Khidair F.doc J Bagh College Dentistry Vol. 25(Special Issue 1), June 2013 Evaluation of Pedodontics, Orthodontics and Preventive Dentistry120 Evaluation of en-masse retraction using microimplant versus conventional techniques: An in vitro study Ahmed G. Mohammed Sharif, B.D.S. (1) Khidair A. Al-Jumaili, B.D.S., C.E.S., D.S.C.O. (2) ABSTRACT Background: The study aimed to investigate the effect of different techniques of en masse retraction on the vertical and sagittal position, axial inclination, rate of space closure, and type of movement of maxillary central incisor. Materials and methods: A typodont simulation system was used (CL II division 2 malocclusion). Three groups were used group 1(N=10, T-loop), group 2(N=10, Time-Saving loop), and group 3(N=10, Microimplant). Photographs were taken before and after retraction and measurements were made using Autodesk AutoCAD© software 2010. Kruskal- Wallis one-way analyses of variance and Mann-Whitney U test (p≤0.05) were used. Results: The rate of space closure showed no significant difference among the three groups (p≤0.05), while results regarding type of tooth movement showed a significant difference among the three groups (p≤0.05), where group 3(0.59±0.09) showed a more degree of controlled tipping than group1(0.33±0.19) while group 2(-0.50±0.09) showed an uncontrolled tipping movement. Conclusions: It is concluded that microimplant anchored sliding mechanics gives better control over the en masse retraction mechanics and greater retraction. Conventional techniques result in extrusion and move the teeth in less degree of translation movement. Key words: Microimplant, retraction, sliding mechanics, axial inclination. (J Bagh Coll Dentistry 2013; 25(Special Issue 1):120-125). INTRODUCTION During premolar extraction treatment, the orthodontist has several options for space closure, a popular method is en-masse space closure with sliding mechanics and coil springs. The use of loops for closing spaces in orthodontics requires the professional to know the force systems offered by the orthodontic treatment mechanics, because if the mechanics associated with loops are used improperly, complications such as loss of anchorage, excessive verticalization of incisors, increase of overbite, dental mobility, root resorption, and an increase in treatment time may result, with irreversible damage to the patient.(1,2)With increased use of preadjusted appliances, various forms of sliding mechanics have replaced closing loop arches. Sliding mechanics might have great benefits, such as minimal wire-bending time and adequate space for activations.(3) The retraction of four incisors after canine retraction is accepted as a method to minimize the mesial movement of the posterior teeth segment, whereas en masse retraction of six anterior teeth may create anchorage problems. In addition, the tipping action built into anterior brackets in preadjusted appliances may produce problems of anchorage. These problems may be aided by the use of a transpalatal bar and extraoral appliances.(3,4) Skeletal anchorage using dental implants provides an absolute anchorage for tooth movement. (1)Master student. Department of POP. College of Dentistry. University of Mosul. (2)Professor. Department of POP. College of Dentistry. University of Mosul. Microimplants have many benefits such as ease of placement and removal and inexpensiveness. Most importantly, because of their small size, they can be placed in the intra- arch alveolar bone without discernable damage to tooth roots. In addition, orthodontic force applications can begin almost immediately after placement in contrast to dental implants.(5,6) In this study a Typodont simulation system is used to show the possible effects of using variable factors on en masse retraction and rate of movement during space closure using microimplant and a conventional retraction technique. MATERIALS AND METHODS A typodont simulation system (Ormco, Japan) is prepared according to manufacturer instructions to be used in the study with a wax form (maxillary arch Cl II division 2 malocclusion) and maxillary metallic teeth. Initial alignment is made by finger pressure on 0.018" stainless steel archwireand preadjusted mini ROTH 0.022"x0.030" slot bracket after immersing the typodont in the water bath,(7) then SS 0.019"x0.025" archwire is used and end with SS 0.0215"x0.025" archwire. The posterior portion of the typodont wax is replaced by cold cure acrylic resin in order to stabilize anchorage teeth (second premolar, first and second molars) and provide a site for microimplant placement. Wood table (length: 23cm, width: 10cm) with a custom made bases to receive and stabilize the typodont and the digital camera (figure 1). J Bagh College Dentistry Vol. 25(Special Issue 1), June 2013 Evaluation of Pedodontics, Orthodontics and Preventive Dentistry121 The digital camera was fixed (10cm) from a vertical ruler which is fixed to the table opposite to the midline between central incisors when the typodont is in place. Horizontal bar was fixed on the ruler and be coincided with a long axis bar (0.022" SS wire) that is fixed to right central incisor by making a groove from lingual fossa to the incisal edge (figure 2), this bar was placed in that groove and fixed with epoxy steel adhesive and adjusted to have the same axial inclination of the tooth. The point of intersection between horizontal and long axis bars is marked and used during repositioning of teeth after each experiment. AutoCAD measurements A. Photograph analysis: The standardized photographs were captured on a scale and transferred to the computer to be analyzed in Autodesk AutoCAD© software 2010 and to measure the accurate readings (figure 3).Photograph analysis is made by drawing three lines: 1. The horizontal line is drawn over the horizontal bar. 2. The long axis line is drown over the long axis bar with a constant length (36mm) and locating the incisal edge (8.25mm) from the tip of long axis bar, the end of this line is considered the apex of the tooth and the estimated midpoint of the root is localized on this line (8.25mm) from tooth apex. 3. The vertical line is drown from the point of intersection between horizontal and vertical bars and extends down vertically. B. Measurements: For each experiment of en masse retraction a photograph was taken before starting retraction process, while another photograph was taken after completing retraction process (i.e. after cooling of the typodont). The two photographs were analyzed by AutoCAD software 2010 and measurements were made as follows: 1. Sagittal movement of incisal edge: The distance from incisal edge to the vertical line was measured in each photograph, and the difference between the two distances will represent the sagittal movement of incisal edge and it is denoted by "SE". 2. Vertical movement of the incisal edge: The vertical distance from incisal edge to the horizontal line was measured in each photograph and the difference between the two distances will represent the change in vertical position of the incisal edge (7). Positive values will indicate extrusion while negative values indicate intrusion of the tooth. 3. Sagittal movement of tooth apex: The distance from tooth apex to the vertical line was measured in each photograph, and the difference between the two distances will represent the sagittal movement of tooth apex and it is denoted by "SA". 4. Vertical movement of the estimated midpoint of the root: The vertical distance from (EMP) of the root to the horizontal line was measured in each photograph, and the difference between the two distances will represent the vertical movement of (EMP) of the root. The vertical change in the position of the (EMP) of the root is used to determine the extent of true intrusion/extrusion (8). Positive values will indicate true extrusion while negative values indicate true intrusion of the tooth. 5. Axial Inclination Change: The angle between long axis line and the vertical line was measured in each photograph and the difference between the two angles will represent the axial inclination change. 6. Rate of Space Closure: The distance between the distal wing of canine bracket and the mesial wing of second premolar bracket was measured in each photograph (9), and the difference between the two distances will represent the rate of space closure. 7. Type of tooth movement: To determine and quantify the movement of the central incisor, the quotient of tooth apex movement (SA) and the incisal edge movement (SE) were calculated. If the apical point moved in the opposite direction to the coronal point, the amount received a negative sign. Tooth movements were classified on the basis of the quotient (R) obtained (SA/SE): < 0, uncontrolled tipping; 0, controlled tipping; >0, controlled tipping and bodily movement; 1, bodily movement; and >1, root movement (10). Reposition of Typodont Teeth After each experiment, typodont teeth was repositioned to their original position by immersing the typodont in the water bath and J Bagh College Dentistry Vol. 25(Special Issue 1), June 2013 Evaluation of Pedodontics, Orthodontics and Preventive Dentistry122 placing an acrylic bite plane made from cold cure acrylic resin (figure4), a precise final alignment for the teeth was done, with SS rectangular archwire of size (0.019"x0.025"), then SS (0.0215"x0.025")(11), these archwires are ligated to typodont teeth with SS ligature. The criteria for successful repositioning of the teeth are passive insertion of SS rectangular archwire of size (0.0215"x0.025") in the bracket slots, the distance between the tip of long axis bar and the vertical bar is (5mm±0.1) measured by digital vernia, the distance between the incisal edge and the vertical bar is (7.6mm±0.1) measured by digital vernia, and the distance between the distal wing of canine bracket and the mesial wing of second premolar bracket is (13mm±0.1) measured by digital vernia. In order to avoid the possible alteration of the characteristics of the wax after successive experiments could interfere in the fidelity of the results, the wax was replaced for each experimental group (11). Placement of Microimplant The C-implant has two components, a titanium head and a screw. The screw is 1.8 mm in diameter and 8.5 mm long. The head has a 0.032" diameter hole and is connected to the screw by friction. A predrilling of implant site between second premolar and first molar buccally (8mm) from the base archwire (12-15) was made through the cold cure acrylic resin that support anchorage teeth then the microimplant is fixed in its place by a thin mix of cold cure acrylic resin and left to set for a few minutes before force application. Experimental groups 1. In group 1 (N=10), en masse retraction with T-Loop (T) (figure 5A), as the height is 7mm and the gingival horizontal part is 8mm and the width of the horizontal part is (2mm), archwire used is SS 0.018"×0.025".(16) 2. In group 2 (N=10), en masse retraction with time-saving closing loop (TS): This loop is made according to the inventor (17)of SS 0.018"x0.025" archwire (figure 5B). This loop is relatively wide (3- 4mm), its height is fairly standard (7- 8mm). Each loop should be bent sufficiently distal to the canine bracket to allow proper oral hygiene. Although the tieback used here is soldered to the wire, it can also be welded, crimped, or bent. Once the space has closed enough that the tieback meets the molar bracket, the loop is squeezed with an optical or how pliers, moving the tieback forward and providing the space for further activation. 3. In group 3 (N=10), en masse retraction with microimplant (MI) and a crimpable hook was crimped on the SS 0.019"x0.025" archwire between lateral incisors and canines through which a force will be applied on the anterior teeth near the center of resistance of upper anterior segment, hook length used is (6mm) from the base archwire, then the force is applied through NiTi closed coil spring from the hook anteriorly to the microimplant posteriorly. (12, 14) Statistical analysis Statistical analysis was undertaken using the Statistical Package for Social Sciences (SPSS Version 11.5) including descriptive statistics (table1). After examining the distribution of the sample, nonparametric tests were used including Kruskal-Wallis one-way analyses of variance (table 2) and Mann-Whitney U test (p≤0.05)(table 3)to compare means among the groups. RESULTS Sagittal movement of the incisal edge: Changes in sagittal position of incisal edge were group 1(1.7±0.22). Group 2 (2.11±0.33). Group 3 (2.84±0.31). Group 3 shows a more degree of retraction than other groups with a significant difference among them (P≤0.05). Vertical movement of incisal edge: Changes in vertical position the tooth were group 1(0.54±0.24), group 2(1.29±0.21), group 3 (- 0.12±0.09). Significant difference was recorded among the three groups (P≤0.05), where extrusion movement in group1 and 2 while intrusion in group 3. Vertical movement of the estimated midpoint of the root: Changes in vertical position of the EMP were group 1 (0.19±0.18), group 2(0.60±0.19), group 3(-0.44±0.11). Significant difference was recorded among the three groups (P≤0.05), where true extrusion movement in group1 and 2 while true intrusion in group 3. Sagittal movement of tooth apex: Changes in sagittal position of tooth apex were group 1(0.25±0.34), group 2(-0.97±0.47), group 3(1.81±0.29). Significant difference was recorded among the three groups (P≤0.05), in group 2apex movement in opposite direction to that of the incisal edge, in group1 and 3 the apex moved in the same direction. Axial inclination change: Changes in axial inclination measurements were group 1(2.06◦±0.87◦), group 2 (7.35◦±0.94◦), group 3 J Bagh College Dentistry Vol. 25(Special Issue 1), June 2013 Evaluation of Pedodontics, Orthodontics and Preventive Dentistry123 (1.84◦±0.65◦). Significant difference was recorded in group 2(P≤0.05). Rate of space closure: No significant difference was recorded among the three groups (P 0.05). Type of tooth movement: The ratio of tooth movement were group1 (0.33±0.19), group 2 (-0.5±0.09),group3(0.59±0.09).Significant difference was recorded among the three groups (P≤0.05). Group 1 and 3 showed controlled tipping movement, while uncontrolled tipping movement was recorded in group2. DISCUSSION The upper incisors were retracted in group 1 and 3 with a combination of tipping and bodily movement. However, the upper incisor in group 2 moved in a relatively uncontrolled tipping manner and showed a resultant extrusion movement of the upper incisal edge.The reason of this observation may be attributed to the type of tooth movement achieved in each group. In group 1 there was a greater sagittal change of incisal edge (1.7mm) and least change in the root apex in sagittal direction (0.25mm), while in group 3 more degree of incisal edge and apex sagittal movement (2.84mm), (1.81mm) respectively, whereas group 2 the root apex moved in sagittal direction opposite to that of the incisal edge (-0.97mm). The reason behind the relatively greater movement of incisal edge in group 1 when compared with group 3 after retraction was mainly due to the wholesome tipping movement that took place around the root apex in group 1 and the translatory movement in group 3.(10; 18; 20) As the force application shifted towards the apex as in group 3, the force applied was more closer to the center of resistance, and the perpendicular distance between the level of force application and the center of resistance of the incisor was reduced resulting in the decrease of the magnitude of tipping moment generated during retraction, and resulting in the maintenance of the torque of the anterior teeth throughout the retraction period.(19) Regarding axial inclination changegroup 3[1.84◦±0.65◦], group 1[2.06◦±0.87◦], and group 2[7.35◦±0.94◦], spaces present between the archwire and the bracket slot 0.019"×0.025" (group 3) and the 0.018"x0.025" (group 1 and 2) lead to a small loss of torque. In addition group 2, the central incisor moved in an uncontrolled tipping manner as a result of producing less M/F ratio than in group 1.(20; 21) Upper incisor was intruded in group 3 and extruded in group 1 and 2 (0.21mm intrusion: 0.54mm, 1.29mm extrusion respectively), suggesting that the microimplant can demonstrate its ability to intrude the upper anterior teeth during retraction due to distal and intrusive force vector, which is in accordance with Ma et al. This appears to be due to the direction of pull by the Ni-Ti closed coil spring from the microimplant head to the hooks on the archwire.(22) From table (1), it can be noticed that vertical position of central incisor is controlled by the change in both (VE) and (EMP) of the root, {in group 1 and 2, nearly two thirds (VE) and one third (EMP) of the root, while in group 3, nearly one fourth (VE) and three fourth (EMP) of the root}. It is concluded that in group 1 and 2 the extrusion of the tooth is attributed to the (EV), while in group 3 the intrusion is attributed to the vertical change in (EMP) of the root. The rate of space closure showed no significant difference among the three groups (p 0.05). This might be due to the effect of immobilization of posterior teeth which might move mesially in conventional retraction techniques. As a conclusion no significant difference existed in the rate of space closure among the three groups. Microimplant achieved better control in both the anteroposterior and vertical directions during en masse retraction.Retraction with time-saving closing loop results in the greatest extrusion, greatest change in axial inclination, and an uncontrolled tipping movement.The intrusion of central incisor with microimplant is mainly a true intrusion, while during retraction with T-loop or time-saving closing loop, tooth extrusion occurs mainly as a result of change in axial inclination of the tooth. REFERENCES 1. Begg PR. Differential force in orthodontic treatment. Am J Orthod Dentofacial Orthop 1956; 42(7): 481- 510. 2. Thiesen G, Rego MVNN, Menezes LM, Shimizu RH. Using different T-loops configurations to obtain optimized force systems. Rev Dent Press Ortod Ortop Facial 2006; 11(5): 57-77. 3. McLaughlin RP, Bennett JC. The transition from standard edgewise to preadjusted appliance systems. J Clin Orthod 1989; 23: 142–153. 4. McLaughlin RP, Bennett JC. 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Sung-Seo Mo, Seong-Hun Kim, Sang-Jin Sung, Kyu- Rhim Chung, Youn-Sic Chun, Yoon-Ah Kook, and Gerald Nelsong. Factors controlling anterior torque during C-implant-dependent en-masse retraction without posterior appliances, Am J Orthod Dentofac Orthop 2011; 140: 72-80. 16. Manhartsberg C, Morton JY, Burstone CJ. Space closure in adult patients using the segmented arch technique. Angle Orthod 1989; 59(3): 205-10. 17. Shigeyuki Matsui, Yuichirou Otsuka, Satoru Kobayashi, Satomi Ogawa, Haruhide Kanegae. Time- saving closing loops for anterior retraction. J Clin Orthod 2002; 36(1): 38-41. 18. Tominaga J, Tanaka M, Koga Y, Gonzales C, Kobayashi M, Yoshida N. Optimal loading conditions for controlled movement of anterior teeth in sliding mechanics. Angle Orthod 2009; 79(6): 1102-7. 19. Prabhuraj B Kambalyal, Arvind M, Tarulatha R Shyagali, Rani Hamsa. Clinical evaluation of the effects of retraction forces applied at varying levels on maxillary anterior segment using implants. J Advanced Dental Res 2010; (1): 27. 20. Ah-Young Lee and Young Ho Kim. Comparison of movement of the upper dentition according to anchorage method: orthodontic mini-implant versus conventional anchorage reinforcement in Class I malocclusion. International Scholarly Research Network Volume 2011, Article ID 321206. 21. Manhartsberg C, Morton JY, Burstone CJ. Space closure in adult patients using the segmented arch technique. Angle Orthod 1989; 59(3): 205-10. 22. Junqing Ma, Lin Wang, Weibing Zhang, Wenjing Chen, Chunyang Zhao, and Roger J Smales. Comparative evaluation of micro-implant and headgear anchorage used with a pre-adjusted appliance system. Eur J Orthod 2008; 30(3): 283–287. Table 1: Linear and angular changes in (Group1, 2 and3) measurements. Measurement Group 1 Group 2 Group 3 Mean SD Mean SD Mean SD SE 1.7 0.22 2.11 0.33 2.84 0.31 VE 0.54 0.24 1.29 0.21 -0.12 0.09 EMP 0.19 0.18 0.60 0.19 -0.44 0.11 SA 0.25 0.34 -0.97 0.47 1.81 0.29 I 2.06 0.87 7.35 0.94 1.84 0.65 SC 1.10 0.57 1.56 0.42 1.41 0.41 R 0.33 0.19 -0.50 0.09 0.59 0.09 Table 2: Kruskal-Wallis analyses of variance SE VE EMP SA I SC R Chi-Square 19.992 25.876 24.586 25.061 19.559 4.254 23.118 df 2 2 2 2 2 2 2 Asymp. Sig. 0.000 0.000 0.000 0.000 0.000 0.119 0.000 Table 3: Mann-Whitney U test. Method SE VE EMP SA I SC R T TS 0.000 0.016 0.001 0.000 0.000 NS 0.000 MI 0.000 0.000 0.000 0.000 NS NS 0.001 TS T 0.000 0.016 0.001 0.000 0.000 NS 0.000 MI 0.000 0.001 0.000 0.000 0.000 NS 0.000 MI T 0.000 0.000 0.000 0.000 NS NS 0.000 TS 0.000 0.001 0.000 0.000 0.000 NS 0.000 NS: No significant difference at p ≤ 0.05 J Bagh College Dentistry Vol. 25(Special Issue 1), June 2013 Evaluation of Pedodontics, Orthodontics and Preventive Dentistry125 Figure 2: Long axis bar on Maxillary right central incisor. Figure 1: Wood table with the vertical and horizontal bars, custom made base for typodont and digital camera fixation. Figure 4: Acrylic bite plane Figure 5: Template used to make the loops operated by Loop application version 1.7. A B Figure 3: Photograph analysis by Autodesk AutoCAD© software 2010: (1) line indicates tooth position before retraction, (2) axial inclination, (3) distance between top of long axis bar and vertical bar, (4) distance between incisal edge and vertical bar, (5) length of long axis bar, (6) distance from apex to EMP of the root (White point), (7) distance between incisal edge and horizontal bar, (8) distance between EMP and horizontal bar, (9) distance between apex and vertical bar.