Determination of the dynamics of restored teeth by 3D electronic speckle pattern interferometry

Biophotonics in Dentistry

The aim of this review paper is to concentrate on the use and application of photonics in dentistry. More than one hundred review and research articles were comprehensively analysed in terms of applications of photonics in dentistry, including surgical applications, as well as dental biomaterials, diagnosis and treatments. In biomedical engineering, various fields, such as biology, chemistry, material and physics, come together in to tackle a disease/disorder either as a diagnostic tool or an option for treatment. Engineers believe that biophotonics is the application of photonics in medicine, whereas photonics is simply a technology for creating and connecting packets of light energy, known as photons. This review paper provides a comprehensive discussion of its main elements, such as photoelasticity, interferometry techniques, optical coherence tomography, different types of lasers, carbon nanotubes, graphene and quantum dots.

Whole-field macro- and micro-deformation characteristic of unbound water-loss in dentin hard tissue

High-resolution deformation measurements in a functionally graded hard tissue such as human dentin are essential to understand the unbound water-loss mediated changes and their role in its mechanical integrity. Yet a whole-field, 3-dimensional (3D) measurement and characterization of fully hydrated dentin in both macro- and micro-scales remain to be a challenge. This study was conducted in 2 stages. In stage-1, a stereo-digital image correlation approach was utilized to determine the water-loss and load-induced 3D deformations of teeth in a sagittal section over consecutively acquired frames, from a fully hydrated state to nonhydrated conditions for a period up to 2 hours. The macroscale analysis revealed concentrated residual deformations at the dentin-enamel-junction and the apical regions of root in the direction perpendicular to the dentinal tubules. Significant difference in the localized deformation characteristics was observed between the inner and outer aspects of the root dentin. During quasi-static loadings, further increase in the residual deformation was observed in the dentin. In stage-2, dentin microstructural variations induced by dynamic water-loss were assessed with environmental scanning electron microscopy and atomic force microscopy (AFM), showing that the dynamic water-loss induced distention of dentinal tubules with concave tubular edges, and concurrent contraction of intertubular dentin with convex profile. The findings from the current macro- and micro-scale analysis provided insight on the free-water-loss induced regional deformations and ultrastructural changes in human dentin.

Impact of Endodontic Treatments on the Rigidity of the Root

The destabilizing effect of endodontic treatment upon teeth is still controversial. The purpose of this study was to investigate the effects of different steps of endodontic treatments upon the rigidity of teeth. Extracted untreated central maxillary anterior teeth were loaded (3.75 N), and deformations of the root were assessed by Speckle pattern interferometry. The following treatments (with subsequent determination of deformability) were conducted sequentially: access preparation, manual instrumentation (Kerr files ISO-40, ISO-60, ISO-80, ISO-110), and tapered and parallel-sided post preparation. It was found that the teeth were increasingly destabilized by any treatment. While the increased deformability was not significant with the manual enlargement (p > 0.05), we found a significant destabilization after access preparation and post preparation (p < 0.05). A corresponding difference was found after conversion of the post preparation from tapered to parallel-sided (p < 0.05). Both substance loss and modifications of the natural root canal geometry play an important role in tooth rigidity.

Effect of cavity design on tooth surface strain

STATEMENT OF PROBLEM

The loss of tooth structure can increase cuspal flexure, thereby reducing the fracture resistance of the tooth, or open the tooth-restoration interface, leading to microleakage.

PURPOSE

The purpose of this study was to evaluate tooth strain in teeth with different cavity preparations after loading and unloading.

MATERIAL AND METHODS

Ten intact human maxillary premolars were selected and embedded in epoxy resin molds. Constantan strain gauges were used and tested as an intact tooth (group I), occlusal cavity (group O), mesio-occlusal cavity (group MO), and finally mesio-occluso-distal cavity (group MOD). All teeth were subjected to gradual nondestructive occlusal loading and unloading (50 N, 70 N, 90 N, 110 N, 130 N, 50 N, 0 N) in a servohydraulic testing machine. All data were analyzed statistically by performing a repeated measures ANOVA with load and cavity as factors to compare the relevant mean strains, and a Bonferroni post hoc test was performed for multiple comparisons (α=.05).

RESULTS

The repeated measures ANOVA did not provide any evidence of an interaction between load and cavity but indicated a significant difference in the mean strains both between the loads (P<.001) and between the cavity groups (P<.001).

CONCLUSIONS

MOD cavities presented statistically significantly higher values of strain than MO, O, or intact teeth, and a significant increase in the values of mean strain for all cavities was observed, even with intact teeth, when nondestructive occlusal loading was increased.

Spatially resolved assessments of composite shrinkage in MOD restorations using a digital-image-correlation technique

OBJECTIVES

To analyze the influence of cavity geometry and lining materials in MOD composite restorations by characterizing the polymerization shrinkage and cusp deflection.

METHODS

Eighty intact molars with similar sizes were collected and randomly divided into eight groups. MOD cavities with various widths and depths were prepared on these teeth: Group I, 2((W)) × 2((D)) mm; Group II, 4((W)) × 2((D)) mm; Groups III, IIIf, IIIg, 2((W)) × 4((D)) mm; and Groups IV, IVf, IVg, 4((W)) × 4((D)) mm. In Groups IIIf and IVf, flowable composite liner was placed prior to composite restoration, while glass-ionomer liner was used in Groups IIIg and IVg. Deformations of restorations resulted from composite shrinkage were recorded for 30 min following light irradiation using a digital-image-correlation (DIC) method to subpixel level. The displacements at the boundaries of the restorations were analyzed using one-way ANOVA and the post hoc test at a 5% significance level. The correlation between the geometric factors and the displacements was also analyzed.

RESULTS

The inward displacements on free surfaces were greater than those on the bonded surfaces. Groups with flowable composite linings showed greater amount of displacements on free and bonded surfaces compared to the unlined and glass ionomer lining groups. The correlation analysis showed that the free surface shrinkage was related with the cavity width and C-factor, while cusp deflections were correlated with the cavity depth and the cusp compliance.

SIGNIFICANCE

The DIC technique measures composite shrinkage on different boundaries of restorations to facilitate the investigation of polymerization kinetics. Using flowable composite lining and increased cusp depth may aggravate the cusp flexure.

Real-time measurement of internal stress of dental tissue using holography

We describe a real-time holographic technique used to observe dental contraction due to photo-polymerization of dental filling during LED lamp illumination. An off-axis setup was used, with wet in-situ processing of the holographic plate, and consequent recording of interference fringes using CCD camera. Finite elements method was used to calculate internal stress of dental tissue, corresponding to experimentally measured deformation. A technique enables selection of preferred illumination method with reduced polymerization contraction. As a consequence, durability of dental filling might be significantly improved.