Shaping ability of the M4 handpiece and Safety Hedstrom Files in simulated root canals

The aim of this study was to assess the shaping ability of the M4 reciprocating handpiece and Safety Hedstrom files in simulated canals. A total of 40 simulated canals of various angles and positions of curvature were prepared with an M4 handpiece using Safety Hedstrom files oriented with the ground, flattened surface towards the inner aspect of the curve. A standard regimen was adopted throughout. Pre- and post-operative longitudinal images of the canals were taken with a video camera and stored and manipulated in a computer with image analysis software. The presence of canal aberrations and the amount and location of resin material removed as a result of preparation were determined from composite images of superimposed pre- and post-operative views. Preparation time varied significantly (P<0.001) between the canal types; overall, 20° canals were prepared more quickly than 40° canals. Zips and elbows were observed in 16 out of the 40 canals with most (11) being created in 40° specimens. Ledges were found in 19 canals and perforations in only 1. There were no significant differences between canal shapes for these aberrations. Excessive removal of material from the inner aspect of the canal at the curve to create a danger zone was found in 20 canals, but only in those with 40° curves. Significant differences in total canal width between the canal types were seen at the zips (P<0.05), elbows (P<0.05) and danger zones (P<0.001). Transportation at the danger zones varied significantly (P<0.001) between canal types. Under the conditions of this study, the M4 handpiece and Safety Hedstrom files created hour-glass preparations in a substantial proportion of canals. In reality, the Safety Hedstrom file with its one flattened surface was ineffective at reducing removal of material along the inner aspect of canal curves in severely curved specimens and clearly has the potential to create strip perforations in teeth.     

On the significance of remodeling space and activation rate changes in bone remodeling

This paper quantifies the relative contributions of the remodeling space and the accumulation of Haversian canals to bone porosity at various ages. It also examines the importance of variations in the rate of bone remodeling that occur during growth and aging, and as a result of trauma and disease. The dependence of the remodeling space (cavities due to resorbing, reversing, and refilling BMUs) and the Haversian canal components of porosity on the Basic Multicellular Unit (BMU) activation frequency are mathematically formulated. A graph is developed using data for the cortex of the human rib which shows the extent to which porosity is primarily due to the remodeling space in children, and to accumulated Haversian canals in adults. It is shown that the diminution of activation frequency between birth and age 35 contributes to the concurrent increase in bone volume fraction, and the increase in activation frequency after age 35 contributes to the subsequent decline of bone volume fraction. An equation is derived for determining the time rate of change of activation frequency using two fluorochrome labels.     

Blood vessels in epiphyseal cartilage of human fetal femoral bone: a scanning electron microscopic study of corrosion casts

Formation of intrachondral vessels (cartilage canals) in the proximal femoral epiphysis was studied in 13- to 22-week-old human fetuses using a corrosion casting technique and scanning electron microscopy. Several successive morphological stages of angiogenesis occurring inside the hyaline cartilage were distinguished. The process of cartilage vascularization starts with the formation of hairpin loops sent off from the perichondrial vascular network into the adjacent cartilage. A capillary glomerulus is then formed at the leading end, and the entire vascular unit grows in length, assuming a mushroom-like shape. Its further elongation is accompanied by a backward expansion of the capillary network which surrounds a pair of main vessels (arteriole and venule) like a manchette. The subsequent branching of such primary vascular units proceeds according to the same morphological patterns. The resulting tree-like vascular formations become interconnected via their lateral branches. This study clearly supports the invasion theory of cartilage canal formation.     

同时性后半规管与水平半规管性良性位置性眩晕

目的：探讨同时性后半规管与水平半规管性良性位置性眩晕（混合性良性位置性眩晕）的诊治方法。方法：联合应用Epley手法和Barbecue翻滚法对4例患者进行治疗，两次治疗间隔1d。结果：4例患者眩晕症状完全消失，随访至今无复发。结论：混合性良性位置性眩晕兼有后半规管与水平半规管性良性位置性眩晕的临床表现，联合采用Epley手法和Barbecue翻滚法治疗该病是可行的。     

碘伏用于超声根管预备预防根管治疗期间痛的临床研究

目的观察碘伏用于超声根管预备对死髓牙根管治疗期间痛(endodontic interappointment pain EIP)发生率的影响及防治效果.方法对159例180颗慢性根尖周炎患者,随机分为3组(每组60颗患牙).第1组为传统手持器械对照组,第2组为超声生理盐水对照组,第3组为超声碘伏治疗组.采用临床观察分析法,观察治疗组与对照组临床反应的差异.结果超声治疗组Ⅱ～Ⅲ级EIP发生率为10%,对照组为36.67%(P＜0.01),有显著差异性.结论碘伏应用于超声根管预备能预防和降低EIP的发生并减轻其疼痛程度.     

The role of ocular torsion in visual measures of vestibular function

This brief review highlights problems in the interpretation of results about perceived postural roll-tilt of human subjects undergoing roll-tilt around their naso-occipital axis, when visual stimuli are used as a means of indicating perception. The otolithic stimulus, which causes the changes in perceived posture, also causes the eyes to roll (or tort). In turn, the altered torsional position of the eye causes the perceived orientation of visual stimuli to change. Consequently, indicators of postural perception, which rely on visual stimuli, are a confounded combination of two factors; the person's perceived postural roll-tilt, and the effect of the otolithic stimulus on ocular torsional position. Consequently, setting of a visual stimulus do not permit direct unambiguous interpretation of a subject's perceived postural roll-tilt.     

Habituation and adaptation of the vestibuloocular reflex: a model of differential control by the vestibulocerebellum

Summary We habituated the dominant time constant of the horizontal vestibuloocular reflex (VOR) of rhesus and cynomolgus monkeys by repeated testing with steps of velocity about a vertical axis and adapted the gain of the VOR by altering visual input with magnifying and reducing lenses. After baseline values were established, the nodulus and ventral uvula of the vestibulocerebellum were ablated in two monkeys, and the effects of nodulouvulectomy and flocculectomy on VOR gain adaptation and habituation were compared. The VOR time constant decreased with repeated testing, rapidly at first and more slowly thereafter. The gain of the VOR was unaffected. Massed trials were more effective than distributed trials in producing habituation. Regardless of the schedule of testing, the VOR time constant never fell below the time constant of the semicircular canals (5 s). This finding indicates that only the slow component of the vestibular response, the component produced by velocity storage, was habituated. In agreement with this, the time constant of optokinetic after-nystagmus (OKAN) was habituated concurrently with the VOR. Average values for VOR habituation were obtained on a per session basis for six animals. The VOR gain was adapted by natural head movements in partially habituated monkeys while they wore ×2.2 magnifying or ×0.5 reducing lenses. Adaptation occurred rapidly and reached about ±30%, similar to values obtained using forced rotation. VOR gain adaptation did not cause additional habituation of the time constant. When the VOR gain was reduced in animals with a long VOR time constant, there were overshoots in eye velocity that peaked at about 6–8 s after the onset or end of constant-velocity rotation. These overshoots occurred at times when the velocity storage integrator would have been maximally activated by semicircular canal input. Since the activity generated in the canals is not altered by visual adaptation, this finding indicates that the gain element that controls rapid changes in eye velocity in the VOR is separate from that which couples afferent input to velocity storage. Nodulouvulectomy caused a prompt and permanent loss of habituation, returning VOR time constants to initial values. VOR gain adaptation, which is lost after flocculectomy, was unaffected by nodulouvulectomy. Flocculectomy did not alter habituation of the VOR or of OKAN. Using a simplified model of the VOR, the decrease in the duration of vestibular nystagmus due to habituation was related to a decrement in the dominant time constant of the velocity storage integrator (1/h ₀). Nodulouvulectomy, which reversed habituation, would be effected by decreasing h ₀, thereby increasing the VOR time constant. Small values of h ₀ would cause velocity storage to approach an ideal integrative process, leading the system to become unstable. By controlling the VOR time constant through habituation, the nodulus and uvula can stabilize the slow component of the VOR. VOR gain adaptation was related to a modification of the direct vestibular path gain g ₁, without altering the coupling to velocity storage g ₀ or its time constant (1/h ₀). The mismatched direct- and indirect-pathway gains simulated the overshoots in the dynamic response to a step in velocity, that were observed experimentally. We conclude that independent distributed elements in the VOR modify its dynamic response, under control of separate parts of the vestibulocerebellum.     

Temporal response properties of lumbar-projecting vestibulospinal neurons to roll tilt in decerebrate cats

In decerebrate cats, rotation about the longitudinal axis of the animal, leading to sinusoidal stimulation of labyrinth receptors, produces a tonic contraction of limb extensors during side-down tilt ( responses) and of dorsal neck extensors during side-up tilt ( responses). These changes in posture are mediated, at least in part, by lateral vestibular nucleus (LVN) neurons, with response characteristics to stimulation of macular and/or canal receptors that have so far been evaluated at the level of either unidentified vestibulospinal (VS) neurons or vestibulo-collic neurons projecting to the upper cervical cord. In the present study we investigated the dynamics of the responses of VS neurons projecting to the lumbosacral segments of the spinal cord to increasing frequencies of tilt (from 0.026 to 0.32 Hz, ±10°). All the recorded units showed an average phase lead with respect to position of +25.6±5.5° (SE) at the tilt frequency of 0.026 Hz. Most of these neurons (n=32) were particularly activated during side-down tilt ( responses) and showed either a stable phase or an increase in phase lead of the responses with increasing frequency of tilt. At the tilt frequency of 0.026 Hz, the smaller the phase lead of the responses, the larger was the response gain. Moreover, the smaller the phase lead of the responses at that frequency of tilt, the smaller the increase in gain but the larger was the increase in lead of the responses obtained by increasing the stimulation frequency up to 0.32 Hz. Through this set of finely organized changes in unit response characteristics, the overall output of this population of neurons increased, while the phase angle of the responses reached the mean value of +64.9±2.6° (SE), thus becoming more related to the velocity than to the positional signal. The remaining units (n=7), which were mainly activated during side-up tilt ( responses), displayed an increase in phase lag of the responses to increasing frequency of stimulation, which reached the mean value of-118.9±14.5° (SE) at 0.32 Hz. The differences in the dynamic properties of these VS neurons projecting to the lumbosacral cord, with respect to those of previously recorded populations of VS neurons, are discussed.     

The role of cartilage canals in endochondral and perichondral bone formation: are there similarities between these two processes?

We investigated the development of cartilage canals to clarify their function in the process of bone formation. Cartilage canals are tubes containing vessels that are found in the hyaline cartilage prior to the formation of a secondary ossification centre (SOC). Their exact role is still controversial and it is unclear whether they contribute to endochondral bone formation when an SOC appears. We examined the cartilage canals of the chicken femur in different developmental stages (E20, D2, 5, 7, 8, 10 and 13). To obtain a detailed picture of the cellular and molecular events within and around the canals the femur was investigated by means of three-dimensional reconstruction, light microscopy, electron microscopy, histochemistry and immunohistochemistry [vascular endothelial growth factor (VEGF), type I and II collagen]. An SOC was visible for the first time on the last embryonic day (E20). Cartilage canals were an extension of the vascularized perichondrium and its mesenchymal stem cell layers into the hyaline cartilage. The canals formed a complex network within the epiphysis and some of them penetrated into the SOC were they ended blind. The growth of the canals into the SOC was promoted by VEGF. As the development progressed the SOC increased in size and adjacent canals were incorporated into it. The canals contained chondroclasts, which opened the lacunae of hypertrophic chondrocytes, and this was followed by invasion of mesenchymal cells into the empty lacunae and formation of an osteoid layer. In older stages this layer mineralized and increased in thickness by addition of further cells. Outside the SOC cartilage canals are surrounded by osteoid, which is formed by the process of perichondral bone formation. We conclude that cartilage canals contribute to both perichondral and endochondral bone formation and that osteoblasts have the same origin in both processes.     

The vestibulo-ocular reflex in three dimensions

The purpose of this paper is to review the kinematics and dynamics of the vestibulo-ocular reflex (VOR) in three dimensions. We give a brief, didactic tutorial on vectors and matrices and their importance as representational schemes for describing the kinematics and dynamics of the angular and linear accelerations that activate the vestibular system. We show how the vectors associated with angular and linear head accelerations are transformed by the peripheral and central vestibular systems to drive the oculomotor system to produce eye movements in three-dimensional space. We also review critical questions and controversies related to the compensatory and orientation behavior of the VOR. One such question is how the central vestibular system distinguishes tilts of the head, which generate interaural linear acceleration from translations along the interaural axis. Another question is how the velocity-position integrator is implemented centrally. The review has been placed in the context of a model that explains the behavior of the VOR in three dimensions. Model processes have been related to peripheral and central neural behavior in order to gain insight into the nature of the three-dimensional organization and the controversial questions that are addressed.