Aluminum oxide is the fourth most abundant compound in the earth’s crust and is the principal component of bauxite, the ore from which the vast majority of the world’s aluminum metal is produced. Synonyms for aluminum oxide include alumina, aluminum trioxide, and corundum powder. Other forms of aluminum oxide are the familiar gems, ruby and sapphire. Aluminum oxide is the primary abrasive in a vast number of polishing and grinding applications. Various forms of aluminum oxide can be found in numerous surgical and dental applications as well. Aluminum oxide is a member of a group of materials called “technical ceramics”. These materials are known for their extreme hardness and chemical inertness.

Physical and Chemical Properties
The hardness of fused, crystalline aluminum oxide is second only to the diamond. It is a granular, white, odorless powder. The chemical formula for aluminum oxide is Al2O3. Aluminum oxide is the highest oxidation state of aluminum and is essentially chemically inert in the microdermabrasion environment. It is insoluble in water. Aluminum oxide is “environmentally friendly” and allowed in landfills. It should be noted that a hydrated, non-crystalline form of aluminum oxide that is the major component of some antacids is called aluminum hydroxide.

Biocompatibility
There is a significant amount of information regarding the safe use of aluminum oxide or alumina in medical applications.

Orthopedic implants made of alumina were introduced in the early 1970’s and have attained widespread use today. Indeed, alumina has been described as “bioceramic”1-3. In a recent review, Christal states “The low-grade tissue reaction induced by the implantation of alumina specimens convinced many investigators to say that this implant material is “bioinert” and to recommend it as a reference material when performing biocompatibility studies,”4. Christal’s review discusses the long-term biocompatibility experience of alumina ceramics used in human orthopedic implants.

Alumina has been the mainstay of dental restorations for decades, and new processing techniques have improved its performance5. The abrasive in dental paste used to polish teeth is a form of aluminum oxide crystals. These crystals are also used in the technique of air abrasion for removal of certain types of dental caries. This technique, first developed in the 1940’s, is experiencing a rebirth, in part due to the introduction of equipment that operates in a similar manner to microdermabrasion equipment8.

Safety Studies
A large number of studies have been performed to investigate the potential toxicity of aluminum oxide. The three studies described below are a few examples. The first two studies address the toxic effects of inhalation of respirable particles of various materials. In order for the test particles to reach the alveoli of the lungs, they must be very small, less than 5 microns. It should be noted that Diamond Crystals are all consistent at 120 microns in size, and most other dermabrasion systems have a variety of crystal sizes of between 53 and 180 microns, with not more than 3% less than 53 microns. If these particles become airborne and are inhaled, they are effectively trapped by the passageways of the nose and the mucosa-coated, ciliated epithelial cells of the upper bronchial tree of the lungs are effectively removed by the clearing of the nose, coughing to the exterior, or swallowing7.

Pigott, et al8 studied the effects of long-term inhalations of alumina fibers in a rat model. Animals were exposed over an 88-week period. Asbestos was selected as a “positive control” and clean air was the “negative control”. Pulmonary reactions to alumina were minimal compared to the expected progressive fibrosis induced by the asbestos. Both benign and malignant tumors were found in the asbestos-exposed animals and no tumors were seen in the animals exposed to alumina. This study shows minimal effects of aluminum oxide on pulmonary tissue and no carcinogenic activity.

Luchtel, and coworkers9 investigated the histopathological responses of rat lung to respirable fractions of various composite fiber-epoxy dusts. Aluminum oxide was chosen as the “negative control” and crystalline silica (quartz) was the “positive control”. Animals received a single intratracheal injection of the test and control material. A semi-quantitative scoring system involving several histopathological parameters showed a score of 1 for saline injection with no test material, a score of 9 for quartz, and a score of 2 for aluminum oxide. The various fiber-epoxy dusts had scores that ranged from 3 to 8. These results demonstrate the minimal histopathological effects of aluminum oxide inhaled into the lung.

Zalic, et al10 examined the reproductive and mutanogenic potential of an aluminum trioxide dental implant in mice. Tween 80 was used as the “negative control” and ethyl-methane-sulphonate was the “positive control”. After intraperitoneal injections, the animals were studied at one-week intervals from 1 to 8 weeks. Similar results were obtained for the aluminum trioxide dental implant compared to Tween 80. The authors state, ”We conclude that aluminum trioxide has a very low rate of embryonal mortality in mice and such a finding is in general agreement with the biocompatibility of aluminum trioxide as an implant material”.

A Word about Aluminum and Alzheimer’s Disease
Two questions are potentially germane to this discussion:
1) is exposure to aluminum a risk factor for the development of Alzheimer’s disease?, and 2) does microdermabrasion expose patients and operators to increased levels of aluminum?

Despite intense research, the pathogenesis of Alzheimer’s disease remains unresolved; however, aluminum does not appear to be involved. The link between aluminum and Alzheimer’s disease was proposed many years ago based on now questionable epidemiological studies and animal studies involving certain aluminum compounds. Recent studies suggest that abnormalities in more fundamental processes at the cellular level, such as oxidative imbalance and genetic factors, are likely to be involved in the primary pathogenesis of Alzheimer’s disease, as opposed to aluminum as a major contributor to the disease. The “Aluminum Hypothesis” originated in 1965 when it was found that injections of aluminum salts into the brains or cerebrospinal fluid of rabbits induced a progressive encephalopathy with histological changes that appeared similar to the lesions associated with Alzheimer’s disease. In ensuing years, with the development of more sophisticated electron microscopy and analytical methods for measuring aluminum in tissue, it became clear that the characteristics of the lesions present in experimentally-induced aluminum encephalopathy were not the same as the lesions present in Alzheimer’s disease. Other recent studies have suggested that the accumulation of aluminum in certain neurons of Alzheimer’s patients may simply be a marker for fundamental alterations in metal metabolism associated with iron accumulation 11,12.

Potential aluminum exposure to patients and operators from microdermabrasion procedures would require that the aluminum in the crystals not only be converted into a biologically active form, but also, be introduced into the bloodstream or tissues of the body. As discussed earlier, the chemical form of aluminum microdermabrasion crystals is aluminum oxide, a compound that is chemically inert. Chemical inertness translates to the fact that the aluminum is very tightly bound to oxygen and is not soluble in water or plasma. Therefore, aluminum in this chemical form cannot ionize or become complexed with other chemical species, and thus, cannot become biologically active.

References

1. Boutin P; Christel P; Dorlot JM; Meunier A; de Roquancourt A; Blanquaert D; Herman S; Sedel; Witvoet J. The use of dense alumina-alumina ceramic combination in total hip replacement. J Biomed Mater Res 1988 Dec: 22(12):1203-32
2. Lemons Jel Biocermanics. Is there a difference?. Clin Orthop 1990 Dec; (261): 153-8
3. Giannini S; Moroni A; Pompill M; Ceccarelli F; Cantagalli S; Pexxuto V; Trinchase L; Zaffe D; Venturini A; Pigato M. Bioceramics in orthapaedic surgery: state of the art and preliminary results. Ital J Orthop Traumatol 1992; 18(4): 431-41
4. Christel PS. Biocompatability of surgical-grade dense polycrystalline alumina. Clin Orthop 1992 Sep; (282): 10-18
5. Deany IL. Recent advances in ceramics for dentistry. Crit Rev Oral Biol Med 1996; 7(2): 134-43
6. Berry EA; Eakle WS; Summit JB. Air abrasion: an old technology reborn. Compend Contin Ed Dentistry 1999 Aug; 20(8): 751-62
7. Guyton AC. Textbook of Medical Physiology. 8th ed, 1991 WB Saunders Co., Philadelphia p410-12
8. Piggot GH; Gaskell BA; Ishmael J. Effects of long term inhalation of alumina fibres in rats. Br J Ex Pathol 1981 Jun;62(3): 323-31
9. Luchtel DL; Martin TR; Boatman ES. Response of the rat lung to respirable fractions of composite fiber-epoxy dusts. Environ Res 1989 Feb; 48(1):57-69
10. Kalic O; Dimitrijevic B; Vasilijevska M; Dujic A; Jekic PC. A dental implant: aluminum trioxide exhibited no effect on mouse reproductive and mutagenic potential. L Clin Periodontol 1998 Nov;25(11 Pt 1): 892-6
11. Munoz DG. Is exposure to aluminum a risk factor for the development of Alzheimer’s disease?-No. Arch Neurol 1998 May; 55:737-9
12. Smith MA; Perry G. What are the facts and artifacts of the pathogenesis and etiology of Alzheimer’s disease? J Chem Neuroanatomy 1998 Dec 16(1): 35-41