The significance ofthe fovea palatini-in complete denture prosthodontics T. t. Lye, B.D.S., F.D.S.R.C.S.*
Faculty o~Dentistry, University o/Singapore, Singapore
T i e fovea palatin i are clinically Visible :pits in the palate which are useful to dentists as surface anatomic landmarks in constructiop of complete dentures (Fig. 1). They are the ductal openings and recipients of distributaries of ducts of the surrounding clusters of mucous glands. They are not constantly:present as are those of the major Salivary glands. They appear to be a peculiarly human feature, as the palatal mucous glands of other animal.,/open iridividually, giving the palate the appearance of an orange peel (Fig. 2). "-/'he foveae are given little or no mention by dental anatomists. Howeyer, for reasons of denture retention, dentists have become interested in these anatomic landmarks, Unfortunately, there are disagreements regarding their location in relation to the soft and hard palates and the vibrating line which is defined as, "the imaginary line across the posterior part of the palate marking the division between the movable and relatively immovable tissues of the palate.". ~ Sicher" described the foveae as:situated immediately behind the boundary between the hard ~and soft palates. According to Nagle and Sears, :~ the foveae mark the posterior limft of the hard palate; while.Anderson and Storer "~ placed them in the glandular region 9 f the soft palate, a View shared by Fenn and associates5 Swenson'; concluded that the vibrating line passes about 2 ram. in front of the fovea palatini. The vibrating line de-termines the useful limit ofthe posterior border of the denture. Silverman r expressed the view that t h e posterior palatal seal could be extended further back (dorsally ,) than:the Vibrating line by about 8.2 ram. to substantially aid i n t h e r e t e n t i 0 n and stability-of theuppe r denture. Skinner and Chung s have experimentally shown the importance of the posterior palatal seal. It complements the border seal :''~' in u-tilizing atmospheric pressure to resist transient lateral thrusts? z The factors of Cohesion,.adhesion , and interfacial surface tension 1:~,~4 maintain the uppe r denture against vertical dislodging forces. In view~ of the importance of the poster!or border of the denture to the vibrating line and the proximity of the foveae, this article reports on an investigation of their *Associate Professor.
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The /ovea palatini and complete dentures
Fig. 1. The fovea palatini are surface landmarks that can be observed clinically in the mouth. Fig. 2. The palate of the pigshowsmultiple openings0f the palatal mucous glands. location in relation to one another, together with the regional innervation and the interrelation of the Underlying soft and hard structures.
CLINICAL STUDIES One-hundred subjects were randomly selected without r e g a r d to sex, age, or race. Clinical Observations revealed that 92 of them showed the presence of fovea palatini. Of these, 18 Subjects (19.56 per cent) had single Pits. In those subjects with the usual double foveae (see Fig. 1), a fibrous band could be seen in some of them running between the openings and disappearing posteriorly and distally into the soft palate. The fovea palatini were visually plotted against the vibrating line. The vibrating line was anterior (ventral) to the foveae in 12 subjects (13.04 per cent). The foveae and vib/'ating line coincided in 16 patients (17.39 per cent). The vibrating line was posterior (dorsal) to the foveae in 64 subjects (69.57 per cent) (Fig. 3). The mean measurement positioned the vibrating line at 1.31 ram. behind the foveae. The readings varied from 3 mm. anterior to 5 ram. posterior to the foveae. The subjects were tested through a second series of measurements. This time, the edge of a mouth mirror was lightly held on the apparent point of vibration as located in the first test (Fig. 4). Observations were made as to when the soft tissues were lifted away from the mirror's edge, thus registering a meaningful point for the vibrating line. It was observed that only 4.12 per cent of the subjects registered palatal movements in front of the foveae, 16.34 per cent registered at the.foveae, and the mirror could be moved back an average 2.16 ram. before movements of the palate became significant in the remaining 79.54 per cent of the subjects.
RADIOGRAPHIC STUDIES Twelve specimens of the palate were collected from accident victims. Each piece measured approximately 4 by 3 cm. (longer anteroposteriorly), with the foveae located approximately in the center. Stainless steel wires of 0.3 ram. gauge were cut to 0.5 mm. lengths and inserted into the foveae. Radiographs were made with tl~e rays aimed at right angles to the surface of the bone of the hard palate, which related the foveae to the palate along the maxillary plane (Fig. 5, A). A second series of radiographs were made to minimize the errors that could arise because the first series of radiographs were not made in a true vertex view. These
J. Vrosthet. Dent, May, 1975
Fig. 3. The distribution in 100 patients of the presence or absence of the foveae and their relationship to the vibrating line.
were lateral views made after the palate had been sectioned along the palatine sutures (Fig. 5, B) All of the radiographs were made of the specimens in their fresh state. The radiographs of both views were enlarged seven times, and tracings of the posterior margins of the bones and the foveae were m a d e (Fig. 6). A straight line was traced through the--P~atine suture in the vertex view. Another line was drawn at. right angles to the first line, passing through the tip of the bone. T h e distance between t h e foveae and second line was indicative of the relationship of the foveae to the edge of the horizontal part of the palatine bone,,which is the anatomic limit of the hard palate. Measurements were also made of the distance separating the two foveae. Similar tracings were made in the lateral view. T h e horizontal line i n this instance passed through the approximate center of the thickness of the palatine and maxillary bones. Again, the length of the vertical line that passedthrough the edge of the bone 'to the foveae was measured. The findings revealed that the foveae were situated in soft tissue :covering the hard palate in all Specimens. The mean distance from the junction of the hard a n d soft palates was 3.58 ram" Variations of 1.85 to 6.14 ram. occurred. The foveae were separated by an average distance of 3.27 ram.
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The [ovea palatini and complete dentures
Fig. 4. The edge of the mirror is used 1:o determine the vibrating line by observing the position at which the soft tissues of the palate lift away from the instrument.
Fig. 5..(A) A vertex radiograph of the palate. (B) A lateral radiograph of the palate. Stainle}s steel markers (F) inserted into the foveae relate them to the edge of the palatine bones (P). HISTOLOGIC STUDIES The foveae of the specimens used for the radiographic investigations were damaged by the insertion of stainless steel points. For the histologic studies, three new specimens were collected. They were carefully sectioned sagittally across the foveae. T h e sections confirmed the radiographic findings that the foveae were located within the region of the bone of the hard pal~/te (Fig. 7). Triehrome differential staining definitely confirmed that there was no direct attachment of muscles to the distal border of the bone. This m e a n t that the vibrating line was located at, or in front of, the foveae as a result of the loose character of the connective and glandular tissues which were more susceptible to the influence of the palatine musculature. I n comparative primate studies, ttle mucosa immediately beneath the tip of the palatine bone was found to be rich in nerve endings."~ , TM This is believed to be important for initiation of the swallowing reflex. In the h u m a n tisgues under study, the c o m p l e x of, nerve endings was found to begin just anterior to the :foveae and spread toward the soft palate (Figs. 8 and 9). T h e significance of this finding is being investigated.
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VERTEX VIEW Fig. 6. Radiographic tracings of Fig. 5. The distances between the foveae (F) and the posterior nasal spine (P) were measured. S is the outline of the soft palate. DISCUSSION T h e fovea palatini were found to be separated from each other by about 3.5 mm. The intervening mucosa in some subjects was thickened because of tile band of fibrous attachment of tile aponeurosis to the nasal spine. Such subjects tended to develop ulcerations when the posterior border of the denture was ended at the foveae. Nerve concentrations were found to begin just anterior to the foveae and spread toward the soft palate. This finding supports the emphasis that the posterior palatal seal should be carefully located and scored so that no soft tissue movement can take place to initiate tile gag reflex. The studies revealed that, ahhough the mean position of tile vibrating line is
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The /ovea palatini and complete dentures
Fig. 7. A cross section of the palate indicates that the foveae are positively anterior to the junction of the hard and soft palates. (Hematoxylin and eosin. Original magnification x2.)
Fig. 8. A histologic section taken just anterior to the foveae (F) shows the anterior limit where ,) the nerve plexus (N) is clearly discernible. (Bodian. Original magnification x_4.) Fig. 9. The cnlargement of area framed in Fig. 8 shows the concentration of nerve endings (N). (Bodian. Original magnification x40.)
1.31 mm. behind the foveae, tile posterior limit of the denture can be extended an additional 2 ram. before soft-tissue movement is sufficient to break tile seal. This position is also approximately at the junction of the soft and hard palates. The fovea palatini serve no other useful purpose than to receive the ducts of the palataI mucous glands around them. Could their unique presence in man mean that the palatal glands are tending to evolve into a distinct pair rather than remaining as clusters of individiml glands as in other animals, and that the fovea are their ducts?
SUMMARY Clinical, radiographic, and histologic studies of the fovea palatini indicate that they were positioned 1.31 ram. (mean of 100 subjects) in [font of tile vibrating line. Radiographically and histologically, the foveae were located in soft tissue covering tile hard palate in all specimens. Histologically, complex nerve endings were found just anterior to the foveae and spreading to the .,oft palate. The findings were related to clinical aspects of complete dentures.
j . Prosthet. Dent. May, 1975
The author expresses his thanks to Dr. T. C. Chao and his staff at the Department of Pathology, O.R.G.H., Singapore, for making available the materials used in this study. His appreciation also goes to Dr. W. K. Yip for his invaluable help, to Dr. Yip's staff for the preparation of the histologic specimens, and to Mr. K: P. Yap and Mr. R. Teo for the photographs.
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Boucher, C. O.: Current Clinical Dental Terminology, ed. 1, St. Louis, 1963, The C. V. Mosby Company, p. 217. Sicher, H~: Oral Anatomy, ed. 2, London, 1952, Henry Kimpton, p. 188. Nagle, R. J., a~nd Sears, V. H.: Dental Prostheties, Complete Dentures, St. Louis, 1958, The C. V. Mosby Company, p. 181. Anderson, J. N . , and Storer, R. : Immediate and Replacement Dentures, Oxford, 1966, Blackwell Scientific Publications, p. 60. Fenn, H. R. B., Liddelow, K. P., and Gimson, A. P.: Clinical Dental Prosthetics, ed. 2, London, 1961, Staples Press, p. I90. Boucher, C. O . : Swenson's Complete Dentures, ed. 6, St. Louis~ 1970, The C. V. Mosby Company, p. 67. Silverman, S. I. : Dimensions and Displacement Patterns of the Posterior Palatal Seal, J. PROSTHET. DENT. 25: 470-488, 1971. Skinner, E. W., and Chung, P.: The: Effect of Surface Contact in the Retention of a Denture, J. PROSTHET. DENT. 1: 229-235, 1951. Ha!l, R. E.: Retention of Full Dentures, Aust. Dent. J. 24: 99-109, 1920. Tyson, K. W.: Physical Factors in Retention of Complete Upper Dentures, J. PROSTHET. DENT. 18:90-97, 1967. Laramie, G. A.: The Retention of Complete Dentures, J. Am. Dent. Assoc. 55: 502-508, 1957. Hardy, I.'R., and Kapur, K. K. : Posterior Border Seal--Its Rationale and Importance, J. PROSTHET. DENT. 8" 386-397, 1958. Stanitz, J. D.: Analysis of the Part Played by the Fluid in Denture Retention, J. Am. Dent. Assoc. 37: 168-172, 1948. Barbenel, J. C.: Physical Retention of Complete Dentures. J. PROSTHET. DENT. 26: 592600, 1971. Gairns, F. W. : The Sensory Nerve Endings of the Human Palate, Q. J. Exp. Physiol. 40: 40-48, 1955. Vii, S., and Kanagasuntheram, R.: Innervation of Oral Tissues in Some Primates, Folia Primatol. 1 I: 289-299, 1969. UNIVERSITY OF SINGAPORE FACULTY OF DENTISTRY SEPOY LINES SINGAPORE 3