To assess the technical quality and clinical outcomes of non-surgical endodontic treatment of immature permanent incisor teeth with three different bioceramic plug materials and highlight variables which may influence treatment and quality outcomes. This cross-sectional analysis forms part of a retrospective service evaluation of the technical quality and clinical outcome of orthograde root canal treatment carried out in the Paediatric Dentistry Department of Charles Clifford Dental Hospital (United Kingdom). Twenty-five cases were identified chronologically, using the electronic patient record system, for three bioceramic plug materials: Mineral Trioxide Aggregate (MTA), Biodentine, and TotalFill Putty. All radiographs were analysed using standard conditions. Intra- and inter-examiner agreement was calculated using Kappa and weighted Kappa tests. Data were collected using a data collection tool, entered into Microsoft Excel, and analysed using descriptive statistics, exploratory analysis with Chi-squared tests, and multivariable analyses (logistic regression). At 12-month review, the success rate for each apexification material was MTA (84%), Biodentine (88%), and TotalFill Putty (92%). MTA had the highest frequency of post-operative coronal discolouration, with Biodentine most associated with apical extrusion. A number of variables and trends that affect the clinical outcome were identified, including the presence of pre-operative resorption, the number of operators involved in treatment, the number of appointments to complete treatment, as well as how non-use of local anaesthetic during apical plug placement had no adverse effect on technical quality or clinical outcome. MTA, Biodentine, and TotalFill Putty are highly effective apexification materials which produce excellent clinical outcomes. As such, logistical and situational factors, such as continuity of care from operators with increased levels of experience, skill and ability, rather than material choice, may be more prognostic regarding the technical quality and clinical outcome of immature endodontic treatment. Further high-quality evidence is required.