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Experimental study on the free transplantation of mucosa and lyophilised dura to the oral cavity
J. max.-fac. Surg. 6 (1978) 64-69
Experimental Study on the Free Transplantation of Mucosa and Lyophilised Dura to the Oral Cavity J/irgen-Friedrich REUTHER,Rudolf WAGNER,Bernhard BRAUN Clinic for Maxillo-Facial Surgery (Head: Prof. H. Scheunemann, M.D., D.M.D.) and Institute of Pathology (Head: Prof. W. Thoenes, M.D.), ]ohannes Gutenberg University, Mainz, W.-Germany
Summary The covering of epithelial defects in the oral cavity presents special problems in preprosthetic surgery, since special requisites for function and quality of mucosal grafts must be satisfied. In animal experiments mucosal defects in the oral cavity of 30 rabbits were repaired with free transplants of autologous mucosa and heterologous lyophilised dura. A comparative clinical and histological assessment of the healing processes showed that there was no essential difference between both methods. Considering the necessary second intervention, the infliction of a second wound, as well as the limited source of mueosa, our results show that the use of lyophilised dura in preprosthetic surgery is preferable.
Key-Words: Transplantation of oral mucosa; Animal experiment; Lyophilised human dura.
Introduction In maxillo-facial surgery there is often the need to cover extensive epithelial defects of the oral cavity. Problems arise especially in preprosthetic and periodontal surgery, where special demands are made on function and quality of the mucosal graft. Split thickness skin graft has been successfully utilised as a substitute for oral mucosa since the original description by Esser was published in 1917. The fact that the epithelium of grafts taken from other sites still retain its original structure after many years (Schwenzer and Wiistenfeld 1970) leads to certain disadvantages especially in function. That was the reason for the recommendation of free transplantation of autologous mueosa in periodontal surgery by Bfi~rn (1968), Cowan (1965), Bernimoulin and Lange (1972), Dreeskamp and Flores de Jacoby (1973), Diedrich and Mulschelhnaus (1974), and in preprosthetic surgery by Proper (1964), Matras (1968), Steinhiiuser (1968, 1969) and Hall and O'Steen 0801-050;3/'78 1300-0064
(1970). The efficacy of this method has, however, been drastically reduced by the limited availability of transplantable mucosa, since the oral cavity appears to be the only donor site. The successful transplantation of intestinal mucosa into the oral cavity by Herbsmann et al. (1957), as well as Steinhiiuser and Schrang (1964) does not appear to have any clinical significance. M a n y specialty fields have reported successful application of lyophilised dura in the replacement of congenital or acquired tissue defects in the past few years. Hering (1969) and Schilli (1969) were the first to publish successful clinical results in the replacement of oral mucosa with lyophilised dura. In experimental animals, we studied the healing processes of grafted heterologous lyophilised dura and autologous mucosa in the oral cavity in order to compare both methods directly, and draw a conclusions about their clinical importance.
Method In standardised experimental conditions a mucosal defect of 2 x 1 cm was made on both sides of the maxillary buccal surface in 30 hybrid rabbits without damage to the periosteum. On the left side lyophilised dura, which was sterilised with gamma rays, was used to cover the mucosal defect and the margin approximately with atraumatic silk sutures (Fig. 1). The mucosa obtained from the left side was placed on a hard support and reduced as much as possible in thi&nessl It was thereafter sutured into the defect on the right vestibulum (Fig. 2). In order better to adapt the grafts, we introduced individually constructed acrylic plates in three animals in a series, while one animal was left without any such dressing (Fig. 3). All operations were performed
$ 05.00 © 1978 Georg Thierne Publishers
Fig. 1 Grafting of lyophilised dura into mucosal defect of the maxillary vestibulum of the oral cavity of a rabbit.
Fig. 2 Free graft of autologous mucosa to cover the mucosal defect in the right maxillary vestibulum of a rabbit.
Fig. 3 Individually constructed protective acrylic plate for additional adaptation of the grafted tissue.
Fig. 4 2 days postoperativeiy: dura transplant lying directly on bone; non-irritated, only minor cellular reaction (experiment with protective plate) (HE, 12x). 5 ,j. u~ax.~fac. Su:g. 1/78
66
],-F. Reuther, R. Wagner, B. Braun
Fig. 5a+ b 4 days postoperatively (a) Resorption of grafted lyo-dura by granulation tissue. Orientation of the macrophages at the connective tissue sepia of the graft (HE, 80x).
Fig. 5 b Enlargement of a section of 5 a): The lyophilised dura is used as a track by the proliferating granulation tissue (HE, 170x).
under intravenous nembutal (35 mg/kg body weight). The grafts were removed after 2, 4, 8, 28 and 42 days.
Findings Two days following the operation in the series with protective acrylic plates, the lyophilised dura and the mucosal graft were found to be clinically intact, firmly adherent to the underlayer and covered with a fine layer of fibrin. The mucosal graft had a whitish-opaque translucent colour. The microscopic picture also showed that lyophilised dura and mucosal grafts were closely attached to the periosteum, and were only
slightly separated from it by an exudate which was poor in fibrin (Fig. 4). Exudation of fibrin was more pronounced at the margin; there was also a collection of leucocytes and histiocytes. The macroscopic picture remained essentially unchanged after four days. But microscopically the margins of the transplants and the periosteum showed granulation tissue which was more developed in the lyophilised dura than in the mucosal graft (Fig. 5a). The macrophages of the granulation tissue migrate into the transplant of dura, thereby using the fibres as guide rails (Fig. 5b). While the lyophilised dura is predominantly replaced by granulation tissue on the 8th day,
Study on the Free Transplantation of Mucosa and Lyophilised Dura
67
Fig. 6 8 days postoperatively: Epithelial tissue radiates into the partially necrotic mucosal graft from the margin (experiment with protective plate (HE, 100x).
Fig. 7 42 days postoperatively: Completion of epithelialisation of the dura transplant in the experimental series with protective plate (HE, 170x). large areas of the surface of the mucosal grafts became necrotic and are resorbed by granulation tissue. Re-epithelisation of the graft begins from the margin of the local mucosa or from the partially intact and remaining mucosal graft. The epithelium grows over the granulation tissue as can be seen in Fig. 6. After 14 days both transplants appear as moderately spongy, highly reddened tissue. Histology of the tyophilised dura shows that it has been completely replaced by granulation tissue and partially covered by a thin epithelium. The mucosal graft appears to be completely re-epithelialised. The squamous epithelium is still very thin
and there is occasional cellular granulation tissue subepithelially. The defects on both sides are completely coated with stratified epithelium 28 days after the operation. Differentiation of both grafted tissues is no longer possible (Figs. 7 +8). In the .series without a protective acrylic plate the lyophilised dura as well as the transplanted mucosa were raised distinctly from the underlayer by an exudate which was rich in fibrin and cells (Fig. 9). Although there was also healing with re-epithelialisation in these c~ses, there was a broad area of fibrous tissue between the periosteum and squamous epithelium.
68
].-F. Reuther, R. Wagner, B, Braun
%
Fig. 8 42 days postoperatively: Condition after complete healing of the free mucosal graft in the experimental series with protective plate (HE, 170x).
Fig. 9 2 days postoperatively without protective plate: The dura transplant is completely raised from bone by an exudation rich in fibrin and cells (HE, 12x).
Discussion Our series of animal experiments explored the efficacy of free transplants of autologous mucosa and heterologous lyophilised dura into the oral cavity. It was found that after the second day after transplantation of the lyophilised dura there was evidence of replacement with marginal and periosteal granulation tissue in those cases in which the graft was held in place with individually constructed protective acrylic plates. Re-epithelisation over the granulation tissue began on the 8th day, and was completed after 28 days. Our findings are comparable with those of Simons (1969) in the regeneration of vesical
mucosa after reconstruction of the defect with lyophilised dura. Similar results have also been reported by Caroll et al. (1974), who grafted mucosal defects of the oral cavity with dry frozen split thickness skin in animal experiments. In free transplant of autologous mucosa in the oral cavity the epithelium remains identifiable up to 4 days after the operation. Thereafter the superficial epithelium and the transplanted subepithelial tissue become partially necrotic. 1Reepithelialisation begins between the 4th and 8th day and is complete after 14 days. The results of our experiment are supported by the findings
Study on the Free Transplantation of Mucosa and Lyophilised Dura of Oliver et al. (1968), Staffileno a n d L e w i (1969) and ]anson et al, (1969), who also found extensive necrosis of the transplanted epithelium. These authors also found that the graft bed was essentially re-epithelialised from ,the neighbourhood. These satisfactory results were obtained only in those experimental animals in which i n d i v i d u a l l y constructed protective plates were used additionally. W h e r e the transplant lay free in the oral cavity a fibrinous layer, which was rich in leucocytes and erythrocytes, developed between the graft bed and the transplanted tissue. Although the defects eventually all re-epithelialised, the result was functionally poor because there was a wide area of fibrous tissue between the squamous epithelium and bone.
69
Conclusion A comparison of both g r a f t e d tissues in our experimental series showed that a p a r t from the slightly shorter period of re-epithelialisation of the mucosal grafts, there was no other clinical or histological difference in the healing processes. Based on these findings, we therefore recommend the use of lyophilised dura in the replacement of mucosal defects of the oral cavity, especially in preprosthetic surgery, where it is necessary to cover larger defects, W i t h the use of this method, there is no limitation in the availability of the graft material. F u r t h e r m o r e the a d d i t i o n a l operation to procure the g r a f t a n d the raw surface at the donor site are obviated. These factors are i m p o r t a n t when intervention in a practice is considered.
References Bernimoulin, ]. P., D. E. Lange: Freie Gingivatransplantate - Klinische Aspekte und Zytologie ihrer Einheilung. Dtsch. zahnSrzth Z. 27 (1972) 357 Bj6rn, H.: Free transplantation of gingiva propria. Odont. Rev. 14 (1963) 323 Caroll, P. B., H. O. Tow, A. R. Vernino: The use of allogenic freeze-dried skin grafts in the oral environment. J. Orah Surg. Med. Path. 37 (1974) 163 Cowan, A.: Sutcus Deeping Incorporating Mucosal Graft. J. Periodont. 36 (1965) 188 Diedrich, P., R. Mutschelknauss: Die Behandlung der isolierten Dehiszenz mit Gingivatransptantaten. Dtsch. zahniirztl. Z. 29 (1974) 399 Dreeskamp, M., L. FIores de Jacoby: Brei~te der Gingiva propria bei der Vestibulumplastik nach Gingivatransplantat. Dtseh. zahn~irztl. Z. 28 (1973) 192 Esser, ].-E.: Studies in Plastic Surgery of the face: I. Use of skin from the Ne& to Replace Defects. II. Plastic Operations about the Mouth. III. The Epidermic Inlay. Ann. Surg. 65 (1917) 297 Hall H. D., A. N. O'Steen: Free grafts of palatal mucosa in mandibular vestibuloplasty. J. Oral Surg. 28 (1970) 565 Herbsmann, H , A. S. Rabson, W. E. Schatten: Experimental Transplantation of Free Grafts of IntestinaI Mucous Membrane. J. Plast. reeonstr. Surg. 20 (1957) 366 Hering, H. ].: Mundschleimhautersatz durch lyophilisierte Dura (LD) bei Mundvorhofplastik. Mcd. Mitt. (Melsungen) 43 (1969) 205 ]anson, W. A., M. P. Ruben, G. M. Kramer, A. A. Bloom, A. Turner: Development of the Blood Supply to Split-thi&ness Free Gin gival Autografts. J. Periodont. 40 (1969) 707 Matras, H.: Zur Anwendung der freien Schleimhaut-
transplantation in der priiprothetischen Chirurgie. O st. Z. Stomat. 65 (1968) 56 Oliver, R. C., H. Loe, T. Karring: Microscopic Evaluation of the Healing and Revascularisation of Free Gingival Grafts. J. Periodont. Res. 3 (1968) 84 Proper, R.: Simplified Ridge Extension using free Mucosal Grafts. J. Oral. Surg. 22 (1964) 469 Schilli, W.: Schleimhautersatz in der MundhShle durch lyophilisierte Dura. Med. Mitt. (Melsungen) 43 (1969) 211 Schwenzer, N., E. Wiistenfeld: Zur Klinik und His,tologie freier Hauttransplantate in der MundhShle. Dtsch. zabn~irztl. Z. 25 (1970) 1049 Simons, E.: Blasendefektde&ung mit lyophilisierter Dura. Med. Mitt. (Melsungen) 43 (1969) 195 Staf[ileno, H., S. Levy: Histologic and clinical Study of Mueosal (Gingival) Transplants in Dogs. J. Periodont. 40 (1969) 311 Steinhiiuser, E.: Freie Schleimhautverpflanzung in der MundhShle - eine Maf~nahme zur Verbesserung des Prothesenhaltes. Schwciz. Mschr. Zahnheilk. 78 (1968) 1046 Steinhiiuser, E.: The Transplantation of Oral Mucosa for Improvment of Denture Retention. J. Oral. Surg. 27 (1969) 955 Steinhiiuser, E., ]. Schrang: A study of the Viability of the Free Transplanted Small Bowel. Army Report, Univ. of Texas Med. Branch, Galveston, Texas 1964 Sullivan, H. C., ]. H. Atkins: Free au,togenous Gin gival Grafts. I. Principles of Successful Grafting. Peri.odontics 6 (1968) 5 Jiirgen-Frledridt Reuther, M.D., D.M.D., Clinic"/orMaxillo[aeialSurgery, Johannes Gutenberg University, 6500Mainz, W.-Germany
Experimental Study on the Free Transplantation of Mucosa and Lyophilised Dura to the Oral Cavity J/irgen-Friedrich REUTHER,Rudolf WAGNER,Bernhard BRAUN Clinic for Maxillo-Facial Surgery (Head: Prof. H. Scheunemann, M.D., D.M.D.) and Institute of Pathology (Head: Prof. W. Thoenes, M.D.), ]ohannes Gutenberg University, Mainz, W.-Germany
Summary The covering of epithelial defects in the oral cavity presents special problems in preprosthetic surgery, since special requisites for function and quality of mucosal grafts must be satisfied. In animal experiments mucosal defects in the oral cavity of 30 rabbits were repaired with free transplants of autologous mucosa and heterologous lyophilised dura. A comparative clinical and histological assessment of the healing processes showed that there was no essential difference between both methods. Considering the necessary second intervention, the infliction of a second wound, as well as the limited source of mueosa, our results show that the use of lyophilised dura in preprosthetic surgery is preferable.
Key-Words: Transplantation of oral mucosa; Animal experiment; Lyophilised human dura.
Introduction In maxillo-facial surgery there is often the need to cover extensive epithelial defects of the oral cavity. Problems arise especially in preprosthetic and periodontal surgery, where special demands are made on function and quality of the mucosal graft. Split thickness skin graft has been successfully utilised as a substitute for oral mucosa since the original description by Esser was published in 1917. The fact that the epithelium of grafts taken from other sites still retain its original structure after many years (Schwenzer and Wiistenfeld 1970) leads to certain disadvantages especially in function. That was the reason for the recommendation of free transplantation of autologous mueosa in periodontal surgery by Bfi~rn (1968), Cowan (1965), Bernimoulin and Lange (1972), Dreeskamp and Flores de Jacoby (1973), Diedrich and Mulschelhnaus (1974), and in preprosthetic surgery by Proper (1964), Matras (1968), Steinhiiuser (1968, 1969) and Hall and O'Steen 0801-050;3/'78 1300-0064
(1970). The efficacy of this method has, however, been drastically reduced by the limited availability of transplantable mucosa, since the oral cavity appears to be the only donor site. The successful transplantation of intestinal mucosa into the oral cavity by Herbsmann et al. (1957), as well as Steinhiiuser and Schrang (1964) does not appear to have any clinical significance. M a n y specialty fields have reported successful application of lyophilised dura in the replacement of congenital or acquired tissue defects in the past few years. Hering (1969) and Schilli (1969) were the first to publish successful clinical results in the replacement of oral mucosa with lyophilised dura. In experimental animals, we studied the healing processes of grafted heterologous lyophilised dura and autologous mucosa in the oral cavity in order to compare both methods directly, and draw a conclusions about their clinical importance.
Method In standardised experimental conditions a mucosal defect of 2 x 1 cm was made on both sides of the maxillary buccal surface in 30 hybrid rabbits without damage to the periosteum. On the left side lyophilised dura, which was sterilised with gamma rays, was used to cover the mucosal defect and the margin approximately with atraumatic silk sutures (Fig. 1). The mucosa obtained from the left side was placed on a hard support and reduced as much as possible in thi&nessl It was thereafter sutured into the defect on the right vestibulum (Fig. 2). In order better to adapt the grafts, we introduced individually constructed acrylic plates in three animals in a series, while one animal was left without any such dressing (Fig. 3). All operations were performed
$ 05.00 © 1978 Georg Thierne Publishers
Fig. 1 Grafting of lyophilised dura into mucosal defect of the maxillary vestibulum of the oral cavity of a rabbit.
Fig. 2 Free graft of autologous mucosa to cover the mucosal defect in the right maxillary vestibulum of a rabbit.
Fig. 3 Individually constructed protective acrylic plate for additional adaptation of the grafted tissue.
Fig. 4 2 days postoperativeiy: dura transplant lying directly on bone; non-irritated, only minor cellular reaction (experiment with protective plate) (HE, 12x). 5 ,j. u~ax.~fac. Su:g. 1/78
66
],-F. Reuther, R. Wagner, B. Braun
Fig. 5a+ b 4 days postoperatively (a) Resorption of grafted lyo-dura by granulation tissue. Orientation of the macrophages at the connective tissue sepia of the graft (HE, 80x).
Fig. 5 b Enlargement of a section of 5 a): The lyophilised dura is used as a track by the proliferating granulation tissue (HE, 170x).
under intravenous nembutal (35 mg/kg body weight). The grafts were removed after 2, 4, 8, 28 and 42 days.
Findings Two days following the operation in the series with protective acrylic plates, the lyophilised dura and the mucosal graft were found to be clinically intact, firmly adherent to the underlayer and covered with a fine layer of fibrin. The mucosal graft had a whitish-opaque translucent colour. The microscopic picture also showed that lyophilised dura and mucosal grafts were closely attached to the periosteum, and were only
slightly separated from it by an exudate which was poor in fibrin (Fig. 4). Exudation of fibrin was more pronounced at the margin; there was also a collection of leucocytes and histiocytes. The macroscopic picture remained essentially unchanged after four days. But microscopically the margins of the transplants and the periosteum showed granulation tissue which was more developed in the lyophilised dura than in the mucosal graft (Fig. 5a). The macrophages of the granulation tissue migrate into the transplant of dura, thereby using the fibres as guide rails (Fig. 5b). While the lyophilised dura is predominantly replaced by granulation tissue on the 8th day,
Study on the Free Transplantation of Mucosa and Lyophilised Dura
67
Fig. 6 8 days postoperatively: Epithelial tissue radiates into the partially necrotic mucosal graft from the margin (experiment with protective plate (HE, 100x).
Fig. 7 42 days postoperatively: Completion of epithelialisation of the dura transplant in the experimental series with protective plate (HE, 170x). large areas of the surface of the mucosal grafts became necrotic and are resorbed by granulation tissue. Re-epithelisation of the graft begins from the margin of the local mucosa or from the partially intact and remaining mucosal graft. The epithelium grows over the granulation tissue as can be seen in Fig. 6. After 14 days both transplants appear as moderately spongy, highly reddened tissue. Histology of the tyophilised dura shows that it has been completely replaced by granulation tissue and partially covered by a thin epithelium. The mucosal graft appears to be completely re-epithelialised. The squamous epithelium is still very thin
and there is occasional cellular granulation tissue subepithelially. The defects on both sides are completely coated with stratified epithelium 28 days after the operation. Differentiation of both grafted tissues is no longer possible (Figs. 7 +8). In the .series without a protective acrylic plate the lyophilised dura as well as the transplanted mucosa were raised distinctly from the underlayer by an exudate which was rich in fibrin and cells (Fig. 9). Although there was also healing with re-epithelialisation in these c~ses, there was a broad area of fibrous tissue between the periosteum and squamous epithelium.
68
].-F. Reuther, R. Wagner, B, Braun
%
Fig. 8 42 days postoperatively: Condition after complete healing of the free mucosal graft in the experimental series with protective plate (HE, 170x).
Fig. 9 2 days postoperatively without protective plate: The dura transplant is completely raised from bone by an exudation rich in fibrin and cells (HE, 12x).
Discussion Our series of animal experiments explored the efficacy of free transplants of autologous mucosa and heterologous lyophilised dura into the oral cavity. It was found that after the second day after transplantation of the lyophilised dura there was evidence of replacement with marginal and periosteal granulation tissue in those cases in which the graft was held in place with individually constructed protective acrylic plates. Re-epithelisation over the granulation tissue began on the 8th day, and was completed after 28 days. Our findings are comparable with those of Simons (1969) in the regeneration of vesical
mucosa after reconstruction of the defect with lyophilised dura. Similar results have also been reported by Caroll et al. (1974), who grafted mucosal defects of the oral cavity with dry frozen split thickness skin in animal experiments. In free transplant of autologous mucosa in the oral cavity the epithelium remains identifiable up to 4 days after the operation. Thereafter the superficial epithelium and the transplanted subepithelial tissue become partially necrotic. 1Reepithelialisation begins between the 4th and 8th day and is complete after 14 days. The results of our experiment are supported by the findings
Study on the Free Transplantation of Mucosa and Lyophilised Dura of Oliver et al. (1968), Staffileno a n d L e w i (1969) and ]anson et al, (1969), who also found extensive necrosis of the transplanted epithelium. These authors also found that the graft bed was essentially re-epithelialised from ,the neighbourhood. These satisfactory results were obtained only in those experimental animals in which i n d i v i d u a l l y constructed protective plates were used additionally. W h e r e the transplant lay free in the oral cavity a fibrinous layer, which was rich in leucocytes and erythrocytes, developed between the graft bed and the transplanted tissue. Although the defects eventually all re-epithelialised, the result was functionally poor because there was a wide area of fibrous tissue between the squamous epithelium and bone.
69
Conclusion A comparison of both g r a f t e d tissues in our experimental series showed that a p a r t from the slightly shorter period of re-epithelialisation of the mucosal grafts, there was no other clinical or histological difference in the healing processes. Based on these findings, we therefore recommend the use of lyophilised dura in the replacement of mucosal defects of the oral cavity, especially in preprosthetic surgery, where it is necessary to cover larger defects, W i t h the use of this method, there is no limitation in the availability of the graft material. F u r t h e r m o r e the a d d i t i o n a l operation to procure the g r a f t a n d the raw surface at the donor site are obviated. These factors are i m p o r t a n t when intervention in a practice is considered.
References Bernimoulin, ]. P., D. E. Lange: Freie Gingivatransplantate - Klinische Aspekte und Zytologie ihrer Einheilung. Dtsch. zahnSrzth Z. 27 (1972) 357 Bj6rn, H.: Free transplantation of gingiva propria. Odont. Rev. 14 (1963) 323 Caroll, P. B., H. O. Tow, A. R. Vernino: The use of allogenic freeze-dried skin grafts in the oral environment. J. Orah Surg. Med. Path. 37 (1974) 163 Cowan, A.: Sutcus Deeping Incorporating Mucosal Graft. J. Periodont. 36 (1965) 188 Diedrich, P., R. Mutschelknauss: Die Behandlung der isolierten Dehiszenz mit Gingivatransptantaten. Dtsch. zahniirztl. Z. 29 (1974) 399 Dreeskamp, M., L. FIores de Jacoby: Brei~te der Gingiva propria bei der Vestibulumplastik nach Gingivatransplantat. Dtseh. zahn~irztl. Z. 28 (1973) 192 Esser, ].-E.: Studies in Plastic Surgery of the face: I. Use of skin from the Ne& to Replace Defects. II. Plastic Operations about the Mouth. III. The Epidermic Inlay. Ann. Surg. 65 (1917) 297 Hall H. D., A. N. O'Steen: Free grafts of palatal mucosa in mandibular vestibuloplasty. J. Oral Surg. 28 (1970) 565 Herbsmann, H , A. S. Rabson, W. E. Schatten: Experimental Transplantation of Free Grafts of IntestinaI Mucous Membrane. J. Plast. reeonstr. Surg. 20 (1957) 366 Hering, H. ].: Mundschleimhautersatz durch lyophilisierte Dura (LD) bei Mundvorhofplastik. Mcd. Mitt. (Melsungen) 43 (1969) 205 ]anson, W. A., M. P. Ruben, G. M. Kramer, A. A. Bloom, A. Turner: Development of the Blood Supply to Split-thi&ness Free Gin gival Autografts. J. Periodont. 40 (1969) 707 Matras, H.: Zur Anwendung der freien Schleimhaut-
transplantation in der priiprothetischen Chirurgie. O st. Z. Stomat. 65 (1968) 56 Oliver, R. C., H. Loe, T. Karring: Microscopic Evaluation of the Healing and Revascularisation of Free Gingival Grafts. J. Periodont. Res. 3 (1968) 84 Proper, R.: Simplified Ridge Extension using free Mucosal Grafts. J. Oral. Surg. 22 (1964) 469 Schilli, W.: Schleimhautersatz in der MundhShle durch lyophilisierte Dura. Med. Mitt. (Melsungen) 43 (1969) 211 Schwenzer, N., E. Wiistenfeld: Zur Klinik und His,tologie freier Hauttransplantate in der MundhShle. Dtsch. zabn~irztl. Z. 25 (1970) 1049 Simons, E.: Blasendefektde&ung mit lyophilisierter Dura. Med. Mitt. (Melsungen) 43 (1969) 195 Staf[ileno, H., S. Levy: Histologic and clinical Study of Mueosal (Gingival) Transplants in Dogs. J. Periodont. 40 (1969) 311 Steinhiiuser, E.: Freie Schleimhautverpflanzung in der MundhShle - eine Maf~nahme zur Verbesserung des Prothesenhaltes. Schwciz. Mschr. Zahnheilk. 78 (1968) 1046 Steinhiiuser, E.: The Transplantation of Oral Mucosa for Improvment of Denture Retention. J. Oral. Surg. 27 (1969) 955 Steinhiiuser, E., ]. Schrang: A study of the Viability of the Free Transplanted Small Bowel. Army Report, Univ. of Texas Med. Branch, Galveston, Texas 1964 Sullivan, H. C., ]. H. Atkins: Free au,togenous Gin gival Grafts. I. Principles of Successful Grafting. Peri.odontics 6 (1968) 5 Jiirgen-Frledridt Reuther, M.D., D.M.D., Clinic"/orMaxillo[aeialSurgery, Johannes Gutenberg University, 6500Mainz, W.-Germany