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

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.

Inclusion criteria

Patients over 18 years of age who had received an Implant Supported Single Crown in the anterior maxilla (canine to canine) were eligible for inclusion.