Morphological Comparison of Residual Ridge in Impression for Removable Partial Denture between Digital and Conventional Techniques: A Preliminary In-Vivo Study.

Although digital impression using an intraoral scanner (IOS) has been applied for removable partial denture (RPD) fabrication, it is still unclear how the morphology of a residual ridge recorded by digital impression would differ from that recorded by conventional impression. This in vivo study investigated the morphological difference in the recorded residual ridge between digital and conventional impressions. Vertical and horizontal displacements (VD and HD) in residual ridges recorded by digital and conventional impressions were assessed in 22 participants (15 female; mean age 78.2 years) based on the morphology of the tissue surface of in-use RPD. Additionally, the mucosal thickness of the residual ridge was recorded using an ultrasound diagnostic device. VD and HD were compared using the Wilcoxon signed-rank test, and the correlation of mucosal thickness with VD and HD was analyzed using Spearman's ρ. The VD of digital impression was significantly greater than that of a conventional impression (p = 0.031), while no significant difference was found in HD (p = 0.322). Meanwhile, the mucosal thickness showed no significant correlation with the recorded morphology of the residual ridge, regardless of the impression techniques. It was concluded that the digital impression would result in a greater displacement in the height of the residual ridge from the morphology of in-use RPD than the conventional impression.

Effect of retention hole designs in artificial teeth on failure resistance of the connection with thermoplastic resin.

This study aimed to evaluate the effect of retention hole designs in artificial teeth on failure resistance of the connection with a thermoplastic denture base resin. Artificial teeth with the following retention hole designs were attached to polyester and polyamide resins: no hole, vertical hole, horizontal hole, and vertical and horizontal holes. An artificial tooth with no hole attached to polymethyl methacrylate was prepared as the control. The load was applied until connection failure occurred between the artificial tooth and resin, and failure resistance was detected. Although the control showed the highest resistance, the artificial tooth with vertical and horizontal holes showed higher resistance than those with other retention hole designs in both thermoplastic resins. Providing vertical and horizontal retention holes in artificial teeth may be effective in improving failure resistance of the connection with thermoplastic resins.

Influence of retainer and major connector designs of removable partial dentures on the stabilization of mobile teeth: A preliminary study.

The purpose of this study was to investigate the influence of retainers and major connector designs on the stabilization of remaining mobile teeth using removable partial dentures (RPDs). We prepared experimental RPDs with several retainer designs and major connectors for lower Kennedy class I models. The simulated RPD insertion and removal test was conducted and retentive force and mobility of mobile remaining teeth with and without RPD placement were measured throughout a simulation test. Regardless of reduction of retentive force, the placement of RPDs using cast clasps and/or lingual plates resulted in reduced mobility of the remaining teeth than use of wrought wire clasps and/or lingual bars. The results suggested that cast clasps and lingual plates are effective for the stabilization of mobile, remaining teeth. Additionally, the stabilizing effect of RPD on abutment teeth was not diminished, despite decreases in retentive force.

Grapefruit seed extract effectively inhibits the Candida albicans biofilms development on polymethyl methacrylate denture-base resin.

This study aimed to investigate the cleansing effects of grapefruit seed extract (GSE) on biofilms of Candida albicans (C. albicans) formed on denture-base resin and the influence of GSE on the mechanical and surface characteristics of the resin. GSE solution diluted with distilled water to 0.1% (0.1% GSE) and 1% (1% GSE) and solutions with Polident® denture cleansing tablet dissolved in distilled water (Polident) or in 0.1% GSE solution (0.1% G+P) were prepared as cleansing solutions. Discs of acrylic resin were prepared, and the biofilm of C. albicans was formed on the discs. The discs with the biofilm were treated with each solution for 5 min at 25°C. After the treatment, the biofilm on the discs was analyzed using a colony forming unit (CFU) assay, fluorescence microscopy, and scanning electron microscopy (SEM). In order to assess the persistent cleansing effect, the discs treated with each solution for 5 min were aerobically incubated in Yeast Nitrogen Base medium for another 24 h. After incubation, the persistent effect was assessed by CFU assay. Some specimens of acrylic resin were immersed in each solution for 7 days, and changes in surface roughness (Ra), Vickers hardness (VH), flexural strength (FS), and flexural modulus (FM) were evaluated. As a result, the treatment with 1% GSE for 5 min almost completely eliminated the biofilm formed on the resin; whereas, the treatment with 0.1% GSE, Polident, and 0.1% G+P for 5 min showed a statistically significant inhibitory effect on biofilms. In addition, 0.1% GSE and 0.1% G+P exerted a persistent inhibitory effect on biofilms. Fluorescence microscopy indicated that Polident mainly induced the death of yeast, while the cleansing solutions containing at least 0.1% GSE induced the death of hyphae as well as yeast. SEM also revealed that Polident caused wrinkles, shrinkage, and some deep craters predominantly on the cell surfaces of yeast, while the solutions containing at least 0.1% GSE induced wrinkles, shrinkage, and some damage on cell surfaces of not only yeasts but also hyphae. No significant changes in Ra, VH, FS, or FM were observed after immersion in any of the solutions. Taken together, GSE solution is capable of cleansing C. albicans biofilms on denture-base resin and has a persistent inhibitory effect on biofilm development, without any deteriorations of resin surface.

Effect of incorporation of surface pre-reacted glass ionomer filler in tissue conditioner on the inhibition of Candida albicans adhesion.

We investigated the effects of incorporation of surface pre-reacted glass ionomer (S-PRG) filler in tissue conditioner (TC) on Candida albicans adhesion. We prepared specimens containing 0, 5, 10, or 20 wt% of S-PRG filler, and measured the amount of C. albicans on the surface using a colony forming unit (CFU) assay and scanning electron microscopic images. In addition, we measured the consistency, penetration depth, and surface roughness (Ra). CFU values for 10 and 20 wt% were significantly lower than that for the control (p<0.05). Hyphal density on the surface was greater in the control. The 10 and 20 wt% specimens showed significantly higher consistency and Ra, lower penetration depth ratio than control (p<0.05). These results suggest that incorporation of S-PRG filler may reduce C. albicans adhesion onto TC surface; however, the optimal amount of filler is dictated by the influence of filler incorporation on mechanical and surface characters of TC.

Superhydrophilic co-polymer coatings on denture surfaces reduce Candida albicans adhesion-An in vitro study.

OBJECTIVE: In this study, we aimed to investigate denture-base-resin coatings prepared with a crosslinkable co-polymer containing sulfobetaine methacrylamide (SBMAm) and the relationship between their surface characteristics and the initial adhesion of Candida albicans (C. albicans). METHODS: Acrylic resin discs were coated with co-polymers containing various concentrations of SBMAm and N,N'-(4,7,10-trioxa-1,13-tridecadiamine) diacrylamide (JDA) as crosslinking agent. Uncoated discs were used as controls. An acquired pellicle was formed on each disc using artificial saliva, and the discs were immersed in a suspension of C. albicans (JCM2085) cells. After incubation, tetrazolium salt (XTT-reduction) and colony forming unit (CFU) assays were performed and the morphogenesis of C. albicans was examined using scanning electron microscopy (SEM). The surface roughness, film thickness, and the water contact angle of each disc surface were measured. RESULTS: All coating groups showed significantly lower amounts of adhered C. albicans in the XTT-reduction and CFU assays than the control, confirmed by the SEM images. Many wrinkle structures were observed on the surfaces coated with co-polymers containing more than 30% SBMAm. There were no significant differences in surface roughness among all groups. The co-polymer films on the coated discs were less than 5.0 µm in thickness, and these surfaces exhibited significantly lower mean water contact angles than the control. CONCLUSION: Crosslinkable co-polymers containing SBMAm can enhance the hydrophilicity of the surface of denture-base resins and reduce the initial adhesion of C. albicans.