Elevation of lesioned palatal shelve in...

/ . Embryol. exp. Morph. Vol. 54, pp. 229-240, 1979 2 2 9Printed in Great Britain © Company of Biologists Limited 1979

Elevation of lesioned palatal shelves in vitro

By L. L. BRINKLEY1 AND M. M. VICKERMAN1

From the Department of Anatomy, Medical School,The University of Michigan

SUMMARYFetuses were obtained from CD-I mice at a time estimated to be 12 h prior to in vivo second-

ary palate closure. One of the palatal shelves of each partially dissected fetal head waslesioned in one of five ways, the other left intact to serve as a control. Single transverse cutsextending the width of the shelf were made at one of three positions along the longitudinalaxis of the shelf: one-third, one-half or two-thirds the shelf length estimated from the rostraledge. Some specimens were cut in two places, dividing the shelf into three equal segments.Another group received a lesion which separated the caudal third of the shelf from itsmaxillary connections. All specimens were cultured for 18 h. At the end of the culture periodthe heads were fixed, examined and the degree of elevation of each shelf piece assessed.

Intact, contiol shelves of all preparations were elevated in the rostral two-thirds of theshelf, while the caudal third was partially elevated. Results seen in lesioned shelves dependedupon both the size of the segment and the region of the shelf contained in the segment.The rostral two-thirds of the shelf, the presumptive hard palate, whether intact or in segmentselevated without physical connections to neighboring shelf tissue. Thus, it is unlikely thatthis elevation requires a wave of contraction be transmitted from the caudal soft palateregion. In contrast, the presumptive soft palate requires continuity with the rostral portionsof the shelf both to maintain structural stability and to elevate.

INTRODUCTION

Closure of the secondary palate involves movement of the palatal shelvesfrom a vertical position on either side of the tongue to a horizontal positionsuperior to it. Extrinsic factors such as tongue displacement, mandibulargrowth, straightening of the cranial base and nonpalatal muscular activityincluding mouth opening, swallowing and neck flexion have been cited ascontributing to shelf elevation (Greene & Pratt, 1976). Intrinsic factors havealso been implicated, of which the most important is 'internal shelf force'(Walker & Fraser, 1956).

The nature of this intrinsic force remains undefined. It was originally postu-lated to reside in an elastic fiber network (Walker & Fraser, 1956); however,subsequently no such network was seen in the shelves at the time of palateclosure (Stark & Ehrman, 1958; Loevy, 1962; Frommer, 1968; Frommer &Monroe, 1968). Other investigators have attributed internal shelf force to

1 Authors' address: Dr L. Brinkley, Department of Anatomy, Medical School, Universityof Michigan, Ann Arbor, Michigan 48109, U.S.A.

230 L. L. BRINKLEY AND M. M. VICKERMAN

properties of the extracellular matrix, glycosaminoglycans and collagen (Larsson1961, 1962; Pratt & King, 1971; Pratt, Goggins, Wilk & King, 1973; Hassell& Orkin, 1976). Hypotheses and evidence have also been put forth suggestingthat a contractile system generates a vector of force that is transmitted alongthe shelf in a caudal to rostral direction (Lessard, Wee & Zimmerman, 1974;Babiarz, Allenspach & Zimmerman, 1975; Wee, Wolfson & Zimmerman,1976). Regardless of the origin of shelf force, it is generally acknowledgedthat this force may allow the palatal shelves to play an active role in their ownelevation.

Several different observations suggest regional differences in the nature ofinternal shelf force. In rodents, the movement of palatal shelves appears todiffer relative to the location along the rostral-caudal axis of the shelf. Themost rostral area of the shelf seems to rotate in an all-or-none manner (Coleman,1965), whereas remodelling of the caudal area seems to involve a medialprotrusion and lateral regression of shelf tissue (Walker & Fraser, 1956;Larsson, 1962; Coleman, 1965; Harris, 1967; Pourtois, 1972; Srivastava & Rao,1979). Whether or not localized internal factors are involved is unknown.There is also disagreement as to the pattern of shelf movement. Some authorsbelieve movement starts caudally (posteriorly) and proceeds in a wave-likemanner rostrally (anteriorly) (Walker & Fraser, 1956; Babiarz et al. 1975).Others suggest that it proceeds from the rostral to the caudal ends of the shelves(Coleman, 1965; Wragg, Diewert & Klein, 1972). It has also been describedas beginning at the junction of the middle and posterior thirds and then extend-ing both rostrally and caudally (Kochhar & Johnson, 1965). To better under-stand the intrinsic factors, it is essential that extrinsic factors be controlled. Oneway to achieve this control is by using an in vitro system.

The process of palate closure has been shown to take place in an in vitrosystem in which many possible extrinsic factors are eliminated (Brinkley,Basehoar, Branch & Avery, 1975). Neither removal of the tongue and brain(Brinkley, Basehoar & Avery, 1978) nor ablation of a large midsagittal regionof the cranial base (Brinkley & Vickerman, 1978) interferes with in vitro palateclosure. In vitro it is possible directly to observe and manipulate the palatalshelves themselves with little or no interference from other extrinsic anatomicalstructures.

The present study on palatal shelf behavior, using our in vitro system,investigates two questions: (1) will elevation occur if the longitudinal axis ofthe shelf is surgically interrupted, thus determining if transmission of a forcealong the longitudinal axis of the shelf is required; and (2) do different areasof the palatal shelf differ in their ability to elevate when freed from theirattachment to the rest of the palatal shelf. If such differences exist it wouldsuggest a possible regionalization of whatever factors constitute internal shelfforce.

Lesioned shelf elevation in vitro 231

MATERIALS AND METHODS

Animals. Timed pregnant CD-I mice were obtained from Charles RiverLaboratories (Charles River, Massachusetts, U.S.A.). The pregnant mice werekilled by cervical dislocation on late day 13 of gestation (plug day = 0), at atime estimated to be about 12 h prior to expected palate closure. Proceduresfor obtaining the fetuses have been described elsewhere (Brinkley et al. 1975).As there is variation in time of fertilization of these commercially suppliedmice, as well as developmental variation within a litter, the age of each fetuswas judged on gestational age, crown-rump length and morphological criteria.Morphological criteria included assignment of a numerical value to the develop-mental status of forefeet, hindfeet, ears, hair follicles and eyes as described byWalker & Crain (1960). Fetuses of morphological rating 7-8, with a crown-rump length of 10-5-10-7 mm were used for this study. Palate closure occursat about 14 days, 8-12 h in CD-I mice at a time when fetuses show a morpho-logical rating of 9-12 and a crown-rump length of approximately 12-5 mm.

Dissections. Fetuses were removed from their membranes and placed in4 °C culture medium for the remainder of the dissection. This and all sub-sequent operations were carried out in an Edgegard Laminar Flow Hood(The Baker Co., Sanford, Maine) using sterile technique. With the aid of adissecting microscope, the head of each fetus was severed from the body anda single circumferential cut around the head was made just above the eyes.This severed tissue and the entire brain and any attached spinal cord wasremoved with fine forceps. The tongue was then entirely removed by pushingit through the floor of the oral cavity with microscissors. The hole throughwhich the tongue was removed was enlarged to form a small vent to the outside.This vent provides both increased medium circulation within the oral cavity,and access to the shelves for lesioning while leaving the maxillary-mandibularrelationship intact. Dissection procedures have been previously shown to bethe optimal ones for palate closure in this culture system (Brinkley et al. 1978).

One of the pair of palatal shelves of each of 103 fetuses was selectively cutat various sites along the rostral-caudal axis of the shelf using microscissorsor an ophthalmological scalpel. The other was left intact. Shelves were given asingle transverse cut across the entire shelf at approximately one-third, one-halfand two-thirds of shelf length, or at both one-third and two-thirds of thelength (Table 1). The width of the lesions ranged from 50 to 100/tm. In anadditional 14 specimens the lateral (maxillary) connections of the caudalone-third of one shelf were severed (Fig. 1A).

The fetal rat palate just prior to closure is assumed to be composed ofapproximately two-thirds presumptive hard palate, divisible anatomically intoanterior, middle and posterior regions, and one-third soft palate (Diewert,1978). This assumption was verified for the mice used in the present experiment.Ten heads were examined to determine the approximate proportion of the total


Table 1. Relationship of the site of a transverse lesionto shelf form after culture

Control shelves (n = 103)

Shell" form after culture

AH* Mil nr s100%

Single Lesion: f

(1) At-J-shelf length (« = 20)

(2) At+shelf length (//. = 29)

(3) Atfshelf length (« = 23)

100%

55%

100%

Two Lesions

(4) At-^ and 3-shelf length

Horizontal,

1mmmm*

Partially elevated, Vertical.

77%

16%

6%

* Postulated anatomical regions of the shelf: All = anterior hard palate: Mil = middlehard palate; I'll = posterior hard palate; S = soft palate.

t The placement of all lesions is described using the rostral edge of the palate as the reference point.

Lesioned shelf elevation in vitro 233shelf length which could be assigned to each of these four regions, using theanatomical criteria of Diewert (1978). The anterior and middle hard palaterepresented approximately 20 % each of the overall length, the posterior hardpalate and soft palate, 30% each as shown in the schematic diagrams inTable 1.

Culture. The preparations were suspended and immersed in circulating,gassed culture medium as previously described (Brinkley et al., 1975). Amodification in the design of the chamber has been made which enhancescirculation of medium and gas exchange (Lewis, Thibault, Pratt & Brinkley,1979). An 18 h culture period was selected to minimize the time available forwound healing, while providing sufficient time for elevation to occur in thissystem (Brinkley et al. 1978). Commercially supplied BGJb medium (GrandIsland Biological Co., Grand Island, N.Y., U.S.A.) with an additional 0-6 mg/mlglutamine and 50/ig/ml gentamicin, supplemented with 10% heat-inactivatedfetal calf serum (KC Biological, Lenexa, Kansas, U.S.A.) was used. Themedium was circulated at a rate of 10 ml/min, gassed with 95 % O2, 5 % CO2

using silicone co-polymer follow fiber devices (NIH, Bioengineering Laboratory,Bethesda, Maryland, U.S.A.), and kept at 34 °C. The POa and PCo2 values ofthe medium were determined with an IL 113 Blood Gas Analyzer. The averagePOa was 525 mmHg, PCQ2 50 mmHg.

Assessment of shelf form. After culture, the heads were removed, fixed inBouin's fluid or phosphate-buffered formalin and the mandible removed. Withthe aid of a dissecting microscope, each portion of the lesioned shelf, as well asthe intact control shelf, was assessed for its degree of elevation and for itsalignment relative to the intact shelf. Fifty-eight preparations were embeddedin paraffin or methacrylate and sectioned to determine the vitality of the tissuesurrounding the lesions.

RESULTS

Intact shelves

The intact, control shelves of all cultured specimens were elevated in therostral two-thirds of the shelf, while the caudal third ranged from partially tofully elevated. As a majority of the caudal thirds were only partially elevated,the control form of this region is reported as partially elevated. These resultsare similar to those seen in fetuses of this age that have both shelves intact(Lewis et al. 1979).

Site of the lesions and shelf form after culture

The relationship between the site of the lesion and the form exhibited byexperimental shelves at the end of the culture period is shown in Table 1.With a single cut placed at the junction of the rostral one-third and caudaltwo-thirds of the palatal shelf (lesion 1) both segments achieved the same shelfform as that of the intact control shelves. However, with a single cut placed


Fig. 1. Photogiaphs of the palatal region of two lesioned specimen after 18 h culture.(A) The caudal third of the shelf has been severed from its lateral maxillary con-nections. The arrows indicate the area and approximate extent of the lesion. Thecaudal region of the lesioned shelf has retained its form and partially elevated.(B) One shelf has been lesioned at approximately one-third and two-thirds the shelflength. The rostral (R) and intermediate (I) thirds have elevated and adhered,whereas the caadal third (C) has moved laterally and has not maintained normalform.

at two-thirds the shelf length (lesion 3), only the large rostral segment appearedsimilar to controls; whereas the caudal third showed no form change. When theshelf was bisected (lesion 2) the rostral one-half achieved control form in 90 %of the cases, whereas the caudal piece did so only 65 % of the time. When theshelf was divided into three approximtely equal segments the shelf formassumed by a given piece was directly related to its location along the longitu-dinal axis of the shelf. The rostral and intermediate segments had the sameform as equivalent regions of an intact shelf in 77 % and 93 % of the cases,respectively, whereas the caudal third never did.

Influence of segment size and region on shelf form

When the data shown in Table 1 are examined by segment size and shelfregion the influence of these two factors can be seen. All of the hard palateregions were more stable than the soft palate. That is, isolated segments ofhard palate behaved alone as they would when in an intact shelf. However, thiswas not true of the soft palate as is seen by the variation in form achieved byshelf thirds. Form similar to controls was achieved by all the intermediatethirds, composed principally of posterior hard palate, 86 % of rostral thirds,principally anterior hard palate, and no caudal thirds, soft palate. In additionthe caudal thirds also lost normal form by moving laterally and becomingrounded (Fig. 1B). Since no piece was predominantly composed of the middle

Lesioned shelf elevation in vitro 235hard palate, no evaluation of its form change when alone was possible. How-ever, middle hard palate composed approximately 40% of rostral thirds and20% of intermediate thirds. In 90% of these segments control shelf form wasobserved.

Rostral halves of palatal shelves, composed entirely of hard palate, achievedform similar to controls in 90% of the cases. On the other hand, caudal halveswhich included more than half (ca. 60%) soft palate, behaved similarly tocontrols only 66 % of the time. The dampening influence of the soft palate wasnot seen, however, in the behavior of the caudal two-thirds segments whichwere composed of approximately equal parts hard and soft palate. In thiscase these regions behaved similarly to the same regions of intact shelves inall cases.

Another type of cut was made to determine more about the behavior of thecaudal area. In 14 specimens the posterior one-third of the shelf was freedfrom its lateral maxillary connections, but remained attached to the rostral areaof the shelf. In all cases the piece retained recognizable shelf form and achievedthe partially elevated control shelf form (Fig. 1A).

Misalignment

In addition to movement to the horizontal plane, the shelves must align withone another in such a way that the corresponding areas along their longitudinalaxes are in register. When two intact shelves elevate this occurs naturally;however, when examining the position of shelf segments, significant misalign-ment was found to occur in pieces of less than or equal to half the shelf length.Rostral halves were misaligned in 68 % of the cases, whereas caudal pieces weremisaligned in 42% of the cases. The proportion of misalignment increaseddramatically when the shelf was divided into three pieces. All of the caudalthirds showed a loss of form. The caudal piece no longer had recognizable shelfcontours and in all cases moved laterally from its original position (Fig. 1B).The rostral thirds maintained normal shelf contours, but were misaligned in53 % of the cases. In sharp contrast, the intermediate thirds were not found tobe misaligned on observation with the dissecting microscope.

Histological findings

Fifty-eight specimens were examined histologically to determine tissue vitalityand to note any evidence of wound healing. Figure 2 illustrates sections im-mediately surrounding and within a lesion. Such tissue appeared vital, despitethe presence of some dead cells in the wound area itself. No evidence of woundhealing was observed.

16 EMB 54


Fig. 2. Coronal sections illustrating shelf behavior and tissue vitality in the regionsimmediately surrounding a typical transverse lesion made at approximately one-third the shelf length. The shelf tissue surrounding the lesion has maintained form,elevated and adhered. (A) Central area of the lesion illustrating its lateral extent.(B) Posterior area of the lesion. (C) Immediately caudal to the lesion. The shelf isagain intact and in contact with the control shelf. (D-F) Higher magnification ofthe tissue immediately adjacent to the lesion. In all sections the cells appear vital,with no evidence of wound healing. Section thickness, 3/«n; stain, toluidine blue.N= nasal septum; PS = palatal shelf.

DISCUSSION

The ability to directly manipulate palatal shelves and follow the outcomein vitro provides a unique opportunity to gain information on the stability ofform and elevation behavior of palatal shelf regions. Our results indicate thatelevation of the rostral two-thirds of the shelf, the presumptive hard palate,is not dependent on elevation of the caudal third, the soft palate. This is inagreement with the observations of Walker & Quarles (1976) that shelf elevationoccurred rostrally in fetuses with tongue stubs which prevented caudal shelf

Lesioned shelf elevation in vitro 237elevation. Present results also demonstrate that the hard palate itself need notbe intact, since segments of presumptive hard palate which are approximatelyone-third the total shelf length will elevate. This clearly indicates that elevationof the hard palate does not require that a vector of force be transmitted fromthe soft palate, thus arguing against the necessity of a 'wave of elevation' orvector of force emanating from the caudal area (Walker & Fraser, 1956;Babiarz et al. 1975; Wee et al. 1976).

Rather than being uniform throughout their length, the palatal shelves displaya striking regionalization of both elevation behavior and stability of form. Thehard palate, particularly the posterior region, displayed an inherent ability toassume the horizontal position even in segments composed of only one-thirdthe total shelf length. In addition, the posterior hard palate was never found tobe misaligned, and therefore seems to be the most structurally stable region.It would seem functionally advantageous for elevation to begin at the moststable region of the shelf, namely the middle third or presumptive posteriorhard palate. This is supported by the observations of Kochhar & Johnson (1965)that palatal shelf movement in rats is initiated at the junction of the anteriortwo-thirds and the posterior one-third of the shelves. We have also observedthis in mice during in vitro palate closure (unpublished observation).

The behavior of the caudal, presumptive soft palate region of the shelfcontrasts sharply to that of the hard palate. Not only is the caudal third unableto elevate when it is isolated from the rest of the shelf, but it does not retainits normal form, as do the regions of the hard palate. Caudal thirds lose theirform by appearing to move or collapse laterally. Skeletal muscle fibers reportedlyinsert from the maxillary area into the buccal side of the most caudal regionof the shelf (Babiarz et al. 1975). The lateral movement of this region when itis freed from most of its connections with the more morphologically stable hardpalate, may reflect contractile actions of these skeletal muscle fibers. Somesupport for this view comes from our observation that the caudal region of theshelf will elevate when severed from its maxillary connections.

Another factor in the failure of the caudal third to elevate may be the localdisruption of epithelial adhesion at the medial edge caused by the experimentaltransverse cuts. That is, a part of caudal elevation may be dependent on a'zippering' effect occurring as the medial edge adhesion of the shelves progressesrostrally and caudally. From our observations it appears that the elevationforce for the soft palate must be coming in part from its connections with thehard palate. Whether this is merely supplying structural stability, or is, in fact,supplying some sort of motive force is unknown.

The primary experimental procedure in the present study, making a transversecut perpendicular to the long axis of the shelf, disrupts the integrity of theepithelial covering in that local area, destroys underlying mesenchymal cells inthe path of the lesion, and disrupts the continuity of any elements which aredisposed along the long axis of the shelf. However such lesions do not, except

16-2


for the localized point of the lesion, affect the maxillary attachments of theshelves. Whatever the intrinsic elements creating the motive force for shelfelevation, they are presumably distributed throughout the hard palate, at least,and are not dependent on the integrity of the whole shelf for their function.Thus, it is logical to look at the structural components of the shelf, the epithelialcells, mesenchymal cells and extracellular matrix, as the potential basis ofintrinsic shelf force. In that regard many proposed roles of these componentsare consistent with the findings of the present study.

The epithelial cells encasing the mesenchymal and extracellular matrix com-ponents may provide part of the shelf force in one of several ways. The surfacearea of the shelf epithelium may be decreased on the nasal (lingual) surface byan increased adhesiveness between epithelial cells. Also, if the surface area ofthe oral epithelium remains constant the formation of rugae could reduce theoverall dimensions of the buccal epithelium, mostly in the rostral-caudaldirection. It has been suggested that these two epithelial activities actingtogether could cause a bulging of the shelf tissue toward the nasal slope (Pourtois,1972).

Many investigators have also suggested that networks or regions of con-centration of mesenchymal cells exist which may play a role in shelf elevation(Walker, 1961; Larsson, 1962; Kochhar & Johnson, 1965; Pourtois, 1972;Babiarz et al. 1975; Wee et al. 1976). For instance, preosteoblastic masses ofmesenchymal cells found in the lateral maxillary areas could act as anchors forother contractile mesenchymal cells or convey tension by some other means(Pourtois, 1972; Babiarz et al. 1975).

Extracellular components of the shelf may also be important. Several workershave demonstrated the presence of glycosaminoglycans throughout rodentpalatal shelves near the time of closure, and have suggested that these molecules,especially hyaluronate, are important in shelf elevation (Larsson, 1960, 1961,1962; Walker, 1961; Kochhar & Johnson, 1965; Pratt et al. 1973; Ferguson,1978; Wilk, King & Pratt, 1978). Evidence from qualitative histochemistryindicates that the middle third of the shelf, or the posterior hard palate,appears to contain the most extracellular matrix (Kochhar & Johnson, 1965).Collagen fibrils have also been reported to be present adjacent to the basementmembrane of the oral epithelium, oriented in a parallel array along the rostral-caudal axis of the shelf (Hassell & Orkin, 1976). However, the cuts used in thepresent study would be expected to disrupt this longitudinal array.

Thus, it seems that elevation of the presumptive hard palate may actuallybe the expression of a pre-existing infrastructure. That is, when the shelves areno longer held in a vertical position by the tongue, they assume a predeterminedform built into them by the quality, quantity and distribution of the cells,extracellular matrix and collagen within the shelves and adjacent maxillaryarea. In contrast, when the soft palate is not part of an intact shelf it does notseem to have sufficient internal stability to maintain its form and elevate.

Lesioned shelf elevation in vitro 239This work was supported by U.S.P.H.S. Grant DE-02774, National Institutes of Health,

Bethesda, Maryland, U.S.A.A portion of this work was presented at the meeting of the International Association of

Dental Research, Copenhagen, Denmark, 1977.

REFERENCESBABIARZ, B., ALLENSPACH, A. L. & ZIMMERMAN, E. F. (1975). Ultrastructural evidence of

contractile systems in mouse palates prior to rotation. Devi Biol. 47, 32-44.BRINKLEY, L., BASEHOAR, G., BRANCH, A. & AVERY, J. (1975). A new in vitro system for

studying secondary palatal development. J. Embryol. exp. Morph. 34, 485-495.BRINKLEY, L., BASEHOAR, G. & AVERY, J. (1978). Effects of craniofacial structures on mouse

palatal closure in vitro. J. dent. Res. 57, 402-411.BRINKLEY, L. & VJCKERMAN, M. (1978). The mechanical role of the cranial base in palatal

shelf movement: an experimental re-examination. / . Embryol. exp. Morph. 48, 93-100.COLEMAN, R. D. (1965). Development of the rat palate. Anat. Rec. 151, 107-118.DIEWERT, V. M. (1978). A quantitative coronal plane evaluation of craniofacial growth and

spatial relations during secondary palate development in the rat. Archs oral Biol. 23,607-629.FERGUSON, M. W. J. (1978). Palatal shelf elevation in the Wistar rat fetus. / . Anat. 125,

555-577.FROMMER, J. (1968). The lack of evidence for elastic fiber involvement in the closure of the

palatal shelves. Anat. Rec. 60, 47.1.FROMMER, J. & MONROE, C. W. (1968). Further evidence for the absence of elastic fibeis

during movement of the palatal shelves in mice. / . dent. Res. 48, 155-156.GREENE, R. M. & PRATT, R. M. (1976). Developmental aspects of secondary palate formation.

J. Embryol. exp. Morph. 36, 225-245.HARRIS, J. W. S. (1967). Experimental studies on closure and cleft formation in the secondary

palate. Sci. Basis Med. Ann. Rev. 356-369.HASSELL, J. R. & ORKIN, R. W. (1976). Synthesis and distribution of collagen in the rat

palate during shelf elevation. Devi Biol. 49, 80-88.KOCHHAR, D. M. & JOHNSON, E. M. (1965). Morphological and autoradiographic studies of

cleft palate induced in rat embryos by maternal hypervitaminosis A. / . Embryol. exp.Morph. 14, 223-238.

LARSSON, K. S. (1960). Studies on the closure of the secondary palate. II. Occurrence ofsulpho-mucopolysaccharides in the palatine processes of the normal mouse embryo. ExplCell Research 21, 498-503.

LARSSON, K. S. (1961). Studies on the closure of the secondary palate. III. Autoradiographicand histochemical studies in the normal mouse embryo. Acta morph. neerl-scan. 4, 349-367.

LARSSON, K. S. (1962). Studies on the closure of the secondary palate. IV. Autoradiographicand histochemical studies of mouse embryos from cortisone-treated mothers. Acta morph.neerl-scan. 4, 369-386.

LESSARD, J. L., WEE, E. L. & ZIMMERMAN, E. F. (1974). Presence of contractile proteins inmouse fetal palate prior to shelf elevation. Teratology 9, 113-126.

LEWIS, C. A., THIBAULT, L., PRATT, R. & BRINKLEY, L. (1979). An improved culture systemfor secondary palatal elevation. In vitro (submitted).

LOEVY, H. (1962). Developmental changes in the palate of normal and cortisone treatedstrong a mice. Anat. Rec. 142, 375-390.

POURTOJS, M. (1972). Morphogenesis of the primary and secondary palate. In DevelopmentalAspects of Oral Biology (ed. H. C. Slavkin & L. A. Bavetta), pp. 81-108. London: AcademicPress.

PRATT, R. M., GOGGINS, J. R., WILK, A. L. & KING, C. T. G. (1973). Acid mucopoly-saccharide synthesis in the secondary palate of the developing rat at the time of rotationand fusion. Devi Biol. 32, 230-237.


PRATT, R. M. & KING, C. T. G. (1971). Collagen synthesis in the secondary palate of thedeveloping rat. Archs oral Biol. 16, 1181-1185.

SRIVASTAAA, H. C. & RAO, P. P. (1979). Movement of palatal shelves during secondarypalate closure in rat. Teratology 19, 87-104.

STARK, R. B. M. & EHRMAN, N. A. (1958). The development of the center of the face withparticular reference to surgical correction of bilateral cleft lip. Plastic reconstr. Surg. 21,177-184.

WALKER, B. E. (1961). The association of mucopolysaccharides with morphogenesis of thesecondary palate and other structures in mouse embryos. / . Embryol. exp. Morph. 9,22-31.

WALKER, B. E. & CRAIN, B. (1960). Effects of hypervitaminosis A on palate developmentin two strains of mice. Am. J. Anat. 107, 49-58.

WALKER, B. E. & FRASER, F. C. (1956). Closure of the secondary palate in three strains ofmice. / . Embryol. exp. Morph. 4, 176-189.

WALKER, B. E. & QUARLES, J. (1976). Palate development in mouse foetuses after tongueremoval. Archs oral. Biol. 21, 405-412.

WEE, E. L., WOLFSON, L. G. & ZIMMERMAN, E. F. (1976). Palate shelf movement in mouseembryo culture: evidence for skeletal and smooth muscle contractility. Devi Biol. 48,91-103

WILK, A. L., KING, C. T. G. & PRATT, R. M. (1978). Chlorcyclizine induction of cleftpalate in the lat: degradation of palatal glycosaminoglycans. Teratology 18, 199-210.

WRAGG, L. E., DIEWERT, V. M. & KLEIN, M. (1972). Spatial relations in the oral cavityand the mechanisms of secondary palate closure in the rat. Archs oral Biol. 17,118-126.

{Received 9 May 1979, revised 16 June 1979)

Elevation of lesioned palatal shelve in...

Documents

Transcript of Elevation of lesioned palatal shelve in...