Purpose: This study systematically reviewed the literature to compare the bond strength of resin composites with that of zirconia-reinforced lithium silicate (ZLS) and lithium disilicate (LD).

Study selection: This review was structured based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) statement. This study was registered at the International Prospective Register of Systematic Reviews (CRD42021256900). Studies were searched via PubMed, Web of Science, and Google Scholar databases without language or publication year limits. In vitro studies that evaluated the bond strength of the resin composites to ZLS and LD were included. The risk of bias in all the included articles was evaluated. Statistical analyses were performed using the Review Manager software (version 5.3, Cochrane Collaboration, Oxford, UK).

Results: Of the 90 potentially related articles, the full texts of 16 articles were evaluated after screening. Finally, seven 
studies were included in the qualitative synthesis and meta-analysis. All the studies presented a medium risk of bias. The results showed no significant difference in bond strength between the ZLS and LD groups (P = 0.94, mean difference=0.08, and 95% confidence interval=-1.93 to 2.10). However, a significant difference was found in the subgroup analysis considering different types of aging treatments (P = 0.0008) and different types of bond strength tests (P < 0.00001).

Conclusion: The bond strength of resin composites was found to be similar to that of ZLS and LD, but different aging treatments and bond strength tests exhibited varying effects on the bond strength.

Purpose: This in-vitro study aimed to compare the accuracy of complete arch scans (CAS) of a fully dentate (FD) and a partially edentulous (PE) maxillary model. Three intraoral scanning systems were used: Omnicam AC (OC), TRIOS 4 (TR), and Primescan (PS).

Methods: Each intraoral scanner was used to take 30 scans each of two clinical scenarios (FD and PE) simulated by a reference model. The PE model simulated a maxilla with six prepared teeth to accommodate a jaw-spanning fixed partial denture (FPD). The missing teeth were then added to create an FD model. Five ceramic precision balls (ball centers P_¹–P_⁵) mounted on metal pins were welded to the metal base on the buccal side of the dental arch. These were later used to determine dimensional (given by each 2 ball centers) and angular changes (given by each 3 or 4 ball centers) between the reference model (digitized with high precision before the tests) and the intraoral scans. Data were statistically analyzed using a type II ANOVA.

Results: The maximum mean absolute distance deviations were as follows. OC: 147 µm (FD) and 139 µm (PE). TR: 133 µm (FD) and 136 µm (PE). PS: 87 µm (FD) and 80 µm (PE). The scanning system used had a significant effect on distance deviations (p < 0.027) and CAS scanning time (p < 0.001). Dental status had no clear effect on distance deviations but did significantly affect angular changes (p < 0.001) and scanning time (p < 0.001).

Conclusion: The manufacture of jaw-spanning FPDs based on a CAS cannot yet be recommended.

Purpose: This randomized controlled trial (RCT) aimed to elucidate the effectiveness of silicone-based resilient denture liners on perceived chewing ability.

Methods: The RCT included completely edentulous patients on both the maxilla and mandible, who were willing to fabricate a new set of complete dentures. A random permuted block method (block size: 4) was used to assign groups to receive maxilla conventional complete denture and mandibular with either a conventional complete denture (CD) or complete demure relined with silicone-based resilient denture liner (RD). The patient-reported chewing ability of six foods, soybean curd, fish sausage, soybean sprout, cubic rice cracker, hard rice cracker, and dry squid, on a 100-mm visual analog scale was measured and reported at the final adjustment and three months after the final adjustment. Mann-Whitney U test was used to analyze the differences between the CD and RD (p < 0.05).

Results: Edentulous patients wearing mandibular complete denture with RD had a higher patient-reported chewing ability than those wearing a CD, but the fish sausage did not in the RD three months after the final adjustment. It also took three months for the patient-reported masticatory ability to improve for cubic rice crackers, hard rice crackers, and dry squid and to show a difference between the RD and CD groups.

Conclusion: Although limited to some food types, mandibular complete dentures relined with silicone-based liners improved patient-reported chewing ability.

Purpose: To investigate the effect of masseter muscle activity during wakefulness and sleep on tooth wear.

Methods: Sixteen participants with no or mild tooth wear (NMTW group) and sixteen participants with moderate-to-severe tooth wear (MSTW group) were enrolled. The severity of tooth wear was evaluated using the occlusal and incisal indices of the tooth wear index. Surface electromyography was performed to record the electrical activity of the left masseter muscle during wakefulness and sleep. Electromyographic activity was detected using an electromyographic threshold of 5% and 20% of maximal voluntary clenching (MVC). The total duration of electromyographic activity and bruxism episodes were calculated.

Results: The mean ages of the NMTW and MSTW groups were 71.75 ± 7.61 years and 71.69 ± 7.49 years, respectively. The mean cumulative duration of electromyographic activity during wakefulness using a threshold of >5% MVC was 6.44 ± 4.52 min/h and 13.62 ± 10.08 min/h for the NMTW and MSTW groups, respectively (p=0.048). The mean total durations of electromyographic activity during wakefulness and sleep using a threshold of >20% MVC were 1.08 ± 1.70 min/h and 1.05 ± 3.02 min/h, respectively, in the NMTW group and 4.78 ± 6.37 min/h and 1.61 ± 1.79 min/h, respectively, in the MSTW group (p=0.048 and p=0.003, respectively).

Conclusion: These results suggest that masseter electromyographic activity during wakefulness and sleep may be related to the severity of tooth wear.

Purpose: To develop a novel resin for provisional prostheses using hyperbranched polyurethane acrylate (HBPUA) and triethylene glycol dimethacrylate (TEGDMA) with promising mechanical properties and low volumetric shrinkage.

Methods: Four groups including TIH3-0 (100 wt% TEGDMA), TIH3-30 (30 wt% HBPUA + 70 wt% TEGDMA), TIH3-60 (60 wt% HBPUA + 40 wt% TEGDMA), and TB-60 (60 wt% bisphenol A-glycidyl dimethacrylate + 40 wt% TEGDMA) were prepared and commercial Luxatemp (DMG) was used for comparison. Fourier transform infrared spectroscopy and gel permeation chromatography were used for material characterization. Mechanical properties including microhardness, flexural strength, flexural modulus, and load energy were measured before and after water immersion. Physical properties measurement included weight changes, solubility, water absorption, surface hydrophobicity, and volumetric shrinkage. Finally, biocompatibility was evaluated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay.

Results: The number- and weight-average molecular weights of the HBPUA were approximately 870 and 1480, respectively. The addition of HBPUA to TEGDMA increased the mechanical strength considerably. Although the weight changes and water absorption of TIH3-60 were higher than those of Luxatemp, the microhardness, flexural strength, flexural modulus, load energy, solubility, shrinkage, and biocompatibility of TIH3-60 were either comparable or superior to those of Luxatemp.

Conclusion: Based on the findings of the present study, TIH3-60 has potential for development as a new provisional material.

Purpose: The purpose of this study was to investigate the inhibitory effect of night denture (ND) placement on abutment tooth mobility in removable partial denture (RPD) wearers with sleep bruxism (SB).

Methods: The participants were selected from RPD wearers diagnosed with SB using BiteStrip® and randomly allocated to one of the following groups: with ND placement or without ND placement (intervention or control group, respectively). The mobility of the RPD abutment tooth was measured using Periotest® at baseline (T0) and at 1 (T1), 3 (T3), and 6 months (T6). BiteStrip® scores were recorded at T0 and T6. Intragroup comparisons of the Periotest® value (PTV) were performed using analysis of covariance. Intergroup comparisons of PTV and BiteStrip® scores were performed using the linear mixed model and Wilcoxon signed-rank test, respectively. Intragroup comparisons of BiteStrip® scores were performed using the Mann–Whitney U test.

Results: At T6, the PTV in the intervention group was significantly lower than that in the control group (p=0.004). PTV was significantly lower at T6 than that at T0 in the intervention group (p=0.030), while PTV was significantly higher at T6 than that at T0 in the control group (p=0.007). There was no significant difference in the BiteStrip® score between the two groups. The BiteStrip® score at T6 was significantly lower than that at T0 only in the intervention group (p=0.011).

Conclusion: ND placement might inhibit the increase in mobility of RPD abutment teeth and be effective in protecting them in RPD wearers with SB.

Purpose: This study explores novel solutions other than standard SBF for biomimetic evaluations of mineralization particularly for resin composites containing bioactive glass (BAG).

Methods: Experimental UDMA/TEGDMA resin composites with 0.0, 1.9, 3.8 or 7.7 vol% of 45S5 BAG fillers were prepared. Besides simulated body fluid (SBF) as control, the specimens were immersed in three other solutions either with bicarbonate which are Hank’s balanced salt solution (HBSS) and cell culture medium (MEM), or without bicarbonate which is a novel Simple HEPES-containing Artificial Remineralization Promotion (SHARP) solution, for 3, 7 and 14 days. These solutions were then analyzed by ICP-OES and pH meter, and the surfaces of the BAG composites were analyzed by SEM, XRD and FTIR.

Results: ICP-OES revealed Ca and P concentration continuously decrease, while Si concentration increases with time in the solutions other than SBF, which showed almost unchanged elemental concentration. Only SHARP solution is able to maintain a constant pH over the immersion time. SEM, together with XRD and FTIR, showed nano-sized octacalcium phosphate (OCP) nanospheres formation on 3.8 and 7.7 vol% BAG composites after 14 days immersion in HBSS (500-600 nm) and MEM (300-400 nm). SHARP solution enabled OCP formation after 3 days and then self-assembled into urchin-like carbonated hydroxyapatite (CHA) microspheres encompassed with nanorods of 100 nm width and 8 µm length after 14 days of immersion for 7.7 vol% BAG composites.

Conclusion: This study suggests SHARP solution can evaluate mineralization biomimetically whereas CHA microspheres can be formed on BAG-containing resin composites.

Purpose: The present study was performed to examine the mandibular deformation during mouth opening in edentulous patients, treated with an implant-supported fixed prosthesis using strain gauges, and identify factors affecting deformation.

Methods: Twenty patients with a fully edentulous mandible who received either 4 or ≥6 implants were included. The distal-most implants were placed mesial to the mental foramen (premolar region) in patients with 4 implants and distal to the mental foramen (molar region) in patients with ≥6 implants. Mandibular deformation during mouth opening was measured using strain gauges in two directions: anteroposterior direction and lateral direction between the distal-most implants on the left and right sides (arch width). The mandibular anatomy was evaluated using computed tomography.

Results: Arch width reduction between the left and right implants during mouth opening ranged from 47.38 to 512.80 µm; the range of deformation was 0.12 to 15.14 µm in the anteroposterior direction. Furthermore, a significant positive correlation was noted between arch width reduction in the premolar region and the ratio between the symphyseal bone height and width (P = 0.0003, r = 0.72).

Conclusion: The reduction in arch width was higher in the molar region than in the premolar region during mouth opening. Moreover, the reduction could be high in the mandibular symphyseal bone because of its greater height and lesser width. The ratio between the symphyseal bone height and width is defined as the mandibular deformation index (MDI) and is used to predict the rate of mandibular bone deformation.

Purpose: To examine the effect of molding angle on the trueness and defects associated with removable partial denture (RPD) frameworks fabricated by selective laser melting (SLM).

Methods: A plaster model of a partially edentulous mandibular arch classified as Kennedy class II modification 1 was used. After obtaining the 3D data of the model (design data), a framework was designed using CAD software. Based on the design data, three different molding angle conditions (0°, 45°, and –45°) were set in the CAM software. The frameworks were fabricated by SLM under each condition, and 3D data were captured (fabrication data). The design and fabrication data were superimposed using 3D inspection software to verify the shape errors. The number of support structures was then measured. To examine the internal defects, micro-computed tomography (µCT) was performed for void analysis. Surface roughness was measured using a laser microscope.

Results: The overall shape errors of the RPD framework were smaller under the 0° condition compared with the others, and the largest number of support structures was observed at 0°. Many internal defects were observed in the large components of the framework at 45° and –45°. The surface roughness was the smallest at –45°.

Conclusion: The trueness and defects associated with the RPD frameworks were affected by the difference in the SLM molding angle.

Purpose: This study aimed to comparatively investigate the effects of accelerated aging on the physical and biological features of zirconia manufactured by digital light processing (DLP) and conventional subtractive manufacturing (SM) with similar composition.

Methods: Both the DLP- and SM-fabricated zirconia samples (7 mm × 7.5 mm × 1.5 mm) were grouped according to aging (134 °C, 0.2 MPa, 100% humidity) times, including 0 h, 5 h, and 10 h. Phase assemblage and surface topography of zirconia manufactured by different technologies were evaluated before and after aging. The biological effects of zirconia on human gingival fibroblast (HGF) cell events, including cell viability, proliferation, morphology and adhesion, were also evaluated by live/dead viability assay, cck-8 assay, scanning electron microscopy and confocal laser scanning microscopy respectively.

Results: The DLP-fabricated zirconia showed a higher initial cubic phase content and rate of phase transformation than the SM-fabricated zirconia. Among the different aging time-based groups, the 5 h-aged group exhibited significantly lower sub-micron scale surface roughness compared with the other groups. Aging did not significantly alter cellular behavior in any zirconia type, except for minor changes in adhesive cell numbers recorded in an aging time/culturing time-dependent manner. In addition to small differences in cell alignment patterns and overall cell morphology, the two zirconia types presented comparable biological performance before and after aging.

Conclusion: Although the microstructure and surface characteristics of DLP-fabricated zirconia can be affected by autoclave aging, this newly manufactured zirconia is likely to maintain desirable long-term biocompatibility as an implant abutment material.

Purpose: The purpose of this study was to determine a reference value for masticatory performance (MP) by measuring the amount of glucose extraction (AGE) from chewing gummy jelly.

Methods: A total of 237 young adults (young group, 20-39 years), 147 middle-aged adults (middle-aged group, 40-59 years), and 177 older adults (old group, 60-87 years) participated in this study. All participants had natural dentition, excluding the third molars. AGE was measured when the participant chewed gummy jelly and used as a parameter of MP. AGE was compared among the three groups. Next, AGE in each group was compared between the habitual chewing side and non-habitual chewing side, and between males and females. The correlation between age and AGE was also investigated.

Results: AGE in the young, middle, and old groups were similar, and no significant differences were observed. AGE was significantly higher in the habitual chewing side compared to the non-habitual chewing side, and in males than that in females. No significant correlations were found between age and AGE. AGE in the habitual chewing side of all ages was 221.9 ± 34.4 mg/dL for males and 206.0 ± 28.7 mg/dL for females. The mean-2SD (standard deviation) value representing the reference value of healthy adults was 153.1 mg/dL for males and 148.6 mg/dL for females, which was close to 150 mg/dL.

Conclusion: It was concluded that the reference value of masticatory performance as measured by the amount of glucose extraction after chewing gummy jelly was 150 mg/dL.

Purpose: Evidence regarding the performance of digital dentures (DDs) fabricated using 3D printing is insufficient. This study aimed to evaluate patient satisfaction with conventional dentures (CDs) and DDs fabricated using 3D printing.

Methods: This randomized controlled trial was conducted between November 2017 and May 2020. In the CD-DD group, CDs were fabricated before DDs, while the protocol was reversed in the DD-CD group. The primary outcome was patient satisfaction, quantified using a 100-mm visual analog scale, which assessed chewing efficiency, pain, stability, retention, comfort, esthetics, ease of cleaning, phonetics, and general satisfaction. Secondary outcomes were quality of life (QOL), number of visits, time required for definitive denture fabrication, number of adjustment appointments, and time required for denture stabilization after denture delivery.

Results: Patient satisfaction with CDs was superior in terms of phonetics, ease of cleaning, stability, comfort, and general satisfaction. Secondary outcomes such as social disability and the number of clinic visits were significantly lower in patients with DDs. However, the two groups showed no significant differences in the other outcomes. Although patient satisfaction with DDs was inferior to that with CDs, 20% of patients preferred and used DDs (12 patients preferred CDs, and three patients opted for DDs).

Conclusion: Although patient satisfaction or QOL with DDs may be somewhat inferior to that with CDs, 20% of patients preferred and used DDs daily. Thus, DDs fabricated using 3D printing may have comparable practicality and efficacy to CDs.

Purpose: We aimed to clarify the relationship between the number of sleep bruxism (SB) bursts at home and in a laboratory equipped with polysomnography with audio-video recording (PSG-AV). We applied an identical single-channel wearable electromyography (EMG) device for both types of SB burst scorings.

Methods: The subjects were 20 healthy student volunteers (12 men and 8 women; mean age, 21.9 years) who were clinically diagnosed with bruxism based on the criteria set forth by the International Classification of Sleep Disorders (ICSD-2). We used a wearable EMG device attached to the masseteric area (the FLA-500-SD [FLA]), for scoring SB bursts at home and in the laboratory. PSG-AV was set within the laboratory environment as well. The mean interval for both sleep studies was 28.8 days. EMG bursts with amplitudes greater than twice the baseline amplitude and with durations of longer than 0.25 s were selected. EMG bursts with amplitudes ≥5% MVC (maximum voluntary contraction), ≥10% MVC, and ≥20% MVC were selected as well. A cluster of bursts was defined as an episode.

Results: In all the conditions for selecting EMG bursts specified above, the number of SB bursts and episodes recorded under laboratory conditions was statistically significantly smaller than that recorded at home. There were no statistically significant differences between the data obtained on the first and second recording days.

Conclusion: The results of this study suggest that the unfamiliar environment of a sleep laboratory equipped with PSG-AV affects the emergence of SB as compared with home conditions.

Purpose: Several studies have evaluated the interest of Low Intensity Pulsed Ultrasound (LIPUS) in the osseointegration of dental implants in murine or rabbit models. However, the thinness and narrowness bones make it difficult to study the effect of LIPUS. The purpose of this study is to assess the ability of LIPUS to stimulate bone formation in contact with a titanium dental implant in a porcine model.

Methods: Eight adults mini-pigs were used. An implant is placed on each tibial crest in the metaphysis. The right side was treated with LIPUS at 1 MHz and 300 mW/cm² of acoustic intensity during 15 minutes per day on 5 consecutive days and during 42 days. The left side was not treated. The Bone Volume/Total Volume ratio (BV/TV), the Intersection Surface (IS) of the volume of interest by the binarized bone and the Trabecular bone Thickness (TbTh) around the implant were analyzed.

Results: At 42 days, BV/TV ratio is significantly higher on the treated side (42,1+/−8,76% versus 32,31+/−10,11%, p < 0,02); as well as TbTh with 0,13+/−0,01 mm versus 0,10+/−0,01 mm (p < 0,01). IS is also significantly higher on the treated side (40,7 +/− 12,68 mm² versus 33,68+/−9,44 mm² at 200 μm from the implant surface; p < 0,01).

Conclusion: The present study showed that LIPUS can significantly increase bone formation and accelerate the healing process at the bone-implant interface in a porcine model. Its low toxicity, low immunogenicity and non-invasion make it a complementary treatment of choice for improving the bone formation around titanium implants.

Purpose: Acquiring adequate attached mucosa is important in restoring masticatory function with a removable dental prosthesis or dental implant. In patients with inadequate attached mucosa, a free gingival graft (FGG) with a custom stent is used. However, it is challenging to apply the conventional method for fabricating a stent with a reshaped cast in patients with reconstructed mandibles because the reconstructed mandible has limitations due to a titanium mesh, skin flap, and unique bone morphology. In the present report, we have proposed a new design and fabrication process for a mucocompressive splint via medical engineering to acquire the attached mucosa for the prosthodontic treatment of reconstructed mandibles.

Methods: Three-dimensional (3D) craniomandibular models were reconstructed from a computed tomography dataset after mandibular reconstruction. The dentition region was replaced with highly precise scan data of the dental casts using a 3D scanner. The alveolar ridge mucosa and teeth were ideally designed using the 3D model while referring to the anatomical structures. The jig used to fabricate the working dental cast with artificial gum in real space was designed and fabricated using a 3D printer. The alveolar ridge was altered into a simulated configuration on the articulator using a jig. A mucocompressive splint was fabricated on an altered dental cast. The splint was immediately seated on the mandible without any major adjustments after the FGG.

Conclusion: Adequate attached mucosa for the prosthodontic treatment of a reconstructed mandible was obtained by the pre-surgical fabrication of a mucocompressive splint through medical engineering.