five-year clinical trial using three attachment systems for implant overdentures

Corina Marilena CristacheLigia Adriana StancaMuntianuMihai BurlibasaAndreea Cristiana Didilescu

Five-year clinical trial using threeattachment systems for implantoverdentures

Authors’ affiliations:Corina Marilena Cristache, Concordia Dent Clinic,Bucharest, RomaniaLigia Adriana Stanca Muntianu, RemovableProsthodontics, Faculty of Dental Medicine,University of Medicine and Pharmacy “CarolDavila”, Bucharest, RomaniaCorina Marilena Cristache, Mihai Burlibasa,Implantology, FMAM, University of Medicine andPharmacy “Carol Davila”, Bucharest, RomaniaAndreea Cristiana Didilescu, Department ofAnatomy, Faculty of Medicine and Pharmacy,“Dunarea de Jos” University, Galati, RomaniaAndreea Cristiana Didilescu, Department ofEmbryology, Faculty of Dental Medicine,University of Medicine and Pharmacy “CarolDavila”, Bucharest, Romania

Corresponding author:Andreea Cristiana Didilescu8, Blvd Eroilor Sanitari, 050474, Bucharest,RomaniaTel.: +40 722536798Fax: +40 21 3131298e-mail: [email protected]

Key words: complications, costs, locator, magnet, prosthetic maintenance, retentive anchor

Abstract

Objective: The objective is to compare, in a prospective randomized clinical trial, three types of

attachment systems for mandibular implant overdenture, focusing on costs, maintenance

requirements and complications from baseline to the end of 5-year follow-up period.

Materials and Methods: Sixty-nine fully mandibular and fully/partially maxillary edentulous

patients received two screw-type Straumann implants, in the mandibular canine region. New

overdentures with three types of attachment systems were inserted according to an early-loading

protocol: Group B (balls, divided into Subgroup B.1 – retentive anchor with gold matrix and

Subgroup B.2 – retentive anchor with titanium matrix) (n = 23), Group M (magnets) (n = 23) and

Group L (locator) (n = 23).

Results: The highest maintenance event number (195) was observed in Group B vs. 31 in Group L

and 15 in Group M. Significantly more complications were recorded in Subgroup B.1 than in

Subgroup B.2, Group M and Group L (P < 0.05). Group M registered the highest prosthetic success

(82.6%) in the 5 years, followed by Group L (78.2%). Subgroup B.1 had the lowest success rate

(50%). The magnet group recorded statistically significant higher costs, comparing with the other

two groups (P < 0.05).

Conclusions: The three attachment systems functioned well after 5 years. The magnets had a low

maintenance requirement and high success rate, despite the relatively increased initial costs.

Retentive anchor with titanium matrix and locator may be a better choice from a financial point of

view, taking into consideration the initial low cost of the components and also the reduced

number of complications.

In case of the edentulous patients, the suc-

cess of the denture therapy depends upon the

biomechanical prodigy of support, stability

and retention (Jacobson & Krol 1983b,c). The

mandibular denture generally presents the

major problem with regard to retention due

to a movable floor of the mouth, which

causes difficulty in establishing a lingual

border seal. Denture stability is minimised

by lack of ideal ridge height and conforma-

tion (Jacobson & Krol 1983a). Due to resorp-

tion, the remaining anatomic regions of the

mandible are not usually essential in provid-

ing dental support (Jacobson & Krol 1983c).

Problems regarding integrating dentures

are observed with a higher incidence for

mandibular than for maxillary dentures

(Mericske-Stern 1998). To overcome these

drawbacks, over the past 35 years, clinicians

have been restoring aesthetics and function in

edentulous patients with implant overdentures

using different retention systems and nowa-

days the cost-effectiveness and the simplic-

ity of treatment become the main issues for

the choice of treatment (Zitzmann et al.

2006). The role of the attachment type is

very important (Kimoto et al. 2009): a rigid

connection between implants and denture

induces stress with potential implant failure

(Menicucci et al. 2006), especially when

hinge movements around the fulcrum line

occurs. Moreover, splinting implants by

means of a bar-clip construction is more

expensive, time-consuming, involves more

complications (Gotfredsen & Holm 2000)

and offers no marked differences in patient

satisfaction when compared with non-splint-

ing attachments (Cune et al. 2010). Due to

these facts, resilient and magnetic attach-

ment for implant overdentures, allowing

several types of movements, are extensively

used. The magnetic anchor is a non-rigid,

Date:Accepted 30 October 2012

To cite this article:Cristache CM, Muntianu LAS, Burlibasa M, Didilescu AC.Five-year clinical trial using three attachment systems forimplant overdentures.Clin. Oral Impl. Res. 25, 2014, e171–e178doi: 10.1111/clr.12086

© 2012 John Wiley & Sons A/S. e171

dynamic anchor. The retentive unit permits

rotary movement of the denture in one or

more directions and/or vertical translational

movements. The magnetic attachment den-

ture has a low resistance to lateral forces,

and the subsequent immediate loss of reten-

tion is associated with a lower level of

implant moment loading, thereby protecting

the implant against unfavourable lateral

forces (Heckmann et al. 2001). The desire

to use the magnetic retention is related to

the simplicity involving minimal time at

the chairside and in the laboratory. Two

different types of alloys were used for the

manufacture of small dental magnets:

cobalt-samarium magnets introduced in the

sixties and an alloy based on iron – neo-

dymium – boron in the eighties, both with

high attractive forces but with a low corro-

sion resistance (Walmsley 2005). Nowadays,

to increase corrosion resistance, the magnets

are encapsulated in stainless steel, titanium

or palladium by using laser-welded coatings

(Haruta et al. 2011).

As resilient anchors, balls (retentive anchors)

are considered the simplest and less costly type

of attachments for clinical application (Cakarer

et al. 2011).

The self-aligning locator system has dual

retention: through both external and internal

mating surfaces, is resilient, retentive and

durable, and has some built-in angulation

compensation (Cakarer et al. 2011). The loca-

tor system has been widely used in the past

three to 4 years, but there is a need of long-

term prospective clinical studies to compare

this system with other attachment systems

(Alsabeeha et al. 2011), particularly with

regard to the treatment’s success, as well as

clinical and prosthetic complications.

Although the recommended number of

implant is established (Feine et al. 2002), no

scientific data to support the use of one

attachment system against another are avail-

able for the edentulous mandible, due to the

fact that functional demands of edentulous

patients are highly variable and the choice of

treatment is strongly influenced by adaptive

capacity, socio-cultural background and also

by financial means (Fitzpatrick 2006).

Therefore, the aim of this study was to com-

pare three types of unsplinted attachment

systems, focusing on costs, maintenance require-

ments and complications, in a prospective clini-

cal trial: retentive anchors (balls, Straumann,

Basel, Switzerland), magnets (Titanmagnetics®

Steco system-technick, Hamburg, Germany) and

locator® (Zest Anchors, Inc., Escondido, CA,

USA), for implant overdenture in the edentulous

mandible. No differences between the attach-

ment systems regarding costs and maintenance

requirements defined the null hypothesis for-

mulated in the present study.

Materials and methods

The study was conducted from September 2004

to March 2012 according to the CONSORT

guidelines for improving the quality of clinical

trials (Altman et al. 2001; Moher et al. 2003;

Schulz et al. 2010) (Data S1). The use of human

subjects in this study was reviewed and

approved by the Romanian Ministry of Health

and written informed consent was obtained

from all participants.

Sixty-nine fully mandibular edentulous

patients (age ranging between 42 and 84 years)

were recruited from the University Hospital of

Dentistry and nine private practices in Bucha-

rest and the surrounding areas (ClinicalTri-

als.gov Identifier: NCT01034930). Their

maxillary status was as follows: 12 (17.4%)

with fixed bridges; 3 (4.3%) with natural teeth;

46 (66.7%) with removable complete dentures

and 8 (11.6%) with removable partial dentures.

The patients were selected based on all the fol-

lowing criteria: complains about the stability

of the existing mandibular denture satisfac-

tory from a technical point of view; patients

included in Class I to III (American College of

Prosthodontists Classification of Complete

Edentulism) (McGarry et al. 2004); acceptance

of a mandibular overdenture retained by two

endosseous implants; agreement for a 5-year

follow-up period.

Exclusion criteria comprised: insufficient

bone volume (height and width) for inserting

of at least a 10-mm implant (diameter 4.1)

(due to extensive residual ridge resorption,

patients in Class IV – American College of

Prosthodontists Classification of Complete E-

dentulism, were excluded); Angle class II rela-

tionship; physical condition that will affect

the minimal invasive surgical procedure or

constitute a hindrance for a 5-year follow-up

(e.g. immunosuppressive therapy, elderly

patients in poor physical condition); history of

radio-/chemotherapy in the head and neck

region; history of pre-prosthetic surgery

(including bone graft procedures) or previous

oral implants.

Selected patients were informed about the

three different treatment options and about

the benefit of treatment with an overdenture

retained by two endosseous implants (Feine

et al. 2002).

The medical status and dental history of

all patients were checked and an oral and

radiographic examination (including oral

hygiene status) was performed before any

treatment procedure.

Surgical procedure

Each patient received two screw-type Strau-

mann (Switzerland) standard soft tissue level

implants 4.1 mm diameter, with sandblasted

large-grit acid-etched (SLA) surface in the

canine region of the mandible with an inter-

connecting line approaching parallelism with

the terminal mandibular hinge axis (Naert

et al. 1998). The implant lengths were 10 or

12 mm. The choice of implant length was

dictated by the preoperative radiographic

assessment of bone height in the canine

region and drilling distance, with the princi-

pal concern of achieving primary stability.

Bone height in the canine region was

assessed on orthopantomograms. Jaw bone

quality was rated during the dental implant

surgery, by the tactile resistance during dril-

ling. The same surgeon for all the cases

performed the implant surgery, allowing an

objective evaluation.

Both clinical and radiographic evaluation

permitted a classification according to the

Lekholm & Zarb (1985) index.

The implants were inserted under local

anaesthesia in a one-stage non-submerged

procedure according to a strict protocol (Wein-

gart & ten Bruggenkate 2000).

Prosthodontic procedure

The mandibular denture was adjusted by

selective grinding at the implant location, Pro-

tefix® (Queisser Pharma, Hamburg, Germany).

Adhesive cushions were provided and patients

received oral hygiene instructions. One, two

and 4 weeks after the surgical procedure,

patients were recalled for follow-up visits. At

the third follow-up visit, the manufacturing of a

new maxillary denture (for the full maxillary

edentulous patients) and a new mandibular

overdenture with metal reinforcement were

initiated. For the maxillary dentate patients,

correct maxillary fixed rehabilitation was

performed prior to implant surgery at the man-

dible.

After 6-week healing period, implants were

loaded using an early-loading protocol (Apari-

cio et al. 2003; Morton 2008; Lethaus et al.

2011). A dental assistant, not involved in this

research project randomly assigned the

patients to one of the three main groups

(Table 1, Fig 1a–g):

1. Group B – (n = 23) received retentive

anchors (Straumann); it was randomly

divided into two subgroups (B.1: with

gold matrix and B.2: with titanium

e172 | Clin. Oral Impl. Res. 25, 2014 / 171–178 © 2012 John Wiley & Sons A/S.

Cristache et al �Different retentions for implant mandibular overdenture

matrix), based on characteristics of the

overdenture attachment.

2. Group M – (n = 23) received magnets

(Titanmagnetics® Steco system-technick.

3. Group L – (n = 23) received locator (Zest

Anchors, Inc).

The random assigning was done using 69

sequentially numbered opaque sealed enve-

lopes (SNOSE) according to the protocol

proposed by Doig & Simpson (2005), regard-

less of the state of the opposing maxilla.

The prosthetic procedure was performed by

experienced prosthodontists, according to the

recommendations of the manufacturer (Strau-

mann Dental Implant System) for retentive

anchors, magnets and the locator system.

Occlusion was assessed both on the articula-

tor and intra-orally to secure a balanced

occlusion in centric relation without anterior

tooth contact (Naert et al. 2004b; Vercruys-

sen et al. 2010).

Patients were scheduled for follow-up visits

at 1-week post-prosthesis insertion and every

6-month post-abutment insertion. At each

follow-up visit, patient received oral hygiene

care and written oral hygiene instructions.

Outcome measurements

Data collection was performed by two inde-

pendent researchers (without knowledge of

the prosthodontist) at baseline assessment

(1 week after insertion of the implant over-

denture) (T0), 6 months (T) and annually (T1–

T5).

Prosthetic maintenance and complications

(related to implant components, structure of

the prosthesis and adjustments of the prosthe-

sis including soft tissue problems) were

assessed from baseline until T5, according to

the number of scheduled (planned and routine

procedures) and unscheduled visits (solicited

by the patients). All the events were prospec-

tively documented using evidence-based crite-

ria from baseline to 5 years and the

prosthodontic success was assessed with the

aid of the six-field table analysis proposed by

Payne et al. (2001). According to this analysis,

the criteria are defined as follows:

Success – no evidence of retreatment except

for accepted maintenance (includes patrix

activation/repair/replacement, matrix acti-

vation/repair/replacement and asymptom-

atic periimplant/interabutment mucosal

enlargement not requiring excision). There

is a limit of two replacements of either pa-

trix or matrix in the first year and five

replacements in 5 years, and one reline of

the overdenture base in 5 years.

Survival – patient cannot be examined

directly, but the patient or another clinician

confirms no evidence of retreatment except

that described for a successful outcome.

Unknown (lost to follow-up) – patient

cannot be traced; surviving or successful

implant overdenture removed to allow —

to provision of a new overdenture, for

example, conversion to another overden-

ture design with additional implants or a

fixed implant prosthesis using the same

or additional implants.

Deceased – patient died during the study

period regardless of whether successful or

surviving criteria were experienced and

recorded before death.

Retreatment (repair) – Treatment of

implant overdenture and/or mucosa where

marginal integrity and associated patrices/

matrices are maintained irrespective of

modifications as long as it continues as an

implant overdenture. This includes more

than two replacements of either patrix or

matrix in the first year or more than five

replacements in the first 5 years. It also

includes replacement of worn or fractured

overdenture teeth/fractured overdentures,

relining of overdenture more than once in

5 years or excision of patrix-associated

mucosal enlargement as a result of infringe-

ment on the shoulder/undersurface of the

patrix.

Retreatment (replace) – part or all of implant

overdenture is no longer serviceable

because of either loss of implants or irrep-

arable mechanical breakdown.

The two subgroups of Group B were analy-

sed separately.

Cost analysis

Costs for each type of attachment were calcu-

lated according to all the procedures and com-

plications at first year (T1) and fifth year (T5)

and were subdivided into direct and indirect

costs, being estimated based on the minimal

clinical charges for the procedures by the sur-

geon, prosthodontist and dental hygienist.

The direct costs included costs of dental labo-

ratory, costs of materials (implants and com-

ponents), pharmaceuticals, radiography and

charges for the procedures by the clinician

and the dental laboratory. The indirect costs

included the patient’s time and out-of-pocket

expenses (Penrod & Takanashi 2003).

In our calculation, the direct costs were

considered. Aftercare was defined as care and

maintenance provided during the evaluation

period, including check ups and cleaning.

Costs of complications (components, prostho-

dontist and dental laboratory fees) were

considered separately.

The costs of dental implants and compo-

nents are from the Romanian Straumann rep-

resentative – February 2009. Costs of the

prosthetic complications per patient were

calculated in the following manner: total costs

of complications per group/subgroup divided

by n (i.e. number of patients in the group/

subgroup) = costs of prosthetic complications

per patient in the respective group/subgroup.

Assessment of implant failure

This was performed according to previously

established criteria (Albrektsson et al. 1986).

Statistical analysis

Data were expressed as mean values, stan-

dard deviations (SD), ranges, medians and

percentages, as appropriate. The Levene test

was used to verify the homogeneity of vari-

Table 1. Groups/subgroups divided upon characteristics of overdenture attachments

Group No. of patients Patrix MatrixRetentive force indicatedby the manufacturer Manufacturer for Straumann

B, Subgroup B.1 12 Retentive anchor abutment,height 3.4 mm, titanium

Gold matrix – Elitor Varied retention (fourlamellae functioninglike a spring)

Straumann, Basel,Switzerland

B, Subgroup B.2 11 Titanium matrix Spring with a definedextraction force: 700–1100 g

Straumann, Basel,Switzerland

M 23 Titanmagnetics insert,height 3.25 mm,titanium housing

Denturetitanmagnetics

Not specified by themanufacturer

Steco system-technick,Hamburg, Germany

L 23 Locator abutment 3 mm,titanium alloy

Denture cap titaniumwith nylon retention

Pink light retention1360 g

Zest Anchors, Inc.,Escondido, CA, USA

© 2012 John Wiley & Sons A/S. e173 | Clin. Oral Impl. Res. 25, 2014 / 171–178


ance. Associations were tested using Pearson

Chi-squared test and Fisher’s exact test.

Analysis of variance was used to test for sig-

nificant differences between means, and the

Scheffe post hoc test analysed the effects

through multiple comparisons. Non-paramet-

ric Kruskal–Wallis and Mann–Whitney U

(Wilcoxon)-tests were performed to compare

the medians between the groups/subgroups

considered. All tests of significance were

two-tailed. StataIC 11 statistical software

(StataCorp LP, College Station, TX, USA,

version 2009) was used for data analysis. A

P-value < 0.05 was considered statistically

significant.

Results

The results confirmed group homogeneity.

There was no statistical difference between

groups for age, bone height in the canine

region and interimplant distance (P > 0.05,

one-way ANOVA test). No association was

recorded between any group and bone qual-

ity, bone quantity, gender or implant length

(P > 0.05, Pearson Chi-squared and Fisher’s

exact tests). No significant difference was

recorded between groups in terms of period

of edentulism (P > 0.05, Kruskal–Wallis test).

Out of the 138 implants placed, four were

lost in three patients (two women and one

man, the last one, a heavy smoker lost both

implants), leading to 97.1% survival rate

during the healing phase (before loading). The

four failed implants (length of 12 mm) were

replaced and healed uneventfully. All patients

could be treated as previously planned with

mandibular two implants overdenture. No

patient dropped out from the study. A mean

number of 3.49 � 5.64 (range 0–21, median 1)

maintenance events in the 5-year period was

recorded for the entire cohort of patients

(n = 69). Table 2 shows the number of main-

tenance events for each group per year.

Baseline group analysis

The summary of the main findings per group

is shown in Table 3.

Occurrence of complications

A mechanical complication occurred in one

patient of Group M, during the fourth year of

the evaluation period: the screw of one of the

abutments was fractured and a part of the

screw was stuck inside the implant. The bro-

ken piece was removed with the aid of a

service set sent by Straumann. A new abut-

ment was inserted and, due to the fracture, a

new denture had to be made.

Significantly more complications were

recorded in Subgroup B.1 than in Subgroup

B.2, Group M and Group L, respectively

(P < 0.05, Kruskal–Wallis and Mann–Whitney

U-tests). The number of maintenance events

was 241 in 5 years, with the following distri-

bution: 195 were observed in Group B (184 in

Subgroup B.1 and 11 in Subgroup B.2), 31 in

Group L and 15 in Group M. All the patients

belonging to Subgroup B.1 required matrix

activation at 6 months up to 1 year. Among

them, four patients needed matrix replace-

ment (eight prosthetic components for two

implants) (Table 4). No statistical significant

differences were recorded between Subgroup

B.2, Group L and Group M (P > 0.05, Kruskal

–Wallis and Mann–Whitney U-tests).

Prosthodontic success

In our study, Group M registered the highest

prosthetic success (82.60%) in 5 years,

followed by Group L (78.26%). Subgroup B.1

had the lowest success rate (50%) (Table 5).

Cost analysis

The subgroups B.1 and B.2 recorded differences

in cost of prosthetic components at the same

surgical, prosthodontic and dental laboratory

fee (B.1 = 1594 Euro/patient and B.2 = 1670

Euro/patient).

Subgroup B.1 registered more expensive

first-year aftercare and complications per

(a) (b)

(d)

(c)

(e)

(f) (g)

Fig. 1. Implant overdenture attachment systems: (a) Group B – Retentive anchor abutments; (b) Subgroup B.1 – Gold

matrix with variable retention; (c) Subgroup B.2 – Titaniummatrix with defined retention; (d) Group M – Magnet abut-

ments; (e) Group M – Magnet denture insert; (f) Group L – Locator abutments; (g) Group L – Locator denture insert.

Table 2. The distribution of maintenance events per year

Group Year 1 Year 2 Year 3 Year 4 Year 5

BB1 31 26 35 48 44B2 7 0 1 0 3

M 8 0 0 6 1L 7 0 0 11 13



patient comparing with the other groups/sub-

group (60 EUR vs. 40 EUR) due to the higher

number of maintenance events.

The costs per patient/group/subgroup are

shown in Table 6. The magnet group recorded

statistically significant higher costs compar-

ing with the other two groups, whilst no

statistical significant differences were

observed between Group B and Group L, after

the 5-year evaluation (Kruskal–Wallis and

Mann–Whitney U-tests). The complication

costs for Subgroup B.1 vs. B.2 during years two

to five were 309.5 Euro/patient and 3.63 Euro/

patient, respectively.

Discussion

The use, in our clinical study, of two implants

as attachment for overdentures is based on the

clearly demonstrated success (Mericske-Stern

& Zarb 1993; Naert et al. 1999, 2004a) of using

fewer (generally two) implants and in accor-

dance with the proposed standard clinical

treatment protocol for edentulous elderly

patients in daily practice (Feine et al. 2002).

The implant survival rate of 97.1% after

5 years, including loss of implants during the

osseointegration period (early failure) is com-

parable with the studies of Buser et al. (1999)

(96.2%), Ferrigno et al. (2002) (95.9%) and

Lethaus et al. (2011) (96.7%), with the use of

the same implant system and the same sur-

face treatment.

The 6-week loading protocol performed in

this study is considered an early-loading pro-

tocol. The absence of implant failures after

loading is in agreement with other studies

(Payne et al. 2002; Roccuzzo & Wilson 2002).

In the light of our findings, the overall num-

ber of prosthetic and soft tissue complications

were relatively low compared with other stud-

ies (Mackie et al. 2011). Most of the mainte-

nance requirements were easy to handle:

screwing loosening abutments or activation of

the matrix to improve retention (Subgroup

B.1). Considerably more prosthetic mainte-

nance requirements were registered in sub-

group B.1, similar to the findings of Walton

et al. (2009), but different from Watson et al.

findings (Watson et al. 2002). The type of gold

matrix used in the present study consisted of

four lamellae functioning like a spring. All the

patients needed at least one activation of the

gold alloy matrix per year (i.e. 100% activation

per year). This result is different from Wal-

ton’s findings who reported, in a 3-year study,

only 73% need of matrix activation (Walton

2003). Four patients needed fully replacement

of the gold matrices due to impossibility of

Table 3. Baseline clinical characteristics of the study groups

GroupsB(n = 23)

M(n = 23)

L(N = 23)

Age (years)Mean (SD) 57.8 (8.8) 63.4 (9.5) 64 (9.6)Median 58 64 65Range [42–76] [47–84] [47–80]

Bone height in canine region (mm)Mean (SD) 25.3 (5.6) 26.2 (4.9) 24.2 (3.7)Median 24 25 24Range [16–44] [18–36] [18.5–30.8]

Bone quality*

N (%)Type I 4 (17.39) 1 (4.35) 4 (17.39)Type II 13 (56.52) 19 (82.61) 14 (60.87)Type III 6 (26.09) 3 (13.04) 5 (21.74)Type IV 0 0 0

Bone quantity*

N (%)Class A 1 (4.35) 0 0Class B 7 (30.43) 11 (47.83) 13 (56.52)Class C 8 (34.78) 9 (39.13) 5 (21.74)Class D 7 (30.43) 3 (13.04) 5 (21.74)

Interimplant distance (mm)Mean (SD) 20.1 (7.3) 20.3 (5.8) 20.1 (4.9)Median 21 22 19.1Range [7–38] [4–31] [11.6–34]

*Lekholm & Zarb (1985).

Table 4. Prosthodontic and soft tissue complications during 5 years of functioning

No. of events

Group B

Group M Group LB.1 B.2

Patrix-related (implant abutment) maintenanceFracture of the abutment screw 0 0 1 0Loosening of the abutment screw 1 2 3 0

Matrix-related (overdenture component) maintenanceActivation of matrix 144 0 0 0Exchange of rubber ring 18 0 0 0Exchange of stainless steel spring 0 0 0 0Exchange of the matrix 8 0 0 0Replacement male locator 0 0 0 22

Overdenture-related maintenanceRelining overdenture 4 2 3 1Fracture of the overdenture 0 0 1 0Fracture of teeth 2 1 1 0New overdenture 2 1 1 1

Soft tissue-related complicationsMucositis, soreness 3 1 2 2Ulcer decubitus 1 2 1 1Hyperplasia 1 2 2 4

Table 5. Six-field table analysis of prosthodontic success after 5 years of functioning according toPayne et al. (2001)

Group BN (%)

Group MN (%)

Group LN (%)

B.1N (%)

B.2N (%)

14 (56.5)Success 6 (50) 8 (72.7) 19 (82.6) 18 (78.3)Surviving 0 0 0 0Deceased 0 0 0 0Unknown 0 0 0 0

9 (39.1)Retreatment (repair) 6 (50) 3 (27.3) 4 (17.4) 5(21.7)Retreatment (replace) 0 0 0 0



activation with breakage of one of the four

lamellae. The high number of maintenance

events usually recorded with this old version

matrix probably led to the replacement with

elliptical gold matrix.

No patrix wear for the retentive-anchor

patients (Group B) as well as no replacement

of stainless steel springs (titanium matrix)

occurred during the 5 years of functioning, in

contrast to previous findings (Watson et al.

2002; Walton 2003). The ball attachment

wear reported in other studies could be due

to misalignment of the implants (Walton

2003).

Prosthodontic success according to the six-

field table analysis (Payne et al. 2001)

(Table 6) was 50% for Group B.1 (retentive

anchors with gold matrix), that is, similar to

Mackie’s findings (Mackie et al. 2011) (54% in

5 years), but higher for Group B.2 (retentive

anchor with titaniummatrix, 72.7%). The pre-

viously mentioned study found a much lower

success rate for titanium matrix in 5 years

(33%).

An abutment fracture was recorded in

Group M. No similar events occurred during

the study. No such mechanical complica-

tions were described in other overdenture

studies with Straumann abutments (Rentsch-

Kollar et al. 2010; Mackie et al. 2011).

No wear or corrosion of magnetic abut-

ments was observed in 5 years of function.

Magnet abutments require lower skills for

wearing and cleaning and, especially due to

lower maintenance requirements, are recom-

mended to be used in elderly patients with

disabilities.

The highest number of events during the

first year was registered in Subgroup B.2 and

Group M, different from previous reported

results (Mackie et al. 2011). In the present

study, the most frequent complications during

the first year were soft tissue-related and acti-

vation of gold matrix (subgroup B.1). However,

the highest number of maintenance events

occurred during the fourth and fifth year of

service for Subgroup B.1 and Group L, mainly

consisting of matrix replacement.

The cost calculation was made taking into

consideration implant and component Strau-

mann prices (2009), for comparison reasons.

Gold matrix was last mentioned in that price

list (replaced with elliptical matrix).

From the cost calculation (Table 6), the

low initial cost for the implant treatment in

Subgroup B.1 has been noted, as opposed to

the high cost of the aftercare for the next

4 years. The lowest overall 5-year cost is

observed in Group B.2, followed in ascending

order by Group L, Subgroup B.1 and Group

M, respectively. Group M had an initially

high cost (components), but low aftercare

requirements. The highest costs represent a

hindrance in the use of magnets as attach-

ment for implant overdentures due to the

lower income of elderly patients and to the

fact that treatment is seldom supported by

the national or private health insurances.

The fact that significant differences were

partially recorded regarding costs and mainte-

nance requirements between the attachment

systems rejected the null hypothesis.

A limitation of the present study was the

heterogeneous maxillary status. Selection of

study participants who are all completely

edentulous in the maxilla would have allowed

for better standardization.

It can be concluded that, after 5-year follow-

up, the three attachment systems (retentive

anchor, magnets and locator) functioned well.

The implant-retained overdenture demands

continuous aftercare, especially when ball

attachment and golden matrix are used.

The magnets had a low maintenance

requirement and high success rate, despite the

relatively increased initial costs.

Retentive anchor with titanium matrix and

locator system may be better choices from a

financial point of view taking into consider-

ation the initial low cost of the components

and also the reduced number of complica-

tions.

The present findings do reflect that there

is variation in the maintenance of overden-

ture attachment systems. Because of this,

costs for maintenance of implant-retained

overdentures have considerable individual

variance and should not be universally inter-

preted.

Acknowledgments: The authors are

grateful to Associate Professor Dr. Roxana

Stegaroiu, Division of Oral Science for

Health Promotion, Department of Oral

Health and Welfare, Niigata University,

Japan, for useful comments and advice. This

study was supported by Grant No. 316/03

and Grant 507-207 from the ITI Foundation

for the Promotion of Oral Implantology,

Switzerland.

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Implants/components 694 770 1118 853Surgery 350 350 350 350Dental technician 200 200 200 200Prosthodontist 350 350 350 350Costs at delivery 1594 1670 2018 1753Costs at delivery per group 1630.34 2018 1753Aftercare and complications first year 60 40 40 40Total costs first year 1654 1710 2058 1793Aftercare 5 years 160 160 160 160Costs of complicationsper patient after 5 years

356.16 67.45 68.34 56.30

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Supporting Information

Additional Supporting Information may be

found in the online version of this article:

Data S1. CONSORT 2010 checklist of infor-

mation to include when reporting a rando-

mised trial*



five-year clinical trial using three attachment systems for implant overdentures

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