|Year : 2014 | Volume
| Issue : 3 | Page : 174-179
Evaluation of the effect of desensitizing agents on the retention of complete cast crowns: An in vitro study
Arun Prakash Chandrasekaran1, Nargunan Deepan2, Bharath Karikurve Rao1, Swathi Pai1, Abhay Sonthalia3, Swapna Venkatesh Bettanpalya1
1 Department of Prosthodontics, Faculty of Dentistry, Melaka Manipal Medical College, Manipal University, Manipal, Karnataka, India
2 Deepam Dental Clinic, Chengam, Tamil Nadu, India
3 Smile O Care, Howrah, West Bengal, India
|Date of Web Publication||14-Aug-2014|
Arun Prakash Chandrasekaran
Faculty of Dentistry, Melaka Manipal Medical College, Manipal University, Manipal - 576 104, Karnataka
Source of Support: None, Conflict of Interest: None
Purpose: Dentin desensitizing agents are commonly used in dental practice. But their effect on crown retention have been anecdotal. This study compared and evaluated the effect of two desensitizing agents on the retention of cast crowns cemented with three commonly used luting cements. Materials and Methods: Recently extracted 81 maxillary first premolars were prepared with flat occlusal surface, 6-degree taper and 4-mm axial height using a custom made paralleling milling device. The prepared teeth were divided into three major groups and further sub-divided into three groups each. GC Tooth Mousse and Seal and Protect were two desensitizing agents. Zinc Phosphate cement, Glass Ionomer Cement and Resin Modified Glass Ionomer Cement were the three cements used. Impressions of the prepared teeth were made and casted with a loop using base metal alloy. The desensitizers were applied on the tooth except the control group, castings were cemented, thermo-cycled and removed along the path of insertion using a universal testing machine. The results were analyzed using Kruskal - Wallis test and Mann - Whitney U test. Results: Resin Modified Glass Ionomer Cement exhibited highest retentive strength of all tested group and Zinc phosphate cement being the least. Retentive strength for Resin modified Glass Ionomer Cement was, Control>with Tooth Mousse> with Seal and protect. For Glass Ionomer Cement, Control > with Tooth Mousse > with Seal and Protect. The lowest of retentive strength was for Zinc phosphate which were Control > with Seal and Protect > with Tooth Mousse. Conclusion: The use of Tooth Mousse desensitizer significantly reduced the retention of Zinc Phosphate. Both tooth mouse and Seal and protect did not affect the retentive property of Glass Ionomer cement and Resin Modified Glass Ionomer Cement significantly, hence can be advocated to use prior to crown cementation.
Keywords: Desensitizing agents, dentin hypersensitivity, luting cements
|How to cite this article:|
Chandrasekaran AP, Deepan N, Rao BK, Pai S, Sonthalia A, Bettanpalya SV. Evaluation of the effect of desensitizing agents on the retention of complete cast crowns: An in vitro study. SRM J Res Dent Sci 2014;5:174-9
|How to cite this URL:|
Chandrasekaran AP, Deepan N, Rao BK, Pai S, Sonthalia A, Bettanpalya SV. Evaluation of the effect of desensitizing agents on the retention of complete cast crowns: An in vitro study. SRM J Res Dent Sci [serial online] 2014 [cited 2022 Dec 8];5:174-9. Available from: https://www.srmjrds.in/text.asp?2014/5/3/174/138730
| Introduction|| |
Healthy natural dentition plays a vital role in speech, esthetics and mastication. The dental health of an individual is affected due to conditions such as malocclusion, dental caries, and periodontal problems. Teeth with coronal destruction and retainers for fixed partial dentures are treated with complete cast coverage restorations.  Around 1-2 million dentinal tubules are exposed during an ideal crown preparation. Patients often experience discomfort in the tooth that is prepared either during the treatment or after the restorative procedure. , Due to exposed dentinal tubules or the chemical nature of the luting cements, about 5-24% of crowns and fixed partial dentures may in time result in pre and postoperative dentinal hypersensitivity.  This phenomenon is best explained by Brannstrom's hydrodynamic theory. He speculated that, "with any stimulus the tubular fluid is displaced. Fluid movement is conveyed to the nerve fibers in the pulp, causing stimulation that result in pain." ,
The areas of the tubules closer to the pulp chamber are wider and the fluid movement away from the pulp activates the nerves associated with the odontoblasts at the end of the tubule which may result in a pain response.  The initial low setting pH of the luting cements is the other possible causes for postoperative hypersensitivity.  The acidic nature of the cement widens the dentinal tubules and removes the smear layer. , The smear layer is the one which is present after the preparation, covers the dentinal tubules physically and seals them from outside stimuli. ,
The use of desensitizing agents after tooth preparation and before cementation of the prosthesis is advocated to reduce the risk of vital teeth sensitivity and to preserve the health of pulpo-dentinal complex. ,, There are many effectively proven commercially available desensitizing agents with seemingly varied chemical forms. Application of desensitizing agent is gaining popularity, but unfortunately their effect on the retention of the crowns has been not consistent. 
The surface property of dentin gets altered after the application of the desensitizing agent. Glass ionomer cement (GIC), resin modified GIC (RMGIC), and resin cements are formulated with adhesive properties, which interact interfacially with the tooth structure and the crown substrate to create bonds. , Desensitizers may affect the bonding mechanism and interfere with the retention of these cements. In either of these categories of cements, the application of desensitizing agents prior to cementation may have some effect on retention of the crown. The purpose of the present study is to evaluate the effect of seal and protect (SP) and tooth mousse (TM) desensitizing agents on the retention of complete cast crowns cemented using zinc phosphate cement, GIC and RMGIC.
| Materials and methods|| |
A total of 81 human premolar teeth of almost similar size were selected for the study. The roots of the premolars were notched buccolingually with a diamond point for retention. They were reinforced with 0.9 mm orthodontic wires and were mounted in auto polymerizing acrylic resin block of dimension 1 cm × 1 cm × 2.5 cm using a putty index [Figure 1].  The teeth were mounted vertically in such a way that the cemento enamel junction was 2 mm above the superior surface of the resin block.
|Figure 1: Natural teeth mounted in the polymethylmethacrylate resin blocks|
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The samples were fixed vertically in the surveying table and secured with a plaster block [Figure 2]. A high speed air-turbine hand piece (Panamax, NSK, Japan) with water spray was mounted to the movable vertical arm of the surveyor using a custom made jig, thus making it a custom made paralleling milling device. , The occlusal surface was sectioned flat with the help of small wheel diamond point. Approximately, 1-1.5 mm of axial tooth structure was prepared using a round end tapering fissure diamond point (102 Regular grit, Shofu, Japan). The vertically held diamond point gave the optimum divergence of 6-10° to the axial walls. ,, The chamfer finish line of about 0.8 mm was kept at the same level all around the tooth, so that 4 mm of axial height from occlusal surface is obtained uniformly.  The hand piece was rigidly secured with the vertical arm of the surveyor and the preparation was done by moving the surveyor base against the diamond point. All the preparations [Figure 3] were terminated in dentin.
The prepared samples were categorized into small, medium and large by measuring the buccolingual and mesiodistal width, keeping the constant axial wall height (4 mm). Randomized control was performed by selecting three samples from each category thereby forming nine clusters to get a uniform distribution of samples. Three groups (Groups 1-3) were made with a control and the two experimental desensitizers each. Each group was divided into three sub-groups (A, B, C) based on the different luting cements used for testing [Table 1].
|Table 1: Grouping of specimens and manufacturers direction for desensitizing agents|
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All the samples in each group were kept together to form a cube within an index. Impressions of the prepared teeth were made using a simultaneous dual-mix technique with an addition silicone impression material (Reprosil, Dentsply, USA). , After inspecting the impression for voids and accuracy, it was poured with Type IV gypsum (Kalrock, Kalabhai, Mumbai, India). The wax-pattern of approximately 1 mm was prepared by using blue inlay wax (Harvard, USA), to simulate a cylinder axially and flat occlusally. A 2 mm sprue wax was made into a loop and attached to the center of the occlusal surface of the wax-pattern for testing in an universal testing machine (Instron Universal Testing Machine, USA) [Figure 4]. , The wax-patterns with loops were sprued and invested with a phosphate-bonded investment (Deguvest CF; Degussa AG, Hanau, Germany) according to the manufacturer's instructions. The test copings were casted using the nickel chromium alloy (Wirolloy, Bego, Bremen, Germany) in an electronic centrifugal induction casting machine (Fornax T, Bego, Bremen, Germany). The castings were retrieved and the internal surfaces were air abraded with 100-150 μm aluminum oxide particles at 40 psi (Santer Labo 16, Confident Dental Suppliers, India). The fit of the completed castings were verified on the preparation.
|Figure 4: Wax copings prepared with a loop attached to the occlusal surface|
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Manufacturer's direction was strictly followed during the application of dentin desensitizing agent [Table 1]. All the cementations were done on the same day [Table 2], immediately following the application of desensitizing agents by a single operator using digital pressure [Figure 5]. Excess cement was removed from the margins of the casting. The test specimens were stored for 24 h at 37°C at 100% relative humidity prior to testing. ,
The crowns were subjected to a vertical dislodgement force until failure on a universal testing machine (Instron, USA) at a cross head speed of 5 mm/min. The castings were pulled along the apico-coronal axis of each tooth using a "J" hook attached to the upper member of the testing machine [Figure 6]. The force at dislodgement and debonding were recorded in megapascals and tabulated.
|Figure 6: Sample mounted for testing in Llyods universal testing machine|
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| Results|| |
Data were analyzed and compared in SPSS software version 16 IBM,USA using Kruskal-Wallis test for multiple comparison and Mann-Whitney U-test for individual comparison with P < 0.05 considered to be statistically significant. Complete failures during withdrawal of the crowns were omitted and a total of seven samples in each sub-group were considered for statistical analysis. The mean values are tabulated in [Table 3] and represented in Graph 1 [Additional file 1].
The highest mean bond strength was shown by the untreated RMGIC 537.2 MPa (C1), whereas the least bond strength was by zinc phosphate cement treated with TM 219.0 MPa (A3).
|Table 3: Mean value of bond strength for all the nine sub-groups in megapascals and the standard deviation|
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When cemented with RMGIC, the highest mean retentive values were shown by the control group 537.2 MPa (C1), which was statistically significant, followed by specimens treated with TM 528.5 MPa (C3) and the least being with SP 379.26 MPa (C2).
With GIC, the mean retentive values were between resin modified glass ionomer and the zinc phosphate. The groups treated with TM 421.46 MPa (B3) showed higher retentive values than the control 416.21 MPa (B1) and the SP group 345.49 MPa (B2). No statistical difference was noted between the tested groups.
When using zinc phosphate cement, the control (A1) showed the highest retentive values (295.12 MPa) than the TM 219.0 MPa (A3) treated groups and the SP 249.25 MPa (A2), the results were not statistically significant.
| Discussion|| |
Dentin hypersensitivity is one of the most common complaints after the crown preparation. To reduce the risk of vital teeth sensitivity and for preservation of the health of pulpo-dentinal complex an alternative approach is the concept of sealing the exposed dentinal tubules with the application of desensitizing or remineralizing agents. ,,,,,
The retentive property of the crown depends on the properties of the luting cement and also the geometry of the preparation. Desensitizing agents are generally either polymerizable or non polymerizable. Both of these types of agents do alter the surface of prepared dentin and also affect the bonding of the luting cements used during cementation thereby affecting the retention of the crown.
In day-to-day practice, GICs and zinc phosphate cements are the most commonly used cement for luting. The frequent complaint in these cements being post cementation hypersensitivity. This study becomes clinically significant as it evaluates the effect of desensitizing agent on the retention of the crown using the commonly used luting cements.
In this study, mounted teeth were prepared to receive complete cast crowns using a custom made paralleling and milling device to standardize the axial inclination of 6-10° and 4 mm axial height from occlusal surface to finish line. ,, Mausner et al. in 1996  and Swift et al. in 1997  advocated the 6-10° taper preparation, which is very much clinically achievable. The use of custom made milling device for the tooth preparation and keeping the axial height of 4 mm was advocated by several authors. ,, The SP (Dentsply Milford, USA) desensitizer is a "one step" dental product which mechanically occludes the open tubules with resin and sealing them from oral environment.  TM (GC Corporation, Japan) contain casein phosphopeptide-amorphous calcium phosphate which remineralizes the tooth structure. 
When TM desensitizer was applied, the mean retentive force to dislodge the crowns cemented with zinc phosphate significantly reduced when compared with the control. This is in conclusion with Yim et al. who stated that the bond strength of those cements which rely on the mechanical configuration of the preparation would decrease as a result of dentin treatment with desensitizers.  When SP was used as the desensitizer for the specimens cemented with zinc phosphate the mean retention values reduced compared with control, but not very significantly. A study in 1996 also concluded that zinc phosphate cement exhibited highest retentive strength without dentin treatment and resulted in the lower retention after dentin treatment.  This could be because the retention in zinc phosphate is mainly obtained by the geometry and the surface roughness of the tooth preparation. , The application of desensitizing agents creates a smooth surface over the prepared tooth, which is also in consistence with the previous studies. , Hence, we can say that for zinc phosphate cement, the application of desensitizers might result in decreased crown retention.
For the crowns cemented with GIC when TM or SP desensitizers were applied there was no significant change in the mean retentive values when compared with the untreated group. This proved that the bonding mechanism of GIC was not altered much by the application of any of these desensitizers. Hence the use of desensitizers could prove effective clinically for the crowns cemented with GIC. Swift et al.  demonstrated that there was no effect of desensitizing agents for the conventional GIC. The results obtained in this study was also consistent with Jalandar et al.  who advocated the judicious use of TM and GLUMA, Heraeus Kulzer, USA, desensitizers prior to cementation of crowns with GIC and RMGIC.
In this study, the highest bond strength was shown by the untreated RMGIC and the lowest bond strength was shown by the samples which were cemented with zinc phosphate cement after treatment with TM. The fact that the RMGIC has superior bond strength when compared with zinc phosphate cement and GIC was not surprising and was similar to previous studies. , This cement hardens by an acid base reaction between fluoroaluminosilicate glass powder and an aqueous solution of polyalkeonic acids modified with pendant methacrylate groups, and by photo-initiated or chemically initiated free radical polymerization of methacrylate units forming a stronger bond. 
When TM, which is non polymerizable was used as the desensitizing agent for the crowns cemented with RMGIC, the mean retentive force to dislodge the crowns were comparable with that of the untreated group. This signifies that the use of TM can be beneficial prior to crown cementation as it will not affect the retention. When SP, which is polymerizable was used as the desensitizing agent for the crowns cemented with RMGIC, the mean retentive values decreased when compared to the control. This was not in concurrent with the previous results and needs further investigation. Yim et al.  stated that the use of polymerizable desensitizer significantly enhanced the retentive values of RMGIC. The SP desensitizer is applied in a thin solution which is capable of penetrating the dentin and is light cured to form a strong protective coat and may work as a self-etching primer to demineralize and seal the dentin.
Crown preparations are the most common procedures in general dental practice. Desensitizing agents should be used for all vital teeth to avoid dentin hypersensitivity. Use of TM and SP desensitizers can be advocated post crown preparation and also prior to crown cementation when using glass ionomer or RMGICs to obtain good clinical results.
| Conclusion|| |
Crown preparation is a frequently performed procedure in routine dental practice. Management of post restorative sensitivity poses a major challenge to the clinician. Application of TM and SP desensitizers over the prepared tooth surface prior to crown cementation may be indicated to reduce dentin hypersensitivity. However in vivo studies are needed to prove its effects. Within the limitation of this study we conclude that.
- TM and SP desensitizers when used prior to the cementation of cast crowns with zinc phosphate cement, reduces the crown retention.
- The use of TM and SP desensitizers for the crowns cemented with glass ionomer and RMGIC did not affect the retentive properties of the cement.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3]