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Effect of different crown contours on periodontal health in dogs. Microbiological results
Journal of Dentistry (2004) 32, 153–159
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Effect of different crown contours on periodontal health in dogs. Microbiological results R.J. Kohala,b,*, K. Pelzc, J.R. Struba a
Department of Prosthodontics, Albert-Ludwigs University, Hugstetter Str. 55, Freiburg 79106, Germany Division of Periodontology, Department of Stomatology, Health Science Center, University of Texas, Houston, TX, USA c Department of Microbiology and Hygiene, Albert-Ludwigs University, Freiburg 79106, Germany b
Received 15 May 2003; revised 10 September 2003; accepted 29 September 2003
KEYWORDS Animal study; Crown contour; Overcontour; Periodontal health; Microbiology; DNA–DNAhybridization
Summary Objectives. In some clinical circumstances, i.e. in cases when the upper anterior region has to be restored by prosthetic means, it is necessary to place the margins of crowns and fixed partial dentures subgingivally. In addition, in periodontally compromised patients the restoration sometimes has to be overcontoured in order to replace the lost interdental papilla. The overcontoured crown margin may influence the subgingival bacterial composition. Therefore, the aim of the present investigation was to evaluate the effect of three different subgingival crown contours in dogs on the composition of the subgingival microbiota. Methods. In four adult beagle dogs the second and third premolars were prepared in three quadrants and restored with single gold crowns. The unprepared second and third premolars in the last quadrant served as controls. The crowns had three different emergence profiles including a normal contour, a 308 and a 508 over-contour. During the entire study period, professional oral hygiene was performed seven times a week. Microbiological samples were harvested from four sites of test and control teeth (mesial, distal, buccal and lingual) at baseline, after 3 months, and after 5 months. Results. The microbiological analysis (DNA –DNA hybridization technique) of the subgingival microbial flora revealed a dominance of P. intermedia, T. denticola and C. showae in all test and control groups at baseline. At three months, the total amount of bacteria increased and a broader variety of bacterial species could be detected. The detection frequency of most bacterial species increased from baseline to the 5-month evaluation. The frequency of detection of some species was higher in the 308 and 508 overcontoured test groups compared to the normal contour group and to the natural teeth. Conclusion. It can be concluded within the limits of this investigation that overcontoured gold crowns placed subgingivally have only slight effects on the microbiological composition in dogs when an intensive oral hygiene regimen was executed. q 2003 Elsevier Ltd. All rights reserved.
Introduction *Corresponding author. Tel.: þ 49-761-270-4906/4977; fax: þ 49-761-270-4925. E-mail address: [email protected]
A number of factors may influence the health condition of the periodontium: the physical or
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chemical properties of crown materials used,1 the marginal fit of a crown restoration,2 – 4 the position of the crown margin,5 – 7 the occlusion of the restoration,8,9 and the crown contour itself.10 – 13 Hence, regarding the influence of artificial crown contours there exist controversial opinions.12,14,15 Several authors have mentioned that from the periodontal point of view, under-contoured crowns are preferred when compared to overcontoured ones.11,12,14,16 Nevertheless, in the esthetic zone of patients with periodontally compromised teeth, it is often mandatory to place the crown margins subgingivally and to overcontour them for esthetic reasons.17 One recent clinical investigation reported on the impact of different emergence profiles of Procera titanium crowns on the quantity and quality of dental plaque.18 Within the limitations of their study, the authors found that titanium crowns with emergence profiles of up to 408 formed less plaque than the healthy controls. There was no higher accumulation of S. mutans in relation to increasing emergence profiles. The investigators did not report on crown contours . 408 nor on the periodontal pathological microbiological composition of the plaque. Therefore, the aim of this animal investigation was to evaluate microbiologically the effect of different subgingival crown contours in dogs. In the first part of our investigation,19 we reported on the clinical outcome of three different crown contours when placed subgingivally. We could show that the Plaque Index increased for the over-contoured (30 and 508) groups. The difference in plaque accumulation could be correlated to the Gingival Index and the Gingival Crevicular Fluid Flow. The Pocket Probing Depths as well as the Clinical Attachment
Figure 1
Levels were higher for the over-contoured groups than for the control group.
Materials and methods The study protocol was approved by the Animal Welfare Committee of the University of Texas Health Science Center at Houston. The study was performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals. The outline of the experiment is shown in Fig. 1. The clinical procedures were presented in detail elsewhere.19 Briefly, four beagle dogs were utilized in this investigation. All teeth were cleaned and a strict oral hygiene program was initiated consisting of tooth brushing with pumice and dental floss seven times a week. The scaling, prosthetic and clinical evaluation procedures were performed under general anesthesia. One month after commencing the oral hygiene regime, the second and third premolars in three quadrants were prepared for crown restorations. A subgingival shoulder was cut on the mesial and distal aspects of the teeth and a chamfer on the buccal and lingual sides. The tooth preparations were placed approximately 0.5 – 1 mm below the gingival margin. The unprepared second and third premolars in one quadrant served as controls. After tooth preparation retraction cords were placed, impressions were taken, and single, high noble gold alloy crowns (Degulor M, Degussa, Pforzheim, Germany) with three different emergence profiles were inserted: (1) normal (tooth) contour, (2) 308 and (3) 508 overcontoured profiles relative to the long axis of the abutments. In each
Outline of the experiment.
Effect of different crown contours on periodontal health in dogs. Microbiological results
Table 1 Preinvestigational means ðxÞ; standard deviations (SD) of organisms £ 106 (in parentheses: mean percentages ðxÞ and standard deviations (SD)). Bacteria
x ^ SD
S. sanguis S. intermedius A. viscosus P. gingivalis P. intermedia F. nucleatum A. actinomycetemcomitans C. showae E. corrodens T. denticola
3.0 ^ 1.0 (2.4 ^ 1.0) 5.9 ^ 3.2 (4.6 ^ 2.6) 23.9 ^ 18.4 (19.9 ^ 16.3) 17.4 ^ 5.4 (13.6 ^ 2.2) 30.3 ^ 10.8 (23.6 ^ 5.1) 5.7 ^ 1.7 (4.5 ^ 1.3) 1.4 ^ 1.2 (1.0 ^ 0.7) 11.6 ^ 7.8 (8.7 ^ 4.7) 8.5 ^ 4.9 (7.0 ^ 4.1) 18.8 ^ 12.7 (14.7 ^ 10.0)
quadrant only one type of crown contour was inserted on the two premolars. The analysis of bacterial species was performed using DNA hybridization according to the ‘Checkerboard’ technique described by Socransky et al.20 After removing the supragingival plaque with sterile cotton pellets, subgingival plaque was harvested using sterile curettes and transferred into tubes containing 100 ml of TE (10 mM Tris – HCl, 1 mM EDTA, pH 7.6), adding 100 ml of fresh prepared 0.5 M NaOH. The samples from the mesial, buccal, distal and lingual tooth sites were pooled. The suspension was boiled for 5 – 10 min and immediately cooled on ice for at least 5 min and then neutralized with 800 ml of 5 M ammonium acetate. Subsequently, the tubes were vortexed and the suspensions were pipetted into the slots of a miniblotter (MiniSlot apparatus, Immunetics, Cambridge, MA) in which a nylon membrane had been placed. The suspensions on the membrane were fixed by ultraviolet light (Stratolinkerw, Stratagene, La Jolla, CA, USA). After fixation, the membranes were wetted with 2 £ SSC and then prehybridized for 1 h at 42 8C. Appropriate DNA probes were mixed with the hybridization solution and placed into the minislots of the prepared miniblotter (board). The board was wrapped with plastic wrap and put into a freezer bag. It was then incubated at 42 8C and hybridized with gentle shaking overnight. After several washing sequences, the membrane was incubated for 1 h at 37 8C with Lumi-Phose 530 (Boehringer, Mannheim, Germany) and exposed to
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a X-ray film for 2 – 4 h. Subsequently, the film was developed. DNA probes of the following 16 bacterial species were utilized: Porphyromonas (P.) gingivalis, Actinobacillus (A.) actinomycetemcomitans, Campylobacter (C.) rectus, Peptostreptococcus (P.) micros, Actinomyces (A.) viscosus, Streptococcus (S.) sanguis, Streptococcus (S.) intermedius, Treponema (T.) denticola, Prevotella (P.) nigrescens, Campylobacter (C.) showae, Fusobacterium (F.) nucleatum, Bacteroides (B.) forsythus, Selenomonas (S.) noxia, Streptococcus (S.) mitis, Eikenella (E.) corrodens and Prevotella (P.) intermedia. For the microbiological data mean percentages ðxÞ and standard deviations (SD) were calculated and the frequency distributions analyzed.
Results Before the initiation of the investigation (i.e. approximately 2.5 months before baseline), the total microbial count in the four animals examined was approximately 5 £ 108. At that timepoint the teeth of all animals harbored large amounts of dental plaque and tartar. The preinvestigational means (x; organisms £ 106) and standard deviations (SD) of the bacterial counts and the mean percentages ðxÞ and standard deviations (SD) of the bacterial groups are shown in Table 1. After the initiation of the oral hygiene regimen (starting two months before the baseline evaluation), including tooth brushing and the use of interdental floss with flour of pumice, the total recoverable amount of the species examined decreased from 5 £ 108 bacteria before oral hygiene was executed to a total bacterial count of 22.5 £ 106 at baseline (total bacterial count at the 3-month evaluation: 31.6 £ 106 and 99.6 £ 106 at the 5-month evaluation). All crown contour groups as well as the control group showed an increase in recoverable total bacterial counts (Table 2). At the 5-month evaluation, no major differences existed between the control group (13.1 £ 106), the normal contour group (13.4 £ 106), and the 508 over-contour group (18.7 £ 106) regarding the total bacterial count. In contrast, the 308 over-contour group (54.4 £ 106)
Table 2 Total bacterial count ( £ 106) at the different evaluation timepoints for the different treatment methods. Groups/time
Control
Normal contour
308 Over contour
508 Over contour
Sum
Baseline Three months Five months
6.5 5.6 13.1
6.1 8.3 13.4
3.0 3.2 54.4
6.9 14.5 18.7
22.5 31.6 99.6
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Table 3 Means ðxÞ ^ standard deviations (SD) (organisms £ 106) at different evaluation timepoints (in parentheses: mean percentages ðxÞ and standard deviations (SD)). Species
Baseline
Three-month evaluation
Five-month evaluation
P. intermedia C. showae T. denticola S. sanguis S. intermedius A. viscosus P. gingivalis F. nucleatum A. actinomycetemcomitans E. corrodens
2.8 ^ 2.5 (57.5 ^ 39.5) 0.06 ^ 0.02 (0.9 ^ 1.3) 2.8 ^ 4.0 (41.1 ^ 39.6) 0 0 0 0 0 0 0
0.3 ^ 0.5 (3.6 ^ 3.7) 1.2 ^ 1.2 (11.7 ^ 7.4) 5.2 ^ 2.4 (74.7 ^ 18.1) 0.1 ^ 0.2 (0.8 ^ 1.60) 0.02 ^ 0.05 (0.2 ^ 0.4) 0 0 0.2 ^ 0.4 (1.5 ^ 2.9) 0.9 ^ 1.3 (7.1 ^ 10.7) 0.02 ^ 0.04 (0.6 ^ 1.1)
16.3 ^ 14.2 (61.1 ^ 14.2) 2.0 ^ 1.4 (14.2 ^ 11.5) 2.8 ^ 3.6 (7.1 ^ 8.4) 0.01 ^ 0.01 (0.04 ^ 0.04) 0.1 ^ 0.2 (0.2 ^ 0.4) 1.6 ^ 3.2 (2.5 ^ 5.0) 0 0.03 ^ 0.03 (0.1 ^ 0.1) 0.1 ^ 0.03 (0.9 ^ 0.6) 2 ^ 1.8 (14.1 ^ 17.0)
depicted a threefold amount of total bacterial count compared to the other groups. Table 3 shows the mean numbers (organisms £ 106) and percentage distribution of the microbiota at baseline, at the 3-month evaluation and at the 5month evaluation, irrespective of treatment groups. Besides P. intermedia, T. denticola, and C. showae no other bacterial species were found at baseline. At three months, the bacterial composition showed a greater diversity and was dominated by T. denticola.
At the 5-month evaluation the bacterial composition was more complex. While only small numbers of A. actinomycetemcomitans were observed, the bacterial composition was dominated by P. intermedia, C. showae and E. corrodens. Changes in the mean amounts of selected periodontopathogenic species at different crown contour profiles are presented in Table 4. P. gingivalis was never observed at all. Both, F. nucleatum and A. actinomycetemcomitans were not detectable at
Table 4 Means ðxÞ and standard deviations (SD) of the periopathogenic bacteria (organisms £ 106) related to the different crown contours at different evaluation timepoints (mean percentages ðxÞ and standard deviations (SD) in brackets). Bacteria
Evaluation timepoint
Control ðx ^ SDÞ
Normal contour ðx ^ SDÞ
308 Over contour ðx ^ SDÞ
508 Over contour ðx ^ SDÞ
P. gingivalis
Baseline Three months Five months
0 0 0
0 0 0
0 0 0
0 0 0
F. nucleatum
Baseline Three months
0 0
0 0
0 0
Five months
0.01 ^ 0.03 (0.1 ^ 0.1)
0.003 ^ 0.005 (0.01 ^ 0.01)
0.008 ^ 0.02 (0.01 ^ 0.03)
0 0.2 ^ 0.4 (1.5 ^ 3.0) 0.005 ^ 0.01 (0.01 ^ 0.02)
Baseline
1.0 ^ 1.4 (12.7 ^ 14.3) 1.1 ^ 0.1 (20.1 ^ 13.1) 0.5 ^ 1.0 (0.8 ^ 1.6)
0.3 ^ 0.3 (6.6 ^ 7.4) 1.6 ^ 0.8 (23.4 ^ 7.4) 0.6 ^ 1.2 (0.9 ^ 1.8)
0.2 ^ 0.2 (3.8 ^ 3.3) 0.5 ^ 0.8 (6.4 ^ 7.4) 1.2 ^ 1.7 (4.7 ^ 7.9)
1.4 ^ 2.5 (18.6 ^ 25.8) 2.0 ^ 1.6 (24.8 ^ 7.7) 0.5 ^ 0.9 (0.7 ^ 1.5)
0.6 ^ 0.7 (11.7 ^ 9.7) 0.03 ^ 0.05 (0.2 ^ 0.4) 2.1 ^ 4.2 (9.9 ^ 19.7)
1.3 ^ 1.3 (26,8 ^ 23.9) 0.02 ^ 0.02 (0.6 ^ 0.8) 1.8 ^ 3.0 (7.1 ^ 8.8)
0.6 ^ 0.5 (10.5 ^ 6.0) 0.04 ^ 0.07 (1.0 ^ 2.0) 9.2 ^ 9.6 (38.1 ^ 1.3)
0.3 ^ 0.3 (8.5 ^ 5.9) 0.2 ^ 0.5 (1.9 ^ 3.8) 3.1 ^ 5.9 (6.0 ^ 8.9)
Baseline
0
0
0
0
Three months
0.1 ^ 0.2 (1.0 ^ 1.9) 0.01 ^ 0.02 (0.1 ^ 0.1)
0.2 ^ 0.5 (1.9 ^ 3.8) 0.01 ^ 0.02 (0.03 ^ 0.04)
0.1 ^ 0.2 (0.9 ^ 1.8) 0.05 ^ 0.03 (0.6 ^ 0.6)
0.4 ^ 0.5 (3.3 ^ 3.9) 0.02 ^ 0.02 (0.2 ^ 0.3)
T. denticola
Three months Five months P. intermedia
Baseline Three months Five months
A. actinomycetemcomitans
Five months
Effect of different crown contours on periodontal health in dogs. Microbiological results
baseline. F. nucleatum was observed at the 3-month evaluation only in one dog in the 508 over-contour group. At the end of the investigation, only low F. nucleatum levels were detected in one dog in each of the four different groups. T. denticola and P. intermedia were present at baseline. The control group and 508 over-contour group contained more T. denticola than the normal contour or the 308 over-contour group. In all groups the amount of recoverable T. denticola increased at the 3-month evaluation, the highest count being observed for the 508 over-contour group. However, all groups, except for the 308 over-contour group, showed a decrease for T. denticola until the end of the investigation. The mean values for the control and the 508 overcontour group dropped below their baseline values. The counts of P. intermedia decreased from baseline to the 3-month evaluation followed by an 100 – 200 fold increase at the 5-month evaluation. A. actinomycetemcomitans showed an elevation from baseline to the 3-month evaluation. In the control, normal contour and 308 over-contour group, one dog each was positive for A. actinomycetemcomitans whereas two dogs were positive in the 508 over-contour group. At five months, all groups returned to almost undetectable levels of A. actinomycetemcomitans, but more dogs were positive for A. actinomycetemcomitans than at the 3-month evaluation.
Discussion Microbial plaque is the principal etiologic factor for periodontal disease.21,22 Plaque retention is greatest in regions where routine oral hygiene measures are problematic; i.e. at interproximal, facial, and lingual cervical areas. There is some controversy in the literature regarding the influence of different crown contours and plaque accumulation. Supporters for natural crown form are of the opinion that the artificial crown has to follow the original anatomy of tooth contour. In this way, the crown permits the functional stimulation and healthy gingival tissues can be maintained.23,24 On the other side, colleagues suggest that the restored crown should be undercontoured for better cleaning and thus for better health of the periodontium.11,14,16 For the microbiological analysis executed in this investigation, the checkerboard DNA – DNA hybridization technique as described by Socransky et al.20 was performed. The advantage of this type of technique is that it allows the examination of 10 – 100 times as many samples as with the culturing
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methods at a time. For the DNA probing no viable bacteria are necessary as compared to the culturing method. The checkerboard DNA – DNA hybridization detected a wide array of bacteria in the preinvestigational flora in this investigation. All animals harbored the periodontal pathogens P. gingivalis, T. denticola, A. actinomycetemcomitans, P. intermedia and F. nucleatum in high numbers and at almost all teeth. The composition of the preinvestigational microbiota in the inflamed gingival situation, i.e. gram-negative anaerobes, is in accordance with that found by other authors using different evaluation techniques.25,26 Cutler and Ghaffar27 for example reported that disease induction in Beagle dogs through ligature placement for 30 days worsened the clinical parameters like gingival and plaque index as well as it resulted in a shift in the microflora from a predominantly aerobic composition to a facultative and anaerobic flora. Gingivitis and periodontal disease in dogs have many features in common with human periodontal disease28,29 and some investigators suggest that there is also a similarity between the oral flora of beagle dogs and humans.25,27 After removal of calculus and soft debris as well as toothbrushing seven times per week for four weeks, the gingiva in the present investigation showed a stage of clinical health. There was a change in bacterial composition of the subgingival microbial flora which consisted predominantly of P. intermedia, T. denticola and C. showae. These organisms could be detected in a high frequency at all teeth, irrespective of the different crown contour groups. Surprisingly, at the baseline examination we could not find other bacterial species, especially no cocci. This finding is in clear contrast to other research data. Bacterial plaque associated with gingival and periodontal health consists primarily of gram-positive and coccoidal forms.30 – 32 Cultural studies have indicated that the predominant organisms are S. sanguis, S. mitis, A. viscosus, A. naeslundii, Staphylococcus epidermis and Veillonella parvula.33 – 35 Since the authors of the present investigation are not aware of any investigation using the checkerboard DNA –DNA technique in dogs, the results will be compared to checkerboard technique investigations performed in humans. When the DNA –DNA hybridization technique was used in healthy subjects, Tanner et al.33 found a microbial flora mainly composed of S. sanguis, V. parvula, S. oralis, S. intermedius. Further investigations also showed a higher prevalence of grampositive species.36,37
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One reasonable explanation as to why no grampositive bacterial species like Streptococci or Actinomyces were found in the present investigation at baseline is that they were below the detection level (, 104). At three months, the total amount of bacteria increased and a broader variety of bacterial species could be detected including the gram-positive, aerobic microbiotes S. sanguis and S. intermedius. At five months, a shift towards a more gram-negative, anaerobic composition of the flora could be found. This shift must not necessarily be a shift in gingival health status since such organisms are also found in the state of gingival health.36,37 The detection frequency of most of the bacterial species increased from baseline to the 5-month evaluation. It seems that—at least for some species—the frequency of detection was higher in the 308- and 508-groups. But a general trend in detection frequency could not be observed. When regarding the periopathogenic bacterial species (P. gingivalis, F. nucleatum, T. denticola, P. intermedia, A. actinomycetemcomitans) no trend could be detected for any of the species during the course of the experiment. However, in most instances the means of the number of the microorganisms and the means for the percentage of the total bacterial load for a given organism were higher in the 308 and 508 group than in the control and normal contour group.
Conclusion Within the limits of this animal experiment it seems that overcontoured subgingivally placed crowns only slightly affect bacterial composition when an intensive oral hygiene regimen is executed. If a longer investigational period would have had a greater influence needs to be demonstrated. The authors are aware of the fact, that the number of the subjects is very small and that there exists an interdependence of the sites within one animal. Therefore, the results have to be interpreted with care.
Acknowledgements The authors would like to thank Dr R.G. Caffesse and Dr Pedro Trejo for their valuable support in the performance of this project. Dr Stan Holt’s support in performing the microbiological analysis is highly appreciated.
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References 1. Karlsen K. Gingival reactions to dental restorations. Acta Odontologica Scandinavica 1970;28:895—904. 2. Waerhaug J. Tissue reactions around artificial crowns. Journal of Periodontology 1953;24:172—85. 3. Lo ¨ e H. Reactions to marginal periodontal tissues to restorative procedures. International Dental Journal 1968; 18:759—78. 4. Lang NP, Kiel RA, Anderhalden K. Clinical and microbiological effects of subgingival restorations with overhanging or clinically perfect margins. Journal of Clinical Periodontology 1983;10:563—78. 5. Waerhaug J. Histologic considerations which govern where the margins of restorations should be located in relation with the gingiva. Dental Clinics of North America 1960;2: 161—76. 6. Silness J. Periodontal conditions in patients treated with dental bridges. II. The influence of full and partial crowns on plaque accumulation, development of gingivitis and pocket formation. Journal of Periodontal Research 1970;5: 219—24. 7. Valderhaug J, Birkeland JM. Periodontal conditions in patients 5 years following insertion of fixed prostheses. Pocket depth and loss of attachment. Journal of Oral Rehabilitation 1976;3:237—43. 8. Nyman S, Lindhe J, Lundgren D. The role of occlusion for the stability of fixed bridges in patients with reduced periodontal tissue support. Journal of Clinical Periodontology 1975;2: 53—66. 9. Coornaert J, Adriaens P, De Boever J. Long-term clinical study of porcelain-fused-to-gold restorations. Journal of Prosthetic Dentistry 1984;51:338—42. 10. Herlands RE, Lucca JJ, Morris HL. Forms, contours and extensions of full coverage restorations in occlusal reconstruction. Dental Clinics of North America 1962;6:147—62. 11. Perel ML. Axial crown contours. Journal of Prosthetic Dentistry 1971;25:642—9. 12. Yuodelis RA, Weaver JD, Sapkos S. Facial and lingual contours of artificial complete crown restorations and their effects on the periodontium. Journal of Prosthetic Dentistry 1973;29:61—6. 13. Ehrlich J, Hochman N. Alterations on crown contour-effect on gingival health in man. Journal of Prosthetic Dentistry 1980;44:523—5. 14. Wagman SS. The role of coronal contour in gingival health. Journal of Prosthetic Dentistry 1977;37:280—7. 15. Becker CM, Kaldahl WB. Current theories of crown contour, margin placement, and pontic design. Journal of Prosthetic Dentistry 1981;45:268—77. 16. Yoshida T. The changes of oral conditions caused by artificial crown contours in severely disabled patients. Kokubyo Gakkai Zasshi 2000;67:240—50. 17. Rufenacht CR. Esthetic management of the dentogingival unit. Chicago: Quintessence; 1990. 18. Sundh B, Ko ¨hler B. An in vivo study of the impact of different emergence profiles of procera titanium crowns on quantity and quality of plaque. International Journal of Prosthodontics 2002;15:457—60. 19. Kohal RJ, Gerds T, Strub JR. Effect of different crown contours on periodontal health in dogs. Clinical results. Journal of Dentistry 2003;31:407—13. 20. Socransky SS, Smith C, Martin L, Paster BJ, Dewhirst FE, Levin AE. ‘Checkerboard’ DNA—DNA hybridization. Biotechniques 1994;17:788—92.
Effect of different crown contours on periodontal health in dogs. Microbiological results
21. Ash MM, Gitlin BN, Smith WA. Correlation between plaque and gingivitis. Journal of Periodontology 1964;35:424—9. 22. Lo ¨e H, Theilade E, Jensen SB. Experimental gingivitis in man. Journal of Periodontology 1965;36:177—87. 23. Amsterdam M, Fox L. Provisional splinting. Principles and techniques. Dental Clinics of North America 1959;3:73—99. 24. Wheeler RC. Complete crown and the periodontium. Journal of Prosthetic Dentistry 1961;11:722—34. 25. Syed SA, Svanberg M, Svanberg G. The predominant cultivable dental plaque flora of beagle dogs with gingivitis. Journal of Periodontal Research 1980;15:123—36. 26. Dahle ´n G, Heijl L, Lindhe J, Mo ¨ller A. Development of plaque and gingivitis following antibiotic therapy in dogs. Journal of Clinical Periodontology 1982;9:223—38. 27. Cutler CW, Ghaffar KA. A short-term study of the effects of SBHAN, a novel compound, on gingival inflammation in the beagle dog. Journal of Periodontology 1997;68:448—55. 28. Lindhe J, Hamp S, Lo ¨e H. Experimental periodontitis in the beagle dog. Journal of Periodontal Research 1973;8:1—10. 29. Lindhe J, Hamp SE, Lo ¨e H. Plaque induced periodontal disease in beagle dogs. A 4-year clinical, roentgenographical and histometrical study. Journal of Periodontal Research 1975;10:243—55. 30. Listgarten MA, Lindhe J, Hellde ´n L. Effect of tetracycline and/or scaling on human periodontal disease. Clinical,
31.
32.
33.
34. 35.
36.
37.
159
microbiological, and histological observations. Journal of Clinical Periodontology 1978;5:246—71. Listgarten MA, Hellde ´n L. Relative distribution of bacteria at clinically healthy and periodontally diseased sites in humans. Journal of Clinical Periodontology 1978;5:115—32. Theilade E, Wright WH, Jensen SB, Lo ¨e H. Experimental gingivitis in man. II. A longitudinal clinical and bacteriological investigation. Journal of Periodontal Research 1966;1: 1—13. Tanner A, Maiden MF, Macuch PJ, Murray LL, Kent RL. Microbiota of health, gingivitis, and initial periodontitis. Journal of Clinical Periodontology 1998;25:85—98. Listgarten MA. The structure of dental plaque. Periodontology 2000;5(1994):52—65. Socransky SS, Manganiello AD, Propas D, Oram V, van Houte J. Bacteriological studies of developing supragingival dental plaque. Journal of Periodontal Research 1977;12:90—106. Haffajee AD, Cugini MA, Tanner A, Pollack RP, Smith C, Kent RL, Socransky SS, Subgingival microbiota in healthy, wellmaintained elder and periodontitis subjects. Journal of Clinical Periodontology 1998;25:346—53. Ali RW, Johannessen AC, Dahle ´n G, Socransky SS, Skaug N. Comparison of the subgingival microbiota of periodontally healthy and diseased adults in northern Cameroon. Journal of Clinical Periodontology 1997;24:830—35.
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Effect of different crown contours on periodontal health in dogs. Microbiological results R.J. Kohala,b,*, K. Pelzc, J.R. Struba a
Department of Prosthodontics, Albert-Ludwigs University, Hugstetter Str. 55, Freiburg 79106, Germany Division of Periodontology, Department of Stomatology, Health Science Center, University of Texas, Houston, TX, USA c Department of Microbiology and Hygiene, Albert-Ludwigs University, Freiburg 79106, Germany b
Received 15 May 2003; revised 10 September 2003; accepted 29 September 2003
KEYWORDS Animal study; Crown contour; Overcontour; Periodontal health; Microbiology; DNA–DNAhybridization
Summary Objectives. In some clinical circumstances, i.e. in cases when the upper anterior region has to be restored by prosthetic means, it is necessary to place the margins of crowns and fixed partial dentures subgingivally. In addition, in periodontally compromised patients the restoration sometimes has to be overcontoured in order to replace the lost interdental papilla. The overcontoured crown margin may influence the subgingival bacterial composition. Therefore, the aim of the present investigation was to evaluate the effect of three different subgingival crown contours in dogs on the composition of the subgingival microbiota. Methods. In four adult beagle dogs the second and third premolars were prepared in three quadrants and restored with single gold crowns. The unprepared second and third premolars in the last quadrant served as controls. The crowns had three different emergence profiles including a normal contour, a 308 and a 508 over-contour. During the entire study period, professional oral hygiene was performed seven times a week. Microbiological samples were harvested from four sites of test and control teeth (mesial, distal, buccal and lingual) at baseline, after 3 months, and after 5 months. Results. The microbiological analysis (DNA –DNA hybridization technique) of the subgingival microbial flora revealed a dominance of P. intermedia, T. denticola and C. showae in all test and control groups at baseline. At three months, the total amount of bacteria increased and a broader variety of bacterial species could be detected. The detection frequency of most bacterial species increased from baseline to the 5-month evaluation. The frequency of detection of some species was higher in the 308 and 508 overcontoured test groups compared to the normal contour group and to the natural teeth. Conclusion. It can be concluded within the limits of this investigation that overcontoured gold crowns placed subgingivally have only slight effects on the microbiological composition in dogs when an intensive oral hygiene regimen was executed. q 2003 Elsevier Ltd. All rights reserved.
Introduction *Corresponding author. Tel.: þ 49-761-270-4906/4977; fax: þ 49-761-270-4925. E-mail address: [email protected]
A number of factors may influence the health condition of the periodontium: the physical or
0300-5712/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2003.09.005
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chemical properties of crown materials used,1 the marginal fit of a crown restoration,2 – 4 the position of the crown margin,5 – 7 the occlusion of the restoration,8,9 and the crown contour itself.10 – 13 Hence, regarding the influence of artificial crown contours there exist controversial opinions.12,14,15 Several authors have mentioned that from the periodontal point of view, under-contoured crowns are preferred when compared to overcontoured ones.11,12,14,16 Nevertheless, in the esthetic zone of patients with periodontally compromised teeth, it is often mandatory to place the crown margins subgingivally and to overcontour them for esthetic reasons.17 One recent clinical investigation reported on the impact of different emergence profiles of Procera titanium crowns on the quantity and quality of dental plaque.18 Within the limitations of their study, the authors found that titanium crowns with emergence profiles of up to 408 formed less plaque than the healthy controls. There was no higher accumulation of S. mutans in relation to increasing emergence profiles. The investigators did not report on crown contours . 408 nor on the periodontal pathological microbiological composition of the plaque. Therefore, the aim of this animal investigation was to evaluate microbiologically the effect of different subgingival crown contours in dogs. In the first part of our investigation,19 we reported on the clinical outcome of three different crown contours when placed subgingivally. We could show that the Plaque Index increased for the over-contoured (30 and 508) groups. The difference in plaque accumulation could be correlated to the Gingival Index and the Gingival Crevicular Fluid Flow. The Pocket Probing Depths as well as the Clinical Attachment
Figure 1
Levels were higher for the over-contoured groups than for the control group.
Materials and methods The study protocol was approved by the Animal Welfare Committee of the University of Texas Health Science Center at Houston. The study was performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals. The outline of the experiment is shown in Fig. 1. The clinical procedures were presented in detail elsewhere.19 Briefly, four beagle dogs were utilized in this investigation. All teeth were cleaned and a strict oral hygiene program was initiated consisting of tooth brushing with pumice and dental floss seven times a week. The scaling, prosthetic and clinical evaluation procedures were performed under general anesthesia. One month after commencing the oral hygiene regime, the second and third premolars in three quadrants were prepared for crown restorations. A subgingival shoulder was cut on the mesial and distal aspects of the teeth and a chamfer on the buccal and lingual sides. The tooth preparations were placed approximately 0.5 – 1 mm below the gingival margin. The unprepared second and third premolars in one quadrant served as controls. After tooth preparation retraction cords were placed, impressions were taken, and single, high noble gold alloy crowns (Degulor M, Degussa, Pforzheim, Germany) with three different emergence profiles were inserted: (1) normal (tooth) contour, (2) 308 and (3) 508 overcontoured profiles relative to the long axis of the abutments. In each
Outline of the experiment.
Effect of different crown contours on periodontal health in dogs. Microbiological results
Table 1 Preinvestigational means ðxÞ; standard deviations (SD) of organisms £ 106 (in parentheses: mean percentages ðxÞ and standard deviations (SD)). Bacteria
x ^ SD
S. sanguis S. intermedius A. viscosus P. gingivalis P. intermedia F. nucleatum A. actinomycetemcomitans C. showae E. corrodens T. denticola
3.0 ^ 1.0 (2.4 ^ 1.0) 5.9 ^ 3.2 (4.6 ^ 2.6) 23.9 ^ 18.4 (19.9 ^ 16.3) 17.4 ^ 5.4 (13.6 ^ 2.2) 30.3 ^ 10.8 (23.6 ^ 5.1) 5.7 ^ 1.7 (4.5 ^ 1.3) 1.4 ^ 1.2 (1.0 ^ 0.7) 11.6 ^ 7.8 (8.7 ^ 4.7) 8.5 ^ 4.9 (7.0 ^ 4.1) 18.8 ^ 12.7 (14.7 ^ 10.0)
quadrant only one type of crown contour was inserted on the two premolars. The analysis of bacterial species was performed using DNA hybridization according to the ‘Checkerboard’ technique described by Socransky et al.20 After removing the supragingival plaque with sterile cotton pellets, subgingival plaque was harvested using sterile curettes and transferred into tubes containing 100 ml of TE (10 mM Tris – HCl, 1 mM EDTA, pH 7.6), adding 100 ml of fresh prepared 0.5 M NaOH. The samples from the mesial, buccal, distal and lingual tooth sites were pooled. The suspension was boiled for 5 – 10 min and immediately cooled on ice for at least 5 min and then neutralized with 800 ml of 5 M ammonium acetate. Subsequently, the tubes were vortexed and the suspensions were pipetted into the slots of a miniblotter (MiniSlot apparatus, Immunetics, Cambridge, MA) in which a nylon membrane had been placed. The suspensions on the membrane were fixed by ultraviolet light (Stratolinkerw, Stratagene, La Jolla, CA, USA). After fixation, the membranes were wetted with 2 £ SSC and then prehybridized for 1 h at 42 8C. Appropriate DNA probes were mixed with the hybridization solution and placed into the minislots of the prepared miniblotter (board). The board was wrapped with plastic wrap and put into a freezer bag. It was then incubated at 42 8C and hybridized with gentle shaking overnight. After several washing sequences, the membrane was incubated for 1 h at 37 8C with Lumi-Phose 530 (Boehringer, Mannheim, Germany) and exposed to
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a X-ray film for 2 – 4 h. Subsequently, the film was developed. DNA probes of the following 16 bacterial species were utilized: Porphyromonas (P.) gingivalis, Actinobacillus (A.) actinomycetemcomitans, Campylobacter (C.) rectus, Peptostreptococcus (P.) micros, Actinomyces (A.) viscosus, Streptococcus (S.) sanguis, Streptococcus (S.) intermedius, Treponema (T.) denticola, Prevotella (P.) nigrescens, Campylobacter (C.) showae, Fusobacterium (F.) nucleatum, Bacteroides (B.) forsythus, Selenomonas (S.) noxia, Streptococcus (S.) mitis, Eikenella (E.) corrodens and Prevotella (P.) intermedia. For the microbiological data mean percentages ðxÞ and standard deviations (SD) were calculated and the frequency distributions analyzed.
Results Before the initiation of the investigation (i.e. approximately 2.5 months before baseline), the total microbial count in the four animals examined was approximately 5 £ 108. At that timepoint the teeth of all animals harbored large amounts of dental plaque and tartar. The preinvestigational means (x; organisms £ 106) and standard deviations (SD) of the bacterial counts and the mean percentages ðxÞ and standard deviations (SD) of the bacterial groups are shown in Table 1. After the initiation of the oral hygiene regimen (starting two months before the baseline evaluation), including tooth brushing and the use of interdental floss with flour of pumice, the total recoverable amount of the species examined decreased from 5 £ 108 bacteria before oral hygiene was executed to a total bacterial count of 22.5 £ 106 at baseline (total bacterial count at the 3-month evaluation: 31.6 £ 106 and 99.6 £ 106 at the 5-month evaluation). All crown contour groups as well as the control group showed an increase in recoverable total bacterial counts (Table 2). At the 5-month evaluation, no major differences existed between the control group (13.1 £ 106), the normal contour group (13.4 £ 106), and the 508 over-contour group (18.7 £ 106) regarding the total bacterial count. In contrast, the 308 over-contour group (54.4 £ 106)
Table 2 Total bacterial count ( £ 106) at the different evaluation timepoints for the different treatment methods. Groups/time
Control
Normal contour
308 Over contour
508 Over contour
Sum
Baseline Three months Five months
6.5 5.6 13.1
6.1 8.3 13.4
3.0 3.2 54.4
6.9 14.5 18.7
22.5 31.6 99.6
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Table 3 Means ðxÞ ^ standard deviations (SD) (organisms £ 106) at different evaluation timepoints (in parentheses: mean percentages ðxÞ and standard deviations (SD)). Species
Baseline
Three-month evaluation
Five-month evaluation
P. intermedia C. showae T. denticola S. sanguis S. intermedius A. viscosus P. gingivalis F. nucleatum A. actinomycetemcomitans E. corrodens
2.8 ^ 2.5 (57.5 ^ 39.5) 0.06 ^ 0.02 (0.9 ^ 1.3) 2.8 ^ 4.0 (41.1 ^ 39.6) 0 0 0 0 0 0 0
0.3 ^ 0.5 (3.6 ^ 3.7) 1.2 ^ 1.2 (11.7 ^ 7.4) 5.2 ^ 2.4 (74.7 ^ 18.1) 0.1 ^ 0.2 (0.8 ^ 1.60) 0.02 ^ 0.05 (0.2 ^ 0.4) 0 0 0.2 ^ 0.4 (1.5 ^ 2.9) 0.9 ^ 1.3 (7.1 ^ 10.7) 0.02 ^ 0.04 (0.6 ^ 1.1)
16.3 ^ 14.2 (61.1 ^ 14.2) 2.0 ^ 1.4 (14.2 ^ 11.5) 2.8 ^ 3.6 (7.1 ^ 8.4) 0.01 ^ 0.01 (0.04 ^ 0.04) 0.1 ^ 0.2 (0.2 ^ 0.4) 1.6 ^ 3.2 (2.5 ^ 5.0) 0 0.03 ^ 0.03 (0.1 ^ 0.1) 0.1 ^ 0.03 (0.9 ^ 0.6) 2 ^ 1.8 (14.1 ^ 17.0)
depicted a threefold amount of total bacterial count compared to the other groups. Table 3 shows the mean numbers (organisms £ 106) and percentage distribution of the microbiota at baseline, at the 3-month evaluation and at the 5month evaluation, irrespective of treatment groups. Besides P. intermedia, T. denticola, and C. showae no other bacterial species were found at baseline. At three months, the bacterial composition showed a greater diversity and was dominated by T. denticola.
At the 5-month evaluation the bacterial composition was more complex. While only small numbers of A. actinomycetemcomitans were observed, the bacterial composition was dominated by P. intermedia, C. showae and E. corrodens. Changes in the mean amounts of selected periodontopathogenic species at different crown contour profiles are presented in Table 4. P. gingivalis was never observed at all. Both, F. nucleatum and A. actinomycetemcomitans were not detectable at
Table 4 Means ðxÞ and standard deviations (SD) of the periopathogenic bacteria (organisms £ 106) related to the different crown contours at different evaluation timepoints (mean percentages ðxÞ and standard deviations (SD) in brackets). Bacteria
Evaluation timepoint
Control ðx ^ SDÞ
Normal contour ðx ^ SDÞ
308 Over contour ðx ^ SDÞ
508 Over contour ðx ^ SDÞ
P. gingivalis
Baseline Three months Five months
0 0 0
0 0 0
0 0 0
0 0 0
F. nucleatum
Baseline Three months
0 0
0 0
0 0
Five months
0.01 ^ 0.03 (0.1 ^ 0.1)
0.003 ^ 0.005 (0.01 ^ 0.01)
0.008 ^ 0.02 (0.01 ^ 0.03)
0 0.2 ^ 0.4 (1.5 ^ 3.0) 0.005 ^ 0.01 (0.01 ^ 0.02)
Baseline
1.0 ^ 1.4 (12.7 ^ 14.3) 1.1 ^ 0.1 (20.1 ^ 13.1) 0.5 ^ 1.0 (0.8 ^ 1.6)
0.3 ^ 0.3 (6.6 ^ 7.4) 1.6 ^ 0.8 (23.4 ^ 7.4) 0.6 ^ 1.2 (0.9 ^ 1.8)
0.2 ^ 0.2 (3.8 ^ 3.3) 0.5 ^ 0.8 (6.4 ^ 7.4) 1.2 ^ 1.7 (4.7 ^ 7.9)
1.4 ^ 2.5 (18.6 ^ 25.8) 2.0 ^ 1.6 (24.8 ^ 7.7) 0.5 ^ 0.9 (0.7 ^ 1.5)
0.6 ^ 0.7 (11.7 ^ 9.7) 0.03 ^ 0.05 (0.2 ^ 0.4) 2.1 ^ 4.2 (9.9 ^ 19.7)
1.3 ^ 1.3 (26,8 ^ 23.9) 0.02 ^ 0.02 (0.6 ^ 0.8) 1.8 ^ 3.0 (7.1 ^ 8.8)
0.6 ^ 0.5 (10.5 ^ 6.0) 0.04 ^ 0.07 (1.0 ^ 2.0) 9.2 ^ 9.6 (38.1 ^ 1.3)
0.3 ^ 0.3 (8.5 ^ 5.9) 0.2 ^ 0.5 (1.9 ^ 3.8) 3.1 ^ 5.9 (6.0 ^ 8.9)
Baseline
0
0
0
0
Three months
0.1 ^ 0.2 (1.0 ^ 1.9) 0.01 ^ 0.02 (0.1 ^ 0.1)
0.2 ^ 0.5 (1.9 ^ 3.8) 0.01 ^ 0.02 (0.03 ^ 0.04)
0.1 ^ 0.2 (0.9 ^ 1.8) 0.05 ^ 0.03 (0.6 ^ 0.6)
0.4 ^ 0.5 (3.3 ^ 3.9) 0.02 ^ 0.02 (0.2 ^ 0.3)
T. denticola
Three months Five months P. intermedia
Baseline Three months Five months
A. actinomycetemcomitans
Five months
Effect of different crown contours on periodontal health in dogs. Microbiological results
baseline. F. nucleatum was observed at the 3-month evaluation only in one dog in the 508 over-contour group. At the end of the investigation, only low F. nucleatum levels were detected in one dog in each of the four different groups. T. denticola and P. intermedia were present at baseline. The control group and 508 over-contour group contained more T. denticola than the normal contour or the 308 over-contour group. In all groups the amount of recoverable T. denticola increased at the 3-month evaluation, the highest count being observed for the 508 over-contour group. However, all groups, except for the 308 over-contour group, showed a decrease for T. denticola until the end of the investigation. The mean values for the control and the 508 overcontour group dropped below their baseline values. The counts of P. intermedia decreased from baseline to the 3-month evaluation followed by an 100 – 200 fold increase at the 5-month evaluation. A. actinomycetemcomitans showed an elevation from baseline to the 3-month evaluation. In the control, normal contour and 308 over-contour group, one dog each was positive for A. actinomycetemcomitans whereas two dogs were positive in the 508 over-contour group. At five months, all groups returned to almost undetectable levels of A. actinomycetemcomitans, but more dogs were positive for A. actinomycetemcomitans than at the 3-month evaluation.
Discussion Microbial plaque is the principal etiologic factor for periodontal disease.21,22 Plaque retention is greatest in regions where routine oral hygiene measures are problematic; i.e. at interproximal, facial, and lingual cervical areas. There is some controversy in the literature regarding the influence of different crown contours and plaque accumulation. Supporters for natural crown form are of the opinion that the artificial crown has to follow the original anatomy of tooth contour. In this way, the crown permits the functional stimulation and healthy gingival tissues can be maintained.23,24 On the other side, colleagues suggest that the restored crown should be undercontoured for better cleaning and thus for better health of the periodontium.11,14,16 For the microbiological analysis executed in this investigation, the checkerboard DNA – DNA hybridization technique as described by Socransky et al.20 was performed. The advantage of this type of technique is that it allows the examination of 10 – 100 times as many samples as with the culturing
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methods at a time. For the DNA probing no viable bacteria are necessary as compared to the culturing method. The checkerboard DNA – DNA hybridization detected a wide array of bacteria in the preinvestigational flora in this investigation. All animals harbored the periodontal pathogens P. gingivalis, T. denticola, A. actinomycetemcomitans, P. intermedia and F. nucleatum in high numbers and at almost all teeth. The composition of the preinvestigational microbiota in the inflamed gingival situation, i.e. gram-negative anaerobes, is in accordance with that found by other authors using different evaluation techniques.25,26 Cutler and Ghaffar27 for example reported that disease induction in Beagle dogs through ligature placement for 30 days worsened the clinical parameters like gingival and plaque index as well as it resulted in a shift in the microflora from a predominantly aerobic composition to a facultative and anaerobic flora. Gingivitis and periodontal disease in dogs have many features in common with human periodontal disease28,29 and some investigators suggest that there is also a similarity between the oral flora of beagle dogs and humans.25,27 After removal of calculus and soft debris as well as toothbrushing seven times per week for four weeks, the gingiva in the present investigation showed a stage of clinical health. There was a change in bacterial composition of the subgingival microbial flora which consisted predominantly of P. intermedia, T. denticola and C. showae. These organisms could be detected in a high frequency at all teeth, irrespective of the different crown contour groups. Surprisingly, at the baseline examination we could not find other bacterial species, especially no cocci. This finding is in clear contrast to other research data. Bacterial plaque associated with gingival and periodontal health consists primarily of gram-positive and coccoidal forms.30 – 32 Cultural studies have indicated that the predominant organisms are S. sanguis, S. mitis, A. viscosus, A. naeslundii, Staphylococcus epidermis and Veillonella parvula.33 – 35 Since the authors of the present investigation are not aware of any investigation using the checkerboard DNA –DNA technique in dogs, the results will be compared to checkerboard technique investigations performed in humans. When the DNA –DNA hybridization technique was used in healthy subjects, Tanner et al.33 found a microbial flora mainly composed of S. sanguis, V. parvula, S. oralis, S. intermedius. Further investigations also showed a higher prevalence of grampositive species.36,37
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One reasonable explanation as to why no grampositive bacterial species like Streptococci or Actinomyces were found in the present investigation at baseline is that they were below the detection level (, 104). At three months, the total amount of bacteria increased and a broader variety of bacterial species could be detected including the gram-positive, aerobic microbiotes S. sanguis and S. intermedius. At five months, a shift towards a more gram-negative, anaerobic composition of the flora could be found. This shift must not necessarily be a shift in gingival health status since such organisms are also found in the state of gingival health.36,37 The detection frequency of most of the bacterial species increased from baseline to the 5-month evaluation. It seems that—at least for some species—the frequency of detection was higher in the 308- and 508-groups. But a general trend in detection frequency could not be observed. When regarding the periopathogenic bacterial species (P. gingivalis, F. nucleatum, T. denticola, P. intermedia, A. actinomycetemcomitans) no trend could be detected for any of the species during the course of the experiment. However, in most instances the means of the number of the microorganisms and the means for the percentage of the total bacterial load for a given organism were higher in the 308 and 508 group than in the control and normal contour group.
Conclusion Within the limits of this animal experiment it seems that overcontoured subgingivally placed crowns only slightly affect bacterial composition when an intensive oral hygiene regimen is executed. If a longer investigational period would have had a greater influence needs to be demonstrated. The authors are aware of the fact, that the number of the subjects is very small and that there exists an interdependence of the sites within one animal. Therefore, the results have to be interpreted with care.
Acknowledgements The authors would like to thank Dr R.G. Caffesse and Dr Pedro Trejo for their valuable support in the performance of this project. Dr Stan Holt’s support in performing the microbiological analysis is highly appreciated.
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References 1. Karlsen K. Gingival reactions to dental restorations. Acta Odontologica Scandinavica 1970;28:895—904. 2. Waerhaug J. Tissue reactions around artificial crowns. Journal of Periodontology 1953;24:172—85. 3. Lo ¨ e H. Reactions to marginal periodontal tissues to restorative procedures. International Dental Journal 1968; 18:759—78. 4. Lang NP, Kiel RA, Anderhalden K. Clinical and microbiological effects of subgingival restorations with overhanging or clinically perfect margins. Journal of Clinical Periodontology 1983;10:563—78. 5. Waerhaug J. Histologic considerations which govern where the margins of restorations should be located in relation with the gingiva. Dental Clinics of North America 1960;2: 161—76. 6. Silness J. Periodontal conditions in patients treated with dental bridges. II. The influence of full and partial crowns on plaque accumulation, development of gingivitis and pocket formation. Journal of Periodontal Research 1970;5: 219—24. 7. Valderhaug J, Birkeland JM. Periodontal conditions in patients 5 years following insertion of fixed prostheses. Pocket depth and loss of attachment. Journal of Oral Rehabilitation 1976;3:237—43. 8. Nyman S, Lindhe J, Lundgren D. The role of occlusion for the stability of fixed bridges in patients with reduced periodontal tissue support. Journal of Clinical Periodontology 1975;2: 53—66. 9. Coornaert J, Adriaens P, De Boever J. Long-term clinical study of porcelain-fused-to-gold restorations. Journal of Prosthetic Dentistry 1984;51:338—42. 10. Herlands RE, Lucca JJ, Morris HL. Forms, contours and extensions of full coverage restorations in occlusal reconstruction. Dental Clinics of North America 1962;6:147—62. 11. Perel ML. Axial crown contours. Journal of Prosthetic Dentistry 1971;25:642—9. 12. Yuodelis RA, Weaver JD, Sapkos S. Facial and lingual contours of artificial complete crown restorations and their effects on the periodontium. Journal of Prosthetic Dentistry 1973;29:61—6. 13. Ehrlich J, Hochman N. Alterations on crown contour-effect on gingival health in man. Journal of Prosthetic Dentistry 1980;44:523—5. 14. Wagman SS. The role of coronal contour in gingival health. Journal of Prosthetic Dentistry 1977;37:280—7. 15. Becker CM, Kaldahl WB. Current theories of crown contour, margin placement, and pontic design. Journal of Prosthetic Dentistry 1981;45:268—77. 16. Yoshida T. The changes of oral conditions caused by artificial crown contours in severely disabled patients. Kokubyo Gakkai Zasshi 2000;67:240—50. 17. Rufenacht CR. Esthetic management of the dentogingival unit. Chicago: Quintessence; 1990. 18. Sundh B, Ko ¨hler B. An in vivo study of the impact of different emergence profiles of procera titanium crowns on quantity and quality of plaque. International Journal of Prosthodontics 2002;15:457—60. 19. Kohal RJ, Gerds T, Strub JR. Effect of different crown contours on periodontal health in dogs. Clinical results. Journal of Dentistry 2003;31:407—13. 20. Socransky SS, Smith C, Martin L, Paster BJ, Dewhirst FE, Levin AE. ‘Checkerboard’ DNA—DNA hybridization. Biotechniques 1994;17:788—92.
Effect of different crown contours on periodontal health in dogs. Microbiological results
21. Ash MM, Gitlin BN, Smith WA. Correlation between plaque and gingivitis. Journal of Periodontology 1964;35:424—9. 22. Lo ¨e H, Theilade E, Jensen SB. Experimental gingivitis in man. Journal of Periodontology 1965;36:177—87. 23. Amsterdam M, Fox L. Provisional splinting. Principles and techniques. Dental Clinics of North America 1959;3:73—99. 24. Wheeler RC. Complete crown and the periodontium. Journal of Prosthetic Dentistry 1961;11:722—34. 25. Syed SA, Svanberg M, Svanberg G. The predominant cultivable dental plaque flora of beagle dogs with gingivitis. Journal of Periodontal Research 1980;15:123—36. 26. Dahle ´n G, Heijl L, Lindhe J, Mo ¨ller A. Development of plaque and gingivitis following antibiotic therapy in dogs. Journal of Clinical Periodontology 1982;9:223—38. 27. Cutler CW, Ghaffar KA. A short-term study of the effects of SBHAN, a novel compound, on gingival inflammation in the beagle dog. Journal of Periodontology 1997;68:448—55. 28. Lindhe J, Hamp S, Lo ¨e H. Experimental periodontitis in the beagle dog. Journal of Periodontal Research 1973;8:1—10. 29. Lindhe J, Hamp SE, Lo ¨e H. Plaque induced periodontal disease in beagle dogs. A 4-year clinical, roentgenographical and histometrical study. Journal of Periodontal Research 1975;10:243—55. 30. Listgarten MA, Lindhe J, Hellde ´n L. Effect of tetracycline and/or scaling on human periodontal disease. Clinical,
31.
32.
33.
34. 35.
36.
37.
159
microbiological, and histological observations. Journal of Clinical Periodontology 1978;5:246—71. Listgarten MA, Hellde ´n L. Relative distribution of bacteria at clinically healthy and periodontally diseased sites in humans. Journal of Clinical Periodontology 1978;5:115—32. Theilade E, Wright WH, Jensen SB, Lo ¨e H. Experimental gingivitis in man. II. A longitudinal clinical and bacteriological investigation. Journal of Periodontal Research 1966;1: 1—13. Tanner A, Maiden MF, Macuch PJ, Murray LL, Kent RL. Microbiota of health, gingivitis, and initial periodontitis. Journal of Clinical Periodontology 1998;25:85—98. Listgarten MA. The structure of dental plaque. Periodontology 2000;5(1994):52—65. Socransky SS, Manganiello AD, Propas D, Oram V, van Houte J. Bacteriological studies of developing supragingival dental plaque. Journal of Periodontal Research 1977;12:90—106. Haffajee AD, Cugini MA, Tanner A, Pollack RP, Smith C, Kent RL, Socransky SS, Subgingival microbiota in healthy, wellmaintained elder and periodontitis subjects. Journal of Clinical Periodontology 1998;25:346—53. Ali RW, Johannessen AC, Dahle ´n G, Socransky SS, Skaug N. Comparison of the subgingival microbiota of periodontally healthy and diseased adults in northern Cameroon. Journal of Clinical Periodontology 1997;24:830—35.