Changes in mechanical properties, surface morphology, structure, and composition of Invisalign material in the oral environment.

INTRODUCTION: The mechanical properties of Invisalign material have rarely been explored because of the inaccessibility of the patent-protected raw material. The purpose of this study was to systematically evaluate the Invisalign thermoformed aligner material before and after clinical application, including mechanical properties, surface morphology, internal structure, and chemical composition changes. METHODS: Twenty sets of "as-received" (0-week) and retrieved (2-week; worn for 2 weeks, 20 ± 2 hours per day) Invisalign aligners were randomly collected from 4 different patients. Tensile tests, stress relaxation, and creep tests were carried out with a dynamic mechanical analyzer to characterize the changes in the mechanical properties of this material, Fourier transform infrared spectroscopy was used to capture the molecular changes on the surface of these aligners, scanning electron microscopy and transmission electron microscopy were used to observe the changes in surface morphology and internal structure, and scanning transmission electron microscopy-energy dispersive x-ray analysis was used to detect any changes in the chemical composition of this material before and after clinical application. RESULTS: The elastic modulus of 0-week and 2-week samples were 842 ± 63 MPa and 806 ± 19 MPa, respectively, with no significant difference. In addition, the relative stress after stress relaxation of 2 hours was 19.89 ± 2.25% and 15.91 ± 6.04% for 0-week and 2-week groups, respectively, with no significant difference. Scanning electron microscopy observations showed voids and signs of delamination on the surface of the 2-week samples, and scanning transmission electron microscopy-energy dispersive x-ray analysis indicated the possible release of trace elements during clinical use, such as aluminum. Results of Fourier transform infrared spectroscopy analysis, and transmission electron microscopy observations were quite stable, indicating that the molecular structure on the surface and the internal structure of this material were relatively stable under the oral environment. CONCLUSIONS: The surface morphology showed some defects after the clinical use of 2 weeks; however, there was no significant difference in mechanical properties. Trace elements may release out during clinical use and may pose a specific danger to allergic patients.

Effectiveness of three-dimensional conformal radiotherapy for treating early primary nasopharyngeal carcinoma.

OBJECTIVE: In 2-dimensional radiotherapy, the irradiating portal is defined mainly by soft tissues and bony structures, so the exact location of nasopharyngeal tumors and many spatial relationships are unknown, resulting in high local-regional relapse rates and radiation toxicities. Three-dimensional conformal radiotherapy (3D CRT) provides more precise targeting of radiation. We studied whether 3D CRT could maintain survival and increase local-regional tumor control whereas reducing the morbidity and severity of radiation toxicity in patients with early primary nasopharyngeal carcinoma (NPC). METHODS: Patients with histologically proven keratinizing or nonkeratinizing undifferentiated NPC (T1₋2N0₋1M0 stage) received a prescribed 3D CRT dose of 70 Gy to the gross tumor volume (GTV(nx)), 60 Gy to the GTV(nx) with an additional 5- to 10-mm margin (CTV(nx)60), 60 to 70 Gy to the region involved by the metastatic lymph nodes (GTV(nd)), and 50 Gy to the prophylactic irradiating region (CTV(nd)50). RESULTS: Of 58 patients enrolled between August 2001 and December 2006, (48 men; median age, 46 years; range, 29-69 years), 15 had stage I and 43 had stage II disease. At 5 years, overall survival was 95% and disease-free survival was 91%; 93% of patients were free of local-regional recurrence and 98% were free of distant metastases. Grade 2 or 3 xerostomia occurred in 7 patients and trismus occurred in 5. Mean standard deviation (SD) dental gap was 37.4 (6.9) mm. Four patients had recurrent lesions, mainly in-field. CONCLUSIONS: The survival and morbidity provided by 3D CRT were excellent in these patients with early NPC.

[Sparing normal oral tissues with individual dental stent in radiotherapy for primary nasopharyngeal carcinoma patients].

BACKGROUND & OBJECTIVE: With the progression of radiotherapy techniques, the 5-year overall survival rate of nasopharyngeal carcinoma (NPC) patients has increased obviously. As the survival time prolonged, more and more attention was paid to various radiation sequelae and the quality of life of the patients. This study was to explore the role of individual dental stent in sparing normal oral tissues for primary NPC patients in radiotherapy by pushing the tongue and a part of oral mucous membrane away from the radiation fields. METHODS: Irradiation dose and volume of the tongue of a NPC patient before and after wearing dental stent was evaluated. A total of 43 patients were randomized into 2 groups: 19 in trial group and 24 in control group. Trial group wore dental stent during radiotherapy, while control group did not. Patients' weight, taste, oral mucous reaction, and tongue mucous reaction before radiotherapy and every week during radiotherapy were examined. RESULTS: Dosimetric analysis proved that the irradiation dose and volume of the tongue decreased obviously in trial group. The occurrence rate of grade 1-2 mucositis of the oral cavity was higher in trial group than in control group (73.68% vs. 62.50%), but the occurrence rate of grade 3-4 mucositis was lower in trial group than in control group (26.32% vs. 37.50%, P=0.470). By the completion of radiotherapy, 4 (21.05%) patients in trial group and 19 (79.17%) in control group suffered from taste dysfunction (P<0.001). CONCLUSION: Individual dental stent is useful in sparing the oral mucous membrane and preserving taste for primary NPC patients in radiotherapy.