Journal of Prosthodontic Research
Online ISSN : 1883-9207
Print ISSN : 1883-1958
ISSN-L : 1883-1958
Volume 64 , Issue 2
Showing 1-21 articles out of 21 articles from the selected issue
Review Article
  • Hidemichi Kihara, Wataru Hatakeyama, Futoshi Komine, Kyoko Takafuji, T ...
    2020 Volume 64 Issue 2 Pages 109-113
    Published: 2020
    Released: July 08, 2020

    Purpose: The digitization of the dental field has been vigorously promoted in recent years. An impression using an intraoral scanner is considered to significantly change future dental treatment. The purpose of this review is to evaluate accuracy and practicality of various intraoral scanners and verification method of intraoral scanners.

    Study selection: This review was based on articles searched through the MEDLINE and PubMed databases. The main keywords that were employed during the search were "Oral Scanner, Intraoral Scanners, Desktop Scanner, and Digital Impression".

    Result: It was reported that illuminance and color temperature affected trueness and precision of intraoral scanners. The repeatability of intraoral scanners indicated the possibility of producing fixed prostheses within the range of being partially edentulous. It is considered difficult to use intraoral scanners in fabricating cross-arch fixed prostheses. However, with intraoral scanners, it may be considered possible to fabricate mouth guards and dentures equivalent to those of desktop scanners. Current intraoral scanner scans are considered more comfortable than traditional impressions that use irreversible hydrocolloid and elastomeric impression materials.

    Conclusion: Since the intraoral scanner is an evolving device, further improvement in accuracy is expected in the future. In addition, verification of the accuracy of intraoral scanners must be conducted accordingly.

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Original Articles
  • A. Gintaute, A.J. Keeling, C.A. Osnes, N.U. Zitzmann, M. Ferrari, T. J ...
    2020 Volume 64 Issue 2 Pages 114-119
    Published: 2020
    Released: July 08, 2020

    Purpose: To compare the precision of maxillo-mandibular registration and resulting full arch occlusion produced by three intraoral scanners in vitro.

    Methods: Six dental models (groups A-F) were scanned five times with intraoral scanners (CEREC, TRIOS, PLANMECA), producing both full arch and two buccal maxillo-mandibular scans. Total surface area of contact points (defined as regions within 0.1 mm and all mesh penetrations) was measured, and the distances between four pairs of key points were compared, each two in the posterior and anterior.

    Results: Total surface area of contact points varied significantly among scanners across all groups. CEREC produced the smallest contact surface areas (5.7-25.3 mm2), while PLANMECA tended to produce the largest areas in each group (22.2-60.2 mm2). Precision of scanners, as measured by the 95% CI range, varied from 0.1-0.9 mm for posterior key points. For anterior key points the 95% CI range was smaller, particularly when multiple posterior teeth were still present (0.04-0.42 mm). With progressive loss of posterior units (groups D-F), differences in the anterior occlusion among scanners became significant in five out of six groups (D-F left canines and D, F right canines, p < 0.05).

    Conclusions: Maxillo-mandibular registrations from three intraoral scanners created significantly different surface areas of occlusal contact. Posterior occlusions revealed lower precision for all scanners than anterior. CEREC tended towards incorrect posterior open bites, whilst TRIOS was most consistent in reproducing occluding units.

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  • Abdullah Barazanchi, Kai Chun Li, Basil Al-Amleh, Karl Lyons, J. Neil ...
    2020 Volume 64 Issue 2 Pages 120-127
    Published: 2020
    Released: July 08, 2020

    Purpose: To investigate the adhesion strength and bonding interface of layered porcelain to powdered cobalt-chromium (CoCr) processed by two different computer-aided manufacturing methods.

    Methods: Sixteen specimens were manufactured from each of Three-dimensionally -printed/laser-sintered (LS) CoCr and milled pre-sintered (SM) CoCr. The specimens were layered with porcelain and 4-point bending was carried out. Nanoindentation was used to calculate changes in elastic modulus and hardness before and after porcelain firing along with adhesion energy. Fracture surface and microstructural changes were examined before and after porcelain firing observed using scanning electron microscopy.

    Results: The adhesion energy of the LS specimens bonded porcelain were higher than the SM specimens (P < 0.05). Analysis of the fracture surfaces showed a predominantly adhesive mode of failure. Elastic-modulus and hardness of the CoCr specimens increased post porcelain firing. Examination using electron-backscatter diffraction (EBSD) showed a fine grain structure for both manufacturing methods. Significant localized changes in the crystal structure post firing were only observed at the surface of the SM specimens.

    Conclusions: Both manufacturing methods showed regular microstructures prior to porcelain firing. Laser-sintered CoCr had stronger bonding to porcelain than milled pre-sintered CoCr and was also more stable microstructurally post-ceramic firing. However, both manufacturing methods were deemed to have satisfactory adhesion strength to porcelain. It was also found that increased hardness of CoCr had an inverse relationship with bonding strength. High strength porcelain bonding and stability following multiple ceramic firings indicate suitability for use of these CoCr materials with implant or tooth supported long-span frameworks.

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  • Lorenzo Arcuri, Alessandro Pozzi, Fabrizio Lio, Eric Rompen, Werner Ze ...
    2020 Volume 64 Issue 2 Pages 128-136
    Published: 2020
    Released: July 08, 2020

    Purpose: To evaluate the influence of implant scanbody (ISB) material, position and operator on the accuracy of a confocal microscopy intraoral scanning (IOS) for complete-arch implant impression.

    Methods: An edentulous maxillary model with 6 internal hexagonal connection analogues was scanned with an extraoral optical scanner to achieve a reference file. Three ISBs made of different materials (polyetheretherketone (Pk), titanium (T) and Pk with a titanium base (Pkt) ) were scanned with IOS by 3 operators. The resulting 45 test files were aligned to the reference file with a best fit algorithm. Linear (ΔX, ΔY and ΔZ-axis) and angular deviations (ΔANGLE) were assessed. Absolute values of the linear discrepancies were summed up to obtain a global measure of linear absolute error (ΔASS). Influence of ISB material, position and operator was statistically assessed using the mixed general linear model.

    Results: At multivariate analysis, whenΔASS was considered as response variable, it was identified a significant influence of material (p < 0.0001) and position (p = 0.0009) while no significant operator effect was detected.

    When ΔANGLE was considered as response variable, material and position significantly influenced the expected ΔANGLE (p = 0.0232 and p < 0.0001) and no operator effect was identified.

    Conclusions: The investigated IOS for complete-arch digital impression was influenced by the ISB material with peek reporting the best results on both linear and angular measurements followed by titanium, peek-titanium resulting as the less accurate. Implant angulation affected significantly the linear deviations while implant position the angular deviations. Operator did not show any significant effect on the IOS accuracy.

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  • Bo Yang, Qin Huang, Brian Holmes, Jiawen Guo, Yuping Li, Young Heo, Ho ...
    2020 Volume 64 Issue 2 Pages 137-144
    Published: 2020
    Released: July 08, 2020

    Purpose: To investigate the effects of different curing modes, including tack cure, on the degree of conversion (DC) and mechanical parameters of dual-cured luting agents for all-ceramic restorations.

    Methods: Immediate light curing, intermittent light curing (2-s tack cure and a 1-min interval before the main cure), delayed light cuing (2-min delay) and chemical or no light curing were used to cure two dual-cured luting agents, RelyX Unicem and PermaCem 2.0, through a 1.5-mm thick lithium disilicate ceramic slide. DC (n = 3), micro-hardness (n = 5), shrinkage strain (n = 4) and shrinkage stress (n = 3) were measured under the aforementioned curing modes. The data were analyzed using two-way ANOVA and post-hoc Tukey HSD test, with the level of significance set at α = 0.05.

    Results: For both luting agents, all the light-curing modes produced similar final DC, but using chemical cure only could significantly reduce the DC. The mechanical parameters followed a similar pattern. There were positive but nonlinear correlations between DC and the other mechanical parameters, with the increase in these parameters with DC being slower initially.

    Conclusions: Provided adequate light curing is applied to a dual-cured luting agent, delaying the light curing or using a tack cure first to facilitate seating of a restoration may not have a significant impact on the luting agent's final degree of conversion. However, using chemical cure only may result in inadequate cure of the luting agent and is recommended only for highly opaque restorations.

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  • Hiroaki Sato, Takuya Kobayashi, Taro Nomura, Norimasa Tanabe, Kyoko Ta ...
    2020 Volume 64 Issue 2 Pages 145-151
    Published: 2020
    Released: July 08, 2020

    Purpose: To determine the appropriate attachment and design of a denture base for mandibular implant overdenture (IOD), the oral mucosa pressure caused by mandibular implant overdentures was measured using edentulous jaw models with various attachments.

    Methods: An experimental edentulous mandibular model with a 1.5-mm thick artificial oral mucosa was used. Two implants were placed at the area equivalent to the bilateral canines of an experimental jaw model. Locator attachments (LA), ball attachments (BA), magnetic attachments (MA), and round-bar attachments (R-BA) were fabricated. Six miniature pressure sensors were placed at the bilateral buccal premolar regions, bilateral buccal shelves, and bilateral lingual molar regions. A precision universal testing machine was used to apply dynamic repetitive loads of 50 N. The load points were the center of the model, which should represent bilateral mastication on both sides (bilateral load), and were equivalent to the left first molar, which should represent unilateral mastication (unilateral load). Statistical analysis was performed using one-way analysis of variance. Multiple comparisons were then performed using the Bonferroni post hoc test. P < 0.05 was considered statistically significant.

    Results: Under the bilateral load condition, the lower oral mucosa pressure value with BA was measured, compared to other attachments at all measurement sites. Under the unilateral load condition, the oral mucosa pressure value of BA was smaller than the other attachments at the measurement site on the loading side.

    Conclusions: BA has exerted the greatest effects on support and bracing, suggesting that, BA is suitable for reducing oral mucosa pressure during mastication.

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  • Seen-Young Kang, Jung-Hyun Park, Ji-Hwan Kim, Woong-Chul Kim
    2020 Volume 64 Issue 2 Pages 152-158
    Published: 2020
    Released: July 08, 2020

    Purpose: This study analyzed the trueness of polymer-infiltrated ceramic and glass ceramic crowns manufactured using the chairside computer-aided design/manufacturing (CAD/CAM) system.

    Methods: The master model designs crowns using a CAD program after acquiring a digital impression with an intraoral scanner. Vita Enamic (VE), Vita Suprinity (VS), and IPS e.max CAD (IPS) were used to manufacture 10 crowns each (total: 30 crowns), using the chairside CAD/CAM system (inLab MC XL). Trueness was evaluated by superimposing the CAD data on the scan data using a three-dimensional program. The Kruskal-Wallis H test, a nonparametric test, and the Mann-Whitney U test were performed by applying the significance level (0.05/3 = 0.016), which was adjusted by post-analysis Bonferroni testing.

    Results: There was a significant difference in the trueness between the samples (p < 0.05). However, there was no statistically significant difference in the outer surface trueness between the samples (p > 0.05).

    Conclusions: These findings show that the milling accuracy of VE is better than that of VS and IPS.

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  • Nick Polychronakis, Panagiotis Lagouvardos, Gregory Polyzois, Nikitas ...
    2020 Volume 64 Issue 2 Pages 159-166
    Published: 2020
    Released: July 08, 2020

    Purpose: The purpose of study was to investigate the long-term effect of staining and/or cleansing solutions on the color stability of two non-metal removable partial denture materials.

    Methods: One hundred disks (25×3 mm) of polyoxymethylene (POM) and polyetheretherketone (PEEK) were immersed in water, wine, coffee, cleanser and combo bath, simulating normal daily use. Color parameters in the CIELAB system was measured every 30 cycles up to 240 using a contact colorimeter and color differences estimated using ΔEab and ΔE00 formulas. Two-way repeated measures ANOVAs and regression analyses were performed at α = 0.05.

    Results: Regression analysis indicated a strong R2 between color changes and number of cycles, for both materials. Tests of within-subjects effects for the ΔEab revealed significant differences among cycles and between the materials in the wine and coffee baths (p < 0.001). Significant materialXcycles interactions were also recorded with all staining baths. ΔE00 values were lower than ΔEab up to 63.6%. Tests within and between-subjects effects for the ΔE00 gave similar but not the same with ΔEab results.

    Conclusions: ΔE00 found to correlate well with ΔEab. Long term exposure of both materials showed a progressive discoloration in all except control baths. POM discolored more than PEEK in coffee, and combo baths but not in cleanser. Discoloration was smaller in combo bath (where a cleanser was also used) indicating the effectiveness of a cleanser to prevent long term discoloration of both materials.

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  • Alexander Schmidt, Christopher R. Benedickt, Maximiliane A. Schlenz, P ...
    2020 Volume 64 Issue 2 Pages 167-174
    Published: 2020
    Released: July 08, 2020

    Purpose: Few investigations have examined the production of single restorations using intraoral scanners (IOS). Data on full-arch scans are rare, and data regarding torsion within the entire arch are very sparsely reported. Therefore, the aim of this study was to examine the deviations of torsion and linear distances in full-arch scans of three IOS based on different scanning principles.

    Methods: A cobalt-chrome-molybdenum alloy master model (CCMM) with four hemispheres was fabricated by laser sintering. The CCMM was digitized using a laboratory scanner (ATOS-Core/GOM) and scanned with three IOS (Omnicam/Sirona (OC); True Definition/3M (TD); TriosII/Cara-Version/Kulzer (TR) ). All scan data were exported in a standard STL-file format and were analyzed with GOM Inspect software (V7.5/GOM). Torsion between the right and left side of the arch and linear accuracy (trueness and precision) were evaluated. After normality was confirmed, all data were subjected to parametric statistical analyses.

    Results: The torsion ranged from 0.07 ± 0.03° (OC) to 0.29 ± 0.14° (TD). Pairwise comparisons showed significant differences between the OC and TD scanners and between the TR and TD scanners. The linear distances ranged from 6 ± 5 μm (OC) to 298 ± 317 μm (TD). Significant differences were observed among all investigated IOS (p = 0.05).

    Conclusions: Although the highest torsion was observed for the TD scanner, it is still not clear whether the differences between the IOS are related to the scanning principle or to the scanning algorithm. Due to the high clinical relevance of full-arch restorations, future studies should consider torsion. Regarding linear accuracy, no general difference related to the scanning principles of the IOSs was observed.

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  • Kodai Hatta, Yasuyuki Gondo, Kei Kamide, Yukie Masui, Hiroki Inagaki, ...
    2020 Volume 64 Issue 2 Pages 175-181
    Published: 2020
    Released: July 08, 2020

    Purpose: Dementia is a growing health problem for countries with aging populations, but few effective dementia treatments are available. However, there is increasing interest in oral health as a modifiable risk factor in interventions to prevent cognitive decline. This study aimed to investigate the impact of oral health on the decline of cognitive function over 3 years among Japanese people aged 70 and 80 years.

    Methods: Participants (n = 860) were community-dwelling older adults who participated in baseline and follow-up surveys (at baseline: 69-71 years n = 423; 79-81 years, n = 437). Registered dentists examined the number of teeth, number of functional teeth, number of periodontal teeth, and occlusal force. The Japanese version of the Montreal Cognitive Assessment was used to evaluate cognitive function. We also evaluated socioeconomic factors, medical history, drinking and smoking habits, physical performance, genetic factors, and C-reactive protein concentration in blood. A generalized estimating equation (GEE) was used to examine how oral health at baseline influenced cognitive decline over 3 years.

    Results: The GEE showed that the number of teeth (non-standardized coefficient: B = 0.031, p = 0.022) and occlusal force (B = 0.103, p = 0.004) at baseline were associated with cognitive function at follow-up, even after adjusting for other risk factors. Furthermore, maintaining more teeth (B = 0.009, p = 0.004) and a stronger occlusal force (B = 0.020, p = 0.040) buffered cognitive decline.

    Conclusions: Number of teeth and occlusal force predict cognitive decline over 3 subsequent years in Japanese older adults aged 70 and 80 years.

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  • Takashi Nakamura, Yoshiro Nakano, Hirofumi Usami, Shinya Okamura, Kazu ...
    2020 Volume 64 Issue 2 Pages 182-187
    Published: 2020
    Released: July 08, 2020

    Objectives: The purpose of this study was to evaluate the fit, fracture load and aging resistance of the monolithic zirconia tooth-borne crowns with conventional and high-speed sintering.

    Methods: The Y-TZP block was machined and sintered with conventional and high-speed sintering furnace. The marginal and internal gap between the crown and abutment was measured using a microscope and a fit checking material. A total of 28 crowns were further divided into an undegraded and a degraded group. An accelerated aging test was carried out on the degraded group. The crown was cemented and a fracture resistance was tested. X-ray diffraction was used to evaluate the crystalline structure. The data were analyzed with Student's t-test, and a one-way ANOVA and Tukey's multiple comparison test.

    Results: There was no significant difference in mean marginal gap between the two groups. The mean internal gap was significantly greater in the speed sintering than in the conventional sintering (P <0.001). The mean fracture load of the conventional sintering crowns was not significantly different from that of speed sintering crowns after aging. The occurrence of monoclinic crystals of degraded crown was significantly higher than that of undegraded crown both in the conventional (P <0.001) and speed-sintering group (P <0.001).

    Conclusions: It was concluded that the monolithic zirconia crowns produced by high-speed sintering showed no significant difference in the marginal gap and the fracture load after aging compared to conventional sintering. Therefore, the high-speed sintering seems a valid method of producing tooth-borne monolithic zirconia crowns.

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  • Yujiro Nakazawa, Takeshi Kikutani, Kumi Igarashi, Yuri Yajima, Fumiyo ...
    2020 Volume 64 Issue 2 Pages 188-192
    Published: 2020
    Released: July 08, 2020

    Purpose: The purpose of this study was to examine how skeletal muscle mass influences the effectiveness of dysphagia rehabilitation.

    Methods: The cross-sectional study and the prospective cohort study were conducted in a clinic, specialized in rehabilitation of patients with dysphagia, located in Tokyo, Japan. Skeletal muscle mass measurement by bioelectrical impedance analysis and tongue strength measurement were performed on 178 outpatients with dysphagia. In addition, the Barthel Index, Mini Nutritional Assessment-Short Form, and Functional Oral Intake Scale values were measured. Dysphagia rehabilitation was performed, and 88 of the patients who were available for follow-up one year later were included in a follow-up study. In the cross-sectional study, the associations between tongue strength and other factors were examined. In the follow-up study, factors associated with rehabilitation effectiveness, shown by tongue strength, were examined.

    Results: Tongue strength and skeletal muscle mass were correlated, and both decreased as eating and swallowing function level decreased. After one year of dysphagia rehabilitation, tongue strength and skeletal muscle mass increased. The factors associated with the amount of increase in tongue strength were initial tongue strength and skeletal muscle mass.

    Conclusions: For patients with dysphagia, maintenance of skeletal muscle mass was associated with improvement of tongue strength in rehabilitation. This indicates that prevention of sarcopenia in dysphagia patients contributes to the effect of rehabilitation.

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  • Lu Yang, Bingzhuo Chen, Hongliang Meng, Huaiqin Zhang, Feng He, Haifen ...
    2020 Volume 64 Issue 2 Pages 193-201
    Published: 2020
    Released: July 08, 2020

    Purpose: This study aimed to evaluate bond durability when applying 2 phosphate ester monomer-containing self-adhesive resin cements alone, versus a combination of phosphate ester monomer-containing primer conditioning plus 2 conventional resin cements requiring primers, to zirconia after different artificial aging methods.

    Methods: We cemented air-abraded zirconia plates to composite resin cylinders with self-adhesive resin cements (MS; RU) alone or cemented them with traditional resin cements (ZRV; ZVN) after pre-conditioning with a zirconia primer. A shear bond strength (SBS) test were performed after subjecting them to 19 different aging conditions (n = 5) comprising 30,000×thermocycles, air storage at room temperature (RT), water storage at RT, or at 37°C for 24 h, 1 week, 1, 3, 6, and 12 months. Zirconia powders mixed with zirconia primer or 2 self-adhesive resin cements were characterized by X-ray photoelectron spectroscopy.

    Results: Groups MS and ZVN obtained the highest SBS after all of aging methods. SBS after 6 months of storage was similar to SBS after 24 h of storage, while both were higher than SBS after 1-year of storage. Water storage at 37°C provided higher SBS than RT water storage did. We detected a Zr-O-P bond in both self-adhesive resin cement/zirconia powder mixtures.

    Conclusions: Application of self-adhesive resin cements alone could be an alternative to pre-conditioning with a zirconia primer followed by the application of conventional resin cements. Formation of Zr-O-P bonds contributed to the bonding improvement of self-adhesive resin cements. Different aging conditions affected SBS values.

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  • Meral Kurt, Merve Bankoğlu Güngör, Seçil Karakoca Nemli, Bilge Turhan ...
    2020 Volume 64 Issue 2 Pages 202-209
    Published: 2020
    Released: July 08, 2020

    Purpose: This study aims to evaluate the effect of different glazing methods on translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP), surface roughness (Ra) and topography of the silicate ceramics.

    Methods: Seventy specimens (10 ×10 ×1 mm) were fabricated from lithium disilicate (IPS e.max CAD, abbreviated as E) and zirconia-reinforced lithium silicate (Vita Suprinity, abbreviated as VS) ceramics and divided into 7 subgroups (n = 10) according to the polishing and glazing procedures: (1) mechanical polishing before-crystallization (m-BC), (2) mechanical polishing after-crystallization (m-AC), (3) glaze powder/liquid after-crystallization (pl-AC), (4) glaze-paste before-crystallization (gp-BC), (5) glaze-paste after-crystallization (gp-AC), (6) glaze-spray before-crystallization (gs-BC), (7) glaze-spray after-crystallization (gs-AC). Color and Ra measurements were performed. CIEL*a*b* and CIEXYZ parameters were recorded and TP, CR, and OP values were calculated. Data were analyzed using two-way ANOVA and Tukey HSD tests (α = 0.05).

    Results: In E groups, the highest Ra value was found in gs-AC (1.66 ± 0.14 μm) while the lowest value was found in pl-AC (0.68 ± 0.08 μm). In VS groups, the highest Ra value was found in gp-BC (1.64 ± 0.25 μm) while the lowest value was found in m-AC (0.77 ± 0.06 μm) (p < 0.05). The mean TP value of E (17.62 ± 0.73) was found to be higher than VS (15.37 ± 1.16). The CR (0.72±0.030) and OP (12.06 ± 0.74) values of VS were found higher than CR (0.57 ± 0.02) and OP (6.72 ± 0.40) values of E.

    Conclusions: Zirconia-reinforced silicate ceramics have higher opalescence and lower translucency values than lithium disilicate ceramics. Increase in surface roughness reduces translucency. Glaze powder/liquid after-crystallization is the most effective way to reduce surface roughness of lithium disilicate ceramics while that is mechanical polishing after-crystallization for zirconia-reinforced silicate ceramics.

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  • Josef Schweiger, Jan-Frederik Güth, Kurt-Jürgen Erdelt, Daniel Edelhof ...
    2020 Volume 64 Issue 2 Pages 210-216
    Published: 2020
    Released: July 08, 2020

    Purpose: The purpose of this study was to evaluate internal porosities, retentive force values and survival of cobalt-chromium (Co-Cr) alloy clasps fabricated by direct metal laser-sintering (DMLS) and compare them to conventionally cast clasps.

    Methods: Embrasure clasps were digitally designed fitting teeth 35 and 36 on identical metal models (N = 32). Sixteen clasps were fabricated using DMLS (group DMLS) and another sixteen clasps were additively manufactured from wax and then cast from a Co-Cr alloy (group CAST). Internal porosities were examined using micro-focus X-ray (micro-CT) and analyzed applying Kolmogorov-Smirnov test, Mann-Whitney test, and T test (significance level: p < 0.050). A universal testing machine was used to determine the retentive force values at baseline and after 1095, 5475, 10,950 and 65,000 cycles of simulated aging. Data were analyzed employing Kolmogorov-Smirnov test, one-way ANOVA, and Scheffé's post-hoc test (significance level: p < 0.050). Survival was estimated for 65,000 cycles of artificial aging using Kaplan-Meier analysis.

    Results: Micro-CT analysis revealed a higher prevalence (p < 0.001), but a more homogeneous size and a significantly smaller mean (p = 0.009) and total volume (p < 0.001) of internal porosities for group DMLS. The groups showed mean initial retentive force values of 13.57 N (CAST) and 15.74 N (DMLS), which significantly declined over aging for group CAST (p = 0.003), but not for group DMLS (p = 0.107). Survival was considerably higher for group DMLS (93.8%) than for group CAST (43.8%) after 65,000 cycles of aging.

    Conclusions: Clasps made by laser-sintering could be an alternative to conventional cast clasps for the fabrication of removable partial denture frameworks.

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  • Seiya Yamazaki, Chihiro Masaki, Tomotaka Nodai, Shintaro Tsuka, Akiko ...
    2020 Volume 64 Issue 2 Pages 217-223
    Published: 2020
    Released: July 08, 2020

    Purpose: We assessed the effects of hyperglycaemia induced by streptozotocin (STZ) on peri-implantitis developing after implant osseointegration.

    Methods: Thirty-six male Wistar rats (4 weeks old) were used. We placed titanium implants 4 weeks after extraction of the maxillary first molars. Healing abutments were attached 4 weeks later. After osseointegration was confirmed, the rats were divided into control, hyperglycaemia (STZ), and STZ with insulin (STZ + INS) groups. Hyperglycaemia was induced by a single injection of 50 mg/kg STZ. Silk ligatures were placed on only the right sides (i.e. ligature sides), not on the left sides. Peri-implant tissues extracted at 4 weeks post-ligation were analysed both radiologically (via micro-computed tomography) and histologically (via toluidine blue staining). Total RNA was also extracted and analysed by quantitative PCR to detect TNF-α, IL-1β and the receptor of advanced glycation end products (RAGE). Additionally, advanced glycation end products (AGEs) were measured by ELISA.

    Results: Radiological and histological analyses showed that bone loss on the non-ligature sides was significantly greater in the STZ than the control group. However, on the ligature sides, bone loss was greater than on the non-ligature sides, and no significant difference was evident among the three groups. The levels of mRNAs encoding TNF-α, IL-1β, RAGE, and AGEs on the ligature sides were significantly upregulated (all P < 0.05) in the STZ compared to the control group.

    Conclusions: Although hyperglycaemia could be associated with bone loss around implants with increased AGE production and RAGE expression, hyperglycaemia does not become a triggering factor of ligature induced peri-implantitis.

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  • Akinori Tasaka, Takahiro Shimizu, Yoshimitsu Kato, Haruna Okano, Yuki ...
    2020 Volume 64 Issue 2 Pages 224-230
    Published: 2020
    Released: July 08, 2020

    Purpose: The present study aimed to compare the accuracy of removable partial denture (RPD) frameworks fabricated by 3D-printed pattern casting and those fabricated by selective laser sintering (SLS).

    Methods: A partially edentulous mandibular model was used for the simulation model. Scanning of the model was performed using a dental scanner. The framework was designed by using CAD software. The 3D-printed resin pattern was formed using a 3D printer and casting was performed (AM-Cast framework), and a direct metal laser sintering machine was used for the framework of SLS (SLS framework). 3D scanning of fabricated two types of framework were performed, and these data were overlapped with design data. Fabrication accuracy was verified using the Mann-Whitney U test to compare the discrepancy between the AM-Cast and SLS frameworks.

    Results: The range of differences for the AM-Cast and SLS framework were -0.185 ± 0.138 to 0.352 ± 0.143 mm and -0.166 ± 0.009 to 0.123 ± 0.009 mm, respectively. Statistically significant differences were observed at the rests, proximal plates, connectors, and clasp arms. Regarding the rests, both lateral and medial displacement in the two types framework was observed in relation to the design data. Large lateral discrepancies of the connectors were observed at the joining area on the tooth-supported side of the lingual bar for the AM-Cast framework. Localized discrepancies were observed at the center of the lingual bar for the SLS framework.

    Conclusion: The accuracies of RPD frameworks fabricated by AM-Cast and SLS differ depending on the specific structural component of the RPD.

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Technical Procedure
  • Heechul Kim, Doyun Lee, Soo Young Lee, Hongso Yang, Sang-Won Park, Hyu ...
    2020 Volume 64 Issue 2 Pages 231-234
    Published: 2020
    Released: July 08, 2020

    Purpose: This paper describes a method for making a customized denture flask using fused deposition modeling (FDM) by three-dimensional (3D) printing. We have proposed a new digital dental prosthesis using conventional dental base materials and artificial teeth.

    Methods: Using the universal development system software, a denture-designed Standard Tessellation Language (STL) file and a denture flask STL file were superimposed, and the denture region was set as an empty space. After setting the offset value to 200 μm between the denture base and teeth for artificial tooth positioning, the flask was created by FDM 3D printing. Conventional artificial teeth were inserted into the 3D-printed flask, and resin packing, finishing, and polishing were performed using the conventional method for fabricating the complete denture.

    Conclusions: The 3D printing materials used to make digital dental prostheses have not yet been fully validated. Therefore, the production of a 3D-printed denture flask, which can use conventional complete denture materials, presents a new alternative to the digital fabrication of dentures.

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Letter to Editor