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The Effects of Resin-Bonded and Conventional Fixed Partial Dentures on the Periodontium: Restoration Type Evaluated
RESEARCH
REPORTS
The purpose of this study was to compare the long-term and short-term periodontal response to three different modalities of fixed prosthodontic tooth replacement. Posterior proximal sites adjacent to abutment teeth supporting etched metal and two designs o f conventional fixed partial dentures (FPDs) were assessed 6 months to 5 years after insertion. For the long-term observation, the etched metal resin-bonded FPDs had significantly greater plaque scores than both o f the conventional designs. The resin-bonded FPD group had statistically, but not clinically, significant increased prob ing depths than the supragingival FPD group. In spite o f the increased levels o f supragingival plaque associated with the etched metal FPD, this type of fixed prosthesis was no more injurious to the periodontium than the subgingival conventional FPD designs.
The effects of resin-bonded and conventional fixed partial dentures on the periodontium: restoration type evaluated
M artin A. F reilich, DDS; C hristine E. N iekrash, D M D , MDS; R alph V. Katz, D M D, P hD ; Richard J. S im on sen , DDS, MS
reparing abutm ent teeth for a fixed partial den tu re (FPD) requires sub sta n tia l to o th re d u c tio n to allow a d e q u a te space fo r the v en e er o r m etal substructure (or both) o f the retainer.11 In addition to the considerable loss of tooth s tr u c tu r e , th e p r o c e d u re s r e q u ir e d to m ake “co n v entional” cast FPDs are often associated with undesirable pulpal” and p eriodontal89 changes. T h e p ro b lem s resulting from th e con struction o f conventional FPDs have lead to th e search for alternative m ethods o f fixed to o th replacem ent. T hese m ethods allow fo r m inim al to o th re d u c tio n and p o te n tia lly d e c re a s e d p u lp a l a n d p e r i odontal hazards. Some o f the m ost popu la r m e th o d s h av e b e c o m e p o ssib le th ro u g h the bonding o f a prosthesis to the to o th en am el with th e use o f com posite resin as d e sc rib e d by R o c h e tte ,10 Howe an d Denehy," Sim onsen ,12 Livaditis,13 and T hom pson and Livaditis.14 T h e e tc h e d m e ta l, r e s in - b o n d e d
P
(M aryland) FPD as described by Livaditis and T hom pson« has becom e particularly p o p u la r as e v id e n c e d by its f r e q u e n t appearance in p red o cto ral d en tal cu rric ula and textbooks,15-'7 and as a continuing education course topic. A survey o f m em bers o f the Academy of General Dentistry in Pennsylvania an d S o u th ern C alifornia found that m ore th an 50% o f those who responded used this particular m ethod of tooth replacem en t in th eir practices.18 In addition, a study in 1982 o f general practi tio n e rs in a New E n g lan d m e tro p o lita n a r e a f o u n d th a t e tc h e d m e ta l, re sin bonded FPDs constituted 20% o f all FPDs in 20- to 29 year-old patients an d 13% of all FPDs in patients aged 70 and older.19 C u r r e n tly , se v e ra l a u t h o r s 2o-22 h av e described the d islodgem ent rates, caries, and framework failure associated with the etched metal, resin-bonded FPD in differ en t populations, b u t little inform ation has been published regarding the periodontal conditions adjacent to these restorations.
C reu g ers23 o b serv ed th a t o v erc o n to u re d ( s u p ra g in g iv a lly lo c a te d ) r e ta in e r s resulted from the usual m inim al ab utm ent tooth preparation m ade for etched m etal resin-bonded FPDs. This overcontour was associated with in creased p laq u e scores. However, increased b leed in g scores were n o t o b serv ed w hen th e a d ja c e n t tissues w ere ev a lu ated afte r 10-day o b se rv a tio n intervals. To date, the long-term periodon tal re sp o n se to th e e tc h e d m etal resin b onded FPD has n o t been rep o rted in the literature. T h e two m ajo r p u rp o ses o f this study are: to com pare, retrospectively, the long term periodontal response to three differ e n t m o d a litie s o f fix e d p r o s th o d o n tic to o th re p la c e m e n t (co n v e n tio n a l FPDs with supragingival m argin placem ent, con v en tio n al FPDs with subgingival m argin p la c e m e n t, a n d e tc h e d m e ta l, re s in b o n d e d FPDs with supragingival m argin p la c e m e n t); a n d to c o m p a re , p ro sp ec tively, the short-term periodontal response JADA, Vol. 121, A ugust 1990 ■ 265
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R E P O R T S
associated with each o f these three m eth ods o f fixed prosthodontic tooth replace m ent. M a te ria ls and methods
Prospective com ponent (short-term)
Retrospective com ponent (long-term)
Selection o f subjects
A total of 87 healthy adult subjects (aged 25 to 70 years) were selected for participa tio n in th is study fro m a g ro u p o f 113 p a t ie n t s w ho h a d re c e iv e d e i th e r an etched metal, resin-bonded FPD, or a con v e n tio n a l FPD in th e p r e d o c to r a l p ro sth o d o n tic clinic at the University of C o n n e cticu t School o f D ental M edicine between 1982 an d 1986. T h e follow ing eligibility crite ria were ap p lied to the 113 potential subjects: an FPD rep lacin g p o sterio r teeth h ad been in se rted 6 m o n th s to 5 years before the proposed time of data collection; a hom ol ogous contralateral control tooth was pres e n t with no proxim al restoration; plaque and gingival index scores o f < 1 and prob ing d epths o f < 4 mm at the potential abut m ent and control sites existed before the initiation o f the tooth replacem ent proce dures; and the subject was in good health and locally available to participate in the study. O f the 36 ad u lt p atien ts who m et these criteria after review o f the p atien t records, 72% (N = 26) en tered and com pleted the study. After the final selection o f subjects who had resin-bonded FPDs (cases), subjects tre a te d w ith “c o n v e n tio n a l” FPDs (c o n trols) were selected. Each control subject possessing a conventional FPD that m et th e criteria was fu rth e r categorized into supragingival or subgingival m argin con tro l g ro u p s. T h e se two c o n tro l g ro u p s w ere ag e a n d g e n d e r m a tc h e d to th e etched metal, resin-bonded group. T h e s e s u b je c t s e le c tio n p r o c e d u re s resulted in the creation o f th ree distinct subject groups. G roup 1 consisted o f 22 individuals who had received conventional FPDs with supragingival margins. G roup 2 was com posed o f 39 subjects with conven tional FPDs with subgingival margins and g ro u p 3 in c lu d e d 26 su b je cts who h ad received etched metal, resin-bonded FPDs with supragingival margins.
Data collection Two paired eligible proxim al sites, one for the posterior abutm ent teeth and one for th e c o n t r a la t e r a l c o n tr o l to o th , w ere selected for each subject before the collec tio n o f any in trao ral data. T h e data col lected to determ ine the periodontal status 266 ■ JADA, Vol. 121, A ugust 1990
Group 1 C onventional FPD w ith supragingival m argin (N = 22)
First examination data GI PI P ro b in g depth BUP Prosthesis evaluation
Group 2 C onventional FPD w ith subgingival m arg in (N = 39)
Scaling and oral hygiene instruction
Group 3 Resin-bonded FPD w ith supragingival m argin (N = 26) Mean tim e = 32.3 + /13.8 m onths
— ->■
------
Second examination data GI PI P ro b in g depth BUP Prosthesis evaluation
____^
Mean tim e = 17.5 + /5.8 days
Fig 1 ■ Flow chart of study design.
o f these sites included th e Plaque Index ( P I I ) o f Silness a n d I.o e ,24 th e Gingival Index (GI) o f Loe and Silness,25 p ro b in g d e p th , an d p re se n c e o f b le e d in g u p o n probing (BUR) to the base o f the sulcus within 30 seconds. T he pro b in g dep th of the sulcus and bleeding on p ro b in g were determ ined using an electronic, pressuresensitive p ro b e (V ine Valley R esearch ) w ith a 0 .5 4 m m d ia m e te r p r o b e tip , Williams markings, and a constant force o f 25 gm. For the latter two assessments, the probe tip was vertically positioned parallel to the buccolingual axis, slightly inclined toward the tooth surface in a location adja cent to the proxim al contact o r FPD con nector. T he P1I and GI assessments were m ade at this same location. All m easure m ents w ere m ade by o n e ex a m in e r who had been calibrated before data collection to attain an acceptable intraexam iner vari ation using subjects with sim ilar resto ra tions an d a sim ilar ex ten t o f p erio d o n tal disease.27 T he initial follow-up exam ination (first exam ination) provided the final outcom e data for the long-term, retrospective study com ponent (Fig 1). After the first exami
nation, each subject received a thorough periodontal scaling, a ru b b er cup prophy laxis, an d a d etailed set o f oral hygiene in s t r u c tio n s fro m o n e o f two tr a in e d d en tal hygienists. After 2 to 3 weeks, all subjects received a second ex am ination, which provided the outcom e data for the short-term , prospective study com ponent.
Data analysis T he two prim ary data analyses consisted of a com parison of p erio d o n tal disease o ut com es betw een the th ree FPD treatm en t modalities: o ne co m p arin g the longterm periodontal outcom e in the retrospective study com p o n en t and one com paring the sh o rt-te rm p e rio d o n ta l o u tc o m e in the prospective study com ponent. The p attern of p erio d o n tal status d ata o b tain ed from th e h o m o lo g o u s, c o n tra la te ra l c o n tro l teeth was used in the final analysis to pro vide in sig h t in to w hether, fo r any given positive finding, th e effect was a p atien t effect (that is, similar changes oil the abut m e n t a n d h o m o lo g o u s , c o n tr a la te r a l te e th ) o r a tr e a t m e n t e f f e c t ( th a t is, noticeable change on the abutm ent teeth
R E S E A R C H
but n ot on the hom ologous, contralateral teeth). All data collected w ere re c o rd e d on a com puter-ready data collection form , key punched an d verified, and analyzed using statistical package fo r th e social sciences (SPSS) on a m ainfram e com puter. A /-test o f in d ep en d en t m eans and a one-way anal ysis o f variance (ANOVA) were perform ed on th e p ro b in g d e p th m easu rem en ts. A Chi-square analysis was perform ed on the n o n p a ra m e tric v a ria b le s (P1I, GI, an d bleeding on probing).
Results T he m ean subject ages were 45 ± 10 years, 4 6 + 1 4 years, and 45 ± 15 years for treat m e n t g ro u p s 1, 2, a n d 3, respectively. Table 1 shows the distribution o f P1I and 1 GI sco res at b o th e x a m in a tio n s fo r all three treatm ent groups. Similarly, Table 2 shows th e fre q u e n c y o f b le e d in g u p o n p ro b in g an d the p ro b in g d ep th reassess m en t at b oth exam inations for the three treatm ent groups. T he statistically significant findings (P < 0.05) observed in these data for the long te rm , re tro s p e c tiv e c o m p o n e n t o f th e study (based on the d ata from both exami n a tio n s ) a r e s u m m a r iz e d in T a b le 3. C o m p a riso n b e tw e e n th e FPD g ro u p s show ed th a t g ro u p 3 (th e resin-bonded FPD g r o u p ) h a d s ig n ific a n tly g r e a te r plaq u e scores th a n g ro u p l( th e conven tional FPD group with supragingival mar gins); g ro u p 1 h ad significantly g re a te r plaque scores than g ro u p 2 (the conven tio n al FPD g ro u p w ith subgingival m ar gins). In ad d itio n , b o th g ro u p s 2 a n d 3 h ad g re a te r m ean p ro b in g d e p th s than group 1 (P < 0.01). F u rth e r analysis com p arin g th e a b u tm e n t sites with th e con tr a l a te r a l c o n t r o l site s w ith in ea ch tre a tm e n t g ro u p show ed th a t th e ab u t m en t sites had significantly greater plaque scores than the control sites for gro u p 3 (P < 0 .0 1 ). S tatistically sig n ific a n t fin d in g s were observed between the treatm ent groups in the short-term , prospective com ponent of th is stu d y (T able 3 ). S tatistic al te stin g revealed significantly g reater plaque scores for group 3 than group 2 (P < 0.05). Two a d d itio n a l o b s e rv a tio n s w ere of clinical interest. First, although no differ ences in GI scores were observed between the three FPD treatm ent groups in either the long- o r short-term study com ponents, b o th ex a m in a tio n s show ed significantly h ig h e r GI scores fo r th e a b u tm e n t sites than control sites (P < 0.01) for groups 2 and 3. Second, although there were no sta
R E P O R T S
Table 1 ■Frequencies of plaque and gingival indexes for FPD abutment sites for long- and short-term examinations. Short-term d istrib u tio n (%)
Long-term d istrib u tio n (%)
G ro u p 0
1
2+3
0
I
2+3
9 28 15
73 64 46
18* 8 39f
32 55 27
46 34 42
23 11 31Ì
59 39 35
41 62 65
0 0 0
68 37 50
32 63 50
0 0 0
PII
1 2 3 GI
1 2 3
* Statistically different than group 2 at P <0.05. t Statistically different than groups 1 and 2 at P X Statistically different than group 2 at P <0.05.
<0.05.
Table 2 ■B leeding on probing frequ en cy and probing depth m easurem ent (millimeters) for FPD abutment sites for long- and short-term examinations. G ro u p
Long-term % BUP*
Short-term % BUP*
14 39 39
23 24 39
Bleeding o n p ro b in g 1 2 3 P ro b in g d ep th 1 2 3
X
(± sd)
X
1.86 2.41f 2.38+
(± 0 .5 6 ) (± 0 .5 5 ) ( ± 0.64)
2.00 2.29 2.27
+
± sd ( ± 0.54) ( ± 0.80) (± 0.53)
* BUP = Bleeding on probing, t Statistically significant from group 1 at P < 0.01.
Table 3 ■ Summary of statistically significant periodontal findings across treatment groups. PII
GI
G ro u p 3 > G ro u p 1 > G ro u p 2
...
G ro u p 3 > G ro u p 2
. ..
C om parison Long-term findings (retrospective co m ponent) Short-term findings (prospective co m ponent)
BUP*
P ro b in g dep th G ro u p 2 > G ro u p I G ro u p 3 > G ro u p 1
* BUP = bleeding on probing.
tistically significant differences for bleed in g on p r o b in g f re q u e n c y o b s e rv e d between the three FPD treatm en t groups in either the long-or short-term study com ponents, the observed difference between tre a tm e n t groups reg ard in g b leed in g on probing was o f clinical interest because of the threefold m agnitude o f the observed difference (Table 2). Discussion T he prim ary objective o f this study was to
exam ine the effects of three different FPD d e s ig n s o n th e p e r io d o n t iu m . It was observed th at the FPD design affected the plaque scores recorded. T he etched metal, resin -b o n d ed FPDs w ere associated with significantly g re a te r p la q u e scores th an both o f the conventional designs as well as th eir own co n tro l sites for th e long-term observation. Also, the etched metal, resinb o n d ed FPDs showed significantly greater plaque scores than the subgingival conven tional FPD design o f the short-term obser v a tio n . T h e s e two g ro u p s , th e e tc h e d
Freilich-O thers: Effects o f fixed p artial den tu res on periodontium ■ 267
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REPORTS
metal, resin-bonded FPD group, and the subgingival conventional FPD group, were found to have significantly greater mean probing depths at the long-term observa tion period and statistically significantly greater GI scores than their own controls at both long- and short -term observations. In regard to the probing depth findings, it should be noted that although the mean p ro b in g d ep th s for the etc h e d m etal, resin-bonded FPD group and subgingival conventional FPD group were statistically greater than the supragingival conven tional FPD group (2.41 mm and 2.34 mm versus 1.86 m m ), this d iffe r e n c e was ju d g ed to be clinically in sign ifican t in regard to p eriod on tal atachm ent level implication. The differences observed are likely to be m ore closely related to the increased penetrability o f the sulcus at th e se sites w h en p ro b ed b eca u se o f in creased in flam m ation at these sites. Coincidentally, these same two FPD design groups also showed a threefold (but statis tically significant, P = 0.09) greater per cen ta g e o f b lee d in g on p rob ing (39% versus 14%) w hen com p ared with the supragingival conventional FPD group at the long-term observation. Bleeding on probing is considered a reliable indicator o f inflammation o f the connective tissue adjacent to and at the base o f the sulcus. 28,29The lack o f a statistically significant dif ference for bleeding on probing may be a result o f a lack o f power to detect statisti cal differences resulting from the number o f subjects available to the investigators for this study. In this study th e resin -b on d ed FPD group had increased supragingival plaque scores, w hereas p reviou s stu d ies have reported in creased subgingival plaque associated with subgingival restoration margins found in subgingival conventional FPDs.8'9-30-31 When these two pieces o f evi dence are combined, it can be concluded that each design has the potential for simi lar effect on the periodontium. Therefore, in spite o f the increased levels of supragin gival p la q u e, th e e tc h e d m etal, resinbonded FPD was no more injurious to the periodontium than the subgingival con ven tio n al FPD d esign , w hich probably remains the standard fixed tooth replace ment (prosthodontic) modality in clinical practice today. However, they both had a less desirable effect on the periodontium than the supragingival conventional FPD design. Whereas the etched metal, resin-bonded FPD appears to have becom e a valuable asset in the fixed prosthodontic armamen tarium o f the restorative dentist, the obser
268 ■JADA, Vol. 121, August 1990
vations m ade in this study support the findings o f Creugers and others 23 who reported higher plaque scores associated with these bulkier restorations. Although no greater injury was seen at the sites adja cen t to these restorations as com pared with the subgingival con ven tional FPD group, the long- and short-term observa tions made in this study found that these restorations appear to be associated with greater periodontal inflam m ation when compared with conventional supragingival FPDs and the unrestored control teeth. In light of this finding, with minor mod ification to the etched metal, resin-bonded FPD technique, it should be possible for a supragingival fixed partial denture to be associated with optim um tissue health resulting from less retainer bulk and lower supragingival plaque levels. It is suggested that this may be achieved for the etched m etal, resin -b on ded FPD by providing greater axial depth o f tooth preparation in enamel to allow for the adequate thickness o f a structurally durable m etal retainer while elim inating excess bulk. Although no data currently exist to directly support this last premise, the data from this study combined with the findings from a related study, 23 suggest that it may be prudent to make tooth preparations for the etched metal, resin-bonded FPD retainer in such a way as to facilitate the removal o f plaque and minimize inflammation to the adja cent periodontium . The authors suggest that appropriate clinical studies designed to provide data pertaining to this issue be done. Conclusions This cohort study compares the long - and short-term periodontal response to three different modalities o f fixed prosthodontic tooth replacem ent. O ne restored (test) and one nonrestored (control) posterior proximal site o f the same tooth type were com pared in 87 subjects, each o f whom had a fix ed partial d en tu re p la ced , 6 months to 5 years before initial data col lection . For th e lo n g -term o b ser v a tio n , the etched metal, resin-bonded FPDs had sig nificantly greater plaque scores than both o f the conventional designs as well as its own control sites. This resin-bonded FPD group and the subgingival conventional FPD group had statistically, but not clini cally, significant increased probing depths than the supragingival FPD group. These same two groups also had significantly greater GI scores than their own control sites at both long-and short-term observa
tions. Therefore the long-and short-term observations made in this study found that the resin-bonded FPDs and the subgingival conventional FPDs were associated with greater periodontal inflam m ation when compared with supragingival conventional FPDs and the unrestored teeth. Moreover, in spite o f the increased levels o f supragin gival p la q u e, th e e tc h e d m etal, resinbonded FPD was no more injurious to the periodontium than the subgingival con ventional FPD design. ---------------------- J !iO A -----------------------
T h e in fo rm e d c o n se n t o f all h u m a n subjects w ho p a r t i c i p a t e d in th e e x p e r im e n ta l in v e s tig a tio n s re p o rte d o r described in this m anuscript was obtained after the n a tu re o f the procedure a n d possible discom forts and risks had b e en fully explained. Each subject received a small m onetary reim bursem ent to com pen sate them for th eir p articipadon time. T h e a u th o rs th a n k Mr. M ichael G ra z ian o fo r his assistance with the im plem entation o f this study. T h is s tu d y was s u p p o r te d by th e U n iv e rs ity o f C onn ecticu t R esearch Foundation G ra n t no. 11722220212-4-00664. Dr. Freilich is assistant professor o f prosthodontics, Dr. N iekrash is assistant professor o f periodontology, a n d Dr. Katz is a sso c ia te p ro f e s s o r o f B e h a v io ra l S c ie n c e s a n d C o m m u n ity H e a lt h , U n iv e rs ity o f C onnecticut, School o f D ental M edicine. Dr. Sim onsen is p ro fessio n al service m a n a g er, U n ite d S tates a n d In te rn a tio n a l D en tal P ro d u cts D ivision, 3M H e a lth C a r e . A d d re s s r e p r i n t re q u e s ts to D r. F r e il ic h , University o f C onnecticut, School o f D ental M edicine, Farm ington, CT 06032.
1. Preston JD , R ational approach to to o th p re p a ra tio n fo r ceram o m etal resto ratio n s. D e n t Clin N o rth Am 1977;21:683. 2. M cL ean JW. V olum e 2: th e scie n c e a n d a rt o f dental ceram ics. Chicago: Q uintessence; 1979> 3. Donovan T. Prince J. An analysis o f m argin con figurations for m etal-ceram ic crowns. J P rosthet D ent 1985;153-9. 4. R o s e n s tie l SF, L a n d MF, F u jim o to J . C ontem porary fixed prosthodontics. St. Louis: Mosby; 1988;135-9. 5. I.an g e la n d K, L a n geland LK. P u lp re a ctio n s to crown preparation, im pression, tem porary crow n fixa tio n , a n d p e rm a n e n t c e m e n ta tio n . J P r o s th e t D en t 1965;15:129. 6. C ollett H . Protection o f the d e n ta l pu lp in con struction of fixed partial d e n tu re prosthesis. J Prosthet D ent 1974;31:637. 7. M orrant GA. D ental in strum entation an d pulpal injury. P art II. Clinical considerations. I Br E ndod Soc 1977;10:55. 8. S iln ess J . P e rio d o n ta l c o n d itio n s in p a tie n ts treated with dental bridges. P a rt II. T h e influence of full and partial crowns on plaque accum ulation, devel o p m e n t o f gingivitis and pocket form ation. I P erio d o n t Res 1970;5:219. 9. V alderhaug J . Periodontal conditions in patients five years following insertion o f fixed partial dentures. J O ral R ehabil 1976;3:237. 10. R ochette A. A ttachm ent o f a splint to enam el of
RESEARCH lower a n te rio r teeth . J Prosthet D en t 1973;30:418-23. 11. Howe DF, D enehy GE. A n terio r fixed partial d en tu re utilizing the acid-€tch te ch n iq u e an d a cast metal framework. J Prosth et D en t 1977;37:28-31 . 12. Sim onsen iy . T h e acid etc h te ch n iq u e in fixed prosthesis: an upd ate. Q uintessence In t 1980;9:33-40. 13. Livaditis GJ. C ast m etal resin -b o n d ed retain ers fo r posterior teeth . JADA 1980;101:926-9. 14. T hom pson VP, Livaditis GJ. E tched casting acid e tc h c o m p o site b o n d e d p o s te r io r b rid g e s. P e d ia tr D ent 1982;4:38-43. 15. S im onsen R, T h o m p so n V, B arrack G. E tch ed cast restorations: clinical a n d la b o ra to ry techniques. Chicago: Q uintessence; 1983. 16. R o s e n s tie l SF, L a n d MF, F u jim o to J . C o n te m p o r a r y f ix e d p r o s t h o d o n t i c s , St. L o u is: Mosby;1988:426-32. 17. D y k e m a RW, G o o d a c r e C J, P h illip s RW. J o h n s to n ’s m o d e rn p ractice in fixed p rosthodontics. Philadelphia: Saunders; 1986:42-9. 18. Landesm an HM, Z im m erm an JL , Bilan JP, Clark MA. How dentists learn ed a b o u t resin-bonded p rosthe sis. J P rosthet D e n t 1986;56:493.
19. G u sta v s e n F, K atz RV. D is tr ib u tio n o f a cid e tc h e d , fix e d a n d re m o v a b le p ro s th e se s in d e n ta l patients. J Pro sth et D ent 1987;57:374-9. 20. Livaditis GJ. R esin-bonded cast restorations: clini cal study. I n tJ P eriodontics Restorative D ent 1981;1:709. 21. C reugers NHJ, van’t H o f MA, V rijhoet MMA. A clinical com parison o f th re e types o f resin-retained cast m etal prosthesis. J Prosthet D ent 1986;56:297-300. 22. Priest GF, D onatelli HA. A four-year clinical eval u a tio n o f re s in - b o n d e d fix e d p a r tia l d e n tu r e s . J Prosthet D en t 1988;59:542-6. 23. C r e u g e r s N H J, S n o e k PA, V og els ALM . O v e rc o n to u rin g in re sin -b o n d e d prosth esis: pla q u e a c c u m u la tio n a n d gingival h e a lth . J P r o s th e t D e n t 988;59: 17-21 . 24. Silness J , L oe H . P e rio d o n ta l disease in p re g nancy. II. C o rrelatio n betw een oral hygiene an d peri od o n tal condition. Acta O d o ntol Scand 1964;22:121 . 25. Loe H , Silness J . P e rio d o n ta l disease in p re g nancy. I. prevalence a n d severity. Acta O d ontol Scand 1963;21:533. 26. Poison RAM, C aton JC , Yeaple RN, Z ander HA.
REPORTS
H istological d e te rm in a tio n o f p ro b e tip p e n e tra tio n in to gingival sulcus o f h u m a n s u sin g a n e le c tro n ic p r e s s u r e - s e n s itiv e p r o b e . J C lin P e r io d o n t o l 1980;7:479-88. 27. Smith LW, Suom i JD , G reene JC , B arbanoJP . A stu d y o f in tr a - e x a m in a r v a ria tio n in s c o rin g o ra l hygiene status, gingival in flam m atio n a n d e p ith e lia l attachm ent level. J Periodontol 1970;41:67l28 . D a v e n p o r t R H , S im p s o n D M , H a ss e ll T M . H istom etric com parison o f active an d inactive lesions o f advanced periodontitis. J P eriodontol 1982;53:285. 29. C ooper PG, C aton JG , Poison AM. Cell p o pula tions associated w ith gingival bleeding. J P erio d o n to l 1983;54:497-502. 30. W aerhaug J. Presence o r absence o f p laque o n subgingival re sto ra tio n s. S cand J D e n t Res 1975;83: 193-201. 31. S altzberg DS, e t al. S c a n n in g e le c tro n m ic ro scope study o f ju n c tio n betw een restorations and gingi val cavosurface m argins. J P ro sth e t D e n t 1976;36:51 7-21 .
Freilich-Others: Effects of fixed partial dentures on periodontium ■269
REPORTS
The purpose of this study was to compare the long-term and short-term periodontal response to three different modalities of fixed prosthodontic tooth replacement. Posterior proximal sites adjacent to abutment teeth supporting etched metal and two designs o f conventional fixed partial dentures (FPDs) were assessed 6 months to 5 years after insertion. For the long-term observation, the etched metal resin-bonded FPDs had significantly greater plaque scores than both o f the conventional designs. The resin-bonded FPD group had statistically, but not clinically, significant increased prob ing depths than the supragingival FPD group. In spite o f the increased levels o f supragingival plaque associated with the etched metal FPD, this type of fixed prosthesis was no more injurious to the periodontium than the subgingival conventional FPD designs.
The effects of resin-bonded and conventional fixed partial dentures on the periodontium: restoration type evaluated
M artin A. F reilich, DDS; C hristine E. N iekrash, D M D , MDS; R alph V. Katz, D M D, P hD ; Richard J. S im on sen , DDS, MS
reparing abutm ent teeth for a fixed partial den tu re (FPD) requires sub sta n tia l to o th re d u c tio n to allow a d e q u a te space fo r the v en e er o r m etal substructure (or both) o f the retainer.11 In addition to the considerable loss of tooth s tr u c tu r e , th e p r o c e d u re s r e q u ir e d to m ake “co n v entional” cast FPDs are often associated with undesirable pulpal” and p eriodontal89 changes. T h e p ro b lem s resulting from th e con struction o f conventional FPDs have lead to th e search for alternative m ethods o f fixed to o th replacem ent. T hese m ethods allow fo r m inim al to o th re d u c tio n and p o te n tia lly d e c re a s e d p u lp a l a n d p e r i odontal hazards. Some o f the m ost popu la r m e th o d s h av e b e c o m e p o ssib le th ro u g h the bonding o f a prosthesis to the to o th en am el with th e use o f com posite resin as d e sc rib e d by R o c h e tte ,10 Howe an d Denehy," Sim onsen ,12 Livaditis,13 and T hom pson and Livaditis.14 T h e e tc h e d m e ta l, r e s in - b o n d e d
P
(M aryland) FPD as described by Livaditis and T hom pson« has becom e particularly p o p u la r as e v id e n c e d by its f r e q u e n t appearance in p red o cto ral d en tal cu rric ula and textbooks,15-'7 and as a continuing education course topic. A survey o f m em bers o f the Academy of General Dentistry in Pennsylvania an d S o u th ern C alifornia found that m ore th an 50% o f those who responded used this particular m ethod of tooth replacem en t in th eir practices.18 In addition, a study in 1982 o f general practi tio n e rs in a New E n g lan d m e tro p o lita n a r e a f o u n d th a t e tc h e d m e ta l, re sin bonded FPDs constituted 20% o f all FPDs in 20- to 29 year-old patients an d 13% of all FPDs in patients aged 70 and older.19 C u r r e n tly , se v e ra l a u t h o r s 2o-22 h av e described the d islodgem ent rates, caries, and framework failure associated with the etched metal, resin-bonded FPD in differ en t populations, b u t little inform ation has been published regarding the periodontal conditions adjacent to these restorations.
C reu g ers23 o b serv ed th a t o v erc o n to u re d ( s u p ra g in g iv a lly lo c a te d ) r e ta in e r s resulted from the usual m inim al ab utm ent tooth preparation m ade for etched m etal resin-bonded FPDs. This overcontour was associated with in creased p laq u e scores. However, increased b leed in g scores were n o t o b serv ed w hen th e a d ja c e n t tissues w ere ev a lu ated afte r 10-day o b se rv a tio n intervals. To date, the long-term periodon tal re sp o n se to th e e tc h e d m etal resin b onded FPD has n o t been rep o rted in the literature. T h e two m ajo r p u rp o ses o f this study are: to com pare, retrospectively, the long term periodontal response to three differ e n t m o d a litie s o f fix e d p r o s th o d o n tic to o th re p la c e m e n t (co n v e n tio n a l FPDs with supragingival m argin placem ent, con v en tio n al FPDs with subgingival m argin p la c e m e n t, a n d e tc h e d m e ta l, re s in b o n d e d FPDs with supragingival m argin p la c e m e n t); a n d to c o m p a re , p ro sp ec tively, the short-term periodontal response JADA, Vol. 121, A ugust 1990 ■ 265
R E S E A R C H
R E P O R T S
associated with each o f these three m eth ods o f fixed prosthodontic tooth replace m ent. M a te ria ls and methods
Prospective com ponent (short-term)
Retrospective com ponent (long-term)
Selection o f subjects
A total of 87 healthy adult subjects (aged 25 to 70 years) were selected for participa tio n in th is study fro m a g ro u p o f 113 p a t ie n t s w ho h a d re c e iv e d e i th e r an etched metal, resin-bonded FPD, or a con v e n tio n a l FPD in th e p r e d o c to r a l p ro sth o d o n tic clinic at the University of C o n n e cticu t School o f D ental M edicine between 1982 an d 1986. T h e follow ing eligibility crite ria were ap p lied to the 113 potential subjects: an FPD rep lacin g p o sterio r teeth h ad been in se rted 6 m o n th s to 5 years before the proposed time of data collection; a hom ol ogous contralateral control tooth was pres e n t with no proxim al restoration; plaque and gingival index scores o f < 1 and prob ing d epths o f < 4 mm at the potential abut m ent and control sites existed before the initiation o f the tooth replacem ent proce dures; and the subject was in good health and locally available to participate in the study. O f the 36 ad u lt p atien ts who m et these criteria after review o f the p atien t records, 72% (N = 26) en tered and com pleted the study. After the final selection o f subjects who had resin-bonded FPDs (cases), subjects tre a te d w ith “c o n v e n tio n a l” FPDs (c o n trols) were selected. Each control subject possessing a conventional FPD that m et th e criteria was fu rth e r categorized into supragingival or subgingival m argin con tro l g ro u p s. T h e se two c o n tro l g ro u p s w ere ag e a n d g e n d e r m a tc h e d to th e etched metal, resin-bonded group. T h e s e s u b je c t s e le c tio n p r o c e d u re s resulted in the creation o f th ree distinct subject groups. G roup 1 consisted o f 22 individuals who had received conventional FPDs with supragingival margins. G roup 2 was com posed o f 39 subjects with conven tional FPDs with subgingival margins and g ro u p 3 in c lu d e d 26 su b je cts who h ad received etched metal, resin-bonded FPDs with supragingival margins.
Data collection Two paired eligible proxim al sites, one for the posterior abutm ent teeth and one for th e c o n t r a la t e r a l c o n tr o l to o th , w ere selected for each subject before the collec tio n o f any in trao ral data. T h e data col lected to determ ine the periodontal status 266 ■ JADA, Vol. 121, A ugust 1990
Group 1 C onventional FPD w ith supragingival m argin (N = 22)
First examination data GI PI P ro b in g depth BUP Prosthesis evaluation
Group 2 C onventional FPD w ith subgingival m arg in (N = 39)
Scaling and oral hygiene instruction
Group 3 Resin-bonded FPD w ith supragingival m argin (N = 26) Mean tim e = 32.3 + /13.8 m onths
— ->■
------
Second examination data GI PI P ro b in g depth BUP Prosthesis evaluation
____^
Mean tim e = 17.5 + /5.8 days
Fig 1 ■ Flow chart of study design.
o f these sites included th e Plaque Index ( P I I ) o f Silness a n d I.o e ,24 th e Gingival Index (GI) o f Loe and Silness,25 p ro b in g d e p th , an d p re se n c e o f b le e d in g u p o n probing (BUR) to the base o f the sulcus within 30 seconds. T he pro b in g dep th of the sulcus and bleeding on p ro b in g were determ ined using an electronic, pressuresensitive p ro b e (V ine Valley R esearch ) w ith a 0 .5 4 m m d ia m e te r p r o b e tip , Williams markings, and a constant force o f 25 gm. For the latter two assessments, the probe tip was vertically positioned parallel to the buccolingual axis, slightly inclined toward the tooth surface in a location adja cent to the proxim al contact o r FPD con nector. T he P1I and GI assessments were m ade at this same location. All m easure m ents w ere m ade by o n e ex a m in e r who had been calibrated before data collection to attain an acceptable intraexam iner vari ation using subjects with sim ilar resto ra tions an d a sim ilar ex ten t o f p erio d o n tal disease.27 T he initial follow-up exam ination (first exam ination) provided the final outcom e data for the long-term, retrospective study com ponent (Fig 1). After the first exami
nation, each subject received a thorough periodontal scaling, a ru b b er cup prophy laxis, an d a d etailed set o f oral hygiene in s t r u c tio n s fro m o n e o f two tr a in e d d en tal hygienists. After 2 to 3 weeks, all subjects received a second ex am ination, which provided the outcom e data for the short-term , prospective study com ponent.
Data analysis T he two prim ary data analyses consisted of a com parison of p erio d o n tal disease o ut com es betw een the th ree FPD treatm en t modalities: o ne co m p arin g the longterm periodontal outcom e in the retrospective study com p o n en t and one com paring the sh o rt-te rm p e rio d o n ta l o u tc o m e in the prospective study com ponent. The p attern of p erio d o n tal status d ata o b tain ed from th e h o m o lo g o u s, c o n tra la te ra l c o n tro l teeth was used in the final analysis to pro vide in sig h t in to w hether, fo r any given positive finding, th e effect was a p atien t effect (that is, similar changes oil the abut m e n t a n d h o m o lo g o u s , c o n tr a la te r a l te e th ) o r a tr e a t m e n t e f f e c t ( th a t is, noticeable change on the abutm ent teeth
R E S E A R C H
but n ot on the hom ologous, contralateral teeth). All data collected w ere re c o rd e d on a com puter-ready data collection form , key punched an d verified, and analyzed using statistical package fo r th e social sciences (SPSS) on a m ainfram e com puter. A /-test o f in d ep en d en t m eans and a one-way anal ysis o f variance (ANOVA) were perform ed on th e p ro b in g d e p th m easu rem en ts. A Chi-square analysis was perform ed on the n o n p a ra m e tric v a ria b le s (P1I, GI, an d bleeding on probing).
Results T he m ean subject ages were 45 ± 10 years, 4 6 + 1 4 years, and 45 ± 15 years for treat m e n t g ro u p s 1, 2, a n d 3, respectively. Table 1 shows the distribution o f P1I and 1 GI sco res at b o th e x a m in a tio n s fo r all three treatm ent groups. Similarly, Table 2 shows th e fre q u e n c y o f b le e d in g u p o n p ro b in g an d the p ro b in g d ep th reassess m en t at b oth exam inations for the three treatm ent groups. T he statistically significant findings (P < 0.05) observed in these data for the long te rm , re tro s p e c tiv e c o m p o n e n t o f th e study (based on the d ata from both exami n a tio n s ) a r e s u m m a r iz e d in T a b le 3. C o m p a riso n b e tw e e n th e FPD g ro u p s show ed th a t g ro u p 3 (th e resin-bonded FPD g r o u p ) h a d s ig n ific a n tly g r e a te r plaq u e scores th a n g ro u p l( th e conven tional FPD group with supragingival mar gins); g ro u p 1 h ad significantly g re a te r plaque scores than g ro u p 2 (the conven tio n al FPD g ro u p w ith subgingival m ar gins). In ad d itio n , b o th g ro u p s 2 a n d 3 h ad g re a te r m ean p ro b in g d e p th s than group 1 (P < 0.01). F u rth e r analysis com p arin g th e a b u tm e n t sites with th e con tr a l a te r a l c o n t r o l site s w ith in ea ch tre a tm e n t g ro u p show ed th a t th e ab u t m en t sites had significantly greater plaque scores than the control sites for gro u p 3 (P < 0 .0 1 ). S tatistically sig n ific a n t fin d in g s were observed between the treatm ent groups in the short-term , prospective com ponent of th is stu d y (T able 3 ). S tatistic al te stin g revealed significantly g reater plaque scores for group 3 than group 2 (P < 0.05). Two a d d itio n a l o b s e rv a tio n s w ere of clinical interest. First, although no differ ences in GI scores were observed between the three FPD treatm ent groups in either the long- o r short-term study com ponents, b o th ex a m in a tio n s show ed significantly h ig h e r GI scores fo r th e a b u tm e n t sites than control sites (P < 0.01) for groups 2 and 3. Second, although there were no sta
R E P O R T S
Table 1 ■Frequencies of plaque and gingival indexes for FPD abutment sites for long- and short-term examinations. Short-term d istrib u tio n (%)
Long-term d istrib u tio n (%)
G ro u p 0
1
2+3
0
I
2+3
9 28 15
73 64 46
18* 8 39f
32 55 27
46 34 42
23 11 31Ì
59 39 35
41 62 65
0 0 0
68 37 50
32 63 50
0 0 0
PII
1 2 3 GI
1 2 3
* Statistically different than group 2 at P <0.05. t Statistically different than groups 1 and 2 at P X Statistically different than group 2 at P <0.05.
<0.05.
Table 2 ■B leeding on probing frequ en cy and probing depth m easurem ent (millimeters) for FPD abutment sites for long- and short-term examinations. G ro u p
Long-term % BUP*
Short-term % BUP*
14 39 39
23 24 39
Bleeding o n p ro b in g 1 2 3 P ro b in g d ep th 1 2 3
X
(± sd)
X
1.86 2.41f 2.38+
(± 0 .5 6 ) (± 0 .5 5 ) ( ± 0.64)
2.00 2.29 2.27
+
± sd ( ± 0.54) ( ± 0.80) (± 0.53)
* BUP = Bleeding on probing, t Statistically significant from group 1 at P < 0.01.
Table 3 ■ Summary of statistically significant periodontal findings across treatment groups. PII
GI
G ro u p 3 > G ro u p 1 > G ro u p 2
...
G ro u p 3 > G ro u p 2
. ..
C om parison Long-term findings (retrospective co m ponent) Short-term findings (prospective co m ponent)
BUP*
P ro b in g dep th G ro u p 2 > G ro u p I G ro u p 3 > G ro u p 1
* BUP = bleeding on probing.
tistically significant differences for bleed in g on p r o b in g f re q u e n c y o b s e rv e d between the three FPD treatm en t groups in either the long-or short-term study com ponents, the observed difference between tre a tm e n t groups reg ard in g b leed in g on probing was o f clinical interest because of the threefold m agnitude o f the observed difference (Table 2). Discussion T he prim ary objective o f this study was to
exam ine the effects of three different FPD d e s ig n s o n th e p e r io d o n t iu m . It was observed th at the FPD design affected the plaque scores recorded. T he etched metal, resin -b o n d ed FPDs w ere associated with significantly g re a te r p la q u e scores th an both o f the conventional designs as well as th eir own co n tro l sites for th e long-term observation. Also, the etched metal, resinb o n d ed FPDs showed significantly greater plaque scores than the subgingival conven tional FPD design o f the short-term obser v a tio n . T h e s e two g ro u p s , th e e tc h e d
Freilich-O thers: Effects o f fixed p artial den tu res on periodontium ■ 267
RESEARCH
REPORTS
metal, resin-bonded FPD group, and the subgingival conventional FPD group, were found to have significantly greater mean probing depths at the long-term observa tion period and statistically significantly greater GI scores than their own controls at both long- and short -term observations. In regard to the probing depth findings, it should be noted that although the mean p ro b in g d ep th s for the etc h e d m etal, resin-bonded FPD group and subgingival conventional FPD group were statistically greater than the supragingival conven tional FPD group (2.41 mm and 2.34 mm versus 1.86 m m ), this d iffe r e n c e was ju d g ed to be clinically in sign ifican t in regard to p eriod on tal atachm ent level implication. The differences observed are likely to be m ore closely related to the increased penetrability o f the sulcus at th e se sites w h en p ro b ed b eca u se o f in creased in flam m ation at these sites. Coincidentally, these same two FPD design groups also showed a threefold (but statis tically significant, P = 0.09) greater per cen ta g e o f b lee d in g on p rob ing (39% versus 14%) w hen com p ared with the supragingival conventional FPD group at the long-term observation. Bleeding on probing is considered a reliable indicator o f inflammation o f the connective tissue adjacent to and at the base o f the sulcus. 28,29The lack o f a statistically significant dif ference for bleeding on probing may be a result o f a lack o f power to detect statisti cal differences resulting from the number o f subjects available to the investigators for this study. In this study th e resin -b on d ed FPD group had increased supragingival plaque scores, w hereas p reviou s stu d ies have reported in creased subgingival plaque associated with subgingival restoration margins found in subgingival conventional FPDs.8'9-30-31 When these two pieces o f evi dence are combined, it can be concluded that each design has the potential for simi lar effect on the periodontium. Therefore, in spite o f the increased levels of supragin gival p la q u e, th e e tc h e d m etal, resinbonded FPD was no more injurious to the periodontium than the subgingival con ven tio n al FPD d esign , w hich probably remains the standard fixed tooth replace ment (prosthodontic) modality in clinical practice today. However, they both had a less desirable effect on the periodontium than the supragingival conventional FPD design. Whereas the etched metal, resin-bonded FPD appears to have becom e a valuable asset in the fixed prosthodontic armamen tarium o f the restorative dentist, the obser
268 ■JADA, Vol. 121, August 1990
vations m ade in this study support the findings o f Creugers and others 23 who reported higher plaque scores associated with these bulkier restorations. Although no greater injury was seen at the sites adja cen t to these restorations as com pared with the subgingival con ven tional FPD group, the long- and short-term observa tions made in this study found that these restorations appear to be associated with greater periodontal inflam m ation when compared with conventional supragingival FPDs and the unrestored control teeth. In light of this finding, with minor mod ification to the etched metal, resin-bonded FPD technique, it should be possible for a supragingival fixed partial denture to be associated with optim um tissue health resulting from less retainer bulk and lower supragingival plaque levels. It is suggested that this may be achieved for the etched m etal, resin -b on ded FPD by providing greater axial depth o f tooth preparation in enamel to allow for the adequate thickness o f a structurally durable m etal retainer while elim inating excess bulk. Although no data currently exist to directly support this last premise, the data from this study combined with the findings from a related study, 23 suggest that it may be prudent to make tooth preparations for the etched metal, resin-bonded FPD retainer in such a way as to facilitate the removal o f plaque and minimize inflammation to the adja cent periodontium . The authors suggest that appropriate clinical studies designed to provide data pertaining to this issue be done. Conclusions This cohort study compares the long - and short-term periodontal response to three different modalities o f fixed prosthodontic tooth replacem ent. O ne restored (test) and one nonrestored (control) posterior proximal site o f the same tooth type were com pared in 87 subjects, each o f whom had a fix ed partial d en tu re p la ced , 6 months to 5 years before initial data col lection . For th e lo n g -term o b ser v a tio n , the etched metal, resin-bonded FPDs had sig nificantly greater plaque scores than both o f the conventional designs as well as its own control sites. This resin-bonded FPD group and the subgingival conventional FPD group had statistically, but not clini cally, significant increased probing depths than the supragingival FPD group. These same two groups also had significantly greater GI scores than their own control sites at both long-and short-term observa
tions. Therefore the long-and short-term observations made in this study found that the resin-bonded FPDs and the subgingival conventional FPDs were associated with greater periodontal inflam m ation when compared with supragingival conventional FPDs and the unrestored teeth. Moreover, in spite o f the increased levels o f supragin gival p la q u e, th e e tc h e d m etal, resinbonded FPD was no more injurious to the periodontium than the subgingival con ventional FPD design. ---------------------- J !iO A -----------------------
T h e in fo rm e d c o n se n t o f all h u m a n subjects w ho p a r t i c i p a t e d in th e e x p e r im e n ta l in v e s tig a tio n s re p o rte d o r described in this m anuscript was obtained after the n a tu re o f the procedure a n d possible discom forts and risks had b e en fully explained. Each subject received a small m onetary reim bursem ent to com pen sate them for th eir p articipadon time. T h e a u th o rs th a n k Mr. M ichael G ra z ian o fo r his assistance with the im plem entation o f this study. T h is s tu d y was s u p p o r te d by th e U n iv e rs ity o f C onn ecticu t R esearch Foundation G ra n t no. 11722220212-4-00664. Dr. Freilich is assistant professor o f prosthodontics, Dr. N iekrash is assistant professor o f periodontology, a n d Dr. Katz is a sso c ia te p ro f e s s o r o f B e h a v io ra l S c ie n c e s a n d C o m m u n ity H e a lt h , U n iv e rs ity o f C onnecticut, School o f D ental M edicine. Dr. Sim onsen is p ro fessio n al service m a n a g er, U n ite d S tates a n d In te rn a tio n a l D en tal P ro d u cts D ivision, 3M H e a lth C a r e . A d d re s s r e p r i n t re q u e s ts to D r. F r e il ic h , University o f C onnecticut, School o f D ental M edicine, Farm ington, CT 06032.
1. Preston JD , R ational approach to to o th p re p a ra tio n fo r ceram o m etal resto ratio n s. D e n t Clin N o rth Am 1977;21:683. 2. M cL ean JW. V olum e 2: th e scie n c e a n d a rt o f dental ceram ics. Chicago: Q uintessence; 1979> 3. Donovan T. Prince J. An analysis o f m argin con figurations for m etal-ceram ic crowns. J P rosthet D ent 1985;153-9. 4. R o s e n s tie l SF, L a n d MF, F u jim o to J . C ontem porary fixed prosthodontics. St. Louis: Mosby; 1988;135-9. 5. I.an g e la n d K, L a n geland LK. P u lp re a ctio n s to crown preparation, im pression, tem porary crow n fixa tio n , a n d p e rm a n e n t c e m e n ta tio n . J P r o s th e t D en t 1965;15:129. 6. C ollett H . Protection o f the d e n ta l pu lp in con struction of fixed partial d e n tu re prosthesis. J Prosthet D ent 1974;31:637. 7. M orrant GA. D ental in strum entation an d pulpal injury. P art II. Clinical considerations. I Br E ndod Soc 1977;10:55. 8. S iln ess J . P e rio d o n ta l c o n d itio n s in p a tie n ts treated with dental bridges. P a rt II. T h e influence of full and partial crowns on plaque accum ulation, devel o p m e n t o f gingivitis and pocket form ation. I P erio d o n t Res 1970;5:219. 9. V alderhaug J . Periodontal conditions in patients five years following insertion o f fixed partial dentures. J O ral R ehabil 1976;3:237. 10. R ochette A. A ttachm ent o f a splint to enam el of
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REPORTS
H istological d e te rm in a tio n o f p ro b e tip p e n e tra tio n in to gingival sulcus o f h u m a n s u sin g a n e le c tro n ic p r e s s u r e - s e n s itiv e p r o b e . J C lin P e r io d o n t o l 1980;7:479-88. 27. Smith LW, Suom i JD , G reene JC , B arbanoJP . A stu d y o f in tr a - e x a m in a r v a ria tio n in s c o rin g o ra l hygiene status, gingival in flam m atio n a n d e p ith e lia l attachm ent level. J Periodontol 1970;41:67l28 . D a v e n p o r t R H , S im p s o n D M , H a ss e ll T M . H istom etric com parison o f active an d inactive lesions o f advanced periodontitis. J P eriodontol 1982;53:285. 29. C ooper PG, C aton JG , Poison AM. Cell p o pula tions associated w ith gingival bleeding. J P erio d o n to l 1983;54:497-502. 30. W aerhaug J. Presence o r absence o f p laque o n subgingival re sto ra tio n s. S cand J D e n t Res 1975;83: 193-201. 31. S altzberg DS, e t al. S c a n n in g e le c tro n m ic ro scope study o f ju n c tio n betw een restorations and gingi val cavosurface m argins. J P ro sth e t D e n t 1976;36:51 7-21 .
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