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    Bond strengths of porcelain laminate veneers to tooth surfaces prepared with acid and Er,Cr:YSGG laser etching

    Aslihan Usumez DDS, PHD, , a and Filiz Aykent DDS, PHDb

    a Assistant Professor, Department of Prosthodontics, Selcuk University, Konya, Turkey
    b Associate Professor, Department of Prosthodontics, Selcuk University, Konya, Turkey

    Abstract
    Statement of problem
    The erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) hydrokinetic laser system has been successful in the ablation of dental tissues. It has been reported that this system is also useful for preparing tooth surfaces for adhesion, but results to date have been controversial.

    Purpose
    This in vitro study evaluated the bond strengths of porcelain laminate veneers to tooth surfaces after etching with acid and Er,Cr:YSGG laser conditioning.

    Material and method
    Forty extracted caries- and restoration-free human maxillary central incisors were used. The teeth were sectioned 2 mm below the cementoenamel junction. The crowns were embedded in autopolymerizing acrylic resin with the labial surfaces facing up. The labial surfaces were prepared with .05 mm reduction to receive porcelain veneers. The teeth were divided into 4 groups of 10 specimens. Thirty specimens received 1 of the following surface treatments before the bonding of IPS Empress 2 laminate veneers: (1) laser radiation from an Er,Cr:YSGG laser unit; (2) 37% orthophosphoric acid; and (3) 10% maleic acid. Ten specimens received no surface treatment and served as the control group. The veneers were bonded with dual-polymerizing resin, Variolink II. One microtensile specimen from each of the cervical and incisal thirds measuring 1.2 × 1.2 mm was prepared with a slow-speed diamond saw sectioning machine with a diamond-rim blade. These specimens were attached to opposing arms of the microtensile testing device with cyanoacrylate adhesive and fractured under tension at a crosshead speed of 1 mm/min, and the maximum load at fracture (Kg) was recorded. The data were analyzed with a 2-way analysis of variance and Tukey HSD tests (=.05).

    Results
    No statistically significant differences were found among the bond strengths of veneers bonded to tooth surfaces etched with Er,Cr:YSGG laser (12.1 ± 4.4 MPa), 37% orthophosphoric acid (13 ± 6.5 MPa), and 10% maleic acid (10.6 ± 5.6 MPa). The control group demonstrated the lowest bond strength values in all test groups. Statistically significant differences were found between the bond strengths of cervical and incisal sections (P<.001). Conclusion
    In vitro microtensile bond strengths of porcelain laminate veneers bonded to tooth surfaces that were laser-etched showed results similar to orthophosphoric acid or maleic acid etched tooth surfaces.

    #9602 Reply

    Glenn van As
    Spectator

    Neat study…….of course it was in enamel but my big big question.

    What were the settings.

    Glenn

    #9595 Reply

    Anonymous
    Guest

    Glenn,
    With the hydrokinetics it doesn’t matter what settings you use 😉

    Actually, I emailed the author and will let you know if I get a response.

    Happy New Year!

    #9603 Reply

    Glenn van As
    Spectator

    Oh darn it all ROn ……….now you tell me HK really does exist and I didnt include it in the text chapter…….

    Oh man guess I better go revise it.

    JUST KIDDING

    Glenn

    #9596 Reply

    Anonymous
    Guest

    Glenn, Dr. Usumez was kind enough to send the whole study.

    Bond strengths of porcelain laminate veneers to tooth surfaces prepared
    with acid and Er,Cr:YSGG laser etching
    Aslihan Usumez, DDS, PHD,a and Filiz Aykent, DDS, PHDb
    Faculty of Dentistry, Selcuk University, Konya, Turkey
    Statement of problem. The erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) hydrokinetic
    laser system has been successful in the ablation of dental tissues. It has been reported that this system is also
    useful for preparing tooth surfaces for adhesion, but results to date have been controversial.
    Purpose. This in vitro study evaluated the bond strengths of porcelain laminate veneers to tooth surfaces after
    etching with acid and Er,Cr:YSGG laser conditioning.
    Material and method. Forty extracted caries- and restoration-free human maxillary central incisors were used.
    The teeth were sectioned 2 mm below the cementoenamel junction. The crowns were embedded in autopolymerizing
    acrylic resin with the labial surfaces facing up. The labial surfaces were prepared with .05 mm reduction
    to receive porcelain veneers. The teeth were divided into 4 groups of 10 specimens. Thirty specimens received 1
    of the following surface treatments before the bonding of IPS Empress 2 laminate veneers: (1) laser radiation
    from an Er,Cr:YSGG laser unit; (2) 37% orthophosphoric acid; and (3) 10% maleic acid. Ten specimens received
    no surface treatment and served as the control group. The veneers were bonded with dual-polymerizing resin,
    Variolink II. One microtensile specimen from each of the cervical and incisal thirds measuring 1.2 1.2 mm was
    prepared with a slow-speed diamond saw sectioning machine with a diamond-rim blade. These specimens were
    attached to opposing arms of the microtensile testing device with cyanoacrylate adhesive and fractured under
    tension at a crosshead speed of 1 mm/min, and the maximum load at fracture (Kg) was recorded. The data were
    analyzed with a 2-way analysis of variance and Tukey HSD tests (.05).
    Results. No statistically significant differences were found among the bond strengths of veneers bonded to
    tooth surfaces etched with Er,Cr:YSGG laser (12.1 4.4 MPa), 37% orthophosphoric acid (13 6.5 MPa), and
    10% maleic acid (10.6 5.6 MPa). The control group demonstrated the lowest bond strength values in all test
    groups. Statistically significant differences were found between the bond strengths of cervical and incisal sections
    (P.001).
    Conclusion. In vitro microtensile bond strengths of porcelain laminate veneers bonded to tooth surfaces that
    were laser-etched showed results similar to orthophosphoric acid or maleic acid etched tooth surfaces.
    (J Prosthet Dent 2003;90:24-30.)
    CLINICAL IMPLICATIONS
    This in vitro study reported no difference in microtensile bond strengths of porcelain veneers
    bonded to tooth surfaces that were etched with an Er,Cr:YSGG laser, 37% orthophosphoric acid,
    or 10% maleic acid.
    Patient demand for the treatment of unesthetic anterior
    teeth has grown. For many years the most predictable
    and durable esthetic correction of anterior teeth has
    been achieved by the preparation of complete crowns.1
    However, this approach is undoubtedly the most invasive
    with the removal of substantial amounts of sound
    tooth substance with possible adverse effects on adjacent
    pulp and periodontal tissues.2,3
    Calamia4 described the clinical and laboratory procedures
    for bonding porcelain laminate veneers to acid
    etched enamel. The popularity of porcelain laminate veneers
    has increased since their introduction because
    tooth preparation is conservative and the restorations
    are esthetic.5 However, an in vitro study has described
    some disadvantages such as marginal adaptation and related
    bonding problems.6
    Traditionally, etching the enamel surface with orthophosphoric
    acid, a concept first proposed by Buonocore,
    7 has been commonly used to increase the bond
    strength between the composite and enamel. The technique
    of etching with orthophosphoric acid is used to create
    an irregular surface of enamel. This allows an increase in
    the prepared surface area available for the retention of the
    composite and an improvement in the marginal adaptation
    of laminate veneers.8 The retentive characteristics of acidconditioned
    enamel surfaces depend on the type of acid,
    etching time, and chemical composition of enamel.9
    aAssistant Professor, Department of Prosthodontics.
    bAssociate Professor, Department of Prosthodontics.
    24 THE JOURNAL OF PROSTHETIC DENTISTRY VOLUME 90 NUMBER 1
    Three types of etching patterns have been described
    by Silverstone et al10 after exposure of the enamel prisms
    to etching solutions: type I, preferential removal of
    prism core material, leaving the periphery intact; type II,
    preferential removal of periphery core material, leaving
    the prism core relatively unaffected; and type III, a more
    random etching pattern in which adjacent areas of the
    tooth surface correspond to types I and II, mixed with
    regions in which the pattern could not be related to
    prism structure. Morphologic information obtained by
    scanning electron microscopy indicated that the surface
    structure resulting from etching with 35% orthophosphoric
    acid and 10% maleic acid is similar.11,12
    Laser devices have been used in dentistry for soft
    tissue surgery, root end sealing and sterilization, and for
    altering enamel and dentin surfaces to increase resistance
    to decay or to facilitate the bonding of composites.13,14
    Laser etching may be an alternative to acid etching of
    enamel and dentin. Laser etching is painless and does
    not involve either vibration or heat, making this treatment
    attractive.15 Furthermore, laser etching of enamel
    or dentin has been reported to yield an anfractuous surface
    (fractured and uneven) and open dentin tubules,
    both apparently ideal for adhesion.15 The surface produced
    by laser etching is also acid-resistant because laser
    radiation of dental hard tissues modifies the calcium-tophosphorus
    ratio, reduces the carbonate-to-phosphate
    ratio, and leads to the formation of more stable and less
    acid-soluble compounds, thus reducing susceptibility to
    acid attack and caries.16
    The ability of erbium:yttrium aluminum garnet (Er:
    YAG) lasers to cut dental biocalcified tissue effectively
    has been demonstrated.15 Furthermore, the cutting ef-
    ficacy is improved when the tooth surfaces are flooded
    with a water layer.15,17,18 The Er,Cr:YSGG pulsed-wave
    laser, when used with an air-water spray, has been shown
    to cut enamel, dentin, cementum, and bone efficiently
    and cleanly.19,20 The Er,Cr:YSGG laser produces microexplosions
    during tissue ablation, resulting in macroscopic
    and microscopic irregularities.21 The Er,Cr:
    YSGG laser initially causes vaporization of water and
    other hydrated organic components of the tissue.21 On
    vaporization, the internal pressure builds within the tissue
    until the explosive destruction of inorganic substance
    occurs before the melting point is reached.21
    The quality of the bond obtained by laser etching of
    enamel relates to the energy densities of the device.22
    With low energy densities, the surface is largely unaffected
    by laser pulses and retention is poor. At intermediate
    exposures surface roughening occurs.22 At high
    energy densities, the enamel is fused and this thin layer
    of fused enamel becomes the weakest link in the chain of
    adhesion.22
    Laser-induced physical changes include melting and
    recrystallization with the formation of numerous pores
    and small, bubble-like inclusions. These profiles have
    been shown by some studies in CO2 laser23 and Nd:
    YAG laser.24,25 In contrast, no melting or recrystallization
    was observed with Er,Cr:YSGG hydrokinetic system.
    19,26
    The purpose of this study was to determine the microtensile
    bond strengths of porcelain laminate veneers
    to acid-etched and Er,Cr:YSGG laser treated enamel,
    with an unetched group serving as the control. The
    enamel morphologic structure after laser etching and
    acid etching was also investigated with scanning electron
    microscopy (SEM). The hypothesis tested was that the
    microtensile bond strength obtained after Er,Cr:YSGG
    laser etching of enamel is similar to that obtained after
    acid etching.
    MATERIAL AND METHODS
    Forty extracted human maxillary central incisors with
    10 mm anatomic crown length and 8 mm mesiodistal
    width were selected. Each tooth was free of dental caries
    and restoration. The teeth were cleaned and stored in
    saline solution at room temperature immediately after
    extraction.
    The teeth were sectioned 2 mm below the cementoenamel
    junction with a slow-speed diamond saw sectioning
    machine (Isomet; Buehler Ltd, Lake Bluff, Ill), and
    the crowns were embedded in autopolymerizing acrylic
    resin (Meliodent; Bayer Dental Ltd, Newbury, UK)
    with the labial surfaces facing up.
    Tooth preparation
    The facial surfaces of the teeth were prepared to accommodate
    veneers of equal thickness. A 0.5-mm facial
    reduction was performed with a chamfered cervical finish
    line and incisal bevel preparation. Self-limiting
    depth-cutting disks of 0.5 mm (834-31-021; Gebr.
    Brasseler, Lemgo, Germany) were used to define the
    Fig. 1. Completed veneer preparation.
    USUMEZ AND AYKENT THE JOURNAL OF PROSTHETIC DENTISTRY
    JULY 2003 25
    depth of the cuts, and then 1.4-mm chamfer diamond
    burs (6844-314-014; Gebr. Brasseler) were selected to
    refine the preparation. All tooth preparations were completed
    without sharp line angles (Fig 1).
    Impression making and master die fabrication
    Impressions of the 40 prepared teeth were made with
    polyvinylsiloxane impression material (Permagum; 3M
    ESPE AG, Seefeld, Germany). The impressions were
    poured with a vacuum-mixed polyurethane die material
    (Alpha Die MF; Schu¨ltz-Dental GmbH, Rosbach, Germany)
    according to the manufacturers’ instructions with
    respect to water/power ratio and mixing time. Dies
    were recovered from the impressions, and 2 layers of die
    spacer (Cement Spacer; Kerr Dental, Orange, Calif)
    were painted 0.5 mm short of the finish lines of the
    preparations.
    Ceramic veneer fabrication
    The veneers were waxed (Yeti Dental produkte;
    GmbH, Engen, Germany), sprued, and then pressed
    after investment. All procedures were performed with
    IPS Empress 2 materials (Ivoclar, Schaan, Liechtenstein),
    following the manufacturer’s recommendations.
    After divestment, the ceramic veneers were finished with
    diamond burs (863-204-016; Gebr. Brasseler) and
    glazed.
    Surface treatment
    The 40 prepared teeth were randomly assigned to 4
    groups of 10 specimens (n 10). Each of 3 groups was
    subjected to a different etching technique (Table I). Ten
    specimens received no surface treatment and served as
    the control group.
    Laser treatment
    An Er,Cr:YSGG hydrokinetic dental laser (Millennium;
    Biolase Technology, Inc., San Clemente, Calif) was
    used for laser etching. This hard- and soft-tissue laser
    creates laser-energized, atomized water droplets that act
    as cutting particles. Laser energy is delivered through a
    fiberoptic system to a sapphire tip terminal 6 mm long
    and 600 m in diameter, bathed in an adjustable air and
    water vapor. It operates at a wavelength of 2.78 m;
    pulse duration of 140 microseconds with a repetition
    rate of 20 Hz. Average power output can be varied from
    0 to 6W, depending on the tissue to be cut. The energy
    and power densities were (5.6 J/cm2) and (111 W/cm2
    at 2W), respectively, and were calculated by the manufacturer
    of the laser unit for the used power adjustment.
    The air and water spray of the hand-piece was adjusted
    to the “30” scale of the laser unit. The beam was aligned
    perpendicular to the enamel at 1 mm distance and was
    moved in a sweeping fashion by hand during an exposure
    period of 15 seconds over the entire area. The irradiated
    specimen was dried with an oil-free air source for
    15 seconds.
    Bonding ceramic veneers
    The ceramic veneers were treated with fluoridic acid
    (Ceramic Etchant; Ceramco, Burlington, NJ) for 1
    minute and neutralized (Ceramic Etchant Neutralizer;
    Ceramco) in accordance with the manufacturer’s instructions.
    Silane (Monobond S; Ivoclar) was first applied
    with a brush to the ceramic veneers for 60 seconds,
    and then a bonding agent (Heliobond; Ivoclar) was applied.
    After the teeth were etched, primer (Syntac Primer;
    Ivoclar) was applied to the tooth surface for 15 seconds,
    adhesive (Syntac Adhesive; Ivoclar) for 10
    seconds, and then a bonding agent (Heliobond; Ivoclar)
    with a brush.
    Cement (Variolink II; Vivadent, Ivoclar), comprising
    a combination of 25% Variolink yellow base, 25% Variolink
    white base, and 50% catalyst was hand-mixed following
    the manufacturer’s directions, and applied to
    both prepared teeth and the ceramic veneers. The ceramic
    veneers were placed on the prepared teeth with
    light finger pressure,27 and excess cement was removed
    with an explorer. Photo polymerization was performed
    with the light-polymerizing unit (Hilux 350; Express
    Dental Products, Toronto, Canada) at 350 mW/cm2
    (with a light tip to specimen distance of 0 mm) for 40
    seconds for incisal, mesial, and distal surfaces.
    Specimen preparation
    After cementation, specimens were stored in distilled
    water for 24 hours. Acrylic resin blocks were mounted in
    a slow-speed diamond saw sectioning machine (Isomet)
    with a diamond-rim blade.
    Two saw cuts were made parallel to the long axis of
    the tooth, and subsequently 4 saw cuts were made perpendicular
    to the long axis. This produced 2 I-shaped
    Table I. Materials used for surface conditioning
    Material Used
    Time of
    etching Brand Manufacturer
    37% orthophosphoric acid 15 s Bisco Bisco Inc, Schaumburg, Ill
    10% maleic acid 15 s Scotchbond Multi-Purpose 3M, St. Paul, Minn
    Er;Cr;YSGG hydrokinetic laser system 15 s Millennium Biolase Tech Inc, San Clemente, Calif
    THE JOURNAL OF PROSTHETIC DENTISTRY USUMEZ AND AYKENT
    26 VOLUME 90 NUMBER 1
    specimens, 1 from the incisal portion, and the other
    from the cervical (Fig. 2, A). The porcelain bonded to
    the facial enamel surface was divided into an array of
    1.2 1.2 5-mm beams (Fig. 2, B), with the top half
    consisting of porcelain and the bonding agent, and the
    bottom half consisting of enamel and dentin.28 Each
    specimen was tested individually.29
    Cyanoacrylate adhesive (Zapit; Dental Ventures of
    America, Corona, Calif) was used to attach the microtensile
    specimens to opposing arms of the microtensile
    testing device (Harvard Apparatus Co. Inc., Dover,
    Mass). The mounting adhesive was applied sparingly to
    the edges of each specimen. The specimen was fractured
    under tension at a crosshead speed of 1 mm/min, and
    the maximum load at fracture (Kg) was recorded. Preparation
    of all specimens and completion of the testing
    were done by the same operator.
    Fracture analysis
    After the specimen was tested and removed from the
    testing apparatus, the fracture sites were observed with a
    stereomicroscope (SZTP; Olympus, Tokyo, Japan) at
    original magnification 22 to identify the mode of failure.
    The fractured surface was classified according to 1
    of 3 types: (1) adhesive failure between the bonding
    resin and the enamel/dentin; (2) cohesive failure in the
    bonding resin; and (3) cohesive failure in the enamel/
    dentin.
    Statistical analysis
    The ultimate stress (MPa) of the porcelain-enamel/
    dentin bonds were calculated as follows:30
    Stress
    Failure Load (Kg)
    Surface area (mm2) 9.8
    The results of testing were entered into a spreadsheet
    (Excel; Microsoft, Seattle, Wash) for calculation of descriptive
    statistics. The obtained data were analyzed by
    2-way analysis of variance and then Tukey HSD tests
    (SPSS/PC, Vers.10.0; SPSS, Chicago, Ill) for pairwise
    comparisons among groups (.05).
    RESULTS
    Microtensile bond strengths
    The 2-way analysis of variance test indicated that tensile
    bond strength was significantly affected by position
    (cervical or incisal) (P.001) and treatment (acid or
    laser) (P.001), and there was no significant interaction
    between the 2 factors (P.05). Because there was no
    significant interaction, all data in each group were
    pooled. When the cervical and incisal data were pooled
    to investigate the effect of a particular surface treatment
    on bond strength, no statistically significant differences
    were found between the bond strength values of veneers
    bonded to 37% orthophosphoric acid (group B) and
    Er,Cr:YSGG laser-etched tooth surfaces (group A).
    Again, no statistically significant differences were found
    between the bond strengths of veneers bonded to 37%
    orthophosphoric (group B) and 10% maleic acid (group
    C) etched tooth surfaces. Statistically significant differences
    were found between the laser etched surfaces
    (group A) and the control (group D) (P.05). There
    were statistically significant differences between the orthophosphoric
    acid etched surfaces (group B) and the
    control (group D) (P.01). Additionally, no statistically
    significant differences were observed between laser
    etched and maleic acid etched tooth surfaces (Table II).
    Mean bond strength values for different treatment
    groups were calculated together with standard deviations
    (Fig. 3). The mean bond strength of group B was
    higher than the laser-treated group (group A) in the
    incisal sections, but in the cervical sections group A was
    higher. The control group (group D) demonstrated the
    lowest bond strength values in all test groups (Table
    III).
    Fig. 2. A, Sections on tooth for specimen preparation (shaded
    area represents section prepared from tooth specimen).
    B, Schematic demonstration of specimen.
    Table II. Microtensile bond strengths (MPa) statistical
    comparison
    Groups X SD
    Tukey
    grouping*
    Group A (Laser) 12.1 4.4 A
    Group B
    (Orthophosphoric acid)
    13.0 6.5 A
    Group C (Maleic acid) 10.6 5.6 A
    Group D (Control) 7.7 3.1 B
    X, Mean; SD, standard deviation.
    *Groups with different letters were statistically significantly different.
    USUMEZ AND AYKENT THE JOURNAL OF PROSTHETIC DENTISTRY
    JULY 2003 27
    Fracture patterns
    In the laser-treated group (group A), most failures
    (17 of 20) were adhesive in nature at the bonding resin/
    enamel interface, and 2 specimens showed cohesive failure
    in the bonding resin. Only 1 specimen showed cohesive
    failure within the enamel. In the group etched
    with orthophosphoric acid (group B), most failures (19
    of 20) were adhesive in nature at the bonding resin/
    enamel interface. One specimen showed cohesive failure
    within the enamel. The specimens in the group etched
    with maleic acid (group C) and in the control group
    (group D) showed adhesive fracture at the resin/enamel
    interface.
    Scanning electron microscopy
    SEM photographs of 37% orthophosphoric acid, 10%
    maleic acid, and Er,Cr:YSGG hydrokinetic laser-treated
    enamel are shown in Figure 4. The enamel surface
    etched with 2 acid solutions and a laser system showed
    different results according to Silverstone’s10 etching
    patterns. The 37% orthophosphoric acid removed the
    periphery core material but left the prism core relatively
    unaffected (type II), producing a very rough enamel
    surface. The 10% maleic acid treatment resulted in preferential
    removal of prism core material and left the periphery
    intact (type I). Er,Cr:YSGG hydrokinetic lasertreated
    enamel showed a more random etching pattern
    in which adjacent areas of tooth surface correspond to
    types I and II, mixed with regions where the pattern
    could not be related to prism structure. There was no
    recrystallization or melting observed.
    DISCUSSION
    The results obtained support the research hypothesis
    of an expected similar adhesive force after laser treatment.
    This result is in accordance with the study of
    Usumez et al26 in which they compared these methods
    for bonding orthodontic brackets to enamel surfaces.
    On the other hand, the results of this study disagree with
    the results from other studies.14,23-25 These differences
    may be related to the different type of laser used, duration
    of exposure, and energy applied to the surface.
    Laser etching may have some advantages, but 1major
    limitation of lasers for dental application includes cost of
    laser units. They are still too expensive to be cost effective.
    This study also compared the microtensile bond
    strengths of specimens in the 10% maleic acid and 37%
    orthophosphoric acid etched groups. The results have
    indicated that there were no significant differences in
    microtensile bond strengths between the 2 groups. The
    results of this study are in agreement with the works of
    Goes et al11 and Hermsen and Vrijhoef.12
    For microtensile testing, the tensile bond strength is
    dependent on the area of the bonded surface.28 In this
    study, failures occurred mostly at the bonding resin/
    enamel interface and did not involve the enamel or ceramic
    except for the 2 specimens which showed cohesive
    Fig. 3. Mean microtensile bond strength values of test groups; groups with different letters are statistically significantly different.
    Table III. Microtensile bond strengths of cervical and
    incisal specimens (MPa)
    X SD
    Group A (laser) Cervical 10.6 4.1
    Incisal 13.5 4.2
    Group B
    (orthophosphoric) Cervical 8.3 3.7
    Incisal 17.7 5.2
    Group C (maleic) Cervical 7.6 3.3
    Incisal 13.5 6.0
    Group D (control) Cervical 5.7 2.5
    Incisal 9.7 2.5
    X, Mean; SD, standard deviation.
    THE JOURNAL OF PROSTHETIC DENTISTRY USUMEZ AND AYKENT
    28 VOLUME 90 NUMBER 1
    failure within the enamel. Microtensile testing should
    more closely approximate clinical applications.28 However,
    microcracks and other defects can possibly occur
    during the production of specimens with a slow-speed
    diamond saw sectioning machine, which may cause premature
    failure of the bond. Therefore the specimens
    must be prepared carefully.29
    Laser-treated enamel demonstrated strong bonding
    to the porcelain laminate veneers. The highest microtensile
    bond strength was achieved with 37% orthophosphoric
    acid for the incisal sections while the highest
    mean bond strength was achieved with laser treatment
    for the cervical sections. It is believed that these differences
    are due to exposure of the dentin layer in the
    cervical portions of specimen because of decreased
    thickness of enamel in this region. Visuri et al15 suggested
    that the greater presence of peritubular dentin,
    which has a greater mineral content than intertubular
    dentin, may result in better bonding to the dentin. In
    their study they obtained higher shear bond strength of
    composite when it was bonded to Er:YAG laser-prepared
    dentin compared with acid-etched dentin. Another
    difference between acid etchant and laser actions
    related to dentin is their effect on the structure of dentin
    tubules. When an acid etchant is applied, the peritubular
    dentin is preferentially etched, resulting in funnelshaped
    openings to the tubules. This structure may contribute
    with polymerization shrinkage to pull the tags
    away from the walls. Laser irradiation produces no demineralization
    of peritubular dentin and the dentinal tubules
    remain open with no widening.21 This effect may
    have contributed to microtensile bond strengths of cervical
    sections where dentinal exposures were present.
    Sources for the large deviations found in this study include
    variations in enamel structure, storage effects, age,
    condition of individual teeth, variations in enamel
    depth, and nonhomogenous laser treatment of surfaces.
    CONCLUSIONS
    Within the limitations of this study, 37% orthophosphoric
    acid (13.0 MPa)– and 10% maleic acid (10.6
    MPa)–treated enamel surfaces showed statistically similar
    bond strength values. Porcelain laminate veneers
    demonstrated the highest bond strengths to 37% orthophosphoric
    acid-etched (13.0 MPa) and
    Er,Cr:YSGG hydrokinetic laser system-conditioned
    tooth surfaces (12.1 MPa). The differences were not
    statistically different.
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    enamel. (Original magnification 1750.)
    USUMEZ AND AYKENT THE JOURNAL OF PROSTHETIC DENTISTRY
    JULY 2003 29
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    Reprint requests to:
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    #9599 Reply

    2thlaser
    Spectator

    Nice Ron,
    Here’s the latest from UCLA….

    Presented at the I3180 Bond Strength of Ceramic to Er,Cr:YSGG Laser Prepared Teeth
    E.M. CHUNG1, E. SUNG1, A.A. CAPUTO1, M. COLONNA2, and I. RIZOIU2, 1 UCLA School of Dentistry, Los Angeles, CA, USA, 2 Biolase Technology Inc, San Clemente, CA, USA
    Objectives: A previous study has shown that composite resin bond strength to primary dentin prepared with an Er,Cr:YSGG laser was comparable or higher than to carbide bur prepared dentin. The purpose of this study was to compare the shear bond strength of bonded ceramic restorations to Er,Cr:YSGG laser prepared and conventionally prepared teeth. Methods: Ten surfaces were prepared into dentin of extracted human molars using each of the following: a) Er,Cr:YSGG hydrokinetic laser (Biolase Technology Inc), b) medium coarse parallel diamond bur (Brassler) with a high speed handpiece (Midwest). Ceramic discs (IPS Empress, Ivoiclar), 4.2 mm in diameter and 2 mm thick, were cemented onto the dentinal surfaces with composite resin cement (RelyX Unicem Aplicap, 3M EPSE). Shear bond strength tests were performed using an Instron test machine. After testing, the failure surfaces of the teeth were examined under 20X magnification. The bond strength data were examined statistically using ANOVA and t-test. Results: The mean values of the shear bond strength of the laser prepared surfaces were 8.23 ± 1.92 MPa and 4.88 ± 1.02 MPa for the conventional bur prepared surfaces. Statistical analysis revealed significant differences between the two groups (p.<0.05). Failure locations varied between the dentin-cement interface and ceramic interface. No predominant location patterns were observed between the laser and bur prepared teeth Conclusions: Higher bond strengths were seen with the laser prepared teeth. These higher values may be due to micromechanical retention or increased surface energy. There was more variability with the laser prepared teeth, indicating the need for a finishing surface treatment with the laser.

    Seq #339 – Cements: Dentin and Ceramic Bonding
    10:15 AM-11:30 AM, Saturday, 13 March 2004 Hawaii Convention Center Exhibit Hall 1-2
    ADR meeting in Hawaii in March…

    We will continue to do more studies as time permits, and Eric and I discuss this study a bit more.

    Mark

    #9597 Reply

    Anonymous
    Guest
    QUOTE
    Quote: from 2thlaser on 1:04 pm on May 6, 2004
    Conclusions: Higher bond strengths were seen with the laser prepared teeth. These higher values may be due to micromechanical retention or increased surface energy. There was more variability with the laser prepared teeth, indicating the need for a finishing surface treatment with the laser.

    Mark

    Mark, the finishing surface treatment refers to a very defocused laser application to remove the byproducts of abaltion (like Graeme recommends), correct?

    As I don’t use Relyx, were the teeth etched?

    Thanks for keeping us up to date with the post,

    #9604 Reply

    Glenn van As
    Spectator

    What settings were used……….what wattage.

    What tip.

    What water concentration.

    What air concentration.

    What was the length of time used for the laser.

    How defocussed.

    Was the enamel scraped afterwards.

    Just other questions I had. The information out there on bonding with lasers is fraught with all kinds of mistakes. There are some studies showing way lower bond strength (particularly class V restorations) and others showing equal bond strength.

    Rare has it been shown to have higher bond strength.

    Neat stuff though , but be very careful suggesting that the laser will increase bond strength as there are many many variables to the equation including what I asked about above.

    Glenn

    #9600 Reply

    2thlaser
    Spectator
    QUOTE
    Quote: from Glenn van As on 6:46 am on May 7, 2004
    What settings were used……….what wattage.

    What tip.

    What water concentration.

    What air concentration.

    What was the length of time used for the laser.

    How defocussed.

    Was the enamel scraped afterwards.

    Just other questions I had.  The information out there on bonding with lasers is fraught with all kinds of mistakes.  There are some studies showing way lower bond strength (particularly class V restorations) and others showing equal bond strength.

    Rare has it been shown to have higher bond strength.

    Neat stuff though , but be very careful suggesting that the laser will increase bond strength as there are many many variables to the equation including what I asked about above.

    Glenn

    Glenn,
    I can appreciate where you are coming from however, until you understand how a crown is prepared with the laser, it’s hard to describe. No contact is made on the tooth. The power settings were my normal settings of 5.5W, 60/30 air/water, and a G-4 tip. The time it took was about 4-6 minutes per tooth to preapare with the laser, mostly in a defocussed mode approximately 3mm from the tooth. When I prepare a tooth for a crown, it’s NOT perpendicular to the tooth, rather more parallel to the surface I am preparing. I prepared all the specimens myself, both with the laser and the high speed specimens. All UCLA, and Eric did was to test the shear strength, and the conclusions you have read. There may be many variables as you stated, but I think you ought to be careful in suggesting that the data might suggest otherwise. This was a VERY controlled study, mainly due to my inquisitive nature on how strong a surface I am creating with the laser for cementation vs. a drilled prepared surface. Now, not being a scientist, but a inquisitive dentist, I tried to take the variables out as much as I could. Oh, and to answer your last question, the surface was not “scraped”. Just a pure lasered surface for cementation, and then shear strength testing. Hope that helps you. I appreciate your questions….!

    Mark

    #9598 Reply

    jetsfan
    Spectator

    Mark .

    For all of those old amalgams we remove with burs and finish off with the laser, perhaps you can quantify the benefit of actually using the laser, i.e, is the shear bond strength greater on a tooth that is just finished off with the laser in a defocused mode, than the tooth bonded without the laser treatment.

    Robert

    #9594 Reply

    Anonymous
    Guest

    Mark, I think what Glenn and I were trying to get at with the questions is that if more details were available then your study could be compared ‘apples to apples’ with some of the other studies. Hopefully it could be discovered what was or wasn’t done in some of the other studies that showed less than stellar results.

    I take it no scraping because you felt all the byproducts of ablation were removed by using the defocused mode, correct?

    #9601 Reply

    2thlaser
    Spectator

    Correct.

    #9605 Reply

    Glenn van As
    Spectator

    Hey Mark…….dont get me wrong. I admire your tenacity for the crown prep and also for doing these studies.

    Kudos to you.

    I am just being the devils advocate and telling you that even in Hibst review of hard tissue lasers he mentions that there are some diagramatically opposed viewpoints on the lasers effect on bond strength. I can give you quotes from my soon to be finished chapter (finally) but suffice it to say that if you look in the research , some of the bonding studies show lasers to be pretty abysmal with respect to bond strength.

    I have seen some fascinating stuff on bone where there is an “ablation “layer in the SEM when using the laser in bone.

    THis leaves a layer which even 18 months after the intial cuts in Rats (Aoki is the author) there still was the ablation layer visible in the histology on rats.

    What does this have to do with bonding?

    Well I sincerely believe that in many of the studies that a “ablation layer” was left behind particularly if there was no etch or Milicich scraping of the enamel after the laser was used.

    You know how I feel about the cutting effects of the Er,Cr:YSGG vs the Er:YAG and the similarities.

    I am proud of you for doing the research and am glad to see an article showing higher bond strengths.

    All I was saying is to be careful when you evaluate the other studies that have been done on hard tissue lasers and bonding or microleakage (Class V) as there are alot of studies showing worse bond strengths or greater leakage with the laser…….

    What did they do differently?

    Interesting debate isnt it?

    I still believe that with the proper technique, settings (not to high), scraping the enamel, and also etching that our bond strengths will be higher……..

    I willl post one case before I turn in for the night…….

    check out what the scope showed.

    Grin

    Glenn

    PS I have the utmost respect for what you are doing, I am on your side full bore…….I think you have done more for my education in lasers than anyone perhaps except for Bob Gregg.

    Just keep that in mind……….ok!!

    Grin

    Glenn

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