- Email: [email protected]
Comparison of Fixation Stability of Resorbable Versus Titanium Plate and Screws in Mandibular Angle Fractures
J Oral Maxillofac Surg 67:1644-1648, 2009
Comparison of Fixation Stability of Resorbable Versus Titanium Plate and Screws in Mandibular Angle Fractures Burak Bayram, DDS, PhD,* Kenan Araz, DDS, PhD,† Sina Uckan, DDS, PhD,‡ and Cenk Balcik, PhD§ Purpose: The aim of this study was to compare the fixation reliability and stability of titanium and
resorbable plates and screws by simulating chewing forces. Materials and Methods: Mandibular angle fractures in 11 sheep hemimandibles were fixed with 4-hole straight titanium plates and 2.0 ⫻ 7–mm titanium screws; in addition, 11 hemimandibles were fixed with 4-hole straight resorbable plates and 2.5 ⫻ 6 –mm resorbable screws according to the Champy technique. The hemimandibles were mounted with a fixation device in a servohydraulic testing unit for compressive testing. Displacement values under 20, 60, 100, 120, 150, and 200 N; maximum displacements; and maximum forces that the model could resist before breakage were recorded and compared. Results: Significant differences were found between resorbable and titanium plates and screws at all forces (20, 60, 100, 120, 150, and 200 N) (P ⬍ .05). We found no statistically significant differences in the breaking force and maximum displacement values (displacement values at the breaking forces) between the groups. Conclusions: The stability of mandibular angle fractures with titanium miniplates under simulated chewing forces was significantly higher than with the resorbable system. Metallic and resorbable fixation systems cannot be used interchangeably to treat mandibular angle fractures under similar loading conditions. © 2009 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 67:1644-1648, 2009 In many studies fractures of the mandibular angle represent the largest percentage of mandibular fractures.1-3 Many treatment approaches have been used for the fixation of angle fractures. However, optimal treatment of angle fractures remains controversial. One of the most frequently used techniques is the Champy technique. In this technique transorally
Received from Baskent University, Ankara, Turkey. *Fellow, Department of Oral and Maxillofacial Surgery, School of Dentistry. †Professor, Department of Oral and Maxillofacial Surgery, School of Dentistry. ‡Professor, Department of Oral and Maxillofacial Surgery, School of Dentistry. §Assistant Professor, Department of Mechanical Engineering. This study was supported and funded by the Baskent University Academic Research Projects Unit. Address correspondence and reprint requests to Dr Bayram: Baskent Universites Dishekimligi Fakultesi, 11.sok No: 26 06490 Bahcelievler, Ankara, Turkey; e-mail: [email protected] © 2009 American Association of Oral and Maxillofacial Surgeons
0278-2391/09/6708-0011$36.00/0 doi:10.1016/j.joms.2009.03.011
placed miniplates secured with monocortical screws are used for fixation.4 Titanium plates have been used for more than 2 decades for internal rigid fixation of mandible fractures. However, the need for a second surgery to remove these plates and screws and other disadvantages of metallic fixations (eg, palpability and growth retardation) have led to the development of resorbable materials. Still, the reliability of resorbable materials at different jaw sites after osteotomies or fractures remains controversial. The purpose of this study is to compare the fixation reliability and stability of titanium and resorbable plates and screws by simulating the chewing forces occurring during the first 6 weeks after fixation.
Materials and Methods The mandibles of 11 healthy sheep aged 9 to 11 months that had been fed a natural diet were studied. The mandibles were stripped of their soft tissues and divided at the anterior midline between the central incisors. Specimens were kept moist and refrigerated until all testing was complete. The models were sectioned in a uniform manner with a reciprocal saw
1644
1645
BAYRAM ET AL
FIGURE 1. Osteotomy line forming a 45° angle with occlusal plane. Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
from the retromolar region on a line that connected to the angle of the mandible. An osteotomy was standardized for all samples. A point 1 cm away from the most concave region of the ascending mandibular ramus toward the last molar tooth was linearly connected to the mandibular angle region, forming a 45° angle with the occlusal plane (Fig 1). Eleven hemimandibles were fixed with 4-hole straight titanium plates and 2.0 ⫻ 7–mm titanium screws; the other eleven hemimandibles were fixed with 4-hole straight resorbable plates and 2.5 ⫻ 6 –mm resorbable screws (Inion CPS System; Inion, Tampere, Finland) according to the principle of Champy. The locations of the fixation plates and screws were standardized. Each plate was inserted to
the upper border of the osteotomy line with the same pattern (Fig 2). A custom-made biomechanical testing model that had been used in our previous biomechanical studies5,6 was adapted to a servohydraulic testing unit (Instron 8874; Instron, Warwick, England), and samples were fixed from the mandibular condyle and incisor regions. The testing unit was equipped with a 2,500-kg load cell (maximum load capacity, 5,000 kg) that was set to produce linear displacement at a rate of 0.1 mm/ min. An occlusal bite force was applied to the posterior mandibles. Each hemimandible was then subjected to a continuous linear compression until a deformation of the plastic was seen. During the test, load and displacement data were recorded digitally, and load-displacement graphs were drawn by dedicated software (Bluehill Software, Warwick, England). Maximum forces (in Newtons) that the models could resist before breaking, maximum displacements (in millimeters) of the models, and displacement values (in millimeters) under 20, 60, 100, 120, 150, and 200 N were compared by use of the Mann-Whitney U test.
Results The displacement values at applied forces were recorded (Table 1). Because of measurement errors, 2 models from the group fixed with resorbable materials and 2 models from the group fixed with titanium materials were withdrawn from the study. The variables that were evaluated statistically are shown in Tables 1 and 2. The Mann-Whitney U test was used to compare the variables and statistically
FIGURE 2. Resorbable and titanium plate fixed for osteotomy. Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
1646
MANDIBULAR ANGLE FRACTURES
Table 1. DISPLACEMENT VALUES OF APPLIED FORCES (20, 60, 100, 120, 150, AND 200 N) FOR RESORBABLE AND TITANIUM GROUPS
Displacement (mm) Resorbable
20 60 100 120 150 200
N N N N N N
Titanium
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
0.76 1.78 2.29 2.51 2.77 3.14
0.14 1.02 1.67 1.98 2.45 3.21
0.91 1.36 1.86 2.03 2.42 3.13
0.16 0.84 1.52 1.84 2.30 2.91
0.19 1.42 1.73 1.98 2.21 2.55
0.10 0.45 1.00 1.48 2.16 2.79
0.23 0.95 1.98 2.25 2.59 3.19
0.65 1.23 1.62 1.76 1.92 2.22
0.82 1.38 1.64 1.89 2.18 2.56
0.25 0.61 1.07 1.29 1.65 2.28
0.18 0.66 1.12 1.40 1.84 2.67
0.29 0.65 0.89 0.96 1.05 1.23
0.09 0.37 0.71 0.89 1.21 1.71
0.16 0.48 0.65 0.74 0.90 1.20
0.10 0.53 1.22 1.42 1.67 2.11
0.08 0.45 1.03 1.31 1.76 2.23
0.05 0.12 0.31 0.43 0.63 1.22
0.08 0.29 0.47 0.59 0.85 1.59
Abbreviation: N, Newton. Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
significant differences for the displacement values at all applied forces (20, 60, 100, 120, 150, and 200 N) (P ⬍ .05). We found no statistically significant differences in the breaking force and maximum displacement values (displacement values at the breaking forces) between the groups (Table 3).
Discussion The angle is one of the most frequent sites of the mandible to fracture after a traumatic event. Metallic plate and screw fixation has been a standard approach in the management of mandibular fractures. Ellis and Walker4 report that the single superior border plate is the simplest and most reliable technique and is associated with few major complications. Because of their high biocompatibility and ease of manipulation, bone plating systems manufactured from titanium are currently used extensively for the fixation of mandibular fractures.7 Recently, titanium particles were discovered in scar tissue and surrounding lymph nodes, leading some clinicians to recommend the removal of titanium materials after fracture healing.8,9 Infection, pain, swelling, and loosening of hardware are other reasons cited for elective removal of fixation.4 In addition, in some areas of the oral cavity, the tissue is thin and movable, making it prone to dehiscence over the hardware. Biodegradable materials were eventually developed for fixation plates to definitively eliminate the need for retrieval.9,10 The resorbable plates and screws used in this study consisted of an amorphous injection-molded copolymer of L-lactide/D-lactide/trimethylene carbonate (Inion CPS System). These plates have been reported to resorb slowly, maintaining 70% of their initial strength at 9 to 14 weeks, with 42% bulk resorption by 40 weeks, and they are completely resorbed in 2 to 4 years (in vitro data obtained by Inion for the US Food and Drug Administration). The mechanism for resorption is hydrolysis. The plates can be bent and rotated
around a central axis. However, disadvantages of resorbable systems are a foreign-body reaction (locally), high cost, easy breakage while adapting, the need for a longer operation time, and the absence of a self-tapping feature. The fresh sheep mandibles used in this study were easy to obtain. They are widely used in biomechanical studies to investigate the many and varied fixation systems because of similarities in size thickness to human mandibles.11-13 Compressive load–imitating chewing forces were applied close to the osteotomy line in the ascending ramus until plastic deformation occurred. In our study, the direction of applied force was parallel to the maximum bite force vector reported by Koolstra et al.14 Bite forces between molars in patients with mandibular angle fractures treated by miniplate osteosynthesis according to the Champy technique amounted to 90 N at the first week and 148 N at the sixth week after fixation.15 Maximum molar bite forces during the first week postoperatively have been reported to be between 90 and 130 N.15,16 In this study, immediate mechanical stability of a mandibular angle fracture fixed with a resorbable plating system compared with a titanium plating system in sheep mandibles was evaluated. A statistically significant difference was found between resorbable and titanium plates and screws up to applied forces of 200 N (20, 60, 100, 120, 150, and 200 N) (P ⬍ .05). We also found that the scale of displacement was less for the titanium plating system compared with the resorbable system. There is only 1 previous study that has compared titanium and resorbable plating systems for the treatment of mandibular angle fractures, in a single cadaveric mandible; that study showed significant biomechanical differences between the 2 materials.7 The findings of our study are similar to those of Chacon et al.7 Although statistically significant differences between displacement values of all the applied forces were ob-
1647
Table 3. P VALUES OBTAINED WITH MANN-WHITNEY U TEST
Variable
P Value
N–breaking force mm–20 N mm–60 N mm–100 N mm–120 N mm–150 N mm–200 N mm–breaking force
.66* .031 .01 ⬍.001 ⬍.001 ⬍.001 .001 .22*
Abbreviation: N, Newton. *No statistically significant difference (P ⬎ .05). Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
Maximum displacement (mm) 6.88 7.32 5.29 4.90 4.44 5.01 9.69 5.78 8.84 6.04 5.45 2.84 10.26 4.01 3.61 6.09 2.03 5.27 Breaking force (N) 471.9 344.7 380.6 307.5 401.8 326.7 468.2 473.5 425.0 447.6 443.5 352.9 842.5 444.1 343.2 298.4 233.4 359.2
5 3 2 1 9 8 7 6 5 4 3 2 1
Resorbable
Table 2. MAXIMUM DISPLACEMENT AND BREAKING FORCE VALUES FOR RESORBABLE AND TITANIUM GROUPS
4
Titanium
6
7
8
9
BAYRAM ET AL
served, we found no statistically significant differences between the 2 groups for breaking forces and maximum displacement values. This may be because of loss of flexibility of the resorbable plating system resulting in the resorbable system showing properties of the titanium system right before the breaking moment. This study has a limitation: under wet conditions, hydrolytic breakdown presumably starts after hydration and may reduce the plate’s resistance. In this study, displacement values in the titanium group were remarkably lower than those in the resorbable group. According to our results, maxillomandibular fixation may be needed to support the absorbable plate and screw fixation system in the early postoperative period after mandibular angle fractures. Although the results of this study could establish a reference for clinical applications in a limited frame, they should be supported by in vivo experiments before clinical decisions are made. In this in vitro study, mandibular angle fractures fixed by resorbable and titanium miniplates showed significant stability differences. On the basis of this finding, metallic and resorbable fixation systems may not be used interchangeably for the treatment of mandibular angle fractures under similar loading conditions. Acknowledgments The authors thank Dr Bulent Dayangac for his help with biomechanical testing.
References 1. Erol B, Tanrikulu R, Görgün B: Maxillofacial fractures. Analysis of demographic distribution and treatment in 2901 patients (25-year experience). J Craniomaxillofac Surg 32:308, 2004 2. Martini MZ, Takahashi A, de Oliveira Neto HG, et al: Epidemiology of mandibular fractures treated in a Brazilian level I trauma public hospital in the city of São Paulo, Brazil. Braz Dent J 17:243, 2006 3. Van Beek GJ, Merkx CA: Changes in the pattern of fractures of the maxillofacial skeleton. Int J Oral Maxillofac Surg 28:424, 1999
1648 4. Ellis E III, Walker LR: Treatment of mandibular angle fractures using one noncompression miniplate. J Oral Maxillofac Surg 54:864, 1996 5. Cilasun U, Uckan S, Dolanmaz D, et al: Immediate mechanical stability of sagittal split ramus osteotomy fixed with resorbable compared with titanium bicortical screws in mandibles of sheep. Br J Oral Maxillofac Surg 44:534, 2006 6. Dolanmaz D, Uckan S, Isik K, et al: Comparison of stability of absorbable and titanium plate and screw fixation for sagittal split ramus osteotomy. Br J Oral Maxillofac Surg 42:127, 2004 7. Chacon GE, Dillard FM, Clelland N, et al: Comparison of strains produced by titanium and poly D, L-lactide acid plating systems to in vitro forces. J Oral Maxillofac Surg 63:968, 2005 8. Jorgenson DS, Mayer MH, Ellenbogen RG, et al: Detection of titanium in human tissues after craniofacial surgery. Plast Reconstr Surg 99:976, 1997 9. Haers PE, Suuronen R, Lindqvist C, et al: Biodegradable polylactide plates and screws in orthognathic surgery: Technical note. J Craniomaxillofac Surg 26:87, 1998 10. Gerlach KL: In-vivo and clinical evaluations of poly(L-lactide) plates and screws for use in maxillofacial traumatology. Clin Mater 13:21, 1993
MANDIBULAR ANGLE FRACTURES 11. Bosanquet AG, Goss AN: The sheep as a model for temporomandibular joint surgery. Int J Oral Maxillofac Surg 16:600, 1987 12. Uckan S, Schwimmer A, Kummer F, et al: Effect of the angle of the screw on the stability of the mandibular sagittal split ramus osteotomy: A study in sheep mandibles. Br J Oral Maxillofac Surg 39:266, 2001 13. Kallela I, Tulamo RM, Hietanen J, et al: Fixation of mandibular body osteotomies using biodegradable amorphous self-reinforced (70L:30DL) polylactide or metal lag screws: An experimental study in sheep. J Craniomaxillofac Surg 27:124, 1999 14. Koolstra JH, van Eijden TM, Weijs WA, et al: A three-dimensional mathematical model of the human masticatory system predicting maximum possible bite forces. J Biomech 21:563, 1988 15. Gerlach KL, Schwarz A: Bite forces in patients after treatment of mandibular angle fractures with miniplate osteosynthesis according to Champy. Int J Oral Maxillofac Surg 31:345, 2002 16. Tate GS, Ellis E III, Throckmorton G: Bite forces in patients treated for mandibular angle fractures: Implications for fixation recommendations. J Oral Maxillofac Surg 52:734, 1994
Comparison of Fixation Stability of Resorbable Versus Titanium Plate and Screws in Mandibular Angle Fractures Burak Bayram, DDS, PhD,* Kenan Araz, DDS, PhD,† Sina Uckan, DDS, PhD,‡ and Cenk Balcik, PhD§ Purpose: The aim of this study was to compare the fixation reliability and stability of titanium and
resorbable plates and screws by simulating chewing forces. Materials and Methods: Mandibular angle fractures in 11 sheep hemimandibles were fixed with 4-hole straight titanium plates and 2.0 ⫻ 7–mm titanium screws; in addition, 11 hemimandibles were fixed with 4-hole straight resorbable plates and 2.5 ⫻ 6 –mm resorbable screws according to the Champy technique. The hemimandibles were mounted with a fixation device in a servohydraulic testing unit for compressive testing. Displacement values under 20, 60, 100, 120, 150, and 200 N; maximum displacements; and maximum forces that the model could resist before breakage were recorded and compared. Results: Significant differences were found between resorbable and titanium plates and screws at all forces (20, 60, 100, 120, 150, and 200 N) (P ⬍ .05). We found no statistically significant differences in the breaking force and maximum displacement values (displacement values at the breaking forces) between the groups. Conclusions: The stability of mandibular angle fractures with titanium miniplates under simulated chewing forces was significantly higher than with the resorbable system. Metallic and resorbable fixation systems cannot be used interchangeably to treat mandibular angle fractures under similar loading conditions. © 2009 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 67:1644-1648, 2009 In many studies fractures of the mandibular angle represent the largest percentage of mandibular fractures.1-3 Many treatment approaches have been used for the fixation of angle fractures. However, optimal treatment of angle fractures remains controversial. One of the most frequently used techniques is the Champy technique. In this technique transorally
Received from Baskent University, Ankara, Turkey. *Fellow, Department of Oral and Maxillofacial Surgery, School of Dentistry. †Professor, Department of Oral and Maxillofacial Surgery, School of Dentistry. ‡Professor, Department of Oral and Maxillofacial Surgery, School of Dentistry. §Assistant Professor, Department of Mechanical Engineering. This study was supported and funded by the Baskent University Academic Research Projects Unit. Address correspondence and reprint requests to Dr Bayram: Baskent Universites Dishekimligi Fakultesi, 11.sok No: 26 06490 Bahcelievler, Ankara, Turkey; e-mail: [email protected] © 2009 American Association of Oral and Maxillofacial Surgeons
0278-2391/09/6708-0011$36.00/0 doi:10.1016/j.joms.2009.03.011
placed miniplates secured with monocortical screws are used for fixation.4 Titanium plates have been used for more than 2 decades for internal rigid fixation of mandible fractures. However, the need for a second surgery to remove these plates and screws and other disadvantages of metallic fixations (eg, palpability and growth retardation) have led to the development of resorbable materials. Still, the reliability of resorbable materials at different jaw sites after osteotomies or fractures remains controversial. The purpose of this study is to compare the fixation reliability and stability of titanium and resorbable plates and screws by simulating the chewing forces occurring during the first 6 weeks after fixation.
Materials and Methods The mandibles of 11 healthy sheep aged 9 to 11 months that had been fed a natural diet were studied. The mandibles were stripped of their soft tissues and divided at the anterior midline between the central incisors. Specimens were kept moist and refrigerated until all testing was complete. The models were sectioned in a uniform manner with a reciprocal saw
1644
1645
BAYRAM ET AL
FIGURE 1. Osteotomy line forming a 45° angle with occlusal plane. Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
from the retromolar region on a line that connected to the angle of the mandible. An osteotomy was standardized for all samples. A point 1 cm away from the most concave region of the ascending mandibular ramus toward the last molar tooth was linearly connected to the mandibular angle region, forming a 45° angle with the occlusal plane (Fig 1). Eleven hemimandibles were fixed with 4-hole straight titanium plates and 2.0 ⫻ 7–mm titanium screws; the other eleven hemimandibles were fixed with 4-hole straight resorbable plates and 2.5 ⫻ 6 –mm resorbable screws (Inion CPS System; Inion, Tampere, Finland) according to the principle of Champy. The locations of the fixation plates and screws were standardized. Each plate was inserted to
the upper border of the osteotomy line with the same pattern (Fig 2). A custom-made biomechanical testing model that had been used in our previous biomechanical studies5,6 was adapted to a servohydraulic testing unit (Instron 8874; Instron, Warwick, England), and samples were fixed from the mandibular condyle and incisor regions. The testing unit was equipped with a 2,500-kg load cell (maximum load capacity, 5,000 kg) that was set to produce linear displacement at a rate of 0.1 mm/ min. An occlusal bite force was applied to the posterior mandibles. Each hemimandible was then subjected to a continuous linear compression until a deformation of the plastic was seen. During the test, load and displacement data were recorded digitally, and load-displacement graphs were drawn by dedicated software (Bluehill Software, Warwick, England). Maximum forces (in Newtons) that the models could resist before breaking, maximum displacements (in millimeters) of the models, and displacement values (in millimeters) under 20, 60, 100, 120, 150, and 200 N were compared by use of the Mann-Whitney U test.
Results The displacement values at applied forces were recorded (Table 1). Because of measurement errors, 2 models from the group fixed with resorbable materials and 2 models from the group fixed with titanium materials were withdrawn from the study. The variables that were evaluated statistically are shown in Tables 1 and 2. The Mann-Whitney U test was used to compare the variables and statistically
FIGURE 2. Resorbable and titanium plate fixed for osteotomy. Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
1646
MANDIBULAR ANGLE FRACTURES
Table 1. DISPLACEMENT VALUES OF APPLIED FORCES (20, 60, 100, 120, 150, AND 200 N) FOR RESORBABLE AND TITANIUM GROUPS
Displacement (mm) Resorbable
20 60 100 120 150 200
N N N N N N
Titanium
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
0.76 1.78 2.29 2.51 2.77 3.14
0.14 1.02 1.67 1.98 2.45 3.21
0.91 1.36 1.86 2.03 2.42 3.13
0.16 0.84 1.52 1.84 2.30 2.91
0.19 1.42 1.73 1.98 2.21 2.55
0.10 0.45 1.00 1.48 2.16 2.79
0.23 0.95 1.98 2.25 2.59 3.19
0.65 1.23 1.62 1.76 1.92 2.22
0.82 1.38 1.64 1.89 2.18 2.56
0.25 0.61 1.07 1.29 1.65 2.28
0.18 0.66 1.12 1.40 1.84 2.67
0.29 0.65 0.89 0.96 1.05 1.23
0.09 0.37 0.71 0.89 1.21 1.71
0.16 0.48 0.65 0.74 0.90 1.20
0.10 0.53 1.22 1.42 1.67 2.11
0.08 0.45 1.03 1.31 1.76 2.23
0.05 0.12 0.31 0.43 0.63 1.22
0.08 0.29 0.47 0.59 0.85 1.59
Abbreviation: N, Newton. Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
significant differences for the displacement values at all applied forces (20, 60, 100, 120, 150, and 200 N) (P ⬍ .05). We found no statistically significant differences in the breaking force and maximum displacement values (displacement values at the breaking forces) between the groups (Table 3).
Discussion The angle is one of the most frequent sites of the mandible to fracture after a traumatic event. Metallic plate and screw fixation has been a standard approach in the management of mandibular fractures. Ellis and Walker4 report that the single superior border plate is the simplest and most reliable technique and is associated with few major complications. Because of their high biocompatibility and ease of manipulation, bone plating systems manufactured from titanium are currently used extensively for the fixation of mandibular fractures.7 Recently, titanium particles were discovered in scar tissue and surrounding lymph nodes, leading some clinicians to recommend the removal of titanium materials after fracture healing.8,9 Infection, pain, swelling, and loosening of hardware are other reasons cited for elective removal of fixation.4 In addition, in some areas of the oral cavity, the tissue is thin and movable, making it prone to dehiscence over the hardware. Biodegradable materials were eventually developed for fixation plates to definitively eliminate the need for retrieval.9,10 The resorbable plates and screws used in this study consisted of an amorphous injection-molded copolymer of L-lactide/D-lactide/trimethylene carbonate (Inion CPS System). These plates have been reported to resorb slowly, maintaining 70% of their initial strength at 9 to 14 weeks, with 42% bulk resorption by 40 weeks, and they are completely resorbed in 2 to 4 years (in vitro data obtained by Inion for the US Food and Drug Administration). The mechanism for resorption is hydrolysis. The plates can be bent and rotated
around a central axis. However, disadvantages of resorbable systems are a foreign-body reaction (locally), high cost, easy breakage while adapting, the need for a longer operation time, and the absence of a self-tapping feature. The fresh sheep mandibles used in this study were easy to obtain. They are widely used in biomechanical studies to investigate the many and varied fixation systems because of similarities in size thickness to human mandibles.11-13 Compressive load–imitating chewing forces were applied close to the osteotomy line in the ascending ramus until plastic deformation occurred. In our study, the direction of applied force was parallel to the maximum bite force vector reported by Koolstra et al.14 Bite forces between molars in patients with mandibular angle fractures treated by miniplate osteosynthesis according to the Champy technique amounted to 90 N at the first week and 148 N at the sixth week after fixation.15 Maximum molar bite forces during the first week postoperatively have been reported to be between 90 and 130 N.15,16 In this study, immediate mechanical stability of a mandibular angle fracture fixed with a resorbable plating system compared with a titanium plating system in sheep mandibles was evaluated. A statistically significant difference was found between resorbable and titanium plates and screws up to applied forces of 200 N (20, 60, 100, 120, 150, and 200 N) (P ⬍ .05). We also found that the scale of displacement was less for the titanium plating system compared with the resorbable system. There is only 1 previous study that has compared titanium and resorbable plating systems for the treatment of mandibular angle fractures, in a single cadaveric mandible; that study showed significant biomechanical differences between the 2 materials.7 The findings of our study are similar to those of Chacon et al.7 Although statistically significant differences between displacement values of all the applied forces were ob-
1647
Table 3. P VALUES OBTAINED WITH MANN-WHITNEY U TEST
Variable
P Value
N–breaking force mm–20 N mm–60 N mm–100 N mm–120 N mm–150 N mm–200 N mm–breaking force
.66* .031 .01 ⬍.001 ⬍.001 ⬍.001 .001 .22*
Abbreviation: N, Newton. *No statistically significant difference (P ⬎ .05). Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
Bayram et al. Mandibular Angle Fractures. J Oral Maxillofac Surg 2009.
Maximum displacement (mm) 6.88 7.32 5.29 4.90 4.44 5.01 9.69 5.78 8.84 6.04 5.45 2.84 10.26 4.01 3.61 6.09 2.03 5.27 Breaking force (N) 471.9 344.7 380.6 307.5 401.8 326.7 468.2 473.5 425.0 447.6 443.5 352.9 842.5 444.1 343.2 298.4 233.4 359.2
5 3 2 1 9 8 7 6 5 4 3 2 1
Resorbable
Table 2. MAXIMUM DISPLACEMENT AND BREAKING FORCE VALUES FOR RESORBABLE AND TITANIUM GROUPS
4
Titanium
6
7
8
9
BAYRAM ET AL
served, we found no statistically significant differences between the 2 groups for breaking forces and maximum displacement values. This may be because of loss of flexibility of the resorbable plating system resulting in the resorbable system showing properties of the titanium system right before the breaking moment. This study has a limitation: under wet conditions, hydrolytic breakdown presumably starts after hydration and may reduce the plate’s resistance. In this study, displacement values in the titanium group were remarkably lower than those in the resorbable group. According to our results, maxillomandibular fixation may be needed to support the absorbable plate and screw fixation system in the early postoperative period after mandibular angle fractures. Although the results of this study could establish a reference for clinical applications in a limited frame, they should be supported by in vivo experiments before clinical decisions are made. In this in vitro study, mandibular angle fractures fixed by resorbable and titanium miniplates showed significant stability differences. On the basis of this finding, metallic and resorbable fixation systems may not be used interchangeably for the treatment of mandibular angle fractures under similar loading conditions. Acknowledgments The authors thank Dr Bulent Dayangac for his help with biomechanical testing.
References 1. Erol B, Tanrikulu R, Görgün B: Maxillofacial fractures. Analysis of demographic distribution and treatment in 2901 patients (25-year experience). J Craniomaxillofac Surg 32:308, 2004 2. Martini MZ, Takahashi A, de Oliveira Neto HG, et al: Epidemiology of mandibular fractures treated in a Brazilian level I trauma public hospital in the city of São Paulo, Brazil. Braz Dent J 17:243, 2006 3. Van Beek GJ, Merkx CA: Changes in the pattern of fractures of the maxillofacial skeleton. Int J Oral Maxillofac Surg 28:424, 1999
1648 4. Ellis E III, Walker LR: Treatment of mandibular angle fractures using one noncompression miniplate. J Oral Maxillofac Surg 54:864, 1996 5. Cilasun U, Uckan S, Dolanmaz D, et al: Immediate mechanical stability of sagittal split ramus osteotomy fixed with resorbable compared with titanium bicortical screws in mandibles of sheep. Br J Oral Maxillofac Surg 44:534, 2006 6. Dolanmaz D, Uckan S, Isik K, et al: Comparison of stability of absorbable and titanium plate and screw fixation for sagittal split ramus osteotomy. Br J Oral Maxillofac Surg 42:127, 2004 7. Chacon GE, Dillard FM, Clelland N, et al: Comparison of strains produced by titanium and poly D, L-lactide acid plating systems to in vitro forces. J Oral Maxillofac Surg 63:968, 2005 8. Jorgenson DS, Mayer MH, Ellenbogen RG, et al: Detection of titanium in human tissues after craniofacial surgery. Plast Reconstr Surg 99:976, 1997 9. Haers PE, Suuronen R, Lindqvist C, et al: Biodegradable polylactide plates and screws in orthognathic surgery: Technical note. J Craniomaxillofac Surg 26:87, 1998 10. Gerlach KL: In-vivo and clinical evaluations of poly(L-lactide) plates and screws for use in maxillofacial traumatology. Clin Mater 13:21, 1993
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