An alternative method to bonding to porcelain restorations
Ahrari F, Heravi F, Hosseini M. CO 2 laser conditioning of porcelain surfaces for bonding metal orthodontic brackets. Lasers Med Sci 2012 September 5 [Epub ahead of print]
Direct bonding to porcelain restorations is a challenge for clinicians. This technique-sensitive procedure will most likely see an increase in its need with more adults seeking orthodontic treatment today. The aims of this study were to evaluate shear bond strengths of metal brackets bonded to porcelain conditioned with a fractional carbon dioxide laser at varying intensities for both glazed and deglazed surfaces, and to compare it with the conventional technique of hydrofluoric acid. Eighty feldspathic porcelain specimens were divided into 4 groups of 20; each group contained half glazed and half deglazed specimens. Groups 1, 2, and 3 were treated with a fractional carbon dioxide laser for 10 s using 10 mJ of energy, frequency of 200 Hz, and powers of 10 W (group 1), 15 W (group 2), and 20 W (group 3), and group 4 was treated with 9.6% hydrofluoric acid for 2 minutes. Shear bond strength in all deglazed specimens conditioned with the carbon dioxide laser had more than double the strength of their glazed counterparts, ranging from 9 to 11 MPa and 4 to 5 MPa, respectively. The hydrofluoric acid control group showed higher mean shear bond strengths for the glazed than the deglazed specimens at 7.31 and 6.25 MPa, respectively. Most studies seem to agree that 6 to 8 MPa of shear bond strength is acceptable for most orthodontic forces during treatment, and the traditional method of using hydrofluoric acid will provide acceptable bond strengths needed for treatment. It seems that a fractional carbon dioxide laser does increase the shear bond strength while bonding to porcelain and possibly decreasing chair time, especially if there are multiple restorations.
Reviewed by Aaron Miyai
Accuracy of orthodontic digital models
Abizadeh N, Moles DR, O’Neill J, Noar JH. Digital versus plaster study models: how accurate and reproducible are they? J Orthod 2012;39:151-9
With recent advances in scanning methods and computer-aided design technology, digital study models are becoming increasingly popular. Plaster models are subject to breakage and loss, and require a large storage space. Virtual models have some limitations in regard to software and scanning procedures. The aim of this study was to compare the measurements between plaster models and their homologous laser-scanned digital models. Plaster models from 112 patients were selected with a relatively equal distribution among Class I, Class II, and Class III malocclusions and mild, moderate, and severe crowding. Digital models were created by ESM Digital Solutions. Sixteen measurements were acquired on the plaster models by using digital calipers and again with the software on the digitally scanned models. This process was repeated a month later to assess reproducibility. The measurements included arch length, intermolar width, intercanine width, overbite, overjet, crown heights of selected teeth, anterior open bite, and midline discrepancy. Analysis showed that for 11 of the 16 variables, the digital measurements were significantly smaller than were the plaster measurements. For half of the variables, the measurements made on the plaster models were more repeatable. Overall, the differences between the measurements were significant but within a reasonable range for clinical use. The authors suggested 2 explanations to account for differences in the digital measurements: errors introduced during scanning or errors due to landmark selection while measuring. Future research with a direct intraoral scan would be an interesting next step to this study. Currently, plaster models measured with digital calipers remain the gold standard for scientific and clinical applications.
Reviewed by Ashley Lestrade