As a novel emerging technology, four-dimensional (4D) printing allows the stimulation of 3D-printed materials in order to change shape, color, functionality, etc, over time. This systematic review is conducted to evaluate the purpose, materials, physiomechanical, and biological properties of 4D-printed scaffolds used for bone tissue engineering. An electronic search was conducted following the PRISMA 2020 guidelines in PubMed, Scopus, Web of Science, and Google Scholar online databases limited to English articles until April 2024. Studies in which scaffolds were fabricated through 3D printing methods responding to external stimulation were included. The quality of in vitro and in vivo studies was evaluated through the modified CONSORT checklist and SYRCLE’s risk of bias tool. The full text of 57 studies were reviewed, and 15 studies met the inclusion criteria. According to the analyzed studies, most scaffolds responded to temperature changes showing shape memory effect. Polyurethane and poly(lactic acid) were the most common shape memory polymers (SMPs), and the most common fabrication method used was fused deposition modeling. A comprehensive systematic review of the studies from the past 10 years demonstrated several findings: (1) Shape memory, drug delivery, and shape morphing are three general purposes of 4D printing for bone regeneration. (2) Smart materials used for 4D printing mostly consist of SMPs. (3) Temperature changes account for the majority of stimulation used for 4D printing. (4) incorporating 4D printing principles does not negatively impact on the physiomechanical properties of the designed scaffold. (5) The 4D-printed scaffolds show a higher osteogenic differentiation capacity than their identical 3D-printed structures in terms of bone regeneration.

Introduction: All-ceramic restorations are being widely used due to its various advantages. However, they have restricted durability and may have to be removed. The conventional procedure for removal is grinding the restoration with rotary instruments which are considered time-consuming and inconvenient. A newer advantageous method is the application of lasers for debonding ceramics from the tooth surface. The objective of this study is to provide a comprehensive literature review on laser-aided ceramic restorations debonding. Methods: We searched PubMed and Google Scholar databases. Seven articles from 2011 to 2018 were identified. Studies were assessed for the efficacy of laser application and the amount of pulpal temperature rise. Results: Studies selected were categorized according to variables including shear bond strength, debonding time and intrapulpal temperature. Oztoprak and Iseri investigated that erbium-doped yttrium, aluminum, and garnet (Er:YAG) laser application reduced shear bond strength of ceramic laminate veneers. The time of debonding took an average of 190 seconds in Rechmann’s study and 106 seconds in Morford’s study. One of the main issues while using the laser is thermal irritation of the pulp. A 5.5°C temperature increase may cause pulpal damage according to Zach and Cohen. Philips et al and Rechmann et al reported no intrapulpal harm due to temperature increase. Additionally, Phillips et al demonstrated that the laser setting affects both the debonding time and the temperature alterations and that a laser adjustment of 2.5 W/25 Hz would be the best safest group. Conclusion: Removal of ceramic crowns and veneers from tooth surfaces can be successfully done by Er:YAG laser application in a less time-consuming procedure and without any harm to the underlying dentin. However, a temperature rise in the pulp may occur which could be overcome by adequate air water cooling.

Comparison of Tooth Color Change After Bleaching With Conventional and Different Light-Activated Methods

Laser-Aided Ceramic Bracket Debonding: A Comprehensive Review