Effect of speed sintering of monolithic zirconia with different yttria contents on color and crystal phase.

This study evaluated the color and microstructure of monolithic zirconia crowns with different yttrium oxide (Y2 O3 ) contents treated by conventional or speed sintering. Four types of zirconia ceramics were assessed: two monolayer zirconia, and two multilayer zirconia. The monolithic zirconia crowns were fabricated using a dental computer-aided design/computer-aided manufacturing (CAD/CAM) system and in two shades (A2 and BL). After milling, the zirconia crowns were sintered using either speed sintering or conventional sintering. For each combination of zirconia (4), shade (2), and sintering condition (2), the color parameters were determined at three positions of each of nine crowns using a non-contact dental spectrophotometer. In addition, the zirconia phases in the specimens were quantified using X-ray diffractometry. Significant differences in the ΔE00 values at different measurement positions were observed for the Multi2 crown of the BL shade group. The color difference resulting from conventional and speed sintering programs was not affected by the difference in yttria content of Mono1, Mono2, and Multi1. However, in Multi2, containing 3Y-TZP and 5Y-PSZ, a color change was caused by the use of speed sintering. Therefore, when performing speed sintering with Multi2, it is necessary to select the color in consideration of these results or take measures for staining.

Daytime masticatory muscle electromyography biofeedback regulates the phasic component of sleep bruxism.

BACKGROUND: Electromyography (EMG) biofeedback (BF) training is potentially an effective cognitive-behavioural approach to regulate bruxism. OBJECTIVE: This study examined sleep bruxism regulation by daytime clenching control using a single-channel auditory EMG BF device. METHODS: Seventeen male subjects (mean age, 24.4 ± 3.1 years; mean ± SD) with self-reported awake/sleep bruxism were recruited and divided into a BF (n = 10) and a control (CO) group (n = 7). All subjects underwent four EMG recording sessions during both daytime and sleep over 3 weeks. During the daytime, in week 2, the BF group received feedback alert signals when excessive EMG activity with certain burst duration was detected while the subjects performed regular daily activities. The CO group underwent EMG recording sessions without receiving any alerts of parafunctional activity. The number of phasic burst events during sleep was compared between the BF and CO groups. RESULTS: While the number of phasic EMG events was not significantly different between the BF and CO groups at baseline, significantly smaller phasic events were observed in the BF compared to the CO group at the follow-up session (week 3) (P = .006, Tukey's HSD). Since daytime BF training is aimed at raising awareness of awake bruxism, it does not interrupt the sleep sequence or involve associated side effects. CONCLUSION: The present results suggest that EMG BF targeting for tonic EMG events during the daytime can be an effective method to regulate phasic EMG events during sleep.

Effects of plasma surface treatment on the bond strength of zirconia with an adhesive resin luting agent.

The purpose of this study was to evaluate the effect of the atmospheric pressure plasma treatment as a surface treatment method on the contact angle and shear bond strength (SBS) of zirconia ceramics and the failure mode between the self-adhesive resin luting agent and zirconia. The zirconia specimens were divided into eight groups based on the surface treatment method: alumina blasting, air plasma, argon plasma (AP), Katana cleaner, ozonated water, ozonated water+AP, Katana cleaner+AP, and tap water+AP. The contact angles, SBS, and fracture modes were tested. AP treatment significantly reduced the contact angle (p<0.0001). The combination of AP and other cleaning methods showed a higher bond strength and more mixed fractures. Our findings indicate that using atmospheric pressure plasma with argon gas, combined with other cleaning methods, results in a stronger bond than when using alumina blasting alone.

Effect of low-temperature degradation and sintering protocols on the color of monolithic zirconia crowns with different yttria contents.

This study investigated the effects of low-temperature degradation (LTD) on the L*, a*, and b* values of highly translucent zirconia crowns. Four types of zirconia disks with different yttria contents (IPS e.max ZirCAD LT, IPS e.max ZirCAD MT, IPS e.max ZirCAD MT Multi, IPS e.max ZirCAD Prime, Ivoclar) and two shades (A2 and BL) were used. A crown was manufactured using four types of zirconia and LTD treated. Color measurements were performed, and the color difference (ΔE00) before and after LTD was calculated. The microstructure was determined through X-ray fluorescence and X-ray diffractometry. Highly translucent zirconia crowns showed greater changes in the a* and b* values than in the L* value after LTD, regardless of the shade. The Multi2 crowns exhibited a discernible color change due to the LTD treatment. The X-ray fluorescence results did not reveal any apparent change in the microstructure between sintering programs for all zirconia specimens.

Assessment of awake bruxism-Combinational analysis of ecological momentary assessment and electromyography.

PURPOSE: No consensus exists regarding the examination methods and assessment criteria for awake bruxism (AB). In this study, masticatory muscle activity measured using electromyography (EMG) was recorded simultaneously with the ecological momentary assessment (EMA) of bruxism events. Data were collected to identify distinctive EMG parameters in AB. METHODS: A total of 104 individuals were classified into the bruxism (BR) or control (CO) groups based on clinical findings. The participants recorded EMA on a tablet device under continuous EMG recording using a data log-type wireless EMG device. For EMA recording, a warning was randomly provided three times each hour for five hours. A receiver operating characteristic (ROC) curve was obtained based on EMA and EMG events. Maximum voluntary contraction (MVC) at the time of maximum bite force was set at 100%. The muscle activity was assessed as a relative value. RESULTS: Based on discriminant analysis, analysis of participants who had four or more positive clenching EMA responses was appropriate. The assessed parameters for the EMG cutoff value determination procedure, which combined EMG and EMA, resulted in a cutoff value that enabled the distinction between the BR and CO groups. The area under the ROC curve was 0.77 and the cut-off value was 3.2 events/hour under the EMG of 20% MVC with a duration of ≥1 s. CONCLUSIONS: This is the first study to report a combined analysis of the EMA and EMG. These results suggest its effectiveness as a cutoff value for AB screening.

Mechanical and surface properties of additive manufactured zirconia under the different building directions.

PURPOSE: This study investigates the mechanical and surface properties of zirconia manufactured using additive manufacturing (AM) technology and the effect of the building direction on the mechanical and surface properties. METHODS: Specimens were prepared using ZrO2 paste (3DMix ZrO2; 3DCeram) and a three-dimensional printing system (CeraMaker 900; 3DCeram) based on the principles of stereolithography (SLA). The mechanical properties (flexural strength, Vickers hardness, fracture toughness, elastic modulus, and Poisson's ratio) and surface properties (chemical composition and surface observation) were evaluated for three building directions (parallel, diagonal, and perpendicular) to investigate the relationship between the building directions and the anisotropy of the mechanical and surface properties of SLA-manufactured zirconia. Statistical analysis was performed using a one-way analysis of variance and Tukey's honestly significant difference test. RESULTS: The highest flexural strength was obtained for a perpendicular building direction. The flexural strength was significantly higher in the perpendicular direction than in the parallel and diagonal directions; it was also significantly higher in the diagonal direction than in the parallel direction (P<0.05). The Vickers hardness, fracture toughness, elastic modulus, Poisson's ratio, and chemical composition did not differ significantly. Microstructural observations revealed that the layers, large crystals, and pores were more prominent in the parallel direction. CONCLUSIONS: The flexural strength and surface structure of the tested SLA-manufactured zirconia were influenced by the building direction; however, other mechanical properties remained unaffected. The layer boundaries affected the anisotropic behavior of the builds to a certain extent, owing to the layer-by-layer production method.

The effect of low-temperature degradation and building directions on the mechanical properties of additive-manufactured zirconia.

This study aimed to investigate the effect of low-temperature degradation (LTD) on the mechanical properties of additive-manufactured zirconia. In addition, the mechanical properties of additive-manufactured were compared with those before aging under similar experimental conditions. This study prepared stereolithography apparatus fabricated zirconia specimens with flexural strength, modulus of elasticity, Vickers hardness, and fracture toughness. The specimen position data were set as parallel (0°), diagonal (45°), and perpendicular (90°) to the direction of the building. The LTD condition was 5 h under 134ºC and 0.2 MPa in an autoclave. It was found that the 0° direction differed significantly from all other conditions before and after aging, and the highest flexural strength was obtained when the additive specimen was manufactured perpendicular to the building direction. However, the results indicate that there is a negligible effect of aging on the mechanical properties of additive-manufactured zirconia.

Prosthodontic treatment can improve the ingestible food profile in Japanese adult outpatients.

PURPOSE: To investigate the effect of prosthodontic treatment on the ingestible food profile in adult Japanese outpatients, and to identify the related risk factors that can deteriorate the profile. METHODS: The participants were 277 outpatients who visited university-based specialty clinics in Japan for prosthodontic treatment. The demographic data, number of present teeth assessed via intraoral examination, and oral health-related quality of life assessed by the total Oral Health Impact Profile (OHIP-J54) scores of all participants were recorded before treatment. Ingestible food profile score (IFS) was recorded using a validated food intake questionnaire. Eligible participants who answered the questionnaire before and after treatment were categorized into five groups based on the prosthodontic treatments they received (i.e., crowns, bridges, removable partial dentures, removable complete dentures, and removable complete and partial dentures). RESULTS: Multivariate analysis of covariance revealed a statistically significant main effect of prosthodontic intervention (time course: before and after treatment) on mean IFS (P=0.035, F=4.526), even after adjusting for covariates (age, number of present teeth, and treatment modality). Multiple linear regression analysis revealed that the low number of present teeth (r=0.427, P<0.001) and a high OHIP-J54 total score (r=-0.519, P<0.001) of the patients at the baseline were significantly associated with their baseline IFSs, even after adjusting for confounding variables. CONCLUSIONS: The findings of this multicenter follow-up study indicate the importance of prosthodontic rehabilitation in improving patients' ingestible food profiles.

Managements of sleep bruxism in adult: A systematic review.

This systematic review aimed to update the management of sleep bruxism (SB) in adults, as diagnosed using polysomnography (PSG) and/or electromyography (EMG). Management methods covered were oral appliance therapy (OAT) with stabilization splints, cognitive-behavioral therapy (CBT), biofeedback therapy (BFT), and pharmacological therapy. A comprehensive search was conducted on MEDLINE, Cochrane Library, and Web of Science up to October 1st, 2021. Reference list searches and hand searches were also performed by an external organization. Two reviewers for each therapy independently performed article selection, data extraction, and risk of bias assessment. The reviewers resolved any disagreements concerning the assortment of the articles by discussion. Finally, 11, 3, 14, and 22 articles were selected for each therapy. The results suggested that OAT tended to reduce the number of SB events, although there was no significant difference compared to other types of splints, that the potential benefits of CBT were not well supported, and that BFT, rabeprazole, clonazepam, clonidine, and botulinum toxin type A injection showed significant reductions in specific SB parameters, although several side effects were reported. It can be concluded that more methodologically rigorous randomized large-sample long-term follow-up clinical trials are needed to clarify the efficacy and safety of management for SB.

Comparative Evaluation of the Reproductive Trueness of Zirconia Crowns Fabricated Using Additive Manufacturing and Conventional Milling.

PURPOSE: To evaluate the occlusal reproductive trueness of zirconia crowns fabricated using additive manufacturing (AM) and to compare the surface roughness of crowns fabricated using AM and conventional milling (CM). MATERIALS AND METHODS: Crowns were manufactured using AM and CM on abutments with total occlusal convergence angles of 16 and 20 degrees. RESULTS: The surface roughness of the AM crowns was less than that of the CM crowns. The differences in reproduction of the occlusal morphology of the abutment crown were greater at 16 degrees than at 20 degrees. CONCLUSION: AM could be an effective method for manufacturing zirconia crowns.

Effects of abutment tooth and luting agent colors on final color of high-translucent zirconia crowns.

PURPOSE: This study aimed to evaluate the effects of the tooth portion evaluated and the colors of the abutment tooth and resin luting agent on the final color of monolithic zirconia crowns. METHODS: Monolithic zirconia crowns were fabricated for left maxillary central incisors using two shades (A2 and A3) of highly translucent monolithic zirconia disks. A model of the abutment tooth was fabricated using resin core materials (white: W; dentin: D). The color of the crowns was measured with try-in pastes (clear: C; brown: B) as a resin-luting agent substitute. The measurement was performed after placing the crown on the model with the attached abutment tooth with try-in paste. The color of three labial portions (cervical, body, and incisal) was evaluated using a dental spectrophotometer. The color difference (ΔE) between the CIELab values of the zirconia disks and the final measurement of zirconia crowns was calculated. RESULTS: The ΔE between the crown of the A2 shade and the zirconia disk of the A2 shade had the highest ΔE value in the body portion with W-B (ΔE=3.92). Similarly, the A3 shade had the highest ΔE value in the cervical portion, with W-B (ΔE=4.27). The results of three-way ANOVA showed that the ΔE values were influenced by the tooth portion evaluated and the color of the abutment tooth. CONCLUSION: The final color of the monolithic zirconia crowns was significantly influenced by the tooth portion evaluated and the color of the abutment tooth.

Effectiveness of the socket shield technique in dental implant: A systematic review.

PURPOSE: Dental implant therapy is a common clinical treatment for missing teeth. However, the esthetic result is not as satisfactory as expected in some cases, especially in the anterior maxillary area. Poor esthetic results are caused by inadequate preparation of the hard and soft tissues in this area before treatment. The socket shield technique may be an alternative for a desirable esthetic outcome in dental implant treatments. STUDY SELECTION: In the present systematic review, PubMed-Medline, Google Scholar, and ScienceDirect were searched for clinical studies published from January 2000 to December 2018. RESULTS: Twenty studies were included, comprising one randomized controlled trial, two cohort studies, 14 clinical human case reports, and three retrospective case series. In total, 288 patients treated with the socket shield technique with immediate implant placement and follow-up between 3-60 months after placement were included. A quality assessment showed that 12 of the 20 included studies were of good quality. Twenty-six of the 274 (9.5%) cases developed complications or adverse effects related to the socket shield technique. Most studies reported implant survival without the complications (90.5%); most of the cases that were followed up for more than 12 months after implant placement achieved a good esthetic appearance. The failure rate was low without the complications, although there were some failures due to failed implant osseointegration, socket shield mobility and infection, socket shield exposure, socket shield migration, and apical root resorption. CONCLUSIONS: The socket shield technique can be used in dental implant treatment, but it remains difficult to predict the long-term success of this technique until high-quality evidence becomes available.

Impact of number of functional teeth on independence of Japanese older adults.

AIM: To examine the relationship between the number of present and functional teeth at baseline and future incidence of loss of independence. METHODS: Participants were community-dwelling older individuals who participated in a comprehensive geriatric health examination conducted in Kusatsu town, Japan, between 2009 and 2015. The primary endpoint was the incidence of loss of independence among participants, defined as the first certification of long-term care insurance in Japan. The numbers of present and functional teeth at baseline were determined via an oral examination. Demographics, clinical variables (e.g., history of chronic diseases and psychosocial factors), blood nutritional markers, physical functions, and perceived masticatory function were assessed. RESULTS: This study included 1121 individuals, and 205 individuals suffered from loss of independence during the follow-up period. Kaplan-Meier estimates of loss of independence for participants with smaller numbers of present and functional teeth were significantly greater than for those with larger numbers of teeth. Cox proportional hazard analyses indicated that a smaller number of present teeth was not a significant risk factor after adjusting for demographic characteristics. However, the number of functional teeth was a significant risk factor after the adjustment (hazard ratio: 1.975 [1.168-3.340]). Additionally, higher hazard ratios were observed in other adjusted models, but they were not statistically significant. CONCLUSIONS: The number of functional teeth may be more closely related to the future incidence of loss of independence than the number of present teeth. This novel finding suggests that prosthodontic rehabilitation for tooth loss possibly prevents the future incidence of this life-event. Geriatr Gerontol Int 2022; 22: 1032-1039.

Clinical evaluation of monolithic zirconia crowns: a failure analysis of clinically obtained cases from a 3.5-year study.

PURPOSE: The primary purpose of this study was to examine the clinical performance of monolithic zirconia single crowns in terms of short-term failure or complications. The secondary purpose was to detect the originating flaws of clinically failed monolithic zirconia crowns to find the causes of failure. METHODS: A short-term prospective cohort study based on record evaluation and clinical examination of patients treated with tooth-supported monolithic zirconia crowns was performed in the Department of Fixed Prosthodontics, Tohoku University Hospital, Japan. The crowns were prepared during the follow-up period from April 2014 to July 2018. The 3.5-year cumulative success and survival rates were set as primary endpoints. Fractures of the crown or fragments were inspected under a scanning electron microscope for descriptive fractography. RESULTS: During the study period, 40 monolithic zirconia crowns were placed. Four crowns experienced clinical complications, including: 1) fracture of the crown (two crowns), 2) abrasion of the crown (one crown), and 3) fracture of the antagonist tooth (one crown). The estimated Kaplan-Meier 3.5-year success and survival rates were 90.5% (95% confi dence interval [CI]: 73.1-97.1) and 92.8% (95% CI: 74.1-98.3), respectively. Fractography revealed that all fractures were initiated from the wear phase on the occlusal surface. CONCLUSIONS: The results of this study suggest that the molar application of monolithic zirconia crowns requires detailed attention to interocclusal clearance and the restoration of the antagonist tooth.

Critical review about two myths in fixed dental prostheses: Full-Coverage vs. Resin-Bonded, non-Cantilever vs. Cantilever.

The purpose of this review was to assess the literature regarding four types of fixed dental prostheses (FDPs)/resin-bonded FDPs (RBFDPs) to provide clinicians with a comparative overview of two myths: "RBFDPs are easy to debond in patients' mouths" and "cantilever RBFDPs still have some clinical problems, especially in terms of overloading the abutment teeth and being easy to debond". A total of 782 papers were identified, 753 of which were judged unsuitable and thus excluded, leaving a total of 29 articles for inclusion in this review. The results indicated that 1) Two-retainer RBFDPs achieve clinical results comparable to full-coverage three-unit FDPs; 2) Cantilever RBFDPs show excellent long-term clinical outcomes (especially in incisor teeth) compared with other FDPs; 3) RBFDPs typically show less catastrophic failure than conventional FDPs, rebonding should be considered when debonding occurs; and 4) Cantilever RBFDPs can be recommended as defect replacement prostheses for maxillary lateral incisors and mandibular incisor teeth. Scientific field: Prosthodontics, Adhesive dentistry, Esthetic dentistry.

Current status and perspective of CAD/CAM-produced resin composite crowns: a review of clinical effectiveness.

The purpose of the present review was to survey the available literature on computer-aided design/computer-aided manufacturing (CAD/CAM)-produced resin composite materials to provide clinicians with a current overview of the key components necessary for daily clinical use. An electronic search was conducted in the PubMed database. Peer-reviewed articles in English language on the use of resin composites in CAD/CAM dental crowns were included. A total of 122 full-text articles were identified, 15 of which were selected during the initial review. Two additional articles were also discovered through a manual search, to obtain a final total of 17 articles included in the present review. Of these, 16 were to in vitro studies, and one was an in vivo study. Findings from the in vitro studies indicate that resin composite block materials for CAD/CAM applications demonstrate excellent physical properties and are appropriate for the clinical restoration of premolars and molars. However, the in vivo study reported a low 3-year success rate, but high survival rate for resin composite CAD/CAM crowns placed in the premolar region. The key to ensuring the successful prognosis of a resin composite CAD/CAM crown is to ensure that all steps-such as proper case selection, abutment tooth preparation, occlusal adjustment, and bonding-are accurately performed.

Clinical outcomes of single crown restorations fabricated with resin-based CAD/CAM materials.

Computer-aided design/computer-aided manufacturing (CAD/CAM) restorative materials have been widely used owing to a number of advantages, including stable quality of the materials, lower costs, and time-saving factors. Resin-based CAD/CAM materials for definitive restorations are classified into two groups: dispersed nanoparticle-filled composite resin and polymer-infiltrated-ceramic-network materials. Resin-based CAD/CAM materials have been applied to single crown restorations as a monolithic structure for the posterior region. In addition, resin-based CAD/CAM restorations have been applied recently for the anterior area. This literature review summarizes clinical outcomes, such as survival rates and clinical complications of single crown restorations fabricated with resin-based CAD/CAM materials.

Number of functional teeth more strongly predicts all-cause mortality than number of present teeth in Japanese older adults.

AIM: Previous studies on the association between intraoral conditions and mortality in community-dwelling older individuals reported that fewer present teeth (PT) are significant risk factors for mortality. However, how the number of PT relative to the number of functional teeth (FT), including both present and rehabilitated teeth, influences mortality has not been investigated fully. This study examined the impact of the number of FT on mortality among community-dwelling Japanese older adults. METHODS: This study was a retrospective, observational and population-based follow-up study, which examined 1188 older individuals who participated in an annual geriatric health examination from 2009 to 2015. The average follow-up period was 1697.0 ± 774.5 days. The primary outcome was all-cause mortality at follow-up. The numbers of PT and FT of each participant were counted during an oral examination. In addition, demographics, clinical variables, blood nutrient markers, physical functions and perceived masticatory function were measured. RESULTS: Kaplan-Meier analysis, followed by a log-rank test, revealed that fewer PT (P < 0.001) and FT (P = 0.002) were significantly associated with a reduced survival rate. Cox's proportional hazard analysis indicated that the number of FT, but not the number of PT, was a significant independent mortality risk factor after adjusting for demographics, clinical variables, nutrient markers and physical functioning (P = 0.036, hazard ratio: 2.089). CONCLUSIONS: Current results suggest that the number of FT more strongly predicts all-cause mortality than the number of PT among community-dwelling older adults. Further studies are necessary to consider the confounding of socioeconomic status and disability status. Geriatr Gerontol Int 2020; ••: ••-••.

Influence of elastic modulus mismatch between dentin and post-and-core on sequential bonding failure.

PURPOSE: Clinical failures of teeth restored with post-and-core are critical issues for the survival of teeth and maintenance of oral functions. A tooth with post-and-core restoration is a complex structure. Cement adhesion is believed to be the weakest component, and breakage in this component leads to changes in stress distribution in the complex structure. The tested hypothesis was that cement breaking processes of prosthetic treated teeth were affected by elastic properties of post-and-cores. METHODS: Finite element analysis focused on sequential adhesion failure between the dentin and cement; the penalty function method was used to analyze stress during each stage of bonding conditions. Failure patterns of adhesion and stress distribution within dentin under load of different materials of post-and-core was observed. RESULTS: Although, an initial failure of cement was observed at the palatal crown margin regardless of the material. Different patterns of adhesion failure between dentin and post-and-cores were observed by different elastic properties of post-and-cores. Stress concentration was observed at the corresponding areas of interface between adhesion failure and continued elements using both post-and-cores. CONCLUSIONS: Using failure criteria for cement adhesion, sequential changes of adhesion failure between dentin and post-and-cores were observed. Local stress concentrations leading to severe destruction of dentin were caused by not only materials of post-and-cores but their adhesive conditions to dentin. Nonlinear finite element analysis (FEA) using complex structure model which deals with alterations of interfacial condition between components could provide the simulation for the clinical failure of teeth restored with post-and-cores.

Importance of interim restorations in the molar region.

Interim restoration protects abutment teeth and periodontal tissues until prosthetic treatment ends with the fabrication of a definitive prosthesis, restores and maintains the functions and morphology of the stomatognathic system, and preserves the occlusal contact relationship. Temporary prostheses are used for a short time, to confirm the diagnosis and treatment plan. However, because interim restorations are used only briefly, their importance in ensuring the success of definitive prostheses is often overlooked. This review includes a comprehensive literature review of interim restoration of molars and summarizes the current clinical understanding and status of this functionally important area. Peer-reviewed publications were identified by searching PubMed in November 2018. An interim restoration, even when used briefly, can help dentists evaluate many aspects of the treatment plan and contribute to accurate prognosis of prosthetic treatment.