rationale for dental implants - psau · rationale for dental implants walton, gardner, and agar 28...

T he ideal goal of modern dentistry is to restore thepatient to normal contour, function, comfort, esthet-ics, speech, and health. A dentist provides this restora-

tion for a living, whether removing caries from a tooth orreplacing several teeth. What makes implant dentistry uniqueis the ability to achieve this ideal goal regardless of the atrophy, disease, or injury of the stomatognathic system.1However, the more teeth a patient is missing, the more chal-lenging this task becomes. As a result of continued research,diagnostic tools, treatment planning, implant designs, mate-rials, and techniques, predictable success is now a reality forthe rehabilitation of many challenging clinical situations.

The number of dental implants used in the United Statesincreased more than tenfold from 1983 to 2002. More than700,000 dental implants are inserted each year. The numberof implants continues to increase steadily, with more than$150 million of implant products sold to North Americandentists in 2002 compared with $10 million in 1983, withan expected growth sustained at 9.4% for the next severalyears.2,3 More than 90% of interfacing surgical specialtydentists currently provide dental implant treatment rou-tinely in their practices, 90% of prosthodontists restoreimplants routinely, and more than 78% of general dentistshave used implants to support fixed and removable pros-theses compared with 65% 15 years ago.4-8

The increased need and use of implant-related treatmentsresult from the combined effect of a number of factors,including the following:1. An aging population living longer2. Tooth loss related to age3. Consequences of fixed prosthesis failure4. Anatomical consequences of edentulism5. Poor performance of removable prostheses6. Consequences of removable partial dentures7. Psychological aspects of tooth loss and needs of aging

baby boomers8. Predictable long-term results of implant-supported

prostheses9. Advantages of implant-supported prostheses

EFFECT OF AN AGING POPULATION

According to the literature, age is related directly to everyindicator of tooth loss.9,10 Therefore the aging population is

an important factor to consider in implant dentistry. WhenAlexander the Great conquered the world, he was only 17 years old; however, life span at that time was only 22 years of age. Since 1910, life expectancy has increasedmore rapidly than in any other time in history. In 1980,30% of the U.S. population was older than 45 years, 21%was older than 50, and 11% was older than 65. In 1995, 15 years later, these individuals were more than 60 years ofage. The over-65 age group is projected to increase to morethan 20% of the population within the next 50 years11

(Fig. 1-1). Life expectancy has increased significantly pastthe age of retirement; in 1965 the average life span was 65 years; in 1990 it was 78 years. Life expectancy in 2001was 85 years for a nonsmoking individual of normalweight.12 A 65-year-old person now can expect to live morethan 20 years; a person 80 years old can expect to live 91/2more years13,14 (Fig. 1-2). One person from a 65-year-oldcouple has a 50% chance of living to 92 years of age and a25% chance of living to 97 years of age. Women representtwo thirds of the population over the age of 65 years.15

A healthy 65-year-old woman has a 50% chance to live to88 years old and a 25% chance to live to 94 years old. For a70-year-old patient to ask “Is it worth it for me to spend$30,000 to repair my mouth at my age?” is not unusual.The response should be positive because the life expectancy ofsuch a person will be more than 2 decades, and the person’scurrent oral situation normally will worsen if not corrected atthis time.

Social pleasures, including dining and dating, continuethroughout advanced life. In the past, geriatric dentistrymeant inexpensive treatment emphasizing nonsurgicalapproaches. Yet the poverty rate for the elderly is less than10%, and retiree median income has grown 8% in recentyears. According to the last census, the median net worth of retirees is 15 times the net worth of those younger than 35 years and 3 times as high as “working families” 35 to 44 years of age.11,15,16 Almost 20% of today’s retirees have anet worth more than a quarter of a million dollars. Today thefull scope of dental services for elderly patients is increasingin importance to the public and the profession because of theincreasing age of society. Treatment alternatives involvingfixed prostheses with implant support should be presented toalmost any patient. Only after discussion of all treatmentoptions can the dentist truly appreciate a person’s desiresrelated to the benefit of implant dentistry.

Rationale for DentalImplants

CHAPTER

1Carl E. Misch

1

AGE-RELATED TOOTH LOSS

Dental services for elderly patients clearly represent a grow-ing demand for the dental profession. In 2000, 28.8% of allincome from a dentist came from patients 60 years andolder, which represented only 12% of dentists’ income in1988. When the dentist is more than 40 years old, incomefrom those patients represents 64.3% of the dentist’sincome, whereas in 1988 it was 30.3%.17 Clearly, the demo-graphics of the population have changed the economics ofdental practice dramatically.

The posterior regions of the mouth often require thereplacement of a single tooth.18-20 The first molars are thefirst permanent teeth to erupt in the mouth and unfortu-nately are often the first teeth lost as a result of decay, failedendodontic therapy, or fracture (usually after endodontics).They are important teeth for maintenance of the arch formand proper occlusal schemes. In addition, the adult patientoften has one or more crowns as a consequence of previouslarger restorations required to repair the integrity of thetooth. Longevity reports of crowns have yielded disparateresults. The mean life span at failure has been reported to be10.3 years. Other reports range from a 3% failure rate at 23 years to a 20% failure rate at 3 years. The primary causeof failure of the crown is caries followed by endodontictherapy.18,21-30 The tooth is at risk for extraction as a resultof these complications, which are a leading cause of singleposterior tooth loss in the adult. One estimate is that a $425crown for a 22-year-old patient will cost $12,000 during thepatient’s lifetime to replace or repair this device.23

D E N TA L I M P L A N T P R O S T H E T I C S2

85

80

75

2001

70

65

60

5519851970

Life expectancy at birthAge

Year

Figure 1-1 Because of the increase in life span over the last 20 years, the population older than 65 years is now approaching20% of the population of the United States. Therefore an invest-ment in the oral health of seniors is more cost-effective than buyinga car, which usually does not last as long.

Mill

ions

ofpe

ople

(U.S

.)

25

75

125

175

225

275

325

4%8.1%

13%21.8%

1900 1950 2000 2050

Total population

Total 65 years andover (% of total)

Figure 1-2 Population older than 65 years as a percentage of U.S. population. Life span of elderly has increased to almost 80 years; 42% of this age group have no teeth. An additional 12 million people have no maxillary teeth opposing some mandibu-lar dentitions. (Redrawn from Misch CE: Contemporary implant den-tistry, ed 2, St Louis, 1999, Mosby.)

SINGLE-TOOTH EDENTULISM

The most common treatment of choice for replacement ofa posterior single tooth is a three-unit fixed partial denture.This type of restoration can be fabricated within 1 to 2 weeks and satisfies the criteria of normal contour, com-fort, function, esthetics, speech, and health. Because ofthese benefits, a fixed partial denture has been the treat-ment of choice for the last 6 decades.29 The bone and softtissue considerations in the missing tooth site are few. Everydentist is familiar with the procedure, which is acceptedwidely by the profession, patients, and dental insurancecompanies.

In the U.S. population, 70% of persons are missing atleast one tooth. Almost 30% of the 50- to 59-year-oldsexamined in a U.S. national survey exhibited single or mul-tiple edentulous spaces bordered by natural teeth. In 1990in the United States, more than 4 million fixed partial den-tures were placed.18-21 Treatments to replace single teethwith a fixed prosthesis represent 7% of the annual dentalreimbursement from insurance companies and more than$3 billion each year. Only one third of the population inthe United States has dental insurance, and many patientswho do have insurance are reimbursed only 50% of treat-ment costs. Hence the entire three- to four-unit fixed par-tial denture costs in the United States may approach morethan $10 billion each year.

A three-unit fixed partial denture also presents sur-vival limitations to the restoration and, more important,to the abutment teeth.27 In an evaluation of 42 reportssince 1970, Creugers, Kayser, and Van’t Hof calculated a74% survival rate for fixed partial dentures for 15 years.26

Rationale for Dental Implants

Walton, Gardner, and Agar28 and Schwartz, Whitsett, andBerry21 have reported mean life spans of 9.6 and 10.3 years,respectively. However, reports are inconsistent, with as littleas 3% loss over 23 years to 20% loss over 3 years.18,20-29

Caries and endodontic failure of the abutment teeth are themost common causes of prosthesis failure.28 Up to 15% ofabutment teeth for a fixed partial denture require endodon-tic therapy, compared with 3% of non–abutment teeth thathave crown preparations. The long-term periodontal healthof the abutment teeth also may be at greater risk, includingbone loss.26

Unfavorable outcomes of fixed partial denture failureinclude not only the need to replace the failed prosthesisbut also the loss of an abutment and the need for additionalpontics and abutment teeth in the replacement bridge. Theabutment teeth of a fixed partial denture may be lost atrates as high as 30% within 14 years.27 Eight percent to 12%of the abutment teeth holding a fixed partial denture arelost within 10 years. The most common reason for single-tooth loss is endodontic failure or fracture of the teeth (usually after endodontic therapy). Because 15% of abut-ment teeth require endodontics and root canal therapy is90% successful at the 8-year mark, many abutment teethare lost. In addition, the abutment teeth are more prone tocaries when splinted together with a pontic. The cariouslesion at the crown margin may render the tooth a struc-tural failure, even if endodontic treatment is possible.

Almost 80% of abutments prepared for a three-unit fixedpartial denture have no restoration or are restored mini-mally. Rather than removing sound tooth structure andcrowning two or more teeth, increasing the risk of decay,endodontic therapy, and splinting together of teeth withpontics, which have the potential to decrease oral hygieneability and increase plaque retention, a dentist may replacethe single tooth with a dental implant (Box 1-1).

SINGLE-TOOTH IMPLANTS

A treatment option to replace a posterior single missing toothis a single-tooth implant. For years, patients were advised toplace their desires aside and accept the limitations of a fixedpartial denture. However, many dentists feel the most naturalmethod to replace a tooth is to use an implant, rather than

preparing adjacent teeth and joining them together with aprosthesis. The primary reasons for suggesting the fixed par-tial denture were its clinical ease and reduced treatment time.However, if this concept were expanded, extractions wouldreplace endodontics and dentures even could replace ortho-dontics. The primary reason to suggest or perform a treatmentshould not be related just to treatment time or difficulty ofperforming the procedure but instead to the best possiblelong-term solution for each individual.

Since 1993, single-tooth implant survival has demon-strated that this procedure is the most predictable methodof tooth replacement. More refereed reports for single-toothimplant replacement occur in the literature than for anyother method of tooth replacement. All reports demon-strate a higher survival rate for single-tooth implants than forany other method of tooth replacement. For example, in1993, Schmitt and Zarb31 reported no failures for 40 implantsplaced in 32 patients (28 in the maxilla, 12 in the mandible,with 27 in the anterior region and 13 in the posterior). Afterup to 6.6 years, all implants were functional. In 1994,Ekfeldt, Carlsson, and Borgeson32 reported a 4- to 7-yearretrospective study of 77 patients who received 93 implants.Two implants were lost, both within the first year of func-tion (2% failure rate, one each anterior and posterior). In1995, Haas et al.33 also reported on 76 single-toothimplants. Their evaluations extended for 6 years, and theyobserved a 2.6% implant loss.

A series of reports in 1991, 1994, and 1996 by Laney andcolleagues reported on a multicenter prospective study con-sisting of 92 patients who received 107 implants with acumulative survival rate of 97.2% at 3 and 5 years.34-36

Plaque and gingival indexes were indicative of soft tissuehealth. In 1996, Malevez et al.37 also presented a retrospec-tive study of 75 patients treated with 84 endosteal screw-type implants (71% of the implants were in the anteriorregion). This study found a cumulative failure rate of only2.4% at 5 years. In 1997, Gomez-Roman et al.38 published a5-year report on 696 endosteal implants in 376 patients.Almost 300 of these were single-tooth implants with a 96%overall survival.

A multicenter prospective clinical study initiated withthe Maestro Dental Implant System from BioHorizons in1996 was reported in 2002.39 The posterior regions of thejaws received a total of 38 single-tooth implants: 15 in themaxilla and 23 in the mandible. The implant survival ratewas 100% over 5 years. Another report by Misch et al.40

yielded 100% success for single-tooth implants in the pos-terior maxilla. Therefore although posterior single-toothreplacement is a relatively new treatment alternative todentistry, many studies have been published since 1990with reported survival rates ranging from a low of 94.6% toa high of 100% for 1 to 10 years. The median of these reportsis a 2.8% implant loss with a mode of 5 years. In compari-son a fixed partial denture failure rate may be as high as 20%within 3 years, and 50% survival at 10 years is expected. Asa result, the single-tooth implant exhibits the highest survival rates presented for single-tooth replacement. As important, no reports indicate a loss of an adjacenttooth, which is a considerable advantage. The longevity ofthe implant crown has not been determined adequately,however, because these reports do not extend as long asthose of other treatment options.

3

Estimated mean life span of fixed partial denture (50% survival) is reported to be 10 years.

Caries most common cause of fixed partial denture failure.Fifteen percent of fixed partial denture abutments require

endodontic treatment.Failure of abutment teeth of fixed partial denture is 8% to

12% at 10 years and 30% at 15 years.Eighty percent of teeth adjacent to missing teeth have

minimal or no restoration.

BOX 1-1

Single-Tooth Replacement: Fixed PartialDenture

Despite some limitations and obvious clinical chal-lenges, the single-tooth implant represents the treatment ofchoice. When adjacent teeth are healthy or when thepatient refuses the preparation for the fabrication of a traditional three-unit fixed partial restoration, a posteriorsingle-tooth implant is an excellent solution. Other advan-tages of this modality over a fixed partial restorationinclude the decreased risk of caries on the abutment teeth,a decrease in risk of endodontics of abutment teeth, theimproved ability to clean the proximal surfaces of the adja-cent teeth (which decreases the risk of decay and periodon-tal disease), a decrease in risk of cold or contact sensitivitywith a brush or scaler on the abutment teeth, improvedesthetics of the adjacent teeth, the maintenance of bone inthe edentulous site, the psychological advantage (especiallywith congenitally missing teeth or the loss of a tooth aftera crown restoration), and the decreased risk of abutmenttooth loss from endodontic failure or caries. These advan-tages are so significant to the health and periodontal con-dition of the adjacent teeth and maintenance of the archform that the single-tooth implant has become the treat-ment of choice in most situations (Box 1-2).

TOTAL EDENTULISM

The present elderly population is benefiting from today’sadvanced knowledge and restorative techniques. In theNational Institute of Dental Research national surveys theoccurrence of total edentulism of a single arch, 35 timesmore frequent in the maxilla, was slight in the 30- to 34-year-old age group but increased at age 45 years to 11% and then began to remain constant after 55 years atabout 15% of the adult population. A total of 12 millionpersons in the United States have edentulism in one arch,representing 7% of the adult population.

Total edentulism occurs in 10.5% of the adult popula-tion or almost 18 million persons. Total edentulism hasbeen noted in 5% of employed adults 40 to 44 years old andgradually increases to 26% at 65 and almost 44% in seniorsmore than 75 years of age.9 As expected, older persons aremore likely to be missing all of their teeth. Gender was notassociated with tooth retention or tooth loss once adjust-ments were made for age (Fig. 1-3).

The percentages of one- or two-arch edentulism translateinto more than 30 million persons or about 17% of theentire U.S. adult population.15 To place these numbers inperspective, 30 million persons represent approximately

the entire U.S. black population or the whole population ofCanada. This number represents 48 million arches. Hencecomplete edentulism remains a significant concern, and theaffected patients often require implant dentistry to solveseveral related problems. If four implants were used to helpsupport each complete edentulous arch, a total of 192 mil-lion implants would be required, yet only 700,000 implantsare inserted each year.

PARTIAL EDENTULISM

The prevalence of partial edentulism is also of interestbecause the number of implants often used in thesepatients is growing. The 1988-1991 survey found that only30% of these patients had all 28 teeth. Partially dentatepatients had an average of 23.5 teeth.9 In the 1987 report ofemployed adults ages 18 to 34, the average number of miss-ing teeth was fewer than two of 28 teeth. However, thisnumber rapidly increases to an average of 10 teeth missingin adults 55 to 64 years old. Partially edentulous seniorsolder than 65 years have lost an average of 17.9 teeth, witholder seniors having lost three more teeth than the youngerseniors. Statistics for partial edentulism are similar for menand women. The greatest transition from an intact dentalarch to a partially edentulous condition occurred in the35- to 54-year-old group.20 The growth rate for this babyboomer portion of the population is approximately 30%,greater than any other age group. Therefore the need forimplant services will increase dramatically during the nextseveral decades.13

The most common missing teeth are molars.19 Partialfree-end edentulism is of particular concern because inthese patients, teeth often are replaced with removable par-tial prostheses. This condition rarely is found in personsyounger than 25 years. Mandibular free-end edentulism is


High success rates (better than 97% for 10 years)Decreased risk of caries of adjacent teethDecreased risk of endodontic problems on adjacent teethImproved hygieneDecreased cold or contact sensitivity of adjacent teethPsychological advantageDecreased abutment tooth loss

BOX 1-2Single-Tooth Implants: Advantages

U.S. Populationcomplete edentulism

Age

45 65 75

44

26

5

Per

cent

18 million people

Figure 1-3 U.S. population completely edentulous rangesfrom 5% after 40 years of age to 44% after 75 years of age. Morethan 18 million persons in the United States have no teeth. Anadditional 12 million people have no maxillary teeth opposing somemandibular dentitions. (Redrawn from Misch CE: Contemporaryimplant dentistry, ed 2, St Louis, 1999, Mosby.)


greater than its maxillary counterpart in all age groups.Unilateral free-end edentulism is more common than bilat-eral edentulism in maxillary and mandibular arches in theyounger age groups (25 to 44 years). About 13.5 million per-sons in these younger age groups have free-end edentulismin either arch.

In 45- to 54-year-old patients 31.3% have mandibularfree-end edentulism and 13.6% have free-end endentulismin the maxillary arch. About 9.9 million persons in the 45-to 54-year-old group have at least one free-end edentulousquadrant, and almost half of these have bilateral partialedentulism.10 The pattern of posterior edentulism evolvesin the 55- to 64-year-old group in which 35% of mandibu-lar arches show free-end edentulism compared with 18% ofmaxillary arches. As a result, about 11 million persons inthis age group are potential candidates for implants. Anadditional 10 million persons show partial free-end eden-tulism at age 65 or older (Fig. 1-4). Additional studies docu-mented that in the population of noninstitutionalized U.S.civilians, one out of five had a removable prosthesis ofsome type.41-43 The total number of potential patients inthe U.S. survey with at least one quadrant of posterior miss-ing teeth is more than 44 million persons.10 If each of thesearches requires three implants to support a fixed prosthesis,132 million implants added to the 192 million for edentu-lous patients would be required.

When the partially edentulous figures are added to theprevious edentulous percentages, almost 30% of the adultsin the United States are candidates for a complete or partialremovable prosthesis. The need for additional retention,support, and stability or the desire to eliminate a removableprosthesis are common indications for dental implants.As a result, 74 million adults and 90 million arches arepotential candidates for dental implants. Because a mini-mum of five appointments is required to implant andrestore a patient, every U.S. dentist would need 20 appoint-ments every month for 20 years to treat the present pos-terior partial and complete edentulous population with

implant-supported prostheses. The population evolution toan increased average age, combined with the existing pop-ulation of partially and completely edentulous patients,guarantees the future of implant dentistry for several gen-erations of dentists.

ANATOMICAL CONSEQUENCES OFEDENTULISM

Consequences on the Bony Structures

Basal bone forms the dental skeletal structure, containsmost of the muscle attachments, and begins to form in thefetus before teeth develop. Alveolar bone first appears whenHertwig’s root sheath of the tooth bud evolves (Fig. 1-5).44

The alveolar bone does not form in the absence of primaryor secondary tooth development. The close relationshipbetween the tooth and the alveolar process continuesthroughout life. Wolff’s law states that bone remodels inrelationship to the forces applied.45 Every time the functionof bone is modified, a definite change occurs in the internalarchitecture and external configuration.46 Bone needs stim-ulation to maintain its form and density. Roberts et al.47

report that a 4% strain to the skeletal system maintainsbone and helps balance the resorption and formation phe-nomena. Teeth transmit compressive and tensile forces tothe surrounding bone. These forces have been measured asa piezoelectric effect in the imperfect crystals of durapatitethat compose the inorganic portion of bone.48 When atooth is lost, the lack of stimulation to the residual bonecauses a decrease in trabeculae and bone density in the area,with loss in external width and then height of the bone vol-ume.49 The width of bone decreases by 25% during the firstyear after tooth loss and an overall 4 mm in height duringthis first year following extractions for an immediate den-ture.50 In a longitudinal, 25-year study of edentulouspatients, lateral cephalograms demonstrated continuedbone loss during this time span; a fourfold greater loss was

5

Max unilat Mand bilat Mand unilat

Partial free-end edentulism

5

10

15

20

25

30

0 25-34(4M)

35-44(9.5M)

45-54(9.9M)

55-64(11M)

65-74+(10M)

Age(population in millions)

44 million people

Max bilat

Per

cent

Figure 1-4 Involvement of mandibular arch (Mand ) andmaxillary arch (Max) in cases of posterior edentulism in U.S. pop-ulation by age group. This common condition can be treated with implants and fixed prostheses. (Redrawn from Misch CE:Contemporary implant dentistry, ed 2, St Louis, 1999, Mosby.)

Figure 1-5 The alveolar bone forms as a result of the toothroot formation. When no tooth bud is present, the alveolar processdoes not form (i.e., ectodermal dysplasia and partial or completeanodontia).

observed in the mandible (Figs. 1-6 and 1-7).51 However,because the mandible begins with twice the bone height ofthe maxilla, maxillary bone loss is also significant in thelong-term edentulous patient.

A tooth is necessary for the development of alveolarbone, and stimulation of this bone is required to maintainits density and volume. A removable denture (complete orpartial) does not stimulate and maintain bone; it acceleratesthe bone loss. The load from mastication is transferred tothe bone surface only, not the whole bone. As a result, bloodsupply is reduced, and total bone volume loss occurs.52 Thisissue, of utmost importance, has been observed but notaddressed in the past by traditional dentistry. Doctors mostoften overlook the insidious bone loss that occurs aftertooth extraction. The patient often is not educated aboutthe anatomical changes and the potential consequences ofcontinued bone loss. The bone loss further accelerateswhen the patient wears a poorly fitting soft tissue–borneprosthesis. Yet patients do not understand that bone is lostover time and at a greater rate under poorly fitting den-tures. Patients do not return for regular visits for evaluationof their condition, but only after several years when den-ture teeth are worn down or can no longer be tolerated.

Hence the traditional method of tooth replacement oftenaffects bone loss in a manner not sufficiently considered bythe doctor and the patient.

Preventive dentistry traditionally has emphasized meth-ods to decrease tooth loss. No predictable therapy wasaccepted by the profession to avoid the bone changesresulting from tooth loss. Today the profession must con-sider not only the loss of teeth but also the loss of bone. Theloss of teeth causes remodeling and resorption of the sur-rounding alveolar bone and eventually leads to atrophicedentulous ridges. Although the patient is often not awareof or informed of the potential consequences, over timeconsequences will occur. The rate and amount of bone lossmay be influenced by sex, hormones, metabolism, para-function, and ill-fitting dentures. Yet almost 40% of den-ture wearers have been wearing an ill-fitting prosthesis formore than 10 years.53 Patients wearing dentures day andnight place greater forces on the hard and soft tissues,which accelerate bone loss. Yet 80% of dentures are wornday and night.54

Atrophic edentulous ridges are associated with anatomicalproblems that often impair the predictable results of tradi-tional dental therapy. Box 1-3 lists several of these anatomicalproblems. The loss of bone first causes decreased bonewidth. The remaining narrow residual ridge often causesdiscomfort when the thin overlying tissues are loadedunder a soft tissue–borne removable prosthesis. The contin-ued atrophy of the posterior mandible eventually causesprominent mylohyoid and internal oblique ridges coveredby thin, movable, unattached mucosa. The anterior residual


4 mm average boneloss in 1 year

Figure 1-6 After the initial loss of teeth the average first-yearbone loss is more than 4 mm in height and 30% in width.

Continuous lossfor 25 years

Figure 1-7 Although the rate is slower, bone loss from toothextraction continues throughout life.

Decreased width of supporting boneDecreased height of supporting boneProminent mylohyoid and internal oblique ridges with

increased sore spotsProgressive decrease in keratinized mucosa surfaceProminent superior genial tubercles, sore spots, and

increased denture movementMuscle attachment near crest of ridgeElevation of prosthesis with contraction of mylohyoid and

buccinator muscles serving as posterior supportForward movement of prosthesis from anatomical

inclination (angulation of mandible with moderate toadvanced bone loss)

Thinning of mucosa, with sensitivity to abrasionLoss of basal boneParesthesia from dehiscent mandibular neurovascular

canalMore active role of tongue in masticationEffect of bone loss on esthetic appearance of lower one

third of faceIncreased risk of mandibular body fracture from advanced

bone lossIncreased denture movement and sore spots during

function caused by loss of anterior ridge and nasal spine

BOX 1-3Consequences of Bone Loss in FullyEdentulous Patients

Figure 1-8 Bone loss in the jaws does not stop with the orig-inal alveolar process but continues to include the basal bone. Thisbone loss is more dramatic than any osteoporotic bone lossobserved in the hip or any other part of the skeleton.


alveolar process also continues to resorb, and the superiorgenial tubercles (which are 2 cm below the crest of bonewhen teeth are present) eventually become the most supe-rior aspect of the anterior mandibular ridge. Little preventsthe prosthesis from moving forward against the lower lipduring function or speech. This condition is compromisedfurther by the vertical movement of the distal aspect of theprosthesis during contraction of the mylohyoid and bucci-nator muscles and the anterior incline of the atrophicmandible compared with that of the maxilla.55

Loss of bone in the maxilla or mandible is not limited toalveolar bone; portions of the basal bone may be resorbedalso (Figs. 1-8 to 1-10), especially in the posterior aspect ofthe mandible where severe resorption may result in morethan 80% bone loss.52 The contents of the mandibularcanal and mental foramen eventually become dehiscentand serve as part of the support area of the prosthesis.56 Asa result, acute pain and transient to permanent paresthesiaof the areas supplied by the mandibular nerve are possible.The body of the mandible is also at increased risk of

7

Sutura coronalis(ossificata)

Processusstyloideus

Linea obliqua

Mandibula (corpus)

Maxilla (processus alveoli atroph)

BA

Figure 1-10 A, Lateral cephalogram of a patient demonstrates the restored verticaldimension of occlusion with a denture. However, because of the advanced basal bone loss in themandible, the superior genial tubercles are twice the height of the residual anterior ridge. Thebody of the mandible is only a few millimeters thick, and the mandibular canal has been com-pletely dehiscent for many years (one body is superimposed on top of the other in this view). Inthe maxillary anterior ridge, only the nasal spine remains (not the original alveolar ridge), and theposterior maxillary bone is paper thin because of basal bone loss at the crest and the pneuma-tization of the maxillary sinus. B, A denture may restore the vertical dimension of the face, butthe bone loss of the jaws can continue until the basal bone is paper thin in the maxilla and themandible becomes the size of a toothpick. (This is a different patient from the one in A.)

Figure 1-9 Atwood described six different stages of resorp-tion in the anterior mandible. Stage I represents the tooth andsurrounding alveolar process and basal bone. Stages II and III illus-trate the initial residual ridge after tooth loss. Stages IV to VIprimarily describe a continuous loss of anterior residual bonein height.


fracture, even under low-impact forces (Fig. 1-11). Themandibular fracture causes the jaw to shift to one side andmakes stabilization and an esthetic result most difficult.

The complete anterior ridge and even the nasal spinemay be resorbed in the maxilla, causing pain and anincrease in maxillary denture movement during function53

(Fig. 1-12). Masticatory forces generated by short facialtypes (brachiocephalics) can be 3 or 4 times that of longfacial types (dolichocephalics). The short facial type ofpatients are at increased risk to develop severe atrophy (Box 1-3).57,58

Many of these similar conditions exist in the partiallyedentulous patient wearing a removable soft tissue–borneprosthesis. In addition, the natural abutment teeth, onwhich direct and indirect retainers are designed, must sub-mit to additional lateral forces. Because these teeth oftenare compromised by deficient periodontal support, manypartial dentures are designed to minimize the forces appliedto them. The net result is an increase in mobility of theremovable prosthesis and greater soft tissue support. Theseconditions protect the remaining teeth but accelerate thebone loss in the edentulous regions (Figs. 1-13 and 1-14).59

Figure 1-11 Resorption of an edentulous mandible may result in dehiscence of themandibular canal and associated paresthesia. The patient may fear that a tumor is growingagainst the nerves. The body of the mandible may continue to resorb until minor trauma causesfracture (i.e., during mastication, the bump of a baby’s head held closely to the face, or an acci-dental bump from the elbow).

Figure 1-12 Panoramic radiograph of a 68-year-old female. The maxillary arch has severeatrophy and almost complete basal bone loss, including most of the nasal spine. Implants wereinserted in the anterior mandible 15 years before this film. The anterior bone has been maintained.The posterior mandible has continued to resorb, and the mandibular canal is dehiscent on one side.


Soft Tissue Consequences

As bone loses width, then height, then width, and thenheight again, the attached gingiva gradually decreases. Athin attached tissue usually lies over the advanced atrophicmandible or is absent entirely. The gingiva is prone to abra-sions caused by the overlaying prosthesis. In addition, unfa-vorable high muscle attachments and hypermobile tissueoften complicate the situation. The thickness of the mucosaon the atrophic ridge also is related to the presence of sys-temic disease and physiologic changes accompanyingaging. Conditions such as hypertension, diabetes, anemia,

and nutritional disorders have a deleterious effect on thevascular supply and soft tissue quality under removableprostheses. These disorders result in a decreased oxygentension to the basal cells of the epithelium. Surface cell lossoccurs at the same rate, but the cell formation at the basallayer is slowed. As a result, thickness of the surface tissuesgradually decreases. Therefore sore spots and uncomfort-able removable prostheses result (Fig. 1-15).

The tongue of the patient with edentulous ridges oftenenlarges to accommodate the increase in space formerlyoccupied by teeth. At the same time, the tongue is used tolimit the movements of the removable prostheses and takesa more active role in the mastication process. As a result,the removable prosthesis decreases in stability. The decrease

9

Figure 1-13 Panoramic radiograph demonstrates that more bone is maintained belowthe anterior periodontal diseased teeth compared with the basal bone loss and severe atrophyof the posterior edentulous segment. Wearing of a mandibular Class I removable partial denturehas escalated the posterior bone loss.

Figure 1-14 Loss of bone height in a mandible may be measured in inches and often is ignored. Such bone loss is oftenmore significant than the bone loss (in millimeters) from peri-odontal disease. The patient should understand that a dentureoften replaces more bone than teeth to restore the proper dimen-sions of the face.

Figure 1-15 Patient with severe mandibular atrophy, show-ing the surrounding muscles above the residual ridge, includingthe floor of the mouth, tongue, and buccinator and mentalis muscles.

in neuromuscular control, often associated with aging, fur-ther compounds the problems of traditional removableprosthodontics. The ability to wear a denture successfullymay be largely a learned, skilled performance. The agedpatient who recently became edentulous may lack themotor skills needed to accommodate to the new conditions(Box 1-4).

Esthetic Consequences

The facial changes that naturally occur in relation to theaging process can be accelerated and potentiated by the lossof teeth. Several esthetic consequences result from the loss ofalveolar bone (Figs. 1-16 and 1-17). A decrease in facial heightfrom a collapsed vertical dimension causes several facialchanges. The loss of labiomental angle and deepening ofvertical lines in the area create a harsher appearance. As thevertical dimension progressively decreases, the occlusionevolves toward a pseudo–Class III malocclusion. As a result,the chin rotates forward and creates a prognathic facialappearance (Fig. 1-18). These conditions result in a decreasein the horizontal labial angle at the corner of the lips; thepatient appears unhappy when the mouth is at rest. Shortfacial types suffer higher bite forces, greater bone loss, andmore dramatic facial changes with edentulism comparedwith others.

A thinning of the vermillion border of the lips resultsfrom the poor lip support provided by the prosthesis andthe loss of muscle tone; the retruded position of the borderis related to the loss of premaxilla ridge and the loss oftonicity of the muscles involved in facial expression.Women often use one of two techniques to hide this cos-metically undesirable appearance: no lipstick and mini-mum makeup to bring as little attention as possible to thisarea of the face or lipstick drawn on the skin over the ver-milion border to give the appearance of fuller lips. A deep-ening of the nasolabial groove and an increase in the depthof other vertical lines in the upper lip are related to normalaging but are accelerated with bone loss. An increase in thecolumella-philtrum angle usually accompanies these changes,which can make the nose appear larger than if the lip hadmore support. Men often grow a moustache to minimize thiseffect. The maxillary lip naturally becomes longer with age asa result of gravity and loss of muscle tone, resulting in lessanterior teeth shown when the lip is at rest. This changehas a tendency to “age” the smile, because the younger the

patient, the more the teeth show in relation to the upper lipat rest or when smiling. The loss of muscle tone is acceler-ated in the edentulous patient, hence the lengthening ofthe lip occurs at a younger age.

The attachments of the mentalis and buccinator musclesto the body and symphysis of the mandible also are affected


Figure 1-16 Esthetics of the inferior third of the face notonly are related to the teeth position but also include the bone andthe muscles that attach to the bone.

Collapseof

edentulousbite

Figure 1-17 A patient often wears a denture for more than15 years. The loss of bone height during this time is associatedwith many extraoral facial changes. The loss of vertical dimensionresults in many changes including closed bite, mandible thatrotates forward, a receding maxilla, reverse smile line, increasednumber and depth of lines in the face, more acute angle betweenthe nose and the face, loss of vermillion border in the lips, jowls,and witch’s chin from loss of muscle attachment.

Attached, keratinized gingiva is lost as bone is lost.Unattached mucosa for denture support causes increased

soft spots.Thickness of tissue decreases with age, and systemic dis-

ease causes more sore spots for dentures.Tongue increases in size, which decreases denture stability.Tongue is more active in mastication, which decreases

denture stability.Neuromuscular control of jaw decreases in the elderly.

BOX 1-4Soft Tissue Consequences of Edentulism


by bone atrophy. The tissue sags, producing “jowls” or a“witch’s chin.” This effect is cumulative because of the lossin muscle tone with the loss of teeth, the associateddecrease in bite force, and the loss of bone in the regionswhere the muscles formerly attached (Fig. 1-19).

Patients are unaware that these hard and soft tissuechanges are from the loss of teeth. Regarding denture wear-ers, 39% have been wearing the same prosthesis for morethan 10 years.52 Dentists are unable to evaluate patientsunless they return for regular yearly visits. Therefore thedentist must explain the consequences of tooth loss to thepartially or completely edentulous patient in the earlyphases of treatment (Box 1-5).

DECREASED PERFORMANCE OFREMOVABLE PROSTHESES

The difference in maximum occlusal forces recorded in aperson with natural teeth and one who is completely eden-tulous is dramatic. In the first molar region of a dentate person, the average force has been measured at 150 to 250 psi.60 A patient who grinds or clenches the teeth mayexert a force that approaches 1000 psi. The maximumocclusal force in the edentulous patient is reduced to lessthan 50 psi. The longer patients are edentulous, the lessforce they are able to generate. Patients wearing completedentures for more than 15 years may have a maximumocclusal force of 5.6 psi.61

As a result of decreased occlusal force and the instabilityof the denture, masticatory efficiency also decreases withtooth loss. Within the same time frame, 90% of the foodchewed with natural teeth fits through a No. 12 sieve; thepercentage is 58% in the patient wearing complete den-tures.62 The tenfold decrease in force and the 40% decreasein efficiency affect the patient’s ability to chew. In personswith dentures, 29% are able to eat only soft or mashedfoods,63 and 50% avoid many foods; 17% claim they eatmore efficiently without the prosthesis.64 A study of 367denture wearers (158 men and 209 women) found that 47%exhibited a low masticatory performance.64 Lower intakesof fruits, vegetables, and vitamin A by women were notedin this group. These patients took significantly more drugs

11

Figure 1-18 Loss of bone height can lead to a closed bitewith rotation of the chin anterior to the tip of the nose.

Figure 1-19 This patient has severe bone loss in the maxillaand mandible. Although she is wearing her 15-year-old dentures,the facial changes are significant. The loss of muscle attachmentslead to ptosis of the chin (witch’s chin), loss of vermillion border(lipstick is applied to the skin), and reverse lip line (decrease in hor-izontal angles, increased vertical lines in the face and lips,increased lip angle under the nose, and a lack of body in the mas-seter and buccinator muscles).

Decreased facial heightLoss of labiomental angleDeepening of vertical lines in lip and faceRotation of chin forward, giving a prognathic appearanceDecreased horizontal labial angle of lip, making patient

look unhappyLoss of tone in muscles of facial expressionThinning of vermillion border of the lips from loss of mus-

cle toneDeepening of nasolabial grooveIncrease in columella-philtrum angleIncreased length of maxillary lip so that fewer teeth show

at rest and smiling, which ages the smilePtosis of buccinator muscle attachment, which leads to

jowls at side of facePtosis of mentalis muscle attachment, which leads to

witch’s chin

BOX 1-5Esthetic Consequences of Bone Loss

(37%) compared with those with superior masticatory abil-ity (20%); 28% were taking medications for gastrointestinaldisorders.

The reduced consumption of high-fiber foods thereforecould induce gastrointestinal problems in edentulouspatients with deficient masticatory performance. In addi-tion, the coarser bolus may impair proper digestive andnutrient extraction functions.65-67 The literature providesseveral reports suggesting that a compromised dental func-tion causes poor swallowing and mastication performance,which in turn may favor systemic changes favoring illness,debilitation, and shortened life expectancy (Box 1-6).68,69

Several reports in the literature correlate patients’ healthand life spans with their dental health.70-73 After conven-tional risk factors for strokes and heart attacks wereaccounted for, a significant relationship was found betweendental disease and cardiovascular disease, the latter stillbeing the major cause of death.65-67,72,74 One may assumelogically that restoring the stomatognathic system of thesepatients to a more normal function may indeed enhancethe quality and length of their lives.75-78

CONSEQUENCES OF REMOVABLEPARTIAL DENTURES

Removable soft tissue–borne partial dentures have one ofthe lowest patient acceptance rates in dentistry. One halfthe number of persons with a removable partial denturechew better without the device. A Scandinavian 4-yearstudy revealed that only 80% of patients were wearing suchprostheses after 1 year. The number further decreased toonly 60% of the free-end partial dentures worn by thepatients after 4 years.79,80

A 5-year survival rate of partial dentures based on toler-ance and use of the prosthesis was about 60% for distalextension prostheses and 80% for tooth-borne prosthe-ses.81-83 The survival rates were reduced to 35% and 60% at 10 years, respectively. In another study, few partial den-tures survived more than 6 years.84 Although one of fiveU.S. adults has had a removable prosthesis of some type,60% reported at least one problem with the prosthesis.42

Reports of removable partial dentures indicate that thehealth of the remaining dentition and surrounding oraltissues often deteriorates (Box 1-7).70,79,85

In a study that evaluated the need for repair of an abut-ment tooth as the indicator of failure, the survival rate ofconventional removable partial dentures was 40% at 5 yearsand 20% at 10 years.81 Those patients wearing the partial

dentures often exhibit greater mobility of the abutmentteeth, greater plaque retention, increased bleeding on prob-ing, more incidence of caries, and accelerated bone loss inthe edentulous regions.82 Aquilino et al.86 reported a 44%abutment tooth loss within 10 years in patients wearing aremovable partial denture. In addition, those patients wearingthe device have accelerated bone loss in the soft tissue sup-port regions. Therefore alternative therapies that improveoral conditions and maintain bone often are warranted.

PSYCHOLOGICAL ASPECTS OF TOOTH LOSS

The psychological effects of total edentulism are complexand varied and range from minimal to a state of neu-roticism. Although complete dentures are able to satisfy theesthetic needs of many patients, some patients feel theirsocial life is affected significantly. They are concerned withkissing and romantic situations, especially if a new friend isunaware of their oral handicap. Past dental health surveysindicate that only 80% of the edentulous population is ableto wear both removable prostheses all of the time.19,20

Some patients wear only one prosthesis, usually the maxil-lary; others are able to wear their dentures for short periodsonly. In addition, approximately 7% of patients are not ableto wear their dentures at all and become dental cripples or“oral invalids.” They rarely leave their home environment,and when they feel forced to venture out, the thought ofmeeting and talking to persons when not wearing theirteeth is unsettling.

Misch and Misch64 reported on 104 completely edentu-lous patients seeking treatment. Of the patients studied,88% claimed difficulty with speech, with one fourth havingdifficult problems. As a consequence, the reported increasecan be correlated easily with concern relative to social activ-ities. Awareness of movement of the mandibular denturewas listed by 62.5% of these patients, although the maxil-lary prosthesis stayed in place most of the time at almostthe same percentage. Mandibular discomfort was listed withequal frequency as movement and was 63.5%; surprisingly16.5% of the patients stated they never wear the denture. Incomparison, the maxillary denture was uncomfortable half asoften (32.6%), and only 0.9% of persons were seldom able towear the denture. Function was the fourth most commonproblem reported. Half of the patients avoided many foods,


• Bite force decreased from 200 psi to 50 psi• Bite force of 15-year denture wearers reduced to 6 psi• Masticatory efficiency decreased• Increased drug use for gastrointestinal disorders• Possible decrease in life span

BOX 1-6Decreased Performance of RemovableProstheses

• Survival rate 60% at 4 years• Survival rate 35% at 10 years• Repair of abutment teeth 60% at 5 years and 80% at

10 years• Increased mobility, plaque, bleeding on probing, and

caries of abutment teeth• Abutment tooth loss of 44% within 10 years• Accelerated bone loss in edentulous region if one wears

a removable partial denture

BOX 1-7Consequences of Removable Partial Dentures


and 17% claimed they were able to masticate more effec-tively without the prostheses. The psychological effects ofthe inability to eat in public can be correlated with thesefindings. Other reports show that the major motivating factors for patients to undergo treatment were related to thedifficulties with eating, denture fit, and discomfort.

The psychological need of the edentulous patient isexpressed in many forms. For example, in 1970, Britonsused about 88 tons of denture adhesive.87 In 1982 morethan 5 million Americans used denture adhesives,88 and areport shows that in the United States more than $200 mil-lion was spent each year on denture adhesives, representing55 million units sold.89 The patient is willing to accept theunpleasant taste, need for recurrent application, inconsis-tent denture fit, embarrassing circumstances, and contin-ued expense for the sole benefit of increased retention ofthe prosthesis. Clearly the lack of retention and psycholog-ical risk of embarrassment in the denture wearer withremovable prostheses are concerns the dental professionmust address.

In contrast, 80% of the patients treated with implant-supported prostheses judged their overall psychologicalhealth improved compared with their previous state ofwearing traditional, removable prosthodontic devices andperceived the implant-supported prosthesis as an integralpart of their body (Box 1-8).90-92

ADVANTAGES OF IMPLANT-SUPPORTED PROSTHESES

The use of dental implants to provide support for prosthe-ses offers a multitude of advantages compared with the useof removable soft tissue–borne restorations. A primary rea-son to consider dental implants to replace missing teeth isthe maintenance of alveolar bone. The dental implantplaced into the bone serves not only as an anchor for theprosthetic device but also as one of the better preventivemaintenance procedures in dentistry. Stress and strain maybe applied to the bone surrounding the implant. As a result,the decrease in trabeculation of bone that occurs after toothextraction is reversed. Bone trabeculae and density increasewhen the dental implant is inserted and functioning. Theoverall volume of bone also is maintained with a dentalimplant. Hence even grafts of iliac bone to the jaws, whichusually resorb within 5 years, are instead stimulated andmaintain overall volume and integration to support the

implant. An endosteal implant can maintain bone widthand height as long as the implant remains healthy.93 As witha tooth, periimplant bone loss may be measured in tenthsof a millimeter and may represent more than a twentyfolddecrease in lost structure compared with the resorption thatoccurs with removable prostheses.

A mandibular denture often moves when the mylohyoidand buccinator muscles contract during speech or mastica-tion. The teeth often are positioned for denture stabilityrather than where natural teeth usually reside. With implants,the teeth may be positioned to enhance esthetics and pho-netics rather than in the neutral zones dictated by traditionaldenture techniques to improve the stability of a prosthesis.

The features of the inferior third of the face are relatedclosely to the supporting skeleton. When vertical bone islost, the dentures only act as “oral wigs” to improve thecontours of the face. The dentures become bulkier as thebone resorbs, making it more difficult to control function,stability, and retention. With implant-supported prosthesesthe vertical dimension may be restored, similar to that withnatural teeth. In addition, the implant-supported prosthesisallows a cantilever of anterior teeth for ideal soft tissue andlip contour and improved appearance in all facial planes.This happens without the instability that usually occurswhen an anterior cantilever is incorporated in a traditionaldenture. The facial profile may be enhanced for the longterm with implants rather than deteriorating over the years,as can occur with traditional dentures.

Occlusion is difficult to establish and stabilize with acompletely soft tissue–supported prosthesis. Because themandibular prosthesis may move as much as 10 mm ormore during function,94,95 proper occlusal contacts occurby chance, not by design. But an implant-supportedrestoration is stable. The patient can return more consis-tently to centric-relation occlusion rather than adopt vari-able positions dictated by the instability of the prosthesis.Proprioception is awareness of a structure in time and place.The receptors in the periodontal membrane of the naturaltooth help determine its occlusal position. Althoughendosteal implants do not have a periodontal membrane,they provide greater occlusal awareness than complete den-tures. Although patients with natural teeth can perceive adifference of 20 mm between the teeth, implant patientscan determine 50-mm differences with rigid implantbridges compared with 100 mm in those with completedentures (either one or two).96

As a result of improved occlusal awareness the patientfunctions in a more consistent range of occlusion. With animplant-supported prosthesis, the restoring dentist controlsthe direction of the occlusal loads. Horizontal forces onremovable prostheses accelerate bone loss, decrease pros-thesis stability, and increase soft tissue abrasions. Thereforethe decrease in horizontal forces applied to implant restora-tions improves the local parameters and helps preserve theunderlying soft and hard tissues.

The success rate of implant prostheses varies, dependingon a host of factors that change for each patient. However,compared with traditional methods of tooth replacement,the implant prosthesis offers increased longevity, improvedfunction, bone preservation, and better psychologicalresults. According to 10-year survival surveys of fixed pros-theses on natural teeth, decay is indicated as the most fre-quent reason for replacement; survival rates are about 75%.

13

• Psychological effects range from minimal to neuroticism.• Tooth loss affects romantic situations (especially in new

relationship).• “Oral invalids” are unable to wear dentures.• Eighty-eight percent of patients claim some difficulty

with speech, and 25% have significant problems.• Patients spend more than $200 million each year on

denture adhesive to decrease embarrassment.

BOX 1-8Psychological Effects of Tooth Loss

In the partially edentulous patient, independent toothreplacement with implants may preserve intact adjacentnatural teeth as abutments, further limiting complicationssuch as decay or porcelain fracture and poorer esthetics,which are the most common causes of fixed prosthesisfailure.28 A major advantage of the implant-supported pros-thesis is that the abutments cannot decay. The implant andrelated prosthesis can attain a 10-year survival of greaterthan 90%.

The maximal occlusal force of a traditional denturewearer ranges from 5 to 50 psi. Patients with an implant-supported fixed prosthesis may increase their maximal biteforce by 85% within 2 months after completion of treat-ment. After 3 years the mean force may reach greater than300% compared with pretreatment values. As a result animplant prosthesis wearer may demonstrate a force similarto that of a patient with a fixed restoration supported bynatural teeth. Chewing efficiency with an implant prosthe-sis is improved greatly compared with that of a soft tissue–borne restoration. Rissin et al.62 evaluated the masti-catory performance of dentures, overdentures, and naturaldentition. The traditional denture showed a 30% decreasein chewing efficiency; other reports indicate that a denturewearer has less than 60% of the function of persons withnatural teeth. The supported overdenture loses only 10% ofchewing efficiency compared with natural teeth. Thesefindings are similar with implant-supported overdentures.In addition, rigid, implant-supported fixed bridges mayfunction the same as natural teeth.63 Beneficial effects suchas a decrease in fat, cholesterol, and the carbohydrate foodgroups intake have been reported, as well as considerableimprovement in eating enjoyment and social life.97-105

The stability and retention of an implant-supported pros-thesis are great improvements over soft tissue–borne dentures.Mechanical means of implant retention are far superior tothe soft tissue retention provided by dentures or adhesivesand cause fewer associated problems. The implant supportof the final prosthesis varies, depending on the number andposition of implants; yet all treatment options demonstratesignificant improvement (Figs. 1-20 and 1-21).

Phonetics may be impaired by the instability of a con-ventional denture. The buccinator and mylohyoid musclesmay flex and propel the posterior portion of the dentureupward, causing clicking, regardless of the vertical dimen-sion.95 As a result, a patient in whom the vertical dimensionalready has collapsed 10 to 20 mm still may produce click-ing sounds during speech. Often the tongue of the denturewearer is flattened in the posterior areas to hold the denturein position. The anterior mandibular muscles of facial expres-sion may be tightened to prevent the mandibular prosthesisfrom sliding forward. The implant prosthesis is stable andretentive and does not require these oral manipulations. The implant restoration allows reduced flanges and palatesof the prostheses, which are of special benefit to the newdenture wearer, who often reports discomfort with the bulkof the restoration. The extended soft tissue coverage alsoaffects the taste of food, and the soft tissue may be tender inthe extended regions. The palate of a maxillary prosthesismay cause gagging in some patients, which can be elimi-nated in an implant-supported overdenture (Box 1-9).


Figure 1-20 Implant prostheses can maintain bone andreduce the bulk of the soft tissue–borne prostheses.

Figure 1-21 Most denture wearers eventually should have a complete implant-supportedrestoration.


S U M M A R Y

The goal of modern dentistry is to return patients to oralhealth in a predictable fashion. The partial and completeedentulous patient may be unable to recover normal func-tion, esthetics, comfort, or speech with a traditional remov-able prosthesis.

The patient’s function when wearing a denture may bereduced to 60% compared with that formerly experiencedwith natural dentition; however, an implant prosthesis mayreturn the function to near normal limits. The esthetics ofthe edentulous patient also are affected because of boneatrophy. Continued resorption leads to irreversible facialchanges. An implant stimulates the bone and maintains itsdimension in a manner similar to healthy natural teeth. Asa result, the facial features are not compromised by lack ofsupport. In addition, implant-supported restorations arepositioned in relation to esthetics, function, and speech,not in neutral zones of soft tissue support. The soft tissuesof the edentulous patient are tender from the effects ofthinning mucosa, decreased salivary flow, and unstable orunretentive prostheses. The implant-retained restoration doesnot require soft tissue support and improves oral comfort.Speech and function are compromised with prostheses fromthe supporting structures during use. The tongue and perioralmusculature may be compromised to limit the movement ofthe mandibular prosthesis. The implant prosthesis is stableand retentive without the efforts of the musculature.

Implant prostheses often offer a more predictable treat-ment course than traditional restorations. Thus the professionand the public are becoming increasingly aware of this dentaldiscipline. Manufacturers’ sales have increased from a fewmillion dollars to more than several hundred million dollars.Almost every professional journal and lay publication now

carries advertisements for implants. Implant dentistry finallyhas been accepted by organized dentistry. All U.S. dentalschools now teach some awareness of implant dentistry. Thecurrent trend to expand the use of implant dentistry will con-tinue until every restorative practice uses this modality forabutment support of fixed and removable prostheses.106

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15

• Bone maintenance• Restoration and maintenance of occlusal vertical

dimension• Maintenance of facial esthetics (muscle tone)• Esthetic improvement (teeth positioned for appearance

versus decreasing denture movement)• Improved phonetics• Improved occlusion• Improvement or allowance for regaining of oral

proprioception (occlusal awareness)• Increased prosthesis success• Improved masticatory performance and maintenance of

muscles of mastication and facial expression• Reduced size of prostheses (eliminate palate and flanges)• Provision for fixed versus removable prostheses• Improved stability and retention of removable

prostheses• Increased survival times of prostheses• Elimination of need to alter adjacent teeth• More permanent replacement• Improved psychological health

BOX 1-9Advantages of Implant-Supported Prostheses

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