Evaluation of Occlusal Adjustment Material Removal on Monolithic Zirconia Blocks: An In Vitro Study

Clinical occlusal adjustment requires precision within tens of micrometers; however, current literature lacks objective data regarding per-stroke material removal during chairside adjustment of monolithic zirconia. As a result, clinical decision-making largely depends on subjective judgment.

Objective

The objective of this study is to quantify material removal per single reciprocating grinding stroke on monolithic zirconia blocks using a silicon carbide grinding stone and to compare performance among operators with different levels of clinical experience.

Methods

Monolithic zirconia specimens (VITA YZ ST; dimensions: 8 × 2 × 15 mm) will be milled, sintered, and embedded into standardized holders. Operators will include 40 fourth-year dental students, 40 sixth-year dental interns, and 40 experienced clinicians. Each participant will perform 100 grinding strokes along an 8-mm linear path at a frequency of 100 strokes per minute, guided by a metronome.

Grinding will be performed using a silicon carbide stone (Dura-Green Stone HP 0031/PC2, SHOFU, Japan) operated at 20,000 rpm. Pre- and post-grinding scans will be obtained using a 3Shape F8 scanner. Scan datasets will be superimposed using feature-based alignment to calculate volumetric loss and thickness reduction, expressed as mm³ per stroke and µm per stroke, respectively.

Statistical Analysis

Mixed-effects models will be applied to evaluate group-by-stroke interactions. Reference intervals for material removal will be established, and results will be translated into a clinically applicable occlusal adjustment guide.

Expected Results

The study is expected to define the magnitude and variability of zirconia material removal per grinding stroke, identify differences in performance between operator experience levels, and highlight areas requiring targeted educational training.

Conclusion

This in vitro investigation will provide the first stroke-level quantitative evidence for monolithic zirconia occlusal adjustment. The findings are expected to enhance the accuracy of clinical decision-making, improve training assessment, and support evidence-based guidelines for zirconia crown adjustment.

Inclusion criteria

Group A: Forty fourth-year dental students who have completed preclinical courses in operative dentistry, complete denture prosthodontics, and fixed prosthodontics (Part I). They have little to no experience in adjusting zirconia.

Group B: Forty sixth-year dental interns. Each participant will be tested twice-once before and once near the end of their clinical training. A questionnaire will also record their prosthodontic clinical experience within the past year.

Group C: Forty licensed clinicians with 0-5 years of post-graduation experience (with practical experience in zirconia adjustment). A questionnaire will also document their clinical experience in prosthodontics.

Exclusion criteria

• Acute upper-limb/hand injuries or postoperative recovery within the past 3 months that may affect grip strength or fine motor control.
• Neuromuscular disorders or tremor/postural control impairments (e.g., essential tremor, peripheral neuropathy, moderate to severe carpal tunnel syndrome) that prevent stable operation.
• Uncorrected or inadequately corrected vision that does not meet the requirements for close-range tasks (e.g., inability to clearly see fine markings at a distance of 30-40 cm even with correction).
• Inability to follow the metronome rhythm (100 beats per minute).