Examination of ceramic/enamel interfacial debonding using acoustic emission and optical coherence tomography

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.

OCT evaluation of the internal adaptation of ceramic veneers depending on preparation design and ceramic thickness

OBJECTIVES

In-vitro evaluation of the influence of preparation design and thickness of ceramic veneers on the interfacial bond using optical coherence tomography (OCT).

METHODS

Sixty-four central incisors were randomly assigned to four preparation designs differing from no to complete dentine exposure (n = 16 each): non-prep (NP), minimal-invasive (MI, no dentine exposure), semi-invasive (SI, 50% dentine) and invasive (I, 100% dentine). Ceramic veneers (IPS InLine Veneer) of two thicknesses (0.2-0.5 mm (T1) and > 0.5-1.2 mm (T2)) were etched, silanized, and adhesively luted (Optibond FL, Variolink Veneer). After water storage (37 °C, 21d), thermocycling (2000 cycles, 5°-55 °C), and mechanical loading (2 + 1 million cycles, 50 + 100 N) specimens were imaged by spectral-domain OCT (Telesto II, Thorlabs). Adhesive defects at the ceramic-composite and tooth-composite interfaces were quantified on 35 equidistantly distributed OCT B-scans (length, %). Statistical differences were verified with Wilcoxon-/Mann-Whitney-U-test (α = 0.05).

RESULTS

Adhesive defects appeared in all groups at both interfaces, albeit to differing extents (0.1 - 31.7%). NP and MI veneers showed no significant differences at the interfaces (p_i > 0.05). In groups, SI and I, significantly more adhesive defects appeared at the tooth-composite compared to the veneer-composite interface (p_i ≤ 0.039). The following preparation designs and veneer thicknesses showed differences (p_i ≤ 0.021): Veneer-composite: NP-T1 < I-T1, MI-T1 < I-T1, I-T1 > I-T2; Tooth-composite: NP-T1 < SI-T1, NP-T1 < I-T1, NP-T2 > MI-T2, MI-T1 < SI-T1, MI-T1 < I-T1, SI-T1 < I-T1, MI-T2 < SI-T2, MI-T2 < I-T2.

SIGNIFICANCE

The interface adhesion of ceramic veneers was influenced by the preparation design and the veneer thickness. A ceramic thickness of at least 0.5 mm and a preparation without exposing dentine is advantageous for the interfacial bond.

Correlation of ultrasound microscopy and Vickers hardness measurements of human dentin and enamel - A pilot study

OBJECTIVE

To investigate if Vickers microhardness of dentin and enamel correlated with acoustic velocity c(l) or acoustic reflection from the sample's top (amplitude).

METHODS

Eight transversal sections of a sound human tooth were investigated with scanning acoustic microscopy (SAM) and Vickers microhardness measurements. Longitudinal acoustic velocity c(l), amplitude and microhardness MHV were evaluated and for each c(l) test point corresponding amplitude and MHV were linearly interpolated and graphically analyzed. Spearman rank order correlation (r_S) was calculated (p<0.05).

RESULTS

c(l) was predominantly 6100-7000ms^-1 in enamel and 3800-4600ms^-1 in dentin and correlated significantly with MHV with 27-420 in enamel and 20-90 in dentin (r_s=0,57). Amplitudes significantly correlated with MHV, too, but even better (r_s=0,77).

SIGNIFICANCE

Acoustic velocity and amplitudes were appropriate to detect microhardness differences of dentin and enamel and certain value ranges of both could be assigned to certain MHV ranges. Further research is needed to differentiate more precisely between the different hard tooth tissues.

Evaluation of adaptation of ceramic inlays using optical coherence tomography and replica technique

Optical coherence tomography (OCT) has generally been used as a nondestructive technique to evaluate integrities of composite restorations. We investigated marginal and internal adaptations of ceramic inlay restorations with OCT and compared them to results with the silicone replica technique. Round-shaped class I cavities were prepared on 16 human maxillary first premolar teeth. Ceramic inlays were fabricated. Silicone replicas from inlays were obtained and sectioned to measure marginal and internal adaptations with a stereomicroscope (Leica Dfc 295, Bensheim, Germany). Inlays were cemented on respective teeth. Marginal and internal adaptations were then measured with the OCT system (Thorlabs, New Jersey, USA) in 200- μm intervals. Replica and OCT measurements were compared with independent samples t-tests. A paired t-test was used to evaluate the marginal and internal adaptations of each group (p < 0.05). Marginal and internal adaptations were 100.97 ± 31.36 and 113.94 ± 39.75 μm, respectively, using the replica technique and 28.97 ± 17.86 and 97.87 ± 21.83 μm, respectively, using OCT. The differences between the techniques were significant (p = 0.00 and p = 0.01, respectively). On evaluation within the groups, internal adaptation values were found to be significantly higher than the marginal adaptation values for the replica technique (p = 0.00) and OCT (p = 0.00). Therefore, the replica and OCT techniques showed different results, with higher values of marginal and internal adaptation found with the replica technique. Marginal and internal adaptation values of ceramic inlays, whether measured by replica or OCT techniques, were within clinically acceptable limits.

The Use of Optical Coherence Tomography in Dental Diagnostics: A State-of-the-Art Review

Optical coherence tomography provides sections of tissues in a noncontact and noninvasive manner. The device measures the time delay and intensity of the light scattered or reflected from biological tissues, which results in tomographic imaging of their internal structure. This is achieved by scanning tissues at a resolution ranging from 1 to 15 μm. OCT enables real-time in situ imaging of tissues without the need for biopsy, histological procedures, or the use of X-rays, so it can be used in many fields of medicine. Its properties are not only particularly used in ophthalmology, in the diagnosis of all layers of the retina, but also increasingly in cardiology, gastroenterology, pulmonology, oncology, and dermatology. The basic properties of OCT, that is, noninvasiveness and low wattage of the used light, have also been appreciated in analytical technology by conservators, who use it to identify the quality and age of paintings, ceramics, or glass. Recently, the OCT technique of visualization is being tested in different fields of dentistry, which is depicted in the article.

Comparison of the marginal adaptation of direct and indirect composite inlay restorations with optical coherence tomography

Objective

The purpose of the study was to use the photonic imaging modality of optical coherence tomography (OCT) to compare the marginal adaptation of composite inlays fabricated by direct and indirect techniques.

Material and Methods

Class II cavities were prepared on 34 extracted human molar teeth. The cavities were randomly divided into two groups according to the inlay fabrication technique. The first group was directly restored on cavities with a composite (Esthet X HD, Dentsply, Germany) after isolating. The second group was indirectly restored with the same composite material. Marginal adaptations were scanned before cementation with an invisible infrared light beam of OCT (Thorlabs), allowing measurement in 200 µm intervals. Restorations were cemented with a self-adhesive cement resin (SmartCem2, Dentsply), and then marginal adaptations were again measured with OCT. Mean values were statistically compared by using independent-samples t-test and paired samples t-test (p<0.05), before and after cementation.

Results

Direct inlays presented statistically smaller marginal discrepancy values than indirect inlays, before (p=0.00001442) and after (p=0.00001466) cementation. Marginal discrepancy values were increased for all restorations after cementation (p=0.00008839, p=0.000000952 for direct and indirect inlays, respectively). The mean marginal discrepancy value of the direct group increased from 56.88±20.04 µm to 91.88±31.7 µm, whereas the indirect group increased from 107.54±35.63 µm to 170.29±54.83 µm. Different techniques are available to detect marginal adaptation of restorations, but the OCT system can give quantitative information about resin cement thickness and its interaction between tooth and restoration in a nondestructive manner.

Conclusions

Direct inlays presented smaller marginal discrepancy than indirect inlays. The marginal discrepancy values were increased for all restorations that refer to cement thickness after cementation.

Biomechanical interactions of endodontically treated tooth implant-supported prosthesis under fatigue test with acoustic emission monitoring

BACKGROUND

This study investigated the biomechanical interactions in endodontically treated tooth implant-supported prosthesis (TISP) with implant system variations under dynamic cyclic loads monitored using the acoustic emission (AE) technique.

METHODS

Macrostructure implants using a taper integrated screw-in (TIS; 2-piece implant) and a retaining-screw (RS; 3-piece implant) connected to an abutment were used for this investigation and their corresponding mechanical resistances in conformity with the ISO 14801 standard were evaluated. The endodontically treated TISP samples were constructed containing TIS and RS implants splinted to the second premolar with fatigue tests performed by applying occlusal force onto the premolar simulating the bending moment effect. The numbers of accumulated AE signals in the fatigue tests and failure modes for the sample were recorded to evaluate the mechanical resistance.

RESULT

The maximum load in the static test for RS (3-piece) implant (797N) was significantly higher than that for the TIS (2-piece) implant (559N). Large deformations were found at abutment screws in both RS and TIS implants. Although the numbers of accumulated AE signals for the TIS implant (72511) were higher than those for the RS implant (437), statistical non-significant differences were found between TIS and RS implants. No obvious damage was noted in endodontically treated TISP samples using RS implants but two of the corresponding TIS implants fractured in the abutment screws.

CONCLUSIONS

Splints with RS (3-piece) implant prosthesis produce better mechanical responses than the TIS (2-piece) implant when connected to an endodontically treated tooth restored with a post core and crown.