Advances in dental materials

Aspects and Principles of Material Connections in Restorative Dentistry-A Comprehensive Review

The combination of two dissimilar materials has always been a serious problem in dentistry. In order to meet this challenge, it is necessary to combine both chemical methods (treatment with silanes, (meth)acrylic functional monomers) and the development of the surface of the joined material in a physical way, e.g., by sandblasting with alumina, alumina with silica, acid etching, the use of lasers and other means. The purpose of this literature review is to present all methods of joining dental composites with other materials such as ceramics, metal, another composite material. This review covers articles published within the period 2012-2022 in journals indexed in the PubMed database, written in English and describing joining different dental materials to each other. All the critical steps of new joint preparation have been addressed, including proper cleaning of the joint surface, the application of appropriate primers capable of forming a chemical bond between ceramics, zirconium oxide or metals and alloys, and finally, the application of new composite materials.

Clinical comparison of a micro-hybride resin-based composite and resin modified glass ionomer in the treatment of cervical caries lesions: 36-month, split-mouth, randomized clinical trial

PURPOSE

The aim of the study was to compare the 36-month clinical performances of a micro-hybride resin based composites (RBC) and a type II resin modified glass ionomer cement (RMGIC) in the treatment of cervical caries lesions.

METHODS

Thirty-three patients (23 females,  10 males) with at least two cervical caries lesions participated in this study. A total of 110 restorations were randomly placed, half using RBC (Spectrum TPH3, Dentsply Sirona) with respective adhesive system (Prime & Bond NT, Dentsply Sirona) the other half using the RMGIC (Riva Light Cure, SDI, Bayswater, Victoria, Australia). Restorations were assessed at baseline, and after 6, 12, 18, 24 and 36 months using modified USPHS criteria. The data were analyzed statistically (p < 0.05).

RESULTS

Recall rate was 90.91% at 36 months. Of the RBC lesions 84.3% (n = 43) and of the RMGIC restorations 92.2% (n = 47) were fully retained at 36 months. There was no significant difference between two materials in terms of retention and marginal adaptation (p > 0.05). No relation was found between caries activity, cavity dimensions and marginal adaptation (p > 0.05) but RMGIC restorations showed significantly more discoloration than RBC restorations after 36 months (p < 0.001).

CONCLUSIONS

Considering the middle-term outcomes, both materials showed clinically successful performance in the treatment of cervical caries lesions.

Direct restoration of endodontically treated maxillary central incisors: post or no post at all?

OBJECTIVES

The aim of this ex-vivo study was to evaluate the impact of cavity size and glass-fiber post (GFP) placement on the load capability of endodontically treated maxillary incisors directly restored with resin composite.

MATERIALS AND METHODS

Ninety-six extracted human maxillary central incisors were endodontically treated and distributed to four groups (n = 24): access cavity (A), access cavity and uni-proximal class III cavity (U), access cavity and bi-proximal class III cavity (B), and decoronated tooth (D). Specimens were restored with resin composite, and 12 specimen of each group received an adhesively placed glass-fiber post (P). Prior to linear loading, specimens were exposed to thermo-mechanical loading (TCML). Statistical analysis was performed using log-rank test after TCML, Kruskall-Wallis and Mann-Whitney U test to compare load capabilities (F_max).

RESULTS

Significantly more failures occurred in group D for specimens without GFP during TCML (p = 0.001). F_max (mean (SD) in N was (A) 513 (124), (AP) 554 (201), (U) 438 (171), (UP) 537 (232) (B) 483 (219), (BP) 536 (281), D 143 (181), and DP 500 (331), and differed significantly among groups (p = 0.003). Pair-wise comparison revealed lower F_max values for group D compared to all other groups (p < 0.034) except group DP.

CONCLUSIONS

Endodontically treated maxillary central incisors with cavity sizes up to bi-proximal class III may be successfully directly restored with resin composite. Post placement shows no additional effect except for decoronated endodontically treated incisors.

CLINICAL RELEVANCE

Endodontically treated incisors with access cavities to class III cavities can be successfully restored with resin composite. Post placement for decoronated ETT is recommended.

Survival rates of anterior composites in managing tooth wear: systematic review

The use of composite restorations for patients with tooth wear is considered as a more conservative treatment option. The aim of this study was to systematically review the literature investigating the survival rates of anterior composite restorations when used in managing tooth wear in patients. PubMed and MEDLINE (Ovid) databases were screened for studies from 1995 to 2015. Cross-referencing was used to further identify articles. Article selection and data extraction were performed in duplication. Languages were restricted to English. A quality appraisal of included studies was carried out using the Strength of Recommendation Taxonomy system. Six hundred and sixty-six articles were initially identified from which eight articles were full-text reviewed. Six articles involving five studies were selected for inclusion. Three studies were prospective and two retrospective. Included studies involved placement of 772 direct and indirect anterior composite restorations in 100 patients with follow-up periods between 5 months and 10 years. The survival rates of anterior composites were >90% and 50% at 2.5 and 5 years, respectively. Posterior occlusion was re-established in 91% of patients within 18 months. Meta-analysis could not be performed due to the heterogeneity of included studies. The systematic review's overall strength of recommendation was graded B. There is evidence to support the use of anterior composite restorations at an increased vertical dimension of occlusion in the short/medium-term management of tooth wear. Long-term reporting of outcomes remains limited. Further research is needed with standardised study design, detailed reporting of outcomes and long-term review.

Comparative study of mechanical properties of dental restorative materials and dental hard tissues in compressive loads

There are two objectives. One is to show the differences in the mechanical properties of various dental restorative materials compared to those of enamel and dentin. The other is to ascertain which dental restorative materials are more suitable for clinical treatments. Amalgam, dental ceramic, gold alloy, dental resin, zirconia, and titanium alloy were processed as dental restorative material specimens. The specimens (width, height, and length of 1.2, 1.2, and 3.0 mm, respectively) were compressed at a constant loading speed of 0.1 mm/min. The maximum stress (115.0 ± 40.6, 55.0 ± 24.8, 291.2 ± 45.3, 274.6 ± 52.2, 2206.0 ± 522.9, and 953.4 ± 132.1 MPa), maximum strain (7.8% ± 0.5%, 4.0% ± 0.1%, 12.7% ± 0.8%, 32.8% ± 0.5%, 63.5% ± 14.0%, and 45.3% ± 7.4%), and elastic modulus (1437.5 ± 507.2, 1548.4 ± 583.5, 2323.4 ± 322.4, 833.1 ± 92.4, 3895.2 ± 202.9, and 2222.7 ± 277.6 MPa) were evident for amalgam, dental ceramic, gold alloy, dental resin, zirconia, and titanium alloy, respectively. The reference hardness value of amalgam, dental ceramic, gold alloy, dental resin, zirconia, and titanium alloy was 90, 420, 130–135, 86.6–124.2, 1250, and 349, respectively. Since enamel grinds food, its abrasion resistance is important. Therefore, hardness value should be prioritized for enamel. Since dentin absorbs bite forces, mechanical properties should be prioritized for dentin. The results suggest that gold alloy simultaneously has a hardness value lower than enamel (74.8 ± 18.1), which is important in the wear of the opposing natural teeth, and higher maximum stress, maximum strain, and elastic modulus than dentin (193.7 ± 30.6 MPa, 11.9% ± 0.1%, 1653.7 ± 277.9 MPa, respectively), which are important considering the rigidity to absorb bite forces.

Comparison of mechanical property and role between enamel and dentin in the human teeth

The mechanical properties of enamel and dentin were studied using test specimens having the same shape and dimensions because these properties might vary with the experimental conditions and specimen shapes and dimensions. Healthy human teeth were used as specimens for mechanical tests. The stress (MPa), strain (%), and elastic modulus (E, MPa) of the specimens were obtained from compression tests. The maximum stresses of the enamel, dentin, and enamel–dentin specimens were 62.2 ± 23.8, 193.7 ± 30.6, and 126.1 ± 54.6 MPa, respectively. The maximum strains of the enamel, dentin, and enamel–dentin specimens were 4.5 ± 0.8%, 11.9 ± 0.1%, and 8.7 ± 2.7%, respectively. The elastic moduli of the enamel, dentin, and enamel–dentin specimens were 1338.2 ± 307.9, 1653.7 ± 277.9, and 1628.6 ± 482.7 MPa, respectively. The measured hardness value of enamel specimens (HV = 274.8 ± 18.1) was around 4.2 times higher than that of dentin specimens (HV = 65.6 ± 3.9). Judging from the measured values of the stress and strain of enamel specimens, enamel tended to fracture earlier than dentin; therefore, it was considered more brittle than dentin. However, judging from the measured hardness values, enamel was considered harder than dentin. Therefore, enamel has higher wear resistance, making it suitable for grinding and crushing foods, and dentin has higher force resistance, making it suitable for absorbing bite forces. The different mechanical roles of enamel and dentin may arise from their different compositions and internal structures, as revealed through scanning electron micrographs of enamel and dentin.

The dentin organic matrix - limitations of restorative dentistry hidden on the nanometer scale

The prevention and treatment of dental caries are major challenges occurring in dentistry. The foundations for modern management of this dental disease, estimated to affect 90% of adults in Western countries, rest upon the dependence of ultrafine interactions between synthetic polymeric biomaterials and nanostructured supramolecular assemblies that compose the tooth organic substrate. Research has shown, however, that this interaction imposes less than desirable long-term prospects for current resin-based dental restorations. Here we review progress in the identification of the nanostructural organization of the organic matrix of dentin, the largest component of the tooth structure, and highlight aspects relevant to understating the interaction of restorative biomaterials with the dentin substrate. We offer novel insights into the influence of the hierarchically assembled supramolecular structure of dentin collagen fibrils and their structural dependence on water molecules. Secondly, we review recent evidence for the participation of proteoglycans in composing the dentin organic network. Finally, we discuss the relation of these complexly assembled nanostructures with the protease degradative processes driving the low durability of current resin-based dental restorations. We argue in favour of the structural limitations that these complexly organized and inherently hydrated organic structures may impose on the clinical prospects of current hydrophobic and hydrolyzable dental polymers that establish ultrafine contact with the tooth substrate.