IMPLANT DENTISTRY / VOLUME 22, NUMBER 5 2013

481

Implant Stability Change andOsseointegration Speed of Immediately
Loaded Photofunctionalized Implants
Senichi Suzuki, DDS, PhD,* Hiroyuki Kobayashi, MD, PhD,† and Takahiro Ogawa, DDS, PhD‡

hotofunctionalization of titanium
implants, the comprehensive
physicochemical and biologicaleffects of ultraviolet (UV)-light treatment, has earned considerable interest
and attention in the ﬁelds of titanium
science, biomaterials research, andimplant therapy.1–6 Photofunctionalization of titanium implants increased thebone-implant contact from 55% to98.2%, approximating an ideal level of
100%, in an animal model.5 Consequently, the strength of bone-implant
integration increases more than 3 times
at the early stage of healing.5 Subsequentin vivo animal studies further revealed
the advantage of photofunctionalization
to overcome challenging conditions.
One of the studies showed that, when
the implant was 40% shorter, thestrength of bone-implant integration
decreased by 50%.7 More importantly,
when 40% shorter implants were photofunctionalized, the strength of boneimplant integration was even greaterthan that of standard-length implants.

P*Director, Lion Implant Center, Kanagawa, Japan.
†Professor, Department of Hospital Administration, Juntendo
University School of Medicine, Tokyo, Japan.
‡Professor, The Weintraub Center for Reconstructive
Biotechnology, Division of Advanced Prosthodontics, Universityof California, Los Angeles, School of Dentistry, Los Angeles, CA.

Reprint requests and correspondence to: Takahiro
Ogawa, DDS, PhD, Laboratory for Bone and Implant
Sciences (LBIS), The Jane and Jerry Weintraub Center
for Reconstructive Biotechnology, Division of Advanced
Prosthodontics, Biomaterials and Hospital Dentistry,
University of California, Los Angeles, School of
Dentistry, 10833 Le Conte Avenue (B3-081 CHS), Box
951668, Los Angeles, CA 90095-1668, Phone: (310)825-0727, Fax: (310) 825-6345, E-mail: togawa@dentistry.ucla.edu.
ISSN 1056-6163/13/02205-481
Implant Dentistry
Volume 22  Number 5
Copyright © 2013 by Lippincott Williams & Wilkins
DOI: 10.1097/ID.0b013e31829deb62

Objectives: This study evaluatedthe degree and rate of implantstability development for photofunctionalized dental implants in humans.
Materials and Methods: Thirtythree implants (7 patients) placed in
the maxilla and immediate loaded
were evaluated. Photofunctionalization was performed by treating implants with ultraviolet for 15 minutes
immediately
beforeplacement.
Implant stability was assessed bymeasuring the implant stability quotient (ISQ) weekly starting from
implant placement up to 3 months.
Osseointegration speed index (OSI),deﬁned as ISQ increase per month,
was also evaluated.
Results: The average ISQ forphotofunctionalized implants at week
6 was 78.0, which was considerably
higher than the average ISQ of 66.1,

reported in literature for various asreceived implants after a longer
healing time of 2 to 6 months. No
stability dip was observed for photofunctionalized implants regardless of
the initial ISQ values. The OSI forphotofunctionalized implants was
6.3 and 3.1 when their initial ISQ
was 65 to 70 and 71 to 75, respectively, whereas the OSI values for asreceived implants calculated fromliterature ranged from −3.0 to 1.17
with an average of −0.10.
Conclusions: Photofunctionalization accelerated and enhanced
osseointegration of dental implants,
providing novel and practical avenues for further advancement in
implant therapy. (Implant Dent
2013;22:481–490)
Key Words: ultraviolet, titanium,
superhydrophilic,hydrocarbon,
super osseointegration

Another study examined the effect ofa periimplant gap in the cortical bone.8
The presence of a periimplant gap,
equivalent to half the implant diameter,
resulted in signiﬁcant reduction of thestrength of bone-implant integration by
70% compared with the implants withcortical support. When photofunctionalized implants were placed in the same
gap healing, the strength of boneimplant integration increased to the samelevel of the implants with cortical support. Detailed microcomputed tomography analysis revealed that the effect canbe explained by an enhanced osteomorphogenesis around photofunctionalized
implants.8 There was robust osteogenesis around photofunctionalized implants,
which initiated at the implant interface
and rapidly spread to and connectedwith the surrounding bone, whereas osteogenesis around untreated implants
initiated at the surface of the remote cortical bone and slowly approached theimplant interface.
The mechanism underlying thebiological effects of photofunctionalization includes 3 property changes on

482

ACCELERATED OSSEOINTEGRATION BY PHOTOFUNCTIONALIZATION  SUZUKI ET AL

titanium surfaces. Photofunctionalization converts titanium surfaces fromhydrophobic to superhydrophilic andfrom electronegative to electropositive.2,3,5,9–13 In addition, titanium surfaces, which are unavoidably covered bya signiﬁcant amount of hydrocarbon during aging, can be cleaned by photofunctionalization.2,3,5,14 Because of thesesurface changes, the recruitment, attachment, retention, spread, proliferation, andthe expression of functional phenotypesof osteogenic cells are remarkably
increased.1,5,8,11,12,15,16 Among cellularbehavior and function, this study paid
attention to the potential beneﬁts obtainedby the enhanced attachment and retentionof the cells. Mechanical stimulation, suchas vibration of the titanium substrate, isknown to detach a large number of cells
from titanium surfaces even after the cells
are adhered.6,10,11,15,17 When an immediate loading protocol is applied to dental
implants, there is a reasonable concernthat only a limited number of remnant
cells could play a subsequent role in osseointegration. If photofunctionalization
is proven to increase cellular attachment
and retention, it may, in particular, help
improve the process of osseointegrationin immediately loaded dental implants.
Measuring implant stability at placement and its subsequent change during
healing provides useful information formonitoring the process of osseointegration, planning a loading protocol, andevaluating various conditions of osseointegration on implant and host sides.18–24
The use of implant stability quotient(ISQ) values based on the resonance frequency analysis has been extensively
reported for its reasonable reliability andvalidity.20,25–30 Periimplant osteogenesis
consists of postsurgical reaction andremodeling of the bone and the initiationand progression of de novo bone formation, which are represented as a reductionin primary stability and development of
secondary stability, respectively.31–33 The
rate of losing primary stability is known
to be faster than the development of secondary stability and, thereby, causesa merging gap between the 2 processes
to maintain overall implant stability,
resulting in the occurrence of a stability
dip32,33 (Fig. 1). The stability dip, including the progressive reduction of overall
stability when the initial stability is high,Fig. 1. A suggested mechanism of theoccurrence of stability dip in dental implants.
The total stability, as determined by theaddition of primary stability and secondary
stability, normally shows a merging gap,
which is called the stability dip. The stability
dip is considered unavoidable in current
dental implants because the rate of losing
primary stability is faster than the development of secondary stability.

is considered difﬁcult to eliminate withcurrent implants, and in fact, ISQ values
are adequately sensitive to detect the stability dip between weeks 1 and 8 after
implant placement.19,21,26,34–37 Becauseof the stability dip, there is a principle inclinical protocol that implants should be
kept unloaded until after the dip has
passed, which limits the application of
immediate and early loading.
Thus, an important question iswhether photofunctionalization iseffective in obtaining similar results inhumans compared with animal studies
and, thereby, providing clinical advantages or therapeutic signiﬁcance. In
particular, we hypothesized that photofunctionalization may affect the commonly understood time course ofa change in implant stability becauseof its capability to expedite and enhanceosseointegration as demonstrated inanimal studies. This is a perspective
cohort study to evaluate the change instability of photofunctionalized dental
implants placed in the edentulous maxilla and immediately loaded during theirearly healing time up to 3 months.

MATERIALS AND METHODSPatients

Among the patients who visited
Lion Implant Center during November
2011 and March 2012 for implant
therapy and who provided consent for

documentation and public presentationof their cases, 7 male patients wereselected consecutively for this study.
Patients were included if they were atleast 20 years old, if they complied withoral health care instructions and necessary visits, and if they showed indications for immediate loading in theedentulous maxilla. Patients with systemic or behavioral conditions that
could potentially affect bone and soft
tissue healing, such as osteoporosis,
diabetes, radiation treatment, bruxism,
or smoking, were excluded. In total, 33
implants were placed in the 7 patients.
The patient and implant information isprovided in Table 1.
Surgical Procedure andPhotofunctionalization of
Dental Implants

Standardized consultation and diagnostic procedures were provided to all
patients, and a treatment plan was presented and approved by the patients.
Following the routine procedures of
local anesthesia and full-thickness ﬂap
reﬂection, implants were placed following the standard surgical procedure
recommended by the manufacturer anddescribed in-depth elsewhere.38,39 Fourto 6 implants were placed per edentulous
maxilla. The implant neck was positioned at bone level. Multiunit straightabutments or 17-degree or 30-degree
angulated abutments were used as
appropriate to correct the ﬁxture inclination. The soft tissues were readapted andsutured.
Implants used in this study had
a tapered root form and identical surface
microscale morphology by oxidation(TiUnite, NobelReplace Tapered Groovy
RP; Nobel Biocare, Yorba Linda, CA).
The dimensions of the implants arepresented in Table 1. All implants were
photofunctionalized by treating with UVlight for 15 minutes using a photo device(TeraBeam Afﬁny; Ushio, Inc., Tokyo,
Japan) at the chair side immediately
before implantation (Fig. 2, A). The photofunctionalization-induced change insurface property from hydrophobic tosuperhydrophilic (deﬁned as a contact
angle of water less than 5 degrees) was
conﬁrmed before patient visits by examining several implants for their wettability to double-distilled water (Fig. 2, B).

Type 219 (57.6%)
13 mm
23 (69.7%)

Diameter

4.3 mm33 (100%)

Total Number

33

10 mm
2 (6.1%)

11.5 mm
5 (15.2%)

Implants

16 mm
3 (9.1%)

Type 18 (24.2%)

Bone Type
LengthType 36 (18.2%)

483

Fig. 2. Photofunctionalization of dental implants and its visualized effects on implant surface
property. A, A photo device (TeraBeam; Afﬁny, Ushio, Inc.) used for photofunctionalization.
Dental implants were treated for 15 minutes immediately before implantation. B, Implants,
which were hydrophobic as received, were converted to superhydrophilic after photofunctionalization. Photographic images of 3 mL of ddH2O droplets placed on implant surfaces
are shown. Two droplets (6 mL) were sufﬁcient to entirely cover a photofunctionalized implant.
C, Clinical images of untreated (as-received) and photofunctionalized dental implants when
they were in contact with an implant site. A hemophilic conversion of the implant surfaces isevidently seen after photofunctionalization. The generated hemophilicity was robust enough tosoak up blood along the implant thread.

These tested implants were from a separate group of the same type of implants
and not used for the patients. Furthermore, photofunctionalized surfaces wereconﬁrmed by watching the patient’s
blood spiral up the implant immediately
after it was in contact with the drilled site,
as typically seen in Figure 2, C. Bonequality was categorized as type 1, 2, 3,
or 4 during the surgery following the criteria proposed by Lekholm and Zarb.40

53–66
59.0 6 5.8
7

Age Range
NumberAge

Immediate Provisional Restoration

Patients

TABLE 1. Patient and Implant Data. All 33 Photofunctionalized Implants were Placed in the Maxilla and Immediately Loaded. The Distribution of Implant Length and Bone
Type is Shown

IMPLANT DENTISTRY / VOLUME 22, NUMBER 5 2013

Full-arch acrylic resin temporary
prostheses were placed on the sameday. The prostheses were fabricatedfollowing the manufacturer’s instructions and as described elsewhere38,39
using autopolymerizing resin (Unifast
II; GC, Tokyo, Japan) and temporary
abutments (Nobel Biocare) in thein-house laboratory. Anterior occlusal
contacts and canine guidance duringlateral movements were preferably
established on the provisional prostheses. No cantilevers contact was givenon the provisional prostheses.

Fig. 3. The ISQ values at implant placement
and week 6 of healing plotted for photofunctionalized implants. Note that all implants
with an initial ISQ that was 75 or lower
showed an increase at week 6, and consequently, the ISQ values at week 6 were all 75
or higher.

484

ACCELERATED OSSEOINTEGRATION BY PHOTOFUNCTIONALIZATION  SUZUKI ET AL

Implant Stability Measurement andOsseointegration Speed Index

Implant stability was evaluated bymeasuring the ISQ at implant

placement (ISQi) and during the healing period with a 1-week interval up
to 11 weeks using Osstell ISQ(Osstell AB, Gothenburg, Sweden).

Furthermore, the rate of establishing
implant stability was evaluated by theosseointegration speed index (OSI)deﬁned as an ISQ increase per month,that is, ([ISQ at week 6] − [ISQi])/1.5.
Statistical Analysis

The effect of healing time on ISQ
values was evaluated by ANOVA; P ,0.05 indicated statistical signiﬁcance.
When the effect was signiﬁcant, further
post hoc analysis of Bonferroni was
performed to compare the ISQi with
the ISQ at each of the subsequent time
points. The ISQ values were comparedamong implants with different lengths
using ANOVA. Furthermore, the effectof different bone types where implants
were placed was evaluated.

RESULTS
Implant Dimensions and Bone TypeThe diameter of all implants used inthis study was 4.3 mm, whereas theirlength varied; 13 mm implants wereused most often (Table 1). A majority of
implants (57.6%) were placed in thetype 2 bone, whereas 24.2% and18.2% implants were placed in the type
1 and type 3 bones, respectively. There
was no type 4 bone because the cases
included in the study were selected for
immediate loading.
Change in Implant Stability

Fig. 4. Change in implant stability for photofunctionalized implants, evaluated by ISQ values at
implant placement and subsequent healing time. Line graphs are drawn in 3 different groups
depending on the initial ISQ values at implant placement (ISQi). A, ISQi 65 -70; B, ISQi 71 –75;
and C, ISQi $ 76. *P , 0.05, **P , 0.01, statistically signiﬁcant difference from the ISQi.

To visualize the overall trend ofchange in implant stability, ISQi values
and the ISQ values at week 6 wereindividually plotted (Fig. 3). The ISQi
varied widely from 65 to 85, whereas
the ISQ values at week 6 were converged to the higher level. There wasa variation in ISQ ﬂuctuation between
the time of implant placement and week
6, an increase, no change, or a decrease,for implants with ISQi that were 77 or
higher. In contrast, all implants with ISQi 75 or lower showed an increase atweek 6. There was a clear trend thatlower the ISQi, the greater the subsequent ISQ increase. As a result, theISQ values at week 6 were all 75 or
higher.
Next, the implants were divided
into 3 groups depending on the range of
their ISQi (ISQi 65–70, ISQi 71–75,
and ISQi $ 76), and the ISQ values

IMPLANT DENTISTRY / VOLUME 22, NUMBER 5 2013

2 times higher than that in ISQi 71 to 75
group. The OSI for ISQi 71 to 75 groupwas 3.1 6 1.2.

Table 2. ISQ Change and OSI in Photofunctionalized Implants
ISQ
Primary Stability Range(ISQi)At
Placement

At Week 6

Change

OSI

65–70
71–75
$76

68.4 6 1.5
73.0 6 1.5
78.5 6 1.6

77.5 6 1.4
78.1 6 2.3
78.1 6 2.1

9.5 6 1.3*
4.6 6 1.8*
−0.3 6 2.1†

6.3 6 0.9
3.1 6 1.2
NA

Implants were divided into 3 groups depending on the initial ISQ value at implant placement. This table shows mean ISQ values at
implant placement and week 6 postimplantation as well as the ISQ change between the 2 time points for each group. Furthermore,
the ISQ change divided by healing time of 1.5 months (6 weeks) is shown as the OSI value. The ISQ change was signiﬁcant andpositive when the initial ISQ was 75 and lower.
*P , 0.01; statistically signiﬁcant change between 2 time points.
†Not signiﬁcant.
NA, not applicable; ISQi, initial ISQ at implant placement; OSI, osseointegration speed index ¼ ISQ increase per month.

starting from the implant placement up to
11th week were plotted in a line graph foreach group (Fig. 4). When the ISQi values was 65 to 70, the ISQ line graphshowed a rapid and continuous increase
up to week 6, followed by the plateau at
the increased level (Fig. 4, A). ANOVA
showed a statistically signiﬁcant effect ofhealing time on the ISQ values (P ,0.05). The post hoc analysis showed that
the ISQ values at week 3 and after week 3
were signiﬁcantly higher than the ISQi,
supporting the rapid increase and subsequent maintenance of ISQ. No signiﬁcant
ISQ decrease was found compared with
the ISQi in the entire assessment period(P . 0.05). There also was no signiﬁcant
ISQ dip (a signiﬁcantly lower ISQ value
compared with neighbor time points)
throughout the healing period (P . 0.05).
Similar to the ISQi 65 to 70 group,
when the ISQi was 71 to 75, thesubsequent ISQ showed an increasing
course of change (Fig. 4, B). Although
the rate of ISQ increase appeared lessthan that in ISQi 65 to 70 group becauseof the higher baseline, the ISQ values in
the later time points appeared to be similar between the ISQi 71 to 75 and ISQi

65 to 70 groups. A signiﬁcant ISQ
increase compared with ISQi was foundstarting at week 2 and continued until
week 11, except at week 3. Comparedwith ISQi, subsequent ISQ values did
not show a signiﬁcant decrease or a signiﬁcant dip throughout the healing
period. In contrast with these 2 results,
there was no time-dependent ISQ
increase, decrease, or dip when the ISQi
was 76 or higher (Fig. 4, C). The mean
ISQ values remained higher than 76
throughout the healing period without
signiﬁcant ﬂuctuation in this group.

Table 3. ISQ in Different Bone Types

Table 4. ISQ in Groups of Different
Implant Length

ISQ
Bone
Type

At
Placement*

At Week
6†

Type 1
Type 2Type 378.6 6 2.0
74.1 6 4.5
74.0 6 2.5

77.0 6 0.0
78.2 6 1.6
78.2 6 3.2

Implants were divided into 3 groups depending on the bonetype in which implants were placed. This table shows mean ISQ
values at implant placement and week 6 postimplantation foreach group. The ISQ values in type 2 and 3 groups increased
between the placement and week 6, and there were no
signiﬁcant difference among the 3 groups at week 6.
*P , 0.05; statistically signiﬁcant difference among the three 3
groups.
†Not signiﬁcant.

485

Osseointegration Speed Index

For each of the ISQi 65 to 70, ISQi
71 to 75, and ISQi $ 76 groups, change
in implant stability between the implant
placement and week 6 was tallied inTable 2. A statistically signiﬁcant ISQ
increase was seen in ISQi 65 to 70 and
ISQi 71 to 75 groups but not in ISQi $76 group. For the signiﬁcant ISQchanges found, the osseointegration
speed index (OSI) deﬁned as the ISQ
increase per month was calculated(Table 2). The OSI in ISQi 65 to 70
group was 6.3 6 0.9 and approximately

ISQ

Implant
Length,mm

At
Placement*

At Week 6*

#11.5
$13

73.6 6 3.6
75.6 6 4.2

77.5 6 3.8
78.1 6 1.6

Implants were divided into 2 groups depending on the implant
length. This table shows mean ISQ values at implant placement
and week 6 postimplantation for each group. Both groups
showed a signiﬁcant increase between the placement and week
6 of healing. Therefore, there was no signiﬁcant difference
between the 2 groups at week 6, indicating that photofunctionalization was effective in increasing ISQ values regardless of theimplant length.
*Not signiﬁcant between the 2 groups.

Effect of Bone Type and Implant Length

To ﬁnd potential speciﬁcity or exclusivity of the effect of photofunctionalization, ISQ values were analyzed indifferent bone types. At implant placement, ISQi signiﬁcantly varied with bonetype (Table 3). The ISQ values were signiﬁcantly lower for the type 2 and 3groups than for the type 1 group at placement. The interbone type difference
became insigniﬁcant at week 6, indicating that photofunctionalization was
effective in increasing the stability of implants with lower initial ISQ in the type 2
and 3 groups. Next, ISQ values were analyzed depending on the implant length(Table 4). The ISQi was not different
between “#11.5-mm” and “$13-mm”
groups. Although ISQ increased in bothgroups at week 6, there was no difference
between the 2 groups, indicating the even
effect of photofunctionalization regardless of the implant length.

DISCUSSION
By using ISQ values, this study
quantitatively evaluated the level,change, and rate of osseointegration ofphotofunctionalized dental implants
under the immediate loading condition.
One of the hypotheses we tested waswhether clinical effects of photofunctionalization similar to those found inanimal studies can be obtained inhumans. As mentioned in Introduction,a series of animal studies demonstrated
the accelerated and enhanced capabilityof osseointegration by photofunctionalization. To compare the osseointegration capability of photofunctionalized
dental implants with that of the asreceived untreated implants, we deﬁned
and calculated the OSI. The proposed
OSI value represents a rate of developing implant stability standardized byhealing time, providing more precise
and reasonable information rather thanthe use of an ISQ per se at a certain time
point or an ISQ increase during undeﬁned period of time and, more importantly, allowing for a comparison
among different sources of data. Table 5
lists ISQ values from 2 time points

486

ACCELERATED OSSEOINTEGRATION BY PHOTOFUNCTIONALIZATION  SUZUKI ET AL

Table 5. ISQ Change and Calculated OSI in the Literature and This Study
ISQ
Initial (atPlacement)

Secondary*

HealingTime (mo)60.1 6 3.6

62.8 6 1.6

4

0.68

63.3 6 6.1

64.3 6 5.3

3

0.33

68.0

63.0

3

−1.67

58.5 6 4.7
61.5 6 9.0
61.9 6 6.6

60.9 6 4.3
60.2 6 6.9
63.5 6 5.7

69.4 6 9.3
69.9 6 8.5
62.8 6 7.2
60.0
65.5 6 5.5
64.2 6 5.0

73.4 6 6.6
74.4 6 6.9
60.7 6 3.6
62.7
62.8 6 5.4
64.1 6 3.5

6
6
6
3
3
3.4
4
3
2.5
1.5
1.5

0.4
−0.2
0.26
−1.8
−3.0
1.17
1.12
−0.7
1.1
−1.8
−0.06

ISQi 68–72

70.2 6 1.5

71.5 6 1.3

2.5

0.52

ISQi $ 72
Type 3 boneType 4 bone
MaxillaGrafted maxilla
Immediate loading,maxillaISQi, 65–70
ISQi, 71–75

76.7 6 3.1
73.6 6 5.8
68.9 6 4.3
62.3 6 5.1
60.7 6 6.1

74.8 6 1.3
74.8 6 5.4
69.9 6 4.3
63.9 6 5.5
61.4 6 5.2

2.5
2
2
6
6

−0.76
0.6
0.51
0.27
0.12

68.4 6 1.5
73.0 6 1.5

77.5 6 1.4
78.1 6 2.3

1.5
1.5

6.3
3.1

Implant Surface

Conditions

TiUnite41 (oxidized)

Immediate/early loading
maxillaImmediate/early loading
maxillaIncludes GBR andextraction socket
Anterior maxilla
Grafted anterior maxilla
Grafted anterior maxilla
ISQi 65–69
ISQi $ 70
Anterior maxilla
Posterior maxilla
Type 1 bone
Mandible
Mandible
Mandible

TiUnite42
TiUnite19†
TiUnite43
TiUnite44
SLA26 (sandblasted, acid-etched)‡
SLA45
SLA18
SLA34†SLA36
SLActive36 (sandblasted, acid-etched,chemically modiﬁed)
Impladent37 (sandblasted, acid andalkali treated)
SPI35 (sandblasted, acid etched)
TiOblast46 (sandblasted)
Photofunctionalized surface(TiUnite, oxidized)

OSI (ISQ
increase/mo)

The ISQ change during healing and calculated OSI are compared between untreated implants in literature and photofunctionalized implants. Note that the OSI values for photofunctionalized implants are
considerably higher than those from literature. In addition, the ISQ values achievable at week 6 of healing (1.5-month healing) in photofunctionalized implants are higher than those in any untreated implants
even after longer healing time.
*Some data were obtained at loading, whereas some at prescheduled follow-up time points.
†Values were read from the graph.
‡Data were provided only for ISQ difference between the implant placement and 3-month follow-up.
ISQi, initial ISQ at implant placement; OSI, osseointegration speed index ¼ ISQ increase per month.

along with the calculated OSI in the literature.18,19,26,34–37,41–46 The OSI values
from this study are also listed at the bottom of the table. Because the initial ISQ
values were all higher than 65 in thisstudy, we focused on the publications
dealing with initial ISQ values higher
than around 60 and at the same time,with data availability at least 2 time
points. The following were the 3 major
ﬁndings (Table 5): (1) a greater increase
between the initial and secondary ISQ
values in photofunctionalized implants
than in literature; (2) the majority of
OSI in literature was lower than 1.0
and the OSI of photofunctionalized implants was notably higher than those inliterature; and (3) the ISQ values atsecondary time points obtained in thisstudy between 77.5 and 78.1 were higher than any values in literature, even
within a shorter healing time of 1.5
months.
The ISQ values are known toincrease when the initial ISQ is lower
than 60, whereas ISQ values mostly stayunchanged or decrease when the initial
ISQ is higher than 60.19,21,26,35,47 This
common understanding can be reafﬁrmed from the data in literature listed
in Table 5, showing OSI of lower than
1.0 or even in the negative range below
0. In this regard, the OSI of 6.3 when theinitial ISQ was 65 to 70 and the OSI of
3.1 even when the initial ISQ was 71 to
75 obtained in this study should beconsidered remarkable. In fact, thecalculated OSI for all as-received conventional implants in Table 5 ranged
from −3.0 to 1.17, with an average of−0.10. If only data with their initial
ISQ being in a similar range to this study(65–75) are selected, the OSI ranged
from −1.8 to 1.17 with an average of
0.21. In both cases, the OSI values inliterature were substantially low.
Although any interpretation should
be carefully made because of the differences in macroscopic design and surface morphology among implants,
considerably high ISQ values obtainedin this study at week 6 may imply theadvantage of photofunctionalization to
not only expedite the process but also

IMPLANT DENTISTRY / VOLUME 22, NUMBER 5 2013

Fig. 5. Proposed mechanisms of appearance and disappearance of stability dip in schematic
description. The stability dip is anticipated for as-received untreated implants as commonly
understood whether the primary stability is high (A) or low (C). In contrast, the stability dip iseliminated by the use of photofunctionalization, regardless of the degree of primary stability (B,D), because of faster (when the primary stability is high) and even faster (when the primarystability is low) development of secondary stability. Note that photofunctionalization did not
only expedite the rate of establishing the total stability but also increased the degree of thetotal stability. Refer to the main text for detailed explanation.

achieve a higher level of osseointegration. The results were particularly surprising because of the following 2
reasons: initial ISQ values of 65 or
higher are not expected to increase
further, as reported in literature, andhigh ISQ values were obtained after
a healing time as short as 6 weeks.
Future studies are needed to follow-up
on the subsequent change of the ISQ
values of photofunctionalized implants.
The higher level of osseointegration
may lead to better success rates andlong-term predictability of implant
therapy, which will be a very interesting
research topic in the future. Thus, thecurrent ISQ data and its comparison
with literature were indeed consistent
with the results obtained from animalstudies that showed highly increased
implant ﬁxation in the early and latestage of healing, accelerated rate ofperiimplant bone formation, and theestablishment of bone-implant contact
nearing 100%,5 supporting the hypothesis that photofunctionalized implants
in humans are as effective as in animal
experiments.
Discussing cases of immediateloading and with a similar type of
implants would be of another particularinterest. A study examined the stabilitychange of implants loaded 1 to 9 days
after implant placement to support
a full-arch ﬁxed bridge in the maxilla.41
A total of 61 oxidized implants (6 or 8
implants per maxilla) were examined.
The mean ISQ, which was 60.1 6 3.6487

at placement, increased to 62.8 6 1.6
after 4 months, giving an OSI of 0.68.
Another study evaluated implants
placed in the partially edentulous maxilla and loaded 0 to 16 days after placement.42 A total of 53 oxidized implants(16 for single tooth replacement and 37
for partial ﬁxed bridges) were examined. The initial ISQ of 63.3 6 6.1slightly increased to 64.3 6 5.3 after 3
months, giving an OSI of 0.33. Again,
there is a general understanding regarding ISQ values that the lower the initialvalue the more increase is expected during the subsequent healing. Despite theinitial ISQ being higher than these studies, OSI values obtained at week 6 inthis study were remarkably greater.
Knowing that these studies were carriedout under a similar clinical protocol andhost conditions to this study and with
the implant texture being identical to anoxidized surface used in this study, thecurrent results may genuinely demonstrate the effect of photofunctionalization in enabling a faster and more
complete process of osseointegration.
As mentioned in Introduction, the clinical beneﬁt of photofunctionalization
was particularly anticipated in such
early/immediate loading cases becauseof the increased attachment and retention of osteogenic cells, which indeed
has been proven by the quantitative
assessment of implant stability.
Another important result of thisstudy was the elimination of the stability dip or signiﬁcant decrease of totalstability throughout the healing period
for photofunctionalized implants. Highinitial ISQ values of approximately 70
to 80 are bound to show a typical dip
during the subsequent healing periodor, if not a typical dip, a decrease andremain at the decreased level.19,21,26,35,47
In this study, as shown in Table 2 andFigure 4, C, implants with very highinitial ISQs (higher than 78) did notexperience a stability dip or signiﬁcantdecrease during the healing period, providing the compelling evidence to support immediate loading. Together withthe rapid ISQ increase observed in theimplants with lower initial ISQ, the current results will help explore a new
strategy for early or immediate loading
protocols. On the basis of the current
results on ISQ dynamics combined with

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ACCELERATED OSSEOINTEGRATION BY PHOTOFUNCTIONALIZATION  SUZUKI ET AL

the common understanding on how thestability dip appears, we propose
a mechanism underlying the disappearance of the stability dip by the use ofphotofunctionalized implants (Fig. 5).
There are 2 scenarios to explain the phenomenon of stability dip, depending on
the level of primary stability. The notions applied to construct the mechanism were as follows: (1) OSI forphotofunctionalized implants was considerably higher than untreated implants reported in literature, which led
to a rapid and steep secondary stability
curve slope during the early healing
period; (2) regardless of the use of photofunctionalization, implants withlower initial ISQ values tend to show
higher OSI as understood commonly;(3) in this study, an OSI with an initial
ISQ of 65 to 70 was, in fact, 2 times
greater than an OSI with an initial ISQof 71 to 75; (4) not only the rate of
implant stability but also the ﬁnal level
was increased by photofunctionalization, which indicates that the level ofsecondary stability could be higher withphotofunctionalized implants than conventional implants; and (5) the rate oflosing primary stability is assumed to be
the same with or without photofunctionalization. In Figure 5, A and C,
high-level and low-level stability dips
unavoidably take place in untreatedconventional implants because of thequicker loss of primary stability thanthe development of secondary stability.
The rate of secondary stability establishment, which is faster in Figure 5, C
than in Figure 5, A, as indicated by “a’. a,” is unlikely to help eliminate thestability dip. In contrast, because of theearly shift of the secondary stability
curve, as indicated by “b . a,” the stability dip is effectively eliminated inphotofunctionalized implants (Fig. 5,
B). The increased level of total stabilityby the increased degree of secondary
stability should not be overlooked. In
addition, because of further increased
rate in the secondary stability, as indicated by “y ¼ 2bx,” the stability dip can
be avoided even when the primary stability was low (Fig. 5, D). We believethat the proposed schemes will help
understand how the overall anchorageof photofunctionalized implants is
uniquely established and provide

a novel platform to build a new strategy
for future clinical protocols and thedevelopment of implant surfaces.
Although the interpretation should
be limited to the results obtained during
the initial period of osseointegration of
up to 3 months, the quantitative analysisof implant stability by the consecutive
measurement of ISQ values in a cohort
design may have provided an invaluable
data set to demonstrate the expedited andenhanced process of osseointegration inphotofunctionalized dental implants andwarrants further clinical studies to establish photofunctionalization as an effective measure to improve the current
implant dentistry in multiple aspects.
Photofunctionalization is a simple, practical, chair-side treatment of dental implants that requires only 15 minutes andhas proven effective on all surface topographies of titanium-based materials
tested, implying the versatile applicability in a wide range of dental andorthopedic implants.9,48–50 If future surface technologies are anticipated to
expand the indications of implant therapy, shorten the healing time, increase
the success rate for compromised bone
conditions, and explore minimally invasive approaches, photofunctionalization
as presented here may provide a novel
insight and a practical avenue to pursue
those goals. Finally, the application ofphotofunctionalization should not be
restricted to use in dental implants.
Orthopedic implants face many, longunsolved challenges. Photofunctionalization can be applied regardless of the
shape and size of implants. Various
orthopedic implants, including but notlimited to spine screws, femoral stem,knee joint implants, plates, and pins,
can potentially be enhanced for theirosteoconduction.

CONCLUSIONSThis study reports a quantitativeevaluation of the effect of photofunctionalization on clinical performance, specifically osseointegration capability, of
dental implants. Photofunctionalization
was conducted by treating implants with
UV light for 15 minutes. The generationof superhydrophilicity and hemophilicity
was conﬁrmed after photofunctionalization. The osseointegration capability ofphotofunctionalized implants placed in
the maxilla and immediately loaded wasassessed by consecutive measurementsof ISQ during the early stage of healing
up to 3 months along with the rate of ISQ
increase per month, deﬁned as the OSI.
Implants with their initial ISQ at placement between 65 and 70 showed a rapid
and robust ISQ increase during the subsequent healing period. Implants with
their initial ISQ between 71 and 75 also
showed a rapid and signiﬁcant increase.
Implants with their initial ISQ of 76 or
greater maintained a high level of ISQ
throughout the healing period without
showing any drop or progressive
decrease in ISQ. Regardless of the initial
ISQ, ISQ values were 75 or greater for all
implants by week 6. The ISQ at week 6
for photofunctionalized implants ranged
from 77.5 to 78.1 with an average of 78.0,
whereas ISQ values after a longer healing
period (mostly 2–6 months) observed inliterature ranged between 60.2 and 74.8
with an average of 66.1. The OSI was
considerably high for photofunctionalized implants (6.3 for implants with an
initial ISQ of 65–70 and 3.1 for implants
with an initial ISQ of 71–75) thanfor untreated conventional implants inliterature ranging from −3.0 to 1.17 withan average of −0.10. In conclusion,
photofunctionalization resulted in theacceleration and enhancement of
osseointegration in commercial dental
implants. As a result, the rate of establishing implant stability was substantially
increased when initial stability was relatively low. When the initial stability was
relatively high, the ISQ was maintained
at a high value, eliminating the commonly accepted phenomenon of the stability dip. In both instances, the level ofstability that implants may experience
was considerably increased. These results imply that photofunctionalization
may provide a novel and practical possibility to further advance implant therapy
for its expanded indications, shortened
healing time, improved predictability inchallenging cases, and the explorationof minimally invasive approaches during
the treatment.

DISCLOSURE
The authors claim to have noﬁnancial interest, either directly or

IMPLANT DENTISTRY / VOLUME 22, NUMBER 5 2013indirectly, in the products or information listed in the article.

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