|Year : 2014 | Volume
| Issue : 5 | Page : 458-461
|Effect of desensitizing treatments on bond strength of resin composites to dentin - an in vitro study
Sameer Makkar1, Meenu Goyal1, Ashih Kaushal1, Vivek Hegde2
1 Department of Conservative Dentistry and Endodontics, National Dental College and Hospital, Derabassi, Punjab, India
2 Department of Conservative Dentistry and Endodontics, Rangoonwala College of Dental Sciences, Pune, Maharashtra, India
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|Date of Submission||19-Mar-2014|
|Date of Decision||04-May-2014|
|Date of Acceptance||24-Jun-2014|
|Date of Web Publication||1-Sep-2014|
| Abstract|| |
Objectives: Hypersensitivity is a common clinical multietiological problem. Many desensitizing treatments are there to overcome hypersensitivity. The aim of this study was to evaluate the effect of different dentin-desensitizing treatments on the tensile bond strength of composite restoration.
Materials and Methods: Twenty-four sound human molars were used. Enamel was wet abraded to expose flat dentin surfaces, polished with sandpaper. The specimens were then divided into three groups (n = 8) based on the type of dentin-desensitizing treatment given. The first group: G1 was the control group where no desensitizing agent was used. The second group: G2 was treated with desensitizing dentifrice containing a combination of potassium nitrate, triclosan, and sodium monoflorophosphate. The third group: G3 was treated with Er:YAG laser. Afterwards, the desensitized specimens were treated with one step self-etch adhesive according to manufacturer's instructions and composite microcylinders were packed. The specimens were then examined for tensile bond strength using universal tensile machine (KMI TM ).
Results: Statistical analysis of the data obtained revealed the mean values for the tensile bond strengths were 10.2613 MPa, 5.9400 MPa and 6.3575 MPa for groups 1, 2 and 3, respectively. These values were statistically significantly different between groups pretreated with laser or dentifrice as compared to control group.
Conclusions: Dentifrice and Laser pre-treated dentin has lower tensile bond strength with resin composites as compared to dentin that is untreated.
Keywords: Dentin desensitization; erbium lasers; potassium nitrate containing dentifrice; tensile bond strength
|How to cite this article:|
Makkar S, Goyal M, Kaushal A, Hegde V. Effect of desensitizing treatments on bond strength of resin composites to dentin - an in vitro study. J Conserv Dent 2014;17:458-61
|How to cite this URL:|
Makkar S, Goyal M, Kaushal A, Hegde V. Effect of desensitizing treatments on bond strength of resin composites to dentin - an in vitro study. J Conserv Dent [serial online] 2014 [cited 2020 Sep 30];17:458-61. Available from: http://www.jcd.org.in/text.asp?2014/17/5/458/139840
| Introduction|| |
Dentin hypersensitivity is one of the most commonly encountered clinical problems. The condition has been defined by an international workshop on DH as follows: "Dentin hypersensitivity is characterized by short, sharp pain arising from exposed dentin in response to stimuli, typically, thermal, tactile, chemical, evaporative or osmotic which cannot be ascribed to any other dental defect or pathology".  Type A delta fibers are supposed to be responsible for dentinal sensitivity being probably activated by the hydrodynamic process. This is in accordance to Branstorm's Hydrodynamic Theory. 
There is a wide range in the reported prevalence of dentinal hypersensitivity, with publications citing prevalence's of 4% and up to 98% depending on the population group. The highest prevalence's are seen in periodontal patients (reported range of 60-98%) and in the general population prevalence's of up to 57% have been reported. , Higher incidences of this condition occur in the 20-40-year-old age group, corresponding with the age at which gingival recession is often seen.  Females tend to be prone to hypersensitivity in comparison to males.  Hypersensitivity tends to be most prevalent on the buccal and cervical regions of the teeth. The most common sites for dentinal hypersensitivity are the cervical margins of the buccal and labial surfaces of teeth, with these sites accounting for 90% of sensitive surfaces. 
According to Landry and Voyer,  there is not an ideal desensitizing agent but any kind of treatment for DH should be effective from the first application and must satisfy these parameters established by Grossman  since 1934:
- Not irritating pulp, nor causing pain,
- Easy application,
- Long-lasting effect,
- Not discoloring or staining teeth,
- Not irritating soft tissues or periodontal ligament,
- Low cost.
In a review article by Bartold PM  2006 about dentinal hypersensitivity, he summarized the treatment strategies into a variety of self care as well as professional treatment strategies designed to depolarize the nerve or occlude and or seal the dentinal tubules. The most common form of management is the placement of a topically applied agent either by a dental professional or by the patient at home. In the last 15 years, the introduction of lasers gave further possibilities to DH therapy. On the other hand, the use of restorative materials is generally an invasive solution to the problem of hypersensitivity. Commonly used materials include composite resins and glass ionomer restorations. Generally this approach is reserved for situations where there has been significant prior loss of cervical tooth structure or as a last resort for a tooth which does not respond to other less invasive desensitizing protocols.
Among the topically applied desensitizing agents the most common "active ingredients" are potassium nitrate, stannous fluoride, sodium fluoride, sodium monofluorophosphate, and strontium chloride.  Potassium nitrate interferes with the transmission of the nerve impulse. It raises the extracellular potassium ion concentrations and affecting polarization.  When this is sustained for a period of time, the nerve excitation is reduced and the nerve becomes less sensitive to the stimuli.
However, the lasers act by photobiomodulating effect on dental pulp which results in production of large quantity of tertiary dentin causing the physiological obliteration of tubules.  Action of lasers is twofold. By one side, the low-level power lasers, also called "soft lasers," act directly on nerve transmission, with a depolarization process that prevents the diffusion of pain to Supra Nuclear Centers; however, their effectiveness seems poorer in higher degrees of DH. By the other side, high-power lasers such as: diode 980 nm and 808 nm, KTP 532 nm, Nd:YAG 1064 nm, CO 2 10600 nm, Er:Cr:YSGG 2780 nm, and Er:YAG 2940 nm act on DH provoking a melting effect with crystallization of dentine inorganic component and the coagulation of fluids contained into the dentinal tubules. 
In case, if the above mentioned two treatment modalities fail to relieve DH, we have to opt for the composite resin restorative material as the last resort.
The purpose of this study is to evaluate the influence of topically applied desensitizing dentifrice containing sodium fluoride as the active ingredient and that of Erbium:YAG laser on the tensile bond strength of dentin with resin composite.
| Materials and methods|| |
Twenty-four teeth were equally divided into three groups. Control group was not pre-treated while others were treated with Thermokind-F Gel and Erbium:YAG laser, respectively. For bonding, self-etch adhesive (3m ESPE Adper Single Bond 2) was applied according to manufacturer's instructions.
Specimen preparation and grouping
Twenty-four occlusal surfaces of sound human molars were used. Enamel was wet abraded to expose flat dentin surfaces, polished with 120 and 320 grit sand paper. Specimens were randomly divided into three groups according to treatment modality (n = 8): G1: Stored in distilled water with no dentin pre treatment; G2: Brushing with Thermokind-F Gel which is commercially available toothpaste with a formula combining the benefits of potassium nitrate, sodium monofluorophosphate and triclosan, G3: Er:YAG laser with these parameters: 2.94 μm, 1.50 W of output power, 15 Hz of frequency, 100 mJ of energy. Brushed specimens were treated for 4 min per day, for a period of 14 days. Lased specimens were treated in a continuous mode for 3 sec. Afterwards, the desensitized specimens were treated with a contemporary one step self etch adhesive according to manufacturer's instructions and composite microcylinders of 3-mm diameter and 5-mm height were packed.
Test procedure for tensile bond strength
Each tooth specimen with its own bonded composite microcylinder was secured with acrylic sheet with the help of cyanoacrylate adhesive to jaws of universal testing machine.
Tensile force was applied via universal testing machine at a crosshead speed of 1 mm/min. The load required for debonding was recorded in Newton.
The recorded values were subjected to statistical analysis using the SPSS software. One-way ANOVA, and Post-hoc Tukey HSD test were performed to evaluate the tensile bond strength values. For the entire evaluation, P < 0.05 was considered to be statistically significant.
Tensile bond strength calculation
The load at failure was divided by bonding area to express the bond strength in MPa:
δ = P/ πr2
where; δ = bond strength (in MPa)
P = load at failure (in N)
π = 3.14
r = radius of microcylinder (in mm)
| Results|| |
The results of the Universal Testing Machine have shown significant (P < 0.05) decrease in tensile bond strength of group 2 and group 3 desensitized with dentifrice and laser, respectively, as compared to the control group [Table 1].
|Table 1: Descriptive statistics and multiple comparisons for the effect of application of desensitizing agent on tensile bond strength of resin composites with dentin|
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This indicates that tensile bond strength of resin composite with dentin was maximum when no pre-treatment was given [Table 2] and there is no significant difference in bond strength between pre-treated groups whether dentin was desensitized with dentifrice or laser [Table 1].
|Table 2: Descriptive statistics for the effect of application of desensitizing agent on tensile bond strength of resin composites with dentin|
Click here to view
| Discussion|| |
It has been well recognized that the main cause of dentin hypersensitivity is attributed to exposed dentinal tubules found in areas where tooth structure has been lost. In attempting to simulate these conditions, the enamel surface has been wet abraded to expose the dentine surface. Freshly extracted caries free human molars were preferred in this study as flat dentin surface could be prepared which would give a wider area of dentin to be treated and bonded to resin substrate. "3M ESPE SINGLE BOND" adhesive was used because it is one of the commonly used bonding agent for anterior and posterior resin restorations. A 5-mm height was kept so that it gives sufficient amount of composite material to hold the acrylic jig. Specimens were kept in distilled water before testing to simulate the oral conditions. A tensile type of test was applied to test the bond strength. Four factors normally influence the final strength of the union of composite resin to the tooth surface, namely wet ability, stress setup by the setting contraction of the resin, filler composition of composite resin, tensile strength of the material. Out of these factors, the role of tensile strength of the material was considered in this study.
Result of present study showed that Er:YAG lasers decreased the tensile bond strength of resin composite to dentin as compared to dentin not pre treated with any desensitizer. These results correlate with the results of Nielli Caetano de Souza et al (2007) who reported that pre treatment with Er:YAG lasers before restoring with resin composites decreases their bond strength as it limits the micromechanical retention of the adhesive system on the conditioned dentin. The results of this study also agrees with similar reported results in which the bond strength of different adhesive systems applied to laser-treated dentin was tested until failure, in micro-tensile or shear mode.
In a study done by Nielle Caetano de Souza et al., (2007) on effect of pulse repetition rate variation of Er:YAG laser on bond strength to dentin, it was concluded that bond strength was higher when pulse repetition rate was 5Hz as compared to when pulse repetition was at 10 or 15Hz.
Thus, parameters used to lace dentin also play an important role in characterizing bond strength of dentin to composite resin.
In previous studies, different types of desensitizers were used, such as monopotassium oxalate, sodium fluoride, strontium chloride + calcium carbonate, Gluma ® desensitizer, etc. These desensitizers, when used with an adhesive system, had given conflicting reports.
Study done by Müjde Sevimay et al.,  (2009) on Microtensile bond strengths of composite to dentin treated with different desensitizers has inferred that bond strength was significantly lower in specimens treated with desensitizers based on Glutraldehyde and HEMA, HEMA and META, and oxalates; as compared to the control group receiving no desensitizing treatment. These results correlate with the present study; however, the desensitizer used in this study has different mechanism of action for reducing sensitivity, i.e., by blocking nerve conductivity. Thermokind-F, whose primary action is blocking conductivity of the nerve, had to some extent a tubule-blocking action after sequential application, and affected the bond strength values in the present study. Dentifrice pre treated group showed the least value of tensile bond strength.
Elhassan et al., (2008) did a study on Microshear Bond Strength Of Self Etch Adhesive To Desensitized Dentin found that there was no significant decrease in bond strength when Relief ACP [0.375 % Amorphous Calcium Phosphate (ACP), 0.22% NaFl, 5% KNO 3 ] or 0.4% stannous fluoride were used as desensitizing agent with Xeno IV (PENTA, Mono, Di and Trimethacrylate resins, cetylamine hydrofluoride, acetone-water) as self-etch adhesive. This difference can be explained by the presence of cetylamine fluoride in Xeno IV composition which could have chemically bonded to the precipitated structures formed by the desensitizing agents to occlude dentinal tubules.
Thus, it is not only the desensitizing agent and its mechanism of action which affects the bond strength but also the adhesive used to bond the composite resin to dentin.
| Conclusions|| |
Dentifrice and Laser pretreated dentin has lower tensile bond strength with resin composites as compared to dentin that is untreated. b) Dentifrice (Thermokind - F gel) showed less bond strength as compared to Laser (Er:YAG). Thus dentin that is not pre treated with any desensitizer showed maximum bond strength with resin composite.
Combination of various desensitizing dentifrice and adhesive agent affects the bond strength. So, further research is required to reach any distinct conclusion. In case of lasers, different outcomes may be produced depending upon the parameters employed. So, special concerns that are required when deciding to use laser irradiation in treatment of dentin hypersensitivity are the precise irradiation parameters for therapeutic laser effects and standardization of treatment protocols.
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Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]
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