Introduction The regular collection of three-dimensional (3D) imaging data is critical to the development and implementation of accurate predictive models of facial skeletal growth. However, repeated exposure to x-ray based modalities such as cone-beam computed tomography (CBCT) have unknown risks that outweigh many potential benefits, especially in pediatric patient populations. One solution is to make inferences about the facial skeleton from external 3D surface morphology captured using safe non-ionizing imaging modalities alone. However, the degree to which external 3D facial shape is an accurate proxy of skeletal morphology has not been previously quantified. As a first step in validating this approach, here we test the hypothesis that population-level variation in the 3D shape of the face and skeleton significantly covary. Methods We retrospectively analyzed 3D surface and skeletal morphology from a previously collected cross-sectional CBCT database of non-surgical orthodontics patients, and used geometric morphometrics and multivariate statistics to test the hypothesis that shape variation in external face and internal skeleton covary. Results External facial morphology is highly predictive of variation in internal skeletal shape (Rv=0.56, p<0.0001; PLS1-13=98.7% covariance, p<0.001) and asymmetry (Rv=0.34, p<0.0001; PLS1-5=90.2% covariance, p<0.001), while age (r2=0.84, p<0.001) and size-related (r2=0.67, p<0.001) shape variation are also highly correlated. Conclusions Surface morphology is a reliable source of proxy data for the characterization of skeletal shape variation, and thus is particularly valuable in research designs where reducing potential long-term risks associated with radiological imaging methods is warranted. We propose that longitudinal surface morphology from early childhood through late adolescence has the potential to be a valuable source of data that will facilitate the development of personalized craniodental planning and treatment plans while reducing exposure levels to “as low as reasonably achievable” (ALARA).
The objective of this in vitro study was to evaluate whether irradiation of enamel with a novel CO 9.3-μm short-pulsed laser using energies that enhance caries resistance influences the shear bond strength of composite resin sealants to the irradiated enamel. Seventy bovine and 240 human enamel samples were irradiated with a 9.3-μm carbon dioxide laser (Solea, Convergent Dental, Inc., Natick, MA) with four different laser energies known to enhance caries resistance or ablate enamel (pulse duration from 3 μs at 1.6 mJ/pulse to 43 μs at 14.9 mJ/pulse with fluences between 3.3 and 30.4 J/cm, pulse repetition rate between 4.1 and 41.3 Hz, beam diameter of 0.25 mm and 1-mm spiral pattern, and focus distance of 4-15 mm). Irradiation was performed "freehand" or using a computerized, motor-driven stage. Enamel etching was achieved with 37% phosphoric acid (Scotchbond Universal etchant, 3M ESPE, St. Paul, MN). As bonding agent, Adper Single Bond Plus was used followed by placing Z250 Filtek Supreme flowable composite resin (both 3M ESPE). After 24 h water storage, a single-plane shear bond test was performed (UltraTester, Ultradent Products, Inc., South Jordan, UT). All laser-irradiated samples showed equal or higher bond strength than non-laser-treated controls. The highest shear bond strength values were observed with the 3-μs pulse duration/0.25-mm laser pattern (mean ± SD = 31.90 ± 2.50 MPa), representing a significant 27.4% bond strength increase over the controls (25.04 ± 2.80 MPa, P ≤ 0.0001). Two other caries-preventive irradiation (3 μs/1 mm and 7 μs/0.25 mm) and one ablative pattern (23 μs/0.25 mm) achieved significantly increased bond strength compared to the controls. Bovine enamel also showed in all test groups increased shear bond strength over the controls. Computerized motor-driven stage irradiation did not show superior bond strength values over the clinically more relevant freehand irradiation. Enamel that is made caries-resistant with CO 9.3-μm short-pulsed laser irradiation showed at least equal or significantly higher shear bond strength to pit and fissure sealants than non-laser-irradiated enamel. The risk of a sealant failure due to CO 9.3-μm short-pulsed laser irradiation appears reduced. If additional laser ablation is required before placing a sealant, the CO 9.3-μm enamel laser-cut showed equivalent or superior bond strength to a flowable sealant.
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