Occlusal Adjustments Needed for Michigan Splints Made Using Different Digital Bite Records

Background Temporomandibular disorders represented a common clinical condition affecting mandibular function and were frequently associated with parafunctional activities such as bruxism or clenching. Clinical features included orofacial pain, joint sounds, restricted mandibular movement, headaches, dental wear, and occlusal instability. Occlusal splints were commonly prescribed to reduce occlusal loading, protect dental structures, and establish a more favourable mandibular position.

Conventional occlusal splint fabrication relied on physical impressions, mechanical articulation, and manual occlusal adjustment. These processes were time-consuming and technique-sensitive. Digital dentistry introduced alternative workflows incorporating intraoral scanning, virtual articulation, and computer-aided design and manufacturing, with the aim of improving accuracy, reproducibility, and efficiency.

Accurate digital recording of the maxillomandibular relationship remained a critical factor influencing occlusal outcomes. Digital bite registration techniques performed at intercuspal position or centric relation, with or without digital facebow transfer, were expected to affect occlusal accuracy and the extent of chairside adjustment required at delivery.

Virtual articulators were developed to simulate mandibular movements using digitally acquired data. These systems required accurate digital impressions, occlusal records, and appropriate orientation of the maxillary arch relative to craniofacial reference planes. Digital facebow systems enabled virtual transfer of maxillary position and were expected to improve mounting accuracy compared with average-value articulators alone.

Study objectives Primary Objectives

• To evaluate volumetric changes on the occlusal surfaces of Michigan splints following clinical adjustment.
• To compare pre-adjustment and post-adjustment occlusal surface volumes across different digital workflows.
• To assess whether an average-value virtual articulator produced occlusal splints at an increased occlusal vertical dimension without the need for clinical registration.

Secondary objectives

• To assess laboratory efficiency and quality control associated with digital workflows.
• To evaluate clinical time and effort required for occlusal adjustment.
• To assess participant comfort during digital recording procedures.

This was a single-centre clinical study involving 10 participants. Each participant received four Michigan occlusal splints, corresponding to four different digital design workflows based on mandibular recording position and the inclusion or exclusion of a digital facebow record. Each of the four digital designs generated for every participant was manufactured as a separate occlusal splint, resulting in four splints per participant.

Clinical and laboratory procedures Visit 1

• Informed consent was obtained.
• Standardised dental photography was performed.
• A digital facebow record was obtained using a digital facebow system equipped with a scannable bite fork (Axiopresia) as part of the registration process, where applicable. The scannable bite fork was positioned intraorally and digitally captured to record the spatial relationship of the maxillary arch relative to craniofacial reference planes.
• Digital impressions of the maxillary and mandibular arches were obtained using an intraoral scanner under standardised clinical conditions.
• Bite registration at centric relation/ retruded articulation position was obtained following neuromuscular deprogramming using a Lucia gauge and intraoral scanner.
• Bite registration at intercuspal position was recorded using the intraoral scanner.

Laboratory procedures

Using computer-aided design software, four distinct digital occlusal splint designs were produced for each participant based on different combinations of mandibular recording position and digital facebow transfer:

Retruded articulation position (centric relation) with digital facebow record Retruded articulation position (centric relation) without digital facebow record Intercuspal position with digital facebow record Intercuspal position without digital facebow record Each digital design was generated using the same virtual articulator parameters and identical splint design settings, differing only in the mandibular position record and the inclusion or exclusion of the digital facebow data. The resulting designs were then manufactured using three-dimensional printing.

Visit 2: Fitting and occlusal adjustment

• Clinical fitting of the occlusal splints was performed during the second visit.
• Occlusal adjustments were carried out to achieve balanced light occlusal contacts at the resting intercuspal position.
• Lateral movements were assessed to confirm canine guidance, and anterior guidance was evaluated during protrusive movements.
• Any occlusal interferences were identified and removed accordingly to achieve a stable and harmonious occlusal scheme.
• Following completion of occlusal adjustments, the splints were digitally scanned via lab scanner for post-adjustment analysis.

Outcome assessment Pre-adjustment and post-adjustment digital scans of each occlusal splint were imported into three-dimensional analysis software ( Geomagic software). Root mean square deviation values were calculated following best-fit alignment to quantify volumetric changes associated with occlusal adjustment. The 3D and 2D Comparisons at six sections were done ( middle of the cingulum of the right and left central incisor, middle of the cingulum of the right and left canines, messy-buccal cusp to disco-palatal cup of the right and left first molar). Occlusal deviation maps were standardised using consistent colour scales to allow comparison between workflows.