## 1 Introduction  
Dental agenesis (DA), i.e., the failure to develop permanent teeth, represents one of the most prevalent developmental anomalies in humans [1, 2]. The absence of permanent teeth often requires complex and interdisciplinary treatment strategies, including the extraction of deciduous teeth or their management as part of restorative approaches [3].  
The incidence and presentation of DA have been reported to vary geographically and depending on patient and anatomic factors. Excluding or including third molars, the incidence of DA has been reported to vary between 2.6 and 11.3% and 9 to 30%, respectively, with females displaying a 1.37 times higher incidence of DA compared to males [4, 5, 6]. The second mandibular premolars, followed by the maxillary lateral incisors, represent the most frequent anatomic sites for DA. Except for the latter location, the condition manifests mainly unilaterally [6].  
While the aetiology of DA remains unclear, both congenital genetic and acquired factors may cause the failure to develop permanent teeth [2]. Inherited genetic factors may, e.g., be associated with systemically broader genetic syndromes, such as Down syndrome or ectodermal dysplasia. Acquired deficiencies leading to DA may, on the other hand, be related to the irradiation of tooth germs, endocrine and metabolic pathologies, trauma, osteomyelitisitis, and unintentional tooth bud removal during primary tooth extraction [2, 6].  
General guidelines define three main treatment options for DA: extraction and space closure, extraction and prosthetic replacement, and retention [3].  
The retention of deciduous teeth may represent an acceptable strategy in young DA patients. However, long-term survival data for this treatment approach remain limited to specific anatomic locations, e.g., second premolars, and relatively young patient populations [2; 7; 8; 9]. Esthetic and functional considerations comprising the evaluation of infra occlusion, root resorption, caries, and periodontal status need to be considered for the prognosis and acceptability of deciduous tooth retention [7; 8; 9; 10].  
Extraction followed by space closure or implant placement may be considered in situations of poor primary tooth prognosis or high esthetic demand [11]. While surgically and restoratively potentially more complex than space closure, implant-restorative approaches have emerged as promising treatment options with high success rates and esthetic potential [12; 13; 14; 15].  
When replacing existing teeth, the timing of implant placement may impact treatment delivery and outcomes at multiple levels [16]. Despite their relatively higher complexity and risk for complications compared to delayed protocols, immediate procedures offer a range of advantages, such as a shorter treatment duration and fewer surgical sessions [16; 17; 18; 19; 20; 21; 22]. Provided case selection and adequate clinical procedures are followed, immediate procedures may also result in favourable bone and soft tissue contours and thus improved aesthetic outcomes at potentially comparable clinical success and survival rates [23; 24; 25; 26; 27]. Regarding DA, [PERSON] et al. have recently reported significant differences in the alveolar ridge dimensions between second premolar agenesis sites missing primary teeth for more than 3 months and sites with primary teeth in situ [28]. This finding suggests that placement timing may also impact the outcome of implant procedures in DA patients, an aspect that, to our knowledge, has not been adequately addressed in the contemporary literature.  
This in-line retrospective clinical pilot study aimed to directly compare relevant clinical and patient-reported outcomes in patients presenting multiple agenesis sites with and without primary teeth in situ that received routine implant treatment, adopting immediate and delayed implant placement procedures, respectively.