Cha

impl

Dae-Ho Nam, D

Presented at the European Associati

aResident, Department of PeriodontbAssistant Professor, Department ofcAssistant Professor, Department ofdProfessor, Department of OrthodoneProfessor, Department of Oral andfProfessor, Department of Periodont

The Journal of Prosthetic

nge in masticatory ability with the

ant restoration of second molars

DS,a Dong-Won Lee, DDS, PhD,b

Chooryung J. Chung, DDS, PhD,c Kyung-Ho Kim, DDS, PhD,d

Kwang-Ho Park, DDS,e and Ik-Sang Moon, DDS, PhDf

Gangnam Severance Dental Hospital, College of Dentistry, YonseiUniversity, Seoul, Korea

Statement of problem. Controversy exists as to whether missing second molars should be replaced to restore masticatoryability.

Purpose. The purpose of this study was to analyze the alteration in masticatory ability associated with the implant restorationof the second molar; the subjective effect of implant treatment on the participant was also assessed.

Material and methods. Twenty-one individuals (13 men and 8 women) participated. Masticatory ability was recorded beforethe cementation of implant-supported single crowns, immediately after cementation, and 1 month after cementation. Theocclusal load (Pa), the load-bearing contact area (mm2), and the maximum occlusal force (N) were calculated. A subjectiveevaluation of masticatory ability was conducted before treatment and 1 month after treatment through the use of aquestionnaire to evaluate chewing difficulties and global satisfaction with treatment. The Wilcoxon signed rank test was usedto analyze the difference in scores.

Results. The load-bearing contact area, maximum occlusal force, and participant satisfaction were found to increasesignificantly 1 month after the cementation of implant-supported single crowns. The restoration of the second molarwith an implant increased both objective masticatory ability and subjective satisfaction 1 month after cementation of theimplant-supported single crowns.

Conclusions. Patients presenting with a missing second molar may benefit from replacement with implant-supported crowns.Longer study periods and larger sample populations are needed to obtain more definitive results. (J Prosthet Dent 2014;111:286-292)

Clinical Implications

Implant-supported restorations can be considered as an appropriateoption for patients with missing second molars and will improvemasticatory ability and patient satisfaction.

Many studies have found that theprevalence of tooth loss increases withage1-4 and that molars are lost morefrequently than other teeth. In partic-ular, the second molar is one of themost frequently lost teeth. A partial

on for Os

ology.PeriodontOrthodontics.Maxillofacology.

Dentis

fixed dental prosthesis is not the idealtreatment for missing second molars,as cantilevered restorations have beenfound to produce unfavorable biome-chanics5; additionally, a partial re-movable dental prosthesis may prove

seointegration annual meeting, Athens, Greece,

ology.tics.

ial Surgery.

try

uncomfortable to the patient in termsof both function and wear.6 Conse-quently, the use of implant-supportedsingle crowns (ISSCs) for secondmolar replacement seems to be a pref-erable treatment. The procedure for

October 2011.

Nam et al

Table I. Age and sex distribution of participants

Sex

Age (y)

Total30 to 39 40 to 49 50 to 59 60 to 69 70 to 79

Male 1 6 5 0 1 13

Female 0 2 2 1 3 8

Total 1 8 7 1 4 21

Table II. Distribution of implant site

Implant SiteMaxillaryRight

MaxillaryLeft

MandibularLeft

MandibularRight Total

No. of participants 4 4 8 5 21

April 2014 287

replacing individual missing teeth withdental implants has high success ratesand does not require preparation of theadjacent natural dentition.7 However,most studies8 of ISSCs have concen-trated on implant survival rates andbiologic and technical complications,and information about the effects oftreatment with ISSCs on oral functionand daily life is limited. The few studies9

that have focused on oral functiondiscuss either occlusal force or mastica-tory performance. They determined thatmasticatory functional improvementmight be expected on a subjective level.

Based on implant survival rate, theplacement of single-tooth implants inthe second molar region was found tobe an effective and reliable treatment.10

However, controversy exists as towhether missing second molars shouldbe replaced. Patients with missing sec-ond molars are sometimes not treatedwith implants because of anatomicpositional limits, such as the maxillarysinus11 and the inferior alveolar nerve.12

Financial issues and questionable mas-ticatory function may also restricttreatment with ISSCs.13

The concept of shortened dentalarches (SDA) was introduced becauseof the tendency to limit the use of ISSCsin the second molar region. The SDAconcept allows for sufficient adaptivecapacity in individuals in whom at least4 occlusal units are left: a pair ofoccluding premolars corresponds to 1unit; a pair of occluding molars corre-sponds to 2 units.14 The SDA modelhas gained acceptance and has a rolein contemporary clinical practice.15-18

However, it has been criticized be-cause loss of molars is associated withreduced masticatory performance andinsufficient masticatory ability.19-21

Edentulous patients treated withprostheses supported by dental im-plants were found to have bettermasticatory function, satisfaction, andquality of life than patients treatedwith a mandibular complete removabledental prosthesis.22-24 Self-reportedmasticatory ability depended on thenumber of remaining teeth.25,26 Inaddition, the masticatory performance

Nam et al

and efficiency, the maximum molarocclusal force, and the maximum ac-tivity in jaw elevator muscles have pos-itive associations with the occlusalcontacts, the occlusal area of naturalteeth, and the number of posteriorteeth.27-30 A previous study31 found asignificant linear relationship betweenthe number of missing occlusal unitsand adverse effects on oral-health-related quality of life.

Evidence suggests that the occlusalunit change caused by the implantrestoration of second molars may causechanges in masticatory ability; however,to date, the authors have identified nopublished investigations of such effects.The purpose of this study was toanalyze the effects of second molarimplant restorations on masticatoryability. In addition, the study investi-gated the subjective effects of theimplant treatment. The null hypothesisof this study was that no correlationwould be found between second molarimplant restorations and masticatoryability.

MATERIAL AND METHODS

Participant selection

All procedures were performed afterobtaining written consent from theparticipant. The Institutional ReviewBoard (IRB) at Gangnam SeveranceHospital, Yonsei University, Seoul, South

Korea, approved the study protocol.Patients who required implant therapyformissing secondmolars were recruitedat the Department of Periodontology,Gangnam Severance Dental Hospital,betweenMarch 2010 and October 2010and were selected as participants for thisstudy. All participants were in goodgeneral health; none had cardiovasculardisease or diabetes. Patients wereexcluded from the study if they lackedopposing teeth, had treatment plans fornumerous implant restorations, or pre-sented with temporomandibular disor-ders, bruxism, or a clenching habit, asany of these conditions precluded inde-pendent evaluation of the masticatoryability of the second molar. The surgicaland prosthetic procedures were thor-oughly explained to each participant. Atotal of 21 individuals (13 men and 8women) participated, with a mean ageof 51 years and an age range of 36 to74 years (Table I). The number of par-ticipants was determined through itsown pilot study. Four right maxillarysecond molar implants, 4 left maxillarysecond molar implants, 8 left mandib-ular second molar implants, and 5 rightmandibular secondmolar implants wereperformed (Table II).

Treatment protocol and studydesign

Masticatory ability was recordedbefore ISSC cementation, immediately

Table III. Questionnaire on daily life

1. Have you had difficulty chewing food in general because of problems withyour teeth?Never experienced (0)Hardly ever (1)Occasionally (2)Fairly often (3)Very often (4)

2. Have you had difficulty chewing different types of foods (hard, tough) because ofproblems with your teeth?Never experienced (0)Hardly ever (1)Occasionally (2)Fairly often (3)Very often (4)

3. Have you had difficulty finishing meals owing to dental problems?Never experienced (0)Hardly ever (1)Occasionally (2)Fairly often (3)Very often (4)

4. Choose 1 of 5 possibilities for your masticatory function.Normal (0)Able to eat anything but it takes a long time (1)Able to eat a soft diet only (2)Difficulty eating even a soft diet and it takes a long time (3)Only liquid diet (4)

5. Evaluate global satisfaction of treatment with scores from 0 (very satisfied) to5 (very dissatisfied).

1 Pressure-sensitive foil (Dental PrescaleFilm 50H, type R; GC, Fuji Film). Occlusalload was measured with this foil.

288 Volume 111 Issue 4

after cementation, and 1 month aftercementation to allow for adaptation(the specific protocol is described later).

The Journal of Prosthetic Dentis

A subjective evaluation of masticatoryability was performed before cementa-tion and 1 month after cementation

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by using the questionnaire (Table III).All implant surgeries were performed byusing a 2-stage method after permittingsufficient healing time. The second sur-gery was performed 6 months later formaxillary implants and 3 months laterfor mandibular implants. The cement-retained implant-supported crown wasinserted 3 weeks after the second sur-gery. All prostheses were made andinserted considering criteria such aslight infraocclusion, narrow occlusaltable, axial loading, and minimal con-tact. The same investigator performedthe examination and all procedures onthe participants.

Measurement of maximum occlusalforce and occlusal contact area

Occlusal load was measured by us-ing a pressure-sensitive foil (DentalPrescale Film 50H, type R; GC, FujiFilm) (Fig. 1) mounted in a holderduring maximum occlusal force in theintercuspal position for 2 seconds.Measurements were performed 3 times,30 seconds apart. The participant wasasked to close the jaw slowly to ensureexact location and to prevent slippageof the foil. During the whole process,the participant’s Frankfurt plane wasmaintained parallel to the floor. Thehorseshoe-shaped foil consisted of alayer of microcapsules of various sizescontaining a colorless dye and a devel-oper layer. When force was applied andthe capsules burst, a chemical reactioncaused the involved area to turn red.The thinnest capsules with the largestdiameter burst at a pressure greaterthan 5 MPa, and with increasingpressure, the thicker capsules withsmaller diameter also burst.32 Afterthe recorded foils were digitized(Occluzer FPD-707; Fuji Film) (Fig. 2),the occlusal load (Pa), the load-bearingcontact area (mm2), and the maximumocclusal force (N) were calculated foreach participant.

Questionnaire

The influence of the oral health sit-uation on daily life in the last month

Nam et al

2 Occluzer FPD-707 (Fuji Film). After recorded foilswere digitized, occlusal load (Pa), load-bearingcontact area (mm2), and maximum occlusal force(N) for each participant were calculated.

Table IV. Normality test (D’Agostino-Pearson test)

VariableBefore

CementationJust After

Cementation1 Month AfterCementation

Occlusal load (Pa) .68 .62 .11

Load-bearing contact area (mm2) .07 <.001 .02

Maximum occlusal force (N) .01 <.001 .16

Questionnaire score .40 Not applicable .29

Table V. Occlusal load alteration

Time Point Occlusal Load (Pa)* PPost hocAnalysis

Before cementation 30.1 �4.730.2 (27.0-32.4)

.005

.0019

.3927Immediately after cementation 33.0 �6.433.0 (29.6-35.0)

.44451 month after cementation 31.5 �6.3

30.2 (27.6-33.3)

P<.05 denotes a statistically significant difference.*Values presented as mean �standard deviation or median (95% CI).

April 2014 289

before and in the first month aftercementation of the ISSCs was expressedas the total sum of the scores of the 3Oral Health Impact Profile33 questionsconcerning masticatory ability. These3 items (questions 1, 28, and 32)

Nam et al

evaluate masticatory difficulties in gen-eral, mastication of different types offood, and difficulties in finishing mealsbecause of dental problems. To furtherevaluate chewing ability, a masticationindex with regard to the participant’s

diet was used; this was modified inaccordance with the method of Yoshidaet al.34 Finally, the participants evalu-ated global satisfaction with treatmentby giving scores from 0 (very satisfied)to 5 (very dissatisfied). The specificquestions are presented in Table III.

Statistical analysis

The D’Agostino-Pearson test wasused to test the normality of the dis-tribution. The Friedman test was usedto analyze the difference in occlusalload (Pa), load-bearing contact area(mm2), and maximum occlusal force(N) among the 3 tests administeredbefore ISSC cementation, just afterISSC cementation, and 1 month afterISSC cementation. Post hoc analysis ofresults was performed by using thepaired Wilcoxon test with correction formultiplicity. The Wilcoxon signed ranktest was used to analyze the differencein scores between the surveys conduct-ed before ISSC cementation and 1month after ISSC cementation. Statis-tical software (MedCalc for Windows,version 11.2.1.0; MedCalc Software)was used to process the data (a¼.05).

RESULTS

The outcome variables exhibitednon-normal distribution except forocclusal load and questionnaire score(Table IV). The mean occlusal load was30.1 �4.7 Pa (mean [mean � standarddeviation]) before cementation; itincreased to 33.0 �6.4 Pa just aftercementation; and it decreased to 31.5�6.3 Pa at 1 month after cementation(P¼.005) (Table V). The difference be-tween occlusal load before and justafter cementation was statistically sig-nificant (P¼.002). The final value forocclusal load was statistically similar tothe initial value.

Before cementation, the load-bearingcontact area was 13.3 �8.3 mm2. Thevalue declined to 11.0 �8.5 mm2 justafter cementation and increased to 15.5�6.8 mm2 at 1 month after cementation(P¼.002) (Table VI). The differencebetween load-bearing contact area

Table VI. Load-bearing contact area

Time PointLoad-Bearing Contact

Area (mm2)* PPost hocAnalysis

Before cementation 13.3 �8.312.1 (8.8-17.3)

.002

.1327

.1054Just after cementation 11.0 �8.59.9 (5.3-14.9)

.00231 month after cementation 15.5 �6.8

14.5 (12.2-17.6)

P<.05 denotes statistically significant difference.*Values presented as mean �standard deviation or median (95% CI).

Table VII. Maximum occlusal force

Time PointMaximum Occlusal

Force (N)* PPost hocAnalysis

Before cementation 405.0 �259.6367.0 (301.2-467.0)

.005

.2443

.1536

.0037

Just after cementation 361.0 �284.2351.8 (171.5-398.8)

1 month after cementation 411.8 �200.3425.0 (333.1-540.9)

P<.05 denotes statistically significant difference.*Values presented as mean �standard deviation or median (95% CI).

Table VIII. Questionnaire score

Variable Before Cementation*1 Month AfterCementation* P

Questionnaire score 5.8 �2.86.0 (3.3-8.0)

2.9 �2.52.0 (1.0-5.0)

.002

P<.05 denotes statistically significant difference.*Values presented as mean �standard deviation or median (95% CI).

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immediately after cementation and 1month after cementation was statisticallysignificant (P¼.002). The final valuemeasured for this parameter was higherthan the first value measured. Maximumocclusal force was found to be 405.0�259.6 N before cementation. Thisvalue decreased to 361.0 �84.2 Njust after cementation and increased to411.8 �200.3 N at 1 month aftercementation (P¼.005) (Table VII). Thedifference between maximum occlusalforce immediately after cementation and1 month after cementation was found tobe statistically significant (P¼.004).

The mean questionnaire scoredecreased from 5.8 �2.8 (beforecementation) to 2.9 �2.5 at 1 month

The Journal of Prosthetic Dentis

after cementation (P¼.002) (Table VIII).Detailed analysis indicated that thenumber of negative answers decreasedand the number of positive answersincreased after final placement of theISSC. Table IX presents changes in ques-tionnaire scores frombefore cementationto afterward.

DISCUSSION

The results of the present study sug-gest that masticatory ability is influencedby second molar implant restoration.Therefore, the null hypothesis wasrejected.

As occlusal units increase in number,the load-bearing area and masticatory

try

force also increase. The association be-tween maximum occlusal force and theamount of occlusal contact is closest inthe posterior region; as a consequence,loss of molar support results in reduc-tion of force.29 In this study, the numberof occlusal units increased with theplacement and cementation of ISSCs.One month after cementation, the load-bearing contact area and the maximumocclusal force were increased comparedwith before the procedure. This resultagreed with previous studies27-30 thatfound that the maximum molar occlusalforce had a positive relationship with theocclusal contacts, the occlusal areaof natural teeth, and the number ofposterior teeth.

Changes in occlusion owing to ISSCplacement could present at first as anocclusal interference. Artificial inter-ferences added to the crown of a molartooth have been found experimentally toalter masticatory muscle activity andjaw movements.35-39 Malocclusion cancause the impairment of masticatoryperformance and efficiency.40,41 Signifi-cant recoveries were found to occurduring the course of repetitive mastica-tory cycles performed under the alteredocclusal condition.42 Similarly, partici-pants in this study did not adaptimmediately to occlusal variation, as thecementation of the ISSCs caused adecline in masticatory ability immedi-ately after placement. At this point intreatment, the load-bearing contact areaand maximum occlusal force decreased.Occlusal load as a function of occlusalforce per unit area increased becausethere was a greater decrease of load-bearing contact area as compared withthe decrease in maximum occlusal force.After 1 month of adaptation, the load-bearing contact area and maximumocclusal force increased to a slightlyhigher level than that before ISSCcementation, whereas occlusal loaddecreased to a level similar to thatmeasured before the procedure.

The replacement of missing teethwith ISSCs was associated with an im-proved oral-health-related quality of lifescore 1 month after crown cementation.The questionnaire score decrease was

Nam et al

Table IX. Questionnaire score alterations

1. Have you had difficulty chewing food in general because of problemswith your teeth?

Before Cementation 1 Month After Cementation

Never experienced (0) 4 12

Hardly ever (1) 8 7

Occasionally (2) 5 2

Fairly often (3) 3 0

Very often (4) 0 0

2. Have you had difficulty chewing in different types of foods (hard, tough)because of problems with your teeth?

Before Cementation 1 Month After Cementation

Never experienced (0) 2 7

Hardly ever (1) 6 7

Occasionally (2) 8 6

Fairly often (3) 5 1

Very often (4) 0 0

3. Have you had difficulty finishing meals owing to dental problems?

Before Cementation 1 Month After Cementation

Never experienced (0) 13 18

Hardly ever (1) 8 3

Occasionally (2) 0 0

Fairly often (3) 0 0

Very often (4) 0 0

4. Choose 1 of 5 possibilities for your masticatory function.

Before Cementation 1 Month After Cementation

Normal (0) 10 15

Able to eat anything butit takes a long time (1)

9 6

Able to eat a soft diet only (2) 2 0

Difficulty eating even a softdiet and it takes a long time (3)

0 0

Only liquid diet (4) 0 0

5. Evaluate global satisfaction of treatment with scores from 0 (very satisfied)to 5 (very dissatisfied).

Before Cementation 1 Month After Cementation

0 w 1 7 15

w2 8 4

w3 1 1

w4 5 1

w5 0 0

April 2014 291

statistically significant in amanner similarto that of a previous study.43 For allquestions posed, the proportion ofnegative answers decreased, whereaspositive answers increased. This indicates

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that the participant’s subjective level ofsatisfaction was improved by theincreased masticatory ability. Tooth losscan be a disabling condition44 and has aprofound effect on such aspects of well-

being as self-confidence and feelings ofrepugnance toward one’s appearance,and it can alter behaviors such as social-izing and forming close relationships. Theresults of this study indicated that psy-chological satisfaction related to com-plete dentition was reflected in thequestionnaire score.

Occlusal load, load-bearing contactarea, and maximum occlusal force areimportant in evaluating masticatoryability, but masticatory efficiency mustalso be considered. However, an exactmethod for evaluating masticatory effi-ciency has not been established, andso various methods are used togetherto determine masticatory efficiency.Masticatory efficiency and maximumactivity in jaw elevator muscles areknown to correlate positively withocclusal area and the number of pos-terior teeth.28,30 Given this information,it can be extrapolated that masticatoryefficiency is improved with increasedload-bearing contact area andmaximum occlusal force. In this study,all prostheses were made and insertedbased on such criteria as light infraoc-clusion, narrow occlusal tables, andminimal contact. These properties weredesirable because osseointegrated im-plants do not permit the same mobilityduring chewing and loading as donatural teeth with periodontal liga-ments.45 Such properties might affectmasticatory efficiency negatively; how-ever, effects due to prosthetic limita-tions were expected to be negligible.Further studies are necessary to deter-mine the masticatory efficiency of sec-ond molar implants.

CONCLUSIONS

Restoration of a missing secondmolar was associated with an objectiveincrease in contact area. The subjectivemeasure of patient satisfaction alsoimproved 1 month after the placementand cementation of ISSCs. Therefore,individuals lacking second molars maybenefit from this treatment. Follow-upover longer periods and with largersample populations is needed to de-termine the effects of this treatment.

292 Volume 111 Issue 4

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Corresponding author:Dr Ik-Sang MoonDepartment of PeriodontologyGangnam Severance Dental Hospital146-92 Dogok-dong, Gangnam-gu, SeoulKOREAE-mail: ismoon@yuhs.ac

Copyright ª 2014 by the Editorial Council forThe Journal of Prosthetic Dentistry.

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