Saul Weiner

The origin of the afferent supply to the mediodorsal thalamic nucleus: Enhancement of HRP transport by selective lesions

Abstract This experiment attempted to identify the cell bodies of origin of axons in the forebrain which supply the mediodorsal thalamic nucleus (MD). Injections of horseradish peroxidase (HRP) were placed into MD in 60 rats. Survival times varied from 1–4 days. Following injections placed into different portions of MD, HRP positively labeled cells were observed in a variety of forebrain structures which lie rostral to the injection sites. Discrete injections of HRP placed into the midline of MD labeled cells situated exclusively in the extreme ventromedial aspect of central levels of the reticular nucleus. HRP injections which included anterior levels of MD labeled cells situated principally in layers V–VI of the sulcal prefrontal cortex, while injections which involved more posterior and lateral portions of MD labeled cells in the deepest layers of the dorsomedial prefrontal cortex. Injections of this region of MD also labeled cells in adjacent portions of the deepest layers of anterior cingulate gyrus, polymorphic cell layer of prepyriform cortex and olfactory tubercle and sites immediately lateral to the vertical limb of the diagonal band and dorsal to its horizontal limb. Positively labeled cells were observed in the cortical, medial, basolateral and basomedial amygdaloid nuclei and adjacent pyriform cortex only when ablations of prefrontal cortex preceded HRP injections of MD. This findings indicates that lesions of the prefrontal cortex dramatically enhance the HRP labeling process in the amygdala and suggests the possibility that the technique involving the placement of selective lesions may be used to advangate in other anatomical systems which receive multiple inputs from widely distributed sources.

An analysis of the efferent connections of the septal area in the cat

The neuroanatomical organization of the efferent connections of the septal area in the cat was analyzed by the use of anterograde ([3H]leucine radioautography) and retrograde (horseradish peroxidase histochemistry) tracing techniques. The results indicate that the lateral septal nucleus projects to the nuclei of the diagonal band, preoptic area, lateral hypothalamus, and supramammillary region. The projections of the septofimbrial nucleus supply the nuclei of the diagonal band and the medial habenular nucleus. Projection targets of the vertical limb of the diagonal band are widespread and include the preoptic area, lateral hypothalamus, anterior limbic cortex, amygdala, medial habenular nucleus, interpeduncular nucleus and hippocampal formation. The projection from the vertical limb to the hippocampal formation is organized in a topographical manner in such a fashion that cells positioned near the midline project to the dorsal hippocampus and adjoining subicular cortex while fibers originating from cells situated more laterally project to more ventral parts of the hippocampal formation. In general, the projections from the horizontal limb were similar to those from the vertical limb, but several differences were noted. Fibers arising from the horizontal limb are distributed to the ventral tegmental area and interpeduncular nucleus but this region seems to lack a projection to either the habenular complex or to the ventral aspect of the hippocampal formation. Fibers arising from the bed nucleus of the anterior commissure are distributed to the preoptic region, lateral hypothalamus, supramammillary region, posterior aspect of the medial mammillary nucleus and lateral habenular nucleus.

An in vitro analysis of implant screw torque loss with external hex and internal connection implant systems.

Purpose:The purpose of this study was to examine, in a controlled environment, effects of connection design upon screw stability. Implant fixtures have 2 types of connections to the abutment: internal connection and external hex. Four implant systems were tested: Bio-Lok (external hex; Bio-Lok International, Inc., Deerfield Beach, FL); Zimmer (internal connection; Zimmer Dental, Carlsbad, CA); Nobel Biocare (external hex; Nobel Biocare USA, Inc., Yorba Linda, CA); and Astra Tech (internal connection; Astra Tech Inc., Waltham, MA). Materials and Methods:Ten samples of each system, including base, implant, abutment, and molar crown, were loaded to 200 N for 1 × 106 cycles. Screws were tightened to manufacturers’ recommendations,and torque audits done at 2.5 × 105, 5 × 105, 7.5 × 105, and 1 × 106 cycles. Results:The Bio-Lok samples lost an average of 10% of the original torque values, the Astra Tech group lost almost all of the torque and loosened, while the Zimmer and Nobel Biocare samples lost an average of 50% of the torque but did not loosen (P ≤ 0.05). Conclusions:It may be concluded from this study that although internal connections are clinically favored, this study did not show any advantage relative to screw loosening. However, screw design may be a significant factor in loosening of the joint.

The Effects of Laser Microtextured Collars Upon Crestal Bone Levels of Dental Implants

Purpose:The purpose of this study was to examine the crestal bone, connective tissue, and epithelial cell response to a laser microtextured collar compared with a machined collar, in the dog model. Materials:Six mongrel dogs had mandibular premolars and first molars extracted and after healing replaced with BioLok implants 4 × 8 mm. Each dog had 3 control implants placed on one side of the mandible and 3 experimental, laser microtextured, implants placed contralaterally. After 3 months, 1 dog was killed. Bridges were placed on the implants of 4 of the dogs. The sixth dog served as a negative control for the duration of the experiment. Two of the dogs were killed 3 months after loading, of the dogs were killed 6 months after loading as was the negative (unloaded) control. Histology, electron microscopy, and histomorpho-metric analysis was done on histologic sections obtained from block sections of the mandible containing the implants. Results:Initially the experimental implants showed greater bone attachment along the collar. With time the bone heights along the control and experimental collars were equivalent. However, the controls had more soft tissue downgrowth, greater osteoclastic activity, and increased saucerization compared with sites adjacent to experimental implants. There was closer adaptation of the bone to the laser microtextured collars. Conclusion:Use of tissue-engineered collars with microgrooving seems to promote bone and soft tissue attachment along the collar and facilitate development of a biological width.

Analysis of changes in implant screws subject to occlusal loading: a preliminary analysis.

Loosening of the abutment screw can present a problem for the stability of the implant-supported crown or prosthesis. The purpose of this study was to understand the parameters of screw loosening, using an in vitro model, including loss of torque, screw head rotation, changes in screw dimension, and distortion of the implant-abutment joint. Implants (4 × 10 mm) were potted in autopolymerizing blocks. Abutments were placed with screws tightened with a 35-Ncm torque and standardized crowns fabricated. There were 3 implant systems used: Nobel Biocare USA, Inc. (Yorba Linda, CA), 3i Implant Innovations, Inc. (Palm Beach Gardens, FL), and Bio-Lok International, Inc. (Deerfield Beach, FL). Seven samples were tested for each system. Samples were loaded with 300-N loads for 50,000 cycles at 1 Hz. Torque turn audits were performed at 10,000, 25,000, and 50,000 cycles. At the conclusion of the loading, counterclockwise rotation of the abutment screw was measured. The screws were retrieved and measurements made compared with the controls. Finally, 1 sample from each group was embedded in resin, sectioned longitudinally, and examined under the standard error of the mean. The Nobel Biocare system showed a 9.4-Ncm loss of torque from the loading protocol. This result was accompanied by a counterclockwise rotation of 7° and a 200-ìm elongation of the screw. Finally, there was compression and distortion of the longitudinally sectioned joint architecture observed with the standard error of the mean. From the 3i and Bio-Lok International groups, no loss of torque, counterclockwise rotation, or lengthening of the screws was observed. Intimate adaptation of the joint without distortion was seen in the longitudinal sections. Screw loosening appears to follow specific parameters that include counterclockwise rotation, lengthening of the screw, and distortion of the screw joint. This process is likely associated with both the physical properties of the screw as well as its configuration.

Effect of an antirotation resistance form on screw loosening for single implant-supported crowns

STATEMENT OF PROBLEM The gold screw of the single tooth implant-supported restoration has frequently been reported to exhibit the problem of screw loosening. PURPOSE This in vitro study considered an antirotation resistance form with an increased moment arm length as a strategy to increase the net effect of the retaining screw preload. MATERIAL AND METHODS Three groups examined included (a) standard abutments (3 mm), (b) modified standard abutments (3 mm) with 4 milled (1 x 1 mm) notches placed equidistant around the periphery, and (c) Estheticone abutments (1 mm). Crown castings of 2% gold-palladium-based alloy were made using plastic and resin patterns molded to fit inside a quarter-inch socket wrench. For testing, each specimen consisted of a 15-mm endosseous threaded implant analog, its abutment (20 N force) and crown casting (10 N force) screwed together and securely clamped in a vise. A clockwise shear (rotational) force was applied using a manual torque driver and the torque recorded to failure of the gold screw or loosening of the abutment screw. RESULTS Analysis revealed that the dislodging force for groups (b) and (c) was similar (69.6 and 71.0 N.cm, respectively), whereas group (a) (standard implant external hex) demonstrated that the smallest moment arm required a significantly smaller dislodging force (21.3 N.cm). CONCLUSION These findings suggest that the addition of an antirotation resistance form increased the length of the moment arm, thereby increasing the effect of preload and reducing the problem of screw loosening.

The subicular cortex of the cat: an anatomical and electrophysiological study.

The anatomic organization of the hippocampal formation in the cat was studied by means of (a) horseradish peroxidase histochemistry, (b) [3H]leucine radioautography, and (c) electrophysiological identification of antidromically activated single units. The data indicate that the CA1 field, prosubiculum, and adjacent subiculum are the source of origin of fibers terminating in the caudal septum. The subiculum and adjacent presubiculum are the only sources of hippocampal efferent fibers which project to the medial mammillary nucleus. The cells of the presubiculum and retrosplenial cortex give rise to the axons which project to the anterior thalamus. Efferent fibers project through the fornix and are topographically distributed to the mammillary bodies and septal area. Specifically, axons arising near the septal pole of the hippocampal formation project to the dorsal aspect of the medial mammillary nucleus or the dorsomedial part the lateral septal nucleus. Axons arising from cells situated progressively more proximal to the temporal pole of the hippocampal formation project to progressively more ventral levels of the medial mammillary nucleus or more lateral parts of the lateral septal nucleus. It was also noted that subicular fibers have slow conduction velocities and that evidence of possible axonal branching of fornix fibers was not obtained.

Effects of temperature on color stability of porcelain stains

The effects of oven firing on the color stability of extrinsic stains used for characterization and color modification of metal ceramic restorations were studied by comparing the color of the stain as initially applied with that observed after it was fired to the fusion temperature. Perceptible changes were noted for all stains studied. Multiple firings of the stain showed only minor effects on the observed color. The effects at fusion temperatures of 1700 degrees F and 1775 degrees F appeared similar. Finally, there appeared to be no marked differences between the color change observed with the use of autoglazing and overglazing techniques.

EFFECTS OF OCCLUSAL LOADING AND THERMOCYCLING ON THE MARGINAL GAPS OF LIGHT-POLYMERIZED AND AUTOPOLYMERIZED RESIN PROVISIONAL CROWNS

STATEMENT OF PROBLEM Resin crowns appear to be increasingly at risk for increases in marginal gap size as a result of thermocycling and occlusal loading. PURPOSE This in vitro study compared the effects of occlusal loading and thermocycling on the margins of provisional crowns made from a conventional autopolymerized provisional acrylic resin (Jet) to those made from a light-polymerized resin (Unifast LC). METHODS AND MATERIAL Crowns made from the 2 materials were thermocycled and loaded on custom dies to simulate 6 to 8 weeks of oral function. Gap sizes were measured before and after thermocycling and occlusal loading. RESULTS Provisional crowns made from light-polymerized resin exhibited smaller changes in marginal gap size than did those made from conventional autopolymerized resin. CONCLUSIONS The improved characteristics of the light-polymerized material may prove useful for provisional crowns that must remain for long periods in the oral environment.

Effects of thermocycling and occlusal force on the margins of provisional acrylic resin crowns

Transitional acrylic crowns were examined for changes in axial contour and increases in marginal gap width after simultaneous thermocycling and occlusal loading. Two groups of 10 crowns--one with a shoulder finish line and another with a chamfer finish line--were treated with 3400 thermocycles and 50,000 load cycles simultaneously within an artificial oral environment chamber in an MTS Dental Materials Testing System. The marginal gaps were increased for both groups after treatment. However, the group of crowns with the shoulder finish lines demonstrated a smaller gap width (x = 90 microns) after treatment than the crowns with chamfer finish lines (x = 210 microns). A statistical comparison identified a significant difference in gap width between groups (p < 0.01). Changes in the axial profile of the groups were similar, but one crown with a chamfer finish line exhibited a cracked margin.