| Abstract|| |
The objective of this in-vitro study was to evaluate the effects of six in-office agents of desensitization on the hydraulic conductance of human dentin by measuring the mean percentage reduction in permeability over a period of one month.
The tested agents were Fluoride varnish (Fluorprotector),resin desensitizer ( Gluma desensitizer ), adhesive resin ( Gluma comfort bond ), laser (Nd: YAG Laser), fluoride iontophoresis (Electric pulp tester, for fluoride iontophoresis) and 3% Potassium oxalate(freshly prepared). Sixty non carious, intact human mandibular third molars were sectioned at mid coronal region and polished to obtain a 1mm thick disc which were divided into six groups. A split chamber device with fluid filtration apparatus was constructed for hydraulic conductance measurements. Permeability of dentin discs was measured at baseline that serves as a control and following the application of the various in-office agents, measurements was recorded post operatively, after 24 hrs, after I week and after 1 month.
Mean percentage reduction in permeability was tabulated and statistically analyzed.
The results of this study indicate that all the tested agents led to a decrease in dentin permeability Nd: YAG laser gave the highest reduction in permeability throughout the entire period of study followed by Gluma desensitizer Gluma comfort bond, Fluoride iontophoresis, and Fluor protector and 3% Potassium oxalate was the least effective.
|How to cite this article:|
Joshua M, Emmanuel, Kandaswamy D. Effects of six in-office agents of desensitization on the permeability of dentin - An in-vitro hydraulic conductance study. J Conserv Dent 2005;8:14-25
|How to cite this URL:|
Joshua M, Emmanuel, Kandaswamy D. Effects of six in-office agents of desensitization on the permeability of dentin - An in-vitro hydraulic conductance study. J Conserv Dent [serial online] 2005 [cited 2020 Feb 24];8:14-25. Available from: http://www.jcd.org.in/text.asp?2005/8/4/14/42593
| Introduction|| |
Hypersensitivity of dentin is one of the commonly encountered problems in the dental office. Dunitz and his co- workers (1982)  stated that 'dentin hypersensitivity is an enigma being frequently encountered yet ill understood. It is defined as short, sharp pain arising from exposed dentin typically in response to thermal, evaporative, tactile, osmotic or chemical stimuli and which cannot be ascribed to any other form of dental defect or pathology.
Although there are many theories about the process of hypersensitivity, the most accepted is the `hydrodynamic theory'  put forth by Brannstrom (1963). This theory proposes that hypersensitive dentin is permeable, whenever any stimuli is applied to exposed dentin. Fluid flow within dentin in either direction stimulates the sensory nerves in the dentin or pulp resulting in sensitivity. Pashley D (1981) studied dentin permeability as a function of hydraulic conductance. It is the ease with which fluid can move across a unit surface area under unit pressure per unit time.
The hydraulic conductance based on Poiseuille's law , is determined by a number of variables such as the pressure moving the fluid across dentin, length of the tubules, viscosity of the fluid and the radius of the tubule. Dentin permeation is directly proportional to the radius of the tubule. Hence the most important variable in reducing the fluid flow (dentinal permeability) is with the reduction of the radius of the tubule (tubule occlusion).
Changes in hydraulic conductance , of dentin have been used as a method of screening the efficacy of various desensitizing agents. Based on this approach, occluding patent tubules to reduce any stimulus-evoked fluid flow movements is an effective method for treating hypersensitive dentin. Although tubular occlusion can be physiologic 
by reparative dentin formation, adhesion of proteins from salivary pellicle etc, these mechanisms cannot give immediate relief in cases of moderate to severe hypersensitivity hence a therapeutic method of intervention either to partially or completely occlude tubules is needed.
The most difficult sites to treat are those where there is no loss or insufficient loss of tooth structure to permit use of restorative treatments" hence the need for in-office agents of desensitization.
The in-office treatment methods that are designed to decrease sensitivity by partial or complete tubule occlusion (Branstrom 1979, Pashleyl986) for such cases include
Primers Containing HEMA
- 5% glutaraldehyde, 35 % HEMA in water
- 35% HEMA in water
Adhesive resin primers
Adhesive resin bonding systems
NON RESIN BASED
Varnishes or precipitants
- 5% sodium fluoride varnish
- Sodium fluoride, stannous fluoride solutions
- Oxalate containing preparations - 3 % potassium oxalate or 6 % ferric oxalate
- Calcium phosphate, calcium hydroxide
USE OF FLUORIDE IONTOPHORESIS LASERS
Hence the objective of this in-vitro study was to evaluate the hydraulic conductance of human dentin by measuring the mean percentage reduction in permeability following the use of six different agents that include a fluoride varnish, a resin desensitizer, an adhesive resin , a laser , an electric pulp tester for fluoride iontophoresis and potassium oxalate paste for a period of one month.
| Materials and Methods|| |
Sixty freshly extracted (caries free) human mandibular third molars were used for this study. They were washed in normal saline and stored in 0.04% sodium azide . The teeth were sectioned , parallel to the occlusal surface from the top of pulp horns and occlusally to an approximate 1mm width using a diamond coated saw. The disc was then polished with 600, 800 grit sandpaper to obtain a thickness of lmm and stored in phosphated buffer saline with sodium azide until use. Prior to permeability measurements the dentin disc were treated with 6% citric acid for a period of two minutes  followed by 20 second rinse with phosphated buffer saline.
After dentin disc preparation, they were randomly assigned into six groups of ten specimens each (n=10).
After treatment with the following agents, they were stored in phosphated-buffered saline with 0.4% sodium azide  between measurements.
Was treated with fluoride varnish (Fluor protector Ivoclar Vivadent Germany). After the disc is isolated using blotting paper, a single coat is applied using a microtip brush (as recommended by the manufacturer) and allowed to dry for a period of 5 minutes.
The sample (dentin disc) was treated with resin desensitizer  (Gluma desensitizer Herzaeus Kulzer). The surface was blot dried and a single coat of the agent was applied using a micro brush and left to dry for 60 seconds and rinsed off.
An adhesive resin system (Gluma comfort bond Herzaeus Kulzer) was used. After acid etching with 37% phosphoric acid for 20seconds and rinsed for 5 seconds with double distilled water and air dry for 10 seconds followed by the single coat application of the bonding agent using the micro tip brush and left in place for l5seconds and light cured for 20 seconds.
Treated with ND:YAG laser(( Nd:YAG continuum SLo l) at 1064nm wavelength at 30mJ intensity ,10pulses per second (pps)and 2 minutes  respectively.
Electric pulp tester was used to simulate for fluoride iontophoresis (Parkell).
An electric pulp tester that delivered the same amount of current -1.5 volts ( at an analogue set at 6) as that of an iontophoresis machine was chosen. A cotton pledget saturated with 2% sodium fluoride solution was placed at the end of the electrode. And an analogue of six was applied to the disc for a period of 2 minutes and then rinsed off with double distilled water for a period of 20 seconds.
This group was treated with 3% potassium oxalate (freshly prepared).A 1: 1 dilution of the solution was freshly prepared in double distilled water and 0.2m1 of the solution was pipetted and added drop by drop to be left in contact with disc for a period of two minutes and rinsed off from with 25cc of double distilled water followed by a 25cc of phosphated buffer saline.
MEASUREMENT OF HYDRAULIC CONDUCTANCE:
A fluid filtration system [Figure 1] with split chamber device , as described by David. H. Pashley (1974) was constructed for hydraulic conductance measurements.
The split chamber device [Figure 2] consists of split housings and two internal plastic spacers with appropriate rubber 'O'rings which were used to seal each half of the chamber to the discs and the smaller `O' rings limited the exposed surface area on the pulpal side of dentin to 0.01981 cm 2 (Dr2 or Dd2/4) ford =5mm, 0.5cm, r=2.5mm, 0 .25cm to the fluid flow.
The fluid filtration system consists of a pressurized nitrogen cylinder , which was connected to a modified pressure cooker containing phosphated buffer saline with foetal bovine serum.
The exit end of this was connected to a softened silicone tube, to which a graduated glass micropipette (1.5mm in diameter) is attached. The end of the micropipette is further connected to a T- tube to which a syringe (containing phosphated buffer saline with foetal bovine serum) is filled and the silicone tube is attached. The other end of the silicone is attached to a split chamber device.
After assembling the device, instead of the tooth sample, a polyethylene disc  was placed and a nitrogen pressure of l5psi was given in order to check the air tightness of the device. After ensuring that there was no leak, the polyethylene disc ,, was replaced with a dentin disc with the pulpal end towards the split chamber and dentinal end facing outside. A solution of foetal bovine serum  and phosphated buffer saline (PBS) in the ratio of 1:3 (as described by Nikaido T, Tigami J) was forced through dentin disc resembling dentinal fluid from the pulpal side to the dentin.
First the solution was forced from the modified pressure cooker through a polyethylene tubing to the split chamber device holding the disc at l5psi  to flush out the debris and any remaining diamond particles. A constant pressure of l0psi was applied to the sample that was maintained throughout the experiment. After introducing an air bubble into the system by a syringe through the T tube, this end of the silicone tube was clamped with artery clamps to make it leak proof.
By measuring the progress of the air bubble through the glass micropipette for a period of six minutes, the amount of liquid that flowed through the dentin was recorded and the fluid movement as a measure of hydraulic conductance was expressed as a function of
LP = Jv/A. P.t.
Lp hydraulic conductance in microlitres, cm- 2 , minutes - 1 , cmH 2 O - 1
Jv fluid flow in microlitres (millimeter recordings is converted into microlitres)
A surface area of the inner 0 ring (0.1981sgcm)
P hydrostatic pressure in cms of H 2 O
t time in minutes
Dentin permeability as a function of hydraulic conductance was measured as a rate for each specimen at baseline and after treatment with each agent. Therefore each disc served as its own control thereby eliminating the biological variability. Prior to treatment, the hydraulic conductance of each specimen was measured. This value represented 100% permeability, which represented baseline permeability for the disc.
Measurements were carried out immediately after application of the agent, after 24hours, following one week and at the end of one month.
Results were tabulated and statistically analyzed using Kruskal Wallis One-Way ANOVA to calculate the p values for the six groups.Mann Whitney U test was employed to identify the significant groups at 5% levels.
Results : Alterations in hydraulic conductance expressed as mean percentage reduction in permeability relative to baseline from preoperative to post operative, after 24hrs, after one week and the end of one month between different study groups are given in [Table 1],[Table 2],[Table 3] and [Table 4] respectively. A graph representing mean percentage reduction and standard deviation is shown in [Figure 3]
POST OPERATIVE MEASUREMENT:
The mean percentage reduction in permeability in Group IV (Nd:YAGlaser)(86.2±11.8) (p<0.05) was significantly higher than the other groups. Followed by Group II resin desensitizer (Gluma desensitizer) (75.7 ± 11.5) and Group V (electric pulp tester) (73.4±7.3)(p<0.05).
Further the mean percentage reduction in permeability in Group III adhesive system Gluma comfort bond) (71.9±17.7) (p<0.05) was significantly higher than Group VI (3% potassium oxalate) (40.6± 12.9) (p<0.05).
AFTER 24 HOURS
The mean percentage reduction in permeability in Group IV (Nd: YAGlaser) (86.4±2.8) (p<0.05) was significantly higher than all the other groups. Followed by Group II resin desensitizer (Gluma desensitizer) (83.0±3.8) and Group III adhesive system (Gluma comfort bond) (74.3± 9.1)(p<0.05).
Further the mean percentage reduction in permeability in Group V (electric pulp tester for iontophoresis) (67.5± 4.4) (p<0.05) was significantly higher than Group I (fluoride varnish Fluor protector) (48.1 ± 6.2) followed by group VI (3% potassium oxalate) (43.8±16.3) (p<0.05).
AFTER ONE WEEK
The changes in mean percentage reduction in permeability in a duration of one week and 24 hours showed a similar pattern. The mean percentage reduction in permeability in Group IV(Nd:YAGlaser)(87.4± 2.5) (p<0.05) was significantly higher than all the other groups. Followed by Group II resin desensitizer (Gluma desensitizer)(86.0 ± 3.8) and Group III adhesive system (Gluma comfort bond)(74.6± 10.8)(p<0.05).Further the mean percentage reduction in permeability in Group V (electric pulp tester for iontophoresis)(62.5± 16.2)(p<0.05) was significantly higher than Group I(fluoride varnish Fluor protector) (53.1±15.2) followed by group VI (3% potassium oxalate)(55.1 ± 0.9)(p<0.05).
AFTER ONE MONTH
The mean percentage reduction in permeability after one month did not show any change for GroupIV(Nd: YAGlaser)(87.4±2.5) and Group II resin desensitizer(Gluma desensitizer) ( 86.0 ± 3.8) (p <0.05).
Further the mean percentage reduction in permeability in Group V (electric pulp tester for iontophoresis)(62.5± 16.2) was significantly higher than Group I (fluoride varnish Fluor protector)(60.2 ±11.8) and Group VI (3% potassium oxalate) (50.6 ± 2.0) (p<0.05).
| Discussion|| |
The tubular nature of dentin makes it permeable especially when enamel or cementum is lost. The concept of tubule occlusion as an effective method of desensitization is a logical conclusion from hydrodynamic theory.
Hydraulic conductance measurements by this method are a non-destructive, sensitive method that allows repeated measurements and also serve as an accurate flow meter. In this in vitro model, the surface area, time, filtration pressure, dentin thickness and viscosity of the fluid were kept constant; only one parameter varied; fluid flow, the dependent variable varied directly with the changes in the tubular radius, the independent variable.
The dentin disc  is a useful screening in-vitro model for assessing the effects of the various agents on fluid flow through dentin. In this study, dentin discs were treated with citric acid to remove smear layer and to simulate patent tubules clinically. Phosphated buffer saline with foetal bovine serum was used to simulate dentin fluid. It is basically an ultrafiltrate of blood in the pulp capillaries resembling plasma.
According to the results of this study none of the tested agents have resulted in 100% reduction in permeability.
Nd:Yag laser, a crystal of YAG (Yittrium, aluminium and garnet) doped with Nd (neodymium)gave the highest mean percentage reduction in permeability throughout the entire period of study. Thermal energy of the laser occludes the tubules by melting the dentin surface and hence closure of tubules  .This was in accordance to a study done by P.RentonHarper and M. Midda (1992)  where an immediate reduction in permeability and after two weeks was observed after lasing with Nd;YAG.
Next to laser,Gluma desensitizer (containing 5% glutaraldehyde, 35%HEMA and purified water) proved to be second best. Glutaraldehyde acts as a protein fixative. Amino groups of the proteins in the dentinal fluid react with the glutaraldehyde and form a protein precipitate , resulting in partial or total occlusion. Studies done by Towbridge,  proved this agent to be an effective desensitizer.
At any given time it was proved to be more effective than the adhesive system (Gluma comfort bond).
In accordance to the study done by Gionvanni Dondi Dall and Werner J Finger (2002)  where Gluma comfort bond was compared with Gluma comfort bond combined with Gluma Desensitizer. The combination was more effective than GCB and the authors concluded that the role of glutaraldehyde was more effective in hampering a fluid shift that could have enhanced the effectiveness of the adhesive (Gluma comfort bond combined with Gluma Desensitizer).
Schupbach et al (1997)  reported the use of Gluma primer (identical to Gluma desensitizer) and glutaraldehyde in causing an intrinsic blocking of tubules.Hence resin desensitizer (Gluma desensitizer) showed an increased reduction in permeability in comparison to adhesive system (Gluma comfort bond ). Tagami et al (1995)  reported the increased efficacy of Gluma primer (identical to Gluma desensitizer) when the tubules contained bovine serum than buffer saline Hence the increased effectiveness of Gluma desensitizer in this study could also be attributed to the use of foetal bovine serum.
Gluma comfort bond (containing methacrylate, 4 META, ethanol and water) proved to be third best. Gluma comfort bond gave a significant reduction immediately after its application, which increased gradually without a statistically significant rise.
After acid etching of dentin with 37% phosphoric acid (for 20 seconds), there is an increase in transdentinal permeability leading to the removal of mineral content in the intertubular dentin thus resulting in the formation of resin tags and hybrid layer (resin infiltrated enamel, dentin / cementum)  . Dayton et al (1984)  evaluated the use of four adhesive resins in comparison to a fluoride varnish for a period of 28 days and concluded the long-term effectiveness of adhesive resins that lasted for 28 days while the varnish was ineffective.
Towbridge (1992)  compared oxalates, fluoride iontophoresis and adhesive resin and concluded that the adhesive resins were more effective.
Fluoride iontophoresis proved to be better than fluor protector and potassium oxalate paste.
The use of iontophoresis was first advocated by Gangarosa  (1983), which involves the use of electric current  to drive relatively high concentration of fluoride into the tubules. In brief, iontophoresis helps in the better permeation of fluoride than topical fluoride.
Fluoride ions are driven deeper into the tubules ,combine with ionised calcium of the dentinal fluid to form a precipitate of calcium fluorides , that occludes the tubules and thereby decreases sensitivity.
Due to the unavailability of this device, electric pulp tester delivering the same amount of current at the analogue set at 6 was used (Kathleen 1985)  . The electric pulp tester used for fluoride iontophoresis gave an immediately post operative reduction in the present study accordance to study done by David A. Kern et Following fluoride iontophoresis, fluor protector proved to be better than potassium oxalate paste. It contains polyurethane lacquer difluorosilane combined with 0.32 % of fluoride in liquid. Silanes are added and serve as effective vehicles in transporting fluorides.
A significant reduction in permeability was noted after 24 hours and a gradual rise after one week to a period of one month. This was in accordance to the study done by ShenC, AutioGold J (2002)  where there was a uniform rise in fluoride release from the tested fluoride varnishes. Hence fluoride varnish can serve as the initial line of treatment for desensitization. Hansen et al ( 1992)  reported that the temporary occlusion of dentinal tubules using fluoride varnish was lost over time (one year).
The loss of effectiveness of fluoride varnish could not be confirmed in this study due to the shorter duration involved (one month).
3% potassium oxalate was the least effective.
Oxalates: are available as potassium oxalate or ferric oxalate. Potassium oxalate was selected in this study over ferric oxalate as they are economical, readily available and have a longer shelf life. Potassium oxalate  combines with ionised calcium of the dentinal fluid to form crystalline complex - calcium oxalate that is relatively insoluble. Indigenous preparation of 3% potassium oxalate was obtained by mixing 3mg of potassium oxalate dissolved in 10ml of double distilled water with the standard dentifrice that contained pumice - 8g, starch1.6 g, methyl salicylate - 1.37 µl, carmine powder 0.03g. 3 % potassium oxalate was effective immediately after application and gradually maintained to reduce the permeability over 24 hours to period of one week but not
AFTER ONE MONTH.
This was in contrast to a study done by Muzzin et al(1989)  where potassium oxalate was effective immediately and after one month but not at one or two weeks The authors concluded that this result could have been due to the significance level that may have been overly rigorous (p<0.0001).
D.H Pashley  reported that oxalates tend to solubilize over time indicating that oxalate solution was only marginally effective.
| Conclusion|| |
- Under the limitations of this study, all the tested agents proved the reduction in permeability of dentin.
- Nd:YAG laser proved to be the best due to the thermal energy that had resulted in effective tubule occlusion.
- Gluma desensitizer was proved to be the second best and performed better than Gluma comfort bond due to the presence of glutaraldehyde.
- Gluma comfort bond was effective over the chemicals used due to the resin bonding being superior to the salt precipitation.
- Electric pulp tester for fluoride iontophoresis was effective over the other chemicals used.
- Fluoride varnish was superior to oxalates due to viscous nature of agent.
- Oxalates were least effective due to the solubility over a period of time.
Initially oxalates or fluoride varnish can be applied as a part of escalation therapy, if found to be ineffective, most definitive therapy that is rapidly effective such as resin desensitizers and adhesive resins are recommended.
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Department of Conservative Dentistry & Endodontics, Meenakshi Animal Dental College & Hospitals, Maduravoyal, Chennai.
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]