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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 34  |  Issue : 3  |  Page : 156-161

Comparative evaluation of different access cavity designs on intracoronal bleaching of endodontically treated teeth using two different agents – An in vitro study


1 Department of Conservative Dentistry and Endodontics, Genesis Institute of Dental Sciences and Research, Firozpur, Punjab, India
2 Department of Paediatric and Preventive Dentistry, Dasmesh Institute of Research and Dental Sciences, Faridkot, Punjab, India
3 Department of Oral Pathology and Microbiology, Dasmesh Institute of Research and Dental Sciences, Faridkot, Punjab, India

Date of Submission02-Jun-2021
Date of Decision27-Nov-2021
Date of Acceptance12-Jan-2022
Date of Web Publication30-Sep-2022

Correspondence Address:
Dr. Prashant Monga
Department of Conservative Dentistry and Endodontics, Genesis Institute of Dental Sciences and Research, Firozpur, Punjab
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/endo.endo_112_21

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  Abstract 


Aim: The present in vitro study was designed to determine the effect of different access cavity designs on intracoronal bleaching of endodontically treated teeth with two different agents.
Materials and Methods: Fifty selected permanent maxillary central incisors were stained. Traditional and contracted access cavity designs and two types of bleaching agents, i.e., 35% carbamide peroxide and 35 percent hydrogen peroxide were used for the study. Color measurements were performed with a spectrophotometer: before staining (T1), after staining (T2), at 7 and 14 days (T3 and T4) post bleaching. The values were calculated and subjected to the statistical analysis.
Results: The results of our study showed that teeth in which traditional access cavity (TAC) was prepared had statistically significant better bleaching results with both 35% carbamide peroxide and 35% hydrogen peroxide than contracted access cavity design. Carbamide peroxide showed better results than hydrogen peroxide irrespective of the access cavity design, but difference was statistically nonsignificant.
Conclusion: The present study concluded that TAC design showed better results than contracted access with both carbamide peroxide and hydrogen peroxide. Whereas, when bleaching agents were compared 35% carbamide peroxide is better than 35% hydrogen peroxide irrespective of access cavity design used.

Keywords: Access cavity designs, carbamide peroxide, hydrogen peroxide, intracoronal tooth bleaching, nonvital


How to cite this article:
Talwar S, Mahajan P, Bajaj N, Monga P, Marya P, Gandhi P. Comparative evaluation of different access cavity designs on intracoronal bleaching of endodontically treated teeth using two different agents – An in vitro study. Endodontology 2022;34:156-61

How to cite this URL:
Talwar S, Mahajan P, Bajaj N, Monga P, Marya P, Gandhi P. Comparative evaluation of different access cavity designs on intracoronal bleaching of endodontically treated teeth using two different agents – An in vitro study. Endodontology [serial online] 2022 [cited 2022 Nov 26];34:156-61. Available from: https://www.endodontologyonweb.org/text.asp?2022/34/3/156/357695




  Introduction Top


One of the initial steps of root canal treatment is proper access preparation to reach pulp space which is followed by further root canal treatment procedure. Access cavity preparation in endodontic treatment is particularly important because it affects all subsequent procedures and finally the outcome. An appropriately designed access cavity assures unobstructed straight-line access to the apical third of the root canal.[1] Access cavity preparation can be done using the various types of access cavity designs. Traditional access cavity (TAC) design involves complete deroofing of the pulp chamber. While contracted access cavity design (CAC) involves partial deroofing of the pulp chamber.[2]

It has been observed that esthetics is one of the main concerns for the patient whose anterior tooth has got discolored due to trauma. Dental trauma can result in penetration and accumulation of hemoglobin in dentinal tubules which may discolor the teeth. Hemolysis of erythrocytes in the dentinal tubules is accompanied by the release of iron, which combines with hydrogen sulfate to form ferric sulfide, a black compound, responsible for the discoloration of the tooth.[3],[4] In these cases, after endodontic treatment of anterior discolored tooth, intracoronal bleaching is a preferred conservative method for improving esthetics if extracoronal restoration is to be avoided.[5]

Carbamide peroxide and hydrogen peroxide in different concentrations are most commonly used intracoronal bleaching agents. Carbamide peroxide is used at different concentrations of 10%−35%. Carbamide peroxide (CP)decomposes on contact with moisture into urea, ammonia, carbon dioxide, and hydrogen peroxide, which releases nascent oxygen needed for bleaching. Another agent used is hydrogen peroxide(HP), which is an active ingredient present in most of the currently used tooth bleaching materials. It is used in dentistry at concentrations ranging from 5% to 35%. Because of its lower molecular weight, this substance can penetrate dentin and release oxygen that breaks the double bonds of the organic and inorganic compounds inside the dentinal tubules.[6],[7]

Irrespective of the bleaching agent used, access cavity prepared should create sufficient space for the placement of bleaching agent for its effectiveness and adequate results.[4] Nowadays, there is increasing trend toward preparation of contracted access cavity designs with a motive to increase fracture resistance of tooth.[2] However, effectiveness of bleaching in teeth with contracted access cavity designs has not been adequately studied yet.[8] Therefore, present in vitro study was designed to determine the effect of different access cavity designs on intracoronal bleaching with two different agents of discolored endodontically treated teeth.


  Materials and Methods Top


Freshly extracted human permanent maxillary central incisors were collected from the Department of Oral and Maxillofacial Surgery of Genesis Institute of Dental Sciences and Research, Ferozepur. Selected teeth were extracted due to weak periodontium. The inclusion criteria included: intact crowns, radiographically visible pulp chamber and single roots with a fully formed apex. Teeth with root resorption, caries, fracture, and immature apex were excluded. Selected teeth were sectioned transversally at 15 mm from the incisal edge toward the apex. The apical end of remaining root portion was enlarged using #6 size Gates Glidden drill (Mani Inc, Japan) from the apical to coronal direction. All samples were immersed in an ultrasonic bath for 10 min containing 17% EDTA (PrevestDenPro Limited, India), followed by 3% NaOCl (Ammdent, Deccan Dental Pvt. Ltd, India) for an additional 10 min to remove pulp remnants. The samples were again placed in ultrasonic bath containing 10% sodium thiosulfate solution to neutralize NaOCl and finally rinsed under running water for 1 h.[8]

The shades of the crowns of selected teeth were recorded at this stage using the spectrophotometer (Vita Zahnfabrik H. Rauter GmbH and Co. KG, Germany) at the time interval named T1. After this, staining procedure was done. Each sample was placed in an Eppendorf tube containing 2 mL fresh bovine blood and centrifuged at 10,000 rpm for 10 min, twice a day for 9 days. Blood was replenished at the 3rd and 6th day. This allowed blood to penetrate into the dentinal tubules. The teeth were then finally washed with distilled water and the crowns polished with a rubber cup and pumice.[8] After the completion of above said staining procedure, color of each sample was evaluated again using same spectrophotometer at the time interval named T2.

Two types of access cavity designs were prepared (a) TAC design and (b) CAC design. In TAC design, access was established with Endo access bur (Dentsply, Maillefer, Ballaigues, Switzerland) to allow straight line access to the canal by removing pulp chamber roof, pulp horns, lingual shoulder of dentin, and further extending the access cavity to the incisal edge.[9] In contracted access cavity design, access was made using Endo guide-EG1A bur (SS White dental, Lakewood, New Jersey), moving the entry point away from the cingulum toward the incisal edge, 1 mm palatal to the incisal edge by creating a small triangular shape or oval-shape cavity, conserving the pulp horns and pericervical dentin and extending the cavity apically along the long axis.[10] Furthermore, two types of bleaching agents were used (1) 35% Carbamide peroxide (Opalescence Quick, Ultradent Products, South Jordan) and (2) 35% Hydrogen peroxide (Polaoffice, SDI, Australia).

The stained samples were divided into five groups of 10 each based on type of access cavity design and bleaching agent used for intracoronal bleaching.

  • Group 1: Positive control group, no access cavity preparation, and no bleaching was performed in this group
  • Group 2: TAC design was prepared and bleaching done with 35% carbamide peroxide
  • Group 3: CAC design was prepared and bleaching done with 35% carbamide peroxide
  • Group 4: TAC design was prepared and bleaching done with 35% hydrogen peroxide
  • Group 5: CAC design was prepared and bleaching done with 35% hydrogen peroxide.


In all the groups, after the completion of access cavity preparation, the apical end of the root was sealed with wax. Standardized root canal procedure was performed and obturation was done using gutta-percha cones (MetaBiomed Co. Ltd, Korea) and AH plus sealer (Dentsply, Maillefer, Ballaigues, Switzerland) using the cold lateral compaction technique. After this gutta percha was removed from coronal part up to 2 mm below the cementoenamel junction and 2 mm-thick glass ionomer cement (GIC) (3M ESPE, Dental Products, Germany) was placed as an orifice barrier just below the cementoenamel junction. Selected bleaching agent was syringed into the pulp chamber for intracoronal bleaching and the access cavity was sealed with cavity. After sealing, all samples were stored in 100% humidity at 37°C for 7 days. After the completion of this period, the color of the crowns was determined using spectrophotometer at the time interval named T3. In all the samples, access was re-established and the bleaching agent removed with air-water spray. The bleaching procedure was repeated and samples again stored in 100% humidity at 37°C for 7 more days before the second color evaluation at the time interval named T4.

Color measurements were performed at four time intervals:

  • (T1) before performing staining procedure
  • (T2) after completion of staining procedure
  • (T3) after the first session of intracoronal bleaching (7 days)
  • (T4) after the second session of intracoronal bleaching (14 days).


Statistical analysis

The comparison of prestaining values (T1) with poststaining (T2), T3 (1 week postbleaching) and T4 (2 weeks postbleaching) in Groups 2, 3, 4, and 5 was done using the paired t-test [Graph 1], [Graph 2], [Graph 3], [Graph 4].Groups 2 and 4 had statistically significant better bleaching outcomes than Groups 3 and 5 [Table 1]. When the comparison was done between Group 2 and Group 4, Group 2 showed better results, but difference was nonsignificant. Between Group 3 and Group 5, Group 3 showed better results than Group 5, but difference was nonsignificant [Table 2].
Table 1: Comparison of T4 (2 weeks postbleaching) values in Group 2, 3, 4 and 5

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Table 2: Inter-group comparison of T4 values

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  Results Top


The results of our study showed that teeth with TAC had statistically significant better bleaching results with both 35% carbamide peroxide and 35% hydrogen peroxide than contracted access cavity design. However, when comparison was done between carbamide peroxide and hydrogen peroxide as a bleaching agent, carbamide peroxide showed better results than hydrogen peroxide irrespective of an access cavity design. Difference in the result was statistically nonsignificant.


  Discussion Top


Trauma to permanent teeth may cause damage not only to hard and supporting soft tissues but also to the pulp vasculature, which may result in internal hemorrhage within pulp chamber. This mechanism leads to discoloration as already explained.

In the present study, to simulate the clinical conditions, the selected teeth were stained or discolored by following a modification of the method purposed by Freccia and Peters[11] using bovine blood. Bovine blood used was withdrawn from livestock under aseptic conditions under the supervision of veterinary officer. The blood used in our study was mixed with anti-coagulant heparin before use, similar to previous studies which also used blood mixed with anti coagulant and achieved desirable staining.[12] This method of staining is reliable, consistent, and easily reproducible.

After access preparation, intracoronal bleaching was prepared. Bleaching is defined as the lightening of the color of the tooth through the application of a chemical agent to oxidize the organic pigmentation in the tooth. The basic mechanism of bleaching agents would be oxidation, or reduction, of such pigments through the “fractioning” of the molecular chains in their configuration.[13] The bleaching process becomes feasible because of the permeability offered by the tooth structure to the hydrogen peroxide, which has the capacity to diffuse through that structure, causing either oxidation or reduction of staining molecules. In contact with the tissue, the hydrogen peroxide molecule breaks up and forms oxygen and peridroxil free radicals. Highly unstable and reactive, these free radicals can “fracture” macromolecular pigments, reducing them to progressively smaller molecules until, by diffusion, these pigments are totally removed.[14],[15] The success of bleaching therapy of tooth is directly related to the ability of the whitening substance to penetrate deep into dentinal tubules and reach the discolored molecules.[12]

This present study has compared the effect of TAC versus CAC design on intracoronal bleaching using 35% carbamide peroxide and 35% hydrogen peroxide in discolored endodontically treated teeth. Color evaluation of samples was done at different time intervals as already explained. While evaluating the effect of access designs with passage of time, color change (ΔE*) and luminosity (L*) values were recorded. ΔE* value signifies color difference between two objects and L* value indicates the level of lightness. Higher the value of ΔE*, larger the color difference which is identified by human eye.

In the present study, for TAC design, L* values significantly decreased from T1 to T2, but from T2 to T3 L* values increased. From T3 to T4, it further gets increased. There was statistically significant change in value from T2-T4. However, when T1 and T4 were compared, result of L values was almost the same. Therefore, the results concluded that the lightness values were re-established with bleaching through the TAC design.

For CAC design, L* values significantly decreased from T1 to T2, but from T2 to T3 L* values increased. From T3 to T4, it further gets increased. There was statistically significant change in value from T2-T4. However, when T1 and T4 were compared, the result of L values was different, i.e., L* value at T4 was less than T1. Therefore, results concluded that the lightness values were never re-established with the CAC design.

TAC design showed better results than CAC design may be because of sufficient removal of necrotic pulpal remnants from chamber and pulp horn areas. This design also allows ease of accessibility, better instrumentation, and minimal iatrogenic complications than contracted access,[16] whereas conservative design with minimal tooth structure removal may hinder adequate placement of bleaching agents. In addition, exposed dentinal surface area in traditional access is greater than those in contracted access permitting more exposure of bleaching agent to the tooth surface. Although the use of CAC design has shown improved fracture resistance in unrestored mandibular premolars and molars, no significant benefit has been demonstrated for maxillary incisors.[17] This conservative design permits preservation of natural tooth structure encouraging minimal invasive dentistry, but according to the results of our present study, compromised bleaching results do not consider this concept as an effective alternate to TAC. The results of our present study correlates with the results of the previous study conducted by Marchesan et al.[8] which also showed that TAC design achieved better bleaching outcome than CAC design. Teeth accessed with TAC had shown statistically significant bleaching outcomes with both 35% CP and 35% HP than CAC in our study.

When the comparison was done between Group 2 (TAC + CP) and Group 4 (TAC + HP), Group 2 showed better results than Group 4, but the results were nonsignificant. When comparison between Group 3 (CAC + CP) and Group 5 (CAC + HP) was done, Group 3 showed better results than Group 5. However, here also the difference was statistically nonsignificant. Hence, it can be inferred that 35% CP is better intracoronal bleaching agent than 35% HP when used in both types of cavity designs. Reason may be that CP penetrates dentin less readily than HP,[18] thus it may remain within dentin where it can effectively break down the chromogens more efficiently as opposed to HP that penetrates dentin more readily. Another contributing factor to the greater efficacy of CP relates to the relationship between pH and rate of reaction of the bleaching reaction; as higher the pH, the more free radicals are available for bleaching. Since pH of 35% HP gel is 3.7 and 35% CP gel is 6.5,[19] CP gel may have appropriate pH for free radical generation.

CP also produces the low levels of hydrogen peroxide diffusion into the periradicular tissues. CP breaks down approximately 12% HP, but results obtained were perhaps surprising, as it was expected that 35% HP would produce a greater bleaching effect than 35% CP. The better effectiveness of CP than HP could be because with HP there is an excess of active ingredient, which simply just diffuses unreacted through the root structure.

A root filling does not adequately prevent diffusion of bleaching agents from the pulpal chamber to the apical foramen.[20],[21] Hansen Bayless and Davis[22] in their studies indicated that a base is required to prevent radicular penetration of bleaching agents. Therefore, sealing the root filling with a base is essential, for which a variety of dental materials such as GICs, resin composites, IRM, zinc-oxide eugenol cement, etc., can be used as an interim sealing agent during bleaching techniques. In the present study, we have used GIC as a barrier to avoid leakage of bleaching agents. Rotstein et al.[23] demonstrated that a 2-mm layer of GIC was effective in preventing penetration of bleaching agents into the root canal. Thus, the use of this material as a base during bleaching presents the additional advantage that it can be left in place after bleaching and serve as a base for the final restoration.

Conventionally, we do visual assessment and color matching with sets of color tabs for shade evaluation. As spectrophotometer is considered as reference instrument in the field of color science and has been used successfully in dentistry for quantitative tooth color measurements.[24],[25],[26],[27] Spectrophotometers are considered the most beneficial, precise and flexible for color matching and measurements in dentistry. It utilizes the Commission International de I'Eclairage's (CIE) L*a*b* system. The CIE L*a*b* system is a three-dimensional uniform colored space with L* (lightness), a* (red to green), and b* (yellow to blue) parameters. Research has showed that observations by the human eye or conventional measuring techniques are 33% less accurate than the spectrophotometer with the latter showing better results almost in 93% of the cases.[25]

There are few limitations of this study. First, this study was conducted in in vitro conditions. Hence, the values of color change may vary in clinical conditions. Second, in the present study, we have used bovine blood instead of human blood, so variation related to staining can be expected. Adverse effects of bleaching such as resorption were not assessed.


  Conclusion Top


The study concluded that TAC design showed better results than contracted access with both carbamide peroxide and hydrogen peroxide. Whereas, when bleaching agents were compared, 35% carbamide peroxide is better than 35% hydrogen peroxide irrespective of access cavity design used.

Acknowledgments

The authors deny any conflict of interests regarding the publication of this article.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Krapež J, Fidler A. Location and dimensions of access cavity in permanent incisors, canines, and premolars. J Conserv Dent 2013;16:404-7.  Back to cited text no. 1
    
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Krishan R, Paqué F, Ossareh A, Kishen A, Dao T, Friedman S. Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod 2014;40:1160-6.  Back to cited text no. 17
    
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Price RB, Sedarous M, Hiltz GS. The pH of tooth-whitening products. J Can Dent Assoc 2000;66:421-6.  Back to cited text no. 19
    
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