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Effects of varied dimensions of surgical guides on implant angulations
Effects of varied dimensions of surgical guides on implant angulations Mijin Choi, DDS,a Elaine Romberg, PhD,b and Carl F. Driscoll, DMDc Baltimore College of Dental Surgery, University of Maryland at Baltimore, Baltimore, Md Statement of problem. Fabrication of a proper surgical guide is critical for success of implant restorations. The effects of the dimensional factors of the surgical guide on implant placement have not been studied.
Purpose. The purpose of this study was to determine the effect of varied dimensions (diameter, length, and distance between the underside of the surgical guide and the implant recipient site) of a surgical guide on the accuracy of implant angulation. Material and methods. In this in vitro study, 240 implant recipient sites were randomly prepared using varied dimensions of a surgical guide. The varied dimensions of the surgical guide’s channel and distance were: channel diameter (2, 3, 4, or 5 mm), channel length (6 or 9 mm), and distance between the underside of the surgical guide and the simulated implant recipient site (2 or 4 mm). From these varying dimensions and distances, 16 combinations of dimensions and distances were tested. For each combination, 15 simulated implant recipient site (SIRS) specimens were prepared. The deviated angulation (DA) from the midpoint of the top surface of the 1- 3 1-inch simulated implant recipient site (each simulated implant recipient acrylic block contained 5 SIRS of 1 3 1 inch), in the right-to-left (DARL) and front-to-back (DAFB) directions, were measured in degrees using a protractor. The data was analyzed using factorial analysis of variance and Tukey’s HSD test (a=.05). Results. The DARL, in degrees, at a channel length of 9.0 mm (2.33 6 1.27) was significantly smaller than at a channel length of 6.0 mm (3.0 6 1.42, P=.0001). The DARL, in degrees, at a distance of 4.0 mm (2.13 6 1.16) was significantly smaller than at a distance of 2.0 mm (3.16 6 1.39, P=.0001). Also, a significant interaction for DARL was found between diameter and distance (P,.05). For DAFB, the varying diameters (P,.05), lengths (P=.0001), and distances (P=.0001) showed significant differences. The DAFB at a channel length of 9.0 mm (2.56 degrees 6 1.51) was significantly smaller than that at 6.0 mm (3.82 degrees 6 1.87). Significant interactions found for DAFB were: diameter by length (P=.0001), diameter by distance (F = 4.547, P=.004), and length by distance (F = 11.512, P=.001). Conclusion. Within the limitations of this study, the results suggest channel length as the primary controlling factor in minimizing deviated angulations. (J Prosthet Dent 2004;92:463-9.)
CLINICAL IMPLICATIONS Within the limitations of this in vitro study, the length of the surgical guide channel was found to be the primary factor in minimizing deviations in implant angulation. The implant angulation is best controlled by fabricating the surgical guide with the longest channel length permitted by the interarch distance.
I
mplant dentistry is divided into 2 phases, surgical and restorative. Often, different clinicians perform these phases. While the surgeon would prefer to position the implant in the most biologically favorable bone site,
Presented at the oral presentation program at the 31st Annual Meeting and Exposition of the American Association for Dental Research, San Antonio, Texas, March 14, 2003. Supported by The Greater New York Academy of Prosthodontics Student Grant. a Third-year Prosthodontic Resident, Postdoctoral Program in Prosthodontics, Department of Restorative Dentistry. b Professor, Department of Oral Health Care Delivery. c Associate Professor and Director of Prosthodontic Residency, Department of Restorative Dentistry.
NOVEMBER 2004
the restorative dentist requires implant placement that allows for optimum function and maximum esthetic value with relative mechanical ease. For the definitive restoration to be successful, therefore, biological, functional, mechanical, and esthetic requirements must be achieved. While the importance of planning for precise implant placement has been stressed in the literature, surgical guides that do not provide exact drill guides may serve as only an approximate guide to the surgeon.1 As a result, it is not uncommon for the implant to be placed in a slightly different position from the originally planned position. Although this discrepancy may be minimal at the time of surgery, it may predispose the implant to an esthetic or functional failure.2 Therefore, fabrication THE JOURNAL OF PROSTHETIC DENTISTRY 463
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of a surgical guide is critical for esthetics, function, and long-term success of the implant-bone prosthesis.3 The need for more accurate placement of implants has led to the development of numerous template designs. These include the labial outline surgical guide made from a wax arrangement of the proposed definitive restoration,4 a clear vacuum-formed matrix,5 a duplicate of the existing restoration,6 and other methods.7 The clear vacuum-formed surgical guide with a guide hole made over the anticipated implant position does not prevent inadvertent deviation of the angle of placement. Significant inaccuracies due to the absence of a guiding channel may occur at the apical portion of the pilot or twist drills close to the edentulous residual ridge. Parel and Funk4 described a surgical guide with the buccal contours of the proposed implant-supported restoration created in the guide. This type of surgical guide may not serve as a direct mechanical guide and site preparation may be performed freehand. Engleman et al8 described a similar surgical guide. This design may not provide accurate spatial information for an implant. In addition, Ku and Shen9 described a surgical guide fabricated with a vacuum-formed matrix filled with clear acrylic resin. In this technique, the guide channel was prepared by drilling through the clear acrylic resin using carbide burs, which had the same diameter as the pilot drill. This technique only allows for correct initial positioning and does not allow for correct inclination at implant placement because the implant cannot be placed with the guide after the initial preparation due to insufficient diameter for the larger pilot drill or twist drill to pass through the channel prepared within the guide. In many situations, surgeons request that the length of the guide channel be reduced in the apical portion to allow for sufficient irrigation and visualization during surgical procedures. This provides the pilot drill more room, allowing for deviation of the implant angulations to occur. Furthermore, due to the narrow diameter of the guide channel, only the 2-mm twist drill is allowed to pass through, causing a surgeon to place implants without the guidance of the surgical guide after the initial preparation. Presently, with the use of computed tomography technology, the fabrication of multiple surgical guides for different diameter surgical drills is feasible. To fabricate a surgical guide that limits the deviation of the drills being used, it is important to examine the factors that may influence accurate placement of an implant when a surgical guide is used during placement. These factors include the diameter of the prepared guide channel, length of the prepared guide channel, and distance between the underside of the surgical guide and the implant site at the alveolar crest. Without careful control of these factors that contribute to the angulation of the implant, the deviation of the pilot drill or twist drill 464
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may cause significant inaccuracies. Thus, the bottom of the guide channel may be too far from the residual ridge, the guide channel may be too short, the diameter of guide channel may be too large, allowing for changes in angulations of the drills, or some combination of these 3 events may occur. The purpose of this study was to investigate the effect of dimensional factors of surgical guides on the accuracy of implant placement. The varying dimensions were diameter (D), length of channel (L), and distance (S) between the surgical guide and the simulated implant recipient site. The hypothesized research predictions for these variables were: (1) a larger diameter would result in a greater deviation, (2) a shorter length would result in a greater deviation, and (3) a larger distance would result in a greater deviation.
MATERIAL AND METHODS In this in vitro study, the surgical guide for simulated implant placement varied in 2 channel dimensions, diameter (D) and length (L) of the channel, and also in the distance (S) between the underside of the surgical guide and the simulated implant recipient site. To investigate the effects of the 3 surgical guide variables, clear acrylic resin blocks (Tap Plastics Inc, Stockton, Calif) were obtained for the fabrication of the testing apparatus. The items fabricated for this study were the simulated surgical guides, spacers to vary the distance between the underside of the surgical guide and the implant recipient site, simulated implant recipient blocks, and a clear acrylic box (1 3 5 3 1.1 inch, Fig. 1). The testing apparatuses were all precision-machined. The 1 3 5-inch surgical guide blocks were first machined with a precision milling machine (Heavy Duty Drilling and Milling Machine A 2 HP; Northern Tool & Equipment Company, Warren, Mich) into channel lengths of 6 mm or 9 mm. Then, 5 channels of each tested diameter were machined with a precision milling machine into appropriate blocks as indicated. The channels were located so that each channel was placed at the midpoint of a 1- 3 1-inch square on the top surface of the 1- 3 5-inch block. To vary the distance between the underside of the surgical guide and the implant recipient site, acrylic spacers were machined with the precision milling machine to dimensions of 1- 3 5-inch blocks with heights of 2 or 4 mm, therefore creating 2- or 4-mm distances from the guide to implant recipient site. The spacers were then hollowed out by precision machining in the middle of each block to allow the surgical drill to reach the implant recipient site without limitation (Fig. 1). The implant sites were simulated with machined 1 3 5-inch clear acrylic blocks, 15 mm in thickness (Fig. 1). A clear acrylic box was then fabricated with 2 screw VOLUME 92 NUMBER 5
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Fig. 1. Schematic diagram of testing apparatus.
knobs (EZ-Flo International, Ontario, Calif) in the front of the box which were used to securely hold the surgical guide, the spacer, and the implant recipient blocks during the simulated implant placement. The surgical guide, the spacer, and the implant recipient block were placed in the clear acrylic box. The order of the blocks placed in the box, from the bottom to top, was as follows: implant recipient block, spacer, and surgical guide. A single operator randomly prepared implant recipient sites, 13 mm in depth from the top of the clear acrylic block through the prepared surgical guide, at the varying distances (thickness of spacer) using a 2.0-mm round drill, a 2.0-mm twist drill, and finally a 2.3-mm twist drill (3i Implant Innovations, Palm Beach Gardens, Fla) with a low-speed handpiece (Titan-3 Low Speed Handpiece system; Star Dental, Lancaster, Pa). After initial preparation of the implant recipient site with a 2.0-mm round drill, the site was prepared using a 2.0-mm twist drill using the surgical guide as far as the surgical drill allowed. The surgical guide was then removed, and the site was further prepared with a 2.3-mm twist drill for each of the 16 varying combinations of dimensions and distances. As a result, a total of 240 implant recipient sites were prepared. For each combination of the 16 varying surgical guide dimensions, 15 specimens were prepared. To measure the deviated angulations (DA), the acrylic blocks with the prepared implant recipient sites were marked at each 1 3 1-inch square to locate the midpoint of the square. A metal rod, 2 mm in diameter (K&S Engineering, Chicago, Ill), was placed in the prepared implant recipient site (Fig. 2). The deviated angulation was measured in both right-to-left (DARL) and front-to-back directions (DAFB) from the midpoint using a protractor (180-degree protractor; Staedtler USA, Chatsworth, Calif). All measurements were made by 1 operator in degrees. NOVEMBER 2004
Fig. 2. Measurement of deviated angulations using protractor. P, Protractor; M, metal rod; IRS, Implant recipient site.
The data were analyzed using a factorial analysis of variance (ANOVA). A power analysis indicated that 240 specimens were needed and the power was 0.77 (a=.05). Tukey HSD tests were used when significant differences were found for the varying dimensions of the surgical guides. In this study, deviated angulations smaller than 1 degree were considered clinically not meaningful based on studies by Weinberg.10-12 According to Weinberg, a 10-degree increase in implant inclination will produce a 5% increase in torque.10-12 Torque is a way of expressing and measuring the result of force applied at an angle to an object and its supporting medium.3,13 Three-dimensional analysis demonstrates that lateral or inclined force applied to the implant produces maximum force to the implant at the level of the third screw thread and to the crestal bone.3,13 For every 1 mm of horizontal implant offset, the torque will increase by approximately 15%.10-12 Therefore, placing the head of the implant as close as possible to the vertical center line of the restoration substantially reduces torque. 465
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Table I. Mean deviated angulations in right-to-left (DARL) and front-to-back (DAFB) directions for each varying dimension Variables
Diameter (D) 4 2 5 3 Length (L) 6 9 Distance (S) 2 4 a, b
Table II. Factorial ANOVA for deviated angulations in right-to-left direction Source
N
Mean DARL (degrees)
SD
Mean DAFB (degrees)
60 60 60 60
2.57a 2.61a 2.64a 2.76a
1.71 1.04 1.40 1.30
2.73a 3.13a,b 3.31a,b 3.60b
1.70 1.58 2.23 1.53
120 120
2.96a 2.33b
1.42 1.27
3.82a 2.56b
1.87 1.51
120 120
3.16a 2.13b
1.39 1.16
3.72a 2.66b
1.80 1.67
SD
Sum of squares
Df
D 3 L 1 S 1 D3L 3 D3S 3 L3S 1 D3L3S 3 Error 224 Total 240 Corrected total 239
1.197 24.029 63.304 7.216 13.815 2.452 5.799 335.770 2134.003 453.581
Mean square
0.399 24.029 63.304 2.405 4.605 2.452 1.933 1.499
F value
0.266 16.030 42.232 1.605 3.072 1.636 1.289
P value
.850 .0001 .0001 .189 .029 .202 .279
Table III. Factorial ANOVA for deviated angulations in front-to-back direction
Groups modified with same letter are not significantly different (P,.05). Source
D L S D3L D3S L3S D3L3S Error Total Corrected Total
Fig. 3. Interaction between diameter and distance for deviated angulations in right-to-left direction - DARL (*smaller than 1 degree difference that is clinically not meaningful).
RESULTS Deviated angulations in the right-to-left direction (DARL) Mean values for the deviated angulations in the rightto-left direction are listed in Table I. The deviated angulation did not differ significantly (P= .85, Table II) when a comparison of the diameters was made. However, there was a significant difference in DARL between the 2 lengths of the surgical guide (P=.0001). The DARL at a length of 9.0 mm (2.33 degrees 6 1.27) was significantly smaller than the DARL at a length of 6.0 mm (2.96 degrees 6 1.42, Table II). An analysis of the 2 different distances also resulted in a significant difference. The DARL at a distance of 2.0 mm (3.16 degrees 6 1.39) was significantly greater than that at a distance of 4.0 mm (2.13 degrees 6 1.16, P=.0001, Tables I and II). 466
df
Sum of squares
3 23.331 1 96.013 1 66.993 3 44.590 3 29.884 1 25.220 3 8.110 224 490.747 240 3224.600 239 784.887
Mean square
7.777 96.013 66.993 14.863 9.961 25.220 2.703 2.191
F value
3.550 43.825 30.579 6.784 4.547 11.512 1.234
P value
.015 .0001 .0001 .0001 .004 .001 .298
The interaction analysis between diameter and distance for DARL was significant (P,.05). While at all diameters, the difference in DARL at a distance of 2.0 mm was larger than at a distance of 4.0 mm, this difference was much larger for diameters 4.0 mm and 5.0 mm than for 2.0 mm and 3.0 mm (P,.05). In addition, the difference at 2.0 mm was not clinically meaningful because in this study, deviated angulations smaller than 1 degree were considered clinically not meaningful based on studies by Weinberg.11,12 No other interactions were significant (Tables I and II and Fig. 3). In summary, deviated angulations in the right-to-left direction did not show significant differences in the diameter of the surgical guide. However, significant differences in DARL were found between the 2 lengths (9.0 mm , 6.0 mm) and with the distances (4.0 mm , 2.0 mm) of the surgical guide, and a significant interaction resulted between diameter and distance.
Deviated angulations in the front-to-back direction (DAFB) The calculated mean deviated angulations in the front-to-back direction are shown in Table I. A significant difference in DAFB was found for the 4 diameters (P=.015). The DAFB at a diameter of 4.0 mm (2.73 VOLUME 92 NUMBER 5
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Fig. 4. Interaction between diameter and length for deviated angulations in front-to-back direction - DAFB (*smaller than 1 degree difference that is clinically not meaningful).
degrees 6 1.70) was significantly smaller than at a diameter of 3.0 mm (3.60 degrees 6 1.53, Table III). There was also a significant difference in DAFB for the 2 lengths of the surgical guide. The DAFB at a length of 9.0 mm (2.56 degrees 6 1.51) was significantly smaller (P=.0001) than the DAFB at a length of 6.0 mm (3.82 degrees 6 1.87, Tables I and III). With distance, a significant difference in DAFB was observed (P=.0001). The DAFB at a distance of 4.0 mm (2.66 degrees 6 1.67) was significantly smaller than the DAFB at a distance of 2.0 mm (3.72 degrees 6 1.80, Tables I and III). The interaction between diameter and length demonstrated significant differences (Table III, Fig. 4). This interaction was significant (P=.0001). While at all diameters, the difference in DAFB at a length of 6.0 mm was larger than at a length of 9.0 mm, this difference was much larger for the diameters of 4.0 mm and 5.0 mm than for the diameters of 2.0 mm and 3.0 mm. In addition, the difference at 3.0 mm was not clinically meaningful. Between diameter and distance, there was also a significant interaction (P=.004, Table III, Fig. 5). DAFB at a smaller distance (2.0 mm) resulted in a greater deviation than at a larger distance (4.0 mm). This interaction demonstrated that, while at all diameters, the difference in DAFB at a distance of 2.0 mm was greater than at a distance of 4.0 mm, this difference was much larger for diameters of 3.0 mm and 5.0 mm. The difference at diameters 2.0 mm and 4.0 mm was not clinically meaningful. Furthermore, the interaction between length and distance was significant (P=.001, Table III, Fig. 6). This interaction demonstrated that, while at both lengths, the difference in DAFB at a distance of 2.0 mm resulted in a greater deviation than at a distance of 4.0 mm, the difference was much larger for a length of 9.0 mm than for a length of 6.0 mm. Also, the difference at a length of 6.0 mm was not clinically meaningful. In summary, there were significant differences with varying diameters, lengths, and distances. The shorter NOVEMBER 2004
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Fig. 5. Interaction between diameter and distance for the deviated angulations in front-to-back direction - DAFB (*smaller than 1 degree difference that is clinically not meaningful).
Fig. 6. Interaction between length and distance for deviated angulations in front-to-back direction - DAFB (*smaller than 1 degree difference that is clinically not meaningful).
length resulted in larger deviated angulations. There were significant interactions between diameter and length, diameter and distance, and length and distance.
DISCUSSION Factors that affect the accuracy of implant placement were shown to include diameter, length, and the distance between the surgical guide and the implant recipient site. The research hypothesis with respect to length was supported. Interactions between length and distance and between length and diameter tended to not support the hypotheses for distance and diameter. In the evaluation of deviated angulations, the length of the surgical guide was found to be the most important factor. A longer length reduced the amount of the deviated angulations significantly, both in the right-to-left and front-to-back direction. This indicates the longer surgical guide limited the deviation of the surgical drills, resulting in decreased deviated angulations. For the interaction between the diameter and the distance for DARL (Fig. 3), the deviated angulations were 467
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larger with a distance of 2.0 mm, although at the smallest diameter the difference was not clinically meaningful. This result is counter to the hypothesized prediction, implying that distance is not the primary controlling factor. One might ask if increased visibility results in greater accuracy. This is unlikely because better visibility does not always equate to improved accuracy, as was previously discussed for a clear vacuum-formed matrix.5 The visibility alone or visibility without an adequate guide may not increase accuracy because the position of the operating clinician and/or the patient during implant placement may not allow for accurate assessment of the angulations of the surgical drill. If better visibility was a possible factor, there would be no inaccuracy without any surgical guide during implant placement. However, this is not the case. A similar result was also seen in the interaction analysis for DAFB (Fig. 5). This result also supported the hypothesis that the length of the surgical guide is the primary controlling factor in minimizing deviated angulations. These results showed that, without the influence of the length factor, the effect of diameter and distance did not make a significant contribution to reducing the deviated angulation. However, at the smallest diameter (2.0 mm), the differences in deviated angulations between the distance at 2.0 mm and 4.0 mm were not clinically meaningful (in this study, deviated angulations smaller than 1 degree were considered clinically not meaningful based on studies by Weinberg10-12), as defined earlier, although the result was contrary to the proposed research hypothesis. Therefore, having an appropriate surgical guide channel diameter that minimizes the movement of the surgical drill becomes an important factor when the length of the surgical guide channel is not sufficient. In simple terms, providing a surgical guide with a smaller diameter alone was not sufficient to reduce the deviated angulation. Furthermore, in the interaction between diameter and length for DAFB, the fact that, at all diameters, the hypothesized prediction that the deviated angulation with a length of 6.0 mm would be greater than with a length of 9.0 mm held true reflects the strong influence of length. Even at the largest diameter, at which the most deviation is possible due to the greater diameter of the surgical guide (Fig. 4), the effect of a longer length contributed to the resulting smaller deviated angulation. The interaction analysis between length and distance for DAFB also supports the result that distance is not the major contributing factor in reducing the deviated angulations. At a longer length (9.0 mm), which was shown to be the primary controlling factor in the minimization of deviation, the distance of 2.0 mm produced a larger deviation than the distance of 4.0 mm (Fig. 6). Therefore, while the research hypothesis for length was supported, the interaction between length and both distance and diameter tended to support the null research hypotheses. 468
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In fabricating surgical guides for the optimal treatment result, one should incorporate an appropriate length and diameter that will minimize the movement of the surgical drill. The surgical guide should provide an adequate length without compromising distance for the surgical handpiece. If the length must be reduced because there is limited distance for the surgical handpiece and drills, the diameter of the surgical guide channel should be the smallest diameter that the selected surgical drill fits. Because this was an in vitro study, reproducing an actual intraoral implant recipient site was not possible. However, this study clearly showed length to be the important controlling factor in fabricating a surgical guide for more accurate implant placement. An in vivo study examining the effect of various types of surgical guides on the accuracy of implant placement is suggested as an area for future research.
CONCLUSION In this study, the effect of varying diameters, lengths, and distances between the underside of the surgical guide and the implant recipient site was explored. For deviated angulations, length was determined to be the primary factor in reducing deviations in implant angulations. Based on this study, the following recommendations are made. For accurate implant angulations: (1) a longer length of a surgical guide channel should be utilized, if interarch distance permits, and (2) the smallest diameter that the selected surgical drill fits should be utilized when the use of the optimal surgical guide channel length is not possible. REFERENCES 1. Lazzara RJ. Effect of implant position on implant restoration design. J Esthet Dent 1993;5:265-9. 2. Dixon DL, Breeding LC. Surgical guide fabrication for an angled implant. J Prosthet Dent 1996;75:562-5. 3. Rieger MR, Mayberry M, Brose MO. Finite element analysis of six endosseous implants. J Prosthet Dent 1990;63:671-6. 4. Parel SM, Funk JJ. The use and fabrication of a self-retaining surgical guide for controlled implant placement: a technical note. Int J Oral Maxillofac Implants 1991;6:207-10. 5. Blustein R, Jackson R, Rotoskoff K, Coy RE, Godar D. Use of splint material in the placement of implants. Int J Oral Maxillofac Implants 1986;1: 47-9. 6. Neidlinger J, Lilien BA, Kalant DC Sr. Surgical implant stent: a design modification and simplified fabrication technique. J Prosthet Dent 1993; 69:70-2. 7. Burns DR, Crabtree DG, Bell DH. Template for positioning and angulation of intraosseous implants. J Prosthet Dent 1988;60:479-83. 8. Engleman MJ, Sorensen JA, Moy P. Optimum placement of osseointegrated implants. J Prosthet Dent 1988;59:467-73. 9. Ku YC, Shen YF. Fabrication of a radiographic and surgical stent for implants with a vacuum former. J Prosthet Dent 2000;83:252-3. 10. Weinberg LA. Reduction of implant loading with therapeutic biomechanics. Implant Dent 1998;7:277-85. 11. Weinberg LA. Therapeutic biomechanics concepts and clinical procedures to reduce implant loading. Part I. J Oral Implantol 2001;27: 293-301.
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12. Weinberg LA. Therapeutic biomechanics concepts and clinical procedures to reduce implant loading. Part II. J Oral Implantol 2001;27:302-10. 13. Clelland NL, Ismail YH, Zaki HS, Pipko D. Three-dimensional finite element stress analysis in and around the Screw-Vent implant. Int J Oral Maxillofac Implants 1991;6:391-8. Reprint requests to: DR MIJIN CHOI DEPARTMENT OF RESTORATIVE DENTISTRY BALTIMORE COLLEGE OF DENTAL SURGERY UNIVERSITY OF MARYLAND AT BALTIMORE
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666 WEST BALTIMORE ST BALTIMORE, MD 21201 FAX: (410) 706-3028 E-MAIL: [email protected] 0022-3913/$30.00 Copyright Ó 2004 by The Editorial Council of The Journal of Prosthetic Dentistry
doi:10.1016/j.prosdent.2004.08.010
469
Purpose. The purpose of this study was to determine the effect of varied dimensions (diameter, length, and distance between the underside of the surgical guide and the implant recipient site) of a surgical guide on the accuracy of implant angulation. Material and methods. In this in vitro study, 240 implant recipient sites were randomly prepared using varied dimensions of a surgical guide. The varied dimensions of the surgical guide’s channel and distance were: channel diameter (2, 3, 4, or 5 mm), channel length (6 or 9 mm), and distance between the underside of the surgical guide and the simulated implant recipient site (2 or 4 mm). From these varying dimensions and distances, 16 combinations of dimensions and distances were tested. For each combination, 15 simulated implant recipient site (SIRS) specimens were prepared. The deviated angulation (DA) from the midpoint of the top surface of the 1- 3 1-inch simulated implant recipient site (each simulated implant recipient acrylic block contained 5 SIRS of 1 3 1 inch), in the right-to-left (DARL) and front-to-back (DAFB) directions, were measured in degrees using a protractor. The data was analyzed using factorial analysis of variance and Tukey’s HSD test (a=.05). Results. The DARL, in degrees, at a channel length of 9.0 mm (2.33 6 1.27) was significantly smaller than at a channel length of 6.0 mm (3.0 6 1.42, P=.0001). The DARL, in degrees, at a distance of 4.0 mm (2.13 6 1.16) was significantly smaller than at a distance of 2.0 mm (3.16 6 1.39, P=.0001). Also, a significant interaction for DARL was found between diameter and distance (P,.05). For DAFB, the varying diameters (P,.05), lengths (P=.0001), and distances (P=.0001) showed significant differences. The DAFB at a channel length of 9.0 mm (2.56 degrees 6 1.51) was significantly smaller than that at 6.0 mm (3.82 degrees 6 1.87). Significant interactions found for DAFB were: diameter by length (P=.0001), diameter by distance (F = 4.547, P=.004), and length by distance (F = 11.512, P=.001). Conclusion. Within the limitations of this study, the results suggest channel length as the primary controlling factor in minimizing deviated angulations. (J Prosthet Dent 2004;92:463-9.)
CLINICAL IMPLICATIONS Within the limitations of this in vitro study, the length of the surgical guide channel was found to be the primary factor in minimizing deviations in implant angulation. The implant angulation is best controlled by fabricating the surgical guide with the longest channel length permitted by the interarch distance.
I
mplant dentistry is divided into 2 phases, surgical and restorative. Often, different clinicians perform these phases. While the surgeon would prefer to position the implant in the most biologically favorable bone site,
Presented at the oral presentation program at the 31st Annual Meeting and Exposition of the American Association for Dental Research, San Antonio, Texas, March 14, 2003. Supported by The Greater New York Academy of Prosthodontics Student Grant. a Third-year Prosthodontic Resident, Postdoctoral Program in Prosthodontics, Department of Restorative Dentistry. b Professor, Department of Oral Health Care Delivery. c Associate Professor and Director of Prosthodontic Residency, Department of Restorative Dentistry.
NOVEMBER 2004
the restorative dentist requires implant placement that allows for optimum function and maximum esthetic value with relative mechanical ease. For the definitive restoration to be successful, therefore, biological, functional, mechanical, and esthetic requirements must be achieved. While the importance of planning for precise implant placement has been stressed in the literature, surgical guides that do not provide exact drill guides may serve as only an approximate guide to the surgeon.1 As a result, it is not uncommon for the implant to be placed in a slightly different position from the originally planned position. Although this discrepancy may be minimal at the time of surgery, it may predispose the implant to an esthetic or functional failure.2 Therefore, fabrication THE JOURNAL OF PROSTHETIC DENTISTRY 463
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of a surgical guide is critical for esthetics, function, and long-term success of the implant-bone prosthesis.3 The need for more accurate placement of implants has led to the development of numerous template designs. These include the labial outline surgical guide made from a wax arrangement of the proposed definitive restoration,4 a clear vacuum-formed matrix,5 a duplicate of the existing restoration,6 and other methods.7 The clear vacuum-formed surgical guide with a guide hole made over the anticipated implant position does not prevent inadvertent deviation of the angle of placement. Significant inaccuracies due to the absence of a guiding channel may occur at the apical portion of the pilot or twist drills close to the edentulous residual ridge. Parel and Funk4 described a surgical guide with the buccal contours of the proposed implant-supported restoration created in the guide. This type of surgical guide may not serve as a direct mechanical guide and site preparation may be performed freehand. Engleman et al8 described a similar surgical guide. This design may not provide accurate spatial information for an implant. In addition, Ku and Shen9 described a surgical guide fabricated with a vacuum-formed matrix filled with clear acrylic resin. In this technique, the guide channel was prepared by drilling through the clear acrylic resin using carbide burs, which had the same diameter as the pilot drill. This technique only allows for correct initial positioning and does not allow for correct inclination at implant placement because the implant cannot be placed with the guide after the initial preparation due to insufficient diameter for the larger pilot drill or twist drill to pass through the channel prepared within the guide. In many situations, surgeons request that the length of the guide channel be reduced in the apical portion to allow for sufficient irrigation and visualization during surgical procedures. This provides the pilot drill more room, allowing for deviation of the implant angulations to occur. Furthermore, due to the narrow diameter of the guide channel, only the 2-mm twist drill is allowed to pass through, causing a surgeon to place implants without the guidance of the surgical guide after the initial preparation. Presently, with the use of computed tomography technology, the fabrication of multiple surgical guides for different diameter surgical drills is feasible. To fabricate a surgical guide that limits the deviation of the drills being used, it is important to examine the factors that may influence accurate placement of an implant when a surgical guide is used during placement. These factors include the diameter of the prepared guide channel, length of the prepared guide channel, and distance between the underside of the surgical guide and the implant site at the alveolar crest. Without careful control of these factors that contribute to the angulation of the implant, the deviation of the pilot drill or twist drill 464
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may cause significant inaccuracies. Thus, the bottom of the guide channel may be too far from the residual ridge, the guide channel may be too short, the diameter of guide channel may be too large, allowing for changes in angulations of the drills, or some combination of these 3 events may occur. The purpose of this study was to investigate the effect of dimensional factors of surgical guides on the accuracy of implant placement. The varying dimensions were diameter (D), length of channel (L), and distance (S) between the surgical guide and the simulated implant recipient site. The hypothesized research predictions for these variables were: (1) a larger diameter would result in a greater deviation, (2) a shorter length would result in a greater deviation, and (3) a larger distance would result in a greater deviation.
MATERIAL AND METHODS In this in vitro study, the surgical guide for simulated implant placement varied in 2 channel dimensions, diameter (D) and length (L) of the channel, and also in the distance (S) between the underside of the surgical guide and the simulated implant recipient site. To investigate the effects of the 3 surgical guide variables, clear acrylic resin blocks (Tap Plastics Inc, Stockton, Calif) were obtained for the fabrication of the testing apparatus. The items fabricated for this study were the simulated surgical guides, spacers to vary the distance between the underside of the surgical guide and the implant recipient site, simulated implant recipient blocks, and a clear acrylic box (1 3 5 3 1.1 inch, Fig. 1). The testing apparatuses were all precision-machined. The 1 3 5-inch surgical guide blocks were first machined with a precision milling machine (Heavy Duty Drilling and Milling Machine A 2 HP; Northern Tool & Equipment Company, Warren, Mich) into channel lengths of 6 mm or 9 mm. Then, 5 channels of each tested diameter were machined with a precision milling machine into appropriate blocks as indicated. The channels were located so that each channel was placed at the midpoint of a 1- 3 1-inch square on the top surface of the 1- 3 5-inch block. To vary the distance between the underside of the surgical guide and the implant recipient site, acrylic spacers were machined with the precision milling machine to dimensions of 1- 3 5-inch blocks with heights of 2 or 4 mm, therefore creating 2- or 4-mm distances from the guide to implant recipient site. The spacers were then hollowed out by precision machining in the middle of each block to allow the surgical drill to reach the implant recipient site without limitation (Fig. 1). The implant sites were simulated with machined 1 3 5-inch clear acrylic blocks, 15 mm in thickness (Fig. 1). A clear acrylic box was then fabricated with 2 screw VOLUME 92 NUMBER 5
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Fig. 1. Schematic diagram of testing apparatus.
knobs (EZ-Flo International, Ontario, Calif) in the front of the box which were used to securely hold the surgical guide, the spacer, and the implant recipient blocks during the simulated implant placement. The surgical guide, the spacer, and the implant recipient block were placed in the clear acrylic box. The order of the blocks placed in the box, from the bottom to top, was as follows: implant recipient block, spacer, and surgical guide. A single operator randomly prepared implant recipient sites, 13 mm in depth from the top of the clear acrylic block through the prepared surgical guide, at the varying distances (thickness of spacer) using a 2.0-mm round drill, a 2.0-mm twist drill, and finally a 2.3-mm twist drill (3i Implant Innovations, Palm Beach Gardens, Fla) with a low-speed handpiece (Titan-3 Low Speed Handpiece system; Star Dental, Lancaster, Pa). After initial preparation of the implant recipient site with a 2.0-mm round drill, the site was prepared using a 2.0-mm twist drill using the surgical guide as far as the surgical drill allowed. The surgical guide was then removed, and the site was further prepared with a 2.3-mm twist drill for each of the 16 varying combinations of dimensions and distances. As a result, a total of 240 implant recipient sites were prepared. For each combination of the 16 varying surgical guide dimensions, 15 specimens were prepared. To measure the deviated angulations (DA), the acrylic blocks with the prepared implant recipient sites were marked at each 1 3 1-inch square to locate the midpoint of the square. A metal rod, 2 mm in diameter (K&S Engineering, Chicago, Ill), was placed in the prepared implant recipient site (Fig. 2). The deviated angulation was measured in both right-to-left (DARL) and front-to-back directions (DAFB) from the midpoint using a protractor (180-degree protractor; Staedtler USA, Chatsworth, Calif). All measurements were made by 1 operator in degrees. NOVEMBER 2004
Fig. 2. Measurement of deviated angulations using protractor. P, Protractor; M, metal rod; IRS, Implant recipient site.
The data were analyzed using a factorial analysis of variance (ANOVA). A power analysis indicated that 240 specimens were needed and the power was 0.77 (a=.05). Tukey HSD tests were used when significant differences were found for the varying dimensions of the surgical guides. In this study, deviated angulations smaller than 1 degree were considered clinically not meaningful based on studies by Weinberg.10-12 According to Weinberg, a 10-degree increase in implant inclination will produce a 5% increase in torque.10-12 Torque is a way of expressing and measuring the result of force applied at an angle to an object and its supporting medium.3,13 Three-dimensional analysis demonstrates that lateral or inclined force applied to the implant produces maximum force to the implant at the level of the third screw thread and to the crestal bone.3,13 For every 1 mm of horizontal implant offset, the torque will increase by approximately 15%.10-12 Therefore, placing the head of the implant as close as possible to the vertical center line of the restoration substantially reduces torque. 465
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Table I. Mean deviated angulations in right-to-left (DARL) and front-to-back (DAFB) directions for each varying dimension Variables
Diameter (D) 4 2 5 3 Length (L) 6 9 Distance (S) 2 4 a, b
Table II. Factorial ANOVA for deviated angulations in right-to-left direction Source
N
Mean DARL (degrees)
SD
Mean DAFB (degrees)
60 60 60 60
2.57a 2.61a 2.64a 2.76a
1.71 1.04 1.40 1.30
2.73a 3.13a,b 3.31a,b 3.60b
1.70 1.58 2.23 1.53
120 120
2.96a 2.33b
1.42 1.27
3.82a 2.56b
1.87 1.51
120 120
3.16a 2.13b
1.39 1.16
3.72a 2.66b
1.80 1.67
SD
Sum of squares
Df
D 3 L 1 S 1 D3L 3 D3S 3 L3S 1 D3L3S 3 Error 224 Total 240 Corrected total 239
1.197 24.029 63.304 7.216 13.815 2.452 5.799 335.770 2134.003 453.581
Mean square
0.399 24.029 63.304 2.405 4.605 2.452 1.933 1.499
F value
0.266 16.030 42.232 1.605 3.072 1.636 1.289
P value
.850 .0001 .0001 .189 .029 .202 .279
Table III. Factorial ANOVA for deviated angulations in front-to-back direction
Groups modified with same letter are not significantly different (P,.05). Source
D L S D3L D3S L3S D3L3S Error Total Corrected Total
Fig. 3. Interaction between diameter and distance for deviated angulations in right-to-left direction - DARL (*smaller than 1 degree difference that is clinically not meaningful).
RESULTS Deviated angulations in the right-to-left direction (DARL) Mean values for the deviated angulations in the rightto-left direction are listed in Table I. The deviated angulation did not differ significantly (P= .85, Table II) when a comparison of the diameters was made. However, there was a significant difference in DARL between the 2 lengths of the surgical guide (P=.0001). The DARL at a length of 9.0 mm (2.33 degrees 6 1.27) was significantly smaller than the DARL at a length of 6.0 mm (2.96 degrees 6 1.42, Table II). An analysis of the 2 different distances also resulted in a significant difference. The DARL at a distance of 2.0 mm (3.16 degrees 6 1.39) was significantly greater than that at a distance of 4.0 mm (2.13 degrees 6 1.16, P=.0001, Tables I and II). 466
df
Sum of squares
3 23.331 1 96.013 1 66.993 3 44.590 3 29.884 1 25.220 3 8.110 224 490.747 240 3224.600 239 784.887
Mean square
7.777 96.013 66.993 14.863 9.961 25.220 2.703 2.191
F value
3.550 43.825 30.579 6.784 4.547 11.512 1.234
P value
.015 .0001 .0001 .0001 .004 .001 .298
The interaction analysis between diameter and distance for DARL was significant (P,.05). While at all diameters, the difference in DARL at a distance of 2.0 mm was larger than at a distance of 4.0 mm, this difference was much larger for diameters 4.0 mm and 5.0 mm than for 2.0 mm and 3.0 mm (P,.05). In addition, the difference at 2.0 mm was not clinically meaningful because in this study, deviated angulations smaller than 1 degree were considered clinically not meaningful based on studies by Weinberg.11,12 No other interactions were significant (Tables I and II and Fig. 3). In summary, deviated angulations in the right-to-left direction did not show significant differences in the diameter of the surgical guide. However, significant differences in DARL were found between the 2 lengths (9.0 mm , 6.0 mm) and with the distances (4.0 mm , 2.0 mm) of the surgical guide, and a significant interaction resulted between diameter and distance.
Deviated angulations in the front-to-back direction (DAFB) The calculated mean deviated angulations in the front-to-back direction are shown in Table I. A significant difference in DAFB was found for the 4 diameters (P=.015). The DAFB at a diameter of 4.0 mm (2.73 VOLUME 92 NUMBER 5
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Fig. 4. Interaction between diameter and length for deviated angulations in front-to-back direction - DAFB (*smaller than 1 degree difference that is clinically not meaningful).
degrees 6 1.70) was significantly smaller than at a diameter of 3.0 mm (3.60 degrees 6 1.53, Table III). There was also a significant difference in DAFB for the 2 lengths of the surgical guide. The DAFB at a length of 9.0 mm (2.56 degrees 6 1.51) was significantly smaller (P=.0001) than the DAFB at a length of 6.0 mm (3.82 degrees 6 1.87, Tables I and III). With distance, a significant difference in DAFB was observed (P=.0001). The DAFB at a distance of 4.0 mm (2.66 degrees 6 1.67) was significantly smaller than the DAFB at a distance of 2.0 mm (3.72 degrees 6 1.80, Tables I and III). The interaction between diameter and length demonstrated significant differences (Table III, Fig. 4). This interaction was significant (P=.0001). While at all diameters, the difference in DAFB at a length of 6.0 mm was larger than at a length of 9.0 mm, this difference was much larger for the diameters of 4.0 mm and 5.0 mm than for the diameters of 2.0 mm and 3.0 mm. In addition, the difference at 3.0 mm was not clinically meaningful. Between diameter and distance, there was also a significant interaction (P=.004, Table III, Fig. 5). DAFB at a smaller distance (2.0 mm) resulted in a greater deviation than at a larger distance (4.0 mm). This interaction demonstrated that, while at all diameters, the difference in DAFB at a distance of 2.0 mm was greater than at a distance of 4.0 mm, this difference was much larger for diameters of 3.0 mm and 5.0 mm. The difference at diameters 2.0 mm and 4.0 mm was not clinically meaningful. Furthermore, the interaction between length and distance was significant (P=.001, Table III, Fig. 6). This interaction demonstrated that, while at both lengths, the difference in DAFB at a distance of 2.0 mm resulted in a greater deviation than at a distance of 4.0 mm, the difference was much larger for a length of 9.0 mm than for a length of 6.0 mm. Also, the difference at a length of 6.0 mm was not clinically meaningful. In summary, there were significant differences with varying diameters, lengths, and distances. The shorter NOVEMBER 2004
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Fig. 5. Interaction between diameter and distance for the deviated angulations in front-to-back direction - DAFB (*smaller than 1 degree difference that is clinically not meaningful).
Fig. 6. Interaction between length and distance for deviated angulations in front-to-back direction - DAFB (*smaller than 1 degree difference that is clinically not meaningful).
length resulted in larger deviated angulations. There were significant interactions between diameter and length, diameter and distance, and length and distance.
DISCUSSION Factors that affect the accuracy of implant placement were shown to include diameter, length, and the distance between the surgical guide and the implant recipient site. The research hypothesis with respect to length was supported. Interactions between length and distance and between length and diameter tended to not support the hypotheses for distance and diameter. In the evaluation of deviated angulations, the length of the surgical guide was found to be the most important factor. A longer length reduced the amount of the deviated angulations significantly, both in the right-to-left and front-to-back direction. This indicates the longer surgical guide limited the deviation of the surgical drills, resulting in decreased deviated angulations. For the interaction between the diameter and the distance for DARL (Fig. 3), the deviated angulations were 467
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larger with a distance of 2.0 mm, although at the smallest diameter the difference was not clinically meaningful. This result is counter to the hypothesized prediction, implying that distance is not the primary controlling factor. One might ask if increased visibility results in greater accuracy. This is unlikely because better visibility does not always equate to improved accuracy, as was previously discussed for a clear vacuum-formed matrix.5 The visibility alone or visibility without an adequate guide may not increase accuracy because the position of the operating clinician and/or the patient during implant placement may not allow for accurate assessment of the angulations of the surgical drill. If better visibility was a possible factor, there would be no inaccuracy without any surgical guide during implant placement. However, this is not the case. A similar result was also seen in the interaction analysis for DAFB (Fig. 5). This result also supported the hypothesis that the length of the surgical guide is the primary controlling factor in minimizing deviated angulations. These results showed that, without the influence of the length factor, the effect of diameter and distance did not make a significant contribution to reducing the deviated angulation. However, at the smallest diameter (2.0 mm), the differences in deviated angulations between the distance at 2.0 mm and 4.0 mm were not clinically meaningful (in this study, deviated angulations smaller than 1 degree were considered clinically not meaningful based on studies by Weinberg10-12), as defined earlier, although the result was contrary to the proposed research hypothesis. Therefore, having an appropriate surgical guide channel diameter that minimizes the movement of the surgical drill becomes an important factor when the length of the surgical guide channel is not sufficient. In simple terms, providing a surgical guide with a smaller diameter alone was not sufficient to reduce the deviated angulation. Furthermore, in the interaction between diameter and length for DAFB, the fact that, at all diameters, the hypothesized prediction that the deviated angulation with a length of 6.0 mm would be greater than with a length of 9.0 mm held true reflects the strong influence of length. Even at the largest diameter, at which the most deviation is possible due to the greater diameter of the surgical guide (Fig. 4), the effect of a longer length contributed to the resulting smaller deviated angulation. The interaction analysis between length and distance for DAFB also supports the result that distance is not the major contributing factor in reducing the deviated angulations. At a longer length (9.0 mm), which was shown to be the primary controlling factor in the minimization of deviation, the distance of 2.0 mm produced a larger deviation than the distance of 4.0 mm (Fig. 6). Therefore, while the research hypothesis for length was supported, the interaction between length and both distance and diameter tended to support the null research hypotheses. 468
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In fabricating surgical guides for the optimal treatment result, one should incorporate an appropriate length and diameter that will minimize the movement of the surgical drill. The surgical guide should provide an adequate length without compromising distance for the surgical handpiece. If the length must be reduced because there is limited distance for the surgical handpiece and drills, the diameter of the surgical guide channel should be the smallest diameter that the selected surgical drill fits. Because this was an in vitro study, reproducing an actual intraoral implant recipient site was not possible. However, this study clearly showed length to be the important controlling factor in fabricating a surgical guide for more accurate implant placement. An in vivo study examining the effect of various types of surgical guides on the accuracy of implant placement is suggested as an area for future research.
CONCLUSION In this study, the effect of varying diameters, lengths, and distances between the underside of the surgical guide and the implant recipient site was explored. For deviated angulations, length was determined to be the primary factor in reducing deviations in implant angulations. Based on this study, the following recommendations are made. For accurate implant angulations: (1) a longer length of a surgical guide channel should be utilized, if interarch distance permits, and (2) the smallest diameter that the selected surgical drill fits should be utilized when the use of the optimal surgical guide channel length is not possible. REFERENCES 1. Lazzara RJ. Effect of implant position on implant restoration design. J Esthet Dent 1993;5:265-9. 2. Dixon DL, Breeding LC. Surgical guide fabrication for an angled implant. J Prosthet Dent 1996;75:562-5. 3. Rieger MR, Mayberry M, Brose MO. Finite element analysis of six endosseous implants. J Prosthet Dent 1990;63:671-6. 4. Parel SM, Funk JJ. The use and fabrication of a self-retaining surgical guide for controlled implant placement: a technical note. Int J Oral Maxillofac Implants 1991;6:207-10. 5. Blustein R, Jackson R, Rotoskoff K, Coy RE, Godar D. Use of splint material in the placement of implants. Int J Oral Maxillofac Implants 1986;1: 47-9. 6. Neidlinger J, Lilien BA, Kalant DC Sr. Surgical implant stent: a design modification and simplified fabrication technique. J Prosthet Dent 1993; 69:70-2. 7. Burns DR, Crabtree DG, Bell DH. Template for positioning and angulation of intraosseous implants. J Prosthet Dent 1988;60:479-83. 8. Engleman MJ, Sorensen JA, Moy P. Optimum placement of osseointegrated implants. J Prosthet Dent 1988;59:467-73. 9. Ku YC, Shen YF. Fabrication of a radiographic and surgical stent for implants with a vacuum former. J Prosthet Dent 2000;83:252-3. 10. Weinberg LA. Reduction of implant loading with therapeutic biomechanics. Implant Dent 1998;7:277-85. 11. Weinberg LA. Therapeutic biomechanics concepts and clinical procedures to reduce implant loading. Part I. J Oral Implantol 2001;27: 293-301.
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12. Weinberg LA. Therapeutic biomechanics concepts and clinical procedures to reduce implant loading. Part II. J Oral Implantol 2001;27:302-10. 13. Clelland NL, Ismail YH, Zaki HS, Pipko D. Three-dimensional finite element stress analysis in and around the Screw-Vent implant. Int J Oral Maxillofac Implants 1991;6:391-8. Reprint requests to: DR MIJIN CHOI DEPARTMENT OF RESTORATIVE DENTISTRY BALTIMORE COLLEGE OF DENTAL SURGERY UNIVERSITY OF MARYLAND AT BALTIMORE
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doi:10.1016/j.prosdent.2004.08.010
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