Amy Isabella Johnston, one of the few women to become registered dentists in New Zealand in the nineteenth century, was born at Greymouth, New Zealand, on 5 April 1872. She was the daughter of Marion Jennings and her husband, Robert James Johnston, a surveyor and later a civil engineer.
Wilson travelled south to Invercargill to set up a new practice soon after Amy Johnston qualified, and she travelled with him and worked as his assistant. The couple appear to have become engaged, but an estrangement occurred, and in 1898 Johnston took the unusual step of buying out Wilson's Blenheim practice for £300, borrowing £250 to do so. It was rare for a woman to run her own practice. Of the four other women dentists registered in 1896, Margaret Caro of Napier and Josephine Duflot of Dunedin worked with their husbands, while Grace Armstrong of Dunedin and Jessie Cox of Auckland were the daughters of dentists and worked in partnership with their fathers and brothers.
In April 1900 Amy Johnston returned to Invercargill in ill health. Her creditors, apparently fearing that she had abandoned the business, forced her to declare voluntary bankruptcy. When she realised her assets, however, she was able to pay her debts easily. She continued in practice until 1908, returning, possibly about 1904, to Invercargill, where she again worked with J. F. Wilson. By 1908 there were 13 registered women dentists, still only about two per cent of the total of 629. All of these women were trained under the apprenticeship system. A greater number of women than this practised dentistry, but Amy Johnston belonged to the minority of registered women dentists who were recognised by the newly formed New Zealand Dental Association.
Johnston was an inaugural member of the Southland Dental Association in 1905, and in 1906 was a delegate to the second conference of the New Zealand Dental Association in Dunedin. She, along with a handful of others, was making an inroad into a male-dominated craft that was rapidly transforming itself into a profession. She also confronted a special practical problem for women in dentistry: the physical strength required to pull teeth. Large-scale extraction was common practice and the main anaesthetic in use, nitrous oxide, could be used for only three minutes before making the patient ill. Yet the elegantly dressed young woman whose portrait appears in the Cyclopedia of New Zealand overcame such difficulties, as well as the lack of confidence revealed by her creditors, to successfully run a practice.
Amy Johnston died of a kidney tumour at Invercargill on 17 September 1908, aged 36. She had set an example that would be only occasionally followed until many years later. The introduction of the School Dental Service in 1921 diverted women away from mainstream dentistry until the late 1970s.