The International Journal of Prosthodontics, 06/2022

Purpose: To compare the speaking space, perceived rotational movement during chewing, and oral health-related quality of life (OHRQoL) of elderly people rehabilitated with new conventional complete dentures (CDs) and single-implant mandibular overdentures (SIMOs) using a paired design. Patient expectations for SIMO use were also evaluated. Materials and methods: The participants were 22 elderly users of unsatisfactory CDs. They received new sets of conventional CDs, and assessment was performed after 2 months of use. Speaking space was recorded with a kinesiograph while participants read a list of words. Participants were asked two questions about perceived posterior rotational denture movement during chewing. The Dental Impact on Daily Living (DIDL) questionnaire was used to examine OHRQoL, and a visual analog scale was used to quantify participants' SIMO expectations. Subsequently, the mandibular CDs were converted to SIMOs, and the assessment was repeated after 2 months of use. Speaking space and OHRQoL data were submitted to ANOVA and Student t test, and perceived mandibular movement and expectation data were examined using likelihood-ratio chi-square test. Results: The speaking space and perceived rotational movement did not differ between CD and SIMO use. General performance and eating restriction DIDL scores increased after SIMO insertion. Participants' SIMO expectations regarding speaking, cleaning, esthetics, and general aspects were met. Conclusion: Relative to CD use, SIMO use did not change the speaking space or perceived rotational movement when chewing among elderly patients. It improved OHRQoL via enhancement of two DIDL dimensions and met most elderly patients' expectations.

Purpose: To compare predoctoral student performance in restorative dentistry related to curricular changes implemented in response to the COVID-19 pandemic and to evaluate the impact of remote education on performance in didactic and preclinical examinations and objective structured clinical examinations (OSCEs). Materials and methods: The study population consisted of 172 students, all members of the DMD graduating classes from 2017 to 2021. Scores in the Final Restorative Treatment (FRTx) course, subdivided into didactic and preclinical lab work, and the OSCEs were assessed and compared between pre-pandemic students and during-pandemic students. Results: Performance in the preclinical lab exercises was statistically significantly higher in the during-pandemic cohort than in the pre-pandemic cohort after adjusting for students' gender and admission scores. Performance in restorative dentistry as measured by the OSCE was not statistically different among during-pandemic students compared to the pre-pandemic students. It was observed that students were more efficient and engaged during the more limited lab sessions with the increased student-to-faculty ratio that allowed for more feedback. Conclusion: Although virtual education cannot replace in-person experiences, this model served students satisfactorily during the COVID-19 pandemic, with added support structures such as flexible scheduling, interactive sessions, and additional small-group discussions to maintain academic performance in predoctoral education.

Purpose: To evaluate correlations of arch size and sex with the interocclusal rest distance (IORD), as well as to estimate proportional variance. Materials and methods: A total of 106 participants were examined. The participants, 38 men and 68 women, were aged 22 to 30 years, were fully dentate, had no signs of abnormal abrasion, and had intact posterior occlusal contacts. Measurements of interocclusal rest distance and tragus-incisal distance were recorded, and the rest angle created between the tragus-incisal distance in maximum intercuspation and in resting vertical dimension were calculated according to the cosine formula. Correlation between the size of the mandible (tragus-incisal distance, mean of left and right sides) and the IORD were calculated using Pearson correlation coefficient. Correlations for sex (calculated separately for male and female) and rest angle were also assessed. Results: The mean (SD) tragus-incisal distance values were 123.38 (6.77) mm for all participants, 120.01 (4.64) mm for women, and 130.72 (5.24) mm for men. The mean (SD) IORD values were 2.76 (1.3) mm for all participants, 2.13 (0.9) mm for women, and 3.87 (1.17) mm for men. The mean (SD) rest angle values were 1.26 (0.55) degrees for all participants, 1.02 (0.41) degrees for women, and 1.7 (0.49) degrees for men. Pearson correlation coefficient between IORD and tragus-incisal distance was significant (P < .05). According to t test, there was a significant difference between men and women for IORD, tragus-incisal distance, and rest angle (P < .01). Conclusion: A correlation exists between IORD and arch size. A statistically significant difference was found between men and women for IORD and arch size values.

Purpose: To evaluate the effects of overnight storage conditions on the dimensional stability and retention of prostheses, as well as participants’ subjective perceptions of these interventions. Materials and Methods: Subjects with maxillary complete prostheses (CRPs) were randomly assigned to receive two interventions in a crossover design: storage of their CRPs overnight in a dry environment or in a wet environment with a cleansing tablet. The denture intaglio surface was scanned, and outcome measures were collected before each intervention (BLN), postintervention (PIS), and after immersion in water for 15 minutes (WOC) following each intervention. Dimensional changes were analyzed for the total surface, anterior flange, palate, and tuberosities. Retention force was measured using a dynamometer, and the participants’ subjective assessments of comfort, fit, and retention of their CRPs were collected. After verifying normal distribution, paired t and Wilcoxon signed rank tests were used to check for statistical significance (α = .05). Results: Ten participants (mean age: 76.5 ± 5.9 years) were recruited. Between BLN and PIS, the dimensional changes after dry intervention were significantly less than the wet intervention for the total surface (P = .009), anterior flange (P = .028), and palate (P = .005). No difference was found between the effects of storage or washout interventions on objectively measured CRP retention. However, after WOC following dry storage, participants perceived a lower retention (P = .021), and after WOC following wet storage, participants perceived a more comfortable palate (P = .018). Conclusion: For dimensional stability, dry overnight storage of removable prostheses can be safely recommended when indicated. Immersion in water for 15 minutes does not seem to add advantages.

Purpose: To answer the following focus question: Are narrow-diameter implants feasible to support fixed dental prostheses (FDPs) and partial removable dental prostheses (PRDPs)? Materials and methods: This review followed the PRISMA statement and was registered in the PROSPERO database (CRD42020153729). Six databases and the gray literature were searched through October 2021 without language, publication time, or follow-up restrictions. The main outcomes were survival, success, and marginal bone loss (MBL). Risk of bias was assessed for each study design, and random-effects meta-analyses were performed (α = .05). Results: Seventeen studies were included in the qualitative analysis, and 3 were included in the meta-analyses. In total, 1,624 NDIs and 339 standard-diameter implants (SDIs) were placed in 1,060 patients. Follow-up varied from 1 to 10 years, and 17 failures (implant loss) were recorded. No differences in survival rate for FDPs supported by NDIs vs SDIs were found (odds ratio [OR] = 0.59, 95% CI: 0.18 to 1.92, P = .38). However, Kaplan-Meier analysis evaluating only NDI performance revealed a higher survival rate of NDIs ≥ 3.3-mm diameter (P = .002), placed with delayed loading (P = .024), and placed in the maxilla (P = .014). FDPs supported by NDIs vs SDIs presented similar success rates (OR = 1.48, 95% CI: 0.41 to 5.34, P = .55); however, MBL was lower in the NDI group (mean difference = -0.23 mm, 95% CI: -0.41 to -0.06, P = .01). Insufficient data regarding PRDPs were available. Conclusion: Despite the limited studies available, FDPs supported by NDIs presented survival and success rates comparable to those supported by SDIs, with slightly lower MBL. For PRDPs, strong conclusions were not possible.

Purpose: To evaluate the effects of nonthermal atmospheric plasma (NTAP) treatment, alone or combined with sandblasting and/or primer application, on the bonding of zirconia ceramics to resin cement. Materıals and Methods: A total of 420 discs of Y-TZP (2 x 15 x 12 mm) were prepared and randomly divided into 10 groups according to surface treatment, as follows: Z (control), SB (sandblasting), Pr (primer), SBPr (sandblasting + primer), P (NTAP), SBP (sandblasting + NTAP), PrP (primer + NTAP), SBPrP (sandblasting + primer + NTAP), PPr (NTAP + primer), and SBPPr (sandblasting + NTAP + primer). After surface treatments, the surface roughness values were evaluated using a profilometer, and the contact angle measurements were performed using a goniometer. Surface characterizations of the groups were analyzed using scanning electron microscopy and x-ray photoelectron spectroscopy analyses. Shear bond strength tests were performed after adhesive cementation in 20 specimens per group, with half (n = 10) subjected to thermocycling (5,000 cycles, 5°C to 55°C). The failure mode was recorded by examining each specimen using a stereomicroscope. One-way and two-way ANOVA followed by Student-Newman-Keuls test (α = .05) were used to analyze the data statistically. Results: Untreated zirconia surfaces (without sandblasting) were found to have a higher wettability and oxygen ratio after NTAP treatment. The clinical application order of NTAP is an important factor, and the best combination for bonding quality was NTAP treatment followed by primer application on untreated zirconia (group PPr), rather than on a sandblasted surface. Conclusıon: NTAP application may be a promising surface treatment method for adhesive cementation of zirconia ceramics as an alternative to sandblasting. To achieve strong adhesion, NTAP should be applied before primer aplication.

Purpose: To test a newly introduced implant-abutment material combination against bacterial endotoxin leakage in a human whole blood assay. Materials and Methods: Two dental implant systems with internal connections and the following material combinations at the implant-abutment interface (IAI) were used (implant material/abutment material): yttrium-stabilized tetragonal zirconium dioxide (Y-TZP)/ polyetherketoneketone (PEKK), and titanium (Ti/Ti). Test implants were inoculated with lipopolysaccharide (LPS) and sealed and submerged in human whole blood. Untreated implants served as the control groups. Changes in gene expression levels of inflammatory markers indicating LPS leakage were assessed after 1, 8, and 24 hours using quantitative real-time polymerase chain reaction. Results: In the Y-TZP/PEKK test group, a significant influence of the implant system (P < .001) on increases in gene expression indicating leakage were detected after 8 hours for TLR-4 and after 24 hours for interleukin 1-β and nuclear factor kappa-lightchain- enhancer of activated B-cells (NF-κB), indicating microleakage of LPS at the IAI. In the Ti/Ti test group, differences in gene expression were found only for NF-κB after 8 hours. Conclusion: The internal hexalobe IAI of two-piece dental implants fabricated from Y-TZP and PEKK do not prevent LPS molecular microleakage.

Purpose: To compare wear behavior, durability during in vitro mastication simulation, and fracture force of an established and a novel lithium disilicate CAD/CAM material, as well as to examine the impact of cementation and reduced ceramic thickness on durability and fracture force. Materials and Methods: Specimens (n = 8 per group) were prepared from lithium disilicate (LS2; IPS e.max, Ivoclar Vivadent) and advanced lithium disilicate (ALD; Cerec Tessera, Dentsply Sirona). Specimens were polished, and two-body wear test and thermocycling were performed (50 N, 120,000 cycles, 1.6 Hz, H2O dist., 5°C/55°C, 600 cycles). Maximum vertical loss, surface roughness, surface roughness depth, and antagonist wear were determined. Single crowns (n = 8 per group; thickness 1.5 mm/1.0 mm) were manufactured from LS2 and ALD and mounted on human molar teeth with adhesive resin (AB; CalibraCeram, Dentsply Sirona), glass-ionomer cement (GIC; Ketac Cem, 3M ESPE), and hybrid glass-ionomer cement (HGIC; Calibra Bio, Dentsply Sirona). Thermocycling and mechanical loading (2 × 3000 × 5°C/55°C, 2 minutes, H20 dist., 1.2 × 106 50 N) were performed. Fracture force was determined by a universal testing machine (1446, ZwickRoell), and one-way analysis and Bonferroni post hoc test (α = .05) were used for statistical analyses. Results: Mean (ALD: 210 ± 42.4 μm; LS2: 264.3 ± 56.1 μm) and maximum (ALD: 391.1 ± 86.3 μm; LS2: 518.3 ± 113.2 μm) wear between groups were significantly different (P ≤ .047). Fracture force varied between 1,911.4 ± 468.4 N (ALD/AB 1 mm) and 2,995.3 ± 880.6 N (LS2/GIC), without significant differences (P ≥ .152). Conclusion: ALD showed better wear behavior than LS2, but provided similar fracture force. Cementation and reduction of ceramic thickness had only minor effects on fracture force.

Purpose: To determine and compare the mechanical properties of 3D-printed yttriastabilized zirconia to milled isostatic pressed yttria-stabilized zirconia, with the following hypotheses: (1) The flexural strength of 3D-printed yttria-stabilized zirconia is comparable to milled yttria-stabilized isostatic pressed zirconia; and (2) thermocycling and chewing simulation do not affect the flexural strength of 3D-printed yttria-stabilized zirconia. Materials and methods: A total of 30 bars of an experimental 3D-printed 3 mol% yttriastabilized zirconia (LithaCon 3Y 230, Lithoz) and 10 bars of milled isostatic pressed zirconia (Prettau Zirconia, Zirkonzahn) were utilized. The printed zirconia bars were divided into three groups (n = 10 bars per group): (1) untreated (control); (2) thermocycled; and (3) tested after chewing simulation. A flexural strength test was performed on all samples using a three-point bend test in an Instron Universal testing machine. One-way analysis of variance on ranks was used to compare milled to printed zirconia. The effects of thermocycling and load cycling on 3D-printed zirconia were also determined. Results: The flexural strength values for milled and printed zirconia were 936.3 ± 255.0 MPa and 855.4 ± 112.6 MPa, respectively. There was no statistically significant difference in flexural strength between the milled and printed zirconia (P = .178). No statistically significant differences were observed between the control 3D-printed zirconia group and the thermocycled (888.4 ± 59.3 MPa) or load-cycled printed zirconia (789.6 ± 133.8 MPa; P = .119). Conclusion: Printed 3 mol% yttria-stabilized zirconia has comparable flexural strength to milled yttria-stabilized isostatic pressed zirconia. The thermocycling and chewing simulation used in this study did not significantly alter the flexural strength of the printed 3 mol% yttria-stabilized zirconia. These results indicate a promising role for 3D printing in the fabrication of zirconia restorations. Additional studies are needed to explore the full potential of this technology.

Purpose: To evaluate the effect of different forms of denture adhesives on the formation of biofilm and on adhesive strength, as well as the effectiveness of hygiene protocols for their removal. Materials and Methods: Samples of a heat-cured polymethyl methacrylate denture base resin were made and divided into four groups: (1) control (no adhesive); (2) Ultra Corega Cream (UCC); (3) Corega Strip Adhesive (CSA); and (4) Ultra Corega Powder (UCP; GlaxoSmithKline). Biofilm formation was evaluated by counting colony-forming units and performing fluorescence microscopy. To evaluate the effectiveness of the hygiene protocols, the samples were divided into five subgroups: (1) brushing with distilled water; (2) brushing with Protex soap; (3) brushing with Colgate toothpaste; (4) immersion in water with Corega Cleaning Tablets (CCT); and (5) immersion in water with CCT followed by brushing with the CCT-water solution itself. The remaining adhesive was quantified with ImageJ software. The adhesive strength was tested at different time intervals after application. After verifying the data distribution using Shapiro-Wilk test, parametric or nonparametric analysis was applied (α = .05). Results: Candida albicans formed more biofilm in the strip (P = .007) and the powder (P = .001), Pseudomonas aeruginosa formed more in the cream (P < .001) and the powder (P < .001), and Staphylococcus aureus formed more in the strip (P < .001). All forms of the adhesives promoted higher biofilm formation when compared to the control (P = .003). Brushing with Colgate toothpaste and Protex soap was most effective for removing the adhesives (P < .05). Independently, the powder had the highest adhesive strength (P < .05). Only the strip showed a change in adhesive strength, with higher values after 3 hours of application (P = .004). Conclusion: Daily treatments with mechanical cleaning of the prosthesis are important for removing the adhesives, since the presence of this material can favor biofilm accumulation. The adhesive strength may vary depending on the commercial type, but all forms can be effective in retaining prostheses for a satisfactory period of time.

Purpose: To assess stress and deformation in telescopic removable partial denture (RPD) frameworks manufactured with polyether ether ketone (PEEK) or graphene-modified polymethyl methacrylate (PMMA), as well as the stress of the underlying mucosa, via nonlinear 3D finite element analysis. Materials and Methods: The 3D model of a full mandible was merged with a 3D-scanned Kennedy Class I model with bilaterally missing molars. The tissues, the telescopic crowns, and the RPD framework were designed and created using dental CAD software. The model was duplicated, and two materials—PEEK and graphenemodified PMMA—were assigned to the telescopic crowns and their frameworks. A force of 200 N was applied perpendicularly to the molars, and constraints were placed in the mandibular ramus and the inferior border. The generated von Mises stress and deformation of the frameworks, as well as the stresses of the telescopic crowns and mucosa, were also assessed. Statistical analysis of the differences between the tested materials was conducted via an independent samples t test at (α = .05). Results: The von Mises stresses of the telescopic crowns and their frameworks in the graphene-modified PMMA model were significantly higher than in the PEEK model. In contrast, the deformation of the telescopic RPD framework of the PEEK model was significantly higher than the graphene-modified PMMA model. The stresses of the mucosa in both models showed an insignificant difference. Conclusion: PEEK material showed better biomechanical performance than the graphene-modified PMMA in telescopic RPDs.

Purpose: To evaluate intraoral scanners, scannable impression materials, and conventional methods for impression-taking with regard to precision and accuracy. Materials and methods: Ten impressions per technique were initially taken from a cobalt-chromium (Co-Cr) master model (chamfer preparation for the maxillary right first molar) for fabricating Co-Cr crown copings. The test specimens, their respective metal master model, and the plaster casts from the conventional impressions were then digitized with the light-optical Atos Triple Scanner. The fit of the dental crown copings was measured in two and three dimensions using computer-aided design software. Global differences between the methods were determined using Kruskal-Wallis test, and pairwise comparisons were performed with Mann-Whitney U test. The significance level was set at .05. Results: The 2D analysis showed that the average absolute marginal distance of the crown copings was 0.026 mm when fabricated with the digital impression method and 0.038 mm when fabricated with the conventional method (P = .028). However, the 3D analysis revealed that the conventional group had a smaller marginal gap (0.028 mm) compared to the digital group (0.06 mm; P = .015). Conclusion: This study showed that, in the field of single-crown prosthetics, digital impressions and the use of scannable impression material could serve as alternatives to conventional methods in the future.

Purpose: To explore the applications of 3D scanning and 3D printing techniques in the restorative treatment of edentulous patients. Materials and methods: A total of 30 edentulous patients (Atwood classes 1 to 4) who visited The 960th Hospital of the People's Liberation Army, Jinan, China, from March 1, 2018 to May 1, 2020 were selected, and the patients were randomly divided into two groups: a traditional complete denture group (group A) and a 3D-printed complete denture group (group B). Each group comprised 15 patients. In group A, the traditional method was used to fabricate complete dentures. In group B, 3D scanning, computer-aided design (CAD), 3D printing, and the duplicate denture technique were used to fabricate the dentures. A single-blinded method was used. Patient satisfaction was measured with a 0-10 visual analog scale (VAS) at four time points: immediately and 1 month, 3 months, and 6 months after denture delivery. SPSS version 22.0 software was used to analyze the data. Results: The ability to speak, ability to chew, and comfort in the two groups gradually improved at the first three time points. VAS scores increased to a satisfactory level after 3 months. The esthetics and stability of the two groups were scored high after the initial delivery. The VAS scores of the two groups regarding esthetics, ability to speak, ability to chew, stability, and comfort were not significantly different (P > .05) at any time point. The number of visits in the 3D-printed complete denture group were significantly decreased in comparison to the traditional group. Conclusion: The use of 3D printing for manufacturing complete dentures can rapidly restore edentulous patients and meet patient demands regarding esthetics and function.

Purpose: To evaluate the long-term survival of IPS Empress 2 and IPS e.max (Ivoclar Vivadent) restorations in a non-university setting. Materials and methods: A retrospective study design was used to evaluate the survival rate of 1,132 Empress 2 and IPS e.max restorations placed in 251 patients with regard to patient age, gender, tooth type, tooth vitality, material, restoration form (inlay vs partial crown vs crown), cementation mode (self-adhesive vs non-self-adhesive), and bruxism activity. Kaplan-Meier and regression analyses were used for statistical analyses. Results: Of the 1,132 restorations, a total of 15 (IPS e.max = 3, Empress 2 = 12) failed. The overall survival rate for all restorations was 98.7% after 15.4 years. A significantly reduced survival rate was found for nonvital teeth (P = .002), patient age > 60 years (P = .002), crowns (vs inlays and partial crowns; P = .002), and self-adhesive resin materials (P = .018). Conclusion: Within the limitations of this study, glass-ceramic single-tooth restorations made of Empress 2 and IPS e.max show good survival rates up to a period of 15 years.