Evaluation of Efficacy of Various Implants in Maxillary Arch Distalization-A Finite Element Analysis

Introduction: Orthodontic correction of Angle’s class II molar relation has, for long, been one of the challenge in orthodontics, with various researchers attempting to correct the class II molar relationship by diverse methods. One of the technique that has gained popularity in recent times is maxillary arch distalization by infrazygomatic screws and miniscrews. The objective of the study is to measure and compare the amount of maxillary arch distalization and its effects, on adjacent teeth, by varying the positions of mini-implants by Finite Element Analysis. Materials & Method: A standard three-dimensional finite element model was constructed to simulate the maxillary teeth, periodontal ligament, and alveolar process. In this study, three models were prepared. Model-1: The (miniscrews) were placed between upper first and second premolar, and between second premolar and first molar bilaterally. Model-2: Infrazygomatic screws was placed between upper first and second molar bilaterally. Model-3: Infrazygomatic screws was placed on the mesiobuccal root of upper first molar bilaterally. The displacement of each tooth was calculated on x, y, and z axes when 200 gm of force was applied on each side. Result: Maximum amount of maxillary arch distalization was seen when infrazygomatic screws placed between upper first and second molar in model-2. Whereas maximum amount of maxillary arch intrusion and less distalization was observed when miniscrews placed between upper first premolar and second premolar and in between second premolar and upper first molar in model-1. The difference was statistically significant (p=0.005*). There was no bucco-palatal rotation of teeth observed among all three finite element models. Conclusion: Thus infrazygomatic screws and miniscrews are the effective means of maxillary arch distalization for the correction of Class II malocclusion.


INTRODUCTION
Maxillary arch distalization is an increasingly popular option to correct the class II malocclusion with nonextraction approach. Headgear has been conventional modality for class II malocclusion through distalization of molars or entire the maxillary dentition. However, its main disadvantage is patient compliance. To avoid this drawback, various non-compliance appliances have been developed including Keles slider, repelling magnets, distal jet, and pendulum. These devices applied continuous forces to distalize maxillary arch, which might lead to distal tipping and extrusion of the first molars and mesial reactive forces might cause anchorage loss and labial flaring of anterior teeth. 1 To overcome unwanted side-effects, recent technique such as maxillary arch distalization by mini-implants are more effective and give good results. Miniscrews were introduced in clinical orthodontics for the purpose of orthodontic anchorage, and these presented the clinician with a versatile option. 2-7 Sugawara et. al. (2006) proposed maxillary dentition distalization by using titanium anchor plates. 8 Miniscrew implants provides absolute anchorage and their ability to retract whole dentitions can eliminate adverse reciprocal movement and maximize the efficiency of the treatment. 9 In addition, miniscrews provides the option, for early loading after placement which reduces treatment time.
The application of monocortical miniscrew type temporary anchorage devices to various clinical situations demanding movement of either a single tooth or teeth segment has been largely successful, with the ease and minimal invasiveness at insertion and removal. 10 The miniscrews placed at the interdental alveolar bone can deliver forces directly to the tooth or archwire, eliminating the need for additional connectors. This versatility of the miniscrews can be very helpful, especially for the posterior segment control, for which extraoral appliances used to be indicated. 11,12 Additional miniscrews in the premolar area appear to facilitate intrusion and distalization of the entire arch according to the position of the force vectors. A new method for distalization of the entire maxillary dentition is using miniscrews implanted in the infrazygomatic crest, as proposed by Liou et. al. 13 and Lin and Liou. 14 They suggested that upper first and upper second molar region is the most ideal safe zone for placing miniscrews in the buccal alveolar bone in the infrazygomatic crest region for maxillary dentition distalization.
Estimation of precise stresses of distalization on the maxillary arch, periodontal ligament and alveolar bone is difficult in in-vivo studies. The stress generated in the periodontal ligament and tooth root can be more accurately studied with the help of an in-vitro numerical finite element model. Finite element analysis was introduced into Orthodontics by Yettram et. al. (1977) in 1972. 15 The FEM is an engineering resource used to calculate stress and deformations in complex structures, and it has been widely applied in biomedical research. 16 In FEM, 3D models allow better understanding of the mechanical and structural behaviour of the dental tissues and structures, providing more realistic and accurate results resembling the actual occurrence in in-vivo studies as recommended by Tajima et.al.

(2009). 17
Hence, this study was undertaken to evaluate the efficacy and effect of various (mini) implants position in maxillary arch distalization by Finite Element Analysis.  hook was also constructed (Fig 1).

MATERIALS AND METHOD
In this study, three finite element models were prepared.

Model-1
The miniscrews were placed bilaterally between maxillary first and second premolar and between second premolar and first molar at the height of 5 mm from alveolar crest 9 (Fig 2). Miniscrews were inserted at the midpoint between adjacent teeth with 45° angulations relative to the occlusal plane and on the mucogingival junction. The crimpable hooks of height 4 mm were attached between lateral incisor and canine and between canine and first premolar on 0.016×0.22 SS on each side. The Niti-coil springs from each miniscrew head to corresponding crimpable hooks with a force magnitude of approximately 200 gm on each side were attached for maxillary arch distalization ( Fig 5).

Model-2
The titanium IZC screws were placed bilaterally between maxillary first molar and second molar on the buccal side of root at an angle of 55-70° to maxillary occlusal plane at height of 11 mm from alveolar crest 9 (Fig 3). The force of 200 gm on each side was applied from Niti-coil spring for maxillary arch distalization (Fig 6).

Model-3
The titanium IZC screws were placed bilaterally on the mesio-buccal root of maxillary first molar on the buccal side at an angle of 55-70° to maxillary occlusal plane at height of 11 mm from alveolar crest 9 (Fig 4). The force of 200 gm on each side was applied from Niti-coil spring for maxillary arch distalization (Fig 7).
The material properties like density, Young's modulus and Poisson's ratio of various components which were used in the study in order to simulate the actual properties of the components are shown in Table 1.
The meshing details of various components used in the study are shown in table 2.          (Table 5).
The individualised effect on teeth's during maxillary arch distalization has been explained in (Fig 8). A standard coordinate system was constructed with the   x-axis corresponding to the bucco-palatal direction, the y-axis the antero-posterior direction, and the z-axis the superior-inferior direction.
The central and lateral incisors were moved distally by 0.6 mm, and canines by 0.7 mm. The first and second premolars were distalized by 0.6 mm. The first and second molars were distalized by 2.1 mm bilaterally, in model 1. (Fig 8.A).
The central and lateral incisors were moved distally by Least intrusion was seen in posterior region. The first and second molars were intruded by 0.1 mm, bilaterally in model 1 (Fig 9.A).   implants were placed between first and second premolar and between second premolar and first molar, as compared to IZC screw. (Fig 9.B). This states from graph 2. The center of resistance (Cres) of the maxillary dentition has been shown to be located around the middle area of the premolar roots.23The more interproximal alveolar bone is available between the maxillary second premolar and first molar roots and between the maxillary first and second molar roots than in other The three dimensional FEM model used in the study provides the freedom to simulate the orthodontic force system applied clinically and allows analysis in the response of the dentition to the orthodontic load in three dimensional spaces. 24 This study was undertaken to evaluate the efficacy In the present study, distalizing force is applied to an

Conflicts of interest
There are no conflicts of interest.