Evaluation of hypermobile teeth deviation during impression taking in a partially edentulous dental arch: An in vitro study comparing digital and conventional impression techniques.

PURPOSE: This study aimed to compare the deviation of hypermobile teeth in partially edentulous dental arches during impression taking using digital and conventional techniques. METHODS: A partially edentulous mandibular model with three target hypermobile teeth (including the left first premolar, #34; left second molar, #37; and right first premolar, #44), was used as the simulation model. After reference data were acquired using a desktop scanner, impressions of the simulation model were obtained using a digital intraoral scanner (IOS) and two conventional techniques (hydrocolloid material with a stock tray and silicone material with a custom tray as impression data (n=12/group). The three-dimensional accuracy (root mean square value) and two-dimensional accuracy (mesiodistal and buccolingual displacements) of the target teeth in each impression dataset were calculated based on the reference data. The comparison among three impression techniques was statistically performed using the Kruskal-Wallis test (α=0.05). RESULTS: For #34 and #44, the three- and two-dimensional accuracies of the impressions fabricated through data acquired through digital scanning (digital impression) were significantly superior to those of the hydrocolloid impression (P < 0.05), whereas no significant difference was found between the digital and silicone impressions. For #37, no significant difference in the accuracy of the impression data for the target teeth was observed among the three impression techniques. CONCLUSIONS: Digital impression acquiring using an IOS is recommended over using a conventional hydrocolloid impression to prevent the deviation of hypermobile teeth in partially edentulous dental arches. Hypermobile tooth deviation in digital impression data depends on the tooth location.

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.

Evaluation of PEEK and zirconia occlusal rest designs for removable partial dentures based on finite element analysis.

Purpose We aimed to assess removable partial denture occlusal rests composed of polyether-ether-ketone (PEEK) and zirconia, using finite element analysis.Methods Three-dimensional PEEK and zirconia rest models, including the occlusal rest (1.5 mm thickness at the basal portion, 3.0 mm width) and minor connector (1.5 mm thickness, 6.0 mm height), and rest seat models with mechanical properties of enamel were constructed. The radius of transitional curvature between the rest and minor connector was 0.1-0.5 mm. The rest and rest seat model interfaces were set as frictional contacts (µ = 0.1), and the base of the rest seat model was restrained in all the directions. A 100 N downward load was applied perpendicular to the bottom surface of the minor connector. The maximum value of the first principal stress (Max-S1) was compared to the flexural and fatigue strengths of each material. Occlusal rests with 1.0-2.0 mm thickness, 2.0-3.5 mm width, and 0.5 mm radius of transitional curvature were analyzed.Results Max-S1 was observed at the transitional part and decreased with increasing radius of the transitional curvature, rest width, and thickness. PEEK rests with at least 1.5 mm thicknesses and 3.0 mm widths showed lower Max-S1 than the flexural strength. Max-S1 of all PEEK rests exceeded the PEEK fatigue strength, whereas Max-S1 of the zirconia rests was lower than the zirconia fatigue strength.Conclusions Zirconia occlusal rests with conventional metal rest designs have sufficient fatigue strength. PEEK occlusal rests have insufficient fatigue strength and may not withstand repeated mastication.

Effect of Scanning Origin Location on Data Accuracy of Abutment Teeth Region in Digital Impression Acquired Using Intraoral Scanner for Removable Partial Denture: A Preliminary In Vitro Study.

The aim of this study was to investigate the effect of scanning origin location on the data accuracy of removable partial denture (RPD) abutment teeth region in digital impressions acquired by an intraoral scanner. A mandibular partially edentulous model including the following target abutment teeth was used: the left second molar (#37); left first premolar (#34); and right second premolar (#45). The following scanning strategies were tested: the strategy starting from #37 to mesial direction (37M); strategies starting from #34 to mesial (34M) and distal directions (34D), and strategies starting from #45 to mesial (45M) and distal directions (45D). The evaluated measures were trueness, precision, and linear accuracy. One-way and two-way ANOVA were performed for the comparison of trueness and linear accuracy, while Kruskal-Wallis test was performed for the precision comparison (α = 0.05). 45M and 45D showed significantly superior trueness of #34 to 37M and 34D. 45M also showed significantly superior trueness of #45 to 34. 45D showed significantly inferior linear accuracy of #34 and superior linear accuracy of #45 compared to other strategies. It was concluded that scanning origin location would have an impact on data accuracy of RPD abutment teeth region in digital impressions acquired by intraoral scanner.

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.