This study was supported by the Minnesota Dental Research Center for Biomaterials and Biomechanics (MDRCBB).

Note: Three dental resin composites were studied using the glass cavities: Z100, Z250 and LS, as listed in Materials List. Among them, LS is known to be a low-shrinkage resin composite with a volumetric shrinkage of around 1.0%, much lower than those of Z250 and Z100 (~2% and ~2.5%, respectively)18-19. The equipment and other materials used in this study are also given in Materials List.
1. Model Cavity Preparation
<ol>
	<li>Cut a long cylindrical glass rod, 10 mm in diameter, into 10-mm long short rods using a low-speed diamond saw.</li>
	<li>Cut a Mesial-Occlusal-Distal (MOD) cavity (Figure&#160;1) measuring 3 mm (width) x&#160;2 mm (depth) in each specimen using an adapted low-speed diamond saw.</li>
	<li>Polish down each cylindrical specimen to create a flat surface perpendicular to the length of the cavity, with dimensions as shown in Figure&#160;1. The flat surface allows precise focusing and image calibration on the restoration. Henceforth, it will be called the observation surface.</li>
	<li>Prepare three specimens for each of the three materials tested: Z100, Z250 and LS; see&#160;Materials table.</li>
</ol>
2. Cavity Filling with Resin Composite
<ol>
	<li>Apply a thin layer of Ceramic Primer with a brush to silanize all the glass cavity surfaces. This allows bonding between the glass surfaces and the resin composites.</li>
	<li>After about 1 min, apply a thin layer of adhesive. Use LS Adhesive system for composite LS and Adper Single Bond Plus for composite Z100 and Z250.</li>
	<li>Cure the adhesive with a curing light and duration (10-20 sec) based on the manufacturer&#8217;s instructions (Materials table).</li>
	<li>Cover all the glass surfaces surrounding the restoration with black tape except the observation surface, as shown in Figure&#160;2. The purpose is to avoid the curing light reaching the resin composite through the surrounding transparent glass, which does not happen in real teeth.</li>
	<li>Bulk-fill the cavity with resin composite and scrape off any excess to flatten all the surfaces.</li>
</ol>
3. Surface Painting
<ol>
	<li>Spray a thin layer of white paint onto the observation surface, which now includes part of the resin composite.</li>
	<li>Sprinkle immediately some black fine charcoal powder onto the paint to create high-contrast speckles. The irregular shapes of the speckles will help the DIC software to identify them and track their movements.</li>
</ol>
4. Sample Mounting, Curing, and Photographing
<ol>
	<li>Referring to Figure&#160;2, place a specimen (E) into the holder (C) and tighten it with a screw (D). Then, place the whole unit at the end of a large horizontal beam.</li>
	<li>Secure a CCD camera and a yellow illumination LED light onto the same beam such that they face the observation surface.</li>
	<li>Using a stand with adjustable clamps, position the curing light such that its tip is about 1 mm above the sample.</li>
	<li>Take a picture of the specimen to provide the reference image prior to curing.</li>
	<li>Cure the resin composite for 20 sec.</li>
	<li>Take another picture at 5 min after curing.</li>
	<li>Place a calibration block at the same position as the observation surface and take a picture. The calibration block contains an array of circular dots with size and spacing precisely known.</li>
</ol>
5. Image Analysis with DIC Software
<ol>
	<li>Import the two pictures taken for each sample, one before and one after curing, into the DIC software.</li>
	<li>Calibrate the dimensions of the images and correct for image distortion using the image of the calibration block. .</li>
	<li>Define the area of interest within the observation surface for analysis.</li>
	<li>Define the size of the square subset windows as 64 x 64 pixels for the first iteration and 32 x 32 pixels for the second iteration20. Define the overlap as 50%.</li>
	<li>Correlate the image taken after curing with the reference image taken before curing to calculate the displacement and strain distributions.</li>
</ol>

<ol>
	<li>Palin, W. M., Fleming, G. J. P., Nathwani, H., Burke, F. J. T., Randall, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+cuspal+deflection+and+microleakage+of+maxillary+premolars+restored+with+novel+low-shrink+dental+composites.">In vitro cuspal deflection and microleakage of maxillary premolars restored with novel low-shrink dental composites.</a> Dental Materials. 21, 324-335 (2005).</li><li>Li, H., Li, J., Yun, X., Liu, X., Fok, A. S. -. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-destructive+examination+of+interfacial+debonding+using+acoustic+emission.">Non-destructive examination of interfacial debonding using acoustic emission.</a> Dental Materials. 27, 964-971 (2011).</li><li>Dijken, J. W., Lindberg, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+effectiveness+of+a+low-shrinkage+resin+composite:+a+five-year+evaluation.">Clinical effectiveness of a low-shrinkage resin composite: a five-year evaluation.</a> J Adhes Dent. 11, 143-148 (2009).</li><li>Yamazaki, P. C. V., Bedran-Russo, A. K. B., Pereira, P. N. R., Swift, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microleakage+Evaluation+of+a+New+Low-shrinkage+Composite+Restorative+Material.">Microleakage Evaluation of a New Low-shrinkage Composite Restorative Material.</a> Operative Dentistry. 31, 670-676 (2006).</li><li>Watts, D. C., Cash, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+polymerization+shrinkage+kinetics+in+visible-light-cured+materials:+methods+development.">Determination of polymerization shrinkage kinetics in visible-light-cured materials: methods development.</a> Dental materials : official publication of the Academy of Dental Materials. 7, 281-287 (1991).</li><li>Gee, A. J., Davidson, C. L., Smith, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+modified+dilatometer+for+continuous+recording+of+volumetric+polymerization+shrinkage+of+composite+restorative+materials.">A modified dilatometer for continuous recording of volumetric polymerization shrinkage of composite restorative materials.</a> Journal of Dentistry. 9, 36-42 (1981).</li><li>Sakaguchi, R. L., Sasik, C. T., Bunczak, M. A., Douglas, W. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strain+gauge+method+for+measuring+polymerization+contraction+of+composite+restoratives.">Strain gauge method for measuring polymerization contraction of composite restoratives.</a> Journal of Dentistry. 19, 312-316 (1991).</li><li>Fogleman, E. A., Kelly, M. T., Grubbs, W. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+interferometric+method+for+measuring+linear+polymerization+shrinkage+in+light+cured+dental+restoratives.">Laser interferometric method for measuring linear polymerization shrinkage in light cured dental restoratives.</a> Dental Materials. 18, 324-330 (2002).</li><li>Arenas, G., Noriega, S., Vallo, C., Duchowicz, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymerization+shrinkage+of+a+dental+resin+composite+determined+by+a+fiber+optic+Fizeau+interferometer.">Polymerization shrinkage of a dental resin composite determined by a fiber optic Fizeau interferometer.</a> Optics Communications. 271, 581-586 (2007).</li><li>Demoli, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Digital+interferometry+for+measuring+of+the+resin+composite+thickness+variation+during+blue+light+polymerization.">Digital interferometry for measuring of the resin composite thickness variation during blue light polymerization.</a> Optics Communications. 231, 45-51 (2004).</li><li>Sharp, L. J., Choi, I. B., Lee, T. E., Sy, A., Suh, B. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Volumetric+shrinkage+of+composites+using+video-imaging.">Volumetric shrinkage of composites using video-imaging.</a> Journal of Dentistry. 31, 97-103 (2003).</li><li>Feilzer, A. J., De Gee, A. J., Davidson, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Setting+stress+in+composite+resin+in+relation+to+configuration+of+the+restoration.">Setting stress in composite resin in relation to configuration of the restoration.</a> Journal of Dental Research. 66, 1636-1639 (1987).</li><li>Li, J., Fok, A. S., Satterthwaite, J., Watts, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+the+full-field+polymerization+shrinkage+and+depth+of+cure+of+dental+composites+using+digital+image+correlation.">Measurement of the full-field polymerization shrinkage and depth of cure of dental composites using digital image correlation.</a> Dental Materials. 25, (2009).</li><li>Chuang, S. -. F., Chang, C. -. H., Chen, T. Y. -. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatially+resolved+assessments+of+composite+shrinkage+in+MOD+restorations+using+a+digital-image-correlation+technique.">Spatially resolved assessments of composite shrinkage in MOD restorations using a digital-image-correlation technique.</a> Dental Materials. 27, 134-143 (2011).</li><li>Arakawa, A., Morita, Y., Uchino, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymerization+Shrinkage+Behavior+of+Light+Cure+Resin+Composites+in+Cavities.">Polymerization Shrinkage Behavior of Light Cure Resin Composites in Cavities.</a> Journal of Biomechanical Science and Engineering. 4, 356-364 (2009).</li><li>Lee, M. R., Cho, B. H., Son, H. H., Um, C. M., Lee, I. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+cavity+dimension+and+restoration+methods+on+the+cusp+deflection+of+premolars+in+composite+restoration.">Influence of cavity dimension and restoration methods on the cusp deflection of premolars in composite restoration.</a> Dental Materials. 23, 288-295 (2007).</li><li>Park, J., Chang, J., Ferracane, J., Lee, I. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+should+composite+be+layered+to+reduce+shrinkage+stress:+Incremental+or+bulk+filling.">How should composite be layered to reduce shrinkage stress: Incremental or bulk filling.</a> Dental Materials. 24, 1501-1505 (2008).</li><li>Weinmann, W., Thalacker, C., Guggenberger, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Siloranes+in+dental+composites.">Siloranes in dental composites.</a> Dental Materials. 21, 68-74 (2005).</li><li>Silikas, N., Eliades, G., Watts, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light+intensity+effects+on+resin-composite+degree+of+conversion+and+shrinkage+strain.">Light intensity effects on resin-composite degree of conversion and shrinkage strain.</a> Dental Materials. 16, 292-296 (2000).</li><li>Yaofeng, S., Pang, J. H. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Study+of+optimal+subset+size+in+digital+image+correlation+of+speckle+pattern+images.">Study of optimal subset size in digital image correlation of speckle pattern images.</a> Optics and Lasers in Engineering. 45, 967-974 (2007).</li><li>Versluis, A., Tantbirojn, D., Pintado, M. R., DeLong, R., Douglas, W. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Residual+shrinkage+stress+distributions+in+molars+after+composite+restoration.">Residual shrinkage stress distributions in molars after composite restoration.</a> Dental Materials. 20, 554-564 (2004).</li><li>Sakaguchi, R. L., Wiltbank, B. D., Murchison, C. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prediction+of+composite+elastic+modulus+and+polymerization+shrinkage+by+computational+micromechanics.">Prediction of composite elastic modulus and polymerization shrinkage by computational micromechanics.</a> Dental Materials. 20, 397-401 (2004).</li><li>Lecompte, D., Bossuyt, S., Cooreman, S., Sol, H., Vantomme, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> , (2007).</li><li>Huang, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Digital+Image+Correlation+with+Self-Adaptive+Gaussian+Windows.">Digital Image Correlation with Self-Adaptive Gaussian Windows.</a> Exp Mech. 53, 505-512 (2013).</li><li>Li, J., Lau, A., Fok, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+digital+image+correlation+to+full-field+measurement+of+shrinkage+strain+of+dental+composites.">Application of digital image correlation to full-field measurement of shrinkage strain of dental composites.</a> J. Zhejiang Univ. Sci. A. 14, 1-10 (2013).</li></ol>

The authors declare that they have no competing financial interests.

The use of glass cavities with the same shape and dimensions for shrinkage strain measurement was to minimize the variation in results due to differences in size, anatomy and material properties of natural human teeth. In addition, the fused silica glass used in this study has a similar Young&#8217;s modulus to enamel, making it a suitable simulant material for natural teeth as far as mechanical behavior is concerned21-22. Although in real tooth restorations, the resin composite is mostly bonded to dentin rath...

Resin composites are widely used in restorative dentistry because of their superior aesthetics and handling properties. However, despite being bonded to the tooth tissues, the polymerization shrinkage of resin composites remains a clinical concern as the shrinkage stress developed may cause debonding at the tooth-restoration interface1-2. Consequently, bacteria can invade and reside in the failed areas and result in secondary caries. On the other hand, if the restoration is well bonded to the tooth, the shrinkage stress may cause cracking in the tooth tissues. Either of these failures will jeopardize the service life of the dental restoration, which will be subjected to a large number of cycles of thermal and mechanical loading.

Measurement of polymerization shrinkage strain and stress has thus become indispensable in the development and evaluation of dental resin composites3-4. Various measuring techniques or methods have been developed5-11 with the main purpose of providing a simple setup for measuring the shrinkage behavior of resin composite materials reliably. While the measurements they provide may be sufficient for comparing the shrinkage behaviors of different materials, they do not help in the understanding of how and where shrinkage stress develops in actual restored teeth. Specifically, a question of great interest is how the cavity walls constrain the shrinkage of composites and leads to the creation of shrinkage stress in dental restorations12. Note that, to create shrinkage stress, part of the shrinkage strain of the resin composite has to be converted into tensile elastic strain. It would therefore be useful if this component of the strain in the restoration can be measured. Recently, the optical full-field strain-measuring technique, Digital Image Correlation (DIC), has been applied to the measurement of free shrinkage of resin composites as well as material flow in dental restorations13-15. The basic idea of DIC is to track and correlate visible patterns on the sample surface from sequential images taken during its deformation whereby the displacement and strain fields over that surface can be determined. Full-field measurement is one of the main advantages of the DIC method, which is especially useful in observing non-uniform deformation and strain patterns13. In this study, DIC was used to uncover the strain patterns in dental resin composite restorations, with the aim of understanding the development of shrinkage stress and identifying potential sites for debonding. This information is not directly available in the works cited above14-15, which only measured the displacement of the restoration due to polymerization shrinkage. The measurement was conducted using models that simulated teeth with mesial-occlusal-distal (MOD) tooth cavities as an attempt to replicate the stress or strain in real dental restorations. Although the use of real teeth is more anatomically representative, the disadvantage of that is the significant inherent differences among teeth in anatomy, mechanical properties, degree of hydration as well as invisible internal defects14 that result in large variations in the results. To overcome such a drawback, some studies have tried to standardize tooth samples by grouping them in terms of the buccal size16 or replaced the teeth altogether with models of a surrogate material17. For example, aluminum models which have a similar Young&#8217;s modulus to enamel (69 and 83 GPa, respectively) have been employed in shrinkage stress measurement, with the level of shrinkage stress being indicated by the cusp deflection17. In this study, silica glass models (cavities) were used instead because the material also has a similar Young&#8217;s modulus (63 GPa) to human enamel and, as it is transparent, any debonding or cracking in the specimens can be readily observed.

<table border="0" cellpadding="0" cellspacing="0" width="790">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:191px;">Dental composite Z100</td>
			<td style="width:167px;">3M ESPE</td>
			<td style="width:175px;">N362979</td>
			<td style="width:259px;">volume shrinkage ~ 2.5%, Young&#39;s modulus ~ 14 GPa</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:191px;">Dental composite Z250</td>
			<td>3M ESPE</td>
			<td style="width:175px;">N326080</td>
			<td style="width:259px;">volume shrinkage ~ 2.0%, Young&#39;s modulus ~ 11 GPa</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:191px;">Dental composite LS</td>
			<td>3M ESPE</td>
			<td style="width:175px;">N240313</td>
			<td style="width:259px;">volume shrinkage ~ 1%, Young&#39;s modulus ~ 10 GPa</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ceramic Primer</td>
			<td>3M ESPE</td>
			<td style="width:175px;">N167818</td>
			<td style="width:259px;">Rely X</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">LS System Adhesive</td>
			<td>3M ESPE</td>
			<td style="width:175px;">N391675</td>
			<td style="width:259px;">Adhesive for compoiste LS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Adper Single Bond Plus</td>
			<td>3M ESPE</td>
			<td style="width:175px;">501757</td>
			<td style="width:259px;">Adhesive for compoiste Z100 and Z250</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glass rod&#160;</td>
			<td>Corning Inc.</td>
			<td>&#160;Pyrex 7740 borosilicate&#160;</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:191px;">Curing light&#160;</td>
			<td>3M ESPE</td>
			<td>Elipar S10&#160;</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:191px;">White paint&#160;</td>
			<td>Krylon Product Group</td>
			<td style="width:175px;"></td>
			<td style="width:259px;">Indoor/Outdoor, Flat white</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:191px;">Charcoal powder&#160;</td>
			<td>Sigma Aldrich, Co.</td>
			<td style="width:175px;">BCBH6518V</td>
			<td style="width:259px;">Fluka activated charcoal</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CCD camera&#160;</td>
			<td>Point Grey Research, Inc.</td>
			<td>Point Grey Gras-20S4C-C</td>
			<td style="width:259px;"></td>
		</tr>
	</tbody>
</table>

shrinkage of dental composite in simulated cavity measured with digital image correlation

Polymerization shrinkage of dental resin composites can lead to restoration debonding or cracked tooth tissues in composite-restored teeth. In order to understand where and how shrinkage strain and stress develop in such restored teeth, Digital Image Correlation (DIC) was used to provide a comprehensive view of the displacement and strain distributions within model restorations that had undergone polymerization shrinkage.
Specimens with model cavities were made of cylindrical glass rods with both diameter and length being 10 mm. The dimensions of the mesial-occlusal-distal (MOD) cavity prepared in each specimen measured 3 mm and 2 mm in width and depth, respectively. After filling the cavity with resin composite, the surface under observation was sprayed with first a thin layer of white paint and then fine black charcoal powder to create high-contrast speckles. Pictures of that surface were then taken before curing and 5 min after. Finally, the two pictures were correlated using DIC software to calculate the displacement and strain distributions.
The resin composite shrunk vertically towards the bottom of the cavity, with the top center portion of the restoration having the largest downward displacement. At the same time, it shrunk horizontally towards its vertical midline. Shrinkage of the composite stretched the material in the vicinity of the &#8220;tooth-restoration&#8221; interface, resulting in cuspal deflections and high tensile strains around the restoration. Material close to the cavity walls or floor had direct strains mostly in the directions perpendicular to the interfaces. Summation of the two direct strain components showed a relatively uniform distribution around the restoration and its magnitude equaled approximately to the volumetric shrinkage strain of the material.

Three specimens were tested for each material. After each test, the specimen was examined by eyes or, if necessary, using a microscope. No apparent debonding at the &#8220;tooth-restoration&#8221; interface or cracking was found.
The resolution of the pictures was 1,600 x 1,180 pixels with a pixel size of 5.8 mm. With a subset window size of 32 pixels, the spatial resolution of the displacement distributions was around 186 mm.
Figure 3 shows a typic...

Watch this Scientific Journal Video about Shrinkage of Dental Composite in Simulated Cavity Measured with Digital Image Correlation at JoVE.com

Shrinkage of Dental Composite in Simulated Cavity Measured with Digital Image Correlation

In order to understand the spatial development of polymerization shrinkage stress in dental resin-composite restorations, Digital Image Correlation was used to provide full-field displacement/strain measurement of restored model glass cavities by correlating images of the restoration taken before and after polymerization.

Polymerization shrinkage of dental resin composites can lead to restoration debonding or cracked tooth tissues in composite-restored teeth. In order to ...

shrinkage-dental-composite-simulated-cavity-measured-with-digital

Research

JoVE Journal

Medicine

13.4K vistas.  University of Minnesota.  Con el fin de entender el desarrollo espacial de la tensión de contracción de polimerización en restauraciones de composite de resina dental, se utilizó la correlación digital de imagen para proporcionar de campo completo de medición de desplazamiento / deformación de las cavidades de vidrio modelo restaurados mediante la correlación de las imágenes de la restauración se toma antes y después de la polimerización. 

Video: Shrinkage of Dental Composite in Simulated Cavity Measured with Digital Image Correlation

Stem Cell Transplantation in an in vitro Simulated Ischemia/Reperfusion Model

Stem cell transplantation protocols are finding their way into clinical practice1,2,3. Getting better results, making the protocols more robust, and finding new sources for implantable cells are the focus of recent research4,5. Investigating the effectiveness of cell therapies is not an easy task and new tools are needed to investigate the mechanisms involved in the treatment process6. We designed an experimental protocol of ischemia/reperfusion in order to allow the observation of cellular connections and even subcellular mechanisms during ischemia/reperfusion injury and after stem cell transplantation and to evaluate the efficacy of cell therapy. H9c2 cardiomyoblast cells were placed onto cell culture plates7,8. Ischemia was simulated with 150 minutes in a glucose free medium with oxygen level below 0.5%. Then, normal media and oxygen levels were reintroduced to simulate reperfusion. After oxygen glucose deprivation, the damaged cells were treated with transplantation of labeled human bone marrow derived mesenchymal stem cells by adding them to the culture. Mesenchymal stem cells are preferred in clinical trials because they are easily accessible with minimal invasive surgery, easily expandable and autologous. After 24 hours of co-cultivation, cells were stained with calcein and ethidium-homodimer to differentiate between live and dead cells. This setup allowed us to investigate the intercellular connections using confocal fluorescent microscopy and to quantify the survival rate of postischemic cells by flow cytometry. Confocal microscopy showed the interactions of the two cell populations such as cell fusion and formation of intercellular nanotubes. Flow cytometry analysis revealed 3 clusters of damaged cells which can be plotted on a graph and analyzed statistically. These populations can be investigated separately and conclusions can be drawn on these data on the effectiveness of the simulated therapeutical approach.

Stem Cell Transplantation in an in vitro Simulated Ischemia/Reperfusion Model

We demonstrate how to set up an in vitro ischemia/reperfusion model and how to evaluate the effect of stem cell therapy on postischemic cardiac cells.

Stem cell transplantation protocols are finding their way into clinical practice1,2,3. Getting better results, making the protocols more robust, and ...

Orthotopic Hind Limb Transplantation in the Mouse

In vivo animal model systems, and in particular mouse models, have evolved into powerful and versatile scientific tools indispensable to basic and translational research in the field of transplantation medicine. A vast array of reagents is available exclusively in this setting, including mono- and polyclonal antibodies for both diagnostic and interventional applications. In addition, a vast number of genotyped, inbred, transgenic, and knock out strains allow detailed investigation of the individual contributions of humoral and cellular components to the complex interplay of an immune response and make the mouse the gold standard for immunological research. 
Vascularized Composite Allotransplantation (VCA) delineates a novel field of transplantation using allografts to replace "like with like" in patients suffering traumatic or congenital tissue loss. This surgical methodological protocol shows the use of a non-suture cuff technique for super-microvascular anastomosis in an orthotopic mouse hind limb transplantation model. The model specifically allows for comparison between established paradigms in solid organ transplantation with a novel form of transplants consisting of various different tissue components. Uniquely, this model allows for the transplantation of a viable vascularized bone marrow compartment and niche that have the potential to exert a beneficial effect on the balance of immune acceptance and rejection. This technique provides a tool to investigate alloantigen recognition and allograft rejection and acceptance, as well as enables the pursuit of functional nerve regeneration studies to further advance this novel field of transplantation.

This novel model for orthotopic hind limb transplantation in the mouse, applying a non-suture cuff technique for super-microvascular anastomosis, provides a powerful tool for in&#160;vivo mechanistic immunological research related to vascularized composite allotransplantation (VCA).

In vivo animal model systems, and in particular mouse models, have evolved into powerful and versatile scientific tools indispensable to basic and ...

Electrophysiological Assessment of Murine Atria with High-Resolution Optical Mapping

Recent genome-wide association studies targeting atrial fibrillation (AF) have indicated a strong association between the genotype and electrophysiological phenotype in the atria. That encourages us to utilize a genetically-engineered mouse model to elucidate the mechanism of AF. However, it is difficult to evaluate the electrophysiological properties in murine atria due to their small size. This protocol describes the electrophysiological evaluation of atria using an optical mapping system with a high temporal and spatial resolution in Langendorff perfused murine hearts. The optical mapping system is assembled with dual high-speed complementary metal oxide semiconductor cameras and high magnification objective lenses, to detect the fluorescence of a voltage-sensitive dye and Ca2+ indicator. To focus on the assessment of murine atria, optical mapping is performed with an area of 2 mm &#215; 2 mm or 10 mm x 10 mm, with a 100 &#215; 100 resolution (20 &#181;m/pixel or 100 &#181;m/pixel) and sampling rate of up to 10 kHz (0.1 ms) at maximum. A 1-French size quadripolar electrode pacing catheter is placed into the right atrium through the superior vena cava avoiding any mechanical damage to the atrium, and pacing stimulation is delivered through the catheter. An electrophysiological study is performed with programmed stimulation including constant pacing, burst pacing, and up to triple extrastimuli pacing. Under a spontaneous or pacing rhythm, the optical mapping recorded the action potential duration, activation map, conduction velocity, and Ca2+ transient individually in the right and left atria. In addition, the programmed stimulation also determines the inducibility of atrial tachyarrhythmias. Precise activation mapping is performed to identify the propagation of the excitation in the atrium during an induced atrial tachyarrhythmia. Optical mapping with a specialized setting enables a thorough electrophysiological evaluation of the atrium in murine pathological models.

This protocol describes the electrophysiological evaluation of murine atria utilizing an optical mapping system with a high temporal and spatial resolution, including dual recordings of the membrane voltage and Ca2+ transient under programmed stimulation through a specialized electrode catheter.

Recent genome-wide association studies targeting atrial fibrillation (AF) have indicated a strong association between the genotype and ...

Contractions of Human-iPSC-derived Cardiomyocyte Syncytia Measured with a Ca-sensitive Fluorescent Dye in Temperature-controlled 384-well Plates

Spontaneously contracting syncytia of cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CM) are a useful model of human cardiac physiology and pharmacology. Various methods have been proposed to record this spontaneous activity and to evaluate drug effects, but many of these methods suffer from limited throughput and/or physiological relevance. We developed a high-throughput screening system to quantify the effects of exogenous compounds on hiPSC-CM's beating frequency, using a Ca-sensitive fluorescent dye and a temperature-controlled imaging multi-well plate reader. We describe how to prepare the cell plates and the compound plates and how to run the automated assay to achieve high sensitivity and reproducibility. We also describe how to transform and analyze the fluorescence data to provide reliable measures of drug effects on spontaneous rhythm. This assay can be used in drug discovery programs to guide chemical optimization away from, or toward, compounds affecting human cardiac function.

Spontaneously contracting syncytia of cardiomyocytes derived from human-induced pluripotent stem cells are useful models of human cardiac physiology and pharmacology. Here we present a high-throughput screening system to quantify the effects of exogenous compounds on beating frequency, using a Ca-sensitive fluorescent dye and a temperature-controlled imaging multi-well plate reader.

Spontaneously contracting syncytia of cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CM) are a useful model of human cardiac ...

Digital Handwriting Analysis of Characters in Chinese Patients with Mild Cognitive Impairment

An increasing amount of evidence shows that cognitive deficits and movement dysfunctions are not separated. Patients with mild cognitive impairment (MCI) can manifest fine motor disorders of the upper extremities. Handwriting is a complex and unique human activity involving both motor and cognitive coordination. Researchers from western countries have discovered that patients with MCI have abnormal handwriting features. However, no relevant studies have been conducted in the Chinese population. Owing to the cross-culture phenomenon of handwriting, the aim of this study is to find new handwriting tasks to demonstrate the differences in handwriting features between elderly patients with MCI and age-matched healthy individuals.

This study proposed a digital handwriting analysis of characters in individuals with mild cognitive impairment to find more information than is revealed by traditional pencil&#8211;paper handwriting analysis.

An increasing amount of evidence shows that cognitive deficits and movement dysfunctions are not separated. Patients with mild cognitive impairment (MCI) ...

A Standardized Approach to Extra-Oral and Intra-Oral Digital Photography

Contemporary dentistry mandates a more comprehensive and personalized analysis of each patient. Technological advances in digital photography have played vital roles in diagnostic accuracy, treatment planning, execution of therapies, and outcome evaluations, including esthetic enhancement. Digital photography also provides an excellent platform for patient education, communication, and co-management of cases with other healthcare providers. However, intra-oral photography often faces challenges such as inaccessibility of areas to be captured, different moveable vs. fixed tissues involved, contamination with saliva or blood, and differing illumination needs on various locations. Thus, a more standardized and systematic approach is proposed for intra- and extra-oral documentation via digital photography to overcome the existing technical challenges. The current work will outline the appropriate equipment specifications (camera bodies, macro lens, and flashes), positions and postures of the operator and patients, proper techniques of tissue retraction, the use of appropriate intra-oral mirrors, and the essential elements such as aperture settings (F-stop), ISO, shutter speed, and white balance. This article aims to provide all dental professionals with an approachable linear array of guidelines to produce simplified and standardized visual tools for more efficient and effective documentation.

The present protocol describes a method to capture intra- and extra-oral photographs for digital documentation in the clinical practice of dentistry. The protocol highlights all the critical components involved and the commonly utilized settings to capture dental photographs for clinical documentation.

Contemporary dentistry mandates a more comprehensive and personalized analysis of each patient. Technological advances in digital photography have played ...

Detection and Removal of Tooth-Colored Composite Resin Using the Fluorescence-Aided Identification Technique

The detection and removal of tooth-colored filling materials is a major challenge for every dentist. The Fluorescence-aided Identification Technique (FIT) is a noninvasive tool to facilitate the distinction of composite resin material from sound tooth substance. Compared to conventional illumination, FIT is a very accurate, reliable, and fast diagnostic method. When composite resin is illuminated with a wavelength of approximately 398 &plusmn; 5 nm, certain fluorescent components make the composite resin appear brighter than the tooth structure. Any fluorescence-inducing light source with the appropriate wavelength can be used for this method. Optimally, this technique is used without additional natural or artificial lighting. The application of FIT can be used for diagnostic purposes, for example, dental charts, and additionally for the complete and minimally invasive removal of composite resin restorations, bracket debonding, and trauma splint removal. The assessment of volumetric changes after composite removal can be provided by overlapping pre- and postoperative scans and subsequent calculation using suitable software.

The Fluorescence-aided Identification Technique is a practicable, fast, and reliable approach for the differentiation of composite resin restorations from tooth substance, and facilitates the minimally invasive and complete removal of composite resin restorations and composite bonded trauma splints.

The detection and removal of tooth-colored filling materials is a major challenge for every dentist. The Fluorescence-aided Identification Technique (FIT) ...

Dynamic Navigation in Endodontics: Guided Access Cavity Preparation by Means of a Miniaturized Navigation System

In the case of teeth with pulp canal calcification (PCC) and apical pathology or pulpitis, root canal treatment can be very challenging. PCC are common sequelae of dental trauma but can also occur with stimuli such as caries, bruxism, or after placing a restoration. In order to access the root canal as minimally invasive as possible in case of a necessary root canal treatment, dynamic navigation has recently been introduced in endodontics in addition to static navigation. The use of a dynamic navigation system (DNS) requires pre-operative cone-beam computed tomography (CBCT) imaging and a digital surface scan. If necessary, reference markers must be placed on the teeth before the CBCT scan; with some systems, these can also be planned and created digitally afterward. By means of a stereo camera connected to the planning software, the drill can now be coordinated with the help of reference markers and virtual planning. As a result, the position of the drill can be displayed on the monitor in real-time during preparation in different planes. In addition, the spatial displacement, the angular deviation, and the depth position are also displayed separately. The few commercially available DNS mostly consist of relatively large camera-marker-systems. Here, the DNS contains miniaturized components: a low-weight camera (97 g) mounted on the micromotor of the electric handpiece utilizing a manufacturer-specific connecting mechanism and a small marker (10 mm x 15 mm), which can be easily attached to an individually manufactured intraoral tray. For research purposes, a post-operative CBCT scan can be matched with the pre-operative one, and the volume of tooth structure removed can be calculated by the software. This work aims to present the technique of guided access cavity preparation by means of a miniaturized navigation system from imaging to clinical implementation.

Dynamic navigation systems (DNS) provide real-time visualization and guidance to the operator during endodontic access cavities preparation. The planning of the procedure requires three-dimensional imaging utilizing cone beam computed tomography and surface scans. After the export of the planning data to the DNS, access cavities can be prepared with minimal invasion.

In the case of teeth with pulp canal calcification (PCC) and apical pathology or pulpitis, root canal treatment can be very challenging. PCC are common ...

Evaluation of Maxillary Posterior Tooth Movement Using Digital Superimposition

Measuring Maxillary Posterior Tooth Movement: A Model Assessment using Palatal and Dental Superimposition

Since the introduction of Invisalign by Align Technology, Inc. in 1999, questions and debates have persisted regarding the precision of Invisalign (clear aligner) therapy, particularly when compared to the use of traditional fixed appliances. This becomes particularly significant in cases involving anteroposterior, vertical, and transverse corrections, where precise comparisons are of paramount importance. To address these inquiries, this study introduces a meticulously devised protocol, placing a primary emphasis on digitally superimposing the movement of maxillary posterior teeth to facilitate accurate analysis. The sample included 25 patients who had completed their first series of Invisalign (clear) aligners. Four maxillary digital models (pre-treatment, post-treatment, ClinCheck-initial, and final models) were digitally superimposed using the palate rugae and dentitions as stable references. A software combination was used for model superimposition and tooth segmentation. Transformation matrices then expressed the differences between the achieved and predicted tooth positions. Thresholds for clinically relevant differences were at &plusmn;0.25 mm for linear displacement and &plusmn;2&#176; for rotation. Differences were assessed using Hotelling's T-squared tests with Bonferroni correction. The mean differences in rotation (2.036&#176; &plusmn; 4.217&#176;) and torque (-2.913&#176; &plusmn; 3.263&#176;) were significant statistically and clinically, with p-values of 0.023 and 0.0003 respectively. De-rotation of premolars and torque control for all posterior teeth were less predictable. All mean differences for the linear measurements were statistically and clinically insignificant, except that the first molars seemed slightly (0.256 mm) more intruded than their predicted position. The clear aligner system appears to meet its prediction for most translational tooth movements and mesial-distal tipping in maxillary posterior teeth for non-extraction cases with mild to moderate malocclusions.

Author Spotlight: 3D Movement Assessment of Maxillary Posterior Teeth in Clear Aligner Treatment

This manuscript presents a comprehensive protocol to evaluate the three-dimensional (3D) movement of maxillary posterior teeth with clear aligners using digital model superimposition, an invaluable tool in orthodontics and dentofacial orthopedics.

Since the introduction of Invisalign by Align Technology, Inc. in 1999, questions and debates have persisted regarding the precision of Invisalign (clear ...

Artificial Intelligence-Based Integration of Dental Images

Reliability of Artificial Intelligence-Based Cone Beam Computed Tomography Integration with Digital Dental Images

This study aimed to introduce cone-beam computed tomography (CBCT) digitization and integration of digital dental images (DDI) based on artificial intelligence (AI)-based registration (ABR) and to evaluate the reliability and reproducibility using this method compared with those of surface-based registration (SBR). This retrospective study consisted of CBCT images and DDI of 17 patients who had undergone computer-aided bimaxillary orthognathic surgery. The digitization of CBCT images and their integration with DDI were repeated using an AI-based program. CBCT images and DDI were integrated using a point-to-point registration. In contrast, with the SBR method, the three landmarks were identified manually on the CBCT and DDI, which were integrated with the iterative closest points method.
After two repeated integrations of each method, the three-dimensional coordinate values of the first maxillary molars and central incisors and their differences were obtained. Intraclass coefficient (ICC) testing was performed to evaluate intra-observer reliability with each method&#39;s coordinates and compare their reliability between the ABR and SBR. The intra-observer reliability showed significant and almost perfect ICC in each method. There was no significance in the mean difference between the first and second registrations in each ABR and SBR and between both methods; however, their ranges were narrower with ABR than with the SBR method. This study shows that AI-based digitization and integration are reliable and reproducible.

Author Spotlight: Advancing CBCT and Digital Dental Image Integration with AI-Assisted Digitization

A process of registering cone-beam computed tomography scans and digital dental images has been presented using artificial intelligence (AI) -assisted identification of landmarks and merging. A comparison with surface-based registration shows that AI-based digitization and integration are reliable and reproducible.