I. for this research, all teeth were scaled

I. Materials:

Two
materials were used in this study, RMGI (Vanish) Fig.(1) and CGI
(Fuji)

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Fig.(2), their composition, manufacturer and batch number
are listed in Table (1).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

*        
HEMA: 2-Hydroxyethyl methacrylate.

**    BIS-GMA: Biphenol A diglycidylmethacrylate.

 

 

 

II. Methods:

II. 1) Selection of teeth :

A total of 20 permanent recently extracted human upper and
lower molars (from patients range 20-40 years old) were selected for this
research, all teeth were scaled and polished with rubber cup after extraction.
Teeth were placed in phosphate buffered saline plus 0.02% thymol to control
bacterial growth until they are used.

 

II. 2) Specimen preparation:

The teeth were mounted on cylindrical
acrylic blocks (2 cm diameter and 4 cm height). An intact buccal view of a
lower molar is shown in Fig.(3-a), an isometric
saw was then used to remove proximal enamel to expose underlying  dentin so that the width of cervical enamel
and dimensions could be measured accurately from the proximal side by using a digital
caliber Fig.(4,5) in order to estimate the amount
of enamel to be removed buccally and lingually from the specimens. The removal
of buccal and lingual enamel was done in Fig.(3-b), while a buccal
view after the removal of enamel buccally is shown in Fig.(3-c).

 

                          

 

 

 

 

 

II.2.a)Removal of buccal and
lingual cervical enamel

Enamel was then removed buccally
and lingually following DEJ as seen from the proximally exposed surface and it
was taken as a guide for cutting in all samples which ranges between 1.5-2 mm.
Soflex discs* were
used to finish and smoothen the surface from the darker course particales disc
to the lighter fine particles disc respectively.

 

II.2.b)EDTA Application

EDTA gel** with concentration 17% (7.5 pH) was used Fig.(6), it was applied by a brush for three min. to the whole buccal and
lingual surfaces of all specimens in order to remove smear layer, then it was
washed away with water and the surface was dried with mini sponge. No air
syringe dryness was made to avoid desiccation.(47,48) 

 

II. 3) Distribution of specimens

The prepared 40 surfaces were
divided into two groups, 20 each according to the type of desensitizing agent
received, therefore 20 buccal surfaces and 20 lingual surfaces. The mesial half
of each surface received the desensitizing material while the other half was
left untreated as a control group knowing that EDTA was applied to both halves
the treated and untreated of each buccal and lingual surfaces. Each group was
subdivided into four subgroups (N=5), the first subgroup faced an abrasion
challenge while the second faced thermocycling, the third faced both abrasion
challenge and thermocycling and the last was left as a control group as shown
in Tables (2,3).

 

*        
Sof-lex discs: 3M ESPE , Grit size : coarse, fine, medium,
multiple grits, superfine.

**    EDTA gel. : Vista
dental product.

 

II.4) Application of desensitizing agent

Each desensitizing agent was
applied to exposed dentin surface according to manufacturer instructions.

 

II.4.a) Application of RMGI

a)     The liquid/paste materials are contained in the clicker dispensing
system manufactured by 3M ESPE. This dispensing system provides simultaneous
dispensing of each component for a consistent ratio. 

b)    After
the exposed dentin surfaces of  half the
buccal surfaces were cleaned polished treated with EDTA it was rinsed with
water then dried with mini sponge.

c)     After
one click on the material applicator clicker, a pre-determined ratio of a paste
and a liquid was put onto a mixing pad, a single click from the clicker would  apply simultinious components that would be
enough to cover one to six teeth surfaces. The mix was done by a clean spatula
for 15 sec. according to the manufacturer instruction (2.5 min. working time).

d)    A very
thin layer was applied to the tooth (1-2 mm or less) using a microbrush, the
coating was then light cured* Fig.(7) at zero
distance for 20 sec.

 

 

 

 

 

 

 

 

 

 

 

*        
Light cure: 3M ESPE , Elipar freelight 2 curing unit.

II.4.b)  Application of CGI

a)    
After the exposed dentin
surfaces of half the lingual surfaces were cleaned, polished and treated with
EDTA, it was rinse thoroughly with water then dried with mini sponge.

b)   
Powder-liquid dispensing: the
standard powder to liquid ratio is 1.8 gm/ 1.0 gm (one level scoop of powder : one
drop of liquid).

c)    
Mixing : the required amount of
powder and liquid were dispensed onto a pad, by using a plastic spatula the
powder was divided into two equal parts, the liquid was spreaded into the pad
and the first portion was mixed with all the liquid for 10 sec., then the
remaining portion was incorporated and the whole amount was mixed for 10-15 sec.
(total time within 25 sec.) Working time is two min. from the start of mixing
according to manufacturer instructions .

d)   
Placement: a brush was used to
apply the mix to the tooth surface and a thin layer was spreaded to the
surface. 

 

II.4.c) Application of the two
desensitizing agents on dentin discs for

imaging depth of penetration

A total of  ten lower molars were used to obtain occlusal
dentin discs, five discs were prepared for each desensitizing material, to
detect the depth of penetration and mode of attachment at the interface between
dentin and the material (of a standard thickness 1mm) using the digital caliber.
All discs received no tooth brush abrasion nor thermocycling. Using a dental
model trimmer, occlusal enamel was removed while the roots were grinded from
its apex towards the occlusal surface until a 1 mm disc was recieved, it was
then smoothened by soflex discs from coarse to fine. EDTA was applied first followed
by the two desensitizing  materials on
the occlusal dentin discs as previously mentioned. A cross section imaging took
place as each dentin disc was then broken into two halves manually with bare
hands to avoid the formation of any smear layer, then it was viewed under the environmental
scanning electron microscope (ESEM)* Fig.(8) and the penetration of the desensitizing agents in the dentinal tubules
was detected.(46) 

 

II.5) Testing of the specimens

II.5.a) Tooth brush abrasion

Half  the samples were subjected to tooth brush
abrasion for a standard time and force.

 

General description of the
toothbrushing machine

A custom made machine was built to simulate brushing
technique,  made and calibrated at the
faculty of engineering, Banha University Fig.(9-12). The machine is
classified as a reciprocating machine, which converts rotational motion to
linear motion. A toothbrush was fixed at the end of a stroke shaft that was
connected to a motor and the tooth sample was fixed in a holder. Tooth-brushing
machine was accomplished with horizontal movements of the toothbrush under a
weight of  350 gm and a traveled course
of  3.8 cm.  The rotation was of  four cycles/s  and  240
cycles/min, the total time of tooth brushing  was 16 min, so total cycles were 3840 cycles.
Toothbrush head was replaced with every new sample. The machine was built to
mimic three years of tooth brushing for each 100 min., So 16 min. will mimic six
months of tooth brushing.(49) 

 

 

 

 

 

 

 

 

* FEI Company, Model Quanta 200 F Field Emission
Scanning Electron Microscope.

 

 

II.5.b)Thermocycling

The samples were thermocycled for 2000 cycles with a dwell time five sec.
and temperature 5 to 55 C. by using a MPM* thermocycling
apparatus.(43) 

Fig.(13).

 

II.6) Evaluation and image
analysis

All samples were observed in an environmental electron microscope at a 2000 magnification
to observe the patent surface area of dentinal tubules. Samples
were dehydrated by placing them in alcohol 96 %. The ESEM was used with SPSS
20** and semaphore software to evaluate depth of penetration of desensitizing
agent inside dentinal tubules and the patency of the dentinal tubules. Semaphore
5.21*** program was used for digital analysis where surface area of each patent
tubules was evaluated and calculated.

II.7) Statistical analysis

Results
were collected, tabulated and statistically analyzed using software  SPSS 20.

 

 

 

 

 

 

 

 

 

*MPM instruments, Bernareggio M1, Italy

**SPSS 20 by IBM company

*** Semaphore 5.21 by Semaphore entertainment group company
research & investing information.

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