Phase transformation and force-deflection responses of niti archwire for bracket assembly in orthodontic treatment_Muhammad Fauzinizam Razali_K4_2018_MYMY
Dawai arkus NiTi digunakan secara meluas di peringkat awal rawatan ortodontik kerana ciri-ciri super-elastik dan biokompatibiliti. Walaupun dawai arkus super-elastik NiTi sering digunakan di setiap peringkat rawatan ortodontik, evolusi penjelmaan fasa dan tingkah laku daya-defleksi dawai ini ketika dilenturkan dalam sistem pendakap masih kurang diketahui. Oleh kerana perubahan lenturan sering ditemui semasa rawatan pengarasan gigi, tahap ubah bentuk dawai dan geseran akan mengubah tingkah laku daya-defleksi dan seterusnya menjauhi kriteria daya optimum. Kajian ini menyiasat evolusi penjelmaan fasa dan daya yang dikeluarkan oleh dawai arkus NiTi semasa rawatan pengarasan. Model unsur terhingga tiga dimensi bagi lenturan dawai arkus NiTi dalam konfigurasi tiga pendakap gigi telah dibangunkan dengan menggunakan subrutin bahan dan interaksi sentuh. Pekali geseran yang diperlukan untuk menentukan hubungan antara dawai dan pendakap keluli tahan karat diperoleh daripada ujian geluncur. Kecekapan model ini diperiksa dengan membandingkan ramalan lengkung daya-defleksi dengan keputusan eksperimen. Penyelidikan ini meningkatkan pengetahuan terkini tentang pengaruh geseran kepada tingkah laku daya-defleksi dawai arkus NiTi melalui kajian kuantitatif pada dua keadaan; melentur dawai pada pelbagai konfigurasi pengarasan (jarak antara pendakap, lenturan dawai dan suhu mulut) dan melentur dengan padanan pendakap yang diperbuat dari bahan yang berbeza (nilai pekali geseran diubah antara 0.1 hingga 0.5). Semasa melentur, hanya sebahagian kecil panjang dawai mengalami transformasi daripada austenit ke martensit manakala selebihnya tidak mengalami sebarang ubahbentuk. Dawai yang diaktifkan pada 2.0 mm menghasilkan tegasan maksimum pada plateau tegasan, menunjukkan bahawa ubah bentuk dawai NiTi disebabkan oleh transformasi martensit yang diaruh tegasan. Dawai yang dilenturkan sehingga 3.0 mm dan 4.0 mm menghasilkan tegasan maksimum pada garis elastik martensit. Penambahan magnitud geseran di pinggir pendakap gigi meningkatkan daya maksimum dan cerun lengkung penyahaktifan dengan ketara, disamping mengurangkan nilai daya minimum. Bagi kes lenturan 4.0-mm, dawai berdiameter 0.4-mm menghasilkan daya di antara 0.13 N sehingga 0.73 N, yang mana dalam julat daya optimum untuk mencapai gerakan gigi yang effektif. Nilai geseran tertinggi bermagnitud 8.33 N dan 3.72 N telah dihasilkan ketika melentur dawai 0.40 × 0.56-mm dan 0.4-mm sebanyak 4.0 mm pada suhu 46°C dengan menggunakan jarak antara pendakap 7.0 mm. Model regresi yang dibangunkan boleh digunakan untuk menjangka daya-defleksi dawai NiTi, khususnya bagi sistem pendakap yang dikaji. Pemadanan dawai bulat dengan pendakap seramik (≥ 0.4) menghasilkan daya bermagnitud sifar di awal urutan penyahaktifan, seterusnya menghalang gerakan gigi yang diperlukan. __________________________________________________________________________
NiTi archwires are used widely during the early stage of orthodontic treatment due to its superelastic and biocompatibility properties. Even though the superelastic NiTi archwires are always preferred in most orthodontic treatments, the evolution of phase transformation and force-deflection behaviour of this wire subjected to bend in the bracket system is still uncertain. Since changes in bending setting are frequently encountered during levelling, the extent of wire deformation and binding friction at the wire-bracket interface would alter the force-deflection behaviour and subsequently defies the optimal force criteria. This study investigated the evolution of phase transformation and forces released by NiTi archwire during orthodontic levelling treatment. For this purpose, a three-dimensional finite-element model of superelastic NiTi wire bends in three-bracket configurations was developed by employing a user material subroutine of superelasticity and contact interaction. The friction coefficient required to define the contact between the wire and stainless steel bracket was obtained from a sliding test. The competency of the bending model was examined by comparing the predicted force-deflection curve with the experimental results. The work further advanced the current knowledge on the influence of binding towards the force-deflection behaviour of NiTi wire by performing a quantitative study at two levelling conditions; bending at different levelling settings (inter-bracket distance, wire deflection and oral temperature) and bending with the presence of different bracket materials (friction coefficient at contact locations were varied from 0.1 to 0.5).
During bending, only a small section of the wire length underwent austenite to martensite transformation, leaving the rest of the length substantially undeformed. The wire activated to 2.0 mm produced the maximum stress on the stress plateau, implying that the NiTi wire was deformed by stress-induced martensitic transformation. The wire activated to 3.0 mm and 4.0 mm essentially produced the maximum stress on the elastic line of martensite. The generation of binding at the bracket edges significantly elevated the maximum force and the slope of the deactivation curve, whilst diminished the minimum force values. The greatest binding of 8.33 N and 3.72 N was generated by the 0.40 × 0.56-mm and 0.4-mm archwires at the maximum deflection (4.0 mm) and temperature readings (46°C), and at the minimum inter-bracket distance (7.0 mm). For the case of large tooth displacement (4.0 mm), the 0.4-mm archwire delivered force in between 0.13 N to 0.73 N, which are within the optimal force range. The developed regression model can be used to predict the force-deflection of NiTi wire for the studied bracket system. Additionally, the archwires coupled with the ceramic brackets (≥ 0.4) produced zero force magnitude at the onset of the deactivation cycle, thus inhibited further tooth movement.
Phase transformation and force-deflection responses of niti archwire for bracket assembly in orthodontic treatment_Muhammad Fauzinizam Razali_K4_2018_MYMY
Phase transformation and force-deflection responses of niti archwire for bracket assembly in orthodontic treatment / Muhammad Fauzinizam Razali