Invited author

Tissue response to dental cariesLangeland K. Tissue response to dental caries. Endod DentTraumatol 1987; 3: 149-71.

Abstract - Caries still represents the most widespread hutnan dis-ease. The pulp tissue sequelae of dentin caries are of utmost im-portance, because prevention ofpulpal damage considerably re-duces the need for extensive restorations and endodontic therapy.There is, however, considerable disagreement in the literature re-garding how early the pulpal response to caries can be detected. Thematerial in this article, gathered from the author's and his co-authors' earlier investigations, deals with pulp reactions from in-itial caries to increasingly extensive caries; caries in combinationwith attrition; the effect of carious dentin in experimental cavities ofintact dentin; the effect of medicaments, restorative proceduresand materials, and indirect pulp capping in the treatment of deepcaries; microbiologic aspects of dentin caries; diagnosis criteria fortreatment; light and electron microscopic study of teeth with cari-ous exposure; periodontal disease and root caries in the geriatricpopulation; pulp biopsies of teeth with periapical lesions, and thebreakdown ofthe remaining pulp and its periapical sequelae. Pul-pal reactions to initial caries detected as early as bacteria reach thedentinal tubules arc also discussed. As in medium and deep caries,this can be reversible following the removal ofthe infected dentin,except for irritation dentin and calcifications on the canal walls orfree in the lumen. Bacteria remaining in dentinal tubules combinedwith iatrogcnesis may be the reason for pulpal disintegration underdeep restorations. Indirect pulp capping is not an acceptable pro-cedure. Pain (or lack thereof) is not a predictable indicator oftheinflammatory stage ofthe pulp. Root caries must be treated early toprevent pulpal destruction. Vital pulp tissue can he found in theroots of teeth with periapical radiolucencies that will ultimatelyshow the presence of bacteria.

Kaare LangelandDepartment of Endodontics, John Dempsey Hospi-tal, University of Connecticut Health Center, Far-mington, Connecticut, USA

Key words: caries, coronal and radicular; micro-

organisms; inflammation, pulpal and periradicular;

calcification; immune response; pain/no pain; pulp,

vitai and non-vital; pulp capping, indirect and direct.

Kaare Langeland, DDS, PhD, Department of Endo-

dontics, John Dempsey Hospital, University of

Connecticut Health Center, Farmington, CT 06032,

USA.

Accepted for publication 12 March 1987.

Caries - despite all prophylactic measures - is stillthe most widespread human disease. Akhough diedisease has heen considerahly reduced in the popula-tions of the West, caries causes tooth destruction ofconsiderable significance, placing great demands onhuman labor and materials. According to the 1979ADA Survey of Dental Practice (1) approximately200 million fillings, 35 million single crowns, and 10rnillion bridges were performed. In addition, therewere 50 million extractions. Almost everything per-formed in the first 3 categories is caries-related. It isalso relevant that 17,390,000 endodontic treatmentsvvere carried out that year. Furthermore, in the endo-dontic clinic ofthe University of Connecticut HealthCenter, approximately 90% of all endodontic ther-apy is carried out in teeth that were restorativelytreated previously. Which part of the pulpal break-

down is caries-related (recurrent caries), of iatro-genic nature, or due to the cumulative effect of allirritants can only be speculated. The reasons for the50 million extractions are not given in the ADA sur-vey; it is ndt known whether the teeth were treatedearlier or if the reason for the extraction is caries orperiodontal disease. It can be assumed that before anindividual has reached 40 years of age most extrac-tions are due to caries, whereas after 40 the extrac-tions are mostly due to periodontal disease or a com-bination of both. Particularly in the geriatric popula-tion, root caries has taken on major proportions andpresents a difficult treatment problem. Thus, cariescontinues to represent a practical and socio-medicalproblem of great economic importance. In this re-gard the pulpal sequelae of dentin caries are of par-ticular interest because prevention of pulpal damage

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considerably reduces the need for extensive restora-tions, and endodontic therapy and its sequelae.

There is disagreement in the literature regardinghow early the pulpal response to caries can be detect-ed (2-6). This is due to lack of acknowledgement ofthe proficiency of the available histologic method-ology. Enamel and dentin caries may be siinul-taneously demonstrated in ground sections. How-ever, the technique of producing ground sections to-tally destroys the pulp and will not allow anyobservations of soft tissue and its cells. On the otherhand, demineralization of mature teeth ~ for the pro-duction of paraffin or Em sections - leads to elimin-ation ofthe enamel. Thus, enamel caries and pulpalreaction cannot be demonstrated simultaneously inthe same section (7,8). However, it was earfier point-ed out that the presence of a few infiammatory cellsin the pulp of clinically intact teeth could be due toclinically undetected caries or doubtful conditionssubjacent to a discolored occlusal fissure (9, 10).

Material and metheds

The material upon which this article is based has ap-peared in a number of earlier investigations. Readersinterested in the details of clinical and histopatholo-gic methodology and how these may clarify aspectsof distinct disagreement are referred to those publi-cations. The investigations deal with: reactions to in-itial caries (7) and to increasingly extensive caries(11); caries in combination with attrition (12); re-actions to the effect of carious dentin inexperimental cavities of intact dentin (13) (with theintent of developing a reproducible model for theevaluation of restorative procedures and materials);reactions to the eflect of medicaments ranging fromsilver nitrate and camphorated monoclorophenol topenicillin and corticosteroids, and reactions to re-storative procedures and materials in carious cavities(14—20); and reactions to indirect capping in thetreatment of deep carious lesions (21). Further inves-tigations deal with: the microbiologic aspects of den-tin caries and their pulpal sequelae (22); the diagnos-tic criteria for the treatment of caries-induced pupitis (23); the light and electron micro-scopic study of teeth with carious exposures (24);periodontal disease and root caries in the geriatricpopuladon (25); pulp biopsies in teeth with peri-apical radiolucencies related to caries (26); and thebreakdown ofthe remaining pulp and its periapicalsequelae involving endodontic therapy (27-29).These studies encompass more than 2,000 teeth. Thepatients represent a cross-section of the populationfrom children all the way through to the geriatricpopulation.

In order to obtain sections of reproducible quality,methods and criteria as used and described in the

quoted references are essential (7, 8, 10-18, 22, 24,26).

Observations

In teeth with only early indications of clinical cariessuch as a discoloration of an occlusal fissure or of anapproximate surface, a minor accumulation of in-fiammatory cells could be observed where the dentintubules involved with caries terminated in the pulp.Clinically, a sharp probe did not catch, and radio-grams did not reveal any interproximal caries. Uponextraction there could be discoloration ofthe proxi-mal surfaces, but no macroscopically observable lossof enamel. However, in typical selected histologic sec-tions taken from the area of a discolored fissure ordiscolored interproximal surface, micro-organismswere only present in the superficial end of the in-volved dentinal tubules.

It should be noted that very minute (if any)changes had occurred in the predentin at this stageof development, and there could be a slightly reducedodontoblast layer where the involved dentinal tu-bules terminated in the pulp. Bacterial stains (e.g..Brown & Brenn) demonstrated the presence of bac-teria in the peripheral end of the dentinal tubules,and also in their side branches. It is evident that de-mineralization of the tubule walls had not takenplace, but it was not necessary for the penetration ofthe bacteria, the diameter of which does not exceedthat ofthe side branches ofthe tubules (Fig. 1). BothBrown & Brenn and PAS/Alcian Blue demonstrateddistinctive stain changes confined to the content ofthe tubules pulpal to the bacteria. Tubules in thesame area that were not invaded by bacteria did notshow these typical color changes. Neither the remain-ing matrix ofthe peri tubular nor intertubular dentinwas involved in this color change.

Caries progress occurred by increases in depth andin width. Bacteria advanced towards the pulp whilewidening the surface area and undermining the en-amel. In general, the severity ofthe pulpal responsealso increased with a significant increase in the num-ber of infiammatory cells.

In addition, a marked increase in dystrophic calci-fication occurred in the pulp chamber, in the rootcanal, and on the canal walls. The calcification couldbecome so extensive that it took up a major part ofthe pulp chamber, narrowed the root canals, andmade the walls extremely irregular (Fig. 2). Thismakes endodontic therapy — if necessary afterwards- more difficult and may, as an end result, jeopardizeor worsen prognosis.

Recording the severity ofthe pulpal response wastotally dependent on the direction and location ofthe sections and their relation to the carious area asdemonstrated in a molar with deep caries: 596 sec-

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Tissue response te dental caries

Fig. J- Tooth with discolored occlusal ri.s.sure, but no attachment of a sharp probe, and thus diagnosed a.s no clinical caries.A. Histologieally, presence of bacteria in some dentinal tubules (horizontal arrows) and where these tubules terminate in the pulp,a concentration of cells in the odontoblast layiM" (oblique arrows, orig. mag. x 32).B. Organic debris and bacterial plaque in the occlusal lissure (vertical arrow in A, orig. mag. x250).C. Bacteria in debris in oeelusal fissure in B (orig. mag. x 1000). -i i l • rD. Bacteria in the peripheral end of the adjacent dentinal tubules and their side branches. Note tlie dearly discernible cliains oibacteria in side branehes (orig. mag. x 1000).E. From area ofleft arrow in A: small concentration ofehronic inllammatory eells (orig. mag. x 250).

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Fig. 2. Maiidibular fust molar, medium to deep caries. No previous uoi- present pain.A. Section, through center of pulp ehamber and the root canal of distal root, ofT center of mesial root. Ofthe 3.5 mm across thepulp chamber of this seetion, 2.7 mm is occupied by calcifications (between horizontal arrows). No orifice, and only part ofthe rootcanal ofthe mesial root, but an area of resorption outside the main canal (vertical arrow). Circumferential apposition on the canalwalls causes narrowness and irregularity of canal (horizontal lower arrows, orig. mag. x 8).B. From area of middle horizontal arrow in A: free ealcification surrounded by ehronic inflammatorv cells and fibroblasts (orie macx250). • • \ b- b-

C. From dense cell concentration in A: small and large lymphoeytes, plasma eells, macrophages, and fibroblasts (orig. mag. x 630).D. Amorphous dystrophie calcification from pulp chamber: left top arrow in A, free in pulp ehamber (orig. mag. x 63).E. Calcification attached to the pulp chamber floor in A. Distance to pulp chamber eeiling 0.1 mm (orig. mag. x 63).Clinical consideraliom. Although ealeifications occur frequently, even in the \m\p of impaeted teeth, they are pathologic entities. Theyoccur by deposition of calcium salts in dead and dying tissue. The capability of pulp tissue to respond to injury is reduced by thesame volume as the calcifications. When endodontic therapy finally becomes necessary, they render the canal irregular and twisted,eausing difficulties in establishing optimal working length and obtaining the smooth clean canal wall required for adequate obturation!

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Tissue response te dental caries

Fig. 3- Photomoniagc from one tooth where caries penetration involves approximately 3/4 of the dentin thickness (but not theirritation dentin) may explain the discrepancy among authors in regard to onset and extent of inllammatory response to canes.A. The farthest penetration of bacteria into the dentinal tubules is indicated by horizontal arrows. The dividing area between prmiaiydentin and irritation dentin (the "calciolraumatic line") is indicated by vertical arrows, pointing upwards. In the subjacent pulp, aconcentration of cells is seen exclusively in the right part.B. Healthy non-inflamed pulp tissue typical of approximately 200 sections cut in lhc left part of this pulp. , . .C. Inflammatory reaction remote from the odontoblast layer, typical of approximately 200 sections cut in the area pomtc-d out witoblique arrow. Note: no inflammatory cells can be seen between the odontoblast layer on top and the concentration ol cells centra y.D. From area of the vertical downward arrow in right part of A. Dense concentration of primarily chronic mllammatory cthroughout the odontoblast layer adjacent to the termination of the involved dentinal tubules. • 1 t inClinical considerations. If seetions had been cut exclusively in the area of B, the diagnosis would have been deep caries, out oinflammation. If they had been cut in the area of C, the diagnosis would have been deep earies, but no 5°'''"'^'^f'°"."'^7;''!f"- ,^inflammation and the termination of the involved dentinal tubules. Only sections including the area in L» wouia gi\e uit us,answer, that an inflammation is caused by deep caries. Thus, different and contradictory results may be arrived at depenaing upondirection and number of sections, unless seetions are cut throughout the entire pulp chamber.

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154

Fig. 4. Mandibular flrst molar. Deep caries treated with indirect pulp capping, permanently leaving soft leathery dentin under therestoration. The remaining "leathery" carious dentin was treated with 10% AgNOj, the carious lesion covered with a thick mix of zincoxide eugenol, and the tooth restored with oxyphosphate cement and amalgam. The observation period was 32 months. The patient hadno previous nor present pain.A. Cavity floor, irritation dentin and adjacent pulp. Extensive layer of solid irritation dentin, but total lack of formation in area under coronal pulp (horizontalarrows) where there are AgNO3 particles and pulp tissue remnants. Dense concentration of cells in coronal part of pulp chamber, a. Empty space (artifact)due to liquefaction necrosis in vivo, and washing out of liquefied tissue during histologic processing. Density of cells tapers oil'to normal with increasing distancefrom carious lesion (orig. mag. x 16).B. From irregular irritation dentin. Note AgNO3 particles in crosscut dentinal tubules and in adjacent odontoblast layer with di.sintegrating ncutropliilicleukocytes (orig. mag. x 1000).C. From area of dense irritation dentin: AgNO;i in dentinal tubules on both sides of calciotraumatic line (vertical arrow in A), and in soft tissue inclusions ofthe irritation dentin.D. Mostly neutropbilie leukocytes along empty spaee a in A. These are the cells responsible for the condition described in A.E. AgNO] particles in pulp and concentrated in cells along vessels (orig. mag. x 1000).Clinical consideralions. Although precipitation of calcium salts occurs in dentinal tuhulcs during the carious process, tubules remain open to penetration, andeven a thick layer of irritation dentin docs not ]5rotect the pulp against irritation and destruction. Absence of pain does not indicate absence of inllammationand destruction. Contrary to Fusayama and Jordan ct al., no carious dentin may be left under a restoration.

Tissue response to dentai caries

Fig. 5. Premolar ol young individual demonstrating the cumulative elfecl of caries restored with a composite lilliii". The patient hadsevere pam, whieh disappeared upon restoration of the cavity and then reappeared after several tnonthsA. Pulp horns seem solidly filled with irritation dentin, which generally is thought to protect the pulp from injury Note onenines in the dentin (arrows) (orig.mag. x25). r r j j ^ 8

B . Less than I mm away, pulp tissue remaining in buccal pulp horn, and lemaining pulp tissue in palatal pulp horn (arrows) (orig. mag. x 25).C . from spaces pointed out with arrows in A. These spaces contain soft tissue with neutrophilic leukocytes as evidence of communication with the pulp tissue

S centrally. Smce the half-hie of neutrophilic leukoeytes is only 7 h, this is fmal evidence of movement ofthe disintegration products ofthe dentinal tubules -I bacterial to.xins, monomer, catalysts, tissue lluid, and odontoblast processes - from the periphery, and a chemotactic movement of neutrophilic leukocytes5 from the pulp tissue into the space where irritation products occur.I D. From the coronal pulp. Large numbersofneutrophilic leukoeytes, lymphocytes, and plasma cells. The inflammatory response-particularly the neutrophilie

leukocytes, which have to be renewed constantly - emphasizes the fact that the pulp has not been protected against the irritants penetrating from the surface,and that the irritation is continuous.Clinical comideratiom. The cuniulative effect of caries and iatrogenesis eaused by a eomposite material can, in the long run, cause total pulp destruetion, leadingto the necessity of endodontic therapy and its sequelae. Prevention of pulpal damage (an endodontic objective) by early and correct treatment prevents thiscostly proeedure.

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Fig. 6. A. Specimen taken from "leathery" dentin after removal of surface debtis and surface carious dentin. Dentinal tubule full ofdead or dying bacteria (orig. mag. x 20,000).B. For gDniparisori ^specirrien JakenJ'rom^dceper part^jf leathery dejitin of mandibular finst molar from another patient; sensitive toheat, cold, and electric stimulation, but not sensitive to pereussion or palpation. These bacteria have attached three-unit membranes,and electrolucent granules in the cytoplasm indicate live baeteria (orig. mag. x 10,000).Clinical consideralions. All leathery dentin must be removed to fulfill the simplest requirement for healing: remove all pathogenic^?bacteria.

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Tissue respense to dental caries

"le. /.i. The man.The mandibular second molar, first lfiolar, and second premolar of a 1 7-yeai-old male had extensive carious lesions with no history of paiii. The teeth were

sted with cold, heat, electric, percussion, and palpation stimuli, which caused responses similar to those in non-involved tcclh in opposite arch. All softrious dentin was excavated. Culture of dentin spiculcs taken from hard cavity floor following exca\-ation identified Slrej)lococciis mulam (types C, D), S.

Fig. 7.

testecarsanguis, and S. mitis. Histologic examination iiU'oK'ed eleetron microscopy of leathery dentin (see Fig. 6).B.-G. Paraflin sections taken from mandibular second molar in A.B. Cavity floor and adjacent coronal pulp. The ealciotraumatic line appears between primary and irritation dentin (\ ertical arrows). Odontoblast layer isreduced, horizontal arrow points to an artifact, a fold ofthe section (orig. niag. x 25).C. From cavity floor. Bacteria in dentinal tubules of hard dentin after removal of all soft carious dentin. Brown c& Brenn stain (orig. mag. x 1000).D. Primary dentin, calciotraumatic line, irritation dentin with fewer dentinal tubules than in primary dentin and reduced odontoblast layer (orig. mag.x250).E. Chronic inflammatory cells, including degratuilated mast cells (orig. mag. x 8t}0).F. Numerous calcifications in coronal pulp tissue (orig. mag. x 63).G. Calcifications take up considerable part of pulp hmien (orig. mag. x 250).Clinical consideralions. Large carious lesions can occur in the absence of pain. Unknowingly, in many cases of deep caries, the clinician will restore teeth withvarying atnounts of bacteria remaining under the cavity. This will contribute to pulpal disintegration in the fultue. Although occurring frequently, calcifi-cations are pathologie entities, resulting at a minimum in less pulp tissue to respond to injury.

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A. Mandibular second premolar and second molar of a 19-year-old male with extensive carious lesions, but no history of pain. Sensitive to cold drinks. Secondpremolar was hypersensitive to cold test, responded normally to heat, electric stimulus, and palpation. Radiographically, there was a slightly ex]:)andedperiodontal space. All soft carious dentin was excavated down to hard dentin without perforation. Culture of dentin spieules from hard cavity lloor identified:Streptococcus mutans (types C, D), 11.8%; S. sanguis, 8.8%; S. mitis, 79.4%.B-G. Paraffin sections taken from second premolar in A. Sections A and C are approximately 0.3 mm apart.B. Gives impression of arrested penetration in irritation dentin (Brown & Brenn, orig. mag. x 25). C demonstrates baeterial penetration into the pulp.C. Bacteria in dentinal tubules and in the adjacent pulp in necrotic (n) area (Brown & lirenn, orig. mag. x 1250).D. Section adjacent to that in C. Area of penetration of bacteria. Disintegrating neutrophilic leukocytes in necrotic (n) area (hematoxylin and eosin, orig.mag. X 1250).E. Large numbers of neutrophilic leukoeytes with a few chronie inflammatory cells intermixed in zone bordering the necrotic zone (orig. mag. x 1000).F. From area deeper in pulp. Chronic inflammatory cells, several with granulated cytoplasm, mast cells (orig. mag. x 1000).G. From root pulp. No inflammation (orig. mag. x 1000).Clinical considerations. Despite inspection of a cavity floor under rubber dam and with the use of a sharp probe a bacterial perforation to the pulp may remainundetected. The clinician would be entitled to (and would) restore this tooth, a treatment whieh would fail after an unpredictable time period. Note: alwaysrecord this on the patient's treatment record, and inform the patient ahout this possibility in cases of deep caries.

158

Tissue respense to dentai caries

Fig. 9. EM. Speeimen from area of penetration of bacteria to the pulp similar to that in Figs. 8 and 16.A. Dendn border (top), adjaeent debris and bacteria of neerotie pulp tissue (n and arrows), part of neutrophilie leukocyte (nl), andremnants of bacteria and their membranes (orig. mag. x6300).B. Neutrophilic leukoeyte with pyknotie nucleus at opening of dentinal tubule with debris (orig. mag. x 2500).Clinical considerations. The attraction of neutrophilic leukocytes to the area of bacterial penetration to the pulp leads to its ultimatedestruction. Following the engulfment of bacteria the leukocytes disintegrate, afier which the engulfed baeteria - dead or alive - arereintrodueed to the pulp, and the enzymes ofthe leukoeytes produee a liquefaction necrosis. If not removed a vicious circle is startedand the liquefaction necrosis will expand.

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Fig. 10. 7; - —Twcnty-year-old male. Filling broke 2 years before. No spontaneous paiu, but slight thill ache 2 3 miu oNo reaction to cold or sweet. The tooth was negative to tests with cold, electric, and heat, but p' ' i»i>"' I'l 1A. Mesial earious cavity reaehing pulp h o " — ~ " ' •"• ' '^ ' - —••••-:

111 stimulation with chcvviug pressure and hot food.c to percussion stimulation.

lorn, recurrent or eontinuing caries under remaining jjart of filling. Periajjical radiolucency both roots,anal orifiee (Brown & Brenn, orig. mag. x 1000).B. Necrosis and bacteria in mesial root

irom main canal (orig. mag. x 200).C. Chronie inflammatory cells mid-root main canal (orig. mag. x 1250).H. Unaltered non-inllained pulp tissue in apical third of main canal (orig. mag. x 1250).Clinical considerations. Although there is necrosis in the entire coronal pulp chamber down to the orifice ofthe root canals and a periapical radioluccncy, thereis 9 mm of vital tissue remaining in the root canal and no inflammation at all iti the ajjieal thir'^ .,r.i.« .,..1., T* CK....I^ K.. :n — n.. ., <«.i (U... .!.....« ...... —baeteria in the remaining vital part ofthe pulp.

ne oritice ot tnc root canals and a pcnapicat raaiotuccncy, ttierelird ofthe pulp. It should be speeifically noted that there are no

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Tissuo respenso to dontal caries

Fig. 11. Maxillary premolar of 20-year-old patient. The patient had no history of pain, tuir present pain. The tooth was diagnosedradiographically during general examination.A, B. Hematoxylin and eosin stained sections detnonstrating root with attached periapieal lesion, and the main canal.A. Including the apical foramen, remnants of neerotie pulp tissue in the main canal, vital tissue in foramen (horizontal arrow).B. Total cut of the main canal, artifact in foraminal area.C. Section stained aeeording to Brown & Brenn. Periapical lesion partly torn away during eutting. Lateral canal with necroticremnants 3/4 into canal, organized vital inflamed pulp tLsstie conneetiiig with periodontal lesion of pulpal origin, 3 mm from apex(vertical arrow). Apieal ramifleations with neerotie remnants 0.8 and 0.3 mm from apex (horizontal arrows).D. Root canal wall with baeteria adjacent to dentin (orig. mag. x 1000).E. Root canal wall. Bacteria in dentinal tubules adjacent to canal with necrotic content (orig. mag. x 1000).F. Lateral canal pointed out by arrow iti C. Necrosis in pulpal part of canal, concentration of neutrophilic leukocytes, and then vitalpulp tissue connecting with periodontal lesion of pulpal origin (orig. mag. x 1000).

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Fig. 12. Specimen taken from root eanal wall of tooth with similar condition to that described in Fig. 11. Presence of necrosis oftheroot pulp was diagnosed clinically. EM section confirms the presence of baeteria in the dentinal tubules of the root eanal wall inpredentin (pd) and mineralized dentin (md). Some of the bacteria are dead: electrodense body and/or separated membrane(horizontal arrows). Some are alive: electrolucent body and attached membrane (vertical arrows) (orig. mag. x 3150).Clinical consideralions. From the point of view of a practical clinical approaeh there are two prineipally different preconditions: 1) inthe presence of a vital root pulp there are no bacteria in the root canal (Figs. 1-12). 2) In the presence of necrosis in the root canaland the lateral canal, there are baeteria in the dentinal tubules ofthe root canal wall (Fig. 11). In the first type, represented by 'Figs. 1-10, sinee no baeteria are present in the root canal, all of them can be treated equally from a biologic point of view ifendodontic therapy becomes necessary. A one-visit technique is permissible, if otherwise desirable and feasible. In the second type, irepresented by Figs. 11 and 12, a one-visit technique is not aeeeptable. The problem is removing or neutralizing the bacteria that ]may have established themselves in the dentinal tubules of the root canal wall. Inability to remove the bacteria adds to endodontic jfailures. j

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Tissuo response to dontal carios

l ! ' '

Fie 13 A. Mandibular right second molar. Patient's chief complaint was pain and a history of pain. Tooth did not respond to pulptests, but was tender to percussion. Radiograph shows a deep earious lesion approaching the pulp ehamber. Wefl-defined penapicatradiolueencies surrounded by selerotie bone are present around the mesial and distal roots.B—H. Pulp tissue extirpated from the chamber and mesiolingual canal of second molar in A.B. Upper segment, coronal pulp; lower segment, root pulp (hematoxylin and eosin; original magnification x 20).

X 1250).F. Intact and degranulated mast cells (hemato.xylin and eosin; orig. mag. x 1250).

i f h i i f l t ll d i h l l ( h m a t xG. Concentration ofehronic inflammatory cells deep in ihe coronal pulp (hematoxylin and eosin; orig. mag.H ' . NO inflammation present in the apical part ofthe root pulp (hematoxylin and eosin; orig. mag. x 1250).Clinical considerations. This case exemplifies the condition in teeth with partial or eomplete periapical lesions and necrosis oi tne coronaipulp. Vital and often non-inflamed pulp tissue still remains in the root canal.

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Fig. 14. Mandibular first molar of 49-ycar-old female. No pain. Clinically caries-free. Caleulus, periodontal disease, and bone lossfrom 2/3 to 3/4 of root.A. Note narrowness of pulp ehamber seen throughout all serial sections (orig. mag. x 8.5).B. Bacterial plaque and adjacent dentinal tubules with bacteria (oblique arrows in A) (orig. mag. x 400).C. Farthest penetration of baeteria in dentinal tubules (vertieal arrow in A) (orig. mag. x400).D. Where dentinal tubules invaded by baeteria terminate in the pulp (horizontal arrow in A), a small but dense accumulation oflymphoeytes and macrophages (a: artifact; pulp tissue torn away from dentin during processing) (orig. mag. x400).

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Tissue responso to dental caries

Fig. 15. Periodontal disease and pocket involving 2/3 3/4 of root. Radiogram demonstrated a periapical lesion, confirnicd histologieally.A. Apieal part of root with attached periapical lesion.B. Mid-root placjue adjacent dentinal tubules with bacteria (Brown & Brenn, orig. mag. x400).C. Pulpal necrosis and bacteria where tubules in B end in pulp.D. Pulp tissue apical to neerotie area, and dense concentration of neutrophilic leukocytes (orig. mag. x800).E. From periapical lesion. Dense concentration of lymphocytes, macrophages, plasma cells, and fibroblasts. No nerves transversingthe lesion in this section.Clinical considerations. When bacteria ]3enetrate to the ])ulp of a root eanal that is greatly reduced in volume and establish necrosis,the circulation to the coronal pulp terminates, neerosis is established in the pulp coronal to the bacterial invasion, and the disintegrationproducts seep back or arc delivered by adjaeent functioning veins to the periapieal tissue and eausc a periapical lesion.

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tions were taken through the carious lesion. In about200 sections there was no inflammatory response atall, and in another 200 sections there was a concen-tration of inflammatory cells centrally in the pulpwith no apparent correlation to the termination ofthe carious tubules. However, in the remaining sec-tions there was a direct correlation between the den-tinal tubules involved in caries and the severe inflam-mation at their pulpal termination (Fig. 3).

When caries was left untreated, it expanded inwidth and depth, and first involved the peritubulardentin and then the intertubular matrix. The bulkofthe lesion was wedge-shaped, with the base ofthewedge towards the surface. Peripherally, more or lessthe entire dentin mass was infiltrated by bacteria, al-though this mass still remained in situ for a long time.

An important aspect of caries related to the pulpaldegeneration was the irritation dentin, the irregulardentin that is laid down and confined to the areawhere the tubules involved with bacteria terminatein the pulp. This dentin was irregular and unpredict-able in amount, just as the dentinal tubules penetrat-ing were irregular in their run. Wherever odonto-blasts had disintegrated their dentinal tubules ter-minated, but did not necessarily occlude. Pulp tissuefrequently remained as cellular fmger-like inclusions.

The variability and unpredictability of this con-dition was expressed by the fact that in some placesno irritation dentin had been formed, whereas in thenear vicinity - within a millimeter - there were largeamounts of irritation dentin, only covered by pulpfibroblasts lying spindle-shaped at a 90° angle to thatofthe end ofthe dentinal tubules.

This condition is exemplified in cases of "indirectpulp capping" (originally suggested by Fauchard) byleaving carious dentin contacting the pulp ratherthan removing it all "of fear of exposing the nerveand make the treatment worse than the disease" (30).The surface carious dentin was removed, 10% silvernitrate was applied to the leathery dentin (assumedby some not to be infected), which was then coveredwith a thick mixture of zinc oxide and eugenol, andthe tooth was restored with zinc oxyphosphate ce-ment and amalgam. The observation period was 32months. A thick layer of irritation dentin was presentunder the major part ofthe cavity, but interrupted insome areas where no irritation dentin had been laiddown, and where an area of necrosis was established.There was evidence of bacterial and silver nitrateparticle penetration in the dentinal tubules, in in-clusions ofthe irritation dentin, and in the adjacentpulp, particularly along vessels (Fig. 4).

Further evidence for the openness and per-meability of such tubules was demonstrated in casesof untreated deep caries. In one example, irritationdentin filled the entire pulp horn of a premolar.Examination of this irritation dentin in the single sec-

tion revealed inclusions of soft tissue, as lakes sur-rounded by dentin. In this case of long-standing car-ies, vital tissue was present in these inclusions. As ulti-mate evidence of penetrability, neutrophilicleukocytes were present in these inclusions (Fig. 5).In the study of the relationship between bacterialpenetration and the hardness ofthe dentin, anaerobicand aerobic culturing on mitis salivarius agar iden-tified Streptococcus mutans (types G, D), S. mitis, S.sanguineous, S. faecalis, and S. hovis in various combi-nations in all cases in the leathery dentin. In aboutone-third ofthe teeth streptococci were also culturedfrom the final culture taken from the hard cavity floorbeneath the leathery dentin.

When these teeth were examined histologieally,EM sections from the outer portion of the leatherydentin demonstrated that massive amounts of bac-teria were also involved with intertubular dentin, butwere confined to dentinal tubules in the deeper areasofthe leathery dentin (Fig. 6). Two typical exampleswill be described - a mandibular second molar (Fig.7) and a mandibular second premolar (Fig. 8) — nei-ther of which involved a clinically observable perfor-ation. In both examples, subculturing of dentin chipsfrom the hard cavity surface showed bacterialgrowth. No spontaneous pain occurred despite deepand extensive cavities that were verified radiograph-ically (Figs. 7, 8). However, the 2 cases were histolo-gieally different: in the molar, bacteria had not per-forated to the pulp, while in the premolar they had,but there was no clinically observable perforation inany of the cases. A light-microscopic section of themolar demonstrated the presence of bacteria in den-tinal tubules under the hard cavity floor following themeticulous removal of all soft carious dentin. In theunderlying pulp, pathologic changes were evident bythe presence of neutrophilic leukocytes and chronicinflammatory cells in addition to extensive calcifi-cation (Fig. 7). In the second example (the mandibu-lar second premolar; Fig. 8), where the patient hadno spontaneous pain either, but had sensitivity tocold, and the excavation similarly did not result inclinically observable perforation, the histologicexamination demonstrated the perforation by bac-teria to the pulp. In the area of bacterial perforationthere was a minor area of necrosis localized to thepenetration of the bacteria (Fig. 8). It should benoted, however, that despite the necrosis, the pres-ence of bacteria in the pulp horn, and a severe inflam-mation in the entire coronal pulp, there was non-in-flamed tissue in the root canal (Fig. 8). The necroticarea was surrounded by a dense accumulation of neu-trophilic leukocytes, and the adjacent pulp showedacellular tissue remnants indicating partial liquefac-tion. Away from the center ofthe breakdown, therewas a typical chronic inflammatory response withlarge numbers of plasma cells, small and large

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Tissue response to dontal carios

lymphocytes, macrophages, fibroblasts, mast cells,and foam cells. At this stage the entire root pulp couldstill remain totally free of inflammatory cells (Fig.8G). The only pathologic condition was dystrophiccalcification centrally in the root pulp and calcifi-cation on the canal walls. The necrosis was verifiedin EM studies where specimens from the area of pen-etration of bacteria demonstrated live and dead bac-teria with tissue debris, and neutrophilic leukocyteswith pyknotie nuclei (Fig. 9).

The next clinically discernible stage of develop-ment was when the entire coronal pulp tissue wasinvolved in the necrosis. Except for expansion in vol-ume ofthe pulpal disintegration, the important prin-cipal difference was the presence of a radio-graphically visible periapical lesion in the presence ofa vital root pulp. Not only was the root pulp vital,but for a long time it was only partially inflamed.Calcification {[ree in the pulp and on the canal walls)and resorption remained as the only evidence of path-ology in the root pulp (Fig. 10).

The last stage in caries-related pulpal destructionwas when necrosis and bacteria entered the root ca-nal. At this time the clinically important differencewas that bacteria could have gone retrogradely intothe tubules of the root canal wafl. This conditioncould (and in this case did) happen in the total ab-sence of pain, similar to the earlier stages. Vital pulptissue with nerves and vessels remained in the mostapical part of the main canal. In addition, where alateral canal was present in an area where necrosiswas established in the main canal, there was necrotictissue in the adjacent part of the lateral canal, fol-lowed by a transition zone of necrosis/neutrophilicleukocytes, and then vital and inflamed tissue con-nected to the periodontal lesion of pulpal origin (Fig.11). Most importantly, it was verified in EM sectionstaken from the root canal wall adjacent to a necroticpulp that live and dead bacteria had establishedthemselves in the adjacent dentinal tubules (Fig. 12).This is what makes a difference in therapy. Since thebacteria involved are anaerobes or facultative an-aerobes, a good prognosis is dependent upon theirelimination.

The fact that vital pulp tissue remained in the rootcanal in the presence of a periapical lesion was con-firmed by taking pulp biopsies by simple extirpationofthe pulp in cases where there was a periapical radi-olucency (Fig. 13) (25). Smears from the coronalpulp demonstrated bacteria, disintegrating blood,and inflammatory cells. The extirpations demon-strated continuous pulp tissue at lengths up to 10 mm.Acute inflammatory cells were present in the mostcoronal part, chronic inflammatory cells in the adjac-ent area, and finally in the apical area, there was vi-tal, and in most cases, non-inflamed tissue (Fig. 13).This cellular interrelationship was maintained as ne-

crosis moved in the apical direction, but the necrosisand bacteria were also confined to the root canal inclinically advanced cases, even in the presence ofswelling.

Root caries and its sequelae has achieved increas-ing importance with the increase ofthe geriatric pop-ulation. The problems are related to the continuousretraction of gingiva and the periodontal ligament,gingival root resorption, and erosion. As the root andthe cementum become exposed, this creates a newenvironment for oral bacteria. Before caries is estab-lished, however, resorption can result in lacunae co-ming in through the cementum into the dentin. De-pending upon the response of the individual in ourstudies, reattachment could occur providing oral hy-giene improved dramatically. If not, the result wasroot caries, either in previous resorption lacunae ordirectly on the cementum surface.

There was no apparent histologic difference be-tween coronal and root caries. Bacteria were presentin the dentinal tubules following the penetration orelimination of cementum by resorption/erosion.Where the carious dentinal tubules terminated in thepulp there was initially a minor inflammation (Fig.14). With increasing involvement a minor area of ne-crosis was established with the presence of bacteria.There were, however, 2 additional problems; 1) themuch shorter distance from the surface ofthe root tothe pulp, and 2) pulp and root canal calcificationconsiderably reduced the amount of pulp tissue cap-able of reacting to injury. Thus, in case of root cariesunder these circumstances, the midroot necrosis maycut off the circulation to the coronal pulp and causea severe reaction in the remaining pulp and a lesionin the periapical tissues (Fig. 15).

Discussion

Because of the limitations of our histologic method-ology it is quite speculative to correlate pulpal inflam-mation and enamel caries (2, 3,6). However, meticu-lous methodology does allow a direct correlation tobe demonstrated between superficial dentin cariesand pulpal inflammation (Fig. 1) (9, 10).

The etiology of pulpal inflammation in superficialcaries should be considered the result of metabolitesand breakdown products of bacteria, disintegrationproducts of odontoblast processes and of the tissuefluid in the dentinal tubules. This condition is indicat-ed by the color changes in the involved dentinal tu-bules in front ofthe bacteria. At this stage, the pulpalinflammation is clinically reversible provided thepioneer bacteria, which are located in the hard den-tin, are removed.

This is in disagreement with Fusayama (31), whomade the statement: "When caries penetrates dentin,softening is always deepest, discoloration is next and

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Langoiand

bacterial invasion is last". Fusayama's use of Knopphardness testing is not a valid method to measure thehardness of fine structures such as dentinal tubules,where the first changes occur (Fig. 1). Further evi-dence contrary to his statement was demonstrated inthe cases of deep caries, where bacteria were found inthe dentinal tubules pulpal to the cavity floor follow-ing the meticulous removal of all soft carious dentin(Figs. 7, 8).

T'here is disagreement among investigators re-garding the severity of pulpal involvement at variousdepths of the carious process. It has been observedthat there was no significant pulpal disturbance whenthe remaining dentin thickness, including irritationdentin, was 1.1 mm (32), or even at an average of0.31 mm (5). Similar observations are also made inindividual cases in our material; however, as the re-sponse is usually seen in 5 |a. paraffin sections or inultrathin EM sections, we can only estimate what thetotal reaction will be, unless the third dimension ofthe reaction is investigated by taking and evaluatingserial sections throughout the entire pulp. Since thiswould be an insurmountable task in a study involvinga large enough number of teeth to be representativeof all aspects of caries, the next most realistic indicatorofthe extent ofthe inflammation is to find the sectiondemonstrating the most severe reaction among all theserial sections. If an insufficient number of sectionshave been cut, or if none ofthe sections have involvedthe reaction area, then contradictory results may beobtained in the same specimen, as demonstrated inFig. 3, where no reaction, an apparently non-relatedreaction, and a severe reaction were demonstrated insections taken from the same pulp.

It has been suggested that stereologic and morpho-metric methods be used to deal with this problem(33-38). Unfortunately, however, such methods de-pend upon random sectioning (34, 35), which is ac-ceptable for a tissue with repetitive structures such asliver or kidney, but which may not be accurate forpulp tissue, as demonstrated in Fig. 3. The accuracywill still depend on the original cut going through thearea ofthe most severe reaction. Also, the morphome-tric measurements are dependent on this procedure.Sections outside that area would represent a falsenegative. Taking as an example the most sophisti-cated equipment for this purpose, the Quantimet900, Nicholsen (39) states: "Agreement among thepathologists and with the Quantimet is good for ex-treme cases. The pathologists do not agree on ran-kings of intermediate dogs and their median rankingdoes not correlate well with the Quantimet".

Thus, when dealing with such superbly preciseequipment one should keep in mind basic principlesfor the use of statistics in biology as expressed bySheps: "A number may be precise but inaccuratewhile a description may be vague but accurate" (40).

It seems that a good deal ofthe disagreements regard-ing pulpal reactions are related to the many variablesin methodology rather than in factual differences inreactions.

Another important aspect of pulpal destruction ispathologic calcification. Following calcification oftissue less pulpal tissue remains to respond to injury.Although calcification occurs in the dental pulp ofclinically intact teeth, and even in the pulp of impac-ted teeth (41), and is therefore recorded as normalby some, the calcifications increase in numbers andamounts during the carious process. Thus, regardlessof the fact that they may be considered normal byfrequency, there is no doubt that biologically theyrepresent precipitation of calcium salts in dead anddying tissue and thus represent pathologic entities(Fig. 2) (42-44).

T'here is a distinct disagreement regarding thefunction ofthe dentin changes due to caries. Gener-ally, it is thought that the calciotraumatic line andthe dentin formed in pulpal direction - alternativelycalled secondary, tertiary, reparative, protective, andirritation dentin (45) - together prevent penetrationof irritants to the pulp.

Two opposing trains of thought are derived fromGerman/Austrian literature from the start ofthe 20thcentury. The discussion is still going on: one groupuses protective dentin - the old German term Schutz-dentin; the opposing group uses irritation dentin - theold German term Reizdenlin. The first term representsthe opinion that the dentin formed under the impactof caries protects the pulp against destruction. Thesecond term represents the observation that the den-tin is formed due to irritation, regardless of what theirritant is (in this case caries). Analyzing these terms,it seems evident that this dentin is not protective, ex-cept possibly in one aspect: where it is laid down therewill be a longer distance for the bacteria to travel inorder to arrive in the pulp itself. In addition, protecti-veness is related to narrowing ofthe dentinal tubules,which may occur by deposition of calcium salts,either hydroxyapatite or whitlockite. Grosscut ofsuch tubules may give the impression that some ofthem are obliterated. However, the area remainsopen, as demonstrated by in vivo penetration of bac-teria, stains, silver nitrate, or radiographic markers,and the presence of neutrophilic leukocytes is firmevidence of penetration (Figs. 1, 3-5, 7—10). Since itis an established fact that leukocytes have a half-lifeof 7 h (46), their presence in the inclusions in theirritation dentin is evidence that irritation products-bacterial disintegration products, metabolites, andtoxins - continuously move from the surface of thecarious lesion into this inclusion, chemotactically at-tracting the neutrophilic leukocytes into movementfrom the vessels ofthe pulp. ;

The presence of neutrophilic leukocytes adjacent!

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Tissue responso to dental caries

to the predentin is further evidence of the penetra-bility ofthe carious dentin. Regardless ofthe irregu-larity, many dentinal tubules remain open to pen-etration (Figs. 1, 3-5). Thus, the old term "protectivedentin" does not seem to be appropriate. The under-lying pulp is in a stage of inflammation and disinte-gration.

Although inflammation is one of the protectivemechanisms ofthe pulp as elsewhere in the body, italso has destructive aspects. When neutrophilicleukocytes disintegrate, lysosomes release enzymesthat are capable of causing liquefaction necrosis ofthe involved tissue (47). When this minor area of ne-crosis is first established, bacteria will thrive underthese conditions, and at this stage the pulpal inflam-mation may be irreversible (Figs. 4, 5, 8-11, 13-15).

The explanation for the development of periapicallesions at this early stage is that the accumulated dis-integration products of the coronal pulp, bacterialdisintegration products, and their toxins - not wholebacteria - are transferred through veins to the peri-apical tissue. Support for this statement may be foundin the experimentation by Barnes & Langeland (48),where circulating antibodies were demonstrated asa result of placing antigens (bovine serum albumin,human gamma globulin, or sheep erythrocytes) intothe pulp chamber of monkeys, or where particles ofKerr sealer were demonstrated in regional lymph no-des after introduction confined to root canals of mon-key teeth (49).

The appearance and disappearance of periapicallesions has led to clinical misunderstanding regardingthe etiology ofthe lesion. In a study of 24 teeth withapical radiolucencies, Jordan et al. (50) used disap-pearance or reduction of the periapical lesion in 11teeth as the basis for a clinical recommendation ofindirect capping procedures. This indicates a misun-derstanding of the biologic sequence. The lesion isthere because of the disintegration products comingfrom the partially necrotic pulp (Figs. 8, 9, 13-15).When the major part of these disintegration productsare removed by excavation of most ofthe carious den-tin in an indirect capping technique, the bulk oftheirritants have been eliminated, and therefore the irri-tation products arriving in the periapical area havebeen reduced. This may allow for a temporary heal-ing of the lesion, but the pulpal disintegration con-tinues and the lesion is re-established. There is pres-ently no medicament or material that kills the bac-teria of carious dentin and does not simultaneouslykill the pulpal cells. Therefore, the remaining pulpdisintegrates at an unpredictable rate, and (of par-ticular interest for long-term clinical success) calcifi-cation will occur, possibly worsening the prognosiswhen endodontic therapy becomes necessary (Figs.2,7, 14, 15) (51).

The fact that pain may be absent is not evidence of

lack of pulpal destruction or inflammation. In a studyof 224 teeth there was severe inflammation with thepresence of numerous neutrophilic leukocytes andpartial necrosis in 81 teeth in the total absence ofpain, previous as well as present (22).

Thus, what necessitates a different clinical ap-proach in the endodontic therapy of pulpal diseaseand its sequelae is not, as was previously believed,presence or absence of a periapical lesion, or a distinc-tion between vital or necrotic teeth - it is the occur-rence of necrotic pulp tissue in the root canal, givingthe bacteria the opportunity to enter the dentinal tu-bules ofthe root dentin (Figs. 11, 12). It is importantto clinically distinguish how far the pulpal necrosisgoes in the apical direction. As has been demonstrat-ed (24, 26), a periapical lesion may be present whilethe entire root canal pulp is vital and not yet invadedby bacteria (Figs. 10, 13). Practically, having estab-lished the presence of a continuous root pulp tissue,the therapy is that of a vital case (or pulp), even inthe presence of necrotic coronal pulp and a periapicallesion. In such a tooth there is no biologic problemwith treatment in one sitting. However, if necrosis isestablished in the root canal, success and long-termprognosis will depend upon the elimination of thebacteria from the dentinal tubules of the root canalwall (Figs. 11, 12). This should be checked by cultu-ring before the obturation of the canal, which pre-cludes a one-visit technique.

The discussion in the literature about whether ornot nerves are present in the periapical lesion hasclinical relevance because ofthe lack of pain in manyinstances of pulpal/periapical lesions. This lack ofpain is not correlated to absence of nerves, since theirpresence has been demonstrated both in the remain-ing apical pulp and in the periapical lesion, whetherthis is a granuloma or a cyst (52).

In the United States in 1980, 11.8% ofthe popula-tion was above the age of 65, and the percentage isexpected to increase to 20% by 2040. The populationover age 75 constituted 4.4% in 1980, and is expectedto rise to 7.6% by 2000, and to 11.5% in 2040 (53).This will have a great impact on the need for dentalcare, with a particular emphasis on the pulpal re-sponse. The clinically important difference in pulpalproblems ofthe geriatric population is that a cariouslesion gingivally to midroot - which would only havecaused local inflammation in the coronal pulp - mayinvolve the entire circumference ofthe reduced vol-ume of the root pulp. When necrosis occurs in theroot canal this may cut off the circulation to the cor- :onal pulp, the contents of which will necrotize andadd to the destruction of the remaining radicularpulp.

Langeland f

Conciusions

1. The pulpal reactions caused by initial caries arereversible following the removal of the infecteddentin.

2. Since many ofthe bacteria in dentin caries arefacultative anaerobes they should be removedbefore restoration of the cavity.

3. The pulpal reactions in medium-deep caries arereversible, except for irritation dentin and pulpalcalcification on the canal walls or free in thelumen.

4. The severity ofthe recorded pulp reactions maydepend upon the location and direction of thesection.

5. Pain (or any type of sensitivity) is not a predict-able indicator of the inflammatory stage of thepulp.

6. In deep caries, bacteria may remain in dentinaltubules of the hard cavity floor. Combined withiatrogenesis, this may be the major reason for theoccurrence of pulpal disintegration under res-toration.

7. The reason for indirect pulp capping failure is thepresence of bacteria and a possible minor areaof pulpal necrosis that is left in contact with thecapping medium. The success of any therapy de-pends on the total removal of all disintegratedtissue.

8. Indirect pulp capping is not an acceptable pro-cedure.

9. Pulpal reactions persist under indirect pulp cap-ping procedures.

10. The apparent clinical success of indirect pulpcapping, pulp capping, and pulpotomy is due tothe removal of the major portion of the disinte-grated tissue.

11. Since no inert material is available - although alldisintegrated tissue has been removed - changesof an inflammatory or degenerative nature willslowly cause disintegration ofthe remaining pulptissue, including calcification, which will jeopar-dize future endodontic therapy.

12. Inspection ofthe pulp after opening through thedentin and washing out all disintegrated tissuewill give valuable information about the extentof remaining vital pulp tissue.

13. Root caries must be treated early to prevent se-vere pulpal destruction.

Acknowledgements-Vor their outstanding contributionto their part ofthe experimental material covered inthis publication, I want to thank the following col-leagues appearing in the list of references: Leena K.Langeland, Leif Tronstad, Gabriel Tobon, Dale M.Anderson, William E. Dowden, William R. Cotton,George E. Clark, Louis M. Lin, Robert Block, Louis

I. Grossman, Kamran E. Safavi, Elizeu A. Pascon,Glover W. Barnes, and Ricard E. Walton.

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