|Year : 2019 | Volume
| Issue : 2 | Page : 127-132
Effects of different dentinal drying methods on the adhesion of glass ionomer restorations to primary teeth
Sherin C Jose, Ektah Khosla, K Korath Abraham, Arun Roy James, Elza Thenumkal
Department of Pedodontics and Preventive Dentistry, Mar Baselios Dental College, Kothamangalam, Kerala, India
|Date of Web Publication||26-Jun-2019|
Dr. Sherin C Jose
Department of Pedodontics and Preventive Dentistry, Mar Baselios Dental College, Kothamangalam, Kerala
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Glass ionomer cements that form an inevitable part of pediatric restorative dentistry are inherently sensitive to moisture. The influence of different drying techniques on the shear bond strength of glass ionomer cements to primary teeth dentin has not been established. Aims: The purpose of the study was to evaluate the effects of different drying methods for different drying time periods on the shear bond strength of GC Fuji IX to primary tooth dentine. Subjects and Methods: A total of 135 caries-free primary teeth were selected and ground to a flat dentinal surface. Specimens were randomly divided into three groups – air dry, blot dry, and suction dry of 45 specimens each. Of these, 15 specimens each were dried for 2 s, 5 s, and 10 s. GC Fuji IX was condensed into Teflon molds, and the specimens were subjected to shear bond strength testing. Results: The mean shear bond strength values for the different time intervals were analyzed with analysis of variance test. In the air-dry group, the maximum shear bond strength values were obtained when the specimens were dried for 5 s and the least when dried for 2 s (P = 0.00). In the blot-dry and suction-dry groups, the highest values were obtained when the specimens were dried for 10 s and least for 2 s (P = 0.039 and 0.000, respectively). Conclusions:Among the three drying methods employed in the study, the maximum shear bond strength of the glass ionomer restoration was observed in the air-dry group.
Keywords: Adhesiveness, glass ionomer cement, shear strength
|How to cite this article:|
Jose SC, Khosla E, Abraham K K, James AR, Thenumkal E. Effects of different dentinal drying methods on the adhesion of glass ionomer restorations to primary teeth. J Indian Soc Pedod Prev Dent 2019;37:127-32
|How to cite this URL:|
Jose SC, Khosla E, Abraham K K, James AR, Thenumkal E. Effects of different dentinal drying methods on the adhesion of glass ionomer restorations to primary teeth. J Indian Soc Pedod Prev Dent [serial online] 2019 [cited 2019 Jul 19];37:127-32. Available from: http://www.jisppd.com/text.asp?2019/37/2/127/261354
| Introduction|| |
Restoring carious teeth is one of the major treatment needs of children. Restorative objectives for children include sealing the cavity, preventing further tooth destruction, rendering the tooth and the tooth–restoration interface caries resistant, and ease of use. In addition, the material selected for the procedure must endure the grueling environment of the mouth for the period in which it is intended to be effective. An ideal material used for restoration should be adhesive, tooth colored, resistant to wear, nontoxic, and biocompatible to the tissue.,
Glass ionomers are considered to be a leading restorative material as they adhere to the tooth structure, have antibacterial activity and negligible dimensional changes, and release fluoride which produces cariostatic and antimicrobial actions., They have less volumetric setting contraction and a similar coefficient of thermal expansion to the tooth structure and can be used in different clinical situations such as luting of indirect restorations, lining, basing, and filling. Glass ionomer cement are water based, and therefore compatible with dentine, which is a water-containing tissue and has a film of odontoblast tubular fluid on the cut surface.
The main limitations of glass ionomer cement are its relative lack of strength and low resistance to abrasion and wear and their early moisture sensitivity. The presence of surface moisture on the dentinal surface interferes with the bonding of glass ionomer cement onto the dentinal surface. The higher the water content, the poorer will be the adhesion.
The effects of moisture on the adhesion of different esthetic restorations have been studied on permanent teeth. However, its effects on the adhesion of glass ionomer restorations to primary teeth have not been established. Thisin vitro study was designed to evaluate the effects of surface moisture on the adhesion of glass ionomer restorations to primary teeth dentin. The shear bond strength of glass ionomer restorations to primary teeth dentin was evaluated following drying the dentinal surface by different drying methods for different time intervals.
| Subjects and Methods|| |
Collection and preparation of sample
A total of 135 extracted, unrestored, caries-free primary teeth were selected for the study. Teeth with fracture, caries, restorations, and dental anomalies were excluded from the study. Depth orientation grooves measuring 1.5 mm were made on the occlusal surface of the tooth with an 836R bur (Diatech Dental AG, Heerbrugg, Switzerland) to ensure uniform reduction of dentine. This was followed by polishing of the dentinal surface using 320,600 and 1200 grit silicon carbide abrasive paper on a polishing machine (Buehler Ecomet V, Buehler Ltd, Lake Bluff, IL, USA) for 10 s to remove the superficial debris.
Mounting and surface treatment of samples
The tooth specimens were mounted on autopolymerizing acrylic resin using a metallic (galvanized iron) casing of 1” × 1” × 1” dimensions. Tooth samples were washed under running water, and the dentinal surfaces were then dried using a three-way syringe. GC Cavity conditioner (GC Corporation, Tokyo, Japan) was applied to the dentinal surfaces using an applicator tip for the next 10 s. After that, the surfaces were thoroughly rinsed with water using a three-way syringe for 10 s. The metallic casing with the mounted tooth sample was then positioned perpendicular to specially designed, adjustable Split Teflon molds with an internal diameter of 3 and 5 mm height.
Grouping of samples
The treated surfaces were then subjected to drying. Depending on the method of drying used, the samples were randomly allocated to the following three groups.
Group 1 – Air-dry group
Forty-five specimens were subjected to air dry with a three-way syringe. The group was again randomly divided into the following three subgroups of 15 specimens each.
- Subgroup 1.1: Air dried for 2 s (15 specimens)
- Subgroup 1.2: Air dried for 5 s (15 specimens)
- Subgroup 1.3: Air dried for 10 s (15 specimens).
Group 2 – Blot-dry group
Forty-five specimens were subjected to blot dry with Kimwipes wipers (Kimberly-Clark Corp., Roswell, GA). The group was again randomly divided into three subgroups of 15 specimens each.
- Subgroup 2.1: Blot dried for 2 s (15 specimens)
- Subgroup 2.2: Blot dried for 5 s (15 specimens)
- Subgroup 2.3: Blot dried for 10 s (15 specimens).
Group 3 – Suction-dry group
Forty-five specimens were subjected to suction dry with a high-speed suction tip (Evacuation Tip-Vented, Starryshine, Anaheim, CA, USA). The group was again randomly divided into three subgroups of 15 specimens each.
- Subgroup 3.1: Suction dried for 2 s (15 specimens)
- Subgroup 3.2: Suction dried for 5 s (15 specimens)
- Subgroup 3.3: Suction dried for 10 s (15 specimens).
Placement of the restorative material
The required amount of GC Fuji IX (GC Corporation, Tokyo, Japan) was mixed as per the manufacturer's instructions. The mixed glass ionomer material was then transferred onto the Teflon cylinders and condensed adequately without incorporating air bubbles. When the material was set, the adjustable split Teflon molds were separated, and GC Fuji Varnish (GC Corporation, Tokyo, Japan) was applied immediately and blow dried.
The treated samples were stored in deionized water at room temperature for 24 h. The shear bond strength of the glass ionomer restorations to the dentinal surface was then evaluated with universal testing machine (Tinius Olsen H10KS Universal Testing Machine) with a crosshead speed of 1 mm/min. The shear bond strength values thus obtained were then subjected to statistical analysis.
Statistical analysis of data
The one-way analysis of variance was used to determine and compare the means of the shear bond strength among the three different drying techniques and drying times. Post hoc analysis was done for intergroup comparisons whenever a significant difference between the means was revealed by SPSS Version 16.0, SPSS Inc., Chicago, (P < 0.05). The statistical analysis of the mean shear bond strength values obtained with different drying methods is shown in [Table 1], and different drying times are shown in [Table 2].
|Table 1: Statistical analysis of the mean shear bond strength values obtained with the different drying methods|
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|Table 2: Statistical analysis of the mean shear bond strength values obtained with the different drying times|
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| Results|| |
The mean shear bond strength values of the glass ionomer material after the defined drying method and time are shown in [Figure 1].
|Figure 1: Plot of the mean shear bond strength values obtained in megapascals|
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Among the three drying methods employed in the study, the maximum shear bond strength of the glass ionomer restoration was observed in the air-dry group regardless of the time of drying. In the blot-dry and suction-dry groups, the maximum shear bond strength was obtained when the specimens were dried for 10 s and the least when dried for 2 s. The results were statistically significant. In the air-dry group, the maximum shear bond strength was obtained when the specimens were dried for 5 s and least when dried for 2 s. The results were statistically significant. When the 2 s, 5 s, and 10 s dry groups were compared, the maximum shear bond strength values were obtained when air dried and minimum when blot dried. The results were statistically significant only in the 5 s group.
| Discussion|| |
Bonding of restorative dental materials to the tooth was studied extensively for many years. Bond strengths of glass ionomers have generally been determined either in shear mode or tension. The shear bond strength produces failure at the tooth adhesion interface and represents the bond strength between the tooth and the material rather than the strength of the material or tooth. Shear mode has the advantage of more closely replicating the patterns of loading that the material experiences under clinical conditions.,
An important requirement for the occurrence of interfacial phenomena called adhesion is that the two materials being joined must be in sufficiently close and intimate relation. Besides an intimate contact, sufficient wetting of the adhesive will occur only if surface tension is less than the surface energy of the adherent. Thus, adhesion to the enamel is much easier to achieve than to the dentin.,
The strength and durability of adhesive bonds depend on several factors including physicochemical properties of the adherent and adhesive, structural properties of adherents, surface contaminants during cavity preparation, development of external stresses that counteract the process of bonding and their compensation mechanisms, and the mechanism of transmission and distribution of applied loads through the bonded joint. Furthermore, the oral environment is subjected to moisture, physical stresses, changes in temperature and pH, dietary habits, and chewing habits, which considerably influences adhesive interactions between materials and tooth tissues.,
In the oral environment, the tooth surface is contaminated by an organic saliva pellicle with a low critical surface tension which impairs adequate wetting by the adhesive. Similarly, instrumentation of the tooth substrate during cavity preparation produces a smear layer with a low surface energy. Therefore, the natural tooth surface should be thoroughly cleaned and pretreated before bonding procedures to increase its surface energy and hence to render it more receptive to bonding.,
For glass ionomers, conditioning is usually carried out with dilute solutions of polyacrylic acid, at concentrations of either 10% or 20% typically for 10–20 s followed by rinsing., The increase in bonding efficiency must be attributed to (a) a cleaning effect, by which loose cutting debris is removed; (b) a partial demineralization effect by which surface area is increased and micro porosities are created; and (c) chemical interaction of the polyalkenoic acid with residual hydroxyapatite.
Adhesive restorations distribute the functional stresses across the bonding interface to the tooth, and they have the potential to reinforce weakened tooth structure. The marked change in the amount of each structural element of dentine with location implies that the nature of the substrate presented for bonding will vary with location. In general, bond strengths are higher in superficial than deep dentin. This probably reflects the difference in the amount of solid dentin available for bonding, as well as differences in moisture content. However, there is also evidence that the dependence is likely to be related to the specific bonding agent or mechanism.
Dentin's intrinsic wetness increases with depth, and moisture is frequently a barrier to good bonding. In contrast to this, for some systems, moist bonding has shown improved bond strengths because the presence of dentinal fluid or water may prevent the shrinkage of demineralized dentin. Dehydration causes the collapse of the exposed collagen scaffold that probably impedes the penetration of bonding resin. Dehydrated specimens show little difference in tensile or bending tests, but are brittle and undergo no plastic deformation in contrast to the hydrated and rehydrated samples. Nearly all changes in the mechanical properties are reversible following rehydration.
In vitro bonding studies by Glantz typically showed that failure of glass ionomer cement of both types is at least partly cohesive, i.e., occurs within the cement, rather than at the interface, which is adhesive failure. Adhesive failure is, therefore, not a measure of the true adhesive bond strength, but rather a measure of the tensile strength of the glass ionomer material. Bond strength is low in immature specimens and not representative of the final value that fully matured cement is likely to have. These considerations show that determining the real strength of the adhesive bond is difficult and that values in the literature are almost certainly not representative of the true strength of the adhesive bond formed. When the effects of salivary contamination on the shear bond strength of glass ionomers to dentin were evaluated, it was found that the modes of failure were mostly cohesive for Fuji IX.
The bonding efficacy of self-adhesive resin cement was studied and it was found that the resin cement showed the best bonding performance when only a small amount of water remained on the dentin surface. Among the different drying methods attempted, it was reported that blot drying of dentin produced a significantly higher water/apatite ratio (3:1) and the bond strengths of all the self-adhesive resin cement decreased significantly when the materials were luted to blot-dried dentin. The results of blot drying the dentinal surface in the present study also suggested the lower bond strength of glass ionomer restorations.
In contrary to these findings, the blot-dry group demonstrated the highest bond strength values to dentine adhesive in studies done by Jayaprakash et al. When blot drying was practiced, most of the water in the interfibrillar spaces remained to support the collagen network. Thus, the monomers infiltrated into the demineralized dentin polymerize and produce a hybrid layer without collapse of the collagen network or separation of the resin from the dentin.
Werle et al. reported that the initial bond strength of adhesive systems can be improved by prolonging the air-drying time. This influence is material dependent, and significantly higher values were found with the prolonged air-drying protocol, probably related to improved solvent evaporation and consequently a less defective adhesive interface. The prolonged airflow could have provided more time for monomer diffusion, leading to better interaction between acidic monomers and the substrate, leading to higher tensile bond strength values. The results of the present study showed similar results with suction dry, with the bond strength values being higher when dried for the maximum duration.
The major difference between air syringe and suction drying lies in the direction of the airflow, that is, from the syringe tip onto the tooth surface under positive pressure versus from the tooth surface into the suction tip under negative pressure. Magne et al. reported that there are no differences in mean tensile bond strength to human dentin using either the air syringe or the suction tip to control the amount of moisture. Even though thorough air drying results in collapsed collagen matrix and precludes optimal resin infiltration, it is not as detrimental as the deficient solvent evaporation that would result from short or insufficient air drying. Suction drying, which seems much less vigorous, might better prevent the collapse of the collagen matrix. The slightly lower (but not significantly different) bond strength values and decreased percentage of cohesive substrate failures observed with suction drying may be attributed to the fact that the suction tip might not have delivered enough negative pressure in order to prevent the accumulation of residual water or other solvents. In the present study, bond strength values obtained in the suction-dry group were not significantly different from that of air-dry group.
In all the studies, the lowest shear bond strength values were obtained when the adhesive system was applied to overwet dentin.,, In the present study also, the lowest bond strength values were obtained when the dentin was dried for a shorter duration among the different drying methods.
When the bond strength of a self-etch system to dentin with varying drying times was evaluated, better adhesion to dentin was obtained when specimens were air dried for 5 s. The present study also reports the highest shear bond strength values of the glass ionomer restorative material when the specimens were air dried for 5 s.
From the studies on various adhesive restorative materials, the better adhesion of the materials to dentin resulted when the optimal amount of moisture was left on the surface. Overdried and overwet surfaces impaired the adhesion of these materials on the dentine surface.
From the present study, it can be summarized that surface moisture plays an important role in the adhesion of glass ionomer restorations to primary teeth. In the present study, removal of excess moisture by air drying with a three-way syringe was the best method that yielded the highest bond strength of the glass ionomer restorative material in primary teeth. Thus, we can conclude that the removal of excess residual moisture with a three-way syringe offered better longevity of the restorative material when it was used for an optimal time period. Too much and too less of drying time inadvertently affect the bonding of the restorative material on the tooth surface.
| Conclusions|| |
From the results of the study, the following conclusions can be drawn:
- Surface moisture plays a significant role in the adhesion of glass ionomer restorations to dentine in primary teeth
- In the air-dry group, the maximum shear bond strength was obtained when the specimens were dried for 5 s and least when dried for 2 s. The results were statistically significant
- In the blot-dry and suction-dry groups, the maximum shear bond strength was obtained when the specimens were dried for 10 s and the least when dried for 2 s. The results were statistically significant
- When the drying times were compared, the maximum shear bond strength values were obtained when air dried and minimum when blot dried. The results were statistically significant only in the 5 s group.
The authors acknowledge Prof. Dr. Paul K Joseph, Dr. Soney Varghese, and Dr. Jacob Kuruvilla for their valuable contributions and support during the study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]