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IMPLANT-BONE INTERFACE OF MINISCREWS TREATED WITH SURFACE LUBRICANTS USING A WATER SOLUBLE-POLYMER OR BONE WAX; AN ANIMAL MODEL STUDY Robert J. Marshall, D.D.S. An Abstract Presented to the Faculty of the Graduate School of Saint Louis University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Dentistry 2010 Abstract Purpose: The purpose of this investigation was to evaluate the change in insertion torque and the effects of the implant-bone interface of miniscrew implants (MSIs) that were treated with a surface lubricant of either bone wax or Ostene®. Methods: MSIs coated with bone wax or Ostene® were compared to control MSIs to determine the acute difference in insertion torque when placed in synthetic bone and pig femur. The pullout strength was also evaluated using the MSIs placed in the synthetic bone. In addition, MSIs coated with bone wax or Ostene® were compared to control MSIs to determine the difference in insertion torque in synthetic bone and pig spare ribs at five second intervals from initial insertion until fully seated using a custom insertion machine. Histological samples of Beagle dogs were evaluated for the cellular response around the MSI controls, MSIs coated with bone wax, and MSIs coated with Ostene® immediately after removal and after two weeks of healing. Results: A significant difference (p<.05) in insertion torque was found between the MSI control group and both the bone wax and Ostene® groups in synthetic bone with the control group requiring the greatest insertion torque. No significant differences (p>.05) were found between any groups for insertion torque 1 when the MSIs were placed in a pig femur or for pullout strength in the synthetic bone. Additional testing showed that at time points T1, T2, T3, and T4 (15, 30, 45, and 60 seconds respectively), the MSI control group required a statistically significant (p<.05) greater torque to insert the MSIs in synthetic bone than when treated with bone wax or Ostene®. No differences were shown when each group was placed in pork spare ribs at any time point. Conclusions: Lubricating MSIs with bone wax or Ostene® reduces the insertion torque in synthetic bone. 2 COMMITTEE IN CHARGE OF CANDIDACY: Professor Rolf G. Behrents, Chairperson and Advisor Assistant Professor Ki Beom Kim Associate Clinical Professor Donald R. Oliver i DEDICATION I dedicate this project to my wife, Jamie, for her support, patience, and constant love as we have and will continue moving forward together. I also what to express a special thanks to my parents for their dedication to and sustaining influence on my pursuit of education over all these years. Finally, may this thesis take part by showing in a very small way the great program that Dr. Ken Marshall devoted so much of his life to creating. ii ACKNOWLEDGEMENTS I would like to acknowledge the following individuals: Dr. Rolf Behrents for guiding and providing direction through this entire project. Your answers to questions that I could not answer provided needed insights and results. Dr. Donald Oliver for providing the technical support and encouragement to finish a professional paper. I appreciate how approachable you are with questions. Dr. Ki Beom Kim for serving on my thesis committee. Your simple questions led to teaching moments. Dr. John Long, Ms. Nancy Roth, and Mr. Frank Strebeck, Jr. and everyone in the Comparative Medicine Department of Saint Louis University for the humane and professional manner in which the animals were handled. This project would not have been started or finished without your help. 3M Unitek and the Imtec Corporation for providing the miniscrew implants and the drivers required to insert and remove them. Mr. Eric Perkins for providing the necessary equipment to further this research. Dr. Robert Spears for his time and knowledge devoted to understanding the intricate cellular responses that must be understood to further science. iii Drs. Ben Lough and Heidi Israel for guiding me through the statistical analysis. iv TABLE OF CONTENTS List of Tables ..........................................vii List of Figures ........................................viii CHAPTER 1: INTRODUCTION ...................................1 CHAPTER 2: REVIEW OF THE LITERATURE Orthodontic Miniscrew Implants .......................4 Placement of MSIs ...............................5 Stability .......................................5 Pullout Strength ................................6 Influences on MSI Failure ............................8 Design of MSIs ..................................8 Bone and MSI Interface ..........................9 MSI Inflammation ...............................11 Insertion Torque ...............................13 MSI Fracture ...................................15 Friction ............................................16 Heat ...........................................16 Lubricants in Medicine .........................19 References ..........................................23 CHAPTER 3: JOURNAL ARTICLE Abstract ............................................29 Introduction ........................................30 Methods and Materials ...............................34 Miniscrew Implants .............................34 Testing Methods ................................35 Synthetic Bone Model ......................35 Pig Femur .................................36 Mechanical Testing .............................36 Placement Torque ..........................36 Pullout Analysis ..........................38 Animals ........................................39 MSI Placement .............................39 MSI Lubricant Evaluation ..................41 Further Research ...............................42 Statistical Analysis ................................44 Results .............................................45 Standard Tests .................................45 Synthetic Bone Model Insertion Torque .....45 Synthetic Bone Model Pullout ..............45 Pig Femur Model ...........................46 Custom Insertion Machine Tests .................47 Synthetic Bone Model ......................47 v Pig Spare Ribs ............................52 Discussion ..........................................57 Conclusions .........................................60 References ..........................................62 Appendix .................................................65 Vita Auctoris ............................................69 vi LIST OF TABLES Table 3.1: Descriptive statistics for MSIs in synthetic bone and pig femur............................45 Table 3.2: Statistical comparison of original measurements..................................45 Table 3.3: Descriptive statistics of MSIs in Synthetic Bone (T1, T2, T3, and T4 equal 15, 30, 45, and 60 seconds respectively)......................50 Table 3.4: Statistical comparison of MSIs in Synthetic Bone (T1, T2, T3, and T4 equal 15, 30, 45, and 60 seconds respectively)......................51 Table 3.5: Descriptive statistics of MSIs in pork spare ribs (T1, T2, T3, and T4 equal 15, 30, 45, and 60 seconds respectively)......................55 Table 3.6: Statistical comparison of MSIs in pork spare ribs (T1, T2, T3, and T4 equl 15,30, 45, and 60 seconds respectively).........................56 vii LIST OF FIGURES Figure 3.1: MSIs used in this research A. Control MSI, B. MSI coated with bone wax, C. MSI coated with Ostene® ..............................33 Figure 3.2: Custom jig securing synthetic bone block with Mecmesin® instrument attached to driver and MSI ...................................36 Figure 3.3: Placement of MSIs (red dots) on dog’s right side ......................................40 Figure 3.4: Placement of MSIs (red dots) on dog’s left side ......................................40 Figure 3.5: Custom insertion torque machine from left side ......................................42 Figure 3.6: Custom torque machine from back showing motor attached under drill press table ....43 Figure 3.7: Individual control MSI’s insertion torque over time in synthetic bone ...............47 Figure 3.8: Individual bone wax coated MSI’s insertion torque over time in synthetic bone ........48 Figure 3.9: Individual Ostene® coated MSI’s insertion torque over time in synthetic bone ........49 Figure 3.10: Average of each group of MSIs’ insertion torque over time in synthetic bone ........50 Figure 3.11: Individual control MSI’s insertion torque over time in pig spare ribs ...............52 Figure 3.12: Individual bone wax coated MSI’s insertion torque over time in pig spare ribs ........53 Figure 3.13: Individual Ostene® coated MSI’s insertion torque over time in pig spare ribs ........54 Figure 3.14: Average of each group of MSIs’ insertion torque over time in pig spare ribs ........55 viii Figure A.1: Individual bath soap coated MSI’s insertion torque over time in synthetic bone ........65 Figure A.2: Individual candle wax coated MSI’s insertion torque over time in synthetic bone ........66 Figure A.3: Individual control MSI’s insertion torque over time in synthetic bone without the help of the custom insertion machine ...........67 Figure A.4: Averages of each group of MSIs’ insertion torque over time in synthetic bone (n=5) ..68 ix CHAPTER 1: INTRODUCTION The necessity for anchorage has been a topic of interest for as long as orthodontists have attempted to move teeth. A wide selection of strategies has been employed in order to establish anchorage for numerous tooth movements with varying levels of success. Common methods of establishing anchorage might include extraoral headgear, differential forces, and intermaxillary elastics. Starting in 1945, animal studies were conducted to evaluate the possibility of using screws in bone to achieve anchorage.1 Since that time, and particularly in the last few years, the use of implants to establish anchorage has become widespread. Their value is based on the fact that miniscrew implants, although they do not always stay perfectly immobile, are a stable anchorage unit.2 While obviously valuable, problems exist and implants fail. Some of the reasons for failure include peri-implant inflammation, site of placement, poor implant design, bone necrosis due to heat generated during placement, and high torque during placement. An aspect of possible miniscrew implant (MSI) improvement is reduction of insertion torque. Increased torque during placement of the MSI leads to decreased 1 mechanical strength and thus earlier failure.3 In an effort to decrease the insertion torque, Lima et al. studied the torque difference when the length, diameter, and shape of the MSIs were altered. They determined that torque was affected most by the diameter, followed by the length, and then the shape.4 Another way to decrease the insertion torque would be to reduce the friction at the bone and MSI interface with lubricants. However, the author could not locate literature that shows that surface lubricants have been applied to MSIs in order to achieve this objective. For years lubricating surfaces has shown favorable results in reducing friction.5 Both bone wax and a water solublepolymer, Ostene®, have been used in medicine for different purposes, and will be used to lubricate the MSIs for this study. Bone wax has been used since the 1800s as a way to achieve hemostasis during surgical procedures.6 Throughout the years it has been widely used because it is inexpensive and typically has few related complications.7 Ostene® is a water soluble-polymer that has gained more acceptance as studies have revealed that it has better biocompatibility and less incidence of infection than bone wax. It has also been shown to increase bone healing at the surgery site. 2 Using 20 rabbits, Wellisz et al. compared the results when placing Ostene® and bone wax on median sternotomies. The histological samples taken after six weeks identified normal bone healing in the soluble-polymer group while the bone wax group showed an absence of new bone formation.8 The long-term objective of this study is to determine whether surface lubricants can reduce the insertion torque of MSIs without affecting adversely the bone-implant interface. If this is the case, then surface lubricants could be used to reduce the friction and heat generated at the bone-MSI interface and possibly decrease the amount of bone necrosis around the MSI. As the amount of insertion torque decreases, the number of MSIs fracturing upon insertion should also decrease. In addition to their lubricating characteristics, the biological response will be evaluated to determine whether there are untoward problems associated with their use in orthodontics. The following review of the literature will give a better understanding of MSIs, their use in orthodontics, some of the problems that are currently faced, and how reducing the friction upon insertion might be beneficial. 3 CHAPTER 2: REVIEW OF THE LITERATURE Orthodontic Miniscrew Implants The correction of misaligned teeth in dentistry has been sought after for more than a century. One of the most difficult tasks is to move teeth that are out of position while preventing correctly aligned teeth from being affected. Throughout the years, many different types of appliances have been used both intraorally and extraorally to achieve anchorage. One of the more recent ways of attaining the objective of absolute anchorage is through the use of MSIs. These devices are relatively small, do not require a complex surgical procedure to place, and aid in achieving better orthodontic results.9 MSIs have many uses. They can be used for the correction of anteroposterior and vertical skeletal discrepancies. Even more commonly, they are being used to effect various tooth movements including molar uprighting, intrusion, or extrusion of single or multiple teeth, and anteroposterior tooth movements.10 Essentially, MSIs have become a very helpful and useful tool in orthodontics. To be useful, each MSI must be placed in the oral cavity in order to perform its function, and inherent in this process arise many variables that affect usefulness. 4 Placement of MSIs The goal of MSI placement is to insert the MSI in bone in such a way that forces can be applied between the MSI and certain teeth with the result being optimal tooth movement while the MSI remains immovable in bone. There is a wide variety of MSIs currently in use. Some of them are self-drilling and others are not. Those that are not self-drilling require a tissue punch and pilot hole be placed prior to MSI insertion.11 The pilot hole is normally 0.2 mm to 0.3 mm smaller in diameter than the MSI.12 The self-drilling MSIs, on the other hand, do not necessarily require a hole punch or pre-drilling and can be inserted directly through the gingival tissues and into the bone. Both types of MSIs are typically placed using one of the following instruments: torque wrench, hand driver, finger/thumb driver, or motorized hand piece with limited torque.10 Stability The subject of stability can be broken down into two different categories. Primary stability, by definition, is a mechanical locking of the bone and MSI upon placement that is directly related to the quality and quantity of 5 local bone. Secondary stability, however, is associated with the changes that occur at the bone to implant interface over time due to the remodeling of the tissues and surrounding bone.13 Without good primary stability, secondary stability generally will not occur. Poor primary stability leads to small movements of the MSI, which does not allow for the necessary bone remodeling and thus secondary stability is not achieved.14 As the implant is moved back and forth due to poor primary stability, micro fracturing occurs which is followed by necrosis. Subsequently a fibrous connective tissue capsule slowly thickens around the implant as bone resorption continues. Eventually the implant may fail due to lack of bone to implant contact.15,16 If primary and secondary stability are achieved, the bone to implant interface becomes osseointegrated, or mechanically locked.17 Pullout Strength One of the more common ways to evaluate the stability of MSIs is to perform a pullout test. This measures the holding power of a MSI.18 As discussed before, the bone to MSI interface is very important in the stability of an implant. It has been shown that the amount of force required to pull out a MSI is directly related to this bone 6 to implant contact.19 This is one of the reasons this test is frequently used. Typically the material that the screw is embedded in is held firmly in a vice while a calibrated machine slowly applies a force in the vertical direction, along the long axis of the MSI, until it is dislodged. The measure of the highest force applied before the implant fails is recorded. It has been found that the diameter and length, both of which affect the amount of bone to MSI contact, are important factors in determining the amount of force that can be withstood on pullout.20-22 Another crucial variable is the material in which the MSI is placed. Huja et al. placed 56 MSIs in four skeletally mature dogs. Two of the 56 MSIs could not be tested because of the inability to prepare the specimens. For the remaining 54 MSIs, the pullout strength was found to be most in the posterior mandible and least in the anterior mandible. There was a significant difference in the data collected from an average of 338.3 N down to 134.5 N. Huja et al. then concluded, “A correlation between cortical bone thickness and pullout strength was obtained. Other factors such as bone density and quality possible play roles in determining pullout strength.”19 7 In another study, Huja et al. evaluated the biomechanical stability of MSIs immediately after placement and also after six weeks of healing. They determined that there was no significant difference in pullout strength between the two times. These results indicate that the holding strength of MSIs is highly dependent on the initial interface between the cortical bone and the MSI.14 Influences on MSI Failure Sometimes MSI failure is defined as loss of ability to hold anchorage.23 However, other studies conclude failure occurs when mobility has reached a predetermined amount.24-26 Such implants may still be functional, but are slightly mobile. There are many reasons for MSI failure and some of them will be discussed in greater detail. Design of MSIs With so many different companies marketing MSIs and each company creating a product that is physically a little different, the options seem endless when choosing which implant is best. However, many studies have been done comparing a few of the different MSI characteristics so that failure is reduced. MSIs has been studied. First, the length and diameter of Mortensen et al. showed recently 8 that immediately loaded 3 mm MSI success rates were significantly lower than 6 mm MSIs in Beagle dogs.15 A different study where 59 MSIs were placed in 29 patients compared the stability of 6 and 8 mm lengths. The success rate was 72.2% for the 6 mm and 90.2% for the 8 mm MSIs.23 Miyawaki et al. followed 134 MSIs of different diameters in the posterior region of the mouth for one year. Among other findings, they concluded that a MSI with a diameter of less than 1.0 mm was associated with increased mobility and failure.26 As recently as 2008, Brinley et al. evaluated the effects of pitch and fluting on primary stability in a synthetic and cadaver bone model. Their work resulted in the findings that, within certain parameters, decreasing MSI thread pitch increases the primary stability. In addition, they concluded that decreasing MSI fluting increases primary stability.27 Bone and MSI Interface As was explained previously, the MSI to bone interface is very important because it directly affects the primary stability of the anchorage unit.14,28 When a MSI is inserted into bone, many events occur. Brunski et al. described some of the cellular responses. Interestingly enough, the 9 first process that takes place is the adsorption of proteins that have come from the blood and tissue fluids. This adsorption causes a small amount of corrosion byproduct that permeates into the tissues. This surface conditioning, or oxidation, plays an important role in the host response that follows.29 Ideally, the host response leads to tissue healing giving a close contact between the MSI and bone. Beginning with a blood clot and moving through an afibrillar interfacial zone, proteins such as osteopontin and bone sialoprotein aid in the process of cell adhesion and mineral binding. This interfacial zone grows in two directions, from the MSI toward the bone and from the bone toward the MSI. Osteoblasts, osteoid, and mineralized matrix are all observed in the interfacial zone as osseointegration occurs.29 Looking at it from a more mechanical perspective, it has been shown that microfractures develop as the implant is placed.30,31 Often, these microfractures are a result of the shear stress that is introduced along the long axis of the MSI upon insertion.32 As the implant is placed farther and farther into the bone, this stress is increased and is partly responsible for the increase in friction and torque that is noted. When a bone is placed under this type of 10 stress and friction, necrosis often occurs at the bone to MSI interface.33 Nkenke et al. showed this necrosis and the fibrous encapsulation of the MSI that can result in seven mini pigs.34 Their study showed that not all of the necrotic bone breaks down at the same time, but is often removed over an extended period of time. They reasoned that if this were not the true process, there would almost always be a loosening and loss of the MSI.34 Nkenke et al. concluded, among other things, that there was no difference between immediately loaded and unloaded implants with regards to the bone mineral apposition rate.34 MSI Inflammation Perhaps one of the greatest predictors of MSI failure is inflammation around the tissues of the implant, or periimplantitis.24 In a very large and thorough study, Park et al. examined 18 different clinical variables in 87 consecutive patients in which a total of 227 MSIs were placed. They followed the patients for 15 months to determine the success rate as determined by loosening, which equated with failure. They reported that the overall success rate was 91.6%. In their study, no statistically significant difference in success rates were found in diameter, length, occlusogingival positioning, angle of 11 placement, timing or type of force application, ligature wire extension, amount of exposed screw head, or oral hygiene. Age and sex also did not show any statistically significant difference. However, the jaw in which the MSI was placed, the side of placement, and inflammation around the implant were all statistically significant reasons for failure.24 Nevertheless, the MSI typically must be placed near the site of the needed anchorage. This makes it difficult for a practitioner to place the MSI in a more ideal location and still achieve the desired results. Therefore it is of importance to note that Park et al. concluded that in order to minimize the failure of MSIs, inflammation must be controlled.24 Park et al. are not alone in concluding that inflammation around the MSI site is a risk factor for failure. Roberts et al., Maino et al., and Johansson and Albrektsson all arrived at similar conclusions.35,36,37 Another study showed that MSIs placed in nonkeratinized tissues have a greater failure rate due to an increased inflammatory response.38 It is safe to conclude from the literature that MSI success rate is inversely related to peri-implantitis. 12 Insertion Torque The amount of torque required to fully insert the MSI is another factor that must be evaluated to reduce failure. In 2006, Motoyoshi et al. recorded the maximum torque on insertion of 124 MSIs in 41 orthodontic patients. The recorded values were between 7.2 Ncm and 13.5 Ncm depending upon the location within the mouth. Although they had not suspected it, it was discovered that the MSIs in the mandible had a significantly higher failure rate than the maxilla, which corresponded to a higher insertion torque in the mandible. They concluded that, “according to our calculations of the risk ratio for failure, to raise the success rate of a 1.6 mm diameter mini-implant, the recommended implant placement torque is within the range from 5 to 10 Ncm.”39 In explaining this finding, the authors theorized the higher torque resulted in a higher stress, which led to bone degeneration at the bone to implant interface, and ultimately the bone turnover in the area was reduced.39 In a follow up study, they placed another 87 implants in 32 patients and set out to determine whether cortical bone thickness and implant placement torque had an effect on stability. With an 87% success rate after six months, 13 they discovered that the cortical bone thickness was significantly greater for the implants that were not mobile than those that had failed. The success group had a mean of 1.42 mm of cortical bone and the failure group only had a cortical thickness of 0.97 mm on average. The success group also had torque values between 8 and 10 Ncm, whereas the failure group tended to fall outside of that range.40 A different study, however, did state that the most stable MSIs are placed in the densest bone.41 This study was performed with several different types of MSIs and in various locations on cadaver bone. After reaching the aforementioned conclusion, the authors noted that there could be a maximum limit after which the bone would be damaged if the insertion torque were too great.41 These same findings were not duplicated by Weichmann et al. and Cheng et al. who both reported higher success rates in the maxilla than in the mandible where the insertion torques were less. It was then deduced that the MSIs were overheating the bone in the thicker cortical plate of the mandible and thus leading to greater failure rates.25,38 As of yet, there does not seem to be a consensus on the maximum or minimum limits to insertion torque throughout the literature. 14 MSI Fracture An obvious reason for MSIs to fail is when the implant itself fractures. While conducting a biomechanical comparison of four different MSIs, Mischkowski et al. discovered that MSIs fracture at different insertion torques depending on the design of the implant itself.42 If the design reveals a weaker portion, a pilot hole may be necessary to minimize the danger of screw fracture. MSIs are typically placed under three phases of mechanical loading throughout their use. Phase one and three are torsional loading when the implant is placed and removed, and phase two is flexural loading when the MSI is loaded during function.43 If the MSI design is flawed, premature mechanical weakening can occur as the insertion torque increases which increases the risk of fracture.43 A significant study by Jolley and Chung indicates that factors that contribute to increased fractures “include the insertion site, bone density, and whether a pilot hole is drilled.”44 They also state that changing the insertion angle during placement, or when placing a MSI into an object with greater density, such as a root, increases the possibility for fracture.44 Another potential characteristic of MSIs that can lead to fracturing is the alloy of the implant itself. 15 Depending on the mixture of metals that are combined to produce the alloy, the MSI can be weakened and thus more prone to fracture at lower torque values. Specifically, MSIs can be more prone to fracture depending on whether hard or soft titanium is used.44 Friction When two or more independent objects are in contact, the motion of moving one of the objects past the other is resisted by friction.45,46 This action of rubbing one surface against the other plays a very important role at the bone to MSI interface. Friction can be reduced or overcome by using some sort of lubricant such as water, oil, or grease between the two surfaces. Types of lubricants used in medicine will be discussed later in greater detail. Heat One definition of heat is “thermal energy transferred between a system and its surroundings.”47 While inserting a MSI, thermal energy is produced in two different ways.48 First, when the drill bit shears the surface layer of a material, the intermolecular bonds are broken and heat is released. Second, as the MSI is inserted into the bone, friction from the non-cutting surfaces of the implant, such 16 as the flank and shaft, all produce thermal energy.48 This heat is dissipated through the blood, tissue fluid, bone, and the bone chips that are removed. Even with these outlets for the heat, bone is a poor heat conductor and it is common for the temperature to rise considerably.48 As early as 500 BC, Hippocrates had a rudimentary idea that heat produced while drilling in the skull was damaging to the bone and tissues. To prevent this, he recommended dipping the drill in cold water frequently.49 All of the negative effects of heat on bone are still not completely understood, but there has been substantial research into this area. It is currently taught that as heat increases, protoplasmic proteins are changed along with the inactivation of enzymes, metabolic processes, and alterations in protoplasmic lipids.47 If the temperature is elevated too much, water is transformed into a vaporous state resulting in several other detrimental occurrences such as dehydration, desiccation, shrinkage, membrane rupture and even carbonization.50 Even more specific are the effects of heat on proteins with their wide variation in thermal resistivity. Lysyl-rRNA-synthetase, for example, is vital for cellular functions and can be denatured at temperatures as low as 45° C that last for five minutes or more. There are small amounts of lysyl-rRNA-synthetase 17 that are denatured at even lower temperatures, around 40° C.51 More resistant proteins include collagen at 60° C and bone alkaline phosphatase at 56° C.47,52 Much more recently, Karmani summarized the effects of drilling on bone. In recapping the literature, the author determined that the drill speed, the condition of the drill, and the use of coolants all had effects on the post surgical reaction of the bone.47 Eriksson et al. recorded the maximum insertion temperature at a distance of 0.5 mm from the periphery of the drill hole. Their study included five rabbits, two dogs, and five humans. Using a constant drill speed, it was discovered that the mean temperatures were as great as 40° C in rabbits, 56° C in dogs, and 89° C in humans. The initial bone temperatures were reported at 32° C in both rabbits and dogs, but was not reported for the human subjects. Eriksson et al. concluded that the difference in temperature was due to the variation in cortical thickness between the three subject groups.53 Because the cortical bone in the mandible is typically thicker than the maxilla, this study may help explain why the findings of others show there is a greater failure rate of MSIs in the mandible. While doing further research Eriksson and Albrektsson determined that the critical threshold at which necrosis 18 occurs is 47° C for one minute in rabbits.54,55 This temperature is under which bone should be kept in order to promote increased stability and decreased bone necrosis. Lubricants in Medicine For many years, lubricants have been applied to various surfaces to reduce friction. Lubricants can be applied either in a solid, mist, or liquid form.5 Wax in particular is often used when either oil or grease is not appropriate.5 The properties of wax have been shown to reduce friction and have good wear resistance.56 As recently as 2008, Quaglini et al. studied the ideal roughness of a metal material with some of the more common lubricants in reducing friction. By applying six different polymer lubricants to steel and measuring the sliding velocity between the metal surfaces, the best lubricant and steel surfaces were determined. They discovered that the ideal interaction for smoothly polished metal surfaces are lubricants with low modulus of elasticity.56 Lubricants that were wax based, although not the best, also showed good friction reducing characteristics in this study.56 Tribology is defined as the “study of friction, wear, lubrication mechanisms, and their interrelationships.”57 Since 1973, biotribology has become a branch of tribology 19 that focuses on friction and lubricants that are used in the body, especially in joints.57 The human body naturally produces various lubricants to reduce friction between articulating surfaces. Some examples of these lubricating components that have shown to reduce friction include synovial fluid, lubricin, hyaluronic acid, surface active phospholipids, and chondroitin sulphate.58 When the body no longer produces enough of these lubricating components, commercially available supplements and replacements are available. Hyaluronic acid derivatives, peptides, synthetic phospholipids, recombinant lubricin, low molecular weight hyaluronate, and high molecular weight hyaluronate have all been approved and marketed to be placed in the human body to lubricate the appropriate sites.59-61,58 Bone wax, essentially sterile bees wax, has been used in medicine since the 1840s.6 Gupta and Prestigiacomo summarized the use of bone wax over more than 100 years and described some of its uses. It has historically been used as a way of controlling bleeding, especially in the cranium. Some of the properties that have made it so desirable in applying it over an exposed bone that is hemorrhaging include being soft, malleable, and nonbrittle.6 Bone wax is also inexpensive and readily available.7 20 Another form of a potential lubricant that is used in medicine is a water-soluble polymer called Ostene®. One of the more significant studies using Ostene® and bone wax involved 20 New Zealand White rabbits. Median sternotomies were performed and either bone wax or Ostene® was sufficiently applied to result in hemostasis. After a six- week time frame, the healing was inspected using x-rays, histology, and mechanical strength testing. The results of the inspections indicated in the Ostene® group normal bone healing had occurred and that the strength was twice as much as the bone wax group. They also demonstrated that in the bone wax group fibrotic scar tissue formed rather than bone.62 One of the major disadvantages of bone wax is it does not inhibit infection. Wellisz et al. compared the infection rates and healing in 24 rabbit tibias between bone wax, Ostene®, and a control group. Immediately after the defects were made and treated according to the study, they were inoculated with Staphylococcus aureaus. After four weeks, all of the bone defects treated with bone wax were infected and osteomyelitis had developed. observed that no bone healing had occurred. It was also However, in the control and Ostene® groups there was a statistically significant lower rate of osteomyelitis and higher rate of 21 healing. This study shows that using a soluble-polymer material, such as Ostene®, rather than bone wax can decrease the rates of postoperative bone infections.8 As we can see, the literature demonstrates that there are many factors influencing MSI failure. Among them, high insertion torque and heat generated by friction are two that can be diminished by a surface lubricant. Two popular FDA approved substances, bone wax and Ostene®, are currently being used in medicine to reduce hemostasis, but potentially can reduce the effects of both high insertion torque and the heat generated by friction on human bone. This could lead to a MSI that provides better anchorage by being more stable and failing less frequently, a type of anchorage that is highly beneficial for the orthodontic profession. 22 References 1. Gainsforth BL, Higley LB. A study of orthodontic anchorage possibilities in basal bone. American Journal of Orthodontics and Oral Surgery. 1945;31:406-17. 2. Liou EJW, Pai BCJ, Lin JCY. Do miniscrews remain stationary under orthodontic forces? Am J Orthod Dentofacial Orthop. 2004;126:42-7. 3. Reicheneder C, Rottner K, Bokan I, Mai R, Lauer G, Richter G, Gedrange T, Proff P. Mechanical loading of orthodontic miniscrews - significance and problems: an experimental study. Biomed Tech (Berl). 2008;53:242-5. 4. Lim S, Cha J, Hwang C. Insertion torque of orthodontic miniscrews according to changes in shape, diameter and length. Angle Orthod. 2008;78:234-40. 5. Warth AH. The Chemistry and Technology of Waxes. New York: Reinhold Publishing Corporation; 1956:413-14. 6. Gupta G, Prestigiacomo CJ. From sealing wax to bone wax: predecessors to Horsley's development. Neurosurg Focus. 2007;23:E16. 7. Yoshida T, Kim W, Tsuchida Y, Hirashima T, Oka Y, Kubo T. Experience of bone bridge resection and bone wax packing for partial growth arrest of distal tibia. J Orthop Trauma. 2008;22:142-7. 8. Wellisz T, An YH, Wen X, Kang Q, Hill CM, Armstrong JK. Infection rates and healing using bone wax and a soluble polymer material. Clin Orthop Relat Res. 2008;466:481-6. 9. Yanosky MR, Holmes JD. Mini-implant temporary anchorage devices: orthodontic applications. Compend Contin Educ Dent. 2008;29:12-20; quiz 21, 30. 10. Mah J, Bergstrand F. Temporary anchorage devices: a status report. J Clin Orthod. 2005;39:132-136; discussion 136; quiz 153. 11. Papadopoulos MA, Tarawneh F. The use of miniscrew implants for temporary skeletal anchorage in orthodontics: a comprehensive review. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007;103:e6-15. 23 12. Melsen B. Mini-implants: Where are we? J Clin Orthod. 2005;39:539-547; quiz 531-532. 13. Meredith N. Assessment of implant stability as a prognostic determinant. Int J Prosthodont. 1998;11:491-501. 14. Huja SS, Rao J, Struckhoff JA, Beck FM, Litsky AS. Biomechanical and histomorphometric analyses of monocortical screws at placement and 6 weeks postinsertion. J Oral Implantol. 2006;32:110-116. 15. Mortensen MG, Buschang PH, Oliver DR, Kyung H, Behrents RG. Stability of immediately loaded 3- and 6-mm miniscrew implants in beagle dogs--a pilot study. Am J Orthod Dentofacial Orthop. 2009;136:251-259. 16. Fritz U, Ehmer A, Diedrich P. Clinical Suitability of Titanium Microscrews for Orthodontic Anchorage—Preliminary Experiences. Journal of Orofacial Orthopedics/Fortschritte der Kieferorthopädie . 2004;65:410-418. 17. Simmons CA, Valiquette N, Pilliar RM. Osseointegration of sintered porous-surfaced and plasma spray-coated implants: An animal model study of early postimplantation healing response and mechanical stability. J. Biomed. Mater. Res. 1999;47:127-138. 18. Cleek TM, Reynolds KJ, Hearn TC. Effect of screw torque level on cortical bone pullout strength. J Orthop Trauma. 2007;21:117-123. 19. Huja SS, Litsky AS, Beck FM, Johnson KA, Larsen PE. Pull-out strength of monocortical screws placed in the maxillae and mandibles of dogs. Am J Orthod Dentofacial Orthop. 2005;127:307-313. 20. Hitchon PW, Brenton MD, Coppes JK, From AM, Torner JC. Factors affecting the pullout strength of self-drilling and self-tapping anterior cervical screws. Spine. 2003;28:9-13. 21. Chapman JR, Harrington RM, Lee KM, Anderson PA, Tencer AF, Kowalski D. Factors affecting the pullout strength of cancellous bone screws. J Biomech Eng. 1996;118:391-398. 24 22. DeCoster TA, Heetderks DB, Downey DJ, Ferries JS, Jones W. Optimizing bone screw pullout force. J Orthop Trauma. 1990;4:169-174. 23. Chen C, Chang C, Hsieh C, Tseng Y, Shen Y, Huang I, Yang C, Chen C. The use of microimplants in orthodontic anchorage. J. Oral Maxillofac. Surg. 2006;64:1209-1213. 24. Park H, Jeong S, Kwon O. Factors affecting the clinical success of screw implants used as orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2006;130:18-25. 25. Wiechmann D, Meyer U, Büchter A. Success rate of miniand micro-implants used for orthodontic anchorage: a prospective clinical study. Clin Oral Implants Res. 2007;18:263-267. 26. Miyawaki S, Koyama I, Inoue M, Mishima K, Sugahara T, Takano-Yamamoto T. Factors associated with the stability of titanium screws placed in the posterior region for orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2003;124:373-378. 27. Brinley C (2008). Effects of MSI design on primary stability. Unpublished master's thesis, Center for Advanced Dental Education at Saint Louis University, St. Louis, MO. 28. Friberg B, Sennerby L, Gröndahl K, Bergström C, Bäck T, Lekholm U. On cutting torque measurements during implant placement: a 3-year clinical prospective study. Clin Implant Dent Relat Res. 1999;1:75-83. 29. Brunski JB, Puleo DA, Nanci A. Biomaterials and biomechanics of oral and maxillofacial implants: current status and future developments. Int J Oral Maxillofac Implants. 2000;15:15-46. 30. Trisi P, Rebaudi A. Progressive bone adaptation of titanium implants during and after orthodontic load in humans. Int J Periodontics Restorative Dent. 2002;22:31-43. 31. Cho HJ. Clinical applications of mini-implants as orthodontic anchorage and the peri-implant tissue reaction upon loading. J Calif Dent Assoc. 2006;34:813-820. 25 32. Hughes AN, Jordan BA. The mechanical properties of surgical bone screws and some aspects of insertion practice. Injury. 1972;4:25-38. 33. Meredith N. Assessment of implant stability as a prognostic determinant. Int J Prosthodont. 1998;11:491-501. 34. Nkenke E, Lehner B, Weinzierl K, Thams U, Neugebauer J, Steveling H, Radespiel-Tröger M, Neukam FW. Bone contact, growth, and density around immediately loaded implants in the mandible of mini pigs. Clin Oral Implants Res. 2003;14:312-321. 35. Roberts WE, Smith RK, Zilberman Y, Mozsary PG, Smith RS. Osseous adaptation to continuous loading of rigid endosseous implants. Am J Orthod. 1984;86:95-111. 36. Maino BG, Maino G, Mura P. Spider Screw: skeletal anchorage system. Prog Orthod. 2005;6:70-81. 37. Johansson C, Albrektsson T. Integration of screw implants in the rabbit: a 1-year follow-up of removal torque of titanium implants. Int J Oral Maxillofac Implants. 1987;2:69-75. 38. Cheng S, Tseng I, Lee J, Kok S. A prospective study of the risk factors associated with failure of mini-implants used for orthodontic anchorage. Int J Oral Maxillofac Implants. 2004;19:100-106. 39. Motoyoshi M, Hirabayashi M, Uemura M, Shimizu N. Recommended placement torque when tightening an orthodontic mini-implant. Clinical Oral Implants Research. 2006;17:109114. 40. Motoyoshi M, Yoshida T, Ono A, Shimizu N. Effect of cortical bone thickness and implant placement torque on stability of orthodontic mini-implants. Int J Oral Maxillofac Implants. 2007;22:779-784. 41. O'Sullivan D, Sennerby L, Meredith N. Measurements comparing the initial stability of five designs of dental implants: a human cadaver study. Clin Implant Dent Relat Res. 2000;2:85-92. 26 42. Mischkowski R, Kneuertz P, Florvaag B, Lazar F, Koebke J, Zöller J. Biomechanical comparison of four different miniscrew types for skeletal anchorage in the mandibulomaxillary area. International Journal of Oral and Maxillofacial Surgery. 2008;37:948-954. 43. Reicheneder C, Rottner K, Bokan I, Mai R, Lauer G, Richter G, Gedrange T, Proff P. Mechanical loading of orthodontic miniscrews - significance and problems: an experimental study. Biomed Tech (Berl). 2008;53:242-245. 44. Jolley TH, Chung CH. Peak torque values at fracture of orthodontic miniscrews. J Clin Orthod. 2007;41:326-328. 45. Andy Ruina RP. Introduction to Statics and Dynamics. Oxford University Press; 2002. 46. Oxford English Dictionary. Ask Oxford. Available at: http://www.askoxford.com/concise_oed/friction?view=uk [Accessed July 15, 2009]. 47. Karmani S. The thermal properties of bone and the effects of surgical intervention. Current Orthopaedics. 2006;20:52-58. 48. Saha S, Pal S, Albright JA. Surgical drilling: design and performance of an improved drill. J Biomech Eng. 1982;104:245-252. 49. Phillips ED. Greek medicine. London: Camelot Press Ltd; 1973. 50. Kuhns JG, Hayes J, Stein M, Helwig EB. Laser injury in skin. Lab. Invest. 1967;17:1-13. 51. Rymo L, Lagerkvist U, Wonacott A. Crystallization of lysyl transfer ribonucleic acid synthetase from yeast. J. Biol. Chem. 1970;245:4308-4316. 52. Viidik A. Functional properties of collagenous tissues. Int Rev Connect Tissue Res. 1973;6:127-215. 53. Eriksson AR, Albrektsson T, Albrektsson B. Heat caused by drilling cortical bone. Temperature measured in vivo in patients and animals. Acta Orthop Scand. 1984;55:629-631. 27 54. Eriksson AR, Albrektsson T. Temperature threshold levels for heat-induced bone tissue injury: a vitalmicroscopic study in the rabbit. J Prosthet Dent. 1983;50:101-107. 55. Eriksson RA, Albrektsson T. The effect of heat on bone regeneration: an experimental study in the rabbit using the bone growth chamber. J. Oral Maxillofac. Surg. 1984;42:705711. 56. Quaglini V, Dubini P, Ferroni D, Poggi C. Influence of counterface roughness on friction properties of engineering plastics for bearing applications. Materials & Design. 2009;30:1650-1658. 57. Norris JA, Stabile KJ, Jinnah RH. An introduction to tribology. J Surg Orthop Adv. 2008;17:2-5. 58. Katta J, Jin Z, Ingham E, Fisher J. Biotribology of articular cartilage--a review of the recent advances. Med Eng Phys. 2008;30:1349-1363. 59. van den Bekerom MPJ, Lamme B, Sermon A, Mulier M. What is the evidence for viscosupplementation in the treatment of patients with hip osteoarthritis? Systematic review of the literature. Arch Orthop Trauma Surg. 2008;128:815-823. 60. Atay T, Aslan A, Baydar ML, Ceylan B, Baykal B, Kirdemir V. The efficacy of low- and high-molecular-weight hyaluronic acid applications after arthroscopic debridement in patients with osteoarthritis of the knee. Acta Orthop Traumatol Turc. 2008;42:228-233. 61. Long X, Chen G, Cheng AHA, Cheng Y, Deng M, Cai H, Meng Q. A randomized controlled trial of superior and inferior temporomandibular joint space injection with hyaluronic acid in treatment of anterior disc displacement without reduction. J. Oral Maxillofac. Surg. 2009;67:357-361. 62. Wellisz T, Armstrong JK, Cambridge J, An YH, Wen X, Kang Q, Hill CM, Fisher TC. The effects of a soluble polymer and bone wax on sternal healing in an animal model. Ann Thorac Surg. 2008;85:1776-80. 28 CHAPTER 3: JOURNAL ARTICLE Abstract Purpose: The purpose of this investigation was to evaluate the change in insertion torque and the effects of the implant-bone interface of miniscrew implants (MSIs) that were treated with a surface lubricant of either bone wax or Ostene®. Methods: MSIs coated with bone wax or Ostene® were compared to control MSIs to determine the acute difference in insertion torque when placed in synthetic bone and pig femur. The pullout strength was also evaluated using the MSIs placed in the synthetic bone. In addition, MSIs coated with bone wax or Ostene® were compared to control MSIs to determine the difference in insertion torque in synthetic bone and pig spare ribs at five second intervals from initial insertion until fully seated using a custom insertion machine. Histological samples of Beagle dogs were evaluated for the cellular response around the MSI controls, MSIs coated with bone wax, and MSIs coated with Ostene® immediately after removal and after two weeks of healing. Results: A significant difference (p<.05) in insertion torque was found between the MSI control group and both the bone wax and Ostene® groups in synthetic bone with the control group requiring 29 the greatest insertion torque. No significant differences (p>.05) were found between any groups for insertion torque when the MSIs were placed in a pig femur or for pullout strength in the synthetic bone. Additional testing showed that at time points T1, T2, T3, and T4 (15, 30, 45, and 60 seconds respectively), the MSI control group required a statistically significant (p<.05) greater torque to insert the MSIs in synthetic bone than when treated with bone wax or Ostene®. No differences were shown when each group was placed in pig spare ribs at any time point. Conclusions: Lubricating MSIs with bone wax or Ostene® reduces the insertion torque in synthetic bone. Introduction Orthodontic miniscrew implants (MSIs) have been widely accepted as a very useful tool in establishing and maintaining nearly absolute anchorage in order to correct various orthodontic problems.1,2 MSIs can be used in many different parts of the oral cavity to establish either direct or indirect anchorage; however, MSIs may come loose and even have the potential to fail. In order to have the greatest success when using MSIs, each potential aspect of failure must be addressed. Many studies have focused on determining the reasons for MSI 30 failure. It has been shown that inflammation around the MSI site is risk factor for failure.3-6 Successful MSI placement must be achieved without fracturing the implant. Each MSI fractures at different torque values depending on the design.7 The location of the insertion site, bone density, insertion angle, potential barriers within the bone and whether a pilot hole has been drilled are all contributing risk factors that also affect MSI fracture.8 Another important aspect of MSI failure can be related to high insertion torque, which leads to increased friction that then produces heat and bone necrosis. Karmani et al. explained that drilling in bone produces heat by breaking intermolecular bonds as each layer of material is sheared off. This often occurs in two ways. First, the cutting surface breaks the molecular bonds, which releases energy, and second, the non-cutting surface of the screw produces friction and heat.9 Thus, the denser the bone, the greater the friction produced. Because bone is a poor conductor of heat, the temperature can rise significantly and damage can occur. This increase in temperature can lead to bone necrosis and later implant failure. The temperature of vital bone in rabbits is approximately 32°C. However, rabbit bone can be damaged if it reaches the threshold of 47ºC for as little 31 as one minute.10 In another study by the same authors, the range for bone damage was determined to be even lower, between 44ºC and 47ºC for one minute.11 Once necrosis has occurred, for a MSI to be successfully stable, the damaged bone from the placement must regenerate.11 Many MSIs are self-drilling, that is, they do not require a pilot hole. Whether a pilot hole is first created, or a self-drilling implant is used, the bone temperature surrounding the MSI can rise beyond the 44ºC47ºC limit and lead to bone necrosis and ultimately MSI failure. In addition, some orthodontists place MSIs without irrigation and with greater speed than is recommended. Both of these technical errors may lead to an increase in temperature as well.11 Biotribology, or the study of friction, wear, and lubrication mechanisms relating to a biological environment, has been researched since 1973.12 As joints in the body lose the natural lubrication that they posses, commercially available supplements such as hyaluronic acid derivatives, peptides, synthetic phospholipids, recombinant lubricin, low molecular weight hyaluronate and high molecular weight hyaluronate all serve to lubricate and reduce friction between bone and cartilage.13-16 This 32 artificial lubrication works to increase the longevity of the original tissue. Bone wax has been used in medicine since the 1800s as a way to maintain hemostasis during surgical procedures.17 Throughout the years it has been widely used because it is not very expensive and typically its use produces few related complications.18 Ostene® is a water soluble-polymer that has gained more acceptance as studies have shown that it has greater biocompatibility and less incidence of infection is seen when it is used. It has also been shown to increase bone healing at the surgery site. Using 20 rabbits, Wellisz et al. compared the results when placing Ostene® and bone wax on median sternotomies. The samples taken after six weeks identified normal bone healing in the soluble-polymer group while the bone wax group showed an absence of new bone formation.19 The purpose of this study was to compare MSIs that were coated in either bone wax or Ostene® to MSIs without a coating to determine whether the amount of friction required to place the implants could be decreased and what the effect on the implant-bone interface would be. 33 Materials and Methods Miniscrew Implants MSIs were randomly assigned to one of three groups: control, surgical wax, or Ostene®. All the MSIs were 3M Unitek 6 mm long and 1.6 mm in diameter IMTEC implant. Nothing was done to the control group and they were used immediately after removal from the sterile package (Fig 3.1). A. Control B. Bone Wax C. Ostene® Figure 3.1 MSIs used in this research A. Control MSI, B. MSI coated with bone wax, C. MSI coated with Ostene® The wax group was dipped in surgical wax heated to 150°F. The MSIs were weighed before and after the coating process to ensure a uniform amount of lubricant was placed. The mean amount of bone wax applied to each MSI was 7.0 mg. Each MSI with the coating cooled completely to room temperature before being inserted. 34 The Ostene® group were dipped in Ostene® heated to 150°F. The MSIs were weighed before and after the coating process to ensure a uniform amount of lubricant was placed. The mean amount of Ostene® applied to each MSI was 7.7 mg. Each MSI with the coating cooled completely to room temperature before being inserted. Testing Methods Two models were used to test the effects of lubricants on MSIs. First, each group of MSIs was inserted into a synthetic bone material that was uniform in nature. Second, each group of MSIs was placed in a pig femur that resembles the density of human bone. Synthetic Bone Model A manufactured block of synthetic polyurethane cancellous bone (Sawbones®, Vashon, WA) was employed to determine the insertion torque and pullout strength of each MSI. Synthetic bone use has become more desired in implant research because of the uniform material properties it exhibits.20-22 The synthetic model had a density of 0.64g/cc, a compressive strength of 31 MPa, a tensile strength of 19 MPa, a shear strength of 11 MPa, and a moduli of 759 MPa, 1000 MPa, and 130 MPa respectively. 35 Ten mm cubes of the synthetic bone were cut from a larger block for testing. 30 MSIs from each of the three groups were tested. Pig Femur A fresh pig femur was used. All remaining soft tissues were removed and the femur was examined for overt pathology. Thirty MSIs of each of the three groups were placed randomly in the articular head. With each MSI insertion, the torque was carefully measured and recorded. Mechanical Testing The effect of the lubricants on the MSI was evaluated by measuring the insertion torque and the pullout strength. The insertion torque was chosen as a way to measure the primary stability of the MSIs because it is a common standard to evaluate stability and has been found to be a good predictor of the bone to implant interface.23 The pullout test was also conducted because it is often used to test implant design on primary stability.24-26 Placement Torque All measurements for insertion torque were recorded using a Mecmesin® Advanced Force and Torque Indicator 36 (Mecmesin, Ltd, West Sussex, UK) and maximum insertion torque (MIT) was recorded in Ncm. The synthetic bone cubes were placed in a base and a jig to secure and guide the placement of the MSIs was attached over the base. The jig allowed each MSI to be placed in a vertical direction until one thread (360°) remained exposed above the level of the synthetic bone. At this point, the Mecmesin® instrument was attached and the torque was recorded for a one-half turn (180°), thus leaving half of a thread exposed (Figure 3.2). This method was used to avoid countersink friction, which is the product of the head of the MSI contacting and compressing the bone, leading to a dramatic spike in the insertion torque.27,28 Mecmesin® torque indicator Custom jig MSI and synthetic bone block Figure 3.2 Custom jig securing synthetic bone block with Mecmesin® instrument attached to driver and MSI 37 The MSIs placed in the pig femur were also hand placed into the specimens in a vertical direction until one thread (360°) remained exposed. At this point, the Mecmesin® instrument was attached and the torque was recorded for a one-half turn (180°), thus leaving half of a thread exposed. Pullout Analysis Following the recording of the insertion torques, all of the MSIs that were placed in synthetic bone were also evaluated to determine the amount of force required to pull them out in a direction coincident with the long axis of the MSI. Each block with the MSI imbedded in it was placed in a custom base with a lid to secure it while an adapter was attached to the head of the implant. The adapter was then secured to an Instron Machine Model 1011 (Instron Corp, Canton, MA). A vertical force at the rate of 10 mm/min was exerted parallel to the long axis of the MSI until failure occurred. load failure in Newtons. The Instron machine recorded peak The pullout strength of a MSI is established as the tensile force required to remove it from a medium.25 38 Animals The sample included two healthy male, 12 month old beagle dogs (approximate weight 8kg). They were obtained from Marshall Bio-Resources (North Rose, NY) and were immediately placed on a soft diet (Canidea® Lamb and Rice, Canidea Corporation, San Louis Obispo, CA and 5006 Canine Diet, PMI Nutrition International, LLC., Brentwood, MO) one week prior to MSI placement. The husbandry was conducted by the Comparative Medicine Department of Saint Louis University Medical School. All procedures were pre- approved by the Saint Louis University Animal Care Committee (Authorization #2010). MSI Placement Both dogs were administered 25 mg/kg of Enrofloxacin (Baytril, Bayer Health Care, LLC., Animal Health Division, Shawnee Mission, KS) intravenously as a prophylactic measure and again for two days post surgery. Carprofen (Rimadyl®, Pfizer Animal Health, Exton, PA) 4mg/kg was administered subcutaneously for analgesia. Induction was obtained using propofol (Propofol®, ABBOTT Animal Heath, Exton, PA) 7 mg/ml. Maintenance for both dogs was achieved using isoflurane (Aerrane, Baxter Healthcare Corporation, Deerfield, IL) 2-3% and an IV drip of 0.9% sodium chloride 39 (Hospira, Inc., Lake Forest, IL) at a rate of 12 ml/kg/hr. Pre-operative lateral head plate radiographs were taken to determine where sufficient bone existed between the teeth in order to place the MSIs. The selected sites were swabbed with 0.12% chlorhexidine gluconate (Acclean®, Henry Schein, Inc., Melville, NY). 15 MSIs were then placed through the soft tissues and into the mandible of each beagle. Five MSIs in each of the three groups, control, bone wax, and Ostene® were randomly assigned to locations in the mandible. On the left side, two MSIs were placed below the 3rd premolar furcation, between the 3rd premolar and 1st molar, below the 1st molar furcation, and between the 1st and 2nd molars (Figure 3.3). On the right side, each dog received one MSI below the furcation of the 3rd premolar and two MSIs between the 3rd premolar and 1st molar, below the furcation of the 1st molar, and between the 1st and 2nd molar (Fig 3.4). No pre-drilling was done and the MSIs were placed using a hand driver. After all MSIs were inserted, a follow-up lateral head plate radiograph was taken to verify that none of the MSIs were touching the roots of any teeth. Both dogs were given 0.2 ml acepromazine maleate (WEDCO, Inc., St. Joseph, MO) IV to calm post anesthetic excitement. 40 Figure 3.3 Placement of MSIs (red dots) on dog’s right side Figure 3.4 Placement of MSIs (red dots) on dog’s left side MSI Lubricant Evaluation Both dogs were allowed to heal for four weeks. After the healing time, the first dog’s MSIs were removed following the same operative procedure used at insertion. This dog was then allowed to heal for two more weeks before it was sacrificed for histological evaluation of the MSI sites. The second dog, after the initial four-week healing time period, was sacrificed with the MSIs still in place and the mandible was sectioned for histological evaluation as well. The two dogs were sacrificed by giving 260 mg of 41 sodium pentobarbital (Fort Dodge Animal Health, Fort Dodge, IA) intravenously. The histological specimens of the two Beagle dogs will be evaluated when they become available and placed in the appendix. Further Research In order to reduce the amount of human error in the project and produce more accurate results, a second series of torque measurements were obtained on both synthetic bone and pig spare ribs using a custom made device. The same type of synthetic bone that was previously used was again tested. A jig to hold the specimen was attached to a motor with a constant rotational speed of nine revolutions per minute (Figures 3.5 and 3.6). Using a drill press that was modified to secure the torque indicator in place, the MSI was lowered by a constant weight (three pounds for the synthetic bone and four pounds for the ribs) attached to the arm of the drill press. As this constant pressure connected the MSI and the rotating specimen, a video camera recorded the amount of torque at all time points for 70 seconds, the time needed to fully insert the MSI up to the tip of the driver. The videotape was then reviewed and the 42 insertion torque for each MSI was graphed at five-second intervals. Drill Press Torque Indicator Rotating Specimen Constant Weight Figure 3.5 Custom insertion torque machine from left side 43 Torque Indicator Rotating Specimen Motor with Constant Rotation Figure 3.6 Custom torque machine from back showing motor attached under drill press table Statistical Analysis Analyses of variance and post hoc tests were used to determine whether significant differences (p<.05) were present regarding the initial torque insertion of the synthetic bone, pig femur, and pullout strength. The nonparametric Mann-Whitney test and independent t-test were used to determine if there were significant differences (p<.05) at T1, T2, T3, and T4 (15, 30, 45, and 60 seconds respectively) between the groups tested with the custom built insertion machine for the synthetic bone and the pig 44 spare ribs. The statistical analysis was processed with SPSS software. (SPSS for Windows, version 16.0, SPSS, Chicago, Ill). Results Standard Tests Synthetic bone model insertion torque MSIs coated with bone wax or Ostene® showed a significant (p<.05) difference for insertion torque when compared to the control (Tables 3.1 and 3.2). Post hoc tests demonstrated that both the MSIs with an application of bone wax or Ostene® resulted in a significantly lower insertion torque than the MSIs without any coating. There was no significant difference (p>.05) found between the MSIs coated with bone wax and Ostene®. Synthetic bone model pullout There was no significant (p>.05) difference between the control, MSIs coated with bone wax, and MSIs coated with Ostene® regarding the amount of force required to pull the MSI out of the synthetic bone in a vertical direction (Table 3.2). 45 Pig femur model There was no significant (p>.05) difference between the control, MSIs coated with bone wax, and MSIs coated with Ostene® for the insertion torque of MSIs placed in a pig femur (Table 3.2). Table 3.1 Descriptive statistics for MSIs in synthetic bone and pig femur ——————————————————————————————————————————————————————————— Control Bone Wax Ostene® Measurements (n=30) (n=30) (n=30) ——————————————————————————————————————————————————————————— Torque in Synthetic Bone (Ncm) Mean 13.0 ± 1.8 9.8 ± 1.9 9.5 ± 2.4 Torque in Pig Femur (Ncm) Mean 8.6 ± 1.7 8.5 ± 1.4 7.9 ± 1.5 Pull-out in Synthetic Bone (N) Mean 18.5 ± 1.9 17.9 ± 2.5 19.7 ± 3.0 ——————————————————————————————————————————————————————————— Table 3.2 Statistical comparison of original measurements ——————————————————————————————————————————————————————————————————————— Diff. in Measurements means p ——————————————————————————————————————————————————————————————————————— Torque in Synthetic Bone (Ncm) Control-Bone Wax 2.97 <.001* Control-Ostene® 3.25 <.001* Bone Wax-Ostene® .28 .837 Torque in Pig Femur (Ncm) Control-Bone Wax .16 .912 Control-Ostene® .76 .122 Bone Wax-Ostene® .60 .261 Pull-out in Synthetic Bone (N) Control-Bone Wax .52 .780 Control-Ostene® -1.22 .257 Bone Wax-Ostene® -1.74 .067 ——————————————————————————————————————————————————————————————————————— * Equals significant difference at p<.05 46 Custom Insertion Machine Tests Synthetic bone model All MSIs in each group are shown in Figures 3.7, 3.8, 3.9. 3.10. The average of each group is represented in Figure At all time points T1, T2, T3, and T4 (15, 30, 45, and 60 seconds respectively), there was a statistically significant difference of insertion torque between the control and bone wax groups (p<.05) tested in synthetic bone with the bone wax coated MSIs requiring less insertion torque (Tables 3.3 and 3.4). This same finding of a statistically significant difference (p<.05) was found between the control and Ostene® groups where the Ostene® group also required less insertion torque. However, when comparing the bone wax and Ostene® groups, there was a statistically significant difference found at time points T2 and T4 (p<.05), but not at T1 and T3 (p>.05). For all time points, Ostene® coated MSIs were shown to require less insertion torque than the control group. 47 Control MSIs in Synthetic Bone 25 20 Screw 1 Screw 2 Screw 3 Screw 4 Screw 5 Torque (Ncm) 15 Screw 6 Screw 7 Screw 8 Screw 9 10 Screw 10 Screw 11 Screw 12 Screw 13 5 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Time (Seconds) Figure 3.7 Individual control MSI’s insertion torque over time in synthetic bone 48 MSIs Coated with Bone Wax in Synthetic Bone 25 20 Screw 1 Screw 2 Screw 3 Screw 4 Screw 5 Torque (Ncm) 15 Screw 6 Screw 7 Screw 8 Screw 9 10 Screw 10 Screw 11 Screw 12 Screw 13 5 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Time (Seconds) Figure 3.8 Individual bone wax coated MSI’s insertion torque over time in synthetic bone 49 MSIs Coated with Ostene® in Synthetic Bone 25 20 Screw 1 Screw 2 Screw 3 Screw 4 Screw 5 Torque (Ncm) 15 Screw 6 Screw 7 Screw 8 Screw 9 10 Screw 10 Screw 11 Screw 12 Screw 13 5 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Time (Seconds) Figure 3.9 Individual Ostene® coated MSI’s insertion torque over time in synthetic bone 50 Figure 3.10 Average of each group of MSIs’ insertion torque over time in synthetic bone Table 3.3 Descriptive statistics of MSIs in Synthetic Bone (T1, T2, T3, and T4 equal 15, 30, 45, and 60 seconds respectively) ——————————————————————————————————————————————————————————— Control Bone Wax Ostene® Time (n=13) (n=13) (n=13) ——————————————————————————————————————————————————————————— T1 Mean 2.07 ± 3.29 .66 ± .30 .46 ± .27 (Ncm) T2 Mean 3.83 ± 1.03 2.77 ± .69 2.23 ± .44 (Ncm) T3 Mean 9.67 ± 1.10 7.51 ± 1.55 6.52 ± 1.10 (Ncm) T4 Mean 15.83 ± 1.27 13.64 ± 1.70 11.97 ± 1.06 (Ncm) ——————————————————————————————————————————————————————————— 51 Table 3.4 Statistical comparison of MSIs in Synthetic Bone (T1, T2, T3, and T4 equal 15, 30, 45, and 60 seconds respectively) ——————————————————————————————————————————————————————————————————————— Independent Mann-Whitney U test t-test(n=13) (n=13) ——————————————————— ———————————————————————————— t p Diff. in p Time means ——————————————————————————————————————————————————————————————————————— T1 Control-Bone Wax 1.53 .138 10.38 <.001* Control-Ostene® 1.75 .092 12.54 <.001* Bone Wax-Ostene® 1.78 .089 5.38 .072 T2 Control-Bone Wax 3.08 .005* 8.92 .002* Control-Ostene® 5.15 <.001* 11.00 <.001* Bone Wax-Ostene® 2.36 .027* 6.54 .029* T3 Control-Bone Wax 4.10 <.001* 9.76 .001* Control-Ostene® 7.31 <.001* 12.70 <.001* Bone Wax-Ostene® 1.89 .071 5.00 .101 T4 Control-Bone Wax 3.73 .001* 9.7 .001* Control-Ostene® 8.39 <.001* 12.92 <.001* Bone Wax-Ostene® 3.00 .006* 7.76 .009* ——————————————————————————————————————————————————————————————————————— * Equals significant difference at p<.05 Pig spare ribs All MSIs in each group are shown in Figures 3.11, 3.12, 3.13. The average of each group is represented in Figure 3.14. At all time points T1, T2, T3, and T4 (15, 30, 45, and 60 seconds respectively), there was no statistically significant (p>.05) difference of insertion torque between the control group, bone wax group, or Ostene® group in pig spare ribs (Tables 3.5 and 3.6). 52 Figure 3.11 Individual control MSI’s insertion torque over time in pig spare ribs 53 Figure 3.12 Individual bone wax coated MSI’s insertion torque over time in pig spare ribs 54 Figure 3.13 Individual Ostene® coated MSI’s insertion torque over time in pig spare ribs 55 Figure 3.14 Average of each group of MSIs’ insertion torque over time in pig spare ribs Table 3.5 Descriptive statistics of MSIs in pig spare ribs (T1, T2, T3, and T4 equal 15, 30, 45, and 60 seconds respectively) ——————————————————————————————————————————————————————————— Control Bone Wax Ostene® Time (n=13) (n=13) (n=13) ——————————————————————————————————————————————————————————— T1 Mean 1.38 ± 1.72 .88 ± .94 1.06 ± .68 (Ncm) T2 Mean 4.43 ± 2.11 3.91 ± 1.38 3.76 ± .82 (Ncm) T3 Mean 8.01 ± 3.12 7.53 ± 2.73 7.33 ± 1.29 (Ncm) T4 Mean 10.32 ± 3.91 9.34 ± 4.17 9.70 ± 2.31 (Ncm) ——————————————————————————————————————————————————————————— 56 Table 3.6 Statistical comparison of MSIs in pig spare ribs (T1, T2, T3, and T4 equal 15, 30, 45, and 60 seconds respectively) ——————————————————————————————————————————————————————————————————————— Independent Mann-Whitney U test t-test(n=13) (n=13) ————————————————————— —————————————————————————— t p Diff. in p Time means ——————————————————————————————————————————————————————————————————————— T1 Control-Bone Wax .919 .367 3.76 .223 Control-Ostene® .629 .535 .38 .920 Bone Wax-Ostene® -.505 .588 -3.38 .960 T2 Control-Bone Wax .749 .461 2.16 .479 Control-Ostene® 1.070 .297 2.84 .362 Bone Wax-Ostene® .329 .745 -.16 .960 T3 Control-Bone Wax .415 .682 .92 .762 Control-Ostene® .723 .477 1.30 .687 Bone Wax-Ostene® .239 .813 .16 .960 T4 Control-Bone Wax .616 .544 1.92 .545 Control-Ostene® .489 .629 1.76 .579 Bone Wax-Ostene® -.273 .787 -.84 .801 ——————————————————————————————————————————————————————————————————————— * Equals significant difference p<.05 Discussion The purpose of this study was to determine if coating MSIs with bone wax or Ostene® would reduce the amount of insertion torque and what histological responses would be noted when these same lubricants were used. During the initial experiments, although the synthetic bone model testing showed that a significant reduction in torque existed when the control group was compared to the bone wax and Ostene® groups, human error and large amounts of variability existed. It is of interest to note that even though the pullout force was not statistically significant 57 when comparing the three groups, more force was required to remove the Ostene® coated MSIs than the others. Even though recording 180º of insertion torque on the final thread has been used often in the past, there is room for inaccuracy. It is at times difficult to determine precisely the final 180º before insertion is complete. Even with jigs and other aids, this final half of a turn is not always easily ascertained and varying even 90º can make a difference. In addition to this challenge, it is even more difficult to keep the Mecmesin® machine from leaning from one side to another and introducing even more torque and variability. Jigs have been used to reduce some of the error when testing uniform pieces of synthetic bone, but testing bones with different dimensions make using a standard and firm jig less feasible. The speed of the final 180º turn can also affect the maximum torque registered. Another area where this particular method of testing was limited is in the ability to know the insertion torque at various points along the insertion path. It is possible the lubricant impacted the insertion torque only at certain position along the way and not others, though the author is unable to account for these differences in this specific study. With these variables and others that are inherent in the system recognized, it was determined to 58 do a second set of experiments using a new custom designed device with the goal of eliminating or greatly reducing the inaccuracies. The data collected from the new custom designed device produced valuable information. As is expected from Figure 3.10, at all time points T1, T2, T3, and T4 (15, 30, 45, and 60 seconds respectively), there was a statistically significant (p<.05) difference of insertion torque between the control and both the bone wax and Ostene® groups in synthetic bone with the bone wax coated MSIs and Ostene® coated MSIs requiring less insertion torque than the control MSIs. When the MSIs were coated with bone wax, the insertion torque was reduced by 68%, 28%, 22%, and 14% at T1, T2, T3, and T4 respectively when compared to the control group. Likewise, the Ostene® coated MSIs reduced the insertion torque by 78%, 28%, 33%, and 24% at T1, T2, T3, and T4 respectively when compared to the control group. This shows that upon insertion, and until the MSI is completely seated in the synthetic bone, MSIs coated with bone wax or Ostene® substantially reduce the amount of torque required to place the MSI. It is hypothesized that this will then reduce the amount of heat generated and therefore less bone damage would be expected. 59 This in turn might produce better primary and secondary stability and decreased MSI failure. However, when comparing the bone wax and Ostene® groups in the synthetic bone, there was a statistically significant difference found at time points T2 and T4 (p<.05), but not at T1 and T3 (p>.05). Time points T1 and T3 were trending toward significance, nevertheless. For all time points, Ostene® coated MSIs were shown to require less insertion torque. Even with the custom insertion machine, the variation within the same pig spare rib and between pig spare ribs proved too much to accurately demonstrate the effects of lubricants on MSIs. There was no significant difference (p>.05) between any of the groups. Conclusions - MSIs coated with bone wax significantly decreases the amount of torque required for insertion in synthetic bone. - MSIs coated with Ostene® significantly decreases the amount of torque required for insertion in synthetic bone. - There is not a significant difference between the bone wax and Ostene® groups at all time points when inserted in synthetic bone. 60 - No significant difference was found in the pullout strength for MSIs coated with bone wax or Ostene® when compared to the control group. - No significant difference was found in insertion torque between the control, bone wax and Ostene® group when placed in pig spare ribs. 61 References 1. Mah J, Bergstrand F. Temporary anchorage devices: a status report. J Clin Orthod. 2005;39:132-136; discussion 136; quiz 153. 2. Liou EJW, Pai BCJ, Lin JCY. Do miniscrews remain stationary under orthodontic forces? Am J Orthod Dentofacial Orthop. 2004;126:42-7. 3. Park H, Jeong S, Kwon O. 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Pull-out strength of monocortical screws placed in the maxillae and mandibles of dogs. Am J Orthod Dentofacial Orthop. 2005;127:307-313. 26. Pfeiffer M, Gilbertson LG, Goel VK, Griss P, Keller JC, Ryken TC, Hoffman HE. Effect of specimen fixation method on pullout tests of pedicle screws. Spine. 1996;21:1037-1044. 27. Salmória KK, Tanaka OM, Guariza-Filho O, Camargo ES, de Souza LT, Maruo H. Insertional torque and axial pull-out strength of mini-implants in mandibles of dogs. Am J Orthod Dentofacial Orthop. 2008;133:790.e15-22. 28. Hughes AN, Jordan BA. The mechanical properties of surgical bone screws and some aspects of insertion practice. Injury. 1972;4:25-38. 64 APPENDIX Throughout this research, several other types of lubricants were experimented with and the data is shown below. Figure A.1 Individual bath soap coated MSI’s insertion torque over time in synthetic bone 65 Figure A.2 Individual candle wax coated MSI’s insertion torque over time in synthetic bone 66 Figure A.3 Individual control MSI’s insertion torque over time in synthetic bone without the help of the custom insertion machine 67 Figure A.4 Averages of each group of MSIs’ insertion torque over time in synthetic bone (n=5) 68 VITA AUCTORIS Robert Jay Marshall was born January 24, 1980, in Bigfork, Montana to Jon and Jean Marshall. He attended Ricks College from September through December of 1998. From 1999 to 2001, he lived in Peru while serving a mission for The Church of Jesus Christ of Latter-day Saints. Upon his return he attended Brigham Young University-Idaho from 2001 to 2003. Robert entered the University of Minnesota School of Dentistry in 2003 and graduated with a Doctor of Dental Surgery in 2007. He continued is his education in pursuit of a master’s degree from Saint Louis University’s Center for Advanced Dental Education in 2007. Upon graduation in January 2010, Dr. Marshall and his family will move to Great Falls, Montana, where he will practice orthodontics. 69