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 Table of Contents  
Year : 2020  |  Volume : 17  |  Issue : 2  |  Page : 45-52

Influence of fabrication techniques on vertical marginal gap distance and internal adaptation of zirconia-reinforced lithium silicate all-ceramic crowns

1 Oral and Maxillofacial Prosthodontic Department, Faculty of Dentistry, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
2 Department of Fixed Prosthodontics, Faculty of Dentistry, October 6 University, Cairo, Egypt

Date of Submission16-Apr-2019
Date of Acceptance27-May-2019
Date of Web Publication26-Sep-2020

Correspondence Address:
Shereen K Salem
Department of Fixed Prosthodontics, Faculty of Dentistry, October 6 University, Cairo
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/tdj.tdj_18_19

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This in-vitro study aimed to evaluate vertical marginal gap distance and internal adaptation of CAD/CAM and heat pressed (HP) zirconia-reinforced lithium silicate (ZLS) all-ceramic crowns.
Materials and methods
A typodont maxillary first premolar was selected in this study and prepared to receive all-ceramic crown. Fifteen ZLS ceramic crowns were constructed and divided into three groups according to their fabrication technique. Group 1: Five CAD/CAM Celtra Duo crowns. Group 2: Five HP Celtra Press crowns using CAD/CAM wax patterns. Group 3: Five HP Celtra Press crowns using conventional wax patterns. After fabrication of the all-ceramic crowns by different techniques, the vertical marginal gap distance between the crown margin and the finish line of the prepared tooth was measured using a digital microscope of ×40 at 16 points/crown. Internal adaptation was evaluated using silicone replica technique. Data were collected, tabulated and statistically analyzed (Tukey post-hoc test) at P value up to 0.05.
The results showed that there was a statistically significant difference between the three groups regarding the vertical marginal gap distance and internal adaptation with the lowest mean value of vertical marginal gap in Celtra Press using CAD/CAM wax patterns crowns and the best internal adaptation was found in CAD/CAM Celtra Duo.
All fabrication techniques used in this study yield marginal and internal adaptation that is within the clinically acceptable range.

Keywords: CAD/CAM, Celtra Duo, Celtra Press, internal adaptation, vertical marginal gap distance, zirconia-reinforced lithium silicate

How to cite this article:
Asaad RS, Salem SK. Influence of fabrication techniques on vertical marginal gap distance and internal adaptation of zirconia-reinforced lithium silicate all-ceramic crowns. Tanta Dent J 2020;17:45-52

How to cite this URL:
Asaad RS, Salem SK. Influence of fabrication techniques on vertical marginal gap distance and internal adaptation of zirconia-reinforced lithium silicate all-ceramic crowns. Tanta Dent J [serial online] 2020 [cited 2020 Oct 31];17:45-52. Available from: http://www.tmj.eg.net/text.asp?2020/17/2/45/296174

  Introduction Top

Ceramics have been improved due to a lot of demands as their superior translucency, enhanced fluorescence and prominent clarity of color from the underlying tooth structure. In addition to esthetics, strength and marginal accuracy are also needed in all-ceramic restorations [1].

The successful longevity of ceramic restorations is significantly affected by both marginal and internal fit [2]. Improper marginal fit might cause cement dissolution, marginal discoloration and leakage causing inflammation of the periodontal tissues, caries and subsequently failure of restoration. So, it is crucial to decrease marginal gaps to minimize the prevalence of correlated problems [3]. In addition to marginal fit, internal fit and accuracy plays an outstanding role for the longevity of a full-coverage restoration as well. Perfect internal fit enhances mechanical properties as strength, resistance and retention [4],[5]. Marginal fit is affected by many aspects as the finish line type and its steepness, construction technique, core thickness, cement material and cementation technique [6],[7].

Nowadays, material-correlated studies target on the evolution of CAD/CAM materials promoting better mechanical strength, associated with sufficient translucency, and time-saving construction [8]. Lithium disilicate (IPS e.max CAD) blocks are presented in a pre-crystallized form. Heat crystallization process causes a controlled growth of the grain size (0.5–5 μm) forming the final form of this glass ceramic with flexural strength of 360 MPa [9].

A new member in the lithium ceramic family is lithium silicate ceramic (Celtra Duo and Celtra Press) that has the same constituents with the recent addition of 7.6% germanium dioxide improving properties like thermal expansion, castabilty, refractive index and increasing the final density resulting in a higher mechanical properties. According to the manufacturers, the mechanical strength of these materials range between 370 and 420 MPa. Recently, the addition of 10% weight zirconium oxide directs to an increased strength [10]. Zirconia has been added to lithium silicate ceramic (referred to as zirconia-reinforced lithium silicate or ZLS) offering a homogeneous, fine crystalline structure with an average crystal size of (0.5–0.7 μm) in comparison to the needle-shaped crystals with an average size of 1.5 μm found in the lithium disilicate ceramic. ZLS-ceramics consist of a two components: small crystalline lithium metasilicate with lithium disilicate crystals (average size: 0.5–0.7 μm). This is considered the major difference from lithium disilicate ceramics, which had only lithium disilicate crystals. The second is the glassy matrix with 10% zirconium oxide. This microcrystalline composition allows for an optimal flexural strength, additionally it still has a high proportion of glassy matrix, that offer good polishing and optical properties [8],[10]. Therefore, the final crystallized ZLS modifications present an ideal integration of reduced fabrication times and high stability. These variations promote the chairside fabrication of posterior all-ceramic prosthesis [11].

The optical, bonding, and mechanical properties of these ZLS-ceramics were investigated in several in-vitro studies. The results of these studies showed fracture strength and marginal accuracy within the clinically acceptable range [12],[13]. Baig et al.[14] and Stappert et al.[15] have shown that the milled restorations had inferior marginal fit compared to pressed ones. However, Miyazaki et al.[16] reported that several progresses have occurred in milling technologies and new systems have been established that declare to produce accurately fitting restorations.

Heat pressing (HP) became one of the most prevalent ceramic fabrication techniques due to ease of construction, accurate marginal adaptation, mechanical properties, translucency, lower porosity, and less brittleness than conventionally fabricated high glass ceramics [17],[18]. First generation of HP ceramic was IPS Empress and more recently IPS e.max Press (lithium disilicate glass-ceramic ingot for the press technique) was launched overcoming the IPS Empress defects [19]. Recently, a new development inpressable ceramics Celtra press (ZLS) was introduced in the market. According to the manufacturer it is characterized by its excellent pressing behavior with all restoration types.

The adaptation of pressable all-ceramic restorations in the laboratory is a sensitive technique that may be affected by many factors like the impression material and technique, the storage time and conditions of the impression before pouring the stone cast, disinfection, application of the die spacer, the investment and casting or pressing process [20]. Also the construction of the wax pattern is the most important step in the fabrication of pressable all-ceramic crowns. So, the wax-up's quality is based on the proficient work of the technician [21]. Wax has several essential drawbacks as thermal sensitivity, softness, high coefficient of thermal expansion and elastic memory [22]. As regard to clarity of automatic margin identification and restoration design compared to manual waxing, it allows most probably to use the CAD/CAM technology wherever possible [23].

After introducing different CAD/CAM systems, these new systems facilitate the fabrication of the wax patterns and put an end to many limitations of conventional wax-up technique. Using CAD/CAM systems allows production of excellent quality restorations using various blocks of materials. Standardizing restoration designing methods and decreasing processing charges, time and effort [24]. Another advantage is the possibility to raise accuracy as they exclude many fabrication steps as waxing and investing [22]. However, some critical points affecting the adaptation of milled restorations can be found as: the precision of the scanner, the software designer, thickness of spacer, the reliability of the milling machine, and the properties of the materials to be milled by CAD/CAM systems [25],[26]. Vojdani et al.[27] stated that conventional wax pattern construction technique allows production over restorations with sufficiently better marginal and internal adaptation than CAD/CAM method.

Akin et al.[28] compared marginal and internal fit of two all-ceramic crowns fabricated with CAD/CAM and HP techniques without cementation. They found that there were no statistically significant differences between CAD/CAM and HP all-ceramic anterior crowns in both marginal and internal adaptation. Anadioti et al.[29] and Farid et al.[30] found that IPS e.max Press crowns have an acceptable marginal fit. Raafattammam[31] concluded that the CAD/CAM fabricated ceramic crowns recorded statistically significant higher vertical marginal fit than HP. He also reported that heat pressed ceramic crowns showed statistically significant higher internal adaptation than CAD/CAM fabricated crowns.

Whether the discrepancy in the composition of the lithium ceramics will allow improvement in their marginal and internal fit or not, is still questionable and needs further investigations. Therefore, the purpose of this study was to evaluate vertical marginal gap distance and internal adaptations of (ZLS) all-ceramic crowns fabricated using different fabrication techniques: CAD/CAM and HP using CAD/CAM fabricated wax patterns and conventional wax patterns.

The null hypothesis for this study was that no difference would be found between (ZLS) all-ceramic crowns fabricated by different techniques in both marginal and internal adaptations.

  Materials and Methods Top

Tooth preparation and scanning

A typodont maxillary first premolar (Frasaco GmbH, Tettnang, Germany) was selected in this study to represent a patient's tooth which was inserted in an acrylic resin mold. The tooth was protruded till 3 mm beyond the finish line. The master tooth was prepared for an all-ceramic crown: 1 mm deep chamfer finish line, 1.5 mm occlusal reduction, 1 mm axial reduction and the total convergence angle of 12°[32] with aid of modified dental surveyor to which hand-piece was fixed to its arm to allow the diamond stone to be parallel to the long axis of tooth during preparation of axial walls [33]. The preparation was carried out with a tapered diamond stone with round end. Scanning was done for the prepared tooth with an intra-oral scanner following a powder free technology (Trios 3; 3Shape, Copenhagen, Denmark) [34]. The scanner was adhered to the tooth from buccal and lingual surfaces by placing the camera at 45° to the tooth axis according to the manufacturer instructions. Then the data were forwarded to the dental lab as a standard tessellation language file.

Samples grouping

Fifteen ZLS ceramic crowns were constructed and divided into three groups according to their fabrication technique; Group 1: Five CAD/CAM Celtra Duo crowns. Group 2: Five HP Celtra Press crowns using CAD/CAM wax patterns. Group 3: Five HP Celtra Press crowns using conventional wax patterns.

Group 1: CAD/CAM fabricated crowns

Each crown was designed in the form of fully contoured monolithic maxillary first premolar with a CAD system software (Dental System; 3Shape) [Figure 1]. The ceramic thickness was set to 1.5 mm at occlusal surface and 1.0 mm at the axial surfaces; the die spacer thickness was set to 30 μm [34]. Finally the designed crowns were exported as standard tessellation language files. Crowns were then milled from Celtra Duo CAD blocks (Dentsply, Sirona GmbH, Munekh, Germany) as full-contour monolithic crowns in a 5-axis milling machine (vhf CAM 5-S1; vhf camfacture AG, Ammerbuch, Germany). After milling of the crowns, the fixation bar of each crown was ground with water-cooled diamond instrument. The crowns were polished with diamond polishing rubbers without addition of glaze firing according to manufacturer recommendation.
Figure 1: Proposed design for fully contoured monolithic maxillary first premolar crown.

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Group 2: Heat pressed using CAD/CAM fabricated wax patterns

Wax patterns were milled according to the design of the CAD/CAM crowns of group 1 using CAD wax (On dent-Wax-On Disc White, Turkey) in a milling machine (vhf CAM 5-S1; vhf camfacture AG). Just before investing, the cervical 2 mm of the milled wax patterns was re-flowed and marginal wax (Bego, Germany) was added (margination) to insure maximum marginal adaptation. The wax patterns were fixed by wax sprue formers with 3 mm diameter and 3 mm length then invested using (Celtra Press investment, Dentsply; Sirona GmbH). The invested mold was transferred to a burnout furnace (Vulcan 3-130; USA) and heated from room temperature to 850°C and hold for 30 min to melt down wax. Then the invested mold was immediately pressed in pressing furnace according to manufacturer instructions by the lost-wax technique using Celtra Press ingots (Degu Dent GmbH, Germany). After HP, the crowns were carefully divested by sandblasting with glass powders (50 μm) at a pressure of three bars to remove investment material. The sprues were cut and finished using diamond disks at low speed following the manufacturer recommendation.

Group 3: Heat pressed using conventional fabricated wax patterns

The external outline form and dimensions of the Celtra Duo crowns were duplicated using polyvinyl siloxane addition silicone (Express XT; 3M ESPE, USA). This (silicone index) was used to standardize the conventionally fabricated wax patterns. Then after setting, the index was sectioned bucco-lingually to evaluate the dimension of the wax pattern. Another impression of the prepared tooth was taken and poured in type IV Stone (Shera premium type IV; SHERA, Germany) following manufacturer guidelines and under standardized conditions. Two layers of die spacer (Cergo; Sienna, Norway) were applied to within 1 mm of the preparation margin on the die according to the manufacturer instructions. The conventionally, manually; fabricated wax patterns were constructed by the help of the previously sectioned rubber index for standardization. The conventionally fabricated five wax patterns (Geo classic opak; Renfert, Germany) were invested, burnt-out, pressed and finished similar to that of group 2.

Testing procedures

Vertical marginal gap distance

The vertical marginal gap distance was measured between each crown and the prepared premolar tooth without cementation [9]. For standardization purposes, a specially designed holding jig was fabricated to hold the crowns on premolar tooth during vertical marginal gap measurement as carried out in different studies [32].

Each crown was positioned onto digital microscope with a built-in camera (Scope Capture Digital Microscope, Guangdong, China) at a fixed magnification of × 40. The images were captured and transferred to an IBM compatible personal computer equipped with the Image-Tool software (Vertical Image J 1.43U; National Institute of Health, USA) to measure and evaluate the gap width of each crown. Shots of the margins were taken for each crown. Then morphometric measurements were done for each shot (four equidistant landmarks) along the circumference for each surface of the crown (buccal, mesial, distal and lingual) 16 points per crown. Then the data obtained were collected, tabulated and subjected to statistical analysis [Figure 2].
Figure 2: Representative microscopic image of buccal surface of the crown showing measurement sites for marginal fit.

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Internal adaptation

It was measured by a replica technique. Light body addition silicone (Elite, Zhermack, Germany) was auto-mixed and applied inside each crown and then seated on the prepared premolar for 2 min till complete setting of light body addition silicone following manufacturer instructions using the specially fabricated holding jig that was used during vertical marginal gap distance. After complete setting of light body addition silicon, the crown was removed from the prepared tooth carefully. Then heavy body addition silicone (Elite) was auto-mixed and injected to fill the inside of the crown to support the light body addition silicone replica. After setting of heavy body addition silicon, the silicone assembly was removed from each crown and sectioned into two halves bucco-lingually then mesio-distally using a blade no. 15 (Matrix, USA) to obtain four equal sections of replica [15].

Each section was placed under digital microscope with built in camera (Scope Capture Digital Microscope, Guangdong, China) at ×25 magnification. The light-body silicone thickness for all replicas was measured in microns representing the distance between the internal surface of the coping and the external surface of the preparation and carried out at a16 points (cervical, axial, occluso-axial and mid-occlusal). Four measurement points were selected for each section cut. Then the data were collected, tabulated and subjected to statistical analysis [Figure 3].
Figure 3: Representative image of silicon replica showing measurement sites for internal adaptation.

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  Results Top

The mean and SD values were calculated for each group in each test. Data were explored for normality using Kolmogorov–Smirnov and Shapiro–Wilk tests, data showed parametric (normal) distribution.

One-way analysis of variance followed by Tukey post-hoc test were used to compare between the tested groups.

The significance level was set at P value up to 0.05. Statistical analysis was performed with IBM SPSS statistics version 20 for Windows.

Vertical marginal gap distance results

Means and SD for vertical marginal gap distance are shown in [Table 1]. A statistically significant difference was found between Celtra Duo and both Celtra Press groups using CAD/CAM wax pattern and Celtra Press using conventional wax pattern.
Table 1: The mean, SD values of vertical marginal gap distance of different groups

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No statistically significant difference was found between the two Celtra Press groups using CAD/CAM wax pattern and Celtra Press using conventional wax pattern.

Means with different small letters in the same column indicate statistically significance difference at P value up to 0.05.

Internal adaptation results

Means and SD for internal adaptation are shown in [Table 2].
Table 2: The mean, SD values of internal adaptation of different groups

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A statistically significant difference was found between Celtra Duo, and both Celtra Press groups using CAD/CAM wax pattern and Celtra Press using conventional wax pattern.

Also, a statistically significant difference was found between Celtra Press groups using CAD/CAM wax pattern and Celtra Press using conventional wax pattern.

  Discussion Top

In this study, a typodont resin tooth was used for all-ceramic preparation to overcome the variations that may showing natural teeth [35]. ZLS ceramic was used as it can be fabricated by two types of fabrication techniques: CAD/CAM and HP. Nowadays, the milled ZLS-ceramics are presented as Celtra Duo (Dentsply) and Suprinity (Vita Zahnfabrik) for chairside as well as lab site processing. The zirconia-reinforced silicate ceramic Suprinity is a pre-crystallized material. Consequently, the CAM processing is comparable with lithium disilicate ceramic materials (crystallization firing after milling to achieve the final density). However, the ZLS variation Celtra Duo is a fully crystallized ceramic. So it is compatible with chairside application, as the final restoration is finished after a short milling time 10–22 min Also, the microstructure of ZLS ceramics is supposed by the manufacturer to allow milling the restorations with acceptable margins [8],[9],[10],[11].

The pressable ZLS used in this study is Celtra Press. It allows the construction of single anterior and posterior crowns, veneers, inlays, on lays and three-unit anterior bridge up to second premolars according to manufacturer recommendation. Celtra Press promotes higher strengths (>500 MPa) than Celtra Duo (370–420 MPa) [10]. Celtra Press ceramic consists of a glass matrix and lithium disilicate crystals having a crystal size of 1.5 μm plus nano-scale lithium phosphate 0.3 μm. In addition to LiO2 and SiO2, Celtra Press contains about 10% zirconia (ZrO2), which is incorporated totally in the glass phase, as in Celtra Duo rather than in crystalline form. According to the manufacturer recommendations, Celtra Press has high strength of about 500 MPa and excellent flow properties during pressing. Additionally with the newly introduced investment, only a minimal reaction layer is formed, leading to an excellent fit and shortening the time required for finishing, as the surface etching step is removed [36]. Celtra Press is easy to polish, only minor corrections are needed in the patient's mouth. Therefore, no postprocessing in the laboratory is required which results in excellent esthetics [37].

The fit of indirect restorations is associated with a minimal marginal gap between the restoration and the prepared tooth. The importance of marginal adaptation is owing to the fact that the significant reasons of indirect restoration failure are recurrent caries and loss of retention due to the dissolution of the luting cement. As important as marginal fit, a minor internal gap is also a necessary characteristic of indirect restorations, as large and inhomogeneous internal gaps may negatively affect the retention and resistance of the restoration [38]. Different levels of adaptation were evaluated in this study: cervical, axial, occluso-axial, mid-occlusal to obtain a complete picture about crown seating.

The vertical marginal gap measurement was chosen in this study as the most commonly used to quantify the accuracy of fit of any restoration [39]. The direct method using the digital microscope was chosen in this study, following Nawafleh et al.[40] who reviewed the methods used to evaluate marginal accuracy of crowns in a systematic review and found that measurements using the direct view method was the most commonly used technique with dependable results. Therefore, good marginal accuracy and adequate internal adaptation are known to be the most important factors for the success and clinical longevity of ceramic crowns [41].

The replica technique was used for quantitative analysis of the marginal and internal adaptation. It is a nondamaging, valid and frequently used technique to detect the marginal and internal adaptation of indirect restorations, as it is simple, relatively economical and does not require long time to be performed [38]. This technique was used in several in-vivo and in-vitro studies and in comparisons of clinical and laboratory results. So it can be considered as a well recorded procedure [15],[42],[43],[44],[45],[46].

The aim of this study was to compare the vertical marginal gap distance and internal adaptation of Celra Duo crowns and Celtra Press crowns fabricated by both conventional wax patterns and CAD/CAM wax patterns. The group of Celtra Press crowns fabricated by CAD/CAM wax patterns was chosen as it is a time saving method having the benefit of absence of any human errors in manufacturing steps that might add a variable. Selection of this technique for wax pattern fabrication was based on the results of Fathi et al.[24] who compared the marginal and internal fit of crowns fabricated using different wax patterns (conventional and milled) and found that marginal and internal fit of milled wax patterns was more accurate than the conventional one. Also, Shamseddine et al.[47] compared the marginal and internal fit of a lithium disilicate crown fabricated from both conventional and CAD/CAM wax patterns and concluded that the CAD/CAM waxing technique resulted in the improved fit of a pressed lithium disilicate crown.

The results in this study showed that there was a statistically significant difference in vertical marginal gap measurements between Celtra Duo, Celtra Press with CAD/CAM wax pattern and Celtra Press with conventional wax pattern groups where Celtra Duo crowns showed higher marginal gap value than both HP groups. This may be due to that in HP technique, the ceramic ingot is pressed under controlled pressure, temperature, and vacuum guaranteeing perfect replication of fine details particularly at the margins in addition to the margination of the wax patterns done just before investing. These results were in agreement to those of Mously et al.[35]who concluded that the e.max lithium disilicate restorations constructed with the HP technique had significantly smaller marginal gaps than those constructed with CAD/CAM technique and Neves et al.[48]who found a significantly smaller marginal gap of e.max lithium disilicate crowns fabricated with the HP technique than max lithium disilicate crowns fabricated with (CAD/CAM E4D) laser scanner. Also, this was in agreement with Burcin et al.[49]who stated that marginal discrepancies of IPS e.max CAD restorations were significantly greater when compared to IPS e.max Press on enamel, but they were not significantly different on dentin.

The findings of this study were not coinciding with those of Ng et al.[50] who compared the marginal gap of IPS e.max Press and IPS e.max CAD (LAVA C.O.S. scanning unit) crowns. They found that the mean marginal gap distance measurements were smaller for the IPS e.max CAD group than that for the IPS e.max Press group. This contradiction maybe attributed to the difference in the scanning protocol between the two studies. Also these results were not in accordance with Raafattammam[31] who concluded that disregarding cementation, it was proved that press group recorded statistically significant higher vertical marginal gap mean value than CAD group. This difference may be due to that wax patterns for IPS e-max Press were not marginated before investing which was different than what was done in this present study. Dolev et al.[51] found no significant differences in marginal gaP values between the CAD/CAM and HP techniques. However, these differences in results may be attributed to different systems for fabrication of CAD crowns as they used a chairside CAD/CAM milling machine.

The vertical marginal gap measurements in this study showed that there was no significant difference between Celtra Press crowns fabricated from CAD/CAM wax patterns and those fabricated from conventional wax patterns. This result can be related to that in the pressable ceramic technique, both wax patterns were marginated directly on the prepared typodont tooth for CAD/CAM wax patterns and on stone die of conventional wax patterns helping the dentist for better shaping, carving, and sealing the margins [52]. But the Celtra Press CAD/CAM fabricated wax pattern had lower marginal gap distance than Celtra Press fabricated from conventional wax pattern as in this later group there was an additional step was done which was pouring of stone die which can be subjected to many errors during its manufacturing steps.

Regarding the internal adaptation results, the CAD/CAM group recorded better adaptation than both HP groups, as there was a statistically significant difference between Celtra Duo (69.76 μm), Celtra Press with CAD/CAM fabricated wax pattern (79.59 μm) and Celtra Press with conventional wax pattern groups (105.45 μm). This finding may be related to the CAD/CAM technology which resulted in restorations with improved adaptation due to the fewer production steps compared to the HP technique and could be a result of new improvements in relation to scanning technology for digitizing the surface of the prepared tooth, advanced software provided accurate determination of the preparation margin, and upgraded milling technique. Also, the justification of these results might be related to the recent development in designing software which has superior features related to automatic identification of the margins of the restorations. In comparison to earlier systems, these recent advancements are supposed to improve internal fit of the milled restorations. On the other hand, the act of removing the wax pattern from the prepared typodont tooth or from the stone die many times to check the margins before and after margination might affect the internal adaptation of the HP groups [53]. The finding of this study coincided with Nejatidanesh et al.[54] who found that CAD/CAM restoration provided better internal adaptation. On the other side, the results were not in-accordance with those of Raafattammam[31] who reported that e-max CAD group recorded statistically significant higher internal gap mean value than press group which may be attributed to the cementation of crowns using self-adhesive cement and total-etch cement. This was also not in accordance with Burcin et al.[49] who stated that the internal adaptation of IPS e.max Press group is higher than the IPS e.max CAD this may be due to difference in preparation designs as they prepared tooth for an onlay restoration.

McLean and von Fraunhofer[55] stated that a marginal gap less than 120 μm is considered clinically acceptable. So the amount of marginal discrepancy present in this study was within the clinically acceptable values.

The limitations of this study include being an in-vitro investigation which cannot reproduce all clinical parameters. The study was carried on one type of ceramic material (ZLS).

The null hypothesis was rejected as the vertical marginal gap distance as well as the internal adaptation, were affected by the method of fabrication of ZLS.

  Conclusion Top

Within the limitations of this study, the followings could be concluded:

  1. Vertical marginal gap distance and internal adaptation of Celtra Duo, Celtra Press fabricated using CAD/CAM wax patterns and Celtra Press fabricated using conventional wax patterns were significantly affected by their fabrication techniques.
  2. HP fabrication technique improved the vertical marginal gap distance while CAD/CAM technique improved the internal adaptation.

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Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]


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