Digital VS Conventional Altered Cast Technique for Mandibular Bilateral Distal Extension RPDs

Partially dentate adults represent an increasing proportion of the population, driven by increased life expectancy and a demographic shift from total edentulism toward partial edentulism. Fabrication of removable partial dentures for distal extension edentulous ridges presents significant clinical complexity because the teeth and residual ridge possess fundamentally different degrees of displaceability. Optimum denture support re-quires recording teeth in anatomical form and the mucosa in functional form .

The altered cast impression technique , introduced by Applegate, remains one of the most widely accepted methods for achieving optimal tissue support and accurate denture base positioning relative to tooth abutments . removable partial dentures fabricated using altered cast impression technique demonstrate improved patient comfort and preservation of oral health . However, despite these advantages, debate persists regarding the clinical significance of altered cast impression technique over single-impression techniques .

Recent advances in computer-aided design and computer-aided manufacturing have transformed the removable partial dentures framework, opening new pathways in the fabrication of RPD through additive and subtractive manufacturing . Digital intraoral scanning offers advantages, including reduced dimensional error, improved efficiency, and real-time feedback on impression accuracy and extension [13-16]. However, intraoral scanning techniques are inherently mucostatic and image-based, rendering the recording of functional impression impossible, a limitation acknowledged as necessary for optimal support in distal extension removable partial dentures . Lab scanning of conventionally prepared altered casts pre-pared by traditional methods fails to eliminate inherited errors from cast separation and reassembly.

Recent studies have introduced hybrid digital workflows that combine functional registration of the edentulous ridge with mucostatic scanning of the remaining oral structures in an effort to reproduce conventional clinical procedures while improving efficiency and precision . Most investigations on digital technology in RPD have concentrated on methods for fabricating metal frameworks and evaluating their performance.

This study aims to compare outcomes of digitally created altered casts with conventional altered casts in mandibular bilateral distal-extension cases.

Inclusion criteria

• Patients presented with bilateral, well-formed mandibular distal extension residual ridges covered by keratinized mucosa, with a minimum thickness of 1.5-3 mm .
• Each participant had a sound first or second premolar serving as the terminal abutment, with a crown-to-root ratio of ≥ 1:2.
• Comprised fully or partially dentate maxillary arches, an Angle Class I molar relationship, and adequate interarch space (7-8 mm) to accommodate the prosthesis .

Exclusion criteria

• The presence of systemic conditions affecting bone metabolism or healing
• pathological conditions in the edentulous area (e.g., residual cysts, retained roots, or severe ridge re-sorption);
• parafunctional habits such as bruxism, clenching, or tongue thrusting
• pro-nounced anatomical undercuts in the lingual mandible or adjacent to abutment teeth that could impede denture fabrication or insertion.