Statement of problem
Dentists must regularly determine the best adhesive cementation protocol for glass-ceramic restorations on posterior teeth. The authors are aware of few in vivo follow-up studies and no meta-analyses, including clinical trials, regarding this clinically relevant topic, which merits further investigation.
The purpose of this systematic review and meta-analysis was to statistically analyze the clinical performance of glass-ceramic posterior restorations by using a descriptive synthesis based on the integrity of the tooth and restoration under different cementation protocols for self-adhesive or conventional resin cements.
Material and methods
The electronic databases Cochrane, LILACS, PubMed/MEDLINE, SciELO, Scopus, and Web of Science were used to identify relevant clinical trials. Non–peer-reviewed literature searches and hand searching were performed to find additional references. Language, participant’s age, or time restrictions were not set. Restoration and tooth integrity were the 2 aspects considered for the meta-analysis. Statistical analyses were performed using a software program in which fixed or random effect models with risk ratios and 95% confidence intervals were applied.
Three prospective randomized or quasirandomized clinical trials, published in English from 2012 onward, were selected and statistically analyzed. The integrity of the tooth and restoration was assessed at the baseline and 1 year after the restorative intervention. The statistical analyses did not show any significant differences between the intervention and control groups in terms of the integrity of the tooth and restoration.
This meta-analysis indicated no clinical differences in the ceramic cementation using a self-adhesive or conventional resin cement after the 1-year follow-up period because both resin cements showed adequate properties for tooth and restoration integrity.
Traditionally, conventional systems are considered the gold standard for adhesive cementation of ceramic restorations. However, attempts have been made to use self-adhesive resin cements to reduce technique sensitivity, postoperative sensitivity, and clinical time. Therefore, if both conventional and self-adhesive resin cement systems present the same clinical performance, then their use according to the criteria for individual clinical applications should be considered.
To satisfy the esthetic and functional requirements in restorative dentistry, cements, cementation techniques, bonding systems, and bonded glass-ceramics have been developed and have become popular. To ensure adequate resistance and esthetics, a product is needed between the tooth and the ceramic restoration. Cements are necessary to provide good marginal adaptation and for ensuring the retention of the restoration. Moreover, they also contribute to the maintenance of the porcelain margin and original color of the restoration.
Adhesive cementation can be achieved using resin cements, which are typically modified composite resins with a higher fluidity to improve flow during cementation. Conventional cementation methods based on dentin and enamel adhesives, besides exhibiting varying results depending on the technique, also require multiple application steps and are time-consuming. Self-adhesive cements have a straightforward application technique and are designed to overcome the limitations of conventional resin cements by combining the favorable characteristics of different cements into a single product. The sensitivity of the adhesive technique was improved by simplifying the application procedure. This single-step technique has eliminated the prior application of an adhesive system or other pretreatments. However, these cements have limited conditioning potential because they can only superficially interact with the dentin. Self-adhesive resin cements are unable to create a distinct hybrid layer due to their high viscosity, which hinders deep penetration of the resin. According to the manufacturers, as the removal of the smear layer is not required, postoperative sensitivity is not expected. Mild inflammatory pulp responses were observed when self-adhesive resin cements were used, whereas moderate responses were observed for conventional methods. In addition, there is some evidence that the material is able to release fluoride.
Previous studies have reported no significant difference in the bonding effectiveness of self-adhesive and conventional systems when the correct protocol is used. However, owing to the lack of long-term scientific evidence, most dentists remain apprehensive about the indications for and long-term response to self-adhesive resin cements.
With respect to the technique itself, adhesive cementation can be considered more difficult as it is more time-consuming and requires improved moisture control in comparison with water-based cementation. Posterior crowns exhibit higher fracture rates than anterior crowns, and indirectly bonded restorations in molars exhibit higher failure rates than those in premolar crowns. The clinical success and reliability of the ceramic systems are directly related to the mechanical integrity of their constituent materials and bond strength at the ceramic-adhesive interface.
Therefore, the purpose of this systematic review and meta-analysis was to analyze the clinical performance of glass-ceramic posterior indirect restorations using resin cements. The null hypothesis was that no difference would be found between the self-adhesive resin cements and conventional adhesive resin cements in terms of both the tooth and restoration integrity.
Material and methods
This systematic review was developed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist and was registered at the International Prospective Register of Systematic Reviews (PROSPERO) under the number CRD42018086472.
Randomized clinical trials in which the main goal was to evaluate the clinical performance of self-adhesive cements compared with conventional resin cements for glass-ceramic indirect posterior restorations were included. There was no restriction with respect to language, participant age, or time.
Studies were excluded based on the following criteria: zirconia restorations; nonvital teeth or those with root canal treatments or fiber posts; implants; indirect restorations’ clinical performance related to orthodontic traction; direct restorations; studies that exclusively compared conventional resin cements or self-adhesive resin cements and in which both the control and intervention groups referred to a single type of resin cement; letters; reviews; book chapters; conference abstracts; personal opinions; descriptive studies; retrospective studies; case reports; and case series.
Studies were screened using a search strategy adapted for the following electronic databases: Cochrane Central Register of Controlled Trials, LILACS, PubMed (MEDLINE), SciELO, SCOPUS, and Web of Science. Hand searches were performed on the reference lists to identify additional studies. In addition, non–peer-reviewed literature was searched by screening the title and abstracts of the first 150 hits (filtered by “relevance”) using Google Scholar. Duplicate studies were excluded using EndNote Web and Rayyan software programs. The search was conducted on January 10, 2018.
The study selection followed 3 steps. First, 2 investigators (S.J.L.S., D.L.N.P.) screened the titles of the studies that appeared to meet the inclusion criteria. In the second phase, the same reviewers independently read the abstracts of potentially relevant articles. Finally, they independently read the full text of the selected articles and excluded those that did not meet the inclusion criteria. Disagreements in any of the 3 steps were resolved by discussion and mutual agreement among the reviewers. If no consensus was reached, a third author (L.V.M.L.R.) was consulted to reach the final decision.
The first investigator (S.J.L.S.) collected the following data from the selected articles: study characteristics (author(s), country of publication, year of publication, study design, and objectives), population characteristics (the total number of participants, the total number of restorations evaluated, sample size, mean age), intervention characteristics (follow-up period, intervention and group sizes, pretreatment and material used), and result characteristics (main results and statistical analyses). The second author (D.L.N.P.) examined all the retrieved information for the analysis. The corresponding authors of the article were contacted when important data were not described in the studies in an attempt to retrieve the missing information.
The risk of bias of the selected studies was assessed using the Meta-Analysis of Statistics Assessment and Review Instrument (MAStARI). Randomized or quasirandomized controlled trials were considered, including judgments regarding sequence generation, blinding of participants, allocation concealment, and other bias sources. The risk of bias was described as high, moderate, or low. Two reviewers assessed the risk of bias independently (S.J.L.S., D.L.N.P.), and differences were resolved in consultation with a third investigator (L.V.M.L.R.). Table 1 shows the criteria for clinical evaluation of the treatments used by the 3 studies.
|Taschner et al, 2012, Germany||Emiroglu et al, 2015, Turkey||Vogl et al, 2016, Germany||Description|
|Alfa 1||Alfa 1||Clinically very good||Perfect|
|Alfa 2||Alfa 2||Clinically good||Slight deviations from ideal performance; correction possible without damage to tooth or restoration|
|Bravo||Bravo||Clinically sufficient||Few defects; correction impossible without damage to tooth or restoration. No negative effects expected|
|Charlie||Charlie||Clinically unsatisfactory||Severe defects; prophylactic removal for prevention of severe failures|
|Delta||Delta||Clinically poor||Immediate replacement necessary|
Meta-analysis was performed using the RevMan 5.3 program, where fixed or random effect models with risk ratios and 95% confidence intervals were applied. Although the selected studies analyzed several variables, for this meta-analysis, only the restoration integrity and tooth integrity were considered. For the data that were not suitable for the meta-analysis, a qualitative analysis was applied. Heterogeneity within the selected studies was evaluated by considering the following characteristics: clinical (participant differences, type of intervention, follow-up periods, and results of the studies), methodological (risk of bias, summary measures, and design of the studies), and statistical (absolute and relative effects of the studies).
The quality of the evidence was assessed using the Grading of Recommendations, Assessments, Development and Evaluations tool (GRADE). The parameters for this assessment were as follows: study design, publication bias, sample size, study limitations, imprecision, indirectness, inconsistency, and magnitude of absolute and relative effects. The quality of the evidence was reported as high, moderate, low, or very low. This tool was created based on the evaluation table of the quality criteria of diagnostic accuracy (QUADAS) by Cochrane.
In phase 1 of the study selection, 1657 citations were identified across the 6 electronic databases. The results from the non–peer-reviewed literature search added 150 references; 11 000 citations were identified using Google Scholar, but only 150 citations were considered for the analysis. After removing duplicate articles, 1019 citations remained. In phase 2, 1625 articles were excluded based on the titles. A thorough screening of 394 abstracts was then conducted, and 384 references were excluded. Hand searches from the reference lists did not identify any additional references. Thus, 10 articles remained for full-text reading. This process led to the exclusion of 7 articles. Finally, 3 studies were selected for the synthesis. Figure 1 details the process of identification, inclusion, and exclusion of the studies.
Table 2 summarizes the characteristics of the included studies. These studies were published in English from 2012 onward. All the selected articles were either prospective randomized or quasirandomized clinical trials, and the follow-up periods were mentioned in all the studies (mean: 18 months, range: 12-24 months). Each study used a different system, and the results are described in Table 2 .
|Study Characteristics||Population Characteristics||Intervention Characteristics|
|Author, Year, Country||Study Design||Objective||Total Number of Participants ( n )||Total Number of Restorations Evaluated or Sample Size ( n )||Age Mean (y)||Follow-up Period (mo)||Clinical Parameters|
|Taschner et al, 2012, Germany||RCT||To compare clinical performances of 2 different cementation procedures to lute IPS empress inlays and onlays.||30||83 (70 inlays/13 onlays) (47 premolars/36 molars)||39||24||Tooth and inlay integrity|
|Emiroğlu et al, 2015, Turkey||QRCT||To evaluate clinical performances of inlays and onlays luted with 2 different resin cements, mixed at different temperatures, and to evaluate marginal adaptation of restorations.||50||100 (18 inlays/82 onlays) (16 premolars/84 molars)||33||12||Tooth and restoration integrity|
|Vogl et al, 2016, Germany||RCT||To evaluate clinical performance of partial ceramic crowns (PCCs) inserted with new universal adhesive, where corresponding luting material used in self-etch or selective etch approach is compared with self-adhesive universal luting material.||48||144 (144 partial ceramic crowns or onlays) (42 premolars/102 molars)||48||18||Tooth integrity, fracture of material, and retention|