FORCEDEFORMATIONANDCHEWINGEFFICIENCY
26. Sherman P. A texture profile of foodstuffs based upon well defined rheological properties. J Food Sci 1969;34:458-62. 27. Vickers ZM. Relationships of chewing sounds to judgements of crispness, crunchiness and hardness. J Food Sci 1981;47:121-4. 28. Luke DA, Lucas PW. The significance of cusps. J Oral Rehabil 1983; 10:197-206. 29. Wang JS, Stohler CS. Textural propel&s of food used in studies of mastication. J Dent Res 1990;69:1546-50. 30. Feldman RS, Kapur KK, Alman JE, Chauncey HH. Aging and mastication: changesin performance and in the swallowing threshold with natural dentition. J Am Geriatr Sot 1980;28:97-103. 31. Chauncey HH, Kapur KK, Feller RP, Wayler AH. Altered masticatory function and perceptual estimates of chewing experience. Spec Care Dent 1981;1:250-5.
ect of removable partial gingival inflammation: A clinical Kenneth R. MeHenry, Lars A. Christersson, State University
32. Wayler AH, Muench ME, Kapur KK, Chauncey HH. Masticatory performance and food acceptability in persons with removable partial dentures, full dentures and intact dentition. J Gerontol 1984;39:284-9. Reprint requests to: DR. A. P. SLAGTER DEPARTMENT OF ORAL FUNCTION AND SPECIAL DENTAL CARE FACULTY OF THE MEDICAL SCIENCES CATHOLIC UNIVERSITY OF NIJMEGEN P.O. Box 9101 6500 HB NIJMEGEN, THE NETHERLANDS
denture model
DDS, MS,a Owe E. Johansson, DDSC
DDS,b
framework
design
on
and
of New York at Buffalo, School of Dental Medicine, Buffalo, N.Y.
A clinical trial using the experimental gingivitis model developed for periodontal clinical research was performed to evaluate the effect of a removable partial denture mandibular major connector design on the surrounding gingival tissues. A comparison of the state of health of adjacent gingival tissues was made between the linguoplate (control) and cingulum bar (test) major connectors. Clinical parameters were recorded in a single-blind crossover experimental gingivitis trial. Subjects were brought to a level of optimal gingival health and then randomly assigned to use one framework design while refraining from any oral hygiene. Measurements were made at ‘I-day intervals for 21 days. The subjects were returned to optimal oral health and repeated the experimental period with the alternate design. Results showed a greater increase in mean gingival inflammation with the control than with the test removable partial denture, suggesting that the cingulum bar has fewer de6rimental effects on gingival tissues than the linguoplate major connector. Results of this study suggest that the experimental gingivitis model can be a useful and valid system for studying the potential effects of a removable partial denture design on surrounding oral tissues. (J PROSTHET DENT 1992;68:799-803.)
ignificant advances have been made in the past three decades in the treatment and prevention of dental caries, mainly through fluoridation, use of fluoridated toothpastes, and increased use of dental sealark These factors, combined with the increase in the elderly population in the United States, have resulted in a substantial portion of the adult population with some remaining teeth requiring removable partial dentures.z, 3 Removable partial denture prostheses, although they
Supported by the New York State Science and Technology Foundation and the Austinal Corporation, Chicago, 111. aAssociate Professor, Department of Removable Prosthodontics. bVisiting Assistant Professor, Department of Oral Biology. CClinical Associate Professor, Department of Oral Biology. 10/l/40962
THEJOURNAL OFPROSTHETICDENTISTRY
serve as an excellent means of replacing missing teeth, may pose a serious threat to a patient’s remaining teeth. Many partial denture designs currently in use contribute to increased or altered oral bacterial flora475 and formation of dental plaque.6,7A removable partial denture may increase the incidence of caries, damage the periodontium, and increasethe amount of stress on the natural teeth.s-lo Therefore the design of a partial denture would seem critical, inasmuch as it must permit maintenance of healthy dental and periodontal conditions for the preservation of remaining teeth. The relationship between periodontal disease and removable partial dentures is of major importance in the long-term oral health of a patient. BergmanI in a review article discussed the relationship of plaque and oral hygiene factors to tissue coverage by a removable partial denture. Although several investigators in his review sug799
McNENRY,
JOHANSSON,
clinical model to studies involving tures.
AND
CHRISTERSSON
removable partial den-
MATERIAL AND METHODS Selection of patients
Fig.
I. Cingulum
bar mandibular
major connector.
gested that good oral hygiene can minimize the effects of tissue coverage, they did not dispute the potential detrimental effects of tissue coverage. Studies that examine the effects of removable partial dentures on the surrounding oral tissues vary greatly in their recommendations for optimal design. These differences in conclusions may be due to the experimental methods used. These studies have utilized clinical methods that either entail multiple variables and long study periods or rely heavily on in vitro simulations. One example of the variation in recommended designs concerns selection of the mandibular major connector for a patient with insufficient gingival space for placement of a lingual bar major connector. In the United States, textbooks advocate either a linguoplate or a continuous bar major connector when a lingual bar cannot be utilized. 12-17Scandinavian investigators, having employed large epidemiologic studies related to their public health system, have suggested a relationship between the occurrence of dental diseases of microbial etiology and factors of partial denture design.lsm21They suggest linguoplate major connectors, which have increased coverage of gingival and dental tissues, may increase food retention and promote plaque formation. The Scandinavian alternative to this extensive coverage is the cingulum, or dental bar major connector, introduced by Carlsson et al.22-24This major connector is used in place of the traditional linguoplate and rests on the lingual surface of the teeth away from the gingival tissues (Fig. 1). Placement of this major connector, which avoids the dentogingival margin, may result in less accumulation of plaque and a more favorable periodontal response. A recent article by Meeuwissen et a1.25reviewed the cingulum bar and discussed its apparent clinical advantages but in summary discussed the need for clinical studies to demonstrate its merits or shortcomings. This pilot study had two objectives: (1) to evaluate the effect of a mandibular major connector design of a partial denture framework on the local gingiva, and (2) to examine the feasibility of applying the experimental gingivitis
800
Eight male students, aged 25 to 30 years, with normal healthy periodontal conditions were selected as subjects. They had no evidence of radiographic bone loss, suppuration on probing, or pockets ~4 mm deep. They were required to have 10 contiguous anterior teeth and at least one posterior mandibular tooth in each quadrant. Subjects who had received systemic antimicrobial therapy within the previous 3 months were excluded, as were subjects with oral plaque-retention factors such as overextended restorations or ill-fitting crown margins. Female subjects were not used in this study to eliminate the possible local effects of cyclic hormonal changes.
Study
design
A single-blind crossover experimental gingivitis trial was used to study the effects of partial denture frameworks on local periodontal tissues (Fig. 2). This design requires that study participants refrain from performing oral hygiene procedures for predetermined periods of time to induce gingivitis. Two different frameworks, a control (linguoplate) design and a test (cingulum bar) design (Fig. 3), were worn in a randomly determined order during either of two 3-week periods. Clinical assessments were made at baseline and at T-day intervals. The frameworks did not replace any teeth and consisted of only the major connector supplied with sufficient rests and clasps for support and retention. The frameworks were constructed so that there was no interference with the subject’s natural occlusion. Impressions for the master casts were made with polysulfide mercaptan rubber (Kerr Manufacturing, Romulus, Mich.) in custom trays, and master casts were poured in improved dental stone (Kerr Manufacturing). Metal castings were fabricated in Vitallium at the Austinal Corporation (Chicago, Ill.) central laboratory, with the use of recommended blockout and relief. Each framework was seated in the mouth before the start of the experiment and checked for accuracy of fit and stability. Any required adjustments were done and affected area was repolished. Before the initiation of the experimental period, subjects were brought to optimal gingival health by repeated professional prophylaxis. Baseline data collection was performed after optimal gingival health was achieved, and one of the two partial denture frameworks was randomly selected to be inserted. The subjects were instructed to wear the framework at all times except when eating and to refrain from performing all forms of oral hygiene in the lower arch during the 3-week experimental period. After measurements were made on the twenty-first day, the subjects reinstituted oral hygiene procedures and were returned to optimal health with repeated prophylaxis over a
NOVEMBER
1992
VOLUME
68
NUMBER
5
FRAMEWORK
DESIGN
AND
GINGIVITIS
Fig. 2. Flow diagram of experimental design. Subjects were randomly assigned to use either test or control connector in phase I and alternate connector in phase II.
3-week period. New baseline data collection was performed, and the second partial denture framework design was inserted (Fig. 2). Periodontal measurements were again made at 7-day intervals. The examiner collecting the periodontal data was blinded from the knowledge of which partial denture design the subjects were wearing.
Clinical
measurement
parameters
The primary outcome variable, gingival inflammation, was recorded by use of the modified gingival index of L$e et a1.26The measurements were made on the lower six anterior teeth on days 7, 14, and 21. Three surfaces, distal, mesial, and midpoint of the lingual aspect of each tooth, were scored. Plaque accumulation was measured by means of a further modification of the plaque index of Quigley and Hein and Turesky et al.,28 developed at the Periodontal Disease Clinical Research Center of the State University of New York at Buffalo. This system emphasizes quantitative changes in the coronal extension of accumulated dental plaque. Three surfaces, distal, mesial, and the midpoint of the lingual aspect of each tooth, were scored. Trace 28 stain (Lorvic Corp. St. Louis, MO.) was used to visualize the accumulated supragingival plaque.
Data analyses
RESULT Seven of eight subjects completed all parts of the study. One subject was withdrawn from the study because of loss of a framework. Therefore data from the S-week examination period are based on one less subject for both groups (n = 7). The data from weeks 1 and 2 were collected to determine the dynamics of the effects of the tissue coverage, but the size of the sample and the variability of the sam-
JOURNAL
OF PROSTHETIC
major connector
experimental
Table I. Change in gingival index between baseline and l-, 2-, and 3-week examinations (mean f SE) Time point (wk)
Control
Test
1 2 3*
+0.5 f 0.1 +0.6 + 0.2 +023 + 0.1
+0.4 i- 0.1 +0.7 k 0.2 +0.5 z!c0.1
*Student’s t test; p < 0.05.
Data are presented as group averages ( f standard error [SE] of the means) based on subject means over all sites. In an experimental study of gingivitis in which no oral hygiene procedures were performed, increases in clinical parameters were expected to occur. The object was to compare differences in the degree of increase between the control and test groups; Student’s t test for paired comparisons was used to compare mean individual changes among subjects in the control and test groups.
TNE
Fig. 3. Test and control frameworks.
DENTISTRY
ples did not result in any demonstrable S-week examination.
Gingival
differences until the
index
Baseline average values for the gingival index (GI) were statistically similar, 0.6 ? 0.1 and 0.7 t 0.1, for the control and test groups, respectively. The GI values were increased in both the control and test groups at the l-, 2-, and 3-week examinations (Table I). The mean GI scores at 3 weeks were increased by 0.8 I 0.1 for the control group and 0.5 + 0.1 for the test group (p < 0.05). The increases from baseline in the percentage of gingival units with observed inflammation, that is the proportion of sites with a gingival index score of ml, also were statistically different (p < 0.05) for the control group (54.9%) compared with the test group (37.5%) (Fig. 4). There were no statistical dif-
801
McHENRY,
JOHANSSON,
AND
CHRISTERSSON
Table II. Change in plaque accumulation between baseline and l-, 2-, and 3-week examinations (mean i SE) Time point (wk)
1 2 3
Test
Control
Fig. 4. Increase in number of surfaces with recorded gingival inflammation from baseline to day 21 (percentage of surfaces receiving score of ~1). Measurements made lingually of six lower anterior teeth at three points per tooth: mesial, midpoint, and distal. T bars indicate standard error of mean (n = 7). Statistical significance was determined by Student’s t test (p < 0.05).
ferences for data collected at the l- and 2-week examinations. l?laque
accumulation
Baseline average values for plaque accumulation (PA) were 1.8 ? 0.4 (SE) and 2.0 i 0.4 (SE), for the control and test groups, respectively. The PA values for both groups then increased to a similar extent and by the 3-week examinationperiodhadincreasedby2.7 & 0.4 (SE) and2.2 + 0.4 (SE) for the control and test groups, respectively (Table II). The increase in PA was not statistically significant between the groups. ISCUSSION The present study, based on results of an experimental gingivitis model with a crossover design, suggests that the placement of a partial denture major connector has an impact on the condition of the adjacent gingival tissues. The control and test frameworks had different influences on the gingival index scores. The data indicate that the increased gingival inflammation caused by cessation of oral hygiene procedures was enhanced by the control design (linguloplate) compared with the test design (cingulum bar). These results indicate the possible benefits of the use of a cingulum bar, which is placed away from the gingival margins, in place of the traditional linguloplate, which covers the marginal gingival tissues, as the partial denture major connector. The differences in gingival inflammation between the plate and dental bar designs suggest that covering more gingival tissue promotes development of gingivitis, which may subsequently predispose an area to periodontal disease.The similar increase in plaque accumulation, based on a quantitative parameter, may be a result of the number of 802
Control
Test
+2.0 f 0.5 +2.4 f 0.5 +2.7 * 0.4
+1.8 + 0.4 +2.1 ri: 0.4 +2.2 2x 0.5
subjects enrolled in the pilot study. More subjects may be necessary to demonstrate differences in plaque accumulation. Alternatively, although the quantitatively recognizable amount of plaque is similar for the two groups, the design of the removable partial denture may affect the composition of the microorganisms in the plaque differently. Linguoplate coverage of the teeth and gingiva may also prevent the flow of saliva into this area and limit its neutralizing effects. Studies in both cariology and periodontology suggest that the quantity of plaque alone does not determine the caries rate, degree of gingival inflammation, or periodontal status, but the quality of the plaque may be a more significant factor.3, 2g-32 Present knowledge of the effects of partial dentures on the surrounding oral environment is derived primarily from three types of investigative data. Empiric or observational information (clinical judgment) represents the largest body of knowledge on the effects and function of a removable partial denture. This kind of data, although readily obtainable, remains subjective and is difficult to evaluate or quantify. In vitro studies are frequently found in the literature on removable partial denture design and function. These studies are appealing because they eliminate numerous variables inherent when utilizing human subjects. However, models of living tissue are extremely difficult to validate and relate to a clinical situation. Clinical studies comprise another method of research in prosthodontic literature. These primarily consist of retrospective cross-sectional or longitudinal studies, which utilize population or convenience samples. When studying populations of convenience samples with heterogeneity among subjects, proper controls are not available; therefore large numbers of subjects are required to demonstrate statistical differences. The differences found only represent associations not directly attributable to cause and effect, inasmuch as many variables are present. In addition, the effects being observed usually are allowed to develop over a natural course of time, which may require a lengthy study. An example of the difficulties in conducting large long-term studies is demonstrated by Chandler et a1.33After a g-year period the study was able to follow only 38 of the original 92 subjects. It would be advantageous to have a model for clinical studies of the effects of removable partial dentures on oral tissues where careful design, reduced variables, and proper experimental controls would enable the investigaNOVEMBER
1992
VOLUME
68
NUMBER
5
FRAMEWORK
DESIGN
AND
GINGIVITIS
tor to draw conclusions from the data by using fewer subjects in a study of reasonable length. The experimental model developed for clinical research on oral hygiene and gingivitis provides an ideal system that may be applicable to studies of removable partial dentures. It is derived from studies by L$e et a1.,26who demonstrated the initial evidence of a cause-and-effect relationship between dental plaque and developing gingivitis. Subsequent studies have shown that the response of each subject to increased amounts of plaque was reproducible and predictable both within and between different groups of subjects.34 Because each subject’s performance can be predicted over repeated trials,35 a crossover design that uses each subject as his or her own control is possible. The advantage of this design is that it requires fewer subjects for statistical analyses and reduces the amount of time needed for a study, since controlled witbholding of oral hygiene procedures accelerates plaque formation and gingivitis. All variables are provided with appropriate experimental controls in this type of study design. Therefore any difference in gingival inflammation between groups can be attributed directly to the parameter being studied. In conclusion, the results of this investigation demonstrated that in vivo studies of removable partial denture framework designs that use an experimental gingivitis model may provide meaningful data concerning their effect on the adjacent gingiva. The model allows valid data to be generated with the use of relatively small numbers of subjects over short periods of time. The use of subjects as their own controls reduces the variability in the data, and the strict control of conditions allows effects to be observed in an accelerated and controlled manner. Further studies evaluating the periodontal parameters of hard and soft tissues of removable partial denture designs are required for a complete understanding of the relationship between periodontal disease and the placement of a removable partial denture major connector. REFERENCES 1. The prevalence of dental caries in United States children 1979-80.The National Dental Caries Prevalence Survey. Washington, DC: United States Department of Health and Human Services,1981.Public Health Service, National Institutes of Health, Publication No. 82-2245. 2. Basic data on dental examination findings of persons 1-74 years United States 1971-1974.Washington, DC: Department of Health, Education, and Welfare. Public Health Service, National Center for Health Statistics. DREW Publication No. PHS 79.1662,11:214. Government Printing Office, 1979:1-31. 3. Oral health of United States adults. National survey of oral health in U.S. employed adults and seniors 1985-86national findings. Washington, DC: Department of Health and Human Services, 1987. National Institutes of Health, Publication No. 87-2868. 4. Salonen L, Allander L, Bratthall D, Hellden L. Mutans streptococci, oral hygiene, and caries in an adult Swedish population, J Dent Res 1990;69:1469-753. 5. Brill N, Tryde G, Stoltze K, El Ghamrawy E. Ecologic changesin the oral cavity caused by removable partial dentures. J PROSTHET DENT 1977;38:138-48.
6. El-Ghamrawy E. Quantitative changesin dental plaque formation related to removabkepartial dentures. J Oral Rehabil 1976;3:115-20. 7. Addy M, Bates JF. Plaque accumulation following the wearing of different types of removable partial dentures. J Oral Rehabil1979;6:111-7.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
8. Douglass C, Gillings D, Solecito W, Gammon M. The potential for increasein the periodontal diseasesof the agedpopulation. J Periodontoi 1984;54:721-30. 9. Bergman B, Hugoson A, Olsson CO. Caries, periodontal and prosthetic findings in patients with removable partial dentures: a ten-year longitudinal study. J PROSTHET DENT 1982;48:506-14. 10. Bergman B, Ericson G. Cross-sectional study of the periodontal status of removable partial denture patients. J PROSTHET DENT 1989;61:20811.
11. Bergman B. Periodontal reactions related to removable partial dentures: a literature overview. J PROSTHET DENT 1987;58:454-8. 12. McGivney G, Castleberry D. McCracken’s removable partial prosthodontics. 8th ed. St. Louis: CV Mosby, 1989:26-34. 13. Renner R, Boucher L. Removable partial dentures. Chicago: QuintessenceBooks, 1987:73-5. 14. Miller E, Grass0 J. Removable partial prosthodontics. 2nd ed. Baltimore: Williams & Wilkins, 1981:184-91. 15. Zarb GA, Bergman B, Clayton JA, MacKay HK. Prosthodontic treatment for partially edentulous patients. St Louis: CV Mosby, 1983:32-40. 16. Krol AJ. Removable partial denture design-outline syllabus. San Francisco: University of Pacific School of Dentistry, 19&1:40-9. 17. Stewart K, Rudd K, Kuebker W. Clinical removable prosthodontics. St. Louis: CV Mosby, 1983:32-g. 18. Koivumaa K, Hedegaard B, Carlsson G. Studies in partial denture prosthesis I. Suom Hammaslaak seur. Tiom. 1960;56:248-306. 19. Markkanen H, Lappalainen R, Honkala E, Tuominen, R. Periodontal conditions with removable complete and partial dentures in the adult population aged 40 and over. J Oral Rehabil 1989;14:355-60. 20. Tuominen R, Ranta K, Paunio I. Wearing of removable partial dentures in relation to periodontal pockets. J Oral Rehabil 1987;16:119-26. 21. Derry A. Bertram U. A clinical survey of removable partial dentures after 2 years usage.Acta Odontol Stand 1970;28:581-98. 22. Carlsson CE, Hedegaard B, Koivuma KK. Studies in partial dental prosthesis II. Acta Odontol Stand 1961;19:215-37. 23. Carlsson CE, Hedegaard B, Koivuma KK. Studies in partial dental prosthesis III. Acta Odontol Stand 1962;20:95-119. 24. Carlsson CE, Hedegaard B, Koivuma KK. Final results of a 4 year longitudinal investigation of dentogingivally supported partial dentures. Study IV. Acta Odontol Stand 1962;23:443-72. 25. MeeuwissenR, Keltjens H, Battistuzzi G. Cingulum bar as a major connector for mandibular removable partial dentures. J PXOSTHET DENT 1991;66:221-3.
26. L$e H, Theilade E, Jensen SB. Experimental gingivitis in man. J Periodontol 1965;36:177-87. 27. Quigley GA, Hein J. Comparative cleansing efficiency of manual and power brushing. J Am Dent Assoc 1962;65:26-9. 28. Turesky S, Gilmore ND, Glickman I. Reduced plaque formation by the chloromethyl analogue of Victamine C. J Periodontol 1970;41:41-3. 29. Socransky SS. Microbiology of periodontal disease-present status and future considerations. J Periodontol 1977;48:497-504. 30. Christersson LA, Zambon JJ, Dunford RG, Grossi S, GencoRJ. Specific subgingival bacteria and diagnosisof gingivitis and periodontitis. J Dent Res 1989;68:1633-9.
31. Christersson LA, Zambon JJ, Genco RJ. Dental bacterial plaques: nature and role in periodontal disease.J Clin Periodontol 1991;18:441-6. 32. Genco RI, Zambon JJ, Christersson LA. The origin of periodontal infections. Adv Dent Res 1988;2:245-59. 33. Chandler J, Brudvik J. Clinical evaluation of patients eight to nine years after placement of removable partial dentures. J PROSTHET DENT 1984;51:736-43.
34. Loesche WJ. Clinical and microbiologic aspects of chemotherapeutic agents used according to the specific plaque hypothesis. J Dent Res 1979;58:2404-12. 35. Theilade E, Wright H, Jensen SB, Loe H. Experimental gingivitis in man. II. A longitudinal clinical and bacteriological investigation. J Periodont Res 1966;1:1-13. Reprint requests to: DR. KENNETH R. MCHENRY 225 SQUIRE HALL SUNY AT BUFFALO SCHOOL OF DENTAL MEDICINE 3435 MAIN ST. BUFFALO, NY 14214
803
26. Sherman P. A texture profile of foodstuffs based upon well defined rheological properties. J Food Sci 1969;34:458-62. 27. Vickers ZM. Relationships of chewing sounds to judgements of crispness, crunchiness and hardness. J Food Sci 1981;47:121-4. 28. Luke DA, Lucas PW. The significance of cusps. J Oral Rehabil 1983; 10:197-206. 29. Wang JS, Stohler CS. Textural propel&s of food used in studies of mastication. J Dent Res 1990;69:1546-50. 30. Feldman RS, Kapur KK, Alman JE, Chauncey HH. Aging and mastication: changesin performance and in the swallowing threshold with natural dentition. J Am Geriatr Sot 1980;28:97-103. 31. Chauncey HH, Kapur KK, Feller RP, Wayler AH. Altered masticatory function and perceptual estimates of chewing experience. Spec Care Dent 1981;1:250-5.
ect of removable partial gingival inflammation: A clinical Kenneth R. MeHenry, Lars A. Christersson, State University
32. Wayler AH, Muench ME, Kapur KK, Chauncey HH. Masticatory performance and food acceptability in persons with removable partial dentures, full dentures and intact dentition. J Gerontol 1984;39:284-9. Reprint requests to: DR. A. P. SLAGTER DEPARTMENT OF ORAL FUNCTION AND SPECIAL DENTAL CARE FACULTY OF THE MEDICAL SCIENCES CATHOLIC UNIVERSITY OF NIJMEGEN P.O. Box 9101 6500 HB NIJMEGEN, THE NETHERLANDS
denture model
DDS, MS,a Owe E. Johansson, DDSC
DDS,b
framework
design
on
and
of New York at Buffalo, School of Dental Medicine, Buffalo, N.Y.
A clinical trial using the experimental gingivitis model developed for periodontal clinical research was performed to evaluate the effect of a removable partial denture mandibular major connector design on the surrounding gingival tissues. A comparison of the state of health of adjacent gingival tissues was made between the linguoplate (control) and cingulum bar (test) major connectors. Clinical parameters were recorded in a single-blind crossover experimental gingivitis trial. Subjects were brought to a level of optimal gingival health and then randomly assigned to use one framework design while refraining from any oral hygiene. Measurements were made at ‘I-day intervals for 21 days. The subjects were returned to optimal oral health and repeated the experimental period with the alternate design. Results showed a greater increase in mean gingival inflammation with the control than with the test removable partial denture, suggesting that the cingulum bar has fewer de6rimental effects on gingival tissues than the linguoplate major connector. Results of this study suggest that the experimental gingivitis model can be a useful and valid system for studying the potential effects of a removable partial denture design on surrounding oral tissues. (J PROSTHET DENT 1992;68:799-803.)
ignificant advances have been made in the past three decades in the treatment and prevention of dental caries, mainly through fluoridation, use of fluoridated toothpastes, and increased use of dental sealark These factors, combined with the increase in the elderly population in the United States, have resulted in a substantial portion of the adult population with some remaining teeth requiring removable partial dentures.z, 3 Removable partial denture prostheses, although they
Supported by the New York State Science and Technology Foundation and the Austinal Corporation, Chicago, 111. aAssociate Professor, Department of Removable Prosthodontics. bVisiting Assistant Professor, Department of Oral Biology. CClinical Associate Professor, Department of Oral Biology. 10/l/40962
THEJOURNAL OFPROSTHETICDENTISTRY
serve as an excellent means of replacing missing teeth, may pose a serious threat to a patient’s remaining teeth. Many partial denture designs currently in use contribute to increased or altered oral bacterial flora475 and formation of dental plaque.6,7A removable partial denture may increase the incidence of caries, damage the periodontium, and increasethe amount of stress on the natural teeth.s-lo Therefore the design of a partial denture would seem critical, inasmuch as it must permit maintenance of healthy dental and periodontal conditions for the preservation of remaining teeth. The relationship between periodontal disease and removable partial dentures is of major importance in the long-term oral health of a patient. BergmanI in a review article discussed the relationship of plaque and oral hygiene factors to tissue coverage by a removable partial denture. Although several investigators in his review sug799
McNENRY,
JOHANSSON,
clinical model to studies involving tures.
AND
CHRISTERSSON
removable partial den-
MATERIAL AND METHODS Selection of patients
Fig.
I. Cingulum
bar mandibular
major connector.
gested that good oral hygiene can minimize the effects of tissue coverage, they did not dispute the potential detrimental effects of tissue coverage. Studies that examine the effects of removable partial dentures on the surrounding oral tissues vary greatly in their recommendations for optimal design. These differences in conclusions may be due to the experimental methods used. These studies have utilized clinical methods that either entail multiple variables and long study periods or rely heavily on in vitro simulations. One example of the variation in recommended designs concerns selection of the mandibular major connector for a patient with insufficient gingival space for placement of a lingual bar major connector. In the United States, textbooks advocate either a linguoplate or a continuous bar major connector when a lingual bar cannot be utilized. 12-17Scandinavian investigators, having employed large epidemiologic studies related to their public health system, have suggested a relationship between the occurrence of dental diseases of microbial etiology and factors of partial denture design.lsm21They suggest linguoplate major connectors, which have increased coverage of gingival and dental tissues, may increase food retention and promote plaque formation. The Scandinavian alternative to this extensive coverage is the cingulum, or dental bar major connector, introduced by Carlsson et al.22-24This major connector is used in place of the traditional linguoplate and rests on the lingual surface of the teeth away from the gingival tissues (Fig. 1). Placement of this major connector, which avoids the dentogingival margin, may result in less accumulation of plaque and a more favorable periodontal response. A recent article by Meeuwissen et a1.25reviewed the cingulum bar and discussed its apparent clinical advantages but in summary discussed the need for clinical studies to demonstrate its merits or shortcomings. This pilot study had two objectives: (1) to evaluate the effect of a mandibular major connector design of a partial denture framework on the local gingiva, and (2) to examine the feasibility of applying the experimental gingivitis
800
Eight male students, aged 25 to 30 years, with normal healthy periodontal conditions were selected as subjects. They had no evidence of radiographic bone loss, suppuration on probing, or pockets ~4 mm deep. They were required to have 10 contiguous anterior teeth and at least one posterior mandibular tooth in each quadrant. Subjects who had received systemic antimicrobial therapy within the previous 3 months were excluded, as were subjects with oral plaque-retention factors such as overextended restorations or ill-fitting crown margins. Female subjects were not used in this study to eliminate the possible local effects of cyclic hormonal changes.
Study
design
A single-blind crossover experimental gingivitis trial was used to study the effects of partial denture frameworks on local periodontal tissues (Fig. 2). This design requires that study participants refrain from performing oral hygiene procedures for predetermined periods of time to induce gingivitis. Two different frameworks, a control (linguoplate) design and a test (cingulum bar) design (Fig. 3), were worn in a randomly determined order during either of two 3-week periods. Clinical assessments were made at baseline and at T-day intervals. The frameworks did not replace any teeth and consisted of only the major connector supplied with sufficient rests and clasps for support and retention. The frameworks were constructed so that there was no interference with the subject’s natural occlusion. Impressions for the master casts were made with polysulfide mercaptan rubber (Kerr Manufacturing, Romulus, Mich.) in custom trays, and master casts were poured in improved dental stone (Kerr Manufacturing). Metal castings were fabricated in Vitallium at the Austinal Corporation (Chicago, Ill.) central laboratory, with the use of recommended blockout and relief. Each framework was seated in the mouth before the start of the experiment and checked for accuracy of fit and stability. Any required adjustments were done and affected area was repolished. Before the initiation of the experimental period, subjects were brought to optimal gingival health by repeated professional prophylaxis. Baseline data collection was performed after optimal gingival health was achieved, and one of the two partial denture frameworks was randomly selected to be inserted. The subjects were instructed to wear the framework at all times except when eating and to refrain from performing all forms of oral hygiene in the lower arch during the 3-week experimental period. After measurements were made on the twenty-first day, the subjects reinstituted oral hygiene procedures and were returned to optimal health with repeated prophylaxis over a
NOVEMBER
1992
VOLUME
68
NUMBER
5
FRAMEWORK
DESIGN
AND
GINGIVITIS
Fig. 2. Flow diagram of experimental design. Subjects were randomly assigned to use either test or control connector in phase I and alternate connector in phase II.
3-week period. New baseline data collection was performed, and the second partial denture framework design was inserted (Fig. 2). Periodontal measurements were again made at 7-day intervals. The examiner collecting the periodontal data was blinded from the knowledge of which partial denture design the subjects were wearing.
Clinical
measurement
parameters
The primary outcome variable, gingival inflammation, was recorded by use of the modified gingival index of L$e et a1.26The measurements were made on the lower six anterior teeth on days 7, 14, and 21. Three surfaces, distal, mesial, and midpoint of the lingual aspect of each tooth, were scored. Plaque accumulation was measured by means of a further modification of the plaque index of Quigley and Hein and Turesky et al.,28 developed at the Periodontal Disease Clinical Research Center of the State University of New York at Buffalo. This system emphasizes quantitative changes in the coronal extension of accumulated dental plaque. Three surfaces, distal, mesial, and the midpoint of the lingual aspect of each tooth, were scored. Trace 28 stain (Lorvic Corp. St. Louis, MO.) was used to visualize the accumulated supragingival plaque.
Data analyses
RESULT Seven of eight subjects completed all parts of the study. One subject was withdrawn from the study because of loss of a framework. Therefore data from the S-week examination period are based on one less subject for both groups (n = 7). The data from weeks 1 and 2 were collected to determine the dynamics of the effects of the tissue coverage, but the size of the sample and the variability of the sam-
JOURNAL
OF PROSTHETIC
major connector
experimental
Table I. Change in gingival index between baseline and l-, 2-, and 3-week examinations (mean f SE) Time point (wk)
Control
Test
1 2 3*
+0.5 f 0.1 +0.6 + 0.2 +023 + 0.1
+0.4 i- 0.1 +0.7 k 0.2 +0.5 z!c0.1
*Student’s t test; p < 0.05.
Data are presented as group averages ( f standard error [SE] of the means) based on subject means over all sites. In an experimental study of gingivitis in which no oral hygiene procedures were performed, increases in clinical parameters were expected to occur. The object was to compare differences in the degree of increase between the control and test groups; Student’s t test for paired comparisons was used to compare mean individual changes among subjects in the control and test groups.
TNE
Fig. 3. Test and control frameworks.
DENTISTRY
ples did not result in any demonstrable S-week examination.
Gingival
differences until the
index
Baseline average values for the gingival index (GI) were statistically similar, 0.6 ? 0.1 and 0.7 t 0.1, for the control and test groups, respectively. The GI values were increased in both the control and test groups at the l-, 2-, and 3-week examinations (Table I). The mean GI scores at 3 weeks were increased by 0.8 I 0.1 for the control group and 0.5 + 0.1 for the test group (p < 0.05). The increases from baseline in the percentage of gingival units with observed inflammation, that is the proportion of sites with a gingival index score of ml, also were statistically different (p < 0.05) for the control group (54.9%) compared with the test group (37.5%) (Fig. 4). There were no statistical dif-
801
McHENRY,
JOHANSSON,
AND
CHRISTERSSON
Table II. Change in plaque accumulation between baseline and l-, 2-, and 3-week examinations (mean i SE) Time point (wk)
1 2 3
Test
Control
Fig. 4. Increase in number of surfaces with recorded gingival inflammation from baseline to day 21 (percentage of surfaces receiving score of ~1). Measurements made lingually of six lower anterior teeth at three points per tooth: mesial, midpoint, and distal. T bars indicate standard error of mean (n = 7). Statistical significance was determined by Student’s t test (p < 0.05).
ferences for data collected at the l- and 2-week examinations. l?laque
accumulation
Baseline average values for plaque accumulation (PA) were 1.8 ? 0.4 (SE) and 2.0 i 0.4 (SE), for the control and test groups, respectively. The PA values for both groups then increased to a similar extent and by the 3-week examinationperiodhadincreasedby2.7 & 0.4 (SE) and2.2 + 0.4 (SE) for the control and test groups, respectively (Table II). The increase in PA was not statistically significant between the groups. ISCUSSION The present study, based on results of an experimental gingivitis model with a crossover design, suggests that the placement of a partial denture major connector has an impact on the condition of the adjacent gingival tissues. The control and test frameworks had different influences on the gingival index scores. The data indicate that the increased gingival inflammation caused by cessation of oral hygiene procedures was enhanced by the control design (linguloplate) compared with the test design (cingulum bar). These results indicate the possible benefits of the use of a cingulum bar, which is placed away from the gingival margins, in place of the traditional linguloplate, which covers the marginal gingival tissues, as the partial denture major connector. The differences in gingival inflammation between the plate and dental bar designs suggest that covering more gingival tissue promotes development of gingivitis, which may subsequently predispose an area to periodontal disease.The similar increase in plaque accumulation, based on a quantitative parameter, may be a result of the number of 802
Control
Test
+2.0 f 0.5 +2.4 f 0.5 +2.7 * 0.4
+1.8 + 0.4 +2.1 ri: 0.4 +2.2 2x 0.5
subjects enrolled in the pilot study. More subjects may be necessary to demonstrate differences in plaque accumulation. Alternatively, although the quantitatively recognizable amount of plaque is similar for the two groups, the design of the removable partial denture may affect the composition of the microorganisms in the plaque differently. Linguoplate coverage of the teeth and gingiva may also prevent the flow of saliva into this area and limit its neutralizing effects. Studies in both cariology and periodontology suggest that the quantity of plaque alone does not determine the caries rate, degree of gingival inflammation, or periodontal status, but the quality of the plaque may be a more significant factor.3, 2g-32 Present knowledge of the effects of partial dentures on the surrounding oral environment is derived primarily from three types of investigative data. Empiric or observational information (clinical judgment) represents the largest body of knowledge on the effects and function of a removable partial denture. This kind of data, although readily obtainable, remains subjective and is difficult to evaluate or quantify. In vitro studies are frequently found in the literature on removable partial denture design and function. These studies are appealing because they eliminate numerous variables inherent when utilizing human subjects. However, models of living tissue are extremely difficult to validate and relate to a clinical situation. Clinical studies comprise another method of research in prosthodontic literature. These primarily consist of retrospective cross-sectional or longitudinal studies, which utilize population or convenience samples. When studying populations of convenience samples with heterogeneity among subjects, proper controls are not available; therefore large numbers of subjects are required to demonstrate statistical differences. The differences found only represent associations not directly attributable to cause and effect, inasmuch as many variables are present. In addition, the effects being observed usually are allowed to develop over a natural course of time, which may require a lengthy study. An example of the difficulties in conducting large long-term studies is demonstrated by Chandler et a1.33After a g-year period the study was able to follow only 38 of the original 92 subjects. It would be advantageous to have a model for clinical studies of the effects of removable partial dentures on oral tissues where careful design, reduced variables, and proper experimental controls would enable the investigaNOVEMBER
1992
VOLUME
68
NUMBER
5
FRAMEWORK
DESIGN
AND
GINGIVITIS
tor to draw conclusions from the data by using fewer subjects in a study of reasonable length. The experimental model developed for clinical research on oral hygiene and gingivitis provides an ideal system that may be applicable to studies of removable partial dentures. It is derived from studies by L$e et a1.,26who demonstrated the initial evidence of a cause-and-effect relationship between dental plaque and developing gingivitis. Subsequent studies have shown that the response of each subject to increased amounts of plaque was reproducible and predictable both within and between different groups of subjects.34 Because each subject’s performance can be predicted over repeated trials,35 a crossover design that uses each subject as his or her own control is possible. The advantage of this design is that it requires fewer subjects for statistical analyses and reduces the amount of time needed for a study, since controlled witbholding of oral hygiene procedures accelerates plaque formation and gingivitis. All variables are provided with appropriate experimental controls in this type of study design. Therefore any difference in gingival inflammation between groups can be attributed directly to the parameter being studied. In conclusion, the results of this investigation demonstrated that in vivo studies of removable partial denture framework designs that use an experimental gingivitis model may provide meaningful data concerning their effect on the adjacent gingiva. The model allows valid data to be generated with the use of relatively small numbers of subjects over short periods of time. The use of subjects as their own controls reduces the variability in the data, and the strict control of conditions allows effects to be observed in an accelerated and controlled manner. Further studies evaluating the periodontal parameters of hard and soft tissues of removable partial denture designs are required for a complete understanding of the relationship between periodontal disease and the placement of a removable partial denture major connector. REFERENCES 1. The prevalence of dental caries in United States children 1979-80.The National Dental Caries Prevalence Survey. Washington, DC: United States Department of Health and Human Services,1981.Public Health Service, National Institutes of Health, Publication No. 82-2245. 2. Basic data on dental examination findings of persons 1-74 years United States 1971-1974.Washington, DC: Department of Health, Education, and Welfare. Public Health Service, National Center for Health Statistics. DREW Publication No. PHS 79.1662,11:214. Government Printing Office, 1979:1-31. 3. Oral health of United States adults. National survey of oral health in U.S. employed adults and seniors 1985-86national findings. Washington, DC: Department of Health and Human Services, 1987. National Institutes of Health, Publication No. 87-2868. 4. Salonen L, Allander L, Bratthall D, Hellden L. Mutans streptococci, oral hygiene, and caries in an adult Swedish population, J Dent Res 1990;69:1469-753. 5. Brill N, Tryde G, Stoltze K, El Ghamrawy E. Ecologic changesin the oral cavity caused by removable partial dentures. J PROSTHET DENT 1977;38:138-48.
6. El-Ghamrawy E. Quantitative changesin dental plaque formation related to removabkepartial dentures. J Oral Rehabil 1976;3:115-20. 7. Addy M, Bates JF. Plaque accumulation following the wearing of different types of removable partial dentures. J Oral Rehabil1979;6:111-7.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
8. Douglass C, Gillings D, Solecito W, Gammon M. The potential for increasein the periodontal diseasesof the agedpopulation. J Periodontoi 1984;54:721-30. 9. Bergman B, Hugoson A, Olsson CO. Caries, periodontal and prosthetic findings in patients with removable partial dentures: a ten-year longitudinal study. J PROSTHET DENT 1982;48:506-14. 10. Bergman B, Ericson G. Cross-sectional study of the periodontal status of removable partial denture patients. J PROSTHET DENT 1989;61:20811.
11. Bergman B. Periodontal reactions related to removable partial dentures: a literature overview. J PROSTHET DENT 1987;58:454-8. 12. McGivney G, Castleberry D. McCracken’s removable partial prosthodontics. 8th ed. St. Louis: CV Mosby, 1989:26-34. 13. Renner R, Boucher L. Removable partial dentures. Chicago: QuintessenceBooks, 1987:73-5. 14. Miller E, Grass0 J. Removable partial prosthodontics. 2nd ed. Baltimore: Williams & Wilkins, 1981:184-91. 15. Zarb GA, Bergman B, Clayton JA, MacKay HK. Prosthodontic treatment for partially edentulous patients. St Louis: CV Mosby, 1983:32-40. 16. Krol AJ. Removable partial denture design-outline syllabus. San Francisco: University of Pacific School of Dentistry, 19&1:40-9. 17. Stewart K, Rudd K, Kuebker W. Clinical removable prosthodontics. St. Louis: CV Mosby, 1983:32-g. 18. Koivumaa K, Hedegaard B, Carlsson G. Studies in partial denture prosthesis I. Suom Hammaslaak seur. Tiom. 1960;56:248-306. 19. Markkanen H, Lappalainen R, Honkala E, Tuominen, R. Periodontal conditions with removable complete and partial dentures in the adult population aged 40 and over. J Oral Rehabil 1989;14:355-60. 20. Tuominen R, Ranta K, Paunio I. Wearing of removable partial dentures in relation to periodontal pockets. J Oral Rehabil 1987;16:119-26. 21. Derry A. Bertram U. A clinical survey of removable partial dentures after 2 years usage.Acta Odontol Stand 1970;28:581-98. 22. Carlsson CE, Hedegaard B, Koivuma KK. Studies in partial dental prosthesis II. Acta Odontol Stand 1961;19:215-37. 23. Carlsson CE, Hedegaard B, Koivuma KK. Studies in partial dental prosthesis III. Acta Odontol Stand 1962;20:95-119. 24. Carlsson CE, Hedegaard B, Koivuma KK. Final results of a 4 year longitudinal investigation of dentogingivally supported partial dentures. Study IV. Acta Odontol Stand 1962;23:443-72. 25. MeeuwissenR, Keltjens H, Battistuzzi G. Cingulum bar as a major connector for mandibular removable partial dentures. J PXOSTHET DENT 1991;66:221-3.
26. L$e H, Theilade E, Jensen SB. Experimental gingivitis in man. J Periodontol 1965;36:177-87. 27. Quigley GA, Hein J. Comparative cleansing efficiency of manual and power brushing. J Am Dent Assoc 1962;65:26-9. 28. Turesky S, Gilmore ND, Glickman I. Reduced plaque formation by the chloromethyl analogue of Victamine C. J Periodontol 1970;41:41-3. 29. Socransky SS. Microbiology of periodontal disease-present status and future considerations. J Periodontol 1977;48:497-504. 30. Christersson LA, Zambon JJ, Dunford RG, Grossi S, GencoRJ. Specific subgingival bacteria and diagnosisof gingivitis and periodontitis. J Dent Res 1989;68:1633-9.
31. Christersson LA, Zambon JJ, Genco RJ. Dental bacterial plaques: nature and role in periodontal disease.J Clin Periodontol 1991;18:441-6. 32. Genco RI, Zambon JJ, Christersson LA. The origin of periodontal infections. Adv Dent Res 1988;2:245-59. 33. Chandler J, Brudvik J. Clinical evaluation of patients eight to nine years after placement of removable partial dentures. J PROSTHET DENT 1984;51:736-43.
34. Loesche WJ. Clinical and microbiologic aspects of chemotherapeutic agents used according to the specific plaque hypothesis. J Dent Res 1979;58:2404-12. 35. Theilade E, Wright H, Jensen SB, Loe H. Experimental gingivitis in man. II. A longitudinal clinical and bacteriological investigation. J Periodont Res 1966;1:1-13. Reprint requests to: DR. KENNETH R. MCHENRY 225 SQUIRE HALL SUNY AT BUFFALO SCHOOL OF DENTAL MEDICINE 3435 MAIN ST. BUFFALO, NY 14214
803
