multivariate study of factors influencing primary dental implant stability

Multivariate study of factorsinfluencing primary dental implantstability

Francisco MesaRicardo MunozBlas NoguerolJuan de Dios LunaPablo GalindoFrancisco O’Valle

Authors’ affiliations:Francisco Mesa, Department of Periodontology,School of Dentistry, University of Granada,Granada, SpainRicardo Munoz, Private Practice, Granada, SpainBlas Noguerol, Private Practice in Periodontologyand Oral Implants, Granada, SpainJuan de Dios Luna, Department of Statistics, Schoolof Medicine, University of Granada, Granada, SpainPablo Galindo, Department of Surgery, School ofDentistry, University of Granada, Granada, SpainFrancisco O’Valle, Department of Pathology, Schoolof Medicine and IBIMER, University of Granada,Granada, Spain

Correspondence to:Dr Francisco MesaFacultad de Odontologıa, Campus de Cartuja s/nUniversidad de GranadaE-18071 Granada, SpainTel.: þ 34 958 240 654Fax: þ 34 958 240 908e-mail: [email protected]

Key words: dental implants, multivariate analysis, Periotests

, primary stability

Abstract

Objectives: The purpose was to determine by multivariate analysis in a large series of

dental implants the variables associated with primary endosseous dental implant stability

(DIS).

Material and methods: A 10-year retrospective study was conducted of 1084 Branemarks

implants placed in 316 patients. Clinical variables (age, gender, smoking habit, and

periodontal status), implant diameter, implant length, and Periotests

values (PTVs) were

analyzed in bivariate and multivariate studies in order to determine their influence on DIS,

using a cut-off PTV value of �2.

Results: The site of implant insertion showed the strongest association with primary DIS

failure among the study variables. Implants in the anterior mandible had a 6.43-fold lower

risk of primary DIS risk vs. those at other sites [95% confidence interval (CI) 3.28–12.61], and

implants in the maxillary had a 2.70-fold higher risk of primary DIS failure vs. those in the

mandible (95% CI 1.82–4). Among other variables, females had a 1.54-fold higher risk of

primary DIS failure vs. males (95% CI 1.88–2.22) and implants o15 mm in length had a 1.49-

fold higher risk of failure vs. longer implants (95% CI 1.09–2.04).

Conclusion: According to these findings, primary DIS failure is more likely in females, at

sites other than the anterior mandible, and with dental implants shorter than 15 mm, at

least when non-threaded titanium implants are used. These data may be of value in the

identification of patients at a high risk of primary DIS failure with immediate implant

loading.

Endosseous dental implant stability (DIS)

can be defined as the capacity of the

implant to withstand loading in axial, lat-

eral, and rotational directions. The clinical

perception of implant stability is often

related to rotational resistance during pla-

cement of the implant (Friberg et al. 1999)

or application of removal torque (Sullivan

et al. 1996). The primary stability of dental

implants depends on the contact of bone

with implant, and various methods have

been used to assess objectively the stability

of the bone–implant interface (Ersanli et al.

2005) at the time of insertion and through-

out the osseointegration period. The Peri-

otests

and resonance frequency analysis

(Osstells

apparatus) (Schulte 1988; Olive

& Aparicio 1990; Meredith et al. 1996;

Ostman et al. 2006) have been described

as useful methods to assess primary DIS

(Goransson & Wennerberg 2005). They

were also reported to yield valuable infor-

mation on favorable or unfavorable changes

in the bone–implant interface after unco-

vering (Morris et al. 2003) and on bone

healing during osseointegration (Huang

Date:Accepted 19 January 2007

To cite this article:Mesa F, Munoz R, Noguerol B, Luna JD, Galindo P,O’Valle F. Multivariate study of factors influencingprimary dental implant stability.Clin. Oral Impl. Res. 19, 2008; 196–200doi: 10.1111/j.1600-0501.2007.01450.x

196 c� 2007 The Authors. Journal compilation c� 2007 Blackwell Munksgaard

et al. 2005). Use of the Periotests

with a

cut-off Periotest value (PTV) of � 2 (� � 2

vs. 4� 2) at first surgery has been found to

offer high sensitivity in the prognosis of

early implant loss and to have a higher

capacity to indirectly evaluate stability

during the osseointegration period com-

pared with a radiographic study (Noguerol

et al. 2006).

There has been limited investigation of

the factors that influence primary stability

or of its predictability at different sites in

the jawbone. The degree of primary stabi-

lity after implant placement has been

related to bone quality, implant design,

patient characteristics, and surgical techni-

que, among other factors (Ostman et al.

2006). The aim of the present study of a

large series of dental implants was to use

multivariate analysis to determine the vari-

ables associated with endosseous primary

DIS, using a PTV cut-off point of � 2.

Material and methods

A retrospective study was conducted of

1084 Branemarks

implants (Nobel Biocare

Iberica, Barcelona Spain) placed in 316

consecutive patients during a 10-year period.

The following data were gathered on all

patients.

Clinical variables

Data were collected on age, gender, and

smoking habit at the time of surgery

(four categories: 0: non-smoking; 1: 1–

10 cigarettes/day; 2: 11–20 cigarettes/day;

3:420 cigarettes/day). Periodontal status

before implant insertion was determined

by clinical probing and radiographic study,

assigning patients to one of three groups

(without periodontitis, with periodontitis,

edentulous). Patients with periodontitis

were treated before implant placement.

The degree of periodontitis was defined as

reported previously (Arbes et al. 1999) by

the percentage of sites with loss of attach-

ment � 3 mm (0%: absent; 0–32%: mild;

33–66%: moderate; 67–100%: severe).

Implant-related variables

Branemarks

implants with different dia-

meters (3.3, 3.75, 4, 5, and 5.5 mm) and

lengths (7, 8, 8.5, 10, 11.5, 12, 13, 15, and

18 mm) were used. Implant diameter and

length were considered as independent

variables. The location of the implant was

recorded as mandibular (n¼ 433) or max-

illary (n¼ 651) and anterior (n¼507) or

posterior (n¼ 577), and it was noted

whether the anchorage was monocortical

or bicortical. Bone quality at surgery was

classified into one of four categories accord-

ing to the criteria proposed by Lekholm &

Zarb (1985). Finally, it was recorded

whether the implant was lost or removed

at an early stage (before or at stage-2

surgery). Implants were considered to

have failed and were removed according

to the clinical criteria of mobility, pain,

and gingival inflammation.

The Periotests

(Siemens AG, Bensheim,

Germany) was used to record PTVs follow-

ing the manufacturer’s instructions, and

the cut-off PTV value was considered to

be �2 in accordance with results obtained

at first-stage surgery in a previous study by

our group (Noguerol et al. in press).

Statistical analysis

A bivariate analysis was carried out using

the method of Rao & Scott (1981) to

identify the variables associated with pri-

mary stability. Multivariate logistic regres-

sion analyses for grouped values were then

performed following the methods proposed

by Binder (1983) and Kish & Frankel

(1974), to determine the independent in-

fluence of each variable. The design, cod-

ing, and debugging of the database and the

statistical analysis were carried out using

STATA PC/Windows version 8.0 (Stata-

Corp LP, College Station, TX, USA).

Results

During a 10-year period, 1084 dental im-

plants were placed at the same clinic in 174

females (55%) and 142 males (45%), a

total of 316 patients with a mean age of

50.7� 12.31 years (range 19–87 years).

Six hundred and five implants were placed

in females (55.8%) and 479 (44.2%) in

males; 651 (60.1%) implants were inserted

into the maxillary and 433 (39.9%) into

the mandible. Table 1 shows the insertion

sites of implants and the remaining study

variables. Fifty-five (5.1%) implants were

considered to have failed during healing

according to clinical criteria (mobility,

pain, and gingival inflammation) and

were removed early, before second-stage

surgery.

A bivariate model to predict primary DIS

(Model 0) was constructed including all

variables of possible interest. Table 2 shows

the associations found between primary

stability failure (PTV�2) and the follow-

ing variables: age, sex, smoking habits, oral

and periodontal health status, maxillary/

mandibular placement, placement site,

bone quality, and implant diameter and

length.

A multivariate logistic regression model

was constructed using the variables that

showed independent influence on primary

Table 1. Description of variables included in the study

Variables Type Category n %

Tobacco Categorical Non-smoker 521 48.1Smoker o10 cigarettes/day 184 17Smoker 10–20 cigarettes/day 166 15.3Smoker 420 cigarettes/day 210 19.4Missing 3 0.3

Periodontal statusn Ordinal Periodontal health 220 20.3Mild periodontitis 12 1.1Moderate periodontitis 70 6.5Severe periodontitis 681 62.9Edentulous 101 9.3

Implant site Categorical Anterior maxilla 317 29.2Posterior maxilla 334 30.8Anterior mandible 190 17.5Posterior mandible 243 22.4

Bone qualityw Ordinal Type I bone 58 5.4Type II bone 449 41.4Type III bone 493 45.5Type IV bone 79 7.3Missing 5 0.5

nPeriodontitis classification according to Arbes et al. (1999).

wBone classification according to Lekholm & Zarb (1985).

Mesa et al . Endosseous primary dental implant stability

c� 2007 The Authors. Journal compilation c� 2007 Blackwell Munksgaard 197 | Clin. Oral Impl. Res. 19, 2008 / 196–200

implant stability (see Models I and II in

Table 2). In the present study, using a PTV

cut-off value of � 2, only four variables

were significantly associated with primary

DIS failure. Thus, females had a 1.54-fold

higher risk of primary DIS failure vs. males

(95% CI, 1.08–2.22); implants placed in

the maxilla had a 2.7-fold higher risk vs.

those in the mandible (95% CI 1.82–4);

implants in the anterior mandible had a

6.43-fold lower risk vs. those at any other

site (95% CI 3.28–12.61); and implants

shorter than 15 mm had a 1.49-fold higher

risk of primary DIS failure vs. longer im-

plants (95% CI 1.09–2.04). No association

was found between risk of primary DIS

failure and patient age, cigarette consump-

tion, bone quality, periodontal status, or

implant diameter.

In the bivariate model (Model 0), a sig-

nificant difference in primary DIS failure

was observed between periodontal and non-

periodontal/edentulous patients, but this

difference disappeared when the model

was adjusted for the remaining variables

(Model II).

Discussion

The primary clinical outcome of implant

placement is its primary stability, i.e., its

rigid fixation within the host bone cavity

and absence of micromotion (Adell et al.

1981; Futami et al. 2000; Meyer et al.

2004). We gathered data on a large series

of patients and constructed a multivariate

model that included variables that can

influence primary DIS, using the Periot-

ests

with a cut-off PTV of �2. Placement

in the maxilla, implant length shorter than

15 mm, and female gender showed a sta-

tistically significant association with a

higher risk of primary DIS failure, with

no significant association found for the

other study variables.

Lachmann et al. (2006a, 2006b) recently

conducted an experimental study in a bo-

vine rib segment to evaluate and compare

the reliability of Osstellt and Periotesttt

devices to assess implant stability. They

reported that these methods were similarly

reliable and yielded strongly associated

classifications of implant stability. The

results obtained demonstrated that reso-

nance frequency analysis and damping ca-

pacity assessment can both be

recommended for clinical use in implant

stability assessment. Our group previously

demonstrated that the Periotests

(with �2

cut-off) offers higher sensitivity vs. radio-

graphy in the prognosis of early implant

loss at first surgery and a better assessment

of implant stability during the osseointe-

gration period (Noguerol et al. 2006). Sta-

tistical analyses were structured on the

basis of these findings.

Some disagreement remains on the

causes of primary DIS failure. It has been

reported that primary stability depends on

the surgical techniques and implant design

(O’Sullivan et al. 2004), and on implant

site (Sennerby et al. 1991; Butcher et al.

2003; Saadoun et al. 2004; Sevimay et al.

2005), while others have identified bone

density and implant diameter/length as

influential factors (Ostman et al. 2006).

Our results indicate that only a small

number of clinical and implant variables

have a statistically significant influence on

primary DIS. These should be taken into

account before implant placement to mini-

mize the risk of failure.

Changes in implant stability that occur

early, during the first 8 weeks after inser-

tion, have been attributed to a delay in

bone healing (Buser et al. 2004). Long-

term success of load-bearing oral implants

requires solid fixation of the implant

within the host bone by osseointegration.

It was reported previously that implants in

the posterior maxilla fail more frequently

than those in the anterior mandible (Buser

et al. 1990; Salonen et al. 1993; Haas et al.

1995; Tricio et al. 1995; Engel et al. 2001),

explained by the higher ratio of compact to

cancellous bone in the latter (Adell et al.

1981; Lazzara et al. 1996). In our patients,

higher PTVs and significantly less primary

DIS were observed for implants placed in

the maxilla than for those in the mandible

and for implants placed in the anterior vs.

posterior mandible, as also found by Tricio

et al. (1995) and Boronat-Lopez et al.

(2006).

Differences in bone mass between males

and females would explain the lower num-

ber of DIS failures in males. In the current

study, PTVs at the time of implant place-

ment were lower in males vs. females.

Similar values were published in a recent

study of the primary DIS of 905 Brane-

marks

implants using Resonance Fre-

quency Analysis (Ostman et al. 2006).

Better primary stability of maxillary im-

plants was demonstrated in males (Buser

et al. 1990; Tricio et al. 1995), whereas no

difference between sexes was observed in

stability during osseointegration (Haas

et al. 1995). The PTVs obtained at second-

Table 2. Bivariate and multivariate models: variables associated with primary dental implant stability

Variables Reference category Risk category Model 0n Model In Model IIn

OR 95% CI OR 95% CI OR 95% CI

Age 460 years �60 years 1.45 [0.97, 2.17]Gender Male Female 1.35 [0.95, 1.92] 1.54 [1.08, 2.22]Tobacco �20 cigarettes/day 420 cigarettes/day 1.36 [0.87, 2.12] 1.12 [0.74, 1.69]Periodontal status Other Severe periodontitis 1.18 [0.79, 1.78] 0.9 [0.47, 1.75]Periodontal status Edent.þnon-per Periodontitis 1.53 [1.01, 2.32] 1.4 [0.66, 2.97]Location Mandible Jawbone 4.35 [3.13, 6.25] 2.78 [1.89, 4.17] 2.70 [1.82, 4]Zone Ant. mandib. Other 13.53 [7.38, 24.8] 6.16 [2.75, 13.83] 6.43 [3.28, 12.61]Bone type Type I Other 1.56 [1.16, 2.08] 1.27 [0.93, 1.75]Diameter (D) o4 mm � 4 mm 1.19 [0.88, 1.61] 0.64 [0.43, 0.95]Length (L) � 15 mm o15 mm 1.56 [1.18, 2.08] 1.67 [1.11, 2.44] 1.49 [1.09, 2.04]Mixed L–D � 15 mm o15 and o4 mm 1.68 [1.17, 2.42]

o15 and �4 mm 1.46 [1.05, 2.04]

nMethods proposed by Binder (1983) and Kish & Frankel (1974).

OR, odds ratio; CI, confidence interval; edent., edentulous; non-per, without periodontitis; ant. mandib., anterior mandible.


198 | Clin. Oral Impl. Res. 19, 2008 / 196–200 c� 2007 The Authors. Journal compilation c� 2007 Blackwell Munksgaard

stage surgery are related to the osseointe-

gration process. Following the placement of

an endosseous implant, primary mechan-

ical stability is gradually replaced by biolo-

gic stability after some weeks post-

placement (Raghavendra et al. 2005). In

this regard, it has been proposed that the

status of implants be continually moni-

tored by the objective measurement of

dental implant mobility (Morris et al.

2003).

The primary DIS results did not differ

according to cigarette consumption. Lind-

quist et al. (1997) and Munoz et al. (2004)

found significant differences in PTVs at

second-stage surgery and demonstrated a

correlation between marginal bone loss

during the first year and the number of

cigarettes/day.

The influence of implant dimension on

primary DIS remains controversial. In the

present series, primary DIS was significantly

associated with implant length, in agree-

ment with Tricio et al. (1995) and Aparicio

(1997), but not with implant diameter.

Greater implant length and diameter in-

crease the contact surface area at the bone–

implant interface and have been found to

result in better (more negative) PTVs (Cra-

nin et al. 1998; Engel et al. 2001; Morris

et al. 2003). Nevertheless, other authors

found no relationship between PTVs and

implant length (Teerlink et al. 1991) and

one group observed a relationship only with

diameter (Deporter et al. 2002). This dis-

crepancy may be explained by the small

samples in the latter studies or by their use

of different implants (not Branemarks

).

According to the present findings in a

wide series, primary DIS failure is more

likely in females, at sites other than the

anterior mandible, and with dental im-

plants shorter than 15 mm, at least when

non-threaded titanium implants are used.

These data may be of value in the identi-

fication of patients at a high risk of primary

DIS failure if immediate implant loading is

performed.

Acknowledgements: The authors

are grateful to Richard Davies for

assistance with the English version. This

investigation was supported in part by

Research Group #CTS-503 (Junta de

Andalucıa, Spain).

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