example, plaque build-up and gingival inflammation were reduced by 11% and 6% respectively after one to three months of use. After three months of use, the reduction observed was even greater – 21% reduction in plaque and 11% reduction in gingival inflammation. Although the scale of these differences in a clinical setting remains questionable, other reviews have reached similar conclusions. Another large review of studies also concluded that power toothbrushes were more effective in removing plaque than manual brushes for children. For patients with limited manual dexterity or where difficulty exists in reaching rear teeth, electric toothbrushes may be especially beneficial. With regards to the effectiveness of different electric toothbrushes, the oscillation rotation models have been found to remove more plaque than manual toothbrushes. More specific studies have also been conducted demonstrating oscillating rotating toothbrush effectiveness to be superior to manual toothbrushes for patients undergoing orthodontic treatment. Notably, only the oscillating rotating power toothbrush was able to consistently provide statistically significant benefit over manual toothbrushes in the 2014 Cochrane Review. This suggests that oscillating rotating power toothbrushes may be more effective than other electric toothbrushes. More recent evidence also supports this as new studies suggest that oscillating rotating toothbrushes are more effective than high frequency sonic power toothbrushes. Overall, oscillating rotating toothbrushes are effective in reducing gingival inflammation and plaque. Other factors that influence effectiveness amongst electric toothbrushes involve factors such as the amount of time spent brushing and the condition of the brush head. Manufacturers recommend that heads be changed every three months or as soon as the brush head has visibly deteriorated. Power source and charging Modern electric toothbrushes run on low voltage, 12 V or less. A few units use a step-down transformer to power the brush, but most use a battery, usually but not always rechargeable and non-replaceable, fitted inside the handle, which is hermetically sealed to prevent water damage. While early NiCd battery toothbrushes used metal tabs to connect with the charging base, some toothbrushes use inductive charging. Environmental concerns According to Friends of the Earth, "Disposable electric toothbrushes are one example of a terrible product ... it's virtually impossible to separate out the tech from the batteries and plastic casing which means valuable and often toxic materials are dumped in landfill or burnt in incinerators." A study published in British Dental Journal found climate change potential of the electric toothbrush was 11 times greater