ABSTRACT
Previously,the choice of prosthetic implant-retained overdentures has depended on data from previous studies about the retention-fatigue strength of the attachment system selected.Little or no data have been available on the correlation between the attachment system selected and the overdenture support configuration.The purpose of the present study was to evaluate the retention force and fatigue resistance of three attachment systems and four support designs of overdenture prosthesis.Four lower edentulous acrylic models were prepared and eight combinations of attachments groups were investigated in the study.These included:O-Rings with mini-dental implants (MDIs),Dalbo elliptic with Dalbo Rotex and fabricated flexible acrylic attachments with both MDI and Dalbo Rotex.The study was divided into four test groups:groups A and B,controls,and groups C and D,experimental groups.Control group A contained three overdenture supports:two free standing MDIs in the canine region and at the midline,and one simulated tooth root with Dalbo Rotex screwed in.Control group B contained four overdenture support foundations:two free standing MDIs in the right canine region and the first premolar region,and two simulated tooth roots with Dalbo Rotex screwed in at the same MDI position,but on the left side of the model.Experimental group C contained three overdenture support foundations:two free standing MDIs in the canine region and at the midline,and one simulated tooth root with MDI screwed in.Experimental group D contained four overdenture support foundations:two free standing MDIs in the right canine region and the first premolar region,and two simulated tooth roots with MDIs screwed in at the same MDI position,but on the left side of the model.Each group was further divided into two subgroups according to attachment type used.Five samples were prepared for each group.Retention force (N) values were recorded initially (0 cycles) and after 360,720,1440 and 2880 insertion and removal cycles.During the tensile test a cross-head speed of 10 mm/min was applied.Values of absolute force (AF) and relative force (RF) were statistically analyzed by two-way ANOVA and multiple comparison Tukey's tests between groups and cycles periods.The results of fatigue tests showed a 50％ reduction in retention force in the subgroups with flexible attachments.A triangular design of overdenture support foundations with O-Ring attachments revealed the lowest value of AF and a relatively high reduction in RF.The four overdenture support designs with flexible acrylic attachments improved the retention force and reduced the fatigue retention.Furthermore,the results of the investigation demonstrate that flexible acrylic attachments for both teeth and implant-supported overdentures offer a wide range of retention forces.
ABSTRACT
Recently,plasma sterilization has attracted increasing attention in dental community for the atmospheric pressure non-equilibrium plasma jet (APNPs),which is driven by a kilohertz pulsed DC power,may be applied to the dental and oral diseases.However,it is still in doubt whether APNPs can effectively kill pathogenic bacteria in the oral cavity and produce no harmful effects on normal oral tissues,especially on normal mucosa.The aim of this study was to evaluate the bacterial-killing effect of APNPs in the biofilms containing a single breed of bacteria (Porphyromonas gingivalis,Pg.),and the pathological changes of the oral mucosa after treatment by APNPs.Pg.was incubated to form the biofilms in vitro,and the samples were divided into three groups randomly:group A (blank control);group B in which the biofilms were treated by APNPs (the setting of the equipment:10 kHz,1600 ns and 8 kV); group C in which the biofilms were exposed only to a gas jet without ignition of the plasma.Each group had three samples and each sample was processed for up to 5 min.The biofilms were then fluorescently stained,observed and photographed under a laser scanning confocal microscope.In the animal experiment,six male Japanese white rabbits were divided into two groups randomly (n=3 in each group) in terms of the different post-treatment time (1-day group and 5-day group).The buccal mucosa of the left side and the mucosa of the ventral surface of the tongue were treated by APNPs for 10 min in the same way as the bacterial biofilm experiment in each rabbit,and the corresponding mucosa of the other sides served as normal control.The clinical manifestations of the oral mucosa were observed and recorded every day.The rabbits were sacrificed one or five day(s) after APNPs treatment.The oral mucosa were harvested and prepared to haematoxylin and eosin-stained sections.Clinical observation and histopathological scores were used to assess mucosal changes.The results showed the obvious P.g.biofilms were formed at 10 days,and most of the bacteria in groups A and C were alive under a laser scanning confocal microscope,but the bacteria in the group B were almost all dead.In animal experiment,no ulcers,anabrosis and oral mucositis were found in both the 1-day and 5-day groups.The average mucous membrane irritation index was -0.83 and -0.67 in the 1-day and 5-day groups,respectively,suggesting that no intense mucosal membrane irritation responses occurred.It was concluded that APNPs could effectively kill P.g.in the biofilms and did not cause any pathological changes in the normal mucosa,suggesting that the plasma jet (APNPs) may be applied to oral diseases as a novel sterilization device in the future.