Impact of altering the dispensing methods of resin-based cements on their physical and bonding qualities.

STATEMENT OF PROBLEM: Despite the advances in dental cements a significant gap remains in understanding how different dispensing and mixing techniques impact the physical properties of resin-based cements. PURPOSE: The purpose of this in vitro study was to investigate how the physical properties, shear bond strengths (before and after thermocycling), and film thickness of resin-based cements change based on the dispensing and mixing methods. MATERIAL AND METHODS: Eight different resin-based cements were evaluated, and specimens were prepared for each method (n=14) by following International Organization for Standardization (ISO) standards. The specimens were desiccated and immersed according to the ISO standard, and measurements were made to determine water sorption, solubility, mass change, and film thickness. Finally, specimens were thermocycled (5-55˚C for 20 000 cycles), and shear bond strength was evaluated. Statistical analysis was then performed with the 1- and 2-way ANOVA and the Tukey post hoc test (α=.05). RESULTS: For Variolink Esthetic (automix, 30.03 µg/mm3), the Wsp was 74.8% greater than Variolink II (hand mix, 17.18 µg/mm3) and 682.3% more soluble (P<.05). The least soluble resin-based cements were RelyX Unicem (3.83 µg/mm3), RelyX Unicem 2 (2.22 µg/mm3), and Variolink II (2.43 µg/mm3). PANAVIA SA automix and G-CEM LinkAce automix had twice the film thickness as their hand mixed counterparts (P<.05). Thermocycling reduced the shear bond strength for most resin-based cements. RelyX Unicem (3.94 MPa), Variolink II (8.52 MPa), and G-CEM Capsule (5.02 MPa) demonstrated significantly higher shear bond strength compared with their automix counterparts (P<.05). CONCLUSIONS: The dispensing methods were found to significantly impact the properties of resin-based cements. Variolink II demonstrated the lowest water sorption and highest shear bond strength among the cements tested. RelyX in both mixing methods exhibited a low solubility rate. Additionally, RelyX showed consistent thickness, regardless of the different dispensing methods.

Effect of simulated toothbrushing on the surface roughness of LOCATOR abutments: An in vitro study.

STATEMENT OF PROBLEM: Studies evaluating the effect of toothbrushing and toothpaste abrasivity on the surface roughness of LOCATOR abutments are lacking. PURPOSE: The purpose of this in vitro study was to compare the surface roughness of LOCATOR abutments before and after simulated toothbrushing with different toothpastes to make recommendations for the home care of patients with LOCATOR abutments. MATERIAL AND METHODS: LOCATOR bone-level overdenture abutments (N=36) were analyzed with a confocal laser scanning microscope (Keyence VK-X1100) at ×5 magnification. Surface scans were made to determine the degree of surface roughness (Ra). Two toothpastes of different abrasivity (Colgate Total and Crest ProHealth) and deionized water were used as the brushing media (n=12). Each toothpaste was mixed with water in a 1:2 ratio. The abutments were brushed using soft nylon toothbrushes for 30 000 cycles in a ZM-3.12 toothbrushing simulator, which has been interpreted as 3 years of regular use. All specimens were then reanalyzed under the microscope. Changes in surface texture were compared by using a repeated measures analysis of variance (ANOVA) statistical test and a pairwise Sídák multiple comparisons test (α=.05). RESULTS: The mean surface roughness value of LOCATOR abutments at baseline ranged between 1.34 µm and 1.35 µm. After 30 000 cycles of toothbrushing simulation, the mean value increased to 1.62 µm (DI water, P=.001), 1.74 µm (Colgate Total, P<.001), and 2.03 µm (Crest ProHealth, P<.001). All brushing media resulted in a statistically significant increase in surface roughness (P<.001). CONCLUSIONS: LOCATOR abutments demonstrated significant increases in surface roughness after being subjected to toothbrushing, regardless of the brushing medium. Whitening toothpaste caused significantly more surface roughness than nonabrasive toothpaste and deionized water. Deionized water resulted in the lowest increase in surface roughness.

Effectiveness of a Chairside Acrylic Adjustment Cabinet in Reducing Dental Acrylic Debris and Aerosols.

PURPOSE: Chairside prosthesis adjustment procedures generate contaminated acrylic particle debris that include visible splatter (particles >50 µm) as well as invisible aerosols (<50 µm). The purpose of this study was to evaluate the effectiveness of a chairside acrylic adjustment cabinet (CAAC) in reducing airborne aerosol particles (<10 µm) and visible acrylic debris, time required for airborne aerosols to return to baseline levels after an acrylic adjustment procedure, and the effect on operatory turnover time. MATERIALS AND METHODS: A total of 40 acrylic adjustment procedures were carried out in a simulated setting with (experiment) and without (control) a CAAC. Standardized acrylic samples of self-polymerized, and heat polymerized polymethylmethacrylate resins, Triad™ and Fastray™ custom tray materials were evaluated. Airborne aerosol measurements were done using a handheld Lase.r Particle Counter for absolute particle counts of sizes 0.3, 0.5, 1.0, 2.5, 5.0, and 10.0 µm before, during, and immediately after adjustment and 10 minutes postadjustment. Spread of aerosols was assessed at three distinct locations within the dental operatory specific to the provider, the patient, and the caregiver/guest. Visible acrylic debris and operatory turnover time were evaluated immediately postadjustments by a blinded investigator. Repeated measures ANOVA was used to estimate group effect, time effect and interaction between group and time for air particle analysis. Independent samples T-tests were used for group differences between operatory turnover time, and time for aerosols to return to baseline. Chi-square test was used for visible surface analysis. RESULTS: In the control group, total aerosol particle counts increased from 6542.7 ± 162.6 particles at baseline to 598378.7 ± 586363.2 and 367569.9 ± 432220.8 particles during and immediately postadjustment, respectively. Adjustments made in the experiment group led to significantly reduced aerosol counts during (97738.9 ± 97866.5) and immediately postadjustment (19786.5 ± 14004.9; F = 17.8, p = 0.006). Similar trends were noted for the patient and guest positions. Time for aerosol particles to return to baseline was significantly lower in the experiment group (20.56 ± 14.5 minutes) compared to the control group (37.9 ± 31.96 minutes; p = 0.03). Visible acrylic debris analysis showed a significant decrease of 78% in the experiment group (p < 0.001). No significant differences were noted in operatory turnover time between the two groups (p = 0.61). CONCLUSIONS: Acrylic adjustment procedures generated aerosols of particle sizes less than 10 µm and were measured in significant quantities throughout the dental operatory for up to 115 minutes. Chairside acrylic adjustment cabinets significantly decreased airborne aerosols, visible acrylic particle debris, and reduced the time for airborne aerosols to return to baseline levels.

Comparative Analysis of Sensory Responses from Dental Implants vs Natural Teeth: An In Vivo Study.

Purpose: To compare subjects' sensory responses to horizontal and vertical forces on tooth- and implant-supported restorations. Materials and Methods: In this prospective study, three protocols simulating the horizontal or vertical forces that occur during mastication were used to obtain subjective responses from subjects. These protocols included the measurement of horizontal force intensity during excursive movements and the identification of initial contact during guided and free vertical closure. Responses were recorded using a 1- to 10-point visual analog scale (VAS) and/ or monitored with electromyography (EMG) and Tekscan. Results: The study included 30 patients with a single implant-supported restoration (ISR) with a contralateral tooth-supported restoration (TSR). For horizontal forces similar to those of mastication (0.6 N), subject VAS scores were similar for both ISRs and TSRs at 6.3 vs 6.1, respectively. At reduced forces (0.2 and 0.4 N), subject responses were greater for the TSR at 3.4 and 5.4, respectively, as opposed to 1.2 and 2.6 for ISR, respectively (P < .01). During vertical guided closure (Test 1) at 25% of maximum bite force (MBF), subjects were more successful at correctly identifying initial contact of TSRs at a rate of 12 out of 17, compared to ISRs, which achieved a rate of 4 out of 13 (P < .1). In vertical free closure (Test 2), subject responses for the correct identification of initial contact at 50% MBF were similar for both TSRs and ISRs at 13 out of 17 and 9 out of 13, respectively. However, comparing the correct responses for subjects whose initial contacts were ISR showed a significant improvement in correct answers from Test 1 to Test 2, from 4 out of 13 correct to 9 out of 13 correct (P < .05). Conclusion: While the mechanism is not clear, subjects' ability to discern the horizontal and vertical forces at levels comparable to mastication appear similar between TSRs and ISRs.