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Application of computational fluid dynamics models for the evaluation of salivary flow patterns and related bacterial accumulation around orthodontic brackets.

OBJECTS
To simulate and compare salivary flow patterns over a tooth surface bonded with different orthodontic appliances using computational fluid dynamics (CFD) and investigate the impact of bracket design on salivary flow in relation to peri-bracket bacterial accumulation.


SETTING AND SAMPLE POPULATION
The models were constructed using computed tomography (CT) data of 81 patients scheduled for fixed orthodontic treatment: 27 patients (10 males, 17 females) for the metal Victory MBT™ bracket; 27 patients (7 males, 20 females) for the ceramic Clarity MBT™ bracket; 27 patients (15 males, 12 females) for the Mini Uni-Twin (MUT) bracket.


METHODS
The salivary flow patterns were simulated by CFD and compared between the groups and the model predictions were validated using a bacteriological experiment.


RESULTS
The MUT bracket was associated with the greatest number of low salivary velocity areas, as it is designed with a connector between double tie-wings and a right contact angle between tooth surface and bracket base. After archwire placement, the centered slot in the bracket and the bilateral sites around the bracket had higher bacterial retention and needed special oral hygiene measures. The obtuse contact angle of the ceramic bracket formed a pocket structure in the tie-wing area, retarding salivary flow and contributing to bacteria retention.


CONCLUSION
With the evaluation of CFD models, we demonstrate that salivary flow patterns over a tooth surface with a bracket vary with bracket designs and further promote bacterial retention in specific locations, suggesting the need for additional oral hygiene measures for specific bracket types.