Gaj finished his undergraduate dental training in 2015 from Bart's and the Royal London Hospital. Following this he spent a year working as a NHS foundation dentist in the competitive South East London deanery.

Whilst working in general practice, Gaj spent the next two years doing a postgraduate diploma in clinical implant dentistry from Newcastle University, which he completed with merit. Having found a passion for periodontology and implantology, Gaj decided to enhance and formalise his skills by embarking upon specialist training. He was accepted onto the specialist training programme in periodontology at the prestigious Eastman Dental Institute, University College London Hospital, where he completed a master’s in Clinical Dentistry.

Following completion of his specialist training, Gaj gained Membership in Periodontics from the Royal College of Surgeons of England. Additionally, he is accredited by the European Federation of Periodontology and was awarded their Certificate of Completion of Specialist training in Periodontology and Implantology.

He is proficient in all aspects of periodontics and implant dentistry, and is accepting referrals for treatment of gum disease, coverage of gum recession, treatment of gummy smiles and rehabilitation of missing teeth with dental implants.

In May 2024 Gaj returned to UCLH as a specialty dentist and clinical lecturer. In addition to being a capable clinician, Gaj has also engaged in research. His research was nominated for the UCL Dean's Research Prize and he has also presented globally.

Outside of dentistry, Gaj is an avid football fan and is happy to talk about all things Arsenal.