Skylab Oral Health Studies

LEE R. BROWN, WILLIAM J. FROME, SANDRA HANDLER, MERRILL G. WHEATCROFT, AND LINDA J. RIDER

ORAL HEALTH CONSIDERATIONS for the Skylab series of manned space flights included three general areas of responsibility. These areas were:

          Clinical dentistry;

Provisions for in-flight care and the In-flight Medical Support System-Dental: and

Research dedicated to the identification of potential oral problems in manned space missions of long duration.

Clinical Dentistry

Clinically, the emphasis in the dental health program was on the prevention of dental disease. This was accomplished by a carefully supervised home care program which was supplemented with oral examinations and evaluations at least every 6 months. Regular topical applications of stannous fluoride were also provided all crewmen. However, because of consideration of other studies during the Skylab missions, the topical fluoride applications were discontinued 6 months preflight for each crew.

Because of risks of inflammation to the dental pulp, no dental restorations were provided the crewman during the last 90 days prior to flight. The oral health of all crewmen was at a sufficiently high level that the 90-day provision was realistic.

Complete oral Panorex radiographs were made of each crewman prior to his mission. These radiographs did reveal two asymptomatic, previously unrecognized areas of pathosis about the apex of the teeth of two crewmen. Both problems were successfully resolved.

During the last 9 months prior to the Skylab missions, six crewmen required treatment for denal problems which were other than routine replacement of restorations and dental prophylaxes. These ranged from a large, symptomatic, recurrent apthous ulcer, to significant inflammation and discomfort from local gingival inflammation, to a periapical abscess. All were resolved successfully with no recurrence.

The possibilty for an unanticipated dental problem occurring in-flight which could significantly impair a crewman’s ability to work effectively was computed at 0.92 percent for a 3-man 28-day mission. This figure was based on studies of dental experiences in other isolated environments, i.e., polar expeditions, United States Navy FBM submarine patrols, and from a 3-year study of the astronaut population. The most likely problems which could impair a crewman’s effectiveness in-flight were judged to be either a painful tooth due to pulpitis or severe, localized gingival inflammation with or without a periodontal abscess. The pulpitis would be most likely to occur in a tooth which had previously been restored with a deep restoration which suddenly had become symptomatic. This is a common ground-based dental problem and the resulting potentially debilitating pain could occur for a number of reasons, including decreased resistance of the host and/or increased virulence of the organisms involved. Dental caries was not considered as a problem in missions of up to 3 months' duration because of the high level of oral health of all crewmen and the frequent dental evaluations they received.

Because of the risks involved, it was decided that a means be developed for treating the most likely ental problems that might arise. To this end the prime and backup crews of all Skylab missions received 2 days of intensive training in pertinent dental procedures at Lackland Air Force Base,Texas. The training included lectures, demonstrations, and supervised clinical procedures. The supervised clinical procedures performed on volunteer patients included complex procedures such as tooth removal. Instruments and medications were provided as the In-flight Medical Support System-Dental. As aids, this In-flight Medical Support System-Dental included a manual with line drawings of complete intraoral radiographs of each crewman as well as integrated, illustrated, diagnostic, and treatment procedures. Examples of these aids are illustrated in figures 6-1a, 6-1b, and 6-1c. Other aids included air-to-ground communication with a dentist and/or surgeon who had as aids intraoral photographs and radiographs, diagnostic casts, complete treatment records with narrative summaries, and complete knowledge of the treatment capabilities of each crewman as he was observed during the training program. No dental problems occurred during the Skylab series of missions which required use of the In-flight Medical Suport System-Dental.

Oral Research

Skylab crewmembers were monitored to assess the effects of their missions on:

            The population dynamics of the oral microflora;

            The secretion of specific salivary components: and

            Clinical changes in oral health.

Not only is oral health important to personal performance during prolonged space missions, but the oral region serves as a portal of entry for pathogenic agents, acts as a reservoir for infectious micro-organisms, and plays a role in cross-contamination and disease transmission.

Laboratory detectable intraoral changes can precede clinical manifestations of acute and chronic infectious disease. Clinically detectable alterations of oral tissue can identify changes caused by local and/or systemic disorders of microbial and nonmicrobial origin.

Oral hygiene procedures consisted of brushing the teeth 2 minutes twice a day and flossing once a day. Tooth brushes with multitufted, nylon, bristles were used in conjunction with an ingestible dentifrice and thin, unwaxed dental floss. Irrigating devices, mouthwashes, topical fluorides, or other oral medication were not used.

All crewmen were placed on a space-food diet at about 21 days preflight. The backup crewmen continued on the space diet until launch and the prime crewmen until 18 days after recovery.

Equipment and Procedures.—Eighteen astronaut crewmembers making up the prime and backup crews for the three Skylab missions were monitored for quantitative changes in oral micro-organisms, saliva partitions considered potentially important to oral health, and alterations in clinical indices of oral health and preexisting dental disease.

Microbiological Assessments.—Specimen collection. Oral specimens were collected from the crew-members weekly or semiweekly from three intraoral sites from 31 days preflight to 18 days postflight for Skylab 2, from 51 days preflight to 20 days postflight for Skylab 3, and from 57 days preflight to 17 days postflight for Skylab 4. All collections took place between 0700 and 0800 hours before oral hygiene procedures or breakfast.

The specimens included dental plaque, crevicular fluid (exudate absorbed from the gingival sulcus area), and stimulated saliva. These parameters were selected because of their ultimate relation to the development of dental caries, periodontal disease, and alveolar bone loss.

Dental plaque was removed using a modification of the technique by Jordan et al. (ref. 1). Crevicular fluid was obtained by inserting a paper point into the gingival sulcus of an upper bicuspid according to the method of Brown et al. (ref. 2). Each specimen was placed aseptically into a sterile tube containing 2 milliliters of 0.1 percent peptone and 0.85 percent sodium chloride. The peptone-saline solution served as both a transport and dilution medium.

To produce stimulated saliva, the crewmembers chewed sterile paraffin and expectorated into a sterile jar until a 5 milliliter indicator mark was reached. The time required for each crewman to collect this volume was recorded and used to calculate the saliva flow rate.

All specimens were transported in cracked ice to the University of Texas Dental Science Institute for immediate processing which occurred about 1 hour after collection.

Speciment Processing.

Serial tenfold dilutions of each specimen were plated onto a variety of bacteriologic media (refs. 3, 4, 5, 6, 7, 8, 9,10,11, 12,13,14) for the enumeration of up to 17 microbial categories. Duplicate platings were incubated at 37° C either aerobically or anaerobically. The bacteriologic media, microbial categories, and an-aerobic procedures are shown in figure 6-2. Specific microbial types from selective and differential media were verified by subculture and by pertinent physiologic reactions when necessary.

In addition to the microbial assessments, stimulated saliva was used to determine total protein, secretory IgA, and lysozyme. Salivary protein determinations were made by the Lowry procedure (ref. 15). Secretory IgA was assayed by electro-immunodiffusion (ref. 16) where the samples are electrophoresed through a medium containing monospecific antisera. Plates were precoated with 0.1 percent agarose in 0.05 percent glycerol and layered with buffered agarose containing antisera. Wells were filled with standards or saliva. Samples were electrophoresed until the point of equivalence with the highest standard was attained. The plates were then processed for staining and the migration distances were measured. Samples with values beyond the standard range required dilution. A plot of log concentration versus log migration distance yielded a linear curve for quantification (ref. 17). Lysozyme values were determined by radial quantitative diffusion using heat-killed Micrococcus lysodeikticus cells as a substrate according to the procedures of Osserman and Lawlor (ref. 18). Plates were layered with a cell suspension in buffered molten agarose. Wells were cut and filled with standards of saliva. Diffusion was allowed to proceed overnight. Values were determined from a plot of log concentration versus diameter of lysed zone.

The microbiologic enumeration and immunologic data were recorded for appropriate statistical analysis. Both a one-way and two-way unbalanced analysis of variance were used for multiple comparisons of individual, paired, and grouped data. Primary comparisons were made within three segments of data: (a) preflight-prespace diet (31 and 21 days preflight or 29 and 19 days preflight), (b) preflight-space diet (14 and 3 days preflight or 13 and 4 days preflight), and (c) recoverey space diet (4,13, and 18 days post-flight from the prime crew only).

Clinical Evaluations

Clinical scores of dental plaque, dental calculus, and gingival inflammation were derived from oral evaluations at two pre-flight and one postflight examination intervals. The examination intervals were relative to the projected duration of each flight. The initial pre-flight oral examination was on days 30, 51, and 57 for Skylab missions 2, 3, and 4, respectively. In all missions the final preflight oral examinations were accomplished on day 4 and the postflight on day 4 after recovery. Following the scoring of gingival inflammation on the initial preflight examination, a thorough prophylaxis was performed. On day 4, the final preflight examination, gingival inflammation, dental plaque, and calculus were scored to calculate a preflight increment (baseline) for each of the oral health indices. All plaque and calculus were again removed to permit recovery scores to be used as in-flight increments. Since gingival inflammation scores could not be brought to a zero baseline, as in the case of plaque and calculus, the difference in scores between the initial and final preflight evaluations was used as the preflight baseline. The difference between the final preflight and recovery scores was used as the in-flight increments of gingival inflammation.

A plaque score was obtained for each astronaut by the use of disclosing wafers which stained the plaque adhering to the tooth surfaces. Calculus scores were obtained for each crewmember by dividing the number of tooth surfaces that had calculus by the number of teeth. The inflammation index was scored according to the method of Loe and Silnes (ref. 19) which graded the gingivae surrounding each tooth.

Dental radiographs were made of each crewmember at 6 months and 30 days preflight to provide baseline records for subsequent comparison. A complete series of oral radiographs were taken at 6 months preflight. To minimize radiation exposure, only bitewing radiographs were taken at 30 days preflight.

The clinical evaluations were statistically compared by "t" analysis using both the means difference and difference between means statistics (ref. 20).

Results.

In Skylab 2 the microbial data showed increases in various anerobic components, i.e., Bacteriodes sp., Veillonella sp., Fusobacterium sp. Other increases were in Neisseria sp. and Streptococcus mutans.

Fewer microbial changes were noted in Skylab 3. For example, in stimulated saliva the anaerobic components showing increases were Veillonella sp., Fusobacterium sp., Leptotrichia sp., and Mycoplasma sp. S. mutans counts were variable. However, in this flight Staphylococcus aureus and enteric organisms showed increasing trends toward the later stages of sampling.

The microbial data from the Skylab 4 mission were very similar to that of the Skylab 3 mission. The anerobic components to show increases in the gingival sulcus fluid were Bacteroides sp. and Veillonella sp. There was also a rise in S. sanguis and Neisseria sp.

Figure 6-3 represents the cumulative preflight data of all 18 crewmen, before and after they were placed on the carbohydrate enriched space diet. At these levels of significance expressed on a percentage basis, there were significant increases after diet of the following total anerobes, Diphtheroids, S. sanguis, Neisseria sp., Bacteroides sp., Veillonella sp., and Fusobacterium sp. Most of the oral microbial changes noted during each mission appeared to be associated with diet change as evidenced by the statistically significant post diet increases.

The saliva partitions—saliva flow rates, salivary lysozyme, and protein concentration levels—assayed in this study of the prime crew of Skylab 2 remained relatively constant throughout this period. But the secretory IgA levels showed pronounced increases beginning just prior to flight and continuing throughout the postflight sample period. It is believed that these changes were probably due to responses to a subclinical viral infection.

The mean values for changes in salivary partitions of the prime crewmembers of Skylab 3 are secretory IgA which showed increases and these increases occurred concurrently with saliva flow rate increases and salivary protein decreases. Reasons for the latter changes are presently unex-plained.

In the Skylab 4 mission secretory IgA levels again increased and the levels of protein and lysozyme as well as saliva flow rates showed trends similar to the Skylab 3 flight. The increase in secretory IgA in the crewmen for the Skylab 4 mission occurred in only two of the three crewmen. The IgA levels of the Scientist Pilot remained relatively constant.

A comparison of clinical scores of oral health before and after the Skylab 4 mission (fig. 6-4) revealed prominently elevated increments of dental calculus and gingival inflammation postflight as compared with the preflight values. This trend was observed for all missions.

While the overall oral health level of all crewmen remained very good postflight, some deterioration had occurred as measured by these indices.

Discussion

The oral microbiological, immunologic, and clinical results of the Skylab series of manned space flight missions were relatively consistent. Oral microbial changes usually occurred after the incorporation of the space diet prior to flight. Statistical comparisons of cumulative preflight data from the 18 (prime and backup) crewmembers, before and after diet inclusion, revealed diet relatedness for the majority of the microbial increases observed during the missions. Some of the changes, although apparent after the inclusion of the diet during the preflight period, were more pronounced after flight. However, the postflight values were excluded in the diet related analysis to avoid any possible flight influence.

Increases in secretory IgA observed in two of the Skylab 4 crewmembers were observed in all three crewmembers of Skylabs 2 and 3. As in the previous studies, the changes were believed to result from subclinical infections. Concurrent fluctuations in salivary protein, lysozyme and saliva flow rates, also observed in previous studies, are unexplained.

In these studies, observed incremental increases of dental calculus and gingival inflammation were consistent, with the exception of the Skylab 3 crew where these changes were not observed to the same degree. Individuals free of oral health problems seem to be less susceptible to detrimental changes under a specific challenge than those with preexisting dental problems.

Conclusion

Skylab crewmembers were monitored for mission related effects on oral health. Those laboratory and clinical parameters considered to be ultimately related to dental injury were evaluated.

Of these, the most distinctive changes noted were:

Increased counts of specific anaerobic and streptococcal components, primarily of the saliva and dental plaque microflora.

Elevations in levels of secretory IgA concurrent with diminutions of salivary lysozyme.

          Increased increments of dental calculus and gingival inflammation.

The microbial changes were mainly diet related rather than flight related. Elevations of secretory IgA were believed to result from a subclinical infection. Concurrent diminutions of salivary lysozyme are unexplained. The clinical changes in oral health were considered to be influenced more by a crewmember’s preexisting state of dental health than by any health hazardous mission related effect.

Assuming no future clinical detection of mission-related intraoral complications, the most significant aspect of these investigations was the relative nonexistence of health hazardous intra-oral changes.

Acknowledgments

We gratefully acknowledge the contributions of John R. Hemby and Darrell G. Fitzjerrell of the General Electric Company for the design and development of the Skylab In-flight Dental Diagnostic and Treatment Manual.

References

1. JORDAN, H.V., B. KRASSE, and A. MOLLER. A method of sampling human dental plaque for certain "caries-inducing" streptococci. Arch. of Oral Biol., 13:919-927, 1968.

2. BROWN, L.R., S.S. ALLEN, M.G. WHEATCROFT, and W.J. FROME. Hypobaric chamber for oral flora study in simulated spacecraft environment. J. of Dent. Res., 50:443-449, 1971.

3. ROGOSA, M., J.A. MITCHELL, and R.F. WISEMAN. A selective medium for the isolation and enumeration of oral lactobacilli. J. of Dent. Res., 30: 682-689, 1951.

4. ROGOSA, M., R.J. FITZGERALD, M.E. MACKINTOSH, and A.J. BEAMAN. Improved medium for selective isolation of veillonella. J. of Bacteriol., 76:455-456, 1958.

5. OMATA, R.R., and M.N. DISRALY. A selective medium for oral fusobacteria. J. of Bacteriol., 72:677-680, 1956.

6. KRAUS, F.W., and C. GASTON. Individual constancy of numbers among the oral flora. J. of Bacteriol., 71:703-707, 1956.

7. RICHARDSON, R.L., and M. JONES. Bacteriologic census of human saliva. J. of Dent. Res., 37:697-709, 1958.

8. SHKLAIR, I.L., M.A. MAZZARELLA, R.G. GUTEKUNST, and E.M. KIGGINS. Isolation and incidence of pleuropneumonia-like organisms from the human oral cavity. J. of Bacteriol., 83:785-788, 1962.

9. MCCARTHY, C., M.L. SNYDER, and R.B. PARKER. The indigenous oral flora of man. I. The new-born to 1-year-old infant. Arch of Oral Biol., 10:61-70, 1965.

10. RITZ, H.L. Microbial population shifts in developing human plaque. Arch. of Oral Biol., 12:1561-1568, 1967.

11. GIBBONS, R.J., and J.B. MACDONALD. Hemin and vitamin K compounds as required factors for the cultivation of certain strains of Bacteroides melaninogenicus. J. of Bacteriol., 80:164-170, 1960.

12. SOCRANSKY, S.S., R.J. GIBBONS, A.C. DALE, L. BORTNICK, E. ROSENTHAL, andJ.B. MACDONALD. The microbiota of the gingival crevice. I. Total microscopic and viable counts of specific organisms. Arch. of Oral Biol., 8:275-280, 1963.

13. SONNENWIRTH, A.C. The clinical microbiology of the indigenous gram-negative anaerobes. Synopsis from Oral Presentation at the Clinical Microbiology Round Table, ASM Meeting, Atlantic City, New Jersey, 1965.

14. FINEGOLD, S.M., A.B. MILLER, and D.J. POSMAK. Further studies on selective media for bacteroides and other anaerobes. Ernahrungsforschung, pp. 617-528. Berlin, 1965.

15. LOWRY, O.H., N.J. ROSEBROUGH, A.L. FARR, and R.J. RANDALL. Protein measurement with the folin phenol reagent. J. of Biol. Chem., 193:265-276, 1951.

16. MERRILL, D., T. HARTLEY, and H. CLAMAN. Electroimmunodiffusion (EID): A simple, rapid method for quantitation of immunoglobulins in dilute biological fluids. J. of Lab. and Clin. Med., 69:151-159, 1967.

17. LOPEZ, M., T. TSU, and N. HYSLOP. Study of electroimmunodiffusion: immunochemical quantitation of proteins in dilute solutions. Immunochemistry, 6:513-526, 1969.

18. OSSERMAN, E.F., and D.P. LAWLOR. Serum and urine lysozyme (muramidase in monocytic, and monocytocytic leukemia). J. of Exp. Med., 124:921-951, 1966.

19. LOE, H. and J. SILNES. Periodontal disease in pregnancy. I. Prevalence and severity. Acta Odontologica Scandinavica., 21:533-551, 1963.

20. SCHEFFE, H. The analyses of variance, pp. 112-119. John Wiley and Sons, Inc., New York, 1959.

 

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