Effect of in vivo crown health

margin

D. A. Felton, D.D.S., M.S.,* B. E. Kanoy, Ph.D.,” and G. P. Wirthman, B.S.***

discrepancies

M.A., D.D.S.,’

S. C. Bayne,

on periodontal M.S.,

University of North Carolina, School of Dentistry, Chapel Hill, N.C. Numerous reports have suggested a relationship between marginal adaptation of dental castings and periodontal tissue health, and this study examined this relationship quantitatively. Forty-two crown restorations in 29 randomly selected patients were selected for this study using three criteria. (1) The crowns were placed at the University of North Carolina School of Dentistry; (2) the crowns were in service for a minimum of 4 years; and (3) the crown margins were within the intracrevicular crevice (subgingival). Replica impressions of the facial margins of specific crowns were made with a vinyl polysiloxane impression material, and poured casts were prepared for scanning electron micrograph evaluation. Marginal discrepancy measurements were identified on each micrograph at 10 equally spaced locations along the margin and averaged for each specimen. Periodontal indices of pocket depths, crevicular fluid volume, and gingival index were accummulated for clinical measurements. Pearson correlation and Bonferroni adjusted probability ,tests were performed, but no significant correlation was found between marginal discrepancy (0.16 + 0.13 mm) and pocket depth (2.4 + 0.9 mm). However, a strong correlation @ < 0.001) existed between marginal discrepancy and gingival index (2 +- 0.8) and between marginal discrepancies and crevicular fluid volume (49.9 + 31.1). These results established that a significant quantitative relationship existed between the marginal discrepancy and periodontal tissue inflammation for subgingivally located crown margins. (J PROSTHET DENT1991;66:357-64.)

T

he extension of an artificial crown or fixed partial denture (FPD) retainer margins into the intracrevicular crevice is justified for severalreasons:(1) subgingival caries,(2) extensionof the preparation marginson soundtooth structure beyond existing restorative materialsor abrasion, (3) to increaseresistanceand retention form for short clinical crowns, and (4) for esthetics. The advent of restorations with castableceramic and porcelain shouldermargins has diminished the incidence of subgingival margins for esthetics. The subgingivalmargins of prostheseshave always been suspectedto have seriousimplications for the periodontal health of the supporting tissues.Christensen1illustrated in vitro that the least accessiblevisually acceptable margin wasopen by 39 ~.lrn.Interproximal and subgingival margins judged asclinically acceptablehad marginal openingsof 74 w. Investigators have repeatedly demonstrated that subgingival marginsproduced gingival inflammation indicated by an elevated gingival index (GI), increasedplaque index (PI), and increasedpocket depths (PD).2-sHowever, other

studies revealed that margin placement had only limited effect on the periodontal indices,gllo but the patients monitored were in strictly supervisedoral homecare regimens. Valderhaug’l compared 339 crowns with subgingival marginswith unrestored controls for 10 years with similar indices and found limited differences between crowned teeth and controls relative to PI and PD, but found an elevated GI in crownswith subgingival margins.Lang et all2 evaluated the bacterial flora associatedwith onlays having 1 mm overhangs compared with onlays with clinically “ideal” margins. They discovered that the castings with overhangsprecipitated the immediate colonization of the subgingival area with microflora resemblingchronic periodontal disease.The “ideal” castingsharbored only bacteria that are found in healthy gingival crevices. Although the controversy remainsasto whether subgingival casting margins adversely affect periodontal health, in vivo measurementof the effects of poor marginal adaptation on periodontal health has not been investigated. This investigation determined whether the relationship between casting margin adaptation and periodontal tissue health could be demonstrated quantitatively.

MATERIAL Research sponsored by NIH/NIDR grant No. RR05333. *Assistant Professo:r, Department of Prosthodontics. “Associate Professor, Department of Operative Dentistry. **‘Research Assistant, Department of Prosthodontics.

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Patients 39 to ‘71years of agewere selectedfor a clinical project to participate in this retrospective study, according to the following criteria: (1) the artificial crowns or FPDs were made at the University of North Carolina School of

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(b)

Fig. 3. Method of determining casting margin adaptation with No. 17 explorer. a, Explorer tip is held perpendicular to long axis of crown when moving apically. b, Explorer tip is held at I°ree angle to crown long axis when moving occlusally. Fig. 1. Facial subgingival margins duplicated with replica impression technique. Enlargement depicts SEM perspective of casting/preparation interface.

Fig. 2. U.N.C. PCP No. 15 periodontal brated markings in 1 mm increments.

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probe with cali-

Dentistry, (2) the restorations were in service for a minimum of 4 years, and (3) the margins were located in the subgingival crevice. The patients (29) yielded a total of 42 restored teeth that involved 34 single crowns and eight FPDs, 25 type III gold alloy, and 17 PFM restorations, and a range in the restorations’ service of 4 to 18.5 years with a mean of 8.6 years. A review of patient records indicated that all of the restored teeth had chamfered margins. Replica impressions of the facial margins of each tooth were made with a low-viscosity vinyl polysiloxane impression material (Mirror 3 Extrude, Kerr Dental Products, Romulus, Mich.). The facial gingival crevice was dried with compressed air, a plastic instrument (FP 1, Hu-Friedy, Chicago, Ill.) was inserted into the crevice, and the tissue was retracted facially from the crown margin. The impression material was injected into the facial crevice, allowed to polymerize for 6 minutes, removed, washed with water, dried, labeled with the patient identification number, and poured with improved stone (Prima Rock, Whip Mix Corp., Louisville, KY.). The stone dies were recovered and sputter-coated with Au Pd for SEM observations (Fig. 1). Periodontal and restorative indices were recorded for each tooth. The periodontal indices included gingival index’s (GI) and crevicular fluid volumei4* l5 (CFV) (Table I). Facial pocket depths (PD) were measured with the U.N.C. PCP No. 15 periodontal probe (Hu-Friedy) calibrated in 1 mm increments (Fig. 2), and were read repeatedly to 0.5 mm. Crevicular fluid volume was measured with the Periotron 6000 (Harco Medical Electronic Devices, Inc., Irvine, Calif.) instrument with small filter papers. Each filter paper wasplaced in the midfacial gingival crevice, removed, and inserted in the Periotron instrument according to the manufacturer’s directions. The facial marginal adaptation was determined with a

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Fig. 4. SEM micrograph demonstrates measuring technique for determining crown to{3th mare$n discrepancies. Note 10 equally spaced locations for measuring discrepancies. C, crow m: T, tooth; A4 (arrow), crown margin; P (arrow?), prepared tooth margin.

-.-

tble I. Fe& d’ontal indices Gingival

Normal gingiva Mild inflammation with slight change in color and slight edema. No bleeding on probing Moderate inflammation with redness and edema glazing. Bleeding on probing present Severe inflammation with marked redness, edema, and ulceration. Spontaneous bleeding

1

2

3

4

Table

Crevicular

index r,GI)

II.

fiuid volume (CFV) (measured

in microliterslmin)

00-20 20-40

Normal gingiva Mild inflammation with slight change in color and slight edema

40-80

Hyperemia, edema, and hyperplasia of tissues

80f

Marked hyperemia, edema, and hyperplasia, with a tendency toward spontaneous bleeding

Criteria for evaluating crown margins Deaeription

Score

Ideal/closed margin (No discrepancy detected at tooth/restoration interface.) Margin underextended/closed (Margin of prepared tooth can be deteded apical to crown margin, but explorer tip cannot be interposed between casting and tooth.) Margin underextended/open (Margin of prepared tooth can be detected apical to crown margin, and explorer tip can be interposed between casting and tooth.) Margin overextended/closed (Margin of prepared tooth cannot be detected apical to crown margin, but explorer tip catches on thick crown margin when moved oeclusally; however, explorer cannot be interposed between casting and tooth.) Margin overextended/open (Margin of prepared tooth cannot be detected apical to crown margin; explorer tip catches on thick crown margin when moved occlusally; and margin can be interposed between casting and tooth.)

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ET AL.

Distribution of material for criteria

Variable

Data

/ Numberof crowns: Marginaldiscrepancy mJ3 Gingivelindex (GI) Crevicukufluid volume (‘XV) Facial pocket depth (PO Margin adaptation 0-l

I

0

0.05

1 0.1

I 0.15

Marginal

1 0.2

I 0.25

Discrepancy

I 0.3

I 0.35

I 0.4

I 0.45

(millimeters)

Fig. 5. Periodontal responseto casting margin discrepanciesas it relates to gingival index (GI).

1001

.

/

Length of crown service Crown material Abutment type

. .

Patient age

0' b

l e 0.65 0.1 I

0.15 I

Marginal

0.2I

0.25 I

Discrepancy

0.3 I

0.35 I

0.4I

0.45 I

(millimeters)

Fig. 6. Periodontal responseto casting margin discrepanciesas it relates to crevicular fluid volume (CFV).

sharp explorer (No. 17, Hu-Freidy) placed on the crown 1 mm above the gingival crest, moved apically onto the submarginal unprepared tooth, and then moved occlusally from the tooth onto the crown. The tip of the explorer was held perpendicular to the long axis of the crown when moving from crown to tooth, and angled occlusally at a 45 degreeangle when moving from tooth onto the crown (Fig. 3). This ensured the detection of minute discrepanciesin tooth/crown marginal adaptation. The criteria for describing the marginal adaptation are outlined in Table II. The prepared dies were photographed in the scanning electron microscope (SEM) (ETEC Autoscan, Hayward, Calif.) at X40 and eachphotomicrograph wasusedto measuremarginal descrepanciesat the tooth/restoration interface. Ten measurementswere recorded at equally spaced locations on each micrograph with a millimeter caliper to the nearest 0.5 mm and averaged for each specimen(Fig.

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N = 42 0.16 k 0.13 mm 2.0 + 0.8 49.8 f 31.1 ul/min 2.4 k 0.9mm 28 Crowns judged as ideal/closed; 9 as underextended/closed; 2 as underextendedlopen; 0 as overextended/open; 3 as overextended/closed Range: 4 - 18.5 years, mean: 8.6 years Gold: N = 25; PFM: N = 17 Single crowns: N = 34 Fixed partial denture abutments: N-8 Range: 39 to 71 years; mean: 56.8 years

4). Thesemarginal discrepancies(MD) were reported with the data from the clinical examinations for statistical analysis. A Pearson correlation, followed by Bonferroni adjusted probability tests were calculated with the Systat statistical analysis program (Systat, Inc., Evanston, Ill.) using a significancelevel of p < 0.01.

RESULTS The characteristics of the entire restoration data are summarizedin Table III and the relationship of each pair of variables is summarizedin Table IV by the correlation coefficients. The results indicated a highly significant correlation between GI and MD (Pearsoncorrelation 0.926, Bonferroni adjusted probability p < O.OOl),and also between CFV and MD (Pearsoncorrelation 0.933,Bonferroni adjusted probability p < 0.001). These relationships are graphically presented in Figs. 5 and 6. No significant correlation was found between MD and PD measurements. The type of restorative material (gold versusPFM) and/ or the ageof the restoration had no influence on the periodontal response.Of interest, there was minimal correlation between the perceived marginal adaptation with the explorer and the actual measuredMD determined by the SEM. The marginal discrepanciesfor all restorations varied from 5 to 430 I.trn (mean 160 pm). Typical marginal discrepanciesare depicted in Figs. 7 and 8. The marginal adaptation in Fig. 7 wasclinically “ideal,” without gingival

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I?ig. 7. Acceptable crown/tooth discrepancies. A, Marginal adaptation was “ideal/closed” and GI and CFV revealed healthy periodontium. B, Marginal adaptation was ideal/closed but GI and CFV revealed mild inflammation. C, Crown; T, tooth; M (arrow), crown margin; P (arrow), prepared tooth margin.

inflammation. The marginal adaptation for those restorations in Fig. 8 were clinically either “underextended/ closed” (Fig. 8, A) or “overextended/closed” (Fig. 8, B). The GI and CFV revealed substantial periodontal inflammation with bleeding during probing. The marginal discrepanciesof these restorations varied from 250 to 430 Mm.

DISCUSSION The adaptation.of castrestorations to the prepared tooth hasbeencapriciously defined as“the fit” of the restoration, although a precisedefinition is lacking. Investigators have

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describedcasting fit by mean marginal openingsbetween the prepared tooth and casting margins,16by the adaptation at multiple points insidethe castings,17by the vertical seatingof the castingson the prepared tooth or die,18p lg or by the distance from the cavosurfaceangleof the preparation to the margin of the casting.20For this investigation, the marginal discrepancy wasmeasuredfrom the apparent margin of the casting to the apparent margin of the prepared tooth. Several conditions are possibleto describe the adaptation of the prosthesesat the tooth/restoration interface

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Fig. 8. Unacceptable crown/tooth discrepancies. A, Marginal adaptation “underextendedlclosed” and GI and CFV revealed moderate inflammation. B, Marginal adaptation was “overextended/closed” and GI and CFV revealed severe inflammation with bleeding. C, Crown; T, tooth; M (arrow), crown margin; P (arrow), prepared tooth margin.

(Fig. 9). Ideally, there are no marginal descrepancies betweenthe tooth and restoration, and the emergenceprofile of the restoration is coincident with the submarginal surfacesof the prepared tooth. Open marginal configurations (Fig. 9, C and E) encouragemicroleakageof bacteria and their by-products during dissolution of the luting cement. This can causesevereeffects on the health of pulpal tissues.21l 22 An overextended restoration can retain periodontal pathogens.i2The underextended/closed restoration margin with the chamfered margin designusedin this investigation can potentially affect periodontal health in two

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ways. The underextendedlclosed margin results in an emergenceprofile that is inconsistent with natural submarginal tooth anatomy. The V-shaped casting/margin discrepancytends to harbor periodontal pathogensand restricts adequate plaque removal apical to the “ledge” resulting from short margins. The exposedprepared tooth structure between the restoration margin and prepared tooth margin is commonly a rough surface,especiallyif prepared with diamonds.Rough surfacesare difficult to clean subgingivally and the periodontium tends to remain chronically inflammed and is susceptible to long-term periodontal breakdown. Whether the

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POSSISLE CROWN MARGINITOQTH REl.ATlONStlIPS FOLLOWING CASilNG CMIlENTATlON

Y

ONLY TYPES A AND I ARE CONSIDERED

CLINICALLY

ACCEPTABLE

I

a: Ideal/ Closed

b: Underextendedl Closed

d: Overextended/ Closed

c: Underextendedl Open

e: Overextended/ Open

9. Crown margin/tooth relationships: (a) Ideal/closed; (b) underextendedklosed; (c) Imderextendedfopen; (d) overextended/closed; (e) overextended/open.

Fig.

Table

IV.

Correlation coefficients

Teat condition Gingival

Margin discrepancy index

GI

0.926 (

Effect of in vivo crown margin discrepancies on periodontal health.

Numerous reports have suggested a relationship between marginal adaptation of dental castings and periodontal tissue health, and this study examined t...
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