Risk Factors Associated With Infraposition of Implant Supported Single Crowns in the Anterior Maxilla

Overview

Losing a tooth in the front part of the upper jaw can affect both appearance and the ability to bite and chew. Treatment to replace missing teeth is therefore often required. Such treatment may be burdensome for the individual and can involve substantial costs for both the patient and society. A common treatment option is placement of a titanium screw (dental implant) in the jawbone. After a healing period, the implant is restored with a crown designed to resemble a natural tooth. Replacement of missing teeth with dental implants in the anterior maxilla can be particularly challenging. Over time, the crown of an implant may appear shorter than the adjacent natural teeth. This occurs because natural teeth may continue to change position throughout adulthood, whereas dental implants remain fixed within the bone. As a result, the implant-supported crown may appear to sink relative to neighboring teeth, a phenomenon referred to as infraposition. The prevalence of infraposition and the factors contributing to its development are not yet fully understood. The aim of this study is to determine the frequency and extent of infraposition and to identify potential contributing factors in individuals treated with a single implant-supported crown in the anterior maxilla. The study also aims to evaluate the aesthetic outcome after treatment from both the patient and the clinician perspective. The study hypothesis is that infraposition occurs in a clinically relevant proportion of patients and that certain factors, such as age at implant placement or individual dental characteristics, may increase the likelihood of its occurrence. It is further hypothesized that infraposition of the implant-supported crown may influence aesthetic appearance and that these changes may be perceived differently by patients and dental professionals. Through longitudinal follow-up and comparison of repeated digital scans, the study seeks to improve understanding of the occurrence of infraposition, its contributing factors, and its potential impact on the aesthetic outcome of implant-supported crowns over time.

This observational cohort study is based on long-term follow-up of patients treated with a single implant-supported crown in the anterior maxilla as part of routine clinical care. Participants are enrolled consecutively from the Departments of Oral Prosthodontics within the Public Dental Service in Region Västerbotten (Umeå) and Public Dental Service Stockholm AB. The study is based on repeated digital recordings of the dentition over time. At the time of crown delivery, a digital impression is obtained using an intraoral scanner to create three-dimensional digital models of the dental arches and their spatial relationship. Additional digital impressions are obtained during scheduled follow-up visits at 1, 3, and 5 years after delivery, in accordance with routine implant follow-up clinical practice. An additional follow-up visit using the same procedures is performed at 10 years. Digital models obtained at different time points are superimposed and compared using proprietary software associated with the intraoral scanner. This enables measurement of positional changes of the adjacent teeth realtive to the implant-supported crown. Changes over time are recorded and used to assess the occurrence and degree of infraposition. At each follow-up visit, participants undergo standard clinical and radiographic evaluation of the implant-supported crown, including assessment of peri-implant soft tissues, marginal bone levels, implant stability, occlusion, and oral hygiene conditions. Radiographic imaging follows standardized regional clinical guidelines and is identical to that used in routine implant follow-up. Data collected for analysis include demographic variables, sex, age at implant placement, medical history and medications, lower anterior face height, pre-prosthetic orthodontic treatment, cause of tooth loss, smile line, type of temporary restoration, implant type (bone-level or tissue-level), implant manufacturer, augmentation procedures, implant position, restoration type (screw-retained or cement-retained), use of a temporary implant-supported single crown, and occlusion or articulation on the implant-supported single crown. The aesthetic outcome of the implant-supported crown is assessed using both objective and subjective evaluation methods. Objective evaluation is based on standardized clinical and digital criteria derived from three-dimensional models and clinical examinations. Subjective evaluation includes patient-reported assessments of aesthetic satisfaction using a questionnaire. Follow-up time points are recorded for all participants. Data are collected using a predefined protocol to ensure standardized documentation across study sites. Source data are obtained from clinical dental records and digital scan files. All data are handled in accordance with national patient data legislation and the General Data Protection Regulation (GDPR). Statistical analyses are planned to explore correlations between infraposition and patient-related, anatomical, and treatment-related factors, as well as correlations between infraposition, marginal bone level changes, and aesthetic evaluations over time.