Effect of patient position on digitally recorded interocclusal distance in prepared teeth: A computer-aided design...

Accurate recording of interocclusal relationships is critical for the success of prosthodontic restorations fabricated using digital workflows. Although intraoral scanners have improved the precision of occlusal recording, clinical factors such as patient positioning during scanning may influence the digitally recorded interocclusal distance. Limited in-vivo evidence exists regarding the effect of dental chair position on interocclusal gap formation during CAD/CAM-based digital impression procedures. The aim of this study was to evaluate the influence of patient chair position on digitally recorded interocclusal distance during intraoral scanning for single full-coverage crown preparation.

The study design was an in-vivo observational study conducted in the Subharti Dental College and Hospital, Meerut, Uttar Pradesh.

Thirty adult participants ( n = 30) requiring a single full-coverage crown with intact opposing dentition were enrolled following ethical approval and informed consent. A priori power analysis (α = 0.05, power = 0.80, effect size = 0.5) determined the sample size. Standardized tooth preparation was performed by a single calibrated operator to eliminate inter-operator variability. Each participant underwent intraoral scanning in two standardized dental chair positions: upright and reclined (120° measured between the backrest and seat base). An intraoral scanner (Omniscan; Dentsply Sirona) was used following a standardized scanning protocol. A 10-minute interval was maintained between scans to minimize neuromuscular adaptation. Bite registration scans were exported as STL files and digitally aligned using a best-fit algorithm in three-dimensional analysis software. Interocclusal distance was measured digitally as the relative vertical separation between maxillary and mandibular arches at corresponding occlusal regions. The same examiner performed all measurements to ensure examiner reliability.

Data normality was assessed using the Shapiro-Wilk test. Interocclusal distance values between chair positions were compared using a paired t -test with the level of significance set at P ≤ 0.05.

The interocclusal distance demonstrated a normal distribution for both upright ( P = 0.392) and reclined ( P = 0.760) positions. Mean interocclusal distance in the upright position was 11.76 ± 1.97 mm, whereas the reclined position showed a mean value of 11.08 ± 1.89 mm. The mean difference between the two chair positions was 0.68 mm. The upright position consistently exhibited greater interocclusal distance values across all participants. Statistical analysis revealed a significant difference between the two chair positions ( t = 9.043; P < 0.001).

Patient chair position significantly influences digitally recorded interocclusal distance during intraoral scanning. Upright positioning resulted in greater interocclusal separation compared with the reclined position. Standardization of patient posture during digital interocclusal recording is recommended to reduce variability and improve the consistency and predictability of CAD/CAM-based prosthodontic outcomes.