OPTIMIZATION OF DRILL DESIGN AND COOLANT SYSTEMS DURING DENTAL IMPLANT SURGERY

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1 University of Kentucky UKnowlege University of Kentucky Master's Theses Grauate School 4 OPTIMIZATION OF DRILL DESIGN AND COOLANT SYSTEMS DURING DENTAL IMPLANT SURGERY Varahalaraju Kaliini University of Kentucky, vkali@uky.eu Recommene Citation Kaliini, Varahalaraju, "OPTIMIZATION OF DRILL DESIGN AND COOLANT SYSTEMS DURING DENTAL IMPLANT SURGERY" (4). University of Kentucky Master's Theses. Paper This Thesis is brought to you for free an open access by the Grauate School at UKnowlege. It has been accepte for inclusion in University of Kentucky Master's Theses by an authorize aministrator of UKnowlege. For more information, please contact UKnowlege@lsv.uky.eu.

2 ABSTRACT OF THESIS OPTIMIZATION OF DRILL DESIGN AND COOLANT SYSTEMS DURING DENTAL IMPLANT SURGERY Dental implants are an effective alternative for the replacement of missing teeth. The success of the implant epens on how well a bone heals aroun the implant, a process known as osseointegration. However, excessive heat generate uring the bone rilling will cause cell eath an may prevent osseointegration of the implant, resulting in early failure. There are many factors which contribute to the heat generation uring rilling. Experiments were carrie out to investigate the affect of variable rilling factors on heat generation uring rilling operation. Natural bone is not an ieal material for such research, as it varies wiely in ensity an other parameters of interest.. It woul be esirable to have a more uniform an consistent material to use in such stuies. However, such a material must be similar to bone to allow the results to be extrapolate to the clinical situation. The current stuy escribes an valiates a moel for use in such stuies. Polymethylmethacrylate (PMMA) is the material chosen for our stuies. A theoretical moel was evelope to stuy the effect of ifferent rilling parameters on temperature rise uring rilling operations. Comparison of observe results obtaine from experiments was mae with the results from theoretical stuy. Comparison of results for PMMA an human bone are also shown explaining how PMMA material can be substitute for human bone. The results suggest that the PMMA moel is an acceptable surrogate for bone in such stuies. Keywors: Dental implants, PMMA, Human bone, Heat generation, Drilling parameters, Coolant system. Copyright Varahalaraju Kaliini 4 Varahalaraju Kaliini Date: /4/4

3 OPTIMIZATION OF DRILL DESIGN AND COOLANT SYSTEMS DURING DENTAL IMPLANT SURGERY By Varahalaraju Kaliini Dr. Kozo Saito (Director of Thesis) Dr. George Huang (Director of Grauate Stuies) Date: /4/4

4 RULES FOR THE USE OF THESIS Unpublishe thesis submitte for the Master s egree an eposite in the University of Kentucky Library are as a rule open for inspection, but are to be use only with ue regar to the rights of the authors. Bibliographical references may be note, but quotations or summaries of parts may be publishe only with the permission of the author, an with the usual scholarly acknowlegements. Extensive copying or publication of the thesis in whole or in part also requires the consent of the Dean of the Grauate School of the University of Kentucky.

5 THESIS Varahalaraju Kaliini The Grauate School University of Kentucky 4

6 OPTIMIZATION OF DRILL DESIGN AND COOLANT SYSTEMS DURING DENTAL IMPLANT SURGERY THESIS A thesis submitte in partial fulfillment of the requirements for the egree of Master of Science in the College of Engineering at the University of Kentucky By Varahalaraju Kaliini Lexington, Kentucky Director: Dr. Kozo Saito, (Professor of Mechanical Engineering) Lexington, Kentucky 4 Copyright Varahalaraju Kaliini 4

7 TO MY FAMILY AND FRIENDS.

8 ACKNOWLEDGMENTS The following thesis, while an iniviual work, benefite from the insights an irection of several people. I woul like to thank my Thesis Chair, Dr. Kozo Saito, for proviing an excellent opportunity to work uner his able guiance. In aition Dr. Mohamme I. Hassan an Dr. Abraham Salazar provie timely an instructive comments an evaluation at every stage of the thesis process, allowing me to complete this project on scheule. Next, I wish to thank the Thesis Committee: Dr. I.S. Jawahir an Dr. Mark V. Thomas. Each iniviual provie insights that guie an challenge my thinking, substantially improving the finishe prouct. This stuy was supporte, in part, by an R&D Excellence Grant from the Kentucky Science an Technology Council (KSEF ; PI: M.. Thomas; Co-I: K. Saito an I. Jawahir). In aition to the technical an instrumental assistance above, I receive equally important assistance from my family an friens. Finally, I woul like to thank my friens from the University of Kentucky College of Dentistry (Division of Perioontology), Drs. Aaron Carner, Neil Lemmerman, an the IAES group, with whom I've share an iscusse this project in several versions. I woul also like to thank Richar an other people from Center for manufacturing in University of Kentucky for helping me to carry out experiments. Their help, avice, an support have been vital throughout. iii

9 TABLE OF CONTENTS ACKNOWLEDGMENTS...iii LIST OF TABLES... vii LIST OF FIGURES...viii LIST OF FILES... ix CHAPTER :INTRODUCTION.... BACKGROUND.... DENTAL IMPLANT SURGERY..... Surgical Placement Uncovering the implant DENTAL IMPLANT FAILURES OBJECTIVES METHODOLOGY THESIS OVERVIEW... 6 CHAPTER :LITERATURE SURVEY BACKGROUND...8. FACTORS AFFECTING HEAT GENERATION Drilling Spee Drilling Status Drilling Depth Drill Design an Flute Geometry Irrigation Systems Drill Sharpness Miscellaneous Factors... CHAPTER 3:MATERIALS & METHODS... 3 iv

10 3. PMMA General Properties Comparison of thermal properties for Human bone an PMMA METHOD Positioning of thermocouples Experimental Setup Experimental Conitions Data Analysis... 9 CHAPTER 4:THEORETICAL EQUATION MODELING APPROACH Thermal Analysis Thermograph Image Assumptions DERIVATION EXPRESSION FOR HEAT FLUX... 8 CHAPTER 5:RESULTS & DISCUSSION EXPERIMENTAL RESULTS Drill spee Drilling epth Drill iameter External Coolant Drill fee rate Single step or Incremental rilling MODEL VALIDATION Comparison for PMMA an human bone Comparison of experimental &theoretical results for pmma Comparison for rilling parameters... 4 CHAPTER 6: SUMMARY AND CONCLUSIONS v

11 6. SUMMARY CONCLUSIONS FUTURE WORK APPENDIX REFERENCES VITA vi

12 LIST OF TABLES Table 3.: Comparison of properties for Bone an PMMA..4 Table 3.: Table of rilling parameters..9 Table 5. Values substitute for PMMA an Bone...4 vii

13 LIST OF FIGURES Figure.: Schematic of Dental Implant..... Figure.: Implants place insie Bone... 3 Figure.3: Root Form Implant... 4 Figure.:Structure of PMMA... 3 Figure 3.: Heat generation recore using infrare camera... 5 Figure 3.: Schematic of the experimental setup... 7 Figure 3.3: Experimental Setup... 7 Figure 3.5 Thermocouple reaings using mm rill at rpm an 6 mm epth... 9 Figure 4.: Thermal analysis on PMMA using ANSYS software... Figure 4.: Heat generation recore using infrare camera... Figure 5.:Temperatures at rilling spee of,8 an RPM Figure 5.: Temperatures measure at rilling epths of 8,,6 mm Figure 5.3: Temperatures measure with rills of,3.5an 4.3 mm iameter Figure 5.4:Temperatures measure when rilling with/without external coolant Figure 5.5: Temperatures measure at ifferent fee rates Figure 5.6: Temperatures when rille continuously & graually for 3.5 an 4.3 mm holes Figure 5.7 Comparison of Results for PMMA an Human bone... 4 Figure 5.8: Comparison of Results from moel an experiments for PMMA... 4 Figure 5.9: Comparisons for Drilling Depth... 4 Figure 5.: Comparison of results for Fee rates Figure 5.: Comparison of results for rill iameter viii

14 LIST OF FILES Kaliini.pf 7 KB ix

15 CHAPTER INTRODUCTION. BACKGROUND Despite significant progress in treatment an prevention of ental isease, many teeth are lost ue to isease an trauma. Life s simple pleasures can cause problems an pain for millions of people who suffer from permanent tooth loss. Men an women of all ages are self conscious about their entures, briges or missing tooth. Some have ifficulty speaking because their entures slip or click. For others, the irritation an pain cause by entures are constant reminers of the limitations they feel. Many are concerne about their appearance an may feel that their tooth loss has age them before their time. Some regularly ecline invitations to social events because they are unwilling to face the uncertainties of eating, speaking an laughing in public. A number of options exist for the replacement of missing teeth. The most recent of these is ental implant. Moern ental implants are the treatment of choice for the replacement of missing teeth. Dental implants offer an excellent alternative to the limitations of conventional entures, briges an missing teeth. Dental implants are changing the way people live, they are reiscovering the comfort an confience to eat, speak, laugh an enjoy life. National surveys have ocumente the increase interest in ental implants on the part of patients an the ental profession. One recent survey reporte that [3]: Dental implant use has nearly triple since 986 an is expecte to continue to rise rapily. People of all ages are turning to ental implants to replace a single tooth, several teeth or a full set of entures. Leaing reasons cite for choosing ental implants are: To restore normal eating an speaking abilities. To enhance facial appearance an confience. To increase enture retention.

16 Accoring to the survey, the reasons for the increase eman are: Growing public awareness of the significant functional an esthetic avantages of ental implants over conventional entures an briges. The availability of ata on the long-term success of ental implants. Dental implants are a great option for patients missing natural teeth, because they act as a secure anchor for artificial replacement teeth an eliminate the instability associate with surface ahesives an removable briges. Natural teeth absorb biting pressure of up to 54 Psi [3]. Longtime enture-wearers can often absorb no more than 5 Psi. Dental implants, when properly place, can withstan 45 Psi of biting pressure. Dental implants are mae of materials that are compatible with human bone an tissue.. DENTAL IMPLANT SURGERY Dental implant surgery, where the entist implants a metallic tooth-root in the bone of human jaw an allows the bone to heal on it for a reasonable perio of time until the bone an the metallic root union is strong enough to support a prosthetic tooth crown. The implant root is mae out of titanium, a metal that is very well tolerate by the human boy. Figure.: Schematic of Dental Implant

17 Dental implant surgery takes place in two stages: ) Surgical placement an ) Uncovering the implant... Surgical Placement A hole is being rille into the bone where the implant is suppose to be place. An implant is screwe or tappe into the surgically prepare site. The gum tissue is close over the implant. After this stage has been complete, an average time between 3 to 6 months is given to allow the bone to heal aroun implant. The suitable time epens upon the bone of the patient. For the first three to six months following surgery, the implants are beneath the surface of the gums, graually boning with the jawbone. During this time, the patient shoul be wearing temporary entures an eat a soft iet. While the implants are boning with the jawbone, new replacement teeth are fashione by entist. The replacement teeth must clip onto the implants, fit securely in the mouth an withstan the ay-to-ay movement an pressure create by chewing an speaking. Figure.: Implants place insie Bone Most currently use ental implants consist of a root-shape portion that is anchore to the bone. Various types of ental restorations (e.g., single crowns, briges, an even complete over entures) can be attache to the root-form implant. The surgical placement of the implant involves preparing a hole in the jaw that correspons in size an shape to the implant. This is known as the osteotomy site. The implant is then threae into the hole (in a manner somewhat similar to woo screw) or is a tight press-fit. Over a perio of time, bone becomes eposite on the implant surface, a phenomenon known as Osseo integration. While the nature of this interface has not been fully eluciate, it is robust. Many stuies have shown implants to be a 3

18 preictable metho of tooth replacement, often achieving successful 5-year survival rates exceeing 95%. Figure.3: Root Form Implant.. Uncovering the implant Once the implants have bone to the jawbone, the secon phase of the proceure begins. At this time, the oral an maxillofacial surgeon uncovers the implants an attaches small posts, which will act as anchors for the artificial teeth. The posts protrue through the gum line but are not visible when artificial teeth are attache..3 DENTAL IMPLANT FAILURES Implants o sometimes fail in service. This may occur ue to a failure to be Osseo integrate (early failure) or uring later service (elaye failure). Early failure is often a result of problems uring osteotomy site preparation. One such problem is overheating the bone uring the rilling process. When the mechanize cutting tools such as saws an rills are use, heat is prouce which raises the temperature of both the tool an the material being cut. In orthopeic an ental practices, high-spee tools are applie to bone, an heat from these operations may result in thermal necrosis [,]. Since thermal necrosis has a negative impact on the outcome of a rilling proceure, bone temperature must be kept below the threshol temperature that results in necrosis. As for the thermal properties of the bone, it is important to note that the relative water content (about 35%), as well as flui movement within the living bone tissue (i.e. bloo an lymph) is significant variables in the ability of bone to withstan thermal amage. Accoringly, 4

19 in thermal conuctivity stuies using living oxen bone tissue, Vacheon et al 967 [4]. For ry versus living oxen bone, the values reporte for thermal conuctivity were.45 * -3 an 5.45 * -3 cal/cm-sec respectively. Bone is a poor conuctor of heat, with thermal conuctivity of fresh cortical bone in the region of J/msK. It has been ocumente that bone cell eath may occur when bone is heate over 47 C [,5]. In the absence of irrigation, bone temperatures may excee C. This may result in a failure of bone to bon to the implant, leaing to early failure. Implant therapy involves some expense an inconvenience to the patient. It is important to improve outcomes an minimizing treatment failures. Given the eleterious effect of heat on bone viability, one strategy for optimizing implant outcomes may be reuction of heat uring osteotomy site instrumentation. This strategy is likely to fin application in other isciplines such as orthopeic an plastic surgery. Various strategies have been employe to reuce heat generation uring implant site preparation, incluing variations in rill esign an coolant elivery. There are many factors that contribute to heat generation uring the rilling operation. However, there is lack of unanimity regaring the optimal combination of rill esign features an coolant elivery an there is relatively little in the implant literature on these topics. The factors can be liste as : ) Drilling spee ) Drill fee 3) Drilling status (continuous or grauate rilling) 4) Drilling epth 5) Drill esign 6) Irrigation (coolant elivery) systems 7) Drill Sharpness 8) Miscellaneous Factors. To check how these factors affect heat generation we carry out a series of experiments uner ifferent conitions. This nees large number of human bone samples, which is a big problem in obtaining. So we looke for an alternative material that can be easily available which is similar to that of a bone in properties an functioning. The material we are consiering here is polymethylmethacrylate (PMMA). 5

20 .4 OBJECTIVES The Primary objective of this research stuy is to reuce the amount of heat generate uring the Osseo integration process an create a thermal moel that can explain how the temperature increases uring rilling process. The main objectives of this thesis can be liste as follows: ) Stuy the effect of ifferent rilling operation parameters on temperature rise uring rilling process on PMMA (as replacement to human bone) by conucting series of experiments. ) Create a thermal moel that can escribe the temperature increase as function of variable rilling parameters. 3) Valiate the thermal moel by comparing its results with the experimental results an explain how it can be interpolate for human bone. 4) To come out with optimal rilling conitions that can help ental surgeons in reucing ental implant failures..5 METHODOLOGY To obtain the objectives liste this stuy is being carrie out in three stages:. Formulating a theoretical moel that can help in explaining the temperature rise uring rilling process.. Carry out series of experiments varying ifferent rilling parameters an check how these factors are going to affect temperature rise. These experiments are performe on PMMA 3. Compare the experimental results with theoretical results to valiate the thermal moel evelope for this case..6 THESIS OVERVIEW Chapter gives the etaile back groun on reasons for ental implant failures. It also explains how previous researchers iffere in their finings about the affect of variable rilling conitions on temperature increase uring the rilling process for placing implants. Chapter 3 explains about the materials an metho use for carrying out experiments. It explains in etail why polymethylmethacrylate(pmma) being consiere instea of human bone for experiments. It also inclues etaile escription of the experimental setup use for experiments an explains t why this setup is being use. Chapter 4 explains moeling approach use for eriving the 6

21 thermal moel to preict temperature rise as a function of rilling parameters. It also inclues in etail the erivation for that equation an nomenclature use. Results obtaine uring experimental stuy are iscusse in chapter 5. Comparisons of results obtaine from thermal moel an experiments are compare in this chapter. Chapter 6 summarizes the whole stuy an results obtaine an also explain about how the future work can be one in this fiel. Copyright Varahalaraju Kaliini 4 7

22 CHAPTER LITERATURE SURVEY. BACKGROUND Dental implant surgery process involves rilling a hole insie the bone. This rilling operation causes heat generation ue to the friction between the rill an bone. Majority of heat generate uring this process is absorbe by rill but bone also absorbs significant amount of heat insie it. Heat absorbe by human bone causes the temperature to rise insie it. The negative affect of heat on bone results in the enaturation of the enzymatic an membrane proteins, hyperemia, necrosis, fibrosis, ecrease osteoclastic an osteoblastic activity, ehyration, an esiccation, which may all contribute to cell eath [5, 6, 7, 8, 9 ]. Historically, temperatures anywhere from 56 o C to 7 o C have been eeme responsible for the enaturation [,]. However, in a lanmark stuy by Eriksson an Albrektsson [,3,4], it was etermine that the critical temperature of bone is in the range of 44 o C to 47 o C. They foun that the threshol temperature for heat inuce bone injury is 47 o C for minute. A temperature of more than 47 o C was shown to result in bone restoration an fat-cell egeneration. Heating the bone to temperatures lower than 47 o C i not seem to affect the bone tissue on the microscopic level, but vascular injury, as seen with increase capillary injury, was seen by others to occur at lower temperatures [5]. As a result of Eriksson an Albrektsson s stuy, the critical temperature is wiely believe to be 47 o C. However, it must be observe that this experiment i not involve rilling of the bone but merely heating the saline solution to a esire temperature, which was in irect contact to the bone.. FACTORS AFFECTING HEAT GENERATION There are many factors that affect the heat generation uring the rilling process. After a etaile literature survey, the factors that can affect temperature raise uring rilling process can be liste as follows: ) Drilling Spee ) Drilling Status (single step or incremental rilling) 3) Drilling Depth 4) Drill Diameter 8

23 5) Irrigation (coolant elivery) systems 6) Drill Sharpness 7) Miscellaneous factors. In this section we escribe how ifferent factors affect the heat generation uring bone rilling. The etails given below are collecte from the results obtaine by ifferent researchers, which are been collecte as part of the literature survey that has been one regaring the project... Drilling Spee There are many varying results from ifferent researchers about the optimal spee for ental implant surgery. Thompson an Pallan,[7,8] measure in vivo the temperature rise in bone increase with rill spee, from 5 rpm to rpm. Eriksson has shown that using high torque an low rpm (5-) are ieal to avoi temperature rise an to increase rilling accuracy. Matthews an Hirsch, [6] however i not fin any significant change in temperature rise with spee (35 to 9 rpm) while rilling in human caaveric femora. Vaughn an Peyton foun that the temperature rise increase with rill spee (from 55 rpm to,3 rpm). In the more recent stuies, Abouzgia an James [9] foun that the maximum temperature rise ecrease with spee, for free running spees from 7, rpm to 97, rpm. Except for the stuy by Matthews an Hirsch [6], there seems to be general agreement that the temperature rise increases with rill spee up to approximately, rpm. Results from the majority of histological stuies an from the temperature measurements from Abouzgia an James [9] appear to inicate that lower temperatures are generate at very high rill spees... Drilling Status Drilling to wien the site to exact iameter of the future implant can be performe either one step or graually. In continuous or one step rilling the hole is being rille in a single step using a single rilling tool. In incremental or multi-step rilling the iameter is increase graually starting from the minimum to the final iameter using a series of rilling tools. Eriksson [] has escribe a single step technique while Branemark [] has recommene an incremental enlargement of the osteotomy site. Branemark s[] hypothesis on the incremental rilling sequence was that each rill bit graually enlarges the osteotomy site, which woul help issipate heat better than a one-stage rill sequence. In a later stuy, Eriksson i an in vivo stuy in which animals an humans are subjecte to either incremental or one- 9

24 stage osteotomy preparation. In this stuy, Eriksson foun that the incremental rilling is better on reucing heat prouction compare to single rilling...3 Drilling Depth Depth of the recipient site is usually etermine by several factors. Corioli an Majzoub [] reporte a significant increase in temperature at epths of 8 mm versus 4 mm, regarless of the iameter of the rill use. However, Tehemar [3] believes that the implant epth may not be as important as having irrigation at the apical extent of the rill that woul thus ecrease heat prouction...4 Drill Design an Flute Geometry Root-form implants vary consierably in esign for biologic an mechanical reasons. Because the en result of the rilling cascae has to be a recipient bony be of the same iameter an shape of the propose implant, the rills usually follow the morphologic an topographic skeleton of the implant. With the great variety of ental systems commercially available, comparison between the ifferent esigns an shapes of rills seems to be impossible. In general, twist rills an taps are use to prepare sites for screw-shape implants, an triflute rills are use to prepare sites for cylinrical implants. Investigations performe on animals an human bone have emonstrate that flute geometry an rill esign contribute to the temperature rise uring rilling. Corioli an Majzoub [] compare the ifferent types of rills on heat generate in bovine bone blocks. They reporte that a triflute rill 4 mm in iameter generate less heat than an 3 mm twist rills an a 3.3 mm triflute rill regarless of the cavity epth. They also foun out that temperature took longer to return to baseline using a smaller iameter rill versus a large iameter rill. However Tehemar [3] believes the opposite. He believes that the wier iameter burs take less bone than the smaller iameter rills which results in wier iameter rills proucing less heat...5 Irrigation Systems In an effort to increase heat issipation uring ental implant rilling an thus, ecrease bone temperature, implant systems have began to use irrigation systems with coolants. There are two types of cooling: internal an external. If one oes not use any coolant, then the critical bone temperature is always exceee. Kirschner an Meyer [4] introuce internally coole rills to entistry. They hypothesize that since the coolant entere closer to the tip of the rill, it woul

25 create a combine rinsing an cooling effect on the bone, which woul surpass the externally coole rill or a rill with no coolant at all. Huhule [5] was the first to propose the internal irrigation system which he believe woul help prevent bone clogging of the implant rill an that its efficacy woul be continuous because all epths of the osteotomy preparation coul be reache with the coolant. Despite the promising results reporte using internal irrigation systems, this issue requires further stuy. The only report present in the literature is that of Haier [6] et al. In their histological an histochemical stuy, this group emonstrate that aitional external cooling seeme to be beneficial for any internal system, particularly in compact bone. Thus, it appears that irrigation is a key implant in implant osteotomy preparation an is worthy of more investigation...6 Drill Sharpness The conition of rill plays a role in regulating the temperature of bone uring rilling. There are many factors that reuce the sharpness of a rill, ensity of bone, use of the rill, the ebris release uring the process, material construction & surface treatment of rill. A worn rill will thus have more heat prouction than a sharper rill. Previous analysis using scanning electron microscopy reveale tangible wear on the cutting eges of trephine rills after to 8 milling proceures. Although the number of sites to be prepare before rill change is usually suggeste by some manufacturers, visual examination or the observation of when the rill fails to progress rapily, frequently inicate the nee for a new rill...7 Miscellaneous Factors The temperature prouce also epens on many factors like rilling time, age of the patient, ensity of the bone, texture of the bone etc. it has been well ocumente that oler patients, certain physiological changes occur. Bony structures ten to become enser an more fragile, the meullary cavity space enlarges faster resulting in a net ecrease of cortical thickness an mass, an healing capability is usually impaire. Although some features of bone have been evaluate in terms of heat, the effect of heat in relation to age has not been stuie. Bone usually varies in ensity from person to person, bone to bone in the skeleton, an from site to site in the same bone. Regaring the effect of ensity on the temperature generate,

26 Yacker an Klein[9] reporte that bone ensity is a far greater inicator of bur temperature than epth of the osteotomy. However, further stuies are necessary to resolve this issue. Time can be consiere as the time of rilling, or the time require for the heate part to return to its normal temperature. The time taken for rilling is irectly proportional to the amount of heat generate uring rilling. Results show that heating bone at 47 C for 5 minutes results in % resumption of original over 3 ays. The ieal fastest time for rilling from the previous results was obtaine as 4 rpm with.4 kg of pressure to rill 7 mm hole with least temperature rise. During the literature survey we fin that there has been ivergence in the opinion between the ifferent researchers regaring how ifferent factors affect the heat generation. More over majority of the observations which are liste above are being observe from an in vitro stuy. But the in vivo situation is ifferent compare to that from in vitro ue to the effects of ambient boy temperature, heat transfer via boily fluis, etc in orer to obtain accurate results we nee to inclue all the factors an the observations must be one in real time. Copyright Varahalaraju Kaliini 4

27 CHAPTER 3 MATERIALS & METHODS To check how ifferent factors as liste in previous chapter affect heat generation, series of experiments are planne uner variable rilling conitions. This nees large number of consistent human bone samples. Since human bone iffer in its ensity an shape epening upon gener, age an other factors, it is extremely ifficult to obtain consistent quality human bone samples. This resulte in looking for an alternative material that can be easily available with consistent quality an similar to that of a human bone in properties an functioning. The material that is being consiere here is poly methyl Methacrylate (PMMA). 3. PMMA Polymethylmethacrylate or acrylic bone cement is the most commonly use non-metallic implant material in orthopeics. PMMA is one of the earliest polymers an is well known aroun the worl by a variety of trae names Lucite, Oroglas, Perspex an Plexiglas, which vary with the country you are in. PMMA (Polymethyl methacrylate) was first iscovere in Germany in 9 by the chemist O. Röhm an was patente in 98. The first meical use of PMMA was in 936 as ental prostheses. The original PMMA was seen as a replacement for glass in a variety of applications an is currently use extensively in glazing applications. The material is one of the harest polymers, rigi, glass-clear with glossy finish an goo weather resistance. PMMA is a member of a family of polymers which chemists call acrylates, but the rest of the worl calls acrylics. PMMA is a vinyl polymer, mae by free raical vinyl polymerization from the monomer methyl methacrylate. Figure.:Structure of PMMA 3

28 PMMA has become essential ingreient in making entures. In mi 95s charnley [3] first introuce a self-curing PMMA to orthopeic surgery. He successfully fixe both the femoral an actebular components in a total hip replacement using PMMA, an with more pioneering efforts, Charnley an his group, revolutionize reconstructive surgery of the hip an other joints as well. Toay most total joint replacement surgery, incluing hip, knee, an ankle, use acrylic bone cement as fixation of the prosthesis to the bone. Bone cement is also often use in the fixation of pathological features, an it has also been utilize in the repair of bone efects. Acrylic bone cement is still utilize as ental cement ue to its low water absorption, nontoxicity, imensional stability, an ease of forming. 3.. General Properties PMMA is a glassy polymer with an amorphous structure. It has a ensity of.9 g/cm3 an has very low water absorption. The refractive inex ranges from.49 to.5 epening on the type. Parts mae of PMMA have high mechanical strength an goo imensional stability. Other properties inclue a high Young's moulus an goo harness with low elongation at break. PMMA oes not shatter on rupture. PMMA is one of the harest thermoplastics an is also highly scratch resistant. 3.. Comparison of thermal properties for Human bone an PMMA PMMA has similar thermal properties compare to the human bone. Properties of both the bone an PMMA can be seen in the following table [3]: Table 3.: Comparison of properties for Bone an PMMA Properties Bone PMMA Thermal conuctivity (W/m K) Specific heat (J/Kg K) 3 4 Thermal iffusivity (m/sec).3*-6.*-6 Density (Kg/m3) 8 4 4

29 3. METHOD To check the effect of variable rilling factors on the temperature rise uring rilling operations series of experiments are planne. Experiments are being carrie out on Drilling machine (HAAS VFOE HP) in CMS (Center for Manufacturing Systems) machine shop at the University of Kentucky. PMMA specimens of 5cm iameter an cm thickness are prepare to perform the experiments. 3.. Positioning of thermocouples The thermocouples locations are chosen base on the images obtaine from infrare thermograph camera uring rilling operation. Images from the infrare thermograph helpe in etermining the isothermal lines istribution aroun the rille hole, as shown in the figure 3.. Figure 3.: Heat generation recore using infrare camera The isothermal lines showe that heat is raially conucte from the rille hole. The images are taken by FLIR IR camera, which has a wavelength ector of 7.5-3µ m. From the table temperatures recore at ifferent positions uring rilling process can be observe. Maximum temperature obtaine uring the rilling process is of main concern. Tip of the 5

30 thermocouples shoul be place where it can recor accurately the maximum temperature absorbe by the specimen uring the rilling process an shoul be careful that thermocouples oes not touch the rill uring the rilling operation. Higher temperatures recore at SPO an SP positions correspons to the temperature absorbe by the rill. SPO3 is the position where the thermocouples can be place to recor maximum temperatures obtaine to the rilling process without any amage to it. Locations for placing thermocouples are calculate using Aobe Photoshop software. To recor the maximum temperatures that are prouce uring rilling, Thermocouple shoul be place at a istance of 6 mm from the top an 6 mm away from the center an Thermocouple is to be place 6 mm below the first one but at the same istance from the center. 3.. Experimental Setup Experimental setup for carrying out these experiments inclue two type K thermocouples for recoring temperatures, Data acquisition equipment for retrieving ata from thermocouples, rilling machine an a PMMA specimen. Two holes are rille into the PMMA specimen for placing thermocouples. These holes are rille in such a way that thermocouples can be inserte easily into the specimen an can reach the exact positions they are suppose to be. These holes are being rille using.9 mm iameter rills. Type K thermocouples (Omega) are use for recoring the temperature rise uring the rilling operation. These thermocouples are connecte to ata acquisition equipment (Data Acquisition System: IO Tech DaqBook/6, 4 channels). This ata acquisition system acquires temperature ata uring the rilling process by the rate of temperatures samples/secon. Data acquisition system is irectly connecte to a laptop, which transfers the ata irectly to Microsoft Excel sheet. Data recoring from thermocouples will be starte an stoppe by manual trigger. For a specific rilling conition, experiments are carrie out on three specimens. Average value of the maximum temperatures obtaine for three ientical specimens uner the same ientical conitions will be taken an that value will be recore as the temperature obtaine for that specific rilling conition. Experiments will be repeate for variable rilling conitions. 6

31 The schematic of experimental setup can be seen from the following figure: Figure 3.: Schematic of the experimental setup Specimen Computer Thermocouple Figure 3.3: Experimental Setup Data Acquisition Equipment 7

32 Figure 3.3 shows thermocouples inserte in the specimen being connecte to the ata acquisition equipment, which in turn is connecte to the computer that collects the ata. Each PMMA specimen is use for performing two experiments. The following figure shows a PMMA specimen that is being use for two series of experiments. We can also observe the holes rille for placing thermocouples. Figure 3.4: PMMA Specimen rille at 3 RPM with 3.5 mm iameter rill 3..3 Experimental Conitions Series of experiments are going to be performe using the above experimental setup to check how ifferent rilling parameters affect temperature. To check each parameter for a rilling conition other rilling conitions an parameters are maintaine constant. Experiments are performe at a stanar conition of RPM, 6 mm epth, using a mm iameter rill an at a fee rate of.58 m/sec. To check a certain conition, i.e. rilling spee, spee is varie from RPM to 8 RPM an then to RPM, other conitions are maintaine same (i.e. epth, iameter an fee rate). Again for every parameter of a certain conition experiments are carrie out on three PMMA specimens. Table 3. shows the list of parameters an conitions uner which rilling operations are going to be performe. Along with these 8

33 parameters, experiments are also carrie out to check how external coolant an incremental rilling proceures affect the temperature change uring rilling operations. Table 3.: Table of rilling parameters CONDITIONS PARAMETERS Drilling Spee (R.P.M), 8, Drilling Depth (mm) 8,, 6 Drill Bit Diameter (mm)., 3.5, 4.3 Drill Fee Rate (m/sec).58,.6, Data Analysis Data Acquisition equipment (IO Tech DaqBook/6) is use to recor temperatures generate uring rilling process. It recors ten temperature samples for every secon an it is connecte irectly to laptop, which allows the ata to be stores in Microsoft Excel software. Following two graphs show the temperatures recore by thermocouples: 6 5 Temperature (in O C) 4 3 Thermocouple Thermocouple Time (in Secons) Figure 3.5 Thermocouple reaings using mm rill at rpm an 6 mm epth 9

34 6 5 Temperature (in O C) 4 3 Thermocouple Thermocouple Time (in Secons) Figure 3.6: Thermocouple reaings using mm rill at rpm an mm epth During the ata analysis, maximum temperatures obtaine uring a rilling operation is of much importance as the main goal of this stuy is to see how these maximum temperatures can be reuce. For every rilling parameter, experiments are performe on three specimens. Average of the maximum temperatures obtaine by rilling three specimens is taken as the maximum temperature obtaine for that rilling parameter. These results are been tabulate an were iscusse in chapter 5. Copyright Varahalaraju Kaliini 4

35 CHAPTER 4 THEORETICAL EQUATION 4. MODELING APPROACH In orer to buil a preictive moel for the temperature an heat flux in the current problem, a global pattern for the heat istribution must be etermine. The preictive moel will help entists to scale the temperature profiles an the amount of heat flux entering into the human bone uring rilling operation. Therefore, proper rilling parameters can be chosen. Finite element analysis is carrie out on PMMA moel an also thermograph images are taken using infrare camera process to check how heat spreas out uring rilling process for formulating a theoretical moel. 4.. Thermal Analysis Thermal analysis is carrie out using finite element analysis software ANSYS. To carry out thermal analysis, a symmetric moel of PMMA cyliner similar to that of specimen use for experiments is esigne. Thermal an physical properties are substitute for this moel an steay state thermal analysis is carrie out on PMMA. Figure 4.: Thermal analysis on PMMA using ANSYS software

36 Results from thermal analysis shows that the heat generate uring the rilling process spreas out in raial irection across the moel. 4.. Thermograph Image Thermograph images of the rilling process are being taken using infrare camera as explaine in chapter 3. Figure 4. is one of the pictures that have been taken using infrare camera. Observations mae from this picture also confirm that heat generate uring rilling process spreas in raial irection. Figure 4.: Heat generation recore using infrare camera 4..3 Assumptions Observations from thermograph images an thermal analysis help us in eveloping one of the main assumptions for our moel, i.e. heat spreas insie the boy in raial irection. Thermal conuctivity of the material is small, which helps us in assuming the boy to be a semiinfinite soli. Following assumptions are use for builing the preictive moel: Heat istribution in the boy is in a raial irection.

37 Boy is consiere to be semi-infinite soli. 4. DERIVATION Drilling proceure insie PMMA cyliner increase temperature. There are many rilling factors like rill spee, epth of the rilling, rill iameter an others, which affect the temperature increase. In this section an equation is erive to preict the temperature rise as the function of these rilling parameters. Equation is being erive base upon the above assumptions. Consier the homogenous ifferential equation of heat conuction in the cylinrical coorination system, T r T T + = r r α t For a r < (4.) Where temperature T is a function of raius r an time t. α is the thermal iffusivity of the material. Bounary conitions are as follows: T q At r = a, = q is the constant heat flux being generate. (4..) r k At T r =, = r we assume heat flux is zero at infinite bounary. (4..) Initial conition: For t =, T = TR T R is the room temperature. (4..3) We efine imensionless parameters to convert non-homogenous bounary conitions into homogenous bounary conitions as follows: T T R θ = T = θ Tc + TR (4..) Tc r η = r =ηrc (4..) r c t = FO = t = tc. (4..3) t c 3

38 Where θ is the imensionless temperature, η is the imensionless raius, is the imensionless time an F O is Fourier number, r c is raius of the rill, t c is the time at which we k k start rilling an we efine Tc = =. qr qa c After substituting the imensionless parameters in Equation (4.) we get the following ifferential equation: θ θ θ + = η η η For η < (4.3) The bounary conitions are as follows: θ At η =, =. (4.3.) η θ At η, =. (4.3.) η At =, θ =. (4.3.3) η The equation (4.3) is epenant on both η an. To solve the problem let us efine =. 4 (4.4) Differentiating (4.4) both with respect to η an we get: η η = η =. (4.4.) η η η = =. (4.4.) 4 4 Substituting the above in Equation (3.) we get θ θ θ + = η η η θ θ θ + = η η η η 4

39 5 θ η η θ η η η θ = + 4 θ η θ θ η 4 4 = + θ θ θ = + Diviing the above equation by we get, θ θ ϑ θ = + = + + θ θ. (4.5) The bounary conitions will be change as follows: As η θ η θ η θ η. 4 = = = = = = (4.5.) As η, = = θ η θ. (4.5.) At =,, = θ. (4.5.3) Let us efine y = θ then the equation (4.5) woul be as follows: = + + y y. (4.6) This equation is of the form: Q Py x y = + (4.7) The solution of the above equation is: + = Px Px Px C e x Qe e y. [33] Comparing the Equation(6) an Equation(7) we have., = + P = Q The solution woul be:

40 6 = + C e y = e C. Also,. θ = e C At bounary conition 4 = we have θ e C e C = = = θ e C =. Integrating on both sies we get, 4 C e C + = θ ν θ. Let us consier the following integral:. ) ( t t e x v v t t e x v t v x v t + Γ = [34] We nee e 4, comparing the above two equations we have 4.5, = = x v hence we get e e + = Γ ) (. (.5) 4 e + Γ = also here [ ] π 4 4 ) ( * * erf e =

41 7 ) ( π erf = Hence we get ). ( * (.5) 4 π erf e + = Γ ) ( * (.5) 4 π erf e = Γ. Hence we have the final equation as ( ) = Γ = π π θ *.775 ) ( erf e erf e Substituting back the value of from our previous assumptions, we get = ) t a ( * erf.775 e a t 4t a α π α θ α But we know that T T qa k k qa T T R R = + = θ θ ) (. Substituting this expression we get the final equation as follows: = ) t a ( * erf.775 e qa t k T T 4t a R α π α α (4.8) The above expression gives expression for temperature rise uring rilling process as a function of heat flux (q), thermal conuctivity (k), time taken for rilling (t), an thermal iffusivity (α ). Here we know the values of thermal conuctivity an thermal iffusivity of PMMA, an also the time taken for rilling process. We nee to etermine the value of heat flux (q) generate uring rilling process.

42 Amount of heat flux generate uring rilling process epens on many rilling parameters. In the next few steps I am going to explain in etail how the expression is erive for heat flux uring rilling process. 4.3 EXPRESSION FOR HEAT FLUX Energy involve in material removal is converte into heat. The heat generate is therefore well approximate by the amount of work one. Q = F S v S t where Q is the heat generate by the cutting action, t is time, the shear plane, vs is the shear velocity. [35] (4.9) F S is the shearing force in 4.3. Calculation of shear velocity The shear velocity v S is relate to cutting velocity v an shear angle φ as v v S = (4.) cosφ Shear angle φ is calculate using the Ernst-Merchant relationship, φ + β α = 9. Where α is rake angle of the cutting tool an the friction angle, β, is equal to.644 [37] An expression for α at a istance r from the rotational axis was evelope by Battacharya an Ham [38], as follows: [ ] cos( p) ( r / D) tanθ tan sin ( / r) sin( p) sin( p) tanα = (4.) where D is the rill iameter, is chisel ege iameter, θ is the helix angle, an p is the halfangle at the point. 8

43 The velocity v can be calculate as follows: πrn v = 6 where N is the rotational spee, in rpm. (4.) 4.3. Calculation of Shear Force The shear force, F, in the material being remove by the rill was calculate from S F S = A [36] (4.3) S S, Where S is the ultimate shear stress an A S is the area of the shear plane. Bone is viscoelastic material an one consequence is that the ultimate stress S varies with the shear rate. Tay et al. as : The expression for maximum shear rate γ in primary eformation zone is calculate by Here a can be calculate from following equation: where C= 6 from Tay et al [39]. v γ = (4.4) 4 a sin 3 [ ] ( φ ) tan( α ) + cot( φ ) = t 6C sin (4.5) a 4 t - uneforme chip thickness: ( φ )[ tan( α ) + cot( φ )]. f / t = sin( p), f is the fee rate of the rill.[4] (4.6) N / 6 The epenence of ultimate shear stress on shear rate was etermine for bone by combining the results of several stuies..6 S γ. [4] To fin the constant of proportionality, the results of saha were use..6 S = 8γ [4] (4.7) Substituting equation (4.4) an equation (4.5) in equation (4.7.) shear stress can be written as follows: 9

44 S = 8 4 6C sin 4 t v ( φ )[ tan( α ) + cot( φ )] sin ( φ )[ tan( α ) + cot( φ )] 3.6 The shear plane area, We know from Equation(3) vc = 8 t[ tan( α ) + cot( φ )].6 ( D ) ( 9 p) sin( p) (4.8) t = (4.9) cos AS F S = A S S Substituting Equation (4.8) an Equation (4.9) in Equation (4.3) we get the expression for shear force: = 8 t vc.6 FS [ tan( α ) + cot( φ )] cos t ( D ) ( 9 p) sin( p). The heat generate is given by the Equation(4.9) as follows: Q = F S v S t (4.) Substituting Equation (4.9) an Equation (4.9) in Equation (4.8) we get : Q = 8 t t vc [ tan( α ) + cot( φ )].6 t * cos ( D ) * v cos ( 9 p) sin( p) φ (4.) The heat generate by cutting conucts to the tool, the chip, an the work piece. Determining the fraction of heat that enters the work piece η is exceeingly ifficult to etermine from the funamentals of mechanics an heat conuction. Q w t Q = η [45] (4.) t 3

45 Substituting Equation(4.) in Equation(4..) we have: Q t w = η * 8 t vc [ tan( α ) + cot( φ )].6 t * cos ( D ) * v cos ( 9 p) sin( p) φ (4.3) Heat Flux Heat flux is calculate as follows: Where Q W t q = [44] (4.4) t π zr Q w - rate of heat generate by the rill that enters the work piece. t z Height of the element where the heat flux us applie. R raius of the rill/hole. t time. Substituting the Equation (4.3) in Equation(4.4) we get the final expression for heat flux: = η * 8 t vc.6 t * cos ( D ) v cos q * [ tan( α ) + cot( φ )] t ( 9 p) sin( p) φ π zr ( D ) ( 9 p) cosφ πn ft = η * 4 ( )( ) (4.5) 5 f sin p tanα + cotφ z* R* cos Equation 5 inclues rilling spee, rilling epth, rill iameter, fee rate an rill esign that can help us in explaining how ifferent rill factors affect temperature rise uring rilling operation FINAL EQUATION Substituting the expression for heat flux (4.5) in the equation (4.8) we get the final expression for temperature rise uring rilling process. The final expression is as follows: T = T R η * 4 5 f k sin tα e πn a 4tα.775 ( p)( tanα + cotφ ) π * erf (.6 a ) tα ft z* R* cos ( D ) ( 9 p) a cosφ (4.6) 3

46 4.5 NOMENCLATURE T R α k t N F z a η D Room temperature Thermal iffusivity of the material. Thermal conuctivity of the material. Time taken for rilling.(sec) Drill spee in R.P.M. Drill fee rate in m/sec. Height of the element where the heat flux is applie or Drilling Depth (m) Raius of the hole (m). Fraction of heat that enters the work piece. Drill iameter (m), Chisel ege iameter of the tool (m), θ p α Helix angle of the cutting tool, Half-angle at the point. Rake angle of the cutting tool. Copyright Varahalaraju Kaliini 4 3

47 CHAPTER 5 RESULTS & DISCUSSION This chapter is ivie into two main sections. In the first section, experimental results obtaine by rilling PMMA with ifferent rilling parameters are being presente. Experiments were carrie out to check how ifferent rilling parameters: spee, epth, bit iameter, fee rate, external coolant an also comparison between temperatures obtaine using single step rilling proceure an incremental rilling proceures were mae on PMMA. Comparisons of temperatures obtaine from theoretical moel an experiments were mae in the secon section of this chapter to valiate thermal moel evelope. Comparison of temperature profiles obtaine from theoretical moel is also mae between PMMA an human bone. 5. EXPERIMENTAL RESULTS This section inclues results obtaine from experiments an a brief iscussion about the results. Series of experiments were carrie out to check how variable rilling conitions woul affect the temperature increase. Number of PMMA samples has been prepare for testing. Experiments are carrie out on three similar PMMA samples for a particular rilling parameter, which is to be teste by having other rilling parameters constant. 5.. Drill spee To stuy the optimum rilling spee experiments are performe for three ifferent spees of, 8 an RPM, while the fee rate is kept constant at.58 m/sec, hole is being rille for 6 mm in epth an rill iameter is mm. Figure 5. shows the maximum temperatures obtaine at ifferent spees. As shown in the figure, increasing the rilling spee as expecte significantly increases temperature. This increase in temperature is ue to the fact that increase in cutting spee causes shear rate to increase which leas to increase in friction between the rill an the work piece. Increase in friction causes more heat generation uring the rilling process, which eventually leas to higher temperature insie the specimen. Plotte ata gives goo information for the entist to avoi the rilling spee that is leaing to temperature that causing gum inflammation. 33