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February 2011
Research
Article 3D-FEA of stress levels and distributions for
different bases under a Class I composite restoration Yan Wang, Zhengyu Liao, Dan Liu,
md, Zhan Liu, phd,
Grant T. McIntyre, phd, Fan Jian,Wei Lv, Abstract: Purpose: To investigate the level and distribution of stresses in
composite-restored mandibular first molars with various
combinations of base materials. Methods:
The finite element package Abaqus was used for the
stress analysis. Several different base materials were evaluated [light-cured
glass ionomer (LC-GI), chemically-cured calcium
hydroxide (CC-CH), and light-cured calcium hydroxide (LC-CH)] in combination
with light-cured composite (LC-CP). Four models of restored molars with Class I
deep cavity preparations were simulated, including (1) LC-GI/LC-CP, (2)
CC-CH/LC-CP, (3) CC-CH/LC-GI/LC-CP, and (4) LC-CH/LC-GI/LC-CP. A 250N static
single-point load was applied vertically on the central fossa
of the tooth to simulate physical loading conditions. Results: In each case, the peak stresses were found to be
concentrated mainly at the interfaces between the various materials and the
dental tissues. In the residual tooth structures, the maximum Von Mises stresses were 20.01 MPa in
model LC-GI/LC-CP, 23.85 MPa in model CC-CH/LC-CP, 23
MPa in model CC-CH/LC-GI/LC-CP and 21.83 MPa in model LC-CH/LC-GI/LC-CP. In the LC-CP restorations,
the maximum Von Mises stresses were 43.68 MPa in model LC-GI/LC-CP, 42.24 MPa
in model CC-CH/LC-CP, 42.29 MPa in model
CC-CH/LC-GI/LC-CP and 42.55 MPa in model
LC-CH/LC-GI/LC-CP. In the bases, the maximum Von Mises
stresses were 5.71 MPa in model LC-GI/LC-CP, 0.85 MPa in model CC-CH/LC-CP, 4.69 MPa
in model CC-CH/LC-GI/LC-CP, and 4.93 MPa in model
LC-CH/LC-GI/LC-CP. (Am J Dent
2011;24:3-7). Clinical significance: This study supports the
conclusions that (1) peak stresses in restored molars were mainly concentrated
at the interfaces between the various materials and the dental tissues; (2) no
clinically important differences were found in the stress levels and
distributions within composite restored molars based with different
combinations of glass-ionomer or calcium hydroxide. Address: Dr. Wenli
Lai, State Key Laboratory of Oral Diseases, Department of Orthodontics, West
China College of Stomatology, Sichuan University,
Chengdu 610041, China. wenlilai@hotmail.com Dr. Zhihe
Zhao, State Key Laboratory of Oral Diseases, Department of Orthodontics, West
China College of Stomatology, Sichuan University,
Chengdu 610041, China. Email: hx_zhaozhihe@yahoo.com.cn Research Article Degree of conversion of
dual-cure resins light-cured through glass-fiber posts Francesca Cerutti, dmd, Pier Antonio Acquaviva,
dmd, Massimo Gagliani, md, dds, Marco Ferrari, md,
dds, Abstract: Purpose: To evaluate the degree of
conversion (DC) of dual-curing materials used to lute glass-fiber posts in a
simulated root canal polymerized by two different modalities. Methods: Artificial root canals were
used to simulate a clinical condition to lute 45 posts by three different dual
curing luting cements (Calibra,
Multilink Automix and Variolink
II). Two light cure modalities were chosen for each luting cement: standard (S group) 400 mW/cm2 for 120 seconds and high-power (H group)
1200 mW/cm2 for 40 seconds. Raman spectra
were collected at different positions in the post surface (1, 3, 5 and 7 mm
from the coronal-most portion of the post covered in cement) and the percentage
degree of conversion was computed. The data were analyzed using ANOVA and
post-hoc Student-Neuman-Keuls
t-test (P= 0.05). Results: The DC of the tested luting composites decreased progressively while increasing
the distance from the light tip. Regardless of the polymerization modality (H
or S) applied. Conversely, the curing modality significantly influenced the DC
of the tested materials, evidencing different responses to the same energy
density: Calibra seemed to be less dependent on
light-curing than the other tested materials, showing a constant behavior.
Multilink Automix reached the highest DCs in the S
group compared to the H mode. Variolink II showed an
interesting drawback in DC at 7 mm when cured in the H model. Dual-cure
materials show adequate monomer conversion but when the distance from the
curing light increased, a variable, but significant lowering in conversion rate
was observed. In addition, the time and power of curing appeared to be
material-dependent and should be calibrated individually. (Am J Dent 2011;24:8-12). Clinical significance: To obtain the best performances
with dual curing luting materials, a careful choice
of the polymerization modality should be taken into account and it could be
provided by manufacturers. Address: Dr. Francesca Cerutti, Department of Materials for Engineering,
University of Brescia, Italy. Email: fc@francescacerutti.it
Morphology and microtensile
bond strength of adhesive systems
FlÁvia Lucisano
Botelho Amaral, dds, ms, Flávia
MartÃo FlÓrio, dds, ms scd,
Abstract:
Purpose: To
evaluate the microtensile bond strength of adhesive
systems to caries-affected dentin formed in
situ after the use of a papain-based chemomechanical removal method. Methods: 84 human dentin specimens (5 x 5 x 3 mm) were sterilized
and randomly distributed on palatal devices of 14 volunteers. Each palatal
device, containing six dentin slabs, was used for 14 days according to a caries
induction design involving plaque accumulation and sucrose use. After this,
fragments were removed from devices and randomly assigned to two groups
according to the caries removal method: (1) Chemomechanical
(papain-based gel followed by curette), or (2)
Mechanical (curette - control group). Specimens were subdivided into three
subgroups according to the adhesive system tested: (SB) a two-step
etch-and-rinse (Adper Single Bond 2); (SE) a two-step
self-etching adhesive (Clearfil SE Bond) and (TriS) a one-step self-etching adhesive (Clearfil
Tri-S Bond) and subsequently restored with microhybrid
composite resin. After 24 hours, resin-tooth blocks were sectioned into 0.9 mm
thick slabs, with one slab of each block being prepared for adhesive interface
analysis by scanning electron microscopy, and the remaining blocks were
sectioned into 0.8-mm2 sticks that were subjected to tensile stress
(0.5 mm/minute). Data were subjected to two-way ANOVA and Tukey’s
test at a 5% level of significance. Results:
The application of the chemomechanical and mechanical
methods to demineralized dentin did not affect the
bond strength values. SB and SE adhesives promoted statistically similar and
significantly higher bond strength values than the TriS.
SEM analysis showed no interference of papain-based
gel in the formation of hybrid layer; SB showed the thickest hybrid layer with
presence of numerous tags; SE showed an intermediate hybrid layer thickness and
quantity of tags and the TriS showed no evidence of
tag formation. (Am J Dent 2011;24:13-19).
Clinical
significance:
The papain-based chemomechanical
method did not affect the bond to caries-affected dentin, but the use of a
one-step self-etching adhesive system should be avoided.
Address:
Prof. Dr. Roberta Tarkany Basting, Faculty of
Dentistry and Center for Dental Research São Leopoldo
Mandic, Department of Restorative Dentistry -
Operative, Rua José Rocha Junqueira,
13, Bairro Swift, Campinas – SP CEP: 13045-755,
Brazil. Email: rbasting@yahoo.com
Research Article Rhoda J. Sword, dmd,
Jeremy
J. Sword, William W. Brackett, dds, msd, Franklin R. Tay,
bdsc, phd, Abstract: Purpose: To adapt a simple gravimetric method to measuring the
permeability of adhesive resin films to liquid water, and to compare this to
the water vapor permeability of the same resins. Methods: Using commercially-available permeability cups designed
for industrial permeability testing, the loss of mass of water vapor or liquid
water from a stainless steel cup sealed with a resin film was measured over 1-2
days. The permeabilities of Parafilm
(control), Clearfil SE Bond adhesive, Xeno IV and One-Up Bond F were compared. Results: The lowest resin film
permeability was obtained with Clearfil SE Bond
adhesive films. The permeabilities
of Xeno IV and One-Up Bond F to liquid water were
2.76 and 3.27-fold higher (P< 0.001) than that of Clearfil
SE Bond adhesive. Liquid water
permeability was always 2.8-3.8-fold higher (P< 0.05) than water vapor
transmission rate. It was concluded that quantitative comparisons of the
permeability properties of resin films can be made gravimetrically. The large
permeability cups that are available commercially may be reduced in size in the
future for measuring dentin adhesive films with smaller surface areas that are
less liable to contain imperfections. (Am
J Dent 2011;24:20-26). Clinical significance: The permeability to liquid water
of adhesive resin films shows promise as a means of screening for adhesives too
permeable to form durable dentin bonds. Address: Dr. William W. Brackett,
Department of Oral Rehabilitation, School of Dentistry, Medical College of
Georgia, Augusta, Georgia 30912-1260, USA.
Email: wbrackett@mail.mcg.edu Research
Article Comparison between water and ethanol wet bonding of
resin composite Salvatore Sauro, phd, Simona Di Renzo, dds, Raffaella Castagnola, dds, Nicola M. Grande, dds,
phd, Abstract: Purpose: To evaluate the bond strength of resin dentin interfaces created
with adhesives applied on root dentin using the water wet or ethanol wet
bonding technique. The morphology of resin dentin interfaces was evaluated
using confocal microscopy. Methods: Four experimental resin adhesives (R#A to R#D) and one
commercial three-step/etch and rinse adhesive were applied to the root canal
dentin of endodontically treated single canal
incisors using the water (control) or ethanol wet bonding technique. The
ethanol wet bonding substrate was achieved by keeping the root canal immersed
in absolute ethanol (100%) for 3 minutes. The root dentin bonded specimens were
sectioned into beams, stored in distilled water (24 hours) and finally tested for
microtensile bond strengths (µTBS). Additional dentin
surfaces were conditioned and bonded as previously described. They were
prepared for the microscopy study and finally observed using confocal microscopy. Results:
The ethanol wet bonding technique gave higher bond strength values for all the
adhesives tested: in Group 1 (water wet bonding technique) no significant
difference was found between the resins tested; the only exception being the
most hydrophilic Resin #4 showing the highest bond strength values (P<
0.05). In Group 2 (ethanol wet bonding technique) no statistical differences
were present between Resin #A and Resin #D. Resin #C showed the highest bond
strength values. Confocal microscopy showed better
resin diffusion and hybrid layer formation when the ethanol wet bonding was
used. (Am J Dent 2011;24:25-30). Clinical significance: The use of
the ethanol wet bonding technique resulted in higher bond strength values with
all the adhesives tested. This technique also offers the possibility to bond
using resin adhesives containing no hydrophilic and/or acidic monomers to root
dentin. Address: Dr. Salvatore Sauro, Biomaterials, Biomimetics
& Biophotonics, King’s College London Dental
Institute at Guy’s, King’s College and St. Thomas’ Hospitals, Floor 17, Guy’s
Hospital, London, UK. Email: salvatore.sauro@kcl.ac.uk Research
Article
Influence of salivary enzymes and alkaline pH
environment
Hesam Mirmohammadi, dds, phd, Cornelis
J. Kleverlaan, phd, Moustafa N. Aboushelib, dds, msc, phd
Abstract: Purpose: To evaluate the effect of enzymatic activity and
alkaline medium on flexural strength and rotary fatigue resistance of direct
and indirect resin composite restorative materials. Methods: Three direct resin composite materials Filtek
Z100, Filtek Z250 and Filtek
Silorane (3M ESPE), and two indirect resin composite
materials; Sinfony (3M ESPE) and an experimental
composite (Heraeus Kulzer)
were used to fabricate bar-shaped specimens (2 x 2 x 25 mm; n = 10) to
determine the flexural strength (Fs) by means of a 3-point bending test
according to ISO 4049. Additional specimens of the same dimensions (n = 20)
were used to prepare hour-glass shaped specimens which were immersed in
distilled water for 48 hours, transferred to one of five aqueous media at 37°C
for 2 weeks; phosphate buffer, distilled water, 0.1N NaOH,
1 unit/ml Amylase, 0.1 unit/ml Esterase, and a group in 0.1N NaOH at 60°C. Rotary fatigue resistance (RFR) was
determined in a rotating-bending cantilever test with the highest stress
located at the constriction of the hour glass. The rotary fatigue resistance
tests were conducted according to the staircase approach (104
cycles, 1.0 Hz) and the mean RFR was calculated using logistic regression
analysis. Results: NaOH produced a significant decrease in Fs of all
materials. The effect of enzymatic biodegradation on Fs of Filtek
Z100 and Filtek Z250 was found to be significant,
however, for Silorane and indirect composites it was
not significant. Except for NaOH the influence of the
different aqueous solutions on RFR was not significant for all tested
materials. For all materials the RFR was about 22-53% lower than the corresponding
Fs. (Am J Dent 2011;24:31-36).
Clinical significance: Beside the deteriorating effect
of fatigue, the mechanical properties of resin composites are also affected by
the chemical and biological degradation in the oral environment.
Address: Prof. Dr. A.J. Feilzer, ACTA, Department of Dental Materials Science, Louwesweg 1, 1066 EA Amsterdam, The
Netherlands. Email: a.feilzer@acta.nl
Research
Article
Shortest exposure time possible with LED
curing lights
Inga
Busemann, dr med dent, Claudia
Lipke, Anke schattenberg, dr med dent,
Abstract: Purpose: To
investigate the shortest exposure time of different light emitting diode
(LED)-curing devices for different resin composites in a clinically relevant
laboratory model. Methods: Nine LED
curing devices (Bluephase, Bluephase
16i, Bluephase G2, Bluephase
20i/Ivoclar Vivadent, DEMI/sds Kerr, Elipar FreeLight 2, Elipar S10/3M ESPE,
Radii plus/SDI, mini LED Autofocus/Satelec) were
investigated to polymerize Tetric EvoCeram
(TEC) and Filtek Supreme XT B (FS) in the shades A1,
A2, A3, A3.5, and A4. The Bluephase 20i was
investigated in its high power and turbo modes. Stainless steel molds (Ø = 5
mm, h = 6 mm, six resin composite test samples per curing device, material, and
shade) were filled in three increments of 2 mm thickness each and incrementally
exposed with the light guide tip in a 7 mm distance from the bottom side to simulate
a Class II curing situation. Surface hardness was measured 10 minutes post
exposure at bottom surfaces of resin samples (n= 3 per sample). A
bottom/top-surface hardness ratio of 80% of a reference surface hardness cured
at a zero-distance (40 seconds) was defined as clinically acceptable for safe
curing. A statistical analysis (Excel) was carried out. Results: To ensure a ratio in surface hardness of at least 80% the
minimal exposure time(s) were: Elipar FreeLight 2, DEMI: TEC and FS: 10 seconds for all shades,
except DEMI FS A4: 20 seconds. Elipar S10: 10 seconds
for both, TEC and FS shades A2-A4 but 5 seconds for shades A1. Bluephase, Bluephase 16i and Bluephase G2: FS: 10 seconds for shades A1-A3.5; 20 seconds
for shade A4. TEC: Bluephase: A1-A3.5: 10 seconds,
A4: 20 seconds. Bluephase 16i: A1-A3: 10 seconds;
A3.5 + A4: 30 seconds. Bluephase G2: A1-A3: 10
seconds; A3.5 + A4: 20 seconds. Bluephase 20i-HIP: 10
seconds for all shades of TEC and FS, Bluephase
20i-Turbo: 10 seconds for all shades of TEC but 5 seconds for all shades of FS:
Radii plus: TEC A1-A3: 10 seconds; A3.5+A4: 20 seconds. FS A1, A2 and A4: 10
seconds; A3+A3.5: 20 seconds. Mini LED Autofocus: TEC A1, A3, A3.5: 10 seconds;
A2: 15 seconds; A4: 20 seconds. FS A1: 5 seconds; A2-A4: 10 seconds. In its
turbo mode with a 5-second exposure time, the Bluephase
20i was able to polymerize all shades of FS, but not of TEC. For the Elipar S10 and the Mini LED Autofocus this was also
possible for the A1 shade of FS; for Elipar S10
additionally for TEC. The higher power of the Bluephase
G2 and the S10 LED allowed the use of an enhanced light guide tip diameter
while the exposure time was not affected compared to their predecessors
equipped with an 7.5 or 8 mm light guide tip diameter
respectively. Nevertheless, 10 seconds should be the minimal exposure time
recommended for lighter shades under optimal circumstances. (Am J Dent 2011;24:37-44).
Clinical
significance: When
using darker shades clinicians should increase the exposure time to improve the
degree of conversion and the mechanical properties of the resin composite.
Additionally, an enhanced light guide tip with an adequate power density should
be preferred to avoid many overlapping polymerization cycles. A possible 5-second
polymerization as claimed by some manufacturers should be employed carefully.
Address:
Dr. Inga Busemann, Department for Operative
Dentistry, University Medical Center, Johannes Gutenberg University Mainz, Augustusplatz 2, 55131 Mainz, Germany. Email: Inga.Busemann@unimedizin-mainz.de
Research
Article
Relationship between caries and dental plaque
composition
Sule Bayrak, dds, phd,
Zeynep Ökte, dds, phd & Ulvi Reha Fidanci, dvm, phd
Abstract: Purpose: To evaluate the relationship between dental caries and
the biochemical composition of dental plaque and to determine the effect of a
10% sucrose solution on the biochemical structure of dental plaque in children.
Methods: 60 children grouped
according to caries status took part in this study [Caries-free (CF), DMFS= 0, df-s= 0; Caries-positive (CP), DMFS ≥ 10, df-s ≥ 10]. Dental plaque samples were collected
before (baseline) and at 3 and 30 minutes after a 1-minute rinse with 10%
sucrose. Fluoride (F), calcium (Ca), and inorganic phosphorus (Pi) levels were
determined using ion chromatography, and insoluble polysaccharide (IEPS)
concentrations were determined using colorimetric analysis. Results: Although the mean baseline Ca
and Pi levels in plaque were higher in the CF group than in the CP group, these
differences were not statistically significant. Baseline IEPS levels were
significantly higher in the CP group than in the CF group. Following exposure
to sucrose, plaque F, Ca and Pi concentrations decreased significantly in both
groups. However, insoluble polysaccharide concentrations increased significantly
in the CF group only. (Am J Dent 2011;24:45-48).
Clinical significance: Insoluble extracellular polysaccharide
concentration in dental plaque may be a marker of dental caries.
Address: Dr. Sule Bayrak, Department
of Pediatric Dentistry, Faculty of Dentistry, University of Ondokuz
Mayıs, 55139, Kurupelit,
Samsun, Turkey. Email: suleb76@yahoo.com
Research
Article
Effect of different concentrations of carbamide peroxide
SÉrgio A.M.
Ourique, dds, ms, Jovana P.S. Magdaleno,
dds, Cesar A.G. Arrais, dds, ms, phd
Abstract:
Purpose: To evaluate the effect of
10% and 16% carbamide peroxide bleaching agents on microhardness of dental ceramics after different periods of
bleaching treatment. Methods: 15
specimens with 5 x 3x 1 mm3 were created with four dental ceramics
following manufacturers' instructions: IPS Classic (Ivoclar-Vivadent);
IPS d.Sign (Ivoclar-Vivadent);
EX3 (Noritake); VMK-95 (Vita). A microhardness tester
with a Knoop diamond with a 100 g load was used to
evaluate the baseline microhardness values of all
ceramics. Afterwards, the specimens were submitted to 6-hour daily bleaching
treatments with 10% or 16% carbamide peroxide
(Whiteness Perfect - FGM) for 21 days, while control groups from each ceramic
system were maintained in artificial saliva. The microhardness
of all groups was evaluated at 18, 42, 84, and 126 hours of bleaching
treatment. The mean value of five indentations performed at each specimen in
each time was obtained and all data were submitted to two-way repeated measures
ANOVA and Tukey’s post-hoc test (α=0.05). Results: No significant differences in
ceramic microhardness were observed among either
bleaching intervals or bleaching treatments. Ceramic restorations are not
affected by carbamide peroxide 10% or 16% gel during
bleaching treatment. (Am J Dent 2011;24:57-59).
Clinical significance: This study provided evidence
that at-home bleaching systems do not cause detrimental effects on dental
ceramics.
Address: Cesar
Augusto Galvão Arrais, Praça Tereza Cristina, 229 – Centro, Guarulhos -SP, CEP: 07023-070,
Brazil. Email: carrais@prof.ung.br
Research Article
Removal of
dental plaque from different regions of the mouth
Kakarla V.V. Prasad,
Abstract:
Purpose: To
assess dental plaque on different regions of the dentition prior to and
immediately after toothbrushing. Methods:
Subjects refrained from oral hygiene for 22-26 hours prior to baseline whole
mouth plaque assessments by the Turesky modification
of the Quigley-Hein Index (TMQH). All subjects brushed with a marketed
soft-bristled toothbrush and a fluoride dentifrice for 1 minute prior to
post-brushing plaque assessments similar to baseline. One calibrated clinical
examiner conducted all measurements. Results: 30 subjects (mean age 23
years) completed the study. Irrespective of arch, posterior teeth harbored
higher frequencies for scores of 3-5 than corresponding anterior teeth prior to
brushing. In comparison to the pre-brushing examination, scores of 0-1 were
more common in the post-brushing evaluation, however, greater frequencies of higher
plaque were observed on posterior than on anterior regions. Irrespective of
gender, subject or arch, anterior teeth harbored lower mean amounts of plaque
than posterior teeth by ANOVA at both clinical examinations (P< 0.0001).
Additionally, irrespective of arch, lower mean scores for plaque were observed
on anterior teeth than from posterior teeth or the whole mouth at both
examinations (P< 0.001). Lingual and molar surfaces consistently harbored
large densities of plaque and represented areas with the least plaque removal
after toothbrushing. Mid-vestibular sites represented
the areas with the highest percent removal of plaque at 65% and harbored
significantly lower levels of plaque than proximal sites during all phases of
the study (P≤ 0.0059). (Am J Dent 2011;24:60-64).
Clinical significance: Anterior
teeth and mid-vestibular surfaces consistently harbored significantly lower
amounts of dental plaque in contrast to higher amounts on molar, lingual and
posterior regions. Significant differences between the dentition for plaque
deposits underscore reasons to evaluate teeth including those accumulating more
dental plaque during oral hygiene examinations.
Address: Dr. Prem K. Sreenivasan, Colgate-Palmolive Company,
Review
Article
Noncarious cervical lesions – A clinical concept based
Raluca Pecie, dr, Ivo Krejci, prof dr med dent, Franklin Garcia-Godoy, dds, ms & Tissiana Bortolotto, dr, phd
Abstract:
Purpose: Due to
an increased prevalence of non-carious cervical lesions (NCCL), a clinical
strategy for this lesion type should be considered. Previous reviews focused
mainly on etiology and prevalence. In Part 1 of this paper, an evidence-based
support for a preventive strategy of NCCL was elaborated. Methods: Literature over the last 10 years available in the MEDLINE
database was reviewed in order to find clinical evidence for a preventive
approach to NCCL. Recommendations were based primarily on systematic reviews,
clinical evaluations and a monograph. Results:
The etiology of NCCL is currently considered to be rather multifactorial,
as clinical investigations found multiple factors associated with this type of
lesions and due to the lack of evidence to support exclusively one or another
factor. Based on the hypothesis of multifactorial
origin, a preventive protocol has been established. No clinical research exists
with respect to the prevention of NCCL and long-term clinical evaluations of
the proposed preventive measures are needed. (Am J Dent 2011;24:49-56).
Clinical
significance: The
slow progression, the high capacity of self-defense by producing sclerotic
dentin, and the lack of evidence for tooth weakening in the absence of a
restoration are evidence-based findings supporting a “wait and see” philosophy.
Restoration could be postponed in the absence of esthetic demands, sensitivity
or threat to the integrity of the tooth. Restoration should not always be the
first treatment of choice, although there still remains to be established to
what extent prevention could replace restoration.
Address:
Dr. Raluca Pecie, Division
of Cariology and Endodontology,
University of Geneva, Rue Barthélemy-Menn 19, CH-1205
Geneva, Switzerland. Email: raluca.pecie@unige.ch
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