Internal adaptation of resin composite restorations with different thicknesses of glass ionomer cement lining

A 3D finite element analysis of stress distribution on different thicknesses of mineral trioxide aggregate applied on various sizes of pulp perforation

OBJECTIVES

The aim of this study was to evaluate the stress distribution on different thicknesses of mineral trioxide aggregate (MTA) placed on various widths of pulp perforations during the condensation of the composite resin material.

MATERIALS AND METHODS

The mandibular molar tooth was modeled by COSMOSWorks program (SolidWorks, Waltham, MA). Three finite elemental analysis models representing 3 different dimensions of pulp perforations, 1, 2, and 3 mm in diameter, were created. The perforation area was assumed as filled with MTA with different thicknesses, 1, 2, and 3 mm for each pulp perforation width, creating a total of 9 different models. Then, a composite resin material was layered on MTA for each model. A 66.7 N load was applied and an engineering simulation program (ANSYS, Canonsburg, US) was used for the analysis. Results were presented considering von Mises stress criteria.

RESULTS

As MTA thickness increased, the stress values recorded within the area between pulp and MTA decreased. Strain was decreased when the thickness of MTA increased.

CONCLUSIONS

Stresses at MTA-pulp interface and strain on MTA decreased with the increase in MTA thickness.

CLINICAL RELEVANCE

In clinical practice, when MTA is required for pulp capping, using a thick layer of the material seems to be a better option in order to reduce the stress under forces of hand condensation of overlying restorative materials.

Cavity Bases Revisited

OBJECTIVE

The aim of this paper was to review the current literature on cavity bases while focusing on the role of zinc oxide eugenol (ZOE) and resin-modified glass ionomers (RMGI) as cavity bases.

MATERIALS AND METHODS

A thorough literature search between 1970 and 2020 was done using Scopus, PubMed, and Google Scholar databases. The keywords of the search strategy were as below: cavity liners and bases, pulp protection, zinc oxide eugenol, and resin-modified glass ionomer. No specific inclusion or exclusion criteria were applied as to what articles would be included in this review.

CONCLUSION

This review emphasizes that the available literature provides very little evidence to support the routine use of a base under amalgam or composite restorations. This review favors the adoption of "no more lining or bases" in shallow and moderate cavity preparations. However, an exception might be a "protective base" of RMGI following the application of calcium hydroxide (CH) liners in deep cavities. Bonded RMGIs are suitable cavity base materials and should always replace zinc oxide eugenol bases in daily practice.

Fracture resistance, gap and void formation in root-filled mandibular molars restored with bulk-fill resin composites and glass-ionomer cement base

AIM

To evaluate fracture resistance and gap/void presence of root-filled mandibular molars restored with 2 bulk-fill and 1 conventional resin composites, with or without a glass-ionomer cement (GIC) base.

METHODS

Coronal access and mesio-occlusal (MO) cavities were prepared, then root canal treatment was performed on 30 mol/L. The teeth were randomly divided, according to the cavity volume, into 6 experimental groups (N = 5) and restored with conventional/light-cured (Ceram-X), bulk-fill/light-cured (SureFil SDR) or bulk-fill/dual-cured (Core-X Flow) with/without a 2-mm thick GIC base. Gaps and voids (%) were determined using microcomputed tomography. Intact teeth and unrestored teeth were used as negative and positive controls. Fracture load (N) was determined using a universal testing machine.

RESULTS

No significant difference in fracture resistance or gap/void formation was found among the 3 resin composites. GIC-base groups revealed significantly lower fracture strength than intact teeth, while fracture strengths of no GIC-base groups were not significantly different from intact teeth. GIC-base groups revealed significantly more gaps and voids in the area of the GIC than the resin composite.

CONCLUSION

Conventional and bulk-fill resin composites provided similar fracture resistance and gaps/voids in root-filled molars with MO cavities. Placing a GIC base decreased fracture resistance and increased gap/void formation.