[show abstract][hide abstract] ABSTRACT: The purpose of this study was to evaluate the nanohardness and elastic modulus of human enamel after treatment with tray and strip bleaching systems.
Fifty-five human enamel samples were exposed to five different bleaching agents. Nanoindentations were made before and after bleaching treatments following the manufacturer's directions using a Nanoindenter XP (MTS Systems Corporation, Oak Ridge, TN, USA). Nanohardness and elastic modulus measurements were obtained and the results were statistically analyzed using a repeated measures analysis of variance with a post-hoc Tukey-Kramer multiple comparison test.
Nanohardness and elastic modulus measurements showed decrease of mean values for each group except the control which remained the same. There were significant differences due to time (before and after treatment) and material effects in nanohardness (P<0.0001) and elastic modulus (P=0.0241). Measurements after treatment showed significant decrease in nanohardness between all groups and the control group. There was a significant difference in hardness between CP and TO after treatment. Additionally, there were significant differences in elastic modulus between the control group when compared to OB and TO after treatment. While there were significant changes in the elastic modulus due to treatment for both CP and TO, there were no significant differences between any of the groups after treatment.
Nanohardness and elastic modulus of human enamel were significantly decreased after the application of home-bleaching systems.
Journal of Dentistry 12/2008; 37(3):185-90. · 3.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: The peer assessment rating (PAR) index is a valid and reliable tool for measuring malocclusion on plaster models, but it has not been shown to be valid and reliable when used to score computer-based digital models. The purpose of this study was to determine whether the PAR index is a valid and reliable measure on digital models.
The study sample consisted of 48 pairs of plaster and digital pretreatment models. One examiner, calibrated in the PAR index, scored the digital and plaster models. The overall PAR scores were examined for reliability and validity by using analysis of variance and the intraclass correlation coefficient (ICC). Reliability of the components of the PAR score was compared with values originally presented by Richmond et al (1992).
No significant differences were found between overall PAR scores of plaster and digital models (P = .82), and scores were highly correlated (ICC = 0.95; lower confidence boundary (LCB) = 0.92; upper confidence boundary (UCB) = 0.97). Intraexaminer reliability was excellent for both plaster models (ICC = 0.98; LCB = 0.97; UCB = 0.99) and digital models (ICC = 0.96; LCB = 0.94; UCB = 0.98). Reliability of all components of the PAR score generated on digital models except for buccal occlusion was similar to those of Richmond et al.
PAR scores derived from digital models are valid and reliable measures of occlusion.
American Journal of Orthodontics and Dentofacial Orthopedics 11/2005; 128(4):431-4. · 1.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: To determine if a specific resorbable plating system provides similar fixation, in terms of strain distribution under load, to a titanium system when the Champy technique is applied for the treatment of a mandibular angle fracture.
A formalin-fixed cadaver mandible was harvested just before the study. A bicortical osteotomy was then made using a diamond disc extending in an oblique direction in the area of the angle. It was then passively fixated with a 4-hole 2.0-mm miniplate. Two stacked rosette strain gauges were bonded to the mandible on either side of the fracture. Each rosette had 3 strain gauges arranged in specific degrees relative to each other. The mandible was then placed on a dynanometer and 30 lb loads were delivered on the ipsilateral molar. Static resistance was placed in the condylar neck region to simulate the glenoid fossa. Loading was repeated 10 times with a period of 3 minutes between loads. Measurements were recorded for each strain gauge after loads were in place for 30 seconds. The same process was repeated using a 4-hole 2.1-mm resorbable miniplate. The strains were then used to calculate the maximum and minimum strains for each rosette. Hooke's law was used to calculate the principal stresses.
Differences were observed between the strain gauges for each individual plating system. There was variability within the resorbable plate measurements as shown by the standard deviation. Using the REML ANOVA test, a significant difference was found between the 2 materials.
In this in vitro study, there were significant biomechanical differences observed between a 2.0-mm titanium miniplate and a 2.1-mm resorbable miniplate when used to treat a mandibular angle fracture following Champy's principles. Based on our finding, both systems cannot be used interchangeably for the treatment of mandibular angle fractures under the same clinical conditions.
Journal of Oral and Maxillofacial Surgery 08/2005; 63(7):968-72. · 1.33 Impact Factor
[show abstract][hide abstract] ABSTRACT: This single-blind controlled clinical study characterized the effects of 30-70% nitrous oxide (N2O) and 0.2-0.8% sevoflurane conscious sedation on quantitative electroencephalographic (EEG) readings of 22 healthy dental students as measured by the bispectral index (BIS). The study verified the 2 previously published BIS/N2O investigations showing no correlation between N2O dosage up to 70% and BIS. Observer's Assessment of Alertness and Sedation scores (OAA/S), however, correlated well with increasing doses of N2O from approximately 35 to 70%. A near linear dose-response relationship was established between OAA/S and end tidal (ET) sevoflurane concentrations of 0.4-0.7%. Only at the highest level of end tidal sevoflurane recorded, 0.7%, was statistically significant BIS depression seen. Subjects evaluated the acceptability of the sedative effect of the 2 gases, showing a slight preference for N2O. Comparable partial anterograde amnesia and sedation (OAA/S) were produced by both agents in administered concentrations of 40-70% N2O and 0.6-0.8% sevoflurane. Female subjects exhibited better memory and significantly less amnesia than males. No statistically significant changes occurred in any of the monitored vital signs. EMG readings demonstrated a statistically significant difference from control values only at the highest, 0.7%, ET concentration of sevoflurane. BIS does not appear useful for evaluating the level of nitrous oxide sedation in the dental setting but may have some value in assessing depth of sedation at deeper levels of sevoflurane sedation.