Background: Based on the role of properties of aligner materials on their efficiency, we aimed to assess their thermomechanical properties after thermoforming and simulated aging. Methods: In this experimental study, 96 samples of polyethylene terephthalate glycol (PETG) aligners (Duran and Erkodur) were prepared and divided to three groups: control (C), after thermoforming (T), after thermoforming and aging (TA). Thermoforming was done through 3D-printed molds, and aging was exerted by 200 thermal cycles after immersion in 37°C distilled water for 24h. Flexural modulus, hardness, glass transition temperature (Tg), elastic and viscous modulus, and loss factor were evaluated. Two-way ANOVA, T-independent, and Tukey HSD tests were done for statistical analysis and significance level was set to 0.05. Results: In both materials, flexural modulus decreased significantly after thermoforming, 88% in Duran and 70% in Erkodur, but did not change significantly after aging. After thermoforming, hardness decreased significantly in both materials (22% in Duran and 7.6% in Erkodur). Dynamic Tg was significantly lower in T and TA in both materials. At all temperatures (25, 37, 55°C) in Duran, the elastic modulus difference was only significant between C and TA, but in Erkodur, it decreased significantly in T, and there was no significant change after aging. Viscous modulus and loss factor showed the same change patterns at all temperatures. In both materials, they increased after thermoforming, but did not change significantly after aging. Conclusion: Thermoforming had more prominent role than aging in diminishing of thermomechanical properties. In general, Duran had greater thermomechanical stability than Erkodur.

One major drawback of orthodontic treatment is its long duration due to slow tooth movement and the pain at the onset of treatment following application of forces. There is controversy regarding the efficacy of laser for decreasing the treatment time and pain of orthodontic treatment. The purpose of this study was to investigate the effect of low level diode laser on the rate of orthodontic tooth movement and the associated pain. In this double blind randomized controlled clinical trial, 12 orthodontic patients referring to Shahid Beheshti School of Dentistry for first premolar extraction were randomly selected and allocated to gallium aluminum-arsenide laser (GA-AL-AS diode laser, 880 nm, 100 mW, 5 j/cm2, 8 points, 80 seconds, continuous mode) or control group. The patients initially underwent leveling and alignment using the sectional system. Force (150 gr) was applied to each canine tooth via sectional closing loops. The loops were activated every month. The rate of tooth movement and pain were monitored over the treatment period and recorded on days 1, 3, 7, 30, 33, 37, 60, 63 and 67. Two-way ANOVA was used for comparison of groups. There was no significant difference in terms of tooth movement and pain scores between the irradiated and non-irradiated sides at any time point (P>0.05). Although laser enhanced orthodontic tooth movement in the upper jaw, we failed to provide solid evidence to support the efficacy of laser for expediting tooth movement or reducing the associated pain.

Mortazavi H, et al. Imaging Sci Dent. 2019 Jun;49(2):87-95. https://doi.org/10.5624/isd.2019.49.2.87

Objective: The aim of this study was to evaluate the effect of agents available in whitening toothpastes (Crest^® and Sensodyne^®) in vitro on the force decay of elastomeric chains used in orthodontics. Materials and Methods: A total of 300 specimens of elastomeric chains were divided into five groups (n = 60) and were evaluated. These groups included (1) the regular Crest® toothpaste and distilled water solution, (2) whitening Crest^® toothpaste and distilled water solution, (3) regular Sensodyne^® toothpaste and distilled water solution, (4) whitening Sensodyne^® toothpaste and distilled water solution, and (5) distilled water as a control group. The samples' force was measured using Instron at intervals of 0, 1, 7, 14, 21, and 28 days. Data were analyzed by SPSS software. Results: At the initial time point, the difference in the force values of elastomeric chain between any of the groups was not significant (P > 0.05). On the 1^st day, there was a significant difference (P < 0.05) between all groups except the groups of whitening Crest^®, regular, and whitening Sensodyne^® (P > 0.05). On days 7, 14, and 28, the rate of decline for all groups was statistically significant (P < 0.05). Conclusions: According to the results obtained in the present study, it seems that toothpastes without whitening agents have less effect on force decay of elastomeric chain over time.

Objectives: This study sought to assess the effect of bracket base design on the shear bond strength (SBS) of the bracket to feldspathic porcelain. Materials and Methods: This in vitro, experimental study was conducted on 40 porcelain-fused-to-metal restorations and four different bracket base designs were bonded to these specimens. The porcelain surfaces were etched, silanized, and bonded to brackets. Specimens were thermocycler, incubated for 24 h and were subjected to SBS. Data were analyzed using Shapiro–Wilk test, Levene's test, one-way ANOVA, and Tukey's honest significant difference test. Adhesive remnant index was calculated and compared using Fisher's exact test. Results: One-way ANOVA showed that the SBS values were significantly different among the four groups (P < 0.001). Groups 1, 2, and 4 were not significantly different, but group 3 had significantly lower SBS (P < 0.001). Fractures mostly occurred at the porcelain-adhesive interface in Groups 1 and 2 while in Groups 3 and 4, bracket-adhesive and mixed failures were more common. Conclusion: The bracket base design significantly affects the SBS to feldspathic porcelain.

The myosin 1H (MYO1H) gene, located on chromosome 12, encodes the unconventional MYO1H protein, which is involved in the intracellular movement and morphology of chondrocytes, and plays a vital role in the prognathism or retrognathism of the mandible. The objective of this study was to assess the relationship between the polymorphisms of the MYO1H gene and mandibular prognathism in the Iranian population. The current project evaluated 64 patients with mandibular prognathism requiring orthognathic surgery and 60 controls with skeletal class I occlusion. Genome amplification was performed using specific primer pairs to assess the rs10850110 and rs11611277 polymorphisms of the MYO1H gene through the polymerase chain reaction (PCR). The restriction fragment length polymorphism (RFLP) technique was used to detect single-nucleotide polymorphisms. The data was analyzed using the χ2 test. The patient and control groups were not significantly different in terms of age or gender (p > 0.05). In all, 3.1% of patients and 6.7% of controls had the rs10850110 polymorphism (p = 0.680), and 1.6% of patients and 5% of controls had the rs11611277 polymorphism (p = 0.602). No significant correlation was noted between the rs10850110 and rs11611277 polymorphisms of the MYO1H gene and mandibular prognathism in the Iranian population. However, the lower frequency of these polymorphisms in the patient group suggests a possible association with mandibular retrognathism, which needs to be investigated with a larger sample size.