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Table of Contents   
ORIGINAL RESEARCH  
Year : 2012  |  Volume : 23  |  Issue : 1  |  Page : 20-25
An evaluation of retention and marginal seating of Ni-Cr alloy cast restorations using three different luting cements: An in vitro study


1 Department of Prosthodontics, Rungta College of Dental Sciences and Research Centre, Bhilai, Chhattisgarh, India
2 Department of Prosthodontics, Nair Dental College and Hospital, Mumbai, Maharashtra, India

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Date of Submission12-Jan-2010
Date of Decision27-Apr-2010
Date of Acceptance31-Aug-2010
Date of Web Publication26-Jul-2012
 

   Abstract 

Context: Clinical and laboratory studies regarding performance of recently introduced luting cements: Adhesive resin cement and resin-modified glass ionomer cement (GIC), are limited.
Aims: To compare the retention and marginal seating of Ni-Cr alloy restorations using newer luting cements: Resin-modified GIC and adhesive resin cement with those of the oldest cement, zinc phosphate.
Materials and Methods: Thirty maxillary premolars of similar sizes were prepared to receive cast metal copings. Copings were placed on the prepared teeth and the marginal opening was examined using a Nikon Measuroscope. The specimens were randomly assigned to three groups. Group I castings were luted with zinc phosphate, Group II castings luted with resin-modified GIC, and Group III castings luted with adhesive resin cement. After cementation marginal seating was measured. Tensile loads required to dislodge the crowns were obtained using MTS machine.
Statistical Analysis Used: Tukey's test, Analysis of Variance (ANOVA).
Results: For zinc phosphate cement, mean marginal seating was 31 microns. Mean retentive strength was 287 Newtons. For resin-modified GIC, mean marginal seating was 29.6 microns. Mean retentive strength was 610 Newtons. For adhesive resin cement, mean marginal seating was 49 microns. Mean retentive strength was 613 Newtons.
Conclusions: Marginal seating of adhesive resin cement was significantly greater than that of zinc phosphate and resin-modified GIC. Retentive strength of adhesive resin cement and resin-modified GIC was significantly greater than that of zinc phosphate There was no significant difference of retentive strength between adhesive resin cement and resin-modified GIC.

Keywords: Dynamic cementation, luting cement, marginal seating, retentive strength

How to cite this article:
Pattanaik BK, Nagda S J. An evaluation of retention and marginal seating of Ni-Cr alloy cast restorations using three different luting cements: An in vitro study. Indian J Dent Res 2012;23:20-5

How to cite this URL:
Pattanaik BK, Nagda S J. An evaluation of retention and marginal seating of Ni-Cr alloy cast restorations using three different luting cements: An in vitro study. Indian J Dent Res [serial online] 2012 [cited 2021 Apr 23];23:20-5. Available from: https://www.ijdr.in/text.asp?2012/23/1/20/99032
Cementation procedure is an important step in fixed restorative procedure. [1] The introduction of new adhesive techniques and materials led to the development of new dental cements with improved bond strength. Recently introduced dental luting materials include adhesive resin cement and resin-modified glass ionomer cement (GIC). Clinical and laboratory studies regarding the performance of these materials are limited. A study was carried out to evaluate the retention and marginal seating of Ni-Cr alloy restorations using newer available luting cement-resin-modified GIC and adhesive resin cement with that of the oldest cement, zinc phosphate.


   Materials and Methods Top


Mounting teeth

Thirty maxillary premolars of similar sizes were collected, washed and stored in 10% formalin solution. A mould was prepared to hold a plastic ring which was then placed on a surveying table (Ney Dental Surveyor, USA). A small plastic ring was filled with cold cure acrylic resin (DPI, Mumbai, India) dough and was kept on the mould. Tooth was mounted on the centre of the ring with help of analyzing arm. The rings were consecutively numbered and samples stored in 100% humidity except during preparation, cementation, crown removal and measurement for the seating procedure.

Tooth preparation

An aluminum attaching jig was attached to the vertical arm of the surveyor. A high-speed, high-torque air rotor hand piece (NSK Nakanishi Inc., Kanuma-Shi, Tochigi, Japan) was attached to the other end of the jig in such a manner that the bur (ManiInc, Utsunomiya, Tochigi, Japan) would remain parallel to the analyzing rod [Figure 1]. The occlusal surface was made flat; the height of the preparation was kept at 4 mm. A chamfer gingival finish line was prepared and positioned above the cemento enamel junction. The axial wall angulation was measured under a Nikon measuroscope (MM-800/LM, Nikon Corporation Instruments Company, Japan). It was maintained between 4-6 degrees.
Figure 1: Air rotor handpiece mounted on the surveyor with an aluminum jig

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Fabrication of the metal coping

Impressions of the prepared teeth were made with putty silicone and light body (Flexitime, HeraeusKulzerGmbh and Co, Hanau, Germany) and poured in die stone (Die Keen, HeraeusKulzer GmbH and Co, Hanau, Germany). A drop of wax (Schuler Dental, Ulm, Germany) was added on the buccal surface of the pattern for orientation. A round wax sprue was shaped as a loop and attached to the occlusal surface of the wax pattern to provide a connection for the tensile testing machine. Patterns were invested (Bella vest, Bego, Bremen, Germany) and casted with base metal alloy (Verabond2, Albadent, Cordelia, California, USA). The castings showed good fit on the prepared teeth [Figure 2].
Figure 2: Cast metal copings with a loop on the prepared teeth

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Cementation

The castings were seated on the tooth with a 5-kg weight; sticky wax was added at two places (mesial and distal surface) on the margin [Figure 3]. The marginal opening was examined under Nikon measuroscope at the mid-buccal and the mid-lingual position [Figure 4]. Then the specimens were randomly assigned to three groups.
Figure 3: Cast metal copings cemented by dynamic cementation procedure with a 5-kg load

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Figure 4: Marginal opening examined under Nikon measuroscope

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  • Group I- Castings luted with zinc phosphate (Harvard Dental International GMbh, Hoppengarten, Germany)
  • Group II- Castings luted with resin-modified GIC (Rely X, 3M, ESPE, St. Paul, MN, USA)
  • Group III- Castings luted with adhesive resin cement (RelyX ARC, 3M ESPE, St. Paul, MN, USA).


Cementation with zinc phosphate

Zinc phosphate was mixed on the glass slab in a powder liquid ratio of 1 g: 0.5 ml. The inner surface of the coping was coated with cement and placed over the tooth under a load of 5 kg. Initially, a stick of wood was placed on top of the coping and subjected to horizontal and vertical movement for 20 sec. Then the load remained static for 10 min.

Cementation with resin-modified GIC

Dentin conditioner (GC Corporation, Tokyo, Japan) was applied on the prepared surface for 20 sec and was rinsed thoroughly with water and dried. Two scoops of powder and two drops of liquid were placed on a mixing pad. Then it was mixed for 30 sec. The cement was then spread over the entire interior surface of the crown and the crown was seated. The same procedure was carried out as with zinc phosphate after this.

Cementation with adhesive resin cement

Adper Etchant (3M ESPE, St. Paul, MN, USA) was applied for 15 sec and was then rinsed with water. Adper Single Bond (3M ESPE, St. Paul, MN, USA) was applied and light cured for 10 sec. The cement was mixed for 10 sec and was applied evenly on the inner surface of the restoration. It was seated similarly to the other cements. The excess cement was cleaned and each margin was cured for 40 sec.

Measuring marginal seating

The cemented crowns were observed under a Nikon measuroscope. The distance between the prepared tooth margin and the apical surface of the casting margin were measured at the mid-buccal and mid-lingual position. The difference between post-cementation and pre-cementation measurements gave the marginal seating.

Measuring retentive strength of cements

The specimens were mounted on an MTS (MTS Systems Corp., Minneapolis, Minn, USA) machine using a special attachment. The attachment was placed at the lower grip and one hook was placed at the upper grip of the MTS machine. The other end of the hook was placed on the loop of the coping [Figure 5]. During testing the lower jaw moved in a downward direction. Force was applied by the testing machine at a cross-head speed of 5 mm/min. The tensile loads required to dislodge the crowns were thus obtained in Newtons.
Figure 5: The specimens were mounted on an MTS machine using a special attachment

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The following formulae were used to statistically analyze the readings obtained in the present study.

  • Mean, Standard Deviation (S.D.)
  • The Analysis of Variance (ANOVA) test
  • Tukey's test.



   Results Top


The data was tabulated and subjected to statistical analysis [Table 1]. The ANOVA test was applied to determine the variability among the different test conditions. The P value gives the level of significance of the difference. There was no significant difference in buccal and lingual pre-cementation values. There was a significant difference in the marginal seating (P<0.001) [Figure 6] and retentive strength (P<0.001)) [Figure 7] of the three cements.
Figure 6: Comparison of all three cements for mean marginal seating

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Figure 7: Comparison of all three cements for retentive strength

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Table 1: Marginal seating (microns) and retentive strength (Newtons) of all three cements

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Tukey's test was applied to compare zinc phosphate and resin-modified GIC. There was no significant difference in marginal seating. The retentive strength of resin-modified GIC was greater than that of zinc phosphate and was significant (P<0.001). Tukey's test was applied to compare zinc phosphate and adhesive resin cement. Marginal seating for adhesive resin cement was significantly greater (P<0.001) than that of zinc phosphate. Retentive strength of adhesive resin cement was greater than that of zinc phosphate and was significant (P<0.001). Tukey's test was applied to compare resin-modified GIC and adhesive resin cement. There was no significant difference in retentive strength. Marginal seating of adhesive resin cement was significantly greater (P<0.001) than that of resin-modified GIC. In case of resin-modified GIC and adhesive resin cementthere were 90 percentage dentinal fractures. In case of zinc phosphate cement there was failure both at the cement-metal and cement-tooth interfaces [Figure 8].
Figure 8: Specimens after tensile strength test

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   Discussion Top


In this study the cervico-occlusal height of the preparation was maintained at 4 mm, with a convergence angle of 4-6 degrees. Any influence of roughened tooth surfaces caused by increasing attrition of the bur as affecting retention was eliminated by using new diamond burs for each test group. Other than taper, there was no retentive component in the prepared surface. The teeth included in the study were comparable in the labio-lingual and mesio-distal dimension. The impressions were registered in addition silicone putty and light body impression materials. Addition silicone is the most dimensionally stable and accurate of the existing impression materials. Patterns were invested immediately. All precautions were taken to standardize all the steps in castings. The tooth preparation factor and the casting factors were standardized. Thus, the differences in retentive value would be due to the type of cement used. A base metal alloy was selected for this study because this alloy has achieved widespread application in the fabrication of fixed partial denture. The resultant castings from this study were within the range of acceptability. A margin is considered to be open if the gap is greater than 50 μm. [1] In all the castings included, marginal gap was less than 50 μm. Those castings demonstrating marginal gap >50 μm were discarded.

Three variations of the cementation technique have been investigated in an effort to obtain improved seating: Vibration, the site of application of cement and magnitude of cementation pressure. Ishikirima [2] found that the cement painted on the inner walls of the crown promoted a better fit than when the crown was completely filled with cement. Ernest, [3] Pegoraro, [4] Gorodovsky [5] applied cement on the inner walls of the crown. Fusayama [6] and Jorgensen [7] reported that the relationship between cement thickness and compressive force applied during cementation was in the form of a hyperbolic curve. Jorgensen [7] noted that an increase in load above 5 kg had little effect on the result. Vibration improved the fitting of crowns. [8] In this study castings were cemented with vibration using a stick. The cement was applied on the inner surface of the castings. Dynamic seating methods generally are superior to static loading and significantly reduce resulting film thickness. [9],[10] The retentive strength of resin-modified GIC and adhesive resin cement was found to be more than zinc phosphate. The results were in accordance with the results of Zidane, [11] Tuntiprown, [12] and Ergin. [13] There was no significant difference in the retentive strength between resin-modified GIC and adhesive resin cements. This was in accordance with the results of Burrow, [14] and Mitchell. [15]

Smear layer consists of coagulated proteins formed from the denaturation of the collagen due to heat formed when using rotary instrument. Inorganic particles originating from the dentin and enamel are present in this pellicle. [10] The treatment of the dentin smear layer before cementation may be important to clinical success. A 1 to 2-μm-thick smear layer is formed during tooth preparation with smear plugs (below the smear layer) usually extending 1 to 2 μm into the dentinal tubules. [10] The smear layer reduces dentin permeability and limits the strength of the dentin bonding agents because of relatively low cohesive forces holding the smear layer together and to the dentin. Its removal results in higher bond strength of dentin adhesives. Resin-modified GIC powder contains fluoroalumino silicate glass and liquid contains polycarboxylate acid modified with pendant methacrylate; hydroxyethyl methacrylate (HEMA). The chemical reaction is an ionic one between calcium of hydroxy apatite and carboxyl ion of polyacrylic acid. Application of polyacrylic acid liquid to the preparation followed by thorough rinsing with water was suggested to achieve a clean surface. Adhesive resin cement contains BIS GMA and triethylene glycol dimethacrylate (TEGDMA) polymer. Scotchbond etchant contains 35% by weight phosphoric acid. Single-bond dental adhesive contains 2-hydroxyethyl methacrylate (HEMA), BIS GMA. If bonding is attempted directly to the smear layer, tensile failure can occur between it and the cement, or within the layer itself. Therefore, to enhance bonding to the tooth structure, the tooth preparation is etched. [10] Etching of both dentin and enamel has been described by Fusamyama [16] in 1979. Acid etching leaves a layer of dentin-anchored collagen fibers on the surface of the demineralized dentin. Hydrophilic resins infiltrated that layer to form a hybrid layer consisting of resin-infiltrated dentin. [17]

The primary retention of a cast restoration cemented with zinc phosphate is influenced by the configuration of the tooth preparation, namely, taper, the length and surface area. [18] The luting ability of the cement is considered a secondary role in retention, which is achieved mainly from mechanical interlocking. [18] It relies on penetration into surface irregularities. Cavity varnish prevents seepage through the dentinal tubule and it reduces micro leakage. The distribution of the mode of failure revealed that fracture occurred at both the cement-metal and cement-tooth interfaces for copings luted with the zinc phosphate cement. In no situation was the cement observed to have completely remained on the prepared tooth. A cohesive dentinal fracture for copings cemented with resin-modified GIC and adhesive resin cement was found in 90% cases. The bond of adhesive resin cement to the tooth structure appeared to be a superior bond. There was no significant difference in the marginal seating of the Ni-Cr alloy cast restoration when luted with zinc phosphate and resin-modified GIC. Marginal seating of the Ni-Cr alloy cast restoration when luted with adhesive resin cement was greater than both the other cements. These results were in accordance with those of White SN, [18] and Kipnis. [19] The nature of the setting reaction affects the film thickness. [20] The faster the cement sets, the less the time available for flow to achieve optimal film thickness. Zinc phosphate, GIC set slowly because of acid base reactions between liquid and filler particles. [21] Resin cements set by polymerization of monomer or oligomers to form large high molecular weight polymers. The viscosity of the liquid increases and it does so at an exponential rate, [20],[21] entrapping the filler particles before they can be reorganized to achieve their minimal film thickness.

A "self-etching" phenomenon was suggested in which the highly acidic unset aqueous luting agents dissolved the surface dentin. [20] This phenomenon in combination with low film thickness of glass ionomer and zinc phosphate created only limited marginal opening. The setting reaction of resin-modified GIC differs from resin cement in that glass filler particles react with the liquid during setting [10] and there is a longer working time to enable escape of excess cement. Both adhesive resin cement and resin-modified GIC cements showed dentinal fracture in 90% of samples examined. This creates concerns about the ease of removing castings cemented with these cements on ideal preparation. Also, these agents would improve the retention of castings on tooth preparations compromised by excess taper or lack of adequate length. When resinous luting agents are used for cementation of a fixed partial denture, the laboratory procedure should also be modified to compensate for their greater film thickness. [20],[21] For intra-coronal castings, the investment expansion ratio could be adjusted, for extra-coronal castings additional die spacer could be applied. The dentist must act quickly when manipulating resin-based luting agents. The castings should not be overfilled before seating and heavy pressure should be applied. [21] Further studies can be carried out in tooth preparations compromised by excessive taper or by lack of adequate length. Despite recent research and development on cements the evaluation of the clinical performance of cements is still difficult. Laboratory test methods do not necessarily simulate the clinical behavior and response of cement. Further in-vivo study is suggested to establish a correlation with the results obtained with the in-vitro study.


   Acknowledgment Top


Department of Mechanical Engineering, Department of Metallurgical Engineering, IIT Mumbai.

 
   References Top

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9.Rosenstiel SF, Gegauff AG. Mixing variables of zinc phosphate cement and their influence on the seating and retention of complete crowns. Int J Prosthodont 1989;2:138-42.  Back to cited text no. 9
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14.Burrow MF, Nopnakeepong U, Phrukkanon S. A comparison of microtensile bond strengths of several dentin bonding systems to primary and permanent dentin. Dent Mater 2002;18:239-45.  Back to cited text no. 14
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15.Mitchell CA, Abbariki M, Orr JF. The influence of luting cement on the probabilities of survival and modes of failure of cast full coverage crowns. Dent Mater 2000;16:198-206.  Back to cited text no. 15
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Correspondence Address:
Bikash K Pattanaik
Department of Prosthodontics, Rungta College of Dental Sciences and Research Centre, Bhilai, Chhattisgarh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.99032

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
 
 
    Tables

  [Table 1]

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