Effects of repeated selective serotonin reuptake inhibitor paroxetine treatments on mouse forced swimming.

Studies were performed in the mouse forced swimming model, a well known experimental depression model, in order to detect the mechanism of the antidepressive effects induced by repeated serotonin reuptake inhibitor (SSRI) dosing. Five-day repeat dosing of a typical SSRI, paroxetine, increased climbing, a distinctive antidepressive behavior, 1 h after but not 1 h before treatment. The coinjection of paroxetine and serum in mice treated with four repeated doses of paroxetine distinctively increased the behavior, but the coinjection of paroxetine and serum in mice without paroxetine did not. These results indicate that repeated dosing of paroxetine produces a serum substance related to the antidepressive effects induced by serotonin neuron activities. Furthermore, the behavior induced by 5-day repeated dosing of paroxetine was decreased by 100 and 10 micrograms/kg of ketanserin (5-HT2 antagonist) and 100 micrograms/kg of LY-278584 (5-HT3 antagonist). The present findings strongly suggest that repeated dosing of paroxetine produces a serum substance stimulating the antidepressive neuronal pathway sensitively mediated by 5-HT2 and 5-HT3 receptor activity.

Changes of subgingival microflora around single-crystal sapphire endosseous implants after experimental ligature-induced plaque accumulation in monkeys.

A study was performed to evaluate the change of subgingival microflora with plaque accumulation around the single-crystal sapphire implant. Four implants were inserted into mandibular and maxillary edentulous regions, and the super-structure was inserted 1 month after implant insertion in each of nine monkeys. Plaque control was maintained for 3 months after insertion to establish the baseline. Plaque was allowed to accumulate on one side by placement of ligatures around the implants and natural teeth with no plaque control. On the other side plaque control was continued for 9 months. Both the implants and natural teeth on the ligature side showed significant increases in proportions of motile rods and spirochetes. No significant difference of microflora was detected between the implants and natural teeth. These findings indicate that plaque control is necessary to maintain the normal microflora around the implant.

Tissue compatibility and stability of a new zirconia ceramic in vivo.

Tissue reaction and stability of partially stabilized zirconia ceramic in vivo was evaluated with the use of the subcutaneous implantation test. During the experimental period, zirconia ceramic was completely encapsulated by a thin fibrous connective tissue with less than 80 microns thickness. No changes of weight and 3-point bending strength were detected after 12 months of implantation. The result suggests that zirconia ceramic is biocompatible and no degradation of zirconia ceramic occurred.

Clinical evaluation of the gingiva around single-crystal sapphire endosseous implant after experimental ligature-induced plaque accumulation in monkeys.

This study was performed to evaluate clinical changes of the gingiva with plaque accumulation around the single-crystal sapphire implant. Four implants were inserted into mandibular and maxillary edentulous regions, and the superstructure was inserted 1 month after insertion of the implants in each of nine monkeys. Plaque control was maintained for 3 months after insertion to set up the baseline. Plaque was allowed to accumulate on one side by placing the ligature around the implant and natural teeth without any plaque control, and on the other side plaque control was continued for 9 months. Both the implant and natural teeth on the ligature side showed a significant increase in the clinical parameters of plaque index, gingival index, and probing depth. No significant difference was obtained between the implant and natural teeth. These findings indicate that plaque control is of great importance for maintaining the health of peri-implant gingiva.

Correlation between clinical and histological evaluations of the peri-implant gingiva around the single-crystal sapphire endosseous implant.

The correlation between clinical periodontal parameters and histological structure of the gingiva around a single-crystal sapphire implant has been evaluated in two volunteer subjects. The implants had functioned after 6 years as the distal abutment of implant bridges in the Kennedy class II mandible. First, clinical evaluation was performed (gingival bleeding index, crevicular fluid volume, plaque index and probing depth) of the gingiva around the implant and natural teeth abutments and then a small piece of peri-implant gingiva was excised from the lingual site of the implant of each subject for histological evaluation. The clinical evaluation using the periodontal parameter indices corresponded with the histological evaluation of the peri-implant gingiva. The result suggests that it is possible for such parameters to be used in practice for judging the success of an implant.

Ultrastructure of the peri-implant junctional epithelium on single-crystal sapphire endosseous dental implant loaded with functional stress.

To elucidate the ultrastructure of peri-implant junctional epithelium (IJE) on single-crystal sapphire dental implants connected to the adjacent teeth by a metal superstructure, the peri-implant gingivae of ten monkeys were examined using a transmission electron microscope (TEM) at 3, 6 and 12 months after implant insertion. At the time of examination, the ultrastructural features of the IJE were almost identical to those of junctional epithelium (JE) attached to natural teeth, i.e. developed Golgi complexes, rough-surfaced endoplasmic reticulum, numerous free ribosomes and mitochondria. The innermost cells of IJE were attached to the implant surface by means of basal lamina-like structures (500-1000 A in thickness) and hemidesmosomes, but lacked a dental cuticle as seen on teeth. Such epithelial attachment of the IJE was often indistinct or absent at the apical portion of the IJE which terminated at the level of alveolar crest. A continuous basal lamina-like structure was also present along basal cells at the interface between the IJE and gingival connective tissue except at its apical portion.

Comparative evaluation of chewing function with removable partial dentures and fixed prostheses supported by the single-crystal sapphire implant in the Kennedy Class II partially edentulous mandible.

Differential chewing function with removable partial dentures (RPDs) and fixed prostheses supported by the single-crystal sapphire implant was evaluated in five subjects with Kennedy Class II partially edentulous mandibles by means of electromyography. Rehabilitation with the single-crystal sapphire implant resulted in regular chewing patterns with a low variation coefficient and higher activity of chewing-side masticatory muscles compared to RPD rehabilitation. This difference in chewing function between the two rehabilitation modalities could be the result of differences in stability of occlusion and neurophysiologic feedback systems.

Single-crystal sapphire endosseous dental implant loaded with functional stress--clinical and histological evaluation of peri-implant tissues.

Peri-implant tissues of the single-crystal sapphire implant connected with neighbouring teeth by a metal bridge-work were examined clinically, radiographically, and histologically in ten monkeys. Professional tooth cleaning was performed during the study. At 3-12 months after insertion, most of the implants were firmly connected to the surrounding tissues and peri-implant gingiva was regarded as healthy, based on various periodontal parameter scores. Destructive changes of the peri-implant bone were not found radiographically. Histologically, peri-implant gingiva was revealed to show similar structure to that of the gingiva around natural teeth. Direct bone-implant interface was observed at 3 months after insertion, while a thin loose fibrous connective tissue layer was present between bone and implant at 6 and 12 months. Such different interrelationship between bone and implant might be attributable to the difference in distribution of functional stress.

Adherence of Streptococcus mutans to implant materials.

The adherence of Streptococcus mutans OMZ-176 to six implant materials (poly-crystal alumina, single-crystal alumina, titanium alloy, cobalt-chromium-molybdenum alloy, hydroxyapatite, and heat-curing polymethylmethacrylate resin) was studied in vitro. The change of free energy, which corresponds to the adherence process, was also evaluated for hydrophobic interaction. Adherence of S. mutans to poly-crystal alumina was lower than adherence to other materials. The adherence of S. mutans to the test materials was highly correlated with the change of free energy, which suggests that hydrophobic interaction plays an important role in the adherence of S. mutans to the implant materials.

Initial bone-implant interfaces of submergible and supramergible endosseous single-crystal sapphire implants.

Three types of bone-single-crystal sapphire implant interfaces were histologically determined in submergible and supramergible implant: direct bone apposition (type I), thin connective tissue with poor collagen fibers (type II), and dense fibrous connective tissue (type III). Type I interface was predominant and type III interface was sparsely seen in submergible implants. In contrast to these findings, type III interfaces frequently appeared in supramergible implants, primarily at the apical region. These differences were considered to occur by the biomechanical variable of postoperative healing.

Tissue reaction to implanted biomaterials.

Tissue reactions to the single-crystal sapphire, titanium, Co-Cr-Mo alloy, and PMMA were histologically evaluated after implantation into the subcutaneous tissue and tibia of rats. In subcutaneous tissue the reaction from early necrotic change and acute inflammation to final encapsulation by fibrous connective tissue was least pronounced around single-crystal sapphire implants. Tissue reactions of a slightly greater degree were found around titanium and Co-Cr-Mo alloy implants. The most prominent tissue reaction was observed around PMMA implants. In the tibia, single-crystal sapphire, titanium, and Co-Cr-Mo alloy implants were encapsulated by newly formed compact bone, but bone was not so evident around PMMA implants. These findings suggest that single-crystal sapphire implants have more favorable tissue compatibility than those of titanium, Co-Cr-Mo alloy, and PMMA.