The effect of endodontic access on all-ceramic crowns: A systematic review of in vitrostudies

Abstract

Objectives

The aim of this systematic review was to identify from in vitro studies the effect of endodontic access on the fracture resistance and damage around the access cavity of all-ceramic crowns.

Data

The articles identified were screened by two reviewers according to inclusion and exclusion criteria. The reference lists of articles advanced to second round screening were hand searched to identify additional potential articles. The risk of bias for the articles was independently performed by two reviewers.

Sources

An electronic search was conducted on PubMed/Medline, Web of Science, Scopus and Embase databases with no limitations.

Study selection

383 articles were identified, of which, eight met the inclusion criteria and formed the basis of this systematic review. Factors investigated in the selected articles included the, presence of microcracks at the access cavity, repair protocol, ceramic type, crown fabrication method, luting agent and grit size of the diamond bur. The risk of bias was deemed to be high for three, medium for two and low for three of the reviewed studies. The high level of heterogeneity across the studies precluded meta-analyses.

Conclusion

Based on the currently available scientific evidence, a ‘best practice’ protocol with regard to improving the fracture resistance of endodontically accessed and repaired all-ceramic crowns cannot be conclusively identified. However, some key factors which potentially impact on the fracture resistance of endodontically accessed and repaired all-ceramic crowns have been isolated. Cautious clinical interpretation of these factors is concluded for the maintenance of the crown as a permanent restoration.

Clinical significance

Key factors which impact on the fracture resistance of endodontically accessed and repaired all-ceramic crowns have been isolated from in vitro studies. Cautious clinical interpretation of these factors is advised for the maintenance of the crown as a permanent restoration.

Introduction

The provision of dental crowns represents a sizeable proportion of treatment units provided to patients presenting to the General Dental Services (GDS) in England and Wales with over 1.1 million dental crowns placed annually . Additionally, dental crowns are frequently the treatment modality of choice for US dentists with approximately one crown being provided to every 2.3 US adult patients in 2012 . The increased incidences of patient treatment with dental crowns in general dental practice is often in preference to less destructive options including bleaching, resin composite (RC) restorations or minor orthodontic treatment . Dental crowns are perceived to be a durable and uncomplicated option whilst simultaneously generating the highest income . However, crown preparation is irreversibly destructive to tooth tissue, typically 62–73% of tooth structure is removed during preparation for anterior all-ceramic crowns . The link between tooth destruction and possible pulpal complications is well documented in the dental literature .

Goodacre et al. reviewed the literature to investigate the incidence of clinical complications of dental crowns over a 50-year period. The authors combined the results of five studies and identified that 3% (27 of 823) of dental crowns required subsequent endodontic treatment. A 2.1% incidence of loss of vitality after all-ceramic crown placement was calculated from a meta-analysis of 34 studies within a 5-year period . A retrospective analysis of 47,474 crowned teeth in the GDS over a ten-year period (1991–2001) highlighted that 10,426 required re-intervention, of which 2.6% (1251 of 47,474) required endodontic treatment . More recent studies reported in the literature highlighted re-intervention for all-ceramic crowns requiring endodontic treatment of 4% (9 of 205), 2.5% (34 of 1335) and 8.6% (19 of 219) for five , 8.5 and seven year follow-up time intervals.

While seemingly low incidences of re-intervention are reported it has been postulated that the actual incidences of pulpal complications may be under-recorded when determination has been made through clinical assessment only and not established through radiographical evidence . Saunders and Saunders reported a conspicuously high incidence (19%) of pulpal complications for periapical radiographs in 87 of 458 crowned teeth, emphasising the asymptomatic potential of pulpal complications. Estimates suggest that 20–50% of non-surgical root canal treatment (NSRCT) is performed through dental crowns . A survey of 543 dental practitioners (endodontists, prosthodontists and general practitioners), highlighted that 72% choose to gain access to the pulp chamber through existing crowns and maintain it as a permanent restoration, rather than remove the crown (17%) or place a temporary crown (11%).

The ‘gold standard’ of care for patients requiring a dental crown has traditionally been a porcelain fused to metal (PFM) restoration . Metal-free restorations are increasingly being prescribed in response to patients demands for increased aesthetic appeal and improvements in mechanical properties are responsible for the extended use of all-ceramics to posterior restorations . NSRCT through all-ceramic crowns is predicted to increase however, providing endodontic care through all-ceramic crowns in situ is a particular challenge with regard to crown perforation given the current availability of high toughness all-ceramic materials (Lithium disilicate, Alumina, Zirconia). Ceramics are brittle materials and their fracture toughness is flaw dependent . Flaws such as microcracks can be present as a result of processing or induced by the operator from grinding with sharp tools such as diamonds with potentially detrimental implications for the mechanical properties of the restoration. Isolation of the key factors which influence the fracture resistance of endodontically accessed and repaired all-ceramic crowns are of critical importance for the maintenance of the crown as a permanent restoration and warrant investigation. Access cavity repair is routinely performed using a RC , which is based on maintaining the crown as a permanent restoration, also ensuring a coronal seal and reducing microleakage.

The current systematic review followed and adapted the ‘Preferred Reporting Items for Systematic Review and Meta-Analysis’ (PRISMA) guidelines for reporting systematic reviews that evaluate healthcare interventions to identify and evaluate the in vitro scientific literature to address the focused questions;

  • 1.

    Which treatment factors influence the fracture resistance of endodontically accessed and repaired all-ceramic crowns? and

  • 2.

    What is the reported evidence of damage around the endodontic access cavity as a result of preparing the cavity in an all-ceramic crown?

Materials and methods

Search methodology

Medical Subject Heading’s (MeSH’s) were selected and refined to develop the electronic search concept; endodontic* OR root canal treatment* OR RCT AND access OR cavity AND ceramic* OR porcelain*. The search was customised ( Table 1 ) and applied to suit the electronic databases of PubMed/Medline (PubMed, www.ncbi.nlm.nih.gov ), Web of Science, Scopus and Embase. No language or date restrictions were applied. A backward and forward author search was carried out for all authors listed on studies forwarded to second round screening, the reference lists of these studies were hand searched for potentially relevant articles. The grey literature (Open Grey) was also consulted. The last search for all databases was run on July 18th, 2016.

Table 1
Database and search methodology.
Database Search methodology
Pubmed (1945-) (endodontic* [All Fields] OR root canal treatment* [All Fields] OR RCT [All Fields]) AND (access [All Fields] OR cavity [All Fields]) AND (ceramic* [All Fields] OR porcelain* [All Fields])
Web of Science (1945-) Topic (endodontic* OR root canal treatment* OR RCT) AND Topic (access OR cavity) AND Topic (ceramic* OR porcelain*)
Scopus (2008-) TITLE-ABS-KEY (endodontic* OR root canal treatment* OR RCT) AND TITLE-ABS-KEY (access OR cavity) AND TITLE-ABS-KEY (ceramic* OR porcelain*)
Embase (1990-) (endodontic* OR root canal treatment* OR RCT) AND (access OR cavity) AND (ceramic* OR porcelain*)
OpenGrey endodontic* OR root canal treatment* OR RCT AND access OR cavity AND ceramic* OR porcelain*

Study selection

The titles and abstracts of all articles identified by the electronic search were read and assessed by two authors (CG, NR). The full text was retrieved where the title and abstract were deemed ambiguous or when no abstract was available. First round exclusion criteria was applied to all articles which were unrelated to endodontics, or dental crowns, which had undergone an endodontic procedure prior to placing a restoration, cohort studies, patents, animal studies and conference proceedings. Articles which met the first round inclusion criteria were retrieved in full and reviewed further according to the second round inclusion criteria. The second round screening process excluded supposition articles, surveys, reviews, in vivo studies, articles which, concerned the endodontic access of crown types other than all-ceramic, finite element analysis (FEA), studies which involved non-anatomical shaped samples and studies which investigated microleakage.

Data extraction

Details from the articles included in the systematic review were extracted (when available) by one author (CG) and checked by a second author (NR). Any potential conflict was resolved by discussion with a third author (FB).

Study quality assessment

A risk of bias was assessed using an adaptation of the methods used in two previous systematic reviews of in vitro studies . Descriptions of the following parameters were used to assess each articles risk of bias: presence of a control group, blinding of the examiner, statistical analysis, evaluation of the access cavity for damage prior to repair, use of samples with similar dimensions and access cavity performed by the same operator. Where the parameter was reported, it was assigned a ‘Yes’ and if the information was absent, it was assigned a ‘No’. Articles were classed as having a high risk of bias if one or two parameters were reported, a medium risk if three or four items were reported and a low risk if five or six items were reported. Two authors (CG, NR) independently assessed the methodological quality of each included study and the third author (FB) checked the assessment.

Materials and methods

Search methodology

Medical Subject Heading’s (MeSH’s) were selected and refined to develop the electronic search concept; endodontic* OR root canal treatment* OR RCT AND access OR cavity AND ceramic* OR porcelain*. The search was customised ( Table 1 ) and applied to suit the electronic databases of PubMed/Medline (PubMed, www.ncbi.nlm.nih.gov ), Web of Science, Scopus and Embase. No language or date restrictions were applied. A backward and forward author search was carried out for all authors listed on studies forwarded to second round screening, the reference lists of these studies were hand searched for potentially relevant articles. The grey literature (Open Grey) was also consulted. The last search for all databases was run on July 18th, 2016.

Table 1
Database and search methodology.
Database Search methodology
Pubmed (1945-) (endodontic* [All Fields] OR root canal treatment* [All Fields] OR RCT [All Fields]) AND (access [All Fields] OR cavity [All Fields]) AND (ceramic* [All Fields] OR porcelain* [All Fields])
Web of Science (1945-) Topic (endodontic* OR root canal treatment* OR RCT) AND Topic (access OR cavity) AND Topic (ceramic* OR porcelain*)
Scopus (2008-) TITLE-ABS-KEY (endodontic* OR root canal treatment* OR RCT) AND TITLE-ABS-KEY (access OR cavity) AND TITLE-ABS-KEY (ceramic* OR porcelain*)
Embase (1990-) (endodontic* OR root canal treatment* OR RCT) AND (access OR cavity) AND (ceramic* OR porcelain*)
OpenGrey endodontic* OR root canal treatment* OR RCT AND access OR cavity AND ceramic* OR porcelain*

Study selection

The titles and abstracts of all articles identified by the electronic search were read and assessed by two authors (CG, NR). The full text was retrieved where the title and abstract were deemed ambiguous or when no abstract was available. First round exclusion criteria was applied to all articles which were unrelated to endodontics, or dental crowns, which had undergone an endodontic procedure prior to placing a restoration, cohort studies, patents, animal studies and conference proceedings. Articles which met the first round inclusion criteria were retrieved in full and reviewed further according to the second round inclusion criteria. The second round screening process excluded supposition articles, surveys, reviews, in vivo studies, articles which, concerned the endodontic access of crown types other than all-ceramic, finite element analysis (FEA), studies which involved non-anatomical shaped samples and studies which investigated microleakage.

Data extraction

Details from the articles included in the systematic review were extracted (when available) by one author (CG) and checked by a second author (NR). Any potential conflict was resolved by discussion with a third author (FB).

Study quality assessment

A risk of bias was assessed using an adaptation of the methods used in two previous systematic reviews of in vitro studies . Descriptions of the following parameters were used to assess each articles risk of bias: presence of a control group, blinding of the examiner, statistical analysis, evaluation of the access cavity for damage prior to repair, use of samples with similar dimensions and access cavity performed by the same operator. Where the parameter was reported, it was assigned a ‘Yes’ and if the information was absent, it was assigned a ‘No’. Articles were classed as having a high risk of bias if one or two parameters were reported, a medium risk if three or four items were reported and a low risk if five or six items were reported. Two authors (CG, NR) independently assessed the methodological quality of each included study and the third author (FB) checked the assessment.

Results

The PRISMA flow diagram provides an overview of the selection process ( Fig. 1 ). The electronic search identified 383 articles: 190 from PUBMED/Medline, 142 from Web of Science, 38 from Scopus, and thirteen from Embase. Further analysis revealed 140 duplicate records which were discarded. As a result 243 articles remained, the titles and abstracts of which were screened for first round inclusion. From these 221 were deemed irrelevant and discarded. After first round screening 22 articles remained, the reference lists of these articles were hand searched and a further four studies were identified. Therefore, a total of 26 articles were retrieved in full text and forwarded for second round screening. Eighteen studies were excluded from the analysis after this point ( Fig. 1 ). Consequently, eight studies formed the basis of this systematic review and the characteristic details extracted (when available) from the articles included in the final study are summarised in Table 2 . The grey literature (OpenGrey) yielded no new information relevant to the topic, no new articles were identified from the backward and forward author search.

Fig. 1
PRISMA flow diagram outlining the study identification and screening process.

Table 2
Characteristics details of the studies included in the current review .
Authors Total number of samples in study (n) Tooth type All-ceramic
crown material
Ceramic processing technique Die replica substrate Luting agent Bur type Access cavity dimension Access cavity
repair material
Failure load (N) recorded from compression testing Contact position with load indenter Reported evidence of damage around the access cavity Catastrophic crown failures during preparation
Teplitsky and Sutherland 56 Mixed Alumina core + veneer Heat pressed+ sintered Extracted
teeth
Temporary cement Diamond (N = 52)
Carbide (N = 4)
Not specified N/A N/A N/A Chips, roughness, vague
Cracks 1.8% (1/56) at access opening
0 crowns fractured
Stokes et al 30 Incisor-maxillary central Alumina Sintered Metal die Glass Ionomer cement Diamond Triangular 3 mm 3 Silux resin composite Control (487.07 ± 10.22) (n = 10)
Access cavity repaired with composite repair (359.05 ± 118.37) (n = 10)
Access cavity repaired with silane and composite repair (354.14 ± 58.4) (n = 10)
Incisopalatal- on ceramic only Not reported Not reported
Sutherland et al. 42 Mixed Fluoromica Cast Extracted
teeth
Temporary cement Diamond or carbide, vague Not specified N/A N/A N/A Craze lines 17% (7/42), chipping 69% (29/42) 2 crowns fractured (4.8%)
Cohen and Wallace 6 Mixed Fluoromica Cast Extracted teeth Zinc phosphate (n = 3)
Polycarboxylate (n = 3)
Diamond Not specified N/A N/A N/A Chipping at access cavity, vague, not quantified 1 crown fractured (17%)
Haselton et al. 28 Premolar Leucite Heat pressed Extracted teeth Dual-cure resin cement
(Variolink)
Diamond (n = 14) or
Tungsten carbide (n = 14)
Not specified N/A N/A N/A Edge chipping 100% (28/28)
Microcracks 14% (4/28)
Fractures 11% (3/28)
3 crowns fractures (11%)
Wood et al 48 Molar-
standardised
Zirconia core + ceramic veneer (n = 24)
Alumina core + ceramic veneer (n = 24)
CAD CAM + heat pressed
CAD CAM + heat pressed
Epoxy resin Resin modified glass-ionomer
(Rely X Luting Plus cement)
Diamond 3.5 mm round diameter XRV Herculite resin composite Alumina intact (1410 ± 111) (n = 12), m = 12.8
Alumina repaired (1436 ± 223) (n = 12), m = 6.2
Zirconia intact (2432 ± 181) (n = 12), m = 13.4
Zirconia repaired (2075 ± 348) (n = 12), m = 5.4
Axial- on ceramic and resin repair Irregularities
Edge chipping 100% (Zirconia)
Radial cracks-Zirconia (4/24)
Edge chipping 100% (Alumina)
Not reported
Qeblawi et al. 60 Molar-maxillary first Lithium disilicate Heat pressed Resin composite Dual polymerising
resin (Multilink Implant) or
Zinc phospahate (Flex’s)
Diamond (126 μm, 150 and 180 μm grit size) Not specified Tetric Evo Ceram resin composite Luted with DPR* intact crown (3316 ± 483) (n = 10)
Luted with DPR, access cavity prepared with 126 μm grit diamond bur (3464 ± 645) (n = 10)
Luted with DPR, access cavity prepared with 150 μm grit diamond bur (2915 ± 569) (n = 10)
Luted with DPR, access cavity prepared with 180 μm grit diamond bur (2354 ± 476) (n = 10)
Luted with ZP** intact crown (2242 ± 369) (n = 10)
Luted with ZP, access cavity prepared with126 μm grit diamond bur (1999 ± 448) (n = 10)
Axial- on ceramic only Not reported Not reported
Bompolaki et al. 40 Molar-standardised Lithium disilicate Heat pressed (n = 20) Milled (n = 20) Epoxy resin Dual-cure resin cement
(Variolink II)
Diamond (126 μm grit size) 3.5 mm
round diameter
Filtek Supreme resin composite Pressed intact (1901 ± 349) (n = 10), m = 5.9
Pressed repaired (1429 ± 384) (n = 10), m = 3.9
Milled intact (1573 ± 267) (n = 10), m = 6.3
Milled repaired (1297 ± 329) (n = 10), m = 4.5
Axial- on ceramic and resin repair Edge chipping 100% (pressed) (4/4)
Edge chipping 100% (milled) (4/4)
Radial crack 25% (milled) (1/4)
Not reported
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Jun 19, 2018 | Posted by in General Dentistry | Comments Off on The effect of endodontic access on all-ceramic crowns: A systematic review of in vitrostudies
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