A Brainstem Neural Substrate for Stopping Locomotion.

Locomotion occurs sporadically and needs to be started, maintained, and stopped. The neural substrate underlying the activation of locomotion is partly known, but little is known about mechanisms involved in termination of locomotion. Recently, reticulospinal neurons (stop cells) were found to play a crucial role in stopping locomotion in the lamprey: their activation halts ongoing locomotion and their inactivation slows down the termination process. Intracellular recordings of these cells revealed a distinct activity pattern, with a burst of action potentials at the beginning of a locomotor bout and one at the end (termination burst). The termination burst was shown to be time linked to the end of locomotion, but the mechanisms by which it is triggered have remained unknown. We studied this in larval sea lampreys (Petromyzon marinus; the sex of the animals was not taken into account). We found that the mesencephalic locomotor region (MLR), which is known to initiate and control locomotion, stops ongoing locomotion by providing synaptic inputs that trigger the termination burst in stop cells. When locomotion is elicited by MLR stimulation, a second MLR stimulation stops the locomotor bout if it is of lower intensity than the initial stimulation. This occurs for MLR-induced, sensory-evoked, and spontaneous locomotion. Furthermore, we show that glutamatergic and, most likely, monosynaptic projections from the MLR activate stop cells during locomotion. Therefore, activation of the MLR not only initiates locomotion, but can also control the end of a locomotor bout. These results provide new insights onto the neural mechanisms responsible for stopping locomotion.SIGNIFICANCE STATEMENT The mesencephalic locomotor region (MLR) is a brainstem region well known to initiate and control locomotion. Since its discovery in cats in the 1960s, the MLR has been identified in all vertebrate species tested from lampreys to humans. We now demonstrate that stimulation of the MLR not only activates locomotion, but can also stop it. This is achieved through a descending glutamatergic signal, most likely monosynaptic, from the MLR to the reticular formation that activates reticulospinal stop cells. Together, our findings have uncovered a neural mechanism for stopping locomotion and bring new insights into the function of the MLR.

CAD/CAM restorations and secondary caries: a literature review with illustrations.

UNLABELLED: The literature related to failures of CAD/CAM restorations, with emphasis on secondary caries, is presented. A good approximal fit of the restoration is important to prevent plaque accumulation that may lead to secondary caries. CAD/CAM restorations allow inspection of the approximal fit prior to cementation and it may explain the relatively few failures due to secondary caries. The longevity of these restorations approaches that of gold restorations. CLINICAL RELEVANCE: The requirement for CAD/CAM restorations has advanced to a stage where high quality restorations with excellent anatomy and fit can be produced. The failure rate is relatively low compared to directly placed restorations.

Research in general dental practice.

Spurred by an initiative by the National Institute of Dental and Craniofacial Research in the USA, this article presents the need for a change in clinical dental research towards practice-based research. It outlines the shortcomings of past and present-day research in dentistry, with emphasis on the lack of clinical relevance of much of the research performed. The slow transfer of sound research findings to clinical practice is also a major problem. The article reviews some problems related to restorative dentistry and how they have adversely affected general dental practice. Practice-based research places emphasis on the problems experienced by clinicians in the routine care of patients. Clinicians should be linked together in research networks. The problems they face in dental practice and the clinical experience they have will form the basis for studies by the network. Experienced clinical researchers will provide guidance and statistical support for the studies initiated by the clinicians.

Evaluation of etching time on dentin bond strength using single bottle bonding systems.

PURPOSE: Incomplete infiltration of the demineralized collagen network may result in a weak zone within the hybrid layer and between the hybrid layer and dentin. The current study evaluates whether reducing the etching time to 5 s from the recommended 15 s or increasing it to 30 s has an effect on dentin bonding. MATERIALS AND METHODS: 108 extracted molars were assigned to 3 bonding agent groups (n = 36): (a) Single Bond (SB), (b) One-Step (OS), and (c) Syntac Single Component (SSC). Each group was further divided into three subgroups (n = 12) of different etching times: 5, 15, and 30 s. All groups were bonded with Z100 composite resin according to the manufacturer's instructions. All specimens were thermocycled 300 times between +/-5 degrees C and +/-55 degrees C, and shear bond strength testing and mode of failure analysis were performed. RESULTS: The bond strength of SB (5 s: 15.5 MPa +/- 4.4; 15 s: 16.5 MPa +/- 3.1; 30 s: 16.8 MPa +/- 3.2) and OS (5 s: 13.7 MPa +/- 1.8; 15 s: 12.4 MPa +/- 3.8; 30 s: 10.6 MPa +/- 3.8) showed no significant differences (p < 0.05) for the different etching times. For SSC, different etching times showed significant differences (5 s: 10.9 MPa +/- 1.8; 15 s: 7.5 MPa +/- 2.5; 30 s: 6.4 MPa +/- 2.1). The mode of failure for SB and OS was adhesive or mixed adhesive/cohesive. For SSC, all failures were adhesive. CONCLUSION: Etching times of less than 15 s do not seem to adversely affect bonding to dentin.

Combined amalgam and composite restorations.

All indirect restorative techniques involving cast metals, ceramics or resin-based materials are expensive compared to directly placed restorations. A restorative technique is presented that combines the esthetic properties of directly bonded resin-based composite material and the wide range of indications for dental amalgam in stress-bearing areas.

Esthetic dentistry in North American dental schools.

OBJECTIVES: Esthetic dentistry is among the most dynamic areas of contemporary clinical dentistry. Teaching programs in dental schools have a strong effect on the practice of dentistry, not only for recent graduates, but also for established clinicians, especially with respect to new techniques and concepts. The purpose of the study reported here was to assess the frequency and extent of the teaching of esthetic dentistry in North American dental schools and to report how it differs among the various schools. MATERIALS AND METHODS: A 19-question survey was mailed to 64 North American dental schools. The questions inquired about the priority given to the teaching of esthetic dentistry in the school; how the subject was taught (through regular curricular courses; through a multidisciplinary approach or through elective classes); the duration of the esthetic dentistry course; the nature of the course content (theoretical or practical); the esthetic procedures taught to undergraduate students; the level of interaction among different disciplines in the teaching of esthetic dentistry; and the techniques and commercial materials used. The responses were summarized as percentages based on the number of schools that responded to each question. RESULTS: Fifty-two (81%) of the 64 dental schools completed and returned the questionnaire. Twenty-five of these schools (48%; designated group A) reported having a course exclusively for the teaching of esthetic dentistry. Twenty-seven schools (52%; designated group B) reported that esthetic dentistry was addressed in multiple courses, i.e., no specific course was available. Four schools in group B (15%) were in the process of developing a separate course for esthetic dentistry. In group A schools, esthetic dentistry was taught mainly in the operative dentistry department or division. The most frequent course duration was 4 to 6 months, but there were marked variations. Thirteen (52%) of these 25 schools had didactic and practical teaching at both the preclinical and the clinical levels. The schools in group B reported that only clinical instruction in esthetic dentistry was provided. Several concerns were addressed in the courses offered in group A schools: extrinsic and intrinsic discoloration, bleaching, diastemas, malformation and malpositioning (the latter including rotation, intrusion and labio-linguoversion), and replacement of amalgam and gold restorations. Only 7 (28%) of the group A schools reported having the support of an inhouse laboratory. The esthetic procedures taught were similar for schools in group A and group B. The use of direct posterior composite restorations, all-ceramic crowns and nonvital bleaching was more common among group B schools. Ceramic inlays, onlays and indirect posterior composite restorations were not taught by 4 (16%) of the schools in group A and 7 (26%) of the schools in group B. CONCLUSIONS: The teaching of esthetic dentistry in North American dental schools is highly variable and in many schools is shared among different disciplines. Dental schools should work together to establish the parameters for teaching this subject and should formulate the necessary standards for education and research in this new field.

The effect of variation in etching times on dentin bonding.

Twelve extracted molars were assigned into four groups of three to observe how different etching times affect the depth of dentin demineralization and the thickness and morphology of the hybrid layer. The four groups were subjected to etching times of 5, 15, 30, and 60 seconds. To study the hybrid layer, another 27 molars were assigned into groups of nine; each group was etched using a different single-bottle bonding agent. In addition, each group was divided into three subgroups, with three different etching times of 5, 15, and 30 seconds. Following the bonding procedure, the specimens were bonded using Z100 composite and processed for observation using a scanning electron microscope. There was a direct correlation between etching time and depth of demineralized zone. The hybrid layer thickness correlated directly to the etching time. Increased etching time demineralized the dentin surface to a depth greater than resin monomers could penetrate, producing a thick, poorly infiltrated hybrid layer. Reducing etching time reduces the depth of the demineralized zone and may be effective for achieving complete penetration and for sealing the dentin surface.