Tissue changes beneath fixed partial dentures

TISSUE

CHANGES J.

PATRICK

HENRY,

DAVID

F. MITCHELL,

Indiana

University,

BENEATH

FIXED

B.D.Sc., M.S.D.,” D.D.S., PH.D.““” School

of

Dentistry,

JOHN

Indianapolis,

PARTIAL F. JOHNSTON,

DENTURES D.D.S.:

M.S.D.,“”

AND

Ind.

TYPES OF I’ONTICS ARE AVAILABLE for the situations that arise in fixed partial prosthodontics. Uut the controversy is centered on whether or not a pontic should contact the ridge tissue, and if so, whether or not it should exert pressure on that tissue. Gold, porcelain, and resins are used, but there is disagrecment as to which is the best material. Clinical and technical procedures have been guided by observation and personal preference with little real basis on scientific fact. The mucosa beneath fixed partial denture pontics is often loosely arranged, devoid of cornification, and frequently edematous.1 Tissue tolerance of gold and porcelain is better than that of acrylic resin.‘,” However, histologically the gingival crevicular epithelium does not react differently to porcelain, gold, or acrylic resin.4s5 Nevertheless, porcelain is more hygienic than gold, 6-11due to its superior surface properties.12-14Many pathologic changes have been reported in association with fixed pontics.l*-l9 Hence, an effort was made to develop a reproducible method whereby the edentulous ridge mucosa beneath pontics of different materials might be studied after varying periods of time. Thus, the nature, significance, and possible consequences of any observed alterations might be determined.

M

ANY

EXPERIMENTAL

PROCEDURE

The subjects were selected from those presenting in the Crown and Bridge Clinic for the construction of fixed partial prostheses. They were divided into groups A and B, corresponding to the final observation periods, three and six months respectively (Table I). Gold, glazed porcelain, and unglazed porcelain pontics were used. Only mandibular ridges were used, so that the following limitations might be imposed : (1) a lessening of the wide range of variables already existing in such a study by involving only one jaw, and (2) to employ sanitary pontics ai often as possible, thus covering the minimal amount of ridge tissue. *Research Fellow, Walter G. Zoller Memorial Dental Clinic. **Professor and Chairman, Crown and Bridge Department. ***Professor and Chairman, Department of Oral Diagnosis. This study was supported in part by a Hackett Studentship from the University Australia, and in part by the U. S. Public Health Grant PHSI 501 F R 05012-01.

of Western

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ET AL

l’he test fixed partial dentures were constructed in an accepted marine? except that precision Gilson Fixable Attachments? instead of soldered joints were used to fix the pontic section to the retainers (Fig. 1). The pontics were fabricated without scraping the ridge so that upon insertion they would touch the mucosa without pressure.20 The detailed method of aligning, adjusting and soldering the attachment has been described.21 A cone-socket handle oral wrench is used for adjusting the male section. A proximal view of a pontic with male section attached is seen in Fig. 2. The excess length of the bolt is to be cut off. The double-acting expanding bolt with the Scullin key and nut are placed inside the split-tube male attachment. The assembled male part of the attachment that is attached to either end of a pontic is seated into the female part that is incorporated into a retainer casting. The wrench can either fix or unfix the attachment so the pontic section can be removed. Thus it was possible to remove the parts and replace them firmly in position. The exposed bolt-end and nut were protected by gutta percha between clinical visits. A partially removed pontic is seen in Fig. 3. DATA

RECORDED

Careful clinical observations of the ridge morphology, irreversible hydrocolloid impressions, casts poured in die-stone, bite-wing roentgenograms of the residual ridges, and intraoral Kodachrome transparencies were made prior to making the test fixed partial dentures.

1

Fig. l.-The fixable-removable attachment. (A) The female part is a flanged open-sided tube with the cervical end enclosed. (B) The male part consists of a split tube which accommodates a douhle actinn snread nut and bolt. (C) and (D) respectively. The arrow indicates a Scullin key which serves to localize the bolt within the split tube. Fig. 2.-A proximal view of a pontic prior to occlusal adjustment of the nut and bolt.

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Whenever possible, a control biopsy was taken from an edentulous area in the mouth that was not included in the experimental area (Table I). Careful clinical observations and serial intraoral Kodachrome transparencies were made when the pontics were removed at intervals of 2 to 4 days, 10 to 14 days, 1 month, 2 months, 3 months, and 6 months for Group B. The same observations as those made before construction was started were repeated at the final observation period. This was 3 months for Group A and 6 months for Group B. At this time also, an elliptically shaped biopsy was taken from beneath each pontic. After fixation in 10 per cent formalin, the specimens were trimmed perpendicular to the epithelial surface and along the long-axis of the elliptically shaped piece of tissue. The specimens were cut in seven micra thicknesses, stained by the periodic acid- Schiff method, and with hematoxylin and eosin. A subdermal implantation technique”’ in rats was used to study the connective tissue reaction to pellets of each of the materials used in the fabrication of the experimental pontics. RESULTS

C’linical Observations.-The response of the mucous membrane to the pontic was the primary consideration. The factors considered were changes in color, contour, and texture of the tissue contacting the pontic. Little difference was noted in the response of the tissues to the different types of materials used in the pontics. No changes occurred which were of such a nature that a change in texture was detectable (Table II). No change in the bony architecture beneath the pontics was revealed by bitewing roentgenograms after the 3 and 6 month intervals. The lamina dura appeared to be the same in all subjects.

‘~ABLIJ

I. QCASTITY

OF THE

-..__

SAMPLE 7

--__-___

___-I_ TYPES

AGE

SUBJECT

I

SEX

/

I

NO. OF UNITS

;: 6

NO. OF PONTICS

POLISHED GOLD

GLAZED PORCELAIN

UNGLAZED PORCELAIN

I

I

2-f t 1 2 3 Gro14P Hf

NO. OF BRIDGES

OF PONTICS

Groz4p

4 65

32

M*

2

59 3.5 31

F* M

1 i 10

Total *Indicates iGroup fGroup

A, B.

control 3 month 6 month

biopsy site. observation observation

unavaijabit?. period. period.

1 1

F 7

:

: 1

-

-

37

5

6

1 3

940

HENRY TABLE

II.

TABLE

ET AL

OF CLINICAL

TIME

SUBJECT

2 TO 4

PONTIC TYPE*

-__----

1 2

GP G GP

3 EP

Group B$ 1 2 3

EP UP G % G GP UP

OBSERVATIONS

OF CLINICAL

DAYS

COL

COL

-

-

OBSERVATION

1 MO.

-. CON

COL

i

Grouf~ At

Pros.Den.

d ctober,1966

10 TO 14

DAYS -____ CON

September-

-

CON

-

!

-

-

-

++ :

i+ -

-

+ + --- ; z : + - + - -

Key. *Pontic type. G, polished gold: GP, glazed porcelain; UP, unglazed porcelain. Co1 refers to change in color of mucosa beneath pontic; con refers to change in contour of mucoea beneath pontic; -, no apparent change in color or contour; +, definite change in color or contour. tGroup A, 3 mo. observation period. fGroup B, 6 mo. observation period.

The stone casts showed evidence of the pontic position when compared to casts from impressions made prior to construction. The difference appeared to be a build-up of the soft tissue around the periphery of the pontic. The proliferation of tissue appeared to be greater on the lingual aspect of the pontic, but this may have been becausethe edentulous ridge generally falls away more sharply on the lingual than on the buccal aspect (Fig. 4). This proliferation of tissue also appeared to be greater over a broad flat ridge, as compared to a more “knife-edged ridge,” when considered bucco-lingually (Fig. 5). The three subjects showing no change in color at the final observation periods (Table II) involved sharp, narrow ridges buccolingually. Hence, the sanitary-type pontic exhibited minimal tissue coverage in that direction. All gold pontics showed evidence of tarnish on the tissue surface. The unglazed porcelain pontics possesseda slight adherent plaque of materia alba on the tissue surface. The unglazed porcelain types appeared quite clean. HistoZogic Observations.-In the evaluation of the results, the responseof the epithelium and connective tissue to the overlying pontic was the primary consideration. An arbitrary classification of “minimum,” “intermediate,” and “maximum” responseswas made. The factors considered in this classification were : (1) change in thickness of the stratum corneum, (2) change in epithelial morphology, (3) alteration in the connective tissue beneath the pontic, (4) degree of vascularity of

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Fig.

d

Fig. Fig.

3.-Following the loosening of the attachment, a test pontic is partially removed. 4.-Three month observation period. A flattened area on the ridge clearly indicates where the pontic has been in position. The build up of tissue (arrow) appears to be more definite on the lingual side of the pontic. Fig. B.-Fourteen day observation period. On the mirror-view, the earliest change in contour of the crest of the ridge is evident as a furrow disrupting an otherwise smooth curve running mesiodistally (arrow).

the region, and (5) degree and type of inflammatory cell infiltrate in the region (Table III). Miniwmm Response.-The epithelium appeared to be thinner directly under the pontic, with loss of rete peg morphology, when compared to the adjacent mu-

942

HENRY

TABLE ___~.___ ---_

ET

III.

BIOPSY

AL

RESULTS

.___ PONTIC TYPE*

SUBJECT

HISTOLOGIC

I Group At

Maximum Intermediate Minimum Minimum Minimum

1

2 3 Group BS

Intermediate Maximum Intermediate Intermediate Intermediate Intermediate Intermediate Intermediate Maximum

1

2 3

Key. iGroup :Group

*Pontic type. G, polished gold: A, 3 mo. observation period. B, 6 mo. observation period.

RESPONSE

I

GP,

glazed

porcelain:

UP,

unglazed

Porcelain.

cosa. The thickness of the stratum corneum appeared to be the same in this region as in the tissue extending buccally and lingually away from the pontic. A slight increase in the number of capillaries was noted, but no inflammatory cells were seen. The papillary collagen of the connective tissue appeared slightly amorphus, with the fibers less dense and apparently finer in texture. These changes were limited to tissue directly beneath the pontic (Figs. 6 and 7). Intermediate Response.-When compared to the minimum response, the papillary collagen was lessdense, and the fibers appeared to be separated, as is seen in interstitial edema. The submucosa was increased in vascularity, and a very mild lymphocytic infiltrate existed (Fig. 8). Maxiwzuwt Response.-This was characterized by a decreased thickness of keratin and thinning of the epithelium. The rete pegs towards the periphery of the pontic area were somewhat blunted, with proliferation of the pegs directly under the pontic. The cells of the stratum spinosum showed a mild degree of intracellular edema, and there appeared to be an occasional break in the basal layer of cells. The papillary layer of connective tissue again showed a decreased density of collagen. Interstitial edema of the connective tissue was present, together with an increased vascularity of the area. An occasional intravascular polymorphonuclear leukocyte was evident, and it was generally marginated. The inflammatory infiltrate was mixed in type, principally lymphocytic (Figs. 9 and 10). No consistent correlation was noted between the histologic response of the tissues and any specific pontic material. This was true of both the biopsy material and the subdermal connective tissue around the materials implanted in the rats. The inflammatory reactions around the implants all were classified as mild. The special stains used did not reveal further pertinent information.

Fig.

Fig .7

Fig. G.-A tissue section from beneath months. A minimum response is seen as the epithelium, with decreased density arrow indicates the pontic position. (x 25.) Fig. ‘7.-Higher magnification (X 50) trate, and complete absence of rete pegs Dontic.

a glazed blunting of collagen of Fig. directly

porcelain pontic. of rete pegs and in the underlying 6 illustrates beneath

the

The biopsy was taken derreased keratinization connective tissue.

the lack of inflammatory cell crest of the ridge, underlying

at 3 of The infilthe

6

HENRY

ET

AI,

September-

Pros. dctober,

Den. 1966

Fig. S.-A tissue section from beneath a glazed porcelain pontic. The biopsy was made at 6 months. Intraand intercellular edema of the stratum spinosum together with decreased keratinization is seen, with a decreased density of collagen under the affected area. A mild chronic cell infiltrate is seen beneath the pontic position indicated by the arrow.

9

Fig. 9.-A tissue section from beneath a glazed porcelain pontic, biopsy at G months. The lack of keratinization and loss of rete peg formation is evident. An inflammatory cell infiltrate is seen together with interstitial edema of the connective tissue. (X 25.) Fig. 10.-A higher magnification of Fig. 9 illustrates an inflammatory infiltrate of a mixed type, principally lymphocytic. An occasional intravascular polymorphonuclear leukocyte was evident, generally marginated. The epithelium shows a degree of intracellular edema. (X 125.)

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DISCUSSION

The validity of clinical studies is difficult to ascertain because of many vari.ables. Age, sex, health status, menstrual cycle, diet, and habits, all have been shown to influence the oral mucous membrane to some degree. The wide range of tissue morphology of different individuals also is recognized. The variables of contour, position, material, and technique of fabrication of the pontic make this problem difficult to analyze. Clinically, there was no evidence that the oral mucosa responded more favorably to any one of the pontic materials during the intervals used. The glazed par.celain pontics were the most hygienic, and are hence, preferable to the other types of material studied, because of this fact alone. This contention is supported by th:, findings of Tylman.23 According to Pini, the characteristic reaction of the gingival mucosa in con-tact with gold or porcelain is sclerosis. This sclerosis is probably comparable to the decreased density and poor staining quality of the papillary collagen seen in this study. The erythema under the pontics probably was due to a combination of factors, including a thinning of the epithelium, particularly the stratum corneum. These features and the increased vascularity of the submucosa would indicate a clinical picture of local irritation. This hypothesis is supported by the fact that those subjects not showing a change in color at the final observation period did not illustrate all of these features. The metabolism of the epithelium is facilitated by the extension of the papilla6 of the connective tissue far up into the epithelium.a5 The exchange of nutrients and waste products seems to take place with the assistance of the tissue fluid. Flattening off of the rete pegs, therefore, seems to indicate an altered metabolism of the epi-. thelium. The changes occurring under complete clentures26 resemble closely the changes in the epithelium recorded in this study. Ostlund26 also reported that the collagenic bundles of the lamina propria were pushed apart, suggesting edema. This total edema provided an increased tissue volume. The proliferation of the ridge tissue toward the pontic could not be clari-. fied histologically. This probably was due to the shrinkage and distortion of the tissue occurring during fixation and subsequent processing. However, it is possible that it could be explained in part by edema of the stratum spinosum and of the connective tissue. This edema may be related to the fact that patients sometimes complain, several months after insertion of a fixed partial denture, that they are not as capable of passing dental floss under the pontic as they were initially. These observations are supported by the findings of WeissZ7 On the basis of the review of the literature and the results of this study, it seems that pontics on fixed partial dentures should be constructed with glazed porcelain contacting the tissue without pressure. The area of contact should be minimal, with the embrasure spaces opened up as much as possible. The pontic should be contoured to ensure self-cleanliness, and should direct the food bolus in. such a manner as to stimulate the mucosa. The patient should follow a vigorous regime of oral physiotherapy to cleanse and stimulate the tissue beneath the pontic.

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Den. 1966

CONCLUSIONS

The first detectable change in tissue morphology beneath pontics occurred within ten days of insertion and was characterized by an apparent proliferation of the adjacent tissue toward the pontics. Within six months, the majority of subjects exhibited a change in color and contour of the mucosa underneath the pontic. These were more ‘noticeable over broad, flat ridges than on sharp, narrow ridges. These changes appeared to be directly related to the effectiveness of the oral hygiene practiced by the subject, and to the amount of tissue covered by the pontic. Glazed porcelain was the most hygienic material used, and it is superior in terms of esthetics and ease of cleaning. However, within six months of insertion, there was no clinical or histologic evidence to suggest that glazed porcelain is superior to unglazed porcelain or polished gold, as far as tissue tolerance is concerned. REFERENCES

1. Wright,

W. H.: Morphological

Changes in the Mucous Membrane Covering Edentulous Process in the Human Mouth, J. D. Res. 18:159-162, 1933. 2. Allison, J. R., and Bhatia, H. L.: Tissue Changes Under Acrylic and Porcelain Pontics, J. D. Res. 37:66-67, 1958. 3. Pine, III y;;;ics for Gold-acrylic Resin Fixed Partial Dentures. J. PROS. DEN. 12:347-

Areas of the Alveolar

Waerhaug, J. : ‘Tissue Reactions Around Artificial Crowns,. J. Waerhaug, J.: Observations on Replanted Teeth Plated With Med. & Oral Path. 9:780-791, 1956. 6. Stamps, H. F. Jr. : Modern Types of Bridge Pontics, Bull. Nat. 7. Schwa;;? {9& : Developmental Trends m Tooth Replacement, 4. 5.

8.

Klaffenbakh,

A. 0.:

27:738-750,

9.

10. 11. 12. 13. 14. 15. 16. 17. :89: 20. 21. 22. 23. 24.

1940.

Some Important

Perio. 24 :172-185, 1953. Gold Foil, Oral Surg., Oral D. A. 7:102-107, 1949. D. Items of Interest 66:242-

Aspects of Fixed Bridge

Restorations,

J.A.D.A.

Study of Tissue Reactions About R.: An Experimental Porcelain Roots, J. D. Res., 13:459-472, 1933. Dobson, N. J.: The Value of Porcelain in Artificial Root Insertion, Cosmos 63:247-248, 1921. Semmelman, J. 0.: Personal communication. York, Pa., 1963. The Dentists’ Supply Co. of New York. Anderson, J. N.: Applied Dental Materials, ed. 2, Oxford, 1961, Blackwell Scientific Publications, p. 272. Roche H. A. P.: An Assessment of the Values of Porcelain Versus Methyl Methacrylate ‘in Jacket Crown and Bridgework, Brit. D. J., 87:25-32, 1949. 1 Shafer, W. G., Hine, M. K. and Levy, B.: A Text-book of Oral Pathology, Philadelphia, 1958, W. B. Saunders Company, p. 618. Mitchell, D. F. : Gingival Pyogenic Granuloma, J. Perio. 27:273-276, 1956. Solomon, H. A., and Burke, E. M.: Giant Cell Reparative Granulomas of the Jaws. J.A.D.A. 65:762-766, 1962. Thoma, K. H., and Robinson, H. B. G.: Oral and Dental Diagnosis, Philadelphia, 1960, W. B. Saunders Company, p. 343. Shafer, W. G. : Oral Cancer in Indiana, J. Indiana D. A. 38 :7-11, 1959. Tylman, S. D. and Tylman, S. G.: Theory and Practice of Crown and Bridge Prosthodontics. St. Louis, 1960, The C. V. Mosby Company, p. 786. Johnston, J. F., Phillips, R. W., and Dykema, R. W.: Modern Practice in Crown and Bridge Prosthodontics, Philadelphia, 1960, W. B. Saunders Company. Gilson, T. D.: A Fixable-removable Prosthetic Attachment, J. PROS. DEN. 9:247-255. 1959. Mitchell, D. F.: The Irritational Qualities of Dental Materials, J.A.D.A. 59:954, 1959. Tylman, S. D.: Co-report: Problems in the Construction of Crowns and Bridges, Internat. D.J. 8:353, 1958. Pini, C. E. : Co-report : Hygienic Considerations in Crown and Bridge Prosthesis. Internat. D.J. 8:357, 1958.

Dewey, K. W., and Zugsmith,

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CHAh’GES

047

25. Sharry, J. J., Editor: Complete Denture Prosthodontics, New York, 1962, McGraw-Hill Book Company, Inc., p. 18. 26. Ostlund, S. G.: The Effect of Complete Dentures on the Gum Tissues, Acta. odont. scandinav. 16 : l-36, 1958. 27. Weiss, M. E.: Technique for Porcelain Pontics, D. Dig. 46:12-14. 1940. 117 TODD AVE., COMO PERTH,

WESTERN

AUSTRALIA