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A5yearprospectiverandomizedclinicaltrialontheinfluenceofsplintedandunsplintedoralimplantsretainingamandibularoverdenture-prostheticaspectsandpatientsatisfaction.pdf

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Journal of Oral Rehabilitation 1999 26; 195 – 202

A 5-year prospective randomized clinical trial on the influence of splinted and unsplinted oral implants retaining a mandibular overdenture: prosthetic aspects and patient satisfaction I . N A E R T *, S . G I Z A N I *, M . V U Y L S T E K E† & D . V A N S T E E N B E R G H E‡ *Department of Prosthetic Dentistry, School of Dentistry, Oral Pathology and Maxillofacial Surgery, Faculty of Medicine, Catholic University Leuven; †Department of

Statistics, Computing Centre, Catholic University Leuven; and ‡Department of Periodontology, School of Dentistry, Oral Pathology and

Maxillofacial Surgery, Faculty of Medicine, Catholic University Leuven, Leuven, Belgium

SUMMARY Prosthetic outcome and patient satisfac- After 5 years of observation, the Bar group pre-

sented the highest retention capacity and the leasttion were evaluated in order to investigate

prosthetic complications but revealed more mu-whether there is a need or advantage to splint two

cositis and gingival hyperplasia. Patient satisfac-implants in the mandible retaining a hinging over-

denture. This study included 36 fully edentulous tion rated similar for all groups although the

Magnet group showed lower retention forces. Allpatients randomly divided into three groups ac-

cording to the attachment system they received: patients would repeat the same treatment even

though the majority of the Magnet group wouldmagnets, ball attachments or straight bars (refer-

ence group). None of the implants failed during prefer a more retentive solution because of limited

denture stability.the whole observation period in any of the groups.

Introduction

Full edentulism can substantially affect oral and gen-

eral health as well as overall quality of life (Gift &

Redford, 1992; Marcus et al., 1996).

Patient satisfaction with dentures is influenced by

various factors including denture quality, the available

denture bearing area, the quality of dentist – patient

interaction, previous experience with dentures, pa-

tient’s personality and psychologic well-being (Boer-

rigter et al., 1995).

Replacing the lost tissues by means of complete den-

tures is challenging both for the dentist and the patient

(Zarb, 1982; Davis, 1990). Nevertheless, some people

do not succeed in acquiring new skills with their den-

tures and thus suffer psychologically because of im-

paired function, comfort, self-image and social

interaction.

Because of the good prognoses of some endosseous

implant systems, these patients can be successfully

treated with implant-retained overdentures. Several

studies reported the clear benefits of overdenture treat-

ment, versus the conventional denture for a number of

aspects such as: aesthetics, speech, chewing, fit and

retention, function and quality of life (Burns et al.,

1994; Cune, Putter & Hoogstraten, 1994; de Grand-

mont et al., 1994). The impact on these aspects of

different attachment systems retaining the overden-

tures is lacking so far.

Therefore, a 5-year randomized clinical trial was set

up to investigate the prosthetic outcome and patient

satisfaction with mandibular hinging overdentures on

different attachment systems. The peri-implant out-

come is discussed in a separate paper (Naert et al.,

1998).

196 I . N A E R T et al.

Fig. 1. The three different attachment systems used for each group: a, Bar group; b, Magnet group; c, Ball group.

Materials and methods

This study included 36 completely edentulous patients

(19 women and 17 men) with a mean age 63·7 years

(range 36 – 85). All of them were edentulous for at least

more than 1 year and all complained about their exist-

ing lower dentures. The exclusion criteria were the

following: insufficient bone volume to harbour at least

two 10 mm implants, Angle class II jaw relationship,

psychological problems for accepting a removable den-

ture, gagging reflexes, less than 1 year of edentulism in

the mandible, absence of a maxillary complete denture

and administrative or physical considerations that

would seriously affect the surgical procedure or consti-

tute a hindrance for a 5-year follow-up.

At the beginning of the treatment the medical status

as well as the dental history of each patient were

recorded. The initial examination also included the

evaluation of the existing dentures, the estimation of

dysfunctional problems and a questionnaire concern-

ing the patient satisfaction of the original denture.

Each patient was provided with two screw shaped

c.p. titanium implants (Brånemark system®*) in the

symphyseal area of the mandible, approximately in the

canine region with a connecting line paralleling the

terminal mandibular hinge axis (Naert et al., 1988).

After 3 – 5 months transmucosal standard Brånemark®

abutments were installed.

A randomization scheme divided the 36 patients into

three groups of equal size according to the retention

system (Fig. 1). In the first group (Bar group), which is

the reference group, the attachment system was an

egg-shaped Dolder bar with continuous clip† splinting

* Nobel Biocare AB, Gothenburg, Sweden. † Cendres et Metaux SA, Biel, Switzerland.

I N F L U E N C E O F S P L I N T E D A N D U N S P L I N T E D O R A L I M P L A N T S 197

Table 1. Summary of the questionnaire split up in three parts: in the first part patients gave their answers on a ordered scale

ranging from 1 (very bad) to 9 (excellent), the second part

includes questions that had to be answered with just yes/no response and in the third part a more descriptive answer was

requested

First part A. How do you find your new prosthesis in general? B. How well does your new prosthesis remain in place? C. How well can you eat with your new prosthesis? D. How well can you talk with your new prosthesis? E. How do you find the appearance of your prosthesis?

Second part F. Do you avoid contact with other people because of fear

loosing your prosthesis? G. Does your new prosthesis bother your mind? H. Does food impaction regularly occur under your prosthesis? I. Does your expectations became real with your new

prosthesis? J. Would you repeat the same treatment?

Third part K. How many times do you take out your prosthesis because

of discomfort? L. If you should repeat the treatment, would you choose: (1)

the same solution or (2) fixed prosthesis?

Table 2. Variables that might interfere with an equal balance for the three treatment groups*

Ball groupMagnet groupBar group

Age (years) 6465 61 5/75/77/5Gender (men/

women) Period of edentulism 15 11·514·8

(years) Bone height in ca- 24·9 25·923·8

nine region (mm) Bone quality†

8 pat.Class 2 4 pat.5 pat. Class 3 7 pat. 8 pat. 4 pat.

Bone quantity†

Class A 1 pat. 0 pat. 0 pat. Class B 2 pat. 3 pat. 3 pat.

7 pat.Class C 7 pat. 6 pat. 3 pat. 2 pat.2 pat.Class D

pat., patients.

* There was not any statistical difference for the variables tested

between the three groups (P\0·05). † According to Lekholm & Zarb (1985).

just a ‘yes/no’ response and a third part of the question- naire demanded a more descriptive answer. Table 1

summarizes the three parts of the questionnaire. Finally,

the temporomandibular joints and masticatory muscles

function was assessed according to an anamnestic and

clinical dysfunction index (Helkimo, 1979).

Statistical analysis

Differences in patient satisfaction per group at the fifth

year, as well as the variation in patient satisfaction over

time were analysed by a non-parametric Kruskal – Wallis

ANOVA test.

Both the objective and the subjective retention of

the overdenture for the whole group was analysed by a

non-parametric Spearman correlation analysis.

both implants. In the second group (Magnet group) two

open-field magnets‡ and in the third group (Ball group),

two ball attachments (SDCB 115-17*) were used. The

occlusion, laterotrusion and protrusion were assessed on

the articulator and intraorally to secure a balanced

occlusion in centric relation without anterior tooth

contact.

Patients were scheduled for follow-up visits at 1 week

post-prosthesis insertion and 4, 6, 12, 24, 36, 48 and

60 months post-abutment installation.

The retention of the overdenture was measured by

means of a dynamometer§ with a maximum capacity of

20 N and the mean of three repeated measurements was

calculated (Naert et al., 1990). The mechanical complica-

tions of the attachment components were recorded as

well as the soft-tissue complications of the denture

bearing area (mucositis, soreness, ulcer decubitus and

hyperplasia) for the whole observation period.

Patient satisfaction was investigated through a ques-

tionnaire. A part of this questionnaire included ques-

tions in which patients gave their answers on a ordered

scale ranging from 1 (very bad) to 9 (excellent). A second

part included questions that had to be answered with

Table 3. Mean retention force (gram, mean of three repeated measurements) of the overdentures measured by means of a

dynamometer at the baseline (prosthesis installation), the first

and the fifth year and the total decrease over time between

baseline and fifth year per group

Ball groupMagnet groupBar group

370 655Baseline 1677 Force 1st year 1855 362 730

5671101240Force 5th year

Total decrease −437 −260 −88 ‡ Dyna Engineering BV, Bergen op Zoom, The Netherlands. § Correx, Bern, Switzerland.

198 I . N A E R T et al.

Table 4. Frequency distribution of the number of prosthetic complications for the 5-year observation period per group

Bar group Magnet group Ball group

Retention element 21 123Wear 21 0Corrosion – 1 11Fracture 0

25100Loosening of abut- ment screw

3 2 –Loosening of gold screw

– –Activation of clip 12 2 –Change of clip –

– – 13Exchange of rubber ring

Exchange of O-box – – 16 53 –Exchange of magnet –

1 3Rebasing 4 0 1 0Remounting

00New denture made 1

one changed address and could not be traced at the

end of the third year follow-up, while from the Ball

group one patient was not able to be present at the

last two control-visits because of severe medical rea-

sons. Finally, from the Magnet group one patient did

not show up at the last control because she was un-

satisfied with the treatment.

When analysing the withdrawn patients regarding

baseline data, such as: age, gender, period of eden-

tulism, bone quality and quantity these did not re-

veal any detectable differences from those followed.

Implant failures

Only one implant failed at the time of abutment

surgery. It was replaced at the same position by an-

other implant without further complications. No im-

plant failed in any of the groups after loading during

the 5-year observation period.

Prosthetic outcome

At year 5, the highest retention of overdentures was

measured in the Bar group (1240 g, range 0 – 2000 g)

and the lowest for the Magnet group (110 g, range

0 – 456 g) (Table 3). Comparing the retention forces

between the baseline (prosthesis installation) and

year 5, a decrease of retention took place over time

for all groups. The steepest decrease of the retention

force over time was observed in the Bar group

(437 g), the least in the Ball group (88 g).

The Magnet and Ball group presented the highest

incidence of prosthetic complications when compared

to the reference group. For example in the Magnet

group frequent renewal of magnets because of wear

and corrosion and in the Ball group frequent tighten-

ing of the abutment screws, besides renewal of the

The level of significance was set at 0·05 unless oth-

erwise stated.

Results

Due to the randomization scheme factors that could

influence the balancing criteria were found not to be

statistically different between the three groups (Table

2).

Patients drop -out

All except five patients were followed during the

whole observation period. From the Bar group two

patients died after 2 years of follow-up and another

Table 5. Frequency distribution of the number of times that denture supporting mucosa complications occurred and the number of patients to whom it occurred during the follow-up visits per group

Bar group Magnet group Ball group

Times Patients Times Patients Times Patients

3Mucositis 322512 000 023Soreness

Ulcer decubitus 6 3 12 4 8 6 33347Hyperplasia 9

I N F L U E N C E O F S P L I N T E D A N D U N S P L I N T E D O R A L I M P L A N T S 199

Magnet group Ball groupBar group

Mean (s.d.) Sum of the ranks Mean (s.d.)Mean (s.d.) Sum of the ranksSum of the ranks

A. How do you find your new prosthesis in general? 105·5000 7·4 (1·8)8·7 (0·4) 133·5000 6·6 (2·2) 139·0000

B. How well does your new prosthesis remain in place? 8·9 (0·3)6·3 (2·4) 185·500092·5000*8·0 (1·5) 100·0000

C. How well can you eat with your new prosthesis? 8·5 (0·8) 167·00008·7 (0·4) 122·0000 6·4 (2·2) 89·0000*

D. How well can you talk with your new prosthesis? 7·3 (1·4) 179·50008·6 (0·9)105·00007·8 (1·4) 93·5000

E. How do you find the appearance of your new prosthesis? 137·00007·7 (0·6)136·00007·7 (1·7)8·2 (0·7) 105·0000

* Statistically different at the 5% level from the other groups.

Table 6. Mean (s.d.) and sum of the ranks from questions answered on an ordered scale ranging from 1 (very bad) to 9 (excellent) per group at year 5

O-rings and the O-ring-boxes were mostly needed.

The most common complication for the Bar group

was the reactivation of the overdenture clips (Table

4).

One denture was remade (Bar group) at the pa-

tient’s request to have a brighter colour of teeth.

Eight dentures had to be relined: one, three and four

in the Bar, Magnet and Ball group, respectively

(Table 4).

Mucositis and hyperplasia more often occurred in

the Bar group, while ulcer decubitus was observed

more often in the Magnet and Ball groups (Table 5).

Patient satisfaction

Patient satisfaction at year 5 derived from questions

concerning general satisfaction, phonetics and aes-

thetics was similar in all groups. On the other hand,

questions related to prosthesis stability and chewing

comfort scored significantly lower in the Magnet

group (P = 0·05) (Table 6). Patient satisfaction for chewing comfort, phonetics

and aesthetics in all groups hardly varied between

baseline and year 5. However, a significant decrease

of the general satisfaction and the denture stability

was noted in the Magnet group (P = 0·03) (Table 7). Food impaction was revealed to occur regularly in

all groups. Patients in all groups would repeat the

same treatment if they had to start again (Table 8).

All patients were satisfied with their overdenture.

The majority seldom removed the overdenture be-

cause of discomfort. Most of the patients preferred

this treatment to a fixed prosthetic solution, except

for half of the Magnet group (Table 9).

Although instructed, only half of the patients took

out their overdentures during the night.

Only a very weak correlation (r = 0·35, P = 0·07) was found between the subjective and objective mea-

sured retention forces of the overdenture at year 5

when the whole group was considered.

Finally, at the end of the observation period only

one patient in the Magnet group reported signs and

symptoms of TMJ-dysfunction, while at the begin-

ning of the study nine patients presented anamnestic

or clinical dysfunction.

Discussion

Five patients could not assist the whole follow-up

scheme, which is not surprising, considering the

rather aged study population.

Although this study was set up to investigate the

prosthetic outcome of splinted and unsplinted oral

implants retaining mandibular hinging overdentures,

the implant outcome was included for completeness.

As shown for the bar-retained hinging overdentures

(Naert et al., 1997b) which is a reliable treatment,

unsplinted implants retaining an overdenture seem to

do as well (Naert et al., 1998).

200 I . N A E R T et al.

The Bar group provides the highest retention force

while magnets the lowest. This is in agreement with

our results at 3-years (Naert et al., 1997a) with previ-

ous reports (Burns et al., 1994; Naert et al., 1994;

Hooghe & Naert, 1997; Petropoulos, Smith & Kousve-

lati, 1997). All three groups presented a decrease of

retention force over time which was more pronounced

in the Bar group. Deactivation of the clip-bar compo-

nents over time can explain this, because reactivation

of the clip only took place on the patient’s request. In

the two other groups the retention elements were

renewed each time the patients complained or when

the components were fractured or showed advanced

wear.

When correlating the subjective with the objective

measured retention force of the overdenture at year 5

for the whole group, only a very weak correlation was

found which is in contrast with the 3-year results,

where a strong correlation was found (Naert et al.,

1997a). This difference may be explained by the fact

that the patients got used to their new overdentures

with time and they did not complain even if the den-

ture retention was not satisfactory.

The Bar group presented the least prosthetic compli-

cations which is in accordance with other studies

(Naert et al., 1994; Hooghe & Naert, 1997). Indeed,

only two clips in the Bar group needed replacement

while in the Magnet and the Ball group 53 magnets

and 29 rubber ring or boxes needed renewal. When

comparing the 3-year (Naert et al., 1997a) with the

5-year results, it becomes apparent that the number of

prosthetic complications in the groups with the un-

splinted implants increased considerably during the last

2 years. This contrasts with the results of Davis, Rogers

& Packer (1996) where the majority of the complica-

tions concentrate during the first year. Our results can

be explained by the keeper’s ageing over time. Indeed,

each time the magnet, the rubber ring and the O-box

had to be renewed, the original keeper was kept in

place. Thus, only the magnet, O-ring or O-ring-box

were changed.

The Bar group patients had more hyperplasia and

mucositis while in the two other groups ulcer decu-

bitus was more frequently observed. A remarkable fact

is that mucositis and ulcer decubitus continued to be

present in the same patients throughout the 5 years,

while hyperplasia was observed in more and more pa-

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I N F L U E N C E O F S P L I N T E D A N D U N S P L I N T E D O R A L I M P L A N T S 201

Table 8. Positive answers to the second part of the question- naire per group at the first and at the last year of the follow-up

period with the new overdentures

Ball groupMagnet groupBar group

1st year 5th year 1st year1st year 5th year5th year

F. Do you avoid contact with other people because of fear loosing your prosthesis?

0/12 2/11 0/121/12 0/110/9

G. Does your new prosthesis bother your mind? 0/12 1/11 0/124/12 0/111/9

H. Does food impaction regularly occur under your prosthesis? 9/12 10/11 8/12 6/117/12 5/9

I. Did your expectations became real with your new prosthesis? 5/11 12/1211/12 9/9 9/1110/12

J. Would you repeat the same treatment? 11/11 10/1112/1211/1212/12 8/9

All patients would prefer the same treatment, if they

had to choose again even though the Magnet group’s

expectations did not became real. This can be ex-

plained by the dramatic improvement when compared

to the previous unretained full dentures (see Naert et

al., 1997a). The impaired denture retention in the

Magnet group, lead those patients to prefer a more

fixed solution, even if they did not consider overden-

ture therapy as a second-class treatment.

Conclusions

(1) The Bar group presented the highest retention

capacity of the overdenture over time. The retention

capacity of the Ball group remained more stable over

time.

(2) The Bar group presented the least prosthetic com-

plications.

(3) The groups with the unsplinted implants presented

more prosthetic complications in the last 2 years of the

study probably because of the ageing of the male reten-

tion elements.

(4) The Bar group revealed more mucositis and gingi-

val hyperplasia while in the unsplinted groups more

decubitus ulcers were observed. The incidence of hy-

perplasia increased for all groups over time indepen- dently of the retention device.

(5) General patient satisfaction rated similar for all

groups but the Magnet group scored lower for the

specific question related to retention and chewing

comfort.

(6) Most of the patients would seek the same kind of

treatment, although in the Magnet group more pa-

tients would prefer a more fixed solution.

tients over time. This applies to all three treatment

groups. However, the plaque index as well as the

bleeding index at year 5 did not significantly differ with

the outcome at year 1 (Naert et al., 1998).

Although half of the patients did not remove their

dentures, the distribution was equal for the three

groups. This underlines the psycho-social impact of

edentulism.

When considering general patient satisfaction no sig-

nificant differences appeared between splinted and un-

splinted implants. However, when specific questions were addressed such as for retention and chewing comfort, magnets scored lower at year 5.

Bar group Magnet group Ball group

5th year 1st year 5th year5th year 1st year1st year

K. How many times do you take out your prosthesis because of discomfort? 9/12�never 5/9�never 10/12�never 9/11�never 12/12�never 10/11�never 2/12�1/day 2/9�1/day

1/11�B5/day2/11�B5/day2/12�B5/day2/9�B5/day1/12�B5/day

L. If you should repeat the treatment, would you choose: (1) the same solution or (2) fixed prosthesis? 11/12�same 7/9�same 9/12�same 6/11�same 10/12�same 11/11�same 1/12�fixed 2/9�fixed 5/11�fixed3/12�fixed 2/12�fixed

Table 9. Answers to the third part of the questionnaire per group at the first and at the last year of the follow-up period with the new overdentures

202 I . N A E R T et al.

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Correspondence: Professor I. E. Naert, Department of Prosthetic

Dentistry, School of Dentistry, Oral Pathology and Maxillofacial

Surgery, Kapucijnenvoer 7, B-3000 Leuven, Belgium. E-mail:

[email protected]

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