early osseointegration events on neoss® proactive and bimodal implants: a comparison of different...

Early Osseointegration Events on Neoss®ProActive and Bimodal Implants:A Comparison of Different Surfaces inan Animal ModelGustavo Augusto Grossi-Oliveira, DDS, MSc;* Antonio Azoubel Antunes, DDS, PhD;†

Carlos Nelson Elias, PhD;‡ Ann Wennerberg, DDS, PhD;§ Lars Sennerby, DDS, PhD;¶

Luiz Antonio Salata, DDS, PhD**

ABSTRACT

Background: Cell interactions, adherence, and osseointegration at the bone-implant interface can be directly influenced bythe surface properties of the titanium implant.

Purpose: To characterize osseointegration of Neoss® implants with conventional (control group) and hydrophilic (testgroup) surface treatments.

Materials and Methods: Six Labrador dogs received Neoss implants with conventional and hydrophilic surfaces. Thebone-implant interfaces were evaluated 1 and 4 weeks after implantation, and osseointegration was evaluated usinghistological, histomorphometric, fluorescence, and resonance frequency analyses. The surfaces were also subjected totopographic and hydrophilicity analyses.

Results: The topographic analyses revealed increased surface roughness in the test group compared with the control group(surface area roughness 0.42 and 0.78 μm, respectively, for control and test group surfaces; p 2 .05). The wettability valueswere higher in the test group (contact angles 67.2° and 27.2° for the control and test group surfaces, respectively; p 2 .05).Implants in the test group also exhibited better stability, more bone-implant contact, and increased bone area comparedwith implants in the control group.

Conclusion: Neoss implants in the test group improved bone formation in the early stages of osseointegration comparedwith implants in the control group.

KEY WORDS: animal model, bone-implant interface, implant surface, surface properties, surface topography

INTRODUCTION

Implant surface properties, including surface topogra-

phy, roughness, ionic interactions, protein adsorption,

and cellular activity, influence healing time.1–3 Predecki4

observed increased rates of bone formation and

mechanical stability on uneven titanium surfaces. This

discovery led to the knowledge that the implant surface

was a modulating factor in bone healing around

implants, and several subsequent studies seeking to opti-

mize the interactions of tissues and implant surfaces,

bone repair, and epithelial regeneration have been

performed.5–8

Biomechanical modification of implant surfaces

with immobilized proteins, enzymes, and peptides can

elicit responses from cells and tissues and control the

*Postgraduate student, Faculty of Dentistry, University of São Paulo atRibeirão Preto, Ribeirão Preto, Brazil; †Postgraduate student, Faculty ofDentistry, University of São Paulo at Ribeirão Preto, Ribeirão Preto,Brazil; ‡adjunct professor, Department of Mechanical Engineering andMaterials Science, Military Institute of Engineering, Rio de Janeiro,Brazil; §professor, Department of Prosthodontics, Faculty of Odontol-ogy, Malmö University, Malmö, Sweden; ¶professor, Departmentof Oral & Maxillofacial Surgery, Institute of Odontology, SahlgrenskaAcademy, University of Gothenburg, Göteborg, Sweden; **associateprofessor, Department of Oral and Maxillofacial Surgery and Periodon-tics, Faculty of Dentistry, University of São Paulo, São Paulo, Brazil

Corresponding Author: Dr. Luiz A. Salata, Department of Oraland Maxillofacial Surgery and Periodontics, Faculty of Dentistry,University of São Paulo at Ribeirão Preto, Avenida do Café s/n –Campus da USP, 14.040–904 – Ribeirão Preto, SP, Brazil; e-mail:[email protected]

© 2014 Wiley Periodicals, Inc.

DOI 10.1111/cid.12213

1

mailto:[email protected]

molecules released near the bone-implant interface.9

Among cellular responses, cell adhesion is considered

the most important, as it is an early event in bone

formation.10 According to Schwartz and Boyan,11 bone

formation on the implant surface requires proliferation

of precursor cells, which differentiate into osteoblasts,

produce nonmineralized extracellular matrix, and

become calcified. This process can be influenced by the

chemical composition, energy, texture, topography, and

roughness of the implant surface.

The hydrophilicity of implant surfaces was recently

identified as another important factor that may influence

bone-implant interactions.12,13 These data emerged from

studies of implant-blood interactions aimed at increas-

ing deposition of proteins around the implant – a factor

that allows early onset of osteogenesis – and increasing

the contact area between the bone and the implant. In

vitro studies in animals have indicated that hydrophilic

surfaces enhance cell attachment, proliferation, differen-

tiation, and gene expression better than hydrophobic

implant surfaces.14,15 In addition, surface wettability

regulates the production of vascular endothelial growth

factor, which promotes osseointegration.16 In vivo

studies suggest that enhanced bone healing associated

with hydrophilic implants significantly increase bone-

implant contact compared with conventional surfaces

within 2 weeks of implantation.14,17–20 Therefore, surface

properties, especially hydrophilicity, have the ability to

induce more efficient osteoblastic responses, increase

bone-implant contact, and enhance osseointegration.5,12

Methods for altering the hydrophilic properties of

implant surfaces are not well described in the literature.

They include exposure to ultraviolet radiation, immer-

sion in isotonic NaCl solutions, elimination of carbon

from the surface, and increasing roughness.15,17,20,21

Recent studies revealing the relevance of the chemical

properties and topography of implant surfaces have led

to the development of a large number of surfaces by

different companies. Changing hydrophilicity has pro-

duced positive results in a limited number of in vivo and

in vitro studies using SLActive surfaces (Straumann,

Basel, Switzerland).12,17,18,20,21 However, to determine

the bone response induced by the hydrophilicity of

implants, qualitative assessments of the surfaces must be

correlated to specific biological responses.

Studies of implant surfaces during osseointegration

have assessed removal torque,17 success rates,22 reso-

nance frequency analysis,23 histomorphometry,24–27 and

in vitro gene expression.28,29 To date, no studies have

comprehensively compared stability, bone-implant

contact, histometric and histological assessments, and

the topographic and hydrophilic properties of the

implant surface. The aim of this study was to compare

the early events of osseointegration, including with

regard to topographic and hydrophilic features, of

Neoss® implants with hydrophilic and conventional

surfaces. Osseointegration dynamics were investigated

using histological, histomorphometric, and fluorescence

parameters and examined sites with bone defects that

left space between the implant and the recipient bed.

We also evaluated stability gains after 4 weeks of

osseointegration in implants with hydrophilic and con-

ventional surfaces using resonance frequency analysis

(RFA).

MATERIALS AND METHODS

Animals

This study was approved by the Ethics Committee

on Animal Use, University of São Paulo (protocol

#10.1.973.53.1). Six young Labrador dogs weighing

20–30 kg were used. The animals were quarantined for

rabies testing and were administered vaccines against

measles, mumps, and rubella; vermifuges; and vitamins.

Animals were kept in individual pens in the vivarium of

the University of São Paulo (FORP-USP) and were given

free access to water and standard laboratory nutritional

feed throughout the experiment. Animals were provided

appropriate veterinary care in the pre- and postopera-

tive periods.

Experimental Design

Surgical bilateral extractions of the mandibular first

molar and premolars were performed. Three months

after the extractions, four Neoss® (Neoss Ltd, Harrogate,

UK) implants were installed in each mandible. Two

implants had conventional surfaces (Bimodal), as

control group, and two had hydrophilic surfaces

(ProActive), as the test group. The control and test

implants were installed alternately over the mandibular

alveolar ridge. The same surgery was performed 3 weeks

later to place implants on the contralateral side. Animals

were sacrificed 1 week after placement of the second set

of implants, and osseointegration was evaluated 1 and 4

weeks after implantation.

2 Clinical Implant Dentistry and Related Research, Volume *, Number *, 2014

Extraction Surgery

Sulcular incisions were made with subsequent detach-

ment of mucoperiosteal flaps. All mandibular premolars

(P1–P4) were removed. Before removal, all two-rooted

teeth were sectioned using separating disks to ease root

extractions. The flaps were adapted for tension-free

wound closure with interrupted and horizontal mattress

sutures. Wounds were carefully cleaned with 0.12%

chlorhexidine digluconate-soaked gauze. Sutures were

removed after seven days.

Implantation Surgeries

Installations of implants were performed 12 and 15

weeks following extraction surgeries. Two dogs received

four implants (two implants with conventional surfaces

and two implants with test surfaces) measuring

4.0 × 11.0 mm. Two dogs received three implants due

to restricted hemimandible space. The implants were

installed in each hemimandibular arch; the implant sites

were selected by the balanced distribution method,

ensuring alternating placement sites by group. After

exposure of the recipient bone bed, the preparation of

bone sites for installation of implants was surgically

standardized with sequential burs and copious irriga-

tion with 0.9% sterile saline. The last bur used was

3.3 mm in diameter.

The four implant sites were created with 11.0 mm

depths. The implants were inserted into the freshly pre-

pared sites. Bone defects were introduced as standard-

ized circles (6.0 mm diameter × 4.0 mm depth) around

the implants, using a trephine drill (Figures 1 and 2).

The defects created a 1 mm space between the implant

surface and the alveolar ridge in the cervical portion.

After placement of the healing cap, the flaps were care-

fully repositioned and secured with absorbable sutures.

The same surgeon performed all surgeries, and aseptic

conditions and sufficient cooling were used to maintain

bone vitality. Postoperative care was the same as after

extraction surgery.

Animal Euthanasia

Ten weeks after the first implantation surgery, euthana-

sia was performed with an overdose of sodium pento-

barbital 0.2 ml intravenously (65 mg/kg, Euthanasia-5®,

Henry Schein Inc., Port Washington, NY, USA). After

euthanasia, the mandibular segments containing the

implants and the surrounding tissues were removed and

dissected into four individual blocks containing the dif-

ferent implants.

Measurement of Implant Stability

Implant stability was measured by RFA using an Osstell

Mentor® device (Integration Diagnostics AB, Göteborg,

Sweden). Implant stability quotient (ISQ) values were

determined, which ranged from 1 to 100. Higher values

indicated increased stability. Measurements were per-

formed according to the manufacturer’s instructions in

the buccolingual and anteroposterior directions and

averaged (Figure 3). Implant stability was measured in

all six dogs at the time of implant placement, prior to the

installation of the healing caps, while the animals were

still anesthetized. Additional measurements were per-

formed after euthanasia, to compare stability after 1 and

4 weeks of osseointegration.Figure 1 Standardization of bone defects with the aid oftrephines and a device made for this purpose.

Figure 2 Occlusal view of bone defect standardization.

Hydrophilic Implant Surface and Osseointegration 3

Fluorescence Analysis

One week after the first implants were installed,

20 mg/kg alizarin red fluorochrome dissolved in 2%

sodium bicarbonate (Sigma-Aldrich, St. Louis, MO,

USA) was administered intravenously. Calcein dye was

infused 2 weeks after the implant installation procedure,

marking the bone matrix deposition in the third and

fourth weeks of osseointegration.

Histological Processing andHistometric Analyses

After removal, bone segments were fixed in a 4% buffered

formaldehyde solution (pH 7) for 48 hours, transferred

to 70% ethanol, and incubated for 3 days. The specimens

were dehydrated using a series of alcohol solutions of

increasing concentrations and embedded in LR White®

acrylic resin (London Resin Company Ltd, Berkshire,

England). The implants were bisected mesiodistally

using the Microslice 2® precision saw (Ultra Tec Manu-

facturing Inc., Santa Ana, CA, USA) and polished using

polishing cloths combined with different granulations

of Al2O3. Two halves and three histological slides were

obtained from each implant. Each slide was worn and

polished to reach approximately 10 mm to 20 mm thick.

Each slide was imaged to quantify fluorescence using the

Microvideo system (Leica DFC300 FX Digital, Leica

Microsystems, Heerbrugg, Switzerland). Fluorescence

analyses were restricted to the bone defect areas.

The same slides were subjected to staining using a com-

bination of Stevenel’s blue with alizarin red, as described

by Maniatopoulos and colleagues30 (Leica DMLB

microscope, Leica Microsystems), and histometric

measurements were performed (LeicaQwin, Leica

Microsystems). Histometric and quantitative fluores-

cence assessments were analyzed without prior knowl-

edge of the experimental specimens. Morphometric

measurements included bone-implant contact (BIC),

bone area (BA) between the implant threads, the distance

between the implant shoulder bone crest and the implant

shoulder’s first point of bone contact (IS-B), and the

bone area rectangle (BAR) placed parallel to the implant.

The rectangle was standardized according to the bone

defect (4.0 mm height and 0.5 mm width).

Fluorescence analyses were conducted differently

for each marker. A rectangular frame of 4 × 1 mm was

positioned over the region corresponding to the bone

defect. Within the frame, the markers used for each

experimental time point were measured. Another fluo-

rescence analysis determined the presence of markers

between implant threads and measured the correspond-

ing area and the percentage of bone formation in this

region.

Surface Wettability

For the hydrophilicity test, 10 titanium disks (20 mm

diameter and 3 mm high, Neoss® Company) were used

to characterize the conventional surfaces. Five disks were

treated to improve hydrophilic properties. A model

FTA100 goniometer (First Ten Angstroms, Inc., Ports-

mouth, VA, USA) was used. Contact angles between the

disks and 1 mL drops of distilled water were measured.

Topography

Topographic analyses were performed by the Depart-

ment of Prosthodontics at the University of Malmö.

An optical interferometer (MicroXam, Phase Shift,

Phoenix, AZ, USA) was used. The tests were performed

on one conventional surface and two modified surfaces

selected at random. Each sample was assessed at three

positions with a measuring area of 250 × 200 μm. A

Gaussian filter with a size of 50 × 50 μm was used to

remove shape errors. Three samples of each type of

implant were analyzed at coronary, medial, and apical

regions to produce 27 measurements for each group.

Particular attention was paid to ensure that the surfaces

of the screws remained perpendicular to the light

source. This ensured that images were of excellent

quality. Average three-dimensional surface roughness

(Sa), peak density (Sds), and developed surface area

ratio (Sdr) were calculated using Scanning Probe Image

Figure 3 Implant stability measurement with Osstell® Mentor.


Processor (SPIP™) image analysis software (Image

Metrology, Hørsholm, Denmark).

Scanning Electron Microscopy

High-resolution images were captured with a Hitachi

S-4800 (Hitachi High-Technologies Corporation,

Tokyo, Japan) scanning electron microscope (SEM)

equipped with a cold field emission electron source and

an in-lens secondary electron detector. One sample was

analyzed for each surface modification. The test surfaces

were analyzed before and after contact with fluids.

The measurements were performed at the Microscopy

Center of the University of Basel, Basel, Switzerland.

Statistics

A database was created for evaluation of the statistical

significance with the aid of the Statistica software for

Windows v. 5.1 (StatSoft Inc., Tulsa, OK, USA).

The results obtained in the analysis of implant sta-

bility, BIC, BA, region of interest (ROI), and fluores-

cence were subjected to paired Student’s t-test for

comparisons between groups. In all tests, the level of

significance was set at 5% (p 2 .05).

RESULTS

All animals tolerated the surgical procedures well. All

three interventions (tooth extraction, the two implant

placements) were performed without complications. No

implants were lost, and no dog had complications that

compromised the results.

RFA

RFA measurements were acquired during implant

installation and after euthanasia. Increased stability was

shown at both time points in both groups. Implants that

underwent 4 weeks of osseointegration had higher sta-

bility values at the time of euthanasia compared with

implants that were in place for only 1 week. Stability

analysis showed greater values in implants of the test

group at both time points compared with the control

group (Table 1).

Histological Analyses

Histological analyses showed similar bone formation

around both implant surface types. One week after

implant installation, granulation tissue was observed in

the bone defects on both surfaces. After 4 weeks, there

was new bone formation at the periphery of the defects

and little bone formation in contact with the implants,

indicating remote osteogenesis (Figure 4).

Histomorphometric Analyses

The histometric analyses of BA assessed the areas

between the implant threads, the bone defect area, and

the area outside the bone defect. Four weeks after

implantation, increased BA was observed in all groups.

The middle third and apical regions, outside the defect

and in close contact with the implant, showed higher BA

values than the threads inside the bone defect. There

were no statistical differences between the test and

control groups when comparing BA in the defect region.

However, the test group demonstrated increased BA

outside the bone defect area, in close contact with the

bone and the implant (Table 2).

To assess the bone-implant contact (BIC), measure-

ments were performed both in threads inside the bone

defects and in threads placed on native bone. BIC values

were substantially higher in the threads installed in

native bone. The test group showed increased BIC values

when compared with the control group in both situa-

tions (Table 3).

TABLE 1 Implant Stability Quotient

1 Week

1-Week Gain

4 Weeks

4-Week GainMean SD Mean SD

Test group Installation 57.73 3.46 63.55 2.29

Sacrifice 62.36 2.59 4.63* 75.64 1.13 12.09*

Control group Installation 61.36 2.16 65.45 1.92

Sacrifice 64.55 1.61 3.19 73.68 1.86 8.23

*Statistically significant difference (p 2 .05) between groups.Measured with radiofrequency analysis.


To assess bone formation in the bone defect region

(ROI), measurements were performed in the bone

defect regions (Table 4). Both implant surfaces showed

increased percentages of newly formed bone after 4

weeks compared with 1 week. There were no statistical

differences between the time points studied (Figure 5,

Table 4).

To determine the distances between the implant

shoulders and bone contacts (IS-B), we analyzed the

shortest distance between the implant shoulders and

the most coronal point of contact between bone and

implants. Both implant surfaces showed similar IS-B

values after 1 week of osseointegration. After 4 weeks of

osseointegration, the IS-B values decreased similarly in

both groups (Figure 6, Table 5).

Fluorescence

By assessing fluorescence markers, we documented

increases in bone matrix formation throughout the

follow-up period. Overall, fluorescence markers were

increased on implants that were in place for 1 week

TABLE 2 Bone Area between Threads (%)

Region Group

Total Gain after3 Weeks

Mean SD

Apical Test 21.77* 9.83

Control 9.75 4.29

Bone defect Test 12.6 4.08

Control 19.68 5.14

*Statistically significant difference (p 2 .05) between groups.

Figure 4 Histological view of bone defect region after 1 week (A) and 4 weeks of osseointegration (B) (×2.5 magnification). Note thepresence of granulation tissue with inflammatory infiltrate after a week of bone repair and the presence of new bone filling the defectafter 4 weeks.

TABLE 3 Bone-Implant Contact (%)

Region Group


Mean SD

Apical Test 25.35* 4.40

Control 12,61 8.01

Bone defect Test 13.11* 4.57

Control 7.45 5.23


TABLE 4 Newly Formed Bone in the Bone DefectRegion (%)

Group


Mean SD

Test 0.30 0.14

Control 0.24 0.22


compared with those that were in place for 4 weeks.

We evaluated bone matrix formation on the implant

threads, and our results indicated that implants in the

test group showed enhanced matrix deposition com-

pared with conventional surfaces (Table 6, Figure 7).

The behavior was similar between the implant surfaces,

and significant increases in the amounts of bone matrix

were observed after 4 weeks of osseointegration com-

pared with 1 week (Table 7, Figure 8).

Optical Interferometry

Optical interferometry results revealed different topo-

graphic values for the implant surfaces. Conventional

surfaces presented surface roughness and densities of

Sa = 0.42 and Sdr = 26.8, respectively. The values for the

test group were Sa = 0.4 and Sdr = 8.0 when the implants

were tested without prior contact with fluids. After the

test-group implants were rinsed and dried, they pre-

sented values of Sa = 0.78 and Sdr = 64.6 (Table 8).

Scanning Electron Microscopy

The implants used in this study received sandblasting

and acid-etching surface treatments. Microscopically,

the conventional surfaces presented uniform irregulari-

ties. At ×5,000 magnification, surface roughness was

formed by multiple heterogeneous gaps, ranging from

0.5 to 1.5 mm in diameter, in the cervical and apical

implants. The test-group implants, before being rinsed

and dried, presented smoother surfaces. At ×5,000

magnification, fewer holes, with larger diameters and

shallower depths, were observed compared with the

conventional surfaces. Morphologically, the surfaces

appeared to be made of particles with average diameters

of 0.3 to 0.5 mm. After rinsing, the particles were no

Figure 5 Bone formation in the bone defect region (×2.5magnification).

Figure 6 Distance between the implant shoulder (IS) and firstbone contact (B) (×10 magnification).

TABLE 5 Implant Shoulder-to-Bone Distance (mm)

Group

1 Week 4 Weeks

Mean SD Mean SD

Test 3.45 0.25 2.62 0.21

Control 3.18 0.38 2.37 0.27

TABLE 6 Bone Formation between Implant Threads(%)

Stain Group


Mean SD

Alizarin Test 2.09* 0.97

Control 0.85 0.67

Calcein Test 2.44 0.42

Control 1.52 0.21



longer present on the surface. At ×5,000 magnification,

the washed test-group implants were composed of mul-

tiple gaps, with more irregularities compared with the

control group (Figure 9).

Surface Wettability

The contact angles between the liquid and titanium

disks were lower in the disks that were subjected to the

hydrophilic surface treatments, consistent with higher

wettability. The same tests performed on the control

surfaces showed larger angles between the distilled water

and the titanium disks (p = .001). Therefore, the control

Figure 7 Fluorescence analysis in the area between implant threads. A, Area stained by calcein. B, Area stained by alizarin (×10magnification).

TABLE 7 Bone Formation in the Bone Defect Region(%)

Stain Group


Mean SD

Alizarin Test 0.22 0.15

Control 0.16 0.10

Calcein Test 0.71 0.25

Control 0.49 0.21

Figure 8 Fluorescence analysis of the bone defect region. A, Area stained by calcein. B, Area stained by alizarin (×2.5 magnification).


group displayed lower surface energies compared with

the test group (Table 9).

DISCUSSION

Modifications to implant surfaces are intended to

increase the quality of bone anchorage around the

implant and reduce the time of osseointegration. These

factors are especially important for patients requiring

rehabilitation at sites where bone quality represents an

obstacle to osseointegration. This study compared two

implant surfaces. Histology, histomorphometry, fluores-

cence, implant stability, surface wettability, and surface

roughness were assessed to determine the interactions

between osteoblasts and implant surfaces. To our knowl-

edge, this is the first experimental study using these

parameters to evaluate the effects of implant surfaces.

Importantly, it should be considered that the bone

metabolism of dogs and humans is different. According

to Roberts and colleagues,31 bone events occur one-third

faster in dogs. Therefore, accounting for all limitations

presented by the chosen animal model, the follow-up

periods of 7 and 30 days used in this study may be

extrapolated to periods of 9 and 40 days for humans.

Histological analyses revealed predominant granu-

lation tissue and no clots at 1 and 4 weeks. Colonization

by osteoblasts and subsequent deposition of bone

matrix on the implant surfaces promotes bone forma-

tion via contact osteogenesis.10 After 4 weeks of bone

repair, we observed immature bone originating from the

bone walls and the defects, similar to observations made

in previous studies of hydrophilic surfaces.12,24,32 Bone

formation was also monitored with fluorescence analy-

sis, which marks bone matrix deposition. In the apical

regions of the implants, bone deposition activities

resembling contact osteogenesis were observed.

In this study, BA values significantly increased over

time when comparing the implants that were in place for

1 week with implants that were in place for 4 weeks.

Test-group implants showed a 12% increase of BA on

the apical region when compared with the conventional-

surface implants. Differences were not observed in the

bone defect areas. This may be explained by the implant

design. As the implants were 2 mm high and had flat

flanges, the 4 mm depths of the bone defects ranged over

approximately three implant threads, reducing the

number of threads assessed for bone area.

TABLE 8 Surface Roughness (μm) and Developed Surface Area Ratio (%)

Control Group Test Group Test Group after Rinse

Sa Sdr Sa Sdr Sa Sdr

Mean 0.42 26.8 0.4 8.0 0.78 64.6

SD 0.1 3.8 0.1 1.7 0.1 1.7

Sa = average surface roughness; Sdr = developed surface area ratio.

Figure 9 Scanning electron micrograph of the control group (A), test group (B), and rinsed test group (C) implant surfaces (×5000magnification).


IS-B values significantly decreased over time when

comparing implants that were in place for 1 week to

those that underwent osseointegration for 4 weeks, indi-

cating coronal-level bone formation. There were no sta-

tistically significant differences between the two implant

surfaces within the two time points. Because other

studies have not evaluated BA and IS-B, comparing

these results with previous studies was not possible.

There were significant increases in BIC values

between the first and fourth weeks of osseointegration.

When the surfaces were compared, increased bone for-

mation around the implants with hydrophilic surfaces

was observed. In a study comparing two surfaces with

similar topographies and different hydrophilicity using

minipigs, Buser12 reported a 20% increase in bone

contact in the hydrophilic surface 2 weeks after installa-

tion. This difference decreased to 15% 4 weeks after

installation, and after 8 weeks of implant installation the

surfaces were equal. In a similar study using dogs,

Borstein18 found a 6% increase in BIC for hydrophilic

surfaces 2 weeks after installation and found no differ-

ences between the groups after 4 weeks. Using the same

evaluation time points as a previous study, Lang and

colleagues25 observed a 16% difference after 4 weeks, and

observed no differences between the groups after 2 and 8

weeks of osseointegration. The results of these previous

studies indicated that BIC values were higher at 2 and

4 weeks in implants with hydrophilic surfaces. In our

study, the test group increased bone formation between

1 and 4 weeks of osseointegration. In the bone defect

areas, the test group implants had 6% greater BIC when

compared with the control group. For the apical area

outside the bone defect, the difference increased to 13%.

By evaluating new bone formation at the defect site,

we found a significant increase in the amount of new

bone formation between weeks 1 and 4 and no differ-

ences between the implant surfaces. In a similar study,

hydrophilic surfaces promoted new bone formation

in the defect sites during the first 4 weeks of osseo-

integration. After 8 weeks, bone formation values were

similar between the two surfaces.24 In previous histologi-

cal analyses of implants placed with fenestration of the

buccal wall, Schwarz and colleagues32 observed early

maturation and proliferation of bone tissue on the

exposed surface of the hydrophilic implant compared

with a conventional surface.

In this study, both surfaces showed increases in ISQ

values between weeks 1 and 4, although increased stabil-

ity values were observed for the test group. This suggests

that the hydrophilic properties of the implants enhanced

bone apposition as compared with the conventional

surface. In a study comparing the ISQ values of conven-

tional and hydrophilic implants after 6 weeks of implan-

tation, Oates and colleagues23 reported loss of stability in

the first 2 weeks of repair for both surfaces. After 4 weeks,

implant stability increased, and both surfaces behaved

similarly. The lack of the 2-week time point in the article

by Oates and colleagues23 precludes stability comparisons

at early time points. However, a small decrease in stability

during the first 3 weeks of repair was reported in a

12-week study of human subjects using RFA. The con-

ventional (SLA) and hydrophilic (SLActive) surfaces

were similar throughout the assessment period. Both

surfaces showed decreased ISQ values during the 3 weeks

following implant installation. After 3 weeks, stability

increased until the end of the follow-up period.33,34 As

found in a study by Abrahamsson,35 implant stability at

the time of installation depends on the imbrication of the

implant with the bone trabeculae. In subsequent weeks, a

remodeling process takes place that involves resorption

followed by bone apposition around the surface. In this

study, the test group had greater stability values com-

pared with the control group. ISQ values increased from

1 week to 4 weeks in both surfaces. These time periods

may correspond to 10 and 40 days in humans.

Implant-surface microroughness has important

influences on osseointegration of implants. In previous

studies, the best results were obtained with moderately

rough surfaces (Sa = 1–2 μm).7,8,36,37 The conventional

surfaces were created by bombardment with ZrO2 balls

(100–300 mm in diameter) and TiO-based irregular

particles (75–150 μm).38,39 Implants with hydrophilic

surfaces undergo the same processes and are also

TABLE 9 Contact Angles of Surfaces Analyzed inTests with Distilled Water (Degrees)

Titanium Disks Control Group Test Group

1 62.97 30.74

2 58.27 29.90

3 67.15 24.40

4 61.84 27.92

5 60.78 23.17

Mean 62.20* 27.22

SD 3.26 3.33



subjected to a process to eliminate carbon from the

surfaces. In the topographic tests performed through

optical interferometry, the test-group and control-group

implants showed modest rugosities. The control group

displayed Sa and Sdr values of 0.42 and 26.8%, respec-

tively. The test group showed larger surface develop-

ment, with Sa of 0.78 and Sdr of 64.6%. In a review of

several surfaces, Wennerberg and Albrektsson7 reported

that most currently used implants have Sa values ranging

from 0.3 to 175 and Sdr values ranging from 24% to

143%. Although there are no previous data on the

implants used in this study, Nanotite surfaces (Biomet

3i, Warsaw, IN, USA) have reported Sa values of 0.5, Sdr

values of 40%, and high success rates 1 year after instal-

lation with immediate load.40 There are treated surfaces

that have lower roughness values compared with

machined implants (Sa = 0.9 and Sdr = 34%) that show

favorable clinical results.7,8 Studies comparing TiUnite

(Nobel Biocare AB, Göteborg, Sweden) and conven-

tional surfaces indicated higher values for Sa (1.1) and

Sdr (37%) for TiUnite.40 In this study, the control group

presented a Sa value of 0.42 and an Sdr value of 26.8%.

Therefore, despite the differences in topographies, both

surfaces showed similar BIC and BA values after 4 weeks

of osseointegration. The differences between surfaces

were not only with regard to the increased hydrophilicity

of the test group but also its enhanced surface irregu-

larities. The difference in surface microroughness may

have contributed to the better results in the test group; in

that case, hydrophilic properties cannot be considered as

the main factor of the improved tissue response in the

test group.

The angles between water droplets and the surface

of titanium disks approximate the ability of the implant

surfaces to break the surface tension of fluids. As

expected, the test-group surface formed a 27.22° angle

with the fluid, while the control-group surface formed

a 62.2° angle with the fluid. Despite the increased

wettability observed for the test-group surface, the

surface tension maintained higher values than Buser and

colleagues31 and Hirakawa and colleagues20 reported for

the SLActive surface. The hydrophilic characteristics of

titanium can be enhanced by removal of carbon from

the surface, hydroxylation of the oxide layer, and storage

in isotonic NaCl, which also prevents contamination.21

Storing implants in isotonic NaCl also helps maintain

surface energy and hydrophilic properties. Although

the implants used in this study were not stored in an

isotonic NaCl solution, they were able to change the

surface energy. This may account for the reported dif-

ferences. Images of test group implants before contact

with fluid revealed particles on the surfaces that may be

responsible for the hydrophilic properties.

The limitations of the study were the small sample

size of the animal model and the absence of a statistical test

on which to base the sample size calculation. Furthermore,

surface chemical and charge analysis could contribute

to elucidate the chemical changes in the test group. Addi-

tional in vivo and in vitro studies are necessary to evaluate

bone formation associated with hydrophilic implants

and to clarify the roles of ProActive surfaces in osseo-

integration and dissociate the effects of hydrophilic pro-

perties from those of the enhanced surface topography

with regard to the encouraging results.

CONCLUSIONS

In conclusion, our results indicate that test-group

(ProActive) surfaces showed larger surface development

values (Sa and Sdr) and increased wettability compared

with the control-group (Bimodal) surfaces. After 4

weeks of osseointegration, all surfaces showed increased

stability, but implants in the test group showed greater

stability increases as compared with implants in the

control group. In addition, implants with ProActive sur-

faces improved bone formation in the early stages

of osseointegration when compared with conventional

surfaces. The improved tissue response in the test group

may have been due not only to hydrophilicity but also to

the improved surface microroughness.

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