|Year : 2017 | Volume
| Issue : 2 | Page : 64-68
The effect of cusp capping with composite resin on fracture resistance of premolars with prepared endodontic access cavities: An in vitro study
Neha Mishra1, Ritesh Garg2, Sonali Taneja3, Pragya Kumar3
1 Department of Endodontics and Conservative Dentistry, DJ College of Dental Sciences, Modinagar, Uttar Pradesh, India
2 Department of Oral and Maxillofacial Surgery, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
3 Department of Endodontics and Conservative Dentistry, ITS-CDSR, Ghaziabad, Uttar Pradesh, India
|Date of Web Publication||8-Jun-2017|
C2c-234a, Pocket 2, Janak Puri, New Delhi - 110 058
Introduction: The purpose of this study was to evaluate the effect of remaining dentinal wall thickness and the effect of remaining cusp height of endodontically treated premolars when restored with composite resin. Materials and Methods: Ninety premolars were divided into 4 test groups (n = 20) and 2 control groups (n = 5). In all groups, except the negative control group (sound teeth), standardized endodontic access cavities were prepared, pulp extirpated, mesioocclusodistal (MOD) cavities prepared and access sealed with Light Cure Glass Ionomer Cement (LC GIC). Test groups were divided as:- Cusp reduction for Groups I and II- 2.5 mm and for Groups III and IV- 1.5 mm. Dentinal wall thickness for Groups I and III- 1-1.5 mm and Groups II and IV- 2-3 mm. The groups were further subdivided into Subgroup A, restored with P60 and Subgroup B, restored with Herculite Precis. Positive control- only access cavity with no cusp reduction and restoration. Fracture resistance was assessed using Universal Testing Machine (UTM). Results: Highest fracture resistance was demonstrated by Group VI and least by Group V. Groups VI, II and I, showed statistically insignificant difference for both the composites (P > 0.05). Groups III and IV showed statistically significant difference only for Subgroup B. Conclusion: When the cusp reduction was 2.5 mm, dentinal wall thickness had no effect on the fracture resistance, for both the composites. When the cusp reduction was 1.5 mm and the remaining dentinal thickness was 1-1.5 mm, Herculite Precis showed inferior results to P60.
Keywords: Composite resin, cusp capping, fracture resistance
|How to cite this article:|
Mishra N, Garg R, Taneja S, Kumar P. The effect of cusp capping with composite resin on fracture resistance of premolars with prepared endodontic access cavities: An in vitro study. SRM J Res Dent Sci 2017;8:64-8
|How to cite this URL:|
Mishra N, Garg R, Taneja S, Kumar P. The effect of cusp capping with composite resin on fracture resistance of premolars with prepared endodontic access cavities: An in vitro study. SRM J Res Dent Sci [serial online] 2017 [cited 2017 Dec 11];8:64-8. Available from: http://www.srmjrds.in/text.asp?2017/8/2/64/207654
| Introduction|| |
Restoring endodontically treated teeth is a challenging procedure. Cusp deforms due to occlusal forces and lateral excursions, leading to tooth fracture. These failures mainly manifest more in root-canal treated teeth with mesio-occluso-distal (MOD) cavity preparation. This type of cavity configuration brings about a significant reduction in tooth strength due to the loss of marginal ridges and microfractures that are caused by applied occlusal forces.,
The traditional methods of restoring endodontic teeth include complex restorations such as bonded amalgam restorations, cast restorations, post and core, and full-coverage restorations. One of the drawbacks of the complex and indirect restorations is the considerable treatment time spent, their high cost, and delay the completion of endodontic therapy and placement of such restorations, which creates a problem of maintaining coronal seal. With advances in composite resin as minimally invasive preparation and maximal conservation of dentinal tissues, it is widely and mostly used in endodontically treated teeth.
Light cure composite resins are being widely used for the restoration of posterior teeth, not only because of their esthetic properties and adhesion to tooth structure, but also because they require minimally invasive preparation and provide maximal conservation of tooth structure, thus enhancing fracture resistance of teeth.
The clinical performance of the newer posterior composites has been significantly improved over the past decade. Two such composites, P60 (3M ESPE, St. Paul, USA) and Herculite Precis (Kerr, Sybron Dental Specialities, USA), are high strength packable composites.
Over the years, it has been seen that the remaining dentinal wall thickness also plays an important role in the restoration of endodontically treated teeth. However, very few studies have been undertaken to determine the effect of remaining dentinal wall thickness and also the effect of remaining cusp height on fracture resistance of endodontically treated teeth when restored with composite resin.
Therefore, the purpose of this study was to evaluate the effect of remaining dentinal wall thickness and the effect of remaining cusp height on fracture resistance of endodontically treated premolars when restored with composite resin.
| Methodology|| |
Ninety freshly extracted noncarious human premolars, indicated for orthodontic extraction, with buccolingual dimension of 9.5 ± 0.5 mm and centric cusp height of 7.0 mm, measured by a digital caliper, were selected. The teeth were stored in 0.1% thymol solution until use. The teeth were randomly divided into four test groups, n = 20 teeth each, and two control groups, n = 5 teeth each. In all groups, except the negative control group, standardized endodontic access cavities were prepared using a cylindrical bur (Dentsply, Maillefer) of 1 mm diameter. Pulp was extirpated and the pulp chamber was irrigated with 5 ml of 5% sodium hypochlorite solution. MOD cavities were prepared with mesial and distal margins located 1 mm above the cementoenamel junction (CEJ). Light cure glass ionomer cement (GC, Tokyo, Japan) was then placed in the canal orifice to the level of cavity floor.
The centric cusp of test groups was reduced as follows [Figure 1]:
- Group I (n = 20): Centric cusp was reduced 2.5 mm keeping the dentinal wall thickness as 1–1.5 mm
- Group II (n = 20): Centric cusp was reduced 2.5 mm keeping the dentinal wall thickness as 2–3 mm
- Group III (n = 20): Centric cusp was reduced 1.5 mm keeping the dentinal wall thickness as 1–1.5 mm
- Group IV (n = 20): Centric cusp was reduced 1.5 mm keeping the dentinal wall thickness as 2–3 mm
- In positive control group, Group V (n = 5): Only access cavity prepared with no cusp reduction and restoration
- In negative control group, Group VI (n = 5): Sound teeth were used.
Groups I, II, III, and IV were further subdivided into two subgroups of 10 samples each depending on the composite resin used for restoration.
- Subgroup A (n = 10): P60 composite resin (3M ESPE, St. Paul, USA)
- Subgroup B (n = 10): Herculite Précis composite resin (Kerr, Sybron Dental Specialities, USA).
The prepared surfaces were etched with 37% phosphoric acid for 15 s and then rinsed with water for 10 s. Adper single bond plus adhesive (3M ESPE, St. Paul, USA) was applied according to the manufacturer's instructions and cured for 10 s with a Quartz Tungsten Halogen light (Dentsply, Baar, Switzerland), with its intensity set at 600 mW/cm 2 and verified with the built-in radiometer. Composite was placed in 2 mm increments with first increment placed on the gingival floor, followed by the second increment which was added along the buccal wall in an oblique direction. The third increment was placed along the lingual wall obliquely. The final increment was added to fill the remainder of the cavity. All the increments were light cured for 20 s.
Restored specimens were then subjected to thermocycling of 500 cycles between 5°C and 55°C, with a dwell time of 15 s [Figure 2].
Fracture resistance test
A customized metal jig was prepared with its base at 30°. A compressive load was applied 30° to the long axis of the teeth until fracture, using a steel ball 3 mm in diameter, in a computerized universal testing machine. The load was applied to the triangular ridge of the palatal cusps at 1.0 mm/min crosshead speed. The force necessary to fracture each tooth was recorded in Newton. Fractures were identified as either restorable, i.e., those ending above the CEJ, or nonrestorable, i.e., those ending below the CEJ.
One-way analysis of variance with post hoc analysis (Tukey honestly significant difference) was applied to assess the significance among the various groups. Multivariate assessment was applied to assess the effect of different variables used in the study on the fracture resistance using SPSS (Statistical Package for the Social Sciences), IBM SPSS Statistics software (2015) version 15, Chicago, US.
| Results|| |
The results have been listed in [Table 1]. Group VI showed highest fracture resistance, followed by Group II, Group I, Group IV, Group III, and Group V for both the subgroups. In Groups VI, II, and I, the difference was statistically insignificant (P > 0.05). In Groups IV and III, the difference was statistically significant (P < 0.05) only for Subgroup B. Majority of the fractures were nonrestorable.
| Discussion|| |
Endodontically treated teeth are more susceptible to fracture than intact teeth. Therefore, there is the need for a restorative material that not only replaces the lost tooth structure but also increases the fracture resistance of the residual tooth and promotes effective marginal sealing.
In the present study, maxillary premolars were chosen as they present with an unfavorable anatomic shape, crown volume, and crown/root proportion, making them more susceptible to cusp fractures than other posterior teeth when submitted to occlusal load application.
Restoration of a MOD cavity in a root-canal treated premolar further poses a significant challenge. Steele and Johnson also reported that the mean fracture strength for unrestored teeth with MOD preparations was 50% less than that of unaltered premolar teeth.
The specimens were subjected to thermocycling for 500 cycles at 5°C–55°C, the temperatures simulating the extreme temperatures of oral environment. Thermocycling is an artificial aging process which increases stress, has a weakening effect on the adhesive bond of teeth, and consequently, leads to a decrease in the fracture resistance of teeth.
The results of our study showed that intact teeth (Group VI) had maximum fracture resistance. This might be because of the presence of palatal and buccal cusps with intact mesial and distal marginal ridges that form a continuous circle of tooth structure which reinforces and maintains the integrity of the tooth. The results are in accordance with many other studies.,,,
The positive control group (Group V), with no restoration in pulp chamber, demonstrated least fracture strength values. Steele and Johnson  have found that mean fracture strength for unrestored root-filled teeth with MOD preparation was 50% less than unaltered teeth.
In our study, P60 composite showed higher fracture resistance than Herculite Precis for all the groups, irrespective of the extent of cuspal reduction (2.5 or 1.5 mm) and remaining dentinal wall thickness (1–1.5 mm or 2–3 mm). This might have been because of the presence of zirconia filler particles present in P60 composite, which are responsible for its better compressive strength and higher fracture resistance. The results are in accordance with Banava and Salehyar, who reported that P60 packable composite demonstrated highest fracture resistance values of all the tested composites. Ranga et al. have stated similar results with P60 where the use of posterior composite P60 with enamel and dentin universal bonding agent gave the maximum strengthening effect in endodontically treated premolars and was as strong as normal teeth.
It was found that P60 showed higher fracture strength values, even when the cusp reduction was insufficient, i.e. 1.5 mm, and dentinal wall thickness was less, i.e., 1–1.5 mm, thus, emphasizing the importance of type of composite resin used for restoring such weakened teeth.
The results of the present study showed that 2.5 mm cuspal reduction had significantly higher fracture resistance than 1.5 mm for both the composites, when the remaining dentinal thickness was 1–1.5 mm. However, when the remaining wall thickness was 2–3 mm, the 2.5 mm cuspal reduction had significantly higher fracture resistance than 1.5 mm for Herculite Precis composite only. This might be because of the presence of 2.5 mm bulk of composite, which strengthened and reinforced the tooth. Furthermore, the reduction of the weak walls might have resulted in lower stresses at the base, thus rendering the tooth more fracture resistant. ElAyouti et al. Mondelli et al. reported that the remaining cusp height inversely influences the fracture resistance of composite restored premolars.
The results of our study showed that when the cusp reduction was 2.5 mm, dentinal wall thickness had no effect on the fracture resistance, for both the composites. This is in accordance with the study conducted by ElAyouti et al., who stated that after cusp reduction, remaining wall thickness of 1, 2, or 3 mm did not influence the fracture resistance of premolars restored with composite. Kantardzic et al. also found that after cusp reduction, cavity wall thickness showed no significant influence on the stress distribution.
However, when the cusp reduction was 1.5 mm, Herculite Precis demonstrated significantly lower fracture strength when the dentinal wall thickness was 1–1.5 mm. This might be because of the presence of very less remaining dentinal wall thickness, which was unable to provide adequate strength to the tooth. In addition, the amount of cuspal coverage provided by Herculite Precis composite resin might not have been sufficient for providing adequate strength.
In the present study, multivariate assessment revealed that the amount of cusp reduction (F = 62.003) played the most significant role on the fracture resistance of endodontically treated teeth, followed by the type of composite resin used (F = 16.232) and remaining dentinal wall thickness (F = 10.354), respectively.
| Conclusion|| |
Within the limitations of the study, following conclusions were drawn.
- P60 composite exhibited significantly higher fracture strength than Herculite Precis composite resin in all the experimental groups. Furthermore, the high strength composite P60 was able to restore teeth with insufficient dentinal wall thickness and insufficient cusp reduction
- Groups with cusp reduction of 2.5 mm demonstrated higher fracture resistance than groups with cusp reduction of 1.5 mm although the difference was significant only with Herculite Precis composite resin
- When the cusp reduction was 2.5 mm, the remaining dentinal wall thickness had no role
- Groups with remaining dentinal wall thickness of 2–3 mm demonstrated significantly higher fracture resistance than groups with remaining dentinal wall thickness of 1–1.5 mm.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]