3D printing vs milling: which dental filling lasts longer?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: Participant-Level Criteria * Adults aged 18-84 years * No active periodontal disease (probing depth ≤ 3 mm, no clinical attachment loss) * No parafunctional habits such as bruxism, clenching, or foreign object chewing * Willingness to attend regular follow-up visits during the study period * Adequate oral hygiene status * No history of systemic disease or medically stable condition if present * No history of similar restorative procedures involving the target teeth Tooth-Level Criteria * Vital posterior teeth (premolars or molars) confirmed by thermal or electric pulp testing; teeth requiring endodontic treatment or with necrosis will be excluded * Permanent posterior teeth located in functional occlusion (premolar or molar region) * Teeth with moderate structural loss suitable for onlay restorations, including mesio-occlusal (MO), disto-occlusal (DO), or mesio-occluso-distal (MOD) cavities with partial crown loss but sufficient remaining tooth structure not requiring full coverage * Periodontally healthy teeth with no mobility, no clinical attachment loss, and probing depth ≤ 3 mm * Teeth that can be matched in contralateral quadrants to allow split-mouth design (structurally and clinically comparable teeth) * Teeth free from cracks, fractures, or internal resorption; supporting tissues without structural defects that may compromise restoration success * Teeth with clearly defined preparation margins located in enamel or sound dentin; subgingival margins extending deep into the sulcus will not be included * Teeth without previous extensive prosthetic restorations (crowns, inlays/onlays, or implant-supported restorations) * Opposing natural teeth in stable occlusal contact with the restored tooth Exclusion Criteria: * Teeth with pulp necrosis or a history of endodontic treatment (previous root canal therapy or non-vital teeth) * Teeth with excessive tissue loss requiring full crown coverage and unsuitable for onlay restoration * Teeth presenting with cracks, fractures, internal or external resorption, or structural defects compromising prognosis * Advanced periodontal disease, including clinical attachment loss, furcation involvement, mobility, or probing depth \> 3 mm * Teeth with subgingival cavity margins extending deep into the gingival sulcus, increasing periodontal risk * Teeth with a history of fixed prosthetic restorations (previous crowns, inlays/onlays, or bridge restorations) * Teeth lacking proximal contacts due to adjacent tooth absence, leading to compromised contact stability and occlusal load distribution * Teeth in regions with orthodontic appliances or fixed retainers that may interfere with restorative procedures or evaluation * Opposing teeth absent or lacking stable occlusal contact with the restoration site * Patients with systemic diseases contraindicate elective dental treatment (e.g., uncontrolled diabetes, immunocompromised status) * Pregnant or breastfeeding women * Patients unable or unwilling to attend scheduled follow-up visits \[baseline (1 week), 6 months, 12 months, and 18 months\]