Relationships between bone mass and micro-architecture at the mandible and iliac bone in edentulous subjects: a dual X-ray absorptiometry, computerised tomography and microcomputed tomography study

Relationships between bone mass and micro-architecture at the mandible and iliac bone in edentulous subjects: a dual X-ray absorptiometry, computerised tomography and microcomputed tomography study Objectives:  To compare bone volume, bone mineral density, cortical thickness and bone micro-architecture in a series of paired mandibular and iliac bone samples analysed by various imagery techniques to see whether relationships exist between the various techniques and between mandibular and iliac bone. Materials and methods:  Bone samples from the mandible and ilium were harvested in 20 cadavers and analysed by dual energy X-ray absorptiometry (DXA), computerised tomography (CT) on a conventional hospital machine and microCT. Results:  Significant correlations were found between Hounsfield density obtained by CT, and bone mass determined by microCT but not with DXA values. Cortical thickness measurements were well correlated between CT and microCT. No relationships were found between mandibular and iliac bone, when considering mineral density, cortical thickness, bone volume or micro-architecture. Conclusion:  In clinical practice, CT remains the most appropriate routine means for bone qualitative and quantitative evaluation at the mandible. In this ex vivo study, these results confirm that mandibular bone status does not reflect the axial skeletal one and assist in the placement of implants with dental prostheses in old or osteoporotic patients

Non-invasive evaluation of an injectable bone substitute.

Colloguium on Model Driven Acquisition, GRENOBLE, FRANCE, NOV 23-24, 2000Despite the increasing number of techniques for the preservation of bone ridges after dental avulsion, no precise evaluation of alveolar filling has been performed to date. The criteria of available measurement techniques (probes, retroalveolar or panoramic radiography, and lateral teleradiography) are not sufficiently reliable and precise. This study investigated the reliability of evaluation based on CT images in comparison with retroalveolar radiography (the most precise radiographic technique, providing standardised images), direct measurements, and images obtained in scanning electron microscopy. After a preliminary investigation ex vivo, a study was performed in vivo on three beagles. Mandibular premolars were extracted, and the corresponding alveoli were filled with an injectable bone substitute composed of a calcium phosphate mineral load associated with hydroxypropyl methylcellulose. Measurements performed on CT images relative to visual and automatic detection of density changes and studies of density curves provided better precision than those obtained by retroalveolar radiography. (C) 2002 Academie des sciences/Editions scientifiques et medicales Elsevier SAS

Mating effort and female receptivity : how do male guppies decide when to invest in sex?

Males vary in the degree to which they invest in mating. Several factors can explain this variation, including differences in males’ individual condition and the fact that males allocate their energy depending on the context they face in each mating attempt. Particularly, female quality affects male reproductive success. Here, we studied whether male guppies (Poecilia reticulata) strategically allocated more mating effort, in terms of mating behaviour and male–male competition, when they were matched with a receptive (R) female than a non-receptive one. In accordance with our prediction, we found that males increased their mating behaviour when they were with a receptive female. Even though male guppies can inseminate non-receptive females, we only found high levels of courtship between males that were with a receptive female rather than a non-receptive one. Although there was little affect of female receptivity on male–male competition, we found that males chased and interrupted courtships more with receptive females than with non-receptive females regardless of odour. Finally, we also studied whether the sexual pheromone produced by receptive female guppies is a cue that males use in order to increase their mating effort. We found that males were more attracted to a female when they perceived the sexual pheromone, but only increased their mating and aggressive behaviours when females showed receptive behaviour. This strategic increase in mating effort could result in higher male reproductive success because mating attempts towards receptive females are likely to be less costly and males could have a greater probability of fertilisation