Translucency of recent zirconia materials and material-related variables affecting their translucency: a systematic review and meta-analysis.

BACKGROUND: Recent forms of translucent zirconia material have been developed, offering a wide range of options and varieties for enhancing aesthetics, making it a preferred choice in the field of prosthetic dentistry. However, there is insufficient understanding regarding the recent types of zirconia materials and their optical behavior. Understanding the variables that influence the translucency of zirconia and identifying strategies to enhance its esthetics are crucial. PURPOSE: The current systemic review highlights a comprehensive understanding of different zirconia generations in relation to their optical characteristics and evaluates material-related variables affecting their translucency. METHODS: The present review studied in-vitro studies that evaluated the optical characteristics of different yttria content of yttria stabilized materials. The topics explored were: (1) the different zirconia material generations and their optical behavior; (2) material-related factors that affect their translucency. The research was restricted to online publication in the English language from July 1, 2010, to July 31, 2023, using PubMed, Scopus, and Science Direct resources. The search key terms and their combinations were "zirconia," "translucent zirconia," "cubic zirconia," "highly translucent zirconia," "yttria partially stabilized zirconia," "monolithic zirconia," "translucency," "optical properties," and "light transmission." RESULTS: The data obtained from fifty-three studies addressed the optical characteristics of various zirconia generations. They reported that changing yttria content had a significant impact on translucency. Different kinds of zirconia ceramics of the same generation have varying translucencies. Achieving optimum aesthetics with monolithic zirconia is challenging due to factors related to material aspects such as the presence of additives, point defects, microstructure, thickness, phase distribution, and sintering conditions. CONCLUSIONS: Newly developed monolithic dental zirconia ceramics have improved aesthetics and translucency. However, additional research is necessary to evaluate their performance and long-term durability. TRIAL REGISTRATION: This systematic review was registered in PROSPERO, under number CRD42023474482.

Distribution and variation in gonadotropin releasing hormone-I (GnRH-I) immunoreactive neurons in the brain of the native Thai chicken during the reproductive cycle.

Gonadotropin releasing hormone-I (GnRH-I) is known to regulate the avian reproductive system. We investigated the roles of GnRH-I in the regulation of the reproductive system of the native Thai chicken. The distribution of GnRH-I neurons and changes in GnRH-I-immunoreactive (-ir) neurons throughout the reproductive stages and between incubating and nest-deprived hens were analyzed utilizing immunohistochemical techniques. The results revealed that GnRH-I-ir neurons were distributed in a discrete region lying close to the third ventricle from the level of preoptic area through the anterior hypothalamus, with the greatest abundance found within the nucleus commissurae pallii (nCPa). The number of GnRH-I-ir neurons in the nCPa was highest in laying hens when compared with that in the other reproductive stages. Nest deprivation caused an increase in the number of GnRH-I-ir neurons in the nCPa of nest-deprived hens when compared with incubating hens. These results indicate that GnRH-I expression is correlated with the reproductive state in the native Thai chicken and may be, in part, regulated by it. This study also confirms a pivotal role of GnRH-I in controlling avian reproduction of this non-seasonal breeding, equatorial species.

The dopaminergic system in the brain of the native Thai chicken, Gallus domesticus: localization and differential expression across the reproductive cycle.

Dopamine (DA) has a pivotal role in avian prolactin (PRL) secretion, acting centrally through D(1) DA receptors to stimulate PRL secretion by operating through vasoactive intestinal peptide (VIP). DA also inhibits PRL secretion by activating D(2) DA receptors at the pituitary level. This study was designed to investigate the distribution of DA neurons in the native Thai chicken, utilizing tyrosine hydroxylase (TH) as a marker for dopaminergic neurons. The differential expression of hypothalamic TH immunoreactive (TH-ir) neurons was also compared across the reproductive cycle. The results revealed that TH-ir neurons and fibers were found throughout the brain of the laying hen and were predominantly located within the diencephalon and mesencephalon. The observed distribution pattern of TH immunoreactivity was consistent with that reported previously in several avian species. However, changes in the number of TH-ir neurons in the nucleus intramedialis (nI) were observed across the reproductive cycle and correlated directly with variations in PRL levels. The population of TH-ir neurons in the nI increased significantly during the egg incubation period, where circulating PRL levels were the greatest. This study indicates, for the first time, that an association exists between DA neurons and the regulation of the reproductive system in the native Thai chicken. There is a paucity of information about the reproductive neuroendocrine regulation of tropical non-seasonally breeding avian species and it is suggested that the differential expression of DA neurons in the nI might play a role in the control of VIP secretion and subsequent PRL release in such birds.