Shedding light on the problem: Proficiency and maintenance practices of light-curing units among dental assistants.

BACKGROUND: Proper light curing is crucial for the success of restorative dentistry and to bond brackets to teeth, yet the responsibility is often delegated to dental assistants (DAs). This study assessed the proficiency and maintenance protocols of DAs when using light-curing units (LCUs) in Saudi Arabia. METHODS: Self-administered questionnaires were distributed to practicing DAs. The questionnaire contained sections on knowledge, adherence to best practices, and how to maintain the LCU. Demographic data were collected as well. Descriptive statistics and linear regressions at a significance level of (p = 0.05) were conducted to identify any relationships that influenced the DAs' LCU knowledge, practice, and maintenance protocols. RESULTS: Among the surveyed DAs, 66% were responsible for using the LCU during treatment, 16% used their fingers for support when light curing, 50% held the LCU tip 1-2 mm from the restoration during curing, and 51% did not have a specific maintenance protocol at their workplace. 70% did not know the output from the LCU, and their educational background correlated with knowledge (b = -14.42, p < 0.001). The type of institution type correlated with adherence to best practices (b = -13.65, p = 0.011), and level of knowledge and adherence to maintenance protocols showed a direct correlation (b = 0.002, p = 0.041). CONCLUSIONS: The findings revealed that a significant percentage of the DAs who replied had insufficient knowledge and did not follow the best practices and maintenance protocols for the LCUs they were using. Their educational background and workplace factors influenced this knowledge gap, while the absence of a maintenance protocol and suboptimal practices were associated with the type of institution. CLINICAL SIGNIFICANCE: To maintain the best practice, clinicians and institutions should improve the education and training of DAs. Otherwise, inadequate light curing by the DAs may jeopardize the long-term success of many dental procedures.

Assessment of internal porosities for different placement techniques of bulk-fill resin-based composites: a micro-computed tomography study.

OBJECTIVES: The aim was to compare the porosity of different bulk-fill resin-based composites (RBCs) placement techniques to the conventional incremental technique using microcomputed tomography (µ-CT). MATERIAL AND METHODS: Occlusal cavities were prepared on extracted human molars, divided into five groups based on the placement technique (n = 10/group). Techniques examined were Monoblock-two-step (SureFil SDR flow + Ceram.X), Monoblock-two-step (Tetric EvoFlow Bulk-Fill + Tetric EvoCeram Bulk-Fill), Monoblock-one-step (Tetric EvoCeram Bulk-Fill), Monoblock with sonic activation (SonicFill2), and incremental technique (Filtek Z250). µ-CT scanning (SkyScan, Bruker, Belgium) assessed the number, volume of closed pores, and total porosity. Analysis of variance on ranks was used (Student-Newman-Keuls method and Mann-Whitney rank-sum test), to determine the significance of RBC viscosity and the sonication placement technique. The Spearman correlation method assessed the correlation between porosity characteristics (α = 0.05). RESULTS: The SonicFill2 presented a higher number of closed pores than the other groups (p < 0.05). The overall porosity within the restoration seemed greater in this order: Filtek Z250 > SonicFill2 > Tetric EvoFlow Bulk-Fill + Tetric EvoCeram Bulk-Fill > Tetric EvoCeram Bulk-Fill > SureFil SDR Flow + Ceram.X. Sonication was associated with increased number (p = 0.005) and volume (p = 0.036) of closed pores. A strong correlation was observed between the number and volume of closed pores (R2 = 0.549, p < 001). CONCLUSIONS: The monoblock technique with sonic activation showed significantly more internal porosity than the other placement techniques. Sonication during application contributed to the higher number and volume of closed pores than the passive bulk-fill application. CLINICAL RELEVANCE: Using bulk-fill materials enhances efficiency, yet void formation remains an issue, depending on viscosity and active/passive delivery of materials. Clinicians must familiarize themselves with effective placement techniques to reduce void formation and optimizing treatment outcomes.

Inorganic Compounds as Remineralizing Fillers in Dental Restorative Materials: Narrative Review.

Secondary caries is one of the leading causes of resin-based dental restoration failure. It is initiated at the interface of an existing restoration and the restored tooth surface. It is mainly caused by an imbalance between two processes of mineral loss (demineralization) and mineral gain (remineralization). A plethora of evidence has explored incorporating several bioactive compounds into resin-based materials to prevent bacterial biofilm attachment and the onset of the disease. In this review, the most recent advances in the design of remineralizing compounds and their functionalization to different resin-based materials' formulations were overviewed. Inorganic compounds, such as nano-sized amorphous calcium phosphate (NACP), calcium fluoride (CaF2), bioactive glass (BAG), hydroxyapatite (HA), fluorapatite (FA), and boron nitride (BN), displayed promising results concerning remineralization, and direct and indirect impact on biofilm growth. The effects of these compounds varied based on these compounds' structure, the incorporated amount or percentage, and the intended clinical application. The remineralizing effects were presented as direct effects, such as an increase in the mineral content of the dental tissue, or indirect effects, such as an increase in the pH around the material. In some of the reported investigations, inorganic remineralizing compounds were combined with other bioactive agents, such as quaternary ammonium compounds (QACs), to maximize the remineralization outcomes and the antibacterial action against the cariogenic biofilms. The reviewed literature was mainly based on laboratory studies, highlighting the need to shift more toward testing the performance of these remineralizing compounds in clinical settings.

Effects of nanohybrid flowable resin-based composites on fibroblast viability using different light-curing units.

PURPOSE: To investigate the in vitro cytotoxic effects of Bis-GMA-containing and Bis-GMA-free flowable resin-based composites (RBCs) on primary human gingival fibroblast cells (hGFc) using direct and indirect curing methods and three different light-curing units (LCUs). MATERIALS AND METHODS: Cells were isolated and cultured in vitro in 24-well plates. The plates were divided into treatment (cells with RBC), control (cells only), and blank (media only) groups. In the treatment groups, two types of nanohybrid flowable RBCs were used: Bis-GMA-free and Bis-GMA groups. Each treatment group was subdivided according to the curing method, i.e., direct curing (RBC was injected into the wells and cured directly on the attached cells) and indirect curing (the samples were pre-cured outside of the well plate and then added to the well plate with cells). To vary the LCU, the subgroups were further divided into three groups: multiple-emission peak light-emitting diode, single-emission peak light-emitting diode, and quartz-tungsten-halogen units. Curing was conducted for 20 seconds. The hGFc cytotoxicity was evaluated via 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay after 24, 48, and 72 hours of culturing. RESULTS: The MTT assay results showed that both RBCs were significantly cytotoxic toward hGFc compared to the control group (p < 0.0001). The Bis-GMA group was significantly more cytotoxic to the cells compared to the Bis-GMA-free group. In addition, the curing method and time interval affected cell viability regardless of the LCU used. CONCLUSION: The Bis-GMA flowable RBC and direct curing method had the highest cytotoxic effects on hGFc regardless of the LCU used. Careful selection of flowable RBCs and proper curing techniques are required to decrease the cytotoxic effects on hGFc and improve the clinical handling of oral tissues.

Polymerization pattern characterization within a resin-based composite cured using different curing units at two distances.

OBJECTIVES: To investigate the relationship of the irradiance-beam-profile areas from six different light-curing units (LCUs) with the degree of conversion (DC), microhardness (KH), and cross-link density (CLD) throughout a resin-based composite (RBC) cured at two clinically relevant distances, and to explore the correlations among them. MATERIALS AND METHODS: A mapping approach was used to measure DC using micro-Raman spectroscopy, KH using a Knoop indentor on a hardness tester, and %KH reduction after ethanol exposure, as an indicator for CLD within a nano-hybrid RBC increment (n = 3) at various depths. These sample composites were cured from two distances while maintaining the radiant exposure, using six different light-curing units: one quartz-tungsten-halogen; two single and three multiple-emission-peak light-emitting-diode units. Irradiance beam profiles were generated for each LCU at both distances, and localized irradiance values were calculated. Points across each depth were analyzed using repeated measures ANOVA. Correlations across multiple specimen locations and associations between beam uniformity corresponding with polymerization measurements were calculated using linear mixed models and Pearson correlation coefficients. RESULTS: Significant non-uniform polymerization patterns occurred within the specimens at various locations and depths. At 2-mm curing distance, the localized DC = 52.7-76.8%, KH = 39.0-66.7 kg/mm2, and %KH reduction = 26.7-57.9%. At 8-mm curing distance, the localized DC = 50.4-78.6%, KH = 40.3-73.7 kg/mm2, and %KH reduction = 28.2-56.8%. The localized irradiance values were weakly correlated with the corresponding DC, KH, and %KH reduction, with only a few significant correlations (p < 0.05). CONCLUSIONS: Although significant differences were observed at each depth within the specimens, the localized irradiance values for all LCUs did not reflect the polymerization pattern and did not seem to have a major influence on polymerization patterns within the RBC, regardless of the curing distance. CLINICAL RELEVANCE: Commonly used LCUs do not produce uniform polymerization regardless of the curing distance, which may contribute to the risk of RBC fracture.

Attitude, Practice, and Knowledge Regarding Fluoridated Toothpaste, Brushing, and Rinse Usage Among Residents of Jeddah City in Saudi Arabia.

Purpose: To evaluate and compare the attitude, practice, and knowledge of individuals who use fluoridated and non-fluoridated toothpaste in Jeddah city, Saudi Arabia. Methods: A digital questionnaire composed of 43 questions were formulated. The questionnaire was divided into five sections: eligibility questions, demographic data, attitude, practice, and knowledge. Content and face validation were done, and convenience sampling was used. The inclusion criteria were any citizen and resident who lives in Jeddah city, Saudi Arabia. Descriptive statistics, Chi-square, and Fischer's tests were conducted to compare fluoridated and non-fluoridated toothpaste users (α=0.05). Results: A total of 473 completed participants' responses were collected. Attitude: 41.8% of fluoridated toothpaste users reported that it was "very important" to rinse to remove the toothpaste compared to non-fluoridated toothpaste users (58.3%) (P-value<0.001). Healthy teeth were the most important to fluoridated toothpaste users (69.1%) (P <0.001). Practice: 28.6% of non-fluoridated toothpaste users have been using non-fluoridated toothpaste for >1 year, and 35.7% of them <2 years. 73.8% of fluoridated toothpaste users used whitening toothpaste. Significantly higher non-fluoridated toothpaste users (29%) used organic toothpaste (P<0.001). Knowledge: 57% of fluoridated toothpaste users believed that a good diet, tooth brushing, and fluoridated toothpaste are important to prevent caries, and the fluoride would strengthen the teeth (P<0.001). Approximately 60% of non-fluoridated toothpaste users did not know the proper age to start using fluoridated toothpaste (P<0.001). Also, 47.6% of non-fluoridated toothpaste users avoid using fluoride because it is toxic. Conclusion: Significantly higher number of Jeddah residents that used fluoridated toothpaste had a better attitude and knowledge than non-fluoridated toothpaste users. Nonetheless, most residents had similar oral hygiene practices. It is suggested to execute educational campaigns to explain the importance of fluoridated toothpaste to the population. Also, individuals should take caution from the source of obtaining their dental information and consult their dentist.

Skill Retention of Light-Curing Technique Using Only Verbal Instructions versus Using an Instructional Video: A 2-Year Follow-Up Study of Dental Students.

Purpose: To evaluate the retention of light-curing skills among dental students after two years of clinical experience and determine if there are any differences in the skills retention between students who received verbal instructions or those who had received an instructional video. The students' satisfaction with past learning, self-confidence, and general knowledge about light-curing were also evaluated. Methods: This study is a 2-year evaluation of previous work. Students had previously been divided into two groups: those who received only verbal instructions, and those who received only an instructional video about the correct light curing technique to use clinically. Each student had light-cured simulated restorations (anterior and posterior) for 10 sec using the Managing Accurate Resin Curing-Patient Simulator (MARC-PS) (BlueLight Analytics, Halifax, Nova Scotia, Canada) and a multiple-emission peak light-emitting-diode (Bluephase N, Ivoclar Vivadent, Schaan, Liechtenstein) curing light. Students then received instructions according to their assigned group and light-cured the simulated cavities again. Two years later, students from both groups light-cured the same simulated cavities. Then, they completed a modified version of the National League of Nursing (NLN) satisfaction and self-confidence questionnaire and answered light-curing knowledge questions. Statistical analysis: The mean radiant exposure values delivered before receiving specific instructions on light curing, immediately after, and two years after instruction for both teaching methods (Friedman test followed by Wilcoxon signed-rank post hoc test), and the difference between both teaching methods was assessed (two-sample Wilcoxon rank-sum test). The satisfaction and self-confidence scores were compared between teaching method groups (Wilcoxon rank-sum test) (p<0.05). Results: The mean and median irradiance values ranged between 194-1777 and 1223-1302 mW/cm2 before instructions, 320-1689 and 1254-1394 mW/cm2 immediately after instructions, and 95-1945 and 1260-1331 mW/cm2 two years later regardless of the simulated restoration or the teaching method. The mean and median radiant exposure values ranged between 2-23 and 12.5-13.6.4 J/cm2 before instructions, 3-28 and 12.8-14.3 mW/cm2 immediately after instructions, and 0.7-20 and 12.8-13.6 mW/cm2 two years later regardless of the simulated tooth being light cured and the teaching method. Students retained their light-curing skills after two years of clinical experience, with no significant differences between both groups. The instructional video group delivered significantly higher radiant exposure values (p=0.021) when light-curing the anterior tooth than the posterior. Students were satisfied with their past learning and confident in their light-curing skills (p=0.020). There were statistical differences in how well the two groups remembered what they had been taught about light-curing. Only 5.7% of students answered all knowledge questions correctly. Conclusion: Students retained their light-curing skills after two years of clinical experience, with no significant difference between verbal instructions or instructional video teaching methods. However, their knowledge about light curing remained very poor. Nevertheless, the students were satisfied with how they had been taught and had confidence in both teaching methods.

Impact of grit, resilience, and stress levels on burnout and well-being of dental students.

OBJECTIVE: Dentistry is demanding and requires a high level of diligence and resilience, resulting in high stress that may impact students' burnout and well-being. The aims were to: (1) investigate the levels of grit, resilience, stress, burnout, and well-being among students at King Abdulaziz University-Faculty of Dentistry; (2) explore age, gender, dentistry as the first career choice, academic level, grit, resilience, and stress as predictors for burnout and well-being among dental students; (3) investigate the correlations among grit, resilience, stress, burnout, and well-being among dental students. METHODS: An electronic questionnaire was distributed, comprised of demographic information and five validated scales: (1) grit (grit-8-item); (2) resilience (The Connor-Davidson resilience scale (CD-RISC)); (3) stress (perceived stress scale); (4) burnout (Oldenburg Burnout Inventory); (5) well-being (World Health Organization-5). The total students number was (n = 1057), number of participants were (n = 355), and the response rate was (33%). Predictors of well-being and burnout (multiple linear regression analyses) and correlations among the scales (Spearman Correlation Coefficient) were performed. RESULTS: Median age (22 years old). Trait levels varied among students. Grit, stress, and academic year were significant predictors for burnout (p < 0.0001), where sixth-year undergraduates showed significantly high, third-year undergraduate and graduates showed significantly low burnout levels. Age, gender, stress, and academic year were significant predictors for well-being (p < 0.0001), where older students and fifth-year undergraduates showed significantly low, and males showed significantly high well-being levels. Burnout had a significant moderate positive relationship with stress and a weak negative relationship with resilience and grit. Well-being had a significant negative moderate relationship with burnout and stress and a weak positive relationship with resilience. CONCLUSION: The levels of grit, resilience, stress, burnout, and well-being, and correlations varied among dental students. The academic level was a common significant predictor between burnout and well-being. We recommend reinforcing existing programs at the school and implementing a resilience program to reduce burnout levels and improve students' well-being.

Effects of aging and light-curing unit type on the volume and internal porosity of bulk-fill resin composite restoration.

This study explores the effects of aging (thermal cycling and cyclic loading-TC/CL) and different light-curing unit (LCU) types on the volume characteristics and internal porosity of a bulk-fill resin-based composite restoration. Occlusal cavities (4 × 4 × 3 mm) were prepared on extracted human molars (n = 5). Tetric N-Bond Universal was applied, and the cavities were restored using Tetric-N-Ceram Bulk Fill. Photoactivation was performed using a quartz-tungsten halogen (QTH) or a multiple-emission peak light-emitting diode (MLED). Digital images for all restorations were obtained using microcomputed tomography (micro-CT) before (baseline) and after (post-aging) TC/CL (5,000 TC cycles in 5-55 °C baths and a dwell time of 30 s followed by 10,000 sinusoidal CL load cycles in an Instron B3000 at 2 Hz and 10-110 N) and storage (37 °C) for three months. For the micro-CT analysis, three-dimensional images were used to determine the restoration volume and internal porosity. Data were analyzed using a two-way ANOVA and Tukey's test (p < 0.05). Restorations photoactivated with QTH exhibited a higher object volume than the LED group at baseline and in post-aging conditions without any significant differences in the other evaluated characteristics. All volume/porosity characteristics increased considerably after TC/CL aging, except for the object volume of the QTH group and the closed porosity of the MLED group. The change in all the volume/porosity characteristics between both LCU groups after TC/CL were not significantly different. Thus, the aging process simulated herein increased the volume and porosity characteristics of the bulk-fill restoration, and no significant differences were obtained between the QTH and MLED equipment.

Effectiveness of Using an Instructional Video in Teaching Light-Curing Technique.

PURPOSE: To investigate dental students' ability to deliver satisfactory amounts of irradiance and radiant exposure to simulated cavities by teaching the light-curing technique using instructional video compared to verbal instructions. METHODS: Students attended the didactic light-curing lecture explaining the light-curing technique. Participants were divided into two groups (n=60). Each participant light-cured a class III and a class I simulated cavities with sensors built-in a Managing Accurate Resin Curing-Patient Simulator (MARC-PS) system, using a multiple-emission-peak light-emitting-diode unit. Each student either 1) watched an instructional video (V) showing the light-curing technique, or 2) received individual verbal instruction (I). The light-curing performance, in terms of the mean irradiance and radiant exposure, was recorded. Each student performed light-curing again on the simulated cavities. Students' feedback for the corresponding teaching method was collected. Comparisons between before and after each instructional method were analyzed using the Wilcoxon signed-rank test. Comparisons between both instructional methods were analyzed using a Mann-Whitney U-test (α=0.05). RESULTS: The students' light-curing performance improved after both methods, as observed on the MARC-PS laptop monitor. The mean irradiance values were anterior-V=1280.6 (183.2), anterior-I=1318.0 (143.5), posterior-V=1337.5 (181.1), posterior-I=1317.6 (248.2) mW/cm2. The mean radiant exposure values were for anterior-V=13.5 (2.7), anterior-I=13.3 (1.6), posterior-V=13.7 (1.9), posterior-I=13.7 (2.5) J/cm2. No significant difference was found between both instruction methods. Students reported that each method was effective. CONCLUSION: Using V was comparable to I and an effective tool for teaching the light-curing technique per the students' ability to deliver sufficient amounts of irradiance and radiant exposure to simulated cavities.

Effect of light-curing distance and curing time on composite microflexural strength.

This study investigated the influence of curing distance on µ-flexural strength (µ-FS) of a nano-hybrid composite, cured using the manufacturer-recommended curing time (MCT), compared to a consistent radiant exposure (CRE) using three different light-curing units (LCUs). Beams (6×2×1 mm) were cured using the MCT or CRE with a quartz-tungsten-halogen (QTH); a single-emission-peak light-emitting-diode (SLED), or a multiple-emission-peak light-emitting-diode (MLED) LCU. Specimens were cured at 0-, 2- or 8-mm distances (n=10) and the bottom irradiance and CRE were measured using a Managing Accurate Resin Curing-Resin Calibrator spectrometer. µ-FS testing was performed, and data analyzed using two-way ANOVA and Tukey multiple comparison tests (α=0.05). Mean bottom irradiance was (25.4-99.7 mW/cm2) and CRE (0.31-1.11 J/cm2). µ-FS was 422.1-516.6 MPa (MCT) and 440.4-490.4 MPa (CRE). Comparing CRE to MCT showed that µ-FS significantly decreased using the CRE at 2-mm (QTH) or the MCT at 2- and 8-mm (SLED). µ-FS may be significantly impacted by the curing protocol.

Dental Students' Didactic and Psychomotor Skills Performance in Dental Anatomy and Preclinical Operative Dentistry Courses in a Saudi Governmental School.

BACKGROUND: Knowledge and psychomotor skills are essential in dental education. The aims were to (1) investigate the correlation between dental students' didactic and psychomotor skills performance in the dental anatomy and preclinical operative dentistry courses and (2) explore the impact of gender on students' performance in both courses. MATERIALS AND METHODS: A retrospective cohort study was performed on dental students' (164 students; 72 males and 92 females) dental anatomy and preclinical operative courses scores of the same class over 2 years (2018-2020). Didactic and practical scores were collected. The didactic scores included examinations. Practical scores included tooth wax carving for the dental anatomy course and class II cavity preparations and restorations for the preclinical operative. Student's t-test and ANOVA were used to analyze the difference between the didactic and psychomotor skills scores of both courses and genders. Pearson's correlation coefficient was used to explore correlations (p < 0.05). RESULTS: Moderate, positive, and significant correlations were found between didactic scores in both courses and between dental anatomy's didactic and psychomotor skills. A weak, positive, and significant correlation existed between the preclinical operative didactic and psychomotor silks (p < 0.05). Females' didactic performance was significantly better than males. Gender had a significant, positive, and moderate correlation in the dental anatomy course, but moderate-weak in preclinical operative (p < 0.05). CONCLUSION: Students' didactic and psychomotor performance correlations in dental anatomy and preclinical operative courses were positive. The correlation was moderate and weak and varied by course. Gender had a significant impact on student performance and varied by procedure and courses investigated.

Variation in composite degree of conversion and microflexural strength for different curing lights and surface locations.

BACKGROUND: Lack of irradiance-beam profile uniformity across the emission area of light-curing units (LCUs) may result in suboptimal properties of composite restorations. The authors' objective for this study was to assess the variation in local cure of 1 composite at 3 different LCU emission area locations cured with 3 different LCUs by means of testing the degree of conversion (DC) and microflexural strength. METHODS: The authors fabricated dual-photoinitiator composite specimens (n = 5), which were cured using either a quartz-tungsten-halogen, a multiple-emission peak, or a single-emission peak light-emitting diode LCU. The specimen's top surfaces received irradiation from either the center, 1.5 millimeters straight to the left of the center, or 1.5 mm straight to the right of the center of the LCU emission area. The authors measured irradiance and DC on top and bottom specimen surfaces using a spectrometer and attenuated total reflection-Fourier transform infrared spectroscopy, respectively. The authors performed micro 3-point bend tests using a universal mechanical testing machine. They used multifactorial analysis of variance (α = 0.05). RESULTS: The irradiance ranged from 452 through 946 milliwatts per square centimeter, and DC ranged from 49.7% through 65.8% on top surfaces. Microflexural strength ranged from 313 through 458 megapascals. CONCLUSIONS: The authors did not find correlations among the LCU irradiance-beam profile of the 3 emission area locations and the investigated material properties, although they found variations in the measured properties. PRACTICAL IMPLICATIONS: The irradiance-beam profile from the different LCUs explored did not have a major influence on the DC and microflexural strength for the investigated composite.

Degree of conversion and cross-link density within a resin-matrix composite.

The aims of this study were to profile light radiated from two light-curing units (LCUs) and evaluate profile relationship to polymerization patterns within a resin-matrix composite (RMC). Beam profiles of one multiple emission peak light-emitting-diode and one quartz-tungsten-halogen curing-unit were measured using a beam profiler/spectrometer system. A camera-based profiler and an integrating sphere/spectrometer assembly were used to evaluate each LCU beam. Polymerization patterns within a nano-hybrid RMC were investigated using a mapping approach by assessing the degree of conversion utilizing micro-Raman spectroscopy and indirectly estimating cross-link-density by repeated microhardness testing before and after exposure to ethanol (%KH reduction, n = 3). The irradiance received on the top and bottom specimen surfaces from both LCUs was measured using a MARC-RC system. The investigated beam profile area from both LCUs was non-uniform and yielded localized discrepancies in DC (55.7-74.9%) and %KH reduction (26.7-54.1%). The LCU irradiance received at the bottom of the specimens was ∼10% of the top value. This study demonstrated that LCU beam profiles were non-uniform in the area explored. Localized differences in DC and %KH reduction existed throughout the RMC specimens but did not follow a specific pattern. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1496-1504, 2018.

Effects of air-abrasion pressure on the resin bond strength to zirconia: a combined cyclic loading and thermocycling aging study.

OBJECTIVES: To determine the combined effect of fatigue cyclic loading and thermocycling (CLTC) on the shear bond strength (SBS) of a resin cement to zirconia surfaces that were previously air-abraded with aluminum oxide (Al2O3) particles at different pressures. MATERIALS AND METHODS: Seventy-two cuboid zirconia specimens were prepared and randomly assigned to 3 groups according to the air-abrasion pressures (1, 2, and 2.8 bar), and each group was further divided into 2 groups depending on aging parameters (n = 12). Panavia F 2.0 was placed on pre-conditioned zirconia surfaces, and SBS testing was performed either after 24 hours or 10,000 fatigue cycles (cyclic loading) and 5,000 thermocycles. Non-contact profilometry was used to measure surface roughness. Failure modes were evaluated under optical and scanning electron microscopy. The data were analyzed using 2-way analysis of variance and χ2 tests (α = 0.05). RESULTS: The 2.8 bar group showed significantly higher surface roughness compared to the 1 bar group (p < 0.05). The interaction between pressure and time/cycling was not significant on SBS, and pressure did not have a significant effect either. SBS was significantly higher (p = 0.006) for 24 hours storage compared to CLTC. The 2 bar-CLTC group presented significantly higher percentage of pre-test failure during fatigue compared to the other groups. Mixed-failure mode was more frequent than adhesive failure. CONCLUSIONS: CLTC significantly decreased the SBS values regardless of the air-abrasion pressure used.

Synthesis and characterization of novel halloysite-incorporated adhesive resins.

OBJECTIVE: To investigate the effects of Halloysite® aluminosilicate clay nanotubes (HNTs) addition on selected physical, mechanical, and biological properties of experimental adhesive resins. METHODS: Experimental dentin adhesive resins were prepared by mixing Bis-GMA, TEGDMA, HEMA (50/25/25wt.%), and photo-initiators. As-received HNTs were then incorporated into the resin mixture at distinct concentrations: 0 (HNT-free, control), 1, 2.5, 5, 7.5, 10, and 20wt.%. The degree of conversion (DC), radiopacity (RP), Knoop hardness (KHN), flexural strength (FS), and cytotoxicity analyses were carried out for each adhesive formulation. The adhesive resin of Adper Scotchbond Multi-Purpose (SBMP) was used as the commercially available reference for both the RP and cytotoxicity tests. Data were statistically analyzed using One-Way ANOVA and Tukey's test (p≤0.05). RESULTS: All adhesives exhibited similar DC (p=0.1931). The RP of adhesives was improved with the addition of up to 5wt.% of HNTs (p<0.001). Adhesives containing 5-10wt.% of HNTs led to greater KHN when compared to the control (p<0.001). The FS was reduced only when 20wt.% of HNTs was added (p≤0.001). None of the prepared adhesives was cytotoxic. CONCLUSION: The incorporation of up to 10wt.% of HNTs into the adhesive resins did not jeopardize the tested physical and biological properties. CLINICAL SIGNIFICANCE: When using HNTs as carriers of drugs/bioactive compounds, the amount of the former added into adhesive resin materials should not exceed 10wt.%; otherwise, a significant reduction in physicomechanical properties may be expected.