Introduction

In this systematic review, the association of occlusal fit, mechanical properties, and success rate of ceramic computer-aided design/computer-assisted manufacturing (CAD/CAM) endocrown is the point of interest in this systematic review. Mechanical properties of the ceramic endocrown are about the tensile strength, elasticity, hardness, fatigue limits, and others. The superior occlusal accuracy of the fabricated endocrowns is also of interest because it determines their success. Today, end crowns are broadly used as alternatives to the traditional fixed partial and post-core dentures [1]. Mechanically, a conventional endodontic fabricated cavity has minimal fractural resistance to a given tooth. On the other hand, ceramic endocrowns’ thickness of the occlusal portion is usually between three and seven millimeters (mm). Empirical studies have demonstrated that the fracture resistance of ceramic endocrowns intensifies when occlusal thickness increases [1]. One is right to reason that when the mechanical properties and the occlusal fit are attained, the success rate of CAD/CAM Designed Ceramic Endocrowns is assured.

Ceramic restorations using ceramic CAD/CAM systems involve the use of feldspathic ceramic blocks [1]. Over the last decade, CAD/CAM technology has gained profound popularity and advances in the material used [2]. Spitznagel et al. (2018) explain that advancements in these technologies and ease of usage facilitated novel therapy concepts and ideologies for contemporary prosthodontics [3]. The different CAD/CAM ceramic restorative procedures are continuously transforming to address the augmented demands for long-lasting, aesthetic, and biocompatible prosthodontics. The latest polymer-infiltrated ceramic CAD/CAM blocks give the specialist a new option and add an innovative treatment approach to the restorations practice.

The high-edge stability of the CAD/CAM ceramic endocrowns facilitates the machinability of thin restoration layers [3]. Furthermore, industrially enhanced feldspathic ceramics are more applicable in CAD/CAM processes than other dental ceramic materials because they have better structural homogeneity and fracture. CAD-CAM endocrowns fabricated using flexible and malleable fused resin blocks are better choices to all-ceramic crowns because of marginal adaptation [4]. According to Sevimli et al. (2015), the comparable flexural strength advantages of these composite ceramic blocks and ferrule outcomes are significant for attaining the desired results [1]. Hassanzadeh et al. (2019) conducted a study to compare and evaluate the marginal and internal “adaptations of chairside CAD/CAM (CEREC) endocrowns and crowns fabricated from lithium disilicate glass-ceramic (IPS e.max CAD), zirconia-reinforced lithium silicate glass-ceramic (VITA Suprinity), and hybrid ceramic (VITA Enamic) [2].” Their results showed that endocrowns had a significantly lower mesial axial wall and occlusal discrepancies than crowns, while distal axial wall revealed a significantly higher contrast. In addition, endocrowns’ floor discrepancy was significantly lower than crowns; however, type material showed no significant consequence [2]. From the discrepancy variations, a knowledge gap would be completed or enriched with additional insights after completing this systematic review.

Materials and Methods

The investigator adopts a systematic review methodology and meta-analyses (PRISMA) guidelines to complete the study. A systematic review involves collecting the evidence after appraising critically pertinent primary studies and extracting befitting data for analysis and inclusion [5]. The Cochrane Handbook for Systematic Reviews of Interventions, “Systematic reviews seek to collate evidence that fits pre-specified eligibility criteria to answer a specific research question” [5]. Ranganathan and Aggarwal (2020) outline six sequential steps for a systematic review [6]. The first step is stating the review question. The second step is listing the eligibility criteria, while the third step is comprehensive research. The fourth stage is the selection and identification of relevant studies. Data extraction and synthesis of the results are steps five and six, respectively [6]. These steps are observed in this study using Cochrane risk of bias assessment and PRISMA guidelines and flowchart.

Inclusion and exclusion criteria 

Inclusion and exclusion criteria are significant for systematic review because they set limits on sample size, availability of relevant articles, quality of papers, and others [7]. Table 1 provides inclusion and exclusion criteria for the current study.

Table 1. Inclusion and Exclusion Criteria

PRISMA flowchart

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) is an evidence-based set of records gathered for reporting in a meta-analysis and systematic reviews. PRISMA assists researchers to enhance the reporting of collected studies and reporting of systematic reviews [8]. It is viable for various types of research; such as randomized trials, evaluations of interventions, and systematic review [8]. It focuses on the documenting and reporting of reviews assessing the effects of interventions and a foundation for reporting systematic reviews with reasons [9]. Figure 1 presents the PRISMA flowchart reporting the steps taken to identify eligible articles based on the inclusion and exclusion criteria. The articles were collected from databases Google scholar and screening entailed publication restrictions (2011 to 2021) and full articles.

Cochrane risk of bias assessment

Assessing risk of bias (RoB) is an integral part of Cochrane systematic reviews (CSRs). Systematic reviews entail collecting and synthesizing relevant studies meeting eligibility criteria set to minimize bias [10]. The primary investigator or author cautiously considers likely limitations of the incorporated studies. The assessment seeks to consider the extent to which the studies were suitable to answer the research question. However, RoB is an essential component of the Cochrane assessment procedure for systematic reviews [10]. Seven principles for evaluating Cochrane RoB are 1) not using quality scales, 2) concentrating on internal validity, 3) assessing in trial results, 4) judgment required, 5) theoretical and empirical domains considered 6) focus on data, and 7) report the specific outcome. Using quality scales makes it difficult to ascertain consistency or predictable assessment criteria [10]. Poor internal validity has high RoB and vice versa.

RoB is assessed based on the results, not methodological or reporting challenges. In a systematic review, a description of the details or lack is applicable for determining RoB. Knowledge and judgment are necessary elements of RoB assessment because they help discern various aspects of the content [10]. Empirical and theoretical considerations help identify the RoB based on the topic and design specific issues associated with the reviews. Data used in a study should focus on evaluating bias rather than reported results, which could have a high or low bias based on input. Lastly, the author should report specific assessments of risks of bias [10]. In assessing the RoB, the Cochrane tool or table engages in six domains, namely selection, detection, performance, reporting, attrition, and other bias [10]. To assess the current studies for this systematic review, the Cochrane RoB table is used as shown in Table 2. The research question is “what are the mechanical properties, occlusal fit, and success rate associated with CAD/CAM designed ceramic endocrowns?

Table 2. Cochrane RoB Table

Source: Adapted from Cumpston (2012) [20]

Results and Discussion

Using the search criteria, the search of the Cochrane database yielded 11 results, while Google Scholars had 1020 results. The first screening was based on duplicates and non-articles, leading to the remaining 250, further screened based on peer reviews and date specification criteria, leaving 60 full-text eligible articles. After reading abstracts, 13 articles had the most relevant content for this systematic review.

Table 3. Summary of findings from Selected Studies