Essentials of Complete Denture Prosthodontics PDF

ESSENTIALS OF m h b numam *- Seco nd edition. -. x t - a... ' Edited by A.I.T.B.S. PUBLISHERS, INDIA ESSENTIALS OF COMPLETE...

ESSENTIALS OF m h b numam Seco nd edition. -. x t - Edited by A.I.T.B.S. PUBLISHERS, INDIA ESSENTIALS OF COMPLETE DENTURE PROSTHODONTICS Second Edition Sheldon Winkler, BA, d d s , f a c d Professor and Acting Chairman Department of Prosthodontics Formerly, Assistant Dean for Research, Advanced Education and Continuing Education Temple University School of Dentistry Philadelphia, Pennsylvania and Editor, Implant Dentistry With twenty-five contributing authors A.I.T.B.S. PUBLISHERS, INDIA DENTAL PUBLISHERS J-5/6, Krishan Nagar, Delhi-110051 (INDIA) Phone: 22549313, 22054798, F a x: 011 -22543416 E-m ail: [email protected] & [email protected] Contents o f the E dentulous M outh 1 lan J. D rinnan 15 22 DENTURES 39 and Lance F. O rtm an 56 81 88 123 142 183 ush Bailey G uidelines fo r C om plete D enture 217 IX Teeth L ance F. O rtm an and C om m unicating With D ental D enture Maintenance 331 341 F. Bow m an 361 W inkler 403 417 427 433 441 Preface first edition— diagnosis and treatm en t planning, nutrition, im m ediate den tu res, maxillofacial prosthetics, and im plants. F our of these chapters have new authors. O th e r chapters w ere ex p an d ed , while som e w ere shortened. Two chap ters rem ain quite lengthy. D ue to the wide vari ety of articulators used in d ental schools today, th e chapter on articulators attem pts to cover as m any o f the com m only used instru m ents as possible. T he chapter on arrangem ent of p osterior teeth has been slightly lengthened. It contains essential inform ation n ot available in any o th er prosthodontic text. A nd finally, a few chapters w ere d ropped from the first edition. Vital inform ation in the d eleted chapters has been incorporated into o th er parts o f the second edition. All of the contributors have given generously of them selves during the prep aratio n of this volum e. T h eir enthusiasm and willingness to co o p erate in spite of m any o th e r com m itm ents are sincerely appreciated and have m ade the e d ito r’s jo b a m ost rew arding and pleasant ex perience. It is also a source o f pride to the editor to include six of his fo rm er students as contribu tors. A ppreciation is expressed to D ean M artin F. T ansy o f T em ple U niversity School of D entistry for his interest and encouragem ent and Tem ple U niversity for its support. D r. G eorge E. M onas- ky, w ho succeeded me as C hairm an of R em ov able P rosthodontics, was of invaluable assistance th ro u g h o u t the en tire revision process and allow ed m e to continue to utilize d epartm ental facilities and services after my reassignm ent to advanced studies and research. D r. A rth u r Nim- m o, while his nam e appears only as senior au th o r of one ch ap te r, w orked closely with the ed ito r and contributed valuable suggestions and assistance. D r. B rien R. Lang, Professor of D entistry and C hairm an o f C om plete D entures at the U niversity of Michigan School of D entist ry, graciously allowed reuse of a num ber of his illustrations from the first edition in C h ap ter 11. D rs. A rth u r N im m o and Julius R osen assisted in p roofreading and Mrs. Sylvia Pearlstein in typ ing and clerical functions. T he invaluable editorial and secretarial assis tance of my wife Sandra is once again acknowl edged. Sandra acted as in-house copy ed ito r and xi Publishing C om pany, whose help and sugges tions w ere m ore than any ed ito r could hope for. PSG Publishing C om pany patiently and diligent ly w orked along with the contributors and editor and has been of invaluable assistance during the p rep aratio n of this textbook. Sheldon W inkler Introduction Prosthodontics Today SHELDON WINKLER, DDS T he m astication o f food with com plete d en tures assists the edentulous patien t in obtaining ad eq u ate nutrition. H ow ever, com plete d en tures constructed even u n d er the m ost ideal con ditions will have a chewing efficiency of only a fraction o f th at of the n atural d entition. T he p atien t m ust und erstan d and accept the reduced efficiency o f the artificial dentition. T o a g reat nu m b er of patients, esthetics is p aram ount. F ortunately, today it is possible for the dental profession to consistently fabricate virtually undetectable com plete dentures th at sim ulate the harm onious positions and rela tionships of the lost natural teeth during speech, m astication, and rest. T he em otional and psy chologic effects of im proved appearance can create a new outlook on life for m any patients. T he unrealistic esthetic dem ands of som e p a tients m ay n ot be possible to achieve for biologic or m echanical reasons. C hanges in the su pport ing structures in later years can necessitate a change in too th position to im prove stability and function th a t m ay adversely affect esthetics. E den tu lo u s p atients should be able to speak clearly and distinctly with com plete dentures. If possible, correction of speech defects as a result o f th e absence of the natural dentition o r from the unsatisfactory arrangem ent of teeth in ex isting den tu res should be incorporated into the new dentures. Artificial teeth should duplicate th e size and con to u r of the missing teeth and xiii nu m b er of prosthodontists is lim ited despite the ever increasing num ber of dentists who en ter specialty training program s, the general practi tio n er will be responsible for providing the vast m ajority of this care. R esearch probably will n ot produce any dram atic change in th e prosthodontic needs of ou r population in the n ear future. T h ere are several reasons for this. D en tal diseases are com plex and th eir prevention has, to date, defied th e efforts of a g reat num ber of sophisti cated researchers. T h ere will be a continued need for com plete dentures until know ledge of the causes, treatm en t, and prevention o f dental caries and p eriodontal disease is com plete. T he research support allotted the profession is grossly inadequate w hen correlated with the m agnitude of dental disease. F u tu re available research m oney could conceivably be used to cope with im proved delivery systems and the increased dem and for dental care ra th e r than investigations into the causes and prevention of dental disease. T he prosthodontic needs of o u r population are m onum ental and m ost probably will rem ain th a t way a t least for the next generation. A m ericans PROBLEMS FACING PROSTHODONTICS Illegal Practice of Dentistry T h ere is a tren d in m any dental schools to have dental technicians perform an ever increasing share o f the laboratory phase o f prosthetic den tistry. D entists already delegate too much of th e fabrication o f dentures to com m ercial laboratories. T he unfo rtu n ate result is a g reater dependency o f the stu d en t and d entist on the laboratory technician, with som e m em bers of the profession relying m ore and m ore on the judgm ent of auxiliary personnel. If a dentist cannot perform all th e phases involved in p ro viding prosthetic service for his patien ts, he can n ot u n d erstan d , prescribe for, and direct the fabrication of a prosthesis for which he alone is responsible. T he com petent d ental technician is an integral p a rt of the dental health team. U nfortunately, too m uch dependence by th e dentist on com m ercial dental laboratories can lead som e tech nicians to believe they know m ore about prosthodontics than dentists and th a t they con sequently should be perm itted to deal directly with th e public. Laws allowing nondentists xv oth ers receiving less. T aylor et a l12 rep o rted an overall decrease in curriculum em phasis on re m ovable prosthodontics during a 15-year period at 33 o f 50 A m erican dental schools th at responded to a recent survey. T he authors con cluded th at educators are losing ground in p ro viding adeq u ate p rep aratio n for dental g rad u ates in rem ovable prosthodontics. U n fo rtu n ate ly, this deem phasis or reduction in pro sth o d o n tic training has resulted in a decrease in student contact hours, both didactic and clinical. T he m ounting dem and for prosthodontic care m andates curriculum com m ittees to m aintain (and perhaps even increase) the tim e devoted to prosthodontics. W hile im proving the quality of instruction and m aking the m ost effective and efficient use o f the hours allotted to pro sth o d o n tics can com pensate in a small way, th ere can be no substitute for clinical experience. A d eq u ate patien t contact hours are essential to develop the skills, m anual dexterity, and clinical ju d g m ent necessary for the successful practice of prosthodontics. pro sth o unsatisfac THE FUTURE W hile the fu tu re will undoubtedly bring new concepts, new techniques, and b e tte r m aterials w ith concurrent im provem ents in diagnosis, treatm en t planning, and d en tu re construction, to d ay ’s problem s m ust be adequately resolved to ensure the highest possible standards of p atien t care. O u r goal m ust always be health ier and happier patients. T h ere will always be som e patients w ho p ut price in front o f quality and may seek o ut illegal o perators. F o r this sm all group of people, th e profession can do nothing. H ow ever, adequate com plete d entures th at m eet minim um stan dards can be and, it is hoped, will continue to be provided for m ost p atients at a fair cost by the m ajority o f general practitioners. This is a m ust, as the am ount of fu tu re prosthodontic needs could very well increase far beyond all expecta tions. T he practice of prosthodontics as we know it today is reaching a crisis. U nless th e profession itself tak es an active p art in m onitoring the fu tu re, th ere may be no future! T h e profession m ust act positively, aggressively, and quickly to m eet to d ay ’s challenges. If dentists do n ot care enough, who else can be expected to act in their behalf? SE C T IO N I The Edentulous Patient factor in biologic evolution. So long as the vital functions o f respiration and digestion are sub served, th e specific anatom ic characteristics of th e oral structures no longer have the im pact on survival they once had in anthropoid, prehom i- nid, and even ex tant prim itive hum an societies. This factor has p erm itted an expanding gene pool to occur th at, in tu rn , has been expressed in th e enorm ous variability seen am ong hum an beings. O ne need think only of the gross differ ences in tooth m orphology, arch configuration, and relative jaw size am ong patients to appreci ate the ex tent o f this variability. T hus, no an atom ic o r physiologic description can do justice to any specific individual. V ariability can be con ten d ed with only by the developm ent of clinical judgm ent, clinical skills, and appreciation and concern for the uniqueness of each individual patient. assum p TOPICAL ORAL ANATOMY T he correlation of topical oral anatom ic struc tures and areas with relevant com plete denture landm arks may be studied in Figure 1-1. and ORAL MUCOUS MEMBRANE m ust be T he oral m ucous m em brane varies in structure from area to area and dem onstrates “ adaptation LANDMARKS Labial frenum Labial vestibule Buccal frenum Buccal vestibule MANDIBULAR ARCH C o ro n o id bulge Residual alveolar ridge M a xilla ry tuberosity H am ular notch Posterior palatal seal region M e d ian palatine raphe Incisive papilla Rugae region Retrom olor p a d j U ngual tubercle M A lveololin gual sulcus f i Alveololingual fold |yg Pfica sublingualis Lingual frenum M asseter groove Pterygom andibular notch Retrom ylohyoid eminence Lingular tubercular fossa M ylo h yo id groo ve M ylo h yo id flange MANDIBULAR IMPRESSION landmarks. (Reproduced by permission of the Block Drug Wernet Division. Block Drug Company, Inc.) consistency o f th e oral m ucous m em b ran e from p a tie n t to p atie n t. Som e p atien ts have alveolar ridges covered with thick, resilient m ucous m em b ran e; o th ers have th in , atro p h ic m em bran es w ith little subepithelial connective tissue. M ost d en tal p ractitio n ers have seen exam ples of th e variations in response to stim uli th a t th e oral m ucous m em b ran e displays. M o d erate o v e r extension o f a d en tu re flange in one p atien t will p ro du ce little discom fort, no u lceratio n , and p erh ap s a hyperplastic response from the tissue. In a n o th e r p a tie n t th ere will be early ulceration and little a tte m p t at rep air. A p a rt from obvious system ic an d local dis eases th at affect th e integrity o f the o ral m ucous m em b ran e, th e clinician m ust rem em b er th a t th e re are general age changes th a t are fre q u e n t ly seen in th e elderly e d en tu lo u s p atie n t. O n e of th e m ost com m on is th e n o d u lar varicose en larg em en t of th e veins on th e v en tral surface of th e tongue (caviar to n g u e ).17 T he o ral m ucosa in those o f advancing age is often thin and easily a b ra d e d , an d p atien ts m ay com plain o f dryness. 3 from the palate (A) shows that keratinizing palatal mucosa has a surface mucosal epithelium (B) does not normally keratinize and the superficial T he basal portion o f th e m andible is, to a large extent, related to th e needs of th e inferior alveolar neurovascular b undle, w hereas the coronoid process largely depends upon an intact and functioning tem poralis muscle. T he form of th e m andibular angle is associated with the m asseter and m edial pterygoid muscles. If these muscles continue to function norm ally, the angular region will n ot appreciably change with age o r following the loss of teeth. T h e m orphol ogy o f th e alveolar process, on th e o th er hand, is intim ately related to th e dentition. T h eir loss has a direct and profound effect on th e alveolar process b u t n o t necessarily on th e o th e r com po nents o f th e m andible or maxilla. A ny changes th a t m ay occur elsew here are indirect and are th e result o f m odified function th a t may have b een required because of th e edentulous situa tion. O cclusal and o th er forces on the n atural teeth are absorbed by the hydrodynam ic effect of tissue fluids, bound w ater, and blood in the p eriodontal ligam ent. A lthough th e obliquely o rien ted principal fibers o f the ligam ent provide a collagen fram ew ork, recent evidence suggests th a t they do n o t prim arily function to resist and ham ulus may becom e extrem ely prom inent relative to the residual alveolar ridges.10 Loss m ay be so severe th at the m ental foram en, once on th e lateral side of the m andible, comes to assum e a position on the top of the ridge. The ridge itself may becom e concave. V ery often it does n ot m aintain cortical bone on its surface, w ith the m edullary spaces having a direct con tinuity with the alveolar m ucosa. T hese variations from typical descriptive an at omy o f the jaw s m ust be considered during com plete d enture construction. T he ability to m anage such m orphologic variability is an essen tial ingredient of successful prosthodontics. effects of THE TEMPOROMANDIBULAR JOINT T his com plex synovial join t m akes up half the bilateral articulation betw een the m andible and cranium — the craniom andibular joint. It m ay be functionally classified as a hinge jo in t w ith a sliding so cket.10 M ost of the hinge or ginglymus m ovem ent takes place betw een the m andibular condyle and its attached articular disc, w hereas th e sliding or arthrodial m ovem ent occurs be tw een the disc and the articular em inence o f the tem poral bone. In understanding the function of this struc tu re, it is im portant to recognize th at the m an dibular (glenoid) fossa does n ot norm ally partic ipate in jo in t activities except for its anterior wall, which, in reality, form s the posterior slope o f th e articular em inence. T he functional bony elem ents of this jo in t, th erefo re, should be p er ceived as two convex structures, nam ely the con dyle and articular em inence. This view is sup p orted by anatom ic, histologic, and physiologic evidence.19 Since the position of the jo in t capsule norm ally denotes the m ovem ent area o f any synovial jo in t, an exam ination of the capsular attach m ents on the tem poral bone serves to illustrate th e func nal limits of the condyle (Fig, 1-3). T he superior and posterior areas of the fossa do n o t p.rticipate in bearing functional loads. Such loads are norm ally borne by the articular em i nence, particularly its posterior slope. T he lateral pterygoid muscle plays a particu larly im portant role in determ ining w here the condyle-disc com plex is located on th e em i nence at any given m om ent. This m uscle, partic ularly its inferior belly, strongly influences the degree of retrusion of the condyle, since it is a \ sive forces, especially in th e den tu lo u s state. It has been hypothesized th a t th e n atu ral d entition carries m uch of th e com pressive load so th a t the jo in t is not. ordinarily req u ired to w ithstand large loads of this type. T he loss of th e n atu ral d entitio n m ay, th ere fo re , place ad ditional com pressive forces on th e tem p o ro m an d ib u lar jo in t, w hich is th en req u ired to ad ap t to th ese new functional dem ands. T he ap p earan ce of cartilage cells and glycosam inoglycans (G A G ) in o ld er jo in ts as areas o f fibrocartilage, as well as jo in t rem o d elin g, rep re se n t physiologic a d ap tatio n s to function. C o n tin u ed loading beyond th e adaptive c ap a bilities o f th e articu lar tissues m ay lead to d eg enerativ e jo in t disease (o steo arth ro sis). T he collagen fibers becom e “ u n m ask ed ” u n d er th e com pressive loads; u n co n tro lled and ab e rra n t rem odeling ensues, and p o rtio n s o f the articular tissues may b reak dow n. T h e p e rfo ratio n o f an articu lar disc is an exam ple o f such deg en eratio n and m ay be accom panied by bizarre rem odeling activity, p articularly o f th e co n d y le.18 If it is tru e th a t th e n atu ral d en titio n relieves th e jo in t from undue com pressive forces, it fol lows th a t loss o f teeth leads to an increase in these forces, u n d o u b ted ly as a result o f m uscular activity in th e presence o f altered biom echanical relationships. T h u s, e d en tu lo u s p atien ts m ay be particularly susceptible to d eg enerative jo in t disease, particularly those individuals w hose tis sues can n o t a d ap t ad eq u ately to th e functional changes. A lth o u g h th e re is no evidence to sug gest th a t pro p erly co n stru cted com plete d e n tu res can reverse th e course o f this disease, ) Sagittal section o f the d ib u lar jo in t from a 67-year- u p p er and low er natural ) Sagittal section o f the tem ib u lar jo in t from an 81-year-old ale w ith co m plete u p p er and recordings from left A s subject clenches in is tapped. A fte r a latency a com pound action poten tial followed by a silent period uration. Blocks rep resen t 0.5 ly. T he sum to tal o f th e electrical events p ro d uced by co n tractio n of th e m o to r units can be reco rd ed by th e use of electrom yography. Its use in studying m an d ib u lar function has g en e ra l ly confirm ed dedu ctio n s m ade from dissections o f the m uscles o f m astication. Such studies have d e m o n strated th a t m an d ib u lar elevation is p ro duced by the tem p o ralis, m asseter, and m edial p terygoids, and d epression by th e in ferio r b e ll/ o f th e lateral pterygoids and th e digastrics. L ateral m ovem ents are p erfo rm ed by th e ipsi- lateral tem p o ralis an d m asseter and by the con tra late ra l m edial and lateral pterygoids. P ro trusion is effected by th e m edial and lateral pterygoids, w hereas retru sio n is effected by the tem p o ralis, chiefly its p o sterio r fibers, th e digas trics, and th e deep p a rt o f th e m assete r.3 R ecen t electrom yographic evidence in m o n k ey 15 and m a n 1"’ has strongly suggested th a t th e inferior belly of th e lateral p terygoid is m ost active during closing an d n o t during o pening o f th e m andible. In ad d itio n , electrom yography as a clinical and research tool has greatly ex p an d ed o u r know ledge o f fu nctional o ral anato m y since its first co n certed use in den tistry by D r. R o b e rt M oyers in 1949. F o r exam p le, it has been show n th a t th e lateral p terygoids, particularly th e in ferio r bellies, a p p ea r to initiate jaw open in g and th a t th e digastrics are im p o rtan t only during m axim um o pening o r open in g against resis t a n c e / E lectro m y o g rap h y has also d e m o n stra te d th a t th e m and ib u lar elev a to r m uscles show stro n g activity during sw allow ing, p articu larly in th e ad u lt o r som atic swallow in w hich occlusal co n tact norm ally occurs. In infantile or visceral sw allows, th e facial and circum oral m us cles a p p ea r to initiate th e sw allow, and th e to n g u e is used to brace th e m andible instead of th e d en titio n. It is in terestin g to n o te th a t after com plete loss o f te e th , th e in fantile p a tte rn of deglu titio n is again se e n.21 T h e insertion o f d e n tu res perm its the p a tie n t to once again utilize th e m ore norm al adu lt sw allow ing p attern. T h e study of m an d ib u lar reflexes m ay also be cited as an im p o rta n t use o f electrom yography. A n exam ple o f this is th e m asseteric silent p erio d th a t can be elicited by a ta p to the chin w hile a su b ject clenches th e te e th in centric occlusion. T h e sh o rt tra n sien t p erio d of inhibi tion during th e o therw ise sustained contraction of th e m asseter m uscles is term e d th e silent p erio d (Fig. 1-5). T h e d u ratio n o f this silent p erio d has b e e n rep eated ly show n :c be lo -g e r. on average, in groups o f pain-dysruncticr. pa tien ts as co m p ared w ith groups l i.r r r : :~ a t;c receptors, particularly in th e p eriodontal m em b rane, gingiva, and p alate, will have an inhibi tory effect on th e alpha m o to r neurons th at supply the m andibular elev ato r muscles. If this is done while these m uscles are contracting, a short m otor pause o r silent period will be observed in th e electrom yographic recordings of those muscles. This p h enom enon is m ediated by the ja w opening reflex, which is a polysynaptic reflex involving the trigem inal system. It is b e lieved by m any th at this reflex is intended, un d er norm al conditions, to p ro tect th e d en ti tion and o th er intraoral structures from undue stress or injury during jaw closure. In the dentu- lous person, it m ost likely is also involved in the learning process th at perm its us to close the m andible into a precise occlusal relationship w hen the head is upright. Since the periodontal receptors have directional capability in addition to th eir sensitivity, the loss o f teeth and their associated periodontal ligam ents should be viewed as much m ore th an ju st a loss of skeletal structure. It is also a deprivation o f an im portant source of neurosensory input, which, in addition to affecting intraoral p erception, decreases the preciseness of jaw closure and o th e r m andibular functions. T he w ell-founded technique of “ balancing” artificial d en tu res is probably ju s tified m ore on the basis o f accom m odating for this loss of neurosensory input and decreased precision closure than of assisting in d en tu re stabilization during lateral excursion of the m an dible. It has also been suggested, but never proven, th a t, w ith the loss of p eriodontal receptors in edentulous p atients, the use o f a retru d ed con dylar position becom es m uch m ore im portant th an it w ould ordinarily be in patients with re m aining natural te e th.6 T he hypothesis is that edentulous p atients are, of necessity, m ore d e p en d en t upon those neurosensory receptors located in the capsule and ligam ents of the tem p o rom andibular jo in ts than are individuals with n atu ral teeth. This view is, at least partly, sup p o rted by evidence th at tem porom andibular jo in t receptors play an im portant role i n , the perception of m andibular position and m ove m ent and in th e reflex modification of m astica tory m uscle activity. T hese receptors have also been im plicated in the intraoral discrim ination of o b ject size. T he m uscle spindles p resen t in the m astica tory muscles provide an o th er extrem ely im por ta n t source o f neurosensory input, particularly in th e closing group or antigravity muscles. 9 b ro u g h t ab o u t by em otional stress, as rep o rted by Y em m.27 T h e degree of em otional tension of an individual is thus a very im p o rtan t consid eratio n in the clinical d eterm in atio n of postural rest position. M ore specifically, it is know n th a t postural rest position of th e m andible is influenced by th e m yotatic (stretch) reflex, which is activated by stretch of th e m uscle spindles in th e elevator m uscles. W hen g ravitational forces act to d e press th e m an d ib le, this reflex causes the ap p ro p riate n u m b er o f m o to r units in th e closing m uscles to be activated, resulting in th e m andi b le being elevated to its original position. This unconscious activity m aintains the p o stu re o f the jaw. H o w ev er, th e response th reshold o f th e m uscle spindle is d eterm in ed by th e activity o f th e gam m a efferent (fusim otor) system. G am m a efferen t activity low ers th e th resh o ld o f th e spin dle in response to stretch. It th en tak es less of a stim ulus to activate th e stretch reflex and bring a b o u t contractio n o f m o to r units w ithin th e ele v ato r muscles. Since th e gam m a efferen t system is excited by th e reticular form ation in th e cen tral nervous system , a link is established be tw een brain and brain-stem activity, muscle spindle th resh o ld levels, and m uscle contraction o r to n e. It is this com plex m echanism th at, to a large ex ten t, accounts for th e clinical observa tion th a t em otional stress o r psychic tension in creases m uscle to n e. A n increase in the to n e of th e m an d ib u lar elevators will decrease rest ver tical dim ension and consequently reduce in te r occlusal distance. T hus, th e psychological status o f th e p a tie n t is an im p o rtan t consideration in all stages of com plete d en tu re construction in which th e p o stu ral rest position is used as a referen ce position o f th e m andible. A ttem p ts have been m ad e to use electrom y ography to m ore precisely determ ine optim al postural rest position. This has n o t been possi ble, particularly since it has b een rep o rted th at m an d ib u lar position during m inim al muscle activity (E M G rest) is at a m o re op en jaw posi tio n, ab o ut 8 - 1 0 m m , th an th e clinically d e te r m ined p o stu ral rest positio n.22 T hus, recognized clinical techniques to register this position are still recom m ended. It is evident th a t postu ral rest position should no t be reg ard ed as a static im m utable position of th e m andible. B esides em otional and psycholog ical effects, th e re are m any o th e r short-term and long-term factors th a t influence p ostural rest position an d , although its clinical im portance and usefulness in com plete d en tu re prostfaodon- ble as occurs during m astication. A lthough the h um an fetus and n ew born can suck and swallow, m ost jaw m ovem ents are relatively random. T he cyclic type o f jaw activity requires learning. T h ro u g h * rep etitio n , the activity will eventually tak e place subconsciously even though its initia tion m ay be a conscious act. E ach person has an individualized p a tte rn o f cyclic m ovem ent, w hat m any clinicians call th e “ occlusal g a it.” A lth o u g h m any factors may influence this gait, few are so im m ed iate and dram atic as the loss of te e th , th e insertion of d e n tu res, o r the co m bina sh ip acts as a sen tion of b o th. N ew p a ttern s of m ovem ent involv ing new learning, often at the conscious level once again , are req u ired to a d ap t to the new fu nctional situ atio n. Successful a d ap ta tio n will lead to m ore au to m atio n and less conscious effo rt on the p a rt o f th e p atien t. In m ost cases, th e occlusal gait will be d ifferent from the p reed en tu lo u s state. T h e d en tu lo u s person usually d em o n strates sm ooth jaw m otion during m astication. It is shaped som ew hat like a te a rd ro p w hen viewed in th e frontal p lane. O n th e o th e r h an d , the ed en tu lo u s p a tie n t will often have a disto rtio n of this m ovem ent w ith the process becom ing m ore ran do m and indiscrim inate. D u ring the closing p art o f th e cycle, the den tu lo u s sub ject will d e c elerate the m ovem ent ju st b efo re to o th contact to d am pen th e effect o f closure on th e den titio n. T he ed en tu lo u s p a tie n t seem s to elevate the jaw at a con stan t velocity with no d eceleratio n n ear th e end of closure. In ad d itio n , the e d en tu lo u s p erson will no t develop th e sam e isom etric te n sion on artificial d en tu res th at is a ttain ed by p eo p le closing on n atu ral te e th ; a red u ctio n o f at least 75 p ercen t is observed. F inally, the preci sion of th e closing occlusal co n tacts will be d e creased in th e ed en tu lo u s individual. R ecen t evidence indicates th a t cyclic jaw m o v em en t is co ntrolled and co o rd in ated by a cen tral p a tte rn g e n e ra to r or “ chew ing c e n te r” in th e brain stem. T his c e n te r m ay be activated by im pulses from higher cen te rs, such as the c ere bral cortex o r from p e rip h eral sensory receptors. T h e im po rtance of neu ro senso ry inp u t has been discussed, particularly in referen ce to th e initia tion of b o th th e jaw open in g and jaw closing reflexes. A t one tim e, it was believed th a t m as tication was th e result o f th e a ltern atio n of these sim ple brain -stem reflex es.12 T his concept has b een replaced by th e idea th a t a cen tral p a tte rn g e n e rato r, once in itiated , co o rd in ates the m us cle co n tractio n sequences th a t pro d u ce the rhythm ic a ltern atio n o f opening and closing m ovem ents th a t co n stitu tes m asticatio n.8 This 11 cial a tte n tio n m ust be paid to th e conto u rin g of th e lingual flange of a low er d en tu re in o rd e r th a t th e d e n tu re is n o t displaced every tim e th e genioglossus m uscle con tracts. T h e dorsal surface o f th e to n g u e is co vered by a specialized m ucosa. T h e a n te rio r tw o thirds o f th e to n g u e displays m any densely packed filiform p apillae. S cattered th ro u g h o u t these p apillae are th e fungiform p apillae th at b ear specialized sensory recep to rs— taste buds. T h e ju n ctio n of the a n te rio r tw o thirds o f th e d orsum o f th e tongue w ith the p o sterio r third is m ore o r less indicated by th e circum vallate papillae. T hese a p p ear as a V -shaped line o f large, ro u n d papillae (th e apex of th e V pointing p o sterio rly ). T h ere are usually 8 - 1 2 circum val late p apillae. E ach is su rro u n d ed by a tro u g h into w hich th e ducts o f the serous E b n e r’s glands open. The circum vallate papillae also serve a taste function. T h ere is a tendency fo r the tasteb u d s to dim inish in n u m b er in old age. “ B ald ” to n g u e, o n e in which the filiform papillae are a tro p h ic, is n o t an uncom m on finding in elderly p eople. A tro p h y o f the lingual p apillae m ay occur in p a tien ts w ith iron-deficiency or vitam in B J2 deficiency an em ia o r those w ith nutritio n al dis o rd e rs, b u t, in m any cases, no satisfactory ex p lan ation can be given for th e presence of a sm ooth to n g u e (Fig. 1-6). T h e lateral b o rd e r o f th e to n g u e is covered w ith sm ooth m ucous m em b ran e except on th e p o sterio r asp ect, w here th ere are several parallel vertical folds of m ucosa (foliate p apillae). T h e foliate p apillae m ay, on occasion, be quite p ro m in e n t, and a p a tie n t m ay be co ncern ed th a t a large foliate papilla m ight rep re sen t oral cancer. T h e v en tral surface o f th e to n g u e is, at rest, norm ally in contact w ith th e floor o f th e m outh an d is covered by sim ple m ucous m em b ran e th at does not display any papillae. In m any elderly p eo p le th e re is a n o d u lar en larg em en t o f the superficial veins on th e v en tral surface o f th e to n g u e. T he presence of such lingual varicosities (“ caviar to n g u e ” ) is not tho u g h t to be of any special significance and should not be reg ard ed as evidence o f disease of th e blood vessels or o f th e cardiovascular system (Fig. 1-7). m ay be of genioglossus SALIVARY GLANDS m andible in Saliva has m any functions. In addition to its p ro tectiv e functions, and its role in taste and d igestion, it is im p o rtan t in the lubrication of the Figure 1-6 This close-up view of the dorsal surface of a “bald” tongue shows that there is a complete absence of filiform and fungiform papillae. The patient had per nicious anemia, a condition that frequently demonstrates a smooth tongue surface. Figure 1-7 An elderly patient with marked varicosities on the ventral surface of the longue. These become more apparent as the patient holds the tongue in the position shown, as the lingual veins are compressed and the varicosities distended with blood. O ccasionally, the relation of the duct orifice to a com plete d en tu re is well dem o n strated , as in Figure 1-8. H ow ever, it is rare for a maxillary d en tu re to p roduce obstruction of S tensen’s duct. T he subm andibular gland is located in the subm andibular fossa of th e lingual aspect of the m andible, and a p a rt o f the gland is w rapped around the p o sterio r p art of th e “ diaphragm a oris,” the m ylohyoid muscle. It is from this p o r tion o f th e subm andibular gland th at W h arto n ’s duct curves forw ard to open at the apex of a small m ucosal papilla in th e anterio r floor of the m outh ju st lateral to th e m idline. E xtension of the lingual flange of a d en tu re in this region can lead to obstruction o f th e subm andibular gland and, in such cases, patients may com plain of developing swellings un d er the jaw s w hen eating (Fig. 1-9). T he sublingual glands are of varying size and, on occasion, may present as large swellings th at may interfere with satisfactory low er d en tu re w earing T h ere are usually 8 -1 2 13 o f Sten- en tu re is clearly show n ably in contact accum u new com plete an 60 years o f age d e r the jaw each f the low er d en tu re (B ). T he loca duct are revealed w hen T he d en tu re covered b lin g u a l g la n d , a n d it 8. Dellow PG : C ontrol mechanisms of mastication. u c e a n y sig n ifican t A n n A ustr Coll Dent Surg 1969;2:81-85. 9. D uBrul EL: Origin and evolution o f the oral apparatus. Front Oral Physiol 1974;1:1-30. te d p e r d a y v a rie s 10. D uBrul EL: Sicher’s Oral A natom y, ed 7. St l. T h e q u a n tity w ill Louis, CV M osby, 1980. ch a s h y d ra tio n , 11. G oodgold J, E berstein A: Electrodiagnosis o f p a tie n t h a b itu a lly Neurom uscular Diseases. Baltim ore, Williams & Wilkins, 1978. , a n d so o n. R e c e n t 12. Jerge CR: The neurologic mechanism underlying e a lth y o ld e r p a cyclic jaw movem ents. J Prosthet Dent 1964; 14: d im in ish w ith ag e. 667-681. c o m p la in o f e x c e s 13. M ahan PE , Wilkinson TM , Gibbs C H , et al: Su perior and inferior bellies of the lateral pterygoid H o w e v e r, b e muscle E M G activity at basic jaw positions. J o f o ld e r p a tie n ts Prosthet Dent 1983;50:710-718. iu re tic s , tra n q u iliz 14. McCall W D , U thm an A A , Mohl ND: Symptom th e r s th a t h a v e a n severity and E M G silent periods. J Dent Res u th (x e ro s to m ia ) 1978;57:709-714. 15. M cN am ara JA : The independent functions of the C e rta in d ise a se s two heads of the lateral pterygoid muscles. A m J l cells o f th e saliv a ry A nat 1973;138:197-206. e s tru c tio n (fo r e x a m 16. M cN am ara JA : Electrom yography o f the m an m ay le a d to th e c o n d i dibular postural position in the rhesus monkey {Macaca mulatto). J Dent Res 1974;53:945. tre s sin g c o n d itio n 17. Miles A EW : “ Sans teeth ” : Changes in oral tissues tio n o f fo o d , a n d with advancing age. Proc R Soc M ed 1972; in d e n tu r e w e a rin g 65:801-806. 18. Mohl ND: A lterations in the tem porom andibular r e , th e d e n tis t joint. Oral Surg Oral M ed Oral Pathol 1973; 36:625-631. e a p o ssib ility in an 19. Mohl N D: Functional anatom y of the tem poro m andibular joint, in Laskin D, Greenfield W, G ale E , et al (eds): The President’s Conference on the Examination, Diagnosis and Management o f Tem porom andibular Disorders. Chicago, A m er ican D ental A ssociation, 1983, chap 1. 20. M ohl N D : The role of head posture in m andibular function, in Solberg W K, C lark G T (eds): A b n o r m al Jaw Mechanics: Diagnosis and Treatment. Chicago, Q uintessence Publishing, 1984, chap 5. 21. Ram fjord SP, Ash MM: O cclusion, ed 3. Phil adelphia, WB Saunders, 1983. 22. Rugh JD , D rago CJ: Vertical dimension: A study of clinical rest position and jaw muscle activity. J Prosthet Dent 1981;45:670-675. 23. Skiba T J, Laskin DM: M asticatory muscle silent periods in patients with M PD syndrome before and after treatm ent. J Dent Res 1981;60:699-706. 24. T en C ate A R : Oral Histology: Development, Structure and Function, ed 2. St Louis, CV M os by, 1985. 25. W idmalm SE: The silent period in the masseter muscle of patients with TM J dysfunction. Acta O dont Scand 1976;34:43-52. 26. Yemm R, B erry DC: Passive control in m andibu lar rest position. J Prosthet Dent 1969;22:30-36. 27. Yemm R: A com parison of the electrical activity of m asseter and tem poral muscles of hum an sub jects during experim ental stress. Arch Oral Biol 1971;16:269-273. m ucosa). C areful inspection of the oral tissues and the oral environm ent is therefore im portant before m aking th e final diagnosis and the prog nosis for the prosthesis. T hus, a consideration of th e nutrition (or m alnutrition) of th e oral tissues becom es an im portant aspect o f the p a tie n t’s ability to to lerate a foreign o bject in the m outh. The technician who can see only the cast on the articulator can n o t do this, no m atter how tech nically skillful he may be. O nly the doctor- clinician can evaluate the denture-bearing tis sues and m ake a prognostic judgm ent. T he fol lowing n utritional factors should be considered: xerostom ia— causes and effects o f negative w ater balance; negative calcium balance— causes and effects on alveolar bone; and nitrogen-protein balance— m uscle w eakness and tissue fragility, and th eir effects on th e o ral tissues. T he con DEHYDRATION W ater is the m ost im portant and essential n u trien t in th e diet of m an. T he body can survive for w eeks w ithout proteins, carbohydrates, fats, o r m inerals and w ithout vitam ins for m onths and years, b u t lack o f w ater for even a few days will lead to death. W ater is essential to all body functions: cell activity, all secretions (including saliva, p erspiration for. tem p eratu re control, and all digestive juices), absorption o f foods, and elim ination of catabolites. W ater lost by kidneys, intestines, lungs, and skin (approxim ately 2500 cc p e r day) m ust be 15 and sebaceous gland secretions dim inish, caus ing th e dryness of th e skin th a t is ch aracteristic o f th e aged. T he n orm al secretions of h y d ro chloric acid in th e stom ach (essential to p ro p e r digestion) and all digestive enzym es in th e in tes tine d ecrease in volum e if w ater in tak e is d e ficient. In the elderly, th e q u an tity and quality of th e saliva m ust be considered during th e assessm ent o f th e o ral enviro n m en t. Eyes X ero p h th alm ia (dry eyes) is due to dim inished secretion o f tears. A bsence o f tears causes irrita tio n , especially w hen th e air is dry and polluted. B ito t spots form at th e inner canthus o f th e eyes. T h ese spots result from an accum ulation o f d e sq u am ated epithelial cells which w ere n o t w ashed away by tears. T hese h eap ed -u p m ounds of d ead epithelial cells are analogous to th e m ateria alba which accum u lates betw een th e te e th w hen n o t rem oved by th e saliva o r foods o r to o th b ru sh in g. T h e cornea becom es dry and w rinkled. O ld p eople do n o t cry with tea rs, “ they cry in sid e.” E xam ination of th e eyes should be included by th e p ro sth o d o n tist in his evaluation o f th e p atien t. Dry mouth X ero sto m ia is d u e to the dim in ished secretion o f saliva. T he oral m ucous m em b ran es becom e h o t, dry, and fragile. D en tu res can n o t be to le ra te d by th e dry and fragile m u cosa. E ven th e m ost skillfully fabricated d e n tu re m ay fail in th e dry m o u th. M ateria alba accum ulates d u e to th e lack o f self-cleansing by saliva. M astication o f dry foods becom es dif ficult, so th a t th e elderly are restricted to soft foods and soups. Tongue T h e to n g u e also changes in th e dry atm o sp h ere o f th e m ou th. A ccum ulation of

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