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ORIGINAL ARTICLE
Year : 2020  |  Volume : 23  |  Issue : 1  |  Page : 1-6

Marginal adaptation and fracture resistance of feldspathic and polymer-infiltrated ceramic network CAD/CAM endocrowns for maxillary premolars


1 Department of Prosthodontics, Faculty of Dentistry, Zonguldak Bülent Ecevit University, Zonguldak, Turkey
2 Department of Prosthodontics, Faculty of Dentistry, Gazi University, Ankara, Turkey

Date of Submission25-Apr-2019
Date of Acceptance21-Aug-2019
Date of Web Publication10-Jan-2020

Correspondence Address:
Dr. G Saglam
Department of Prosthodontics, Faculty of Dentistry, Zonguldak Bulent Ecevit University, 67600 Kozlu, Zonguldak
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_231_19

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   Abstract 


Objective: The aim of this study was to evaluate the marginal adaptation and fracture resistance of feldspathic and Polymer-Infiltrated Ceramic Network (PICN) CAD/CAM endocrowns for maxillary premolars. Materials and Methods: Twenty extracted human permanent maxillary premolars were randomly divided into two groups (n = 10); Group CEREC (GC), which was produced by feldspathic ceramic and the Group Enamic (GE), which was produced by PICN. All teeth were endodontically treated and decoronated horizontally at 2 mm above the cemento-enamel junction. Endocrown preparations were done with 4 mm depth into the pulp chamber. Endocrowns were manufactured using CAD/CAM from ceramic blocks. Following adhesive cementation, all specimens were subjected to thermocycling. Marginal adaptation evaluated under SEM at 200 × magnification. Each specimen was fixed in a universal testing machine and a compressive load was applied at 45° to long axis of the teeth until failure. Failure load was recorded and failure modes were evaluated. Statistical analyses were performed with SPSS 19.0 software and data were compared using Mann-Whitney U test. Results: There were no significant differences in the marginal adaptation between two groups (P > 0.05). GE presented significantly higher fracture resistance when compared to GC (P < 0.05). Failure pattern was similar and characterized by the tooth-ceramic fracture on the force-applied side. Conclusions: CAD/CAM fabricated feldspathic ceramic and PICN endocrowns provide sufficient marginal adaptation, but the PICN endocrowns shows higher fracture resistance than the feldspathic ceramic endocrowns.

Keywords: Endocrown, feldspathic ceramic, fracture resistance, marginal adaptation, polymer-infiltrated ceramic network


How to cite this article:
Saglam G, Cengiz S, Karacaer O. Marginal adaptation and fracture resistance of feldspathic and polymer-infiltrated ceramic network CAD/CAM endocrowns for maxillary premolars. Niger J Clin Pract 2020;23:1-6

How to cite this URL:
Saglam G, Cengiz S, Karacaer O. Marginal adaptation and fracture resistance of feldspathic and polymer-infiltrated ceramic network CAD/CAM endocrowns for maxillary premolars. Niger J Clin Pract [serial online] 2020 [cited 2020 Jan 18];23:1-6. Available from: http://www.njcponline.com/text.asp?2020/23/1/1/275616




   Introduction Top


An endodontically treated tooth with severe coronal hard tissue loss becomes predisposed to biomechanical failures and is usually restored with a full crown and a postcore.[1],[2] However, intracanal posts have been reported to only increase the retention of the crown prosthesis and that the preparation for postplacement weakens the tooth structure and increases the fracture risk.[3],[4],[5]

With the development of adhesive dentistry and restorative materials, endocrown restorations have become popular in recent years. An endocrown is a “monoblock” restoration that consists of a crown part and a central retainer inside the pulp chamber. It provides retention by using the pulp chamber and the cavity margins to achieve stability with adhesive cementation.[6] Previous studies reported that endocrown restorations exhibited comparable fracture load values compared with conventional crowns and provided adequate function and esthetics while protecting the tooth integrity of molars and premolars.[7],[8] According to a finite element analysis, endocrowns showed lower stress values than conventional crowns, and their resistance to stress was better than that of conventional crowns with post systems.[9],[10] Moreover, endocrowns have been recommended for the restoration of teeth with calcified or curved root canals that make postcore restoration impossible.[11]

In parallel with the advances in adhesive and digital dentistry, endocrowns, which are manufactured by CAD/CAM, have been frequently used to restore endodontically treated teeth. A more acceptable marginal fit, appropriate strength, and esthetics of restoration can be achieved through CAD/CAM technologies.[12] Moreover, using CAD/CAM for endocrown restoration has the advantage of minimizing chair time.[13] CAD/CAM endocrowns can be created from feldspathic ceramic or reinforced ceramic blocks.[14]

As adhesive bonding affects endocrown retention, the use of prosthetic materials that are bonded to tooth tissues is important. Glass ceramic and feldspathic ceramic endocrowns were investigated in several clinical studies.[7],[15],[16],[17] Glass ceramics can be etched like feldspathic ceramics and bonded to the resin cement effectively with hydrofluoric acid and silane application.[18] Moreover, CAD/CAM composites, which have been recently released to the market, have been recommended for manufacturing monolithic cemented restorations. CAD/CAM composites are divided into two types, namely, hybrid and polymer-infiltrated ceramic network (PICN) materials.[19] A PICN material consists of 75% glass ceramic and dimethacrylate monomer polymerized at high pressure and temperature by volume, therefore combining the properties of ceramic and polymer.[20] A PICN material contains a hybrid network structure with two interpenetrating phases throughout the microstructure. It comprises an 86% inorganic phase, including feldspathic ceramic as the dominant phase, and a 14% organic phase composed of dimethacrylates. The dominant ceramic network provides resistance to deformation and wear, but it is susceptible to fracture.[21]

The clinical success and quality of a dental restoration depend on many factors, such as esthetic value, resistance to fracture, and marginal adaptation. The marginal adaptation of restoration is an important factor to achieve clinical success because inadequate adaptation causes dental caries due to plaque accumulation, microleakage, and endodontic or periodontal inflammation.[22],[23] This in vitro study aimed to investigate the marginal adaptation and fracture resistance of feldspathic and PICN CAD/CAM endocrowns for maxillary premolars.


   Materials and Methods Top


The brands, manufacturers, types, compositions, and batch numbers of the materials used in the study are shown in [Table 1]. Twenty extracted human permanent maxillary premolars with a similar size and morphology, free of restorations, caries and root canal treatment were selected for the study. The organic tissue and other remnants, such as dental plaque or calculus, were removed ultrasonically and the teeth were stored in distilled at 37°C water. Endodontic access cavities were prepared, and the working length was determined. Then, the root canals were prepared with nickel-titanium rotary instruments (ProTaper Universal, Dentsply, Maillefer, Ballaigues, Switzerland). Irrigation was performed with 1% sodium hypochlorite solution. The root canals were dried and filled with a sealer and gutta-percha. After the endodontic treatment, the teeth were decoronated horizontally at 2 mm above the cemento-enamel junction.
Table 1: The brands, manufacturers, types, compositions and batch numbers of the materials used in the study

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Endocrown preparations were done by one operator with a 4 mm depth into the pulp chamber. The depth of the cavity was standardized with occlusal reduction burs. The cavity walls of the pulp chamber were prepared with a 4° inclined diamond chamfer burs, which expanded toward the occlusal. The prepared specimens were scanned using the CEREC scanner (Cerec Omnicam, Sirona Dental Systems, Bensheim, Germany). The teeth were randomly divided into two groups according to the endocrowns produced by different restorative materials: GC, which was produced by feldspathic ceramic (CEREC Blocks, Sirona Dental Systems, Bensheim, Germany), and GE, which was produced by PICN (Vita Enamic, Vita Zahnfabrik, Bad Säckingen, Germany) (n = 10). Endocrowns were designed with CEREC software version 4.3 (Sirona Dental Systems, Bensheim, Germany) and milled (Cerec MC XL, Sirona) according to the original anatomy that was previously stored in the database [Figure 1].
Figure 1: Design of endocrown with the CEREC software (version 4.3, Sirona Dental Systems)

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After being removed from the milling unit, the endocrowns were placed into the cavities 2and the fit of restoration were checked. The finishing and polishing processes of the restorations were performed with Al2O3 coated disks (Sof-Lex Spiral, 3M ESPE, St. Paul, USA) and a ceramic polishing set (EVE Diapol, EVE Ernst Vetter GmbH, Pforzheim, Germany). The enamel and dentin surfaces of the prepared teeth were etched with 37% phosphoric acid (Total Etch, Ivoclar Vivadent, Schaan, Liechtenstein) for 30 s and 15 s, respectively. Then, the cavity surfaces were rinsed for 20 s and dried with air. A primer (Syntac Primer, Ivoclar Vivadent, Schaan, Liechtenstein) was applied for 15s and allowed to dry for 10 s. Adhesive resin (Syntac Adhesive, Ivoclar Vivadent, Schaan, Liechtenstein) was applied for 10s and spread gently with air. The cementation surface of all restorations was etched with 5% hydrofluoric acid (IPS Ceramic Etching Gel, Ivoclar Vivadent Schaan, Liechtenstein) for 60 s and then rinsed with water for 30 s, dried and silane coupling agent (Monobond-S, Ivoclar Vivadent, Schaan, Liechtenstein) was applied for 60 s. A bonding agent (Heliobond, Ivoclar Vivadent) was applied to restoration and teeth cementation surfaces and air blown to a thin layer for 15 s.

All specimens were luted with dual-cure resin cement (Variolink II, Ivoclar Vivadent, Schaan, Liechtenstein) under a constant load and excess material was removed. All specimens were subjected to thermocycling (Mod Dental, Esetron, Ankara, Turkey) for 5,000 times between 5°C and 55°C with a dwell time of 20 s in each bath.

Marginal adaptation was evaluated with scanning electron microscopy (SEM) (Quanta FEG 450 Oxford Instruments, Netherlands) under 200 × magnification, and a marginal gap was measured using the software [Figure 2]. Marginal gap was measured from five different points per each side of the sample, and thus 20 measurements in total were taken from each sample. The image of the measured surfaces and the marginal gap values were recorded.
Figure 2: (a) SEM arrangement for marginal gap measurement of groups, (b) SEM image (×200) of distal margin of a specimen. D dentin, LC luting cement, E endocrown

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Specimens were placed in a silicone mold and embedded in autopolymerizing acrylic resin (ProBase Cold, Ivoclar Vivadent, Schaan, Liechtenstein) at a height of 2 mm from the cemento-enamel junction with long axis perpendicular to the ground plane. Each specimen was fixed in a universal testing machine (Lloyd LRX, Lloyd Instruments, Fareham, UK) for the fracture resistance test [Figure 3]. A compressive load was applied at a crosshead speed of 1 mm/min with 45° to the long axis of specimens at the buccal incline of the palatinal cups using a 2.5 mm diameter stainless steel round load cell until failure. The maximum force at which fracture occurred was recorded in Newton (N). The failure load values were recorded, and the failure types were evaluated with a stereomicroscope (Leica EZ4 D, Leica Microsystems, Wetzlar, Germany). The failure types were classified as follows; Type I: Cohesive failure in the endocrown material, Type II: Adhesive failure between the endocrown material and the dentin, Type III: Cohesive failure in the enamel/dentin, Type VI: Fracture extending to the root.[24]
Figure 3: Position of the specimen fixed in universal testing machine for the fracture resistance test

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Statistical analyses were performed with SPSS 19.0 (SPSS Inc., Chicago, IL, USA) software. The Mann–Whitney U test was used to compare the two groups in terms of marginal adaptation and fracture resistance. The variables were expressed as the mean ± standard deviation. The Spearman correlation analysis was performed to determine the relationship between the continuous variables. The Chi-square test was used to evaluate the fracture types. A P value of less than 0.05 was considered statistically significant for all tests.


   Results Top


The mean, standard deviation, and minimum and maximum values for both marginal gap and fracture strength of two investigated CAD/CAM blocks are presented in [Table 2]. No significant differences were found in the marginal adaptation between the two groups (P > 0.05). The GE (434.56 ± 134.51 N) presented a significantly higher fracture resistance than the GC (236.29 ± 32.12 N) (P < 0.05). Failure modes are presented in [Table 3]. The failure types were mainly cohesive failure in the endocrown material for the GC. The failure types of the GE group were characterized by cohesive failure in the enamel/dentin. No correlation was found between the marginal adaptation and the fracture resistance of CAD/CAM-fabricated feldspathic ceramic and PICN endocrowns (P > 0.05).
Table 2: Marginal gap and fracture strength results (mean±standard deviation, minimum, maximum) (Newton) of experimental groups

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Table 3: Failure modes of two groups

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   Discussion Top


The marginal adaptation and fracture resistance of feldspathic and polymer-infiltrated ceramic endocrowns for the restoration of maxillary premolars were evaluated in thisin vitro study. The reason for using premolar teeth in the present study is that the application of monochromatic restorations to the upper premolars may require esthetic adjustments. Moreover, mesio-distal furcations and right-angled occlusal anatomy between the cusps make these teeth susceptible to vertical fractures in the mesio-distal direction.[25]

In the present study, the periodontium around the roots was not stimulated. Nevertheless, teeth were embedded into acrylic resin, with the vertical distance between the cemento-enamel junction and the acrylic resin level set to 2 mm, to simulate the alveolar bone. The simulated periodontium is necessary to mimic the clinical situation inin vitro tests of full ceramic bridges because the connector increases the tensile forces in the gingival part of the region. However, some disadvantages of coating the roots with silicon or different material in single crowns have been reported.[26] During the fracture test, the movement of specimens according to the ligament simulation material can change the fracture resistance results and failure modes positively.[27]

Different techniques, such as digital photography, stereomicroscopy, SEM, and micro-computed tomography, are used to measure the marginal discrepancy.[14],[28],[29],[30] SEM evaluation was used for the marginal discrepancy measurement in the present study. Previous studies reported that using SEM is one of the most reliable and realistic methods for evaluating the marginal adaptation of indirect restorations.[31] In this method, the measurement of the marginal discrepancy can be performed in a short time period with low cost because processes such as cross-section or replica preparation are not required for the sample. Additionally, the absence of intermediate stages reduces error risks.[32]

According to the results of the present study, no significant difference was observed between the GC and GE in terms of the marginal discrepancy. The marginal discrepancy values were found within clinically acceptable limits in both groups. McLean and von Fraunhofer reported that the clinically acceptable range of a marginal gap limit is less than 120 mm.[33] In the present study, the mean marginal gap values for the GC and GE were 83.34 μm and 69.70 μm, respectively. In the literature, no study has been found to compare the marginal adaptation of feldspathic ceramic and PICN endocrowns. However, consistent with our study, Yıldırım et al.[30] evaluated the marginal adaptation of three different hybrid and nanoceramic crowns, including PICN, and found that the marginal discrepancy values of PICN and others were clinically acceptable.

Many factors affect the fracture strength or failure modes, and the force-loading method is one of these factors. In the present study, occlusal loading was applied at an angle of 45° to the long axis to mimic the loads in both lateral and long-axis directions. Similarly, Gou et al.[34] applied force at an angle of 45° to the long axis in their study that compared the fracture strengths of endocrown and glass fiber postcore restorations. The buccal face of the lingual tubercle was used instead of the central fossa for the loading position to simulate the clinical situations.

In complicated restorations with multiple interfaces, many factors affect the mechanical behavior of the tooth-restoration system. Factors such as thickness of the restorative material, elastic modulus differences among the restoration material, adhesive cement, and dentin, quality of the adhesive surfaces between these layers, bonding strength and the presence of microleakage play a role in the behavior of these restorations.[35] According to the results of the present study, polymer-infiltrated ceramic endocrowns showed a significantly higher fracture resistance than the feldspathic ceramic endocrowns. These results are consistent with those of previous studies comparing these two materials in different restoration types.[36],[37] Kanat-Ertürk et al.[37] compared the fracture strength of different endocrown materials, including feldspathic ceramic and PICN materials, with different preparation depths. Similar to the present study, they reported that feldspathic ceramic showed significantly lower fracture strength than PICN restorations.

The fracture modes of each group were also analyzed in the present study. According to the results, the GC presented mainly cohesive failure in the restorative material. In the GE, cohesive failure in enamel/dentin was mainly observed. These two failure modes were repairable in which the re-treatment of the restoration is possible.[24],[38]

This study has its limitations. First, this study used only one type of adhesive and bonding cement system. Using different systems may lead to different results. Second, many new materials are available in the market for use in CAD/CAM dentistry. Therefore, future studies should also focus on examining the fracture strength and marginal adaptation of premolar endocrowns manufactured with different materials.


   Conclusion Top


Restoration of endodontically treated premolars with excessive coronal hard tissue loss is a challenge in restorative dentistry because of having a higher risk for biomechanical failure. CAD/CAM fabricated endocrowns are an option for restoration of endodontically treated teeth but their use on premolars must be evaluated carefully. Feldspathic ceramic and PICN endocrowns manufactured by CAD/CAM seems to be promising for clinical application. Both CAD/CAM fabricated feldspathic ceramic and PICN endocrowns provide clinically acceptable marginal adaptation, but the PICN endocrowns shows higher fracture resistance than the feldspathic ceramic endocrowns.

Presentation at a congress

This study was presented as poster presentation at 22nd BaSS Congress 4-6 May 2017 in Thessaloniki, Greece.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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