Bond strength and marginal adaptation of resin composites and correlations with clinical results

OBJECTIVES

Due to innumerable confounding factors and a high number of types and brands of dental restorative materials, the clinical performance of restorative materials are sought predicted by various in vitro tests. However, only few such tests have been found to correlate well with clinical findings. Thus, the present study determined the in vitro dentin bond strength and marginal adaptation of Class II restorations and correlated the results to their clinical outcomes.

METHODS

Dentin bond strength (µTBS and µSBS) and marginal gap formation of Class II restorations (replica technique and SEM) were measured after 24 h and 6 m water storage using eight combinations of adhesive and resin composite. Clinical outcomes (mean survival time, Hazard Ratio, annual failure rate; n = 10.695) were gained from a data set of a retrospective multicenter study of direct restorations.

RESULTS

Significant differences were found for dentin bond strength and marginal gap formation between the restorative material groups, and negative effects of long-term storage were observed. µTBS correlated significantly with certain clinical outcomes of Class I restorations, while µSBS correlated with certain clinical outcomes of Class II, III, IV and V restorations. Marginal gap formation in enamel and number of paramarginal fractures correlated with certain clinical outcomes of Class II restorations.

SIGNIFICANCE

Using the same restorative materials in vitro as in vivo, gave significant, but weak correlations between in vitro bond strength or marginal adaptation and clinical outcomes, lending support to the use of in vitro tests in early stages of material selection.

The clinical performance of dental resin composite repeatedly preheated: A randomized controlled clinical trial

OBJECTIVES

To assess the clinical performance of class II restorations performed by repeatedly preheated resin composite "RC" at 68 °C up to ten times.

METHODS

105 patients were selected and randomized into three groups, each comprising 35 patients. Each patient was provided with a single class II Bulk-fill resin composite "BF-RC" posterior restoration based on the number of preheating cycles; group I (H0): The BF-RC was packed non-heated, group II (H1): BF-RC preheated once, and group III(H10): BF-RC preheated ten cycles. These restorations were evaluated at 1, 3,6, and 12 months, using the modified United States Public Health Service "USPHS". Statistical analysis was performed using Kruskal-Wallis test, Mann Whitney U test, and Friedmann test, where p = 0.05.

RESULTS

All the 105 restorations did not suffer from any clinical situation that recommended replacement regarding retention, fracture, secondary caries, or anatomical form. Although all performed restorations did have Alpha and Bravo scores with good clinical performance, the non-preheated RC restorations"" suffered from relatively inferior clinical performance through the follow-up period regarding marginal adaptation, marginal discoloration, and color matching when compared to preheated groups. One and ten times of preheating conducted better clinical performance.

CONCLUSIONS

After 12-months follow-up, although no restoration needed replacement or repair in the 3 tested groups, restorations with single and ten times of preheating aided in better clinical performance of RC restorations compared to the non-preheated restorations. Preheating of RC for 10 times could be used safely with good clinical performance of restorations.

CLINICAL SIGNIFICANCE

By continually preheating RC syringe up to ten times, the dentist will not only benefit from the enhanced clinical performance and easiness of application but also will use preheated RC syringes without hesitation, relying on the absence of drawbacks related to multiple preheating cycles.

Impact of repeated preheating of bulk-fill resin composite on postoperative hypersensitivity; a randomized controlled clinical trial

BACKGROUND

This clinical study was conducted aiming to evaluate the impact of repeated preheating of bulk-fill resin composite on postoperative hypersensitivity.

METHODS

A total of 105 eligible, consenting adults were recruited. Patients had posterior teeth suffering from proximal decay with no signs of irreversible pulpitis. Patients were prepared for Class II restorations and restored with bulk-fill resin composite. Patients were randomized into three groups of 35 patients according to the number of preheating cycles for the resin composite syringe used; group I: no preheating; control group at room temperature, group II: Resin composite preheated once, and group III: Resin composite preheated ten cycles. Patients were assessed for postoperative dentin hypersensitivity using the visual analogue scale (VAS) at three-time intervals: day one, one week and by the end of one month after restorative treatment. Statistical analysis was performed; ANOVA with a single factor was used to test for significance at a p value ≤ 0.05. For nonparametric data, the Kruskal‒Wallis test was used to compare the three testing groups. Friedman's test was used to study the changes within each group. Dunn's test was used for pairwise comparisons when the Kruskal‒Wallis test or Friedman's test was significant.

RESULTS

The scores of the three groups through the three time intervals were almost zero except for the first day where VAS scores were recorded with maximum score of 3 for groups I and II. Groups II and III; there was no statistically significant change in hypersensitivity scores by time with P-values 0.135 and 0.368, respectively. However, for group I there was a significant difference from VAS score recorded on first day and the two following time intervals.

CONCLUSION

The repeated preheating cycles of bulk-fill resin composite prior to curing had no adverse effect on the patients regarding postoperative dentin hypersensitivity. This information could be of utmost significance, as the same resin composite syringe can undergo numerous preheating cycles clinically before it is completely consumed with the advantage of improvement on the handling properties.

TRIAL REGISTRATION

The protocol of the current study was registered at www.

CLINICALTRIALS

gov , with the identification number NCT05289479 on 21/03/2022. All procedures involving human participants were performed in accordance with the ethical standards of the Research Ethics Committee of the Faculty of Dentistry, Minia University, Egypt, under the approval number 73/440 on 11/09/2020.

Effect of repeated preheating on monomer elution from a bulk-fill composite resin

Background

Due to incomplete polymerization of composite resin restorations, residual monomers adversely affect their mechanical properties and biocompatibility. Preheating of composite resins is advised to increase the degree of conversion and reduce monomer elution. This study aimed to analyze the effect of preheating and repeated preheating on the amount of monomer released from a bulk-fill composite resin.

Methods

Forty samples were prepared using Filtek One Bulk Fill Restorative composite resin. Samples in one group were fabricated at room temperature, whereas the composite resins in the other groups were cured after 1, 10, or 20 repeated preheating cycles (55 °C), 10 in each group. Eluted urethane dimethacrylate (UDMA) and bisphenol-A-glycidylmethacrylate (BisGMA) monomers were measured with high-performance liquid chromatography (HPLC) 24 hours and 30 days after immersion. The data were evaluated using one-way ANOVA and post hoc Tukey tests. Paired-sample t tests were used to test the differences between time intervals.

Results

At both time intervals, the greatest amounts of released BisGMA, UDMA, and total monomers were obtained from the control group, whereas 10 preheating cycles resulted in the least monomer elution. The decrease in monomer elution was not statistically significant after 10 preheating cycles compared with that after one preheating cycle (P>0.05). The group with 20 preheating cycles showed a greater amount of monomer elution compared to that with 1 and 10 cycles, which was statistically significant (P < 0.05). The amount of released monomers on day 30 was significantly higher than on day 1 (P<0.01).

Conclusion

Preheating of the bulk-fill composite resin was shown to be effective in reducing monomer elution. However, monomer elution was adversely affected after repeated preheating cycles of 20.

Examining the Impact of Preheating on the Fracture Toughness and Microhardness of Composite Resin: A Systematic Review

The objective of this comprehensive study was to systematically evaluate the effects of preheating on two critical mechanical properties, microhardness and fracture toughness, in resin composite materials. The overarching goal was to provide valuable insights into the potential benefits and limitations of this technique for enhancing the overall mechanical performance of such materials. To achieve this, an extensive and systematic electronic search was conducted across multiple reputable databases, including MEDLINE/PubMed, SCOPUS, ProQuest, SpringerLink, Web of Science, ScienceDirect, and Google Scholar, with data collection extending until June 2023. This rigorous search process resulted in the identification of 29 pertinent articles, which were subjected to a thorough risk of bias assessment employing the Quality Assessment Tool For In Vitro Studies (QUIN). The findings of this comprehensive investigation revealed several noteworthy trends. First, concerning microhardness, all the studies consistently demonstrated a positive effect of preheating on this mechanical property. This uniformity in results corroborates the initial hypothesis that preheating indeed enhances microhardness in resin composite materials. Second, with respect to fracture toughness, a majority of the studies provided evidence supporting the notion that preheating has a favorable influence on this particular mechanical property. This alignment of outcomes suggests that preheating can be a beneficial technique for improving fracture toughness in resin composites. However, it is essential to note that there were a few exceptions within the collected data, where preheating appeared to lead to a decrease in fracture toughness. Additionally, one study reported no statistically significant effect on fracture toughness. These deviations from the general trend highlight the complexity of the relationship between preheating and fracture toughness, indicating that other factors or material-specific nuances may come into play. In conclusion, the results of this study indicate that preheating resin composites can improve microhardness and fracture toughness, offering potential benefits for dental restorations. Yet, conflicting data warrants further research to uncover the reasons behind these discrepancies. Future studies should also investigate preheating's broader impact on composite resin materials to gain a comprehensive understanding of its applications and limitations in the field.

In Vitro Mechanical Properties of a Novel Graphene-Reinforced PMMA-Based Dental Restorative Material

Recent studies suggest that the incorporation of graphene in resin-based dental materials might enhance their mechanical properties and even decrease their degree of contraction during polymerization. The present study aimed at comparing the three-point flexural strength (FS), the compressive strength (CS), and the Vickers hardness (VH) of a CAD/CAM poly-methylmethacrylate (PMMA)-based resin, a recently introduced graphene-reinforced CAD/CAM PMMA-based resin (G-PMMA), and a conventional dental bis-acryl composite resin (BACR). No significant differences (p > 0.05) were detected among the materials in terms of flexural strength. On the other hand, a mean flexural modulus value of 9920.1 MPa was recorded in BACR group, significantly higher compared to the flexural modulus detected for G-PMMA (2670.2 MPa) and for conventional PMMA (2505.3) (p < 0.05). In terms of compressive modulus (MPa) and compressive strength (MPa), BACR was significantly stiffer than PMMA and G-PMMA. Concerning VH measurements, a significantly increased hardness emerged comparing the BACR group (VH 98.19) to both PMMA and G-PMMA groups (VH 34.16 and 34.26, respectively). Based on the finding of the present study, the graphene-reinforced (PMMA)-based polymer herein tested was not superior to the conventional PMMA and seemed not able to be considered as an alternative material for permanent restorations, at least in terms of hardness and mechanical response to compressive stress. More research on the mechanical/biological properties of G-PMMAs (and on graphene as a filler) seems still necessary to better clarify their potential as dental restorative materials.

Retrospective clinical evaluation of a no-prep porcelain veneer protocol

STATEMENT OF PROBLEM

Porcelain laminate veneers without tooth preparation (no-prep veneers) might represent a convenient and conservative option for the esthetic rehabilitation of anterior teeth. However, controversy exists about their predictability.

PURPOSE

The purpose of this clinical study was to retrospectively evaluate the performance of no-prep porcelain veneers placed as per the recently proposed "CH no-prep" protocol, which claimed to overcome many of the drawbacks of previous no-prep veneer solutions.

MATERIAL AND METHODS

One hundred eight no-prep porcelain laminate veneers based on the CH no-prep protocol were placed in 21 patients between 2015 and 2017. All participants were contacted, and 15 received a recall examination: a total of 78 veneers were evaluated as per the Clinical-Photographic-Micromorphologic coding. Plaque and gingival indexes and any increase in gingival recession were recorded. Pulp vitality was verified. A survival rate based on the count of absolute failures and a success rate summarizing the effect of both absolute and relative failures were calculated.

RESULTS

The mean observation period was 43.1 months, with an observation interval of 36 to 60 months and a survival rate of 97.4%. From the 5 relative failures (3 minimal fractures or chips and 2 limited marginal discolorations) and the 2 absolute failures (unrepairable fractures), an overall success rate of 91.0% was recorded, with 71 restorations that were judged excellent in terms of clinical acceptance after the recall examination. From the Clinical-Photographic-Micromorphologic evaluation, 5 restorations (6.4%) showed minimal issues for marginal integrity, while a limited porcelain overhang was identified on 2 restorations (2.8%). Micromorphologic analyses confirmed the clinical evaluations. No periodontal recession was observed, and plaque and gingival indexes appeared stable.

CONCLUSIONS

Porcelain laminate veneers placed as per the CH no-prep protocol demonstrated excellent performances after 36 to 60 months of clinical service. The achieved outcomes, in terms of color match and overall esthetic and anatomic integration, confirmed that a prepless approach may be safely adopted provided that strict rules for patient selection and finish line placement are adopted.

Comparison of Mechanical Properties of a Self-Adhesive Composite Cement and a Heated Composite Material

(1) Background: Due to the limitations of composite cements, the authors carried out tests to compare such materials with preheated composite materials because the latter may be an alternative to cements in the adhesive cementation procedure. (2) Methods: The materials used in the adhesive cementation procedure, i.e., Enamel Plus Hri (Micerium, Avegno, Italy), a heated composite material, and RelyX U200 Automix (3M, Maplewood, MN, USA), a dual composite cement, were tested for microhardness, compressive strength, flexural strength, diametral compressive strength, and elastic modulus. Composite material was heated to the temperature of 50 degrees Celsius before polymerisation. (3) Results: Higher values of microhardness (by 67.36%), compressive strength (by 41.84%), elastic modulus (by 17.75%), flexural strength (by 36.03%), and diametral compressive strength (by 45.52%) were obtained using the Enamel Plus Hri composite material compared to the RelyX U200 self-adhesive cement. The survey results revealed statistically significant differences. (4) Conclusions: Due to its better mechanical properties, the heated composite material (Enamel Plus Hri) is a beneficial alternative to composite cements in the indirect restoration placement procedure. As the strength parameters of the heated composite material increase, a higher resistance to the compressive and bending forces present in the oral cavity, and hence a greater durability of the created prosthetic reconstructions can be expected.

Composite Resin Preheating Techniques for Cementation of Indirect Restorations

Purpose

Resin-based materials have been preheated by using different techniques and commercial devices. However, a consensus on the clinical protocol for cementing with preheated composite resins is lacking. The aim of this scoping review was to identify the different methods used for heating composite resins as used for cementing indirect adhesive restorations and to determine the benefits and limitations. Study Selection. A search was performed on PubMed/MEDLINE, Embase, Cochrane, Web of Science, Scopus, LIVIVO, and the nonpeer-reviewed literature database. Studies on preheating composite resins for cementing indirect restorations were included, with no restrictions on the type of study, year of publication, or language. The following data were extracted: preheating technique, the device used for preheating, preset temperature, and warming time.

Results

In total, 304 studies were identified. After removing duplicates, 270 articles were selected, and 14 articles were included in the final evaluation. Half of the included studies reported similar preheating techniques using the Calset device for composite resins. The temperatures of 54°C and 68°C were most frequently reported, with a mean warming time of 5 minutes.

Conclusions

Preheating composite resins for the cementation of indirect restorations reduces viscosity, but the material must be used promptly after removal from the device. Practical Implications. Different methodologies for preheating composite resins have been reported and used in clinical dental practice. To achieve good results and guide the clinician on use, the techniques for heating composite resins for cementation need to be standardized. Keeping the material warm until the restorative procedure, the thickness of the indirect restoration, and the composition of the composite resins can directly affect the outcome of the procedure.

One-year clinical evaluation of bulk-fill composite resin restorations plasticized by preheating and ultrasonics: A randomized clinical trial

Introduction:

Aim:

Methodology:

Results:

Conclusion:

Effect of Light-Sources and Thicknesses of Composite Onlays on Micro-Hardness of Luting Composites

The aim of this study was to compare three different light-curing-units (LCUs) and determine their effectiveness in the adhesive cementation of indirect composite restorations when a light-curing resin cement is used. Two resin composites were selected: Enamel Plus HRI (Micerium) and AURA (SDI). Three thicknesses (3 mm, 4 mm and 5 mm) were produced and applied as overlays and underlays for each resin composite. A standardized composite layer was placed between underlay and overlay surfaces. Light curing of the resin-based luting composites was attained through the overlay filters using LCUs for different exposure times. All specimens were allocated to experimental groups according to the overlay thickness, curing unit and curing time. Vickers Hardness (VH) notches were carried out on each specimen. Data were statistically evaluated. The curing unit, curing time and overlay thickness were significant factors capable of influencing VH values. The results showed significantly decreased VH values with increasing specimen thickness (p < 0.05). Significant differences in VH values were found amongst the LCUs for the various exposure times (p < 0.05). According to the results, a time of cure shorter than 80 s (with a conventional quartz–tungsten–halogen LCU) or shorter than 40 s (with a high-power light-emitting diode (LED) LCU) is not recommended. The only subgroup achieving clinically acceptable VH values after a short 20 s curing time included the 3 mm-thick overlays made out of the AURA composite, when the high-power LED LCU unit was used (VH 51.0). Composite thickness has an intense effect on polymerization. In clinical practice, light-cured resin cements may result in insufficient polymerization for high thickness and inadequate times. High-intensity curing lights can attain the sufficient polymerization of resin cements through overlays in a significantly shorter time than conventional halogen light.

One-Year Clinical Aging of Low Stress Bulk-Fill Flowable Composite in Class II Restorations: A Case Report and Literature Review

Bulk-fill flowable composites provide functional and aesthetic restorations while eliminating incremental composite layering and saving time. The degradation of the adhesive interface with subsequent gap formation is a concern when adhesively luted restorations are placed. Moreover, the number of adhesive interface failures increases when they are exposed to long-term water storage. The aim of the present study was to evaluate the morphological characteristics of the tooth-composite interface in class II cavities restored with a low stress bulk-fill flowable composite after aging in an oral environment. We describe a case of a patient with class II cavities in four premolars restored with a low stress bulk-fill flowable composite Surefil SDR (Dentsply DeTrey GmbH, Konstanz, Germany). The occlusal part was restored with nano-hybrid resin composite Ceram X Mono (Dentsply DeTrey GmbH). After one year of clinical function, the teeth were extracted and examined in a scanning electron microscope (SEM). It can be concluded that the application of bulk-fill covered with conventional composite seems to provide the homogeneous and stable bond to tooth structure after one year of aging in an oral environment. However, some defects within the dentin-resin composite interface were observed.

The effect of preheating resin composites on surface hardness: a systematic review and meta-analysis

Objectives

This paper presents a systematic review and meta-analysis of the effect of preheating on the hardness of nanofilled, nanoceramic, nanohybrid, and microhybrid resin composites.

Materials and Methods

An electronic search of papers on MEDLINE/PubMed, ScienceDirect, and EBSCOhost was performed. Only in vitro studies were included. Non-English studies, case reports, clinical trials, and review articles were excluded. A meta-analysis of the reviewed studies was conducted to quantify differences in the microhardness of the Z250 microhybrid resin composite using the Comprehensive Meta-Analysis software.

Results

Only 13 studies met the inclusion criteria for this systematic review. The meta-analysis showed that there were significant differences between the non-preheated and preheated modes for both the top and bottom surfaces of the specimens (p < 0.05). The microhardness of the Z250 resin composite on the top surface in the preheated mode (78.1 ± 2.9) was higher than in the non-preheated mode (67.4 ± 4.0; p < 0.001). Moreover, the microhardness of the Z250 resin composite on the bottom surface in the preheated mode (71.8 ± 3.8) was higher than in the non-preheated mode (57.5 ± 5.7, p < 0.001).

Conclusions

Although the results reported in the reviewed studies showed great variability, sufficient scientific evidence was found to support the hypothesis that preheating can improve the hardness of resin composites.

The effect of repeated preheating of dimethacrylate and silorane-based composite resins on marginal gap of class V restorations

Background. One of the problems with composite resin restorations is gap formation at resin‒tooth interface. The present study evaluated the effect of preheating cycles of silorane- and dimethacrylate-based composite resins on gap formation at the gingival margins of Class V restorations.

Methods. In this in vitro study, standard Class V cavities were prepared on the buccal surfaces of 48 bovine incisors. For restorative procedure, the samples were randomly divided into 2 groups based on the type of composite resin (group 1: di-methacrylate composite [Filtek Z250]; group 2: silorane composite [Filtek P90]) and each group was randomly divided into 2 subgroups based on the composite temperature (A: room temperature; B: after 40 preheating cycles up to 55°C). Marginal gaps were measured using a stereomicroscope at ×40 and analyzed with two-way ANOVA. Inter- and intra-group comparisons were analyzed with post-hoc Tukey tests. Significance level was defined at P < 0.05.

Results. The maximum and minimum gaps were detected in groups 1-A and 2-B, respectively. The effects of composite resin type, preheating and interactive effect of these variables on gap formation were significant (P<0.001). Post-hoc Tukey tests showed greater gap in dimethacrylate compared to silorane composite resins (P< 0.001). In each group, gap values were greater in composite resins at room temperature compared to composite resins after 40 preheating cycles (P<0.001).

Conclusion. Gap formation at the gingival margins of Class V cavities decreased due to preheating of both composite re-sins. Preheating of silorane-based composites can result in the best marginal adaptation.