Affiliations: Department of Orthodontics, Yenepoya University, Mangalore, India
Correspondence:
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Corresponding author: Shahista Parveen, Department of Orthodontics, Yenepoya University, Mangalore, India. Tel.: +91 988 679 4150; Fax: +91 824 220 4663; E-mail:drshahistaparveen@yahoo.com
Abstract: The problems that often arises in orthodontic treatment of adult patients is
the presence of periodontal disease and loss of bone support. As a
consequence of this, the center of resistance of the tooth is altered.
Excessive orthodontic force with advanced periodontal bone loss may
traumatize the periodontium. Force dosage during orthodontic treatment is
one of the most difficult problems at this stag.the purpose of the study is
to simulate the effect of orthodontically induced stress in the periodontal
ligament of maxillary molar at different levels of bone loss. The study is
carried out to estimate the reduction in magnitude of force at different
levels of bone loss (2.5 mm, 5 mm and 6.5 mm) necessary to achieve evenly
distribution of stress in the periodontal ligament of the tooth as obtained
without bone loss and to determine the change in counterbalancing M/F ratio
to induce uniform stress distribution in the PDL. A 3-dimensional finite
element model of a tooth comprises of maxillary first molar with periodontal
ligament and alveolar bone with different levels of bone height was
constructed. Bone loss that ranged from 2.5 thrugh 6.5 mm was simulated in a
model. Necessary reduction in the magnitude of force and the increase in
moment to force (M/F) ratio was determined to obtain evenly distributed
stress in the periodontal ligament of a tooth. The results showed that lesser
force magnitude is required in simulated 2.5 mm bone loss (80%), 5 mm bone
loss (60%), 6.5 mm bone loss (35%) as compared to the initial load
applied to the tooth without bone loss. The counter tipping moment to force
ratio should be increased from no bone loss (9.65) through 6.5 mm bone loss
(12.8) to maintain the same range of stress in the PDL as was obtained
without bone loss. The counter rotation moment to force ratio should
decrease from no bone loss (5.65) through 6.5 mm bone loss (4.0) to maintain
the same range of stress in the PDL as was obtained without bone loss.
Combination of decreased force magnitude and increased counter tipping
moment to force ratio will bring about uniform stress in the periodontal
ligament of a tooth with varying degree of bone loss.
Keywords: Finite element analysis, adult patient, simulated bone loss, force magnitude, moment to force ratio
