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Mechanical properties of collagen membranes: Are they sufficient for orbital floor reconstructions?
Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 260e263
Contents lists available at ScienceDirect
Journal of Cranio-Maxillo-Facial Surgery journal homepage: www.jcmfs.com
Mechanical properties of collagen membranes: Are they sufficient for orbital floor reconstructions? € rg Wiltfang a Falk Birkenfeld a, *, Eleonore Behrens a, Matthias Kern b, Volker Gassling a, Jo a b
Department of Oral and Maxillofacial Surgery, Christian-Albrechts University at Kiel, Kiel, Germany Department of Prosthodontics and Dental Materials, Christian-Albrechts University at Kiel, Kiel, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Paper received 10 September 2014 Accepted 21 November 2014 Available online 27 November 2014
Introduction: The most common reconstruction materials for orbital floor fractures are PDS (polydioxanone) foil and titanium meshes. These materials have advantages and disadvantages. Therefore, new materials are needed to improve surgical outcomes. Materials and methods: Three resorbable collagen membranes (Smartbrane®, BioGide®, Creos®) were tested for their mechanical properties (puncture strength) in mint and artificially aged (3, 6, 8 weeks) conditions and were compared to PDS foil, titanium meshes (0.25 mm, 0.5 mm) and human orbital floors (n ¼ 7). Results: The following puncture strengths were evaluated: human orbital floor, 0.81 ± 0.49 N/mm2; 0.25 mm titanium mesh, 5.36 ± 0.25 N/mm2; 0.5 mm titanium mesh, 16.08 ± 5.17 N/mm2; Smartbrane, 0.74 ± 0.31 N/mm2; BioGide, 1.65 ± 0.45 N/mm2; and Creos, 2.81 ± 0.27 N/mm2. After artificial aging, the puncture strengths were significantly reduced (p 0.05) at 3, 6 and 8 weeks as follows: Smartbrane, 0.05 ± 0.03 N/mm2, 0.03 ± 0.02 N/mm2, and 0.01 ± 0.01 N/mm2, respectively; BioGide, 0.42 ± 0.06 N/mm2, 0.41 ± 0.12 N/mm2, and 0.32 ± 0.08 N/mm2, respectively; and Creos, 2.02 ± 0.37 N/mm2, 1.49 ± 0.42 N/mm2, and 1.36 ± 0.42 N/mm2, respectively. Conclusion: The tested materials showed sufficient puncture strength for orbital floor reconstruction in mint condition. Moreover, after artificial aging, the Creos and BioGide membranes showed sufficient resistance, while Smartbrane showed equivocal data after eight weeks. Therefore, collagen membranes have adequate properties for further in vivo investigations for orbital floor reconstructions. © 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Keywords: Orbital floor Collagen membrane Orbital trauma Titanium mesh
1. Introduction Orbital floor fractures are a common challenge in maxillofacial surgery (Polligkeit et al., 2013, Salentijn et al., 2013). The symptoms of orbital floor fractures are hematoma, hyposphagma, hypesthesia of the infraorbital nerve, reduced globe motility, and enophthalmos (Arangio et al., 2014, Carinci et al., 2006). The reduced globe motility follows swelling and herniation of the orbital contents into the maxillary sinus. Orbital rehabilitation is appropriate to remedy the enophthalmos, to relieve the infraorbital nerve, and to prevent
* Corresponding author. Department of Oral and Maxillofacial Surgery, University Hospital Schleswig-Holstein, Campus Kiel, ArnoldeHellereStraße 16, 24105 Kiel, Germany. Tel.: þ49 431 597 2831; fax: þ49 431 597 2839. E-mail address: [email protected] (F. Birkenfeld).
scarred malformation of the orbital content by averting reduced globe motility. The orbital floor measures approximately 600 mm2, with a convex and concave profile. The orbital content weighs approximately 30 g (0.3 N), resulting in 0.0005 N/mm2 of static mechanical stress. Orbital floor fractures measure approximately 30e350 mm2, resulting in 0.01e0.0008 N/mm2 of static mechanical stress on reconstruction materials (Czerwinski et al., 2008, Tabrizi et al., 2013). Currently, two different common materials are used for orbital floor reconstruction, PDS (polydioxanone) foils and titanium meshes (Dietz et al., 2001, Essig et al., 2013). PDS foils are completely resorbable within approximately 30 weeks and are replaced with scar tissue without any adherence to the orbital content (Merten and Luhr, 1994). However, due to the rigidity of these materials, it is challenging to repair a convex orbital floor, but there is no need for surgical removal. Titanium meshes might
http://dx.doi.org/10.1016/j.jcms.2014.11.020 1010-5182/© 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
F. Birkenfeld et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 260e263
261
require surgery for removal, and orbital adherence syndrome has been described (Lee and Nunery, 2009), but the meshes can be adapted to the orbital floor in three dimensions (Metzger et al., 2006). There has been controversy regarding both materials in the literature; however, thus far, there is no evidence demonstrating the superiority of either of these materials. Moreover, there is little available information regarding the demand for reconstruction materials. Recently published studies have investigated the demand for reconstruction materials (Birkenfeld et al., 2011, Birkenfeld et al., 2012a,b,c). However, there is also little available information regarding the mechanical properties of the human orbital floor. This study had two objectives: (1) to investigate the puncture strength of human orbital floor bone specimens and (2) to compare this strength with the puncture strengths of titanium meshes, PDS foils, and three resorbable collagen membranes in mint condition and after artificial aging for 3, 6, and 8 weeks to determine their potential for orbital floor reconstruction.
2. Materials and methods A Zwick Z010 TN1 universal testing machine (Zwick GmbH, Ulm, Germany) was used for the puncture strength investigations (Fig. 1). The materials were positioned under a height-adjustable horizontal traverse with a high-definition force transducer and a punch (diameter of 5.5 mm [23.758 mm2]). The start position (approximately 20.0 cm above the materials) and end position (approximately 1.0 cm behind the materials) were set before the measurement was performed, and the same conditions were used for all tested materials. The measurement process began, and the punch was lowered approximately 2.0 mm toward the material. From this position, the feed speed was 0.2 mm*s1 until the end position was reached. Puncture strength and punch height were recorded. Seven specimens were tested for each material, as summarized in Table 1. Three resorbable porcine collagen membranes (Smartbrane®, BioGide®, Creos®) were tested for their initial puncture strengths and their strengths after simulated aging. For simulated aging, the membranes were stored in fetal calf serum (GIBCO, FBS South American, Ref. 41F3496K, Catalog No. 10270-106, Invitrogen, Darmstadt, Germany) in an incubator at 37 C for 3, 6, and 8 weeks. The titanium meshes (0.25 mm and 0.5 mm), PDS foil (0.15 mm), and human orbital floors were tested only for their initial puncture strengths. The human orbital floor bones were harvested from body donors to the anatomical course at the Institute of Anatomy of the Christian-Albrechts University at Kiel. Unfortunately, personal identifications of sex and age were not possible due to the anonymity of the donors. After harvesting the specimens, the under surface (rims of the maxillary sinus, zygomatic bone) were carefully shaped with a bone pliers for balanced position. To prevent slip away, the specimens stood on sandpaper and were partially supported with small rubber rips from the side. The specimens were positioned under the punch 10 mm behind the orbital rim and beneath the bony canal of the infraorbital nerve (Fig. 1D).
2.1. Ethical approval All cadavers were available from the Institute of Anatomy at the first author's institution and were used according to the institutional and national ethical and legislative frameworks. The human skulls were obtained from bequeathed body donations to the Institute of Anatomy of the Christian-Albrechts University at Kiel.
Fig. 1. A Zwick Z010 universal testing machine. (A) An overview of the machine (white frame close-up in B, C, and D). (B) Before the testing procedure, a collagen membrane is positioned over the aperture. (C) Punch while testing the membrane. (D) A human orbital floor positioned under the punch. The arrowhead indicates the testing punch (5.5 mm in diameter). The arrow indicates the zygomatic bone. The star indicates the infraorbital nerve foramen. Table 1 An overview of the tested materials.
Orbital floor Smartbrane Creos BioGide Titanium Titanium PDS
Thickness (mm)
Material/source
Manufacturer
0.1e0.5 0.1 0.2 0.4 0.25 0.5 0.15
Bone/human Collagen/porcine Collagen/porcine Collagen/porcine Titanium Titanium Polydioxanone
x Regedent, Zurich, Switzerland € ln, Germany Nobel Biocare, Ko Geistlich, Wolhusen, Switzerland Stryker, Duisburg, Germany Stryker, Duisburg, Germany Ethicon, Norderstedt, Germany
262
F. Birkenfeld et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 260e263
2.2. Statistical analysis WinSTAT add-in software for Microsoft Excel (Version 2012.1, R. Fitch Software, Bad Krotzingen, Germany) was used for the statistical analysis. First, the puncture strength data were tested for parametric distribution with the KolmogoroveSmirnov test. Based on a p-value > 0.05, the data had a parametric distribution. Therefore, further statistical analysis was performed with ANOVA (analysis of variance), with a significance level of p 0.05. 3. Results The puncture strength testing results are summarized in Table 2. The Smartbrane was the single material with a puncture strength comparable to that of the human orbital floor in mint condition (p ¼ 0.75). The puncture strength of the Creos membrane was similar to that of the PDS foil (p ¼ 0.11). Artificial aging significantly decreased the puncture strength of the tested collagen membranes (p 0.05). However, the three membranes showed different aging processes. After 8 weeks, the puncture strength of the Smartbrane was decreased by approximately 98% of the initial value, that of the Creos was decreased by approximately 50%, and that of the BioGide was decreased by approximately 80%. The Smartbrane and BioGide showed no significant differences between their own values after 3, 6, or 8 weeks of aging. The greatest decrease in puncture strength was observed after 3 weeks and then was constant for the Smartbrane and BioGide membranes. After 3 weeks of aging, the Creos membrane showed significantly greater (p 0.05) strength compared to that after 6 weeks; however, there was no difference between 6 weeks and 8 weeks, although there was a difference between 3 weeks and 8 weeks (p 0.05). The human orbital floor showed the highest standard deviation due to the greatest differences in thickness. The titanium meshes showed up to sixteenfold greater puncture strength values than the other materials. 4. Discussion This study was the first to provide data concerning the puncture strength of the human orbital floor compared to those of resorbable collagen membranes in mint condition and after artificial aging. The human orbital floor can withstand a puncture strength of approximately 0.8 N/mm2 (a thickness of approximately 0.1e0.5 mm). The force required for an orbital floor fracture is approximately 1.2 Je1.6 J for globe-directed and infraorbital rimdirected traumas, respectively (Ahmad et al., 2003). These data indicate that the mechanical properties of the orbital floor are comparatively poor. Under normal circumstances, peak forces of the orbital content onto the orbital floor are not experienced, indicating that a titanium mesh with a puncture strength of
Table 2 Summarized results of the puncture strength of the materials. Initial (N/mm2) Orbital floor Smartbrane Creos BioGide Titanium 0.25 mm Titanium 0.5 mm PDS
0.81 0.74 2.81 1.65 5.36 16.08 2.57
± ± ± ± ± ± ±
0.49 0.31 0.27 0.45 0.25 5.17 0.32
3 weeks (N/mm2)
6 weeks (N/mm2)
8 weeks (N/mm2)
x 0.05 ± 0.03 2.02 ± 0.37 0.42 ± 0.06 x x x
x 0.03 ± 0.02 1.49 ± 0.42 0.41 ± 0.12 x x x
x 0.01 ± 0.01 1.36 ± 0.42 0.32 ± 0.08 x x x
approximately 5 N/mm2 can be used. The puncture strengths of the tested collagen membranes indicated that the membranes might be an adequate alternative to reconstruction to shorten the wound healing time. However, it is still problematic if reconstruction of the concave and convex orbital floor anatomy is required (Forouzanfar et al., 2013). Non-resorbable polyethylene computer-aided manufactured implants were evaluated to for complex forms in reconstructing the orbital floor, however, thicknesses up 1.5 mm of the implants were reported, with may lead to esthetic disadvantages (Kozakiewicz et al., 2013). A clinical evaluation of orbital floor reconstruction with a collagen membrane showed comparable results to reconstruction with PDS foils (Becker et al., 2010). A survey of clinical data regarding the anatomical study of maximal loads on the orbital floor and our puncture strength results for the collagen membranes provide increasing evidence supporting the clinical use of these membranes (Birkenfeld et al., 2012a,b,c). However, titanium meshes should retain their indications for complex traumas and for three-dimensional reconstruction of the orbital floor, with their combined concave and convex profile. The current study had several limitations, including the small number of tested human orbital floors. However, it is challenging to harvest a large number of specimens from human body donors due to their small number of human body donors'. In addition, the puncture strength testing procedure used here tested only the continuous increasing force until the materials ruptured. The expected force in a human after orbital floor reconstruction is more likely a dynamic rather than a static force. Finally, artificial aging could only approximately simulate the in vivo process due to the lack of enzymatic collagen degradation. However, wound healing with the development of scar tissue might increase the resistance of the reconstructed orbital floor to prevent prolapse into the maxillary sinus. 5. Conclusion The tested materials showed sufficient puncture strength for orbital floor reconstruction in mint condition. Moreover, after artificial aging, the collagen membranes showed sufficient resistance. Therefore, collagen membranes have adequate properties for further in vivo investigations for orbital floor reconstruction. Conflict of interest There were no conflicts of interest. Acknowledgments The membranes were provided free for disposal by Regedent (Zurich, Switzerland), Nobel Biocare (Cologne, Germany), and Geistlich (Wolhusen, Switzerland). References Ahmad F, Kirkpatrick WN, Lyne J, Urdang M, Garey LJ, Waterhouse N: Strain gauge biomechanical evaluation of forces in orbital floor fractures. Br J Plast Surg 56: 3e9, 2003 Arangio P, Vellone V, Torre U, Calafati V, Capriotti M, Cascone P: Maxillofacial fractures in the province of Latina, Lazio, Italy: review of 400 injuries and 83 cases. J Craniomaxillofac Surg 42: 583e587, 2014 €ller B, Wiltfang J: Comparison of Becker ST, Terheyden H, Fabel M, Kandzia C, Mo collagen membranes and PDS for reconstruction of orbital floor after fractures. J Craniofac Surg 21: 1066e1068, 2010 Birkenfeld F, Steiner M, Becker ME, Kern M, Menzebach M, Wiltfang J, et al: Forces charging the orbital floor after fractures. J Craniofac Surg 22: 1641e1646, 2011 Birkenfeld F, Steiner M, Becker ME, Kern M, Wiltfang J, Lucius R, et al: Forces charging the orbital floor after trauma: a cadaver study. J Craniofac Surg 23, 2012a in press € ller B, Lucius R, et al: Forces affecting Birkenfeld F, Steiner M, Kern M, Wiltfang J, Mo orbital floor reconstruction materials e a cadaver study; 2012, in press
F. Birkenfeld et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 260e263 Birkenfeld F, Steiner M, Kern M, Witlfang J, Moller B, Lucius R, et al: Maximum forces applied to the orbital floor after fractures. J Craniofac Surg 23: 1491e1494, 2012c Carinci F, Zollino I, Brunelli G, Cenzi R: Orbital fractures: a new classification and staging of 190 patients. J Craniofac Surg 17: 1040e1044, 2006 Czerwinski M, Izadpanah A, Ma S, Chankowsky J, Williams HB: Quantitative analysis of the orbital floor defect after zygoma fracture repair. J Oral Maxillofac Surg 66: 1869e1874, 2008 Dietz A, Ziegler CM, Dacho A, Althof F, Conradt C, Kolling G, et al: Effectiveness of a new perforated 0.15 mm poly-p-dioxanon-foil versus titanium-dynamic mesh in reconstruction of the orbital floor. J Craniomaxillofac Surg 29: 82e88, 2001 Essig H, Dressel L, Rana M, Rana M, Kokemueller H, Ruecker M, et al: Precision of posttraumatic primary orbital reconstruction using individually bent titanium mesh with and without navigation: a retrospective study. Head Face Med 9: 18, 2013 Forouzanfar T, Salentijn E, Peng G, van den Bergh B: A 10-year analysis of the “Amsterdam” protocol in the treatment of zygomatic complex fractures. J Craniomaxillofac Surg 41: 616e622, 2013
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Kozakiewicz M, Elgalal M, Walkowiak B, Stefanczyk L: Technical concept of patientspecific, ultrahigh molecular weight polyethylene orbital wall implant. J Craniomaxillofac Surg 41: 282e290, 2013 Lee HB, Nunery WR: Orbital adherence syndrome secondary to titanium implant material. Ophthal Plast Reconstr Surg 25: 33e36, 2009 Merten HA, Luhr HG: Resorbable synthetics (PDS foils) for bridging extensive orbital wall defects in an animal experiment comparison. Fortschr Kiefer Gesichtschir 39: 186e190, 1994 Metzger MC, Schon R, Weyer N, Rafii A, Gellrich NC, Schmelzeisen R, et al: Anatomical 3-dimensional pre-bent titanium implant for orbital floor fractures. Ophthalmology 113: 1863e1868, 2006 Polligkeit J, Grimm M, Peters JP, Cetindis M, Krimmel M, Reinert S: Assessment of indications and clinical outcome for the endoscopy-assisted combined subciliary/transantral approach in treatment of complex orbital floor fractures. J Craniomaxillofac Surg 41: 797e802, 2013 Salentijn EG, van den Bergh B, Forouzanfar T: A ten-year analysis of midfacial fractures. J Craniomaxillofac Surg 41: 630e636, 2013 Tabrizi R, Langner NJ, Pouzesh A, Arabion H: Evaluation of the biodegradable plates (PG910/PDO) for reconstruction of various sizes of orbital floor defects in the blow-out fractures. Craniomaxillofac Trauma Reconstr 6: 187e190, 2013
Contents lists available at ScienceDirect
Journal of Cranio-Maxillo-Facial Surgery journal homepage: www.jcmfs.com
Mechanical properties of collagen membranes: Are they sufficient for orbital floor reconstructions? € rg Wiltfang a Falk Birkenfeld a, *, Eleonore Behrens a, Matthias Kern b, Volker Gassling a, Jo a b
Department of Oral and Maxillofacial Surgery, Christian-Albrechts University at Kiel, Kiel, Germany Department of Prosthodontics and Dental Materials, Christian-Albrechts University at Kiel, Kiel, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Paper received 10 September 2014 Accepted 21 November 2014 Available online 27 November 2014
Introduction: The most common reconstruction materials for orbital floor fractures are PDS (polydioxanone) foil and titanium meshes. These materials have advantages and disadvantages. Therefore, new materials are needed to improve surgical outcomes. Materials and methods: Three resorbable collagen membranes (Smartbrane®, BioGide®, Creos®) were tested for their mechanical properties (puncture strength) in mint and artificially aged (3, 6, 8 weeks) conditions and were compared to PDS foil, titanium meshes (0.25 mm, 0.5 mm) and human orbital floors (n ¼ 7). Results: The following puncture strengths were evaluated: human orbital floor, 0.81 ± 0.49 N/mm2; 0.25 mm titanium mesh, 5.36 ± 0.25 N/mm2; 0.5 mm titanium mesh, 16.08 ± 5.17 N/mm2; Smartbrane, 0.74 ± 0.31 N/mm2; BioGide, 1.65 ± 0.45 N/mm2; and Creos, 2.81 ± 0.27 N/mm2. After artificial aging, the puncture strengths were significantly reduced (p 0.05) at 3, 6 and 8 weeks as follows: Smartbrane, 0.05 ± 0.03 N/mm2, 0.03 ± 0.02 N/mm2, and 0.01 ± 0.01 N/mm2, respectively; BioGide, 0.42 ± 0.06 N/mm2, 0.41 ± 0.12 N/mm2, and 0.32 ± 0.08 N/mm2, respectively; and Creos, 2.02 ± 0.37 N/mm2, 1.49 ± 0.42 N/mm2, and 1.36 ± 0.42 N/mm2, respectively. Conclusion: The tested materials showed sufficient puncture strength for orbital floor reconstruction in mint condition. Moreover, after artificial aging, the Creos and BioGide membranes showed sufficient resistance, while Smartbrane showed equivocal data after eight weeks. Therefore, collagen membranes have adequate properties for further in vivo investigations for orbital floor reconstructions. © 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Keywords: Orbital floor Collagen membrane Orbital trauma Titanium mesh
1. Introduction Orbital floor fractures are a common challenge in maxillofacial surgery (Polligkeit et al., 2013, Salentijn et al., 2013). The symptoms of orbital floor fractures are hematoma, hyposphagma, hypesthesia of the infraorbital nerve, reduced globe motility, and enophthalmos (Arangio et al., 2014, Carinci et al., 2006). The reduced globe motility follows swelling and herniation of the orbital contents into the maxillary sinus. Orbital rehabilitation is appropriate to remedy the enophthalmos, to relieve the infraorbital nerve, and to prevent
* Corresponding author. Department of Oral and Maxillofacial Surgery, University Hospital Schleswig-Holstein, Campus Kiel, ArnoldeHellereStraße 16, 24105 Kiel, Germany. Tel.: þ49 431 597 2831; fax: þ49 431 597 2839. E-mail address: [email protected] (F. Birkenfeld).
scarred malformation of the orbital content by averting reduced globe motility. The orbital floor measures approximately 600 mm2, with a convex and concave profile. The orbital content weighs approximately 30 g (0.3 N), resulting in 0.0005 N/mm2 of static mechanical stress. Orbital floor fractures measure approximately 30e350 mm2, resulting in 0.01e0.0008 N/mm2 of static mechanical stress on reconstruction materials (Czerwinski et al., 2008, Tabrizi et al., 2013). Currently, two different common materials are used for orbital floor reconstruction, PDS (polydioxanone) foils and titanium meshes (Dietz et al., 2001, Essig et al., 2013). PDS foils are completely resorbable within approximately 30 weeks and are replaced with scar tissue without any adherence to the orbital content (Merten and Luhr, 1994). However, due to the rigidity of these materials, it is challenging to repair a convex orbital floor, but there is no need for surgical removal. Titanium meshes might
http://dx.doi.org/10.1016/j.jcms.2014.11.020 1010-5182/© 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
F. Birkenfeld et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 260e263
261
require surgery for removal, and orbital adherence syndrome has been described (Lee and Nunery, 2009), but the meshes can be adapted to the orbital floor in three dimensions (Metzger et al., 2006). There has been controversy regarding both materials in the literature; however, thus far, there is no evidence demonstrating the superiority of either of these materials. Moreover, there is little available information regarding the demand for reconstruction materials. Recently published studies have investigated the demand for reconstruction materials (Birkenfeld et al., 2011, Birkenfeld et al., 2012a,b,c). However, there is also little available information regarding the mechanical properties of the human orbital floor. This study had two objectives: (1) to investigate the puncture strength of human orbital floor bone specimens and (2) to compare this strength with the puncture strengths of titanium meshes, PDS foils, and three resorbable collagen membranes in mint condition and after artificial aging for 3, 6, and 8 weeks to determine their potential for orbital floor reconstruction.
2. Materials and methods A Zwick Z010 TN1 universal testing machine (Zwick GmbH, Ulm, Germany) was used for the puncture strength investigations (Fig. 1). The materials were positioned under a height-adjustable horizontal traverse with a high-definition force transducer and a punch (diameter of 5.5 mm [23.758 mm2]). The start position (approximately 20.0 cm above the materials) and end position (approximately 1.0 cm behind the materials) were set before the measurement was performed, and the same conditions were used for all tested materials. The measurement process began, and the punch was lowered approximately 2.0 mm toward the material. From this position, the feed speed was 0.2 mm*s1 until the end position was reached. Puncture strength and punch height were recorded. Seven specimens were tested for each material, as summarized in Table 1. Three resorbable porcine collagen membranes (Smartbrane®, BioGide®, Creos®) were tested for their initial puncture strengths and their strengths after simulated aging. For simulated aging, the membranes were stored in fetal calf serum (GIBCO, FBS South American, Ref. 41F3496K, Catalog No. 10270-106, Invitrogen, Darmstadt, Germany) in an incubator at 37 C for 3, 6, and 8 weeks. The titanium meshes (0.25 mm and 0.5 mm), PDS foil (0.15 mm), and human orbital floors were tested only for their initial puncture strengths. The human orbital floor bones were harvested from body donors to the anatomical course at the Institute of Anatomy of the Christian-Albrechts University at Kiel. Unfortunately, personal identifications of sex and age were not possible due to the anonymity of the donors. After harvesting the specimens, the under surface (rims of the maxillary sinus, zygomatic bone) were carefully shaped with a bone pliers for balanced position. To prevent slip away, the specimens stood on sandpaper and were partially supported with small rubber rips from the side. The specimens were positioned under the punch 10 mm behind the orbital rim and beneath the bony canal of the infraorbital nerve (Fig. 1D).
2.1. Ethical approval All cadavers were available from the Institute of Anatomy at the first author's institution and were used according to the institutional and national ethical and legislative frameworks. The human skulls were obtained from bequeathed body donations to the Institute of Anatomy of the Christian-Albrechts University at Kiel.
Fig. 1. A Zwick Z010 universal testing machine. (A) An overview of the machine (white frame close-up in B, C, and D). (B) Before the testing procedure, a collagen membrane is positioned over the aperture. (C) Punch while testing the membrane. (D) A human orbital floor positioned under the punch. The arrowhead indicates the testing punch (5.5 mm in diameter). The arrow indicates the zygomatic bone. The star indicates the infraorbital nerve foramen. Table 1 An overview of the tested materials.
Orbital floor Smartbrane Creos BioGide Titanium Titanium PDS
Thickness (mm)
Material/source
Manufacturer
0.1e0.5 0.1 0.2 0.4 0.25 0.5 0.15
Bone/human Collagen/porcine Collagen/porcine Collagen/porcine Titanium Titanium Polydioxanone
x Regedent, Zurich, Switzerland € ln, Germany Nobel Biocare, Ko Geistlich, Wolhusen, Switzerland Stryker, Duisburg, Germany Stryker, Duisburg, Germany Ethicon, Norderstedt, Germany
262
F. Birkenfeld et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 260e263
2.2. Statistical analysis WinSTAT add-in software for Microsoft Excel (Version 2012.1, R. Fitch Software, Bad Krotzingen, Germany) was used for the statistical analysis. First, the puncture strength data were tested for parametric distribution with the KolmogoroveSmirnov test. Based on a p-value > 0.05, the data had a parametric distribution. Therefore, further statistical analysis was performed with ANOVA (analysis of variance), with a significance level of p 0.05. 3. Results The puncture strength testing results are summarized in Table 2. The Smartbrane was the single material with a puncture strength comparable to that of the human orbital floor in mint condition (p ¼ 0.75). The puncture strength of the Creos membrane was similar to that of the PDS foil (p ¼ 0.11). Artificial aging significantly decreased the puncture strength of the tested collagen membranes (p 0.05). However, the three membranes showed different aging processes. After 8 weeks, the puncture strength of the Smartbrane was decreased by approximately 98% of the initial value, that of the Creos was decreased by approximately 50%, and that of the BioGide was decreased by approximately 80%. The Smartbrane and BioGide showed no significant differences between their own values after 3, 6, or 8 weeks of aging. The greatest decrease in puncture strength was observed after 3 weeks and then was constant for the Smartbrane and BioGide membranes. After 3 weeks of aging, the Creos membrane showed significantly greater (p 0.05) strength compared to that after 6 weeks; however, there was no difference between 6 weeks and 8 weeks, although there was a difference between 3 weeks and 8 weeks (p 0.05). The human orbital floor showed the highest standard deviation due to the greatest differences in thickness. The titanium meshes showed up to sixteenfold greater puncture strength values than the other materials. 4. Discussion This study was the first to provide data concerning the puncture strength of the human orbital floor compared to those of resorbable collagen membranes in mint condition and after artificial aging. The human orbital floor can withstand a puncture strength of approximately 0.8 N/mm2 (a thickness of approximately 0.1e0.5 mm). The force required for an orbital floor fracture is approximately 1.2 Je1.6 J for globe-directed and infraorbital rimdirected traumas, respectively (Ahmad et al., 2003). These data indicate that the mechanical properties of the orbital floor are comparatively poor. Under normal circumstances, peak forces of the orbital content onto the orbital floor are not experienced, indicating that a titanium mesh with a puncture strength of
Table 2 Summarized results of the puncture strength of the materials. Initial (N/mm2) Orbital floor Smartbrane Creos BioGide Titanium 0.25 mm Titanium 0.5 mm PDS
0.81 0.74 2.81 1.65 5.36 16.08 2.57
± ± ± ± ± ± ±
0.49 0.31 0.27 0.45 0.25 5.17 0.32
3 weeks (N/mm2)
6 weeks (N/mm2)
8 weeks (N/mm2)
x 0.05 ± 0.03 2.02 ± 0.37 0.42 ± 0.06 x x x
x 0.03 ± 0.02 1.49 ± 0.42 0.41 ± 0.12 x x x
x 0.01 ± 0.01 1.36 ± 0.42 0.32 ± 0.08 x x x
approximately 5 N/mm2 can be used. The puncture strengths of the tested collagen membranes indicated that the membranes might be an adequate alternative to reconstruction to shorten the wound healing time. However, it is still problematic if reconstruction of the concave and convex orbital floor anatomy is required (Forouzanfar et al., 2013). Non-resorbable polyethylene computer-aided manufactured implants were evaluated to for complex forms in reconstructing the orbital floor, however, thicknesses up 1.5 mm of the implants were reported, with may lead to esthetic disadvantages (Kozakiewicz et al., 2013). A clinical evaluation of orbital floor reconstruction with a collagen membrane showed comparable results to reconstruction with PDS foils (Becker et al., 2010). A survey of clinical data regarding the anatomical study of maximal loads on the orbital floor and our puncture strength results for the collagen membranes provide increasing evidence supporting the clinical use of these membranes (Birkenfeld et al., 2012a,b,c). However, titanium meshes should retain their indications for complex traumas and for three-dimensional reconstruction of the orbital floor, with their combined concave and convex profile. The current study had several limitations, including the small number of tested human orbital floors. However, it is challenging to harvest a large number of specimens from human body donors due to their small number of human body donors'. In addition, the puncture strength testing procedure used here tested only the continuous increasing force until the materials ruptured. The expected force in a human after orbital floor reconstruction is more likely a dynamic rather than a static force. Finally, artificial aging could only approximately simulate the in vivo process due to the lack of enzymatic collagen degradation. However, wound healing with the development of scar tissue might increase the resistance of the reconstructed orbital floor to prevent prolapse into the maxillary sinus. 5. Conclusion The tested materials showed sufficient puncture strength for orbital floor reconstruction in mint condition. Moreover, after artificial aging, the collagen membranes showed sufficient resistance. Therefore, collagen membranes have adequate properties for further in vivo investigations for orbital floor reconstruction. Conflict of interest There were no conflicts of interest. Acknowledgments The membranes were provided free for disposal by Regedent (Zurich, Switzerland), Nobel Biocare (Cologne, Germany), and Geistlich (Wolhusen, Switzerland). References Ahmad F, Kirkpatrick WN, Lyne J, Urdang M, Garey LJ, Waterhouse N: Strain gauge biomechanical evaluation of forces in orbital floor fractures. Br J Plast Surg 56: 3e9, 2003 Arangio P, Vellone V, Torre U, Calafati V, Capriotti M, Cascone P: Maxillofacial fractures in the province of Latina, Lazio, Italy: review of 400 injuries and 83 cases. J Craniomaxillofac Surg 42: 583e587, 2014 €ller B, Wiltfang J: Comparison of Becker ST, Terheyden H, Fabel M, Kandzia C, Mo collagen membranes and PDS for reconstruction of orbital floor after fractures. J Craniofac Surg 21: 1066e1068, 2010 Birkenfeld F, Steiner M, Becker ME, Kern M, Menzebach M, Wiltfang J, et al: Forces charging the orbital floor after fractures. J Craniofac Surg 22: 1641e1646, 2011 Birkenfeld F, Steiner M, Becker ME, Kern M, Wiltfang J, Lucius R, et al: Forces charging the orbital floor after trauma: a cadaver study. J Craniofac Surg 23, 2012a in press € ller B, Lucius R, et al: Forces affecting Birkenfeld F, Steiner M, Kern M, Wiltfang J, Mo orbital floor reconstruction materials e a cadaver study; 2012, in press
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