- Email: [email protected]
A Comparison of Torque Forces Used to Apply Intermaxillary Fixation Screws
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
CRANIOMAXILLOFACIAL TRAUMA
A Comparison of Torque Forces Used to Apply Intermaxillary Fixation Screws Arjan Bins, DDS,* Jacques A. Baart, DDS,y Tymour Forouzanfar, DDS, MD, PhD,z and Jack J. W. A. van Loon, MSc, PhDx
Q8
Purpose:
When establishing intermaxillary fixation (IMF) using bone screws, fracture of a screw is a potential complication. This study was conducted to investigate the forces that arise at bone screw insertion and to determine safety margins between torque for manually tightened insertion and torque until breakage for 3 different IMF screw systems, which could ultimately favor the use of 1 IMF screw system based on decreased risk of complications.
Materials and Methods:
IMF screws were placed into porcine mandibles by 3 oral and maxillofacial surgeons. The porcine mandibles were evaluated for cortical thickness and suitable insertion sites by cone-beam computed tomography. Measurements of torque until failure were performed on predrilled aluminum plates by the primary author. A digital torque screwdriver measured 180 data points per second as continuous data and recorded the measurements.
Results:
Measurements indicated clear differences in torsion forces between manually tightened insertions and torque until breakage for all 3 IMF screw systems. No statistical difference in safety margins was found among the IMF screw systems.
Q2
Conclusions: Because no statistical differences in safety margins were found among the IMF screw systems, this study indicates that IMF screw selection should be based on other clinical factors, such as ease of use or economic factors. Future prospective studies are necessary to fully determine evidence-based criteria for IMF screw selection. Ó 2015 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg -:1-9, 2015
Intermaxillary fixation (IMF) screws are frequently used as a quick and easy alternative to arch bars in mandibular fracture treatment.1,2 Several manufacturers provide IMF screw systems for this technique of IMF. Since the screws were first introduced, they have undergone several geometric changes to optimize treatment results. Self-drilling screws, with no need to predrill a hole before insertion, are often used and supposedly are safer against damage to tooth roots.3 Because of forces exceeding
the maximum tolerated torque at insertion, screws have been reported to break.4,5 This negatively influences treatment, causing delay and an increase in costs. Because there is a difference in design and material among IMF screw systems, there is most likely a difference in applied and maximum tolerated forces at insertion. Ideally, there is a substantial difference between the forces required to manually tighten a screw in a clinical setting, providing primary stability to allow wire or elastic band
*PhD Student, Department of Oral and Maxillofacial Surgery/Oral
Address correspondence and reprint requests to Dr Bins: Depart-
Pathology, VU University Medical Center, Amsterdam, The
ment of Oral and Maxillofacial Surgery/Oral Pathology, VU University
Netherlands.
Medical Center, PO Box 7057, 1007 MB, Amsterdam, The
yMaxillofacial Surgeon, Department of Oral and Maxillofacial
Netherlands; e-mail: [email protected]
Surgery/Oral Pathology, VU University Medical Center/Academic
Received July 3 2015
Center for Dentistry Amsterdam, Amsterdam, The Netherlands.
Accepted September 12 2015
zProfessor and Department Head, Department of Oral and Maxillofacial Surgery/Oral Pathology, VU University Medical
Ó 2015 American Association of Oral and Maxillofacial Surgeons
Center/Academic Center for Dentistry Amsterdam, Amsterdam,
http://dx.doi.org/10.1016/j.joms.2015.09.001
0278-2391/15/01267-7
The Netherlands. xResearch Associate, Department of Oral and Maxillofacial Surgery/Oral Pathology, VU University Medical Center/Academic Center for Dentistry Amsterdam, Amsterdam, The Netherlands.
1 FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112
113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168
2
TORQUE FORCE FOR INTERMAXILLARY SCREW FIXATION
Table 1. SCREW CHARACTERISTICS OF INCLUDED IMF SCREW SYSTEMS
Company Stainless steel Synthes
Screw
IMF screw
Screw Model Diameter Shaft Alloy (mm) (mm) (mm)
316L
8.0
Titanium KLS Amsterdam Ti Al 12.0 6V4 Martin IMF screw Ti Al 10.0 Jeilmed Dual Top 6V4 Anchor System JA
2.0
10.0
2.0
7.5
2.0
10.0
Abbreviation: IMF, intermaxillary fixation. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
traction for IMF, and the maximum tolerated torque that causes the screw to break.6,7 When there is little difference between the manually tightened and maximum tolerated torque, screws are more likely to break. The aim of this study was to assess and compare torque measurements for 3 different IMF screw systems and provide a recommendation for screw selection. To determine safety margins, manually tightened torque and maximum tolerated torque were compared. Although such tests might have been performed during the manufacturing process, the manufacturers do not specify any of these characteristics. A major difference in safety margins could clearly favor the use of one particular IMF screw system, because such a screw would break less easily and would decrease complication rates and operative time. The authors hypothesized that all screws would show a substantial margin between manually tightened and breakage torque.
Materials and Methods STUDY DESIGN
Q3
Three different IMF screw systems were used in this study. All screws were self-tapping and self-drilling systems. Characteristics and geometry of the screws, provided by KLS Martin (Umkirch, Germany), Synthes (Solothurn, Switzerland), and Jeilmed (Seoul, Korea), are presented in Table 1 and Figures 1 to 3. The tests in this study were conducted on porcine cadaveric mandibles obtained from pigs that were intended for human consumption. Four mandibles
FIGURE 1. Geometry of Synthes intermaxillary fixation screw. Q7 Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
Q1
169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224
3
BINS ET AL
225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280
FIGURE 2. Geometry of KLS Martin intermaxillary fixation screw. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
Q4 Q5
Q6
were scanned by cone-beam computed tomography (CBCT; 8 mA and 60 kV; Pax-Zenith3D, Vatech, Gyeonggi-do, Korea) to assess cortical bone thickness and suitable insertion sites away from the tooth roots. Cortical thickness was analyzed (Ez3D Plus, Vatech) in coronal sections at fixed points, A (anterior) and P (posterior), on the buccal mandible. In a sagittal plane, point A is on the line between the 2 most posterior permanent premolars and point B is on a line through the middle of the second molar (Figs 4, 5). For the torque measurements, a digital torque screwdriver (range, approximately 0.2 to 4.0 N-m; accuracy 0.5% from full scale; Cedar DID-4, Sugisaki Meter Co, Ibaraki, Japan) was used. Continuous data
FIGURE 3. Geometry of Jeilmed intermaxillary fixation screw. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336
print & web 4C=FPO
TORQUE FORCE FOR INTERMAXILLARY SCREW FIXATION
FIGURE 4. Sagittal section of porcine mandible showing lines A (anterior) and P (posterior), where cortical thickness was measured. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
print & web 4C=FPO
337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392
4
FIGURE 5. Buccal cortical thickness assessment (3.5 mm) at the posterior point. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448
5
BINS ET AL
were collected directly into an Excel spreadsheet (Microsoft, Redmond, WA) using a USB cable measuring a maximum of 180 data points per second. For the tests, 3 departmental oral and maxillofacial surgeons were asked to drive the screws into the porcine mandibular bone. All specialists manually tightened 8 screws of each IMF screw system in the mandibular bone, as they would do in normal human patients. To limit the surgeons’ time, the screws were pre-inserted one half the length by the primary author along a fixed path of 7 cm, with a distance of 1 cm between each screw. The remaining half was inserted by the surgeons using the insertion torque screwdriver, which recorded torque (Newton meters) as continuous data (Fig 6). Matching screw heads were mounted on the insertion torque screwdriver bits for this purpose. Failed screws were not replaced. Then, the primary and secondary authors removed the screws from the mandibles using the same screwdriver that recorded torque and failure when applicable. For tests of torque until failure, the primary author applied 8 screws of each system in an aluminum (51ST) plate with predrilled 1.7-mm-diameter holes until the screw broke. Four of these screws had already been used in the porcine mandible tests. The other 4 were never-used screws. No ethical approval by the institutional review board was required for this study.
STATISTICAL ANALYSIS
Descriptive analysis, including means, standard deviations, confidence intervals, and ranges, were calculated using SPSS 20.0 (SPSS, Inc, Chicago, IL). Independent t test and Mann-Whitney U test were performed to compare means between manually tightened and breakage torsion forces, with a P value less than .05 considered significant. One-way analysis of
variance was used to compare peak torsion means between screws and surgeons.
Results CBCT SCANS
The CBCT scans showed that at a mandible height of one third measured from the inferior cortical border (Fig 5), root contact is unlikely to occur at screw insertion. Therefore, this was regarded a safe screw insertion height and cortical thickness was assessed at the fixed points at this height. Placing the screws in alveolar bone was not possible without tooth root interference. The cortical thickness measured on the buccal side from point P ranged from 3.4 to 4.2 mm. Cortical thickness measured on the buccal side from point A ranged from 2.3 to 3.1 mm. This was not considered an interference with the measurements. TORQUE FORCES
When peak torsion data of the 3 different surgeons were pooled for each screw, mean torque forces and standard deviation were calculated for manual tightening and breakage (Fig 7). Table 2 presents an overview of the descriptive analysis for manual tightening, breakage, and removal forces. Mean maximum torque for torque until failure (breakage test) was substantially higher for all screws compared with manual tightening (Table 2, Fig 7). Measurements of 10 screws (13.9%) showed failed manually tightened insertion; 2 screws (2.8%) failed because the software did not produce a clear outcome and 8 failed because the screws broke or were stripped at insertion. Exact failure rates are presented in Table 3. When analyzing the results for manual tightening (Fig 7), mean peak torque for the Synthes system was significantly higher (P = .02) than that for the
print & web 4C=FPO
449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504
FIGURE 6. Example of typical manual tightening continuous data in Newton meters for 8 screws as recorded by the torque screwdriver (surgeon 1, Jeilmed screw). Clearly seen is the increased force required when a longer part of the screw is within the bone. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560
561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616
6
TORQUE FORCE FOR INTERMAXILLARY SCREW FIXATION
FIGURE 7. Mean peak forces (Newton meters) and standard deviation for manual tightening, removal, and breakage tests. *P < .05 (significant difference). HT, manual tightening. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
KLS Martin system. Removal of the screws from the porcine mandibles showed no statistical difference in mean torque forces between screw systems (Fig 7). Failure rates during removal are presented in Table 3. Test results for torque until failure (Fig 7) showed that the mean peak failure torque of the KLS Martin system was significantly lower than those of the Synthes
(P < .001) and Jeilmed (P < .001) systems. No statistical difference was found between the used and neverused screws in this test for torque until failure. Overall, there was no statistical difference among surgeons for manually tightened torque forces. Manually tightened torque measurements for each surgeon per screw are shown in Figure 8. For Jeilmed screws,
Table 2. DESCRIPTIVE ANALYSIS
Force (N-m) Screw
Total Screws
Manually tightening Synthes KLS Martin Jeilmed Breakage Synthes KLS Martin Jeilmed Removal Synthes KLS Martin Jeilmed
95% Confidence Interval (N-m)
Range (N-m)
Mean
SD
LB
UB
Minimum
Maximum
20 20 22
0.447* 0.380* 0.409*
0.085 0.093 0.090
0.407 0.336 0.368
0.487 0.423 0.449
0.286 0.228 0.226
0.640 0.544 0.582
8 8 8
0.624* 0.534* 0.607*
0.011 0.010 0.042
0.614 0.529 0.571
0.633 0.546 0.642
0.610 0.523 0.528
0.640 0.552 0.658
20 19 20
0.450 0.428 0.490
0.111 0.119 0.081
0.398 0.371 0.452
0.502 0.486 0.528
0.280 0.240 0.370
0.670 0.660 0.670
Abbreviations: LB, lower bound; SD, standard deviation; UB, upper bound. * P < .001 for all comparisons (significant difference) between manual tightening and breakage per screw. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672
7
BINS ET AL
Table 3. TOTAL NUMBER AND PERCENTAGE OF SCREW FAILURE RATES
Screw
Breakage
Stripped
Manually tightened insertion Synthes 4 (16.7%) 0 KLS Martin 1 (4.2%) 3 (12.5%) Jeilmed 0 0 Removal Synthes 0 0 KLS Martin 1 (5.0%) 0 Jeilmed 4 (16.7%) 0
Missing Data
Total Screws
0 0 2 (8.3%)
24 24 24
0 0 0
20 20 24
Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
surgeon 1 had significantly higher (P = .02) torque forces than surgeon 2, whereas for KLS Martin screws, surgeon 2 applied the highest force. This average torque was significantly higher for surgeon 2 (P = .03) compared with surgeon 3.
Discussion In the treatment of mandibular fractures, bone screws are an alternative to arch bars.2,5 The possible fracture of a screw is a known complication
for bone screw use.4 Breakage of bone screws is associated with root contact and an increase of insertion torque forces.8 This study was conducted to investigate the forces that arise at bone screw insertion and to determine margins among different IMF screw systems for regular clinical forces and forces at screw breakage under the hypothesis that all included screws would have substantial margins. The clinical relevance relates to the fact that a substantial difference in safety margins among screw systems could favor a particular system, given the likely decreased complication rate and operative time. With a digital torque screwdriver, forces were measured in Newton meters for manual tightening insertion and removal using porcine mandibles. On a predrilled aluminum plate, torque forces for torque until breakage were measured. To analyze and exclude major variances in cortical thickness, CBCT scans were obtained for 4 porcine mandibles. Scans showed some variation in cortical thickness; however, these variations are similar to those found in human studies with cortical thickness averaging 1.7 to 5.4 mm.9,10 Values for increased torques with increased insertion length (Fig 6) are comparable to previous studies.11 Bone quality assessment using CBCT is inferior to multislice or micro-CT and results can vary among different CBCT systems.12
print & web 4C=FPO
673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728
FIGURE 8. Mean manual tightening peak forces per surgeon for each screwing system. *P < .05 (significant difference). Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784
785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840
8
TORQUE FORCE FOR INTERMAXILLARY SCREW FIXATION
Therefore, although some studies have found correlations between CBCT values and bone quality, the authors did not attempt to make such an assessment.13,14 Clinically, bone screws are placed mostly at the mucogingival junction between the teeth roots.2 However, space limitations in the interradicular bone forced the screws to be placed in the basal bone below. The correlation between manual tightening and torque until failure is in accord with a study by Buijs et al6 who found an important correlation between manual tightening and torque until failure for their pure titanium plate locking screws. Five screws broke during manually tightened insertion and sometimes manual tightening torque values exceeded those for torque until failure. This shows that measurements are not always repeatable and that other factors, such as screwdriver positioning or rotation velocity, might contribute to screw failure. The substantially higher mean torque value for manual tightening of the Synthes system can be explained by the longer thread (10.0 mm) compared with the KLS Martin system (7.5 mm); however, Jeilmed screws have a similar thread length (10.0 mm) and showed no difference from the KLS Martin system. Other variations in screw geometry and cortical thickness might have contributed to this difference.11 Variations in cortical thickness and bone quality could well explain the substantial differences in torque forces among surgeons for similar IMF screw systems, because pooled data of all 3 IMF screw systems showed no overall difference in manual tightening among the surgeons.9,10 Cumulative manual tightening torque values were significantly higher (P = .03) for the 4 most anteriorly placed screws compared with the 4 most posteriorly placed screws. All 5 screws that broke at insertion were placed in this anterior segment. The CBCT scans showed a larger cortical bone portion in the anterior mandible compared with the posterior mandible, which could explain these higher values. The Jeilmed screwdriver bit has a somewhat looser fit on the screw head compared with the very precise fit of the Synthes and KLS Martin bits. A somewhat loose fit provides less danger of breaking a screw owing to bending when the direction of the applied force onto the screw is not exactly parallel to the main shaft of the screw. Although the number of samples is very limited, this might be reflected during the screw placement procedure (Table 3). Most screws seem to break at the shaft at or near the bone level. Jeilmed screws also break at the screw head, allowing easier removal. It has been reported that higher insertion torque forces can cause local ischemia and damage to cortical bone.15,16 However, a certain amount of insertion torque is required to achieve primary stability.7 Meur-
singe Reynders et al17 did not find higher success rates for specific insertion torque forces for orthodontic mini-implants in their systematic review. Because no difference was found in breakage forces between never-used and used screws, it seems that these IMF screws can be reused after initial incorrect placement without increased risk of breakage. With the absence of clear results favoring the use of one specific screw system with regard to risk for breakage, other factors are likely to determine screw selection. Although these results were not systematically obtained, all surgeons favored the screw head and screwdriver geometry of the Jeilmed screwing system, because of the ease of engagement. However, results might be biased because the surgeons were already familiar with this particular system. In contrast to the Synthes and Jeilmed screw systems, the wide diameter of the KLS Martin screw head facilitates ease for multiple elastic appliances, which seems to be a clinical advantage. In conclusion, this study showed no important differences among the 3 screw systems for safety margins, defined as the difference between manual tightening and breakage torque forces. All IMF screw systems had substantial margins between manual tightening and breakage torque forces. This means screw selection should be based on clinical factors, such as ease of use or elastic application for IMF or other economic factors. Future prospective clinical studies are necessary to further determine evidencebased IMF screw selection. Acknowledgments The authors thank Jeilmed, KLS Martin, and Synthes for the supply of their screws. Specialist staff members E.A.J.M. Schulten, J.A. Baart, and J.E.H. Wolff are much appreciated for their skilled support in applying the screws. They also thank Sjoerd te Slaa and Frank Verver for their assistance in facilitating the tests.
References 1. Ansari K, Hamlar D, Ho V, et al: A comparison of anterior vs posterior isolated mandible fractures treated with intermaxillary fixation screws. Arch Facial Plast Surg 13:266, 2011 2. West GH, Griggs JA, Chandran R, et al: Treatment outcomes with the use of maxillomandibular fixation screws in the management of mandible fractures. J Oral Maxillofac Surg 72:112, 2014 3. Widar F, Kashani H, Kanagaraja S, et al: A retrospective evaluation of iatrogenic dental root damage with predrilled vs drillfree bone anchor screws for intermaxillary fixation. Dent Traumatol 28:127, 2012 4. Coburn DG, Kennedy DW, Hodder SC: Complications with intermaxillary fixation screws in the management of fractured mandibles. Br J Oral Maxillofac Surg 40:241, 2002 5. Rai A, Datarkar A, Borle R: Are maxillomandibular fixation screws a better option than Erich arch bar in achieving maxillomandibular fixation? A randomized clinical study. J Oral Maxillofac Surg 69:3015, 2011 6. Buijs GJ, van der Houwen EB, Stegenga B, et al: Torsion strength of biodegradable and titanium screws: A comparison. J Oral Maxillofac Surg 65:2142, 2007
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896
9
BINS ET AL
897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912
7. Motoyoshi M, Hirabayashi M, Uemura M, et al: Recommended placement torque when tightening an orthodontic miniimplant. Clin Oral Implants Res 17:109, 2006 8. Brisceno CE, Rossouw PE, Carrillo R, et al: Healing of the roots and surrounding structures after intentional damage with miniscrew implants. Am J Orthod Dentofacial Orthop 135:292, 2009 9. Motoyoshi M, Yoshida T, Ono A, et al: Effect of cortical bone thickness and implant placement torque on stability of orthodontic mini-implants. Int J Oral Maxillofac Implants 22:779, 2007 10. Nkenke E, Hahn M, Weinzierl K, et al: Implant stability and histomorphometry: A correlation study in human cadavers using stepped cylinder implants. Clin Oral Implants Res 14:601, 2003 11. Lim SA, Cha JY, Hwang CJ: Insertion torque of orthodontic miniscrews according to changes in shape, diameter and length. Angle Orthod 78:234, 2008
12. Parsa A, Ibrahim N, Hassan B, et al: Bone quality evaluation at dental implant site using multislice CT, micro-CT and cone beam CT. Clin Oral Implants Res 26:e1, 2015 13. Brosh T, Yekaterina B, Pilo R, et al: Can cone beam CT predict the hardness of interradicular cortical bone? Head Face Med 10:12, 2014 14. Parsa A, Ibrahim N, Hassan B, et al: Reliability of voxel gray values in cone beam computed tomography for pre-operative implant planning assessment. Int J Oral Maxillofac Implants 27:1438, 2012 15. Lee NK, Baek SH: Effects of the diameter and shape of orthodontic mini-implants on microdamage to the cortical bone. Am J Orthod Dentofacial Orthop 138:8.e1, 2010 16. Meredith N: Assessment of implant stability as a prognostic determinant. Int J Prosthodont 11:491, 1998 17. Meursinge Reynders RA, Ronchi L, Ladu L, et al: Insertion torque and success of orthodontic mini-implants: A systematic review. Am J Orthod Dentofacial Orthop 142:596, 2012
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928
CRANIOMAXILLOFACIAL TRAUMA
A Comparison of Torque Forces Used to Apply Intermaxillary Fixation Screws Arjan Bins, DDS,* Jacques A. Baart, DDS,y Tymour Forouzanfar, DDS, MD, PhD,z and Jack J. W. A. van Loon, MSc, PhDx
Q8
Purpose:
When establishing intermaxillary fixation (IMF) using bone screws, fracture of a screw is a potential complication. This study was conducted to investigate the forces that arise at bone screw insertion and to determine safety margins between torque for manually tightened insertion and torque until breakage for 3 different IMF screw systems, which could ultimately favor the use of 1 IMF screw system based on decreased risk of complications.
Materials and Methods:
IMF screws were placed into porcine mandibles by 3 oral and maxillofacial surgeons. The porcine mandibles were evaluated for cortical thickness and suitable insertion sites by cone-beam computed tomography. Measurements of torque until failure were performed on predrilled aluminum plates by the primary author. A digital torque screwdriver measured 180 data points per second as continuous data and recorded the measurements.
Results:
Measurements indicated clear differences in torsion forces between manually tightened insertions and torque until breakage for all 3 IMF screw systems. No statistical difference in safety margins was found among the IMF screw systems.
Q2
Conclusions: Because no statistical differences in safety margins were found among the IMF screw systems, this study indicates that IMF screw selection should be based on other clinical factors, such as ease of use or economic factors. Future prospective studies are necessary to fully determine evidence-based criteria for IMF screw selection. Ó 2015 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg -:1-9, 2015
Intermaxillary fixation (IMF) screws are frequently used as a quick and easy alternative to arch bars in mandibular fracture treatment.1,2 Several manufacturers provide IMF screw systems for this technique of IMF. Since the screws were first introduced, they have undergone several geometric changes to optimize treatment results. Self-drilling screws, with no need to predrill a hole before insertion, are often used and supposedly are safer against damage to tooth roots.3 Because of forces exceeding
the maximum tolerated torque at insertion, screws have been reported to break.4,5 This negatively influences treatment, causing delay and an increase in costs. Because there is a difference in design and material among IMF screw systems, there is most likely a difference in applied and maximum tolerated forces at insertion. Ideally, there is a substantial difference between the forces required to manually tighten a screw in a clinical setting, providing primary stability to allow wire or elastic band
*PhD Student, Department of Oral and Maxillofacial Surgery/Oral
Address correspondence and reprint requests to Dr Bins: Depart-
Pathology, VU University Medical Center, Amsterdam, The
ment of Oral and Maxillofacial Surgery/Oral Pathology, VU University
Netherlands.
Medical Center, PO Box 7057, 1007 MB, Amsterdam, The
yMaxillofacial Surgeon, Department of Oral and Maxillofacial
Netherlands; e-mail: [email protected]
Surgery/Oral Pathology, VU University Medical Center/Academic
Received July 3 2015
Center for Dentistry Amsterdam, Amsterdam, The Netherlands.
Accepted September 12 2015
zProfessor and Department Head, Department of Oral and Maxillofacial Surgery/Oral Pathology, VU University Medical
Ó 2015 American Association of Oral and Maxillofacial Surgeons
Center/Academic Center for Dentistry Amsterdam, Amsterdam,
http://dx.doi.org/10.1016/j.joms.2015.09.001
0278-2391/15/01267-7
The Netherlands. xResearch Associate, Department of Oral and Maxillofacial Surgery/Oral Pathology, VU University Medical Center/Academic Center for Dentistry Amsterdam, Amsterdam, The Netherlands.
1 FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112
113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168
2
TORQUE FORCE FOR INTERMAXILLARY SCREW FIXATION
Table 1. SCREW CHARACTERISTICS OF INCLUDED IMF SCREW SYSTEMS
Company Stainless steel Synthes
Screw
IMF screw
Screw Model Diameter Shaft Alloy (mm) (mm) (mm)
316L
8.0
Titanium KLS Amsterdam Ti Al 12.0 6V4 Martin IMF screw Ti Al 10.0 Jeilmed Dual Top 6V4 Anchor System JA
2.0
10.0
2.0
7.5
2.0
10.0
Abbreviation: IMF, intermaxillary fixation. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
traction for IMF, and the maximum tolerated torque that causes the screw to break.6,7 When there is little difference between the manually tightened and maximum tolerated torque, screws are more likely to break. The aim of this study was to assess and compare torque measurements for 3 different IMF screw systems and provide a recommendation for screw selection. To determine safety margins, manually tightened torque and maximum tolerated torque were compared. Although such tests might have been performed during the manufacturing process, the manufacturers do not specify any of these characteristics. A major difference in safety margins could clearly favor the use of one particular IMF screw system, because such a screw would break less easily and would decrease complication rates and operative time. The authors hypothesized that all screws would show a substantial margin between manually tightened and breakage torque.
Materials and Methods STUDY DESIGN
Q3
Three different IMF screw systems were used in this study. All screws were self-tapping and self-drilling systems. Characteristics and geometry of the screws, provided by KLS Martin (Umkirch, Germany), Synthes (Solothurn, Switzerland), and Jeilmed (Seoul, Korea), are presented in Table 1 and Figures 1 to 3. The tests in this study were conducted on porcine cadaveric mandibles obtained from pigs that were intended for human consumption. Four mandibles
FIGURE 1. Geometry of Synthes intermaxillary fixation screw. Q7 Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
Q1
169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224
3
BINS ET AL
225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280
FIGURE 2. Geometry of KLS Martin intermaxillary fixation screw. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
Q4 Q5
Q6
were scanned by cone-beam computed tomography (CBCT; 8 mA and 60 kV; Pax-Zenith3D, Vatech, Gyeonggi-do, Korea) to assess cortical bone thickness and suitable insertion sites away from the tooth roots. Cortical thickness was analyzed (Ez3D Plus, Vatech) in coronal sections at fixed points, A (anterior) and P (posterior), on the buccal mandible. In a sagittal plane, point A is on the line between the 2 most posterior permanent premolars and point B is on a line through the middle of the second molar (Figs 4, 5). For the torque measurements, a digital torque screwdriver (range, approximately 0.2 to 4.0 N-m; accuracy 0.5% from full scale; Cedar DID-4, Sugisaki Meter Co, Ibaraki, Japan) was used. Continuous data
FIGURE 3. Geometry of Jeilmed intermaxillary fixation screw. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336
print & web 4C=FPO
TORQUE FORCE FOR INTERMAXILLARY SCREW FIXATION
FIGURE 4. Sagittal section of porcine mandible showing lines A (anterior) and P (posterior), where cortical thickness was measured. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
print & web 4C=FPO
337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392
4
FIGURE 5. Buccal cortical thickness assessment (3.5 mm) at the posterior point. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448
5
BINS ET AL
were collected directly into an Excel spreadsheet (Microsoft, Redmond, WA) using a USB cable measuring a maximum of 180 data points per second. For the tests, 3 departmental oral and maxillofacial surgeons were asked to drive the screws into the porcine mandibular bone. All specialists manually tightened 8 screws of each IMF screw system in the mandibular bone, as they would do in normal human patients. To limit the surgeons’ time, the screws were pre-inserted one half the length by the primary author along a fixed path of 7 cm, with a distance of 1 cm between each screw. The remaining half was inserted by the surgeons using the insertion torque screwdriver, which recorded torque (Newton meters) as continuous data (Fig 6). Matching screw heads were mounted on the insertion torque screwdriver bits for this purpose. Failed screws were not replaced. Then, the primary and secondary authors removed the screws from the mandibles using the same screwdriver that recorded torque and failure when applicable. For tests of torque until failure, the primary author applied 8 screws of each system in an aluminum (51ST) plate with predrilled 1.7-mm-diameter holes until the screw broke. Four of these screws had already been used in the porcine mandible tests. The other 4 were never-used screws. No ethical approval by the institutional review board was required for this study.
STATISTICAL ANALYSIS
Descriptive analysis, including means, standard deviations, confidence intervals, and ranges, were calculated using SPSS 20.0 (SPSS, Inc, Chicago, IL). Independent t test and Mann-Whitney U test were performed to compare means between manually tightened and breakage torsion forces, with a P value less than .05 considered significant. One-way analysis of
variance was used to compare peak torsion means between screws and surgeons.
Results CBCT SCANS
The CBCT scans showed that at a mandible height of one third measured from the inferior cortical border (Fig 5), root contact is unlikely to occur at screw insertion. Therefore, this was regarded a safe screw insertion height and cortical thickness was assessed at the fixed points at this height. Placing the screws in alveolar bone was not possible without tooth root interference. The cortical thickness measured on the buccal side from point P ranged from 3.4 to 4.2 mm. Cortical thickness measured on the buccal side from point A ranged from 2.3 to 3.1 mm. This was not considered an interference with the measurements. TORQUE FORCES
When peak torsion data of the 3 different surgeons were pooled for each screw, mean torque forces and standard deviation were calculated for manual tightening and breakage (Fig 7). Table 2 presents an overview of the descriptive analysis for manual tightening, breakage, and removal forces. Mean maximum torque for torque until failure (breakage test) was substantially higher for all screws compared with manual tightening (Table 2, Fig 7). Measurements of 10 screws (13.9%) showed failed manually tightened insertion; 2 screws (2.8%) failed because the software did not produce a clear outcome and 8 failed because the screws broke or were stripped at insertion. Exact failure rates are presented in Table 3. When analyzing the results for manual tightening (Fig 7), mean peak torque for the Synthes system was significantly higher (P = .02) than that for the
print & web 4C=FPO
449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504
FIGURE 6. Example of typical manual tightening continuous data in Newton meters for 8 screws as recorded by the torque screwdriver (surgeon 1, Jeilmed screw). Clearly seen is the increased force required when a longer part of the screw is within the bone. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560
561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616
6
TORQUE FORCE FOR INTERMAXILLARY SCREW FIXATION
FIGURE 7. Mean peak forces (Newton meters) and standard deviation for manual tightening, removal, and breakage tests. *P < .05 (significant difference). HT, manual tightening. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
KLS Martin system. Removal of the screws from the porcine mandibles showed no statistical difference in mean torque forces between screw systems (Fig 7). Failure rates during removal are presented in Table 3. Test results for torque until failure (Fig 7) showed that the mean peak failure torque of the KLS Martin system was significantly lower than those of the Synthes
(P < .001) and Jeilmed (P < .001) systems. No statistical difference was found between the used and neverused screws in this test for torque until failure. Overall, there was no statistical difference among surgeons for manually tightened torque forces. Manually tightened torque measurements for each surgeon per screw are shown in Figure 8. For Jeilmed screws,
Table 2. DESCRIPTIVE ANALYSIS
Force (N-m) Screw
Total Screws
Manually tightening Synthes KLS Martin Jeilmed Breakage Synthes KLS Martin Jeilmed Removal Synthes KLS Martin Jeilmed
95% Confidence Interval (N-m)
Range (N-m)
Mean
SD
LB
UB
Minimum
Maximum
20 20 22
0.447* 0.380* 0.409*
0.085 0.093 0.090
0.407 0.336 0.368
0.487 0.423 0.449
0.286 0.228 0.226
0.640 0.544 0.582
8 8 8
0.624* 0.534* 0.607*
0.011 0.010 0.042
0.614 0.529 0.571
0.633 0.546 0.642
0.610 0.523 0.528
0.640 0.552 0.658
20 19 20
0.450 0.428 0.490
0.111 0.119 0.081
0.398 0.371 0.452
0.502 0.486 0.528
0.280 0.240 0.370
0.670 0.660 0.670
Abbreviations: LB, lower bound; SD, standard deviation; UB, upper bound. * P < .001 for all comparisons (significant difference) between manual tightening and breakage per screw. Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672
7
BINS ET AL
Table 3. TOTAL NUMBER AND PERCENTAGE OF SCREW FAILURE RATES
Screw
Breakage
Stripped
Manually tightened insertion Synthes 4 (16.7%) 0 KLS Martin 1 (4.2%) 3 (12.5%) Jeilmed 0 0 Removal Synthes 0 0 KLS Martin 1 (5.0%) 0 Jeilmed 4 (16.7%) 0
Missing Data
Total Screws
0 0 2 (8.3%)
24 24 24
0 0 0
20 20 24
Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
surgeon 1 had significantly higher (P = .02) torque forces than surgeon 2, whereas for KLS Martin screws, surgeon 2 applied the highest force. This average torque was significantly higher for surgeon 2 (P = .03) compared with surgeon 3.
Discussion In the treatment of mandibular fractures, bone screws are an alternative to arch bars.2,5 The possible fracture of a screw is a known complication
for bone screw use.4 Breakage of bone screws is associated with root contact and an increase of insertion torque forces.8 This study was conducted to investigate the forces that arise at bone screw insertion and to determine margins among different IMF screw systems for regular clinical forces and forces at screw breakage under the hypothesis that all included screws would have substantial margins. The clinical relevance relates to the fact that a substantial difference in safety margins among screw systems could favor a particular system, given the likely decreased complication rate and operative time. With a digital torque screwdriver, forces were measured in Newton meters for manual tightening insertion and removal using porcine mandibles. On a predrilled aluminum plate, torque forces for torque until breakage were measured. To analyze and exclude major variances in cortical thickness, CBCT scans were obtained for 4 porcine mandibles. Scans showed some variation in cortical thickness; however, these variations are similar to those found in human studies with cortical thickness averaging 1.7 to 5.4 mm.9,10 Values for increased torques with increased insertion length (Fig 6) are comparable to previous studies.11 Bone quality assessment using CBCT is inferior to multislice or micro-CT and results can vary among different CBCT systems.12
print & web 4C=FPO
673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728
FIGURE 8. Mean manual tightening peak forces per surgeon for each screwing system. *P < .05 (significant difference). Bins et al. Torque Force for Intermaxillary Screw Fixation. J Oral Maxillofac Surg 2015.
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784
785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840
8
TORQUE FORCE FOR INTERMAXILLARY SCREW FIXATION
Therefore, although some studies have found correlations between CBCT values and bone quality, the authors did not attempt to make such an assessment.13,14 Clinically, bone screws are placed mostly at the mucogingival junction between the teeth roots.2 However, space limitations in the interradicular bone forced the screws to be placed in the basal bone below. The correlation between manual tightening and torque until failure is in accord with a study by Buijs et al6 who found an important correlation between manual tightening and torque until failure for their pure titanium plate locking screws. Five screws broke during manually tightened insertion and sometimes manual tightening torque values exceeded those for torque until failure. This shows that measurements are not always repeatable and that other factors, such as screwdriver positioning or rotation velocity, might contribute to screw failure. The substantially higher mean torque value for manual tightening of the Synthes system can be explained by the longer thread (10.0 mm) compared with the KLS Martin system (7.5 mm); however, Jeilmed screws have a similar thread length (10.0 mm) and showed no difference from the KLS Martin system. Other variations in screw geometry and cortical thickness might have contributed to this difference.11 Variations in cortical thickness and bone quality could well explain the substantial differences in torque forces among surgeons for similar IMF screw systems, because pooled data of all 3 IMF screw systems showed no overall difference in manual tightening among the surgeons.9,10 Cumulative manual tightening torque values were significantly higher (P = .03) for the 4 most anteriorly placed screws compared with the 4 most posteriorly placed screws. All 5 screws that broke at insertion were placed in this anterior segment. The CBCT scans showed a larger cortical bone portion in the anterior mandible compared with the posterior mandible, which could explain these higher values. The Jeilmed screwdriver bit has a somewhat looser fit on the screw head compared with the very precise fit of the Synthes and KLS Martin bits. A somewhat loose fit provides less danger of breaking a screw owing to bending when the direction of the applied force onto the screw is not exactly parallel to the main shaft of the screw. Although the number of samples is very limited, this might be reflected during the screw placement procedure (Table 3). Most screws seem to break at the shaft at or near the bone level. Jeilmed screws also break at the screw head, allowing easier removal. It has been reported that higher insertion torque forces can cause local ischemia and damage to cortical bone.15,16 However, a certain amount of insertion torque is required to achieve primary stability.7 Meur-
singe Reynders et al17 did not find higher success rates for specific insertion torque forces for orthodontic mini-implants in their systematic review. Because no difference was found in breakage forces between never-used and used screws, it seems that these IMF screws can be reused after initial incorrect placement without increased risk of breakage. With the absence of clear results favoring the use of one specific screw system with regard to risk for breakage, other factors are likely to determine screw selection. Although these results were not systematically obtained, all surgeons favored the screw head and screwdriver geometry of the Jeilmed screwing system, because of the ease of engagement. However, results might be biased because the surgeons were already familiar with this particular system. In contrast to the Synthes and Jeilmed screw systems, the wide diameter of the KLS Martin screw head facilitates ease for multiple elastic appliances, which seems to be a clinical advantage. In conclusion, this study showed no important differences among the 3 screw systems for safety margins, defined as the difference between manual tightening and breakage torque forces. All IMF screw systems had substantial margins between manual tightening and breakage torque forces. This means screw selection should be based on clinical factors, such as ease of use or elastic application for IMF or other economic factors. Future prospective clinical studies are necessary to further determine evidencebased IMF screw selection. Acknowledgments The authors thank Jeilmed, KLS Martin, and Synthes for the supply of their screws. Specialist staff members E.A.J.M. Schulten, J.A. Baart, and J.E.H. Wolff are much appreciated for their skilled support in applying the screws. They also thank Sjoerd te Slaa and Frank Verver for their assistance in facilitating the tests.
References 1. Ansari K, Hamlar D, Ho V, et al: A comparison of anterior vs posterior isolated mandible fractures treated with intermaxillary fixation screws. Arch Facial Plast Surg 13:266, 2011 2. West GH, Griggs JA, Chandran R, et al: Treatment outcomes with the use of maxillomandibular fixation screws in the management of mandible fractures. J Oral Maxillofac Surg 72:112, 2014 3. Widar F, Kashani H, Kanagaraja S, et al: A retrospective evaluation of iatrogenic dental root damage with predrilled vs drillfree bone anchor screws for intermaxillary fixation. Dent Traumatol 28:127, 2012 4. Coburn DG, Kennedy DW, Hodder SC: Complications with intermaxillary fixation screws in the management of fractured mandibles. Br J Oral Maxillofac Surg 40:241, 2002 5. Rai A, Datarkar A, Borle R: Are maxillomandibular fixation screws a better option than Erich arch bar in achieving maxillomandibular fixation? A randomized clinical study. J Oral Maxillofac Surg 69:3015, 2011 6. Buijs GJ, van der Houwen EB, Stegenga B, et al: Torsion strength of biodegradable and titanium screws: A comparison. J Oral Maxillofac Surg 65:2142, 2007
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896
9
BINS ET AL
897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912
7. Motoyoshi M, Hirabayashi M, Uemura M, et al: Recommended placement torque when tightening an orthodontic miniimplant. Clin Oral Implants Res 17:109, 2006 8. Brisceno CE, Rossouw PE, Carrillo R, et al: Healing of the roots and surrounding structures after intentional damage with miniscrew implants. Am J Orthod Dentofacial Orthop 135:292, 2009 9. Motoyoshi M, Yoshida T, Ono A, et al: Effect of cortical bone thickness and implant placement torque on stability of orthodontic mini-implants. Int J Oral Maxillofac Implants 22:779, 2007 10. Nkenke E, Hahn M, Weinzierl K, et al: Implant stability and histomorphometry: A correlation study in human cadavers using stepped cylinder implants. Clin Oral Implants Res 14:601, 2003 11. Lim SA, Cha JY, Hwang CJ: Insertion torque of orthodontic miniscrews according to changes in shape, diameter and length. Angle Orthod 78:234, 2008
12. Parsa A, Ibrahim N, Hassan B, et al: Bone quality evaluation at dental implant site using multislice CT, micro-CT and cone beam CT. Clin Oral Implants Res 26:e1, 2015 13. Brosh T, Yekaterina B, Pilo R, et al: Can cone beam CT predict the hardness of interradicular cortical bone? Head Face Med 10:12, 2014 14. Parsa A, Ibrahim N, Hassan B, et al: Reliability of voxel gray values in cone beam computed tomography for pre-operative implant planning assessment. Int J Oral Maxillofac Implants 27:1438, 2012 15. Lee NK, Baek SH: Effects of the diameter and shape of orthodontic mini-implants on microdamage to the cortical bone. Am J Orthod Dentofacial Orthop 138:8.e1, 2010 16. Meredith N: Assessment of implant stability as a prognostic determinant. Int J Prosthodont 11:491, 1998 17. Meursinge Reynders RA, Ronchi L, Ladu L, et al: Insertion torque and success of orthodontic mini-implants: A systematic review. Am J Orthod Dentofacial Orthop 142:596, 2012
FLA 5.4.0 DTD YJOMS56956_proof 28 September 2015 5:45 pm CE AH
913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928