Abstracts in endodontics

ABSTRACTS IN ENDODONTICS These abstracts have been selected from recent issues qf O r a l monthly journal published by the American Dental Association. pubtbhed regularly as a service to the readers of the J o u r n a l information about ORA is available from the ADA Subscription

Fixation with intracanalicular endosteal pins of anterior teeth in monkeys with experimental horizontal fractures. G. Dietz (Univ Dent Clim Goethestrasse 70, Munich, West Germany). Drsch Zahnaerztt Z 31(2):89-91 Feb, 1976 (Get; summaries in Eng and FreL Horizontal fractures were produced with a chisel in the mandibular anterior teeth in anesthetized rhesus monkeys. The fractures w'ere produced in each of 3 monkeys at the apical, middle, or cervical parts of the roots. The apical fragments of the lateral incisors were removed. In the central incisors a periapicaI cavity was prepared in the bone, and subsequently the apical fragment was again adapted to the coronal fracture surface. All fractured and mobile teeth were fixed by means of an endodontic pin introduced through the root canal into the bone, After an average of 104 days the animals were killed, and histological sections were made of the decalcified mandible with teeth after the metal pins had been removed. In 8 incisors with fractures at the apical or middle parts of the roots with or without maintenance of the apical part, the mobility was reduced after 104 days of fixation; this was also true for 4 teeth with a cervical fracture, Radiographs showed that adaptation of the fracture surfaces did not succeed. Histologically, there was often root resorption. Root canal treatment never resulted in a round cross section of the canal. The bone around the pin always showed severe inflammation, but farther away from the pin there was fibrosis of the spongious bone. The present technique of fixation was not successful in cervical fractures. However, good results can be obtained in fractures in other parts of the root. Removal of the apical part of the root gives better fixation; maintenance of this part never results in good adaptation of the fracture, In monkeys the anatomical relations are more complicated than in man; thus the results of this study cannot be trans%rred directly to man. 1. S, Levij

An apparatus to determine pulp vitality by cold, I. Erdelsky and J. Dedik (lnst Postgrad Training Stomatol Clin, Bratislava, Czechoslovakia). Prakt Zub Lek 24(2):55-7 March, 1976 (Slo). A new pulp vitality testing cryoapplicator, using compressed CO2 snow, was designed and tested. Its construction and function are described and documented. The cryoapplicator is designed according to principles of the Bock-Pichler applicator, yet is modified and improved. Improvement is based on visible handling because of plastic (Plexiglas) construction of the removable piece, Its endpiece consists of stainless steel metal rods which are shaped directly for use on either anterior or lateral teeth. The 2 L flask of 5 kg weight contains 40-60 doses of CO~ snow to be used in vitality testing. Its use and manipulation are safe and effective, Anna Plackova

W o u n d healing after root resection in the dog, II. Results of a scanning electron microscopic investigation. J, Svejda, M, Janota and O. Krejza (Inst Dent Res, Prague,. Czechoslovakia). Cesk Stomatol 76(2):8I-8 March, t976 (Cze; summaries in Rus and Eng). In 6

dogs the region of root resection was investigated by SEM at time intervals of 33-2i 8 days af{er the surgical procedures. Results of SEM i5ndings were Compared with histological findings. After apicectomy the histological findings showed hard tissue: resorption in the resected root area. Lacunae in the dentin were filled with cementum or fibrous tissue. Resorp~,ive lacunae Were seen also in the cemental area of the periodontal tissue in the vicinity of the resection region. Collagen fibers ran parallel to the resection plane;

Research

Abstracts,

a

Selected abstracts wilt be o f E n d o d o n t i c s , More Department.

these could be observed with both light and SEM microscopy. Ligaments attached vertically to the resection plane with cement apposition were rare findings. Zinc oxyphosphate root canal filling showed in SEM a spongelike, porous structure; thus forming a large surface area (not considered favorable for the healing process), Neither structural renewal of the periodontal membrane area with anchored ligaments nor a cement layer enclosing the root canal surface were seen. The orifice of the root canal was mostly covered by chronic inflammatory or scar tissue. The healing process, however, cannot be considered as a failure. Chronic inflammatory lesions, if limited to small areas, can be controlled by the organism's defense mechanism. Anna Ptackova

Comparison of success rates of root treatment with and without periapical surgery, lmre Vigh, Eva Boros and Z, Nagy (Univ Dent Sch, Budapest, Hungary). Fogorv Szemle 69(5): 139-42 May, 1976 (Hun; summaries in Rus and Get). Five hundred and forty-six teeth with root fillings were controlled by serial radiographs for 10 yr, In 198 teeth apical resection had been carried out, and there was a success rate of 88%. In teeth without apical resection the success rate was 84%. In the group of apical resected teeth there was a higher frequency of periodontal (marginal) involvement than in the other group (41 extractions among 54 teeth in the reseeted group and 8 among 32 in the group without apical resection necessary because of periodontal involvement). P Adler

Histophotometry of acid mucopolysaecharides in the healing process of dental pulp after protection with calcium hydroxide, Formagen, and zinc oxide and eugenol. Sergio Augusto Catanzaro Guimaraes and Vicente G. lsaia (Univ Sao Paalo Sch Dent, Bauru, Brazil). Estomatol Cult 9(1):83-6 Ja~v'June. 1975 (Por; summary in Eng) (Published in 1976). High reactivity for acid mucopolysaccharides was tkmnd in the fast coagulation necrosis zone, in the intercellular ground substance, and in the cytoplasm of fibrobtasts and neutrophils of the proliferative zone. The metachromatic stainable material was analyzed quantitatively by histophotometry. The amount of acid mucopolysaccharides was high in pulps capped with Na(OH)~. Formagen and ZnO and eugenol developed intermediate values, Luiz Casati Alvares

Radiographic evaluation of endodontie treatment need. K~ Kerekes and S. F, A. Bervell (Univ Oslo Sch Dent, Oslo, Norway). Norske T(mnlaeg~J~ren Tid 86(6):248-54 June, I976. tn order to estimate the need for endodontic treatment in a population group, the intraorat radiographs of 200 patients admitted to the Department of Operatire Dentistry~ University of Oslo, were examined. The number of remaining teeth, endodontically treated teeth, and teeth with periapicat pathological changes were recorded. The average number of remaining teeth varied from 29.6 in the age group below 20 yr to t8 in the age group over 60 yr. Periapical changes were present in 2.8% of the teeth. In the total material, 6% of the teeth had root fillings. Among these~ 60",4 she,wed normal periapical structure, 24% had definite pathological changes, and 16% were uncertain. When the periapical findings were compared with the quality of the root filling, it appeared that 93% of those root fillings which had an optimal length and apical seal were free of periapical changes. Knut A. Selvig

29

J O U R N A L O F E N D O D O N T I C S ! V O L 4, N O 1, JANUARY 1978

Treatment of non-vital permanent incisors with calcium hydroxide. Miomir Cvek, Lars Hollender and Cart-Erik Nord (Eastman Inst, Stockholm. Sweden). Odontol Revy 27(2):93-t08, 1976 (Eng; summary in Swe). The effect of Ca(OH)e was studied as a temporary root canal filling when inserted in the same sitting as mechanical cleansing and flushing with sterile saline or 0.5 or 5.0% NaCIO solution in permanent, non-vital, maxillary incisors with a mature or immature root, infected or uninfected root canal, and with or without radiologically demonstrated periapical bone changes. The data are derived from 141 teeth of 132 children, 6-I7 yr old. It is not necessary to add any antibacterial substance to the Ca(OH)~ especially as many of them may irritate the tissue. When necessary, treatment in 1 sitting can be done routinely, irrespective of the initial status. If the periodontium or the periapical bone are not injured during cleansing procedures or if necrotic rests are not pressed out through the apical foramen, no complications need be feared. After 6 months, periapical bone healing was noted in 61 teeth, regression or periapical bone lesions in 64, and no l~eriapicat healing in 6. Teeth flushed with 5% NaCIO had poorer healing than those with the 0.5% NaCIO or saline flusheS. John Haefele

A fundamental study of iontophoresis in endodontic therapy. The effect of patent and closed apex of the human tooth. Toshikazu Akashi (Nihon Univ Grad Sch Dent, Tokyo, Japan). Jap J Conservative Dent 19( 1): I-8 April, 1976 (Jap; summary in Eng), Extracted human teeth with an artifically closed apex or with a patent apex were prepared and stored in 0.2 M phosphate buffer (pH 7.4) for 1 wk. Five hundredths milliliter of zinc iodid-iodine solution was applied in the root canal, and a cathode current of 3 mA was applied for 10 mira The distribution ofl was examined by iodostarch reaction on sectioned root dentin, and the degree of I penetration was assessed by a dentin permeability index. In controls, root canals with a closed apex were given an application of zinc iodid-iodine solution without current. The migration of 1 in root dentin was remarkable in experimental teeth as compared with control teeth. The degree of migration of I into root dentin was higher in cervical and middle areas as compared with the apical area. The majority of applied zinc iodid-iodine migrated beyond the root apex, and a small amount of it migrated into the roo~ dentin in the teeth with a patent apex. The condition of the apex, closed or opened, aft:ects the degree of migration in iontophoresis. Y. Tsuchitani

The apical level of root fillings. Olav Molven (Univ Bergen Sch Dent, Bergen, Norway). Acra Odontol Scand 34(2):89-105, 1976. An investigation compared the apical level of root fillings completed by general practitioners (GP's), undergraduate students, and an endodonfist, The analysis was based on 3,003 root fillings in 2,581 roots. The fillings were assigned to 3 classes: partial root fillings (class A), flush with radiographic apex or overfilling of not more than I mm (class B), and fillings with moderate (1-2 ram) or extreme ( > 2 mm) excess. G-P's had very few Class A or B (7.6%) fillings, whereas such fillings accounted for 40-50% of the total number of root fillings made by undergraduate students or the endc,dontist, More than 60% of the G-P's fillings were more than 2 m m from the apex. The undergraduates had completed a higher relative number of root fillings in Class C than the endodontist. Roots of 3-rooted teeth were filled closer to the radiographic apex by the endodontist than by 30

the undergraduates. The G-P had not filled any closer to the apex on simple, single-rooted teeth than the endodontist had on difficult, multirooted teeth. The difference in length of root fillings made by the G-P and those made by the undergraduate students and the endodontist cannot be explained by differences in the morphology of the roots and the pathological diagnosis within the samples. The difference could be explained by the G-P's lack of adherence to accepted principles for root canal preparation and filling, and not by differences in training and clinical experience of the operator groups. The differences between undergraduates and endodontist could be related to lack of clinical experience. The training and experience of the endodontist allow him to treat multirooted and more difficult teeth with greater success. Many references. Carl L, Tinkelman

Pain perception to electrical stimulation of the periapical tissues in human subjects and the possible influence of disease. Arch Oral Blot 21(2):95~7, 1976. Electrical stimulation of teeth is practiced for the diagnosis of pulpal conditions, the effectiveness of analgesic drugs, and investigation of the physiology and anatomy of the trigeminat system. Electrical stimulation gives relatively crude information regarding pulp vitality, but is useful clinically to indicate if a tooth is vital or not. The investigation described concerned the level of current required to excite nerve fibers in the periapical area. Fifty patients undergoing routine endodontic treatment fi~r maxillary incisors and canines were studied. The root canals in these teeth were reamed to a relatively broad diameter which facilitated inserting the electrode high in the canal. Threshold values tended to be higher in those with radiographicatly evident apical lesions, this difference being greater in the subjects under 25 yr of age. However, the wide spread of the results and the possible variability of the current path suggest that the method will not prove clinically useful, Charles C. Ailing

Effect of Sani paste on living tissues in vivo and in vitro. Bozena Kaczor~ Halina Jastrzebska and Waclawa Tartowska (ul Miodowa 18, Warsaw, Poland). Czas Stomatol 29(3):193-8 March, 1976 (Pol; summaries in Rus and Eng). The cytotoxic effect of Sani paste (for root canal fillings) was examined in vivo and in vitro. The paste, which belongs to the resorcin-formalin group, was introduced into glass tubes and added to tissue cultures. Histopathologic examination of the periapical area of 14 teeth was made on tissues obtained through apiceetomies. A cytotoxic effect was obvious in both conditions. In tissue cultures pyknotic nuclei, lack of cells in the mitotic stage, and malalignment of cells were observed. In the histopathologic examinations lymphocytic infiltration and, later, necrotic areas in the periapex were observed. Sani paste should be used very cautiously for root canal filling, and overfilling should be avoided. 24 references. Ilana Brunn

Biologic tests of a proposed pulp-capplng agent (Reocap). Leif Tronstad and Alf Wennberg (Univ Lund Sch Dent, Malmo, Sweden). Odontol Revy 27(2):109-14, I976 (Eng; summary in Swe). A Ca(OH)2-containing cement (Reocap), delivered as a 2-component product in a capsule, was tested as a pulp capping agent. The pulp of 34 monkey teeth was exposed, and Reocap was applied to the pulp wound and the cavity floor. The cavities were then filled with amalgam. After 8 days, a hecrotic area was seen in the pulp subjacent to the pulp capping agent and the

J O U R N A L OF E N D O D O N T I C S [ VOL 4, N O I, JANUARY 1978

surrounding tissue was inflamed. After 80 days, hard tissue formation was observed at the exposure site in 21 teeth. The hard tissue enclosed areas of necrotic or vital tissue or both, and a complete bridge had not formed. In 7 teeth the pulp was necrotic, whereas 3 teeth had pulp free of inflammation. In the remaining teeth the pulp showed a chronic inflammatory reaction. Reocap is not as good a pulp capping agent as pure Ca(OH)2 or certain other commercial Ca(OH)2-containing products. The importance of biologic testing of dental materials is emphasized, particularly those used for the treatment of exposed pulp. John Haefele

Apical infiltration shown by silver nitrate and gentian violet in human molars filled by the lateral condensation method. J. H. Gutierrez and E. Cortes (Sch Dent, Concepcion, Chile). Rev Assoc Paul CirDent 30(2):84-8 Jan-Feb, 1976 (Por; summary in Eng). The root canals of 10 maxillary molars and 10 mandibular molars were filled with guttapereha cones and Grossmann's cement+ using the lateral condensation method. The pulp chamber was filled with Cavit. Immediately after root canal filling, the molars were immersed in distilled water for 12-24 hr for better hardening of the Grossmann's cement. Next, the crowns and roots were covered with paraffin, with only the foramen remaining exposed. Five maxillary and 5 mandibular molars were placed in an aq 30% solution of silver nitrate for 6 hr, and the other molars were immersed in a 2% aq Imlution of gentian violet for 6 hr. All teeth were washed, radiographed. and studied microscopically. A 30c,-~silver nitrate solution neutralized with 10% formol is useful for meast, ring the apical infiltration of the roots of human molars filled by the lateral condensation method with gutta-percha cones and Grossmann's cement. Among the 25 molar roots thus filled, 64% showed infi Itration when silver nitrate was used; 52% showed infiltration with gentian violet. The silver nitrate solution showed good penetration, especially for roots with narrow canals, and gentian violet penetrated better into roots with larger diameters. Hans Freudenthal

Fast desensitization of tooth roots by topically applied SnF2 and SrCIz in dogs. Deborah A. Penney and U. L. Karlsson (Univ Iowa Coil Dent Med, Iowa City, Iowa). Arch Oral Biol 21(6):339-47, 1976. Forty incisors and canines were taken from 5 dogs, anesthetized by Na pentobarbital after mucoperiosteal elevation and reduction of interdenlal and facial bone by 4-5 mm. The exposed roots were curetted and the flap, without attached gingiva, was replaced and sutured. After 2-4 days, Sensitivity of the exposed roots was measured by withdrawal responses and eyelid reflexes in the anesthetized animals (after Vitapulp stimulation). The roots in 1 quadrant were brushed with pumice and etched with 0.5 M Perchloric acid for 5 sec. In another quadrant no etchant was applied, and in the third quadrant they were brushed with a soft nylon brush and water only. The fourth quadrant remained as the control. Sensitivity tests were taken immediately and 30 rain after treatment and again after application of a 10% solution of SnF2 for 30 rain to 2 dogs and of a 10% Sr'CI2 to 2 other dogs. Tooth specimens were prepared and examined in a Cambridge scanning electron microscope. Other samples were prepared for electron microprobe analysis, and concentration gradients for Ca, Sn, F, and Sr were reCOrded with an ARL EMX Electron Microprobe. Only SnF2 treatment lowered sensitivity and then only when etched and pumiced or pumiced 0nly. Microprobe analysis revealed greater penetration of Sn and F into the

tooth in etched specimens than in pumiced or brushed material. In the St-treated material, Sr appeared further from the root surface in the brushed than in the etched and pumiced specimens. M . S . Simpson

Dental root resportion. Experimental study in dogs. Jorge Mema Bernaba, Valdir de Souza and Miguel Carlos Madeira (Sch Dent. Aracatuba, Brazil). Rev Assoc Paul Cir Dent 30(3):150-6 March-April, 1976 (Pot; summary in Eng). Eight young mongrel dogs. age 9-10 wk, were anesthetized. The complete dental pulp was removed from their maxillary fight deciduous incisors and canines. After hemorrhage was controlled, the coronary portion was sealed with fast-setting ZnO-eugenol cement. The corresponding teeth of the left side were left untouched and served as controls. Every 7-14 days after the pulpectomy, the state of root resorption was observed radiographically. The age of 9-10 wk was chosen because at that time the roots were complete and their resorption had not started. After that age, resorption began. Compared with the control teeth, 20 treated teeth had resorption earlier, 2 were normal, and 10 were delayed. The pulp of the deciduous maxillary incisors and canines of the dogs studied did not participate in the mechanism of root resorption. Hans Freudenthal Quantitative study of the penetration of phosphoric acid from zinc phosphate cement into pulp protecting material containing calcium hydroxide. Aldevina Campos de Freitas, Zuleika Rothschild and Ruy Barbosa Rosetino (Univ Sao Paulo Sch Dent, Ribeirao Preto, Brazil). Estomatol Cult 9(2):221-8 July-Dec, 1975 (Eng; summary in Pot) (Published in 1976). The infiltration of H3PO4, from Zn phosphate cement, into layers of different thicknesses of Ca(OH)2-containing materials was measured quantitatively. The highest concentrations of P were found in samples of the alkaline material close to tne contact with the acid cement (0-0.16 ram). These concentrations differed significantly according to the alkaline material used. In samples obtained in thicknesses higher than 0.16 ram, up to 2.00 ram, the percentage of P was reduced drastically for all materials used. However, the values obtained were significantly different between materials. 28 references. Luiz Casati Alvares

Endodontic therapy of non-vital teeth with open apices. M a t i n Levin (Univ Pennsylvania, Philadelphia, Pennsylvania). J DC Dent Soc 11-20 Spring, 1976. Non-vital teeth with open apices are now treated routinely with Ca (OH)2 root end closure techniques, followed by orthograde gutta-percha obturation. A review of the literature and 2 case reports are presented. A discussion indicates that endodontic treatment of non-vital teeth with open apices is difficult. The Ca (OH}z root end closure technique is currently the treatment of choice. Several reasons are given for the elimination of surgical intervention. The Ca (OH)2 used in root canals should be chemically pure. Numerous materials have been advocated as vehicles for the Car(OH)z. Local anesthetic solutions are used because of their availability, sterility, and tissue tolerance. 25 references. Leonard A. Ahemus Fine structure of the human dental pulp after cavity preparation. Shigeji Yamada (Osaka Dent Univ, Osaka, Japan). J Osaka Odontol Soc 39(3):357-86 June, 1976. After cavity preparation and pulp capping, human premolars were studied. Electron microscopic 741

J O U R N A L OF E N D O D O N T I C S

observations were made immediately, 1 day, 3 days. 5 days, 7 days. 10 days. 14 days. 20 days, and 30 days postoperatively. Then the teeth were extracted, fixed in 6.25% glutaraldehyde and 1% OsO4 made into ultrathin sections, and stained with 2% uranyl acetate and lead citrate solutions to be examined with a Hitachi HU-12A electron microscope. After cavity preparation vacuolar formation, destroyed and absent cristae, and swollen mitochondria occurred in the odontoblast layer. In five days the rough surface endoplasmic reticulum, free ribosome, and lipid were increased. Then appeared changes as disintegrated mitochondria, atrophy, destruction. and a loss of cells. Normal odontoblasts were partially present. Increased numbers of pinocytotic vesicles and vacuoles appeare in the endothelial cell of the capillaries. Erythrocyles increased in the lumen; bleeding occurred, marginal flaps and lysosomes increased. In the latter phase, bleeding increased greatly and the capillary became atrophic. The basal lamina was either swollen or absent; pinocytotic vesicles and marginal flaps increased. In the nerve fiber vacuolar tbrmation occurred in the axon. Subsequent changes included a swollen Schwann cell envelope, swollen nuclear envelope, and condensed and fused neurofilaments. Initial changes of the pulp after pulp capping in the odontoblast layer were similar to those of cavity preparation. Then disintegrated mitochondria and the absence of cytoplasm were noted. In 30 days the rough surface endoplasmic reticulum and free ribosome increased significantly, and near-normal odonloblasts appeared. The initial capillary findings were similar to those of cavity preparation. Then a few vacuoles appeared in the endothelial cell, and there were a number of almost normal capillary vessels. Findings in the nerve fiber were similar to those of cavity preparation. Masakazu Mori

I VOL

4, N O 1, JANUARY 1978

Paraformaldehyde-containing pastes in endodontic therapy Worth Gregory, Ben Brown and Alvin Goodman. J Alabanu Dent Assn 60( 1):26-31 Jan, 1976. The goals of endodontic therapy are tl remove as much necrotic, or potentially necrotic, material from the roe canal system as possible and to seal off the root canal system from th periapical tissues and the oral environment. These goals are accomplishe~ by careful and thorough debridement of the canal system and by fillinI canals with a sterile, inert, relatively nonresorbable filing material. Thus damage to the periapical tissues is kept to a minimum. Paraformaldehyde containing pastes are not indicated for the filling of root canals. Thes~ pastes may be useful in temporary' vital pulpotomy procedures, but defini tire endodontic therapy will probably be required for long-term success Powered instrumentation may cause ledging and perforations. The use n hand instruments with careful digital control is the safest method of debrid ing and enlarging root canals. Trephination of the bone is a valid therapeu tic measure whenever surgical drainage is indicated, but is seldom neces sary in routine endodontic practice. Charles C. AllinI

Technique for filling root canals by means of ultrasound. J Soulie. Actual Odonto,~tomatol (Paris) (I 12):591-600 Dec, 197'. (Fre: summaries in Eng. Get, lta, Spa, Por, and Rus). In vitro and in vivg tests indicate that injection into a root canal with a filling material subjectel to supersonic,.vibration seals,the canals, regardless of morphology, evel with very low pressure. Density of the material is increased, accessor canals filled, use of the lentulo spiral eliminated, risk of fracture reduced and the possibility of creating a periapical lesion avoided. Carroll G. Benne~

Endodontic surgery periodontal consideration for flap design. Roger Spott and Mark Winnick (Sinai Hosp Baltimore, Baltimore, Maryland). J DC Dent Soc 29-31 Spring, 1976. The semilunar flap is used most commonly in endodontic surgery. Two basic flap designs satisfy most conditions that occur in endodontic surgery and also the periodontal complications. These flap designs are the full flap procedures and the common semilunar flap. Seven factors to be considered for tissue flap design are presented. Comparisons of factors relative to the use of the 2 different flap designs indicate the full flap to be superior. The 2 categories of full flap superiority are in periodontal conditions and the improved tissue characteristics which enhance reapproximation and wound healing. Leonard A. Altemus

Response of the pulp-dentin system to drugs. P. Gangler (Med Acad Stomatol Clin. Erfurt, East Germany), Stomatol DDR 26~51:327-30 May, 1976 (Ger: summaries in Rus and Eng). Pulp reactions to drugs used routinely in pulp treatment were tested by a window technique and vital microscopy in rat incisors. The microcirculation can be observed very well. The modes of action of H202, local anesthetic, and antiphlogistic drugs as propipocaine (Falicaine), Falipulpin, and myrex (used for direct and indirect pulp capping) were studeid. HzO2 produces an emphysema of the pulp tissue, associated with slowing of the circulation and with partly irreversible capillary stasis. Propipocaine compound preparations iFalicid and Myrex) cause, by way of hemolysis, injuries that involve entire areas of the pulp. For this reason, H:~O,, should not be used for cleaning cavities. Myrex is well suited for symptomatic treatment to relieve pain. if removal of the inflamed pulp ensues. Anna Plackova 32

Pupal response to acid etching agents. Donald R. Heys, Ronal! J. Hcys, Charles F. Cox, and James K. Avery (Univ Michigal Sch Dent, Ann Arbor, Michigan). J Mit'h Dent Assn 58(41:221-32 April 1976. The effect of lactic and phosphoric acid on healthy pulps of monk~ teeth was measured using the specifications of the American Standard Committee MD+ 156 for criteria. Six rhesus monkeys were subjected to: thorough prophylaxis before a single class V cavity was prepared in tl~ buccal surface of each tooth with use of high speed with water spray, i shallow and deep cavity preparation were used: the former extended jus through enamel and the latter, approximately 0.5 mm from the pulp. Phos phoric acid, 5 0 ~ , and lactic acid, 20%, were tested. The cavities wen dried and acid etched for I rain using a saturated cotton pellet. A composil, (Smile), a ZnO-eugenol (Cavitec), and a silicate (MQ) were used as con trois, and testing was done at 3 days and at 5 and 8 wk, with 5 test teeth pc time period for each material. Histological examination was conducted o decalcified and hematoxylin and eosin stained sections. After 5 wk th measurement of reparative dentin indicated that acid etchants produce more reparative dentin than Smile, ZnO-eugenol, and Silicate controh both shallow and deep preparations had approximately the same amount c reparative dentin. After 8 wk the same observation was made. The control at 8 wk showed ZnO-eugeno] with the least and Silicate with the too.' response. Approximately 500-600/xm of the remaining dentin is sufficiet for the placement of these materials. Fifty percent phosphoric and 20q lactic acids placed for 1 min produce histological responses similar to thos from the placement of Smile without an etchant, especially after the 5- an 8-wk test periods. Robert G. Cra[