Force of dislodgement of crimpable attachments with different types and dimensions of archwire: An in vitro study , Dr Amit Srivastava Post graduate student Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, Modinagar Dist- Ghaziabaad, Uttar Pradesh, India Email- srivastavamit0224@gmail.com Dr Mudita Srivastava Senior Lecturer Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, Modinagar Dist- Ghaziabaad, Uttar Pradesh, India Email- mudi2007@rediffmail.com Dr Puneet Batra Professor and Head of the Department Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, Modinagar Dist- Ghaziabaad, Uttar Pradesh, India Email- drpuneetbatra@gmail.com Dr Saurabh Sonar Professor Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, Modinagar Dist- Ghaziabaad, Uttar Pradesh, India Email- saurabhsonar@hotmail.com ADDRESS FOR CORRESPONDENCE – Dr Amit Srivastava Post graduate student Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, ModinagarDist- Ghaziabaad, Uttar Pradesh, India Email- srivastavamit0224@gmail.com Abstract The objective of this study was to measure the force required to dislodge crimpable hooks crimped to rectangular archwires of two different types (stainless steel and beta titanium). In vitro testing of hooks and wires of 0.016 x 0.022 inch, 0.017 x 0.025 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch of both stainless steel and beta titanium was carried out using Instron Universal Testing machine. The results demonstrated that there was a significant difference in dislodgement force for stainless steel and beta titanium archwires. The dislodgement force increases with the increasing dimension of the archwire. The clinical relevance of dislodgement force is discussed. Key words: Instron Universal Testing machine, Crimpable hooks, Stainless steel, beta titanium, Force of dislodgement. Introduction With the advent of pre-adjusted edgewise orthodontic bracket systems, archwire fabrication has been considerably simplified. Archwires that are devoid of any loops or customizing bends can be utilized. These include fabricated tie-back loops, soldered brass hooks, pre-posted archwires and crimpable archwire hooks. Soldering requires chairside or laboratory equipment, is time consuming and may lead to annealing of the archwire. Crimpable archwire attachment allows quick and simple placement of the attachment in any desired position along the archwire in or out of the mouth.1 Crimpable attachments have the potential for reducing the chairside time and cost savings in both time and materials with minimum discomfort. However, excessive force during crimping can cause distortion of the wire and the introduction of unwanted force into the wire.2 Griffith and Farracane (1998) examined the effect of addition of sandblasting and/or adhesives on the stability of crimpable hooks when positioned and crimped onto surgical archwires. The combination of sandblasting and dental adhesive increased the force required to dislodge the hook by a factor of 10.3 Johal et al (1999) did a study to evaluate the force of dislodgement of crimpable hooks on stainless steel wire and found that archwire size makes little difference to the force of dislodgement.2 The demand for speedy and efficient orthodontic treatment has been increasing in recent years. To meet this demand sliding mechanics has become popular throughout the world. The use of crimpable attachments readily achieve controlled movement of the anterior teeth. Studies of various biomechanical factors affecting tooth movement in sliding mechanics such as flexural rigidity of archwire, friction and height of retraction force have been reported.4-5 Nevertheless, optimal loading condition for controlled movement of anterior teeth in sliding mechanics by using crimpable attachments is not fully understood and little research has been undertaken to evaluate the crimpable attachment despite their extensive use in everyday clinical orthodontic practice. The aims of this research were – To compare the force required to dislodge the hooks on two different types of wires (stainless steel and beta titanium wire) To compare the effects of wire dimensions on the force required to dislodge a single type of hook. Materials and methods The force of dislodgement of crimpable hooks was evaluated with the Instron Universal machine (Model No WDW5, SERIAL NO -20070802, BANBROS ENGINEERING Pvt. Ltd) (Figure1). Stainless steel and beta titanium wires of 0.016 x 0.022 inch, 0.017 x 25 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch dimensions were used. Fig.1: INSTRON UNIVERSAL MACHINE (MODEL NO WDW5, SERIAL NO. 20070802, BANBROS ENGINEERING PVT. LTD.) USED IN THE STUDY A 4 cm length of wire was cut and was cleaned with ethanol and was allowed to air dry. Crimpable hooks (Ormco Corporation) were then attached to the wire with a crimping plier (3M Unitek) without gabling the wire (Figure 2 and 3) by a single operator. The wire was then mounted on an Instron Universal machine. The force required to move the hook was then determined at a rate of 0.5 mm/min similar to the study of Johal et al.2 This procedure of attachment of crimpable hooks to the wire was done 10 times taking a new crimpable hook each time and the force was measured by taking the mean of 10 values. Fig. 2: HOOK CRIMPED ON 0.019×0.025 INCH STAINLESS STEEL WIRE WITH CRIMPING PLIER Fig. 3: 4cm 0.019×0.025 INCH STAINLESS STEEL WIRE WITH CRIMPABLE HOOK Results and data analysis Data was analyzed using SPSS (version 19). Significance was predetermined at p =0.05. A one way analysis of variance was used to compare between the two groups of wire. Bonferroni multiple test was used to compare the mean force value of different dimensions within the groups. Table 1 and table 2 shows the mean value of force required to dislodge the hooks on various dimensions of stainless steel and beta titanium wire. Table 3 shows the difference between force value between stainless steel and beta titanium. STAINLESS STEEL WIRES Mean ± SD (Newton) f-value Sig. 0.016X0.022 INCH 14.80 ± 2.83 47.045 0.000* 0.017X0.025 INCH 15.70 ± 2.42 0.019X0.025 INCH 19.79 ± 4.57 0.021X0.025 INCH 23.09 ± 6.29 TABLE 1:THE FORCE REQUIRED TO DISLODGE THE CRIMPABLE HOOKS CRIMPED ON STAINLESS STEEL WIRES BETA TITANIUM WIRES Mean ±SD(Newton) F-value Sig. 0.016X0.022 INCH 18.59 ± 4.09 39.187 0.000* 0.017X0.025 INCH 20.45 ± 4.82 0.019X0.025 INCH 29.64 ± 6.02 0.021X0.025 INCH 32.18 ± 4.39 TABLE 2:THE FORCE REQUIRED TO DISLODGE THE CRIMPABLE HOOKS CRIMPED ON BETA TITANIUM WIRES WIRE MEAN ± SD (Newton) MEAN DIFFERENCE t VALUE p VALUE STAINLESS STEEL 18.34 ± 5.33 -6.82 4.71 0.000* BETA TITANIUM 25.21 ± 7.52 TABLE 3: THE COMPARISON OF FORCE REQUIRED TO DISLODGE THE CRIMPABLE HOOKS CRIMPED ON STAINLESS STEEL AND BETA TITANIUM WIRES Discussion Force of dislodgement of crimpable attachments In the present study hooks were crimped on two different types (stainless steel and beta titanium) of wires and the force required to dislodge the hooks was tested. The dimensions of wire that were used were 0.016 x 0.022 inch, 0.017 x 0.025 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch. These two wires have different properties and are widely used in orthodontics. Stainless steel rectangular wires are used for retraction during sliding mechanics. During sliding mechanics crimpable attachments can be a suitable replacement for soldered attachments thereby saving time, without altering the properties of the wire as it happens with soldered attachments. It becomes clinically important to know the force of dislodgement of these attachments as force is applied through it for retraction. So in the present study the force of dislodgement of crimpable hooks on rectangular stainless steel wire was tested. Torque is best expressed in beta titanium wire therefore it is more frequently used and preferred over stainless steel wires by orthodontic clinicians to give torque in the anterior segment along with elastics during the finishing stages of treatment for the proper inclination of anterior teeth. Crimpable hooks on TMA can be of great advantage during finishing stages, so in the present study we have tested the dislodgement force on beta titanium wires, also. 10 hooks were crimped on every wire and the average force of dislodgement was recorded to minimize the error. Stainless Steel In stainless steel wires, hooks were crimped on 0.016 x 0.022 inch, 0.017 x 0.025 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch dimension of wire. No study has previously tested the dislodgement force of crimpable hooks on 0.016 x 0.022 inch, 0.017 x 0.025 inch and 0.021 x 0.025 inch wire. Ethanol was used to clean the wires so that any impurities on the wires were removed that could affect the dislodgement force. It was found that different dimensions have different dislodgement force, and also the dislodgement force increases with the increased dimensions in the stainless steel category. For 0.016 x 0.022 inch the mean was 14.8 N and for 0.021 x 0.025 inch mean value was 23.09 N so there was a difference of 9 N between the highest and lowest dimensions. This can be explained by the fact that as the dimension increases, the stiffness increases, thereby increasing the dislodgement force. Thus, hooks are better crimped on higher dimension wires. The results of the present study are contrary to that of Johal et al 2 where hooks were crimped on 0.019 x 0.025 inch and 0.018 x 0.025 inch stainless steel and concluded that there are no differences in the dislodgement force with the two wires and they stated that the dimensions of the wire do not make any difference to the dislodgement force. In the present study the mean force to dislodge hooks for 0.019 x 0.025 inch stainless steel was 19.79 N which was much higher than the force evaluated by Johal et al 2 which was 11.7 N for TP hooks and 6.75 N for AO hooks. In the study done by O’Bannon et al 6 the mean force of dislodgement for 0.019 x 0.025 inch stainless steel wire was 49.9 N for coated crimpable hooks and 31.3 N for ribbed crimpable hooks. In the study of O’Bannon et al 6 the force of dislodgement was much higher than the present study, but they tested torsional displacement instead of sliding displacement. Higher values for torsional dislodgement vs. sliding along a rectangular wire are to be expected. This higher force of dislodgement in the present study as compared to Johal et al 2 is also because a single male operator crimped 10 hooks on each wire without gabling the wire. This is in accordance that the force used by clinicians to crimp hooks on stainless steel archwires differs with different gender as studies by Johal et al 7 and Evans et al 8 that suggested that male operators apply more force as compared to female operators while crimping the hooks. The more force of dislodgement in the present study can also be explained by the fact that all the hooks were crimped outside the mouth, placing the hooks outside the mouth enables a higher force value to be used, which is in accordance with studies by Johal et al 7 that suggested that placement of crimpable hooks outside the mouth which provides greater clinical reliability rather than inside the mouth. In the present, no adhesives were assessed to increase the stability of hooks as the force of dislodgement is already much higher than that of a clinically applied force used for retraction. Griffith and Ferracane 3 stated that when sandblasting or adhesives are used the force required to dislodge the hooks increases by a factor of 10. Nattrass et al 9 in their comparison of the different force delivery systems, reported that clinicians apply extremely wide ranges of force (0.44–3.54 N) to the dentition during space closure. Furthermore, Frost 10 reported that lower levels of force are required to achieve bone remodeling and tooth movement. In the present study, the force required to dislodge hooks is much more than what is applied clinically. Thus, it would appear that the magnitude of force required to dislodge the hooks during retraction in sliding mechanics may not be reached clinically. So the use of adhesives or sandblasting for increasing the dislodgement force is not required. Beta Titanium (TMA) The force of dislodgement of crimpable hooks was tested on similar dimensions as in stainless steel for beta titanium, also. Wires used were 0.016 x 0.022 inch, 0.017 x 0.025 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch. No previous study has tested the force of dislodgement of crimpable hooks on beta titanium wire. The force of dislodgement increased as the dimensions of the wire was increased in the beta titanium group, also. The mean amount of force for dislodgement in the beta titanium group was highest for 0.021 x 0.025 inch which is significantly higher than 0.021 x 0.025 inch stainless steel. When the wires were compared among themselves the mean force of dislodgement were 12.32 ± 7.58 N for stainless steel and 18.78 ± 8.82 N for beta titanium. So the mean force of dislodgement for stainless steel was significantly less as compared to beta titanium. This can be explained as beta titanium has higher titanium content which makes the surface of beta titanium rough,11 so more force is required to dislodge the crimped hook. It was concluded from the present study that the force of dislodgement increases with the increase in dimension of the wires. The force required to dislodge the hook for stainless steel is significantly less as compared to beta titanium. The force of dislodgement was found to be much higher than what is applied clinically. Conclusion 1. The force of dislodgement of crimpable hooks increases with the increase in dimension of the wires in both stainless steel and beta titanium. 2. The force required to dislodge the hook for stainless steel wire is significantly less compared to beta titanium. 3. The force of dislodgment measured in the study was much higher than that of clinically applied force during retraction in sliding mechanics. Acknowledgement The authors would like to thank ITS engineering college Greater Noida for providing the Instron Universal Machine. References Algers DW. Arch marking technique for soldering intermaxillary hooks. J Clin Orthod 1987;21:538-9. Johal A, Harper CR, Sherriff M. Properties of crimpable archwire hooks a laboratory investigation. Eur J Orthod 1999;21:679-83. Griffin JT, Ferracane JL. Laboratory evaluation of adhesively crimped surgical ball hooks. Int J Adult Orthod Orthognathic surg 1998;13:169-175. Moore JC, Waters NE. Factors affecting tooth movement in sliding mechanics. Eur J Orthod 1993;15:235-41. Sia SS, Koga Y, Yoshida N. Determining the centre of resistance of maxillary anterior teeth subjected to retraction forces in sliding mechanics. Angle Orthod 2007;77:999-1003. 0’Bannon SP, Dunn WJ, Lenk JS. Comparison of torsional stability of 2 types of split crimpable surgical hooks with soldered brass surgical hooks. Am J Orthod Dentofacial Orthop 2006;130:471-5. Johal A, Loh S, Heng JK. A clinical investigation into the behavior of crimpable archwire hooks. J Orthod 2001;28:203-5. Evans RD, Jones ML. Laboratory evaluation of surgical ball hook crimping pliers. Int J Adult Orthod Orthognathic surg 1991;6:57-60. Nattrass C, Ireland AJ, Sherriff M. An Investigation into the placement of force delivery systems and the initial forces applied by clinicians during space closure. Br J Orthod 1997;24:127–31 Frost HM. Skeletal structural adaptations to mechanical usage (SATMU): 1. Redefining Wolff’s Law: the bone modeling problem. Anatomical Record 1990;226:403–13 Brantley WA, Eliades Theodore. Orthodontic Materials: Scientific and clinical aspects. New York:Theim;2007. , http://bit.ly/17pZf5e

Force of dislodgement of crimpable attachments with different types and dimensions of archwire: An in vitro study , Dr Amit Srivastava Post graduate student Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, Modinagar Dist- Ghaziabaad, Uttar Pradesh, India Email- srivastavamit0224@gmail.com Dr Mudita Srivastava Senior Lecturer Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, Modinagar Dist- Ghaziabaad, Uttar Pradesh, India Email- mudi2007@rediffmail.com Dr Puneet Batra Professor and Head of the Department Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, Modinagar Dist- Ghaziabaad, Uttar Pradesh, India Email- drpuneetbatra@gmail.com Dr Saurabh Sonar Professor Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, Modinagar Dist- Ghaziabaad, Uttar Pradesh, India Email- saurabhsonar@hotmail.com ADDRESS FOR CORRESPONDENCE – Dr Amit Srivastava Post graduate student Department of Orthodontics and Dentofacial Orthopedics Institute of Dental studies and Technologies, Modinagar NH- 58, Kadrabaad, ModinagarDist- Ghaziabaad, Uttar Pradesh, India Email- srivastavamit0224@gmail.com Abstract The objective of this study was to measure the force required to dislodge crimpable hooks crimped to rectangular archwires of two different types (stainless steel and beta titanium). In vitro testing of hooks and wires of 0.016 x 0.022 inch, 0.017 x 0.025 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch of both stainless steel and beta titanium was carried out using Instron Universal Testing machine. The results demonstrated that there was a significant difference in dislodgement force for stainless steel and beta titanium archwires. The dislodgement force increases with the increasing dimension of the archwire. The clinical relevance of dislodgement force is discussed. Key words: Instron Universal Testing machine, Crimpable hooks, Stainless steel, beta titanium, Force of dislodgement. Introduction With the advent of pre-adjusted edgewise orthodontic bracket systems, archwire fabrication has been considerably simplified. Archwires that are devoid of any loops or customizing bends can be utilized. These include fabricated tie-back loops, soldered brass hooks, pre-posted archwires and crimpable archwire hooks. Soldering requires chairside or laboratory equipment, is time consuming and may lead to annealing of the archwire. Crimpable archwire attachment allows quick and simple placement of the attachment in any desired position along the archwire in or out of the mouth.1 Crimpable attachments have the potential for reducing the chairside time and cost savings in both time and materials with minimum discomfort. However, excessive force during crimping can cause distortion of the wire and the introduction of unwanted force into the wire.2 Griffith and Farracane (1998) examined the effect of addition of sandblasting and/or adhesives on the stability of crimpable hooks when positioned and crimped onto surgical archwires. The combination of sandblasting and dental adhesive increased the force required to dislodge the hook by a factor of 10.3 Johal et al (1999) did a study to evaluate the force of dislodgement of crimpable hooks on stainless steel wire and found that archwire size makes little difference to the force of dislodgement.2 The demand for speedy and efficient orthodontic treatment has been increasing in recent years. To meet this demand sliding mechanics has become popular throughout the world. The use of crimpable attachments readily achieve controlled movement of the anterior teeth. Studies of various biomechanical factors affecting tooth movement in sliding mechanics such as flexural rigidity of archwire, friction and height of retraction force have been reported.4-5 Nevertheless, optimal loading condition for controlled movement of anterior teeth in sliding mechanics by using crimpable attachments is not fully understood and little research has been undertaken to evaluate the crimpable attachment despite their extensive use in everyday clinical orthodontic practice. The aims of this research were – To compare the force required to dislodge the hooks on two different types of wires (stainless steel and beta titanium wire) To compare the effects of wire dimensions on the force required to dislodge a single type of hook. Materials and methods The force of dislodgement of crimpable hooks was evaluated with the Instron Universal machine (Model No WDW5, SERIAL NO -20070802, BANBROS ENGINEERING Pvt. Ltd) (Figure1). Stainless steel and beta titanium wires of 0.016 x 0.022 inch, 0.017 x 25 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch dimensions were used. Fig.1: INSTRON UNIVERSAL MACHINE (MODEL NO WDW5, SERIAL NO. 20070802, BANBROS ENGINEERING PVT. LTD.) USED IN THE STUDY A 4 cm length of wire was cut and was cleaned with ethanol and was allowed to air dry. Crimpable hooks (Ormco Corporation) were then attached to the wire with a crimping plier (3M Unitek) without gabling the wire (Figure 2 and 3) by a single operator. The wire was then mounted on an Instron Universal machine. The force required to move the hook was then determined at a rate of 0.5 mm/min similar to the study of Johal et al.2 This procedure of attachment of crimpable hooks to the wire was done 10 times taking a new crimpable hook each time and the force was measured by taking the mean of 10 values. Fig. 2: HOOK CRIMPED ON 0.019×0.025 INCH STAINLESS STEEL WIRE WITH CRIMPING PLIER Fig. 3: 4cm 0.019×0.025 INCH STAINLESS STEEL WIRE WITH CRIMPABLE HOOK Results and data analysis Data was analyzed using SPSS (version 19). Significance was predetermined at p =0.05. A one way analysis of variance was used to compare between the two groups of wire. Bonferroni multiple test was used to compare the mean force value of different dimensions within the groups. Table 1 and table 2 shows the mean value of force required to dislodge the hooks on various dimensions of stainless steel and beta titanium wire. Table 3 shows the difference between force value between stainless steel and beta titanium. STAINLESS STEEL WIRES Mean ± SD (Newton) f-value Sig. 0.016X0.022 INCH 14.80 ± 2.83 47.045 0.000* 0.017X0.025 INCH 15.70 ± 2.42 0.019X0.025 INCH 19.79 ± 4.57 0.021X0.025 INCH 23.09 ± 6.29 TABLE 1:THE FORCE REQUIRED TO DISLODGE THE CRIMPABLE HOOKS CRIMPED ON STAINLESS STEEL WIRES BETA TITANIUM WIRES Mean ±SD(Newton) F-value Sig. 0.016X0.022 INCH 18.59 ± 4.09 39.187 0.000* 0.017X0.025 INCH 20.45 ± 4.82 0.019X0.025 INCH 29.64 ± 6.02 0.021X0.025 INCH 32.18 ± 4.39 TABLE 2:THE FORCE REQUIRED TO DISLODGE THE CRIMPABLE HOOKS CRIMPED ON BETA TITANIUM WIRES WIRE MEAN ± SD (Newton) MEAN DIFFERENCE t VALUE p VALUE STAINLESS STEEL 18.34 ± 5.33 -6.82 4.71 0.000* BETA TITANIUM 25.21 ± 7.52 TABLE 3: THE COMPARISON OF FORCE REQUIRED TO DISLODGE THE CRIMPABLE HOOKS CRIMPED ON STAINLESS STEEL AND BETA TITANIUM WIRES Discussion Force of dislodgement of crimpable attachments In the present study hooks were crimped on two different types (stainless steel and beta titanium) of wires and the force required to dislodge the hooks was tested. The dimensions of wire that were used were 0.016 x 0.022 inch, 0.017 x 0.025 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch. These two wires have different properties and are widely used in orthodontics. Stainless steel rectangular wires are used for retraction during sliding mechanics. During sliding mechanics crimpable attachments can be a suitable replacement for soldered attachments thereby saving time, without altering the properties of the wire as it happens with soldered attachments. It becomes clinically important to know the force of dislodgement of these attachments as force is applied through it for retraction. So in the present study the force of dislodgement of crimpable hooks on rectangular stainless steel wire was tested. Torque is best expressed in beta titanium wire therefore it is more frequently used and preferred over stainless steel wires by orthodontic clinicians to give torque in the anterior segment along with elastics during the finishing stages of treatment for the proper inclination of anterior teeth. Crimpable hooks on TMA can be of great advantage during finishing stages, so in the present study we have tested the dislodgement force on beta titanium wires, also. 10 hooks were crimped on every wire and the average force of dislodgement was recorded to minimize the error. Stainless Steel In stainless steel wires, hooks were crimped on 0.016 x 0.022 inch, 0.017 x 0.025 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch dimension of wire. No study has previously tested the dislodgement force of crimpable hooks on 0.016 x 0.022 inch, 0.017 x 0.025 inch and 0.021 x 0.025 inch wire. Ethanol was used to clean the wires so that any impurities on the wires were removed that could affect the dislodgement force. It was found that different dimensions have different dislodgement force, and also the dislodgement force increases with the increased dimensions in the stainless steel category. For 0.016 x 0.022 inch the mean was 14.8 N and for 0.021 x 0.025 inch mean value was 23.09 N so there was a difference of 9 N between the highest and lowest dimensions. This can be explained by the fact that as the dimension increases, the stiffness increases, thereby increasing the dislodgement force. Thus, hooks are better crimped on higher dimension wires. The results of the present study are contrary to that of Johal et al 2 where hooks were crimped on 0.019 x 0.025 inch and 0.018 x 0.025 inch stainless steel and concluded that there are no differences in the dislodgement force with the two wires and they stated that the dimensions of the wire do not make any difference to the dislodgement force. In the present study the mean force to dislodge hooks for 0.019 x 0.025 inch stainless steel was 19.79 N which was much higher than the force evaluated by Johal et al 2 which was 11.7 N for TP hooks and 6.75 N for AO hooks. In the study done by O’Bannon et al 6 the mean force of dislodgement for 0.019 x 0.025 inch stainless steel wire was 49.9 N for coated crimpable hooks and 31.3 N for ribbed crimpable hooks. In the study of O’Bannon et al 6 the force of dislodgement was much higher than the present study, but they tested torsional displacement instead of sliding displacement. Higher values for torsional dislodgement vs. sliding along a rectangular wire are to be expected. This higher force of dislodgement in the present study as compared to Johal et al 2 is also because a single male operator crimped 10 hooks on each wire without gabling the wire. This is in accordance that the force used by clinicians to crimp hooks on stainless steel archwires differs with different gender as studies by Johal et al 7 and Evans et al 8 that suggested that male operators apply more force as compared to female operators while crimping the hooks. The more force of dislodgement in the present study can also be explained by the fact that all the hooks were crimped outside the mouth, placing the hooks outside the mouth enables a higher force value to be used, which is in accordance with studies by Johal et al 7 that suggested that placement of crimpable hooks outside the mouth which provides greater clinical reliability rather than inside the mouth. In the present, no adhesives were assessed to increase the stability of hooks as the force of dislodgement is already much higher than that of a clinically applied force used for retraction. Griffith and Ferracane 3 stated that when sandblasting or adhesives are used the force required to dislodge the hooks increases by a factor of 10. Nattrass et al 9 in their comparison of the different force delivery systems, reported that clinicians apply extremely wide ranges of force (0.44–3.54 N) to the dentition during space closure. Furthermore, Frost 10 reported that lower levels of force are required to achieve bone remodeling and tooth movement. In the present study, the force required to dislodge hooks is much more than what is applied clinically. Thus, it would appear that the magnitude of force required to dislodge the hooks during retraction in sliding mechanics may not be reached clinically. So the use of adhesives or sandblasting for increasing the dislodgement force is not required. Beta Titanium (TMA) The force of dislodgement of crimpable hooks was tested on similar dimensions as in stainless steel for beta titanium, also. Wires used were 0.016 x 0.022 inch, 0.017 x 0.025 inch, 0.019 x 0.025 inch and 0.021 x 0.025 inch. No previous study has tested the force of dislodgement of crimpable hooks on beta titanium wire. The force of dislodgement increased as the dimensions of the wire was increased in the beta titanium group, also. The mean amount of force for dislodgement in the beta titanium group was highest for 0.021 x 0.025 inch which is significantly higher than 0.021 x 0.025 inch stainless steel. When the wires were compared among themselves the mean force of dislodgement were 12.32 ± 7.58 N for stainless steel and 18.78 ± 8.82 N for beta titanium. So the mean force of dislodgement for stainless steel was significantly less as compared to beta titanium. This can be explained as beta titanium has higher titanium content which makes the surface of beta titanium rough,11 so more force is required to dislodge the crimped hook. It was concluded from the present study that the force of dislodgement increases with the increase in dimension of the wires. The force required to dislodge the hook for stainless steel is significantly less as compared to beta titanium. The force of dislodgement was found to be much higher than what is applied clinically. Conclusion 1. The force of dislodgement of crimpable hooks increases with the increase in dimension of the wires in both stainless steel and beta titanium. 2. The force required to dislodge the hook for stainless steel wire is significantly less compared to beta titanium. 3. The force of dislodgment measured in the study was much higher than that of clinically applied force during retraction in sliding mechanics. Acknowledgement The authors would like to thank ITS engineering college Greater Noida for providing the Instron Universal Machine. References Algers DW. Arch marking technique for soldering intermaxillary hooks. J Clin Orthod 1987;21:538-9. Johal A, Harper CR, Sherriff M. Properties of crimpable archwire hooks a laboratory investigation. Eur J Orthod 1999;21:679-83. Griffin JT, Ferracane JL. Laboratory evaluation of adhesively crimped surgical ball hooks. Int J Adult Orthod Orthognathic surg 1998;13:169-175. Moore JC, Waters NE. Factors affecting tooth movement in sliding mechanics. Eur J Orthod 1993;15:235-41. Sia SS, Koga Y, Yoshida N. Determining the centre of resistance of maxillary anterior teeth subjected to retraction forces in sliding mechanics. Angle Orthod 2007;77:999-1003. 0’Bannon SP, Dunn WJ, Lenk JS. Comparison of torsional stability of 2 types of split crimpable surgical hooks with soldered brass surgical hooks. Am J Orthod Dentofacial Orthop 2006;130:471-5. Johal A, Loh S, Heng JK. A clinical investigation into the behavior of crimpable archwire hooks. J Orthod 2001;28:203-5. Evans RD, Jones ML. Laboratory evaluation of surgical ball hook crimping pliers. Int J Adult Orthod Orthognathic surg 1991;6:57-60. Nattrass C, Ireland AJ, Sherriff M. An Investigation into the placement of force delivery systems and the initial forces applied by clinicians during space closure. Br J Orthod 1997;24:127–31 Frost HM. Skeletal structural adaptations to mechanical usage (SATMU): 1. Redefining Wolff’s Law: the bone modeling problem. Anatomical Record 1990;226:403–13 Brantley WA, Eliades Theodore. Orthodontic Materials: Scientific and clinical aspects. New York:Theim;2007. , http://bit.ly/17pZf5e , via Dental Teach " Daily Dental Info " https://www.facebook.com/photo.php?fbid=647949808562905&set=a.588953107795909.1073741858.110664842291407&type=1