Self-drilling and self-tapping screws: an ultrastructural study.

OBJECTIVE: The aim of the current study was to compare self-drilling and self-tapping screws with regard to bone contact and the production of bone debris using scanning electron microscopy. MATERIALS AND METHODS: Three New Zealand rabbit calvariae were used. Self-tapping and self-drilling screws were inserted into the outer surface of the skull with and without saline solution irrigation. All screws were 5 mm in length and were inserted until their tips projected through the endosteal side. Sixteen screws were used--8 with a head diameter of 1.5 mm and 8 with 2.0 mm. All self-tapping screws were inserted through a drill bit hole (1.6 mm for 2.0-mm screws and 1.3 mm for 1.5-mm screws). RESULTS: There was no damage to the screws after insertion. Bone damage occurred when irrigation was not used during the installment of the self-tapping screws. Bone debris formed during the installment of the self-drilling screws, which is considered beneficial. CONCLUSIONS: Because the insertion of self-drilling screws is performed with manual pressure, irrigation is not essential. Unlike the drilling that occurs with self-tapping screw, the bone debris formed with self-drilling screws is not the result of the heat generated, but rather the result of biologically active bone tissue capable of reacting with the screw and improving its performance. The animal model used proved highly appropriate for comparisons with human beings because the bone structures of the head have the same density and thickness.

Surface bone histology of the occipital bone in humans and chimpanzees.

Human and chimpanzee occipital bones are thought to grow and develop in distinctly opposite bone remodeling patterns. Preliminary research examining growth-remodeling fields (GRFs) from the surfaces of the occipital bone in modern humans and chimpanzee indicates this may not be entirely correct. By using vinyl/resin-casting techniques, coupled with scanning electron and reflected-light microscopy, GRF profiles from a cross-sectional sample of humans and chimpanzees have documented the ongoing histological activities that reflect developmental processes through which taxon-specific ontogenetic trajectories alter bone morphology. Surface bone profiles aid in explaining how the posterior skull takes shape, thereby aiding in our understanding of the developmental processes that may contribute to the morphological variation in the posterior skull in humans and chimpanzees.

Interpretation of scanning electron microscopic images of abraded forming bone surfaces.

The experimental abrasion of forming bone surfaces was conducted so that such surfaces could be characterized. This is particularly important to bone remodeling studies utilizing scanning electron microscope (SEM) imaging of archeological material. Forming surfaces derived from subadult macaque cranial bone were treated by particle abrasion, water abrasion, sliding abrasion, brushing, manual rubbing, weight, exfoliation, chipping and replication. Acetic acid treatments were also performed. The effects of abrasive agents are specific but generally fall into rough (particle and water abrasion) and smooth (sliding abrasion, brushing, rubbing and weight) categories. Protohistoric human and Plio-Pleistocene hominid subadult craniofacial remains were observed with the SEM for comparison with experimental data. The more recent material appeared smooth, probably as a result of specimen preparation procedures using brushes. Surfaces were still interpretable as forming, however, using a more abrasion-resistant feature called intervascular ridging (IVR) described in this study. The IVR pattern is also recognized on the hominid sample, confirming the possibility of performing remodeling studies on abraded fossil material. The abrasion characteristics are somewhat more difficult to classify, however. Abrasion is defined and discussed relative to remodeling studies and taphonomy. The usefulness of the experimental data reported here, however, in paleoenvironmental reconstruction, has yet to be fully realized. Acid and mechanical preparation techniques are briefly addressed. It is concluded that it is possible to characterize a forming surface as abraded according to the findings of this study and that acid, if handled with care, will more likely preserve microanatomical surface detail. It would also be in everyone's interest to employ a less abrasive cleaning regime on archeological specimens.

Embryogenesis of the human occipital bone.

From an original study of fetal specimens, the embryogenesis of the human occipital bone is described. The occipital bone in man is derived from cartilage, except for the interparietal segment which has a membranous origin. Normally there is no midline cerebellar fissure or synchondrosis.