placement of the retrograde . Retrograde amalgam filling: The third case (Fig 3) was initially treated without periapical surgery, but a scanning electron because of postoperative pain, a ret- rograde amalgam filling was placed two weeks later. The tooth was finally microscopic study extracted five months later because of the patient's persistent pain.

Materials and Methods The three clinical specimens were Richard M. Moodnik, DDS; Marc H. Leveu DDS; Martin A. Besen, BS; placed in 10% buffered Formalin and Bernard G. Borden, DMD, New York fixative. After sectioning the apical third of the root, the apices were postfixed in 2.5% glutaraldehyde for 48 hours. The specimens were dehy- drated by passage through a graded The scanning electron microscope retrofillings. However, Jorgensen 11 ethanol series (ethanol was replaced was used to examine four retro- has noted that zincfree amalgam tends by amyl acetate). A critical point grade amalgam fillings in three to corrode more readily than amalgam drying apparatus was used. The speci- human teeth and an extracted containing ; therefore, he rec- mens were mounted on aluminum ommends amalgam containing zinc. tooth. Micrographs showed large stubs with colloidal . They then Kopp and Kresberg 9 listed the dis- interfaces or defects between the were placed on a rotating table in a advantages of amalgam: introduction amalgam and the prepared root; high-vacuum evaporator and were of into the periapical tissues; the measurements of the defects coated with approximately 200 A of scattering of amalgam particles into carbon and a 200 A layer of gold- ranged between. 6/x and 150/x. adjacent tissues; introduction of a The significance of the defects nonsterile material into the body; is unknown. corrosion; and a slow setting time that allows change in dimensions and con- lamination of fluid. In the past two decades, retrograde obturation of the root canal has been Description of specimens an increasingly favored adjunct to Three of the specimens that were apicoectomy. Various materials for examined were human teeth where retrograde filling have been advocated, apical amalgams had been successful but amalgam appears to be the most in effecting periapical repair after the acceptable material. 1-5 However, failure of conventional endodontic Cavit,0 Biobond, 7 zinc oxide and therapy. A fourth specimen was of a eugenol, s and gold foil~ also have retrograde amalgam completed on an been recommended. exlracted tooth; it was used as a con- Orr a listed the advantages of trol. The first specimen was a maxil- amalgam; it is easy to manipulate, lary canine (Fig 1). Complete healing available in all dental offices, radio- had followed the placement of the paque, well tolerated by tissues, retrograde amalgam, but three years slightly bacteriostatic, and seals ac- later, the tooth was extracted for ceptably. A position has been advo- prosthetic reasons. The second speci- Fig 1--Radiographs of retrograde cated that only zincfree amalgam be men was a mandibular second molar amalgam in maxillary leJt canine in used since OmnelP ~ has shown (Fig 2). The tooth was extracted as case 1; dates are June 16, 1970 (A); electrolysis with precipitation of zinc a result of periodontal involvement June 16, 1970 (B); June 16, 1970 carbonate around regular amalgam that occurred two years after the (C); and July 20, 1973 (D).

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Fig 2--Radiographs o/retrograde amalgam in distal Fig 3--Radiographs of retrograde root of mandibular right second molar in case 2; amalgam in maxillary le[t [irst pre- dates are July 9, 1971 (A); Oct 10, 1971 (B); Jan 8, molar in case 3; dates are Aug 8, 1973 1972 (C); and Oct 24, 1973 (D). (A) and Aug 20, 1973 (B).

to render the specimens electrically conductive. The specimens were examined with a scanning elec- tron microscope operated at 20 kv. Micrographs were obtained at various magnifications ranging from X20 to X4,000. The micrographs were com- pared and evaluated.

Findinqs Gouges were created by the bur during mechanical preparation of the apex in case 1 (Fig 4A). There was a lack of close adaptation between the amalgam filling and the beveled root; the dentinal tubules were ex- posed (Fig 4B). The interface be- tween the amalgam seal and the prepared apex measured between 10/z and 40/x; there was an average separation of 24/z (Fig ,~C,D). An apparent adaptation of the apical amalgam to the beveled root was shown in case 2 (Fig 5A). In a micrograph with greater magnifica- tion, the actual adaptation of the amalgam to the root can be seen; the average defect was 15/z (Fig 5B). Another area along the dentinal- amalgam interface is shown; it de- picts an average defect of 13/x be- tween the two surfaces (Fig 5C). In another portion of the interface, there was a large cavernous opening into the depths of the dentinal Fig 4--Scanning micrographs o] retrograde amalgam in tubules; the average separation was maxillary le[t canine in case 1. Symbols are amalgam, A; 140/z (Fig 5D). dentin, D; and root, R (orig mag X40 {A); X90 {B); The apical preparation of case 3 X700 {C); and X1350 {D)).

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Fig 5--Scanning micrographs of retrograde amalgam in distal root of mandibular right second molar in case 2. Symbols are amalgam, A; dentin, D; and root, R (orig mag XSO {A); X320 (B); X3200 (C); and X800 (D) .)

showed a submerged retrofiUing (Fig Discussion 6A,B). The measurements of inter- The purpose of the retrograde seal facial defects averaged 100# (Fig is to obturate the main apical fora- 6c). men by using a surgical approach. The control case was prepared on This is not done as a substitute for an extracted tooth and was imme- conventional endodontic therapy, but diately processed (Fig 7A,B). Again, rather in cases that are not amenable there was a lO/x deficit along the to conservative treatment. dentinal-amalgam interface. Three cases of human teeth It should be noticed that on several deemed successful by radiographic areas of the specimens, a few minor evaluation, and a case that was corn- dentinal cracks were observed that were probably caused by mechanical manipulation as a result of extraction Fig 6--Scanning micrographs or apical beveling with a bur. These of retrograde amalgam in max- cracks were not seen in other teeth illary left first premolar. Sym- that were examined and prepared in bols are amalgam, A, and den- a similar manner to the teeth in this , D (orig mag XSO (A); X320 study. (B); and X320 {C)).

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analyzed micrographically. Smooth preparation or beveling of the apex of the root is difficult to achieve clinically. Often, the prepared surface is left gouged; the dentinal tubules are grossly exposed. The significance of the defects is unknown. The authors thank Lynda Marchese for technical assistance and Drs. Alan Prot- zell, Harold Kresberg, William Kopp, David Schwartz, and Betram Blum for the specimens. Dr. Moodnik is the director of the division of endodontics; Dr. Levey has completed his residency in endodontics; Mr. Besen is the director of electron microscopy; and Dr. Borden is the chair- man of the department of , Nas- sau County Medical Center, East Mea- dow, NY. Requests for reprints should be directed to Dr. Richard M. Moodnik, Department of Dentistry, Nassau County Medical Center, 2201 Hempstead Turn- Fig 7--Scanning micrographs pike, East Meadow, NY 11554. of retrograde amalgam in con- References trol tooth. Symbols are amalgam, A, and dentin, D (orig mag X30 1. Grossman, L.I. Endodontic prac- (A) and X770 (B)). tice, ed 8. Philadelphia, Lea & Febiger, 1974, p 367. 2. Trice, F.B. Periapical surgery. Dent Clin North Am 3:735 Nov 1959. 3. James, G.A. Simplified techniques in surgical periapical treatment. Dent Clin North Am 7:375 July 1963. 4. Ingle, J.I. Endodontics. Philadelphia, Lea & Febiger, 1967, p 528. 5. Orr, J., Jr. Simplified retrograde endodontics. J Mo Dent Assoc 51:7 April 1971. 6. Nord, P. G. Retrograde root fillings pleted on an extracted tooth were harbor bacteria and other toxic prod- with Cavit: a clinical :and roentgenologic study. Sven Tandlak Tidskr 63:261 April examined under the scanning electron ucts. The exposed dentinal tubules as 1970. microscope. Micrographs showed well as the corrosive properties of the 7. Nordenram, A. Biobond for retro- large interfaces or defects between the materials could be a source of in- grade root filling in apicoectomy. Scand amalgam and the prepared root; the flammation. J Dent Res 78:251, 1970. 8. Nicholls, E. Retrograde filling of measurements of the defects ranged Summary the root canal. Oral Surg 15:463 April between 6/z and 150/~. The mag- 1962. nitude of the interfacial discrepancy A scanning electron microscopic 9. Kopp, W.K., and Kresberg, H. varied from case to case. Even when study of four teeth showed that de- Apicoectomy with retrograde gold foil. NY State Dent J 39:8 Jan 1973. an apical amalgam was placed under fects between the amalgam-dentinal 10. Omnell, K.A. Electrolytic precip- controlled conditions in an extracted interface varied between 6/x and itation of zinc carbonate in the jaw. An tooth, a substantial defect could be 150/z after the insertion of the retro- unusual complication after root resorp- clearly demonstrated. grade amalgam filling. tion. Oral Surg 12:846 July 1959. 11. Jorgensen, K.D. Amalgams in den- The radiographic depiction of the It is not possible to relate any clini- tistry, no. 354. US Dept of Commerce, cal significance to the discrepancies. apical seal did not correlate with the Dental Materials Research, National Speculatively, these defects could completeness of the seal when it was Bureau of Standards Sp Pub, 1972, p 33.

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