Literature on edge chipping test applied to dental materials and structures has been systematically reviewed with regard to the evaluation methods and parameters used.
A systematic search of the literature retrieved 3484 relevant studies. After removing duplicates, 1848 records were screened by titles and abstracts and 1797 were excluded; 51 papers were assessed full text for eligibility. Twenty papers were included in this study and they were organized according to the dental materials and structures tested as follows: 2 studies on human tooth, 9 on dental ceramics, 5 on polymer-based composites, and 4 studies evaluated both ceramic and polymer-based materials.
MEDLINE/PubMed, Scopus and Web of Science databases were searched up to June 2019 without restriction on date and language.
In vitro studies using edge chipping test on dental materials and structures were included.
Different methods have been used for edge chipping test, regardless of reported parameters. There is significant evidence that edge chipping test is a relevant approach to predict chipping behavior of dental materials and tooth tissues because chips produced from most edge chipping studies are similar to clinically reported chipping failures.
Despite of the continued evolution of dental material sciences, masticatory and parafunctional occlusal forces can cause mechanical failure and degradation of dental restorative materials [ ]. Previous studies have shown that chipping is a relatively frequent mechanical problem for dental hard tissues [ , ], ceramic materials [ ], and polymer-based materials [ , , , , ], especially when subjected to excessive masticatory forces [ ]. Clinically, minor chipping often causes marginal infiltration and/or discoloration of the tooth-restoration interface, which may result in restoration loss [ , ]. As a consequence, in the worst-case scenario, patient will need replacing the restoration with additional tooth tissue loss [ , ] or, at least, a repair to adjust the affected structure [ ].
More specifically, a chip is a small broken or spall-off piece from a brittle material. Chipping can either be the primary mode of fracture or a secondary, minor resultant from the fracture process. In clinical dentistry, chipping usually occurs when a load near an edge of a tooth or restoration causes to chip off a portion of it. Such fracture process initiates beneath a concentrated contact by sub-surface crack formation that propagates unstably towards a free edge (adjacent surface) to form the chip. For in vitro evaluation of the process, researches have used the edge-chipping test that applies an increasing force near the edge of a sample until a chip forms [ , ]. The force to cause fracture depends upon the shape of the object that applies the contacting force, the distance from the edge, the direction of the applied force, the angle of the edge, and the material’s fracture resistance and toughness. In general, the larger the distance away from an edge, the greater the force that is necessary to create a chip [ , ]. The test has demonstrated to be an useful mean to assess the edge chipping resistance of dental materials and structures [ ] with significant clinical relevance since chips are similar to clinical failures [ , , , ]. In addition, thermo-mechanical properties [ ] have been evaluated and finite element analysis [ , ] and fatigue methods [ ] have been used to assist on understanding the chipping process.
The edge chipping test was originally developed at the National Physical Laboratory (NPL), London, UK, in the 1980s to evaluate hard metals [ ]. Quinn et al. [ ] introduced it to Dentistry to evaluate brittle structures, such as human teeth and restorative dental materials, with the purpose of measuring the force necessary to generate a chip. A crack is intentionally created near the edge of a structure using an indenter, which is linked to a load cell [ ]. A specific device (CK 10, Engineering Systems, Nottingham, UK) has been used to perform the test, but universal testing machines were also used. Yet, studies have reported different parameters based on slightly different materials and methods. Therefore, this comprehensive narrative work based on a systematic review aimed to present a qualitative analysis of studies published on edge chipping test of dental materials and structures focusing on the diversity of test methods and parameters reported to evaluate the data and on the clinical relevance of the edge chipping test.
Materials and methods
This study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement [ ], centered on the following review question: “Do the different methods and parameters reported on edge chipping test are effective in assessing the chipping resistance of dental materials and structures?”
The present work included published in vitro studies that used the edge chipping test to evaluate dental structures ( e.g. , teeth) and materials ( e.g. , ceramic- and polymer-based dental materials). Accordingly, the exclusion criteria were as follows: in vivo studies; animal studies; studies evaluating materials not applied in dental practice; literature reviews, comments and conference abstracts.
Electronic search was conducted in three different databases (MEDLINE/PubMed, Scopus and Web of Science) with no restriction for language and publication, with last search performed on 14/06/2019. The search strategy was outlined based on PubMed MeSH terms and adapted for each database. Search strategy is described in Table 1 .
|Search||Topic and terms|
|#6||Search #1 OR #2 OR #3 OR #4 AND #5|
|#5||Edge Chipping Test:|
|“edge chipping” OR “edge-chipping” OR “chipping” OR “chippings” OR “edge toughness” OR “edge-toughness” OR “edge strength” OR “edge-strength” OR “edge fracture” OR “CK 10″ OR “CK-10”.|
|“composite resins” [Mesh] OR “composite resin” OR “resins” OR “Composite” OR “resin based” OR “resin-based” OR “resin-based composite” OR “resin-based composites” OR “resin based composite” OR “resin based composites” OR “resin composite” OR “resin-composite” OR “dental composite” OR “flowable” OR “flowable resin” OR “flowable resins” OR “filled resin composite” OR “filled resin composites” OR “fiber reinforced composite” OR “fiber-reinforced composite”.|
|“denture bases” [Mesh] OR “denture base” OR “prosthodontic” [Mesh] OR “prosthodontics” OR “ceromer” OR “polymethyl methacrylate” [Mesh] OR “denture materials” OR “polymer based provisional crown” OR ” polymer-based provisional crown” OR “denture, fixed partial” [Mesh] OR “fixed partial denture materials” OR “fixed-partial denture materials”.|
|“ceramics” [Mesh] OR “ceramic” OR “ceramics” OR “dental ceramic” OR “dental-ceramic” OR “dental ceramics” OR “dental-ceramics” OR “all ceramic” OR “all ceramics” OR “all-ceramic” OR “all-ceramics” OR “metal free ceramic” OR “metal free ceramics” OR “metal-free ceramic” OR “metal-free ceramics” OR “dental porcelain” [Mesh] OR “porcelain” OR “porcelains” OR “dental porcelain” OR “dental porcelains” OR “dental-porcelain” OR “dental-porcelains” OR “feldspathic porcelain” OR “feldspathic porcelains” OR “glass ceramics” [Mesh] OR “glass ceramic” OR “glass ceramics” OR “machinable glass ceramics” OR “glass-ceramic” OR “glass-ceramics” OR “lithia disilicate” [Mesh] OR “lithia disilicate” OR “lithium disilicate” OR “lithium disilicate ceramic” OR “lithium disilicate ceramics” OR “yttria stabilized tetragonal zirconia” [Mesh] OR “yttria stabilized tetragonal zirconia” OR “zirconia” OR “zirconia ceramic” OR “zirconia ceramics” OR “yttria-stabilized zirconia” OR “polymer infiltrated ceramic network” OR “polymer-infiltrated ceramic network” OR “polymer infiltrated ceramic network material” OR “polymer-infiltrated ceramic network material” OR “hybrid ceramic” OR “PICN” OR “Computer-Aided Design” [Mesh] OR “computer-aided design” OR “computer aided design” OR “computer-aided manufacturing” OR “computer aided manufacturing” OR “CAD/CAM” OR “CAD-CAM” OR “computer-aided-design” OR “computer-aided-machine” OR “computer-aided machine” OR “computer aided machine” OR “CAD-CAM ceramics “OR “CAD-CAM ceramic systems” OR “CAD/CAM ceramics “OR “CAD/CAM ceramic systems”.|
|“tooth” [Mesh] OR “teeth” OR “dental enamel” [Mesh] OR “enamel” OR “dentin” [Mesh] OR “dentine” OR “human dentin” OR “human dentine” OR “bovine dentin” OR “bovine dentine”.|
Search results were duplicated using EndNote software (EndNote X7, Thomson Reuters, New York, NY). Two reviewers (SBNB and MLV) independently screened all titles and abstracts. Records meeting the eligibility criteria or classified as unclear were retrieved for full text analysis, which was performed independently by the two reviewers. The exclusion reasons were collected. Discrepancies in the screening were resolved through a discussion between the two reviewers with assistance of a third reviewer (ADB), if necessary. In case of missing information or data, the authors from such papers were contacted up to three times by e-mail.
The articles that met the inclusion criteria were subjected to critical appraisal, which was carried out by two reviewers (SBNB and MLV) independently. Standardized data extraction form was created in an Excel spreadsheet (Microsoft Corporation, Redmond, WA, EUA) to collect the following data:
Publication details: authors, country, year and journal of the publication.
Study characteristics: objectives, materials and methods, results and conclusions.
Materials characteristics: dental trademark, geometry and size of specimens.
Methods characteristics: equipment and devices, type of indenter, edge distance (in mm) and parameters used.
A descriptive analysis of the findings was used to summarize the data. Due to the narrative characteristic of present study, a quantitative analysis was considered impractical and only a qualitative data synthesis was performed.
Fig. 1 presents a PRISMA flow chart for the study selection, including the reasons for exclusions. From the initial 1848 studies identified after the removal of duplicates, 51 were screened full text to assess for eligibility, and 20 studies were included in the qualitative analysis.
Table 2 shows the included studies in the review after systematic search, as well as the variables of interest that were collected. Studies were organized by the dental structure or material tested. Two studies performed edge chipping test in human teeth (10%), nine in ceramic materials only (45%), five in polymer-based and resin-based composites (RBC) (25%) and four studies evaluated ceramics and polymer-based or RBC materials (20%). Specimen geometry varied among studies, with bar-shaped (rectangular) specimens being the most popular (65%), followed by disk-shaped specimens (20%), and 15% of tooth-shaped specimens (crowns and roots).
|Structure or material tested||Author (Year), Journal||Objective||Specimen geometry||Main test equipment||Indenter type||Edge distance (in mm)||Reported parameter a|
|Human tooth||Chai et al. [ ],
J Mech Behav Biomed Mater
|To investigate chipping in teeth by carrying out in-situ fracture tests on extracted human molars.||Crowns||Universal Testing Machine||Vickers||0.2–4.0||F vs. d|
|Whitbeck et al. [ ],
J Res Natl Inst Stand Technol
|To evaluate changes in fracture resistance in fully developed human teeth treated with calcium hydroxide using an edge chipping test and to evaluate the suitability of this test.||Roots||CK 10||Conical 120°||0.1 – 0.5||T e|
|Ceramics||Quinn et al.
Mach Sci Technol
|To evaluate the effect of material properties and the role of “edge toughness” as a practical predictor of machining behavior in brittle materials.||Bars||CK 10||Conical 180°||0.1 – 0.5||T e|
|Chai and Lawn [ ],
|To conduct chipping tests on brittle materials using a Vickers indenter loaded at prescribed distances from polished orthogonal edges.||Bars||Universal Testing Machine||Vickers||0.2 – 2.5||T e|
|Quinn et al.
|To investigate the chipping resistance of veneered zirconia specimens and compare it to the chipping resistance of porcelain fused to metal (PFM) specimens.||Bars||CK 10||Conical 120°||0.1 – 0.5||F vs. d|
|Zhang et al.
J Dent Res
|To conduct chipping tests on graded zirconia crowns with anatomically correct geometries.||Crowns||Universal Testing Machine||Vickers||0.05 – 3.0||F vs. d|
|Zhang et al. [ ],
|To evaluate the chipping resistance for lithium disilicate glass-ceramics and modified zirconia materials.||Bars||Universal Testing Machine||Vickers||0.05 – 1.0||T e|
|Quinn et al. [ ],
J Am Ceram Soc
|To measure the fracture resistance of alumina/alumina-zirconia laminated structures with edge chipping test.||Bars||CK 10||Conical 120°||0.1 – 0.6||T e|
|Argyrou et al. [ ],
J Prosthet Dent
|To measure the edge chipping resistance of the polymer infiltrated ceramic network and resin nanoceramic materials and compare them with 2 commonly used feldspathic ceramic and leucite reinforced glass-ceramic CAD/CAM materials that share same clinical indications.||Bars||Universal Testing Machine||Conical 120°||0.1 – 0.7||T e|
|Taufer and Della Bona [ ],
J Mech Behav Biomed Mater
|To evaluate the edge chipping resistance of two CAD/CAM monolithic ceramics bonded to a dentine analogue substrate.||Bars||Universal Testing Machine||Vickers||0.1 – 0.6||R eA|
|Tanaka et al. [ ],
|To describe an edge chipping method developed with the use of an universal testing machine and to verify the accuracy of this method to determine the influence of residual thermal stresses on the chipping fracture resistance of veneering porcelain.||Bars||Universal Testing Machine||Vickers||0.1 – 1.2||T e|
|Polymer-based and composites||Kim and Watts [ ],
|To evaluate in vitro the edge-strength of polymer-based provisional crown and fixed partial denture materials at increasing distances from an edge.||Disks||CK 10||Conical 120°||0.4 – 1.0||S E|
|Baroudi et al. [ ],
|To evaluate in vitro the failure forces of flowable composites at different distances from an interface edge of a bulk material.||Disks||CK 10||Vickers||0.4 – 1.0||S E|
|Watts et al. [ ],
|To evaluate the applicability of an edge strength measurement device in an in vitro test to determine the force required to fracture flakes of material by a Vickers indentation at progressively increasing distances from an interface edge of bulk material.||Disks||CK 10||Conical 120°||0.4 – 1.0||S E|
|Quinn and Quinn [ ],
|Determination of material and fractographic properties of a dental indirect resin composite material.||Bars||CK 10||Conical 120°||0.05 – 0.3||T e|
|Quinn et al. [ ],
|To compare the edge chipping fracture resistances of polymethylmethacrylate (PMMA) based and two filled resin composite denture tooth materials.||Bars||CK 10||Conical 120°||0.05 – 0.6||T e|
|Ceramics and Polymer-based composites||Ereifej et al. [ ],
|To evaluate the edge strength and fracture patterns of different all-ceramic and indirect composite materials used in prosthodontic applications.||Bars||CK 10||Vickers;||0.4 – 1.0||S E|
|Quinn et al. [ ],
|To measure the fracture resistance of CAD/CAM dental restoration ceramics and resin composites with edge chipping test.||Bars||CK 10||Vickers||0.1 – 0.6||T e|
|Quinn et al. [ ],
|To analyze the edge chipping resistance of brittle materials evaluated in Part 1, to determine why some force-distance trends were linear and others were nonlinear and account for differences in chipping resistance with indenter type.||Bars||CK 10||Conical 90°||0.1 – 0.6||T e|
|Pfeilschifter et al. [ ],
|To investigate the edge force of CAD/CAM materials as a function of material, thickness and distance from the margin.||Disks||Universal Testing Machine||Vickers||0.4 – 1.0||S E|