A photoelastic study of the stress distribution by multiloop edgewise arch wire / 대한치과교정학회지

The purpose of this study was to investigate the force mechanism of Multiloop Edgewise Arch Wire and the intensity and distribution of stresses with vertical and intermaxillary elastics. The obtained results were as follows. 1. When plain wires were inserted and vertical and intermaxillary elastics were used in the upper and lower arch, the stresses of the anterior and posterior ends of wires were observed greatly but the stresses of the premolar were very small. 2. When MEAW were inserted in upper and lower arch, the upper 1st and 2nd premolar and the lower 1st premolar were extruded greatly. 3. In the area of the upper 1st molar and the lower 2nd premolar and the lower 1st molar, any stresses were not observed. 4. The vertical elastic counteracted the intrusion force of the MEAW in the anterior teeth but could not affect on posterior teeth. Using with the Class II elastics, the distal tipping force and extrusion force were exerted in the upper anterior teeth and the intrusion forces of the lower anterior teeth were relieved. Using with the Class III elastics, the extrusion force were exerted in the upper and lower anterior teeth, the distal tipping force were increased in the lower posterior teeth. 5. The Class II elastic counteracted the anterior intrusion force of the MEAW and extruded and tipped mesially the lower 2nd molar. The intrusion force of the MEAW also could not overcome the extrusion force of the class II elastics. 6. When the Class III elastics were engaged, the upper 2nd molar was extruded in spite of the intrusion forces of the MEAW and the extrusion forces of the lower anterior teeth and distal tipping forces in the posterior teeth were observed.

The increase of enamel crack in debonding teeth / 대한치과교정학회지

The aim of this study was to clarify whether bonding/debondmg procedure will affect the occurance of enamel crack. The frequency of enamel crack was compared between before-bonding and after-debonding on 200 human extracted teeth Each facial surface of the tooth was divided in 9 fragments A presence of crack, which was classified by its direction as vertical, horizontal and oblique crack, was surveyed in each fragment. Number of all cracks in facial surface was 1355 at before-bonding, and 1605 at after-debonding, so it revealed significant increase rate of 18.5%, but compared by fragment, cracks were significantly increased in OC, OD, CC and GC fragments. All kinds of cracks were significantly increased, especially increase rate of oblique crack reached 54.9%. The increase rate of cracks was not superior at any fragment or region, but some evidence was seen in CC fragment. Judging from the above, increase of crack is unavoidable with bonding/debonding procedures.