Periodontal Configuration Martin Ralph University

effects of fixed and location

partial

denture

retainer

A. Freilich, DDS,a Christine E. Niekrash, DMD, IvIDS,~ V. Katz, DMD, PhD,C and Richard J. Simonsen, DDS, MSd of Connecticut

Health

Center,

School

of Dental

Medicine,

Farmington,

Conn.

0ur purpose was to study the periodontal response to posterior fixed partial denture (FPD) retainers with different marginal configurations and locations. One posterior proximal site restored with a clinically acceptable FPD and one matched, unrestored poster& proximal site were examined in 60 subjects. Assessments were made of the FPD retainers and the periodontal responses to both the lopgterm and short-term use of these retainers. Periodontal examination included assessment of probing depth and bleeding on prdbing and determination of plaque index and the gingival index scores. Statistical analysis showed that “clinically acceptable” FPDs, which had clinically detectable deviations from an ideal (flat) retainer/tooth configuration, were not associated with increased probing depth or bleeding on probing when compared to the matched, unrestored teeth at both examinations. As a group, sites adjacent to subgingival retainer margins were not associated with greater probing depths than sites adjacent to supragingival retainer margins. These findings suggest that long-term exposure to variations of FPD margin configuration and location, within clinically acceptable but less than ideal parameters, are not associated with the destruction of the supporting periodontaltissues.(J PROSTHET DENT 1992;67:184-90.)

he location of the apical extent of the cast fixed partial denture (FPD) retainer margin has been discussed at great length in the dental literature. Along with cast restoration marginsin general, many authors have suggested the extension of these margins to a subgingival location. The rationale for subgingival marginal placement has included the enhancementof estheticsand tooth preparation retention form, and the notion of the gingival sulcus asa caries-free zone. There has not, however, been agreement asto the degreeof subgingival extension. Various investigators have suggestedthat the margin should be placed at the baseof the gingival sulcus,l 3 mm from the alveolar crest,2-40.5 mm from the coronal extent of the junctional epithelial attachment,5 half the distance between the base of the sulcus and the gingival margin,6 slightly below the gingival margin,7,8 or at the crest of the gingival margin.g The theory of a caries-free zone was originally disputed by Orbanl’ in 1941 and by data from later clinical tri-

Supported by the University of Connecticut Research Foundation grant 1172-22-20212-4-00664. Presented at the International Association for Dental Research meeting, Dublin, Ireland. aAssistant Professor, Department of Prosthodontics. bAssistant Professor, Department of Periodontology. CAssociate Professor, Behavioral Sciences and Community Health. Qrofessional Service Manager, U.S. & International, Dental Products Division, 3M Health Care, St. Paul, Minn.; Professor, General Dentistry, University of Tennessee, School of Dentistry, Mempkis, Tenn.

10/l/28255 184

als.ll>l2 Additionally, there is considerableevidence that the subgingival retainer margin is often associatedwith an undesirable periodontal response.g, 11-14Bacterial plaque retained on relatively rough restoration surfacesand on the exposeddental cement betweenthe tooth and the restoration is diflkult for the patient and dentist to remove, and is responsiblefor the inflammatory changesseen in the periodontium adjacent to subgingival restoration margins.15-lgIn recent times, this evidence has led to the increasinglypopular notion that restorationmarginsshould be placed supragingivally wheneverpossible.Additionally, from this evidence one might hypothesize that the more apical the subgingivalmarginal placement,the more apical the observed inflammatory changes.At present, only one sourceof evidence supports this hypothesis.20 The configuration of the FPD retainer margin has also beenof concernto both the restorative dentist and the periodontist. A horizontal overextension of this margin has commonly been referred to asan ouerhang.21-27 Data from a number of studieshave shownthe detrimental periodontal effects of the overhang, or horizontally overextended margin,24,26,28-32 but there are no data demonstrating the effects of the short, or horizontally underextended, restoration margin. There is evidence that the horizontally underextended, aswell asthe overextended, retainer margin/ tooth configuration occurs quite frequently in clinical practice. Therefore the periodontal effects associatedwith both of these types of retainer configurations are of clinical interest. The purpose of this analysiswas to study the periodontal responseto posterior FPD retainers with different

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MARGINS

marginal configurations (horizontally overextended VS. horizontally underextended) and with different marginal locations (subgingival vs. supragingival).

MATERNAL

AND

METHODS

Sekection of subjects. Sixty adult subjects (25 to ‘75 years of age) were selected for participation in this study from patients who had received a conventional FPD replacing a posterior tooth in the predoctoral prosthodontic clinic at the University of Connecticut School of Dental Medicine between 1982 and 1986. All participants were systemically healthy and had demonstrated plaque and gingival indexes of less than 2 and probing depths (PD) of less than 5 mm at the abutment teeth before prosthodontic therapy, but after initial therapy. Additionally, all subjects who were selected for this study had an unrestored posterior tooth of the same tooth type with no proximal restoration. Informed consent was obtained from all subjects after the nature of the procedure and possible discomfort and risks had been fully explained. Each subject received a $25 reimbursement to compensate them for participation time and travel expenses. Study design. This article reports the analysis of a secondary research question applied to the data obtained in a published cohort study, 33whose primary question was the comparison of the periodontal effects associated with etched-metal FPDs as compared to conventional FPDs. This secondary data analysis was, of course, limited by the size and the nature of the subject population assembled to perform the primary data analysis. Collection ofdata. Clinical examinations for this study occurred 6 months to 5 years (mean, 32.3 +- 13.8 months) after the placement of the conventional FPDs at sites just proximal to the line angle on both the buccal and lingual aspects of the proximal surfaces of posterior teeth. Two paired eligible sites, one for the abutment tooth and one for the matched, unrestored tooth, were selected from each subject in either the maxilla or mandible before any intraoral data were collected. The data collected to determine periodontal status at these study sites included the plaque index (PlI) of Liie and Silness3* and the gingival index (GI) of Lae and Silness, 35 PD, and presence of bleeding on probing (BP) to the base of the sulcus within 30 seconds. The criteria for both the PlI and the GI can be seen in Fig. 1. Additionally, the FPD retainer was categorized as to its marginal location and configuration with the use of an explorer tip attached perpendicular to a thin calibrated periodontal probe at all of the restored (retainer) sites. The PD measurement of the sulcus and BP were determined by using an electronic, pressure-sensitive probe (Vine Valley Research, Middlesex, N.Y.) with a 0.54 mm diameter probe tip, Williams markings, and a constant force of 25 gm. 36 The probe tip was vertically positioned parallel to the buccolingual axis and slightly inclined

THE

JOURNAL

OF PROSTHETIC

DENTISTRY

Plaque

Index

Score 0

=

1

=

2

=

3

=

Gingival

Criteria

No plaque

A film of plaqueadheringto thefreegingival

marginandadjacentareaof thetooth. Theplaque maybeSeenin situonly aftertheapplicationof disclosingsolution,or by usinga probeon the tooth surface. Moderateaccumulation of softdepositswithin the gingivalmarginwhichcanbe seenwith the naked ~Z&lance of soft matterwithin thegingival pocketand/oron thetoothandgingivalmargin.

Index Criteria

Score 0

=

2

=

3

=

1 =

Absenceof inflammation. Mild inflamation- slightchangein colorand little changein texture. Moderateinflammation- moderate glazing, redness,edemaandhypertrophy. Bleedingon pressure at entranceof sulcus. Severeinflammation- markedredness and hypertrophy.Tendencyto spontaneous bleeding, ulceration.

Fig. 1. Criteria of plaque index and gingival index (Lije and Silness34, 35).

toward the tooth surfacein a location adjacent to the proximal contact or FPD connector. The PlI and GI assessments were made at this samelocation before PD and BP were assessed. The retainer margin configuration and location were determined at the end of each examination with an “outward” or “inward” facing explorer tip attached to a thin calibrated periodontal probe at the two endsof this instrument. The “outward” facing tip of this double-ended instrument is shown in Fig. 2. The explorer tip of this instrument was positioned perpendicular to the proximal axial surfaceto determine both the configuration of the retainer margin and its location with respect to the gingival margin. The configuration of the retainer marginswasdetermined by moving the perpendicularly held explorer tip in both apicocoronaland coronoapicaldirections while this tip wasin contact with the proximal axial surfaces.While the tip washeld at the retainer margin, the calibrated probe part of the instrument was positioned alongsidethe proximal axial surface to measurethe distance between the subgingival retainer margin and the gingival margin at the experimental site. The distance between supragingival retainer marginsand the gingival margin wasmeasuredwith a periodontal probe tip. All measurementswere made by one examiner who had been calibrated before data collection to attain an acceptable intraexaminer variation in examining subjects with similar prosthesesand a similar extent of periodontal disease.37 The details of the study designaregraphically presented 185

FREILICH

ET AL.

Secondary intrasubject comparisonsmade between each restoration group and its own matched unrestored surfaces were used merely as a means to ensure that differences found betweenthe periodontal responsesto the restoration groups were not a result of a “patient effect.” A t-test of independent meansand a one-way analysisof variance with a Scheffe multiple range test option were usedto comparecontinuous data obtained from PD measurements. A chi-square analysis was performed on the discrete data resulting from the assessments of PlI, GI, and BP scores. RESULTS

Fig. 2. Custom-designed explorer/periodontal probe used to determine configuration and location of FPD retainer margins evaluated in this study.

in Fig. 3. The first examination provided the final outcome data for the long-term, retrospective study component. Subsequent to the first examination, each subject received a thorough periodontal scaling, a rubber cup prophylaxis, and a detailed set of oral hygiene instructions from one of two trained dental hygienists. After a period of 2 to 3 weeks, all subjects received a second examination that provided the outcome data for the short-term, prospective study component. Statistical analysis. All data collected were recorded on a computer-ready data collection form, keypunched, verified, and analyzed with an SPSS software package (SPSS Inc., Chicago, Ill.) on an IBM PS/2 computer (IBM Corp., Armonk, N.Y.). Analysis of these data resulted in the comparison of FPD retainers of various marginal location and configuration. For the comparisons related to marginal configuration, the matched unrestored surfaces were used to provide periodontal responses to a flat retainer/tooth configuration. This was necessary because only two of the retainers examined were found to have flat configuration and thus the number of flat surfaces was inadequate for comparison with the horizontally overextended and underextended retainers. Therefore the primary comparison to study the effects of marginal configuration was between the restoration groups and their own matched unrestored teeth. This was an intrasubject comparison.Intersubject comparisonswere alsomadebetweenthe overextended and underextended treatment groups. The effect of marginal location wasdetermined by direct comparison between the periodontal responsesto the retainer margins located apical to the gingival crest (the subgingival group) versus the retainer margins located coronal to and at the gingival crest (the at-crest/supragingival group). Therefore the intersubject comparisonmade between thesetreatment groups wasthe primary comparison for studying the effect of retainer margin location.

186

Unless otherwise specified, statistically significant differencesbetweenthese comparisonswere declaredwhen p valuesdid not exceed0.05.A summary of thesestatistically significant findings from the primary comparisonscan be found in Table I. Marginal configuration. With regard to the intrasubject comparison,sites adjacent to horizontally overextended retainers (n = 30) had greater GI scoresthan their matched unrestored teeth for the long-term observation only. When only the subgingivally placed overextended restorations were compared to their matched unrestored teeth, these retainers were associatedwith significantly greater GI scoresfor both long-term and short-term observations. Underextended retainers (n = 29) were associated with significantly greater GI scoresthan the unrestored controls in the samesubjects for both the long-term and short-term observation periods,and with greater PlI scores at the short-term observation. These intrasubjeet comparisonscan be seenin Table II. An intersubject comparison showedno significant difference betweenhorizontally overextended and underextended retainers with regard to PlI and GI scoresat the long-term observation. The 61 scores for the sites adjacent to underextended retainers were, however, significantly greater than the scoresat sitesadjacent to overextended retainers at the short-term observation. No differences in BP or PD were noted betweenthe sites adjacent to the underextended or overextended retainers or betweeneither of thesegroupsand their matched unrestored teeth. Margin Location. No difference was found between retainers of different marginal location either asa result of 1) a lack of statistical differencesbetween the primary intersubject comparisonsor (2) a failure of the intrasubject comparisonto support a difference observedfor the intersubject comparisons. Relationshipsbetween retainer margin location and PlI and GI scoresare seenin Table III. Note that the number of sites in both the subgingival and the at-crest/supragingival groupschangedfrom the first (long-term) to the second (shortterm) examination, likely as a result of the gingival recessionand decreasedinAammation often associated with scaling and improved oral hygiene. The primary intersubject comparisonshowedthat subgingival retamers

FEBRUARY

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MARGINS

PROSPECTIVE COMPONENT (Short-term)

RETROSPECTIVE COMPONENT (Long-term) b

e Mean Time= 17.5 +I5.0 Days

Mean Time 32.3 4 13.8 Months

Posterior Conventional Group (N=60)

First Exam Data FPD GI PI Probing depth BP Prosthesis Evaluation

Second Data

c Scaling lygiene

Exam

GI Pi Probing depth BP

& Oral instruction

Prosthesis Evaluation

Fig. 3. Schematic

of study design.

Table I. Summary of statistically significant (p < 0.05) findings resulting periodontal effects of FPD retainer margin configuration and location Comparison Marginal

PI1

configuration

(intrasubject

GI

Marginal

Underextended > matched unrestored teeth

location

(intersubject

-

Underextended > matched unrestored teeth Subgingival overextended > matched unrestored teeth

-

PD

comparison)

At-crest/supragingival subgingival

>

Subgingival > at-crest/ supragingival

(n = 27) were associated with significantly greater GI scores than retainer margins in the at-crest/supragingival group (n = 33) for the short-term examination, despite the significantly greater PlI scores observed adjacent to the supragingival retainers at this examination. No statistically significant difference was detected between the supragingival or subgingival groups with respect to BP at either the long-term or short-term examination, despite the finding that the subgingival retainer group bled

OF

to determine

-

Short-term (prospective component)

JOURNAL

BP

Underextended > matched unrestored teeth Overextended > matched unrestored teeth

Long-term (retrospective component)

THE

comparisons

comparison)

Long-term (retrospective component)

Short-term (prospective component)

from primary

PROSTHETIC

DENTISTRY

2-3 mm subgingivai > at-crest/supragingival and 1 mm subgingival

twice as frequently as the supragingival group. Whereas no differences were found in mean PD between the subgingival and supragingival retainer groups for either observation period, a further comparison, illustrated in Table IV, found that the apical extent of the retainer margin had an effect on the PD measurements at the short-term examination. Specifically, there was a statistically significant difference between those sites adjacent to the FPD retainer margins that are 2 to 3 mm apical to the gingival margin and the

187

FREILICH

Table II. Frequency distribution of PlI and GI scores at experimental overextended FPD retainer margins versus their matched unrestored (intrasubject comparisons) Long-term

0

1

24

66

sites adjacent to underextended and teeth for long-term and short-term examinations Short-term

distribution

(W)

2+3

Statistical significance

ET AL.

distribution

(%) Statistical significance

0

1

2+3

48

35

17

21

65

14

47

40

13

37

53

10

31

69

-

79

21

_

1

63

37

83

13

-3

1

PlI

Underextended

retainers

10 No

(rl = 29)

Matched unrestored teeth

17

62

21

Overextended retainers (n = 30) Matched unrestored teeth

20

70

10

20

67

13

Underextended retainers (n = 29) Matched unrestored teeth

48

52

-

79

21

Overextended retainers

43

57

Yes I

No !

No I

GI Yes -

1 Yes

(n = 30)

Matched unrestored teeth

80

17

-13

sites adjacent to both the retainers in the at-crest/supragingival group and those retainers that were located 1 mm apical to the gingival margin. This first subgroup exhibited a mean PD of 3.50 + 0.58 mm; this measurement was statistically different from that of the at-crest/supragingival group, which had a mean PD of 2.00 f 0.50 mm, and that of the 1 mm subgingival group, which had a mean PD of 2.22 L 0.80 mm. Additionally, when the secondary intrasubject comparison was made, the mean PD for the 2 to 3 mm subgroup was also found to be significantly different from that of its own matched unrestored teeth, which had a mean PD of 2.50 f 0.58 mm.

DISCUSSION The primary objectives of this study were to examine the effects of conventional FPD retainer margin location and configuration on the periodontium. Both the horizontally underextended and overextended retainers had significantly greater GI scores than their matched unrestored -teeth at the first, or long-term, examination. The retainers that were underextended and those that were both subgingival and overextended also had significantly greater GI scores than had their matched unrestored teeth at the second, or short-term, examination. In addition, the underextended retainers were associated with significantly greater GI scores than were the overextended retainers at the second examination. In this study the variation in retainer configuration had no effect on BP scores or PD measurements. The only difference in periodontal response observed between the different retainer/tooth configurations and between either of these configurations and their matched restored teeth was seen at the gingival margin where the GI scores are taken. The periodontal effects or changes in inflammation were, therefore, limited to the superficial regions of the periodontium. Additionally, most 188

Yes

-

No

GI scores in all experimental groups were 0 and 1, and these scores are representative of relatively mild gingival inflammation. No differences were found in the long-term periodontal response to differences in retainer margin location. However, some short-term differences were observed at the second examination, which occurred 2 to 3 weeks after scaling and reinforcement of patient education. Despite the observation that retainer margins located at or coronal to the gingival crest were associated with significantly greater PI scores than were subgingivally located retainer margins, the subgingival margins exhibited higher GI scores. Although no statistically significant difference in BP between the retainer margin location groups was found, the subgingival group bled twice as often as the at-crest/ supragingival group. The inability to declare this clinically interesting difference to be statistically significant may be the result of the limited power to detect this difference, which was the result of the modest size of the subject population. Retainer margins that were located 2 to 3 mm apical to the gingival margin exhibited significantly increased mean PD measurements than those retainer margins that were located either at, coronal to, or 1 mm apical to the gingival crest. This finding supports the hypothesis that the more apical the subgingival margin placement, the greater the inflammatory changes observed. This hypothesis is supported by the work of Newcomb, who also found that more apical margin placement is associated with deeper PDs. The increased PD measurements found in both studies are likely more closely related to the increased penetrability of the gingival sulcus to periodontal probing as a result of increased inflammation rather than to actual differences in periodontal attachment levels.38 The differences in PD associated with retainer margin location in the FEBRUARY

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EFFECTS

OF RETAINER

MARGINS

III. Frequency distribution of PlI and GI scores at experimental sites adjacent to FPD retainers of different marginal location for long-term and short-term examinations (intersubject comparison)

Table

Long-term

P11 At-crestisupragingival

distribution

n

0

1

25

16

68

(%)

Short-term

Statistical significance

2+3

16

distribution

n

0

1

33

30

46

24

27

61

29

4

33

64

36

27

30

70

(W) Statistical significance

2f3

No Subgingival GI At-crest/supragingival

35

25

66

25

60

40

9

-

Yes

Yes

No

Subgingival

35

34

66

-

IV. Mean PD measurements at sites adjacent to FPD retainers of different marginal locations (intersubject comparisons)

second, or short-term, examination were probably absent in the first, or long-term, examination because of the longterm effect of plaque at these sites and the resultant gingival inflammation and hypertrophy that may have obscured the effect of retainer margin location in all groups. Given the similarity of clinical findings for most of the comparisons made in this study, which did not produce statistically significant differences, the lack of power to detect differences for these analyses is only a modest concern. In other words, the lack of observed statistical differences was generally accompanied by a lack of observed clinical differences.

Table

CLINICAL

Therefore, this study has also shown that the placement of “clinically acceptable” FPD retainer margins apical to the gingival crest has not proved to have a significant adverse effect on the periodontium when compared to FPD retainer margins of similar quality placed at or coronal to the gingival crest.

IMPLICATIONS

OF RESULTS

Although the restorative dentist strives to produce a flat retainer margin/tooth configuration, it appears from the results of this study and others2s that this goal is rarely achieved. The data collected during this study have shown that FPDs that were judged “clinically acceptable,” with clinically detectable deviation from the flat configuration, may be associated with increased marginal inflammation (GI scores). However, it is somewhat reassuring to discover that two groups of conventional FPDs with either slightly overextended or underextended retainer margin/tooth configurations are not associated with greater PD measurements or BP scores than matched contralateral unrestored teeth in the same subjects. Therefore these less than ideal configurations do not seem to have caused any irreversible harm during this observation period, which ranged from 6 months to 5 years. Evidence from many studies has shown that placing FPD retainer margins coronal to the gingival crest whenever possible is certainly preferable. Data from this study have shown that subgingival retainer margins are associated with increased marginal inflammation and that further increases in the apical extent of subgingival marginal placement result in increased PD measurements over short-term observation periods. These effects, however, were absent over long-term observation periods. This suggests that the effects of retainer margin location have been “canceled out” by the long-term presence of plaque, even in this relatively well-maintained dental school patient population. THE

JOURNAL

OF PROSTHETIC

DENTISTRY

Long-term

At-crest/supragingival 1 mm subgingival 2-3 mm subgingival *Statistically

different

from

n

Mean

SD

n

Mean

SD

25

1.92 2.26 2.67

0.57 0.54 0.49

33 23 4

*2.00 *2.22 3.50

0.50 0.80 0.58

23

12 2

Short-term

to

3

mm subgingival

group at p < 0.05.

SUMMARY This analysis studied the periodontal response to posterior conventional FPDs with different marginal configurations (horizontally overextended vs. horizontally underextended) and with different marginal locations (subgingival vs. supragingival). One posterior proximal site restored with a clinically acceptable FPD and a matched unrestored posterior proximal control site were examined in 60 subjects with conventional FPDs. Eligibility criteria for subjects enrolled in this study included PI1 and GI scores of less than 2 and PDs less than 5 mm before prosthodontic therapy. Both the FPD retainers and the periodontal responses to the long-term effects of these retainers were assessed at the first examination, which occurred 6 months to 5 years (mean, 32 t 14 months)-after FPD placement. A prophylaxis was given to all subjects after this first examination. Subjects were then recalled 2 to 3 weeks later for a second examination, where the short-term periodontal responses were observed. The location and configuration of the FPD retainers were determined with the use of a customdesigned explorer/periodontal probe. Periodontal examination included assessment of PD and BP by means of an 189

electronic pressure-sensitive probe, and the determination of PI and GI scores. Statistical analysis showed that both the horizontally underextended and overextended retainers had significantly greater GI scores than had their own matched unrestored teeth at the first, or long-term, examination. The retainers that were underextended and those that were both subgingival and overextended also had significantly greater GI scores than had their matched unrestored teeth at the second, or short-term, examination. In addition, the underextended retainers were associated with significantly greater GI scores than the overextended retainers at the second examination. The variation in retainer configuration had no effect on BP scores or PD measurements. No long-term periodontal effects resulted from differences in retainer marginal location, but some short-term differences were observed at the second examination, which occurred 2 to 3 weeks after scaling and reinforcement of patient home care. Despite the observation that retainer margins located at or coronal to the gingival crest were associated with significantly greater PlI scores than subgingivally located retainer margins, the subgingival margins were associated with the higher GI scores. At the second examination there was no statistically significant difference in BP scores detected between the retainer marginal location groups, but some differences in PD were seen. Specifically, retainer margins located 2 to 3 mm apical to the gingival crest exhibited significantly increased mean PD measurements than either those retainer margins that were located 1 mm apical to the crest or those in the at-crest/supragingival group. These effects, however, were absent over long-term observation periods. These results suggest that the effects of retainer margin location were “canceled out” by the long-term presence of plaque.

1. Stein R, Glickman I. Prosthetic considerations essential for gingival health. Dent Clin North Am 1960;4:177-88. 2. Nevins M, Skurow GM. The intracrevicular restorative margin, the biologic width, and the maintenance of the gingival margin. Int J Periodontics Restorative Dent 1984;4:30-49. 3. Fugazzatto PA. Periodontal restorative interrelationships: the isolated restoration. J Am Dent Assoc 1985;110:915-7. 4. Silvers J, Johnson GM. Periodontal and restorative considerations for crown lengthening. Quintessence Int 1985;16:833-6. 5. Wilson RD, Maynard 6. Intracrevicular restorative dentistry. Int J Periodontics Restorative Dent 1981;1:34-49. 6. Tylman SD. The theory and practice of crown and fixed partial prosthodontics. 6th ed. St Louis: CV Mosby Co, 1970:94. 7. Herlands R, Lucca J, Morris M. Forms, contours, and extensions of full coverage in occlusal reconstruction. Dent Clin North Am 1962;6:147-62. 8. Weinberg LA. Esthetics and the gingiva in full coverage. J PROSTHET DENT 1960;10:737-44. 9. Marcum J. The effect of crown marginal depth upon gingival tissue. J PROSTHET DENT 1967;17:479-87. 10. Orban IS. Biologic considerations in restorative dentistry. J Am Dent Assoc 1941;28:1069-79. 11. Silness J. Peridontal conditions in patients treated with dental bridges. Part III. The relationship between the location of the crown margin and the periodontal condition. J Periodont Res 1970$x225-9. 12. Valderhaug J, Birkeiand JM. Periodontal conditions in patients 5 years

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FEBRUARY1992

YBEUMEW

NUMBER2

Periodontal effects of fixed partial denture retainer margins: configuration and location.

Our purpose was to study the periodontal response to posterior fixed partial denture (FPD) retainers with different marginal configurations and locati...
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