Purpose: The present review aimed to investigate autoclave sterilization of dental handpieces based on available studies.

Study selection: The sterilizing efficiency of dental handpieces with autoclave is mainly affected by the types of apparatus (N, B, and S), the packaging with sterilizing pouch, cleaning, and lubrication. These subjects were reviewed based on the in vitro experimental studies.

Results: Dental handpieces can be sterilized, including inactivation of heat-resistant bacterial spores, with type B or type S sterilizers, regardless of the use of a sterilization pouch. In contrast, although type N autoclaves are capable of sterilization of general bacteria such as Streptococcus salivarius even in a sterilization pouch if instruments are washed beforehand, complete sterilization of the wrapped handpiece is not always achieved. Therefore, to achieve sterilization efficiency with type N autoclaves, processing without any packaging is recommended. As regards cleaning of handpiece, although contamination decreases with irrigation and wiping of handpieces, all reports concluded that these treatments alone do not achieve complete decontamination of reusable handpieces.

Conclusion: Although type B and type S autoclaves allow us to sterilize the dental handpieces, it is important to realize that complete sterilization of the handpiece is not always achieved by type N autoclave. Understanding autoclave processing of handpieces is essential for dental practice to deliver the safe dental care.

Purpose: Masticatory changes in the older adult population may cause nutritional impairment, so epidemiological studies are important to allow specific public health interventions. Thus, this study aims at constructing and validating an instrument for screening for masticatory disorders in older adults (SMDOA).

Methods: Validation study. First step: validity evidence based on test content. Defining the construct and elaborating the questions by a panel of experts and evaluating the representativeness and relevance of the items in relation to the construct by a committee of 28 experts. Analysis was performed through the Content Validity Index for Items (CVI-I) and the Content Validity Index (CVI). Second stage: validity evidence based on response processes. The questionnaire was applied to 40 older adults (≥60 years) using the cognitive interview strategy. Quantitative and qualitative analysis of the responses was carried out. Third stage: validity evidence based on the internal structure. The instrument was applied to 295 older adult patients and a confirmatory factorial analysis was performed to fit the model.

Results: The first version of SMDOA consisted of 16 issues related to chewing. The CVI and CVI-I were satisfactory, and only one question was excluded. The instrument with 15 questions was well evaluated by the older adults, only requiring minor adjustments to the morphosyntax. After the confirmatory factorial analysis, adjustments were made in its internal structure resulting in the 9-question model in two factors regarding function and masticatory perception.

Conclusions: The SMDOA presented good evidence of validity in its content, response processes and internal structure.

Purpose: Polyetheretherketone (PEEK), a high-strength, aesthetic, and non-allergic thermoplastic polymer, recently became a candidate for replacing metallic components in dental prosthesis. However, as PEEK is flexible, the need for retention presents a key challenge in terms of its clinical application. In this study, clasps prepared using PEEK were optimized and evaluated to provide the mechanical properties required by dentures.

Methods: Seventy-two three-dimensional rod-shape models, based on four thickness/width ratios, three base widths, and six taper ratios were created. These models were analyzed using finite-element methods to determine which modified clasp arm shape provided the most appropriate mechanical properties. Three shape-optimized PEEK specimens and one standard-shape Co-Cr alloy specimen were then fabricated. Constant-displacement fatigue testing was performed to calculate load values and deformations after ten years of clinical use.

Results: Shape optimization indicated a maximum stress concentration that was consistently located at the base of the specimen, a correlation between mean load values and thickness that was greater than that with the width, and a correlation between taper ratio and mean load values. Fatigue testing showed that although PEEK exhibited significantly lower average load values than the Co-Cr alloy, these were sufficient for clinical use. All specimens exhibited significant deformation during the first period of cycling; however, there was no significant difference in the deformation between the two materials after fatigue testing.

Conclusions: PEEK exerts fewer stresses on abutments compared to standard-alloy clasps, provides adequate retention, and satisfy aesthetic demands, indicating that PEEK presents a promising alternative to conventional metal clasps.

Purpose: This study aimed to investigate the effect of removable denture prostheses on the comminution progress in elderly people.

Methods: Twenty-two denture wearers of Eichner' s classification B and C (75.1±5.3 years old) and 20 young fully dentate subjects (27.6±1.9 years old) participated in the masticatory examination, which used a combined test food from 5 daily food materials. Full masticatory cycles lasting until subjects needed to swallow and the half number of the cycles were adopted as masticatory conditions. Digital images of food particles under wet conditions were obtained for each bolus, and particles were analyzed by calculating the homogeneity and particle size indices.

Results: The characteristic properties of the food particles were observed using a homogeneity index in the elderly denture group for half masticatory strokes. Their homogeneity index was significantly higher than that of the young dentate group. By contrast, no significant difference was observed in the indices for particles immediately before swallowing between two groups.

Conclusions: The comminuted particle size before swallowing in healthy denture wearers was not significantly different from that in the natural dentate group. The comminution of the first-half process in denture wearers was typical and could be one possible focus for meal property specifications in future studies.

Purpose: This study evaluated the effect of the use of a powder-type adhesive on masticatory performance and oral health related quality of life (OHRQoL) in patients with normal and resorbed mandibular ridges during adaptation period with complete dentures.

Methods: Forty-two edentulous subjects (12 men, 30 women) were distributed in four groups: normal mandibular ridges with adhesive, n = 10; normal mandibular ridges without adhesive, n = 10; resorbed mandibular ridges with adhesive, n = 11; resorbed mandibular ridges without adhesive, n = 11. Masticatory performance was evaluated by sieving method and OHRQoL by Oral Health Impact Profile in Edentulous Adults (OHIP-EDENT) inventory at 30, 60 and 90 days after the insertion of new complete dentures. Data were analyzed using 2-way ANOVA test and Generalized Estimating Equations (GEEs), α = 0.05.

Results: The use of adhesive resulted in better masticatory performance at 30 (35.76 ± 12.63%) and 60 days (30.06 ± 10.54%) after the insertion of the dentures and did not influence on OHRQoL in participants with normal ridges during the adaptation period. The use of adhesive did not interfere on masticatory performance during adaptation period and had a negative effect on masticatory discomfort/disability subscale OHRQoL at 30-day period [5.2 (3.6, 6.8) ] for resorbed mandibular ridges with new complete dentures.

Conclusions: The use of adhesive can improve masticatory performance of new complete dentures users with normal mandibular ridges in the initial adaptation period up to 60 days after insertion. For resorbed ridges subjects, the use of adhesive had a negative impact on masticatory discomfort/disability OHRQoL at 30 days after insertion.

Purpose: The purpose of this study was to evaluate the effect of pretreatment using phosphoric acid, sodium hypochlorite and sulfinic acid sodium salt on the bonding of one-step self-etching adhesives to root canal dentin.

Methods: Thirty-six single-rooted sound human premolars were randomly assigned into three groups before applying the one-step self-etching adhesive. These comprised a control group with no pretreatment, an NC group that received phosphoric acid and subsequent sodium hypochlorite gel pretreatments, and an NC + AC group that received an additional treatment with sulfinic acid sodium salt following the same pretreatment applied to the NC group. Microtensile bond strength measurements, bonding interface observations by scanning electron microscopy (SEM), elemental analyses by X-ray photoelectron spectroscopy (XPS) and degree of polymerization (DOP) analyses by Raman spectroscopy were subsequently performed.

Results: The bond strength was significantly higher in the NC + AC group than in the other two groups (Control: P = 000.1 and NC: P = 0.004). SEM observations showed that resin tags were present in the dentinal tubules in the NC and NC + AC groups. Compared to the control group, the adhesive resin layer had a lower DOP in the NC group, while the DOP for the NC + AC group was higher than that of the NC specimens.

Conclusions: Bonding to root canal dentin was improved by applying sulfinic acid sodium salt in addition to treatment with phosphoric acid followed by sodium hypochlorite. The DOP of the adhesive resin was reduced by sodium hypochlorite and subsequently restored by applying sulfinic acid sodium salt.

Purpose: The purpose of this study was to investigate the effect of denture adhesives on oral moisture in a 10-center parallel randomized clinical trial.

Methods: Two hundred edentulous subjects wearing complete dentures were allocated into three groups: cream-type adhesive, powder-type adhesive and control groups. The adhesives (and saline solution in the control group) were applied to the mucosal surface of the dentures for 4 days, and baseline data and data after the intervention for eight meals over 4 days were obtained. For the main outcome, oral moisture was measured with a moisture checking device. Secondary outcomes were denture satisfaction, masticatory performance, denture retention, and occlusal force. In addition to between-group and within-group comparisons of oral moisture, investigations for secondary outcomes were undertaken in subgroups classified according to the degree of oral moisture at baseline (normal subgroup and dry mouth subgroup). Intention-to-treat analysis was also performed.

Results: Between-group and within-group comparisons of oral moisture showed no significant differences. The cream-type and powder-type denture adhesives were significantly effective in the dry mouth group for denture satisfaction ratings of ability to masticate, stability, retention, and comfort of mandibular dentures (p < 0.05). The masticatory performance and retentive force of the dry mouth denture adhesive using groups were significantly improved after intervention (p < 0.05).

Conclusions: The oral moisture of complete denture wearers was not influenced by the use of denture adhesives. Our findings showed that denture adhesives improved subjective denture satisfaction, masticatory performance, and retention for complete denture patients with oral dryness.

Purpose: This study aimed to investigate the relationship between the bilateral maximum occlusal force (MOF) of full dental arches and all-cause mortality in a group of community-dwelling older males and females in Japan.

Methods: This 13-year prospective cohort study was conducted among 815 older adults (395 male and 420 female) aged 70-years or over (mean age ± standard deviation: 75.1 ± 4.5-years). Bilateral MOF in the intercuspal position was recorded with horseshoe-shaped pressure-sensitive film. Participants were grouped by gender into tertiles according to MOF. Demographic variables, chronicity, comorbidity, physical status, cognitive and psychological status, social functioning, and blood chemistry data were also assessed. Information regarding all-cause mortality and migration was obtained from the Sendai Municipal Authority. Cox proportional hazard modeling was performed to assess all-cause mortality during the follow-up period.

Results: In total, 159 male and 109 female participants died over a median 12.9-year follow-up period, and the cumulative mortality significantly increased with lower MOF in both males and females. The multivariate Cox proportional hazard model demonstrated a significant increase in the risk of all-cause mortality associated with lower tertiles of MOF, relative to the upper tertile in males (hazard ratio: 1.62; 95% confidence interval: 1.05-2.51) and females (hazard ratio: 1.94; 95% confidence interval: 1.10-3.56).

Conclusions: There was a significant and independent association of bilateral MOF with all-cause mortality in community-dwelling elderly males and females in Japan. These findings suggested that maintenance of oral functioning contributes to general health.

Purpose: Maxillofacial prosthetic rehabilitation replaces missing structures to recover the function and aesthetics relating to facial defects or injuries. Deep learning is rapidly expanding with respect to applications in medical fields. In this study, we apply the artificial neural network (ANN) -based deep learning approach to coloration support for fabricating maxillofacial prostheses.

Methods: We compared two machine learning algorithms, ANN-based deep learning and the random forest algorithm, to determine the compounding amount of pigment. We prepared 52 silicone elastomer specimens of varying colors and measured the CIE 1976 L* a* b* color space information using a spectrophotometer on the input dataset. The output of these algorithms indicated the compounding amount of four pigments. According to the algorithms' pigment compounding predictions, we prepared the specimens for validation analysis and measured the CIE 1976 L* a* b* values. We determined the color differences between the real skin color of five research participants (22.3 ± 1.7 years) and that of the silicone elastomer specimens fabricated based on the algorithm predictions using the CIEDE00 ΔE₀₀ color system.

Results: The color differences (ΔE₀₀ value) between the real skin color and silicone elastomer validation specimens were 3.45 ± 0.87 (ANN) and 5.54 ± 1.41 (random forest), which indicates that the deep ANN approach produced superior results with respect to the ΔE₀₀ value compared with the random forest algorithm.

Conclusions: These results suggest that applying deep ANN is a promising technique for the coloration of maxillofacial prostheses.

Purpose: To compare the effect of different surface treatments (pre-treatments and bonding agents) on the bond strength between glass-fiber post and composite resin, and the topographic alterations of the treated post surface.

Methods: Thirty-six glass-fiber blocks (12 mm × 10 mm × 8 mm) were specifically manufactured for this study and randomly assigned into 12 groups considering two factors: 'pre-treatments' (-cleaning with 70% alcohol; air-abrasion with silica-coated aluminum oxide particles; 35% hydrogen peroxide) and type of 'bonding agent' (no bonding agent; application of Monobond Plus; RelyX Ceramic Primer; Single Bond Universal). After that, 6 cylindrical templates ( 1mm high × 1 mm Ø) were fixed on each block, filled with composite resin (n = 18) and light-cured. Specimens were stored under 37 °C for 24 h and microshear tests (wire loop Ø = 0.2 mm) were performed. Topographic, roughness and failure analyses were also performed.

Results: Different surface pre-treatments led to different topographic and roughness alterations; a higher surface alteration was noted after silica particles air-abrasion, while a slight surface alteration in the hydrogen peroxide group and a smooth pattern were observed in the cleaning group. The factors 'pre-treatments' (p < 0.05), 'bonding agent' (p < 0.05) and their interaction (p < 0.05) influenced the bond strength. Silica coating, apart from bonding agent application, or Single Bond Universal application without pre-treatment promoted the highest bond values. The main failure type was adhesive at the resin-post interface.

Conclusions: In terms of pre-treatments, silica coating promotes the best bonding performance, but pre-treatments can be dispensable when applying Single Bond Universal.

Purpose: This study aimed to elucidate the effects of hydrogen peroxide (H₂O₂) and sodium fluoride (NaF) on titanium surfaces under conditions mimicking those encountered during dental treatment.

Methods: Titanium samples were immersed in artificial saliva (AS), 1 M H₂O₂, 1 M H₂O₂ with catalase, 1000 ppmF NaF, 1 M H₂O₂ with 1000 ppmF NaF, or 9000 ppmF NaF (9000 ppmF NaF: pH 5.3, other solutions: pH 6.5) for 3 min. The electrochemical properties of the titanium samples were analyzed before and after the immersion procedures using a potentiostat. The amounts of titanium eluted into each solution were measured using inductively coupled plasma mass spectrometry. The post-immersion color changes (ΔE*ab) and gloss values of the titanium samples were determined using spectrophotometry. Moreover, the solution-treated titanium samples were subsequently immersed in AS and analyzed electrochemically at 1, 2, 3, 4, 6, 8, and 24 h.

Results: The immersion of titanium in any of the solutions except 1000 ppmF NaF caused significant increases in corrosive and passive currents and significant reductions in polarization resistance. No titanium elution or color changes were observed, except when 9000 ppmF NaF was used. After immersion in AS, the electrochemical properties of all of the titanium samples, except the 9000 ppmF NaF-treated samples, recovered within 24 h.

Conclusions: One M H₂O₂ and 1000 ppmF NaF can be used alone or in combination in the clinical setting without causing significant titanium corrosion because the corrosive properties they induce is reversible. However, highly concentrated acidic fluorides can cause irreversible corrosion.

Purpose: The objective of the present study was to evaluate fracture loads of screw-retained implant-supported zirconia prostheses after artificial aging.

Methods: Four types of screw-retained implant-supported prostheses were fabricated (n = 11 each); porcelain-veneered zirconia prosthesis (PVZ), indirect composite-veneered zirconia prosthesis (IVZ), porcelain-fused-to-metal prosthesis (PFM), and monolithic zirconia prosthesis (ML). The specimens were subjected to 10,000 thermocycles and cyclic loading for 1.2 million cycles. Fracture loads were measured, and the data were analyzed with the Kruskal-Wallis and Steel-Dwass tests (α = 0.05).

Results: All specimens survived the artificial aging procedures. The fracture loads for the PVZ (1.52 kN), IVZ (1.62 kN), and PFM groups (1.53 kN) did not significantly differ; however, the fracture load for the ML group (6.61 kN) was significantly higher than those for the other groups. The fracture load for the IVZ group was comparable to those for the PVZ and PFM groups.

Conclusions: The monolithic zirconia prostheses exhibited significantly higher fracture loads than the bilayered prostheses. All the investigated types of screw-retained implant-supported zirconia prostheses appear sufficient to resist posterior masticatory forces during long-term clinical use.

Purpose: The purpose of this study was to evaluate the effectiveness of both a resin primer containing methyl methacrylate (MMA) and a silanizing agent on bonding to indirect resin composite blocks, using two types of build-up hybrid resin composites.

Methods: SHOFU BLOCK HC (Shofu) specimens were blasted with alumina, after which one of two surface treatments was applied: CERA RESIN BOND (Shofu, the Silane group) or HC primer (Shofu, the MMA group). Resin composites made using either Solidex Hardura (SDH, Shofu) or Ceramage Duo (CMD, Shofu) were built up and micro-tensile bond strength (μTBS) values were measured after storage in water for either 24 h or 6 months (n = 24 per group). The fracture surfaces after μTBS measurements and the resin block/build-up resin interfaces were observed by scanning electron microscopy (SEM).

Results: The bond strength of the Silane/SDH group significantly decreased after 6 months (p < 0.001), whereas in the MMA group there was no significant loss after 24 h or 6 months (p = 0.99). In the CMD group, the bond strength after 6 months was significantly lowered in both the Silane group (p < 0.001) and the MMA group (p < 0.001), but the latter still showed greater adhesion. SEM images demonstrated that the matrix resin was partially destroyed at the fracture surfaces of the MMA group and fracture surface unevenness was observed.

Conclusions: A primer containing MMA produced stronger bonding to CAD/CAM resin even after long-term aging compared to a silane treatment.

Purpose: To evaluate the different cooling procedures on the mechanical properties of five heat-cured polymethyl methacrylate (PMMA) denture materials.

Methods: 250 specimens were made equally from Meliodent (ME), Paladon 65 (PA), Probase Hot (PB), Stellon QC-20 (QC) and Vertex Rapid Simplified (VE) implementing five different cooling procedures (n = 10/procedure): A) removal from water bath, bench-cooling (10 min) and cooling under water (15 min), B) remain in water bath till room temperature, C) removal from water bath and cooling in water for 15 min, D) removal from water bath and bench cooling till room temperature and E) removal from water bath, bench cooling for 30 min and cooling under water for 15 min. The specimens were immersed in distilled water (15 days/37 °C) and then subjected to Instrumented Indentation Testing for Martens Hardness (HM), indentation modulus (E_IT) and elastic index (η_IT). Results were statistically analyzed by two- and one-way Analysis of variance (ANOVA) plus Tukey post hoc tests (α = 0.05).

Results: The highest values for HM were recorded for QC, PA, VE with B cooling procedure, PB with A and ME with E, for E_IT for QC, PB with A, for PA, VE with B and ME with E, and for η_IT for QC, PB with B, PB with E, ME with C and VE with D.

Conclusions: The cooling procedures recommended for PB resulted in the lowest mechanical properties. A and B may be considered as universal short- and long-cooling procedures respectively providing the highest mechanical properties for the materials tested.

Purpose: To evaluate failure rates and incidence of chipping for metal-ceramic and all-ceramic implant-supported single crowns (SCs).

Methods: Six hundred and fifty-two implant-supported SCs placed in 404 patients (mean age: 57.8 years; 193 male; mean SCs per patient: 1.6) were evaluated up to 12.8 years. The frameworks of the SCs were made from Au alloys (n = 319), CoCr (n = 37), zirconia (n = 286), or lithium disilicate (n = 10). Full-coverage ceramic veneers were placed on 319 Au SCs, 34 CoCr SCs, and 92 zirconia SCs. One hundred and fifty-two monolithic zirconia SCs were not veneered. A partial veneer was placed on the buccal surface only of a further 42 zirconia SCs.

Results: A total of 26 failures were caused by loss of implants (n = 6), ceramic fractures and chipping (n = 15), loosening of the abutment (n = 4), or swallowing of a de-cemented SC (n = 1). Kaplan-Meier analysis revealed a probability of survival of 96% after five years and 92% after 10 years. A greater incidence of failure was observed for lithium disilicate and zirconia SCs than for metal-ceramic SCs (p <.05). Separate analysis of the most frequent complication, chipping (n = 61), revealed that zirconia and lithium disilicate frameworks were significant risk factors for chipping (p < 0.05). Furthermore, a significantly greater incidence of chipping was observed for SCs with full-coverage veneers than for monolithic zirconia SCs and for SCs with partial veneers (p <.05).

Conclusion: Avoidance of full-coverage veneers significantly improves the clinical performance of implant-supported crowns, primarily reduces the incidence of chipping.

Purpose: An increasing number of clinical reports describe the use of dental implants as abutments in implant-assisted removable partial dentures (IARPD). We used three-dimensional finite element analysis to evaluate IARPD as a unilateral mandibular distal extension denture. Specifically, the mechanical effects of implant position and abutment height on the abutment tooth, denture, and denture-supporting tissue were assessed.

Methods: The models analyzed were defects of the left mandibular second premolar and first and second molars prosthetically treated with an IARPD using one implant for each tooth position. There were two abutment heights: one equal to that of the mucosa and another that was elevated 2 mm above the mucosa. Six models were constructed.

Results: For mucosal-level abutments, movement of the abutment tooth was lower for implants positioned distal to the abutment tooth than for those positioned medial to the abutment tooth. For elevated abutments, movement of the abutment tooth was lower for implants positioned medial to the abutment tooth than for those positioned distal to the abutment tooth.

Conclusions: The mechanical effects on abutment teeth at the same implant position differed in relation to implant abutment height.

Purpose: The association between periodontal disease and carotid atherosclerosis has been widely discussed, but to our knowledge, no population-based studies have been conducted on the association between masticatory ability and carotid atherosclerosis. We aimed to clarify the hypothesis that objectively accessed masticatory performance is related to increased intima-media thickness (IMT) in a general urban population.

Methods: We studied 1,484 Japanese (mean age: 66.9 y) from the Suita study. Masticatory performance was measured using test gummy jelly, and periodontal status was evaluated using the Community Periodontal Index (CPI). Carotid ultrasonography was performed to measure maximum IMT (max-IMT) in the entire area of the carotid arteries. Analysis of covariance was used to compare max-IMT according to quartiles of masticatory performance adjusted by cardiovascular risk factors and periodontal status.

Results: Multivariable-adjusted max-IMT (standard error) was significantly higher in the lowest masticatory performance quartile group (decreased group) (1.58 ± 0.03 and 1.44 ± 0.03 mm) than in the 2nd to 4th quartiles combined (non-decreased groups) in both sexes (1.48 ± 0.02 mm, trend P = 0.038) and in women (1.34 ± 0.02 mm, trend P = 0.013), respectively. In participants without cardiovascular risk factors (n = 250), multivariable-adjusted max-IMT was significantly higher in the decreased (1.54 ± 0.06, 2.08 ± 0.22, and 1.42 ± 0.06 mm) than in the non-decreased groups in both sexes (1.31 ± 0.04 mm, trend P = 0.006), in men (1.41 ± 0.12 mm, trend P = 0.028), and in women (1.28 ± 0.04 mm, trend P = 0.073).

Conclusions: These findings suggest that decreased masticatory performance may be related to carotid IMT progression in the general urban Japanese population.

Objectives: To evaluate the long-term clinical outcome of posterior metal-ceramic crowns fabricated with CAD/CAM-based laser-sintering technology (BEGO Medical, Bremen, Germany).

Materials and Methods: Sixty posterior crowns were placed in 39 patients. After tooth preparation, impression taking and model casting, the stone dies were scanned to create STL data, followed by manufacturing of crown frameworks with laser-sintering technology. A base metal alloy (CoCr) and a precious alloy (AuPt) were used for 31 and 29 posterior crowns, respectively, which were veneered using the layering technique. All crowns were cemented using glass-ionomer cement.

Results: The mean observation period was 10.5 ± 3.9 years. Six patients with 10 crowns were regarded as dropout. Nine crowns had been removed, three of them were intact but they were removed due to a new prosthetic treatment plan. The cumulative survival rate of all crowns was 81% after 14.7 years. When comparing the survival rates related to the alloy used, the Gehan-Wilcoxon test showed no significant differences between both alloys. Biological complications were most commonly reported, while technical complications did not affect the function of the crowns.

Conclusion: The long-term clinical outcome of posterior metal-ceramic crowns fabricated with CAD/CAM-based laser-sintering technology is very promising, so that this novel technique could be an alternative to the traditional lost wax casting process.