Adaquate fixation of plates for stability during mandibular reconstruction.
OBJECTIVE
To determine the most appropriate plate fixation for dispersing the stress around screws in mandibular reconstruction.


METHODS
Forty-eight three-dimensional reconstructed mandibular models with Central (C) or right Lateral (L) defects were created and divided into three groups, fixed with: (1) two screws on each side, (2) three screws on the left side with the third (middle one) located distally, or (3) three screws on the left side with the third (middle one) located proximally. A 300N vertical load was applied to the left molar region. The maximum stress was calculated using a finite element method and statistically evaluated.


RESULTS
Stress was concentrated around the screw at the distal end of the mandibular halves on the loaded side ('crucial screw'). For the C defect, stress concentrated around the 'crucial screw' was greater when there were only two screws for fixation (20.55MPa) than when there were three screws (16.17MPa; p=0.022). No significant difference was found between the two groups with three screws for fixation. For the L defect on the other hand, stress on the 'crucial screw' was relatively greater when there were three screws for fixation (18.9MPa) than when there were only two screws for (12.83MPa; p=0.051). No significant difference was found between the two groups with three screws for fixation. As for the reconstruction plate, the stresses on the plates were not different among the various screw groups for fixation nor among the C and L defects.


CONCLUSIONS
This paradoxical result is explained by plate bowing. Thus in large defects screw positions should take into consideration the potential for plate bowing.
Kimura
Akiko
A
Department of Plastic and Reconstructive Surgery, Keio University, School of Medicine, Tokyo, Japan. 941736@infoseek.jp
Nagasao
Tomohisa
T
Kaneko
Tsuyoshi
T
Tamaki
Tamotsu
T
Miyamoto
Junpei
J
Nakajima
Tatsuo
T
D001732:Bite Force; D001860:Bone Plates; D001863:Bone Screws; D001842:Bone and Bones / Q000502:physiology; D003198:Computer Simulation; D015921:Dental Implants; D003799:Dental Stress Analysis / Q000379:methods*; D020342:Finite Element Analysis; D006801:Humans; D008334:Mandible / Q000601:surgery*; D008341:Mandibular Prosthesis; D008409:Mastication; D008410:Masticatory Muscles / Q000502:physiology; D008953:Models, Anatomic; D019647:Oral Surgical Procedures / Q000295:instrumentation; D011474:Prosthesis Design; D019651:Plastic Surgery Procedures / Q000295:instrumentation; D013314:Stress, Mechanical
D015921:Dental Implants