- Email: [email protected]
The construction and application of templates in the surgical reduction of mandibular prognathism
T H E C O N S T R U C T I O N A N D A P P L I C A T I O N OF T E M P L A T E S IN THE S U R G I C A L R E D U C T I O N OF M A N D I B U L A R PROGNATHISM
By C. C. KNOWLES, M.D.S., D.D.O., R.F.P.S.(Glas.) Consultant Orthodontist, Burns and Plastic Unit, Whiston Hospital, Prescot, Lancs. IN considering the causes of some failures in the treatment of mandibular prognathism by means of horizontal osteotpmy of the ramus the following factors may be considered. If a " b l i n d " osteotomy is performed using a Gigli saw passed around the inner aspect of the ramus, one is then unable to : (a) be sure to avoid the inferior dental bundle ; (b) control the swing of the upper fragment and perhaps only have a point contact of the bone ends with the possibility of non-union or fibrous union which will later contract. This will lead to a fore-shortening of the ramus and gagging in the molar region (Fig. I, 13and c) ;
]FIG. I - - - A ; An arbitrary line across the ramus. B, U n controlled swing of the upper fragment. Only point contact can be achieved, and this only if the upper fragment does not swing inwards. C, A fore-shortened ramus after delayed fibrous union. T h e loss of height is indicated by the amount of overlap. D, Incorrect (upper), and correct (lower), lines of section. E, Good alignment of the bone ends if the correct line is followed. Lateral displacement of the upper fragment if the incorrect upper line is followed.
C
D
E
(c) ensure that the direction of the section corresponds to the direction of movement of the lower fragment into its new position. Should this not be the case, then the bone ends will be in faulty apposition from this cause in addition to the likely displacement of the upper fragment. In Figure I, D and E, the lower line is the correct direction, but if the upper line were followed, the bone ends would over-ride so that the upper fragment would necessarily be displaced. If, therefore, horizontal osteotomy of the ramus is to be successful, then there is only one direction of cut that can be employed. It was perhaps because of the uncertainty of the outcome of the horizontal osteotomy of the ramus that other techniques were developed such as the sagittal splitting of Obwegeser (1964), the " L " shaped osteotomy of Trauner (I955), and various forms of subcondylar osteotomy and ostectomy which have been described many times. Thoma (I96I) gives a selection of techniques and Van Zile 0963) shows a modification which he has employed since I955. As 6I
62
B R I T I S H J O U R N A L OF P L A S T I C SURGERY
the objections to simple osteotomy of the ramus seem to be centred on the questions of non-union and the uncertainty of the eventual occlusal outcome it was thought that if good apposition of the bone ends could be achieved, horizontal osteotomy of the ramus could regain favour, leaving only the objection of the external approach to be considered. It has been found that the only external mark left after a few months' time is a thin line indistinguishable from a normal skin crease. This would seem a small price to pay for the ease of approach that the external approach offers. The time factor was mentioned by Caldwell and Letterman (1954) when they described a vertical osteotomy of the ramus involving decortication so that the anterior and posterior parts of the divided
/ MM •
-7¢
FIG. 2 L i n e " B " is t h e correct level a n d direction o f section d e t e r m i n e d after positioni n g t h e m i n o r tracing (dotted outline). T h e u p p e r edge o f t h e t e m p l a t e p a t t e r n c o r r e s p o n d s to " B ". T h e s h a d e d areas are b e n t over, in order to fit a r o u n d t h e anterior, posterior a n d lower b o r d e r s o f t h e m a n d i b l e as in F i g u r e 3.
FIG. 3 T o s h o w h o ' - t h e t e m p l a t e fits into place. T h e t h i r d flange fits a r o u n d t h e anterior border.
ramus could overlap. They mention an operating time of between 4 and 6 hours. Using a template to ensure correct alignment of the bone ends, it is possible to complete a simple horizontal osteotomy of the ramus in about 2 hours giving time for careful dissection to avoid the marginal branch of the 7th nerve. The precision splints (Knowles, 1961) which are cemented the day before, can be fixed with the elastics in a few minutes and the bone ends also quickly fastened with the interosseous wires as will be described later. The R a m i - s e c t i o n T e m p l a t e . - - T h e application of cephalometric X-rays to the construction of templates has been previously described (Knowles et al., 1963) , but
TEMPLATES IN MANDIBULAR PROGNATHISM
63
the method may perhaps be repeated because modifications have been made to the template over a period of some four years before the present design was evolved. The left and right sides of the dental arches and the jaws can easily be traced separately with practice and with the aid of study models. On a separate piece of tracing paper the mandibular teeth and part of the ascending ramus are copied, including the cross marked on the anterior border (Fig. 2). With the help of the study models, the left and right copy tracing may be moved into the new position of occlusion (Fig. 2), bearing in mind the need to allow a sufficient degree of over-correction of the lower incisor region for the eventual proclination of the lower incisors that will take place as Hogeman (I95I) has shown. The cross on the copy tracing will now be found further back on the outline of the ramus of the main tracing (Fig. 2), and if the two crosses are joined, the line so formed (A, Fig. 2) will mark the correct direction for the osteotomy, because it represents the direction taken by the teeth in moving to their new position. However, the height is obviously wrong, and since it is desired to perform the osteotomy in the thickest possible part of the rarnus, the level can now be dropped to fall just above the X-ray outline of the mandibular foramen (B, Fig. 2). A section at this level, cutting at 45 ° to the outer plate of the ramus, will emerge on the inner aspect well clear of the inferior dental bundle. A paper pattern of the template is now drawn over the combined tracings and extended, as shown (Fig. 2), beyond the anterior, posterior and lower borders of the ramus and angle. When this has been done, the width and height of the template are reduced by IO per cent. which is the degree of magnification of the X-ray image over normal size. The corrected paper shape is now stuck down to a sheet of German silver metal and cut out. Before the paper is removed, the lines indicating the anterior and posterior borders are scribed through. A handle is soldered on and the template polished. Finally, the locating flanges may be bent over according to the lines scribed through. The template will now fit as shown in Figure 3. There can, of course, be only one correct position for the template, that is, with all three flanges fitting around their respective borders of the mandible. In this position, the upper border represents the correct direction and height of section. The template is applied to the mandible after the bone has been exposed from an external approach and the masseter and internal pterygoid muscles have been stripped off. A tungsten carbide fissure bur is used to mark the line of section and then the template may be withdrawn. Osteotomy is taken through the outer plate with the fissure bur held at 45 ° to the external surface as already described and the separation is completed with an osteotome with its edge in the same plane as the bur cut and cutting from behind forwards through the inner cortical plate. In this way, a clean smooth surface can be obtained so that there is no need for any trimming to be carried out in order for the bone ends to be properly approximated. Figure 4 shows a part ofa cephalometric X-ray taken two weeks post-operatively showing the degree of accuracy with which the bone end may be approximated. It can also be seen how the height of the section passes just above the level of the mandibular foramen and the interosseous wire. Note the step on the posterior border between the upper and lower fragments. The degree of this is carefully measured from the tracings at the time the interosseous wire is tightened. Firm union is achieved at the sixth week in young subjects, those between 20 and 30 years of age being left for two more weeks. In prognathism with asymmetry, cephalometric planning by the method described illustrates the need to follow slightly differing directions on the two sides and also clearly shows the variation in the amount of the posterior border step between the two sides. Careful note is made of these differing steps when the interosseous wires are applied. Such a case is illustrated in Figures 5 and 6. Some cases, particularly those with an anterior open bite, are best corrected by means of a body or angle ostectomy. It is not the purpose of the present paper to
64
B R I T I S H J O U R N A L OF P L A S T I C SURGERY
FIG. 4 P r i n t taken f r o m a cephalometric film to s h o w : T h e line o f section (white) ; posterior b o r d e r step ; interosseous wires.
r
~
j
R
FIG. 5 R i g h t a n d left tracings of t h e case s h o w n in F i g u r e 6. N o t e : Different direction o f section o n each side ; a larger posterior b o r d e r step on t h e right side.
TEMPLATES IN MANDIBULAR PROGNATHISM
65
discuss the reasons for the election of these sites. This has been well done by Rowe (I96o). Although it is an easy matter to measure the width of the osteotomy from study models, it is not very easy to mark out with pen and ink upon the bone surface. With a template made as shown in Figure 7, marking out is simplified. The width of the template is given by a superimposition of two tracings in a similar manner as for osteotomy of the ramus. The completed template (Fig. 7A), has cut-outs made down each side,
FIG. 6 Case of asymmetry and prognathism before and after an osteotomy of both rami according to the plan in Figure 5.
which are of the same width as the diameter of the fissure bur to be used. The upper crosspiece indicates the full width, that at the bottom which is shaded in is to be bent to fit under the lower border of the mandible. Two small notches, indicating the level of the mandibtflar canal, are cut in. A handle may be soldered on in such a way that the template will retain sufficient flexibility to enable it to be bent to the contour of the outer aspect of the mandible (Fig. 7, B). When the outer aspect of the mandible has been exposed, the template may be located centrally between the standing teeth on either side of the ostectomy site, the flange fitting along the lower border of the mandible. The fissure bur can now be run along each side of the template and a mark can also be made to IE
BRITISH JOURNAL OF PLASTIC SURGERY
66
I
?i I
: Ij.
'
b
FIG. 7 Tracing and template for body osteotomy. The shaded portion is bent to fit along the lower border of the mandible. The central portion of the template is narrowed to allow for the thickness of the fissure bur. Notches mark the line of the mandibular canal. It may also be seen how the template has been curved to fit the contour of the bone. Solid line, major tracing ; dotted line~ minor tracing.
FIG. 8 Tracing and template for angle osteotomy. The shaded parts are bent to fit the anterior and posterior borders of the mandible. Small pointers mark the line of the canal because the template is thin only when allowance has been made for the thickness of the fissure bur. Solid line, major tracing, dotted line, minor tracing.
FIG. 9 A template in place for angle ostectomy. The upper picture shows the inferior dental bundle displayed through the window cut according to the markers on the template. The osteotomy has been performed and holes for interosseous wires are about to be made.
TEMPLATES IN M A N D I B U L A R
r
/
PROGNATHISM
67
/Y J
FIG. i2 T r a c i n g of a c e p h a l o m e t r i c film from which the template shown in F i g u r e 13 was m a d e .
FIG, ! 0
T r a c i n g to s h o w t h e w e d g e - s h a p e d piece to be r e m o v e d in order to allow r e d u c t i o n of t h e anterior o p e n bite.
FIG. I I
Profiles before a n d after wedge o s t e o t o m y as in F i g u r e IO. T h e lips n o w close w i t h o u t conscious effort. N o t e t h e line o f t h e incision a n d t h a t a r h i n o p l a s t y has b e e n carried out.
68
BRITISH JOURNAL OF PLASTIC SURGERY
correspond to the notches indicating the line of the mandibular canal. When the template ~s removed, the ostectomy may be proceeded with, usually starting with the exposure of the inferior dental bundle through a window cut around the line which has been marked. Exactly the same procedure is followed for an angle ostectomy (Figs. 8 and 9). In the case of a large anterior open bite, a wedge-shaped piece is removed as in the case illustrated by Figures IO and II. In this instance, the fissure bur was run
FIG. 13 Template to indicate the a m o u n t of bone to be removed from the lower border of the mandible. T h e slots represent the line of the mandibular canal.
on the inner aspect of the two arms of the template. The line of the mandibular canal was marked by two small pointers. The template principle may be adapted to other procedures where a measured amount of bone is to be reinoved. In Figure I2 a tracing is shown of a case of unilateral hypertrophy and it was intended to remove sufficient lower border of the mandible on the affected side to restore symmetry. The template (Fig. r3) was constructed from the tracing illustrated and it was possible to indicate the points where the inferior dental bundle crossed the line of section in two places. Using this method, it was possible to trim the affected side to match exactly the shape of the normal.
SUMMARY A method of constructing templates from cephalometric films is described. These templates are intended to be placed directly upon that part of the mandible in which the osteotomy is to be performed. Although cephalometric films have been used by Converse (I963) and Joffe (I964) as an indirect aid to treatment planning, and by many such as Goldstein (I947) and Poulton, Taylor and Ware (I963) for the post-operative evaluation, there does not seem any instance of their use for the manufacture of templates to be used at operation. HillerstrSm and Nyquist (x954) were able to indicate the correct direction of a ramus osteotomy by mechanical means on a special articulator, but regarded their apparatus as more of scientific than of clinical interest. Although there have been instances where an operator will not count it of importance to sever the inferior dental bundle as Winter et al. (r949) reported, it would seem
TEMPLATES IN MANDIBULAR PROGNATHISM
69
much more worth while to take pains to avoid damage to these structures if possible and the use of templates as described is a simple way of doing this.
The author wishes to thank Mr. M. Bayliss, medical photographer at Whiston Hospitals for his help in preparing the illustrations. REFERENCES CALDWELL,J. B., and LETTERMAN,G. S. (1954). J. oral Surg., 12, 185. CONVERSE,J. M. (I963). Br. ~. plast. Surg., 16, 197. GOLDSTEII%A. (1947). Angle Orthod., 17, 59HILLERSTROM, K., and NYQUIST~G. (1954). Acta odont, scand, 12, 65. HOGEMAN, K. E. (1951). Acta chir. scan&, Supp. 159. JOFFE, B. M. (1964). Dent. Practnr., I4, 5o8. KNOWLES,C. C. (1961). Br. J. plast. Surg. 14, 315. KNOWLES, C. C., KERNAHAN,D. A., and BURSTON,W. R. (I963). Br. J. plast. Surg., 16, I8O. OBWEGESER,H. (1964). Br. J. oral Surg., .I, 157. POULTON,D. R., TAYLOR,R. C., and WARE,W. H. (1963). Oral Surg., 16, 807. ROWE, N. L. (196o). Br. dent. J., io8, 45 and 77. THOMA, K. H. (1961). Oral Surg., 14, 23. TRAUNER,R. (1955). Ost. Z. Stomat., 52, 361. VAN ZlLE, W. N. (1963). J. oral Surg., 21, 3. WINTER, L., WINTER,R. E., and WINTER,L. jun. (1949). Oral Surg., 2, 15o6.
By C. C. KNOWLES, M.D.S., D.D.O., R.F.P.S.(Glas.) Consultant Orthodontist, Burns and Plastic Unit, Whiston Hospital, Prescot, Lancs. IN considering the causes of some failures in the treatment of mandibular prognathism by means of horizontal osteotpmy of the ramus the following factors may be considered. If a " b l i n d " osteotomy is performed using a Gigli saw passed around the inner aspect of the ramus, one is then unable to : (a) be sure to avoid the inferior dental bundle ; (b) control the swing of the upper fragment and perhaps only have a point contact of the bone ends with the possibility of non-union or fibrous union which will later contract. This will lead to a fore-shortening of the ramus and gagging in the molar region (Fig. I, 13and c) ;
]FIG. I - - - A ; An arbitrary line across the ramus. B, U n controlled swing of the upper fragment. Only point contact can be achieved, and this only if the upper fragment does not swing inwards. C, A fore-shortened ramus after delayed fibrous union. T h e loss of height is indicated by the amount of overlap. D, Incorrect (upper), and correct (lower), lines of section. E, Good alignment of the bone ends if the correct line is followed. Lateral displacement of the upper fragment if the incorrect upper line is followed.
C
D
E
(c) ensure that the direction of the section corresponds to the direction of movement of the lower fragment into its new position. Should this not be the case, then the bone ends will be in faulty apposition from this cause in addition to the likely displacement of the upper fragment. In Figure I, D and E, the lower line is the correct direction, but if the upper line were followed, the bone ends would over-ride so that the upper fragment would necessarily be displaced. If, therefore, horizontal osteotomy of the ramus is to be successful, then there is only one direction of cut that can be employed. It was perhaps because of the uncertainty of the outcome of the horizontal osteotomy of the ramus that other techniques were developed such as the sagittal splitting of Obwegeser (1964), the " L " shaped osteotomy of Trauner (I955), and various forms of subcondylar osteotomy and ostectomy which have been described many times. Thoma (I96I) gives a selection of techniques and Van Zile 0963) shows a modification which he has employed since I955. As 6I
62
B R I T I S H J O U R N A L OF P L A S T I C SURGERY
the objections to simple osteotomy of the ramus seem to be centred on the questions of non-union and the uncertainty of the eventual occlusal outcome it was thought that if good apposition of the bone ends could be achieved, horizontal osteotomy of the ramus could regain favour, leaving only the objection of the external approach to be considered. It has been found that the only external mark left after a few months' time is a thin line indistinguishable from a normal skin crease. This would seem a small price to pay for the ease of approach that the external approach offers. The time factor was mentioned by Caldwell and Letterman (1954) when they described a vertical osteotomy of the ramus involving decortication so that the anterior and posterior parts of the divided
/ MM •
-7¢
FIG. 2 L i n e " B " is t h e correct level a n d direction o f section d e t e r m i n e d after positioni n g t h e m i n o r tracing (dotted outline). T h e u p p e r edge o f t h e t e m p l a t e p a t t e r n c o r r e s p o n d s to " B ". T h e s h a d e d areas are b e n t over, in order to fit a r o u n d t h e anterior, posterior a n d lower b o r d e r s o f t h e m a n d i b l e as in F i g u r e 3.
FIG. 3 T o s h o w h o ' - t h e t e m p l a t e fits into place. T h e t h i r d flange fits a r o u n d t h e anterior border.
ramus could overlap. They mention an operating time of between 4 and 6 hours. Using a template to ensure correct alignment of the bone ends, it is possible to complete a simple horizontal osteotomy of the ramus in about 2 hours giving time for careful dissection to avoid the marginal branch of the 7th nerve. The precision splints (Knowles, 1961) which are cemented the day before, can be fixed with the elastics in a few minutes and the bone ends also quickly fastened with the interosseous wires as will be described later. The R a m i - s e c t i o n T e m p l a t e . - - T h e application of cephalometric X-rays to the construction of templates has been previously described (Knowles et al., 1963) , but
TEMPLATES IN MANDIBULAR PROGNATHISM
63
the method may perhaps be repeated because modifications have been made to the template over a period of some four years before the present design was evolved. The left and right sides of the dental arches and the jaws can easily be traced separately with practice and with the aid of study models. On a separate piece of tracing paper the mandibular teeth and part of the ascending ramus are copied, including the cross marked on the anterior border (Fig. 2). With the help of the study models, the left and right copy tracing may be moved into the new position of occlusion (Fig. 2), bearing in mind the need to allow a sufficient degree of over-correction of the lower incisor region for the eventual proclination of the lower incisors that will take place as Hogeman (I95I) has shown. The cross on the copy tracing will now be found further back on the outline of the ramus of the main tracing (Fig. 2), and if the two crosses are joined, the line so formed (A, Fig. 2) will mark the correct direction for the osteotomy, because it represents the direction taken by the teeth in moving to their new position. However, the height is obviously wrong, and since it is desired to perform the osteotomy in the thickest possible part of the rarnus, the level can now be dropped to fall just above the X-ray outline of the mandibular foramen (B, Fig. 2). A section at this level, cutting at 45 ° to the outer plate of the ramus, will emerge on the inner aspect well clear of the inferior dental bundle. A paper pattern of the template is now drawn over the combined tracings and extended, as shown (Fig. 2), beyond the anterior, posterior and lower borders of the ramus and angle. When this has been done, the width and height of the template are reduced by IO per cent. which is the degree of magnification of the X-ray image over normal size. The corrected paper shape is now stuck down to a sheet of German silver metal and cut out. Before the paper is removed, the lines indicating the anterior and posterior borders are scribed through. A handle is soldered on and the template polished. Finally, the locating flanges may be bent over according to the lines scribed through. The template will now fit as shown in Figure 3. There can, of course, be only one correct position for the template, that is, with all three flanges fitting around their respective borders of the mandible. In this position, the upper border represents the correct direction and height of section. The template is applied to the mandible after the bone has been exposed from an external approach and the masseter and internal pterygoid muscles have been stripped off. A tungsten carbide fissure bur is used to mark the line of section and then the template may be withdrawn. Osteotomy is taken through the outer plate with the fissure bur held at 45 ° to the external surface as already described and the separation is completed with an osteotome with its edge in the same plane as the bur cut and cutting from behind forwards through the inner cortical plate. In this way, a clean smooth surface can be obtained so that there is no need for any trimming to be carried out in order for the bone ends to be properly approximated. Figure 4 shows a part ofa cephalometric X-ray taken two weeks post-operatively showing the degree of accuracy with which the bone end may be approximated. It can also be seen how the height of the section passes just above the level of the mandibular foramen and the interosseous wire. Note the step on the posterior border between the upper and lower fragments. The degree of this is carefully measured from the tracings at the time the interosseous wire is tightened. Firm union is achieved at the sixth week in young subjects, those between 20 and 30 years of age being left for two more weeks. In prognathism with asymmetry, cephalometric planning by the method described illustrates the need to follow slightly differing directions on the two sides and also clearly shows the variation in the amount of the posterior border step between the two sides. Careful note is made of these differing steps when the interosseous wires are applied. Such a case is illustrated in Figures 5 and 6. Some cases, particularly those with an anterior open bite, are best corrected by means of a body or angle ostectomy. It is not the purpose of the present paper to
64
B R I T I S H J O U R N A L OF P L A S T I C SURGERY
FIG. 4 P r i n t taken f r o m a cephalometric film to s h o w : T h e line o f section (white) ; posterior b o r d e r step ; interosseous wires.
r
~
j
R
FIG. 5 R i g h t a n d left tracings of t h e case s h o w n in F i g u r e 6. N o t e : Different direction o f section o n each side ; a larger posterior b o r d e r step on t h e right side.
TEMPLATES IN MANDIBULAR PROGNATHISM
65
discuss the reasons for the election of these sites. This has been well done by Rowe (I96o). Although it is an easy matter to measure the width of the osteotomy from study models, it is not very easy to mark out with pen and ink upon the bone surface. With a template made as shown in Figure 7, marking out is simplified. The width of the template is given by a superimposition of two tracings in a similar manner as for osteotomy of the ramus. The completed template (Fig. 7A), has cut-outs made down each side,
FIG. 6 Case of asymmetry and prognathism before and after an osteotomy of both rami according to the plan in Figure 5.
which are of the same width as the diameter of the fissure bur to be used. The upper crosspiece indicates the full width, that at the bottom which is shaded in is to be bent to fit under the lower border of the mandible. Two small notches, indicating the level of the mandibtflar canal, are cut in. A handle may be soldered on in such a way that the template will retain sufficient flexibility to enable it to be bent to the contour of the outer aspect of the mandible (Fig. 7, B). When the outer aspect of the mandible has been exposed, the template may be located centrally between the standing teeth on either side of the ostectomy site, the flange fitting along the lower border of the mandible. The fissure bur can now be run along each side of the template and a mark can also be made to IE
BRITISH JOURNAL OF PLASTIC SURGERY
66
I
?i I
: Ij.
'
b
FIG. 7 Tracing and template for body osteotomy. The shaded portion is bent to fit along the lower border of the mandible. The central portion of the template is narrowed to allow for the thickness of the fissure bur. Notches mark the line of the mandibular canal. It may also be seen how the template has been curved to fit the contour of the bone. Solid line, major tracing ; dotted line~ minor tracing.
FIG. 8 Tracing and template for angle osteotomy. The shaded parts are bent to fit the anterior and posterior borders of the mandible. Small pointers mark the line of the canal because the template is thin only when allowance has been made for the thickness of the fissure bur. Solid line, major tracing, dotted line, minor tracing.
FIG. 9 A template in place for angle ostectomy. The upper picture shows the inferior dental bundle displayed through the window cut according to the markers on the template. The osteotomy has been performed and holes for interosseous wires are about to be made.
TEMPLATES IN M A N D I B U L A R
r
/
PROGNATHISM
67
/Y J
FIG. i2 T r a c i n g of a c e p h a l o m e t r i c film from which the template shown in F i g u r e 13 was m a d e .
FIG, ! 0
T r a c i n g to s h o w t h e w e d g e - s h a p e d piece to be r e m o v e d in order to allow r e d u c t i o n of t h e anterior o p e n bite.
FIG. I I
Profiles before a n d after wedge o s t e o t o m y as in F i g u r e IO. T h e lips n o w close w i t h o u t conscious effort. N o t e t h e line o f t h e incision a n d t h a t a r h i n o p l a s t y has b e e n carried out.
68
BRITISH JOURNAL OF PLASTIC SURGERY
correspond to the notches indicating the line of the mandibular canal. When the template ~s removed, the ostectomy may be proceeded with, usually starting with the exposure of the inferior dental bundle through a window cut around the line which has been marked. Exactly the same procedure is followed for an angle ostectomy (Figs. 8 and 9). In the case of a large anterior open bite, a wedge-shaped piece is removed as in the case illustrated by Figures IO and II. In this instance, the fissure bur was run
FIG. 13 Template to indicate the a m o u n t of bone to be removed from the lower border of the mandible. T h e slots represent the line of the mandibular canal.
on the inner aspect of the two arms of the template. The line of the mandibular canal was marked by two small pointers. The template principle may be adapted to other procedures where a measured amount of bone is to be reinoved. In Figure I2 a tracing is shown of a case of unilateral hypertrophy and it was intended to remove sufficient lower border of the mandible on the affected side to restore symmetry. The template (Fig. r3) was constructed from the tracing illustrated and it was possible to indicate the points where the inferior dental bundle crossed the line of section in two places. Using this method, it was possible to trim the affected side to match exactly the shape of the normal.
SUMMARY A method of constructing templates from cephalometric films is described. These templates are intended to be placed directly upon that part of the mandible in which the osteotomy is to be performed. Although cephalometric films have been used by Converse (I963) and Joffe (I964) as an indirect aid to treatment planning, and by many such as Goldstein (I947) and Poulton, Taylor and Ware (I963) for the post-operative evaluation, there does not seem any instance of their use for the manufacture of templates to be used at operation. HillerstrSm and Nyquist (x954) were able to indicate the correct direction of a ramus osteotomy by mechanical means on a special articulator, but regarded their apparatus as more of scientific than of clinical interest. Although there have been instances where an operator will not count it of importance to sever the inferior dental bundle as Winter et al. (r949) reported, it would seem
TEMPLATES IN MANDIBULAR PROGNATHISM
69
much more worth while to take pains to avoid damage to these structures if possible and the use of templates as described is a simple way of doing this.
The author wishes to thank Mr. M. Bayliss, medical photographer at Whiston Hospitals for his help in preparing the illustrations. REFERENCES CALDWELL,J. B., and LETTERMAN,G. S. (1954). J. oral Surg., 12, 185. CONVERSE,J. M. (I963). Br. ~. plast. Surg., 16, 197. GOLDSTEII%A. (1947). Angle Orthod., 17, 59HILLERSTROM, K., and NYQUIST~G. (1954). Acta odont, scand, 12, 65. HOGEMAN, K. E. (1951). Acta chir. scan&, Supp. 159. JOFFE, B. M. (1964). Dent. Practnr., I4, 5o8. KNOWLES,C. C. (1961). Br. J. plast. Surg. 14, 315. KNOWLES, C. C., KERNAHAN,D. A., and BURSTON,W. R. (I963). Br. J. plast. Surg., 16, I8O. OBWEGESER,H. (1964). Br. J. oral Surg., .I, 157. POULTON,D. R., TAYLOR,R. C., and WARE,W. H. (1963). Oral Surg., 16, 807. ROWE, N. L. (196o). Br. dent. J., io8, 45 and 77. THOMA, K. H. (1961). Oral Surg., 14, 23. TRAUNER,R. (1955). Ost. Z. Stomat., 52, 361. VAN ZlLE, W. N. (1963). J. oral Surg., 21, 3. WINTER, L., WINTER,R. E., and WINTER,L. jun. (1949). Oral Surg., 2, 15o6.