Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
AN EVALUATION OF THE INSERTION TORQUE OF ORTHODONTIC MINISCREW IMPLANTS IN RELATION TO TOOTH ROOT CONTACT. Michael B. McEwan, B.S., D.D.S An Abstract Presented to the Graduate Faculty of Saint Louis University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Dentistry (Research) 2012 Abstract Introduction: Miniscrew impants (MSIs) are a useful tool when absolute orthodontic anchorage is required. While helpful in many regards, problems can still arise. The purpose of this study was to quantify how insertion torque changes during insertion of a self-drilling MSI with tooth root contact. Methods: MSIs from two manufacturers (3M Unitek™ TAD and Dentaurum tomas® pin) were inserted in pig cadaver mandibles and divided into three groups: Control (miss), Glance, and Direct Hit. Cone-beam computed tomography (CBCT) was used to verify MSI location. Insertion torque was continuously recorded during MSI insertion and inspected for fracture or damage upon removal. Scatterplots of time vs insertion torque were created. Results: 3M Unitek MSIs showed higher insertion torque than Tomas MSIs in control groups. Self-drilling MSIs were unable to directly penetrate the roots. Self-drilling MSIs which contact teeth show a higher insertion torque than control groups with no contact. Tomas® MSIs showed higher fracture rates at the tip, possibly due to a weaker thread-cutting design. Conclusions: Contact with a tooth root with a self-drilling MSI causes an increase in insertion torque and thus tactile feedback may help the experienced clinician determine if root contact has occurred. 1 Additionally, thread-cutting tips appear to be more prone to breakage when a tooth root is contacted. 2 EVALUATION OF INSERTION TORQUE OF ORTHODONTIC MINISCREW IMPLANTS IN RELATION TO TOOTH ROOT CONTACT. Michael B. McEwan, B.S., D.D.S A Thesis Presented to the Graduate Faculty of Saint Louis University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Dentistry (Research) 2012 COMMITTEE IN CHARGE OF CANDIDACY: Professor Rolf G. Behrents, Chairperson and Advisor Associate Clinical Professor Donald R. Oliver Professor Eustáquio Afonso Araújo i DEDICATION To my parents, for their unconditional love and support. They once told me I could do anything I wanted to and I have relied on that statement many times when the going got tough! To my wife and best friend, Lea. You are an amazing person and I don’t tell you that enough! Thanks for the love, patience, and support. I’m excited for all the new adventures that await us! To my two girls, Mazy and Evey. Sorry I haven’t been around to play very much lately – I’ve been busy finishing this thesis! You two mean the world to me! ii ACKNOWLEDGEMENTS Thanks to… Dr. Rolf Behrents for his support and guidance throughout this thesis and my time here at SLU. Dr. Donald Oliver for his time, attention to detail, and willingness to serve. Dr. Eustáquio Araújo for his time and contributions to this project. Dr. Heidi Israel for help with the statistical analysis. Mr. Don Larabell for help in customizing our instrumentation for this project. Gary Schwend, Jeanette Deiters, and the employees at Trenton Processing for accommodating my weird requests and helping me acquire samples to test. 3M Unitek and Dentaurum for providing the miniscrew implants used for this project. Saint Louis University Orthodontic Education and Research Foundation, for financial support. iii TABLE OF CONTENTS List of Tables..................................................v List of Figures................................................vi CHAPTER 1:INTRODUCTION..........................................1 CHAPTER 2:REVIEW OF THE LITERATURE History and Contemporary Use...........................4 Nomenclature and Miniscrew Implant Design..............5 MSI Failures and Success...............................8 Role of Primary Stability in Success..............9 Insertion Torque..................................11 Tooth Root Contact.....................................15 MSIs and Tooth Contact............................19 Consequences of Tooth Contact.....................20 Tactile Perception................................24 Summary................................................27 Works Cited............................................28 CHAPTER 3:JOURNAL ARTICLE Abstract...............................................38 Introduction...........................................39 Materials and Methods..................................42 Results................................................46 Insertion Torques vs Time.........................47 MSI Fractures.....................................54 Discussion.............................................55 Conclusions............................................62 Works Cited............................................63 Vita Auctoris....................................................67 iv LIST OF TABLES 3.1: Mean maximum insertion torques............................54 v LIST OF FIGURES 3.1: Pig mandible area of interest.............................42 3.2: MSIs tested...............................................43 3.3: Custom insertion torque measuring device..................44 3.4: Close up view of insertion device.........................45 3.5: Control sample image and photo............................47 3.6: CBCT image of glance group................................48 3.7: 3M Unitek control group insertion torque..................49 3.8: Tomas control group insertion torque......................49 3.9: Mean control groups insertion torque .....................50 3.10: Direct hit example.......................................50 3.11: Mean direct hit insertion torque.........................51 3.12: 3M Unitek glance group insertion torque..................52 3.13: Tomas glance group insertion torque......................52 3.14: Mean 3M Unitek glance and control group insertion torque.53 3.15: Mean Tomas glance and control group insertion torque.....53 3.16: Close up of fractured Tomas MSIs.........................55 vi CHAPTER 1:INTRODUCTION Miniscrew implants (MSIs) are a treatment adjunct designed to provide absolute skeletal anchorage in orthodontics. They have gained in popularity due to their simple placement, low cost, patient-acceptance, and ability to eliminate patient compliance issues in treatment. MSIs are a relatively new offering for most practices. In a 2008 survey of orthodontists, only 7.8% had reported using MSIs more than five years, and yet 60-91% of orthodontists report an active case using an MSI.1–3 A recent survey showed 45.5% of orthodontists reported not placing their own implants. Potential root contact and damage was cited by 32.8% as the main reason for delegation to other practitioners.1 Severe, irreversible damage can be caused by MSIs contacting the roots of teeth.4–7 Fortunately, damage caused by MSI contact most often results in minor damage that heals uneventfully.8–10 Root contact should also be of concern to the practitioner since it has been shown to dramatically increase MSI failure rates.5,11 Many authorities on MSIs state that a clinician will be able to feel if he or she contacts a tooth root during insertion, as there will be a dramatic increase in torque and resistance.12–16 Only a few studies have evaluated the claim that insertion torque changes when a tooth root is contacted.8,17,18 1 These studies looked at MSIs which required predrilling a pilot hole. Newer self-drilling MSI designs, which require no pilot hole, have been introduced. A self-drilling MSI is preferred by clinicians due to the simplicity of the procedure.19–21 Only 10.5% of clinicians report using a pilot hole “mostly” or “always.”1 Insertion torque has been typically measured as the “maximum insertion torque” and is often derived from MSIs being placed to almost their final length and then measuring the insertion torque of the last turn or measuring just the highest value encountered during insertion.8,17,18 It would be more valuable to measure insertion torque continuously, which better emulates what happens clinically and will provide more information as to what happens when a tooth root is contacted and the rate of change seen. Currently, no studies have investigated tooth contact using newer self-drilling MSI designs. Additionally, torque-limiting drivers to place MSIs are becoming more commonplace.20 Added information as to appropriate values to use as the maximum torque values and whether torque-limitations can be used to detect tooth contact could prove valuable. The purpose of this research is to quantify what happens to insertion torque when a self-drilling MSI is inserted and contacts a tooth. Insertion torque will be continuously recorded so the rate of change can be studied. 2 This study addresses the following questions: Does insertion torque increase with root contact? How much and how quickly does it change? Could this change be used to detect root contact? 3 CHAPTER 2: REVIEW OF THE LITERATURE Miniscrew implants (MSIs) provide exciting opportunities to treat orthodontic patients in ways that were not previously possible and, at the same time, avoid reliance on patient compliance. As a result, MSIs have attracted great interest, generated hundreds of articles published in the last few years, and have become a “standard in the modern orthodontic practice.”19,20 Miniscrews are a recent addition to the clinician’s armamentarium, only 7.8% of orthodontists in a recent survey had been using MSI more than five years.1 Usage of MSIs has increased dramatically. Various surveys have shown usage rates varying from 60-91% of orthodontists using miniscrews at least once in the past year, and the majority are placing their own miniscrews.1–3 History and Contemporary Use The history of MSI use in orthodontics is an interesting story. Brånemark’s work in the late 1950s and early 1960s is considered the pioneering work establishing the potential for osseointegration with titanium implants, though it was preceded by the attempts of others to replace teeth using biocompatible materials which, due to failure, fell into disuse.12,22 Today, 4 osseointegrated titanium dental implants have become commonplace and have success rates exceeding 95%.23 The first published report of successful miniscrew use for orthodontic anchorage appeared in 1983 when Creekmore and Eklund inserted a vitallium bone screw just below the anterior nasal spine in a 25 year-old female to intrude and torque the maxillary incisors.24 It wasn’t until 14 years later in 1997 that Konami wrote of a small, 1.2mm diameter titanium, modified bone screw designed specifically for orthodontic use.25 The next year Costa et al., introduced a screw with a bracket-like head, and was the first MSI to approximate the designs in use today.26 Rapidly, a number of MSIs were developed and introduced, each with varying designs. In 2007, there were 13 FDA-approved miniscrew implants approved for orthodontic use, with each major orthodontic manufacturer offering MSI options for clinicians.27 When compared to traditional larger endosseous implants, MSIs are smaller, more versatile, easier to place, less expensive, can be immediately loaded, and create less discomfort for the patient.28 Nomenclature and Miniscrew Design It is important for students, orthodontists, and researchers to use similar nomenclature and terms when working with MSIs to facilitate communication. What has been referred to 5 so far as miniscrew implants or MSIs, have also been referred to as: microimplant, microscrew implant, mini-implant, mini dental implant, miniscrew, temporary anchorage device (TAD), and OrthoImplant.12,27 Cope explains that, in his view, micro- is an inappropriate term, since it is derived from microscopic, or something so small that it can only be visualized with a microscope.12 The term mini- is derived from miniature, which is merely something smaller. Sung et al., disagrees saying that micro- can be used to emphasize small size such as in the terms micrognathia, microsomia, microdontia and that micro- should be used for implants smaller than 1.9mm and mini- for implants greater than 1.9mm, but still much smaller than traditional dental implants.29 Additionally, using the word screw is valuable, since an implant is “any device…surgically placed in the bone of upper or lower jaw” and MSIs are defined by having screw components such as a body with threads and a defined head/end for orthodontic use.12 Again Sung et al., disagrees, saying that implant is defined by the MDD (European equivalent of the FDA), as a device left in the body more than 30 days.29 The nomenclature preferred by Cope has been the most frequently used since 2004 and will be used throughout this study.27 Another point of confusion is the use of the terms, selftapping (or pre-drilling), self-drilling (or drill-free), and nondrill—free.12,27,29 Many papers refer to self-tapping as screws 6 that require a pilot hole the entire length of the screw and have a blunted tip.18 Cope feels that the term self-tapping should be discarded, since self-tapping is simply the ability of the screw to create its own thread and advance itself, which all MSIs do.12 In this study the term self-drilling will be used to refer to a screw design with a very sharp tip, which is inserted without a pilot hole and pre-drilled, which requires a pilot hole either through the cortex of bone only or the entire length of the screw. It is unclear if there is a difference in clinical success between self-drilling and pre-drilled MSIs. Kim and Choi reported loss rates of 64% for self-drilling and 34% of predrilled MSIs.29 Kim et al., however, favored self-drilling implants since they showed less mobility and more bone-to-metal contact.30 Suzuki and Suzuki did not detect a difference in success rates in self-drilling and pre-drilled MSIs.31 Both selfdrilling and pre-drilled designs can be successful and clinical success may have more to do with insertion torque encountered and bone quality and quantity than with screw design.20 A selfdrilling MSI is preferred by clinicians due to the simplicity of the procedure.19–21 Only 10.5% of clinicians report using a pilot hole “mostly” or “always.”1 Lastly, there are two types of screws designs that are common, thread-forming and thread-cutting. Both feature sharp 7 threads for forming the internal threads in the bone when the screw is advanced, but a thread-cutting screw has a notch removed parallel to the long axis of the screw at the tip of the screw. As the screw is advanced, it actually cuts and removes bone from the advancing threads and aids in removing the swarf, or the bone debris.12 A disadvantage is that the screw is weakened by removing the notch and some claim that the already smaller screw size being reduced weakens the screw too much and can lead to excessive fracture.12 MSI Failures and Success Failure rate is one of the biggest concerns of clinicians using MSIs.1 Failure is defined differently by various clinicians, varying from any mobility or inflammation to the most accepted definition of loss or mobility of the screw that renders the MSI inoperative.12 Failure rates of 10-30% are frequently published.32–34 As such, causes for failure have been explored by many researchers.11,27,35–37 Miyawaki et al. found that the diameter of a MSI of 1.0 mm or less, inflammation of the peri-implant tissue, and a high mandibular plane angle (i.e., thin cortical bone), were associated with mobility (i.e., failure).34 Excessive forces placed on the MSI and a large lever arm (i.e., the result of incomplete insertion due to such things as thick mucosa) were 8 associated with higher failure rates.38,39 Other authors noted such factors as patient manipulation, poor hygiene, and periimplant soft tissue character contribute to failure.27,33,40–42 Of particular interest in overcoming failure has been our understanding of the importance of primary stability and insertion torque on clinical success. Role of Primary Stability in Success Much of what we know about MSIs is derived from our experiences with osseointegrated dental implants. It is known that a dental implant’s prognosis is highly correlated to its primary stability.43–45 Primary stability refers to a mechanical stability derived from the bone-to-implant contact which results in a lack of implant mobility immediately after placement. Primary stability is crucial for development of secondary stability.46 Secondary stability refers to the remodeling and regeneration of the bone/implant interface as the bone that was damaged by the implant insertion heals and forms a stable biocompatible interface with the titanium screw. Similar to the experience with endosseous implants, primary stability and the resulting secondary stability has been also deemed crucial for long-term MSI success.19,20,28,47–49 Lack of primary stability would allow the MSI to have micromotion, 9 leading to a fibrous capsule formation, inflammation in the area, and lack of bone-to-implant contact.46 Ure et al. studied primary stability and the transition to secondary stability of MSIs using a non-destructive method of resonance frequency analysis in dogs.50 They showed that the overall stability of an MSI decreases over the first three weeks as primary stability decreases and healing and bone remodeling occur at the bone/screw interface and secondary stability increases almost to previous levels by from weeks 5-8 weeks. The MSIs primary stability holds the MSI tight and overcomes the “stability dip” in the transition from primary to secondary stability, thus primary stability is an important predictor for success in MSI placement.51 Primary stability also allows for immediate loading of the MSI.47,51 Immediate loading is preferred by clinicians for its simplicity and efficiency.1 Primary stability can be measured by a variety of methods. Histological assessment allows one to visualize the bone-toimplant contact, but is limited to only looking at the areas selected for inspection.30 Resonance frequency analysis has been routinely used in traditional dental implant literature, but only recently have studies used it to look at MSIs.50,52,53 Unfortunately, these studies used custom methods to analyze the MSIs and no commercial attachments are available from the vendor 10 for MSIs. Lastly, and most commonly, insertion torque has been a common measure of primary stability. It has been used since the 1960s for evaluating screws in bone and currently in MSI studies.33,51,54 Insertion Torque Primary stability is almost synonymous with insertion torque.18,20 Insertion torque is the measure of the rotational force needed to insert the MSI into bone and is reported in most literature as Newton cm.55 Insertion torque is determined by bone quality, implant design and size, and insertion methods such as pilot-hole drilling.51 Bone thickness and density has a positive linear relationship with insertion torque.51,56 The bone’s outer cortex thickness and density plays a large role in what the insertion torque will be.51 Such areas of thick, dense cortex are often found in the human mandible and implant site preparation, such as pre-drilling, has been recommended to decrease insertion torque in this area.20,51 Screw design can have a strong influence on insertion torque. As expected, larger diameter screws require greater insertion torques.54 Similar diameter screws can show great variation in insertion torque.51,56,57 One factor is a conical body vs a cylindrical body. A conical MSI design shows increased 11 insertion torque compared to cylindrical designs.54,57,58 An additional benefit of the conical design is the MSI is more likely to miss contacting teeth, since it is narrower in the apical portion.12,59 An additional design consideration is a thread-cutting vs. a thread-forming design. As mentioned previously, a threadcutting design features a notch in the tip which actively cuts the internal threads of the bone at the apex.12 Thread-cutting designs are common in osteosythesis screws, used to fixate bone fractures, and are thought to alleviate bone stress and voids between the screw and bone.60 Kuhn et al. studied bone deformation between thread-cutting and thread-forming predrilled osteosythesis screws.61 Less bone deformation and lower insertion torque was seen in the thread-cutting screws. Though the fracture rate of thread-cutting MSIs has not been specifically addressed in any MSI study, they may be more prone to fracture at the tip.12,62 The last major influence of insertion torque is implant site preparation, namely pilot hole drilling. Drilling a pilot hole decreases insertion torque.18,51,56 Self-drilling MSIs tout the benefit that they require no pilot hole. Kim et al. found less mobility and more bone/implant contact with self-drilling MSIs compared to pre-drilled MSIs after 12 weeks in beagle 12 dogs.30 He attributed this difference to the surgical trauma of pilot-hole drilling and resultant bony damage. High insertion torque results in high primary stability, thus higher insertion torque is favorable, up to a point.51 Too high of an insertion torque might result in fracture of the MSI. A number of studies using MSIs have experienced screw fracture with high insertion torques.51,54 Additionally, excessively high insertion torques can lead to hoop stress from excessive bone compression, which leads to microcracks, local ischemia, and bone necrosis.43,63,64 Wawrzinek et al. documented increased microfractures in overtightened MSIs in pig bone.65 Lee and Baek also documented increased microfractures in rabbit tibias in MSIs with larger insertion torques due to conical design or larger diameters.66 Wilmes et al. advocates predrilling just through the bone cortex even with self-drilling MSIs in the entire mandible and in the palate to avoid MSI fracture and bone damage.67 Other authors have made similar statements.20 Lehnen et al. found that patients have no overall preference between self-drilling and pre-drilled MSIs. Patients disliked the sound of the pilot hole drill in the pre-drilled group and they disliked the increased pressure sensation in the self-drilling group, but overall there was no difference in overall preference.68 13 The idea that there is an ideal insertion torque in MSI placement has not been investigated in depth. Motoyoshi et al. investigated the relationship between insertion torque and clinical success of MSIs.69 A total of 124 MSIs (8mm length and 1.6mm diameter, Biodent Co, Tokyo Japan) were placed in 41 patients in both the maxilla and mandible with pilot holes using a 1.3mm drill. Maximum insertion torque values were recorded and the implants were immediately loaded. Torque values were used to divide the groups into three groups, <5 Ncm, 5-10 Ncm, and >10 Ncm and the success rates of each group were compared. The group of 5-10 Ncm had a success rate of 96.2% compared to 72.7% for the <5 Ncm groups and 60.9% for the >10 Ncm group. They recommended that insertion torque be monitored and changed by varying the diameter of MSI and using a pilot hole to obtain an optimal torque value of 5-10 Ncm. This is in contrast to a study by Chaddad et al., who tested an experimental surface-roughened MSI vs a commercial smooth-surfaced MSI and found no difference in success rates between the two.70 They did, however, find that MSIs with insertion torques over 15 Ncm had 100% success rates and MSIs with insertion torques less than 15 Ncm had 69% success rates, thus showing that the ideal torque value for MSIs is still not established. 14 Both studies only investigated pre-drilled MSIs, however, a more recent study did compare a self-drilling vs pre-drilled MSIs and found that although self-drilling had higher maximum insertion torque (14.5 Ncm) vs pre-drilled (9.2 Ncm), there was no statistically significant difference in success rates and they called into question Motoyoshi’s claim of determining an ideal placement torque.31 Tooth Root Contact In a 2008 survey of orthodontists, 45.5% of orthodontists reported not placing their own implants. Potential root damage was cited by 32.8% as the main reason for delegation to other practitioners, despite the fact that orthodontist-placed MSIs have higher success rates.1 One complicating factor is that due to tooth anatomy, locations for MSI placement are limited. Although “safe zones” have been developed to guide clinicians in their MSI placement locations, anatomy is different for each patient.71,72 The buccal area continues to be favored by clinicians, but offers the least flexibility in placement.71 A recent study by Antoszewska et al. had 35 orthodontists place MSIs in the maxilla of typodonts.73 Fear level of the orthodontists was surveyed on a 10-point visual analog scale and root contacts were counted. Root contacts occurred in 23.5% of 15 the insertions. Fear level before MSI insertion (4.6) was significantly decreased after insertion (3.2). Clinicians cited their fear stemmed from the potential of hitting teeth or the maxillary sinus. Another recent study investigated the surgical site and clinician experience in MSI/tooth contact using typodonts mounted realistically in mannequin heads with lips and cheeks.74 The study was divided into a group of eight orthodontists experienced in MSI placement and another group of 20 inexperienced general dentists. Inexperienced clinicians had a higher frequency of root contacts (21.3%) than did the experienced group (13.5%). The inexperienced group had contacts roughly equal in all quadrants. For the experienced group, vulnerable sites were the maxillary right and mandibular left posterior regions, especially the lower left first molar and the upper right first molar (all but one of the subjects were righthanded). On the left, most contacts were on the mesial of the root and on the right, most contacts were on the distal. Experienced clinicians held their posture steady and kept movements in relation to the mannequin to a minimum. MSIs can be used in a number of locations in the mouth. The interradicular spaces between teeth are the most common sites, however these sites also carry the greatest risk for root damage.74 Additionally, although MSIs are commonly assumed to be 16 absolutely stable, Liou et al. found that MSIs move up to 1.5 mm and therefore a clearance of 2.0mm from adjacent teeth is recommended.75 Maino et al., however, recommend a distance of only 1mm.76 Although interradicular space increases as one moves apically on a tooth, this may lead to MSIs being placed in unattached gingiva, which can lead to soft-tissue inflammation and overgrowth, leading to screw failure.33 The apprehension about contacting tooth roots has resulted in a myriad of techniques that have been developed to avoid tooth root contact, such as using the palate or areas of the buccal bone with more interradicular space, using panoramic or periapical radiographs before and after, radiographic stents or guides, and angled placement.77–82 Placing MSIs requires practice and experience as there is a tendency for the clinician to inadvertently change the angle of insertion by pulling the driver toward the body.4 Miyazawa et al. emphasized that blind placement of miniscrews is difficult and in his study 53% of surgical guides fabricated on models required adjustment of angulations or position after being reviewed with threedimensional radiography (cone-beam computed tomography).83 In a study of tooth root contact in swine, it was found that although the researchers thought they had contacted roots, in 26.2% of cases no actual root contact had occurred.84 17 Fear of iatrogenic damage by MSI contact with tooth roots is justified. Much information is to be gleaned from the oromaxillofacial traumatology literature and the use of fixation screws. The risk of pulpitis or ankylosis is low after contact with screws. Fabbroni et al. conducted a prospective study evaluating the placement of 232 intermaxillary fixation screws in 55 patients.85 These screws are placed after a pilot hole was drilled. Twenty-six screws (11.2%) had “minor” contact, meaning that <50% of the hole overlapped the root and 37 screws had “major” contact, meaning >50% of the hole overlapped the root. Seventeen teeth tested non-vital, however only 6 showed contact with the screw. They determined that skilled doctors trying to avoid roots would still hit them, but fortunately most teeth appear to do well after the traumatic injury. In a prospective audit of intermaxillary fixation screws, Farr and Whear found radiographic evidence of tooth root damage in 13 of 31 cases (43.3%) and the pulp chamber was entered in 4 of the 13 cases (30.8%).86 The authors emphasized that although the placement of screws appears to be a simple procedure, root damage frequently occurs. Additionally, fixation screws are not typically placed interradicularly, so the likelihood of tooth contact using oral surgery data would likely be underestimated. It is recommended that surgeons try and feel for a change in resistance when the pilot hole drill penetrates the bone cortex. 18 If no change in resistance is felt, then consider that a tooth is being contacted. It must be noted that the screws often used in the oral surgery literature are pre-drilled and require a pilot hole the entire length of the screw. This is in contrast with contemporary MSIs which are placed with either a pilot hole through the bone cortex only or with no pilot hole and placed directly through the gingiva into the bone. MSIs and Tooth Contact In an article describing the Imtec® implant, Herman and Cope claim that it is “nearly impossible, even with the selftapping property, to place the OrthoImplant directly into the tooth root.”87 This claim is in direct contrast to Lee et al., who warns of the risk of root injuries from MSI placement, and show a case of a tooth root which had been perforated. Due to loss of vitality and the presence of vertical root fracture this tooth had to be extracted.13 Also, Sung et al. states that selfdrilling MSIs can penetrate roots without heavy resistance and shows photographs of various perforated teeth.29 Other authors have mentioned the possibility of damaging the tooth’s nerve, periodontal ligament or root.88,89 Studies were conducted by Lee to develop a “safe” MSI with a blunted tip to prevent root perforations, however the study 19 showed disappointing results with a 59% failure rate. They speculated that blunt tip interferes with final seating of the MSI and achieving primary stability.13 Consequences of Tooth Contact Healing typically occurs uneventfully when tooth roots are damaged experimentally, as long as the area is 2mm x 2mm or smaller.90,91 Contact with traditional endosseous implants also appears to heal by forming a cementum layer around the teeth.92 Screw proximity has been linked with increased risk of failure.5,11 Kang et al. found that 79.2% of MSIs that contacted teeth in beagle dogs failed, with an average failure time of 16 days.5 One theory is that when a screw contacts a tooth root, biting forces are transferred to the screw, causing an intermittent force and interruption of healing and bone remodeling.93,94 Root damage is one of the most commonly cited potential complications of MSI placement.1,4,76 Potential serious complications of root contact with MSIs include ankylosis, osteosclerosis, and loss of tooth vitality.4,93 A study in beagle dogs noted root cracking and fracture and ankylosis in roots that were contacted directly.6 20 The first study looking at MSI contact with teeth and healing was a study by Asscherickx et al., who described tooth root repair in beagle dogs after MSI placement.93 A study examining a new type of miniscrew design was placed between the roots of the teeth of the beagle dog and removed after 24 weeks. Three of the twenty MSIs contacted teeth accidentally and penetrated the dentin of the teeth. Subsequent histology revealed complete healing of the root with cementum after 12 weeks of healing following removal. A number of studies used dogs to evaluate sequelae and healing of teeth contacted with MSIs.8–10,17,84 Similar results were found in each study, namely that damaged dog teeth healed and reestablished a periodontal ligament, and bone filled in the damaged area. Cementum repair occurred on the tooth when teeth were only partially contacted. Some damage was extensive, however, resulting in inflammation, tooth necrosis and ankylosis, particularly when the tooth fractured or the pulp chamber was compromised.8,84 Healing typically started as early as week 4 and was complete by week 12. Concave outlines on the root remained, indicating that osteoblastic activity of bone was higher than cementoblastic activity.17 No spots of ankylosis was noted, unless severe damage occurred such as the root splitting.10 MSIs left in damaged roots for a period of time consistently showed inflammatory reactions and uneven surface 21 resorption on roots.17 These inflammatory reactions are probably responsible for MSI loosening and failure after root contact. Chen et al. recommends immediate removal of MSIs contacting teeth to prevent additional resorptive damage.17 A more recent paper using a swine model and self-drilling MSIs investigating root-surface healing was done by Kim and Kim.95 Results were similar to the previous canine studies, however histologic analysis revealed evidence of root resorption caused indirectly by the MSI even when the MSI was up to 1mm away from the tooth root. Another study in beagle dogs noted resorption when MSIs were 0.6mm away from the root.6 This was attributed to compression of bone which was transmitted to the PDL. During healing, damaged tissues are removed by osteoclasts and macrophages. Not only are necrotic tissues removed, but also adjacent bone and cementum. Additionally, when dentin was contacted, the teeth would quickly deposit tertiary dentin. In all instances when MSIs were immediately removed, healing occurred with cementum or dentin deposition and reestablishment of the PDL. Maino et al. investigated MSI contact in vivo using premolars treatment planned for extraction.76 First they placed MSIs mesial to the tooth root and pushed the teeth into the MSI for 2 months and extracted the teeth. There was a resorptive crater in the tooth root and little repair. In another tooth 22 root, they pushed for two months and then stopped pressure for 2 months. A slight residual defect was seen, but cellular cementum had been deposited to fill the crater. In another tooth that had been contacted with a drill and then contacted with an MSI and removed, there was incomplete repair after 2 months with cellular cementum, but some of the original contour was present. Inflammatory cells were seen in the periodontal ligament. Another similar study using human premolars treatment planned for extraction showed similar results.96 There are reports of root perforations due to MSI placement, subsequent necrosis, and the need for endodontic treatment. In one case report, a mandibular incisor root was perforated by an MSI during orthodontic treatment, and after 8 months a large periapical lesion was discovered via a routine radiograph.7 The patient was asymptomatic. Conventional root canal treatment was attempted, but was unsuccessful and surgical repair was initiated which resolved the lesion. Roncone recommends diverging the adjacent roots at the start of treatment if the use of an MSI is planned.97 Other authors recommend a myriad of techniques to avoid tooth root contact, such as using the palate or areas of the buccal bone with more interradicular space, using panoramic or periapical radiographs before and after, radiographic stents or guides, and angled placement.77–82 23 A number of clinicians advocate avoiding profound anesthesia, so as to elicit a patient reaction if a tooth is contacted.12,98 Usually the patient will feel a dull pain if the periodontal ligament is contacted.97 Patient reactions can serve as false positives however as patients may confuse pressure from MSI placement as pain. Tactile Perception Many authorities on MSIs state that a clinician will be able to feel if he or she contacts a tooth root, as there will be a dramatic increase in torque and resistance.8,12–16 These statements have mostly been made when referring to pre-drilled MSIs, however. In contrast, Sung et al. states that selfdrilling MSIs can be inserted and contact teeth without the clinician feeling any increased resistance.29 He states that a self-drilling MSI has a sharper point and is more likely to damage a root. A pre-drilled MSI is less likely to penetrate a root.29 All these claims are not evidence-based and merely anecdotal. Three studies, however, did measure insertion torque changes when an MSI contacts teeth. Wilmes et al. placed predrilled MSIs in pig mandibles.18 In this study the researchers pre-drilled the entire length of the screw, due to difficulty with screw fracture in pilot tests. They measured resistance to 24 pilot hold drilling and found an increase in resistance when a tooth was contacted. Additionally, they placed MSIs by hand and then had a torque-measuring robot perform the final 80 degree turn and measured the peak insertion torque. Torque values were higher in MSIs that had contacted teeth. A similar study by Chen et al. found that maximum insertion torque was higher in predrilled MSIs that contacted teeth vs. no contact.17 Briceno et al. placed 56 pre-drilled MSIs in the mandibles of beagle dogs with intentional root contact and evaluated the short and long-term effects of root contact.8 Predrilling was done through the cortex and the mean maximum insertion torque without root contact was 23.8 Ncm vs. 50.7 Ncm with root contact. A simultaneous study using the maxilla of the same dogs was also performed.84 This study did not report insertion torques, but noted that clinically, more resistance was felt when teeth were contacted. The author noted that tactile resistance wasn’t always accurate as 26.2% of the time the clinician felt the MSI had hit the root, but histologically there showed no contact. Using only tactile feedback, there was tendency to have false-positives. The operator could not tell the difference between root fracture and merely hitting the cementum. They also warn that self-drilling MSIs with sharpened tips to facilitate placement may not show such a change in 25 resistance.84 At present there are no studies investigating selfdrilling MSI torque changes when contacting a tooth. Roncone cautioned against an overreliance on tactile feedback pointing out that bone density in identical sites often varies widely among different individuals, thus what may feel like root impingement in an individual may only be particularly dense bone.97 It may be wise for clinicians to use torque-measuring or torque-limiting drivers when placing MSIs. Torque-limiting driver use is associated with higher success rates.1 Baumgaertel advocates using these instruments to avoid excessive bone damage and potential MSI breakage, especially in the mandible.20 Wilmes also recommends that clinicians monitor torque values, modify MSI diameters, and use pilot holes as necessary to limit excessive torque.54 McManus et al. proposed that a torque-driver with an audible click be produced when 5 Ncm and 10 Ncm were reached to help clinicians know if they are in the ideal insertion torque range according to Motoyoshi et al.69,99 A study by Schätzle investigated the accuracy of commercially available MSI torque-limiting drivers and found that after 100 sterilization cycles, significant variations were observed from the true torque values.100 26 Summary As MSIs become commonplace in modern orthodontics, practitioners desire evidence-based recommendations when providing treatment.101 Currently, no studies have investigated tooth contact using newer self-drilling MSI designs. All previous studies have drilled pilot holes, most of which drilled the entire length of the MSI, which is almost never the case in clinical practice. These data will be useful because it will evaluate the claim that one can “feel” if a tooth is encountered. Additionally, torque-limited drivers to place MSIs are becoming more commonplace. Information as to appropriate values to use as the maximum torque values and whether torquelimitations can be used to detect tooth contact could prove valuable. Lastly, studies that continuously measure insertion torque as the MSI is inserted, as opposed to just the final turn of the screw, better emulates clinical practice and will provide more information as to what happens when a tooth root is contacted. 27 Works Cited 1. Buschang PH, Carrillo R, Ozenbaugh B, Rossouw PE. 2008 survey of AAO members on miniscrew usage. J Clin Orthod. 2008 Sep;42(9):513–8. 2. Keim RG, Gottlieb EL, Nelson AH, Vogels DS 3rd. 2008 JCO study of orthodontic diagnosis and treatment procedures, part 1: Results and trends. J Clin Orthod. 2008 Nov;42(11):625–40. 3. Hyde JD, King GJ, Greenlee GM, Spiekerman C, Huang GJ. Survey of orthodontists’ attitudes and experiences regarding miniscrew implants. J Clin Orthod. 2010 Aug;44(8):481–6. 4. Kravitz ND, Kusnoto B. Risks and complications of orthodontic miniscrews. Am J of Orthod and Dentofacial Orthop. 2007 Apr;131(Suppl):S43–51. 5. Kang Y-G, Kim J-Y, Lee Y-J, Chung K-R, Park Y-G. Stability of mini-screws invading the dental roots and their impact on the paradental tissues in beagles. Angle Orthod. 2009 Mar;79(2):248–55. 6. Lee Y-K, Kim J-W, Baek S-H, Kim T-W, Chang Y-I. Root and bone response to the proximity of a mini-implant under orthodontic loading. Angle Orthod. 2010 May;80(3):452–8. 7. Hwang Y-C, Hwang H-S. Surgical repair of root perforation caused by an orthodontic miniscrew implant. Am J of Orthod and Dentofacial Orthop. 2011 Mar;139(3):407–11. 8. Brisceno CE, Rossouw PE, Carrillo R, Spears R, Buschang PH. Healing of the roots and surrounding structures after intentional damage with miniscrew implants. Am J Orthod Dentofacial Orthop. 2009 Mar;135(3):292–301. 9. Dao V, Renjen R, Prasad HS, Rohrer MD, Maganzini AL, Kraut RA. Cementum, pulp, periodontal ligament, and bone response after direct injury with orthodontic anchorage screws: A histomorphologic study in an animal model. J Oral Maxillofac Surg. 2009 Nov;67(11):2440–5. 28 10. Renjen R, Maganzini AL, Rohrer MD, Prasad HS, Kraut RA. Root and pulp response after intentional injury from miniscrew placement. Am J Orthod and Dentofacial Orthop. 2009 Nov;136(5):708–14. 11. Kuroda S, Yamada K, Deguchi T, Hashimoto T, Kyung H-M, Takano-Yamamoto T. Root proximity is a major factor for screw failure in orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2007 Apr;131(Suppl):S68–73. 12. Cope JB. Orthotads: The Clinical Guide and Atlas. Dallas:Under Dog Media; 2007. 13. Lee JS, Ph.D., Kim JK, Ph.D., Park Y-C, Vanarsdall RL. Applications of Orthodontic Mini-Implants. Hanover Park:Quintessence Pub Co; 2007. 14. Ludwig B. Mini-implants in Orthodontics: Innovative Anchorage Concepts. London:Quintessence Pub Co; 2008. 15. Paik C-H, Park I-K, Woo Y, Kim T-W. Orthodontic Miniscrew Implants: Clinical Applications. St. Louis:Mosby; 2008. 16. Nanda R, Uribe FA. Temporary Anchorage Devices in Orthodontics. St.:Louis:Mosby; 2008. 17. Chen Y-H, Chang H-H, Chen Y-J, Lee D, Chiang H-H, Yao C-CJ. Root contact during insertion of miniscrews for orthodontic anchorage increases the failure rate: An animal study. Clin Oral Implants Res. 2008 Jan;19(1):99–106. 18. Wilmes B, Su Y-Y, Sadigh L, Drescher D. Pre-drilling force and insertion torques during orthodontic mini-implant insertion in relation to root contact. J Orofac Orthop. 2008 Jan;69(1):51–8. 19. Baumgaertel S. State of the art of miniscrew implants: An interview with Sebastian Baumgaertel. Interviewed by Robert P. Scholz. Am J Orthod Dentofacial Orthop. 2009 Aug;136(2):277–81. 20. Baumgaertel S. Predrilling of the implant site: Is it necessary for orthodontic mini-implants? Am J Orthod Dentofacial Orthop. 2010 Jun;137(6):825–9. 21. Heidemann W, Gerlach KL, Grobel K-H, Kollner H-G. Drill free screws: A new form of osteosynthesis screw. J Cranio Maxill Surg. 1998;26(3):163–8. 29 22. Brånemark PI. Vital microscopy of bone marrow in rabbit. Scand J Clin Lab Invest 1959;11(Supp 38):1–82. 23. Ring ME. A thousand years of dental implants: A definitive history--part 1. Compend Contin Educ Dent. 1995 Oct;16(10):1060, 1062, 1064 passim. 24. Creekmore TD, Eklund MK. The possibility of skeletal anchorage. J Clin Orthod. 1983 Apr;17(4):266–9. 25. Kanomi R. Mini-implant for orthodontic anchorage. J Clin Orthod. 1997 Nov;31(11):763–7. 26. Costa A, Raffainl M, Melsen B. Miniscrews as orthodontic anchorage: A preliminary report. Int J Adult Orthodon Orthognath Surg. 1998;13(3):201–9. 27. 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 May;103(5):e6–15. 28. Melsen B. Mini-implants: Where are we? J Clin Orthod. 2005 Sep;39(9):539–47. 29. Sung J, Kyung H, Bae S, Kwon O, McNamara J. Microimplants in Orthodontics. Daegu:Dentos; 2006. 30. Kim J-W, Ahn S-J, Chang Y-I. Histomorphometric and mechanical analyses of the drill-free screw as orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2005 Aug;128(2):190–4. 31. Suzuki EY, Suzuki B. Placement and removal torque values of orthodontic miniscrew implants. Am J Orthod Dentofacial Orthop. 2011;139(5):669–78. 32. Cacciafesta V, Bumann A, Cho HJ, Graham JW, Paquette DE, Park H-S, et al. JCO Roundtable. Skeletal anchorage, part 2. J Clin Orthod. 2009 Jun;43(6):365–78. 33. Cheng S-J, Tseng I-Y, Lee J-J, Kok S-H. A prospective study of the risk factors associated with failure of miniimplants used for orthodontic anchorage. Int J Oral Maxillofac Implants. 2004 Feb;19(1):100–6. 30 34. 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 and Dentofacial Orthop. 2003 Oct;124(4):373–8. 35. Chen Y, Kyung HM, Zhao WT, Yu WJ. Critical factors for the success of orthodontic mini-implants: A systematic review. Am J Orthod Dentofacial Orthop. 2009 Mar;135(3):284–91. 36. Schätzle M, Männchen R, Zwahlen M, Lang NP. Survival and failure rates of orthodontic temporary anchorage devices: a systematic review. Clin Oral Implants Res. 2009 Dec;20(12):1351–9. 37. Lim H-J, Eun C-S, Cho J-H, Lee K-H, Hwang H-S. Factors associated with initial stability of miniscrews for orthodontic treatment. Am J Orthod Dentofacial Orthop. 2009 Aug;136(2):236–42. 38. Büchter A, Wiechmann D, Koerdt S, Wiesmann HP, Piffko J, Meyer U. Load-related implant reaction of mini-implants used for orthodontic anchorage. Clin Oral Implants Res. 2005 Aug;16(4):473–9. 39. Wiechmann D, Meyer U, Büchter A. Success rate of mini- and micro-implants used for orthodontic anchorage: A prospective clinical study. Clin Oral Implants Res. 2007 Apr;18(2):263–7. 40. Tsaousidis G, Bauss O. Influence of insertion site on the failure rates of orthodontic miniscrews. J Orofac Orthop. 2008 Sep;69(5):349–56. 41. Fritz U, Ehmer A, Diedrich P. Clinical suitability of titanium microscrews for orthodontic anchorage-preliminary experiences. J Orofac Orthop. 2004 Sep;65(5):410–8. 42. McGuire MK, Scheyer ET, Gallerano RL. Temporary anchorage devices for tooth movement: A review and case reports. J Period. 2006 Oct;77(10):1613–24. 43. Meredith N. Assessment of implant stability as a prognostic determinant. Int J Prosthodont. 1998 Oct;11(5):491–501. 31 44. Ottoni JMP, Oliveira ZFL, Mansini R, Cabral AM. Correlation between placement torque and survival of single-tooth implants. Int J Oral Maxillofac Implants. 2005 Oct;20(5):769–76. 45. Friberg B, Sennerby L, Meredith N, Lekholm U. A comparison between cutting torque and resonance frequency measurements of maxillary implants: A 20-month clinical study. Int J Oral Maxillof Surg. 1999 Aug;28(4):297–303. 46. Piattelli A, Trisi P, Romasco N, Emanuelli M. Histologic analysis of a screw implant retrieved from man: Influence of early loading and primary stability. J Oral Implantol. 1993;19(4):303–6. 47. Melsen B, Costa A. Immediate loading of implants used for orthodontic anchorage. Clin Orthod Res. 2000 Feb;3(1):23–8. 48. Cornelis MA, Scheffler NR, De Clerck HJ, Tulloch JFC, Behets CN. Systematic review of the experimental use of temporary skeletal anchorage devices in orthodontics. Am J of Orthod and Dentofacial Orthop. 2007 Apr;131(Suppl):S52– 8. 49. 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 Oct;22(5):779–84. 50. Ure DS, Oliver DR, Kim KB, Melo AC, Buschang PH. Stability changes of miniscrew implants over time. Angle Orthod. 2011 Nov;81(6):994-1000. 51. Wilmes B, Rademacher C, Olthoff G, Drescher D. Parameters affecting primary stability of orthodontic mini-implants. J Orofac Orthop. 2006 May;67(3):162–74. 52. Suzuki EY, Suzuki B, Aramrattana A, Harnsiriwattanakit K, Kowanich N. Assessment of miniscrew implant stability by resonance frequency analysis: A study in human cadavers. J Oral Maxillofac Surg. 2010 Nov;68(11):2682–9. 53. Su Y-Y, Wilmes B, Hönscheid R, Drescher D. Application of a wireless resonance frequency transducer to assess primary stability of orthodontic mini-implants: An in vitro study in pig ilia. Int J Oral Maxillofac Implants. 2009 Aug;24(4):647–54. 32 54. Florvaag B, Kneuertz P, Lazar F, Koebke J, Zöller JE, Braumann B, et al. Biomechanical properties of orthodontic miniscrews. An in-vitro study. J Orofac Orthop. 2010 Feb;71(1):53–67. 55. Collinge CA, Stern S, Cordes S, Lautenschlager EP. Mechanical properties of small fragment screws. Clin Orthop Relat Res. 2000 Apr;373:277–84. 56. Wilmes B, Drescher D. Impact of bone quality, implant type, and implantation site preparation on insertion torques of mini-implants used for orthodontic anchorage. Int J Oral Maxillofac Surg. 2011 Jul;40(7):697–703. 57. Wilmes B, Ottenstreuer S, Su Y-Y, Drescher D. Impact of implant design on primary stability of orthodontic miniimplants. J Orofac Orthop. 2008 Jan;69(1):42–50. 58. Kim J-W, Baek S-H, Kim T-W, Chang Y-I. Comparison of stability between cylindrical and conical type miniimplants. Mechanical and histological properties. Angle Orthod. 2008 Jul;78(4):692–8. 59. Carano A, Lonardo P, Velo S, Incorvati C. Mechanical properties of three different commercially available miniscrews for skeletal anchorage. Prog Orthod. 2005;6(1):82–97. 60. Sowden D, Schmitz JP. AO self-drilling and self-tapping screws in rat calvarial bone: An ultrastructural study of the implant interface. J Oral Maxillofac Surgy. 2002 Mar;60(3):294–9. 61. Kuhn A, Mc Iff T, Cordey J, Baumgart FW, Rahn BA. Bone deformation by thread-cutting and thread-forming cortex screws. Injury. 1995;26(Suppl 1):12–20. 62. Ansell RH, Scales JT. A study of some factors which affect the strength of screws and their insertion and holding power in bone. J Biomech. 1968 Dec;1(4):279–302. 63. Huja S., Katona T., Burr D., Garetto L., Roberts W. Microdamage adjacent to endosseous implants. Bone. 1999 Aug;25(2):217–22. 33 64. Büchter A, Kleinheinz J, Wiesmann HP, Kersken J, Nienkemper M, Weyhrother H von, et al. Biological and biomechanical evaluation of bone remodelling and implant stability after using an osteotome technique. Clin Oral Implants Res. 2005 Feb;16(1):1–8. 65. Wawrzinek C, Sommer T, Fischer-Brandies H. Microdamage in cortical bone due to the overtightening of orthodontic microscrews. J Orofac Orthop. 2008 Mar;69(2):121–34. 66. Lee N-K, Baek S-H. Effects of the diameter and shape of orthodontic mini-implants on microdamage to the cortical bone. Am J Orthod Dentofacial Orthop. 2010 Jul;138(1):e1–8. 67. Wilmes B, Panayotidis A, Drescher D. Fracture resistance of orthodontic mini-implants: A biomechanical in vitro study. Eur J Orthod. 2011 Aug;33(4):396–401. 68. Lehnen S, McDonald F, Bourauel C, Baxmann M. Patient expectations, acceptance and preferences in treatment with orthodontic mini-implants. A randomly controlled study. Part I: Insertion techniques. J Orofac Orthop. 2011 Mar;72(2):93–102. 69. Motoyoshi M, Hirabayashi M, Uemura M, Shimizu N. Recommended placement torque when tightening an orthodontic mini-implant. Clin Oral Implants Res. 2006 Feb;17(1):109– 14. 70. Chaddad K, Ferreira AFH, Geurs N, Reddy MS. Influence of surface characteristics on survival rates of mini-implants. Angle Orthod. 2008 Jan;78(1):107–13. 71. Poggio PM, Incorvati C, Velo S, Carano A. “Safe zones”: A guide for miniscrew positioning in the maxillary and mandibular arch. Angle Orthod. 2006 Mar;76(2):191–7. 72. Chaimanee P, Suzuki B, Suzuki EY. “Safe zones” for miniscrew implant placement in different dentoskeletal patterns. Angle Orthod. 2011 May;81(3):397–403. 73. Antoszewska J, Trześniewska P, Kawala B, Ludwig B, Park HS. Qualitative and quantitative evaluation of root injury risk potentially burdening insertion of miniscrew implants. Korean J Orthod. 2011;41(2):112–20. 34 74. Cho U-H, Yu W, Kyung H-M. Root contact during drilling for microimplant placement affect of surgery site and operator expertise. Angle Orthod. 2010;80(1):130–6. 75. Liou EJ., Pai BC., Lin JC. Do miniscrews remain stationary under orthodontic forces? Am J Orthod and Dentofacial Orthop. 2004 Jul;126(1):42–7. 76. Maino BG, Weiland F, Attanasi A, Zachrisson BU, Buyukyilmaz T. Root damage and repair after contact with miniscrews. J Clin Orthod. 2007 Dec;41(12):762–6. 77. Martinelli FL, Luiz RR, Faria M, Nojima LI. Anatomic variability in alveolar sites for skeletal anchorage. Am J Orthod and Dentofacial Orthop. 2010 Sep;138(3):e1–e9. 78. Ludwig B, Glasl B, Kinzinger GSM, Lietz T, Lisson JA. Anatomical guidelines for miniscrew insertion: Vestibular interradicular sites. J Clin Orthod. 2011 Mar;45(3):165–73. 79. Bae S-M, Park H-S, Kyung H-M, Kwon O-W, Sung J-H. Clinical application of micro-implant anchorage. J Clin Orthod. 2002 May;36(5):298–302. 80. Kim S-H, Kang J-M, Choi B, Nelson G. Clinical application of a stereolithographic surgical guide for simple positioning of orthodontic mini-implants. World J Orthod. 2008;9(4):371–82. 81. Morea C, Dominguez GC, Wuo ADV, Tortamano A. Surgical guide for optimal positioning of mini-implants. J Clin Orthod. 2005 May;39(5):317–21. 82. Noble J, Karaiskos NE, Hassard TH, Hechter FJ, Wiltshire WA. Stress on bone from placement and removal of orthodontic miniscrews at different angulations. J Clin Orthod. 2009 May;43(5):332–4. 83. Miyazawa K, Kawaguchi M, Tabuchi M, Goto S. Accurate presurgical determination for self-drilling miniscrew implant placement using surgical guides and cone-beam computed tomography. Eur J Orthod. 2010 Dec;32(6):735–40. 84. Hembree M, Buschang PH, Carrillo R, Spears R, Rossouw PE. Effects of intentional damage of the roots and surrounding structures with miniscrew implants. Am J Orthod Dentofacial Orthop. 2009 Mar;135(3):e1–9. 35 85. Fabbroni G, Aabed S, Mizen K, Starr DG. Transalveolar screws and the incidence of dental damage: A prospective study. Int J Oral Maxillofac Surg. 2004 Jul;33(5):442–6. 86. Farr DR, Whear NM. Intermaxillary fixation screws and tooth damage. Br J Oral Maxillofac Surg. 2002 Feb;40(1):84–5. 87. Herman R, Cope JB. Miniscrew implants: IMTEC mini ortho implants. Sem Orthod. 2005 Mar;11(1):32–9. 88. Melsen B, Verna C. Miniscrew implants: The Aarhus anchorage system. Sem Orthod. 2005 Mar;11(1):24–31. 89. Maino BG, Mura P, Bednar J. Miniscrew implants: The Spider Screw anchorage system. Sem Orthod. 2005 Mar;11(1):40–6. 90. Garrett S, Bogle G, Adams D, Egelberg J. The effect of notching into dentin on new cementum formation during periodontal wound healing. J Periodont Res. 1981 May;16(3):358–61. 91. Helldén L. Periodontal healing following experimental injury to root surfaces of human teeth. Scand J Dent Res. 1972;80(3):197–205. 92. Gray JL, Vernino AR. The interface between retained roots and dental implants: A histologic study in baboons. J Periodontol. 2004 Aug;75(8):1102–6. 93. Asscherickx K, Vannet BV, Wehrbein H, Sabzevar MM. Root repair after injury from mini‐screw. Clin Oral Implants Res. 2005 Oct 1;16(5):575–8. 94. Asscherickx K, Vande Vannet B, Wehrbein H, Sabzevar MM. Success rate of miniscrews relative to their position to adjacent roots. Eur J Orthod. 2008 Aug;30(4):330–5. 95. Kim H, Kim T-W. Histologic evaluation of root-surface healing after root contact or approximation during placement of mini-implants. Am J Orthod and Dentofacial Orthop. 2011 Jun;139(6):752–60. 96. Kadioglu O, Büyükyilmaz T, Zachrisson BU, Maino BG. Contact damage to root surfaces of premolars touching miniscrews during orthodontic treatment. Am J Orthod Dentofacial Orthop. 2008 Sep;134(3):353–60. 36 97. Roncone CE. Complications encountered in temporary orthodontic anchorage device therapy. Sem Orthod. 2011 Jun;17(2):168–79. 98. Costello BJ, Ruiz RL, Petrone J, Sohn J. Temporary skeletal anchorage devices for orthodontics. Oral Maxillofac Surg Clin North Am. 2010 Feb;22(1):91–105. 99. McManus MM, Qian F, Grosland NM, Marshall SD, Southard TE. Effect of miniscrew placement torque on resistance to miniscrew movement under load. Am J Orthod and Dentofacial Orthop. 2011 Sep;140(3):e93–8. 100. Schätzle M, Golland D, Roos M, Stawarczyk B. Accuracy of mechanical torque‐limiting gauges for mini‐screw placement. Clin Oral Implants Res. 2010 Aug 1;21(8):781–8. 101. Madhavji A, Araujo EA, Kim KB, Buschang PH. Attitudes, awareness, and barriers toward evidence-based practice in orthodontics. Am J Orthod and Dentofacial Orthop. 2011 Sep;140:309–16.e2. 37 CHAPTER 3: JOURNAL ARTICLE Abstract Introduction: Miniscrew impants (MSIs) are a useful tool when absolute orthodontic anchorage is required. While helpful in many regards, problems can still arise. The purpose of this study was to quantify how insertion torque changes during insertion of a self-drilling MSI with tooth root contact. Methods: MSIs from two manufacturers (3M Unitek™ TAD and Dentaurum tomas® pin) were inserted in pig cadaver mandibles and divided into three groups: Control (miss), Glance, and Direct Hit. Cone-beam computed tomography (CBCT) was used to verify MSI location. Insertion torque was continuously recorded during MSI insertion and inspected for fracture or damage upon removal. Scatterplots of time vs insertion torque were created. Results: 3M Unitek MSIs showed higher insertion torque than Tomas MSIs in control groups. Self-drilling MSIs were unable to directly penetrate the roots. Self-drilling MSIs which contact teeth show a higher insertion torque than control groups with no contact. Tomas® MSIs showed higher fracture rates at the tip, possibly due to a weaker thread-cutting design. Conclusions: Contact with a tooth root with a self-drilling MSI causes an increase in insertion torque and thus tactile feedback may help the experienced clinician determine if root contact has occurred. 38 Additionally, thread-cutting tips appear to be more prone to breakage when a tooth root is contacted. Introduction Miniscrew implants (MSIs) provide exciting opportunities to treat orthodontic patients in ways that were not previously possible and, at the same time, avoid reliance on patient compliance. As a result, MSIs have attracted great interest, generated hundreds of articles published in the last few years, and have become a “standard in the modern orthodontic practice.”1,2 Miniscrews are a recent addition to the clinician’s armamentarium, only 7.8% of orthodontists in a recent survey had been using MSI more than five years.3 Usage of MSIs has increased dramatically. Various surveys have shown usage rates varying from 60-91% of orthodontists using miniscrews at least once in the past years.3–5 Severe, irreversible damage can be caused by MSIs contacting teeth.6–8 Fortunately, root damage caused by MSI contact most often results in minor damage that heals uneventfully.9–13 Root contact should also be of concern to the practitioner since apart from damage, it has been shown to dramatically increase failure rates.6,7 39 In a 2008 survey of orthodontists, 45.5% of orthodontists reported not placing their own implants. Potential root damage was cited by 32.8% as the main reason for delegation to other practitioners, despite the fact that orthodontist-placed MSIs have higher success rates.3 A recent study by Antoszewska had 35 orthodontists place MSIs in the maxilla of typodonts.14 Fear level of the orthodontists was surveyed on a 10-point visual analog scale and root contacts were counted. Root contacts occurred in 23.5% of the insertions. Fear level before MSI insertion (4.6) was significantly decreased after insertion (3.2). Clinicians indicated that their fears stemmed from the risk of injury to the teeth and maxillary sinus. Many authorities on MSIs state that a clinician will be able to feel if he or she contacts a tooth root, as there will be a dramatic increase in torque and resistance.12,15–19 Only a few studies have evaluated the claims that insertion torque changes when a tooth root is contacted.10,12,20 These studies looked at MSIs which required predrilling a pilot hole. Newer selfdrilling MSI designs, which require no pilot hole, have been introduced. A self-drilling MSI is preferred by clinicians due to the simplicity of the procedure.1,2,21 Only 10.5% of clinicians report using a pilot hole “mostly” or “always.”3 Insertion torque has been typically measured as the “maximum insertion torque” and is often derived from MSIs being 40 placed to almost the final length and then measuring the insertion torque of the last turn or measuring just the highest value encountered during insertion.10,12,20 More valuable would be a system that measures insertion torque continuously, which better simulates what occurs clinically and will provide more information as to what happens when a tooth root is contacted and the rate of change seen. Currently, no studies have investigated tooth contact using newer self-drilling MSI designs. Additionally, torque-limited drivers to place MSIs are becoming more commonplace. Added information as to the appropriate values to use as the maximum torque values and whether torque-limitations can be used to detect tooth contact could prove valuable. The aim of this research is to quantify the insertion torque when an MSI is inserted and contacts a tooth. Insertion torque will be continuously recorded so the rate of change can be studied. This study addresses the following questions: Does insertion torque increase with root contact? How much and how quickly does it change? Could this change be used to detect root contact? 41 Materials and Methods Resected, frozen pig mandibles were prepared to include the posterior premolar teeth (Figure 3.1). Samples were thawed and Figure 3.1 CBCT-derived image depicting pig mandible area used in this study (left) and diagrammatic representation of swine dental arcade with area of interest outlined (right). two commercially-available, self-drilling miniscrew implants were selected to be placed without predrilling or incision of soft tissue. The two MSIs in this study were a 1.8mm diameter, 6mm long 3M Unitek™ TAD (Monrovia, CA, USA) and a 1.6mm diameter, 6mm long Dentaurum tomas® pin (Ispringen, Germany)(Figure 3.2). Torque measurements were continuously measured as the MSI was inserted until the collar of the miniscrew approximates the gingiva. Torque measurements were made using a custom insertion torque measuring device. This 42 Figure 3.2 MSIs tested in this study. 3M Unitek™ TAD (left) and Dentaurum tomas® pin (right) method reduces human error in testing, allows for continuous torque measurement during insertion, and has been proven a reliable method to measure insertion torque of miniscrew implants in previous studies.22,23 The device consists of an aluminum jig that securely holds the sample and is rotated at 9 revolutions per minute by a high torque motor (Model 016-2240108, Display Devices Inc., Arvada, CO, USA). A torque sensor (Mecmesin Ltd., West Sussex, UK) is securely mounted above and is fitted with the proprietary driver bit for the MSI. It is lowered using a using a modified drill press (Model 220-01, Dremel, Robert Bosch Tool Corp., Racine, WI, USA) into the revolving sample (Figure 3.3 and Figure 3.4). It was determined in pilot testing that approximately five and one-half pounds (5.48 lbs, 2.49 kg) was needed to adequately advance the MSIs. 43 Figure 3.3 Custom insertion torque measuring device As this constant weight was applied at the lever arm and the motor rotated the sample, insertion torque was recorded via a computer with appropriate software (Emperor ™ lite, ver. 1.17015, Mecmesin Ltd., West Sussex, UK) Imaging was performed with a 3-dimensional cone-beam computed tomography (CBCT) i-CAT scanner (Imaging Sciences 44 A B C Figure 3.4 Close-up view of torque sensor (A), MSI driver and MSI (B), and aluminum jig with sample held securely with washers and bolts (C) International, Hatfield, Pa) and viewed with Dolphin 3-D (Dolphin Imaging Version 11.0, Premium Chatsworth, CA). Lead markers were placed on the bone sections and were used to select locations for MSI insertion. MSIs were inserted first without root contact into the mandibular sections between the roots of the first, second, and third premolars. After imaging and removal, MSIs were inserted directly into the tooth roots. On the contralateral side, MSIs were placed closer to the teeth to 45 produce a “glance” where contact occurred and less than half the diameter of the MSI was in the root. CBCT was again used to verify MSI placement and root contact. MSIs were removed and examined for fractures; fracture incidence and location was recorded and photographed. Pilot tests with pig mandibles showed that the MSIs could be placed accurately. Power analysis using pilot data showed that a sample size of at least 10 miniscrews per group would give an 80% probability of detecting a real difference between the groups at a statistically significant level of 5%. Scatterplots of time vs insertion torque measurements were made using Microsoft Excel® 2007 (Microsoft Corporation, Redmond, WA) and statistical analysis was conducted using SPSS software (SPSS for Windows, Version 15.0, Chicago, IL). Due to the small sample size and possibility of skewed data, nonparametric analysis using the Mann-Whitney U test was used to determine significant differences (p<.05) among the mean torque values of the control group vs. the experimental group at different times. Results Cone-beam computed tomography (CBCT) was able to accurately locate the position of the MSI in relation to the tooth. Figure 46 Figure 3.5 CBCT-derived image representing a control (miss) sample (above) and a photograph of the same sample (below) 3.5 is an example of the three dimensional view of the mandible in the control group. Additionally, slices can be made to verify the position of the MSI such as Figure 3.6, which shows an example of a glance group coronal slice. Insertion torques vs time Both of the control (miss) groups showed a positive linear relationship with increasing insertion torque as the MSI 47 Figure 3.6 CBCT-derived images. Above is a coronal slice from the 3-dimensional image below. The above image confirms partial root contact with the MSI advanced (Figure 3.7 and Figure 3.8). The average insertion torque of the 3M Unitek MSIs was higher than the Tomas MSIs at similar timepoints (Figure 3.9). The MSIs assigned to the direct hit group were unable to penetrate the tooth (Figure 3.10 and 3.11). They would enter the bone, and as expected torque would increase, but then the MSI would stop advancing and just spin and strip the bone. The insertion torque at this point would plateau at a low value, 48 Figure 3.7 Insertion torque values for the control (miss) group from time = 0 to full engagement for 3M Unitek MSIs Figure 3.8 Insertion torque values for the control (miss) group from time = 0 to full engagement for Dentaurum Tomas MSIs 49 Figure 3.9 Mean insertion torque from time = 0 to full engagement for both control groups Figure 3.10 MSIs attempted to penetrate directly into the tooth root were unable to penetrate the root and would just partially insert and then spin as seen above 50 Figure 3.11 Mean insertion torque from time = 0 to full engagement for direct hit group thus only five MSIs of each brand were attempted and the data wasn’t included in statistical analysis. The data from the glance groups showed a deviation from the tight linear relationship see in the control group (Figure 3.12 and Figure 3.13). Figure 3.14 and 3.15 illustrates the mean insertion torque for the 3M Unitek and Tomas MSIs glance groups respectively. Although the lines start out similar to the control group, one can appreciate that the lines exhibit an inflection point where the rate of increase (slope of the line) suddenly increases and the insertion torque become higher than the control group. There was a statistically significant 51 Figure 3.12 Insertion torque values for the glance group from time = 0 to full engagement for 3M Unitek MSIs Figure 3.13 Insertion torque values for the glance group from time = 0 to full engagement for Tomas MSIs 52 Figure 3.14 Mean insertion torque from time = 0 to full engagement for the 3M Unitek control and glance groups Figure 3.15 Mean insertion torque from time = 0 to full engagement for the Tomas control and glance groups 53 Table 3.1 Mean maximum insertion torques every 0.1 mins (6 secs) 3M Unitek Miss (control) Glance p-value Tomas Miss (control) Glance p-value N T=0.1 min Mean Maximum Insertion Torque (Ncm) T=0.2 min T=0.3 min T=0.4 min T=0.5 min 10 10 3.08 3.44 5.45 6.12 7.20 10.23 9.42 14.81 11.71 17.00 0.324 0.211 0.002 0.001 0.000 1.88 2.43 3.56 4.57 5.22 7.91 6.91 11.67 8.76 12.86 0.555 0.009 0.001 0.001 0.001 10 7 difference between the glance group and control group at time = 0.3 min (18 seconds) and greater for the 3M Unitek MSI and for the Tomas MSI at time = 0.2 min (12 seconds) and greater (Table 3.1). MSI Fractures Three of the 10 Tomas MSIs advanced partially and then stopped advancing, only achieving approximately 7-9 Ncm of torque. Upon removal it was found that the tip of the three MSIs had fractured and were not included in the analysis (Figure 3.16). 54 Figure 3.16 Close-up view of a control and two of the three Tomas screws whose tips fractured during insertion Discussion Few studies have measured how insertion torque changes with tooth root contact. A study by Wilmes et al. used pig mandibles and randomly placed 320 pilot holes drilled the entire length of the MSI in 11 bones and placed MSIs by hand until the last 0.2mm, which was then done by a robot which measured the insertion torque.20 The control group and the partially contacted roots group had insertion torque of 16.1 Ncm and 18.5 Ncm respectively. This difference was small, but statistically significant and the authors note that clinicians may not be able to detect this small a difference clinically. A similar in-vivo study by Chen et al. again drilled the entire length of the MSI in mongrel dogs and placed miniscrews by hand and then measured the last few turns with a torque meter.10 They also found 55 slightly higher insertion torque in root contact vs no contact MSIs (20.3 vs 17.4 Ncm respectively). A weakness of these studies is that they pre-drilled, not just through the cortex, but the entire length of the MSI. This technique is not used clinically since a pilot hole the entire length of the screw is unnecessary, creates greater trauma to the bone, and leaves a void between the MSI tip and bone.24 Because it was the pilot drill which contacted the teeth first and removed part of the tooth before MSI placement, this may have diminished the differences seen. The difference may be greater using the more conventional pilot-hole through the cortex only or with the newer self-drilling MSIs. Another shortcoming in these studies is they measured only the last turn of the MSI and called it the maximum insertion torque. It would be better to continuously measure the insertion since the true maximum insertion torque may occur before the final turn, especially in studies looking at tooth contact. Also, the last turn involves the miniscrew body/neck interface. The transmucosal neck has no threads and can give a torque increase simply because the miniscrew can no longer advance. An animal study by Brisceno et al. also looked at insertion torque when tooth roots are contacted.12 They predrilled through the bone cortex only due to very high insertion torques which were encountered and caused MSI breakage. The maximum insertion 56 torque encountered was recorded and was higher in contacted teeth (50.7 Ncm) than non-contacted teeth (23.8 Ncm). This study was an improvement, since only the cortex was drilled, but doesn’t provide a continuous picture of how the torque changes during insertion, just that the overall value was higher. Another study involving tooth root contact and healing using the maxilla of these same dogs was done simultaneously. The authors reported that there was higher insertion torque using only tactile feedback, but 26.2% of the time there was a falsepositive where the clinician felt a contact, but none had occurred histologically.9 The use of hand drivers introduces inconsistency due to the operator and how hard he or she pushes on the MSI and variably rotates the driver. The method used in this study is superior since it eliminates the “human” variability, uses current placement techniques, and offers continuous data for the entire placement. In this study two commercially-available orthodontic miniscrew implants were compared in terms of their insertion torque when placed normally between roots and when contacting teeth. Both control (miss) groups performed similarly with a positive, linear relationship to time. The 3M Unitek MSIs had higher torque values when compared to Tomas MSIs in the control groups at the same timepoints. One reason for this is the 3M 57 Unitek MSI is 1.8mm diameter compared to the 1.6mm for the Tomas MSI. Larger diameters have been correlated with higher insertion torques.25,26 Barros et al. found diameter changes of as little as 0.1 mm caused significant insertion torque differences in MSI placement.27 Another reason for the higher insertion torque seen in the 3M Unitek MSI may be due to the design of the miniscrew, as the 3M Unitek MSI has a different taper than the Tomas MSI. Conical designs have a higher insertion torque due to the upper part of the tapered body having a larger diameter than the lower part and this factor creates a tighter contact with the bone.25,26,28 Additionally, the pitch and thread count is different between the screws. Wilmes et al. showed that for similar sized MSIs, there was a wide variation in insertion torque due to the various design differences such as thread pitch and shape.25,29 Perhaps one should choose various screw designs for different locations in the mouth to vary the insertion torque. Directly drilling into a tooth with a self-drilling MSI was not successful with either brand MSI. Perforation is one of the most serious potential complications.30 A clinician might prefer a self-drilling MSI, since he or she knows that it is highly unlikely to perforate the tooth without the use of a drill. In each case where a tooth was contacted, there is a deviation from linearity; the slope of the line suddenly increases and the value at similar timepoints to the control 58 group is higher. This can only be attributed to contact with the tooth root, since other variables are controlled. This confirms quantitatively what clinicians have claimed anecdotally, namely that insertion torque does increase with tooth root contact. This finding also agrees with the previously mentioned studies using pre-drilled MSIs and pilot holes who found torque increased with tooth contact.10,12,20 When the mean insertion torque is compared to control there was a statistically significant difference after .2 min (12 seconds) for the 3M Unitek MSI and at .3 min (18 seconds) for the Tomas MSI. This may be due to the difference in pitch of the MSIs, which would affect the rate at which they entered the bone. Torque-limited or torque-measuring drivers are available for many of the MSI kits. Some researchers advocate their use to avoid excessively high insertion torque, which could lead to MSI fracture and bone damage.1,31,32 The use of a torque-limited driver could also help prevent complications due to tooth root contact. MSI contact with tooth roots has been shown to dramatically decrease success rates.6,7 If only partially contacted, most roots heal normally, but in some cases severe damage can occur which can lead to necrosis, ankylosis, or root fractures that may require endodontic therapy or tooth removal.8,30 These data show that there is a higher insertion torque caused by tooth 59 root contact. If an operator notices higher than normal torque values and is unsure of his position, it may be worthwhile to adjust angulation or location. Additional research using human cadaver bone and in vivo studies could better determine the safe ranges for insertion torque. Ideal insertion torque values have not been established. Motoyoshi et al. claimed that insertion torque values between 510 Ncm are ideal for a 6 mm long 1.6 mm diameter MSI, but Chaddad et al. claims insertion torques over 15 Ncm are more successful in similar screws.33,34 Both of these studies used the older predrilled MSIs and a recent study by Suzuki and Suzuki called into question the previous claims of ideal insertion torque ranges since they found no difference in success rates of higher torque self-drilling MSIs (14.5 Ncm) and lower torque pre-drilled MSIs (9.2 Ncm).35 If ideal insertion torques were established, then torquelimited drivers could be set to alert the clinician when this value has been exceeded, which could avoid damage to bone, possible MSI fractures, and possible tooth root contact. An experienced clinician could determine normal torque values encountered in his office, and if the MSI suddenly increased in torque he or she could detect root contact and remove the MSI and choose a better location. In pilot testing using hand 60 drivers, the researcher in this study felt he was able to determine via tactile feedback when a tooth root was contacted. MSIs and their proximity to tooth roots were easily visible on the CBCT images, and higher insertion torques were consistently found in the samples that showed tooth root contact. Clinicians with access to CBCT imaging might find it useful to check position of MSIs if they are unsure of root proximity. One finding was the thread-cutting Tomas tip was more prone to fracture when contacting a tooth. The fractures seemed to happen when a glance was occurring. The MSI would contact the root and then stop advancing and not pass the root. By creating a cutting tip, metal is removed, which weakens the tip.15,36 On the other hand, thread-cutting designs are claimed to cause less compression and alleviate bone stress, thus allowing for a more less traumatic insertion.37,38 There have been no studies specifically comparing thread-forming to thread-cutting MSIs used in orthodontics. This study was not designed to compare thread-forming to thread-cutting MSI design on insertion torque, since the miniscrew’s design varied in other ways which could also influence results. More studies should be done to investigate what the benefits, if any, of a thread-cutting design are, since they potentially have the weakness of increased fracture. 61 Conclusions 1. 3M Unitek MSIs showed higher insertion torque than Tomas MSIs in control groups. 2. Self-drilling MSIs which contact teeth show a higher insertion torque than control groups with no contact. 3. It may be possible to detect tooth root contact by using a torque-sensitive driver. 4. Tomas MSIs showed higher fracture rates at the tip when a tooth was contacted, possibly due to the weaker threadcutting design. 62 Works Cited 1. Baumgaertel S. Predrilling of the implant site: Is it necessary for orthodontic mini-implants? Am J Orthod Dentofacial Orthop. 2010 Jun;137(6):825–9. 2. Baumgaertel S. State of the art of miniscrew implants: An interview with Sebastian Baumgaertel. Interviewed by Robert P. Scholz. Am J Orthod Dentofacial Orthop. 2009 Aug;136(2):277–81. 3. Buschang PH, Carrillo R, Ozenbaugh B, Rossouw PE. 2008 survey of AAO members on miniscrew usage. J Clin Orthod. 2008 Sep;42(9):513–8. 4. Keim RG, Gottlieb EL, Nelson AH, Vogels DS 3rd. 2008 JCO study of orthodontic diagnosis and treatment procedures, part 1: Results and trends. J Clin Orthod. 2008 Nov;42(11):625–40. 5. Hyde JD, King GJ, Greenlee GM, Spiekerman C, Huang GJ. Survey of orthodontists’ attitudes and experiences regarding miniscrew implants. J Clin Orthod. 2010 Aug;44(8):481–6. 6. Kuroda S, Yamada K, Deguchi T, Hashimoto T, Kyung H-M, Takano-Yamamoto T. Root proximity is a major factor for screw failure in orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2007 Apr;131(Suppl):S68–73. 7. Kang Y-G, Kim J-Y, Lee Y-J, Chung K-R, Park Y-G. Stability of mini-screws invading the dental roots and their impact on the paradental tissues in beagles. Angle Orthod. 2009 Mar;79(2):248–55. 8. Hwang Y-C, Hwang H-S. Surgical repair of root perforation caused by an orthodontic miniscrew implant. Am J Orthod Dentofacial Orthop. 2011 Mar;139(3):407–11. 9. Hembree M, Buschang PH, Carrillo R, Spears R, Rossouw PE. Effects of intentional damage of the roots and surrounding structures with miniscrew implants. Am J Orthod Dentofacial Orthop. 2009 Mar;135(3):e1–e9. 10. Chen Y-H, Chang H-H, Chen Y-J, Lee D, Chiang H-H, Yao C-CJ. Root contact during insertion of miniscrews for orthodontic anchorage increases the failure rate: An animal study. Clin Oral Implants Res. 2008 Jan;19(1):99–106. 63 11. Renjen R, Maganzini AL, Rohrer MD, Prasad HS, Kraut RA. Root and pulp response after intentional injury from miniscrew placement. Am J Orthod Dentofacial Orthop. 2009 Nov;136(5):708–14. 12. Brisceno CE, Rossouw PE, Carrillo R, Spears R, Buschang PH. Healing of the roots and surrounding structures after intentional damage with miniscrew implants. Am J Orthod Dentofacial Orthop. 2009 Mar;135(3):292–301. 13. Dao V, Renjen R, Prasad HS, Rohrer MD, Maganzini AL, Kraut RA. Cementum, pulp, periodontal ligament, and bone response after direct injury with orthodontic anchorage screws: A histomorphologic study in an animal model. J Oral Maxillofac Surg. 2009 Nov;67(11):2440–5. 14. Antoszewska J, Trześniewska P, Kawala B, Ludwig B, Park H-S. Qualitative and quantitative evaluation of root injury risk potentially burdening insertion of miniscrew implants. Korean J Orthod. 2011;41(2):112–20. 15. Cope JB. Orthotads: The Clinical Guide and Atlas. Dallas:Under Dog Media; 2007. 16. Lee JS, Ph.D., Kim JK, Ph.D., Park Y-C, Vanarsdall RL. Applications of Orthodontic Mini-Implants. Hanover Parl:Quintessence Pub Co; 2007. 17. Ludwig B. Mini-implants in Orthodontics: Innovative Anchorage Concepts. London:Quintessence Pub Co; 2008. 18. Paik C-H, Park I-K, Woo Y, Kim T-W. Orthodontic Miniscrew Implants: Clinical Applications. St. Louis:Mosby; 2008. 19. Nanda R, Uribe FA. Temporary Anchorage Devices in Orthodontics. St. Louis:Mosby; 2008. 20. Wilmes B, Su Y-Y, Sadigh L, Drescher D. Pre-drilling force and insertion torques during orthodontic mini-implant insertion in relation to root contact. J Orofac Orthop. 2008 Jan;69(1):51–8. 21. Heidemann W, Gerlach KL, Grobel K-H, Kollner H-G. Drill free screws: A new form of osteosynthesis screw. J Craniomaxillofac Surg. 1998;26(3):163–8. 64 22. Bartschi NJ. Insertion torque and fracture characteristics of orthodontic miniscrew implants [MS thesis]. St. Louis:Saint Louis University; 2011. 23. Shah, A. P. Effect of miniscrew characteristics (length and outer diameter) and bone properties (cortical thickness) on insertion torque and pullout strength [MS thesis]. St. Louis:Saint Louis University; 2011. 24. Wilmes B, Rademacher C, Olthoff G, Drescher D. Parameters affecting primary stability of orthodontic mini-implants. J Orofac Orthop. 2006 May;67(3):162–74. 25. Wilmes B, Ottenstreuer S, Su Y-Y, Drescher D. Impact of implant design on primary stability of orthodontic miniimplants. J Orofac Orthop. 2008 Jan;69(1):42–50. 26. Florvaag B, Kneuertz P, Lazar F, Koebke J, Zöller JE, Braumann B, et al. Biomechanical properties of orthodontic miniscrews. An in-vitro study. Journal Orofac Orthop. 2010 Feb;71(1):53–67. 27. Barros SE, Janson G, Chiqueto K, Garib DG, Janson M. Effect of mini-implant diameter on fracture risk and self-drilling efficacy. Am J Orthod Dentofacial Orthop. 2011 Oct;140:e181– 92. 28. Kim J-W, Baek S-H, Kim T-W, Chang Y-I. Comparison of stability between cylindrical and conical type mini-implants. Mechanical and histological properties. Angle Orthod. 2008 Jul;78(4):692–8. 29. Wilmes B, Drescher D. Impact of bone quality, implant type, and implantation site preparation on insertion torques of mini-implants used for orthodontic anchorage. Int J Oral Maxillofac Surg. 2011 Jul;40(7):697–703. 30. Kravitz ND, Kusnoto B. Risks and complications of orthodontic miniscrews. Am J Orthod Dentofacial Orthop. 2007 Apr;131(Suppl):S43–51. 31. Wilmes B, Panayotidis A, Drescher D. Fracture resistance of orthodontic mini-implants: A biomechanical in vitro study. Eur J Orthod. 2011 Aug;33(4):396–401. 32. Wawrzinek C, Sommer T, Fischer-Brandies H. Microdamage in cortical bone due to the overtightening of orthodontic microscrews. Journal Orofac Orthop. 2008 Mar;69(2):121–34. 65 33. Motoyoshi M, Hirabayashi M, Uemura M, Shimizu N. Recommended placement torque when tightening an orthodontic mini-implant. Clin Oral Implants Res. 2006 Feb;17(1):109–14. 34. Chaddad K, Ferreira AFH, Geurs N, Reddy MS. Influence of surface characteristics on survival rates of mini-implants. Angle Orthod. 2008 Jan;78(1):107–13. 35. Suzuki EY, Suzuki B. Placement and removal torque values of orthodontic miniscrew implants. Am J Orthod Dentofacial Orthop. 2011;139(5):669–78. 36. Ansell RH, Scales JT. A study of some factors which affect the strength of screws and their insertion and holding power in bone. J Biomech. 1968 Dec;1(4):279–302. 37. Sowden D, Schmitz JP. AO self-drilling and self-tapping screws in rat calvarial bone: An ultrastructural study of the implant interface. J Oral Maxillofac Surg. 2002 Mar;60(3):294–9. 38. Kuhn A, Mc Iff T, Cordey J, Baumgart FW, Rahn BA. Bone deformation by thread-cutting and thread-forming cortex screws. Injury. 1995;26(Suppl):12–20. 66 Vita Auctoris Michael Berry McEwan was born February 28th, 1980 in Provo, UT to Robert and Sandra McEwan. He grew up in Henderson, IL and graduated from Galesburg High School in 1998. He attended Brigham Young University from 1998-1999. He interrupted his education to spend two years serving a religious mission for The Church of Jesus Christ of Latter-day Saints in Mexico from 19992001. Afterward, he resumed his studies at Brigham Young University where he received a Bachelor of Science in Food Science in 2004. From 2005 to 2009 he attended the University of Iowa College of Dentistry, where he received his Doctorate of Dental Surgery in 2009. It is anticipated that Michael will graduate from Saint Louis University’s Center for Advanced Dental Education in January 2012 with a certificate of specialty in orthodontics and a Master of Science in Dentistry (Research). Dr. McEwan married Lea Janine McEwan in 2004 and they are the proud parents of Mazy and Evey. Upon graduation, Dr. McEwan will enter private orthodontic practice in Colorado. 67