Special Report Reparative dentin: factors affecting its deposition Charles F. Cox^'^ / Kevin C. White^* / Dean L. Ramus* ^ / John B. Farmer** /H, Mllner Siiuggs** Results of this study showed no correlation between the thickness or amotmt of reparative dentin deposited and the type of dental restorative material piaced at either 5 or 8 weeks in controlled Class V cavity preparations in monkey teeth. Factors stich as preparation trauma from the bttr, operator hand instrumentation, and microleakage of bacterial toxins played a greater role in the stimulation of reparative dentin than did materiai irritation or to.xicity Some differences in the thickness of the reparative dentin deposited were noted when teeth were grouped according to the amotmt of remainitig dentin. (Quintessence !nt 1992:23:257-270.) Introduction Dentin is the hardest vital tissue of the htiman body; it contains odontoblastie processes, neural eietnents, and plasma proteins from the dental pulp. It is vital throughout the life of the tooth unless pathologically altered.' Galen" was perhaps the first to descrihe the dentin of a tooth as a core of bony material. Von Leeuwenhoek^ observed parts of teeth with his then newly developed microscope and described dentin as a tnhular material. Kölliker"' first reported the mero- crine function of odontoblasts, and Huxley' discussed the mesenchymal origin of odontoblasts. Human dentin is first deposited at the cusp tips in increments of approximately 4.0 ftm per day.'' This outermost zone of preeruptive mineralized dentin is called mantle for primary) dentin (Fig la). Mantle dentin has few imperfections, because its deposition and mineralization result from a unique interaction of ' Assoeiate Professor. Department ai Restorative Dentislry. University of Alabama at Birmingham, Setiool of Dentistry, UAB Station, Birmingham, Alabama 35294, '* Assistant Professor, Department of Restorative Dentistry, University of Alabama al Birmingham. Presented at the 69lh General Session of the International AssociD- tion for Dental Research, Acapulco, Mexico, April 17-21, t991 (abstr No, 2354), ameloblasts and odontoblasts.' Most dentinal ttibules contain odontoblastic processes extending perpendic- ular to the dentinoenamel junction." All mineralized dentin deposited after tooth eruption is referred to as secondar)' dentin. Secondary dentin is deposited in an inward circumpulpal (centripetal') manner throtjghout the life of the tooth (Fig la). Secondary dentin is deposited in increments of approximately Ü.5 ^m per day. unless systemic factors intervene to cause irregularities.* The capacity of secondary dentin to respond to pathologic or physiologic irritation was reviewed by Fish.'*' who demonstrated that a front of sclerotic, hypermineralized dentin. impervious to the penetration of dyes, proceeds caries. The more central zone of hypomineralized, earious dentin, which allows the uptake of various dyes, is composed of dead tracts (Fig lb), Reparative dentin is a localized area or zone of dentin that is deposited in response to some external stimula- tion. Albrecht" first described this as "dentin of repair," suggesting it was deposited to prevent the pulpal tissue from becoming exposed. Baume'- characterized any dentin underneath occlusal attrition as a kind of re- placement dentin. In the dental literature, the terms for dentin of repair have included cellular, acellular, irregular, secondary, secondary irregular, tertiary, repara- tive, irritation, response, and reactiot!ary'~~^^ (Table 1). Ail these terms refiect a change in quantity (thickness) as well as quaiity of dentin. For additional reading re- Quintessence International Volume 23. Number 4/1992 257
Transcript
Special Report
Reparative dentin: factors affecting its depositionCharles F. Cox ' / Kevin C. White^* / Dean L. Ramus* ^ / John B. Farmer** /H, Mllner Siiuggs**
Results of this study showed no correlation between the thickness or amotmt ofreparative dentin deposited and the type of dental restorative material piaced at either5 or 8 weeks in controlled Class V cavity preparations in monkey teeth. Factors stich aspreparation trauma from the bttr, operator hand instrumentation, and microleakage ofbacterial toxins played a greater role in the stimulation of reparative dentin than didmateriai irritation or to.xicity Some differences in the thickness of the reparative dentindeposited were noted when teeth were grouped according to the amotmt of remainitigdentin. (Quintessence !nt 1992:23:257-270.)
Introduction
Dentin is the hardest vital tissue of the htiman body; itcontains odontoblastie processes, neural eietnents,and plasma proteins from the dental pulp. It is vitalthroughout the life of the tooth unless pathologicallyaltered.' Galen" was perhaps the first to descrihe thedentin of a tooth as a core of bony material. VonLeeuwenhoek^ observed parts of teeth with his thennewly developed microscope and described dentin as atnhular material. Kölliker"' first reported the mero-crine function of odontoblasts, and Huxley' discussedthe mesenchymal origin of odontoblasts.
Human dentin is first deposited at the cusp tips inincrements of approximately 4.0 ftm per day.'' Thisoutermost zone of preeruptive mineralized dentin iscalled mantle for primary) dentin (Fig la). Mantledentin has few imperfections, because its depositionand mineralization result from a unique interaction of
' Assoeiate Professor. Department ai Restorative Dentislry.University of Alabama at Birmingham, Setiool of Dentistry,UAB Station, Birmingham, Alabama 35294,
'* Assistant Professor, Department of Restorative Dentistry,University of Alabama al Birmingham.
Presented at the 69lh General Session of the International AssociD-tion for Dental Research, Acapulco, Mexico, April 17-21, t991(abstr No, 2354),
ameloblasts and odontoblasts.' Most dentinal ttibulescontain odontoblastic processes extending perpendic-ular to the dentinoenamel junction." All mineralizeddentin deposited after tooth eruption is referred to assecondar)' dentin. Secondary dentin is deposited in aninward circumpulpal (centripetal') manner throtjghoutthe life of the tooth (Fig la). Secondary dentin isdeposited in increments of approximately Ü.5 ^mper day. unless systemic factors intervene to causeirregularities.*
The capacity of secondary dentin to respond topathologic or physiologic irritation was reviewed byFish.'*' who demonstrated that a front of sclerotic,hypermineralized dentin. impervious to the penetrationof dyes, proceeds caries. The more central zone ofhypomineralized, earious dentin, which allows theuptake of various dyes, is composed of dead tracts(Fig lb),
Reparative dentin is a localized area or zone of dentinthat is deposited in response to some external stimula-tion. Albrecht" first described this as "dentin of repair,"suggesting it was deposited to prevent the pulpal tissuefrom becoming exposed. Baume'- characterized anydentin underneath occlusal attrition as a kind of re-placement dentin. In the dental literature, the termsfor dentin of repair have included cellular, acellular,irregular, secondary, secondary irregular, tertiary, repara-tive, irritation, response, and reactiot!ary'~~^^ (Table 1).Ail these terms refiect a change in quantity (thickness)as well as quaiity of dentin. For additional reading re-
Quintessence International Volume 23. Number 4/1992 257
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s _ _ _1ci
-A 1
fFig la (M) Mantle (primary) dentin; (C) circumpulpal (sec-ondary or Incremental) dentin.
Fig 1b (S) Sclerotic dentinal tubules with an outer hyper-mineralized zone and an inner hypomineralized zone; ft)lamella or enamel imperfection.
Table 1 Timeline of dentinal terminologies
Term Author Journal/book title Yr
Mantle
Primary
Secondary
Orban BSisea RF
Tomes CSBeust TBHoffman MMKuttler YStanley HRAtkinson ME
Hunter JHulme RTWedlCToni es JSalter SJATomes CSBodecker CFW
•"• Black G V
"•' BnntingRWNoyes FB
* Hopewell-Smith A* Fasoli GZ
Oral Histology and Embryology, ed 1Calcif Tissue Res, 9;1-16
Manual of Dental Anatomy; Am Dent Assoc, 21:646-657Anat Rec, 78:233-25]Oral Surg Oral Med Oral Pathol, 12:996-1001Oral Surg Oral Med Oral Pathol, 21:180-189Arch Oral Biol, 21:67-^8
On the Anatomie of the Human TeethTrans Coll DentPathology of the TeethSystem of Dental Surgery, p 307Dental Pathology and SurgeryManual of Dental AnatomyDent Cosmos, 21:354-359Operative DentistryDent Cosmos. 54:157-169Dental Histology, p 184Dent Items Interest, pp 477-498Stomatol 22:225-232
19291972
192319341950195919661976
17731861187218731875187618791908191)191219181924
258 Quintessence International Volume 23, Number4/1992
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Table I Timeline of dentinal terminologies (cont)
Term Author Journal/book title Yr
Secondary * Orban B Oral Histology and Embryology, ed 1* Byrnes RR J Am Dent Assoc, 18:449-458* BeustTB JAmDentAssoc,18:f060-1073* BoulgerEP J Dent Res, If :257-265* FishEW BrDentJ.53:351-363* KronfeldR HistopaihologyoftheTeethand
Their Surrounding Strnetures* ManleyEB BrDentJ. 60:32f-331* Gottlieb B J Dent Res 25:29-32* Scelig A NY State Dent ,T, lfi:54O-553* Hoffman MM Anatomical Record, 78:233-251* Kuttler Y Oral Surg Oral Med Oral Pathol, 12:996-1001* Mitchell DF J Am Dent Assoc, 59:954-959* Klein AJ J Am Dent Assoc, 63:76-84* El-Kafrawy AH J Dent Res, 42:874-884* CorbettEM BrDentJ, 114:142-147* BanmeU BrDentJ, 116:254-259* StanleyHR OralSurgOralMedOralPathol,21:180-189* Kaplan NL J Dent Child, Ju!y:237-242* Rowe AHR BrDentJ, 122:291-300* ShoveltonDS Int Dent J, 18:392^05* BergenholtzG ScandJDentRes,83:153-158* Plant CG BrDentJ, 140:373-377* Brcivik M Scand J Dent Res. 85:392-395* HasselgrenGS ActaOdontolScand,35:289-295* Rayner JA J Dent, 7:39^2* Roulet J-F Schweiz Monatsschr Zahnmed, 90:1116-1126
Mjor IA Dentine and Dentine Reactions inthe Oral Cavity, pp 27-31
BodeckerCF* KntllerY^ Baume I J* Stanley HR* Fischer FM* TaintorJF
Santini AMjorIA
Fish EWMUllerOLangeland KSchmidt CNKlaiber B
^ TaintorJFMjörlAWarfvinge JBeerVR
Müller O
Albrecht EHohlR
Oral Histology atid Embryology, ed 1Dentin and Dentinogenesis, vol 1, pp81-134Detitin and Dentine Reactions inthe Oral Cavity, pp 17-26Dentine and Dentine Reactions inthe OralCavity,pp 27-31
Oral Histology and Embryology, ed I ,p44
J Oral Pathol, 8:28-*6
Tufts Dent Outlook, vol 19J Am Dent Assoc, 33:1233-1238J Am Dent Assoc, 58:49-59J Oral Rehabil, 4:335-340
Arch Oral Biol. 13:755-763JDcnt Res,53:565-570Oral Surg Oral Med Oral Pathol, 43:135-140Oral Surg Oral Med Oral Pathol, 45:123-130JDentChild,33:1-5ScandJDentRes,88:187-192Oral Surg Oral Med Oral Pathol, 54:232-237J Dent Res 66:78-83
Int DentJ,20:309-315BrDentJ , 130:99-107Calcif Tissue Res, 24:215-222Acta Odontol Seand, 47:41-52
J Am Dent Assoc, 26:527-530Oral Surg Oral Med Oral Pathol, 12:996-1001BrDeiitJ416:254-259Oral Surg Oral Med Oral Pathol ,21:180-189JDentRes,49:1537-1540Oral Surg Oral Med Oral Pathoi, 51:442-449BrDentJ , 155:151-154Dentine and Dentine Reactions inthe Oral Cavity, pp 27-31
Br DentJ,53:.351-363Über das Elfenbein als Wurzelfüllung der PulpaOdontol Tidskr. 65:306-363Sehweiz Monatsschr Zahnheilkd, 84:391-426Dtsch Zahnärztl Z, 34:503-505Oral SiirgOral Med Oral Pathol, 51:442^49Dentin and Dentinogenesis, pp 1-19JDetit Res, 64:1046-1050Zahn Mund Kieferhetlkd, 74:675-682
Über das Elfenbein als WnrzelfüUungder Pulpa
Die Krankheiten der ZähneÜber Neubildungen der Zähne
192919841987
1987
1929
1979
1945194619591977
196819741977197S1979198019821987
1970197119771989
19391959196419661970198119831987
193219381957197119791981198219851986
1938
18581868
260Quintessence International Volume 23, Number 4/10
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Table I Timeline of dentinal terminologies (cont)
AtJthor Journal/book title Yr
Shroff FR Oral SmgOral Med Oral Pathoi, 5:51-57Massler M J Tenn Dent Assoc, 35:353-374James VE J Am Dcnt Assoc, 59:903-910Weider SR Oral Surg Oral Med Oral Pathol, 9:221-232Going RE J Am Dent AKSOC, 60:285-300Kozlowska I Czas Stomatol, 13:375-380Swerdlow H Oral Surg Oral Med Oral Pathol, 15:499-508Shankle RF Oral StirgOral Med Oral Pathol, 15:1121-1128Kuwabara RK J Dent Child, 33:190-204Stanley HR Oral Stirg Oral Med Oral Pathol, 21:180-189Diamond RD J Prosthet Dent, 16:1127-1134Sayegh FS J Dent Child, 34:471-477Anderson AW Oral Surg Oral Med Oral Pathol, 26:837-847Phaneuf RA J Dcnt Child, 35:61-76Giltnore HW J Prosthet Dent, 23:434^39Goto G Btiin okyo Dent Coll, 13:251-256McWalter GM Oral SiirgOral Med Oral Pathol, 36:90-100Brazda O Acta Uiiiv Caro! [Metí] (Praha), 19:399-404Cotton WR Oral SurgOral Med Oral Pathol, 38:441^50RetiefDH JOral Pathol,3:114-122I leys DR J Oral Pathol ,5:129-148Eriksen HM Scand J Dent Res, 84:297-303Atkinson ME Arch Oral Biol, 21:67-68Myers GE J Dent Res, 55:259-264Bloch WW J Oral Pathol, 6:278-284TobiasRS BrDent J, 144:345-350Rieth VP Dtsch Zahnärztl Z, 9:593-672Brännström M J Prosthet Dem, 41:290-295Pitt Ford TR J Br Endod Soc, 12:67-72Isermatin GT J Endod. 5:322-327Tomeck CD J Endod. 6:719-723Cox CF J Dent Res. 59:109-115Dick HM J Endod, 6:641-644Negm M ProcFinn Dent Soc, 79:25-27Scherman B J Dent AssocSoulh Afr, 37:849-853BergenholtzG J Oral Pathol, 11:439-450Bender IB J Am Dent Assoc, 107:595-600Dowden WE J Prosthet Dent, 50:497-504NilvéusR J Periodont Res, 18:420-428SantiniA BrDent J, 155:151-154Karjalainen S Secondary and Reparative Dentin
Formation, pp 107-117Jerrell RG J Dent Child, 51:34-38Ohya-misu M Btjl! Tokyo Dent Coll, 26:15-33Ichino R Shikwa Gakuho, 85:255-299WarfvingeJ Endod Dent Traumatol, 2:256-262Mjör IA Dentine and Dentine Reactions in
the Oral Cavity, pp 27-31ten Cate JM Dentine and Dentine Reactions in
the Oral Cavity, pp 67-76
Mjör IA Dentine and Dentine Reactions inthe Oral Cavity, pp 27-31
ten Cate JM Dentine and Dentine Reactions inthe Oral Cavity, pp 67-76
Individuals who have etnployed a different term to describe the localized deposition of reparative dentin.
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R — ^ ^ ^ \ "
R
f1iV
\
]Fig 2a Physiologie ctianges associated with areas of (R)reparative dentin; (A¡ occlusal attrition; (E) cervical erosion;(T) dentinal tubules. Areas of reparative dentin are locatedrelative to tubule orientation.
garding the historical perspective on the terminologyof dentin, the interested reader is referred to TheDental Cosmos'" of 1882 and a more recent article byShroff, ' who first proposed the use of "reparativedentin as a much more suitable term."
Several mechanisms have heen postulated to stimu-late formation of reparative dentin. Beust " considereddeposition of reparative dentin to he either a conse-quence of naturally occurring physiologic factors, suchas occlusal attrition, fracture, erosion, abrasion, andaging (Fig 2a), or of pathologic effects, such as caries,periodontal disease, orofacial infections, and instrumen-tation trauma during tooth preparation (Fig 2b).Numerous dental articles have alleged that such factorsas the alkaline pH of calcium hydroxide (CafOHJi)bases, unset monomers from composite resins, hand ormechanical condensation pressure, thermal conductiv-ity, and microleakage may stimulate either localizedreparative dentin deposition or eventual obliterationof the pulp canals.""*""'"'
Reparative dentin has heen studied in animal andhuman models. Stanley'"* and Stanley et aP^ reportedthicker zones of reparative dentin in those humanteeth that have undergone extensive operative restora-
tion, while teeth restored with zinc oxide and eugenol(ZOE) only show thin reparative dentin after 90 days.Human studies by Diamond et al'^ and rat sttidies hyWeider et al'' indicated that deep cavity preparationsproduce thicker reparative dentin, Swerdlow and Stan-ley ^ reported an exaggerated pulpal response in ex-perimental procedures compared to similar proceduresin clinical practice. However, neither irregular or re-parative dentin is observed in noncarious teeth, as isthe case when cavities are prepared in carious teeth.Heys et al""* reported no significant correlation be-tween cavity depth and reparative dentinal thicknessin monkey teeth at 5 or 8 weeks. Others have reportedthat plaeement of certain calcium hydroxide-containingliners and bases will stimulate thicker reparative dentinthan will ZOE materials.*'°^-
Until now, there has been a lack of substantive lon-gitudinal research data to either support or refutethese empirical suppositions. The purpose of thisretrospective study was to evaluate whether differenttypes of restorative materials stimulate depositioti ofthicker reparative dentin than do others. Nonexposed,Class V, facial restorations were statistically analyzedfor thickness of reparative dentin.
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Method and materials
Data for this study were collected from tissues obtainedfrom more than 40 rhesns monkeys. A total of 246 non-exposed, facial. Class V cavities were prepared andrestored with a variety of restorative materials includ-ing amalgam, self-curing composite resin, light-curingcomposite resin, calcium hydroxide, sihcate, and zincoxide and eugenol.
Experimental [procedure
Each animal was initially tranquilized with an intra-muscular injection of ketamine hydrochloride (10 mg/mL) and then given an intravenous injection of sodiumpentobarbitol (25 tng/mL) for final sedation. Oneoperator was responsible for all cavity preparations, toreduce operator variability. A new No. 33 invertedcone carbide bur was used after every fourth tooth.All cavities were cut under constant water irrigationwith an ultra-high-speed air-driven handpiece at ap-proximately 250,000 rpm. No rubber dam was used.No effort was made to remove the smear layer or dis-infect the dentin. All materials were placed accordingto manufacturer's recommendations.
Following either 5-week or 8-week placetnent inter-vals, tissues were collected using techniques previouslydescribed by Cox et al."* All teeth were demineralizedin 0.5 M of e thy lenedi ami ne tetra acetic acid, rinsed indistilled water, dehydrated in N-butyl alcohol, embed-ded in Paraplast Plus (Sherwood Medical), and seriallysectioned at 7-/.im on a Leitz microtome. Alternateserial shdes were stained with hematoxyhn and eosin,Preece's trichrome for connective tissue, and McKay'sstain for bacteria. The mesiodistal dimension of eachreparative dentinal area was estabhshed by countingthe number of 7-fi.m serial sections through the entiremesiodistal dimension. This established the midpor-tion of each reparative dentinal area. A camera lucidatracing of each midsection was made using a LeitzOrtholux microscope with a magnification attachmentof x3.5. The dimensions for each of these tracings(Fig 3) were measured using a cahbrated graphic tab-let (Apple I) Pins computer and Apple Graphic Tab-let, Macintosh) following the techniques ofWarfvinge.''"'
Ten specific dimensions were analyzed:
1, Area of the reparative dentin (ARPD)2. Ineisal or occlusoapical length of each reparative
dentinal area along the calciotraumatic line separat-ing the secondary and reparative dentin (LRPD)
Fig 3 Dimensions for camera lucida tracings: (ARPD) areaof reparative dentin; (LRPD) length of reparative dentin;(TRPD) thickness of reparative dentin; (TBL) dentinal tubulelength; (TDT) total dentinai thickness; (RD) remaining dentin;(OL) occlusal cavity wall length; (AL) axial wall length; (CL)cervical cavity wall length.
3. Thickness of each reparative dentinal area at themidsection (TRPD)
4. Area of the cavity as measured at the midsection(ACAV)
5. Thickness of the remaining dentin at the deepestportion of the cavity measured along the naturalcurvature of the remaining dentinal tubules (TBL)
6. Total dentinal thickness measured jnst cervical tothe cavity preparation and perpendicular to thepulp-dentin interface (TDT)
7. Tliickness of the remaining dentin at the deepestportion of the cavity measured perpendicular tothe pulp-dentin interface (RD)
8. Length of the dentinal cavity wall along its occlu-soaxial line angle (OL)
9. Occlusocervical axial wall length of the midportioncavity section (AL)
10. Length of the dentinal wall along its cervicoaxialline angle (CL)
Each tooth was independently measured by twoindividuals, and the data were stored in a computerfile for later statistical analysis. Standard error
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Table 2 Cavity preparation and reparative dentin measurements of teeth treated with various re.storative agents
5 Wk (43)8Wk(27)
5Wk(21)8Wk{31)
5Wk(22)8Wk(19)
5Wk(35)8Wk(25)
5Wk(12)8Wk(n)
ACAV(fim-)
1562 ± 6611557 ± 633
1670 ± 7441896+544
1469 ± 478*1877 ± 740
1777 + 6121460 ± 664
1566 ± 6701609 ± 494
ARPD(um-)
121 + 76125 ± 106
127 ±108171 + 117
99 ± 62*224 ± 145
127± 71154 ± 105
69 ± 53*132± 85
AL(um)
Calcium hydroxide
1944 + 6351937 ±519
Zinc oxide-eugenol
1933 ± 3361856 ± 562
Amalgam
1795 ± 3501973 ± 443
Composite resin
1915 ±4101771± 509
Silicate
1832 ±5461954 ± 468
RD(um)
768 ± 330649 ± 263
675 ± 425701 ±411
625 ± 415667 ±316
790 ± 348746 ± 332
869 ± 379706 ± 275
TBL([im)
1098 ± 403964 ± 356
1Ü08 ± 588994 ± 585
1031 ± 5431038 ± 471
1136 + 4591061± 393
1290 ± 4391009 ± 340
TDT(|im)
1648 ± 279*1509 ±218
1546 ±3181655 ± 249
1504 ± 226*1634 ± 173
1756 ± 2881735 ±217
1684 ± 2461648 ± 264
Numbers in parentheses represent (he number of teeth in the category,* Statistically significatit difference between 5 and 8 weeks (P < ,05).
of measurement of this system was computed usingdata collected from ten consecutive tracings of a singlecamera lucida tracing of known dimension. Standarderrors of measurement for the measuring system wereless than 5% for all types of measurements.
Statistical analysis
All data were initially analyzed by one-way analysis ofvariance (ANOVA) at the ,05 level. Differences be-tween the variables within the ANOVA were comparedusing unpaired Student's t tests (P < ,05), All of thestatistical tests were performed using the InteractiveData Analysis System at the University of Alabamacomputing center. All data were grouped so that theycould be analyzed according to the following: (1) typeof restorative material: (2) cavity depth; and (3) anteriorversus posterior teeth.
Results
AH groups of restorative materials showed similarthicknesses of reparative dentin at the 5-week and 8-week time periods (Table 2). There was no statisticalcorrelation at the ,05 level between the thickness orlength of the reparative dentin and ihe cavity depth(inner, middle, and outer) (Table 3). However, datademonstrated that the deeper the cavity preparation,the thinner the remaining dentin (P < ,05), Within thevarious types of materials, there were significant butinconsistent correlations between remaining dentin,the area of the cavity preparation, the area of repara-tive dentin, the length of the axial wall, and the occlu-socervical length of the reparative dentin.
Following are the results of comparisons betweenmaterials analyzed without respect to cavity depth(Table 2 and Fig 4):
1, There was no statistically significant difference in
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Table 3 Measurements of reparative dentin of teeth treated with various restorative agents placed in inner, middle,and outer thirds of dentin
Numhers in parentheses represent the number of teeth in the category.* Statistically significant differenee between 5 atid 8 weeks ( P < .05).
the thickness of reparative dentin between mate-rials at 5 or 8 weeks if the data were stratified byeavity depth.
2. Comparisons within various groups of materials at5 weeks and 8 weeks showed that reparative dentinwas significantly thicker at 8 weeks {P < .03).
3. Linear regression analysis showed a correlation be-tween dentinal measurements for remaining dentinand the tubule length along the curvature of re-maining dentinal tubules: RD = 4.2 ± 0.7 ¡imTBL[P = .000).
4. Linear regression analysis showed a correlation be-tween occlusoapical axial wall length and occluso-
apical length of the reparative dentin: AL = 1501.1± 0.3 im LRPD {P = .000).
When materials were atialyzed aeeording to eavitydepth, in general, there were no statistically significantdifferences between material types at either 5 or 8weeks (Table 3 and Fig 5). Exceptions were in the fol-lowing areas:
1. There was a significant difference in the thicknessof reparative dentin at 5 weeks between Ca(OH)2and amalgam only when the cavity preparation wascut in the inner (pulpal) third of dentin. In this
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Fig 4 Representative cameralucida tracings depicting reparativedentin under materials placed for(A) 5 weeks and (B) 8 weeks.
Fig 5 Representative cameralucida tracings showing the re-lationship betviieen thickness ol re-parative dentin and depth of thecavity. Cavity prepared in the (A)outer third of dentin, (B) middlethird of dentin, and (C) inner third ofdentin.
case, reparative dentin under Ca(OH)2 was signi-ficantly thicker than reparative dentin under amal-gam (P = .007).There was a significant difference in reparativedentinal thit:kness at 8 weeks between Ca(0H)2and amalgam when the cavity preparation wascut within the inner third of the dentin. In theseteeth, the reparative dentin nnder Ca(OH)2 was
less thick than was the reparative dentin underamalgam.When the 5-week and 8-week intervals were com-pared within material types, it was found that, inthe outer third of dentin, there were no statisticallysignificant differences in any measurements. Incavities in the middle third of dentin, the area ofreparative dentin for amalgam was significantly
266 Quintessence International Volume 23, Number 4/1992
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Table 4 Cavity preparation and reparative dentin measurements of anterior and posterior teeth
greater at 8 weeks than at 5 weeks {P = ,016), Thethickness of reparative dentin beneath Ca(OH)2,composite resin, and amalgam was significantlygreater at 8 weeks than at 5 weeks (P — ,013,P = ,001, and P — ,004, respectively). In cavities inthe inner (pulpal) ihird of dentin, the thickness ofreparative dentin under both amalgam and ZOEwas significantly greater at 8 weeks than at 5 weeks(P - .000 and P = .006, respectively). The area ofreparative dentin under amalgam was greater at8 weeks than at 5 weeks.
Some differences between anterior and posteriorteeth were observed at 3 and 8 weeks (Table 4). Ingeneral, the area of the eavity, the area of reparativedentin, and the incisoaxial length of the reparativedentin were greater in anterior teeth than in posteriorteeth (P < .05). When comparisons were made withingroups, no statistically significant differences werefound between variables in maxillary and mandibularteeth. The data showed that, as the incisoapical lengthand area of the cavity axial wall increased, the lengthand area of the reparative dentin also increased.
Discussion
Various authors have reported that certain dentalmaterials stimulate thicker reparative dentin, due totheir irritational properties.''""'^ Stanley""' has reportedthat calcium hydroxide stimulates thicker reparativedentin than does ZOE. The present data demotistratedno statistically significant difference between the tliick-
ness of reparative dentin in nonexposed cavities restoredwith either Ca(OH)j and that of cavities restored withZOE.
Statistically significant differences were noted whenanterior teeth were compared to posterior teeth. An-terior facial Class V restorations produced a larger areaof reparative dentin than did posterior restorations.This difference may result because anterior teeth pro-vide a greater incisocervical dimension for clinicalaccess, possibly resulting in larger cavity preparations.The values for the area and length of reparative dentinwere also greater in anterior teeth, but the value forthickness was not.
There were no statistically significant differences inthe thickness of reparative dentin deposition betweenmaterial types placed at 5 or 8 weeks. Teeth with facialClass V cavities prepared in the middle or outer thirdof dentin showed no differences in reparative dentinthickness, regardless of the type of restorative mate-rial placed. However, when the data were stratified,there was an increased thickness of reparative dentinin teeth whose cavities were cut in the inner (pulpal)third of dentin.
At 5 weeks, cavities restored with a Ca(0H)2 basehad a significantly thicker amount of reparative dentinthan did those restored with amalgam. However, at8 weeks, cavities restored with amalgam presentedthicker reparative dentin than did Ca(OH)2-restoredcavities. Since both groups of cavity preparations wereprepared within the inner (pulpal) third of remainingdentin, these differences were most likely not relatedto the trauma of the cavity preparation, but to micro-
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leakage factors that exist for both material types.Another considetation may be that, in ¡imalgam, deposi-tion of reparative dentin ¡s inbibited by galvanic corro-sion for up to 5 weeks.
Weider et al"" reported that cavity depth was moresignificant in determining the thickness of reparativedentin than were the different restorative materials(ie, the deeper the cavity depth, the thicker theamount of reparative dentin). The present data indi-cated no correlation between the overall thickness ofreparative dentin and cavity depth and the type ofrestorative material placed, at either 5 or 8 weeks. Inaddition, these data also suggested that, irrespectiveof the depth of the cavity, thicker reparative dentinwas deposited at 8 weeks than at 5 weeks. Nîlvéus andSelvig'' reported that reparative dentin is thicker inteeth that have reeeived deep root planing than it is inteeth that have received superficial root planing, butthat no differences in inflammatory reactions in thepulp were observed.
Differences were observed within material typeswhen the 5-week and 8-week depositions were com-pared in cavities prepared in the inner and middlethirds of dentin. No statistically significant differencesin reparative dentinal thickness were seen between 5and 8 weeks when cavity preparations were placed inthe outer third of dentin. This data demonstrated thatwhen detital materials are tested for usage at these timeintervals, they must be placed in the inner (pulpal)third for any difference in reparative dentinal thicknessto be measured.
As the postoperative time increased from 5 to 8weeks, a thicker reparatjve dentin was observed. Thisobservation agrees with reports of Stanley,* who re-ported this same phenomenon in human teeth. Thesefindings raise questions about the long-term effects ofreparative dentinal deposition as discussed by McWalteret al,-** Barnes and Kidd,"" and Lewin.'" Clarke'*''suggested that Ca(OH)2-induced dentinogenesis mighteventually stimulate the eoronal pulp to become oblit-erated. However, long-term pulp capping studies byMcWalter et al**'' and Cox et aP" have not supportedthis suggestion.
The 5-week and 8-week format of data measuredfrom this stndy does not allow a prediction of dailyincremental reparative dentinal deposition. Will therate of deposition decrease after several years? An ap-proach io determine the rate of incremental depositionmight be to employ a hard tissue tetracycline markerat regular time intervals following cavity preparationand material plaeement. Simpson ' reported that tet-
racycline remains bound to the organic complex ofhard tissues after ethylenediaminetetraacetic acid de-mineralization, making it an acceptable hard tissuemarker for future pulpal studies.
Underlying all of this discussion is what, if any, isthe most important stimulus for deposition of repara-tive dentin? Stanley '' concluded that the thickness ofremaining dentin does not appear ro affect the totaldeposition of reparative dentin, bnt that traumaticoperative procedures are capable of stimulating re-parative dentin. The present data showed that cavitiesmust be placed in the inner third of dentin tt) stimulatethicker reparative dentin. Reparative dentin may resultfrom increased operative trauma from the deeper cavitypreparations. In addition, reparative dentin may alsoresult from irritating effects of microieakage or bacte-rial contaminants at the cavity margins," " "*
Manley^^ speculated that two dissimilar materials,"coming into contact with a living tissue, would pro-duce different reactions in the pulp." Since 1936, theliteratutc has discussed this issue from many aspects.However, the present data indicated that there was nocorrelation between material irritation and the thick-ness of reparative dentin. This result is in agreementwith that of Kronfeld,^'' who reported, "Secondai)'(reparative) dentine formation in the teeth of youngdogs begins immediately after a cavity has been drilled,and in experiments of this kind it apparently does notmake a difference whether such an artificial cavity isfilled with any kind of filling material, or whether itis left open; the mere faet that dentinal tubules itithe periphery have been mechanically injured is thedeciding factor that stimulates secondary (reparative)dentine formation,"
Conclusions
These data demonstrated several trends;
1. There was no correlation between the types of re-storative dental materials employed in this studyand the thickness of reparative dentin,
2. Reparative dentin was thicker at 8 weeks than at 5weeks for all material types studied.
3. The thickness of the remaining dentin was only af-feeted when the depth of the cavity extended to theinner (pulpal) third of dentin.
4. A direct correlation was observed between the re-maining dentinal thickness and the dentinal tuhnlelength.
266 Quintessence Internationai Voiume 23, Numh,s
Special Report
5. There was no difference in the thickness of thereparative dentin between anterior and posteriorteeth.
6, The area and length of reparative dentin weregreater in anterior teeth.
Acknowl edgm ent s
Data for this report were supported in part by Department ofRestorative Dentislry grant Nos. 3t87t3, 317712, 33379Ü, and638 US,
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