One of the major challenges of fixed clinical orthodontics is the correction of deep overbite. Mini screw implants are ideally suited for absolute intrusion because they make it possible to apply light continuous forces of known magnitudes without producing any reciprocal reactionary effect on posterior teeth. The purpose of this FEM study was to evaluate and compare the stresses generated in maxillary anterior region during absolute en masse intrusion of six maxillary teeth using mini-implants at strategic locations. Materials and methods: Finite element model was generated using FEM software ANSYS and, on the same model, two different analyses were carried out for two groups with different points of force application as Group I consisted of two bilateral implants for en masse intrusion of maxillary anteriors and Group II consisted of a single mid implant. Results: Soft and hard bones showed significantly high stress distribution in Group I as compared to Group II. The total tooth deformation was found to be more with single point of force application which produced oblique force vectors. Conclusion: Stresses on the teeth are higher and distributed more evenly, when the point of force application is bilateral rather than a single source. Bilateral implants generate less stresses which are evenly distributed with minimum detrimental effect on the teeth during absolute intrusion.

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Introduction. The purpose of this study is to evaluate the effect of change in vertical placement of bracket and effect of tooth morphology on stress developed on periodontal ligament with the help of three dimensional finite element modeling. Methods. A three-dimensional model of the maxillary bone, maxillary right central incisor, lateral incisor and canine was designed based on the average dimensions of the anatomy and morphology given by Wheeler’s and standard edgewise bracket with Slot of 0.022″ X 0.028″ inch was designed using the finite element method. Brackets were placed on each tooth, on the mentioned labial surface at variable distances from the cusp tip, and a full size archwire was virtually engaged into the bracket, then optimum orthodontic load of 2N is applied and PDL stress were calculated. Results. The lowest stress values were measured as bracket position changes from crest of teeth to the apical direction. By displacing the bracket gingivally from 1.5 to 6 mm, a 16.2% decrease in stress level for central incisor, for lateral incisor the stress level decrease by 25.8% and for canine the stress level decrease by 21.6% thus our study confirms that variation in vertical bracket position results in change in resultant stress in PDL. Conclusion.It can be concluded that the variation in the vertical position of the bracket on different tooth can have an important effect on the stresses developed in the PDL.

Objectives: Deep bite or increased overbite correction often offers a challenge to the clinician during orthodontic treatment. Bite opening with conventional mechanics in high angle cases which require intrusion of anteriors cause reciprocal forces in the posteriors which is undesired. Absolute or true en masse intrusion mechanics using mini-implants are ideal for such cases. This study explores the rate, amount of intrusion and torque changes of maxillary anteriors over a period of 6 months using mini-implants between canine and lateral incisors bilaterally. Materials and methods:Bilateral mini-implants made by Dentos were placed between lateral incisors and canines and a force of 45 gm per side was applied. Pre-and postlateral cephalograms were evaluated for the rate, amount of intrusion and torque changes.Results: Rate of intrusion of incisors was found out to be 0.43 mm/month and rate of intrusion of canines was found out to be 0.18 mm/month and the torque changes observed were nonsignificant. Conclusion:Mini-implants were used to deliver light continuous forces of optimal magnitudes and they were observed to be efficient and stable source of anchorage for en masse intrusion of the maxillary anterior teeth. The amount of intrusion achieved for six maxillary anterior teeth was statistically and clinically significant without significant torque changes.

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