Palatal orthodontic miniscrew insertion using a CAD-CAM surgical guide: description of a technique

The aim of this report was to describe a new computer-guided technique for a controlled site preparation and palatal orthodontic miniscrew insertion using a dedicated software. A surgical guide was designed after planning the appropriate insertion sites on three-dimensional images created by the fusion of cone-beam computed tomography (CBCT) and digital dental model images. Pre- and postoperative CBCT images were compared and the angular, coronal, and apical deviations between the planned and the placed miniscrews were calculated. The mean coronal and apical deviations were 1.38 mm (range: 3.48–0.15 mm; standard deviation (SD): 0.65) and 1.73 mm (range: 5.41–0.10 mm; SD: 1.03), respectively, while the mean angular deviation was 4.60° (range: 15.23–0.54°; SD: 2.54). The present surgical guide allows a controlled and accurate palatal miniscrew placement in three dimensions.     

Accuracy of position of cutting and drilling guide for sagittal split guided surgery: a proof of concept study

The benefits of three-dimensional planning and guided surgery have been realised over the last few years in maxillofacial surgery. Reproducing the exact positioning of the cutting and drilling guides on the flat mandibular angles defined by the engineer is a challenge for the surgeon and for the reliability of guided bilateral sagittal split osteotomy. Reference screws positioned on the skeleton before the acquisition of medical computed tomographic data can provide a fixed landmark that can be used during surgery and by the engineer during the design phase. The objective of this proof of concept in vitro study is to calculate the accuracy obtained for guides positioned by inserting a reference screw. The precision obtained for 30 guides following the insertion of 30 reference screws on 15 mandibular models was analysed. The models were scanned using an optical scanner and compared to CAD-CAM projects. The mean (SD) absolute position (in)-inaccuracy is 0.1616 (0.1141) mm for the entire guide surface and 0.13143 (0.0835) mm for the rim surface. The results indicate that the use of reference screws is efficient, and so they can be used to position guides accurately during guided bilateral sagittal split osteotomy.     

In vitro study of fracture strength of provisional crown materials

PURPOSE

The purpose of this report was to evaluate the effect of the fabrication method and material type on the fracture strength of provisional crowns.

MATERIALS AND METHODS

A master model with one crown (maxillary left second premolar) was manufactured from Cr-Co alloy. The master model was scanned, and the data set was transferred to a CAD/CAM unit (Yenamak D50, Yenadent Ltd, Istanbul, Turkey) for the Cercon Base group. For the other groups, temporary crowns were produced by direct fabrication methods (Imident, Temdent, Structur Premium, Takilon, Systemp c&b II, and Acrytemp). The specimens were subjected to water storage at 37℃ for 24 hours, and then they were thermocycled (TC, 5000×, 5-55℃) (n=10). The maximum force at fracture (Fmax) was measured in a universal test machine at 1 mm/min. Data was analyzed by non-parametric statistics (α=.05).

RESULTS

Fmax values varied between 711.09-1392.1 N. In the PMMA groups, Takilon showed the lowest values (711.09 N), and Cercon Base showed the highest values (959.59 N). In the composite groups, Structur Premium showed the highest values (1392.1 N), and Acrytemp showed the lowest values (910.05 N). The composite groups showed significantly higher values than the PMMA groups (P=.01).

CONCLUSION

Composite-based materials showed significantly higher fracture strengths than PMMA-based materials. The CAD-CAM technique offers more advantages than the direct technique.     

Retention Forces of Monolithic CAD/CAM Crowns Adhesively Cemented to Titanium Base Abutments—Effect of Saliva Contamination Followed by Cleaning of the Titanium Bond Surface

The aim of this study was to investigate the effects of saliva contamination and the cleaning of the bond surface of titanium base (ti-base) abutments on the bonding stability and retention force values. The bond surface of the ti-base abutments was treated with airborne-particle abrasion. After contamination, the ti-base abutments underwent different cleaning protocols: water spray (H₂O); alcohol (ALC); suspension of zirconium particles (SZP); reapplied airborne-particle abrasion (APA); and a control condition without contamination and cleaning (CTR). All lithium disilicate crowns were bonded to the ti-base abutments using a primer and a self-curing composite. Bonded specimens underwent thermo-mechanical aging. Bond failure analysis and pull-off testing were performed. Bond failure occurred more frequently in groups H₂O, ALC, SZP, and APA (p < 0.05). Significant differences in retention force values were only found between CTR and ALC (p < 0.05). Specimens which did not show bond failure after ageing had higher retention force values than the specimens that showed bond failure (p < 0.05). Saliva contamination with cleaning can degrade the bonding properties to titanium. For the retention force values, only the protocol with alcohol after contamination could not restore the values.     

Flexural resistance of heat-pressed and CAD-CAM lithium disilicate with different translucencies

Objective

To compare flexural strength of CAD-CAM and heat-pressed lithium disilicate.

Experimental Study Regarding the Behavior at Different pH of Two Types of Co-Cr Alloys Used for Prosthetic Restorations

Cobalt-chromium (Co-Cr) alloys are widely utilized in dentistry. The salivary pH is a significant factor, which affects the characteristics and the behavior of dental alloys through corrosion. This study aimed to evaluate the corrosion behavior in artificial saliva with different pH values (3, 5.7, and 7.6) of two commercial Co-Cr dental alloys manufactured by casting and by milling. Corrosion resistance was determined by the polarization resistance technique, and the tests were carried out at 37 ± 1 °C, in Carter Brugirard artificial saliva. After the electrochemical parameters, it can be stated that the cast Co-Cr alloy has the lowest corrosion current density, the highest polarization resistance, and the lowest speed of corrosion in artificial saliva with pH = 7.6. In the case of milled Co-Cr alloy, the same behavior was observed, but in artificial saliva with pH = 5.7, it recorded the most electropositive values of open circuit potential and corrosion potential. Although both cast and milled Co-Cr alloys presented a poorer corrosion resistance in artificial saliva with a more acidic pH value, the milled Co-Cr alloy had better corrosion behavior, making this alloy a better option for the prosthetic treatment of patients suffering from GERD.     

CEREC陶瓷修复体的临床应用

在临床修复中，传统的瓷嵌体等修复体的制作，至少需要二次就诊时间。随着光学扫描方法和计算机辅助制作嵌体技术的应用，省去了目前操作的印模、灌模、蜡型等技术。CEREC系统运用光学印模方法以及CAD-CAM技术，将一预成陶瓷块铣磨成修复体，使牙科医生能在牙体预备后即制作一个色泽自然的陶瓷修复体，并即时粘固于预备牙上，这不仅提高了工作效率，更重要的是提高了修复体的质量。该系统不仅可以制作嵌体和高嵌体，而且还可制作各种贴面。本文的目的是介绍和描述CEREC系统制作修复体的方法步骤，并就临床应用中的有关问题加以探讨。