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Lasers in Surgery and Medicine

Minimally Invasive Skin Rejuvenation With Erbium:

YAG Laser Used in Thermal Mode

Karin Kunzi-Rapp, MD, 1,2 * Christine C. Dierickx, MD, 3,4 * Bernard Cambier, MD, 5 and

Michael Drosner, MD, PhD 6,7

1

Institute for Laser Technologies in Medicine and Metrology, University of Ulm, Germany

2

Department of Dermatology and Allergology, University of Ulm, Germany

3

Laser Skin Center, Boom, Belgium

4

Wellman Laboratories of Photomedicine, Havard Medical School, Boston

5

Laser Clinic, Gent, Belgium

6

Cutaris Zentrum für Haut, Venen und Lasermedizin, Munich, Germany

7

Department of Dermatology and Allergology, Technical University of Munich, Germany

Background and Objectives: To evaluate the efficacy

and safety of a thermal mode Erbium:YAG laser several invivo

morphological as well as clinical changes were

monitored in a multi-center investigation.

Study Design/Materials and Methods: An Erbium:YAG

laser was used at a thermal mode with sub-ablative

fluences of 2.1 and 3.1 J/cm 2 with parallel air cooling to

treat either periorbital, perioral rhytides or patients with

post-traumatic or acne scars. Two treatments were applied

2 months apart, with follow-up at 1, 3, 6, and 12 months

post-treatment. Photographs were taken before and at each

follow-up visit and evaluated by three blinded independent

reviewers. Histology and immunohistochemistry for procollagen

expression were investigated. Optical coherence

tomography (OCT) was performed before, and at 4, 14, and

28 days after single pass treatment with Erbium:YAG

thermal pulses.

Results: The improvement of rhytides at 1–3 months

follow-up was graded as excellent in 19%, good in 19%, fair

in 31%, and no improvement in 31%. At the 6- to 12-month

follow-up, the improvement was excellent in 40%, good in

40%, fair in 20%, and no improvement in 0%. The

improvement of scars at 3–6 months follow-up was graded

as excellent in 50%, good in 25%, fair in 25%, and no

improvement in 0%. Intra- and post-operative discomfort

was described as mild by the patients. OCT, histological

sections and immunohistochemistry demonstrated production

of new collagen bundles.

Conclusions: Thermal Erbium:YAG pulses can induce

collagen neogenesis, as proved by temperature elevation

and morphological changes in the upper dermis. This leads

clinically to visible and long lasting reduction of wrinkles

and scars after applying multiple passes with minimal sideeffects.

Lasers Surg. Med.

ß 2006 Wiley-Liss, Inc.

Key words: Er:YAG; thermal pulses; collagen neogenesis;

histology; immunohistochemistry; minimally invasive

resurfacing; optical coherence tomography (OCT);

scar reduction; temperature recording; wrinkle reduction

ß 2006 Wiley-Liss, Inc.

INTRODUCTION

Patients and physicians look for less invasive techniques

to improve rhytides and scars. For many years, ablative

lasers (CO2 and more recently Er:YAG lasers) have been

used successfully for the treatment of wrinkles and scars

[1–5], but their use is limited by the pain and down time for

the patient and the relatively high risk of side effects and

complications for the physician [6]. Therefore, the market

of non-ablative techniques is growing fast and all kinds of

different methods are available that claim to be efficient for

reduction of wrinkles and scars. But after critical review

and assessment of current literature in terms of their

efficacy, all these non-ablative methods are not a comparable

alternative to the ablative skin resurfacing [7–10].

Both physician and patient should be willing to accept

subtle, incremental, and gradual improvements. Also, a

relatively high proportion of non-responders limit the

clinical success rate [11]. Additionally these methods often

need multiple treatments, are time consuming, and sometimes

painful which makes them less attractive than

originally intended. Finally, the non-ablative rejuvenation

treatment modalities are based on newly developed

technologies. Therefore, these new devices with modest

efficacy are often expensive for the practitioner.

Compared to the CO2 laser, the main advantage of the

Er:YAG laser for skin resurfacing, is precise ablation with

limited residual thermal damage (RTD). This results in

faster reepithelialization and an improved side effect

profile. On the other hand, immediate collagen shrinkage

and delayed new collagen formation is reduced together

with poor intra-operative hemostasis.

Karin Kunzi-Rapp and Christine C. Dierickx contributed

equally to the work.

*Correspondence to: Dr. Karin Kunzi-Rapp, Institute for Laser

Technologies and Metrology in Medicine, University of Ulm,

Helmholtzstr. 12, D-89081 Ulm, Germany.

E-mail: karin.rapp@ilm.uni-ulm.de

Accepted 15 June 2006

Published online in Wiley InterScience

(www.interscience.wiley.com).

DOI 10.1002/lsm.20380


2 KUNZI-RAPP ET AL.

In an attempt to overcome the limitations of the shortpulsed,

ablative Er:YAG lasers, modulated (short- and

long-pulsed) Er:YAG systems were introduced. With the

addition of significant coagulative properties, modulated

Er:YAG systems combine precise control of ablation with

the ability to improve hemostasis and induce dermal

collagen formation by means of thermal injury.

However, compared to non-ablative skin rejuvenation

techniques, conventional CO2 and erbium resurfacing

techniques cause thermo-mechanical tissue ablation with

the implication of visible and longer healing times. This has

caused that traditional CO2 and erbium resurfacing

techniques are nowadays largely abandoned, but has

stimulated the search for techniques to deliver energy with

these lasers, deeper in the skin without the unwanted

ablation.

The main effect of CO 2 and Er:YAG laser resurfacing is

the stimulation of new collagen growth in the dermis.

Histologically, it has been shown that these new collagens

replace the elastotic collagen of the connective tissue

matrix associated with wrinkles and photodamaged skin

in the upper dermis. Because water is the target chromophore

of these lasers, they ablate the full epidermis before

the laser energy affects the papillary dermis by heat

diffusion.

Theoretically, animal and clinical studies have shown

that it is indeed possible to deliver CO 2 or erbium laser

energy deeper in the skin without causing unwanted

epidermal ablation [12–20]. Ross et al. 1999 [12] described

the effect of stacking pulses of a CO 2-laser causing a less

distinct line between denatured and intact collagen and an

increased depth of the RTD. Using heat transfer models as

well as animal models, it could be shown, that an erbium

laser pulse can achieve greater RTD by lengthening the

pulse width [13–15].

The goal of our study was to determine whether an

Er:YAG laser used with a sequence of sub-ablative pulse

fluences below the ablation threshold, a so called thermal

mode, could produce enough dermal injury without complete

epidermal ablation to cause new collagen synthesis.

To evaluate the efficacy and safety for rejuvenation of a

laser system already established in the dermatological

practice the thermal mode of an Er:YAG laser was used for

the treatment of facial wrinkles. In a first preliminary

study we used a sub-ablative setting. A group of 29

volunteers were treated twice at a 6-month interval at 33

areas (periorbital 19, upper lips 11, lower lips/chin 2, cheeks

1) with a single pass of Er:YAG thermal laser pulses at subablative

fluences of 3.1–4.2 J/cm 2 , using parallel cooling

with cold air. The clinical efficacy was evaluated by

comparing pre- and post-photographs taken at baseline,

1, 3, 6, and 12 months after the two treatments. Although

the wrinkles were improved transitory at months 1 and 3,

the 6 and 12 months follow-up photographs revealed no

improvement, evaluated by the volunteers themselves,

by the physicians or by uninvolved, blinded interpreters

(Fig. 1).

As some individuals showed good clinical responses [21]

and some investigations reported histological changes

Fig. 1. Periorbital wrinkles treated with a single pass of

Erbium:YAG thermal laser pulses at sub-ablative fluences of

2.4 J/cm 2 , parallel cooling with cold air, (A) before, (B) 7 months

after treatment with mild structure changes.

[22–24], a second study was initiated. In this study, the

efficacy of multiple passes of Er:YAG thermal laser pulses

at fluences below the ablation threshold was evaluated by

clinical means, by histology and immunohistochemistry, by

optical coherence tomography (OCT) and by in vitro/in vivo

temperature measurements.

MATERIALS AND METHODS

Laser

Two variable pulsed Er:YAG lasers (SupErb XL and

BURANE XL, WaveLight Laser Technologie AG, Erlangen,

Germany) were used. We used the laser in a special thermal

mode consisting of a sequence of 9–11 short pulses each

with a fluence below the ablation threshold with an overall

pulse duration of 200–270 milliseconds and a total energy

density of 2.1–3.1 J/cm 2 . The parameters of this pulse


sequence were determined by temperature calculations as

well as Monte–Carlo simulations in order to optimize

heat penetration by conduction. Sub-ablative thermal

Er:YAG laser pulses heat the stratum corneum and the

epidermis due to absorption by the water content and

cause temperature increase of the upper dermis by heat

conduction.

Histology

The tissue samples were fixed in 4% freshly prepared

paraformaldehyde, paraffin embedded, cut in 3 mm sections

and stained with hematoxylin and eosin for histopathology.

A specialized procedure to pronounce collagen fibers was

done by Alcian blue staining.

Immunohistochemistry

Paraffin sections were mounted on poly-L-lysine coated

slides. After deparaffinizing and rehydrating antigen

retrieval of sections was done by protein kinase K at 378C

for 10 minutes. Non-specific binding sites were blocked

with goat serum. Human pro-collagen Type I C-peptide

mouse monoclonal antibody (TaKaRa, Bio Europe S.A.,

Gennevillier, France) was applied according to the manufacturer

protocol. The highly sensitive Histostain-Plus

streptavidin peroxidase staining procedure (Zymed

Laboratories, Inc., San Francisco, CA) was used with

DAB chromogen staining. At optimal color development

sections were immersed in sterile water, counterstained

with Mayer’s hematoxylin and covered.

Quantitative assessment of pro-collagen expression.

To determine pro-collagen expression, positive staining

fibroblasts were evaluated at 100 magnification using

an optical microscope (Axiophot, Carl Zeiss, Jena, Germany)

with a CCD camera (Sony MC-3249) and calculated

as percentage of the total number of fibroblasts by an

imaging analysis software (OPTIMAS, MediaCypernetics,

Silverspring MD). The numbers in Figure 5 represent

averaged values of four counts.

Optical Coherence Tomography (OCT)

OCT (ISIS Optronics GmbH, Mannheim, Germany) was

performed before, and at 4, 14, and 28 days after single pass

treatment of the outer forearm in two volunteers with

Er:YAG thermal pulses (fluence 4.2 J/cm 2 , spot size 5 mm),

parallel cooling with cold air.

Temperature Recording

For temperature measurements we used a digital

temperature probe (80 TK thermocouple module, Fluke

Cooperation, Everett WA).

Patient Selection

Patient selection for the morphological (biometrical)

study. Tissue biopsies were taken from seven

volunteers scheduled for blepharoplasty or abdominoplasty

with Fitzpatrick skin types 2–3 after informed written

consent was obtained before, 2 and 4 weeks after treatment

with Er:YAG thermal pulses at the same body side.

MINIMALLY INVASIVE SKIN REJUVENATION WITH ER:YAG 3

Patient selection for the clinical study. Subjects

with wrinkles or scars were included in the clinical

study. The first group consisted of 20 female subjects with

peri-orbital, peri-oral, or wrinkles on the cheeks. The

Fitzpatrick phototypes ranged from I to III and the ages

varied from 38 to 78 years (mean 55 years).

A second group included 12 patients with scars. Six

female and six male patients with phototypes I–III and

ages ranging from 12 to 39 years (mean 29 years) were

treated. The scars were either post-traumatic in nature and

located on the face and extremities or were atrophic facial

scars due to acne.

Treatment Protocol

All patients were treated with a 2,940 nm, variable pulse

Erbium:YAG laser (SupErb XL or BURANE XL, Wave-

Light Laser Technologie AG) in the thermal mode program.

Thermal mode pulse sequences (total pulse duration 200–

270 milliseconds) at sub-ablative fluences were used at

total energy density of 2.1–3.1 J/cm 2 for a 5 mm spot size

and at a frequency of 3 Hz. All procedures were performed

without local anesthesia. Eyes were protected with eye

shields. Parallel to the application of thermal laser pulses

cooling was provided with a constant flow of cold air level 1

(Cryo 5 skin cooling system, Zimmer MedizinSystems, Neu-

Ulm, Germany). No pre-cooling was performed. At each

treatment, the entire treatment area was irradiated with

3–5 consecutive laser passes with minimal overlap. No

wiping was performed between the passes. Additional

passes over the wrinkles or scars were given until the

clinical endpoint of skin whitening was obtained (Fig. 2).

The number of passes needed to reach the skin whitening

depended on the humidity of the skin and coincidences with

thermally induced necrosis of the stratum corneum and the

epidermis. Normally, more than five passes were necessary.

All treatment sites received two treatments with an

interval of 2 months. Post-exposure skin care consisted of

Fig. 2. Clinical endpoint (whitening of the epidermis) for the

Er:YAG treatment of wrinkles with multiple passes of Er:YAG

thermal laser pulses at sub-ablative fluences of 2.1 J/cm 2 and

parallel cooling with cold air.


4 KUNZI-RAPP ET AL.

an antibiotic ointment for reepithelialization and moistening

purposes. Sun blocks were recommended once healing

was complete. Patients came in for follow-up at 1, 3, 6, and

12 months post-treatment. Photographs were taken at each

follow-up visit and side effects were noted. Pre-and postoperative

photographs were captured with a digital Sony

camera (Cyber-shot 3.3 megapixels, DSC-F505V, Sony

Electronics) and were compared to evaluate treatment

response. Assessments were done by three blinded independent

reviewers, using a five-point improvement scale

(Table 1).

RESULTS

Biometrical Results

Histology. Examination of the biopsies taken 2 weeks

after treatment under light microscopy H&E staining

revealed a hypertrophic epidermis, caused by a thickened

stratum spinosum. In the papillary dermis we found

vasodilatation and a mild perivascular infiltration of

inflammatory cells. Four weeks after treatment the

epidermis flattened and the upper dermis demonstrated

more tightly packed collagen bundles with parallel orientation

to the skin surface (Fig. 3).

Structural evaluation of the treated samples compared to

non-treated samples showed a decrease in clumping of

collagen bundles and an increased amount of thin collagen

fibers with regular orientation in the upper dermis

extending from the basement membrane zone.

Immunohistochemistry. Immunhistological staining

4 weeks after treatment (Fig. 4) showed a marked increase

of pro-collagen expression in dermal fibroblasts till a depth

of about 320 mm. When we compared different treatment

modalities, mild ablation with two passes at a fluence of 5 J/

cm 2 as well as ablation followed by one pass of the

combination mode (ablative pulses in combination with

the thermal pulses) induced pro-collagen expression in

40.1% of the fibroblasts. Two passes of thermal pulses alone

showed a pro-collagen expression in 25.5%. In untreated

skin 5.6% of the fibroblasts were activated (Fig. 5).

Optical coherence tomography. OCT is a noninvasive

technique for high resolution imaging in the

tissue. It is based on the same concept like ultrasound:

waves are backscattered by tissue inhomogenities and

analyzed over time of flight to obtain spatial resolved

resolution. Before laser treatment OCT pictures of normal

skin clearly showed the epidermal–dermal junction separated

by a small band with a low scattering structure. In the

upper dermis clearly demarcated homogeneous dark

structures indicated the blood vessels. Four days after

thermal Er:YAG laser pulses crusting and edema were still

TABLE 1. Grading Scale

Worse 0

No improvement 1

Fair improvement 2

Good improvement 3

Excellent improvement 4

obvious. After 2 weeks OCT images could still detect

inflammatory cells in the tissue marked by blurred skin

structures. Four weeks after treatment dense reflecting

structures in the upper dermis were indicating an increase

of collagen fibers (Fig. 6).

Fig. 3. Histological sections H&E stained before and 4 weeks

after Er:YAG thermal laser pulses (original magnification

100 ): (A) before Er:YAG laser treatment and (B) 4 weeks after

Er:YAG thermal laser pulses; the epidermis flattened and in

the upper dermis (*) new collagen bundles and less elastosis

became obvious. [Figure can be viewed in color online via

www.interscience.wiley.com.]


Fig. 4. Immunhistochemical sections stained with mAb

against pro-collagen: (A) before and (B) 4 weeks after single

pass treatment with Er:YAG thermal laser pulses at subablative

fluences of 3.5 J/cm 2 , parallel cooling with cold air. The

brown staining indicates the pro-collagen expression of dermal

fibroblasts (original magnification 100 ).

Temperature recording. The basic approach of the

thermal pulses was to heat up the upper dermis to a

sublethal temperature and maintain this temperature for a

time period up to 300 milliseconds to induce collagen

remodeling. Monte–Carlo simulations as well as heat

transfer calculations resulted in temperature profiles at

different depths of the skin. These simulations resulted in a

pulse sequence consisting of short pulses with different

pulse energies below the ablation threshold. The calculations

determined the temperature increase till a maximum

of about 608C in the depth of the upper dermis (150 mm) was

reached. This temperature was maintained for more than

30 milliseconds. Temperature profiles were verified by

temperature measurements with a digital temperature

probe in ex vivo human skin samples. Different programs of

thermal pulses showed characteristic temperature elevations

in the epidermis shown in Figure 7.

MINIMALLY INVASIVE SKIN REJUVENATION WITH ER:YAG 5

% positive cells

45

40

35

30

25

20

15

10

5

0

25,5

In one volunteer, the temperature profile was measured

in vivo by placing the temperature probe into the dermis of

the forearm in a depth of 335 mm. The depth of this probe

was controlled by OCT. After application of one thermal

Er:YAG laser pulse sequence temperature profile was

recorded. In this depth the temperature increase was about

38C after a single thermal pulse sequence with a fluence of

3.5 J/cm 2 and a spot size of 5 mm. It took about 40 seconds to

reach the initial skin temperature (Fig. 7c). If cooling was

performed during repetitive pulses the time to reach the

value of the initial temperature was reduced to about

1 second (picture not shown).

Clinical Results

Average post-operative follow-up was 6–12 months for

the wrinkle group and 3–6 months for the scar group. The

wrinkle reduction or scar improvement was significant in

most cases and improved over time. Improvement of

rhytides at 1–3 months follow-up was graded as excellent

in 19%, good in 19%, fair in 31%, and no improvement in

31%. At the 6–12 months follow-up, the improvement was

excellent in 40%, good in 40%, fair in 20%, and no

improvement in 0% (Figs. 8 and 9). Improvement of scars

at 3–6 months follow-up was graded as excellent in 50%,

good in 25%, fair in 25%, and no improvement in 0%

(Figs. 10 and 11).

Intra- and post-operative discomfort was described as

mild by the patient. Superficial crusting occurred and

reepithelialization was complete in 3–4 days. Mild postoperative

erythema persisted for 3–4 weeks. In one patient

with a history of herpes simplex, a reactivation of latent

labial herpes simplex virus infection occurred after the first

laser treatment. When acyclovir was given prophylactically

40,1

TP 3.5 J/cm² ablation 5 J/cm² control

Fig. 5. Quantitative assessment of pro-collagen expression

calculated as a percentage of total number of fibroblasts (the

numbers represent averaged values of four counts). Biopsies

taken 4 weeks after single pass treatment with Er:YAG laser:

TP 3.5 J/cm 2 : thermal pulses at sub-ablative fluences of 3.5 J/

cm 2 ; ablation 5 J/cm 2 : ablative Er:YAG laser pulses at ablative

fluences of 5 J/cm 2 ; control: untreated skin in the same

individual of the same location (either eyelid or abdominal

skin).

5,6


6 KUNZI-RAPP ET AL.

Fig. 6. Optical coherence tomography (OCT) before and after

single pass treatment with Er:YAG thermal laser pulses at

sub-ablative fluences of 4.2 J/cm 2 , parallel cooling with cold air:

(A) before laser treatment OCT pictures clearly showed the

epidermal–dermal junction separated by a small band with a

low scattering structure (dotted line). In the upper dermis

clearly demarcated homogeneous dark structures indicated

the blood vessels *. B: Four days after Er:YAG thermal laser

before the second treatment, another outbreak could be

prevented. No hyper- or hypopigmentation, textural

changes or scarring were observed in this patient group

with skin types I–III. Average post-operative follow-up was

6–12 months for the wrinkle group and 3–6 months for the

scar group.

DISCUSSION

CO2 or erbium resurfacing is a well-established method

to treat facial rhytides associated with photoaging [1–5].

These techniques completely disrupt or remove the

epidermis. Subsequent loss of barrier function results in

discomfort, edema, transudation, and focal crusting.

Epidermal loss also increases the risk of infection, pigmentary

changes and scarring [6].

Non-ablative skin rejuvenation, which does not remove

the epidermis, was specifically developed as a bettertolerated

alternative to ablative laser resurfacing. The

objective is to achieve selective, heat-induced denaturation

of dermal collagen that leads to subsequent new collagen

deposition with as little damage to the epidermis as

pulses crusting and edema were still obvious (bars indicate

thickness of the crusts). C: After 2 weeks OCT images could

still detect inflammatory cells in the tissue marked by blurred

skin structures. The epidermal–dermal junction is not

demarcated. D: Four weeks after treatment dense reflecting

structures in the upper dermis were indicating an increase of

collagen fibers. [Figure can be viewed in color online via www.

interscience.wiley.com.]

possible. The main problem with non-ablative skin rejuvenation,

however, is poor and/or unpredictable efficacy

compared with ablative treatments [7–11,25,26].

Microscopic changes associated with wrinkles occur

primarily in the dermis [27–30]. Wrinkle reduction, by

means of thermal damage to the dermis, is based on the

induction of synthesis of new collagen and other components

of extracellular matrix [13,25]. In this study, a

thermal mode Er:YAG laser was used to examine the effect

on wrinkle/scar reduction by dermal heating.

At commonly utilized ablative Er:YAG parameters, the

zone of RTD typically does not exceed 50 mm [33,34]. The

amount of thermal damage is dependent on the repetition

frequency, while the laser fluence is of much less importance

for the depth of necrosis [35,36]. The thermal pulse

structure in this study was composed of a sequence of short

Er:YAG pulses (200–270 milliseconds) below the ablation

threshold. It was developed in such a way to increase the

temperature in the upper dermis to about 608C in order to

induce collagen denaturation. In our ex/in vivo studies we

could confirm the temperature increase to 608C only for the


A

temperature / °C

B

temperature / °C

C

temperature / °C

80

60

40

20

0

0 10 20

time / s

30 40

100

80

60

40

20

0

0 5 10 15 20 25 30

time / s

33

32

31

30

29

28

27

0 20 40 60 80

time / s

Fig. 7. Temperature measurements with a digital temperature

probe: (A) at the epidermis in ex vivo skin samples after a

single Er:YAG thermal laser pulse (fluence 3.5 J/cm 2 , spot size

5 mm); (B) at the epidermis in ex vivo skin samples after a

single Er:YAG thermal laser pulse with a fluence of 4.2 J/cm 2 ;

(C) in vivo by placing a temperature probe into the dermis of

the forearm at a depth of 330 mm (OCT controlled) after a single

Er:YAG thermal laser pulse (fluence 3.5 J/cm 2 , spot size 5 mm);

the temperature profile was recorded for 70 seconds. It took

about 40 seconds to reach the initial skin temperature.

layers near the basal membrane zone. In deeper dermal

layers the temperature increase was only very mild after

application of only one pulse. However, in our clinical

study, we used multiple passes over the wrinkles. This most

likely resulted in a thermal build up by heat conduction

because the thermal relaxation of the treated tissue is very

slow (Fig. 7). After desiccation of the tissue the main

chromophore for the Er:YAG laser radiation deprived. As a

result, the optical penetration depth was enlarged, resulting

in further diminished ablation efficiency, enhanced

deposition of heat, and increased the zone of thermal injury.

MINIMALLY INVASIVE SKIN REJUVENATION WITH ER:YAG 7

% Patients

50

45

40

35

30

25

20

15

10

5

0

none slight moderate dramatic

1-3 months 6-12 months

Fig. 8. Wrinkle improvement in 20 female subjects with

periorbital, perioral, or wrinkles on the cheeks treated with

multiple passes of Er:YAG thermal laser pulses at sub-ablative

fluences of 2.1 J/cm 2 , parallel cooling with cold air. Assessments

were done on photographs taken at 1–3 months or 6–

12 months follow-up by three blinded independent reviewers,

using a five-point improvement scale (Table 1).

This finding can be understood by recalling that the

threshold fluence for skin ablation with the Er:YAG laser

is between 0.5 and 1 J/cm 2 [14,33,35]. At pulse fluences

below these values, the coagulation depth increases

linearly with the applied fluence [36]. Longer pulse

durations increase the ablation threshold [15]. A higher

ablation threshold simply enables a larger heat deposition

into the tissue and the elevated temperature persists for a

longer time due to the lower temperature gradients at these

depths.

While non-ablative skin rejuvenation with intense

pulsed light sources, visible or near-infrared light sources

or radiofrequency cause no epidermal damage at all, a

thermal mode Er:YAG laser damages the epidermis but

does not remove it [10].

After two passes of thermal pulses clinical as well as OCT

data revealed limited thermal damage of the epidermis. In

an in vivo skin model we could show 4 days after laser

treatment mostly upper epidermis was injured but basal

Fig. 9. Wrinkle improvement at 12 months follow-up in a 56year-old

woman treated with multiple passes of Er:YAG

thermal laser pulses at sub-ablative fluences of 2.1 J/cm 2 ,

parallel cooling with cold air.


8 KUNZI-RAPP ET AL.

% Patients

60

50

40

30

20

10

0

no slight moderate dramatic

Fig. 10. Scar improvement in 12 patients (6 female, 6 male)

with post-traumatic or acne scars located on face and

extremities treated with multiple passes of Er:YAG thermal

laser pulses at sub-ablative fluences of 2.1 J/cm 2 , parallel

cooling with cold air. Assessments were done on photographs

taken at 3–6 months follow-up by three blinded independent

reviewers, using a five-point improvement scale (Table 1).

keratinocytes were preserved [22,23]. The damaged epidermis

was not removed and acted as a wound dressing.

After reepithelialization, a hypertrophic epidermis as well

as inflammatory cells in the upper dermis persisted for

more than 2 weeks. This indicated that the reparative

phase was not finished at that time. Immunhistochemical

findings still showed activated fibroblasts with pro-collagen

1 expression in the upper dermis 4 weeks after treatment.

The number of these fibroblasts was significantly higher

than the basal expression of pro-collagen 1 in untreated

skin, but it was not as high as the expression after a mild

ablative treatment. Because the temperature increase in

the upper dermis in ablative resurfacing is less than after

sub-ablative thermal pulses the effect seems not only to be

based on the temperature. Fatemi et al. [37] focused on the

early histological changes after non-ablative laser treatment

with a 1,320 nm Nd:YAG laser. They concluded that

immediate vascular damage, recruitment of inflammatory

cells, and release of mediators may be responsible for

the clinical improvements associated with non-ablative

Fig. 11. Scar improvement at 6 months follow-up in a 49-yearold

woman treated with multiple passes of Er:YAG thermal

laser pulses at sub-ablative fluences of 2.1 J/cm 2 , parallel

cooling with cold air. [Figure can be viewed in color online via

www.interscience.wiley.com.]

resurfacing. Recently Drnovsˇek-Olup et al. [38] found a

sub-epidermal regeneration zone to a depth of about 120–

240 mm after treatment with non-ablative Er:YAG laser

fluences of 1.5 and 1.75 J/cm 2 . This zone consisted of

edematous tissue with stellate appearing cells with

immunhistochemically positive staining to smooth muscle

actin monoclonal antibody. These activated fibroblasts did

undergo an epidermal–mesenchymal transition (EMT)

which indicated the proliferative phase of wound healing

with production of extracellular matrix components [39].

The last phase of wound healing is characterized by

remodeling of the granulation tissue. In this stage collagen

3 is replaced by collagen 1 and proteoglycans are synthesized.

This neocollagen brings an indispensable support to

the dermis and fills the wrinkle. Furthermore myofibroblasts

in wound healing are responsible for wound

contraction and fibroplasia [40,41].

The purpose of our clinical study was to determine the in

vivo response to dermal injury without complete epidermal

ablation. We therefore used a 2,940 nm Er:YAG laser in a

thermal mode with sub-ablative settings: fluence of 2.1–

3.1 J/cm 2 , 200–270 milliseconds, slight overlapping, a spot

size of 5 mm, a repetition rate of 3 Hz and multiple pulse

stacking mode. These laser settings were chosen on the

base of results of theoretical studies of repetitive Er:YAG

treatments [14,36].

We showed that the thermal damage pattern included

limited epidermal damage, but no epidermal removal. A

rapid repair response was initiated with complete recovery

of the epidermis within 3–4 days with minimal discomfort.

Since the dermis was uniformly denatured by the multiple

pulse stacking technique, we introduced a way to reproducibly

induce denaturation of the treated tissue area

and thus may allow to achieve more reproducible therapeutic

results: in the wrinkle group up to 80% of patients

obtained moderate to dramatic improvement of wrinkles

while 75% of patients obtained the same results in the scar

group.

Although clinically observable results were present in

most of the patients, overall patient satisfaction was low.

The in vivo response to tissue damage consists namely of

three consecutive phases: an inflammatory phase, a

proliferation phase, and a remodeling phase [31,32]. This

explains why clinically observable results were only seen

between 3 and 6 months after initial treatment, with

further improvement between 6 and 12 months. This

relatively long period before clinically observable results

were seen, may lead to low patient satisfaction grade.

Additional topical or other non-invasive treatment modalities

might help to speed up the results and increase the

patient satisfaction.

CONCLUSIONS

Thermal mode Er:YAG laser pulses can induce collagen

neogenesis, as proved by temperature elevation and

morphological changes in the upper dermis, which leads

clinically to visible and long lasting reduction of wrinkles

and scars after applying multiple passes with minimal

side-effects.


ACKNOWLEDGMENTS

The authors thank Detlev Russ, Institute for Laser

Technologies in Medicine and Metrology at the University

of Ulm for providing the theoretical data and for the

performance of the temperature measurements.

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