Finite element analysis of the biomechanical effect of clear aligners in extraction space closure under different anchorage controls.

INTRODUCTION: Clear aligners (CAs) have attracted increasing attention from patients and orthodontists because of their excellent esthetics and comfort. However, treating tooth extraction patients with CAs is difficult because their biomechanical effects are more complicated than those of traditional appliances. This study aimed to analyze the biomechanical effect of CAs in extraction space closure under different anchorage controls, including moderate, direct strong, and indirect strong anchorage. It could provide several new cognitions for anchorage control with CAs through finite element analysis, further directing clinical practice. METHODS: A 3-dimensional maxillary model was generated by combining cone-beam computed tomography and intraoral scan data. Three-dimensional modeling software was used to construct a standard first premolar extraction model, temporary anchorage devices, and CAs. Subsequently, finite element analysis was performed to simulate space closure under different anchorage controls. RESULTS: Direct strong anchorage was beneficial for reducing the clockwise occlusal plane rotation, whereas indirect anchorage was conducive for anterior teeth inclination control. In the direct strong anchorage group, an increase in the retraction force would require more specific anterior teeth overcorrection to resist the tipping movement, mainly including lingual root control of the central incisor, followed by distal root control of the canine, lingual root control of the lateral incisor, distal root control of the lateral incisor, and distal root control of the central incisor. However, the retraction force could not eliminate the mesial movement of the posterior teeth, possibly causing a reciprocating motion during treatment. In indirect strong groups, when the button was close to the center of the crown, the second premolar presented less mesial and buccal tipping but more intrusion. CONCLUSIONS: The 3 anchorage groups showed significantly different biomechanical effects in both the anterior and posterior teeth. Specific overcorrection or compensation forces should be considered when using different anchorage types. The moderate and indirect strong anchorages have a more stable and single-force system and could be reliable models in investigating the precise control of future tooth extraction patients.

Colour stabilities of three types of orthodontic clear aligners exposed to staining agents.

The aim of this study was to evaluate and compare the colour stabilities of three types of orthodontic clear aligners exposed to staining agents in vitro. Sixty clear orthodontic aligners produced by three manufacturers (Invisalign, Angelalign, and Smartee) were immersed in three staining solutions (coffee, black tea, and red wine) and one control solution (distilled water). After 12-h and 7-day immersions, the aligners were washed in an ultrasonic cleaner and measured with a colourimeter. The colour changes (ΔE*) were calculated on the basis of the Commission Internationale de I'Eclairage L*a*b* colour system (CIE L*a*b*), and the results were then converted into National Bureau of Standards (NBS) units. Fourier transformation infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) were conducted to observe the molecular and morphologic alterations to the aligner surfaces, respectively. The three types of aligners exhibited slight colour changes after 12 h of staining, with the exception of the Invisalign aligners stained with coffee. The Invisalign aligners exhibited significantly higher ΔE* values (ranging from 0.30 to 27.81) than those of the Angelalign and Smartee aligners (ΔE* values ranging from 0.33 to 1.89 and 0.32 to 1.61, respectively, P<0.05). FT-IR analysis confirmed that the polymer-based structure of aligners did not exhibit significant chemical differences before and after the immersions. The SEM results revealed different surface alterations to the three types of aligner materials after the 7-day staining. The three types of aesthetic orthodontic appliances exhibited colour stability after the 12-h immersion, with the exception of the Invisalign aligners stained by coffee. The Invisalign aligners were more prone than the Angelalign and Smartee aligners to pigmentation. Aligner materials may be improved by considering aesthetic colour stability properties.

[Correlation of high-risk HPV 16/18 infections with prostate cancer].

OBJECTIVE: To study the correlation of high-risk human papillomavirus 16 and 18 (HPV16/18) infections with the risk of prostate cancer (PCa) and their association with the clinicopathologic indexes of PCa. METHODS: We collected tissue samples from 75 cases of PCa and 73 cases of benign prostatic hyperplasia (BPH). We detected HPV16/18 infections in the samples by immunohistochemistry and PCR combined with reverse dot blot (RDB) assay. RESULTS: Immunohistochemistry revealed 16 cases of HPV16/18 positive in the PCa (21.3%) and 7 cases in the BPH samples (9.5%), with statistically significant difference between the two groups (P=0.049). PCR combined with RDB assay showed 17 cases of HPV16 infection (22.6%) and 13 cases of HPV18 infection (17.8%), including 4 cases of HPV16/18 positive, in the PCa group, remarkably higher than 6 cases of HPV16 infection (8.2%), 3 cases of HPV18 infection (4.1%) and no HPV16/18 positive in the BPH controls (P=0.001). No significant differences were observed between the result of immunohistochemistry and that of PCR combined with RDB assay (P=0.069). The risk of HPV16/18 infections was found to be correlated with the clinical T-stage and Gleason score of PCa (P<0.05 ) but not with the patient's age, PSA level or lymph node metastasis (P>0.05 ). CONCLUSIONS: High-risk HPV16/18 infections are correlated with the risk of prostate cancer.