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ORIGINAL RESEARCH  
Year : 2021  |  Volume : 24  |  Issue : 2  |  Page : 190-194
Comparative evaluation of marginal and internal fit of endocrowns using lithium disilicate and polyetheretherketone computer-aided design - computer-aided manufacturing (CAD-CAM) materials: An in vitro study


Department of Prosthodontics and Crown and Bridge, MA Rangoonwala College of Dental Sciences and Research Centre, Pune, Maharashtra, India

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Date of Submission24-Oct-2020
Date of Decision17-Jan-2021
Date of Acceptance19-Feb-2021
Date of Web Publication09-Oct-2021
 

   Abstract 


Purpose: To evaluate the marginal and internal fit of endocrowns with different computer-aided design/ computer-aided manufacturing (CAD-CAM) materials by measuring them with a stereomicroscope (μm).
Materials and Methods: A mandibular first molar typodont tooth was prepared to receive an endocrown. The preparation was scanned using an extra-oral scanner. Endocrowns (n = 20) were fabricated using lithium disilicate (IPS e. max CAD LT block; CEREC Ivoclar Vivadent, Liechtenstein) and polyetheretherketone (PEEK) (breCAM. BioHPP®; Bredent, UK) using CAD-CAM technique. Marginal gap was evaluated using a stereomicroscope at the midpoint of all four surfaces (mid buccal, mid lingual, mid mesial, mid distal). This was followed by sectioning of the endocrowns in a sagittal plane along with the prepared tooth to evaluate the internal fit at four different points (A, B, C, D) using a stereomicroscope. Statistical analysis was performed using one-way analysis of variance test.
Results: Mean values of marginal gap of lithium disilicate and PEEK endocrowns are 56.6 ± 6.1 μm and 81.3 ± 10.1 μm, respectively. Mean value internal gaps of lithium disilicate and PEEK endocrowns are 158.2 ± 11.1 μm and 199.1 ± 13 μm, respectively. Results in the present study have shown that the marginal and internal fits of lithium disilicate endocrowns are superior to that of PEEK endocrowns.
Conclusions: Based on the outcomes of this in vitro study, the marginal and internal fit of lithium disilicate endocrowns is better than PEEK endocrowns. The marginal gap clinically acceptable is <120 μm. The marginal gap values recorded in this study are within the acceptable range for both materials.

Keywords: Accuracy; computer-aided design; computer-aided milling; crown; endodontically treated tooth

How to cite this article:
Godil AZ, Kazi AI, Wadwan SA, Gandhi KY, S. Dugal RJ. Comparative evaluation of marginal and internal fit of endocrowns using lithium disilicate and polyetheretherketone computer-aided design - computer-aided manufacturing (CAD-CAM) materials: An in vitro study. J Conserv Dent 2021;24:190-4

How to cite this URL:
Godil AZ, Kazi AI, Wadwan SA, Gandhi KY, S. Dugal RJ. Comparative evaluation of marginal and internal fit of endocrowns using lithium disilicate and polyetheretherketone computer-aided design - computer-aided manufacturing (CAD-CAM) materials: An in vitro study. J Conserv Dent [serial online] 2021 [cited 2021 Nov 30];24:190-4. Available from: https://www.jcd.org.in/text.asp?2021/24/2/190/327854



   Introduction Top


The restoration of severely damaged endodontically treated teeth still remains a challenge in restorative dentistry. The stiffness and fracture resistance of endodontically treated teeth is reduced mainly due to the loss of structural integrity associated with caries, trauma, and extensive cavity preparation; rather than dehydration or physical changes in the dentin.[1] It has been observed that the use of intracanal retainers only promoted retention of the prosthetic crown. Posts have known to weaken an abutment root because of the forces acting on it which can eventually fracture. Furthermore, the invasive nature of this type of restoration often excludes the possibility of further intervention. Contrastingly, in an endocrown, occlusal stresses will be resisted by the cross-sectional area of tooth/core material located theoretically at the level of the crown or ferrule margin, with minimal or no stress put on the tooth root.[2],[3]

In 1995, Pissis, described the monoblock technique which was the forerunner of the endocrown. Bindl and Mormann were the first to describe the term “Endocrown” in 1999 as an adhesive monolithic ceramic restoration anchored in the pulp chamber, exploiting the micromechanical retention properties of the pulp-chamber walls.[4] The results of clinical and in vitro studies have shown that endocrowns are an excellent treatment solution for extensively damaged endodontically treated teeth. Excellent survival rates, good clinical performance, and fewer catastrophic failures have been reported in long term for molars compared to other treatment modalities.

A high-performance polymer, polyetheretherketone (PEEK) has been a popular choice of restorative material among researchers since the last decade. Various modifications of PEEK have been advocated to attain desirable properties for restorative implications. The major advantage of modified PEEK material (20% ceramic fillers) is a 3.6–4 GPa modulus of elasticity, making it as elastic as bone and allowing it to act as a stress breaker and reduce the forces transferred to the restoration and the tooth root accordingly.[5] Furthermore, surface modifications of this material can yield good adhesion to tooth structures when luted with resin cements. It has been used for the fabrication of implant fixtures, fixed and removable dental prosthesis frameworks and could be a viable alternative endocrown material.[6] Ceramic-based endocrowns have shown better marginal and internal fit than resin-based endocrowns.[7] Ouqba Ghajghouj and Simge Tasar-Faruk stated that PEEK endocrowns had higher fracture resistance compared to lithium disilicate and zirconia reinforced glass ceramic endocrowns without any significant difference in the depth of coronal preparations.[7]

For the longevity of any endocrown, marginal and internal adaptation, fracture strength along with adhesive properties play an important role. The marginal and internal fit of PEEK as an endocrown material has not been reported in the literature. Therefore, this study was undertaken with the objectives to evaluate and compare the marginal fit and internal fit of PEEK with lithium disilicate endocrowns, which are the current gold standard. The primary research question was to investigate any statistically significant differences in the marginal and internal gap of endocrowns using the two materials. The null hypothesis of the study was that; there is no difference in marginal and internal gap between PEEK and computer-aided design/ computer-aided manufacturing (CAD CAM) lithium disilicate endocrowns.


   Materials and Methods Top


A mandibular ivorine first molar on a typodont (Prosthetic Restoration Jaw Model, Nissin Dental Products Inc.; Japan) was prepared using a high speed super torque hand piece (Dyna LED Handpiece, NSK; USA) to receive an endocrown following the guidelines by Fages and Bennasar [Figure 1]a.[8] The preparation was done by placing occlusal depth grooves of 2 mm as a guide using a tapered flat (TF-12) diamond bur (Dia-Burs; Mani, Inc; Japan) followed by a complete reduction of the occlusal surface by 2 mm using a blue diamond wheel bur (WR-13). The pulp chamber was prepared by keeping the TF blue diamond bur orientated along the long axis of the tooth, followed by flattening of the pulp chamber using a blue diamond wheel bur up to an intra-pulpal depth of 3 mm. These measurements were done using a graduated probe. A shoulder margin, 1 mm wide was given along the entire circumference of the tooth using a TF blue diamond bur. The entire preparation was finished and polished using polishing burs (TF-12EF) [Figure 1]b and [Figure 1]c.
Figure 1: (a) Mandibular first molar on typodont for endocrown preparation, (b) Prepared teeth on typodont to receive endocrown: sagittal view, (c) Prepared teeth on typodont to receive endocrown: occlusal view

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This preparation was scanned using an extra-oral lab scanner (T500 Lab Scanner, Medit; Korea). The digital scan was saved as an STL file. A dental design software (exocad, exocad GmbH; Germany) was used to design the endocrown on the scanned digital model [Figure 2]a and [Figure 2]b. This endocrown design was converted into 20 STL files and milled in two different materials; Group 1; lithium disilicate (IPS e. max CAD LT block; CEREC Ivoclar Vivadent, Liechtenstein) (n = 10) and Group 2; PEEK (breCAM. BioHPP®, Bredent; UK) (n = 10) using a 5-axis milling machine (×5 − 200, ARUM; USA). All the endocrowns were finished according to their manufacturer's guidelines [Figure 3]a and [Figure 3]b. Each endocrown was placed on the prepared typodont tooth. The midpoint of all four surfaces (mid buccal: MB, mid lingual: ML, mid mesial: MM, and mid distal: MD) were evaluated for marginal gap using a stereomicroscope (Model: XTL 3400E, Magnification: ×10, Wuzhou New Found Instrument Co. Ltd; China) [Figure 4]. The prepared typodont tooth was sectioned first with a long diamond point in the mid-sagittal plane. The sectioned typodont tooth was then partially embedded in a putty matrix and the endocrown was stabilized over it with sticky wax on the buccal surface. This was followed by sectioning of the endocrown with a carborundum disc along the inclines of the mid-sagittal plane of the prepared sectioned typodont tooth. This was done for all the samples from both the groups. The internal gap was evaluated at four different points (Point A– mesio-axial-occlusal, Point B– mesio-axial-pulpal, Point C– disto-axial-pulpal, Point D–disto-axial-occlusal) using a stereomicroscope [Figure 5]a, [Figure 5]b, [Figure 5]c and [Figure 6].
Figure 2: (a) Computer-aided design /-computer aided manufacturing designing of endocrown: In occlusion, (b) Computer-aided design /-computer aided manufacturing designing of endocrown: intaglio surface

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Figure 3: (a) Lithium disilicate endocrown, (b) Polyetheretherketone endocrown

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Figure 4: Assessment of external marginal discrepancy of endocrown using stereomicroscope

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Figure 5: (a) Four points marked for measurement of internal discrepancy of endocrown, (b) Sectioned (mid-sagittal) lithium disilicate endocrown, (c) Sectioned (mid-sagittal) polyetheretherketone endocrown

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Figure 6: Assessment of internal (pulpal) discrepancy of endocrown using stereomicroscope

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A total of 160 measurements were made for the 2 groups (4 measurements × 2 sections × 10 endocrowns × 2 groups). All data were saved in a spreadsheet (Microsoft Excel 2016; Microsoft Corp.; USA). One-way analysis of variance tests were performed using the Statistical Package for the Social Sciences (SPSS version 21.0, IBM Corporation, USA) for MS Windows to assess differences in marginal and internal gap in between both groups (P < 0.05 was considered statistically significant).


   Results Top


The results showed a statistically significant difference in between both the groups for marginal as well as internal gap (P < 0.05). Group 1 showed better marginal and internal fit compared to Group 2 [Table 1]. The mean marginal gap of Group 1 (56.5 ± 6.1 μm) was lesser than that of Group 2 (81.3 ± 10.1 μm). The smallest mean marginal gap was observed at MB point (49.72 μm) followed by MM, MD and ML points in Group 1. The smallest mean marginal gap was observed at MB point (75.67 μm) followed by MD, ML, and MM points for Group 2. Furthermore, the mean internal gap recorded for Group 1 (158.2 ± 11.1 μm) was lesser than Group 2 (199.1 ± 13 μm). The largest mean internal gap was observed at Point B (172.99 μm) followed by Point C, D, and A for Group 1. The largest mean internal gap was observed at Point C (214.25 μm) followed by Point B, D, and A for Group 2.
Table 1: Lithium Disilicate vs PEEK Marginal and Internal Fit Comparison - One way ANOVA Test

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   Discussion Top


Endocrowns are in use for restoring extensively damaged endodontically treated teeth, their main advantage being preservation of the remaining tooth structure and utilizing it in aiding retention and stability without the use of additional retentive aids, especially in clinically compromised situations. A finite element analysis done by Dejak and Młotkowski stated that teeth restored by endocrowns are more resistant to failure than those with posts.[9] In the current scenario; metal ceramic, composite resin, zirconia, and lithium disilicate are the materials frequently used in fabrication of endocrowns. Altier et al. compared the fracture resistance of three different endocrowns, made of lithium disilicate ceramic and two different indirect resin composites (Solidex composite and Gradia composite) and concluded that lithium disilicate ceramic endocrowns exhibited higher fracture strength than the indirect composite groups.[10] In 2018, a study stated that resin nanoceramics and lithium disilicate showed the highest values of fracture resistance followed by polymer infiltrated ceramics, thereby favoring their use as endocrown restorations.[11] Literature states that endocrowns made of lithium disilicate-based ceramics are considered among the best restorative materials because of their good adhesive properties and micromechanical interlocking with resin cement.[12] Gudugunta et al. and Dolev et al. compared the marginal fit between CAD-CAM and hot-press lithium disilicate crowns and concluded that the marginal fit of crowns fabricated by CAD-CAM technique was better than by pressed technique.[13],[14] Therefore, in the current study CAD-CAM technique of fabrication was employed.

In 2015, Zoidis et al. proposed that PEEK can also be used as an alternative material for endocrown restorations as it can successfully withstand physiologic occlusal forces.[5],[15] Acid-etched (98% sulfuric acid) PEEK surfaces provide a good shear bond strength with the adhesive resin cements and therefore have favorable bonding properties.[16] Modification of PEEK with carbon fibers can provide greater elasticity up to 18 GPa which is very close to that of cortical bone (15 GPa). Furthermore, it is very rigid with a flexural strength of 140–170 MPa.[17] These properties help to dampen the occlusal forces protecting weakened tooth structures better than the brittle ceramic materials.[5],[18] Another advantage of PEEK is its property of radiolucency, thereby making it easy for diagnosing secondary caries. Moreover, it has excellent polishing properties, low plaque affinity, high biocompatibility, good wear resistance, and nonmetallic taste.[19]

A prime factor governing the success of any restoration is its marginal adaptation.[20] Plaque accumulation leading to secondary caries and periodontal disease are consequences of poor marginal adaptation. Roy et al. compared the marginal fit of porcelain fused to metal (PFM) and PEEK full coverage crowns using a stereomicroscope and concluded that the marginal fit of PEEK crowns was higher than PFM crowns.[21]

The results of the current study have shown that CAD-CAM endocrowns fabricated with lithium disilicate have better marginal and internal fit compared to PEEK endocrowns. However, the marginal gap of both the CAD-CAM materials were within the clinical acceptable range of ≤120 μm and the internal gap was in the range of 150–220 μm.[22] These values are lesser compared to those observed by Shin et al. and Kim et al. for CAD-CAM endocrowns. They reported the internal discrepancies in the range of 200–300 μm.[23],[24] These differences in the results can be attributed to the fact that the internal fit of endocrowns is dependent on the cavity depth, variations in materials and processing techniques. However, there is no consensus regarding the clinically acceptable values of maximum internal gap for endocrowns. The possible reason for discrepancies in marginal and internal gaps of lithium disilicate and PEEK could be due to the semi crystalline structure of PEEK which contains fillers embedded in resin matrix, therefore creating differences in the milling of the two materials. Furthermore, the accuracy of the milling process is highly affected by the specifications of the milling machine.[25]

The promising properties of PEEK make it a sought-after material for endocrown restorations. However, further clinical investigation with PEEK endocrowns is required to know more about the longevity of the restoration.

Limitations

Since this study was performed under in vitro conditions, further clinical evaluation of PEEK endocrowns must be assessed in terms of their flexural and bond strength to provide reliable results.


   Conclusions Top


The current study shows a statistically significant difference in which lithium disilicate showed a better marginal and internal fit compared to PEEK. However, the marginal fit of both materials is within the clinical acceptable range. Hence, both the materials can be used as endocrown materials.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Correspondence Address:
Dr. Arshi Ilyas Kazi
Department of Prosthodontics and Crown and Bridge, MA Rangoonwala College of Dental Sciences and Research Centre, Hidayatullah Road, Azam Campus, Pune - 411 001, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JCD.JCD_547_20

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