Michal Staninec

Bonding of amalgam to tooth structure: Tensile adhesion and microleakage tests

Amalgam can be bonded to etched enamel by a thin coat of Panavia resin cement with a resulting mean bond strength of 1404 psi to enamel and 469 psi to dentin as tested in tension. Less microleakage was observed in resin-bonded amalgam restorations than in Copal varnish-lined or unlined restorations. The technique could be used clinically with possible implications for cavity design, fracture resistance of restored teeth, and recurrent caries. These properties as well as the variables affecting bond strength need further exploration.

Effect of bonded amalgam on the fracture resistance of teeth

The purpose of this study was to determine whether amalgam bonded to tooth structure with an adhesive resin cement can increase the fracture resistance of restored teeth. Extracted paired upper premolars were prepared for G.V. Black type mesioocclusodistal amalgam restorations. In one tooth of each pair (the experimental group), the enamel walls were etched with phosphoric acid and were painted with an adhesive resin (Panavia), and amalgam was condensed and carved. For the other tooth in each pair (the control group), amalgam was placed in the same manner but was not etched and lined with resin. The teeth were thermocycled and mounted for testing and then were loaded until fracture. A significant difference (p less than 0.05, the paired Students t-test) was found in the force needed to fracture the bonded amalgam group (70.5 +/- 21.6 kg) compared with that needed to fracture the conventional amalgam group (60.3 +/- 16.8 kg). SEM examination of fractures at the interface occurred predominantly within the resin.

Imaging artificial caries under composite sealants and restorations

Polarization-sensitive optical coherence tomography (PS-OCT) is used to monitor the progression of simulated caries lesions on occlusal surfaces and image the lesions underneath composite sealants. The polarization-sensitive system, recording images in both the parallel and perpendicular axes, is useful for enhancing the image contrast of the artificial caries and minimizing the interference of the strong reflections at surface interfaces. Using the perpendicular-axis signal, the mean reflectivity increase from day 0 to day 14 is 5.1 dB (p<0.01, repeated-measures analysis of variation, Tukey-Kramer). For imaging lesions underneath the sealants, the mean reflectivity of the enamel underneath 250, 500, 750, and 1000 microm of composite is calculated for demineralized and control samples. The artificial lesions can be detected under 750 microm of visibly opaque sealant, with a 5.0-dB difference from the control samples (t-test, p<0.001). Tooth colored sealants allow deeper imaging depth. The artificial lesions could be detected under 1000 microm of sealant, with a 6.6-dB difference from the control samples (t-test, p<0.001). This study demonstrates that PS-OCT can be used to track lesion progression on occlusal surfaces nondestructively with or without sealants.

Multispectral near-IR reflectance and transillumination imaging of teeth

NIR imaging methods do not require ionizing radiation and have great potential for detecting caries lesions (tooth decay) on high-risk proximal and occlusal tooth surfaces and at the earliest stages of development. Previous in vitro and in vivo studies at 1300-nm demonstrated that high contrast reflectance and transillumination images could be acquired of caries lesions on tooth proximal and occlusal surfaces where most new decay is found. Water absorption varies markedly between 1200 and 1600-nm and the scattering properties of enamel and the underlying dentin have not been characterized in this region. Hyperspectral reflectance studies show lower reflectivity from sound enamel and dentin at NIR wavelengths with higher water absorption. The purpose of this imaging study was to determine which NIR wavelengths between 1200 and 1600-nm provide the highest contrast of demineralization or caries lesions for each of the different modes of NIR imaging, including transillumination of proximal and occlusal surfaces along with cross polarization reflectance measurements. A tungsten halogen lamp with several spectral filters and a Ge-enhanced CMOS focal plane array (FPA) sensitive from 400 to 1600-nm were used to acquire the images of caries lesions on extracted teeth. Artificial interproximal lesions were created on twelve tooth sections of 5 & 6-mm thickness that were used for transillumination imaging. Fifty-four extracted teeth with suspected occlusal lesions were also examined in both occlusal transillumination and reflectance imaging modes. Cavity preparations were also cut into whole teeth and filled with composite and used to compare the contrast between composite and enamel at NIR wavelengths. NIR wavelengths longer than 1400-nm are likely to have better performance for the transillumination of occlusal caries lesions while 1300-nm appears best for the transillumination of proximal surfaces. Loss of mobile water in enamel markedly reduced the transparency of the enamel at all NIR wavelengths. Significantly higher contrast was attained for reflectance measurements at wavelengths that have higher water absorption, namely 1460-nm. Wavelengths with higher water absorption also provided higher contrast of composite restorations.

Adhesion and microleakage tests of a new dentin bonding system

Adhesion to dentin and microleakage of a new dentin bonding system was studied. The new system includes a low viscosity lightly filled Bis-GMA based resin liner which is placed between the phosphate ester-containing adhesive layer and the composite. This system was compared to dentin bonding agents based on: 1) HEMA and Bis-GMA and 2) PMDM and NTG-GMA. The phosphate ester system was used with and without the low viscosity resin. Each system was used with its corresponding posterior composite. All groups were tested by shear and tensile bond testing immediately and up to 6 mon after bonding. Microleakage of the three systems was tested in Class V restorations by dye penetration. The results of the shear and tensile tests indicated that significant changes within groups occurred with time, and significant differences appeared between groups at various times. The use of low viscosity resin with the phosphate ester system resulted in decreased leakage. The amount of leakage observed was related to early shear bond strength. This study suggests that the properties of the layer immediately adjacent to the adhesive may affect the performance of the system.

Clinical assessment of early tooth demineralization using polarization sensitive optical coherence tomography

The aims of this study were to test the hypothesis that polarization sensitive‐optical coherence tomography (PS‐OCT) can be used to non‐destructively measure and quantify the severity of the early demineralization of enamel on buccal and occlusal surfaces and assess the inhibitory effect of fluoride varnish in vivo.

Dentin Erosion Simulation by Cantilever Beam Fatigue and pH Change

Exposed root surfaces frequently exhibit non-carious notches representing material loss by abrasion, erosion, and/or abfraction. Although a contribution from mechanical stress is often mentioned, no definitive proof exists of a cause-effect relationship. To address this, we examined dimensional changes in dentin subjected to cyclic fatigue in two different pH environments. Human dentin cantilever-beams were fatigued under load control in pH = 6 (n = 13) or pH = 7 (n = 13) buffer, with a load ratio (R = minimum load/maximum load) of 0.1 and frequency of 2 Hz, and stresses between 5.5 and 55 MPa. Material loss was measured at high- and low-stress locations before and after cycling. Of the 23 beams, 7 withstood 1,000,000 cycles; others cracked earlier. Mean material loss in high-stress areas was greater than in low-stress areas, and losses were greater at pH = 6 than at pH = 7, suggesting that mechanical stress and lower pH both accelerate erosion of dentin surfaces.

Dentin shear strength: effect of distance from the pulp

OBJECTIVE Dentin structure varies with orientation and location. Ultimate shear strength (USS) has also been found in previous studies to vary with location. The present study further explores this relationship between USS and various locations in coronal dentin as well as distance from the pulp. METHODS Stick specimens were prepared from coronal dentin located in the center or under cusps of human molar teeth. These were tested in the shear mode at various distances from the pulp. RESULTS Median values ranged from 52.7 (range 29.0-73.1) MPa near the pulp to 76.7 (range 53.9-104.0) MPa near the dentino-enamel junction. No differences were found among the buccal, central or lingual locations, however, the USS near the pulp was found to be significantly lower. SIGNIFICANCE The properties of coronal dentin vary with distance from the pulp, which may affect adhesion and other aspects of restorative dentistry.

Weakening of dentin from cracks resulting from laser irradiation

UNLABELLED Cracking of tooth structure is a frequent mechanism of clinical failure necessitating treatment. Some laser conditions, particularly those without sufficient water cooling, may cause surface cracking of dentin. Surface cracks may serve as initiation sites for the onset of catastrophic fracture under mechanical stress, resulting in failure of the dentin. In this study, the hypothesis that laser initiated cracks result in lower bending strength of dentin was tested. Dentin beam specimens were prepared from human molar teeth, 1.1 mm x 1.1 mm x approximately 9 mm, and divided into groups C (control), W (wet), D (dry) of 12 beams each. In groups W and D, the middle of each beam on one surface (buccal) was irradiated with either a Er-YAG or Q-switched Er-YSGG laser and measured under a microscope, noting the dimensions in the irradiated area and immediately adjacent to irradiated area. Each beam was placed in a mechanical testing machine in a four-point bend jig and tested with a monotonically increasing load at a displacement rate of 1mm/min until failure. The bending strengths for groups C, W (Er-YAG laser) and D (Q-switched Er-YSGG laser) were, respectively, 141.6, 114.0, and 90.9 MPa. A one-way ANOVA determined a significant difference between groups C and D, p<0.001. CONCLUSION The Q-switched Er-YSGG laser without water caused cracks in the surface that significantly decreased the bending strength of dentin.

In vivo near-IR imaging of approximal dental decay at 1,310 nm.

The high transparency of dental enamel in the near‐IR (NIR) light at 1,310‐nm can be exploited for imaging dental caries without the use of ionizing radiation (X‐rays). We present the results of the first in vivo imaging study in which NIR images were acquired of approximal contact surfaces.