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ORIGINAL ARTICLE
Year : 2006  |  Volume : 24  |  Issue : 3  |  Page : 122-126
 

A comparative evaluation of four restorative materials to support undermined occlusal enamel of permanent teeth


Department of Pedodontics and Preventive Dentistry, Bapuji Dental College and Hospital, Davangere, India

Correspondence Address:
A R Prabhakar
Dept of Pedodontics and Preventive Dentistry, Bapuji Dental College and Hospital, Davangere - 577 004
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-4388.27892

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   Abstract 

The purpose of this study was to test the support to undermined occlusal enamel provided by posterior restorative composite (FiltekTM P60, 3M Dental products USA), polyacid modified resin composite (F2000 compomer, 3M Dental products, USA.), radiopaque silver alloy-glass ionomer cement (Miracle Mix. GC Corp, Tokyo, Japan) and Glass Ionomer cement (Fuji IX GP). To test each material, 20 human permanent mandibular third molars were selected. The lingual cusps were removed and the dentin supporting the facial cusps was cut away, leaving a shell of enamel. Each group of prepared teeth was restored using the materials according to the manufacturer's instructions. All the specimens were thermocycled (250 cycles, 6C- 60C, dwell time 30 seconds) and then mounted on an acrylic base. Specimens were loaded evenly across the cusp tips at a crosshead speed of 5 mm /minute in Hounsfield universal testing machine until fracture occurred. Data obtained was analyzed using analysis of variance and Studentized- Newman- Keul's range test. No significant differences were detected in the support provided by P-60, F 2000, Miracle Mix or Fuji IX GP groups. The support provided to undermined occlusal enamel by these materials was intermediate between no support and that provided by sound dentin. Without further development in dental material technology and evidence of its efficacy, restorative materials should not be relied upon to support undermined occlusal enamel to a level comparable to that provided by sound dentin.


Keywords: Bonding, carious dentin, occlusion, reinforcement, undermined enamel


How to cite this article:
Prabhakar A R, Thejokrishna P, Kurthukoti A J. A comparative evaluation of four restorative materials to support undermined occlusal enamel of permanent teeth. J Indian Soc Pedod Prev Dent 2006;24:122-6

How to cite this URL:
Prabhakar A R, Thejokrishna P, Kurthukoti A J. A comparative evaluation of four restorative materials to support undermined occlusal enamel of permanent teeth. J Indian Soc Pedod Prev Dent [serial online] 2006 [cited 2019 Jul 20];24:122-6. Available from: http://www.jisppd.com/text.asp?2006/24/3/122/27892



   ntroduction Top


Enamel is the hardest mineralized structure in the body; designed perfectly by nature to endure the greatest of mechanical, thermal and chemical insults in the oral cavity. Man is yet to make a material similar to it. In addition to its esthetic qualities, natural healthy enamel is superior to most of the restorative materials available. Most of its noble features are undoubtedly related to the underlying " dentin cushion" on which it rests. In fact dentin absorbs all the shock from a variety of insults that enamel is subjected to in the oral cavity.

The sound enamel, once undermined of its dentinal bed, loses its features and just flakes away under functional load. The removal of all occlusal enamel, not supported by sound dentin has been advocated since the time of G. V. Black.[1],[2]

Studies have shown that unsupported occlusal enamel could be attached internally to a restorative material via bonding and thus reinforced.[3] This procedure showed significantly higher cuspal reinforcement than did the non-bonded procedures.[4] So the present in-vitro study was designed to test the ablity of four restorative materials having chemical or micro-mechanical bonding to tooth structure, to reinforce undermined occlusal enamel.


   Materials and Methods Top


Surgically extracted human mandibular permanent 3rd molars, with no caries, restorations or signs of fractures were selected from the Dept of Oral and Maxillofacial Surgery and stored in tap water. All the specimens were disinfected in 5% sodium hypochlorite for 15 mins and then cleaned with rubber cup, prophy brush and pumice. Mesiodistal and Buccolingual diameters were determined using a dial caliper (Mitutoyo Corp, Japan). The mean values obtained were 9.5 mm for mesiodistal and 8.6 mm for buccolingual dimensions. Samples presenting a difference of 20% from the mean were discarded leaving a total sample of 120 molars.

Cusp removal procedure: All 120 teeth thus selected were subjected to the procedure of removal of lingual cusp. A separating disk in a handheld straight hand piece with water irrigation [Figure - 1] was used and the first cut, was in a vertical direction parallel to the long axis of the tooth and placed 1 mm buccal to the central groove in the mesiodistal direction through, the mesial and distal marginal ridges, to a depth extending approximately 1 mm below cemento-enamel junction from the occlusal surface. The second cut, using the TR-24 (ISO 197/018: MANI, Japan) bur held in a friction grip airotor handpiece, began approximately 2 mm apical to the CEJ on the lingual surface of each tooth and followed an obtuse angle to join the first cut [Figure - 2].

20 teeth were randomly selected from the total sample group (after cusp removal) and labeled as Group I (positive control).

Occlusal enamel undermining procedure: On the remaining 100 teeth; coarse grit diamond (TF-13C - ISO: 197/016. MANI, Japan) was used in a high-speed hand piece with water spray to remove all, but a thin layer of the dentin in the facial cusps. The remaining layer of dentin was removed using a super fine finishing bur (TR-25EF-ISO 199/016 MANI, Japan), in a slow speed hand piece under water spray. A light brushing motion at stall out speed was used so that there was less likelihood that the remaining enamel shell would be weakened.

Visual and tactile evaluation using a magnifying glass and a graduated William's probe respectively were used to determine the dentin within the facial cusps removed and thus standardize the width of occlusal enamel table. The width of the occlusal table of the enamel shell subjected to loading was maintained between 1.0-1.5 mm.

A dial caliper (Mitutoyo Corp, Japan), was used to measure the thickness of the remaining tooth structure at the mesial, central and distal limits of the enamel shell obtained after the undermining procedure and a consistent occlusal enamel thickness between 0.8 mm to 1.2 mm was maintained [Figure - 3].

Twenty molars from the common lot were randomly selected and labeled as Group II (negative control).

The remaining 80 molars were randomly divided into four groups of 20 teeth each (Group III through Group VI).

Group III: The cavities in the 20 molars of this group were etched with 37% phosphoric acid gel and Single bond dental adhesive was applied to the walls as per manufacturer's instructions. The posterior restorative composite (FiltekTM P60, 3M Dental products USA) was applied as per manufacturer's instructions.

Group IV: A similar etching and bonding method as used in Group III was followed and the Compomer (F2000 compomer, 3M Dental products, USA.) was applied as per manufacturer's instruction.

Group V: The cavities in the 20 molars of this group were conditioned with the Dentin conditioner (GC Dental industrial Corp, Japan), as per manufacturer's instructions and radiopaque silver alloy- glass ionomer cement (Miracle Mix TM, GC Corp, Tokyo) was mixed and placed as per the manufacturer's instructions.

Group VI: A similar cavity conditioning procedure as used in Group V was followed and Fuji IX glass ionomer cement (GC Corp, Tokyo, Japan) was mixed and placed as per manufacturer instructions. Fuji varnish was applied over the restored surfaces of Group V and VI samples.

In samples of all the Groups the restorative material was inserted and contoured so that its surface was flush with the vertical cut in each molar.

All specimens were thermocycled for 250 cycles at 6oC to 60oC, with a dwell time of 30 seconds. Roots were notched and embedded in acrylic to a level approximately 1 mm apical to the lingual extent of the second cut. The acrylic was contained in a 3/4th inch diameter PVC pipe of 2 cm length to standardize the size of the base.

A flat ended rod was held vertically by a Ney surveyor and was used to position the molar during mounting so that the lingual inclines of the facial cusps were approximately horizontal, to do this; the inclines were attached to the flat end of the rod with sticky wax. The cusp ridges of the lingual inclines of the facial cusps in each specimen were then flattened slightly using a horizontally mounted separating disk to assure that the cusps would be loaded simultaneously. The inclines were then loaded to failure using Hounsfield universal testing machine [Figure - 4]. Failure was defined as the first deflection on the "stress strain chart" recorder. The results were tabulated and statistically analyzed.

Throughout the study, when the specimens were not being mounted, sectioned, treated or tested, they were stored in tap water at room temperature.


   Results Top


The present study was carried out to evaluate and compare the support of undermined occlusal enamel provided by four restorative materials in human permanent mandibular third molars. The failure load was recorded using Hounsfield universal testing machine [Figure - 4]. The recorded values were statistically analyzed using ANOVA and Newmans-keul studentized range test.

The mean failure load and standard deviation for each group were calculated. Analysis of variance (ANOVA) showed f= 9.71 P <0.01 [Table - 1], indicating a significant difference among the groups. A Studentized Newman-Keul's test showed that the mean loads required to cause failure in Groups I and II were significantly different from each other, with each being significantly different from Groups III, IV, V and VI. There was no significant difference in mean failure loads among Groups III, IV, V and VI.

Observations from Graph 1

Graph 1 shows comparison of failure load between the various experimental groups. There were no statistically significant differences in the support provided by Group III (P-60, Posterior composite), Group IV (F2000, Compomer), Group V (Miracle Mix) and Group VI (Fuji IX GP).

Observations from Graph 2

Graph 2 compares the failure load between the positive control and other groups. In comparison to the positive control Group II (negative control) showed a mean difference of 126.32 (31%), which was statistically highly significant ( P <0.01). While Group III (P-60 Posterior composite) and Group VI (Fuji IX GP) showed a mean difference of 46.95 (74%) and 51.49 (72%) respectively, that was not statistically significant. Group IV (Compomer) and Group V (Miracle Mix) showed a mean difference 59.84 (67%) and 63.72 (65 %) respectively, which was statistically significant ( P >0.05) in providing less support to undermined occlusal enamel.


   Discussion Top


Occlusal enamel that is not supported by sound dentin has the propensity to fracture during function. This is often seen in teeth with extensive carious dentinal involvement undermining the occlusal enamel. Hence it would be advantageous if the extensive caries-softened dentin could be removed by the clinician, leaving sound, uninvolved occlusal enamel intact and then replacing the lost dentin by a suitable restorative material to support and reinforce the undermined enamel. The reinforced occlusal enamel could then serve the dual purpose of restoring function and maintaining esthetics and the extent of invasive treatment needed for the tooth could be minimized. This procedure would also avoid extensive reconstruction and complete coverage restorations for these teeth.[5]

The profession has been in quest for such an adhesive material since a long time. The internal acid-etch technique offers interesting possibilities for supporting undermined enamel in posterior teeth.[3] Another suitable option available is the chemically bonding Glass-Ionomer cement and its variants. As a restorative material, glass ionomer offers the advantage of being the only material with a true chemical bond to tooth structure.[6],[7]

Mandibular molars were used in the study, as molars are most commonly affected by caries and the most frequently restored teeth. These unerupted/partially erupted third molars were not subjected to attrition; hence the occlusal enamel thickness obtained was optimal and relatively consistent.

The lingual cusps were removed as they were the non-holding cusps and were relatively smaller than the buccal cusps. Also this would facilitate in the complete removal of dentin beneath the occlusal enamel of buccal cusps.

All the samples were subjected to compressive stress in a universal testing machine (Hounsfield Corp, UK). A flat end tool was placed against the slightly flattened lingual inclines of each cusp. This was done to simulate the occlusal load on the functional cusps of lower molars i.e., buccal cusps.

Samples in all groups showed a wide range of values of failure load during testing in spite of our best efforts of standardization of the teeth, procedure of undermining occlusal enamel and the occlusal enamel thickness and width. This could be attributed to the morphological variations of shape and size commonly seen in third molars.

Limitations of in-vitro investigations is well recognized and in this case a factor, which must be taken into account, is that all the teeth were surgically extracted that had no or less exposure to oral environment. The single compressive force used in this study does not simulate the cyclical nature of mastication or parafunction. However, it serves to compare the reinforcing abilities of various adhesive restorative systems.

In our study, comparison of the failure load between the negative control group and the other experimental groups excluding Miracle Mix showed statistically highly significant ( P <0.01) difference in better reinforcement. The posterior composite group provided maximum reinforcement to the undermined occlusal enamel, followed by Fuji IX GP group and the Compomer group. However, the reinforcement provided by Miracle Mix was not highly significant ( P <0.01).

When inter comparison among the experimental groups was done, the results of our study demonstrated that posterior composite and FujiIX GP supported undermined occlusal enamel better than Compomer and Miracle Mix, even though it was statistically insignificant compared to the Positive Control group.

The physical and mechanical properties of posterior composite resins are excellent. Studies have reported the compressive strength of Filtek P60 (posterior composite) to be in the range of 360-380 MPa. The shear bond strength of posterior composites is also satisfactory (20 MPa), when cured in 2.5 mm thick increments.[8] The excellent interfacial bonding of composite to the enamel, which is obtained by the use of a Fifth Generation Dentin Bonding Agent (AdperTM Single Bond, 3M) could have also contributed to the good performance of this material in our study.

The reinforcement of undermined occlusal enamel by FujiIX GP was close to Posterior composite. Fuji IX GP is a self-adhesive restorative material having sufficient strength to dissipate stress and protect the integrity and quality of the critical tooth - restorative interface.[9] Several studies have shown that the greater reinforcing effect of the glass ionomer cement is closely related to its ability to adhere to the tooth structure.[10]

The F2000 (Compomer group) provided reinforcement intermediate to that of Fuji IX GP and Miracle Mix cement. The absence of chemical bonding between the large fluoro-silicate glass particles and resin matrix contributes to the low fracture toughness of Compomers, when compared to Composites. The absence of a true chemical bond to the tooth structure warrants the use of a dentin-bonding agent in order to provide mechanical adhesion.[11] Also in view of the poorer resistance to crack propagation, Compomers are not recommended for use in stress bearing areas. So the relatively unsatisfactory performance of Compomers in our study could be attributed to the above mentioned reasons.

The poor capability of Miracle Mix in reinforcing undermined occlusal enamel was not a surprise. The absence of interfacial bonding in Miracle Mix provides a reason why this material in spite of metal addition has not proved to be any stronger or more durable than their metal free counterparts. Studies have shown complete de-cohesion of the matrix-metal particle interface under rapid fracture conditions.[12]

Our experience with Fuji IX GP and Miracle Mix was very similar to that of Yap et al , who have shown that the properties of Fuji IX GP were significantly better than that of Miracle Mix. Hence they recommended the substitution of Miracle Mix by Fuji IX GP when ever possible.

In this study, neither Fuji IX GP (Glass Ionomer cement), P60 (Posterior composite), F2000 (Compomer) nor Miracle Mix (Metal reinforced glass ionomer), provided support for undermined occlusal enamel that was comparable to that provided by sound dentin, which is similar to results of studies conducted by Latino et al[5] and Grisanti et al .[13]

All the materials tested in our experimental group did not provide reinforcement comparable to that provided by "Sound Dentin". Dentin is a unique biologic tissue, composed of a near perfect combination of organic and inorganic constituents, along with a "fluid" component that provides the right cushioning for enamel, the hardest tissue found in the human body. No available restorative material can replace this unique creation of nature.

With future advances in dental material technology, restorative support of undermined occlusal enamel will hopefully some day be an option. Until such capability exists, unsupported occlusal enamel that is retained during cavity preparations should be viewed as a site prone for fracture during function, even with the use of adhesive restorative materials that were used in our study.

  1. The order of performance of the restorative materials in supporting undermined occlusal enamel was Posterior composite (P60)> Glass ionomer cement (Fuji IX GP) >Compomer (F2000)> Silver alloy- glass ionomer cement (Miracle Mix).
  2. Posterior composite (P-60), Compomer (F2000), Fuji IX GP and Miracle Mix, provided support for undermined occlusal enamel that was intermediate to the support provided by sound dentin and no support at all.


Without further evidence, current direct adhesive restorative materials should not be relied upon to reinforce occlusal enamel to a level comparable to the support provided by sound dentin. However results of the present study should be corroborated with further investigations to reach a definitive conclusion.

 
   References Top

1.Black GV. A work on operative dentistry. Vol 2. Medical - Dental: Chicago; 1980. p. 111.  Back to cited text no. 1    
2.Roberson TM, Sturdevant CM, Barton RE, et al . Fundamentals in cavity preparation. In : Sturdevant CM, Robertson TM, Heymann HO, Sturdevant JR, editors. The art and science of operative dentistry, 2nd ed. Mosby yearbook: St Louis; 1995. p. 306.  Back to cited text no. 2    
3.Denehy GE, Torney DL. Internal enamel reinforcement through micromechanical bonding. J Prosthet Dent 1976;36:171-5.   Back to cited text no. 3  [PUBMED]  
4.Herrin HK. Use of a posterior composite resin to restore teeth and support enamel: Report of case. J Am Dent Assoc 1986;112:845-6.  Back to cited text no. 4  [PUBMED]  
5.Latino C, Troendle K, Summitt JB. Support of undermined occlusal enamel provided by restorative materials. Quintessence Int 2001;32:287-91.  Back to cited text no. 5  [PUBMED]  
6.Mount GJ. Clinical placement of modern glass-ionomer cements. Quintessence Int 1993;22:99-107.  Back to cited text no. 6    
7.Mount GJ. Glass ionomer cements and future research. Am J Dent 1999;7:286-92.  Back to cited text no. 7    
8.Mount GJ, Hume WR. Preservation and restoration of tooth structure. Mosby Publication: 1998.  Back to cited text no. 8    
9.Powis DR, Folleras T, Merson SA, Wilson AD. Improved adhesion of glass ionomer cements to enamel and dentine. J Dent Res 1982;61:1416-22.  Back to cited text no. 9  [PUBMED]  
10.Yap AU, Chung SM, Chow WS, Tsai KT, Lim CT. Fracture resistance of Compomer and Composite restoratives. Oper Dent 2004;29:29-34.  Back to cited text no. 10  [PUBMED]  
11.Moodley D, Grobler SR, Rossoauw RJ, Oberholzer TG, Patel N. In vitro evaluation of two adhesive systems used with compomer filling materials. Int Dent J 2000;50:400-6.  Back to cited text no. 11    
12.Nakajima H, Watkins JH, Arita K, Hanaoka K, Okabe T. Mechanical properties of glass ionomers under static and dynamic loading. Dent Mater 1996;12:30-7.  Back to cited text no. 12  [PUBMED]  
13.Grisanti LP 2nd, Troendle KB, Summitt JB. Support of occlusal enamel provided by bonded restorations. Oper Dent 2004;29: 49-53.  Back to cited text no. 13  [PUBMED]  


    Figures

[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6]

    Tables

[Table - 1]


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