Impaired hippocampal-dependent learning and functional abnormalities in the hippocampus in mice lacking serotonin(1A) receptors.

The hippocampus is a major limbic target of the brainstem serotonergic neurons that modulate fear, anxiety, and learning through postsynaptic serotonin(1A) receptors (5-HT(1A) receptors). Because chronic stress selectively down-regulates the 5-HT(1A) receptors in the hippocampus, we hypothesized that mice lacking these receptors may exhibit abnormalities reminiscent of symptoms of stress-related psychiatric disorders. In particular, a hippocampal deficit in the 5-HT(1A) receptor could contribute to the cognitive abnormalities often seen in these disorders. To test whether a deficit in 5-HT(1A) receptors impairs hippocampus-related functions, we studied hippocampal-dependent learning and memory, synaptic plasticity in the hippocampus, and limbic neuronal excitability in 5-HT(1A)-knockout (KO) mice. 5-HT(1A)-KO animals showed a deficit in hippocampal-dependent learning and memory tests, such as the hidden platform (spatial) version of the Morris water maze and the delayed version of the Y maze. The performance of KO mice was not impaired in nonhippocampal memory tasks such as the visible platform (nonspatial) version of the Morris water maze, the immediate version of the Y maze, and the spontaneous-alternation test of working memory. Furthermore, paired-pulse facilitation in the dentate gyrus of the hippocampus was impaired in 5-HT(1A)-KO mice. Finally, 5-HT(1A)-KO mice, as compared with wild-type animals, displayed higher limbic excitability manifested as lower seizure threshold and higher lethality in response to kainic acid administration. These results demonstrate that 5-HT(1A) receptors are required for maintaining normal hippocampal functions and implicate a role for the 5-HT(1A) receptor in hippocampal-related symptoms, such as cognitive disturbances, in stress-related disorders.

An in vitro study of the tensile strength of the resin bond between chemically etched non-noble alloy and enamel.

A model was made to represent the in vivo situation for resin-bonded restorations using metal bonded to enamel. The tensile bond strength of chemically etched metal bonded to enamel was compared with that obtained with electrolytically etched metal. Four resin luting agents were used with the following results: the tensile bond strength of chemically etched non-noble alloy bonded to enamel was lower than strengths obtained for electrolytically etched alloy. The differences, however, were not statistically significant. Of the four luting resins, Comspan Regular gave the highest mean bond strength.

The effect of three different surface treatments on the tensile strength of the resin bond to nickel-chromium-beryllium alloy.

The effect of three different metal surface treatments on the tensile strength of the resin bond to non-noble nickel-chromium-beryllium alloy was studied by bonding metal to metal. Chemical etching of the metal for 1 hour obtained the highest strength, followed by air-abraded bond specimens. Lowest strength was obtained with the gel-etch method. All resulted in clinically acceptable values.

Dimensional accuracy of two denture base processing methods.

The mucosal surfaces of maxillary complete dentures processed using the SR-Ivocap injection technique and the Lucitone heat-polymerized compression molding technique were compared to a metal master impression to determine if one method of denture processing produced a more accurate denture base. Comparisons were made before and after polishing the prepared bases to determine if changes occur as a result of this procedure. The dental comparator, described by Rupp and others in 1957, was used to compare selected points on the palatal surface of the denture bases. No statistical differences were found in the accuracy of the denture bases processed using either of the two techniques.

Radiostrontium clearance and bone formation in response to simulated internal screw fixation.

Changes in radiostrontium clearance (SrC) and bone formation (tetracycline labeling) were observed in the femurs of skeletally mature dogs following the various operative steps involved in bone screw fixation. Drilling, but not periosteal stripping, produced a small but statistically significant increase in SrC and endosteal bone formation in the distal third of the bone. Strontium clearance values equivalent to those produced by drilling alone were recorded after screw fixation at low or high torque (5 versus 20 inch pounds), as well as by the insertion of loosely fitting stainless steel implants. Bone formation (equals the percentage tetracycline-labeled trabecular bone surfaces) was increased by 30% when SrC values exceeded 3.5 ml/100 g bone/min, and the relationship was linear when SrC values ranged between 1.0 and 7.0 ml/100 g bone/min. The changes in SrC and bone formation one-week after bone screw application are primarily those associated with a response to local trauma caused by drilling.

In vitro evaluation of circadian patterns of bone collagen formation.

The circadian patterns of bone collagen formation were studied in vitro to ascertain whether the biorhythmic profiles previously measured in vivo reflect true differences in collagen synthesis. Alteration of amino acid pool sizes did not negate the circadian-stage differences in bone collagen production. Evaluations of proline uptake and transport, as well as collagenous protein turnover, demonstrated that the intracellular assembly and secretion of bone collagenous protein during the dark span is truly decreased relative to that during the light period. It was further affirmed that PTH is essential for maintenance of the normal circadian collagen synthesis rhythms.

A comparative study of the centrifugal and vacuum-pressure techniques of casting removable partial denture frameworks.

A study was undertaken to evaluate two techniques for casting accuracy on removable partial denture frameworks: centrifugal casting and vacuum-pressure casting. A standard metal die with predetermined reference points in a horizontal plane was duplicated in refractory investment. The casts were waxed, and castings of nickel-chrome alloy were fabricated by the two techniques. Both the casts and the castings were measured between the reference points with a measuring microscope. With both casting methods, the differences between the casts and the castings were significant, but no significant differences were found between castings produced by the two techniques. Vertical measurements at three designated points also showed no significant differences between the castings. Our findings indicate that dental laboratories should be able to use the vacuum-pressure method of casting removable partial denture frameworks and achieve accuracy similar to that obtained by the centrifugal method of casting.

An occlusal prosthesis to assure airway patency in the comatose patient.

Ruminatory reflex chewing activities in the comatose patient and the associated prostheses used in their treatment have been well documented in the literature. The comatose patient, whose condition is further complicated by the need for oral-endotracheal intubation, requires the aid of a prosthesis which will allow for long-term patency of the tube to maintain proper ventilation.

Vital root retention in humans: a final report.

A research protocal for submucosal vital root retention in humans has been developed based on laboratory animal studies. Procedures, patient management, and statistical results have been reported in a series of three articles. Changes in techniques have also been reported, along with explanation of a flowchart for tooth root retention and alveolar ridge preservation. Some ideas for future investigations are presented. Vital root retention in humans appears to be a valid means of retaining residual bony ridge tissues to a greater degree than when patients are rendered totally edentulous.

The effect of various clasping systems on the mobility of abutment teeth for distal-extension removable partial dentures.

Three clasping systems were placed in five patients, and measurements of abutment tooth mobility were made. These data were compared to previously established baselines and statistically analyzed. The findings of the study are: 1. There was no difference in abutment tooth mobility during the 4-week test period with each of the three clasping systems. The important factor may have been the fit of the distal-extension denture base over the residual ridge, which provides the stability to prevent increases in abutment mobility. 2. Any mobility increases were in a buccal direction only, or toward the flexible retentive clasp arm. There was never any change in lingual mobility. 3. All five patients chose the I-bar retainer as the design of choice due to its increased resistance to dislodgment. Periodic recall of distal-extension removable partial denture patients is mandatory to ensure proper stress distribution and prevent increases in abutment tooth mobility.

Vital root retention in humans: an interim report.

A protocol based upon findings in laboratory animal studies was established for the retention of vital roots for overdenture support in humans. Ten patients with a mean age of 54.5 years and a postsurgical mean time of 11.1 months had 45 vital teeth buried submucosally under complete overdentures. Of the 45 teeth, 37 remained vital, seven were endodontically treated due to acute pulpal response following surgery, and one tooth has been extracted. A mean interproximal bone loss of 1.1 mm had occurred at the time the data were tabulated for this report. This project included a cross section of patient types, tooth selection, and surgical and prosthodontic management that varied slightly from the methods utilized in earlier patient treatment. The inclusion of maxillary teeth, the increased thoroughness of root surface roundings, and the utilization of root canal therapy with subsequent reburying of apulpally involved teeth expanded the scope of this research. A final report on this project will be forthcoming when all patients have been followed for a 24-month period.

Vital root retention in humans: a preliminary report.

With increasing experience in the technique, it has become apparent that more generous contouring of the retained root after amputation is desirable. The effect is to produce a more rounded ridge instead of the "boxy" one that would result from mere horizontal sectioning of the crown structure. The surgical sectioning of vital teeth, followed by anequate mucoperiosteal eversion suturing, has proved to be successful. Periodontal evaluation of each tooth seems to be paramount to success or failure. Accurate impression-making and postsurgical treatment including soft acrylic resin relines and removal of pressure spots appear to be next in importance. Age of the patient, condition of the clinical crowns, and length of surgical procedures did not seem to affect normal healing in the patients involved in the project.