Simulation of Initial Forces and Moments on a Curve of Spee Malocclusion with Labial and Lingual Orthodontic Appliances

  • Author / Creator
    Yeung, Silas Kwun-Yee
  • OBJECTIVES: Orthodontic movement is determined by the acting forces and moments exerted onto teeth, which are difficult to predict and calculate with continuous archwires. Levelling the curve of Spee is a fundamental objective in orthodontic treatment. The forces and moments exerted by labial and lingual orthodontic fixed appliances using three archwire forms (labial straightwire, lingual straightwire, and lingual mushroom) on mandibular teeth in a curve of Spee malposition were compared. An increased understanding may have clinical implications pertaining to orthodontic appliance design in preventing adverse effects such as undesirable tooth movement and root resorption.

    METHODS: The Orthodontic SIMulator (OSIM) measured the three-dimensional forces and moments on each tooth of a mandibular arch (excluding third molars) set in a curve of Spee malposition with the first premolar intruded 1.5mm and the canine and second premolar intruded 0.75mm. Labial and lingual brackets were bonded to the mechanical teeth initially in a levelled position. Attached load cells measured the forces and moments as the dental analogs, with an archwire engaged, moved to the curve of Spee position. Three treatment groups (archwire forms) were assessed: labial straightwire, lingual straightwire, and lingual mushroom. The primary forces and moments of interest were occlusal-gingival forces (Fz), labial-lingual forces (Fy), and labial-lingual moments (Mx).

    RESULTS: Similarities and differences were observed between the archwire forms. All archwire forms generally exerted forces in the same direction on the mandibular teeth but at different magnitudes. Teeth positioned below the occlusal plane received occlusal forces relative to their displacement, while the lateral incisor received large gingival forces with all groups. The lowest force magnitudes were noted with labial straightwires at each tooth position. The first premolar and first molar had different directional labial-lingual moments between labial and the two lingual archwire forms. The standard deviations of horizontal moments on the first premolar were substantially large with lingual archwire forms.

    CONCLUSION: The initial forces and moments of interest (Fz, Fy, and Mx) on mandibular mechanical teeth in a curve of Spee malposition were different between labial and lingual archwire forms. The majority of the recorded forces and moments were above the clinically significant threshold for tooth movement. Similar pattern of labial-lingual and occlusal-gingival forces were exerted been labial and lingual archwire forms. The lateral incisor received large gingival forces and labial crown tipping forces, which has increased concerns of root resorption. Labial straightwires exerted the lowest magnitudes at each tooth position and have increased transverse effects on the crowns of posterior teeth. With both lingual archwire forms, the first premolar resulting labial-lingual incliniation could be highly variable, as it had large standard deviation of labial-lingual moments.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.