenon between doses. The literature concerning the use of this new formulation of alprazolam in panic disorder is reviewed.

Anxiety Disorders↗
PubMed1980

Failure of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate to enhance sister chromatid exchange, mitotic segregation, or expression of mutations in Chinese hamster cells.

The potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) was tested for its ability (a) to induce sister chromatid exchange, (b) to increase the rate of transition at the adenine phosphoribosyltransferase (apt) locus from the presumptive heterozygous state ((+/- to the homozygous state (-/ - or -), and (c) to enhance the frequency of mutations expressed after ultraviolet radiation mutagenesis. We have found no significant effect of TPA in any of these experiments. Sister chromatid exchange frequencies in both V79 and Chinese hamster ovary cells remained unchanged by TPA treatment under various conditions, a result inconsistent with the hypothesis that an important effect of TPA might be to increase the rate of chromosomal mitotic recombination (and hence segregation of recessive mutations) in a manner akin to increased chromatid recombination. We have also been unable to obtain evidence for mitotic recombination affecting the aprt locus in Chinese hamster ovary cells for which the rate of change to a high level of resistance to azaadenine was measured. The rate of 8.6 X 10(-7) mutation (and/or segregations) per cell generation assessed by fluctuation analysis was not increased by the continuous presence of TPA, 4 microgram/ml, in the medium. In the third set of experiments, mutant frequencies in Chinese hamster ovary cells after ultraviolet mutagenesis were measured for the markers ouabain resistance, thioguanine resistance, and azaadenine resistance, under conditions with and without pretreatment with TPA before mutant selection. No convincing enhancement in mutation expression was observed. In summary, these results argue that promotion by TPA does not proceed by a mechanism involving genetic recombination or the altered expression of newly mutated alleles.

Animals↗
PubMed1993

Seasonal energy stress in an Ethiopian rural community: an analysis of the impact at the household level.

The household integrated response to seasonal fluctuations in food availability and work load was assessed in a longitudinal study in two villages of southern Ethiopia. The household response to energy stress was estimated by pooling weight changes of all members of the family, accounting for the diverse biological and functional meaning of weight losses of different age and sex groups, and levels of nutritional status. On average, seasonal energy stress experienced by the households was modest (3.3%, P < 0.05 by Tukey test). The cumulative weight change of poor households was twice as large as that of rich ones, and evidence was obtained of their further deterioration over the following agricultural year. Household food availability fluctuated seasonally, with evident socio-economic gradient: in the early pre-harvest season food stocks of poor households were 6.5 times smaller than those of better-off families (P < 0.001 by ANOVA). Unlike rich households, poor families markedly decreased the time devoted to agriculture in the pre-harvest season. Crop selection, quality of land management and time employed in agricultural work might have synergistically concurred to cause the stress situation.

Adolescent↗
PubMed2004

Applying the partitioned multiobjective risk method (PMRM) to portfolio selection.

The analysis of risk-return tradeoffs and their practical applications to portfolio analysis paved the way for Modern Portfolio Theory (MPT), which won Harry Markowitz a 1992 Nobel Prize in Economics. A typical approach in measuring a portfolio's expected return is based on the historical returns of the assets included in a portfolio. On the other hand, portfolio risk is usually measured using volatility, which is derived from the historical variance-covariance relationships among the portfolio assets. This article focuses on assessing portfolio risk, with emphasis on extreme risks. To date, volatility is a major measure of risk owing to its simplicity and validity for relatively small asset price fluctuations. Volatility is a justified measure for stable market performance, but it is weak in addressing portfolio risk under aberrant market fluctuations. Extreme market crashes such as that on October 19, 1987 ("Black Monday") and catastrophic events such as the terrorist attack of September 11, 2001 that led to a four-day suspension of trading on the New York Stock Exchange (NYSE) are a few examples where measuring risk via volatility can lead to inaccurate predictions. Thus, there is a need for a more robust metric of risk. By invoking the principles of the extreme-risk-analysis method through the partitioned multiobjective risk method (PMRM), this article contributes to the modeling of extreme risks in portfolio performance. A measure of an extreme portfolio risk, denoted by f(4), is defined as the conditional expectation for a lower-tail region of the distribution of the possible portfolio returns. This article presents a multiobjective problem formulation consisting of optimizing expected return and f(4), whose solution is determined using Evolver-a software that implements a genetic algorithm. Under business-as-usual market scenarios, the results of the proposed PMRM portfolio selection model are found to be compatible with those of the volatility-based model. However, under extremely unfavorable market conditions, results indicate that f(4) can be a more valid measure of risk than volatility.

Journal Article↗
PubMed1987

The genetic structure of natural populations of Drosophila melanogaster. XX. Comparison of genotype-environment interaction in viability between a northern and a southern population.

In order to examine the operation of diversifying selection as the maintenance mechanism of excessive additive genetic variance for viability in southern populations in comparison with northern populations of Drosophila melanogaster, two sets of experiments were conducted using second chromosomes extracted from the Ogasawara population (a southern population in Japan) and from the Aomori population (a northern population in Japan). Chromosomal homozygote and heterozygote viabilities were estimated in eight kinds of artificially produced breeding environments. The main findings in the present investigation are as follows: (1) Significant genotype-environment interaction was observed using chromosomes extracted from the Ogasawara population. Indeed, the estimate of the genotype-environment interaction variance for heterozygotes was significantly larger than that of the genotypic variance. On the other hand, when chromosomes sampled from the Aomori population were examined, that interaction variance was significant only for homozygotes and its value was no more than one quarter of that for the chromosomes from the Ogasawara population. (2) The average genetic correlation between any two viabilities of the same lines estimated in the eight kinds of breeding environments for the chromosomes sampled from the Ogasawara population was smaller than that for the chromosomes from the Aomori population both in homozygotes and in heterozygotes, especially in the latter. (3) The stability of heterozygotes over homozygotes against fluctuations of environmental conditions was seen in the chromosomes from the Ogasawara population, but not from the Aomori population. (4) From the excessive genotype-environment interaction variance compared with the genotypic variance in heterozygotes, it was suggested for the chromosomes from the Ogasawara population that the reversal of viability order between homozygotes took place in some environments at the locus level. On the basis of these findings, it is strongly suggested that diversifying selection is operating in a southern population of D. melanogaster on some of the viability polygenes which are probably located outside the structural loci, and the excessive additive genetic variance of viability in southern populations is maintained by this type of selection.

Alleles↗
PubMed1998

Active brood care in an amphipod: influences of embryonic development, temperature and oxygen.

Female amphipods (Crustacea) carry their fertilized eggs in an external brood pouch until the fully formed juveniles emerge (passive brood care). They may also direct specific maternal activities towards the brood (active brood care). We show that Crangonyx pseudogracilis, which typically populates fresh-waters subject to wide fluctuations in temperature and dissolved oxygen, engages in a highly responsive form of active brood care. This involves a flexing motion by the female that expands the brood pouch and increases the suspension of the eggs in the surrounding medium, accompanied by ventilation of the brood pouch and the 'cycling' of eggs therein. Females also selectively eject nonviable eggs from their broods. We investigated the expression of this brood care behaviour in relation to intrinsic and extrinsic factors relevant to the development of broods. The time spent by females in this behaviour initially increased as embryos developed, but decreased once advanced embryos began to self-ventilate and to have a heart pulse. In addition, both increased temperature and decreased oxygen concentration resulted in increased levels of brooding behaviour. We thus propose that this behaviour functions to ameliorate the microclimate of the brood pouch and serves the changing metabolic demand of the brood, as influenced by the interaction of embryonic development with temperature/dissolved oxygen regime. In addition, this behaviour may be a key adaptation facilitating the success of this North American species as an invader of disturbed and polluted freshwaters in Europe and elsewhere. Evidence is emerging that other amphipods associated with harsh environmental conditions also show such active maternal brood care. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Thermal cycling procedures for laboratory testing of dental restorations.

OBJECTIVES: Exposure of restorations in extracted teeth to cyclic thermal fluctuations to simulate one of the many factors in the oral environment has been common in many tracer penetration, marginal gap and bond strength laboratory tests. Temperature changes used have rarely been substantiated with temperature measurements made in vivo and vary considerably between reports. Justification and standardization of regimen are required. DATA, SOURCES AND STUDY SELECTION: An assessment of reports describing temperature changes of teeth in vivo is followed by an analysis of 130 studies of laboratory thermal cycling of teeth by 99 first authors selected from 25 journals. A clinically relevant thermal cycling regimen was derived from the in vivo information, and is suggested as a benchmark standard. CONCLUSIONS: Variation of regimens used was large, making comparison of reports difficult. Reports of testing the effects of thermal cycling were often contradictory, but generally leakage increased with thermal stress, although it has never been demonstrated that cyclic testing is relevant to clinical failures. However, should this be done, the standard cyclic regimen defined is: 35 degrees C (28 s), 15 degrees C (2 s), 35 degrees C (28 s), 45 degrees C (2 s). No evidence of the number of cycles likely to be experienced in vivo was found and this requires investigation, but a provisional estimate of approximately 10,000 cycles per year is suggested. Thermal stressing of restoration interfaces is only of value when the initial bond is already known to be reliable. This is not the case for most current restorative materials.

Benchmarking↗