Anatomy of the Mouth and its Relation to Upper and Lower Full Denture Construction*

A N A T O M Y OF THE M O U T H A N D ITS RELATION TO UPPER A N D LOWER FULL DENTURE C ON STRU CTION * By HAROLD LYTTON HARRIS, D.D.S., Minneapolis, M inn. C O M P R E H E N S I V E and th o r­ ough know ledge of the anatom y of the m outh is essential if one is to keep pace w ith the progress th a t is being m ade today in prosthetic dentistry. W h e n one stops to consider th a t th e various technics th a t are before th e profession to­ day for the construction of upper and low er fu ll dentures m ust necessarily have the same sta rtin g place, th a t is to say, an impression of the seating area of th e den­ tu re, it becomes of p aram o u n t im portance th a t th e operator possess a thorough know ledge of the anatom y of the m outh, regardless of the technic he m ay use, if the d en tu re th a t he builds is to be a t all times in harm ony w ith the anatom ic structures involved in the seating area.

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A survey w hich I have m ade of the lite ra tu re of the past ten years on the sub­ je c t of prosthetic dentistry in five of the leading dental m agazines has show n th a t the greatest num ber of w riters by fa r have been interested more p articu larly in a rticu latio n and occlusion th an in any o th e r p a rt of the subject. M a te ria ls and th e ir handling have been second in im ­ p ortance, and esthetics has been th ir d ; w hile the field in w hich w e w ork, w hich is the basis of operation and the sta rtin g p o int fo r any technic, has been am ong *R ead before the Section on Full D en tu re P rosthesis a t the Seventy-Second A n n u a l Ses­ sion of the A m erican D ental A ssociation, D enver, Colo., Ju ly 24, 1930.

Jour. A .D . A ., July, 1931

the least to receive consideration from authors on this subject. I appreciate th a t there is a divergence of opinion as to th e relative value to the finished case of a thorough technic in im ­ pression taking, w hich obviously entails a thorou g h know ledge of th e anatom y in ­ volved, and the articu latio n and occlusion of the case. T h e re are some w h o hold the opinion th a t the a rtic u la tin g in stru m en t to be used, and th e balanced occlusion to be obtained, are of m uch m ore im por­ tance in assuring a satisfactory p erfo rm ­ ance of th e finished case th a n is the m ethod of im pression taking. T h is opin­ ion I believe to be w ro n g ; n o t th a t I be­ lieve the reverse to be tru e, b u t I do be­ lieve th a t the one step is as im p o rtan t as the oth er in relation to a satisfactory resu lt in the finished case. T h e theory th a t a p atien t w ill m ore successfully w ear a poor-fitting set of dentures having a bal­ anced occlusion th a n he w ill a w ell-fitting set w ith malocclusion is perhaps accept­ able, b u t I believe th a t w e w ill have more successful cases w hen w e pay as m uch a t­ tention to w o rk in g in harm ony w ith the anatom y of th e seating area, as w e do to w orking in harm ony w ith the anatom y of th e tem porom andibular articulation. T h e r e are certain fund am en tals in up­ per and low er fu ll d en tu re construction w hich have come to be universally recog­ nized. R ussell W . T en ch , of N ew Y o rk C ity, presented these in a m ost interesting

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H arris— A n a to m y of the M o u th and valuable paper at the Chicago M id ­ w in te r C linic last Ja n u a ry . D r. T en c h believes the consensus of opinion am ong leading prosthodontists to be th a t the peripheral borders of th e dentures should rest on soft tissues, and th a t the operator should be skilled in a sound technic of impression taking to accom plish th a t re­ su lt. In coordination w ith my discussion on anatom y, therefore, may I review for you a w ell-know n m ethod of impression technic w hich, in the opinion of m any op­ erators the country over, accomplishes for them the desired results. T h e anatom y of the m outh and jaw s, from th e point of view of prosthesis, m ust necessarily be divided into three sections; namely, th a t p a rt of th e anatom y w hich deals w ith the foundation and border of th e d en tu res; secondly, th a t w hich has more to do w ith the function of the den­ tures, the glenoid fossa w ith its su rro u n d ­ ing anatom y and the muscles of m astica­ tion, and, thirdly, th a t w hich has to do w ith the esthetics of the dentures, or the muscles of expression. I t is the purpose of this paper to con­ sider the first of these sections; namely, th a t p a rt of the anatom y w hich concerns the underlying stru ctu re s and the periph­ eral border of th e upper and low er den­ tures, w ith the m axilla and the m andible, discussed according to ( 1 ) osteology; (2 ) muscles and lig am ents; ( 3 ) blood vessels and nerves, and ( 4 ) mucosa, w ith a re­ view of the anatom y of the structures form ing the definite and specific border o utline of the upper and low er dentures, w hich w ill be of in terest to those who accept the theory th a t to obtain peripheral seal, it is necessary to build the periphery o f the dentures in soft tissue. F irst, a review of the difference in osseous stru ctu re of the m axilla and m an­ dible w ould be tedious and probably u n ­ interesting. C ertain portions of each are

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im portant, i. e., w herein muscles attach, glands lie or blood vessels and nerves leave or enter. T h e m axilla w ill be considered from the standpoint of its p alatal anatom y and the tuberosity. T h e h ard palate, w hich is form ed by th e ju n ctio n of the m axillae along the m edian line, varies in shape in various m ouths, from an inconspicuous form ation, as seen in the m outh w ith the high v au lt, to a decided protuberance. In all cases, it is a nonstress bearing area as it is invariably covered only by a th in layer of mucosa. Posteriorly, it is form ed by the spine of the p alate bone, and, in certain cases, this spine lies posteriorly from the m ovable tissu e; while, in others, it term inates an terio rly from the m ov­ able tissue from 2 to 6 mm. on the m edian line. W e m ay classify the upper portion of the m o u th according to the w id th of the area betw een the distal border of the h ard p alate and the an terio r border of the m ovable tissues of the soft palate, or in other w ords, th ro a t f o rm : Class 1, those cases in w hich there is a distance of 5 mm., or m ore, betw een these tw o points ; and the th ro a t form consists of a gentle curve from before b a c k w a rd ; Class 3, those cases in w hich th e h ard area con­ tinued backw ard and the cu rtain of soft tissue dropped d o w nw ard ab ru p tly from i t ; Class 2, those interm ediate cases offer­ ing a fair am ount of area capable of w ith ­ standin g the postdam pressure. In Class 3 cases, the operator, in b u ilding the pos­ terio r plate line, is faced w ith tw o a lte r­ natives, both of w hich are unfavorable. H e may either stop the d en tu re a n te ri­ orly, so th a t it rests on h ard tissu e,'o r he m ay extend it distally so th a t it covers a sm all am ount of m ovable soft tissue. I t is decidedly b etter to choose the lesser of these tw o evils, th a t is, extend the border of the d en tu re distally and the postdam

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on soft tissue, w ith the hope th a t th e pa­ tie n t w ill be able to to lerate the tickling sensation th a t is usually caused by so do­ ing. Stopping the denture on a h a rd area w ill result only in atrophy of the u n d er­ lying tissue and a loss of den tu re seal, w hich w ill cause the op erato r no end of trouble. T h e tuberosity is the inferior angle of the m axilla, articulated w ith the tuberos­ ity of the palate bone. Its size and shape is effected to a g reat ex ten t by the life history of the th ird m o lar and the m an ­ ner in w hich it consequently w as re ­ moved. T h e tuberosity high on its pos­ terio r surface gives rise to a few fibers of both the in tern al and ex tern al ptery­ goid muscles. A n osseous stru ctu re, n o t a p a rt of the m axilla but in close relation to the tu b er­ osity, greatly concerns the operator in denture w ork. I t is the h am u lar process of the m edial pterygoid plate of the sphe­ noid bone. I t lies posteriorly and m edi­ ally from the tuberosity form ing a tr i­ an g u lar area betw een these tw o osseous stru ctures in w hich th e re is a resilient pad of soft tissue, th e only area in th a t portion of the m outh capable of w ith ­ standing the pressure exerted by the post­ dam . T h e ham ulus serves to deflect the bursa or tendon of the tensor veli palatini, and the tip of the ham ulus gives insertion to the pterygom andibular raphe. T h e h am u lar process is also a landm ark for the g rea ter or posterior palatine foram en, w hich lies anteriorly from it on the p alatal portion of the m axilla. T h is foram en transm its the g rea ter palatine branch of the descending palatine artery, along w ith the an terio r palatine nerve. T h e incisive, or a n te rio r palatine, canal lies in the m edian line posteriorly from the incisor teeth. I t is form ed by the ju n ctio n of the tw o m axillae, and consists of a la rg e opening a t the bottom

of w hich are fo u r foram ina, tw o sm aller ones, the foram ina of Scarpa, being lo­ cated directly on the m edian line. T h e y serve to tran sm it the nasopalatine nerves, the le ft passing th ro u g h the an terio r and the rig h t passing th ro u g h the posterior. T h e other tw o are som ew hat larger, and lie la terally from the m edian line, these being the foram ina of Stenson, tran sm it­ tin g te rm in al branches of the descending palatine artery . T o apply the postdam pressure accu­ rately, as w ill be recognized, the oper­ a to r m ust m ake a careful study of this area from the tuberosity on one side across the soft palate to the tuberosity on the other side. T h e pressure exerted m ust vary w ith the depth and resiliency of the soft tissue w hich is to w ith stan d the pres­ sure. T o accomplish this accurately, it is necessary to have an impression of th a t area w ith the tissues com pletely a t rest, u nder no pressure w hatsoever. F o r the case, an upper tray is selected th a t is from one-eighth to one-quarter inch over-size on the labial and buccal aspects and long enough distally to include th e area of the h am u lar process. C om pound is softened, adapted in the tray, inserted in the m outh and pressed to place w ith a firm pres­ sure. I t is allow ed to cool, an d th en re­ m oved from the m outh. T h e com pound is chilled thoroughly. T h e surface is then heated by gentle p ain tin g w ith a sm all flame, tem pered in w ate r of about 110 degrees and reseated in the m outh u nder firm pressure, tissue detail and m arkings being thus brought out. T h e excess com­ pound is trim m ed back to the tray , the tra y removed and the com pound fu rth e r c u t back to the height of convexity of the buccal an d labial folds. F ro m this point on, freq u en t chilling of the com pound in icew ater, precluding any possibility of w arpage, is essential. T h e com pound tra y is now ready for

H a rris— A n a to m y o f the M o u th muscle trim m ing. T h e buccal flange, fro m tuberosity to cuspid, is gently heated w ith a sm all flame a t the periphery on one side at a tim e, tem pered in w arm w ate r and inserted in th e m outh under pressure, the p a tie n t’s cheek being draw n dow n a t the same tim e w ith the other hand. T h e flange is then rem oved and chilled and the excess appearing on the buccal is trim m ed aw ay. T h is process is repeated u n til no m ore excess appears to be folded over by the tissues. T h e oppo­ site side is now done in th e same m anner, also the labial from cuspid to cuspid, the lip being pulled dow nw ard, side to side, and folded lingually over the process to insure accurate ad aptation of the labial flange. In the m uscle-trim m ing, it w ill be noted th a t the border tissues have been pulled beyond th e ir norm al functional range. T h e space m aking up the differ­ ence betw een the established range and the functional range w ill be taken up and accurately established by the plaster wash. T o achieve an impression of the area to be postdam m ed w ith the tissues u nder no pressure w hatsoever, the com pound over the h ard area to be relieved and across the postdam area is reduced by from onesixteenth to one-eighth inch in thickness, only the horseshoe-shaped stress-bearing area and the muscle trim being le ft in­ tact. A th in m ix of quick settin g plaster is poured into the com pound impression, replaced in the m outh and forced to place by a pressure of about 25 pounds exerted at a 45 degree angle to the occlusal plane. W h e n the plaster has set thoroughly and the impression has been rem oved from the m outh, the com pound over the alveolar area should show th ro u g h the plaster com pletely, and there should be a heavy plaster impression 2 or 3 m m . thick of the hard area to be relieved and the entire posterior border of th e im pression cover­ ing the area to be postdam m ed.

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By th e use of an egg-shaped burnisher, or a sim ilar in stru m en t, the exact w id th and length of th e h ard area is determ ined and charted w ith an indelible pencil on the tissue, extending always fa r enough an terio rly to include the an terio r palatine foram en. T h e n , w ith a m outh m irro r, the notch betw een the h am u lar process and the tuberosity is located and m arked w ith th e indelible pencil. T h e posterior m argin of the plate on the m edian line is then noted by having the p atien t say “ ah ” and placing an indelible m ark 1 m m . an terio rly from the movable tissue, and the plate line is com pleted by con­ necting the tuberosity m arkings w ith a gentle curve th ro u g h the m edian line m arking. T h e impression is then replaced in the m outh in o rd er th a t the p alatal m arkings m ay be tran sfe rred to the plaster. T h is m arks th e impression accurately as to the location of th e h ard and postdam areas. I n those cases in w hich th ere is a decided u n d ercu t in th e region of the tuberosities, these areas should be studied, an d the p alata l m arkings placed before the plas­ te r w ash im pression is taken. T h e h ard area is relieved by scraping aw ay 1 or 2 mm. of p laster over th a t area, the am ount depending on the prom inence of the area. By th e use of a sharp pointed instrum ent, the posterior p late line is grooved in the m iddle of th e indelible m arking, so th a t an embossed line w ill appear on the cast. T h e cast is poured, and th e bite plate co n stru cted ; and w hen the patient re ­ turn s, th e case is ready fo r postdam m ing. T h e postdam area is divided into five sm aller sections of equal size. S tartin g on the le ft w h ere the buccal and posterior plate m argins m eet, passing posteriorly around the tuberosity betw een it and the h am u lar process is A rea 1. M ed ially from the process to a p o in t 5 mm. from the m edian lin e is A rea 2, and A rea 3 is

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the m edian line area, consisting of about 10 m m ., th a t is, 5 m m . on either side of the m edian line. A reas 4 and 5 are sim i­ la r to A reas 2 and 1, respectively. N ow , w ith an egg-shaped burnisher, the tissue in A rea 1 betw een the tuberosity and h am u lar process is com pletely com­ pressed. T h e distance the burnisher tra v ­ eled to compress this tissue is judged as carefully as possible. T w o -th ird s of the distance is com puted, and is tran sfe rred to th e cast by the use of a N o. 10 round bu r in the straig h t handpiece. A N o. 10 b u r is used because it is the w idth of the narro w est p a rt of the postdam , the w idth of th e area betw een the tuberosity and the h am u lar process. A groove is cut in the cast along the embossed line indicating th e posterior plate line in A rea 1 to the depth as com­ puted. N ex t, the am ount of compression in A rea 3, or m edian line area, is com­ puted, w hich is obviously the least com­ pressible of the five areas, and tran sfe rred to the cast. A reas 1 and 3 are then con­ nected by th e groove through A rea 2, the depth of w hich has been com puted as in A reas 1 and 3, and w hich is usually g rea ter than in either of those tw o areas. A reas 5 and 4 are then handled in the same way, the result being a n a rro w groove across the posterior plate line vary ing in depth according to the tissues in the m outh w hich are to bear the pres­ sure thus exerted. T h e next step is to w iden th e postdam according to the stru c ­ tu re of the soft tissue of the palate. In A reas 1 and 5, the postdam , as stated before, is never w ider th an the groove m ade by a N o. 10 round bu r, for the reason th a t the distance betw een the tuberosity and ham ulus is constant, w ith only m inute v a ria tio n s; therefore, m erely the sharp edges of the groove are rounded over, a sharp knife being used fo r this purpose. W id en in g the postdam a t this

point w ould resu lt in soreness on the tu ­ berosity an d atro p h y to the underlying tissues. P osteriorly, it w o u ld resu lt in an inflam m ation of th e bursa of the tensor veli palatini, as it is deflected around the ham ulus. In A reas 2 and 4, soft tissue is found an terio rly beyond the posterior palatine foram en. T h is pad of soft tissue norm ally is thicker by fa r th an any other area of the postdam , and therefore is capable of being an d should be post­ dam m ed. By the use of a sharp knife, this tria n g u la r area of so ft tissue is scraped from the deepest p a rt of the groove a n ­ terio rly to a fea th er edge, the depth of the postdam as it passes over the posterior palatine foram en thus being lessened. In A rea 3, or the m edian line area, the w id th of the postdam area is exactly th a t of the distance betw een th e posterior plate line and the distal border of the h ard palate, and is postdam m ed as be­ fore w ith a knife, the plaster being scraped an terio rly to a feath er edge at the b ord er of the h ard tissue. W h e n this is com pleted, the posterior portion of the biteplate is w arm ed and molded into the postdam depression of the cast. Postdam m ing w ith com pound on th e impres­ sion w ill not, in the first place, allow the operator to w o rk w ith the tissues a t rest, and, secondly w ill n o t consequently allow an accurate an d definite com putation of the w id th and depth of the postdam . T h e muscles involved in the m axillary area are ( 1 ) the b u ccin ato r; ( 2 ) the levator veli p alatini, and ( 3 ) th e tensor veli palatini. T h e buccinator originates from three areas: the buccal aspect of the m o lar portion of the m axilla, the co rre­ sponding area on th e m andible and the pterygom andibular raphe, an d is supplied by the buccal branch of the facial nerve. Its fibers converge an d are attached in the group of muscle fibers know n as the orbicularis oris a t the angle of th e m outh.

H a rris— A n a to m y of the M o u th T h e levator veli palatini arises partly from the inferior surface of the petrous portion of th e tem poral bone and partly from the low er portion of th e cartilage form ing the eustachian tube. I t is a t­ tached in the aponeurosis of the soft pal­ ate. T h e nerve supply is from the pharyn­ geal branch of the vagus. T h e tensor veli palatini originates from the scaphoid fossa of the sphenoid, w ith some fibers from the la te ra l side of the cartilage of the eustachian tube. I t passes forw ard, and is deflected by the h am u lar process, passing m edially to be attached along the spine of the palate bone and partly in the aponeurosis of the soft palate. Its nerve supply is from the m andibular branch of the trigem inal through the otic ganglion. T h e mucosa overlying the abovem en­ tioned portions and stru ctu res varies in thickness and therefore in resiliency. T h e thickness of th e mucosa over the h ard palate varies directly w ith th e prom i­ nence of th a t a re a ; th a t is, the g reater the prom inence of the hard area, the thinner the mucosa. I t is stric tly a nonstress bearing area, an d m ust be relieved in every case. T h e m ucosa overlying the alveolar crest, w hich is norm ally from 5 to 7 mm. thick, is capable of w ith stan d ­ ing at all points the m asticating stress of the upper denture. T h e mucosa overly­ ing the posterior palatine foram en in five specimens averaged 8 m m . in thickness, postm ortem m easurem ent, and it is know n to be invariably thicker th an any other overlying mucosa on the m axilla. As the nerve and blood vessels em anating from this foram en ru n an terio rly in a groove, this area is capable of w ith stan d in g a slight am ount of postdam pressure, rath e r th an necessitating relief. T h e incisive foram en area is thinly cov­ ered, and therefore m u st alw ays be re ­ lieved. T h e mucosa betw een the tu b e r­ osity and the h am u lar process has been

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described previously and is capable of w ithstan d in g considerable postdam pres­ sure. N ea r the posterior m arg in of the hard palate, there is, on each side of the m edian line, a sm all pit, a fam iliar la n d ­ m ark for determ ining the posterior b o r­ der of the d enture. T h ese pits, the foveola palatinae, usually m ark the begin­ ning of the m ovable tissue of the soft palate. T h e m andible, from the standpoint of peripheral anatom y of the low er denture, presents m any sites of interest. A d m it­ tedly the largest and strongest bone of the face, the edentulous m andible varies in size and shape according to the history and condition of the n a tu ra l teeth d u rin g th e ir retention and th eir investing tissues, and, of course, according to age. I t p re­ sents three surfaces in the areas in w hich w e are a t present p articu la rly in te reste d ; nam ely, the lateral, m edial and alveolar surfaces. T h e la te ra l surface presents, near the m edian line, or symphysis, a de­ pression know n as th e incisive fossa in w hich arise th e m entalis and incisivus labii inferioris muscles. U n d e r the second bicuspid area is the m ental foram en, from w hich em anate the m ental nerve and blood vessels. T h e ex ternal oblique line arises from the m ental tubercle, passes u pw ard and backw ard below the m ental foram en, passes m edially to th e attach ­ m ent of the buccinator muscle in the re­ gion of the m olars and continues on up the ram us helping to form p a rt of the retro m o lar triangle. T h e m edial surface presents near the symphysis four sm all tubercles, w hich collectively are called genial tubercles, or the m ental spine, and m ark th e origin of the genioglossus and geniohyoid muscles. B eginning ju st below th e m en tal spine, and extending u p w ard an d backw ard, the mylohyoid line reaches its greatest prom i­ nence in the region of the distal cusp of

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the second artificial m olar, then disap­ pears on up the ram us. T h e mylohyoid line serves as the point of attachm ent along its entire length from the m ental spine to a point directly beneath the dis­ tal cusp of the second artificial m olar for the m ylohyoid m uscle. F ro m the distal m argin of the mylohyoid muscle, the m y­ lohyoid line is void of tissue attachm ents fo r approxim ately 5 m m .; and then, in w h at is the posterior fifth of th e line, is attached the m ylopharyngeal, or th ird head, of the superior constrictor muscle of the pharynx. A bove the mylohyoid line beginning at its an terio r border and extending to the distal aspect of the first bicuspid area is a depression on the m an­ dible know n as the fovea sublingualis, or fossa for the sublingual gland. Below the mylohyoid line in the m o lar area is an ­ o ther depression fo r the subm axillary gland. T h e buccinator muscle, w hich form s the periphery of the m olar area of the low er denture buccally, has its broad a t­ tachm ent directly inferior to the external oblique line, the fibers ru n n in g up w ard and backw ard to join w ith the m axillary and raphe attachm ents. I t, therefore, moves approxim ately a t rig h t angles to the denture, any overextension of w hich w ill tend to cause the buccinator to lift the den tu re from the ridge. Stopping the d en tu re short of the attach m en t allow s no seal for the periphery as the m andible a t the point of the external oblique line is covered only w ith a th in layer of mucosa. A uxiliary buccinator attachm ents fre­ quently occur in the regions of th e bi­ cuspid. N o other muscle comes in contact w ith the buccal or labial peripheral area, but as the distal border of th e denture crosses the crest of the ridge, it passes over a pad of soft tissue, an area know n as the retrom olar triangle, th e area lying distally

from the last m olar form ed by the ex­ te rn al and in te rn al oblique lines. In this area are attached a few term in al fibers of the tem poral muscle, and these fibers, w ith th e overlying mucosa, furnish a soft tissue sealing area resilient enough to w ith stan d a slight postdam pressure. T h e m ylohyoid muscle, referred to be­ fore, arises along the an terio r four-fifths of th e m ylohyoid line, its fibers passing dow n w ard and in w ard form ing a convex­ ity w hich is the floor of the m outh. T h e muscle is attached to the v en tral surface of the hyoid bone, and its nerve supply is from the mylohyoid nerve, a branch of the m asticator, or portia m inor. I t also functions a t rig h t angles to the border of the d en tu re from a point beneath the second bicuspid to a point beneath the dis­ ta l cusp of the second artificial m olar. A ny overextension of the denture border along this line causes the den tu re to be lifted from its seating area by the action of the tongue, because of the com plete co­ ordin atio n of action betw een the m ylo­ hyoid and geniohyoglossus muscles. A ny underextension w ould resu lt in loss of seal, as th e periosteum is covered only by a th in layer of mucosa. T h e m ylopharyngeus muscle is in ­ volved in the distolingual peripheral area of the low er denture, th a t area know n as the retro m o lar or lateral pressure area. T h e m ylopharyngeus, in reality one of the three divisions of th e superior con­ stricto r muscle, derives its name from its origin on the posterior fifth of the m ylo­ hyoid line approxim ately 5 mm. from the distal end of the origin of the mylohyoid muscle, and from its insertion in the great fibrous raphe of the pharynx. T h e other tw o divisions of the superior constrictor are th e buccopharyngeus, or th a t p a rt arising from the pterygom andibular raphe, and the pterygopharyngeus, or th a t p a rt arising from the h am u lar process of

H arris— A n a to m y of the M o u th the pterygoid plate. T h is group of muscles, w ith the m iddle and inferior constrictor of the pharynx, all have their nerve supply from the pharyngeal plexus. T h e action of the m ylopharyngeus is p a r­ allel to the surface of the overlying den­ tu re, and therefore does not tend a t any tim e to dislodge the den tu re from its seat­ ing area, m erely form ing a soft tissue area for obtaining peripheral seal. T h e pterygom andibular raphe is a fibrous band of tissue ru n n in g from the tip of th e h am u lar process to the internal oblique line of the retro m o lar triangle on the m andible. I t serves to give origin to the m iddle o r second division of the buccinator m uscle ru n n in g an terio rly ; and, posteriorly, it gives rise to the buccopharyngeus, o r second division, of the su­ perior constrictor, w hich furnishes, a t its attachm ent, a soft tissue sealing area at th e point w here th e b order of th e denture crosses the in te rn al oblique line of the retro m o lar triangle. T h e classification of th ro a t form in the low er m outh is based upon the action of the palatoglossus muscle, and its overlying tissue attachm ent to th e m andible. T h e palatoglossus is a cylindrical band of muscle having its origin on the oral surface of the palatal aponeurosis of the soft palate, and its insertion in th e super­ ficial muscle layer on th e side and under surface of the tongue. B etw een its origin and insertion, it form s the anterio r pillar of the fauces o r to n sillar crypt. T h e muscle moves fo rw ard upon the extension of the tongue, carrying w ith it in a sweep­ in g action its overlying mucosa, w hich is attached to the m andible. In a Class 1 case, then, there is a large am ount of la t­ eral pressure area le ft distally from the mylohyoid line w hen the tongue is ex­ tended to a point one-eighth inch below the red line of the low er lip. T h is lateral pressure area, w hich has had such m is­

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nom ers as “ the p reto n sillar area,” “ flange area,” o r “u n d ercu t area,” is practically obliterated in a Class 3 case, as th e c u r­ tain of overlying tissue comes fo rw ard alm ost to the m ylohyoid line on the ex­ trusion of th e tongue the distance given before. Class 2 cases, obviously, are in te r­ m ediate of these tw o extremes. T h e sublingual gland w ith its overlying mucosa comes in direct contact w ith the lingual m arg in of the den tu re from the fren u m to the second bicuspid area. Its m edial surface lies in a cry p t m ade up of the mylohyoid, geniohyoid and genioglossus m uscles; and w hen those muscles, together w ith the floor of th e m outh, rise in the act of d eglutition or in the act of extrusion of the tongue, the gland rises u p w ard against the den tu re. Its nerve supply is derived from th e sublingual branch of the lin g u al nerve. A m ost in terestin g situ atio n lies in the proxim ity of the lingual nerve to the bor­ der of the low er d en tu re, necessitating, in some patients, specific relief at th a t point. T h is large nerve tru n k , th e forem ost of the branches of the m an d ib u lar in posi­ tion, passes m edially from th e inferior alveolar nerve, descending on the m edial side of the external pterygoid muscle, w here it is joined by the chorda tym pani, a branch of the glossopalatine nerve w hich furnishes the sensory fibers to the tongue. I t th en passes betw een the in ­ te rn al pterygoid m uscle and the ram us, continuing on over the fibers of the mylo­ pharyngeus, passing fo rw ard behind the last m olar area ju s t above the mylohyoid line at its m ost prom inent point. A t this point, th e lingual nerve is covered by the th in m ucous m em brane overlying the periosteum . T h e nerve th en dips dow n­ w ard and fo rw ard to w ard th e tip of the tongue, touching th e la te ra l surface of the styloglossus, hypoglossus and genio-

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T h e Jo u rn a l of the A m erican D e n ta l Association

glossus muscles, in close proxim ity to W h a r to n ’s duct of th e subm axillary gland. T h e mucosa of the alveolar ridge of the m andible is n orm ally th in n e r a t the crest of the ridge th an it is on the labial or lingual slopes. T h erefo re, the crest of the alveolar ridge should not have, as it cannot w ith stan d , the am ount of pres­ sure th a t may be applied to the sloping sides. J u s t the opposite is tru e in the m axilla, w here the alveolar ridge is so covered th a t it is capable of w ithstanding the force of m astication. T h e mucosa overlying the lingual nerve, as it lies m e­ dially from the m ylohyoid line in the region of the th ird m olar, is usually very thin, and, in m ost cases, the pressure ex­ erted by the den tu re m ust be less than the pressure applied elsew here. T h e m u­ cosa and underlying stru ctu res in the la t­ eral pressure area are capable of w ith ­ standing a fair am ount of pressure, w hich, being lateral, is unaffected by m asticat­ ing force and rem ains constant a t all times. T o o m uch la te ra l pressure w ould resu lt in unbearable pain, and too little w ould result in loss of peripheral seal. T h e pressure applied is best tested in the rebased den tu re by placing the index fin­ ger over the incisors and tipping the den­ tu re linguolabially, w hen the denture in the la te ra l pressure area should move up and dow n a t least 3 mm. T o get an impression of the entire area desired fo r th e low er denture, it is neces­ sary to take the low er impression in sec­ tions, it becoming, a t its best, m erely a prelim inary impression. A stock tray is selected, long enough distally to include the retro m o lar triangle, and the distolin g ual cu rv atu re of the tra y trim m ed to an angle of 45 degrees to the occlusal plane, along the area of the mylohyoid line. A com pound impression is then taken of the ridge, the operator determ in­

ing th a t th e com pound has included all the desired peripheral tissues. A fte r the chilling and rem oval from the m outh, the distolingual portion of one side is cut back to the border of the tra y along the trim m ed edge. A piece of softened com­ pound the size of an olive is tacked to this b order of tra y and com pound; the im ­ pression is seated, and, w ith th e index finger a t rig h t angles to the cu t border of the tray, the com pound is forced gently u nder about 5 pounds pressure into the la teral pressure area. T h e m aterial is chilled and removed. A groove is cu t in the com pound on the back of the im pres­ sion along the trim m ed b o rd er of the tray, and the added extension is broken off cleanly and laid aside. T h e opposite side of the impression is com pleted in like m anner, an d the broken side is then re­ placed and attached w ith sticky w ax. T h e impression is now ready for the pouring, w hich is done w ith o rd in ary plaster. A fte r separation, the cast is ready for the study relative to m arking on it the anatom ic outline of the d enture. T h e tendency should be to overbuild the biteplate so th a t it may be trim m ed back to toleration of the functional range of the border tissues. T h erefo re, labially, the outline is m arked w ell into the soft tis­ sue attachm ents. Buccally, the outline should be extended w ell to w ard the ex­ tern al oblique line. O n the lingual as­ pect, the outline should dip as fa r as pos­ sible below th e second bicuspid area, pro­ ceeding u p w ard and backw ard along the m ylohyoid line to the second artificial m olar area, w hen, u n d er the distal cusp area of th a t tooth, the outline should cross the mylohyoid line into th e la te ra l pres­ sure area, dipping 1 mm. and m aking a half circle u p w ard to m eet the buccal outline. T h e biteplate is built, and, a t th e next appointm ent of the patient, the tria l plate

H a rris— A n a to m y o f the M o u th is trim m ed to toleration. I t is trim m ed on all borders so th a t the peripheral tis­ sues in th e ir m axim um range do n o t u n ­ seat the tria l plate. In the la te ra l pres­ sure area, th e tria l plate is trim m ed to allow th e tongue to p ro tru d e one-eighth inch below th e verm ilion border of the lo w er lip, w hich does n o t allow the tongue its m axim um range, b u t does allow all the range ever required by the patient. T h e den tu re vulcanized to the to ler­ ated outline m ust not be considered a finished denture. I t is a den tu re w ith grossly inaccurate peripheral borders, w ith th e various pressures dem anded by the underlying mucosa u n d e r no control w h atso ev e r; fo r example, the pressure ex­ erted on th e crest of the ridge by this prelim inary den tu re is the same as on the sloping sides of th e ridge. I t is a denture w ith the la te ra l pressure a rb itra rily set w ith a definite pressure, w hich m ay or may n o t be accurate fo r th a t case. T h e re ­ fore, to correct th e situation, th e denture m ust be reb a sed ; fo r it is not possible for anyone, no m a tte r how skilled he may be in the h an d lin g of impression m aterials, to build a low er d en tu re to th e proper p eripheral tissues, and, a t the same tim e, exert the desired pressure on th e tissues capable of w ith stan d in g those pressures, and incorporate th e necessary relief w here it may be needed. T h is again, it m ust be stated, cannot be done from a single or m aster impression of the low er m outh. T h e denture should be rebased, and re ­ based u n d er a definite, equalised pres­ sure, com parable to, o r accom plished only by, perfect balanced occlusion. T h e low er den tu re should be rebased im m ediately a fte r th e first vulcanization. T o equalize the pressure exerted by the u pper d en tu re in centric occlusion, the teeth m ay either be m illed to a balance, o r a strip of com pound laid along the

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bicuspids and m o lars of the u pper den­ ture, th e com pound being w arm ed and tem pered eyenly in hot w a te r and placed in position in the m outh, and the low er then bro u g h t up in to a centric relation to a point alm ost th ro u g h the com pound, thus avoiding cusp contact. T h e com­ pound is chilled and the low er den tu re rem oved. T h u s, it is recognized th a t the pressure of the u pper den tu re in this cen­ tric relation w ill be equalized, and the operator may be assured the case is in the centric relation ju s t established. T h e low er d en tu re is now trim m ed, one-sixteenth inch of vulcanite being re­ moved from the tissue surface of the den­ tu re a t all points, w ith th e exception of the la te ra l pressure areas. A fter this is accomplished, an ad d itio n al one-sixteenth inch is rem oved fro m the periphery, the border being beveled p arallel w ith the surface of th e un d erly in g tissue. W ith a trac in g stick, com pound is now applied to the d en tu re along the buccal, labial an d lin g u al borders, w ith the ex­ ception of in the la te ra l pressure a re a ; the com pound is heated by means of a m outh blow pipe, o r any other sm all flame, tem pered in w a te r and placed in the m outh, and th e teeth are b ro u g h t to ­ gether steadily in centric occlusion. T h e application of th e com pound along the border allow s th e crest of the ridge to be free of pressure, as the com pound com ­ presses th e tissues on the sloping sides of the ridge, flow ing to m eet the com pound of the opposite side a t th e crest of the ridge, and flow ing u n d er the border of the den tu re as excess. T h e d en tu re is re­ moved, and any im perfection in the flow of com pound is corrected by the addition of com pound an d reseating u n d er pres­ sure. T h e excess of com pound on the labial and buccal is trim m ed aw ay w ith a sharp knife, and the b o rd er w arm ed and re­

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T h e Jo u rn a l o f th e A m erican D e n ta l A ssociation

seated in centric occlusion. T h e p atien t is w hich the lin g u al nerve comes in greatest th en instructed to pucker the lips, as in proxim ity to the overlying mucosa. the act of kissing, then to p ull back the T h e vulcanite in the lateral pressure corners of the m outh as in a w ide grin. area is now covered w ith com pound and T h is brings th e border tissues, including the den tu re seated in the m outh in cen­ the buccinator muscle, into the p a tie n t’s tric occlusion. T h e m outh is opened, and functional range, and trim s the com pound the d en tu re held in place w ith finger pres­ accordingly by folding or rollin g it up sure, w hile th e p atien t is instructed to over th e buccal and labial m argin of the extru d e, elevate an d move th e tongue d enture. T h is is repeated u n til no excess from side to side. T h e d en tu re is removed, is noticeable on th e buccal and labial and the process is repeated u n til all excess periphery. • has been rem oved, an d th e border is in T h e excess is then trim m ed aw ay ac­ harm ony w ith th e peripheral tissues. T h e cordingly on the lin g u al aspect, the com ­ size of this area, as has been explained pound w arm ed an d tem pered an d the previously, is dependent entirely on the d en tu re seated in th e m outh. T h e denture action of th e palatoglossus m uscle and its is held in th e m outh by finger pressure, curtain-like soft tissue attach m en t to the and th e p atien t is instructed to extrude m andible. In a C lass 3 case, th e area the tongue and also to elevate th e tongue w ould be sm a ll; in a Class 1 case, the to touch th e roof of th e m outh. T h is ac­ area w ou ld be large. T h e perfect h alf tion of the tongue produces the functional circle form of the b o rd er should always range of the lingual fre n u m ; the coordi­ be m aintained. T h e corresponding area of th e oppo­ nated action of th e genioglossus an d the geniohyoid muscles raising the sublingual site side is then prep ared and rebased the g lan d against the m argin of th e denture, same w ay. T h e n , th e entire seating area and also the functional range of th e my­ w ith the exception of the la teral pressure lohyoid muscle. T h e den tu re is removed areas is b u t slightly w arm ed by a gentle and the process repeated u n til all excess p ain tin g w ith the flame, dipped in w ater disappears, and an accurate anatom ic and placed in th e m outh, and the p atien t b o rd er crosses th e mylohyoid line, one- is instructed to close in centric occlusion. pletely rebased, w ith the exception of the T h e den tu re is no w tested for lateral la te ra l pressure areas, w hich are rebased pressure by attem p tin g to tip the denture singly. T h e only p a rt of th a t area of the labiolingually. I f so m uch pressure is be­ vulcanite d en tu re to be trim m ed previous ing exerted th a t the den tu re does not to rebasing is the border itself. B egin­ move, it should be removed from the m outh, scraped slightly w here the lateral n in g a t a point on the lingual m argin an­ pressure is being exerted, b u t n o t a t the te rio r fro m the place w here the denture periphery, w arm ed slightly and retu rn ed b order crosses the mylohyoid line, oneto th e m outh. T h is should be repeated sixteenth inch of vulcanite is removed u n til the den tu re w ill respond to the tip ­ along the border aro u n d the half circle ping force by m oving up and dow n at over the m ylopharyngeus to the retro- least 3 m m . in th e la te ra l pressure area. m o lar tria n g u la r area, to allow the tissues T h e rebasing technic is now com pleted to form a com pound border to the denture and the d en tu re m ay be tested fo r sta­ in th is are a on extrusion of the tongue, bility and seal. I t w ill be noted th a t the an d also to give relief over th e area in den tu re is in com plete harm ony w ith the

H a rris— A n a to m y of the M o u th functional range of the b o rd er tissues, th a t th e desired pressure has been applied and controlled in the areas capable of w ith stan d in g pressure, and those areas dem anding relief have been tre a te d in accordance w ith th eir anatom ic and his­ tologic stru ctu re. In review , m ay I outline the peripheral border of th e upper denture fo r those w ho w ish to build dentures to soft tissue as follow s: I f w e s ta rt at the crest of the ridge in th e central area, passing labially, the first so ft tissue encountered is the frenum of the lip. In the lateral area, we go beyond the frenum to the fold or cu rv a tu re of the soft tissue to the lip. T h e same holds tru e fo r the cuspid area. Above th e tw o bicuspids, one usually finds accessory attachm ents of the buccinator muscle, along w ith strong plicae of soft tissue. T h e first m olar area indicates the attachm ent of the buccinator muscle. T h e second m olar area is bordered by the soft tissue fold of the cheek. T h e re being ob­ viously no lingual border of the upper denture, the peripheral border is form ed by the posterior plate line, w hich is de­ term ined by definite anatom ic landm arks. T h is area, as noted before, is divided into five sections from tuberosity to tuberosity, A reas 1 and 5 from the buccal aspect of the tuberosity m edially through the tr i­ angular notch betw een the tuberosity and the h am u lar process; A reas 2 and 4 m a rk ­ ing the insertion of the palatinus. A rea 3 is the m idline area distally fro m the bor­ der of the palate bone, and anteriorly from the border of the m ovable tissue of the soft palate. T h e periphery of th e low er den tu re is som ew hat m ore com plicated. I f w e sta rt, as before, a t the crest of the ridge in the central area and passing labially, the first soft tissue m et is th e fren u m of the lip. T h e la teral and cuspid areas are sim ilar in th a t they pass labially from th e soft

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tissue of the lip. T h e bicuspid area is m arked as in th e upper d en tu re by stro n g plicae of soft tissue and by au x iliary a t­ tachm ents of th e buccinator muscle. T h e border in the m o lar area goes buccally to w ard th e ex tern al oblique line to the broad attachm ents of the buccinator m uscle. O n the lingual aspect, the cen tral area passes d o w n w ard to the fren u m of the tongue. T h e la te ra l area is bordered by the a n te rio r portion of the sublingual gland. T h e cuspid area is bordered by the m iddle or highest portion of the sublin­ g ual gland as it passes u p w ard an d back­ w ard in a gentle curve, passing do w n w ard and backw ard beneath the first bicuspid area. T h e deepest point in the lingual outline of th e low er den tu re is reached at a point directly undern eath the second bicuspid area, as th a t point m arks the sm all space betw een the distal end of the sublingual g lan d and the first noticeable portion of th e mylohyoid line and its muscle. T h e first m olar area is bordered by the fu n ctio n al range of the mylohyoid m uscle as it passes u p w ard and backw ard und ern eath th e second m o lar area to the distal cusp of th a t tooth, w here th e border of the d en tu re slips over th e mylohyoid line, as th e re are no muscle attachm ents on th e mylohyoid line from the d istal end of th e m ylohyoid muscle to th e mesial end of the m ylopharyngeus. T h e outline of the d en tu re th en dips 1 m m . and continues d ow nw ard, u p w ard , and fo rw ard slightly in a perfect h alf circle, the size of w hich is dependent on the action of the soft tissue curve from the m andible to the palatoglossus muscle, w hich is th e an terio r p illar of th e tonsil. T h e outline continues over the m ylo­ pharyngeus an d th e pterygom andibular raphe attach m en t on the m edial border of the retro m o la r tria n g u la r area and passes w ell distally over the retro m o lar tria n g u ­ la r pad of so ft tissue overlying th e te r­

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T h e Jo u rn a l of th e A m erican D e n ta l Association

m inal fibers of the tem poral muscle, jo in ­ ing th e buccal border a t this point. T h u s is the field in w hich w e w ork composed, not as the resu lt of opinion or hypothetical surm ise b u t of actu al dissec­ tion. T h is is the anatom ic stru c tu re w ith w hich w e, as den tu re men, are w orking every day, and it necessitates only our careful endeavor to w ork in harm ony w ith it. W h ile the anatom ic stru ctu res, as outlined, appear w ith alm ost u n varying constancy, it becomes apparent th a t one m ust thoroughly know the no rm al in o rd er th a t one m ay recognize both m ajor and m inor abnorm alities. T h e ability of any operator to recognize the abnorm al in anatom y varies directly w ith his know l­ edge of the n o rm a l; th a t is to say, th e less his know ledge, the g rea ter his ability to recognize the abnorm al only by its gro ­ tesqueness, m inor abnorm alities, w hich m ay in terfere greatly w ith the success of the case, slipping by unnoticed and unrec­ ognized. T h erefo re, w h a t I hope to have accomplished is to review the anatom y as w e w ere ta u g h t it in our u n d erg rad ­ u ate days, to bring back to m ind th e rela­ tion of the various anatom ic structures involved in the seating areas, and to em ­ phasize th e fact th a t there is a definite anatom ic outline, regardless of th e tech­ nic used, for those w ho w ish to build the periphery of th e dentures in soft tissue. B u ild ing to this outline, applying pres­ sure and relief in harm ony w ith th e resil­

iency of the u n d erly in g tissues, w ith an equal effort to secure and establish a bal­ anced occlusion, and to produce pleasing effects, n o t only enables the operator to discharge faith fu lly his professional re ­ sponsibility as reg ard s the p atien t’s com ­ fort, health and happiness, b u t fu rth e r affords th a t added satisfaction th a t comes w ith the know ledge of a piece of w ork well done. D IS C U S S IO N

C lyde H . Schuyler, N e w Y o rk C ity: T oo few o f us h a v e an ap p reciatio n of the value of exam ination of d e n tu re borders in the mouth, com plete exam ination and ch arts of the case, before s ta rtin g the construction of dentures. I think th e re is no w a y th a t one can fa m ilia riz e him self so thoroughly w ith m outh conditions as by h a v in g a complete c h art fo r each in d iv id u a l m outh. In m any instances, w e p e rh ap s enter into the construc­ tion of a prosthetic appliance a n d -th e n find difficulties th a t should h av e been observed b e ­ fo re w e started . A thorough exam ination of the m outh is im pressive to a patien t and aids us in acq u irin g his confidence. T h e re are m any things essential to success in full den­ tu re construction. O ne m ay be a m aste r of the h a n d lin g of p la s te r com pound o r w ax, but if he does not h av e a thorough know ledge of d enture a re a s a n d the tissues he is dealing w ith, he cannot expect the ultim ate of success. E w e ll N e il, N a sh v ille , T e n n .: T h e upper technic has not been changed in about tw enty years, except fo r a change m ade about tw elve y ears ago. T h e lo w e r technic had its incep­ tion in the M e h a rry D ental College of N a sh ­ ville, T e n n . T h e clinical m ate ria l offered in the anatom ic la b o ra to ry of th a t g re a t school m ade it possible fo r us to sta rt this technic.