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An in vitro evaluation of miniplate fixation techniques for fractures of the atrophic edentulous mandible
Int. J. Oral Maxillofac. Surg. 2005; 34: 174–177 doi:10.1016/j.ijom.2003.10.024, available online at http://www.sciencedirect.com
Research and Emerging Technologies Trauma
An in vitro evaluation of miniplate fixation techniques for fractures of the atrophic edentulous mandible
B. -H. Choi1, J. -Y. Huh2, C. -H. Suh3, K. -N. Kim4 1
Department of Oral and Maxillofacial Surgery, College of Dentistry, Yonsei University (Brain Korea 21 Project for Medical Science), Seoul, South Korea; 2Department of Dentistry, Gangneung Asan Hospital, Ulsan University, Gangneung, South Korea; 3 Department of Dentistry, College of Medicine, Dongguk University, Gyungju, South Korea; 4Department of Dental Materials, College of Dentistry, Yonsei University, Seoul, South Korea
B. -H. Choi, J. -Y. Huh, C. -H. Suh, K. -N. Kim:An in vitro evaluation of miniplate fixation techniques for fractures of the atrophic edentulous mandible. Int. J. Oral Maxillofac. Surg. 2005; 34: 174–177. # 2004 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Abstract. This study was undertaken to evaluate the biomechanical stability of various miniplate fixation techniques in varying degrees of atrophy and to determine optimal fixation techniques for fractures of the atrophic edentulous mandible. A total of 78 bovine ribs were randomly divided into 13 groups of six each; one non-atrophic group and twelve atrophic groups. Each one of the 13 sets of six ribs was formed based on the vertical dimension (40, 20, 15 or 10 mm) and osteotomized. The segments so produced were then reduced and fixed using various miniplate fixation techniques. The stability of various miniplate fixations in ribs showing varying degrees of atrophy (10, 15 and 20 mm) was compared with that of one miniplate fixation in non-atrophic ribs (40 mm), used as a standard. Atrophic groups utilizing single miniplate were significantly less stable than the non-atrophic group, whereas atrophic groups fitted with double miniplates, such as two 4-hole or two 6-hole miniplates, were significantly more stable than the non-atrophic group. The two miniplate fixation technique is recommended for the provision of adequate fracture site stability when open reduction is indicated in cases of atrophic edentulous mandibular fractures.
Although the treatment of mandibular fractures with miniplates has been proven a successful technique for open reduction and fixation in dentate patients, the situation is completely different when one has to deal with fractures of the atrophic edentulous mandible. Because of the unfavorable conditions produced by the reduced cross-sectional area of the mandible and the smaller contact area of the fractured ends, many surgeons favor more rigid fixation techniques1,9,12,15. BRUCE & ELLIS2 reported that in the atrophic mandible, bone plates 0901-5027/020174+04 $30.00/0
of greatest rigidity should be applied, and SIKES et al.14 recommended the use of a 2.4-mm reconstruction plate. However, a large reconstruction plate requires wider stripping of the periosteum for placement and involves less periosteal contact with bone after placement. In addition, large bicortical screws may violate the inferior alveolar nerve or be an instrument of further jaw fracture11. In order to avoid these problems, attention has been directed to the treatment of fractures of the edentulous mandible by miniplate osteosynthesis. FROST et al.7
Key words: mandibular fractures; atrophic mandible; miniplate. Accepted for publication 16 October 2003 Available online 10 November 2004
and IATROU et al.10 used either longer or more miniplates to increase the stability of fixation in edentulous mandibular fractures. However, no reports are available on investigation into the various miniplate fixation techniques with respect to varying degrees of bone resorption. The relation between the height of the mandible and the stability of plating techniques is self-evident14. Therefore, the aim of this study was to determine the relative biomechanical stability of various miniplate fixation techniques in varying degrees of atrophy, and to decide
# 2004 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Atrophic edentulous mandible fractures whether the use of miniplate fixation provides sufficient stability in simulated atrophic mandibular fractures. Materials and methods
This investigation was designed to compare various miniplate fixation techniques in ribs showing varying degrees of atrophy with one miniplate fixation technique in non-atrophic ribs. Our study used ribs from recently killed cows. Ribs that resembled the contours and dimensions of human edentulous mandibles were selected and stripped free of soft tissues. A total of 78 ribs similar in size were chosen and randomly divided into 13 groups of six each; one non-atrophic group and twelve atrophic groups. Each rib was cut into 20-cm lengths and the average overall and cortical thicknesses were then measured. Each one of the 13 sets of six ribs was formed based on the vertical dimension (40, 20, 15 or 10 mm) and osteotomized perpendicularly to the long axis of the rib, at a point exactly 5 cm from the proximal end of the rib. The segments were then reduced and fixed in four different ways. The constructs and configurations investigated are depicted schematically in Fig. 1, and included: (group 1) a 4-hole miniplate applied at the superior border of the rib with a 40-mm vertical dimension; (group 2) a 4-hole miniplate applied at the
superior border of the rib with a 20-mm vertical dimension; (group 3) a 6-hole miniplate applied at the superior border of the rib with a 20-mm vertical dimension; (group 4) two 4-hole miniplates applied at the superior and inferior borders of the rib with a 20-mm vertical dimension; (group 5) two 6-hole miniplates applied at the superior and inferior borders of the rib with a 20-mm vertical dimension; (group 6) a 4-hole miniplate applied at the superior border of the rib with a 15-mm vertical dimension; (group 7) a 6-hole miniplate applied at the superior border of the rib with a 15-mm vertical dimension; (group 8) two 4-hole miniplates applied at the superior and inferior borders of the rib with a 15-mm vertical dimension; (group 9) two 6-hole miniplates applied at the superior and inferior borders of the rib with a 15-mm vertical dimension; (group 10) a 4-hole miniplate applied at the superior border of the rib with a 10-mm vertical dimension; (group 11) a 6-hole miniplate applied at the superior border of the rib with a 10-mm vertical dimension; (group 12) two 4-hole miniplates applied at the superior and inferior borders of the rib with a 10-mm vertical dimension; (group 13) two 6-hole miniplates applied at the superior and inferior borders of the rib with a 10-mm vertical dimension. All miniplates and screws used in this experiment were made of titanium alloy
Fig. 1. Schematic representation of the test constructs.
175
(Martin Medizin Technik, Tuttlingen, Germany; screw diameter 2 mm, plate thickness 1 mm, screw length 5 mm). After the application of the miniplates, the stability of the fixation was measured for each sample using the method described by SIKES et al14. The distal portion of the rib was held in a mounting jig, and the proximal portion was inserted into a slotted cylinder with positional thumb screws to minimize torsional forces (Fig. 2). The cylinder was fixed on the load actuator of an Instron machine (Instron Inc., Canton, MA, USA). Using a constant distance between the loading point and the mounting jig for all specimens, load was applied at a rate of 10 mm/min. The load versus displacement relationship, load for permanent deformation, and maximum load at fracture were recorded using an Instron chart recorder. Permanent deformation was defined as the initial point that the load–displacement relationship was no longer linear. Maximum load was defined as the greatest load recorded just before any sudden decrease in the load level. Six specimens were tested in each group. The data obtained were processed in the program SPSS 7.5 (SPSS Inc., Chicago, IL, USA). ANOVA was performed to evaluate the statistical differences between the average sizes of the specimens in the 13 groups, and unpaired t-test was used to
176
Choi et al.
Fig. 2. Photograph showing the rib loading in the Instron.
calculate the significances of group stability differences. Results
ANOVA showed no significant differences (P < 0:05) in the average specimen size in the different test groups. The average permanent deformation and maximum loads for the individual groups are summarized in Table 1. With a second plate, the stability increased significantly in the atrophic ribs. The atrophic groups (i.e., groups 2, 3, 6, 7, 10 and 11) utilizing a single miniplate, such as one 4-hole or one 6-hole miniplates, were found to be significantly less stable (P < 0:05) than group 1. The atrophic groups (groups 4, 5, 8, 9, 12 and 13) fitted with double miniplates, Table 1. Load for permanent deformation and maximum load for each of the 13 groups
Group 1 2 3 4 5 6 7 8 9 10 11 12 13
Load for permanent deformation (N) 99 84 86 132 140 79 81 123 129 74 76 110 119
9 8 9 21 29 12 14 22 24 15 18 7 14
Maximum load (N) 318 246 254 537 556 215 222 492 522 188 201 443 470
29 38 13 41 34 26 16 64 136 31 29 36 84
such as two 4-hole or two 6-hole miniplates, were significantly more stable (P < 0:05) than group 1, indicating that double miniplate fixation techniques in the atrophic mandible provide greater stability than one miniplate technique in the non-atrophic mandible; see Table 2. Screw number comparisons showed that the mean permanent deformation and maximum loads afforded by one 6-hole miniplate was greater than provided by a single 4-hole miniplate. However, the difference was not statistically different. Discussion
SIKES et al.14, in 2000, undertook a study intended to provide guidelines as to whether less rigid, less invasive techniques may be used in the treatment of atrophic edentulous mandibular fractures. Unfortunately, the study was flawed by comparisons made between the strength of fixations stabilized with a single miniplate and a larger reconstruc-
tion plate in a bovine rib mandible model. Moreover, they did not include different miniplate fixation techniques. They concluded that atrophic mandible fixation is probably better treated with a reconstruction plate than with a miniplate. We undertook the present study for the same reason. However, we compared the stability of various miniplate fixation techniques in ribs showing varying degrees of atrophy with that of one miniplate applied in the tension zone of non-atrophic ribs. The superior border one miniplate technique is in line with the osteosynthesis method described by CHAMPY et al.3 for the mandibular angle fracture or body fracture in the fully dentate patient. The present study demonstrated that osteosynthesis of a fracture in a simulated atrophic mandible may be achieved by means of miniplates and monocortical screws. The advantage of this fixation system is that with very few exceptions, fixation can be achieved by an intraoral approach. This technique, thus allows the avoidance of facial scarring and the preservation of the facial nerve branches. In addition, monocortical screws disturb the inferior alveolar nerve to a lesser extent, even in cases of significant atrophy, where inevitably the canal is vulnerable. Treatment of mandibular fractures in the non-atrophic mandible with a superior border one miniplate is often successful4–6, whereas the use of similar plates for treating the atrophic edentulous mandibular fracture often results in plate fracture2. The key factor to failure seems to be the relative lack of bony buttressing in the atrophic mandible. The effect of bony buttressing on fixation systems decreases as the vertical dimension of the mandible decreases14. The current experimental study showed that a miniplate in atrophic ribs (10–20 mm) provides lesser stability than a miniplate in 40-mm vertical
Table 2. Plate system groups showing significant differences P Group Group Group Group Group Group Group Group Group Group Group
1 vs. groups 2–13 2 vs. groups 4, 5, 8, 9, 12, 13 3 vs. groups 4, 5, 8, 9, 12, 13 4 vs. groups 6, 7, 10–12 5 vs. groups 6, 7, 10–12 6 vs. groups 8, 9, 12, 13 7 vs. groups 8, 9, 12, 13 8 vs. groups 10, 11 9 vs. groups 10, 11 10 vs. groups 12, 13 11 vs. groups 12, 13
<0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05
Atrophic edentulous mandible fractures dimension (non-atrophic) ribs, whereas fixations reinforced with a second miniplate provides greater stability, even in severely atrophic ribs. Therefore, in order to compensate for the lack of bony buttressing, double miniplates should be chosen. HAUG8 showed that increased stability of miniplate fixation is obtained by increasing the screw number to a maximum of three screws per segment when using miniplates. In his investigation, the stability of approximately 10 N increased when screw numbers were increased from 2 to 3 screws per segment. In our study similar increases in stability of miniplate fixation were achieved by increasing the screw number from 2 to 3 screws per segment. The mean increased maximum load obtained was 9.3 N for the single miniplate and 25.3 N for the double miniplates. An interesting finding in the present study was that the stability achieved with two miniplates (two 4-hole or two 6-hole miniplates) was more than twice that achieved with one miniplate, even in the severely atrophic rib models (10 mm vertical dimension). Whereas increasing screw numbers from 2 to 3 screws per segment in either single or double miniplate fixations resulted in a slight improvement in the stability. In view of the fact that a two 6-hole miniplate fixation might be a more traumatic procedure than two 4-hole miniplate fixations, we suggest that the two 4-hole miniplate fixation techniques should be considered in cases of atrophic edentulous mandibular fractures. Atrophic edentulous mandibles have been classified by LUHR et al.12 as Class 1 (16–20 mm), Class 2 (11–15 mm), and Class 3 (10 mm or less). Mandibles with 30–40 mm vertical height were considered as non-atrophic. According to this classification, in the present study, 20, 15 or 10 mm vertical dimension of the bovine ribs were used as the atrophic edentulous mandible models and 40 mm vertical dimension of the ribs as the non-atrophic mandible mod-
els. Bovine rib is similar in contour and in dimension to the body and angular region of the human mandible, and it also possesses cortical and cancellous bone of similar thickness. This model appears to have the advantage of minimizing variations and of allowing standardization for comparison, and thus it has been used in biomechanical research8,13,14. Further investigations on the results of clinical series using two 4-hole miniplates in atrophic edentulous mandibular fractures are desirable to decide whether the results of our experimental study in the ribs are in accord with clinical findings. Acknowledgments. This work was supported by Grant No. R13-2003-13 from the Medical Science and Engineering Research Program of the Korea Science & Engineering Foundation. References 1. Bruce RA, Strachan DS. Fractures of the edentulous mandible: The Chalmers J. Lyons Academy of Study. J Oral Surg 1976: 34: 973–977. 2. Bruce RA, Ellis E. The second Chalmers J. Lyons academy study of fractures of the edentulous mandible. J Oral Maxillofac Surg 1993: 51: 904–911. 3. Champy M, Lodde JP, Schmitt R, Must D. Mandibular osteosynthesis by miniature screwed plates via a buccal approach. J Maxillofac Surg 1978: 6: 14–21. 4. Champy M, Kahn JL. Fracture line stability as a function of the internal fixation system: an in vitro comparison using a mandibular angle fracture model (Discussion). J Oral Maxillofac Surg 1995: 53: 801–802. 5. Ellis E, Walker LR. Treatment of mandibular angle fractures using one noncompression miniplate. J Oral Maxillofac Surg 1996: 54: 864–871. 6. Feller KU, Richter G, Schneider M, Eckelt U. Combination of microplate and miniplate for osteosynthesis of mandibular fractures: an experimental study. Int J Oral Maxillofac Surg 2002: 31: 78–83.
177
7. FROST D, TUCKER M, WHITE R. Small plate fixation for fixation of mandibular fractures. In: Tucker MR, Terry BC, White R, et al., eds: Rigid Fixation in Maxillofacial Surgery. Philadelphia, PA: Lippincott 1991: 104–121. 8. Haug R. The effect of screw number and length on two methods of tension band plating. J Oral Maxillofac Surg 1993: 51: 159–162. 9. Hibi H, Sawaki Y, Ueda M. Modified osteosynthesis for condylar neck fractures in atrophic mandibles. Int J Oral Maxillofac Surg 1997: 26: 348–350. 10. Iatrou I, Samaras C, Lygidakis NT. Miniplate osteosynthesis for fractures of the edentulous mandible: a clinical study 1989–1996. J Craniomaxillofac Surg 1998: 26: 400–404. 11. Iizuka T, Lindqvist C. Sensory disturbances associated with rigid internal fixation of mandibular fractures. J Oral Maxillofac Surg 1991: 49: 1264–1268. 12. Luhr HG, Reidick T, Merten HA. Results of treatment of fractures of the atrophic edentulous mandible by compression plating. J Oral Maxillofac Surg 1996: 54: 250–254. 13. Sikes JW, Smith BR, Mukherjee DP, Coward KA. Comparison of fixation strengths of locking head and conventional screws. J Oral Maxillofac Surg 1998: 56: 468–473. 14. Sikes JW, Smith BR, Mukherjee DP. An in vitro study of the effect of bony buttressing on fixation strength of a fractured atrophicedentulous mandible model. J Oral Maxillofac Surg 2000: 58: 56–61. 15. SPIESSL B. Universal plate system, contral angle fractures, use of the EDCP and reconstruction plate internal fixation of the mandible. In: Spiessl B, ed.: Internal Fixation of the Mandible. New York, NY: Springer-Verlag 1989: 19292. Address: Byung-Ho Choi Department of Oral and Maxillofacial Surgery Wonju Christian Hospital Yonsei University 162 Ilsan-Dong Wonju, Kangwon-Do South Korea. Tel: þ82 33 741 0672 Fax: þ82 33 748 2025 E-mail: [email protected]
Research and Emerging Technologies Trauma
An in vitro evaluation of miniplate fixation techniques for fractures of the atrophic edentulous mandible
B. -H. Choi1, J. -Y. Huh2, C. -H. Suh3, K. -N. Kim4 1
Department of Oral and Maxillofacial Surgery, College of Dentistry, Yonsei University (Brain Korea 21 Project for Medical Science), Seoul, South Korea; 2Department of Dentistry, Gangneung Asan Hospital, Ulsan University, Gangneung, South Korea; 3 Department of Dentistry, College of Medicine, Dongguk University, Gyungju, South Korea; 4Department of Dental Materials, College of Dentistry, Yonsei University, Seoul, South Korea
B. -H. Choi, J. -Y. Huh, C. -H. Suh, K. -N. Kim:An in vitro evaluation of miniplate fixation techniques for fractures of the atrophic edentulous mandible. Int. J. Oral Maxillofac. Surg. 2005; 34: 174–177. # 2004 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Abstract. This study was undertaken to evaluate the biomechanical stability of various miniplate fixation techniques in varying degrees of atrophy and to determine optimal fixation techniques for fractures of the atrophic edentulous mandible. A total of 78 bovine ribs were randomly divided into 13 groups of six each; one non-atrophic group and twelve atrophic groups. Each one of the 13 sets of six ribs was formed based on the vertical dimension (40, 20, 15 or 10 mm) and osteotomized. The segments so produced were then reduced and fixed using various miniplate fixation techniques. The stability of various miniplate fixations in ribs showing varying degrees of atrophy (10, 15 and 20 mm) was compared with that of one miniplate fixation in non-atrophic ribs (40 mm), used as a standard. Atrophic groups utilizing single miniplate were significantly less stable than the non-atrophic group, whereas atrophic groups fitted with double miniplates, such as two 4-hole or two 6-hole miniplates, were significantly more stable than the non-atrophic group. The two miniplate fixation technique is recommended for the provision of adequate fracture site stability when open reduction is indicated in cases of atrophic edentulous mandibular fractures.
Although the treatment of mandibular fractures with miniplates has been proven a successful technique for open reduction and fixation in dentate patients, the situation is completely different when one has to deal with fractures of the atrophic edentulous mandible. Because of the unfavorable conditions produced by the reduced cross-sectional area of the mandible and the smaller contact area of the fractured ends, many surgeons favor more rigid fixation techniques1,9,12,15. BRUCE & ELLIS2 reported that in the atrophic mandible, bone plates 0901-5027/020174+04 $30.00/0
of greatest rigidity should be applied, and SIKES et al.14 recommended the use of a 2.4-mm reconstruction plate. However, a large reconstruction plate requires wider stripping of the periosteum for placement and involves less periosteal contact with bone after placement. In addition, large bicortical screws may violate the inferior alveolar nerve or be an instrument of further jaw fracture11. In order to avoid these problems, attention has been directed to the treatment of fractures of the edentulous mandible by miniplate osteosynthesis. FROST et al.7
Key words: mandibular fractures; atrophic mandible; miniplate. Accepted for publication 16 October 2003 Available online 10 November 2004
and IATROU et al.10 used either longer or more miniplates to increase the stability of fixation in edentulous mandibular fractures. However, no reports are available on investigation into the various miniplate fixation techniques with respect to varying degrees of bone resorption. The relation between the height of the mandible and the stability of plating techniques is self-evident14. Therefore, the aim of this study was to determine the relative biomechanical stability of various miniplate fixation techniques in varying degrees of atrophy, and to decide
# 2004 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Atrophic edentulous mandible fractures whether the use of miniplate fixation provides sufficient stability in simulated atrophic mandibular fractures. Materials and methods
This investigation was designed to compare various miniplate fixation techniques in ribs showing varying degrees of atrophy with one miniplate fixation technique in non-atrophic ribs. Our study used ribs from recently killed cows. Ribs that resembled the contours and dimensions of human edentulous mandibles were selected and stripped free of soft tissues. A total of 78 ribs similar in size were chosen and randomly divided into 13 groups of six each; one non-atrophic group and twelve atrophic groups. Each rib was cut into 20-cm lengths and the average overall and cortical thicknesses were then measured. Each one of the 13 sets of six ribs was formed based on the vertical dimension (40, 20, 15 or 10 mm) and osteotomized perpendicularly to the long axis of the rib, at a point exactly 5 cm from the proximal end of the rib. The segments were then reduced and fixed in four different ways. The constructs and configurations investigated are depicted schematically in Fig. 1, and included: (group 1) a 4-hole miniplate applied at the superior border of the rib with a 40-mm vertical dimension; (group 2) a 4-hole miniplate applied at the
superior border of the rib with a 20-mm vertical dimension; (group 3) a 6-hole miniplate applied at the superior border of the rib with a 20-mm vertical dimension; (group 4) two 4-hole miniplates applied at the superior and inferior borders of the rib with a 20-mm vertical dimension; (group 5) two 6-hole miniplates applied at the superior and inferior borders of the rib with a 20-mm vertical dimension; (group 6) a 4-hole miniplate applied at the superior border of the rib with a 15-mm vertical dimension; (group 7) a 6-hole miniplate applied at the superior border of the rib with a 15-mm vertical dimension; (group 8) two 4-hole miniplates applied at the superior and inferior borders of the rib with a 15-mm vertical dimension; (group 9) two 6-hole miniplates applied at the superior and inferior borders of the rib with a 15-mm vertical dimension; (group 10) a 4-hole miniplate applied at the superior border of the rib with a 10-mm vertical dimension; (group 11) a 6-hole miniplate applied at the superior border of the rib with a 10-mm vertical dimension; (group 12) two 4-hole miniplates applied at the superior and inferior borders of the rib with a 10-mm vertical dimension; (group 13) two 6-hole miniplates applied at the superior and inferior borders of the rib with a 10-mm vertical dimension. All miniplates and screws used in this experiment were made of titanium alloy
Fig. 1. Schematic representation of the test constructs.
175
(Martin Medizin Technik, Tuttlingen, Germany; screw diameter 2 mm, plate thickness 1 mm, screw length 5 mm). After the application of the miniplates, the stability of the fixation was measured for each sample using the method described by SIKES et al14. The distal portion of the rib was held in a mounting jig, and the proximal portion was inserted into a slotted cylinder with positional thumb screws to minimize torsional forces (Fig. 2). The cylinder was fixed on the load actuator of an Instron machine (Instron Inc., Canton, MA, USA). Using a constant distance between the loading point and the mounting jig for all specimens, load was applied at a rate of 10 mm/min. The load versus displacement relationship, load for permanent deformation, and maximum load at fracture were recorded using an Instron chart recorder. Permanent deformation was defined as the initial point that the load–displacement relationship was no longer linear. Maximum load was defined as the greatest load recorded just before any sudden decrease in the load level. Six specimens were tested in each group. The data obtained were processed in the program SPSS 7.5 (SPSS Inc., Chicago, IL, USA). ANOVA was performed to evaluate the statistical differences between the average sizes of the specimens in the 13 groups, and unpaired t-test was used to
176
Choi et al.
Fig. 2. Photograph showing the rib loading in the Instron.
calculate the significances of group stability differences. Results
ANOVA showed no significant differences (P < 0:05) in the average specimen size in the different test groups. The average permanent deformation and maximum loads for the individual groups are summarized in Table 1. With a second plate, the stability increased significantly in the atrophic ribs. The atrophic groups (i.e., groups 2, 3, 6, 7, 10 and 11) utilizing a single miniplate, such as one 4-hole or one 6-hole miniplates, were found to be significantly less stable (P < 0:05) than group 1. The atrophic groups (groups 4, 5, 8, 9, 12 and 13) fitted with double miniplates, Table 1. Load for permanent deformation and maximum load for each of the 13 groups
Group 1 2 3 4 5 6 7 8 9 10 11 12 13
Load for permanent deformation (N) 99 84 86 132 140 79 81 123 129 74 76 110 119
9 8 9 21 29 12 14 22 24 15 18 7 14
Maximum load (N) 318 246 254 537 556 215 222 492 522 188 201 443 470
29 38 13 41 34 26 16 64 136 31 29 36 84
such as two 4-hole or two 6-hole miniplates, were significantly more stable (P < 0:05) than group 1, indicating that double miniplate fixation techniques in the atrophic mandible provide greater stability than one miniplate technique in the non-atrophic mandible; see Table 2. Screw number comparisons showed that the mean permanent deformation and maximum loads afforded by one 6-hole miniplate was greater than provided by a single 4-hole miniplate. However, the difference was not statistically different. Discussion
SIKES et al.14, in 2000, undertook a study intended to provide guidelines as to whether less rigid, less invasive techniques may be used in the treatment of atrophic edentulous mandibular fractures. Unfortunately, the study was flawed by comparisons made between the strength of fixations stabilized with a single miniplate and a larger reconstruc-
tion plate in a bovine rib mandible model. Moreover, they did not include different miniplate fixation techniques. They concluded that atrophic mandible fixation is probably better treated with a reconstruction plate than with a miniplate. We undertook the present study for the same reason. However, we compared the stability of various miniplate fixation techniques in ribs showing varying degrees of atrophy with that of one miniplate applied in the tension zone of non-atrophic ribs. The superior border one miniplate technique is in line with the osteosynthesis method described by CHAMPY et al.3 for the mandibular angle fracture or body fracture in the fully dentate patient. The present study demonstrated that osteosynthesis of a fracture in a simulated atrophic mandible may be achieved by means of miniplates and monocortical screws. The advantage of this fixation system is that with very few exceptions, fixation can be achieved by an intraoral approach. This technique, thus allows the avoidance of facial scarring and the preservation of the facial nerve branches. In addition, monocortical screws disturb the inferior alveolar nerve to a lesser extent, even in cases of significant atrophy, where inevitably the canal is vulnerable. Treatment of mandibular fractures in the non-atrophic mandible with a superior border one miniplate is often successful4–6, whereas the use of similar plates for treating the atrophic edentulous mandibular fracture often results in plate fracture2. The key factor to failure seems to be the relative lack of bony buttressing in the atrophic mandible. The effect of bony buttressing on fixation systems decreases as the vertical dimension of the mandible decreases14. The current experimental study showed that a miniplate in atrophic ribs (10–20 mm) provides lesser stability than a miniplate in 40-mm vertical
Table 2. Plate system groups showing significant differences P Group Group Group Group Group Group Group Group Group Group Group
1 vs. groups 2–13 2 vs. groups 4, 5, 8, 9, 12, 13 3 vs. groups 4, 5, 8, 9, 12, 13 4 vs. groups 6, 7, 10–12 5 vs. groups 6, 7, 10–12 6 vs. groups 8, 9, 12, 13 7 vs. groups 8, 9, 12, 13 8 vs. groups 10, 11 9 vs. groups 10, 11 10 vs. groups 12, 13 11 vs. groups 12, 13
<0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05
Atrophic edentulous mandible fractures dimension (non-atrophic) ribs, whereas fixations reinforced with a second miniplate provides greater stability, even in severely atrophic ribs. Therefore, in order to compensate for the lack of bony buttressing, double miniplates should be chosen. HAUG8 showed that increased stability of miniplate fixation is obtained by increasing the screw number to a maximum of three screws per segment when using miniplates. In his investigation, the stability of approximately 10 N increased when screw numbers were increased from 2 to 3 screws per segment. In our study similar increases in stability of miniplate fixation were achieved by increasing the screw number from 2 to 3 screws per segment. The mean increased maximum load obtained was 9.3 N for the single miniplate and 25.3 N for the double miniplates. An interesting finding in the present study was that the stability achieved with two miniplates (two 4-hole or two 6-hole miniplates) was more than twice that achieved with one miniplate, even in the severely atrophic rib models (10 mm vertical dimension). Whereas increasing screw numbers from 2 to 3 screws per segment in either single or double miniplate fixations resulted in a slight improvement in the stability. In view of the fact that a two 6-hole miniplate fixation might be a more traumatic procedure than two 4-hole miniplate fixations, we suggest that the two 4-hole miniplate fixation techniques should be considered in cases of atrophic edentulous mandibular fractures. Atrophic edentulous mandibles have been classified by LUHR et al.12 as Class 1 (16–20 mm), Class 2 (11–15 mm), and Class 3 (10 mm or less). Mandibles with 30–40 mm vertical height were considered as non-atrophic. According to this classification, in the present study, 20, 15 or 10 mm vertical dimension of the bovine ribs were used as the atrophic edentulous mandible models and 40 mm vertical dimension of the ribs as the non-atrophic mandible mod-
els. Bovine rib is similar in contour and in dimension to the body and angular region of the human mandible, and it also possesses cortical and cancellous bone of similar thickness. This model appears to have the advantage of minimizing variations and of allowing standardization for comparison, and thus it has been used in biomechanical research8,13,14. Further investigations on the results of clinical series using two 4-hole miniplates in atrophic edentulous mandibular fractures are desirable to decide whether the results of our experimental study in the ribs are in accord with clinical findings. Acknowledgments. This work was supported by Grant No. R13-2003-13 from the Medical Science and Engineering Research Program of the Korea Science & Engineering Foundation. References 1. Bruce RA, Strachan DS. Fractures of the edentulous mandible: The Chalmers J. Lyons Academy of Study. J Oral Surg 1976: 34: 973–977. 2. Bruce RA, Ellis E. The second Chalmers J. Lyons academy study of fractures of the edentulous mandible. J Oral Maxillofac Surg 1993: 51: 904–911. 3. Champy M, Lodde JP, Schmitt R, Must D. Mandibular osteosynthesis by miniature screwed plates via a buccal approach. J Maxillofac Surg 1978: 6: 14–21. 4. Champy M, Kahn JL. Fracture line stability as a function of the internal fixation system: an in vitro comparison using a mandibular angle fracture model (Discussion). J Oral Maxillofac Surg 1995: 53: 801–802. 5. Ellis E, Walker LR. Treatment of mandibular angle fractures using one noncompression miniplate. J Oral Maxillofac Surg 1996: 54: 864–871. 6. Feller KU, Richter G, Schneider M, Eckelt U. Combination of microplate and miniplate for osteosynthesis of mandibular fractures: an experimental study. Int J Oral Maxillofac Surg 2002: 31: 78–83.
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