Purpose: The aim of this systematic review and meta-analysis was to evaluate the microbial colonization at the implant-abutment interfaces (IAI) on bone-level implants and to identify possible association with peri-implant conditions.

Study selection: The focus question aimed to answer whether two-piece osseointegrated implants, in function for at least 1 year, in human, relate to higher bacterial count and the onset of periimplantitis, compared to healthy peri-implant conditions. Search strategy encompassed the on-line (MedLine, Google scholar, Cochrane library) literature from 1990 up to March 2015 published in English using combinations of MeSH (Medical Subject Headings) and search terms. Quality assessment of selected full-text articles was performed according to the ARRIVE and CONSORT statement guidelines. For data analysis, the total bacterial count of Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Prevotella intermedia, and Fusobacterium nucleatum was calculated and compared to IAI with or without peri-implant pathology.

Results: A total of 14 articles, reporting data from 1126 implants, fulfilled the inclusion criteria and subjected to quality assessment. The selected studies revealed contamination of the IAI, in patients who received two-piece implant systems. Meta-analysis indicated significant difference in total bacterial count between implants affected by periimplantitis versus healthy peri-implant tissues (0.387±0.055; 95% CI 0.279–0.496). Less bacterial counts were identified in the healthy IAI for all the investigated gram-negative bacteria except for T. forsythia.

Purpose: Sleep bruxism (SB) is classified as a sleep-related movement disorder characterized by grinding and clenching of the teeth during sleep, which is responsible for a variety of clinical problems such as abnormal tooth attrition and fracture of teeth or roots. Little is known about the etiology of SB. Our previous study identified a genomic association of the serotonin 2A receptor (5-HT2A) single nucleotide polymorphism (SNP), rs6313 C>T, with SB, where the C allele carrier is associated with a 4.25-fold increased risk of SB. Based on this finding, the aim of this study was to generate of neural cells using SB patient-specific induced pluripotent stem cells (iPSCs).

Methods: Two SB patients with C/C genotype of rs6313 and two controls with T/T genotype were screened by laboratory-based polysomnographic recordings and the TaqMan genotyping assay. Four lines of iPSCs, two from SB patients and two from controls, were established from peripheral blood mononuclear cells by introduction of reprogramming factors. We performed quality control assays on iPSCs using expression of markers for undifferentiated pluripotent cells, immunostaining for pluripotency markers, a three-germ layer assay, and karyotype analysis. The established iPSCs were differentiated into neurons using the neurosphere culture system. 5-HT2A gene expression in these neurons was evaluated by quantitative real-time PCR.

Results: Patient-specific iPSCs were successfully differentiated into neurons expressing 5-HT2A.

Purpose: Phytic acid (IP6) works well as an etchant in dentin bonding to remove the smear layer due to its acidity and chelating effect. This study compared the etching effect of IP6 with phosphoric acid (PA) and ethylenediaminetetraacetic acid (EDTA) on resin–dentin bond strength, micromorphology of the etched dentin surface and nanoleakage formation along resin–dentin interfaces and compared the protecting effect against collagen degradation.

Methods: Dentin disks and flat dentin surfaces were obtained from extracted human teeth. Specimens were etched with 35% PA (15s), 0.5M EDTA (30s) or 1% IP6 (30s). The surfaces and longitudinal sections of the etched dentin disks were observed using field emission scanning electron microscope (FE-SEM). An etch-and-rinse adhesive was used to create composite build up-specimens for microtensile bond strength (mTBS) testing and nanoleakage observation. To evaluate the effect on collagen degradation, demineralized bovine root dentin blocks were challenged with bacterial collagenase and then observed under light microscope.

Results: PA- and EDTA- treated groups showed significantly lower mTBS when compared to IP6-treated group. PA showed distinct nanoleakage and severe collagen degradation. Only slight nanoleakage was detected in IP6 group. IP6 showed better effect than EDTA in preventing collagen degradation induced by bacterial collagenase.

Conclusions: IP6 effectively removed the smear layer and etched dentin, providing high bond strength values and causing minimal nanoleakage and slight collagen degradation.

Purpose: There are no studies on the prevention of temporomandibular joint and/or masticatory muscle pain (TMD pain) associated with oral appliance (OA) therapy in patients with obstructive sleep apnea (OSA). The aim of this study was to determine the effect of jawopening exercise on TMD pain associated with OA therapy in OSA patients.

Methods: Twenty-five OSA patients without pain-related TMD were consecutively enrolled into a two-arm, randomized, double-blind, placebo-controlled trial. One group performed jaw-opening exercise (JE, n=13), and the other group performed placebo exercise (PE, n=12) for 1-month, and had started 2-weeks prior to insertion of an adjustable OA. TMD sign using the Research Diagnostic Criteria for Temporomandibular Disorders and TMD pain intensity using a visual analog scale (VAS) in the morning and daytime were evaluated at baseline (preexercise) and at 2-weeks, 1-month, and 3-months after OA insertion.

Results: Pain-related TMD was not observed in the JE-group at all evaluation periods, although one subject in the PE-group was diagnosed with arthralgia at the 1-month evaluation. The JEgroup showed lower morning and daytime VAS scores than the those of the PE-group at all evaluation periods, and significant group differences were found in terms of chewing pain and jaw-opening pain in the morning at the 1-month evaluation, and of jaw-opening pain during daytime at the 3-month evaluation (P<0.05).

Conclusions: Within the limitations of the study, jaw-opening exercise prior to OA therapy reduced the risk of TMD pain associated with OA use. Therefore, jaw-opening exercise may contribute to the prevention of TMD pain.

Purpose: The present study compared the clinical prognosis of double crown-retained removable dental prostheses (D-DRPs) with that of clasp-retained removable dental prostheses (C-RDPs).

Methods: Clinical records of 201 patients who had received 52 D-RDPs with 144 abutment teeth (D-teeth) and 199 C-RDPs with 399 abutment teeth (C-teeth) at the Prosthetic Dentistry Clinic in Hokkaido University Hospital between April 2005 and June 2015 were analyzed. Survival and complication probabilities of the two types of prostheses and abutment teeth were evaluated using the Kaplan–Meier method and compared using the log-rank test. Cox regression analysis was used to determine the impact of covariates on abutment teeth survival and complications such as gender, age, type of retainer, Eichner classification, jaw, type of tooth, endodontic therapy performed, type of edentulous space, and presence of opposing teeth.

Results: Statistical analysis showed no significant differences between the two types of prostheses in terms of prostheses survival, prostheses complication, and abutment teeth survival. However, a significant difference was observed for complications of abutment teeth. Decementation was the most frequent cause of failure, which occurred in 76.9% of Dteeth and 28.3% of C-teeth. Patient's age, jaw, endodontic therapy performed, and type of edentulous space affected the survival of abutment teeth, whereas the type of retainer and edentulous space affected complications of abutment teeth.

Conclusion: The prognosis of both types of prostheses was considered to be acceptable. Although D-RDP had lower complication-free rates for abutment teeth, most of the observed complications were decementation, which was considered to be reparable.

Purpose: A single machine platform that integrates repeated laser sintering and high-speed milling for one-process molding has been developed.

Methods: The Akers clasp was designed using the CAD system (DWOS Partial Frameworks, Dental Wings) and fabricated using repeated laser sintering and a high-speed milling machine (LUMEX Advance-25, Matsuura) with 50-μm Co–Cr particles (CAM clasp). As controls, cast clasps of the same forms were also prepared using conventional casting methods with a Co–Cr alloy and CP titanium Grade 3. After the surface roughness was measured, the gap distance between the clasps and the tooth die was assessed using the silicone film method. The initial retentive force and changes in retention up to 10,000 cycles were also measured. The data were analyzed using two-way ANOVA and Tukey's multiple comparison test (α=0.05).

Results: CAM clasps exhibited significantly smoother surfaces than those of cast Co–Cr and CP Ti clasps (p<0.05). However, the gap distances of the CAM clasps were significantly greater than those of the cast clasps (p<0.05). The retentive forces of both CAM and cast Co–Cr clasps were significantly higher than those of CP Ti clasps. (p<0.05). The retention of CAM clasps demonstrated a constant or slight decrease from 1000 up to 10,000 cycles.

Conclusions: The CAM clasp made by repeated laser sintering and high-speed milling can be used effectively as an RPD component.

Purpose: Due to the bite force importance in functionality of the masticatory system, this study aimed to characterize it in dolichofacial and brachyfacial individuals.

Methods: A sample comprised by 190 patients was divided into two groups: 90 severe dolichofacial, and 100 severe brachyfacial individuals classified according to the VERT index and the face height ratio (Jarabak quotient). Bite force was measured by using an adjusted digital dynamometer and proper methodology.

Results: The sample met the parametric assumptions and presented statistical significance when right and left sides of dolichofacial and brachyfacial individuals were compared. However, within the same group, no differences between the left and right sides were found. Generally, bite force was higher for male, left masticator, age between 41–50 years, weighing over 100kg and between 1.81 and 1.90m tall.

Conclusions: Based on the results of this cross-sectional study, it was possible to conclude that the bite force in severe brachyfacial individuals was significantly higher than in severe dolichofacial individuals, being influenced by gender, weight and height.

Purpose: This study aimed at developing the Arabic version of the Orofacial Esthetic Scale (OES-Ar) and to investigate its psychometric properties among Arabic-speaking population with and without esthetic impairments.

Methods: Translation and cross-cultural adaptation was done according to the standard guidelines. Internal consistency was assessed on 230 participants. For test-retest reliability, 50 subjects with natural teeth were recalled within a period of 2 weeks. Validity of the OES-Ar was tested by construct, convergent, and discriminant validity tests. Responsiveness to esthetic changes was assessed in 60 patients.

Results: The results showed excellent internal consistency with Cronbach's alpha value of 0.92 and inter-item correlation average value of 0.60. The ICC values ranged from 0.87 to 0.96 which indicated excellent agreement. Construct validity of the OES-Ar was confirmed to be one-factor structure (one-dimensional). For convergent validity, a significant correlation was found between OES summary score and overall impression of the orofacial esthetic as well as between OES summary score and the summary score of the three questions of the OHIP-49Ar related to esthetic. The discriminant validity test revealed significant differences between different study groups (P<0.001). Responsiveness to treatment was confirmed by significant differences between pre- and post-treatment OES total summary score (P<0.001).

Conclusion: The OES-Ar has excellent psychometric properties making it valuable instrument to assess orofacial esthetics in Arabic-speaking patients.

Purpose: The aim of this study is to investigate the effects of different electrolytes on the titanium–porcelain bond strength after micro-arc oxidation (MAO) treatment.

Methods: Three electrolytes at the same concentration were used as MAO reaction solutions: Na₂SiO₃, KF, and MgSiF₆. Blasting treatment was chosen as a control. After MAO treatment in each electrolyte, the titanium–porcelain bond strengths were measured by the three-point bending test, as described in ISO 9693. The morphologies and elemental compositions of the MAO coating on the titanium substrate were evaluated by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The interface between the titanium and porcelain was also observed by SEM and EDS.

Results: The MAO coatings created in different electrolytes exhibited completely different morphologies and compositions. The bond strengths of the Na₂SiO₃ and MgSiF₆ groups were significantly higher than those of the other groups (p<0.05). Additionally, the titanium– porcelain interfaces were compact in the former two groups, whereas pores and cracks were visible at the interfaces in the other groups.

Conclusions: These results indicate that MAO treatment with an appropriate electrolyte could be an effective method to increase the titanium–porcelain bonding strength. According to ISO 9693, titanium–porcelain restorations subjected to MAO treatment with an appropriate electrolyte could be appropriate for clinical use.

Purpose: The purpose of this study was to determine if the optical properties of zirconia and glass–ceramic (e.max) were affected by low-temperature degradation (aging).

Methods: Experiment samples were fabricated with seven zirconia brands (n=10): Zenostar, Zirlux, Katana, Bruxzir, DD-BioZX², DD-cubeX², NexxZr; and e.max were used as a control. This resulted in a total of 80 samples in the experiment. The L*, a* and b* were measured for each sample, and then the optical properties including translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP) were calculated. The samples were aged (20, 40, 60, 80, 100h), and the optical properties were calculated after each interval.

Results: Most zirconia brands had lower L*, higher a*, higher b* with increased aging, which visually corresponds to darker, redder, and more yellow. Aging also increased CR, lowered TP, and lowered OP. e.max was also affected by aging but still had the highest TP (23.9±2.8), L* (81.7±3.4), and lowest CR (0.41±0.05) compared to any zirconia. The Zenostar had the closest TP (24.1±0.4), and L* (90.2±0.5) values to e.max before aging. However, after 100h of aging, the DD-cubeX² was least effected and had the highest TP (22.2±0.6) and lowest CR (0.43±0.01) compared with other zirconia samples and highest OP (11.3±0.2) of all ceramic samples.

Conclusions: The optical properties of zirconia and e.max materials were affected by aging with the effects increasing with time. The magnitude of change was affected by seven brands of dental zirconia.

Purpose: This cross-sectional study analyzes how bone resorption affects the masticatory function and investigates the relation between perceived and measured masticatory function.

Methods: Thirty complete dentures wearers were divided in two groups according to mandible bone atrophy based on the classification criteria from Cawood & Howell. Retention and stability of the mandibular complete denture, masticatory performance (MP) indexes (X_50 and B) and masticatory efficiency (ME, sieves 4 and 2.8) were evaluated. Geriatric Oral Health Assessment Index (GOHAI) and Dental Impact on Daily Living (DIDL) questionnaires were completed by the patients.

Results: A strong correlation between bone atrophy and poor retention was found (P=0.0132). Neither masticatory performance indexes nor GOHAI and DIDL domains showed statistical differences (P>0.05) when patients were compared according to the atrophy criteria. Mandibular length showed a negative correlation with ME4, showing a positive association (R²=0.17, β=-0.67, P=0.029). Mandibular denture retention was significantly correlated with MPB (P=0.01) and ME2.8 (P=0.01). GOHAI showed a positive association between the physical and the functional domains and ME2.8 (R²=0.17; b=1.22; P=0.02). DIDL showed a negative association between ME4 and oral comfort domain (R²=0.16; β=-2.94; P=0.02).

Conclusion: Mandibular bone height does not directly affect the masticatory function and is inversely correlated with the self-perceived masticatory ability.

Purpose: The purpose of this study was to investigate the influences of bone quality and implant size on the maximum equivalent elastic strain (MES) in peri-implant bone using finite element (FE) analysis, and to minimize implant size via optimized calculation based on MES.

Methods: Three-dimensional FE models consisting of a mandible and a titanium implant with a superstructure were constructed and applied a vertical load or an oblique load of 60N. We investigated the effects of four variables: the thickness of the cortical bone (C), Young's modulus of the trabecular bone (T), and the diameter (D) and length (L) of the implant. According to the variables determined using Latin hypercube sampling, 500 FE models were constructed and analyzed under each of the loads following the construction of response surfaces with the MES as a response value. D and L were minimized by optimized calculation with the MES limited to the physiological limit with reference to the mechanostat theory.

Results: The MES was significantly influenced by D more than L, and could be restricted to the physiological limit unless both C and T were small. Larger MES than physiological limit was observed around the bottom of implants.

Conclusions: From the viewpoint of the mechanostat theory, we calculated minimum size of implants according to the bone quality. However, the results should be verified with more detailed FE models made using CT data, animal studies and clinical prognoses.

Purpose: This report presents our evaluation system that assesses sleep bruxism. The characteristics and fabrication process of our novel designed splint, and the analysis process of our system are presented.

Methods: The subjects were 17 volunteers. The splint was fabricated with a self-curing resin compounded with an amino-acid powder for easy wear on the semi-adjustable articulator, and adjusted for a full-balanced occlusion. An impression of the splint, located on the cast, was taken before and after it was worn. The analytical casts were made and scanned via a dental 3D scanner. The datasets were superimposed using two kinds of regions of interest (palate and occlusal surface). The differences between the two datasets were quantitatively presented with pseudo-color mapping. The maximum differences in coronal and apical directions were calculated on the selected area in the occlusal surface when the occlusal surface was used as a region of interest for registration. The relationship between the EMG activities and the change of occlusal surface of the splint were investigated.

Results: In all subjects, deformation and wear facets on the splint were observed. The differences in the apical direction, which indicate wear depth, were correlated with the maximum muscle activity during sleep (p=0.036).

Conclusion: From our results, it is suggested that we are not able to eliminate the influence of parafunction for the prosthesis only by designing the surface of occlusal splint using the semi-adjustable articulator. Our splint may have the potential to detect specific facets due to parafunctions as nocturnal bruxism.

Purpose: To compare the failure behaviour of zirconia-reinforced lithium silicate (Celtra Duo, DeguDent) with that of lithium disilicate (IPS e.max CAD, Ivoclar Vivadent) and feldspar (Mark II, VITA) ceramics.

Methods: Three groups of sixteen glazed maxillary incisor crowns were produced. The inner surfaces of the crowns were etched, then luted to metal dies with self-adhesive cement. Single load-to-failure tests were performed before and after thermo-mechanical ageing. To simulate clinical conditions, the specimens were thermocycled (10,000 cycles between 6.5°C and 60°C) and underwent chewing simulation (1,200,000 cycles, F_max=86N). Statistical analyses were performed by use of non-parametric Kruskal–Wallis and Mann–Whitney U-tests.

Results: Before ageing, all the monolithic incisor crowns fractured at test forces >285N. Mean fracture loads were highest for zirconia-reinforced lithium silicate (725N, SD 162N), slightly lower for lithium disilicate (701N, SD 276N), and lowest for feldspar (554N, SD 190N). The differences between the results were not statistically significant. After ageing, fracture resistance decreased for all materials except zirconia-reinforced lithium silicate. Mean fracture loads were highest for zirconia-reinforced lithium silicate (766N, SD 98N) and significantly lower for both lithium disilicate (485N, SD 64N) and feldspar (372N, SD 116N).

Conclusion: Monolithic restorations fabricated from zirconia-reinforced lithium silicate retain high fracture resistance after extensive thermo-mechanical ageing. This preclinical study suggests that cohesive failures of monolithic anterior crowns produced of these ceramics will not be a major problem in dental practice.