Implant Complications and Failures_The Complete Overdenture

8/13/2019 Implant Complications and Failures_The Complete Overdenture

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2 34 Dental Update June 2001

P R O S T H O D O N T I C S

Abstract:The implant-retained overdenture has been advocated as an effectivemethod of restoring the edentulous patient with an appliance that offers significant

benefits over conventional prosthetics. However, the success and survival of suchappliances have been shown to vary considerably, depending on which jaw is treated:

implants supporting overdentures in the maxilla have a significantly higher failure

rate. The restoration also requires considerable maintenance, which is both time

consuming and costly. The purpose of this paper is to look at common restorative

complications and maintenance problems following the placement of dental implants to

support an overdenture. A number of implant systems have been reviewed and the

results of the authors clinical experiences with referred and their own cases are

reported.

Dent Update 2001; 28: 234-240

Clinical Relevance: Implant-retained overdentures require all the prosthetic skills

of conventional treatment combined with a clear appreciation for the need for careful

long-term maintenance. Planning the implant position is essential. Using attachmentsthat are easy to replace can simplify maintenance and reduce ongoing costs.


C.J. Watson,BDS, FDS RCS, PhD,Senior Lecturer/Honorary Consultant in Restorative Dentistry, D.Tinsley, BDS, MDSc, MFDS RCS, Lecturer in

Restorative Dentistry, and S. Sharma, BDS, FDSRCS,Staff Grade in Restorative Dentistry, LeedsDental Institute, Leeds.

mplant-retained overdentures make

an attractive alternative to

conventional complete dentures.

Patients find their prosthesis more

stable and retentive and have improved

oral function. The treatment has a high

success rate with minimal reported

morbidity. The long-term reliability of

implant-retained overdentures is well

documented, particularly when they are

placed in the mandible.13The provision

of these restorations is thought to be

one of the more economical forms of

implant treatment,3and hence more

affordable to patients. The surgery is

relatively simple because fewer implants

are generally required to support an

overdenture, as the occlusal load

generated is shared between the

alveolar ridge and the implants. For the

patient with extensive bone resorption,

an overdenture with its associated

flanges can provide excellent soft-tissue

support, particularly in the upper arch.4

Positioning of the implants is also less

critical than may be required with fixed

bridgework, giving the surgeon a greater

degree of freedom in selecting sites with

optimal bone quality and quantity. It

must be noted, however, that success

rates in the maxillary arch can be as low

as 78.7%.5This may be related to the

placement of short implants in highly

vascular, low-density, poor-volumebone.6

For the prosthodontist, construction

of the implant-retained overdenture is

relatively straightforward, as the

techniques used are similar to those for

conventional overdentures using naturalteeth. However, it has to be appreciated

that the costs of long-term maintenance

of these restorations can be high710in

both time and money and this should be

explained to the patient before treatment

is undertaken. The overdenture needs to

be carefully reviewed as potential

resorption of the alveolar bone in the

saddle areas means that frequent relines

or replacement of the denture may be

necessary.10,11

The purpose of this paper is todiscuss the common problems

encountered with implant- retained

overdentures in a review and referral

clinic at the Leeds Dental Institute.

PLACEMENT ANDPOSITIONAL PROBLEMS

The ideal placement of implants can be

compromised by a lack of alveolar bone

width or height, due to alveolar bone

resorption following the loss of natural

teeth. This can result in non-optimal

positioning with the implants being

divergent, or positioned outside of the

arch (Figure 1).

Certain implant systems dictate that

the anchorage abutment is placed before

recording the impression. In these

circumstances recording an accurate

working impression of grossly divergent

implants may prove to be difficult if

there are significant undercuts present.

This can restrict the choice of retention

systems that can be used; for example,ball or O-ring attachments would not

be recommended as they require

Implant Complications and Failures:The Complete Overdenture

C.J. WATSON, D. TINSLEYANDS. SHARMA

I


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Dental Update June 2001 235

acceptable implant alignment.

When restoring implants placed in the

maxilla, the implants should be splinted

by means of a bar. This will ensure that

occlusal loads are shared more

favourably to the linked implants. To

restore markedly divergent implants,

some systems may require the

connecting bar to be of a split design in

order to allow different paths of insertion.

This increases the complexity and cost of

the technical work and reduces the

number of implants that are splinted

together (Figure 2).

Malaligned implants can compromise

the oral hygiene, as access may be

difficult because of the close proximity of

the anchorage and abutment or conflict

with the lip or cheek or tongue. Inaddition, the bulk of the final overdenture

may have to be increased in order to

allow room for the implants, together with

the housings for the retentive

components. Even mildly divergent

implants will increase the incidence of

fracture and wear of the retentive

components (Figure 3).

The buccallingual positioning of the

implants is critical (Figure 4). Implants

placed away from the centre of the ridge

may cause the overdenture to encroach

into the tongue space or distend the

labial/buccal soft tissues. This may lead

to ulceration or instability of the

prosthesis. Many of these positional

complications can be avoided by the use

of a surgical stent (Figure 5) a clear

acrylic denture, often manufactured bycopying the original denture. The

prosthetist can indicate to the surgeon

optimal implant position and alignment

by preparing pilot holes in the stent. The

stent shown in Figure 5 is designed to

give the surgeon some flexibility in

deciding the final implant position.

There is little doubt that the longer the

implant the higher the chance of success.

Wider implants, which contact the outer

and inner cortical bony plates, may also

be advantageous. Short implants, whichare often used in the maxillary ridge

because of poor bone volume, can lead to

an imbalance in the implant abutment

ratio (Figure 6). With the overdenture in

place, the resulting torque can lead to

high cantilevering forces. The use of

short implants has been associated with

an increased rate of bone loss and

eventual implant failure.12,13

Figure 7a demonstrates an atrophic

mandible where three short implants have

been placed to support a bar-retained

overdenture. In this case the implants

were placed with a large thickness of

mucoperiosteum remaining, which

resulted in relatively tall transmucosal

elements. One consequence of this was

an unfavourable suprastructure to

implant ratio, resulting in bone loss

adjacent to the distal implants; another

was that the tall transmucosal element led

to the development of a long epithelial

junction which is poorly attached to the

titanium abutment. This may result in the

development of a pocket that is difficult

to clean (Figure 7 b and c); subsequently

soft tissue hyperplasia can develop.

When using an overdenture there is no

advantage in placing the implant well

below the mucosal cuff, as the emergenceprofile is of less importance in this

situation.

RESTORATIVE PROBLEMS

Temporization Phase

Tissue conditioners are often used to

reline the existing denture during the

healing phase, but they require frequent

replacement and maintenance. Theplacement of healing abutments at

exposure necessitates further extensive

modification of the patients existing

denture. Such alterations may weaken the

denture, leading to fracture. It may be

necessary to consider the use of some

form of strengthener within the patients

denture at this stage. If cobalt chromium

has been used as the denture base

material in the original denture,

adjustments may be extremely difficult

and in some cases construction of a new

acrylic temporary denture may be

Figure 1.An example of divergent implants.

Figure 2.Split-bar as a solution to the divergentimplants shown in Figure 1.

Figure 3. Damaged rubber O-rings, possibly asa result of mildly divergent implants.

Figure 4. (a)Lingually placed implant causing trauma to the lingual frenal attachments. (b)Labially placed implants supporting magnets.

a b


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necessary: this requires pre-planning.

Patients undergoing more complex

surgery, such as ridge augmentation,

before or at the time of implant placement,present particular difficulties during the

temporization phase. Radical denture

adjustment followed by frequent relines

using tissue-conditioning materials may

be required. The patient must be warned

of the difficulties they are likely to

experience through the initial healing

period.

Impression Stage

It is important to realize that, although the

denture is implant-retained, standard

prosthetic principles apply. It is essential

to record an accurate mucocompressive

impression of the free-end saddle to

distribute the masticatory loads evenly

and reduce rocking around the

attachments. Greenstick low-fusing

impression compound in a special tray

can be very useful in achieving this result

when recording the working impression.

Occlusal ProblemsLack of interocclusal space restricts the

type of attachment that can be used. It

may also lead to a thin weak denture,

which will be prone to fracture (Figure 8).

Patients with a clenching or grinding

habit will rapidly wear down or fracture

acrylic teeth. The use of teeth with a hard

wear resistance surface (for example

Ivoclar-Vivadent teeth; Ivoclar-Vivadent

UK Ltd, Leicester, UK) will reduce the

incidence of this problem. Bruxists also

apply high non-axial loads to the implants

via the prosthesis and attachments. This

may be especially important if the

implants are not splinted in the maxilla.

Restoring one arch with an implant-

retained prosthesis, which generates

higher occlusal forces, can result in the

patient becoming more aware of thelimitations of the opposing denture. This

now becomes a source of complaint, and

relines and remakes may be necessary.

Maintenance

There is already a large body of evidence

that overdentures require significant

postinsertion maintenance: during the

first year after insertion, a higher than

expected number of review visits were

required to adjust attachments and easedentures in a number of studies.1,7,14

Workers have reported as many as 25%

of maxillary overdentures failing within

the first 3 years.15This high maintenance

should be explained to the patient at the

start of treatment so that they are aware

of the necessity for regular reviews.14

There are three commonly used

techniques for retaining overdentures:

bar and retentive clips;

magnets;

ball attachments with various retentive

elements housed in the denture.

The maintenance factors of each are

discussed below.

Bar and Clip Design

Walmsley13stated that the bar and clip

design is relatively costly in clinical and

technical time. The most common

prosthetic complication that can arise isfracture of the clip or loss of retentive

capacity. This is one of the main reasons

for patient re-attendance. The clip may be

of metal or plastic. The metal clip is

usually more durable and easily adjusted

to improve retention, but can be prone to

fracture (Figure 9) and the bar can wear.

The use of plastic clips is

advantageous as they are more easily

replaced and usually less expensive than

metal. In addition, plastic clips may

produce less wear of the metal bar thanmetal clips.16If the plastic clip becomes

non-retentive it usually requires

replacement; the complexity of this

procedure depends on the system in

question. With many systems, the clips

are retained by a metal plate secured in

Figure 5. Clear copy of maxillary denturemodified to form a maxillary stent.

Figure 6. Failing maxillary implant, possibly due toocclusal overload on short implants in vascular bone.

a b

c

Figure 7. (a) Radiographic appearance offailing Brnemark implants. (b)Inflammation around failing implants. (c)The transmucosal element with debrisclearly visible around the neck.


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the prosthesis, which is designed for

easy replacement without the need for

remake of the prosthesis.

There is considerable variation in the

shape and design of the bar. In a study

that compared cantilevered with non-cantilevered bars, Dunnen et al.9found

that the suprastructure was more likely to

fracture in the cantilever group. In

contrast, Engquist et al.12found no

evidence of increased fracture in

cantilevered cast bars. Our experience

with cantilevered cast bars is limited but

from the referrals that we have seen their

predisposition to fracture would seem to

contraindicate their use (Figure 10).

Magnets

Magnets may be used to simplify

restorative and technical procedures.

They are helpful when a limited number

of implants have been placed, or when

short implants are necessary. Magnets

can overcome angulation or positional

problems and their use reduces non-axial

loading from forces generated during

mastication, because the magnetic forces

are greatest in the vertical plane but allow

horizontal movement of the denture.

Magnetic keepers attached to the implant

head keep the height to a minimum andtake up less room within the denture than

some other types of attachment, which

could be helpful when inter-ridge space is

limited. They are economical, easy to

clean and replacement costs are low.

Patients with dexterity problems findremoval of magnet-retained dentures

easier.

However, there have been reports of

corrosion and wear of magnets,13,17and a

high incidence of loosening of the keeper.

Components can fracture (Figure 11) and

the magnets may lose their ability to aid

retention with time.17Patients may

complain of a clicking when chewing due

to metal-on-metal contact when the

denture moves during function. The

denture may be prone to rock as it moves

over the magnetic keeper. Over a longerperiod of time it has been found that

magnets need replacement because of

wear or perforation through the titanium

cover box.18

Ball Attachments with Various Retentive

Elements

The use of free-standing implants to

retain the overdenture has a number of

advantages:

the implant and attachments take upless room within the denture;

the implant abutments are easier to

clean by the patient;

the prosthetic treatment is easier and

more economical;

routine maintenance, such as relines,

is easier to manage.

However, in general, the attachments

tend to lose retention over time (Figure

12) due to wear and fracture of

components. In our experience, the

simple rubber O-ring system has proved

reliable. It is easy to replace the O-ring

and maintain the overdenture.

Regardless of the retentive element

used, it is important that overdentures

are carefully reviewed and the fit over the

free-end saddle assessed. Bone

resorption in the saddle area will result in

movement of the denture. Untreated, a

pronounced rock may develop, which will

result in significant rotational forces

being applied to the retaining implant.

This may result in failed attachments orcervical bone loss around the implants.

Regular relines of the saddle areas can

help to reduce this complication.

SUMMARY

Implant-supported overdentures provide

an economic and reliable means of

restoring an edentulous ridge. The

prosthesis offers support to the facial

muscles and can aid aesthetics in

patients with a high smile line. It also

offers greater latitude in implant position

and angulation than a fixed prosthesis.

However, provision is not without

complications and, as with all restorative

treatments, case selection and careful

treatment planning is the key.

Practitioners must be aware that thistreatment is associated with a higher

implant failure rate especially in the

atrophic maxilla, which has low-density

bone.

It is quite clear, however, that in the

long term all overdentures require a high

degree of maintenance. The attachment

often proves to be the weakest link, and

the incidence of fracture and wear is

high. The necessity for relining becomes

common after the first year due to ridge

crest changes in the edentulous regions.The requirement for significant ongoing

maintenance is something that the

patient and clinician need to be aware of

when considering this form of treatment.

Figure 8. Fracture of an overdenture due to thinacrylic over attachment housing.

Figure 9. Fractured gold clip.

Figure 10.A fractured distal cantilever bar.

Figure 11. Fracture of a magnetic keeper.


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ACKNOWLEDGEMENTSWe are grateful for the support from the Department

of Medical and Dental Illustrations, Leeds Dental

Institute.

REFERENCES1. Hemmings KW, Schmitt A, Zarb GA. Complications

and maintenance requirements for fixed

prostheses and overdentures in the edentulous

mandible: A 5-year report. Int J Oral Maxillofac

Implant 1994; 9:191196.

2. Davis DM. Implant supported overdentures

the Kings experience.J Dent 1997; 25:S33S37.

3. Cooper LF, Scurria MS, Lang LA et al.Treatment

of edentulism using Astra Tech Implants and ball

abutments to retain mandibular overdentures.

Int J Oral Maxillofac Implant1999; 14:646653.

4. Zitzmann NU, Marinello CP. Implant-supported

removable overdentures in the edentulous

maxilla: Clinical and technical aspects.Int J

Prosthodont 1999; 12:385390.

5. Goodacre CJ, Kan JYK, Rungcharassaeng K.

Clinical complications of osseointegrated

implants.J Prosthet Dent 1999; 81: 537552.

6. Watson RM, Jemt T, Chai J et al.Prosthodontic

treatment, patient response, and the need for

maintenance of complete implant-supported

overdentures: an appraisal of 5 years of

prospective study. Int J Prosthodont1997; 10:

345354.

7. Chan MFW-Y, Johnston C, Howell RA.

A retrospective study of the maintenance

requirements associated with implant stabilised

mandibular overdentures. Eur J Prosthodont

Restor Dent 1996; 4: 3943.

8. Watson RM, Davis DM. Follow up and

maintenance of implant supported prostheses: acomparison of 20 complete mandibular

overdentures and 20 complete mandibular

fixed cantilever prostheses.Br Dent J 1996; 181:

321327.

9. Dunnen ACL, Slagter AP, Baat C, Kalk W.

Adjustments and complications of mandibular

overdentures retained by four implants. A

comparison between superstructures with and

without cantilever extensions. Int J Prosthodont

1998; 11:307311.

10. Walton JN, MacEntee MI. A retrospective study

on the maintenance and repair of implant-

supported prostheses. Int J Prosthodont 1993; 6:

451455.

11. Tinsley D, Watson CJ, Russell JL. A comparison

Figure 12.Replacement of small metal clip,which is easily damaged during normal function.

of hydroxylapatite coated implant retained fixed

and removable mandibular prostheses over 4 to

6 years. Clin Oral Implant Res2001; 12:159166.

12. Engquist B, Bergendal T, Kallus T et al. A

retrospective multicenter evaluation of

osseointegrated implants supporting

overdentures. Int J Oral Maxillofac Implant1988;

3:129134.

13. Walmsley AD, Frame JW. Implant supported

overdentures the Birmingham experience.J

Dent1997; 25: 4347.

14. Jemt T, Book K, Linden B, Urde G. Failures and

complications in 92 consecutively inserted

overdentures supported by Brnemark implants

in severely resorbed edentulous maxillae: A study

from prosthetic treatment to first annual check-

up. Int J Oral Maxillofac Implant1992; 7: 162167.

15. Hutton JE, Heath MR, Chai JYet al. Factors

related to success and failure rates at 3-year

follow-up in a multicenter study of overdentures

supported by Brnemark implants. Int J OralMaxillofac Implant 1995; 10:3342.

16. Walton JN, Ruse ND. In vitrochanges in clips and

bars used to retain implant overdentures.J

Prosthet Dent1995; 74:482486.

17. Naert I, Gizani S, Vuylsteke M, Van Steenberghe

DV. 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.J Oral

Rehab1999; 26:195202.

18. Naert I, Quirynen M, Hooghe M, Steenberghe D.

A comparative prospective study of splinted and

unsplinted Brnemark implants in mandibular

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Prosthet Dent1994; 71:486492.

BOOK REVIEW

Periodontics: Current Concepts and

Treatment Strategies. By P.N. Galgut,

S.A. Dowsett and M.J. Kowolik. Martin

Dunitz Ltd, London, 2000 (208pp.,

49.95). ISBN 1-85317-981-7.

Periodontology is a fast moving subject

and, although some of the basicprinciples of treatment havent

changed, there is an ever increasing

amount of new research, which has

implications about how we treat our

patients.

Its important that students, general

practitioners and specialists keep up-

to-date with current research, which

can be difficult with the ever increasing

number of research papers published.

So any textbook that offers a review of

the subject is welcomed.

This textbook gives an overview of

current research and its implications

from a clinical point of view. The book

contains 14 chapters and covers the

following:

The Periodontium in Health and

Disease

Epidemiology in the Study of

Periodontal Disease

The Microbiology of Periodontal

Diseases

The Host Response in Periodontal

Diseases Systemic Influences and Periodontal

Health

Gingival Disease and Hyperplasia

Early Onset Periodontal Disease

Diagnosis and Treatment Planning in

the Periodontitis Patient

Mechanical Treatment of Periodontal

Diseases

The Role of Surgery in Periodontal

Treatment

Chemotherapeutic Agents in the

Management of Gingivitis and

Periodontal Diseases

Restorative Considerations in the

Periodontitis Patient

Peri-implantitis

Current Dilemmas and Future Solutions

The chapter Peri-implantitis covers,

Reasons for failure, Implant management

in practice (including monitoring and

management),Instrumentation and

management of the failing implant. As

more implants are being placed, it is

inevitable that we will all see more failed

cases in our routine practice, andinformation on how to manage such cases

is obviously very helpful.

The final chapter gives insights into

where research might be leading in the

next few years, and includes sections on

Advances in diagnosis,Risk factors,

Therapeutics and tissue repair.

In summary, this colour hardback

textbook is clearly written and well

illustrated and offers anyone with an

interest in this specialty a fascinating

update, and I would thoroughly

recommend it.Mike Milward

Birmingham Dental School

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Implant Complications and Failures_The Complete Overdenture