Journal of Prosthodontic Research
Online ISSN : 1883-9207
Print ISSN : 1883-1958
ISSN-L : 1883-1958
Current issue
Showing 1-27 articles out of 27 articles from the selected issue
Editorial
Original article
  • Tsuyoshi Kitagawa, Yasuhiro Tanimoto, Takashi Iida, Hiroshi Murakami
    Type: Original article
    2020 Volume 64 Issue 4 Pages 359-367
    Published: 2020
    Released: August 08, 2020
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    Purpose: The aim of this study was: (1) to compare the coefficients of friction between commercially pure titanium (cpTi), titanium (Ti) alloy, and yttria-stabilized zirconia (YSZ) and: (2) to investigate the dynamic behavior of an implant system before, during, and after loading, by transient dynamic three-dimensional finite element analysis (FEA).
    Methods: Coefficients of friction were measured by a ball-on-disk frictional wear testing device. The preload in the screw shaft was calculated from geometric parameters. Two abutment model designs were created, namely a Ti alloy abutment model with a porcelain-fused-to-metal super structure and a YSZ abutment model with a porcelain-fused-to-zirconia super structure. Transient dynamic three-dimensional FEA was performed on ANSYS Workbench Ver. 15.0.
    Results: The coefficients of friction of YSZ/cpTi, YSZ/Ti alloy, Ti alloy/cpTi, and Ti alloy/Ti alloy were 0.4417, 0.3455, 0.3952, and 0.3489, respectively. The preload generated in the abutment screw of the FEA model was set to be 158 N. Significantly differences were not found in the maximum von Mises equivalent stress between the Ti alloy and YSZ abutment models before, during, and after loading.
    Conclusion: The findings indicate differences in the coefficients of friction of cpTi, Ti alloy, and YSZ before, during, and after loading. Fractures caused by stress did not depend on the use of different materials (Ti alloy and YSZ) at the abutment.
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  • Jin-Hun Jeon
    Type: Original article
    2020 Volume 64 Issue 4 Pages 368-372
    Published: 2020
    Released: August 08, 2020
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    Purpose: The purpose of this in vitro study was to determine the precision evaluation of blue light scanning of abutment teeth impressions and dental stone casts according to different 3D superimposition methods.
    Methods: Impressions and dental stone casts of the maxillary canine, 1st premolar, and 1st molar were fixed; they were repeatedly scanned 11 times, (6 types, total n = 66). Stereolithography (STL) files were superimposed one by one, and used to obtain 10 root mean square (RMS) values with the 2 superimposition methods (best-fit-alignment, no control). Statistical analysis included the independent t test and one-way ANOVA with Tukey honest significant differences (α = 0.05).
    Results: RMS ± Standard Deviation (SD) values for the best-fit-alignment method of the abutment teeth impressions of the maxillary canine, 1st premolar, and 1st molar was 8.07 ± 0.76, 5.03 ± 0.23, and 6.59 ± 0.24, respectively, and those of the no control method were 9.36 ± 0.82, 7.10 ± 1.14, and 8.17 ± 0.36 respectively. RMS ± SD values for the best-fit-alignment method for the dental stone casts were 4.07 ± 0.27, 3.39 ± 0.07, and 3.29 ± 0.07, respectively, and those for the no control method were 6.26 ± 2.50, 4.98 ± 1.16, and 4.55± 0.74, respectively.
    Conclusions: Using different 3D superimposition methods, blue light scanning of abutment teeth impressions and dental stone casts shows high precision. The no control method showed lower precision best-fit-alignment. However, the results may help advance the digital dental CAD/CAM research and the clinical field of Prosthodontics
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  • Takeshi Saito, Takeshi Wada, Keitaro Kubo, Takayuki Ueda, Kaoru Sakura ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 373-379
    Published: 2020
    Released: August 08, 2020
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    Purpose: This study aims to investigate the effect of mechanical and chemical cleaning on the surface roughness ofPurpose: silicone soft relining materials.
    Methods: We selected silicone soft relining materials with the highest (Soft) and lowest (Supersoft) Shore A hardness. In the abrasion test, specimens were cleaned 50,0 0 0 times using a kitchen sponge (Sponge), a soft (Soft brush) or hard (Hard brush) denture brush, or stored in water (No cleaning). In the immer- sion test, specimens were immersed in either water (Water), neutral peroxide denture cleanser (Neutral), alkaline peroxide denture cleanser (Alkaline), or hypochlorite denture cleanser (Hypochlorite) for 1440 h. Surface roughness of the arithmetic mean height of the surface (Sa) and maximum height (Sz) were measured before and after the tests. Data were analyzed using the Kruskal–Wallis and Mann–Whitney U tests.
    Results: In the abrasion test, significant differences were observed for Sa and Sz with Soft relining ma- terials, but not for No cleaning and Sponge. In the immersion test, significant differences were observed for Sa and Sz with Soft relining materials, but not between Water and Neutral or Water and Alkaline. Significant differences were observed with Supersoft, except between Water and Neutral or Water and Alkaline for Sa and between Water and Neutral for Sz.
    Conclusions: Mechanical cleaning using a sponge did not increase the surface roughness of the mate- rial with a high Shore A hardness. Furthermore, neutral peroxide denture cleanser did not increase the roughness of materials with high and low Shore A hardness.
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  • Takeshi Wada, Takayuki Ueda, Kuniko Morita, Yuichi Nezu, Keitaro Kubo, ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 380-383
    Published: 2020
    Released: August 08, 2020
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    Purpose: The purpose of this study was to compare the adhesiveness of chewing gum to hard and soft denture base materials to investigate food retention associated with the basal surface of the denture.
    Methods: Test specimens were fabricated using acrylic resin[Re], cobalt-chromium alloy[Co], zirconia[Zr], silicone soft relining material[SS], and acrylic soft relining material[AS]. Samples were set on a top-andbottom pair lifting platform equipped with a digital force gauge. The experimenter chewed 3.0 g of chewing gum for 5 min. After surface saliva was wiped off, the chewing gum was placed on the lower test fragment and compressed until the distance between the upper and lower test fragments decreased to 1 mm. The upper test fragment was pulled at a crosshead speed of 100 mm/min. Adhesiveness was measured under dry conditions, and under wet conditions with inter-positioned artificial saliva.
    Results: Under dry conditions, the adhesive strength was 17.04 ± 1.99 N for Re, 12.88 ± 2.20 N for Co, 3.80 ± 1.03 N for Zr, 5.76 ± 1.41 N for SS, and 12.54 ± 2.44 N for AS. Under wet conditions, the adhesive strength was 5.26 ± 1.64 N for Re, 0.96 ± 0.21 N for Co, 3.32 ± 0.40 N for Zr, 5.20 ± 1.35 N for SS, and 6.78 ± 1.97 N for AS.
    Conclusions: Among the hard denture base materials, zirconia recorded low adhesiveness and Re recorded high adhesiveness under both wet and dry conditions. The adhesiveness of Co was low under wet conditions but high under dry conditions. Among the soft denture base materials, SS under dry conditions recorded lower adhesiveness than that of AS. The adhesiveness of SS was low under both wet and dry conditions.
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  • Aya Elkabbany, Matthias Kern, Amr H. Elkhadem, Sebastian Wille, Ashraf ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 384-390
    Published: 2020
    Released: August 08, 2020
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    Purpose: To evaluate the change in the retention of novel metallic and non-metallic combinations for double-crown-retained mandibular overdentures on implants.
    Methods: Cylindrical bases were used to insert four implants arranged in an arch, with 10 mm inter- implant spacing anteriorly, and 35 mm posteriorly. Five groups ( n = 8 each) of different materials combi- nations were tested for retention: zirconia abutments/PEEK framework (ZP), PEEK abutments/PEEK frame- work (PP), titanium abutments/PEEK framework (TP), titanium abutments/CoCr framework (TC), and ti- tanium abutments/gold copings/cobalt-chromium framework as the control group (TG). The abutment retention height was 4 mm with 1 ° convergence angle. The retention was measured in a wet condition using a chewing simulator initially, and then at 10 0, 20 0, 50 0, 1,0 0 0, 2,0 0 0, 3,0 0 0, 5,0 0 0, 8,0 0 0, and 10,0 0 0 insertion/separation cycles, which simulates the removing and inserting of an overdenture three times daily for 10 years of function.
    Results: The initial median retention of all groups ranged from 10.0 to 33.3 N. After 10,0 0 0 inser- tion/separation cycles, the median retention ranged from 10.3 to 35.0 N. The change in the retention after 10,0 0 0 cycles was not statistically significant within groups ZP and TG. For groups PP and TP, there was a slight increase in retention with partial significance. The retention of group TC showed fluctuation with a partially significant decrease in retention.
    Conclusions: The use of novel metallic and non-metallic combinations in the construction of double- crown-retained mandibular overdentures on implants resulted in acceptable levels of retention and might be recommended for clinical application.
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  • Shane N. White, Chad C. Green, Robert M. McMeeking
    Type: Original article
    2020 Volume 64 Issue 4 Pages 391-396
    Published: 2020
    Released: August 08, 2020
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    Purpose: Porcelain fused to zirconia prostheses are widely used, but porcelain chipping, fracture, spalling and delamination are common clinical problems. Conventional bond strength testing is inherently un- suited for studying interfacial failure by cracking in brittle materials. Instead, fracture toughness is a more meaningful parameter because it can assess the robustness of the interface when subjected to loading, but fracture mechanics approaches have only rarely been used. Our purpose was to develop a novel, sim- ple, 3-point flexural methodology and mathematical analysis to measure the fracture toughness of the porcelain to zirconia interface.
    Methods: Equations were derived to estimate the fracture toughness of the bond by computing the inter- facial energy release rate for a novel simple 3-point flexural test model. The test was validated using two different configurations of layered zirconia/porcelain beams ( n = 10), approximating the dimensions of a fixed dental prosthesis, fabricated from a tetragonal polycrystalline zirconium dioxide partially stabilized with yttria and a feldspathic dental porcelain.
    Results: Cracking along the bimaterial interface was produced and measured as a discrete event. Frac- ture toughness means (standard deviations) computed from the measured energy release rate, for the porcelain to zirconia interface in two different specimen configurations were 7.9 (1.3) and 5.3 (1.6) J/m 2 .
    Conclusions: Equations were derived to measure interfacial fracture toughness of brittle materials using a novel simple 3-point flexural test method. The test was then validated; estimates for the fracture tough- ness for the porcelain to zirconia bond, overlapped with previously published data derived from more complex 4-point notched tests.
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  • Sayuri Koga, Yoichiro Ogino, Natsue Fujikawa, Machiko Ueno, Yuki Kotak ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 397-400
    Published: 2020
    Released: August 08, 2020
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    Purpose: The purpose of this study was to evaluate the effect of oral rehabilitation (maxillofacial prosthetic intervention and oral hygiene instruction) on oral health-related Quality of Life (OHRQoL) and oral hygiene condition in patients with maxillofacial defects and to explore the correlation between them in these patients.
    Methods: Twenty-five patients with maxillofacial defects who had been treated since April 2016 to March 2018 were included in this study. The scores of the Oral Health Impact Profile (OHIP) and O’Leary’s Plaque Control Record (PCR) were also identified as the scores of OHRQoL and oral hygiene condition, respectively. Statistical analyses were performed to compare between the scores of “pre” and “post” prosthetic treatment and to evaluate patient-related factors influencing these variables (age, the number of residual teeth and occlusal supports, and occlusal units (OUs)). The effect of combined chemo-radiotherapy (CRT) on each score was also assessed statistically. Furthermore, the correlation of OHIP and PCR scores was explored statistically.
    Results: Both oral rehabilitations could significantly improve OHIP and PCR scores. Significant correlations of the change of OHIP scores with age and OUs were detected. CRT had no significant effect on OHIP and PCR scores. No correlations between OHIP and PCR were observed.
    Conclusions: Although oral rehabilitation such as maxillofacial prosthetic treatment and oral hygiene instruction would be highly effective for improvement of OHRQoL and oral hygiene condition in patients with maxillofacial defects, there was no correlation between them.
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  • Saori Muta, Masaomi Ikeda, Toru Nikaido, Mahmoud Sayed, Alireza Sadr, ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 401-407
    Published: 2020
    Released: August 08, 2020
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    Purpose:The purpose of this study was to evaluate the dimensional accuracy of crowns fabricated using a polyvinyl alcohol (PVA) dental model.
    Methods: An intraoral scanner (LAVA TDS) was used to scan a prepared molar abutment as a master model. The STL file obtained from the scanning process was transferred into the FDM 3D printer (Value 3D Magix MF-10 0 0) and then models were fabricated with PVA filament. In order to compare with the conventional method, an impression of the master model was taken using silicone impression material to fabricate the conventional stone cast model (Conv). An indirect resin composite (Gradia) and self- cured acrylic resin (Curergrace) were used to fabricate crowns ( n = 20) according to the manufacturer’s instructions. Surface accuracy of the Conv and PVA models and internal accuracy of the crowns set on the models were measured using two methods; 3D digital analysis and silicon-fitting evaluation. Statistical analysis of the results was done using t -test and Willcoxon signed rank test with Bonferroni correction at 5% significance.
    Results: Digital analysis showed the Root Mean Square (RMS) value of PVA model surface was higher than that of Conv, while there was no significant difference between the two crown materials. However, the silicon-fitting analysis showed marginal discrepancy of crowns fabricated on PVA model were within 100 μm.
    Conclusion: 3D printed PVA model can be used for chairside crown fabrication with an acceptable accu- racy.
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  • Ana Paula Rodrigues Magalhães, Carla Müller Ramos-Tonello, Mateus Zamo ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 408-416
    Published: 2020
    Released: August 08, 2020
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    Purpose: To evaluate the shear bond strength (SBS) between Y-TZP and a resin luting agent, after 1 of 2 enhancing strategies with TiO2--nts was applied, either to the resin luting agent or the Y-TZP mass, in different concentrations.
    Methods: In the Strategy TiO2-nts on ceramic, the resin luting agent Panavia F2.0TM (Kuraray) and an experimental Y-TZP with added concentrations of TiO2--nts (0%, 1%, 2%, and 5% vol/vol) and a commercial Y-TZP, comprised 5 different groups (n = 10). In the Strategy TiO2-nts on cement, the resin luting agent RelyX U200TM (3 M ESPE) was added with different concentrations of TiO2--nts (0%, 0.3%, 0.6%, 0.9% wt/wt) luted to a commercial Y-TZP, comprising 4 different groups (n = 10). The Y-TZP discs were included in acrylic bases, and a cylinder (3 × 3 mm) of the correspondent luting agent for each respective group was applied over them. After 24 h, specimens were subjected to SBS assessments in a universal testing machine. Field emission scanning electron microscopy and energy dispersive X-ray spectroscopy analyses were also performed on Y-TZP surfaces. Data were analyzed via analysis of variance and Tukey tests (α = 0.05).
    Results: TiO2-nts on ceramic influenced the bond strength significantly, but not linearly; TiO2-nts on cement did not influence bond strength when analyzed separately, nor in comparison with the first.
    Conclusion: Y-TZP enhancements with TiO2-nts led to a higher SBS with Panavia F2.0, a 5% TiO2--nt concentration presented the highest bond strength. Modified Rely X U200 did not improve SBS.
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  • So Furokawa, Suguru Kimoto, Nobuhiko Furuse, Yoshiteru Furuya, Takahir ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 417-423
    Published: 2020
    Released: August 08, 2020
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    Purpose: This randomized controlled trial aimed to study the effects of lining mandibular complete den- tures with silicone-based resilient denture liners, especially with respect to sensation.
    Methods: The trial included completely edentulous patients who were willing to fabricate new set of complete denture. A random permuted block method (block size: 4) was used to assign participants to one of the following groups: mandibular conventional denture (CD) group or mandibular denture with resilient denture liner (RD) group. The outcomes were evaluated using both, objective measures (current perception threshold (CPT) and pain threshold (PT)) for external stimuli measured using the Neurometer CPT® and subjective measures (physical pain and psychological discomfort measured using the Japanese version of Oral Health Impact Profile for Edentulous patients—OHIP-EDENT-J). The outcomes were mea- sured twice, at immediately after completion of denture adjustments (first measurement), and 3 months after the completion of denture adjustments (second measurement). All outcomes were analyzed using the Student t -test. A p -value of <0.05 was considered statistically significant.
    Results: CPT was significantly higher with RD than CD only at second measurement with frequency level of 20 0 0 Hz and 5 Hz. The pain thresholds were significantly higher in the RD group than the CD group. The physical pain and psychological discomfort scores were significantly lower in the RD group than in the CD group.
    Conclusion: This study concludes that edentulous patients wearing mandibular complete dentures with silicone-based resilient denture liners dull perception mandibular ridge mucosa and felt less pain than those without the liners.
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  • C. Monaco, A. Arena, L. Corsaletti, V. Santomauro, P. Venezia, R. Cava ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 424-430
    Published: 2020
    Released: August 08, 2020
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    Purpose: To compare the 2D and 3D positional accuracy of four guided surgical protocols using an analysis of linear and angular deviations.
    Methods: DICOM and .STLs files obtained from a CBCT and a digital impression were superimposed with software to plan implant position. Fifty-six patients were subdivided into 4 groups: FGA group (template support [Ts]: teeth [T]; bed preparation [Bp]: fully guided [FG]; implant insertion [Ii]: 3D template [3Dt]; device [D]: manual adapter [MA], FGM group (Ts: T; Bp: FG; Ii: 3Dt; D: fully guided mounter [FGM]), PG group (Ts: T; Bp: FG; Ii: manual; D: none) and MS group (Ts: mucosa; Bp: FG; Ii: 3Dt; D: FGM). The position of 120 implants was assessed by superimposing the planned and final position recorded with a digital impression.
    Results: In FGA group, 3D deviations were 0.92 ± 0.52 mm at the implant head and 1.14 ± 0.54 mm at the apex, and the angular deviation (ang. dev.) was 2.45 ± 1.24°. In FGM group, were 0.911 ± 0.44 mm (head) and 1.11 ± 0.54 mm (apex), and the ang. dev. was 2.73 ± 1.96°. In PG group, were 0.95 ± 0.47 mm (head) and 1.17 ± 0.488 mm (apex), and the ang. dev. was 3.71 ± 1.67°. In MS group, were 1.15 ± 0.45 mm (head) and 1.42 ± 0.45 mm (apex), and the ang. dev. was 4.19 ± 2.62°. Ang. dev. of MS group was different from the other groups (P < 0.05).
    Conclusions: Guided surgery showed a sufficient accuracy
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  • N.K. Sonnahalli, R. Chowdhary
    Type: Original article
    2020 Volume 64 Issue 4 Pages 431-435
    Published: 2020
    Released: August 08, 2020
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    Purpose: The purpose of this study was to evaluate the impact of silver nanoparticle incorporation into maxillofacial silicone material on its hardness, tear strength and color stability.
    Methods: A total of 180 silicone specimens were fabricated according to the specification of American so- ciety for material and testing (ASTM) No. D142 and No. D624. The control samples were fabricated with- out silver nanoparticles and test samples were fabricate with 20 ppm concentration of silver nanoparti- cles. For outdoor weathering specimens were placed in a metal cage, which was suspended from the roof for a period of one month. Digital shore A hardness tests (Yuzuki, DIN 53505, ASTM D2240) was used to measure hardness, for tear strength the specimen was placed in the jaws of the universal testing machine (Lloyd instruments, LR 50 K) and stretched at a rate of 500 ram⁄rain, for color stability Spectrophotome- ter had been employed and the data recorded in the CIE L∗ a ∗ b ∗ system. The independent sample’s “t” test was used to test significant differences.
    Results: The mean difference for hardness between control and test group was 0.54 and t value was 2.08 and ( p ‹ 0.05).tear strength 0.66 and “t” value was 0.93 and ( p ‹ 0.05) and for color stability it was -0.02 and t value was -0.92 and ( p ‹ 0.05).
    Conclusion: The present study findings suggest that addition of silver nanoparticles at 20 ppm concentra- tion decreased the hardness of Teksil 25(S25) silicone elastomer, and it did not affect tear strength and color stability.
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  • Tsubasa Naoe, Akira Hasebe, Rumi Horiuchi, Yoji Makita, Yohei Okazaki, ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 436-443
    Published: 2020
    Released: August 08, 2020
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    Purpose: The mechanical properties, antimicrobial activity, and biocompatibility of a novel antimicrobial tissue conditioner containing cetylpyridinium chloride with montmorillonite (CPC-Mont) were evaluated.
    Methods: To examine the mechanical properties of the novel material, hardness, consistency, and penetration tests were conducted. Antimicrobial activity against Candida albicans (C. albicans) and Staphylococcus aureus (S. aureus) was evaluated. Cell viabilities of fibroblasts and epithelial cells using eluates from materials were measured to evaluate cytotoxicity. In addition, to assess tissue response, animal experiments were conducted.
    Results: The hardness test results were similar to those of other commercially available materials. The novel tissue conditioner showed good antimicrobial activity against C. albicans and S. aureus compared with other materials. This effect was sustained for a week for C. albicans. In the case of S. aureus, microbial growth was suppressed for up to 3 weeks. Cell viability of the novel material for the eluate at 1 day was significantly less than those of other material for both cells. However, the cell viability at 7 days showed no significant difference. Animal experiments demonstrated that inflammatory responses around materials were not observed on the oral mucosa as other material.
    Conclusion: Within the limitations of this in vitro and in vivo study, the results suggest that the newly developed tissue conditioner containing CPC-Mont has not only excellent antimicrobial properties, but also the same mechanical properties and biocompatibility as tissue conditioners on the market.
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  • Gary Hack, Leila Liberman, Joerg P. Tchorz, Sebastian B.M. Patzelt, Zi ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 444-453
    Published: 2020
    Released: August 08, 2020
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    Purpose: Within the specialty of prosthodontics, oral impressions are ubiquitous tools utilized to transfer intraoral characteristics such as teeth, implants, and soft tissue into a physical state (stone cast) that is processable in a laboratory setting for the fabrication of dental restorations. In recent years, optical impression systems have become ubiquitous in clinical practice replacing the conventional method of impression making. The purpose of the present study was to evaluate the feasibility and accuracy of computerized optical impression making of edentulous jaws in an in vivo setting.
    Methods: 29 edentulous patients (27 maxillae and five mandibles) underwent conventional impressions as well as computerized optical impressions. The conventional impressions and the resulting stone casts were digitized and superimposed over the computerized/digitized optical impressions in order to obtain information on differences between the two datasets. Statistical analyses were performed to identify rel- evant deviations.
    Results: The overall mean difference between the stone cast, digital scans and the computerized optical scans were 336.7 ± 105.0 μm ( n = 32), 363.7 ± 143.1 μm ( n = 24), and 272.1 ± 168.5 μm ( n = 29), respectively. The visual evaluations revealed highest deviations ( ≥ 500 μm) in the areas of the soft palate, the sublingual areas, and the vestibule (peripheral seal zone).
    Conclusions: Within the limitations of the present study, the investigated scanners were not able cur- rently to fully replace a conventional impression for the fabrication of a complete denture.
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  • Shuhei Arita, Tomoya Gonda, Hitomi Togawa, Yoshinobu Maeda, Kazunori I ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 454-459
    Published: 2020
    Released: August 08, 2020
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    Purpose: The purpose of this study was to determine the influence of mandibular free-end partial edentulism and the wearing of removable partial dentures in the partially edentulous area on the force exerted on maxillary anterior teeth.
    Methods: A commercially available jaw model with exchangeable teeth was used. Seven experimental conditions of mandibular free-end edentulism were set up and a distal extension removable partial denture to replace missing posterior teeth was fabricated. Strain gauges were attached to the root surface of the maxillary left central incisor, canine, first premolar and first molar, and the force exerted on them was calculated based on the calibration coefficient. An occlusal load of 49 N was applied and the forces were compared with the Kruskal–Wallis test (P < 0.05).
    Results: The force exerted on the maxillary anterior teeth increased significantly as the number of remaining teeth decreased. The force exerted on the maxillary anterior teeth decreased significantly with use of a removable partial denture.
    Conclusions: When the number of remaining teeth decreases in mandibular free-end partial edentulism, the burden on the maxillary anterior teeth increases. Our findings suggest that for patients with mandibular free-end partial edentulism, wearing a removable partial denture is effective in preserving the remaining teeth by reducing excessive stress.
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  • Shohei Suzuki, Yasuhiro Katsuta, Kazuhiko Ueda, Fumihiko Watanabe
    Type: Original article
    2020 Volume 64 Issue 4 Pages 460-467
    Published: 2020
    Released: August 08, 2020
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    Purpose: The purpose of this study was to compare the marginal and internal fit of three-unit fixed dental prostheses (FDPs) fabricated using CAD/CAM with two designs, two cement space (CS), and two zirconia types.
    Methods: A master model with two zirconia abutments and a missing tooth was scanned with an intraoral scanner. FDPs were fabricated with two designs (Full contour: FC, Framework: FW), two zirconia types (multi-layer: L, single-layer: W), and two CS values (30 and 45 μm for L and 30 μm for W). There were six experimental groups. The fit of the FDPs was evaluated using the replica method. The space between an abutment and the FDPs in the marginal (MO), chamfer (CH), axial (AX), and occlusal (OC) areas was measured under an optical microscope and the data was statistically analyzed using three-way ANOVA and Bonferroni test (p < 0.05).
    Results: FW-l-45 μm showed a significantly smaller space than those for the FC in MO (p = 0.011), CH (p = 0.001) and AXE (p = 0.003). FW-l-30 μm showed a significantly smaller space than that for the 45 μm in AXE (p = 0.000) and OC (p = 0.016). FW-W-30 μm showed a significantly smaller space than that for the L in MO (p = 0.000), CH (p = 0.000), AXE (p = 0.000), and OC (p = 0.002).
    Conclusions: The design and CS of the FDPs affected the fit. FDPs with single-layer zirconia showed better fit than that obtained with multi-layer zirconia.
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  • Kazuya Takahashi, Mana Torii, Toyoki Nakata, Noboru Kawamura, Hidemasa ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 468-477
    Published: 2020
    Released: August 08, 2020
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    Purpose: Laboratory and clinical assessment of cast titanium dentures were reported, little is known about additive manufacturing (AM) frameworks. This study evaluated in vitro AM titanium alloy clasps for clinical use.
    Methods: After scanning the stainless steel dies to simulate the first molar, an Akers clasp was designed by CAD. AM clasp specimens were manufactured using laser sintering and AM machines from CP titanium grade 2 (CPTi), Ti-6Al-4V (Ti64), and Ti-6Al-7Nb (Ti67) powders. As controls, cast titanium clasps were conventionally made with same three titanium alloys. After nondestructive inspection and surface ele- ment analysis, surface roughness, fitness accuracy, initial retentive forces, and changes in retentive forces were measured.
    Results: Although few porosities and little contamination of AM clasps were confirmed, the AM clasp arm and tip indicated slightly worse fitness accuracy as compared to cast clasps. The initial retentive forces of all titanium clasps showed appropriate retentive forces within the acceptable ranges, AM clasps tended to have lower decreases in retentive forces with up to 10,0 0 0 insertion/removal cycles as compared to those of the cast clasps.
    Conclusions: AM titanium clasps would be acceptable for clinical use similar to that of cast titanium clasps.
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  • Rong Li, Hu Chen, Yong Wang, Yongsheng Zhou, Zhijian Shen, Yuchun Sun
    Type: Original article
    2020 Volume 64 Issue 4 Pages 478-484
    Published: 2020
    Released: August 08, 2020
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    Purpose: The aim of this in vitro study was to evaluate the three-dimensional trueness and margin quality of monolithic zirconia restorations fabricated by additive 3D gel deposition, compared with those by subtractive milling.
    Methods: Ten single crowns and ten 4-unit FPDs of different occlusal geometries and margin thickness were fabricated by additive 3D gel deposition (additive group) and subtractive milling (subtractive group). An intraoral scanner was used to digitalize the restorations. 3D deviation analysis was applied and root mean square (RMS) was used to assess the trueness. Margin quality was characterized using optical stereomicroscopy and 3D laser scanning microscopy.
    Results: For single crowns with shallow fossae and grooves and normal margin, RMS value of additive group and subtractive group showed no significant difference in external surface, while additive group showed higher RMS value in intaglio surface. As for 4-unit FPDs with deep fossae and grooves and thin margin, RMS value of additive group in external surface was significantly lower than that of subtractive group and in intaglio surface there was no significant difference between two groups. With a 0.5 mm chamfer design, single crowns in additive group showed flawless margin with a smooth contour line, whereas minor flaws could be observed in 4-unit FPDs with thin margin. In subtractive group, restorations showed minor flaws or defects of various number and severity.
    Conclusions: Monolithic zirconia restorations fabricated by additive 3D gel deposition have comparable trueness and better margin quality than those fabricated by subtractive milling. Besides it is more capable of enabling complex geometry.
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  • Takashi Matsuda, Kosuke Kurahashi, Naoki Maeda, Takaharu Goto, Tetsuo ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 485-489
    Published: 2020
    Released: August 08, 2020
    JOURNALS RESTRICTED ACCESS
    Purpose: The present study aimed to examine three methods for imaging a complete denture form and to discuss the geometric assessment and availability of these methods.
    Methods: Three methods were used: cone-beam computed tomography (CBCT), desktop dental scanning (DDS), and handheld optical scanning (HOS). Three sides of a cuboid resin block of a known size were measured on the captured images. Ten upper and lower complete dentures were digitized using each of the three methods. The denture forms in the standard triangulated language format were reconstructed using the computer aided design software with three resolutions: 0.1, 0.5 and 1.0. The two images were superimposed through a least-square algorithm, and the mean differences were examined among the three types of imaging methods and resolutions.
    Results: The smallest mean differences and variations were obtained for CBCT and DDS, followed by HOS in the experiment using resin block. The lengths of longitudinal and horizontal sides were shortened in CBCT and DDS, whereas the height was shortened in HOS. The variations in each direction were very small by repetitive imaging within every imaging method. The difference between the CBCT and DDS was significantly smaller than that in the other two groups in experiment using actual dentures. The influence of resolution was comparatively low.
    Conclusions: The results suggested that CBCT and DDS had a similar geometric assessment, but that of the HOS was lower.
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  • Nor Haliza Mat-Baharin, Masfueh Razali, Shahida a Mohd-Said, Junaidi S ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 490-497
    Published: 2020
    Released: August 08, 2020
    JOURNALS RESTRICTED ACCESS
    Purpose: Not all elements with β-stabilizing properties in titanium alloys are suitable for biomaterial applications, because corrosion and wear processes release the alloying elements to the surrounding tissue. Chromium and molybdenum were selected as the alloying element in this work as to find balance between the strength and modulus of elasticity of β-titanium alloys. This study aimed to investigate the effect of Titanium-10Molybdenum-10Chromium (Ti-10Mo-10Cr), Titanium-10Chromium (Ti-10Cr) and Titanium-10Molybdenum (Ti-10Mo) on the elemental leachability in tissue culture environment and their effect on the viability of human gingival fibroblasts (HGFs).
    Methods: Each alloy was immersed in growth medium for 0–21 days, and the elution was analyzed to detect the released metals. The elution was further used as the treatment medium and exposed to seeded HGFs overnight. The HGFs were also cultured directly to the titanium alloy for 1, 3 and 7 days. Cell viability was then determined.
    Results: Six metal elements were detected in the immersion of titanium alloys. Among these elements, molybdenum released from Ti-10Mo-10Cr had the highest concentration throughout the immersion period. Significant difference in the viability of fibroblast cells treated with growth medium containing metals and with direct exposure technique was not observed. The duration of immersion did not significantly affect cell viability. Nevertheless, cell viability was significantly affected after 1 and 7 days of exposure, when the cells were grown directly onto the alloy surfaces.
    Conclusions: Within the limitation of this study, the newly developed β-titanium alloys are non-cytotoxic to human gingival fibroblasts.
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  • Michael H. Walter, Jens Dreyhaupt, Torsten Mundt, Ralf Kohal, Matthias ...
    Type: Original article
    2020 Volume 64 Issue 4 Pages 498-505
    Published: 2020
    Released: August 08, 2020
    JOURNALS RESTRICTED ACCESS
    Purpose: This analysis focused on periodontal health in shortened dental arches (SDAs).
    Methods: In a randomized controlled clinical trial, patients with missing molars in one jaw and at least one premo-lar and canine on both sides were eligible for participation. In the partial removable dental prosthesis (PRDP) group ( n = 79), molars were replaced with a precision attachment retained PRDP. In the SDA group ( n == 71), the SDA up to the second premolars was either left as is or restored with fixed den- tal prostheses. Outcome variables were vertical clinical attachment loss (CAL-V), pocket probing depth (PPD), bleeding on probing (BOP) and plaque index (PLI). For CAL-V and PPD, the changes at six mea- suring points per tooth were analyzed. For BOP and PLI, patient related rates were calculated for each point in time. Statistical methods included linear regression analyses.
    Results: In the intention-to-treat (ITT) analysis for CAL-V in the study jaw, the 10 year patient related mean changes were 0.66 mm in the PRDP group and −0.13 mm in the SDA group. The resulting mean patient related group difference of 0.79 mm (95% CI: 0.20 mm–1.38 mm) was significant ( p = 0.01). There were no significant differences in the ITT analyses for PPD. For BOP and PLI, significant group differences with more favorable results for the SDA group were found.
    Conclusions: In view of lacking substantial differences for CAL-V and PPD, the overall differences were considered of minor clinical relevance. The results add confirmatory evidence to the shortened dental arch concept and its clinical viability (controlled-trials.com ISRCTN97265367).
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Technical procedure
  • Rubén Agustín-Panadero, Ignazio Loi, Lucía Fernández-Estevan, César Ch ...
    Type: Technical procedure
    2020 Volume 64 Issue 4 Pages 506-514
    Published: 2020
    Released: August 08, 2020
    JOURNALS RESTRICTED ACCESS
    Purpose: This article describes a digital technique used to record gingival emergence profiles modeled for the prosthetic restoration of teeth prepared using biologically oriented preparation technique (BOPT).
    Materials and methods: The description of the technique of intraoral recording, manipulation of digital files, and chairside protocol of prosthetic restorations is developed in the present manuscript on two an- terior teeth treated with vertical and subgingival dental preparations for restoration with ceramic crowns. The manipulation of the digital files registered with an intraoral scanner with software that allows its alignment (best-fit) and the performance boolean of operation manages to create a virtual gingival emer- gency like the one it presents when it is adapted on the cervical part of the interim prosthesis.
    Conclusions: The technique allows the dentist and laboratory technician to obtain a digital reproduction of the subgingival soft tissues around the prosthetic crown, unaffected by the collapse of the gingival sulcus when the provisional crown is removed, as well as an exact copy of the provisional restoration, making it possible to fabricate a definitive prosthesis that ensures precise anatomy, and so good compat- ibility with periodontal tissues.
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