[Analysis of situations prone to insufficient spaces in tooth surface preparation with the fixed-depth groove method]

Digitally collect data on the preparation space of the molar occlusal surface for full crown restoration and analyze the minimum preparation spaces and areas prone to insufficient preparation.

A total of 846 molars (excluding third molars) designated for repair with zirconium dioxide crowns were selected. All molars were prepared by using the fixed-depth groove method under visual guidance. A digital impression was collected, and the occlusal surface of the preparation was divided into regions: mesiobuccal area, mesiolingual area, distobuccal area, distolingual area, mesial marginal ridge, and distal marginal ridge. Image measurement software (3Shape Unite) was employed to record the smallest preparation space on the molar occlusal surface, and a space of <1 mm was defined as insufficient preparation. The chi-square test was utilized for the statistical analysis of data.

Significant differences were observed in the areas with the smallest preparation space on the occlusal surface of molars across different quadrants (P<0.05). Notably, the area with the smallest preparation space on the occlusal surface of the maxillary first molar was most frequently found in the mesiobuccal area, whereas the smallest preparation spaces on other molars were predominantly located in the distolingual area. The insufficient preparation of the occlusal surface occurred in 41.0% (347 cases) of teeth. The distribution of prone areas corresponded with the distribution of the smallest spatial areas.

Although the fixed-depth groove method is employed, the preparation space on the molar surface unavoidably remains uneven under visual guidance. The identification of the areas prone to minimum preparation spaces can serve as a valuable guide for clinicians to prevent insufficient preparation.