Survival of directly placed ormocer-based restorative materials: A systematic review and meta-analysis of clinical trials

Highlights

  • Ormocers demonstrated no difference in success compared to conventional composites.

  • Although non-significant, the global failures was higher for ormocers.

  • A significantly higher failure rate due to sensitivity was observed for ormocer-based materials than for other composites.

  • Methodological quality should be improved, using CONSORT and Cochrane guidelines.

  • Future RCT should test a new family of ormocers, dimethacrylate-diluent-free.

Abstract

Objectives

In-vitro experiments on ormocers (ORganically MOdified CERamics) have provided controversial results. Consequently, the objectives of this meta-analysis were to (1) compare clinical performances of first generation ormocers versus conventional composite restorations, (2) explore the influence of various clinical factors and the impact of the quality of studies on published results.

Methods

The following databases were explored until 2017/01/08: Ovid MEDLINE In-Process, Pubmed, CENTRAL, HTA, DARE, LILACS and Google Scholar.

Studies of more than two years with quantitative comparisons between ormocers and control groups were selected. Outcome was the failure of a restoration (need to repair, remove or replace). Multivariate random-effects Poisson’s regression was used to obtain a summary estimate.

Results

75% of the 8 included trials concerned Class I/II restorations. Although non-significant, the global failures were higher for ormocers (0.22 [−0.16; 0.61]). For Class I/II restorations, a significantly higher sensitivity was observed for ormocer-based materials compared to other composites (0.75 [0.01; 1.50]). An increase of the number of restorations per patient was associated with higher marginal adaptation failures for ormocers in Class I/II obturations (0.59 [0.11; 1.08]).

Significance

This study did not identify clear advantages of using the first generation of ormocer-based fillings rather than conventional composites. Given the recent development of new, dimethacrylate-diluent-free ormocer matrices, potentially more stable and resistant, new randomized clinical trials should be developed comparing this new family of pure ormocers with current composites.

Introduction

To replace part of the dental organ in a sustainable way and to meet increasing esthetic demand from patients, modern resin-based dental composites have undergone important improvements . Even though sufficient mechanical properties have been obtained to consider them suitable for placement in load-bearing areas in posterior teeth, the stability and longevity of composite resin restorations should nevertheless be further optimized . Controlling the degree of cure, polymerization shrinkage of the matrix and adhesion to adhesive systems is critical to improve biofunctional and biocompatibility properties . The materials are subjected to stresses not only during the polymerization but also during aging in the oral environment. The aqueous medium of saliva, associated with masticatory and thermal variations and pH, exerts a degradative effect on the resin matrix and fillers . To overcome these phenomena, new matrices have been developed and the filler content increased.

Ormocer is the acronym for ORganically MOdified CERamic. These materials were developed by the Fraunhofer Institute for Silicate Research (ISC) and have been commercialized in dentistry since 1998 . They are composed of inorganic-organic co-polymers with inorganic silanated filler particles . The solution and gelation process (sol-gel process) induces polymerization of multi-functional urethane and thioetheroligo(meth)acrylate alkoxysilanes , producing a silica glass by hydrolysis of the alkoxy groups followed by water and alcohol polycondensation . This results in a matrix of long inorganic silica chain backbones with organic lateral chains, able to react during curing using conventional photoinitiators . The larger size of the monomer molecules may reduce polymerization shrinkage, wear, and leaching of monomers , and the materials are expected to combine the advantages of both organic polymers ( e.g. flexibility and impact resistance) and inorganic materials ( e.g. thermal stability, mechanical strength and chemical resistance) . Currently, the available ormocer-based composites Admira ® (Voco GmbH, Germany), Definite ® (Degussa AG, Germany) and Ceram X ® (Dentsply DeTrey GmbH, Germany) are associated with conventional methacrylate diluents, which may reduce their ability to fulfill their initial promises . A higher toxicity of this first generation of ormocers is suspected: in-vitro studies have revealed higher 3T3 fibroblast cytotoxicity of polymerized disks of Admira compared to Tetric Ceram or Z 250, which could be linked to the higher release of bis-GMA . The coefficient of thermal expansion has been shown to be similar to that of natural tooth structure . Shear bond strength is also equivalent to that of traditional bis-GMA matrix containing composites and in-vivo sealing ability and polymerization shrinkage are equivalent to packable composite . Despite only 3 brands of ormocers are available for comparison, they are expected to exhibit similar mechanical properties to hybrid, nano-hybrid and packable composites (flexural strength, flexural modulus, diametric tensile and compressive strength) after storage in water for 24 h . However, after one year of aging in saliva, ormocers obtained the lowest values for flexural strength and Vickers hardness . Ormocers are used in conjunction with nanoparticles. For example, they may contain ZrO2 nanoparticles . This should also increase the microsurface hardness and thus the polishability of the restoration; roughness values after polishing were found to be similar to those of nanofill composites . Nevertheless, ormocer matrix seemed to be sensitive to degradation processes, with greater degradation of optical properties, particularly in acidic media . In vitro studies have shown limitations when attempts have been made to translate findings into real life and analysis of clinical trials is necessary to obtain information about the clinical performances of ormocer restorations, and the differences among them . A previous study pointed out some poor clinical behavior of ormocers but an in-depth meta-analysis for ormocers is still lacking in the literature.

Consequently, the objectives of this meta-analysis were to (1) compare clinical performance (such as survival rates or quality of restorations) of the first generation of ormocer-based fillings against those of conventional composite restorations and (2) explore the influence of different clinical factors and the impact of the quality of studies on published results.

Materials and methods

Search strategy

We followed the PRISMA guidelines (Supplementary File S1 ) to identify any controlled trials, randomized or not, with patients or teeth randomly allocated to at least one ormocer based material, with follow-up of more than two years. There was no restriction on language of publication. The extraction of data from reports using a data extraction form was performed twice by one investigator (PM), at one-month interval to confirm data. File S1

We used the terms “ormocer” or their trade names (“Admira”, “Definite” or “Ceram X”) and searched the following databases: Cochrane Central Register of Controlled Trials, Health Technologies Assessment (HTA), Database of Abstracts of Reviews of Effects (DARE), Ovid MEDLINE In-Process and Other Non-Indexed Citations via OvidSP, the databases of MEDLINE (1950 to present) via Pubmed, Biosis (1997 to present) via OvidSP ® , and LILACS via the Virtual Health Library search form (1982 to present). Details of the search strategy are provided in Supplementary File S2 . File S2

Reference lists of query studies were inspected to identify any additional relevant published or unpublished data. For literature that is difficult to trace, the so-called “grey literature”, we sought out unpublished and on-going trials by searching the World Health Organization (WHO) International Clinical Trials Registry Platform, which provides access to several trial registries including ClinicalTrials.gov and the International Standard Randomized Controlled Trial Number Register (ISRCTN). We also searched for Conference proceedings from the International Association for Dental Research meeting (IADR) sessions and the Academy of Dental Materials. Google Scholar was also queried to identify additional references such as theses, using the same search strategy. The last search was conducted on 2017/01/08.

Extraction of data from primary studies

Outcomes

Studies with quantitative comparisons between ormocers (OR) and control groups were selected and included in the quantitative analysis . Control materials could be conventional composite (CC), polyacid-modified resin composite (CP), silorane (SI) or glass ionomer (GI). Studies about different techniques of placing the same material were not included. In accordance with FDI guidelines, failure of a restoration was defined as the need to repair, remove or replace it .

Subgroup and sensitivity analyses

Characteristics of included studies

As stated in the Cochrane Handbook , the I 2 statistic was used to quantify the amount of heterogeneity as probably not important (0%–40%), moderate (30%–60%), substantial (50–90%) or considerable (75%–100%). Meta-regression, subgroup and sensitivity analyses were planned to explain such statistical heterogeneity and determine whether difference in the efficacy of ormocer restorations compared to other materials was influenced by methodological factors (such as risk of bias) and/or clinical factors (variability in the participants and interventions). The year, duration of study, mean number of restorations per patient, mean age, gender ratio, isolation method and main source of funding were extracted in order to perform sensitivity analyses and meta-regression. The quality of studies and risk of biases were also assessed. For quality assessment, each trial was judged as Low, High or Unclear risk of bias for random sequence generation, allocation concealment, blinding, incomplete outcome data or selective reporting, using the Cochrane Risk of bias list .

Characteristics of restorations

We also extracted different clinical characteristics of the restorations in order to perform subgroup analyses. The positions of restorations were identified and classified as Class I, II or V according to their location. Finally, we also extracted, when available in the original publication, the type of isolation method (cotton rolls or rubber dams), and the bonding method, classified as etch and rinse (ER) or self-etch (SE).

Characteristics of teeth

Both permanent and primary teeth were considered.

Statistical analyses

The restoration was considered as the statistical unit. Split mouth and parallel studies were both included. For each study, event incidence rates were calculated as the total number of events divided by the total restoration exposure time in years. For each study, the last time point was considered. The number of events was considered to follow a Poisson distribution for a given sum of exposure years . Consequently, a multivariate random-effects Poisson’s regression ( metafor R package ) was used to obtain a summary estimate, either for global results or subgroup analyses (according to the brand of ormocer or type of restoration). Sensitivity analyses were also performed using such multivariate regression to investigate whether event rates were influenced by the factors mentioned above (age, gender, isolation method, number of restorations per patient). Survival curves were built from the data for all time points of each study to compare them between ormocers and other biomaterials.

Materials and methods

Search strategy

We followed the PRISMA guidelines (Supplementary File S1 ) to identify any controlled trials, randomized or not, with patients or teeth randomly allocated to at least one ormocer based material, with follow-up of more than two years. There was no restriction on language of publication. The extraction of data from reports using a data extraction form was performed twice by one investigator (PM), at one-month interval to confirm data. File S1

We used the terms “ormocer” or their trade names (“Admira”, “Definite” or “Ceram X”) and searched the following databases: Cochrane Central Register of Controlled Trials, Health Technologies Assessment (HTA), Database of Abstracts of Reviews of Effects (DARE), Ovid MEDLINE In-Process and Other Non-Indexed Citations via OvidSP, the databases of MEDLINE (1950 to present) via Pubmed, Biosis (1997 to present) via OvidSP ® , and LILACS via the Virtual Health Library search form (1982 to present). Details of the search strategy are provided in Supplementary File S2 . File S2

Reference lists of query studies were inspected to identify any additional relevant published or unpublished data. For literature that is difficult to trace, the so-called “grey literature”, we sought out unpublished and on-going trials by searching the World Health Organization (WHO) International Clinical Trials Registry Platform, which provides access to several trial registries including ClinicalTrials.gov and the International Standard Randomized Controlled Trial Number Register (ISRCTN). We also searched for Conference proceedings from the International Association for Dental Research meeting (IADR) sessions and the Academy of Dental Materials. Google Scholar was also queried to identify additional references such as theses, using the same search strategy. The last search was conducted on 2017/01/08.

Extraction of data from primary studies

Outcomes

Studies with quantitative comparisons between ormocers (OR) and control groups were selected and included in the quantitative analysis . Control materials could be conventional composite (CC), polyacid-modified resin composite (CP), silorane (SI) or glass ionomer (GI). Studies about different techniques of placing the same material were not included. In accordance with FDI guidelines, failure of a restoration was defined as the need to repair, remove or replace it .

Subgroup and sensitivity analyses

Characteristics of included studies

As stated in the Cochrane Handbook , the I 2 statistic was used to quantify the amount of heterogeneity as probably not important (0%–40%), moderate (30%–60%), substantial (50–90%) or considerable (75%–100%). Meta-regression, subgroup and sensitivity analyses were planned to explain such statistical heterogeneity and determine whether difference in the efficacy of ormocer restorations compared to other materials was influenced by methodological factors (such as risk of bias) and/or clinical factors (variability in the participants and interventions). The year, duration of study, mean number of restorations per patient, mean age, gender ratio, isolation method and main source of funding were extracted in order to perform sensitivity analyses and meta-regression. The quality of studies and risk of biases were also assessed. For quality assessment, each trial was judged as Low, High or Unclear risk of bias for random sequence generation, allocation concealment, blinding, incomplete outcome data or selective reporting, using the Cochrane Risk of bias list .

Characteristics of restorations

We also extracted different clinical characteristics of the restorations in order to perform subgroup analyses. The positions of restorations were identified and classified as Class I, II or V according to their location. Finally, we also extracted, when available in the original publication, the type of isolation method (cotton rolls or rubber dams), and the bonding method, classified as etch and rinse (ER) or self-etch (SE).

Characteristics of teeth

Both permanent and primary teeth were considered.

Statistical analyses

The restoration was considered as the statistical unit. Split mouth and parallel studies were both included. For each study, event incidence rates were calculated as the total number of events divided by the total restoration exposure time in years. For each study, the last time point was considered. The number of events was considered to follow a Poisson distribution for a given sum of exposure years . Consequently, a multivariate random-effects Poisson’s regression ( metafor R package ) was used to obtain a summary estimate, either for global results or subgroup analyses (according to the brand of ormocer or type of restoration). Sensitivity analyses were also performed using such multivariate regression to investigate whether event rates were influenced by the factors mentioned above (age, gender, isolation method, number of restorations per patient). Survival curves were built from the data for all time points of each study to compare them between ormocers and other biomaterials.

Results

Description of studies

We screened 524 studies and 40 full-text articles were retrieved based on titles and abstracts. Finally, 11 of them were included, corresponding to 8 unique trials (see flow diagram in Supplemental File S2 ). Some studies were split into two different articles to present intermediate and final results ( e.g. Bottenberg et al. with the three- and five-year results data ). Details on included studies are provided in Table 1 . Most studies concerned Class I/II restorations (6 unique studies (75%)). Two studies, one for Class I/II and one for Class V, lasted 8 years . Other studies lasted 3–5 years.

Table 1
Description of included studies with at least one ormocer tested.
Country Method of isolation Np Nr Female (%) Mean age Type of restorations Follow-up (years) Composite: bonding comparisons
Bottenberg 2007/2009 Belgium Rubber dam 32 135 56 38 Class I/II 0.5, 1, 2, 3, 4, 5 Admira: ER; definite: SE; tetric ceram: ER
Demirci 2015 Turkey Cotton roll 30 147 73 20 Class I/II 1, 2, 3, 4 Ceram X: ER; filtek supreme XT: ER
dall’Orologio 2014 Italy Rubber dam 50 150 58 Class V 4, 6, 8 Ceram X: ER; esthet X: ER
Mahmoud 2013 Egypt Cotton roll 40 140 33 Class I/II 1, 2, 3 Ceram X: ER; admira: ER; filtek supreme: ER; tetric ceram: ER
Schirrmeister 2006/2009 Germany Rubber dam 37 73 54 Class I/II 1, 2, 3, 4 Ceram X: ER; tetric ceram: ER
Schmidt 2011/2015 Denmark Rubber dam 72 158 82 46 Class I/II 1, 5 Ceram X: SE; filtek silorane: SE
van Dijken 2011/2015 Sweden Cotton roll 78 158 56 53 Class I/II 1, 2, 3, 4, 5, 6, 7, 8 Ceram X: SE; ceram X: ER
Yaman 2014 Turkey Cotton roll 24 144 46 45 Class V 1, 2, 3 Ceram X: ER; ceram X: SE; filtek silorane: SE
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Nov 22, 2017 | Posted by in Dental Materials | Comments Off on Survival of directly placed ormocer-based restorative materials: A systematic review and meta-analysis of clinical trials
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