Perforation of a tooth resulting in the communication of the root canal with the periodontal structures occasionally occurs during endodontic treatment. They may be induced iatrogenically or by resorption or caries. Prognosis of the tooth depends on the location of the perforation, the duration that the perforation is open to contamination, feasibility of sealing the perforation, and accessibility of the main canal. The manner in which the problem may be resolved both surgically and nonsurgically is considered.
Endodontic perforations: their prognosis and treatment Irving H. Sinai,
DDS, P h ila d e lp h ia
Practitioners unfortunately sometimes must contend with the perforation of a tooth during endodontic treatment. Perforations may be in duced iatrogenically or by resoiptive processes or caries. Iatrogenically caused perforations may be produced by powered rotary instruments dur ing the attempt to gain access to the pulp (Fig 1) or during instrumentation for a post (Fig 2). Inju dicious or improper manipulation of endodon tic instruments (Fig 3) may also lead to a perfor ation of the root. The resorptive process, given an adequate amount of time, can produce a communication between the pulp canal and the periodontal struc tures. This resorptive process (Fig 4) may be in ternal and caused by an inflamed pulp or external and caused by trauma; the latter generally ends in the destruction of the root (Fig 4, right) and the loss of the tooth. External resorption also may be idiopathic, which generally results in the blunting of the apex. The nature of this resorp tive process is probably systemic and its occur rence is infrequent. There is no treatment for this problem, and it will not be considered here. 90
■ JADA, V o l. 95, J u ly 1977
Caries, by invading the floor of the pulp cham ber and extending through to the furcation, may cause a perforation in instances of gross neglect (Fig 5). Caries that extends down the side of a root may expose the pulp. However, this is not generally considered an endodontic perforation but rather a restorative-periodontal problem.
P rognosis
The prognosis for a tooth with a perforation de pends on the location of the perforation, the time the perforation is open to contamination, the possibility of sealing the perforation, and acces sibility of the main canal. ■ Location in relation to the gingival sulcus: Perforation of the crown or root produces in flammatory changes and subsequent breakdown in the periodontium. This breakdown may ex tend to the gingival sulcus, producing a deep, nonmanageable periodontal defect. In my ex perience, a perforation in the middle or apical third of the root is less serious in this regard, and
Fig 2 ■ P e rfo ra tio n (P) p ro d u c e d
in p re p
a ra tio n o f to o th fo r post. M a te ria l (M ) fo rc e d F ig 1 ■ P e rfo ra tio n o f m esial a sp e ct o f flo o r
o u * ° * ro ° * d u rin g p re p a ra tio n and ce m en -
o f c h a m b e r (P) in a tte m p t to lo c a te m esial
ta tio n o f post,
ca na ls.
Fig
3 ■ M esial
fro m
im p ro p e r
p e rfo ra tio n
(P)
re s u ltin g
use o f e n d o d o n tic
in s tru
m ents.
THE AUTHOR F ig 5 ■ E xte n sive ca rie s (C) p e rfo ra tin g p u lp c h a m b e r.
flo o r o f
Dr. S ina i is d ir e c to r o f th e u n d e rg ra d u a te d iv i s io n and a s s o c ia te p ro f e s s o r in t h e d e p a r t m e n t o f e n d o d o n to lo g y , S c h o o l o f D e n tis tr y , T e m p le U nive rsity, 3223 N B ro ad St, 19140.
P h ila d e lp h ia ,
SINAI
S in a i: P ER FO R ATIO N S ■
91
the inflammatory changes will probably subside, if treated, before the periodontal breakdown can extend to the gingival sulcus. In contrast, per forations in the coronal third of the root or through the floor of the pulp chamber into the furcations of multirooted teeth may create more serious problems. In these instances, the trauma of the perforation and the subsequent inflamma tion may rapidly produce communication with the gingival sulcus and a noncorrectable perio dontal lesion. I believe it is especially impor tant that a perforation in this area be sealed im mediately after the root canal or canals have been located, to isolate the traumatized area and avoid further irritation and to allow it to heal quickly. ■ The time that the perforation is open to con tamination: The time the perforation is open to contamination has been shown to be a factor in the degree of inflammatory change and break down in the periodontium .1 As mentioned pre viously, those perforations in the coronal third of the root and in the floor of the chamber should be sealed immediately. For those located further apically, it is not essential that the seal of the per foration be placed immediately, but it is impor tant to protect the area from contamination to reduce the possibility of bacterial irritation and inflammatory changes. Therefore, in teeth with perforations in the apical two thirds, it is espe cially important that endodontic treatment be per formed under a rubber dam and that the tooth not be left open between visits under any circum stances. This approach will reduce the possibil ity of further breakdown of the periodontium adjacent to the perforation until a seal can be achieved. ■ The possibility o f achieving a seal o f the per foration: To ensure a favorable prognosis for the tooth, it is essential to seal the perforation. If this were not possible because of the size of the defect or an anatomic consideration either in the tooth itself or its position, the prognosis would be questionable. ■ The accessibility o f the main canal: A per foration may reduce the practitioner’s options during the performance of endodontic treatment. For example, a perforation in the coronal por tion of the tooth may occur during the process of locating the main canal. The perforation and its resultant change in the anatomy increase the 92 ■ JAD A, V o l. 95, J u ly 1977
Fig 6 ■ G utta-percha cones (C) leaving root through
perforation
(P) of curved canal.
difficulty of locating the canal. If it cannot be lo cated and treated endodontically, the apical end of the canal must be sealed directly, using a sur gical approach, and the perforation must be sealed, for repair to occur. A perforation in the apical two thirds of the root may be a result of failure to negotiate the curvature of the root (Fig 6). If the perforation is a short distance from the apex and the apical end of the canal can be negotiated, it may be possible to fill the perforation and the apical end of the canal. However, if this is not possible, I suggest that the apical end of the canal should be left un filled; a surgical approach to remove or seal the unfilled portion of the canal would be necessary if healing fails to occur.
T re a tm e n t
The correction of perforations usually can be achieved by one of six treatment approaches. ■ Perforations sealed during routine endodon tic treatment: There are two possible instances for this treatment. First, the perforation may be sealed if it occurs near the apex in a curved canal and if sealing of the canal with the use of pres sure forces the material into both the perforation and the main canal. Second, in instances of inter nal resorption, a small perforation may be sealed. Again, with a gutta-percha and solvent technique or a gutta-percha, root canal sealer, and pres sure technique, the material can be made to ex trude into and through the perforation, thereby sealing it (Fig 7). ■ Perforations sealed as an additional canal: A perforation extending diagonally through the root wall for a distance so that a canal-like effect is created may be treated as an additional root
Fig 7 • Top, (1) canal to be cleaned; (2) canal cleaned but perforated (P) near apex; (3) gutta percha cone (C) fitted at perforation; (4) filling forced into main canal and perforation. Bottom left, internal resorption (I) that has perforated dis tal root causing bone resorption (B). Bottom right, filling of area of internal resorption (I) using pres sure tech niq ue with extrusion of filling material (F) sealing perforation.
canal in that tooth. The perforation can be cleaned, shaped, and filled as would be done in the main canal (Fig 8). ■ Perforations sealed with amalgam via the chamber: In the location of a canal that has been narrowed considerably because of calcification, the floor of the pulp chamber may be perforated. As mentioned previously, this type of perfora tion should be sealed immediately. After the canal has been located, a retentive preparation
should be made in the chamber in the region of the perforation. Insertion into the canal of a paper point or of a lubricated metal instrument protects the canal. The area of the perforation then is gently packed with amalgam via the ac cess opening (Fig 9). Care must be exercised to avoid extrusion of the material through the per foration into the periodontal ligament. If the per foration is extensive, indium foil may be cut and laid over the perforation before placement of the amalgam to prevent its extrusion. The amalgam and the indium foil will coalesce to provide a sat isfactory seal .2 ■ Perforations sealed with amalgam using a sur gical approach: Use of the surgical approach is
Fig 8 ■ Filling “second can al” perfor ation. Gutta-percha cones (C) have been fitted to both canals.
Fig 9 ■ Perforation, created during ac cess, sealed via access with am algam (A). S in a i: PER FO R ATIO N S ■ 93
Fig 10 ■ Left, ro o t p e rfo ra tio n as a re su lt o f e x te n sive in te rn a l
re s o rp tio n
p e rfo ra te d
area se ale d w ith
Canal
been
h as
sealed
w ith
(I). R ight,
a m a lg a m
(A).
g u tta -p e rc h a
c o n e (C) a n d la te ra l co n d e n s a tio n .
usually limited to those situations that are not amenable to other treatment modalities. Place ment of an amalgam seal after routine filling of the canal can be used in instances of an exten sive perforation (Fig 10) or when the apical end of a canal cannot be negotiated. If a perforation was caused in the preparation of the tooth for a post, a coronal approach as previously described may be used. If this is not feasible, then the post can be prepared and cemented short of the per foration, and the perforation can be approached surgically and sealed with amalgam. There is lit tle likelihood of disturbing the cemented post. ■ Perforations repaired by stimulation o f calci fication: Calcium hydroxide is known to be in volved in the induction of calcification of tissue external to the tooth. This phenomenon is ap plied in the technique of apexification of the in
completely formed root end .3 The technique en tails cleansing the canal as thoroughly as possi ble, drying the canal, and then filling the canal with a calcium hydroxide paste. This is repeated as necessary until the desired calcification has occurred. Use of the approach has also been sug gested in instances of internal resorption and other pathoses that produce a defect too exten sive to be sealed by routine filling techniques .4 I have had success using this technique in the case of a multiple root fracture in a child (Fig 11). ■ Apicoectomy, root amputation, or hemisection: There are instances in which the use of an amalgam filling is not feasible or necessary. One example would be failure to negotiate a curved canal, thereby causing a perforation near the apex of the root. If an absence of healing resulted from the fail
Fig 11 ■ Left, m u ltip le ro o t fra c tu re s (F) as a re s u lt o f tra u m a . B o n e re s o rp tio n (R) has o c c u rre d a d ja c e n t to fra c tu re . C en te r, g u tta -p e rc h a c o n e (C) th ro u g h m esial g in g iv a l s u lc u s in to area o f b on e re s o rp tio n . R ig h t, b one (B) has d e p o s ite d a d ja c e n t to fra c tu re . G in g iva l s u lc u s no lo n g e r c o m m u n ic a te s w ith area o f ro o t fra c tu re .
94
■ JADA, V ol. 95, Ju ly 1977
Fig 12 ■ Left, m e s io b u c c a l ro o t (M ) to be re m o ve d . R ig h t, d is to b u c c a i (D) ro o t fille d , p a la ta l
ro o t fille d
and space p ro v id e d fo r
p o s t (S), and m e s io b u c c a l ro o t re m ove d (M).
ure to seal the last few millimeters of the canal, an apicoectomy could be performed removing the root structure to a point coronal to the per foration and unfilled canal. This would leave a root that is well filled to its new apex. The practitioner can encounter additional dif ficulties, as well as options, in the treatment of multirooted teeth. In these teeth, the perfora tion may occur in a surgically inaccessible area such as the lingual surface of the mesiobuccal root of a maxillary molar or the distal surface of the mesial root of a mandibular molar. In these instances, a root amputation (for example, re moval of the mesiobuccal root of the maxillary tooth as shown in Figure 12) or a hemisection (for example, removal of the mesial half of the mandibular tooth including the crown) may be performed.
S u m m ary
Causes of tooth perforation include resorption, caries, and operator performance. The progno sis for a tooth with a perforation is related to the location of the perforation, negotiability of the canal, contamination, and treatment. Alterna tive treatment approaches include routine endo dontic treatment, correction via the chamber, surgical correction, and stimulation of calcifica tion. In most instances, a perforation can be treated so that satisfactory healing will occur.
1. S e ltz e r, S.; S ina i, I.; and A u g u s t, D. P e rio d o n ta l e ffe c ts o f ro o t p e rfo ra tio n s
b e fo re and d u rin g
e n d o d o n tic
p ro c e d u re s .
J D e n t Res 49:332 M a rc h -A p rll 1970. 2. A u s lä n d e r, W.P., and W e in b e rg , G. A n a to m ic re p a ir o f in te r nal p e rfo ra tio n s w ith in d iu m fo il and s ilv e r a m a lg a m : o u tlin e o f a m e th o d . NY J D en t 39:454 D ec 1969. 3. F ra n k, A.L. T h e ra p y fo r th e d iv e rg e n t p u lp le s s to o th by c o n tin u e d a p ic a l fo rm a tio n . JA D A 72:87 Jan 1966. 4. F ra n k, A .L., and W eine, F.S. N o n s u rg ic a l th e ra p y fo r th e p e r fo ra tiv e d e fe c t o f in te rn a l re s o rp tio n . JA D A 87:8 63 O ct 1973.
S in a i: PER FO R A TIO N S ■
95
Endodontic perforations: their prognosis and treatment Irving H. Sinai,
DDS, P h ila d e lp h ia
Practitioners unfortunately sometimes must contend with the perforation of a tooth during endodontic treatment. Perforations may be in duced iatrogenically or by resoiptive processes or caries. Iatrogenically caused perforations may be produced by powered rotary instruments dur ing the attempt to gain access to the pulp (Fig 1) or during instrumentation for a post (Fig 2). Inju dicious or improper manipulation of endodon tic instruments (Fig 3) may also lead to a perfor ation of the root. The resorptive process, given an adequate amount of time, can produce a communication between the pulp canal and the periodontal struc tures. This resorptive process (Fig 4) may be in ternal and caused by an inflamed pulp or external and caused by trauma; the latter generally ends in the destruction of the root (Fig 4, right) and the loss of the tooth. External resorption also may be idiopathic, which generally results in the blunting of the apex. The nature of this resorp tive process is probably systemic and its occur rence is infrequent. There is no treatment for this problem, and it will not be considered here. 90
■ JADA, V o l. 95, J u ly 1977
Caries, by invading the floor of the pulp cham ber and extending through to the furcation, may cause a perforation in instances of gross neglect (Fig 5). Caries that extends down the side of a root may expose the pulp. However, this is not generally considered an endodontic perforation but rather a restorative-periodontal problem.
P rognosis
The prognosis for a tooth with a perforation de pends on the location of the perforation, the time the perforation is open to contamination, the possibility of sealing the perforation, and acces sibility of the main canal. ■ Location in relation to the gingival sulcus: Perforation of the crown or root produces in flammatory changes and subsequent breakdown in the periodontium. This breakdown may ex tend to the gingival sulcus, producing a deep, nonmanageable periodontal defect. In my ex perience, a perforation in the middle or apical third of the root is less serious in this regard, and
Fig 2 ■ P e rfo ra tio n (P) p ro d u c e d
in p re p
a ra tio n o f to o th fo r post. M a te ria l (M ) fo rc e d F ig 1 ■ P e rfo ra tio n o f m esial a sp e ct o f flo o r
o u * ° * ro ° * d u rin g p re p a ra tio n and ce m en -
o f c h a m b e r (P) in a tte m p t to lo c a te m esial
ta tio n o f post,
ca na ls.
Fig
3 ■ M esial
fro m
im p ro p e r
p e rfo ra tio n
(P)
re s u ltin g
use o f e n d o d o n tic
in s tru
m ents.
THE AUTHOR F ig 5 ■ E xte n sive ca rie s (C) p e rfo ra tin g p u lp c h a m b e r.
flo o r o f
Dr. S ina i is d ir e c to r o f th e u n d e rg ra d u a te d iv i s io n and a s s o c ia te p ro f e s s o r in t h e d e p a r t m e n t o f e n d o d o n to lo g y , S c h o o l o f D e n tis tr y , T e m p le U nive rsity, 3223 N B ro ad St, 19140.
P h ila d e lp h ia ,
SINAI
S in a i: P ER FO R ATIO N S ■
91
the inflammatory changes will probably subside, if treated, before the periodontal breakdown can extend to the gingival sulcus. In contrast, per forations in the coronal third of the root or through the floor of the pulp chamber into the furcations of multirooted teeth may create more serious problems. In these instances, the trauma of the perforation and the subsequent inflamma tion may rapidly produce communication with the gingival sulcus and a noncorrectable perio dontal lesion. I believe it is especially impor tant that a perforation in this area be sealed im mediately after the root canal or canals have been located, to isolate the traumatized area and avoid further irritation and to allow it to heal quickly. ■ The time that the perforation is open to con tamination: The time the perforation is open to contamination has been shown to be a factor in the degree of inflammatory change and break down in the periodontium .1 As mentioned pre viously, those perforations in the coronal third of the root and in the floor of the chamber should be sealed immediately. For those located further apically, it is not essential that the seal of the per foration be placed immediately, but it is impor tant to protect the area from contamination to reduce the possibility of bacterial irritation and inflammatory changes. Therefore, in teeth with perforations in the apical two thirds, it is espe cially important that endodontic treatment be per formed under a rubber dam and that the tooth not be left open between visits under any circum stances. This approach will reduce the possibil ity of further breakdown of the periodontium adjacent to the perforation until a seal can be achieved. ■ The possibility o f achieving a seal o f the per foration: To ensure a favorable prognosis for the tooth, it is essential to seal the perforation. If this were not possible because of the size of the defect or an anatomic consideration either in the tooth itself or its position, the prognosis would be questionable. ■ The accessibility o f the main canal: A per foration may reduce the practitioner’s options during the performance of endodontic treatment. For example, a perforation in the coronal por tion of the tooth may occur during the process of locating the main canal. The perforation and its resultant change in the anatomy increase the 92 ■ JAD A, V o l. 95, J u ly 1977
Fig 6 ■ G utta-percha cones (C) leaving root through
perforation
(P) of curved canal.
difficulty of locating the canal. If it cannot be lo cated and treated endodontically, the apical end of the canal must be sealed directly, using a sur gical approach, and the perforation must be sealed, for repair to occur. A perforation in the apical two thirds of the root may be a result of failure to negotiate the curvature of the root (Fig 6). If the perforation is a short distance from the apex and the apical end of the canal can be negotiated, it may be possible to fill the perforation and the apical end of the canal. However, if this is not possible, I suggest that the apical end of the canal should be left un filled; a surgical approach to remove or seal the unfilled portion of the canal would be necessary if healing fails to occur.
T re a tm e n t
The correction of perforations usually can be achieved by one of six treatment approaches. ■ Perforations sealed during routine endodon tic treatment: There are two possible instances for this treatment. First, the perforation may be sealed if it occurs near the apex in a curved canal and if sealing of the canal with the use of pres sure forces the material into both the perforation and the main canal. Second, in instances of inter nal resorption, a small perforation may be sealed. Again, with a gutta-percha and solvent technique or a gutta-percha, root canal sealer, and pres sure technique, the material can be made to ex trude into and through the perforation, thereby sealing it (Fig 7). ■ Perforations sealed as an additional canal: A perforation extending diagonally through the root wall for a distance so that a canal-like effect is created may be treated as an additional root
Fig 7 • Top, (1) canal to be cleaned; (2) canal cleaned but perforated (P) near apex; (3) gutta percha cone (C) fitted at perforation; (4) filling forced into main canal and perforation. Bottom left, internal resorption (I) that has perforated dis tal root causing bone resorption (B). Bottom right, filling of area of internal resorption (I) using pres sure tech niq ue with extrusion of filling material (F) sealing perforation.
canal in that tooth. The perforation can be cleaned, shaped, and filled as would be done in the main canal (Fig 8). ■ Perforations sealed with amalgam via the chamber: In the location of a canal that has been narrowed considerably because of calcification, the floor of the pulp chamber may be perforated. As mentioned previously, this type of perfora tion should be sealed immediately. After the canal has been located, a retentive preparation
should be made in the chamber in the region of the perforation. Insertion into the canal of a paper point or of a lubricated metal instrument protects the canal. The area of the perforation then is gently packed with amalgam via the ac cess opening (Fig 9). Care must be exercised to avoid extrusion of the material through the per foration into the periodontal ligament. If the per foration is extensive, indium foil may be cut and laid over the perforation before placement of the amalgam to prevent its extrusion. The amalgam and the indium foil will coalesce to provide a sat isfactory seal .2 ■ Perforations sealed with amalgam using a sur gical approach: Use of the surgical approach is
Fig 8 ■ Filling “second can al” perfor ation. Gutta-percha cones (C) have been fitted to both canals.
Fig 9 ■ Perforation, created during ac cess, sealed via access with am algam (A). S in a i: PER FO R ATIO N S ■ 93
Fig 10 ■ Left, ro o t p e rfo ra tio n as a re su lt o f e x te n sive in te rn a l
re s o rp tio n
p e rfo ra te d
area se ale d w ith
Canal
been
h as
sealed
w ith
(I). R ight,
a m a lg a m
(A).
g u tta -p e rc h a
c o n e (C) a n d la te ra l co n d e n s a tio n .
usually limited to those situations that are not amenable to other treatment modalities. Place ment of an amalgam seal after routine filling of the canal can be used in instances of an exten sive perforation (Fig 10) or when the apical end of a canal cannot be negotiated. If a perforation was caused in the preparation of the tooth for a post, a coronal approach as previously described may be used. If this is not feasible, then the post can be prepared and cemented short of the per foration, and the perforation can be approached surgically and sealed with amalgam. There is lit tle likelihood of disturbing the cemented post. ■ Perforations repaired by stimulation o f calci fication: Calcium hydroxide is known to be in volved in the induction of calcification of tissue external to the tooth. This phenomenon is ap plied in the technique of apexification of the in
completely formed root end .3 The technique en tails cleansing the canal as thoroughly as possi ble, drying the canal, and then filling the canal with a calcium hydroxide paste. This is repeated as necessary until the desired calcification has occurred. Use of the approach has also been sug gested in instances of internal resorption and other pathoses that produce a defect too exten sive to be sealed by routine filling techniques .4 I have had success using this technique in the case of a multiple root fracture in a child (Fig 11). ■ Apicoectomy, root amputation, or hemisection: There are instances in which the use of an amalgam filling is not feasible or necessary. One example would be failure to negotiate a curved canal, thereby causing a perforation near the apex of the root. If an absence of healing resulted from the fail
Fig 11 ■ Left, m u ltip le ro o t fra c tu re s (F) as a re s u lt o f tra u m a . B o n e re s o rp tio n (R) has o c c u rre d a d ja c e n t to fra c tu re . C en te r, g u tta -p e rc h a c o n e (C) th ro u g h m esial g in g iv a l s u lc u s in to area o f b on e re s o rp tio n . R ig h t, b one (B) has d e p o s ite d a d ja c e n t to fra c tu re . G in g iva l s u lc u s no lo n g e r c o m m u n ic a te s w ith area o f ro o t fra c tu re .
94
■ JADA, V ol. 95, Ju ly 1977
Fig 12 ■ Left, m e s io b u c c a l ro o t (M ) to be re m o ve d . R ig h t, d is to b u c c a i (D) ro o t fille d , p a la ta l
ro o t fille d
and space p ro v id e d fo r
p o s t (S), and m e s io b u c c a l ro o t re m ove d (M).
ure to seal the last few millimeters of the canal, an apicoectomy could be performed removing the root structure to a point coronal to the per foration and unfilled canal. This would leave a root that is well filled to its new apex. The practitioner can encounter additional dif ficulties, as well as options, in the treatment of multirooted teeth. In these teeth, the perfora tion may occur in a surgically inaccessible area such as the lingual surface of the mesiobuccal root of a maxillary molar or the distal surface of the mesial root of a mandibular molar. In these instances, a root amputation (for example, re moval of the mesiobuccal root of the maxillary tooth as shown in Figure 12) or a hemisection (for example, removal of the mesial half of the mandibular tooth including the crown) may be performed.
S u m m ary
Causes of tooth perforation include resorption, caries, and operator performance. The progno sis for a tooth with a perforation is related to the location of the perforation, negotiability of the canal, contamination, and treatment. Alterna tive treatment approaches include routine endo dontic treatment, correction via the chamber, surgical correction, and stimulation of calcifica tion. In most instances, a perforation can be treated so that satisfactory healing will occur.
1. S e ltz e r, S.; S ina i, I.; and A u g u s t, D. P e rio d o n ta l e ffe c ts o f ro o t p e rfo ra tio n s
b e fo re and d u rin g
e n d o d o n tic
p ro c e d u re s .
J D e n t Res 49:332 M a rc h -A p rll 1970. 2. A u s lä n d e r, W.P., and W e in b e rg , G. A n a to m ic re p a ir o f in te r nal p e rfo ra tio n s w ith in d iu m fo il and s ilv e r a m a lg a m : o u tlin e o f a m e th o d . NY J D en t 39:454 D ec 1969. 3. F ra n k, A.L. T h e ra p y fo r th e d iv e rg e n t p u lp le s s to o th by c o n tin u e d a p ic a l fo rm a tio n . JA D A 72:87 Jan 1966. 4. F ra n k, A .L., and W eine, F.S. N o n s u rg ic a l th e ra p y fo r th e p e r fo ra tiv e d e fe c t o f in te rn a l re s o rp tio n . JA D A 87:8 63 O ct 1973.
S in a i: PER FO R A TIO N S ■
95
