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Implant-supported fixed prostheses inthe edentulous maxilla: 8-yearprospective results

Christian MertensHelmut G. Steveling

Authors’ affiliations:Christian Mertens, Helmut G. Steveling, Departmentof Oral and Maxillofacial Surgery, University ofHeidelberg, Heidelberg, Germany

Corresponding author:Dr Christian Mertens

Department of Oral and Maxillofacial SurgeryUniversity of HeidelbergIm Neuenheimer Feld 40069120 HeidelbergGermanyTel.: þ 49 6221 56 39705Fax: þ 49 6221 56 4222e-mail: [email protected]

Key words: dental implants, edentulous maxilla, fixed prostheses, long-term follow-up, impla

survival, marginal bone loss

Abstract

Objective: The purpose of this prospective study was to evaluate the long-term survival and succe

rates of implants and screw-retained, full-arch prostheses placed in edentulous maxillae over 8 years

function.

Materials and methods: A total of 106 Astra Tech implants were placed in the maxillae of 17

edentulous patients in a one-stage surgical approach. After a healing period of 6 months, the patien

received fixed screw-retained bridges. Follow-up visits, including clinical and radiographic

examinations, were performed after 6 months and at yearly intervals. Implant survival, implant

success, and marginal bone-level changes were defined as the primary outcome variables. The

secondary aims were to report periodontal pathogens at 5 years’ follow-up and patients’ satisfactio

at the 8-year follow-up.

Results: The overall observation time was 8 years. One patient died during the study and one impla

failed during the healing period, yielding an 8-year cumulative implant survival rate of 99%. The

prosthetic survival rate was 100%. The mean crestal bone loss amounted to 0.3 0.72mm. Patien

subjective evaluations demonstrated an overall high level of satisfaction. In all cases, except for on

microbiologic probing of the peri-implant sulcus after 5 years showed no higher incidence of

periodontal pathogens.

Conclusions: Screw-retained, full-arch restorations on six implants in an edentulous maxilla are a

predictable and highly successful treatment concept as observed throughout this study with an

observation period of 8 years of function, in particular with respect to low crestal bone loss and hig

patient satisfaction.

Introduction and objective

A lower density frequently characterizes maxil-

lary bone, as opposed to mandibular bone. The

anatomic and morphologic structure of the max-

illa and the reduced bone volume caused by a

high degree of alveolar ridge resorption are con-

sidered to be critical to the success of dental

implants. The literature shows that maxillary

implants are generally less successful than those

in the mandible (Esposito et al. 1998). Implant-

retained maxillary overdentures seem to be af-

fected most frequently, and they show higher

failure rates, as well as greater marginal bone

loss, compared with mandibular implants. In a 3-

year follow-up report by Hutton et al. (1995), the

implant failure rate in cases of mandibular im-

plant-supported overdentures was 3.3%, whereas

it was 27.6% for maxillary overdentures.

Schwartz-Arad et al. (2005) reported a 10-year

implant survival rate for removable maxillary

implants of 83.5%, while the success rate w

only 41.9% when using the Albrektsson et

(1986) success criteria.

On the contrary, fixed prostheses in the maxi

are more successful than removable dentures. P

spective long-termstudies presentimplantsurvi

rates ranging from 95.5% to 97.9% when evalu

ing fixed full-arch bridges in the maxilla.(Bergkv

et al. 2004; Rasmusson et al. 2005; Fischer et

2008). Gallucci et al. (2009) have concluded th

fixed-implant prostheses in the edentulous maxi

are a scientifically validated treatment optio

Offsetting their high survival rates, phonetic pr

blems have been reported frequently for implan

supported maxillary fixed bridges, resulting in lo

patient satisfaction (Lundqvist et al. 1992a, 1992

Heydecke et al. 2004). The gap between muco

and fixed prostheses is thought to be a major cau

of speech difficulties (Lundqvist et al. 1992

Minimizing this gap, however, leads to impa

ment of hygienic procedures.

Date:Accepted 21 June 2010

To cite this article:

Mertens C, Steveling HG. Implant-supported fixedprostheses in the edentulous maxilla: 8-year prospectiveresults.Clin. Oral Impl. Res. 22, 2011; 464–472.doi: 10.1111/j.1600-0501.2010.02028.x

464 c 2010 John Wiley & Sons A

mailto:[email protected]:[email protected]


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The aim of this study was to investigate

whether appropriately designed, screw-retained,

full-arch prostheses retained by six to eight im-

plants are a feasible treatment option for the

edentulous maxilla.

To ensure complete assessment of this pros-

thetic design, not only implant and prosthetic

survival but additional parameters were also

evaluated during the observation period. The

primary objectives were implant survival as

well as marginal bone-level changes and implant

success, according to the Albrektsson success

criteria. The secondary outcome objectives were

patient satisfaction for assessment of all func-

tional aspects, such as phonetics. Plaque accu-

mulation and soft tissue reactions were measured

at every follow-up to evaluate the clinical para-

meters and the success of patients’ hygienic

procedures, because fixed restorations may be

difficult to clean. Additionally, microbiologic

probing of the peri-implant sulcus was performed

to determine a possible higher incidence of perio-

dontal pathogens and whether any specific mi-

crobiota composition could be identified. All

technical complications were recorded as well.

Patients included in this prospective clinical

trial were followed up over a period of 8 years,

and data were statistically evaluated because

long-term observations in prospective studies

can help validate the predictability of this treat-

ment modality.

Material and methods

Patient selection

The study protocol was approved by the ethics

committee for clinical studies of the Medical

Faculty, University of Heidelberg.

To be included in the study, patients had to

meet the following criteria: 18–75 years of age,

edentulous maxilla, and sufficient bone to sup-

port implants at least 9 mm in length. The

exclusion criteria were as follows: (1) need for

bone augmentation, (2) simultaneous tooth ex-

traction and implant placement, (3) Class 4 bone

quality according to the Lekholm & Zarb classi-

fication (1985; assessed by the surgeon during

fixture installation), (4) any systemic disease or

condition that could compromise postoperative

healing or osseointegration, and (5) taking sys-

temic corticosteroids or any other medication

that could compromise postoperative healing or

osseointegration. Smokers, bruxers, and patients

with poor oral hygiene were not excluded from

this study.

Each patient was thoroughly informed about

the study, and each signed an informed consent

form before entering the study. All patients were

treated between January and October 1999 in the

Department of Oral and Maxillofacial Surgery of

the Heidelberg University by the same experi-

enced clinician.

Surgical procedure

After clinical and radiographical examination

(including intraoral and panoramic radiography)

and verification that the patient fulfilled the

inclusion criteria and that none of the exclusion

criteria applied, he or she was scheduled for

implant surgery. All patients had been edentu-

lous in the maxilla for 6 months or longer. No

simultaneous tooth extractions were performed

during implant surgery.

All patients received prophylactic antibiotics

1 h before surgery, which was performed under

local anaesthesia. After crestal incision and eleva-

tion of a full-thickness muco-periosteal flap, six to

eight implants were placed using a standardized

surgical procedure. The number and location of

implants depended on the anatomic and morpho-

logic conditions of the bone. Implants were evenly

distributed in the anterior and posterior segments

of the edentulous maxilla, depending on the size,

curvature, and shape of the ridge. No surgical

templates were used. Inclination of the implants

was adapted to the opposing dentition. The quan-

tity and quality of the alveolar bone were assessed

during surgery according to the index described by

Lekholm and Zarb (1985). Insertion depth of the

implant was determined by the surrounding bone

to ensure that the implant neck and the alveolar

ridge were at the same level.

The implants (TiOblastt, Astra Tech AB,

Mölndal, Sweden) were moderately rough tita-

nium, screw shaped, and parallel walled. The

fixtures had a coronal portion equipped with

minute threads (MicroThreadt, Astra Tech

AB). Only implants of 3.5 and 4 mm diameter

and having a length of 9–15 mm were used,

depending on the bone dimensions. The implants

were placed using a one-stage surgical procedure.

After connection of healing abutments (Healing

Abutment Zebrat, Astra Tech AB), the flap was

closed and sutured. No postoperative antibiotics

were prescribed. The sutures were removed 7

days after the operation. Throughout this period,

mouth rinsing with chlorhexidine was pre-

scribed. Patients were not allowed to use their

existing complete upper denture until suture

removal. At that time, any pressure from the

denture base on the healing abutments was

relieved, and a resilient relining material was

applied to the base.

Prosthetic procedure

Prosthetic rehabilitation began after a healing

period of 6 months. The healing abutments

were removed and replaced by permanent, on

piece titanium abutments (Uni-Abutmentt, A

tra Tech AB), which were connected using

insertion torque of 20 Newton-centimet

(N cm), according to the manufacturer’s guid

lines. Abutment height was selected clinical

taking into account the mucosal thickness a

interocclusal space. After abutment connectio

impressions were taken using an individual op

tray, screw-retained transfer copings, and a po

ether impression material (Impregums

, 3

ESPE, Seefeld, Germany). Subsequently,

screw-retained registration of jaw relations

centric occlusion was taken. Fitting of the com

plete functional wax-up with assessment of o

clusion, phonetics, and aesthetic parameters a

fitting of the cast framework were perform

during the next appointment. The framewo

needed to fit passively without tension. Canti

vers were not to exceed 10 mm distal to t

position of the most distal implant. As occlus

concepts, either a bilateral balanced occlusion

canine guidance was applied, depending on t

opposing dentures. Finally, the permanent, on

piece, fixed reconstruction was manufactur

To allow for optimal oral hygiene, the relatio

ship between the gingival mucosa and the base

the bridge was evaluated. To avoid muco

irritations by impaired cleaning, the base of t

full-arch restoration was provided with a conve

bridge-like design, slightly contacting the o

mucosa. Concavities of the base should be com

pletely avoided (Figs 1–3). Additionally, the a

rylic base had to be free from porosities and sho

well-polished surfaces. After the denture w

screwed onto the abutments, the openings

Fig. 1 and 2. To avoid mucosal irritations by impai

cleaning, the acrylic base should have a convex surf

design.

Mertens & Steveling Implant-supported fixed prostheses in the edentulous max

c 2010 John Wiley & Sons A/S 465 | Clin. Oral Impl. Res. 22, 2011 / 464–4


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the screw holes were sealed with composite.

Hygiene instructions, including the use of in-

terdental brushes and floss, were given to all

patients.

Follow-up protocol

After delivery of the bridge, follow-up visits were

scheduled after 6 months, 12 months, and at

yearly intervals thereafter.

During the follow-ups, the following clinical

parameters were evaluated in accordance with

Mombelli et al. (1987):

Assessment of plaque accumulation – Modi-

fied Plaque Index:

Score 0: no detection of plaque;

Score 1: plaque recognized only by running a

probe across a smooth marginal surface of the

implant;Score 2: plaque can be seen at a glance;

Score 3: abundance of soft matter.

Assessment of bleeding – Modified Bleeding

Index:

Score 0: no bleeding when the periodontal

probe is passed along the gingival margin

adjacent to the implant;

Score 1: isolated bleeding spots visible;

Score 2: blood forms a confluent red line on

the margin;

Score 3: heavy or profuse bleeding.

Both bleeding and plaque accumulation were

obtained on the buccal, lingual, mesial, and distal

surfaces and were calculated per implant as one

unit. The bridges were not routinely removed at

the follow-ups. Only the 60-month follow-up

included completely unscrewing the denture to

test the implants for mobility (Fig. 4). A non-

mobile implant had to resist torquing of the

abutment to 20 N cm. Any implant mobility or

painful response was defined as implant failure.

Additionally, microbiologic probing of the peri-

implant sulcus was performed (ParoChecks

I Kit,

Lambda GmbH, Freistadt, Austria). Pooled sub-

gingival plaque samples were collected from all

implants of each individual patient. To avoid

contamination, samples were not taken before

supragingival plaque removal and isolation of the

area with cotton rolls. Around each abutment,

samples were obtained using two sterile paper

points, which were inserted into the sulcus until

resistance was met and left there for 15 s. All tips

used for one patient were transferred into a single

transport container.

The purpose of this test was to investigate

the composition of the microbiota of the peri-

implant sulcus in edentulous patients wearing

fixed restorations for many years. Because fixed

restorations are often suspected of having exces-

sive plaque accumulation owing to impaired

cleaning, the goal was to determine whether

there was a higher incidence of periodontal patho-

gens and whether any specific pattern could be

identified.

Radiographic examination

In addition to clinical assessments, radiographic

examinations were performed after implant sur-

gery, at prosthetic loading (radiographic baseline),

and at follow-up visits, which began 6 months

after prosthetic loading and then at yearly inter-

vals. The distance between the implant shoulder

and the first visible bone–implant contact was

measured (in mm) at the mesial and distal aspect

of each implant using periapical radiographs ta-

ken using the long-cone technique. (Arvidson

et al. 1998; De Bruyn et al. 2008). To correct

dimensional distortion, the apparent dimension

of each implant was measured on the radiograph

and compared with the actual implant size. To

ensure reproducibility between examinations,

radiographs were taken with the parallel techni-

que using film holders. Care was exercised to

ensure that threads on both the mesial and distal

sides of the implants were clearly imaged (Bergk-

vist et al. 2004; Fischer et al. 2008). All radio-

graphs were analysed by the same examiner, who

had not previously been actively involved in this

study. For evaluations and measurements, the X-

rays were digitalized and analysed using the

computer program Friacom Dental Office V

sion 2.5 (Friadent, Mannheim, Germany).

Statistical method

Data were evaluated using SPSS (SPSS In

Chigaco, IL, USA) and SAS Software (SAS, H

delberg, Germany). Statistical tests were appli

for descriptive and explorative reasons. T

Mann–Whitney test was used to compare t

variables between the groups (Lehmann 199

Associations between two variables were esta

lished based on Spearman’s rank-correlationco

ficient (Lehmann 1998). A P value of 0.05 w

considered to indicate an exploratory significa

difference. Arithmetic mean and standard err

were given for descriptive purposes.

Technical complications

Any problems with respect to implants, ab

ments, prostheses, or treatment as such w

recorded as complications. Survival was definas implants or prostheses not requiring replac

ment and still in function after 8 years. T

Albrektsson (1986) criteria were applied to det

mine implant success.

Prostheses presenting complications, such

fractures of metal frameworks or smaller repai

such as repair of acrylic parts, were consider

survivors but not successful.

Patients satisfaction

At the 8-year-follow-up, patients were asked

fill in questionnaires related to satisfaction a

the psychological effects concerning their iplant-supported bridges. Evaluation of functio

involving both chewing and phonetics, a

thetics, and overall satisfaction were recorde

Response alternatives for patients were as f

lows: 1 ¼ very satisfied, 2 ¼ satisfied, 3 ¼ neutr

4 ¼ dissatisfied, and 5 ¼ very dissatisfied. In a

dition, patients were asked whether they wou

have chosen the same treatment again, knowi

what this particular treatment consisted of.

Results

Patients

A total of 106 Astra Tech dental implants we

placed in the edentulous maxillae of 17 patien

(12 female, 5 male). On the day of surge

patients’ ages ranged from 41 to 69 years, wi

a mean of 55.6 7.3 years.

Eight patients were smokers (47%), four we

previous smokers (23.5%), and five were no

smokers (29.4%).

All patients had an opposing denture in t

mandible at the time of implant surgery to ensu

stable occlusion. Three patients had natu

teeth, nine had removable partial prosthes

Fig. 3. Bridge-like design with slight contact to the oral

mucosa, permitting the use of interdental brushes and

flossing techniques.

Fig. 4. Clinical situation after 60 months of function.

Screw-retained prostheses were removed for the first time

for microbiologic probing of the periimplant sulcus. Only

minimum mucosal irritations are visible.

Mertens & Steveling Implant-supported fixed prostheses in the edentulous maxilla

466 | Clin. Oral Impl. Res. 22, 2011 / 464–472 c 2010 John Wiley & Sons A


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two had fixed partial prostheses, and one patient

had an implant-supported denture. Only two

patients had a complete denture.

Implants

In aggregate, 99 implants could be evaluated and

assessed throughout an observation period of 8

years (mean observation period, 8.34 0.53

years). Originally, 106 implants had been placed

in 17 patients eligible for clinical evaluation.

During the first year after installation, one pa-

tient died from cancer (six implants) and one

patient lost one implant during the healing per-

iod, which was not replaced. No further implant

losses occurred during the course of the study.

Patients received six to eight implants at surgery.

In most patients ( n ¼ 15), six implants were

placed to retain the fixed full-arch bridge

(88.2%). The 8-year cumulative implant survival

rate was 99%. When applying the Albrektsson

implant success criteria, an implant is defined as

being successful if the marginal bone loss is

1 mm or less within the first year after insertion

of the prosthesis and not greater than 0.2 mm in

each subsequent year of function. Using these

radiographic criteria on our patients, crestal bone

loss after 8 years of function should not exceed

2.4 mm in total. Throughout this study, only

four individual implants failed to meet these

criteria. Additionally, all implants were tested

individually for mobility and were found to be

clinically stable, no peri-implant radiolucency

was identified around any of the implants, and

no signs or symptoms of pain were reported.

Thus, the overall success rate according to Al-

brektsson et al. (1986) was 96% after 8 years.

Clinical examination

According to Mombelli’s plaque index, 92% of

the implants had a satisfactory oral hygiene

status (grades 0 and 1; Table 1) at the 8-year

follow-up. Bleeding on probing was also evalu-

ated, showing an incidence of bleeding in the

peri-implant mucosa of around 45% of the im-

plants. A high tendency towards bleeding wasfound in only one implant site.

Microbiologic probing of the periimplant su

cus showed normal flora in all cases, except f

two, after 60 months of function (Table 2).

Radiographic examination

Radiographic examination of the remaining

implants after 8 years of loading revealed a memarginal bone resorption of 0.3 0.72m

(minimum: 0 mm, maximum: 4.48mm). M

sially, a bone loss of 0.28 0.87mm was

corded; the distal value was 0.33 0.68m

Altogether, 62 implants (63% of all examin

implants) remained without any evidence

crestal bone-level changes or angular defects

the proximal sites. An additional 24 implan

(87% of all implants) showed a marginal bo

loss of less than 0.5 mm. Fig. 5 summarizes t

results of the radiographic assessment. Only fo

implants (4%) showed a bone loss greater th

2.4 mm. All four of these implants showed fomesial measurements worse than 2.4 mm, b

Table1. Scores of the clinical examination after 8years

Periimplant parameters 8 years

MPI MBI Mobility

Score 0 49 54 99

Score 1 42 38 0

Score 2 6 6 0

Score 3 2 1 0

Score range 0–3 in accordance with Mombelli et al.(1987).

MPI, Modified Plaque Index; MBI, Modified Bleeding

Index.

Table2. Results of microbiologic probing per patient analyzed after 60 months of function

Results of microbiologic probing

1 2 3 4 5 6 7 8 9 10 11 1 2 13 14 15 16

Actinobacillus actinomycetemcomitans

Actinomyces viscosus ( þ )

Tannerella forsythensis ( þ ) þ þ ( þ ) ( þ ) þ þ

Campylobacter rectus þ þ þ ( þ )

Treponema denticola ( þ ) þ ( þ )

Eikenella corrodens

(þ

)

(þ

) þ

Prevotella intermedia þ ( þ ) ( þ ) þ þ

Peptostreptococcus micros þ ( þ )

Porphyromonas gingivalis þ þ ( þ ) þ þ ( þ ) þ

Fusobacterium nucleatum þ ( þ ) þ þ þ þ

Actinomyces odontolyticus ( þ ) ( þ ) ( þ ) þ þ ( þ ) ( þ ) ( þ ) þ þ ( þ ) ( þ ) þ þ ( þ )

Campylobacter concisus

Campylobacter gracilis þ þ þ

Capnocytophaga gingivalis ( þ ) ( þ ) þ þ

Prevotella nigrescens ( þ )

Eubacterium nodatum

Streptococcus constellatus

Streptococcus gordonii þ þ

Streptococcus mitis ( þ ) þ þ ( þ ) þ þ ( þ ) ( þ ) þ þ ( þ )

Veillonella parvula þ þ þ þ þ þ þ þ þ ( þ ) þ þ þ ( þ ) ( þ ) þ þ þ

, negative; ( þ ), weakly positive; þ , positive; þ þ , strong positive; þ þ þ , very strong positive.

0%

20%

40%

60%

80%

100%

0

n=62

2

n=4

Marginal bone loss [mm]

mean: 0.3 mmSD: 0.72 mmmin: 0 mmmedian: 0 mmmax: 4.48 mmsample size: 99

Fig. 5. Frequency distribution including descriptive statistics of marginal bone loss after 8 years in function.




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only three of these (3%) also had distal bone loss

measurements above 2.4 mm.

The analysis of marginal bone-level changes in

relation to implant length and diameter indicates

that shorter implants (9 and 11 mm) showed no

greater bone resorption than longer implants (13

and 15 mm). The Spearman rank correlation

coefficient showed an association between im-

plant length and bone loss ( r ¼ 0.22, P ¼ 0.03),

with higher losses with increasing implant length

(Fig. 7).

Large-diameter implants showed somewhat

less bone loss than small-diameter implants,

but without statistical significance (P ¼ 0.146).

Implants with a 3.5mm diameter showed a

marginal bone loss of 0.33mm; implants of

4 mm diameter showed a marginal bone loss of

0.2mm (Fig. 6).

The mean marginal bone loss around implants

related to smoking is presented in Table 3; no

exploratory differences were found between smo-

kers and nonsmokers.

Technical complications

The survival rate of the suprastructure was

100%. After 8 years, all patients were still wear-

ing the same fixed bridges. The most common

complications observed were related to the resin

part of the prostheses, that is, chipping of acrylic

teeth (three patients), ageing of the acrylic base,

or discolorations at the contact area between the

teeth and the acrylic base (six patients). All of

these complications were reparable without hav-

ing to replace the prosthesis or entailing high

costs, as compared with ceramic works. No

complications were recorded concerning fractures

of the metal frameworks or loosening or fracture

of abutments or abutment screws. During the

observation period, loss of the composite seals

over screw holes was recorded as well. The

prosthetic success rate was 82.4%.

Patients satisfaction

The results of the 8-year evaluation of function,

aesthetics, speaking, and overall patient satisfac-

tion ranged from highto very high (Table 4). After

8 years, all patients declared that they wouldchoose the same treatment concept again.

Discussion

Because of anatomical structure and specific bone

quality, implant treatment of the completely

edentulous maxilla is often associated with

higher implant failure rates and higher marginal

bone loss as compared with mandibular implants.

In this study, patients received fixed, screw-

retained, full-arch bridges with distal cantilevers

on six to eight implants, and they were examinedannually over a period of 8 years. A high homo-

geneity of the data was achieved by treating all

patients for the same indication. The prospective

study design, combined with the fact that almost

all patients were available for the complete ob-

servation period, is another strength of this study.

Additionally, not only implant survival but also

marginal bone loss, clinical parameters, micro-

biologic probing, and patient satisfaction were

observed and assessed.

With respect to implant survival, the results

this study are comparable with the outcome

similar studies analysing patients with fix

screw-retained implant dentures in the eden

lous maxilla ranging from 95.5% to 97.9% (F

rigno et al. 2002; Bergkvist et al. 200

Rasmusson et al. 2005; Fischer et al. 2008).

Further, literature search reveals that the su

vival rates of implants with rough surfaces a

significantly higher than those of machined im

plants. Moreover, the survival rates of machin

implants were found to decrease continuou

over the years, whereas the rates for roug

surface implants remained stable for up

10 years of follow-up (Lambert et al. 200

Lambert concludes that a rough surface on den

implants is important for stable, long-term

sults of fixed-implant rehabilitation of the ede

tulous maxilla.

The aspect of marginal bone stability is a

positively influenced by rough surface implan

as compared with machined implants (Web

et al. 2000; Watzak et al. 2006), consequen

leading to an increase in the overall impla

success (Van de Velde et al. 2007; De Bru

et al. 2008). Le Guéhennec et al. (2007) co

cluded in a review on surface roughness that

means of increased surface roughness not on

osseointegration can be enhanced, but also t

prevention of bone resorption.

Measurement of marginal bone-level loss ov

time is a valuable indicator in evaluating t

clinical performance of implants, because t

gradual loss of marginal bone eventually lea

to implant failure. By measuring each impla

mesially and distally, very accurate objecti

results can be obtained. All implants in t

present study were evaluated radiographica

on a regular basis. Initial intraoral radiograp

were taken after implant placement, followed

radiographs taken 6 months later at the tim

of prosthetic loading. After a further 6-mon

period, the first radiographic follow-up w

obtained, followed by annual radiographic co

trols. The accuracy of marginal bone-level me

surements is influenced by the precision of bo

the radiographic technique and the measureme

technique. To ensure reproducibility betwe

examinations, radiographs were taken using t

parallel technique, using commercially availab

film holders. Care was exercised to ensure th

threads on mesial distal sides of the implan

were clearly imaged (Bergkvist et al. 2004, 200

Fischer et al. 2008). To correct dimension

distortion, the apparent dimension of each i

plant was measured on the radiograph and com

pared with the actual implant size. Radiograp

were not standardized using individually fab

cated film holders for each implant at th

time, although the standardization of radiograp

0

0.5

1

1.5

2

2.5

3

3.5

4

3.5 4

implant diameter [mm]

m a r g i n a l b o n e

l o s s [ m m ]

Spearman's rank

correlation of implant

length and marginalbone loss: r = –0.15

(p=0.146)

Fig. 6. Marginal bone loss in relation to implant diameter.

0

1

2

3

4

5

9 11 13 15

implant length [mm]

m a r g i n a l b o n e l o s s [ m m ] Spearman's rank

correlation of implant

length and marginal bone

loss: r = 0.22 (p=0.030)

Fig. 7. Marginal bone loss in relation to implant length.




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would have further increased the comparability

and accuracy of the data. The measurement

technique used in this study, however, is iden-

tical to that used in most investigations analyzing

marginal bone levels in the edentulous maxilla

(Bergkvist et al. 2004; De Bruyn et al. 2008;

Fischer et al. 2008).

With respect to marginal bone stability around

the implants (mean marginal bone loss: only

0.3 mm after 8 years), the treatment outcome

can be rated as high. Our results in terms of

maintained marginal bone corroborate the long-

term results of other authors using the same

implant system – although for different indica-

tions (Rasmusson et al. 2005; Gotfredsen 2009;

Vroom et al. 2009).

From a statistical point of view, implant data

have to be considered as dependent data observa-

tions when assessing marginal bone-level

changes related to individual implants retaining

a full-arch restoration. Chuang et al. (2001)

statistically validated three different models for

estimating implant survival. The models they

used for studying a total of 660 patients were

based on (1) a random selection of one implant

per patient only; (2) the inclusion of all implants,

assuming independence among all implants of

the same subject; and (3) the inclusion of all

implants, assuming dependence among all im-

plants of the same subject. They were not able to

demonstrate significant differences and con-

cluded that both the survival point estimates as

well as the standard-error estimates varied very

little among the three models. Considering the

number of patients in this study, the indepen-

dence model was selected as appropriate to ana-

lyse the data available on implant level.

The analysis of marginal bone-level data with

respect to implant length in this study demon-

strated that shorter implants involve no higher

bone loss than longer implants.

These findings are supported by the recent

literature on short implants. While studies using

short machined implants document far lower

survival rates than longer implants (Winkler

et al. 2000; Herrmann et al. 2005), studies with

rough surface implants reported that implant

length did not influence the survival rates (Buser

et al. 1997; Testori et al. 2001; Feldman et al.

2004). Implant surface topography seems to be

one of the main factors influencing implant

survival. An unfavourable implant-to-crown ra-

tio was believed to cause overloading. The in-

creased bone stress leads to atrophy and higher

marginal bone loss (Rangert et al. 1997). A

systematic review by Blanes (2009), however,

demonstrated that implant-to-crown ratios do

not influence marginal bone loss. One article

showed even less marginal bone loss with higher

crown-to-implant ratios (Blanes et al. 2007).

Marginal bone loss was further assessed using

the Albrektsson success criteria (Albrektsson

et al. 1986). With an implant survival of 99%

and a respective implant success of 96% after 8

years, the difference between implant survival

and success was only minor. Albrektsson et al.

(1981) had already described the following factors

as preconditions for successful osseointegration:

implant material, implant design, surface quality,

status of the bone, surgical technique, and im-

plant loading conditions.

The exceptional use of native bone in this

study could have also contributed to the high

success rates, because patients requiring augmen-

tation procedures were excluded. Lambert et al.

(2009) showed that the survival rates of ma-

chined implants were significantly higher when

placed in native bone compared with implants in

augmented bone. However, this study also fou

that the survival rates for rough-surface implan

were the same whether placed in native

regenerated bone. Survival of machined implan

placed in augmented maxillary bone, in contra

decreased significantly over the years.

Concerning the number of implants necessa

to retain a fixed, full-arch restoration in t

edentulous maxilla, this study shows that t

use of six implants seems to be sufficient

providing long-term stability, because all, exce

for two, patients received six implants. Oth

studies report that for fixed maxillary reconstru

tions, eight implants distributed strategically a

necessary for long-term success (Lambert et

2009). However, our 8-year data demonstr

that six implants seem to be able to provi

long-term, stablereconstruction. Even with oth

loading modalities, such as early or immedia

loading, the survival rates of rough-surfaced i

plants are comparable to conventional loadi

protocols. Fischer et al. (2008) showed that the

were no significant differences between early a

delayed loading in the edentulous maxilla usi

five or six implants for implant-supported, fix

prostheses. Bergkvist et al. (2009) reported sim

lar survival rates, comparing conventiona

loaded and immediately loaded implants. A

fixed, screw-retained reconstructions were

tained by six implants.

The use of fixed implant rehabilitations of t

edentulous maxilla also seems to improve im

plant survival and reduce marginal bone loss

contrast to removable solutions (Hutton et

1995; Schwartz-Arad et al. 2005). Comparis

of various fixed prosthetic concepts such as eig

strategically distributed implants with retaini

segmented rehabilitations, that is, four thre

unit fixed bridges (Gallucci et al. 2004, 200

with one-piece, full-arch reconstructio

yielded no statistical differences (Lambert et

2009).

The advantages of screw-retained, full-ar

prostheses are – besides high hard- and soft-tiss

stability – the capability to compensate for com

plications such as divergent implant axes, lo

teeth, wide interdental spaces, missing cong

ence of implant location, and tooth position,

well as compensating for sagittal miscorrelatio

between jaws. Such adverse morphologi

Table3. Marginal bone loss around implants related to smoking

Exposure of implants

to smoking

Mean SE Minimum Median Maximum Sample size P -value

Mean bone loss (mm) – 0.15 0.04 0 0 1.62 57 0.07

þ þ 0.51 0.16 0 0 4.48 42

Marginal bone loss (mesial) (mm) – 0.08 0.03 0 0 1.46 57 0.12

þ þ 0.54 0.20 0 0 5.76 42

Marginal bone loss (distal) (mm) – 0.21 0.06 0 0 2.63 57 0.26

þ þ 0.48 0.13 0 0 3.21 42

Table4. Scores of the item denture satisfaction questionnaire 8 years after treatment

Satisfaction 8 years

Patients (N ) Function (eating) Speaking Appearance Satisfaction

Score 1 14 13 12 13

Score 2 2 3 4 3

Score 3 0 0 0 0

Score 4 0 0 0 0

Score 5 0 0 0 0

Scale range 1–5: 1 ¼ very satisfied, 2 ¼ satisfied, 3 ¼ neutral, 4 ¼ dissatisfied, 5 ¼ very dissatisfied.




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