Biaxial flexural strength of high-viscosity glass-ionomer cements heat-cured with an LED lamp during setting

Evaluation of the Mechanical Properties of Three Resin-Modified Glass-Ionomer Materials

This study is aimed at evaluating the flexural strength (FS), fracture toughness (FT), and diametral tensile strength (DTS) of three resin-modified glass-ionomer cements (RMGICs): Ketac Nano, Riva Light Cure, and Fuji II LC. One hundred twenty specimens were prepared from the RMGIC materials ( $n=10$ ). The cements were mixed and inserted into different mould sizes according to the test performed: FS: rectangular Teflon mould ( $32\text{mm}\times 3.15\text{mm}\times 2\text{mm}$ ); FT: notchless triangular prism (NTP) Teflon mould ( $6\text{mm}\times 6\text{mm}\times 6\text{mm}\times 12\text{mm}$ ); and DTS: ring road stainless steel mould ( $6\text{mm}\times 3\text{mm}$ ). Specimens were light cured for 20 seconds on each surface and stored in distilled water at ${37}^{°}\text{C}\pm 2^{°}\text{C}$ for seven days prior to tests. To evaluate the influence of storage in the mechanical properties of the RMGIs, specimens tested for DTS were stored in distilled water at ${37}^{°}\text{C}\pm 2^{°}\text{C}$ for 32 days prior to test. Data were analyzed by ANOVA and Tukey’s test ( $\alpha =0.05$ ). Fuji II LC presented significantly higher values for all tests employed when compared to Ketac Nano and Riva LC RMGIs. There was no significant difference on DTS before and after the 32-day storage for each material. Fuji II LC presented superior mechanical properties when compared to Ketac Nano, and Riva LC storage showed no influence on the mechanical properties of the RMGI materials tested.

Randomized Clinical Trial of Heated High Viscosity Glass Ionomer Class II Restorations in Deciduous Molars: 12 Months Follow Up

Objective: New generation High Viscosity Glass Ionomer Cements (HVGICs) have enhanced physical and mechanical properties. By effectively closing the restoration margin, it ensures that the restorations will last longer. The aim of this study was to investigate the clinical performances of heat-cured versus non heated HVGIC in class II restorations of deciduous molars. Methods: This randomized, split mouth, multicentre study was performed in four different centres. A total of 250 deciduous molars from 88 individuals were randomly allocated to one of the following groups: 1) non-heated (n = 125) 2) heated (n = 125) and restored with a HVGIC using LED light for heat application. Restorations were clinically evaluated according to the modified USPHS at the baseline, 6 months and 12 months. The survival analysis was performed by Kaplan Meier and Life Tables. This study was retrospectively registered to the ClinicalTrials.gov with the ID number of NCT04291872 at 2nd March 2020. Results: No statistically significant differences were found between the groups regarding to modified USPHS criteria (p>0.05). Success rate in retention criteria was 94.1% of the heat-cured and 92.6% of the non-heated restorations after 12 months. The mean survival time was 11.8 ±0.1 months in the heated group, while 11.9±0.1 months in the non-heated group. Conclusion: The heat treated HVGIC for Class II restorations did not show any significant differences in 12 months’ follow-up compared with the conventional technique.

Retention Ability of a Glass Carbomer Pit and Fissure Sealant

Dental sealants are an excellent means to prevent pits and fissure decay. Currently, there are multiple commercially available sealant materials. The purpose of this study was to assess the retention of glass carbomer fissure sealant and the incidence of secondary caries over a period of 24 months in comparison with a resin-based sealant. Materials and Methods: We included 32 children in the study, with ages between six and eight years and an average age of 6.8 years old. For each child, we sealed four permanent molars (totaling 128 teeth). The study group was divided into sub-groups. Sub-group A was represented by 64 first permanent molars which underwent dental sealing procedures with composite resin-based fissure sealant, Helioseal F™, and sub-group B was represented by 64 first permanent molars which underwent dental sealing procedures with glass carbomer cement, GCP Glass Seal™. The sealants were assessed clinically at 6, 12, 18, and 24 months. Results: The 6-month follow-up evaluation showed no statistically significant differences between the two materials neither regarding sealant retention nor new carious lesions formation (p > 0.05). At the 12-month recall, 57 molars had good retention (89.06%) from sub-group A and 44 molars (68.75%) from sub-group B; there was a statistically significant difference (p = 0.0187) between the two treatment choices only regarding material retention. At the last recall after 2 years, sub-group A had a higher number of molars with perfect sealing (47–73.43%) and 8 molars (12.5%) with new caries lesions and sub-group B had 23 (35.93%) molars with perfect sealing and 15 molars (23.44%) with new caries lesions; there was a statistically significant difference (p < 0.0001) between the two treatment choices only regarding material retention. Conclusions: The glass carbomer retention is very inferior to the resin-based material. The glass carbomer sealant was effective in preventing new caries development, comparable with the conventional resin-based sealant.

Clinical performance of high-viscosity glass ionomer and resin composite on minimally invasive occlusal restorations performed without rubber-dam isolation: a two-year randomised split-mouth study

OBJECTIVE

The aim of this clinical trial was to evaluate the 2-year clinical performances of high-viscosity glass ionomer and nanohybrid resin composite restorations performed without rubber dam isolation.

MATERIALS AND METHODS

Occlusal carious lesions on the right and left mandibular second molars of 56 patients (26 female, 30 male patients) were restored in a split-mouth design. High-viscosity glass ionomer (Hv-GIC) (Equia, GC) and nanohybrid resin composite (GrandioSO, Voco) were used as restorative materials. Clinical evaluations of the restorations were performed according to the Fédération Dentaire Internationale criteria. Data were analysed using the Friedman's analysis of variance and Mann-Whitney U tests (α=0.05).

RESULTS

After 2 years, the success rate of Hv-GIC restorations was 96% and that of resin composite restorations was 100%. Hv-GIC showed lower marginal discoloration and greater surface wear and loss of anatomic form (p<0.05). Resin composite showed significantly better surface lustre.

CONCLUSION

The 2-year performance of resin composite was similar to that of Hv-GIC for the occlusal restorations of mandibular second molars, in spite of being performed without rubber-dam isolation.

CLINICAL RELEVANCE

Saliva contamination can be a clinically significant problem for dental restorations. High-viscosity glass ionomers are a satisfactory alternative to resin composites with the advantage of fast application in such situations.

TRIAL REGISTRATION

Clinical Trials Registration number-date: NCT04488380-22/07/2020, retrospectively registered.

Comparative Evaluation of the Mechanical Properties of Zinc-reinforced Glass Ionomer Cement and Glass Ionomer Type IX Cement: An In Vitro Study

Aims and objectives

The aims and objectives of this study were to evaluate and compare the flexural strength and microhardness of zinc reinforced glass ionomer cement and glass ionomer type IX cement.

Materials and methods

The sample size of twenty each of group I (zinc-reinforced glass ionomer cement) and group II (glass ionomer type IX cement) were selected. The samples were prepared in the customized steel molds and subjected to test for flexural strength and microhardness. The flexural strength was determined by the three-point bending test. After determining the flexural strength, the fragments were used to determine Vickers Hardness by means of an automatic microhardness indenter. The flexural strength and microhardness was calculated for all samples and subjected to statistical analysis. Two sample t-test with unequal variances were used, as the data are found to be from the same material. The normality was checked by using the usual normal probability plot. For flexural strength, p value was found to be 0.007530. Hence, zinc-reinforced glass ionomer cement was superior to glass ionomer type IX cement. For microhardness the p value was found to be 0.0023. So, glass ionomer type IX cement was superior to zinc reinforced glass ionomer cement.

Conclusion

The zinc-reinforced glass ionomer cement showed enhanced flexural strength when compared to glass ionomer type IX cement, thus increasing the longevity whereas glass ionomer type IX cement had a better microhardness than zinc-reinforced glass ionomer cement. Hence, the mechanical properties of various materials should be considered for the long-term clinical success by selecting the appropriate material based on the clinical condition.

How to cite this article

Patil K, Patel A, Kunte S, et al. Comparative Evaluation of the Mechanical Properties of Zinc-reinforced Glass Ionomer Cement and Glass Ionomer Type IX Cement: An In Vitro Study. Int J Clin Pediatr Dent 2020;13(4):381–389.

Mechanical properties and water sorption of two experimental glass ionomer cements with hydroxyapatite or calcium fluorapatite formulation

In this study the mechanical behavior and water sorption (Ws) of experimental glass-ionomer-cements (GICs) with hydroxyapatite (HA) or calcium fluorapatite (CFA) prototype formulations were examined. Specimens from two experimental and one commercially available GIC were prepared in three protocols; (1) according to the manufacturer's instructions, (2) with coating and (3) with heat application. The specimens were stored in distilled water or artificial saliva at 37°C for 7- and 30-days. Flexural strength (FS), Vickers hardness (VHN) and Ws of GICs were evaluated. Experimental GICs showed higher FS values than commercial GIC (p<0.001). Higher FS and VHN values were observed when GICs were prepared according to manufacturer's recommendation. FS was affected only by GIC-type (η²=0.027), whereas VHN was affected by GIC-type (η²=0.331), treatment-protocols (η²=0.067), storage-medium (η²=0.100) and increased storage-duration (η²=0.317). The tested parameters did not significantly influence the Ws of all tested GICs (p>0.05). The GICs with HA or CFA formulations might represent a promising approach due to their FS, VHN and Ws characteristics.

Long-term clinical performance of heat-cured high-viscosity glass ionomer class II restorations versus resin-based composites in primary molars: a randomized comparison trial

OBJECTIVE

To evaluate the long-term clinical performance of heat-cured high-viscosity glass ionomer (GIC) and posterior composite resin (CR) restorations in primary molars over a 3-year period.

METHODS

Photographs and radiographs of EQUIA GIC and Filtek™ P60 restorations were assessed. Study sample is comprised of healthy preschool/school children with proximal surface caries in primary molars.

RESULTS

70 GI restorations were placed in 45 patients (aged 78 months ± 25) and were evaluated at 33 months ± 7. 61 composite resin restorations were placed in 42 patients (age 82 months ± 19) and were evaluated at 39 months ± 13. GI restorations failure was 17.1%, a significantly greater rate compared with 4.9% in the CR group. GI failures were due to either significant loss of the restoration or to loss of marginal ridge integrity. CR failures were due to loss of marginal ridge integrity.

CONCLUSION

Both GI and CR restorations were clinically successful during a 3-year period. GI restorations may be considered as an intermediate-lasting restoration option for proximal lesions in primary molars, with 83% of the restorations functioning up to 36 months. CR restorations showed a higher success rate than GIC during the same period.

Alkaline Phosphatase Controls Lineage Switching of Mesenchymal Stem Cells by Regulating the LRP6/GSK3β Complex in Hypophosphatasia

Lineage differentiation of bone marrow mesenchymal stem cells (BMMSCs) is the key to bone-fat reciprocity in bone marrow. To date, the regulators of BMMSC lineage switching have all been identified to be transcription factors, and researchers have not determined whether other genes control this process. This study aims to reveal a previously unknown role of tissue-nonspecific alkaline phosphatase (TNSALP) in controlling BMMSC lineage selection. Methods: We compared the characteristics of cultured BMMSCs from patients with hypophosphatasia (HPP), which is caused by mutations in the liver/bone/kidney alkaline phosphatase (ALPL) gene, and an ALPL knockout (ko) mouse model. We performed ALPL downregulation and overexpression experiments to investigate the regulatory role of ALPL in BMMSC lineage switching. Using the PathScan array, coimmunoprecipitation experiments and pathway-guided small molecule treatments, we explored the possible mechanism underlying the regulatory effects of ALPL on cell differentiation and evaluated its therapeutic effect on ALPL ko mice. Results: BMMSCs from both patients with HPP and ALPL ko mice exhibited defective lineage differentiation, including a decrease in osteogenic differentiation and a parallel increase in adipogenic differentiation. Mechanistically, TNSALP directly interacted with LRP6 and regulated the phosphorylation of GSK3β, subsequently resulting in lineage switching of BMMSCs. Re-phosphorylation of GSK3β induced by LiCl treatment restored differentiation of BMMSCs and attenuated skeletal deformities in Alpl+/- mice. Conclusion: Based on our findings, TNSALP acts as a signal regulator to control lineage switching of BMMSCs by regulating the LRP6/GSK3β cascade.

Maturation processes in glass-ionomer dental cements

Glass-ionomer cements are used for a variety of tooth-repair functions in clinical dentistry. They are formed by reaction of a basic glass powder with a solution of polymeric water-soluble acid, usually polyacrylic acid. After the initial neutralization reaction, by which the cement hardens, various maturation reactions occur. Changes induced by these maturation reactions are identified as: increase in strength; reduction in plasticity; improvement in opacity; and increase in proportion of tightly bound water. In addition, in contact with the tooth, an ion-exchange interfacial layer is gradually formed. This is mechanically strong and chemically-resistant. These changes are described in the current paper, which reviews the extent to which they occur, and reports what is know about the chemistry that underlies them. Processes involving slow diffusion of various ions and of water through the set cement bring about these changes. They include a secondary setting reaction to form a phosphate-based phase, binding of water to co-ordination sites around metal cations and to a hydration sheath around the polymer molecules, and possibly reaction of water with glass particle surfaces to form silanol groups. Evidence from a wide range of literature sources is used to be build up a detailed picture of the chemistry of the maturation processes, and gaps in our understanding are highlighted. The article concludes that, given the importance of glass-ionomers in contemporary dentistry, it is important to know the extent to which such maturation processes occur in current cement formulations, and also to determine how rapidly they take place.

Clinical Performance of Heat-Cured High-Viscosity Glass Ionomer Class II Restorations in Primary Molars: A Preliminary Study

OBJECTIVES

The present preliminary study evaluated the clinical and radiographic performances of heat-cured high viscosity glass ionomer (HCHVGI) in class II restorations of primary molars.

STUDY DESIGN

A retrospective study on a cohort of patients who had dental caries restored at a private practice was conducted. Restorations were evaluated radiographically and photographically by two separate examiners.

RESULTS

Ninety-three Class II restorations in 44 patients (average age: 108 months ± 25.3, 24 males, 20 females) were examined. Average recall time was 22.2 months ± 4.2. All but three restorations (96.8%) were present and intact, with no incidents of secondary caries. Three additional restorations had occlusal defects that required retreatment, resulting in an overall success rate of 93.5%. Ninety-seven percent of the restorations were rated optimal for marginal integrity with no staining of the restoration surfaces. No patients complained of post-operative sensitivity. The most common flaw found was a concavity on the proximal wall of the cavity box (27%, mean age 16 months ± 3.9).

CONCLUSION

The findings in this preliminary study suggest that heat cured high viscosity glass ionomer cement may be an effective restorative material for Class II restorations in primary molars that are a year or two from shedding.

The effect of atraumatic restorative treatment on adhesive restorations for dental caries in deciduous molars

BACKGROUND

Minimal invasive approaches to managing caries, such as partial caries removal techniques and atraumatic restorative treatment (ART), are showing increasing evidence of improved outcomes over the conventional complete caries removal.

OBJECTIVE

To evaluate clinically and radiographically the effect of ART on restorations using restorative cement and glass ionomer cement (GIC) for dental caries in the deciduous molars of children aged between 4 and 8 years.

SETTINGS AND DESIGN

The study design was a split-mouth, randomized, blind clinical trial.

MATERIALS AND METHODS

Eighty-six patients had 108 restorations placed with GIC (Ketac Molar Easy Mix - 3M ESPE) and 108 restorations placed with composite resin (CR) (Filtek Z250 - 3M ESPE). The restorations were assessed by means of images obtained with a digital camera and periapical radiographs at baseline and after 12 months of follow-up.

STATISTICAL ANALYSIS

The Student's t-test, Pearson Chi-squared test, and Bonferroni paired comparison test were used to evaluate the differences in proportions and correlations between the variables.

RESULTS

After 12 months of follow-up, the restorations were considered clinically successful in 89.3% of cases and radiographically successful in 80.5% of cases. There was statistical difference neither between the two restorative materials used nor between the numbers of restored surfaces.

CONCLUSIONS

GIC and CR can be used successfully for restorations of one or two dental surfaces after ART.

In-vitro Study on Temperature Changes in the Pulp Chamber Due to Thermo-Cure Glass Ionomer Cements

The application of the Glass Ionomer Cements in clinical dentistry is recommended due to properties such as fluoride release, chemical adhesion to tooth, negligible setting shrinkage, and coefficient of thermal expansion close to tooth, low creep, and good color stability. However, the cement is vulnerable to early exposure to moisture due to slow setting characteristics. The uses of external energy such as ultrasound and radiant heat (Thermo-curing) have been reported to provide acceleration of the setting chemistry and enhance physical properties. Aim: The aim of this in vitro study was to analyze temperature changes in the pulpal chamber when using radiant heat to accelerate the setting of GICs. Material and Methods:The encapsulated GIC Equia Forte was used for this study. The temperature changes in the pulp were measured using thermocouple in the cavities which were 2,6 and 4,7mm deep with and without filling. Results:The results showed that a temperature rise (ΔT) in the pulp chamber was 3,7°C. ΔT for the 2.6mm and 4.7mm deep cavity and without placing any restoration the temperature was 4,2°C and 2,6°C respectively. After the restoration has been placed, the ΔT range in the pulp chamber was lower ranging from 1.9°C to 2.4°C. Conclusion: It could be concluded that Thermo-curing of the GIC during the setting is safe for the pulp and can be recommended in clinical practice.

One year survival of ART and conventional restorations in patients with disability

Background

Providing restorative treatment for persons with disability may be challenging and has been related to the patient’s ability to cope with the anxiety engendered by treatment and to cooperate fully with the demands of the clinical situation. The aim of the present study was to assess the survival rate of ART restorations compared to conventional restorations in people with disability referred for special care dentistry.

Methods

Three treatment protocols were distinguished: ART (hand instruments/high-viscosity glass-ionomer); conventional restorative treatment (rotary instrumentation/resin composite) in the clinic (CRT/clinic) and under general anaesthesia (CRT/GA). Patients were referred for restorative care to a special care centre and treated by one of two specialists. Patients and/or their caregivers were provided with written and verbal information regarding the proposed techniques, and selected the type of treatment they were to receive. Treatment was provided as selected but if this option proved clinically unfeasible one of the alternative techniques was subsequently proposed. Evaluation of restoration survival was performed by two independent trained and calibrated examiners using established ART restoration assessment codes at 6 months and 12 months. The Proportional Hazard model with frailty corrections was applied to calculate survival estimates over a one year period.

Results

66 patients (13.6 ± 7.8 years) with 16 different medical disorders participated. CRT/clinic proved feasible for 5 patients (7.5%), the ART approach for 47 patients (71.2%), and 14 patients received CRT/GA (21.2%). In all, 298 dentine carious lesions were restored in primary and permanent teeth, 182 (ART), 21 (CRT/clinic) and 95 (CRT/GA). The 1-year survival rates and jackknife standard error of ART and CRT restorations were 97.8 ± 1.0% and 90.5 ± 3.2%, respectively (p = 0.01).

Conclusions

These short-term results indicate that ART appears to be an effective treatment protocol for treating patients with disability restoratively, many of whom have difficulty coping with the conventional restorative treatment.

Trial registration number

Netherlands Trial Registration: NTR 4400

Do light cured ART conventional high-viscosity glass-ionomer sealants perform better than resin-composite sealants: a 4-year randomized clinical trial

OBJECTIVE

The hypotheses tested were: the cumulative survival rates of dentin caries lesion-free pits and fissures of ART conventional high-viscosity glass-ionomer sealants with light-curing (high-intensity LED) and glass-carbomer sealants are higher than those of conventional ART sealants and resin-composite sealants after 4 years.

METHODS

The randomized controlled clinical trial covered 405 children (mean age 8-years). Three dentists placed sealants in pits and fissures of high caries-risk children. Evaluation by two independent evaluators was conducted after 0.5, 1, 2, 3 and 4 years. The Kaplan-Meier survival method, ANOVA and t-test were used in data analyses.

RESULTS

1304 first permanent molars were sealed. 12.3% of children and 15.4% of sealants dropped out. 46 re-exposed pits and fissures, 39 (occlusal) 7 (free smooth surfaces), in 42 children developed a dentin carious lesion. The cumulative survival of dentin caries lesion-free occlusal pits and fissures in ART plus LED group (98%) was statistically significantly higher than in the resin-composite group (96.4%) and in the glass-carbomer group (94.5%). The cumulative survival of dentin caries lesion-free occlusal pits and fissures in the glass-carbomer group was statistically significantly lower than that in the conventional ART group (97.3%). For the free smooth surfaces, there was no statistically significantly difference among the four sealant groups.

SIGNIFICANCE

Light-cured ART conventional high-viscosity glass-ionomer sealants prevented the occurrence of dentin cavities best.