Lasers in Periodontology Today and Tomorrow

The concept of periodontal treatment has radically changed over the past decades from a very aggressive surgical approach of pocket elimination to a conservative treatment. The treatment objective today is just removing the periodontal disease causing agents. Regarding this aspect the use of lasers in periodontal treatment may be the next step towards a more conservative treatment.Selective ablation of calculus requires preferential absorption by the material to be removed compared to the healthy tissues.In Periodontology the use of the Nd:YAG laser is restricted to the field of soft tissue management, no ablation of calculus is possible. Using conventional CO₂ lasers runs the risk of thermal overheating of the pulp. Moreover due to the absorption characteristics uncontrolled destruction of gingival tissue as well as cementum and enamel occurs. Excimer and Er:YAG lasers can be used to remove calculus but uncontrolled ablation of healthy tooth structure takes place. The frequency doubled Alexandrite (377 nm) laser allows a selective ablation of calculus based on natural differences in absorption. Calculus and microbial plaque are removed quickly and easily while cementum and other healthy tooth structures remain unchanged.In order to establish clinically healthy gingiva and to prevent further loss of attachment the use of the frequency doubled Alexandrite laser seems to be a very promising step for the future of periodontal therapy. Moreover the expectation of a sound maintenance therapy will be fulfilled by using this laser.     

倍频Nd：YAG激光小梁成形术疗效分析

为评价倍频Ｎｄ：ＹＡＧ激光小梁成形术的临床疗效。对２２例３８只临床用药物不能控制病情发展的原发性开角型青光眼，采用倍频Ｎｄ：ＹＡＧ激光实施小梁成形术，所有病例均治疗下半部１８０°小梁，５０个光凝点，局部组织产生苍白反应。结果：随访期内眼压平均下降０．７５ｋＰａ（５ｍｍＨｇ），眼压降幅与术前眼压水平成正相关。结论：倍频Ｎｄ：ＹＡＧ激光是行小梁成形术的有效激光，治疗参数为：光斑直径５０μｍ，功率０．７～１．２Ｗ，曝光时间０．１ｓ。     

Theoretical and experimental assessment of genome-based prediction in landraces of allogamous crops

Discovery and enrichment of favorable alleles in landraces are key to making them accessible for crop improvement. Here, we present two fundamentally different concepts for genome-based selection in landrace-derived maize populations, one based on doubled-haploid (DH) lines derived directly from individual landrace plants and the other based on crossing landrace plants to a capture line. For both types of populations, we show theoretically how allele frequencies of the ancestral landrace and the capture line translate into expectations for molecular and genetic variances. We show that the DH approach has clear advantages over gamete capture with generally higher prediction accuracies and no risk of masking valuable variation of the landrace. Prediction accuracies as high as 0.58 for dry matter yield in the DH population indicate high potential of genome-based selection. Based on a comparison among traits, we show that the genetic makeup of the capture line has great influence on the success of genome-based selection and that confounding effects between the alleles of the landrace and the capture line are best controlled for traits for which the capture line does not outperform the ancestral population per se or in testcrosses. Our results will guide the optimization of genome-enabled prebreeding schemes.

Genetic improvement is essential to secure sustainable crop production. Future crops will have to combine high yield potential with major sustainability factors, such as stress tolerance and resource efficiency. To meet these demands, plant breeding will require a reservoir of genetic variation much larger than what is currently found in commercial varieties (1). For maize, it has been estimated that US breeding populations represent only 2% of the entire maize germplasm (2). In contrast, seed banks around the world harbor thousands of untapped landrace accessions (1, 3, 4). Revisiting this vast diversity of landraces is considered promising for elite germplasm improvement (1, 5–9), and developments in molecular, computational, and quantitative genetics open new avenues to make native diversity accessible.Landraces have been shown to harbor beneficial alleles for traits with limited genetic variation in breeding populations (10), but for most agronomically important traits, they exhibit a substantial performance gap compared with elite germplasm (11–13). While for qualitative traits targeted introgression of favorable alleles discovered in landraces is possible, many traits have a polygenic foundation, which is determined by a large number of genes with small effects. Consequently, marker-based introgression of individual alleles is limited for those traits. Extracting inbred lines directly from landraces and selecting them for superior performance can close the performance gap only partially. Therefore, recurrent population improvement with additional rounds of recombination and selection is necessary to increase the frequency of favorable alleles before introducing landrace-derived genetic material into elite populations. Genome-based selection can accelerate this process, but the theoretical basis of its implementation in prebreeding still needs to be developed.In outcrossing species, population improvement generally includes three distinct phases (14): 1) sampling candidates from the population to establish progeny for evaluation, 2) evaluating them in multienvironment field trials, and 3) recombining the best candidates to form the next cycle. In genome-based recurrent selection, genomic data are collected in the first phase, and together with data from the second phase, a statistical model is trained for prediction of breeding values of untested candidates from the same or future breeding cycles. The success of this approach depends strongly on the prediction accuracy that can be achieved with the training data. One major determinant is the type of progenies that can be derived from the ancestral landrace (e.g., inbred lines, full- or half-sib families). Additional factors are the quality of phenotyping expressed as the heritability (h²) of the target traits, the sample size (N), and the number of markers (M).Here, we developed the quantitative genetic framework for two fundamentally different concepts for establishing training populations from landraces. The two concepts are displayed in Fig. 1 and differ with respect to the proportion of landrace genome and technical steps for their production. The “pure” approach entails the production of fully homozygous doubled-haploid (DH) lines from the ancestral landraces. The DH lines exhibit twice the additive genetic variance of the ancestral landrace and allow high-precision phenotyping. The “admixed” approach captures gametes of the landraces in a cross with an inbred (capture) line of different genetic background followed by subsequent selfing of the offspring. When the aim of the prebreeding program is the immediate development of superior inbred lines, a natural choice for the capture line would be a high-performing elite line to increase the usefulness of the resulting population compared with the pure approach. However, the use of an elite capture line has been shown to carry a high risk of reconstructing the elite genome, associated with a loss of landrace alleles in later selection steps (15). We, therefore, investigated the role of the capture line for the genetic improvement of landrace-derived populations with a focus on genome-based recurrent selection. We link generic theory with population-specific molecular parameters and experimental results on several traits, including yield, in four unique populations representing the pure and the admixed approach as well as two ancestral landraces.Open in a separate windowFig. 1.Scheme of population development for the pure and admixed approaches.     

Wavelengths for laser treatment of port wine stains and telangiectasia

Background and Objective: This report presents analytical modelling of the influence of wavelength on the amount of volumetric rate of heat produced in dermal blood vessels by millisecond laser radiation. Study design/Materials and Methods: A new anatomical model is proposed that represents port wine stains as well as telangiectatic lesions. It consists of a target blood vessel, representing the deepest dermal blood vessel that requires irreversible injury, and a layer of whole blood, representing all other dermal blood vessels above the target vessel. The laser light that interacts with the blood vessels is assumed to be diffuse. Selective photothermolysis is the basis for the analysis. We consider wavelengths between 577 nm and 600 nm, the argon laser wavelengths at 488/515 nm, and the frequency doubled Nd:YAG laser wavelength at 532 nm. Results: The rate of volumetric heat production of absorbed laser light in the target blood vessel is expressed analytically as a function of blood absorption, the concentration of additional dermal blood, and the depth of the target vessel. Conclusion: The model explains why 585 nm is a good compromise for treating port wine stains that vary widely in number of dermal blood vessels. It predicts that wavelengths between 577 nm and 582 nm are excellent for the treatment of port wine stains in young children, and it suggests a possible explanation as to why the argon laser is sometimes said to be capable of treating dark mature port wine stains. The copper vapour laser wavelenght at 578 nm, and the frequency doubled Nd:YAG laser wavelength at 532 nm, are predicted to be suitable for the treatment of port wine stains that contain, respectively, a small to moderate and a moderate number of dermal blood vessels. When laser beam spotsize becomes smaller, the best wavelength for producing maximal rate of heat in the target vessel is predicted to shift to 577 nm. © 1995 Wiley-Liss, Inc.     

Correlations between observability of the spatial frequency doubled illusion and a multi-region pattern electroretinogram

A glaucoma screening device based on the visibility of the spatial frequency doubled (FD) illusion will be marketed by Welch Allyn Ltd in the next year (ANU Patents (Australia) 611 585, (USA) 5 065 767 and application PL 3130). An underlying assumption of the method is that retinal processes are being tested. To test this assumption we compared the visibility of the FD illusion over a range of conditions and in the same spatial locations as a multi-region pattern electroretinogram (PERG). Grating speed and contrast were good predictors of the psychometric functions and PERG amplitude and phase.