Int. J. Oral Surg. 1975: 4:27-31 (Key words:
fl'actures; inandible, Jraetures; osteosynthesis)
Photoelastic behavior of osteosynthesis plates with different arrangement of screw holes for mandibular fractures H. NIEDERDELLMANN, W. SCHILLI, R. EWERS AND E. AKUAMOA-BOATENG
Department of Maxillo-Facial and Oral Surgery, University of Frelburg, Breisgau, GerllTally
In the treatment of fractures of the mandible, considering its biomechanics and topography, it is not enough to achieve just a horizontal compression with the osteosynthesis plate, as was previously the goal, since compression in parts far away from the osteosynthesis plate is equally essential. This double function is attainable by means of a new arrangement of the screw holes. The photoelastic experiment is performed to demonstrate that compression forces which develop in the two types of plates differ according to the arrangement of the screw holes. Whereas there is practically no change in compression forces in plates with a horizontal screwing mechanism, a new traction strapping plate shows clearly the development of compression forces in areas far away from the plate. ABSTRACT --
(Received for publication 10 June, accepted 20 October 1974)
In the treatment o.f mandibular fractures the physiologic and mechanical aspects of the m a n d i b l e should be considered, in order to achieve absolute stabilization and thus maintain correct anatomic positioning of the f r a c t u r e fragments during healing. A c c o r d i n g to PAUWELSs, it is essential to p e r f o r m osteosynthesis in regions of maximal tension caused by muscular pull. MARX~ mad WEBER-TI-IE.DY13, in model experiments, as well as JUNOa, in human
beings, have demonstrated that under physiologic loading, tension occurs in the alveolar region and compression in the lower border of the body o f the mandible. The work of MARX~ is 0s much importance for the treatment of mandibular fractures and for the correct design and placing of osteosynthesis plates. Owing to its topography and the thickness of the compact bone, it is only the inferior margin, that is, the region of corn-
* Lecture given 6 September 1974 during a colloquium on biomechanics organized by the Frannhofer Association, Institut far Festktirpermechanlk Freiburg, in Freiburg, Breisgau.
28
N I E D E R D E L L M A N N , SCHILLI, EWERS AND AKUAMOA-BOATENG In order to demonstrate visually the difference in behavior between the plate with onZy axial screwing and that with axial and an additional oblique screwing mechanism, we tried to give a qualitative impression os the difference in behavior of these two plates by means of a photoelastic experiment.
p!t!fl!H1rIitl,llttttll l ttmtlmtllmtttllI' !tti / lt Fig. 2. The two different plates used. Upper: titanium plate with axial screwing mechanism. Lower: traction strapping plate.
pression of the mandible, w h i c h needs to be considered in using osteosynthesis plates to treat m a n d i b u l a r fractures. It is therefore understandable that almost all known methods of osteosynthesis have been used in that region, which is rather biomechanically v e r y unsuitable. It was very tempting also, as in the t r e a t m e n t of fractures of the long bones, to apply the principle of traction strapping to neutralize mandibular fractures 1,~,,,2. Owing to the complicated nature of this operative m e t h o d and its limited application, it a p p e a r e d necessary to develop a new type o f plate which takes the abovementioned p r o b l e m s into consideration, embodies the principle of traction strapping and thus makes a functionally stable osteosynthesis possibleT. It differs from the ordinary plates (Fig. 1 upper) in the new arrangement of the screw holes, which causes an initial compression in the alveolar region, i.e. away f r o m the plate (Fig. 1 lower). All the holes of these plates contain the original D C P holes of the A O '~j or ASIF. In this way it is possible to brace the plates, thus bringing about a compression zone in the alveolar region. Thus, under functional strain, forces of tension and bending are eliminated in the alveolar region.
Material and methods The photoelastic method is based on using circularly polarized light to visualize the distribution of tension in an isometric material. Under tension, these materials are capable of separating polarized light into two waves, the direction of which corresponds to the direction of the main tension. On entering the material, these waves show a difference in phase which is proportional to the thickness of the material and difference in the major tensions. Darkness results when many half wavelengths add up to an uneven number to produce a phase difference, but this applies only to monochromatic light. Maximal brightness occurs when identical phases of the partial waves meet together, that is, phase difference of an even number of several 2/2. Only those rays which parallel the direction of transmission of the analyzer can go through the latter. Monochromatic light produces dark and bright bands, whereas white light causes colored bands. These bands are called isochromates. They appear not only as open or closed lines but can also be recognized as areas or points. In such areas or points, the major tension is the same in all directions, that is, in this area there is the same hydrostatic pressure or traction. A single isochromate always connects points of equal major tensional differences. The major tensional difference increases with the order of the isochromates. With the aid of colored isochromates it is now possible to identify the order of the isochromates, because the order of the isochromates increases from yellow or red towards green and decreases in the opposite direction~4. Only the isochromate of zero-order is black. Two different osteosynthesis plates with different arrangements of the screw holes were studied. As an example of purely axial cornpress[on screwing, the titanium plate was selected and compared with screwing phases of
P H O T O E L A S T I C OSTEOSYNTHESIS the traction strapping plate, which has screw holes arranged horizontally in the inner part and lateral screw holes arranged at an angle of 45 ~. T h e metal plates, measuring 150 • 30 • 19 ram, are screwed to Araldid B| a n arti-
29
ficial material possessing very active p h o t o elastic properties. O n e expects different tensional fields and consequently different optical pictures from this Araldid model because of the different arrangement of the screw holes of the two types of osteosynthesis plates.
Fig. 2. Pictures showing photoelastic changes during screwing. Left: using titanium plate. Right: using traction strapping plate.
30
NIEDERDELLMANN, SCHtLLI, EWERS AND AKUAMOA-BOATENG
In order to. avoid interfering tensions, only unbroken models were used, and to show clearly the horizontal and the oblique forces, only the lateral screw holes were used for fixing the metal plate. For the sake of completeness, pictures are shown depicting all four screws being used to stabilize each plate.
Results Looking at the phot0elastic pictures, the upper part, w h e r e there is no plate~ should be noted especially, In t h a t area, the isochromates r u n n i n g parallel t o the upper edge o:f the plate can b e interpreted as a line of constant tension, since the second major tension disappears. I n the series of pictures, where the titanium plate is u s e d (Fig. 2 left), the upper edge r e m a i n s photoelastically inactive. With increasing screwing, the n u m b e r of the isochromates increases - this is shown in the first picture. A f t e r final screwing, ~ of the height of the m o d e l b e c o m e s photoelastically activated. E v e n at this stage the upper third of the m o d e l remains photoelhsticalIy inactive, a n d thus free f r o m compressional forces. T h e o r d e r of the isochromates, as seen in the o r d e r of t h e colors, increases from the u p p e r edge downwards. I n t h e series o f pictures where the traction strapping p l a t e (Fig. 2 right) was used, there is m u c h difference. In all pictures the u p p e r edge of t h e m o d e l shows isochromates of the o r d e r N r O. T h e very first picture of this series shows at the same stage of screwing, unlike that of the former one, an isochromate. W i t h increasing screwing the o r d e r o f isochromates clearly increases. T h e last picture shows obviously the greatest n u m b e r of isochromates. Their n u m b e r decreases from the u p p e r edge of the m o d e l across the m i d d l e part, laterally, and increases upwards a n d downwards. The nail-test2 (Fig. 3 upper) at the upper edge of the m o d e l indicates that the appearance of a lower o r d e r of isocbromates shows the
Fig. 3, Photoelastic pictures. Upper: "nail-test" (see text) using traction strapping plate. Middie: titanium plate finally screwed tight. Lower: traction strapping plate finally screwed tight.
presence of compressional forces far away from the plates in the fracture region. W h e n both osteosynthesis plates are finally screwed, the resulting pictures are similar. In the titanium plates (Fig. 3 middle) there is indeed slight activity away from the plate; this indicates increasing compression forces in the peripheral parts of the plates. This additive function of extra compression screws is described by HESS 8.
PHOTOELASTIC OSTEOSYNTHESIS In the traction strapping plates (Fig. 3 lower), however, there are a relatively large number of isoehromates in the periphery, which indicates increases of compression forces in the upper regions away from the plate.
Discussion The use of ordina~2r osteosynthesis plates in the treatment of mandibular fractures, as done by Ll_rltR5 and SPIESSL:t2~does not permit sufficient compression in the alveolar parts. This, however, is essential for the optimal neutralization of the fracture. This insufficiency can be demonstrated photoelastically. Many authot's~,X~, ~-~, from their own clinical experience, know the necessity of introducing additional aids, such as a tension boom in the form of plates or wiring in the alveolar region, or dentally fixed splints, if intermaxillary immobilization was not done after the plate osteosynthesis~~ We consider these additional aids to be superfluous provided the biomechanics of the mandible have been studied toe advantage during the design of the osteosynthesis plates.
References 1. BRONS, R. & BOERING, G.: Fractures of the mandibular body treated by stable internal fixation: a preliminary report. Y. Oral Surg. 1970: 28: 407-415. Address: Klinik /iir Zahn-, Mund- und KieferKrankheiten der Universitiit 78 Freibttrg L Br. Hugstette~wtr. 55 Germany
31
2. F/JPPL, L. & Mt3NCH, E.: Praktische Spannungsoptik. Springer-Verlag, HeidelbergNew York 1972, p. 58. 3. HEss, H. In: OTTE, P. & SCmmGEL, K. F. (ed.): Die Spaanungskriifle der Druckplattenos_seosynthese. Enke-Verlag, Stuttgart 1972, p. 31. 4. JtrNG, F.: Die Elastizitiit der Skeletteile des Gebil3systems. Stoma 1952: 5: 74-93. 5. LtmR, H. G.: Zur stabilen Osteosynthese bei Unterkieferfrakturen. Dtseh. Zahnaerztl. Z. 1968: 23: 754. 6. MARX, H.: Die /unktionsbedingten elastischen De]ormierungen der menschlichen Mandibula. Thesis. Mainz 1966. 7. NIEDERDELLMANN, H. • SCHILLI, W.: ZLlr Plattenosteosynthese bei Unterkieferfrakturen. Dtseh. Zahnaerztl. Z. 1973: 28: 638639. 8. PAtrWELS, S.: Grundril3 einer Biomechanik der Frakturheilung. Verb. Dtsch. Orthop. Ges. 1940: 34: 62-1.08. 9. PERREN, S. M.) RUSSENBERGER,l'q., STEINE= MANN, S., MUELLER, M. E. & ALLGOWER, M.: A dynamic compression plate. Acta Orthop. Seand. 1969: Suppl. 125: 29-41_. 10. REICHENBACH, E.: Traunmtologie im Kiefer-Gesichtsbereich. Barth-Verlag, Mtinchen 1969, p. 276. ]1, SNELL, J. A. & DOTT, W. A.: Internal fixation of certain fractures of the mandible by bone plating. Plast. Reconstr. Surg. 1969: 43: 281-286. 12. SI'IESSL, B., SCKAR~I_IS,G. & SCHROLL, K," Die stabile Osteosynthese bei Frakturen des unbezahnten Unterkiefers. Schweiz. Monatsschr. Zahnheifkd. 1971: 81: 39-53[. 13. WEBER-TrlEDY, K. W.: Die Zuggurtungsfunktion der Wurzelhaut oder wie die Toleranzquint die Wurzelhaut bewertet. Dtsch. Zahnaerztl. Z. 1964: 19: 426--433. 14. WOLF, H.: Spannungsoptik. Springer Verlag, Berlin-GtSttingen-Heidelberg 1971, p. 107.
fl'actures; inandible, Jraetures; osteosynthesis)
Photoelastic behavior of osteosynthesis plates with different arrangement of screw holes for mandibular fractures H. NIEDERDELLMANN, W. SCHILLI, R. EWERS AND E. AKUAMOA-BOATENG
Department of Maxillo-Facial and Oral Surgery, University of Frelburg, Breisgau, GerllTally
In the treatment of fractures of the mandible, considering its biomechanics and topography, it is not enough to achieve just a horizontal compression with the osteosynthesis plate, as was previously the goal, since compression in parts far away from the osteosynthesis plate is equally essential. This double function is attainable by means of a new arrangement of the screw holes. The photoelastic experiment is performed to demonstrate that compression forces which develop in the two types of plates differ according to the arrangement of the screw holes. Whereas there is practically no change in compression forces in plates with a horizontal screwing mechanism, a new traction strapping plate shows clearly the development of compression forces in areas far away from the plate. ABSTRACT --
(Received for publication 10 June, accepted 20 October 1974)
In the treatment o.f mandibular fractures the physiologic and mechanical aspects of the m a n d i b l e should be considered, in order to achieve absolute stabilization and thus maintain correct anatomic positioning of the f r a c t u r e fragments during healing. A c c o r d i n g to PAUWELSs, it is essential to p e r f o r m osteosynthesis in regions of maximal tension caused by muscular pull. MARX~ mad WEBER-TI-IE.DY13, in model experiments, as well as JUNOa, in human
beings, have demonstrated that under physiologic loading, tension occurs in the alveolar region and compression in the lower border of the body o f the mandible. The work of MARX~ is 0s much importance for the treatment of mandibular fractures and for the correct design and placing of osteosynthesis plates. Owing to its topography and the thickness of the compact bone, it is only the inferior margin, that is, the region of corn-
* Lecture given 6 September 1974 during a colloquium on biomechanics organized by the Frannhofer Association, Institut far Festktirpermechanlk Freiburg, in Freiburg, Breisgau.
28
N I E D E R D E L L M A N N , SCHILLI, EWERS AND AKUAMOA-BOATENG In order to demonstrate visually the difference in behavior between the plate with onZy axial screwing and that with axial and an additional oblique screwing mechanism, we tried to give a qualitative impression os the difference in behavior of these two plates by means of a photoelastic experiment.
p!t!fl!H1rIitl,llttttll l ttmtlmtllmtttllI' !tti / lt Fig. 2. The two different plates used. Upper: titanium plate with axial screwing mechanism. Lower: traction strapping plate.
pression of the mandible, w h i c h needs to be considered in using osteosynthesis plates to treat m a n d i b u l a r fractures. It is therefore understandable that almost all known methods of osteosynthesis have been used in that region, which is rather biomechanically v e r y unsuitable. It was very tempting also, as in the t r e a t m e n t of fractures of the long bones, to apply the principle of traction strapping to neutralize mandibular fractures 1,~,,,2. Owing to the complicated nature of this operative m e t h o d and its limited application, it a p p e a r e d necessary to develop a new type o f plate which takes the abovementioned p r o b l e m s into consideration, embodies the principle of traction strapping and thus makes a functionally stable osteosynthesis possibleT. It differs from the ordinary plates (Fig. 1 upper) in the new arrangement of the screw holes, which causes an initial compression in the alveolar region, i.e. away f r o m the plate (Fig. 1 lower). All the holes of these plates contain the original D C P holes of the A O '~j or ASIF. In this way it is possible to brace the plates, thus bringing about a compression zone in the alveolar region. Thus, under functional strain, forces of tension and bending are eliminated in the alveolar region.
Material and methods The photoelastic method is based on using circularly polarized light to visualize the distribution of tension in an isometric material. Under tension, these materials are capable of separating polarized light into two waves, the direction of which corresponds to the direction of the main tension. On entering the material, these waves show a difference in phase which is proportional to the thickness of the material and difference in the major tensions. Darkness results when many half wavelengths add up to an uneven number to produce a phase difference, but this applies only to monochromatic light. Maximal brightness occurs when identical phases of the partial waves meet together, that is, phase difference of an even number of several 2/2. Only those rays which parallel the direction of transmission of the analyzer can go through the latter. Monochromatic light produces dark and bright bands, whereas white light causes colored bands. These bands are called isochromates. They appear not only as open or closed lines but can also be recognized as areas or points. In such areas or points, the major tension is the same in all directions, that is, in this area there is the same hydrostatic pressure or traction. A single isochromate always connects points of equal major tensional differences. The major tensional difference increases with the order of the isochromates. With the aid of colored isochromates it is now possible to identify the order of the isochromates, because the order of the isochromates increases from yellow or red towards green and decreases in the opposite direction~4. Only the isochromate of zero-order is black. Two different osteosynthesis plates with different arrangements of the screw holes were studied. As an example of purely axial cornpress[on screwing, the titanium plate was selected and compared with screwing phases of
P H O T O E L A S T I C OSTEOSYNTHESIS the traction strapping plate, which has screw holes arranged horizontally in the inner part and lateral screw holes arranged at an angle of 45 ~. T h e metal plates, measuring 150 • 30 • 19 ram, are screwed to Araldid B| a n arti-
29
ficial material possessing very active p h o t o elastic properties. O n e expects different tensional fields and consequently different optical pictures from this Araldid model because of the different arrangement of the screw holes of the two types of osteosynthesis plates.
Fig. 2. Pictures showing photoelastic changes during screwing. Left: using titanium plate. Right: using traction strapping plate.
30
NIEDERDELLMANN, SCHtLLI, EWERS AND AKUAMOA-BOATENG
In order to. avoid interfering tensions, only unbroken models were used, and to show clearly the horizontal and the oblique forces, only the lateral screw holes were used for fixing the metal plate. For the sake of completeness, pictures are shown depicting all four screws being used to stabilize each plate.
Results Looking at the phot0elastic pictures, the upper part, w h e r e there is no plate~ should be noted especially, In t h a t area, the isochromates r u n n i n g parallel t o the upper edge o:f the plate can b e interpreted as a line of constant tension, since the second major tension disappears. I n the series of pictures, where the titanium plate is u s e d (Fig. 2 left), the upper edge r e m a i n s photoelastically inactive. With increasing screwing, the n u m b e r of the isochromates increases - this is shown in the first picture. A f t e r final screwing, ~ of the height of the m o d e l b e c o m e s photoelastically activated. E v e n at this stage the upper third of the m o d e l remains photoelhsticalIy inactive, a n d thus free f r o m compressional forces. T h e o r d e r of the isochromates, as seen in the o r d e r of t h e colors, increases from the u p p e r edge downwards. I n t h e series o f pictures where the traction strapping p l a t e (Fig. 2 right) was used, there is m u c h difference. In all pictures the u p p e r edge of t h e m o d e l shows isochromates of the o r d e r N r O. T h e very first picture of this series shows at the same stage of screwing, unlike that of the former one, an isochromate. W i t h increasing screwing the o r d e r o f isochromates clearly increases. T h e last picture shows obviously the greatest n u m b e r of isochromates. Their n u m b e r decreases from the u p p e r edge of the m o d e l across the m i d d l e part, laterally, and increases upwards a n d downwards. The nail-test2 (Fig. 3 upper) at the upper edge of the m o d e l indicates that the appearance of a lower o r d e r of isocbromates shows the
Fig. 3, Photoelastic pictures. Upper: "nail-test" (see text) using traction strapping plate. Middie: titanium plate finally screwed tight. Lower: traction strapping plate finally screwed tight.
presence of compressional forces far away from the plates in the fracture region. W h e n both osteosynthesis plates are finally screwed, the resulting pictures are similar. In the titanium plates (Fig. 3 middle) there is indeed slight activity away from the plate; this indicates increasing compression forces in the peripheral parts of the plates. This additive function of extra compression screws is described by HESS 8.
PHOTOELASTIC OSTEOSYNTHESIS In the traction strapping plates (Fig. 3 lower), however, there are a relatively large number of isoehromates in the periphery, which indicates increases of compression forces in the upper regions away from the plate.
Discussion The use of ordina~2r osteosynthesis plates in the treatment of mandibular fractures, as done by Ll_rltR5 and SPIESSL:t2~does not permit sufficient compression in the alveolar parts. This, however, is essential for the optimal neutralization of the fracture. This insufficiency can be demonstrated photoelastically. Many authot's~,X~, ~-~, from their own clinical experience, know the necessity of introducing additional aids, such as a tension boom in the form of plates or wiring in the alveolar region, or dentally fixed splints, if intermaxillary immobilization was not done after the plate osteosynthesis~~ We consider these additional aids to be superfluous provided the biomechanics of the mandible have been studied toe advantage during the design of the osteosynthesis plates.
References 1. BRONS, R. & BOERING, G.: Fractures of the mandibular body treated by stable internal fixation: a preliminary report. Y. Oral Surg. 1970: 28: 407-415. Address: Klinik /iir Zahn-, Mund- und KieferKrankheiten der Universitiit 78 Freibttrg L Br. Hugstette~wtr. 55 Germany
31
2. F/JPPL, L. & Mt3NCH, E.: Praktische Spannungsoptik. Springer-Verlag, HeidelbergNew York 1972, p. 58. 3. HEss, H. In: OTTE, P. & SCmmGEL, K. F. (ed.): Die Spaanungskriifle der Druckplattenos_seosynthese. Enke-Verlag, Stuttgart 1972, p. 31. 4. JtrNG, F.: Die Elastizitiit der Skeletteile des Gebil3systems. Stoma 1952: 5: 74-93. 5. LtmR, H. G.: Zur stabilen Osteosynthese bei Unterkieferfrakturen. Dtseh. Zahnaerztl. Z. 1968: 23: 754. 6. MARX, H.: Die /unktionsbedingten elastischen De]ormierungen der menschlichen Mandibula. Thesis. Mainz 1966. 7. NIEDERDELLMANN, H. • SCHILLI, W.: ZLlr Plattenosteosynthese bei Unterkieferfrakturen. Dtseh. Zahnaerztl. Z. 1973: 28: 638639. 8. PAtrWELS, S.: Grundril3 einer Biomechanik der Frakturheilung. Verb. Dtsch. Orthop. Ges. 1940: 34: 62-1.08. 9. PERREN, S. M.) RUSSENBERGER,l'q., STEINE= MANN, S., MUELLER, M. E. & ALLGOWER, M.: A dynamic compression plate. Acta Orthop. Seand. 1969: Suppl. 125: 29-41_. 10. REICHENBACH, E.: Traunmtologie im Kiefer-Gesichtsbereich. Barth-Verlag, Mtinchen 1969, p. 276. ]1, SNELL, J. A. & DOTT, W. A.: Internal fixation of certain fractures of the mandible by bone plating. Plast. Reconstr. Surg. 1969: 43: 281-286. 12. SI'IESSL, B., SCKAR~I_IS,G. & SCHROLL, K," Die stabile Osteosynthese bei Frakturen des unbezahnten Unterkiefers. Schweiz. Monatsschr. Zahnheifkd. 1971: 81: 39-53[. 13. WEBER-TrlEDY, K. W.: Die Zuggurtungsfunktion der Wurzelhaut oder wie die Toleranzquint die Wurzelhaut bewertet. Dtsch. Zahnaerztl. Z. 1964: 19: 426--433. 14. WOLF, H.: Spannungsoptik. Springer Verlag, Berlin-GtSttingen-Heidelberg 1971, p. 107.
