|Year : 2010 | Volume
| Issue : 4 | Page : 258-263
Comparative evaluation of the effect of cavity disinfectants on the fracture resistance of primary molars restored with indirect composite inlays: An in vitro study
MD Indira, B Nandlal
Department of Pedodontics and Preventive Dentistry, JSS Dental College and Hospital, A Constituent College of JSS University Mysore - 570 015, India
|Date of Web Publication||25-Jan-2011|
M D Indira
Department of Pedodontics and Preventive Dentistry, JSS Dental College and Hospital, A constituent College of JSS University Mysore - 570 015, Karnataka
| Abstract|| |
A study was conducted to evaluate and compare the effect of cavity disinfectants on the fracture resistance of primary molars restored with indirect composite inlays. Thirty-six non-carious primary second molars were selected and divided randomly into three groups (n = 12): control group (no disinfectant), chlorhexidine group (disinfected with 2% chlorhexidine for 40 seconds) and sodium hypochlorite group crowns (disinfected with 2% chlorhexidine for 40 seconds). The inlays were fabricated by indirect method using Ceram X nanocomposite on plaster die. All the groups were submitted to compression mechanic test in a Hounsfield universal testing machine at 1 mm/min cross-head speed and the results were calculated in Newtons. Descriptive statistics, independent t test, and one way analysis of variance (ANOVA) test revealed the mean fracture resistance of three groups, i.e., control group, chlorhexidine group and sodium hypochlorite group to be 2260.66, 1858.08 and 1310.66, respectively. When intragroup comparisons were made, a significant difference was observed in all the groups (P<0.001). Scheffe's post hoc test revealed that control group had the highest fracture resistance, followed by chlorhexidine group, and sodium hypochlorite group had the least fracture resistance. Each value differed significantly from the other (P<0.05). Cavity disinfectants used in the present study had detrimental effect on the fracture resistance of primary molars. Among the disinfectants employed in the present study, chlorhexidine showed a better resistance to fracture than sodium hypochlorite.
Keywords: Chlorhexidine, composite resins, fracture resistance, inlays, sodium hypochlorite
|How to cite this article:|
Indira M D, Nandlal B. Comparative evaluation of the effect of cavity disinfectants on the fracture resistance of primary molars restored with indirect composite inlays: An in vitro study. J Indian Soc Pedod Prev Dent 2010;28:258-63
|How to cite this URL:|
Indira M D, Nandlal B. Comparative evaluation of the effect of cavity disinfectants on the fracture resistance of primary molars restored with indirect composite inlays: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2010 [cited 2013 Jun 20];28:258-63. Available from: http://www.jisppd.com/text.asp?2010/28/4/258/76153
| Introduction|| |
Dental caries is one of the most common diseases, affecting approximately 80% of the population in developed countries. , Finding a material that could restore the lost tooth structure and combining physical, chemical and esthetic properties which are optimal have been the goal of research for many years. In pediatric dentistry, it is common to observe the occurrence of the fast and severe decay causing greater loss of dental structure. Despite the development of pediatric dentistry, dental decay is still one of the diseases of greater prevalence, mainly in children. 
When direct composite resin is placed, polymerization may be inherently incomplete to the depth of several hundred microns within the polymer. This occurs secondary to the fact that radical polymerization is inhibited by ambient oxygen resulting in incomplete surface polymerization referred to as surface dispersion film.  The placement of direct posterior resin composite is accomplished by many problems like polymerization shrinkage, microleakage and wear.  The main shortcoming being polymerization shrinkage, when direct composite is placed in a large cavity, the mass to be polymerized is so large that the shrinkage forces win out, producing marginal defect and gaps, despite careful application and use of adhesive techniques. 
The indirect composite restoration shows many advantages compared to direct technique such as replacement of natural convexities of teeth, control of occlusal and proximal contact points, better marginal fit especially in the gingival wall, minimal shrinkage polymerization due to cement agents, good polishing and finishing possibilities, shorter clinical section and less contamination risk.  Furthermore, the additional cure of composite in indirect technique is not necessary because this could increase the wear resistance of some composites commercially available. 
Secondary decay can also be the result of the action of bacteria left under restoration. Investigations have shown the presence of bacteria in dentin after the removal of infected dentin even after the removal of dye stainable dentin. The use of disinfectant solutions such as fluorides, chlorhexidine and sodium hypochlorite is an alternative procedure to reduce or eliminate bacteria from cavity preparation. 
Hence, the present study was conducted to evaluate the effect of cavity disinfectants on resistance of fracture of primary molars restored with indirect composite inlays and to compare the effect of two different cavity disinfectants on fracture resistance of primary molars restored with indirect composite inlays.
| Materials and Methods|| |
Thirty-six extracted, intact mandibular second primary molars were selected for this study. Teeth were selected for similarity in size, shape and root anatomy. Hard and soft deposits were removed with hand scaling instruments.
The following criteria for teeth selection were included in this study:
This was done so that the teeth of similar dimensions could be evenly distributed between groups. The tooth was stored in distilled water except during restoration and experimental testing.
- Teeth with not less than one-third of the root;
- Teeth with no caries/cracks and
- Teeth selected were within the normal range of mesio-lingual and bucco-lingual width.
- The following teeth were excluded from this study:
- Teeth with visible initial carious when viewed under magnification and
- Teeth with less than one-third of root.
All selected teeth were mounted in a wooden jig of standardized dimension. The acrylic resin was placed up to a point approximately 2 mm below cemento-enamel junction to approximately the height of healthy alveolar bone with standard inclination and parallelism.
The specimens were randomly divided into three groups of 12 samples each and color-coded with colored adhesive tapes and numbered. The numbered coding of samples included alphabetical initials of the color group they belonged to. The groups included control group (yellow), the chlorhexidine group (red) and the sodium hypochlorite group (black).
Cavity preparation for composite inlay
In order to standardize cavity preparation, a custom made jig was made [Figure 1]. The jig consisted of a vertical arm and a horizontal arm. To the vertical arm, provision was made so that it could move in both vertical and horizontal directions. Airotor, used to cut the cavity, was attached to the vertical arm. In the horizontal arm, a slot was made to place the mounted tooth. The cavity was prepared by moving the vertical arm in horizontal direction. The depth of the cavity was kept constant by moving the vertical arm in vertical direction using a movable attachment. The depth was measured by viewing the scale attached to the vertical arm.
Based on the ideal design of cavity preparation for inlays, the cavity cutting was done on the occlusal surface of the selected mandibular second primary molars using diamond trunk conic burs. For the purpose of standardization, the cavity was not extended to the grooves and fissures. The depth of the cavity was placed 0.5 mm pulpally from the cemento-enamel junction/2.5 mm below the tallest cusp and the bucco-lingual width of the cavity was 2 mm. The pulpal floor was made flat [Figure 2].
The prepared cavity was rinsed with water and dried with cotton. Impressions from the preparation were taken using polyvinyl siloxane putty and soft rubber impression material [Figure 3]. The die was prepared using die stone type IV [Figure 4]. Die was separated using isolant solution. Indirect restoration (inlays) was fabricated using nanocomposite M2 Shade, by incremental technique beginning with proximal box followed by occlusal box. Each increment was photocured for 20 seconds using the soft start polymerization unit [Figure 5].
The prepared cavity was treated with 2% chlorhexidine for group II, and 1% sodium hypochlorite for group III was applied using disposable 5 ml syringe for 40 seconds, then washed off and dried [Figure 6]. After the disinfectant was applied on the prepared cavity, the dentine surface was etched with 37% phosphoric acid for 15 seconds, washed and dried with adsorbent paper, followed by one bottle primer and adhesive application (Prime and bond NT), followed by curing for 10 seconds.
The inner surface of the inlay was cleaned and bonding agent was applied [Figure 7]. The resin luting cement was inserted on the inner surface of inlay and to the cavity walls; the inlay was fixed by finger pressing, simulating the clinical situation. The excess cement was removed after an initial cure of 10 seconds using an explorer. Then, each surface (buccal, lingual, mesial, and distal) was cured for 40 seconds. The finished restorations were stored in 100% humidity at 37°C for 24 hours, followed by testing.
The fracture resistance test was performed using Hounsfield universal testing machine [Figure 8]. The compressive load was applied on the occlusal surface with steel, 3 mm diameter ball end head at a cross-head speed of 1 mm/min [Figure 9].
The results were obtained at the specimen fracture and calculated in Newtons. The data were subjected to statistical analysis using descriptive statistics, one-way analysis of variance (ANOVA), independent samples "t" test and Scheffe's post hoc test.[Table 1], [Table 2], [Table 3] and [Table 4]
|Table 1 :Descriptive statistics of peak failure load (Newtons) for various groups |
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|Table 2 :Results of one-way ANOVA for peak failure load (Newtons) for various groups |
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|Table 4 :Summary of comparison between various groups using independent samples "t" test |
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| Results|| |
As shown in [Table 1], the mean fracture resistance of the three groups, control group, chlorhexidine group and sodium hypochlorite group, were 1117.00, 906.67 and 767.42, respectively, during first load application.
Further, Scheffe's post hoc test [Table 2],[Table 3] revealed that the control group had highest fracture resistance followed by chlorhexidine group, and sodium hypochlorite group had the least fracture resistance [Figure 10]. Each value differed significantly from the other (P < 0.05).
Between the groups also, a significant difference was found in the fracture resistance at load application. Further, the group statistics and independent t test [Table 3],[Table 4] revealed that between control and chlorhexidine groups, control group had the highest resistance to fracture (1117.00) compared to chlorhexidine group (906.6). Between control and sodium hypochlorite groups, the control group showed a higher resistance to fracture (1117.00) compared to sodium hypochlorite group (767.42). Between chlorhexidine and sodium hypochlorite groups, chlorhexidine group had a higher resistance to fracture (906.67) compared to sodium hypochlorite group (767.42).
| Discussion|| |
Residual microorganisms under restorations can cause recurrent caries and limit the dentin sealing ability of the bonding agents. Therefore, the cavity sterilization has become an important sequence in restorative procedure.  Phosphoric acid etchant materials demonstrate antimicrobial activity against some of the bacteria involved in caries.  However, some studies have shown that even after using the newest dentin bonding agents, a certain microleakage is apparent which allows the entrance of the oral fluids that can be used by residual bacteria as a nutritional requirement and bacterial entry. , This mechanism is responsible for secondary caries. It would be necessary or advisable to place an additional disinfectant to treat dentin surfaces prior to the placing of restoration.
The resistance to fracture of a restored tooth may be considered to be associated with many factors, including cavity dimension , and restorative system utilized. , For indirect composite restorations, it may also be considered that the use of adhesive luting cement would enhance the resistance of fracture of the restored unit.
Chlorhexidine solutions have been indicated to be placed after cavity preparation to disinfect dentin. , Chlorhexidine, a cationic agent, is the most widely used antibacterial agent. The cationic nature of chlorhexidine promotes the connection with anionic compound at the bacterial surface and alters its integrity and results in cell death. However, the remnants of chlorhexidine left after its application could interact with calcium and phosphate present in dentin and therefore inhibit bonding ability of bonding agents. 
Sodium hypochlorite is one of the most widely used irrigants. However, various studies have shown the effect of sodium hypochlorite as a cavity disinfectant on bond strength. The present study was conducted to evaluate the effect of sodium hypochlorite as a cavity disinfectant on the fracture resistance of tooth.
Sodium hypochlorite breaks down to sodium chloride and oxygen, which causes oxidation of some components in the dentin matrix,  and consequently, decreases the elastic modulus and flexural strength of dentin.  Sodium hypochlorite could affect the resin penetration into the dentin structure and/or the polymerization of monomer in the dentin and also could influence the restoration's quality. 
In the present study, the disinfectants were applied before acid etch technique, which was in accordance with the studies conducted by Meiers and Kresin  and De Sousa Vieira and Da silva.  They found that the use of cavity disinfectant after tooth preparation and before the application of a dentin bonding agent could help reduce the potential for residual caries. They stated that cavity disinfectant used with composite resin restoration might be material specific regarding their interactions with various dentin bonding systems' ability to seal the dentin.
Polymerization shrinkage, and consequently, development of shrinkage stress is the main problem associated with the curing of composite dental materials. As a result of this phenomenon, debonding of the curing material from the dental tissues occurs, enabling the occurrence of marginal gaps. ,
Thus, with the clinicians looking for an alternative, the use of indirect resin composite restoration was first recommended in order to avoid some of the shortcomings of direct posterior resin composite restoration. Their mechanical and physical properties were reported to be enhanced and side effects of polymerization were reported to be reduced. ,,
Ausiello et al,  and Wendt et al,  affirmed that the efficacy of the bonding to dentin is based on hybridization, although their studies were carried out in permanent teeth. Ausiello et al,  using the finite element analysis (FEA), described the importance of adhesive systems on stress distribution in direct composite restorations because the stress difference is transferred to adhesive layer, generating a deformation.
With the results of the present study, it can be stated that use of cavity disinfectants reduces the fracture resistance of tooth. However, when chlorhexidine was used as a disinfectant, it showed a better resistance to fracture than using sodium hypochlorite as a disinfectant, within the limitations of this study. Hence, it can be suggested that whenever a clinical situation arises to restore a decayed deciduous teeth, it is advisable to use cavity disinfectants.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
[Table 1], [Table 2], [Table 3], [Table 4]