Purpose: In recent years, the application of restorations and fixed dental prostheses to molars by computer-aided design-computer-aided manufacturing (CAD/CAM) with composite resin has been increasing. Titanium and titanium alloy having a high tissue affinity and good biocompatibility are suitable for cases where CAD/CAM fabrications are inadequate, such as allergic reaction to metal. Many studies have reported methods of production with titanium and titanium alloys. The purpose of this review is to survey the clinical application of titanium and titanium alloy restorations and fixed dental prostheses with various fabrication systems.

Study selection: A literature search in PubMed was performed for various fabrication systems of titanium and titanium alloy from 2010 through 2019. The search keywords were "titanium", "titanium alloy", "CAD/CAM", "cast", "fabrication system", "marginal gap", "internal gap", and "clinical performance". Only relevant studies are summarized and discussed in this review.

Results: With any fabrication system, titanium and titanium alloy restorations and fixed dental prostheses fabricated with various systems were within the clinically acceptable ranges of marginal gap and internal fit. Additionally, these restorations were considered to have less effect on the periodontal issues. Although metal–ceramic restoration has clinical performance problems, such as ceramic fracture, fabrications with only titanium and titanium alloy were reported to have good clinical performance.

Conclusions: Regardless of the fabrication system, titanium and titanium alloy restorations and fixed dental prostheses can be applied clinically. Titanium and titanium alloys are thought to be a promising alternative to the dental metals currently used.

Purpose: Intraoral scanners may offer an alternative to traditional impressions. That intraoral scanners produce precise scans is essential. Popular methods used to evaluate precision tend to rely on mean distance deviation between repeated scans. Mean value measurements may underestimate errors resulting in misleading conclusions and clinical decisions. This study investigated the precision of six intraoral scanners using the traditional method of measuring mean error, and a proposed method considering only the most extreme and clinically relevant aspects of a scan.

Methods: An edentulous model was scanned five times using six intraoral scanners. The repeated scans were aligned, uniformly trimmed and mean surface deviation measured across all 20 scan combinations within each scanner group. All scan combinations were then measured by arranging scan vertices from greatest to smallest unsigned distance from its compared scan and measuring the median value within the 1% of most greatly deviating points. Traditional mean deviation results and upper-bound deviations were compared.

Results: The upper-bound deviation within a scan reported errors up to two times greater than those found when measuring global mean distances. Results revealed clinically relevant errors of more than 0.3 mm in scans produced by the Planmeca and Dentalwings scanners, findings not seen when measuring mean distance error of the complete scan.

Conclusions: Upper-bound deviation of a cropped scan may provide a clinically useful metric for scanner precision. The Aadva, 3Shape, CEREC and TDS produced scans potentially appropriate for clinical use while Planmeca and Dentalwings produced deviations greater than 0.3 mm when measuring the upper- bound deviation.

Purpose: To characterize the effect of two processing techniques (pressing and CAD/CAM — Computer Aided Design/Computer Aided Machining) of lithium-disilicate (LD) based crowns on the microstructure, topography, roughness, fractal dimension, internal and marginal adaptation.

Methods: One-hundred identical preparations for monolithic crowns were made with dentin analogue material (G10 epoxy resin). One of the preparations was scanned and a monolithic crown in lithiumdisilicate was planned in the CAD system. Fifty crowns were milled in a wax pattern and subjected to pressing (IPS e.max Press), while 50 crowns were machined at CAD/CAM (IPS e.max CAD) and posteriorly crystallized. Internal and marginal adaptation were assessed via replica technique at four manufacturing moments (Milled wax pattern; LD^PRESS; Milled LD^CAD; Crystallized LD^CAD) and considering 5 regions (margin, cervico-axial angle, axial wall, axial-occlusal angle and occlusal wall). Complementary analysis considering microstructure and topography, roughness and fractal dimension were performed in Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).

Results: The processing technique resulted in different ceramic microstructure, topography, roughness and fractal dimension, whereas CAD/CAM lead to smoother, more homogeneous but more complex topography features (higher fractal dimension) in comparison to the pressing technique (P < 0.05). Regarding marginal and internal fit, LD^PRESS crowns showed to be more adapted at the margin, while LD^CAD were more adapted at the occluso-axial angle; other regions were not statistically different (α = 0.05).

Conclusions: CAD/CAM and the pressing techniques for manufacturing LD crowns lead to completely different ceramic surface characteristics and affect crown adaptation at the margin and at occluso-axial angle.

Purpose: This randomised cross-over trial aimed to comparatively investigate patient preference and satisfaction with thermoplastic resin removable partial dentures (TR-RPDs) and conventional metal clasp-retained removable partial dentures (MC-RPDs).

Methods: Twenty-eight partially dentate subjects were enrolled and randomised to receive MC-RPDs followed by TR-RPDs or vice versa (n = 14, each group). The subjects were asked to score overall satisfaction and denture-related parameters 3 months after delivery of each denture. Additionally, they were asked to choose their preferred denture type at the end of the trial.

Results: Of the 28 subjects, 24 (86%; mean age, 67.3 years) completed the trial. The overall satisfaction scores and ratings for oral appearance with TR-RPDs were significantly higher than those with MC-RPDs (P < 0.05). Moreover, 75% (18/24) and 83% (20/24) of the subjects reported greater overall satisfaction and better oral appearance with TR-RPDs than with MC-RPDs (P < 0.001, both). Scores for mucosal pain and food impaction were significantly better with TR-RPDs than with MC-RPDs (P < 0.05). Relative to MC-RPDs, TR-RPDs provided slightly better oral comfort and speech, although the differences were not statistically significant (P > 0.05). Scores for chewing ability, denture stability, and ease of denture cleaning were almost identical for both types of dentures.

Conclusions: These results suggest that TR-RPDs hold an advantage over MC-RPDs in terms of oral appearance and can offer greater satisfaction than MC-RPDs in partially dentate arches with at least an occluding pair in the posterior region.

Clinical trial registration: UMIN Clinical Trials Registry (UMIN000007310).

Purpose: Comparison of outcomes of maxillary implant overdentures retained by use of either locator attachments or bars in a 1-year randomized controlled trial.

Methods: Fifty edentulous participants received four maxillary implants. They were allocated to two groups (n = 25) differing in type of prosthetic attachment used to retain the maxillary prosthesis: either locator attachments or bars were applied. After one year, implant and overdenture survival was assessed. Peri-implant hygiene (Plaque-index, presence of calculus), soft tissue conditions (Gingiva-index, Sulcus Bleeding-index and pocket probing depth) and patient satisfaction (oral health impact profile (OHIP-49), denture complaints questionnaire and general satisfaction score (GSS) ) were compared. The peri-implant bone level was estimated using intra-oral radiographs (student T-test).

Results: Implant survival was 96.7% in the locator group and 97.9% in the bar group. No overdentures had to be remade. Patient satisfaction was significantly greater in the bar group when rated by OHIP-49 sum score and by GSS. When comparing the denture complaints questionnaire and the separate OHIP-49 item scores, no significant difference was found. There was not a significant difference in hygiene and soft tissue conditions. Marginal bone loss was estimated 0.58 ± 0.71 mm for locators and 0.31 ± 0.47 mm for bars.

Conclusions: Maxillary overdentures on four implants retained by bars or locators were compared. Bone loss was within an acceptable range for both groups after 1 year. However, less bone was lost in the bar group. Even though both treatment options improved patient satisfaction, bars seem to be particularly beneficial with regard to OHIP-49 sum score.

Purpose: To reveal the impact of titanium dioxide-based scanning powder for intraoral digital impression on the biological activity of oral fibroblasts.

Methods: Murine L929 cells and human periodontal ligament (PDLF) and gingival fibroblasts (GF) were treated with ten-fold serial dilutions of scanning powder and the corresponding conditioned medium (filtrate of overnight incubation of powder in medium) starting with 30 mg/ml. Bicinchoninic acid protein assay, formazan- and resazurin-based toxicity assays, live/dead and annexin V/propidium iodide (PI) staining and immunoassays for interleukin (IL) -6 and IL-8 were performed. Powder composition was analyzed using energy dispersive X-ray spectroscopy (EDS).

Results: Formazan and resazurin conversion was lesser in L929 cells than PDLF and GF in the presence of scanning powder. Induction of cell death was caused by 30 mg/ml of powder in L929 cells but not in PDLF and GF. No pronounced impact of the conditioned medium was seen in cytotoxicity assays or live/dead-, and annexin V/PI staining. In PDLF and GF IL-6 expression was increased by the powder, while there was a decrease in IL-8. Powder particles did not deplete protein from medium. EDS showed a heterogeneous mixture consisting predominantly of titanium dioxide.

Conclusions: Scanning powder decreased cell activity and induced cell death in L929 cells at high concentrations. Human oral fibroblasts showed an increase in IL-6 levels but more resistance to the cytotoxicity of the powder. Within the limitations of an in vitro study our results suggest that proper cleaning after scanning is of clinical relevance to avoid potential unwanted effects of the powder.

Purpose: Rhythmic masticatory muscle activity (RMMA), a biomarker of sleep bruxism (SB), has been associated with mild hypoxia and/or big breaths in some adults with non-sleep-disordered breathing. The purpose of this study was to investigate that concurrent oxygen and carbon dioxide fluctuations are among the physiological variables that contribute to RMMA onset.

Methods: Twelve subjects (5 female, 7 male, mean age: 43 ± 11) underwent polysomnography recording in a sleep laboratory. RMMA index and apnea-hypopnea index were calculated. Oxygen saturation (SpO₂) was estimated by finger pulse oximeter and end-tidal CO₂ (ETCO₂) by nasal airflow cannula before and after RMMA onset. Given the expected response time delay between actual arterial hypoxemia and fingertip pulse detection, we adjusted the SpO₂ desaturation onset to the onset of masseter muscle activity using a 17 s criterion based on ETCO₂ shifts.

Results: SpO₂ was slightly but significantly lower than at baseline (max: -0.6%) in the 6–4 s before RMMA onset and significantly higher in the 6–18 s after onset (0.9%; p < 0.05). Although ETCO₂ before RMMA onset did not differ from baseline, it decreased at 8–10 s after onset (-1.7 mmHg: p < 0.05). No changes in SpO₂ or ETCO₂ in relation to RMMA onset reached a critical clinical threshold.

Conclusions: The mild transient hypoxia observed before RMMA onset was not associated with a change in ETCO₂. The mild and brief oxygen fluctuations before RMMA onset may reflect a physiological response that seems to have little influence on SB genesis.

Purpose: Masticatory performance can be measured through elution of glucose or beta-carotene from comminuted gummy jelly. However, these methods require special devices. Additionally, occasional/unintentional swallowing or inadequate collection of comminuted particles of gummy jelly in the oral cavity may cause measurement errors. Therefore, we devised a new photographic method to estimate the increase in surface area and weight of comminuted gummy jelly. This study aimed to verify the accuracy of this method.

Methods: Initially, fifty images depicting the comminuted pieces in a special box were prepared. Then, the increase in surface area was measured using a fully-automated method, and the weight was measured. The size and angle of each image were adjusted based on markers located at the four corners of the box. From these photographic images, the area, perimeter, color average, color deviation, side area, and amount of surface roughness for each particle was calculated, and multiple regression analysis was performed to estimate the surface area and weight. The relationship between the estimated values and the values measured with the fully-automated device and by weight were analyzed.

Results: The intra-class correlation coefficient between the estimated value and the value from the fully-automated method was r = 0.956. This high correlation was also obtained under different photographic conditions. Furthermore, for determining whether 80% or less gummy jelly was collected, the sensitivity was 100% and the specificity was 91%.

Conclusions: The newly developed photographic method is valuable because it is accessible and may assist in achieving reliable evaluation of masticatory performance.

Purpose: The presented technique describes the intraoral scanning workflow to capture scans of edentulous arches and occlusion rims, align them as per maxillo-mandibular relationships registered in the occlusion rims, and incorporate data for tooth arrangement.

Methods: On preliminary intraoral scans of the edentulous arches, design the baseplates for the occlusion rims, make a 3D print of them and finalize by adding wax. Use occlusion rims to make jaw relation record and definitive intraoral scans. Use the "Pre-preparation scan" function to link scans of occlusion rims to scans of edentulous arches and align each other.

Conclusions: Making and aligning, in a single procedure, intraoral scans of the edentulous arches and occlusion rims incorporating maxillo-mandibular relationships and information for tooth arrangement, allow to proceed directly with the denture design, thus, being sensible from the treatment time efficiency point of view. The technique is applicable to both partial and complete edentulous maxillary and mandibular arches. Nonetheless, care should be taken in stabilizing occlusion rims, whose shape is characterized by a reduction in size of the baseplates. In addition, its accuracy in comparison with the current clinical best practice based on conventional procedure requires to be addressed by further research.

Purpose: To compare the effects of airborne-particle abrasion protocols on the surface morphology, the phase transformation and the resin bond strength of highly translucent zirconia (M) and conventional zirconia (Z).

Methods: Thirteen groups (N = 12) of Z and M specimens were prepared. Except for the control group, the specimens were sandblasted with conditions involving different grit sizes (50 μm or 110 μm), treatment times (10 s or 20 s) and pressures (0.1 MPa, 0.3 MPa or 0.6 MPa). The surface morphology was analyzed using scanning electron microscope (SEM) and the phase analysis was conducted with X-ray diffraction (XRD). The Ra and the shear bond strength (SBS) were measured and statistically analyzed, and the failure mode was determined by optical microscope.

Results: The surface morphologies were strongly dependent on treatment conditions. Larger particle size and higher pressure resulted in higher Ra for bothmaterials. Longer blasting time resulted in higher Ra for Z but not M. Overall, the SBS increased with increasing Ra; the highest average SBS was achieved by M and exceeded 18 MPa. The monoclinic transformation was not found in any treatment for M, but was found in Z.

Conclusions: Z and M showed different dependence on the airborne-particle abrasion parameters in terms of Ra, SBS and phase transformation. The conditions for maximizing SBS included a 110 μm particle size and 20 s treatment for both, with pressures of 0.3 MPa and 0.6 MPa for the M and Z, respectively.

Purpose: The aim of this study was to evaluate the biaxial flexural strength and translucent characteristics of dental lithium disilicate glass ceramics with different translucencies.

Methods: Two heat pressed lithium disilicate glass ceramics (IPS e.max Press and an experimental ceramic) and one computer aided design/ computer aided manufacture (CAD/CAM) lithium disilicate glass ceramic (IPS e.max CAD) with different translucencies were evaluated. Disk-shaped specimens of each group were subjected to a biaxial flexural strength (BFS) test. Translucent parameters (TP) were also tested at 0.5 mm and 1.0 mm thickness, respectively. X-ray diffraction (XRD) and SEM were used for crystalline and microstructural analysis.

Results: BFS values of two heat pressed lithium disilicate glass ceramics were significantly higher than the CAD/CAM counterpart. No difference in BFS between two heat pressed glass ceramic was found. There were significant differences in BFS and TP values among the tested subgroups with different translucencies for IPS e.max Press and IPS e.max CAD. No difference in crystalline composition was found among the tested glass ceramics, but microstructure with shorter and wider crystal was revealed for IPS e.max CAD ceramics.

Conclusions: Lithium disilicate glass ceramics with different translucencies demonstrated different BFS and TP values.

Purpose: We investigated the effects of denture adhesives (cream (Cr), powder (Po), and cushion (Cu) ) on growth and adhesive-related morphological transformation of Candida albicans. For this purpose, the numbers of adherent C. albicans, hyphae-specific gene expressions, and the SEM images were examined.

Methods: Acrylic resin blocks were prepared as controls (Co). Cr, Po, and Cu were thinly spread on the surface of the resin block.C. albicans suspension was seeded on the specimens and incubated at 4°C for 2 h. The numbers of C. albicans adhering to each specimen at each incubation time period (1, 2, 3, 6, 12, and 24 h) were quantified using real-time RT-PCR. The hyphae-specific genes expressions were examined. The surface of each specimen was observed under the SEM to detect the transformation to the hyphal form.

Results: The initial adhesion rates in all groups were not statistically significant. The numbers of C. albicans adhering increased with time in all groups, and those adhering to the Cr, Po, and Cu were significantly greater than that adhering to the Co. In the Cr and Po, the hyphal-specific genes expressions were higher after incubation for 6 h. The transformation to the hyphal form was identified in the Cr and Po after incubation for 6 and 12 h.

Conclusions: The denture adhesives used in this study accelerated the growth of C. albicans. Moreover, the early transformation to the hyphal form on the Cr- and Po-type adhesives was observed, suggesting that we should carefully use Cr- and Po-type adhesives.

Purpose: To investigate occlusal wear of resin denture teeth in partial removable dental prostheses worn by partially edentulous patients.

Methods: Thirty patients with partial removable dental prostheses were included in the study. Thirty-two patients with complete dentures served as a reference group. Occlusal wear after two years was evaluated indirectly using gypsum casts and a three-dimensional laser-scanner device. Overall wear of complete occlusal surfaces and maximum wear of occlusal contact areas were measured. Patient and prosthesis data were analyzed using univariate and multiple linear mixed models.

Results: Overall wear of denture teeth in partial removable dental prostheses was 91 (SD 85) μm, and maximum wear of occlusal contact areas was 329 (SD 204) μm (means and standard deviations). Average and maximum wear values for teeth in complete dentures were both lower than those for teeth in partial removable dental prostheses. However, differences between wear of different types of denture did not reach statistical significance after adjustment for gender, type of tooth, dental status of the opposing jaw, and antagonist material. Statistical analysis revealed that wear was greater for denture teeth occluding with ceramic crowns and/or fixed partial dentures as antagonists.

Conclusions: Resin denture teeth in partial removable and complete dental prostheses are subjected to clinically important occlusal wear that might destabilize occlusion and cause further problems. Patientrelated factors and dental status affect wear behavior and should be taken into consideration when treating patients with removable dentures.

Purpose: The purpose of this study was to clarify the validity of assessment of sleep bruxism (SB) by using single-channel electromyogram (EMG) and a cut-off value with optimum sensitivity and specificity.

Methods: The subjects were twenty volunteers with clinical diagnosis of SB. Assessment by masseteric EMG data only by using a wearable EMG was compared with reference standard assessment by masseteric EMG data using polysomnography with audio-visual recording (PSG-AV). From EMG activities recorded by single-channel EMG, bursts of more than two times the baseline amplitude with a duration of 0.25 s or more were selected by a burst unit (EMG-burst-all). Furthermore, from EMG-burst-all, bursts that were more than 5–20% of the maximum voluntary contraction value (EMG-burst-5%, EMG-burst- 10%, EMG-burst-20%) were selected. By an episode unit, phasic, tonic, and mixed episodes were selected by single-channel EMG (EMG-episodes). Among the EMG-episodes, further, reference standard episodes of SB (PSG-episodes) were selected by PSG-AV assessment.

Results: Sixteen subjects were diagnosed as bruxers based on PSG-AV (PSG-episodes/h >2). By a burst unit and an episode unit, there were significant correlations between assessment variables of SB by singlechannel EMG and PSG-AV except for EMG-burst-20%/h. When the cut-off value in EMG-episodes/h was 5.5/h for sleep bruxers, both sensitivity and specificity were 100%. As for variables by a burst unit, EMG-burst-all/h and EMG-burst-5% had higher values of sensitivity and specificity.

Conclusions: The results suggested that single-channel EMG is valid for diagnosis of SB if a cut-off value that is appropriate for single-channel EMG is used.

Purpose: This technical procedure report introduces a newly developed method for removable partial denture (RPD) fabrication using computer-aided design and computer-aided manufacturing (CAD/CAM) and rapid prototyping (RP) technologies.

Methods: Full-arch digital impressions of the partially edentulous jaw were made by an IOS or the conventional method. The denture framework, artificial teeth, and denture base were designed by commercially available CAD software. Each of the denture components including connectors, clasps, and artificial teeth and the denture bases were fabricated separately by the CAM machine or the three- dimensional (3D) printer, and then assembled using an adhesive material.

Conclusions: RPDs were successfully fabricated using fully digital workflow and delivered to the patient, and no clinical complications were reported. Within the limitations of this report, the newly developed RPD fabrication techniques have the potential to change clinical and laboratory workflow from analog to digital.

Patients: This case report presents a novel method to remove glass fiber-reinforced composite root posts in a minimally invasive way while simultaneously shaping the canal for a new post-endodontic restoration. A multi-morbid, handicapped 62-year-old patient was referred with a horizontally fractured maxillary incisor presenting approximately 1 mm residual coronal tooth height. Endodontic revision was necessary, which required removal of a glass fiber-reinforced composite post. A cone-beam computed tomography (CBCT) scan was imported into conventional implant-planning software and matched to a stone cast of the intraoral situation. Position, length, and axis of the future post were planned virtually. Based on this planning, a tooth-supported splint was three-dimensionally (3D) printed. This splint allowed use of a 2.2-mm spiral drill for removal of the fractured post and shaping of the root canal for a new cast post-and-core. This metal post-and-core was adhesively cemented and prepared for a zirconia single crown veneered in the labial aspect.

Discussion: This method currently requires use of CBCT-based, ionizing 3D imaging. Additional refinements to this approach can be made regarding spiral drill design and coating as well as regarding the post-and-core workflow.

Conclusions: 3D-guided post-endodontic management is feasible. More research is needed to balance higher radiation doses against therapeutic success.