Dental post-operative sensitivity associated with a gallium-based restorative material

Liquid metal biomaterials for biomedical imaging

Liquid metals (LMs) not only retain the basic properties of metallic biomaterials, such as high thermal conductivity and high electrical conductivity, but also possess flexibility, flowability, deformability, plasticity, good adhesion, and so on. Therefore, they open many possibilities of extending soft metals into biomedical sciences including biomedical imaging. One of the special properties of LMs is that they can provide a controllable material system in which the electrical, thermal, mechanical, and chemical properties can be controlled on a large scale. This paper reviews the preparation and characteristics of LM-based biomaterials classified into four categories: LM micro/nanoparticles, surface modified LM droplets, LM composites with inorganic substances, and LM composites with organic polymers. Besides, considering the most important requirement for biomaterials is biocompatibility, the paper also analyzes the toxicity results of various LM biomaterials when used in the biomedical area, from different levels including body weight measurement, histology evaluation, and blood biochemistry tests. Next, the applications of LMs in X-ray, CT, MRI, photoacoustic imaging, and molecular imaging are introduced in detail. And finally, the challenges and opportunities of their application in medical imaging are also discussed.

Self-Powered Gallium-Based Liquid-Metal Beating Heart

Mercury beating heart is a well-known phenomenon that consists of a mercury droplet covered with aqueous acid and an iron nail. However, mercury is highly poisonous, and its vapor is especially dangerous. Thus, related studies and applications on mercury have often been hindered. Here, we proposed another beating heart but employed a different material, i.e., GaIn alloy with low toxicity. A stainless steel wire was utilized to touch the side of the liquid-metal droplet in basic solution. Based on this method, periodic oscillation could be kept continuous and steady. This finding suggests a more feasible and safer way to realize beating behaviors, which would shed light on a variety of future applications, such as pump and mixer for the mini device.

Alternating-Magnetic-Field-Mediated Wireless Manipulations of a Liquid Metal for Therapeutic Bioengineering

As emergent multifunctional materials, room temperature liquid metals (LMs) display many unique properties. Here we show that applying an external alternating magnetic field (AMF) to an LM induces various physical phenomena, such as exothermic behavior, controlled locomotion, electromagnetic levitation, and transformations of the LMs between different morphologies and configurations, in a non-contact manner. Additional interesting therapeutic bioengineering applications of LMs demonstrated herein include in vitro and in vivo effective cancer magnetic hyperthermia via wireless AMF, remote manipulation of a pill-shaped microdevice based on an LM/hydrogel composite, and spatiotemporal controlled release of drug molecules from the microdevice. Overall, as an innovative therapeutic bioengineering technology, this platform and the described performance traits of LMs enable the development of biocompatible smart devices with a wide range of dynamic components that can be wirelessly controlled in a manner that solves issues related to the powering of devices and biocompatibility.

Liquid metal bath as conformable soft electrodes for target tissue ablation in radio-frequency ablation therapy

BACKGROUND

Radio-frequency ablation has been an important physical method for tumor hyperthermia therapy. The conventional rigid electrode boards are often uncomfortable and inconvenient for performing surgery on irregular tumors, especially for those tumors near the joints, such as ankles, knee-joints or other facets like finger joints.

MATERIAL AND METHODS

We proposed and demonstrated a highly conformable tumor ablation strategy through introducing liquid metal bath as conformable soft electrodes. Different heights of liquid metal bath electrodes were adopted to perform radio-frequency ablation on targeted tissues. Temperature and ablation area were measured to compare the ablation effect with plate metal electrodes.

RESULTS

The recorded temperature around the ablation electrode was almost twice as high as that with the plate electrode and the effective ablated area was 2-3 fold larger in all the mimicking situations of bone tumors, span-shaped or round-shaped tumors. Another unique feature of the liquid metal electrode therapy is that the incidence of heat injury was reduced, which is a severe accident that can occur during the treatment of irregular tumors with plate metal boards.

CONCLUSIONS

The present method suggests a new way of using soft liquid metal bath electrodes for targeted minimally invasive tumor ablation in future clinical practice.

The injectable neurostimulator: an emerging therapeutic device

Injectable neurostimulators are currently applied in clinical trials to minimize the side effects such as discomfort, risk of infection, and post-surgery trauma, which can be pronounced with conventional, bulky implantable neurostimulators. Owing to its smaller size, wireless-updatable software, and wireless power supply, the injectable neurostimulator is presumably less invasive, 'smarter', and has a longer lifetime. We discuss the concept and development of the injectable neurostimulator, persistent implementation challenges, and obstacles to be overcome in its evolution. We survey the use of new materials, technologies, and design methods for injectable electrodes, batteries, antennas, and packaging to enhance reliability and other features. These advances in the field are accompanied by progress in electrophysiology, neuroscience, neurology, clinical trials, and treatments.

Injectable 3-D fabrication of medical electronics at the target biological tissues

Conventional transplantable biomedical devices generally request sophisticated surgery which however often causes big trauma and serious pain to the patients. Here, we show an alternative way of directly making three-dimensional (3-D) medical electronics inside the biological body through sequential injections of biocompatible packaging material and liquid metal ink. As the most typical electronics, a variety of medical electrodes with different embedded structures were demonstrated to be easily formed at the target tissues. Conceptual in vitro experiments provide strong evidences for the excellent performances of the injectable electrodes. Further in vivo animal experiments disclosed that the formed electrode could serve as both highly efficient ECG (Electrocardiograph) electrode and stimulator electrode. These findings clarified the unique features and practicability of the liquid metal based injectable 3-D fabrication of medical electronics. The present strategy opens the way for directly manufacturing electrophysiological sensors or therapeutic devices in situ via a truly minimally invasive approach.

Biomedical implementation of liquid metal ink as drawable ECG electrode and skin circuit

BACKGROUND

Conventional ways of making bio-electrodes are generally complicated, expensive and unconformable. Here we describe for the first time the method of applying Ga-based liquid metal ink as drawable electrocardiogram (ECG) electrodes. Such material owns unique merits in both liquid phase conformability and high electrical conductivity, which provides flexible ways for making electrical circuits on skin surface and a prospective substitution of conventional rigid printed circuit boards (PCBs).

METHODS

Fundamental measurements of impedance and polarization voltage of the liquid metal ink were carried out to evaluate its basic electrical properties. Conceptual experiments were performed to draw the alloy as bio-electrodes to acquire ECG signals from both rabbit and human via a wireless module developed on the mobile phone. Further, a typical electrical circuit was drawn in the palm with the ink to demonstrate its potential of implementing more sophisticated skin circuits.

RESULTS

With an oxide concentration of 0.34%, the resistivity of the liquid metal ink was measured as 44.1 µΩ·cm with quite low reactance in the form of straight line. Its peak polarization voltage with the physiological saline was detected as -0.73 V. The quality of ECG wave detected from the liquid metal electrodes was found as good as that of conventional electrodes, from both rabbit and human experiments. In addition, the circuit drawn with the liquid metal ink in the palm also runs efficiently. When the loop was switched on, all the light emitting diodes (LEDs) were lit and emitted colorful lights.

CONCLUSIONS

The liquid metal ink promises unique printable electrical properties as both bio-electrodes and electrical wires. The implemented ECG measurement on biological surface and the successfully run skin circuit demonstrated the conformability and attachment of the liquid metal. The present method is expected to innovate future physiological measurement and biological circuit manufacturing technique in a large extent.

Clinical Assessment of Postoperative Sensitivity in Posterior Composite Restorations

Posterior teeth restored with resin composite have been known to exhibit postoperative sensitivity. The type, size and design of the cavity, material properties and handling technique may influence the incidence of this sensitivity.

Do adverse effects of dental materials exist? What are the consequences, and how can they be diagnosed and treated?

OBJECTIVES

All dental biomaterials release substances into the oral environment to a varying degree. Various preclinical biocompatibility test systems have been introduced, aiming at an evaluation of the potential risks of dental materials. Potential pathogenic effects of released substances from dental materials have been demonstrated. For the biocompatibility of a biomaterial, it is not only important that minimal diffusable substances are released when it is in body contact--the material must also fulfill the function for which it has been designed. This is also very much dependent on the material properties and its handling properties. The aim of this review was to generate an overview of the present status concerning adverse reactions among patients and personnel.

MATERIALS AND METHODS

A systematic review was performed using a defined search strategy in order to evaluate all MEDLINE-literature published between 1996 and 2006.

RESULTS

The compilation of the literature available has revealed that the majority of studies have been carried out on patients compared with personnel. Adverse reactions towards dental materials do occur, but the prevalence and incidence are difficult to obtain. The results were essentially based on cohort studies. Clinical trials, especially randomized-controlled trials, are in the minority of all studies investigated, with the exception of composite and bonding studies, where clinical trials, but not randomized-controlled trials, represent the majority of studies. Patients and personnel were treated separately in the manuscript. Amalgam studies show the lowest degree of verified material-related diagnosis. Even if objective symptoms related to adverse reactions with polymer resin-based materials have been reported, postoperative sensitivity dominates reports concerning composites/bondings. Verified occupational effects among dental personnel show a low frequency of allergy/toxic reactions. Irritative hand eczema seemed to be more common than in the general population.

CONCLUSIONS

Patient- and personnel-related studies are of variable quality and can be improved. There is a need for a better description of the content of materials. A registry for adverse effects of dental materials would be useful to detect the occurrence of low-incidence events.

Dimensional change of a calcium aluminate cement for posterior restorations in aqueous and dry media

OBJECTIVES

A calcium aluminate cement has recently been developed, with claims of being an alternative to dental amalgam and resin composites in posterior cavities. However, its' mechanical properties are not well evaluated and the aim of the study was therefore, to evaluate its' dimensional stability over time.

METHODS

The dimensional changes of the cement, Doxadent, and two composite resins, Esthet-X and InTen-S, were tested during 360 d. The specimens were stored at 37+/-1 degrees C either in 100% air humidity (dry) or immersed in distilled water (wet), except for the first 24h when all specimens were stored at 100% air humidity and 37+/-1 degrees C.

RESULTS

During the first 24h, Doxadent decreased in volume with 0.04%, while InTen-S and Esthet-X decreased with 1.60 and 1.75%, respectively. From d 1-360, the dry Doxadent specimens increased in volume with 2.0% and in weight with 5.5%, while the corresponding increase for the wet specimens were 4.1 and 6.3%, respectively. The volume of both composites increased 0.8% or less in dry and wet conditions, while the increase in weight for InTen-S was 1.2% for the wet specimens and 0.6% for the dry. The corresponding figures for Esthet-X were 0.7 and 0.2%.

SIGNIFICANCE

Doxadent was less dimensionally stable than the composites tested. Doxadent increased 2 times more in volume immersed in water than in 100% air humidity, while the increase in weight was almost similar. The clinical implications of the results found in the present study are uncertain. A material that continues to absorb water during prolonged periods and continues to react is questionable for clinical use.

A 3-year longitudinal, controlled clinical study of a gallium-based restorative material

AIM

The aim of this three-year longitudinal controlled study was to compare the clinical performance of Galloy versus a high copper, mercury based Dispersalloy filling material.

METHODS

Moderate to large class I and class II cavities or replacement restorations were selected and 25 Galloy restorations and 25 Dispersalloy controls were placed in 14 adult patients by a single operator. Restorations were photographed and a silicone impression recorded at baseline, 6 months, 1 year, 2 years and 3 years.

RESULTS

At 3 years all 22 Dispersalloy restorations but only 4 Galloy restorations were still in situ. Three Dispersalloy restorations were lost to follow-up. Tooth fracture was observed in 15 (60%) of the Galloy restorations by the end of the 3 years, compared to one (4%) Dispersalloy restoration, which failed due to tooth fracture. A further six Galloy restorations had to be removed due to complaints of persistent pain. Four teeth restored with Galloy required endodontic treatment but none of the Dispersalloy restored teeth required endodontics. Of the four Galloy restorations remaining in situ, three were relatively small restorations and the fourth a moderate sized restoration required a marginal repair.

CONCLUSION

The clinical performance of Galloy restorations was so grossly inferior to the Dispersalloy controls that Galloy cannot be recommended for clinical use in moderate to large or multi-surface cavities.