Effect of vertical reference point deviations on crown inclination

Abstract

Purpose

The influence of vertical deviations of the reference point from the facial axis (FA) point on crown inclination (CI) has not been fully clarified. Therefore, this study aimed to identify the tooth type with the largest adverse effect on CI.

Materials and methods

Forty dental casts of non-orthodontic normal occlusion were analysed with a laser scanning system. The clinical crown height (CCH) for each tooth was measured and divided into tenths. From 30% to 70% level of CCH were used to identify the reference points for CI. Cl at the FA point (CI₅₀) and that measured at occlusally and gingivally deviated positions (CI₄₀ and CI₆₀, respectively) were measured using 10% of the CCH. CI₄₀, CI₅₀, and CI₆₀ were compared by one-way ANOVA with post-hoc Tukey’s test. Changes from CI₅₀ to CI₄₀ (CI_50–40) and from CI₆₀ to CI₅₀ (CI_60–50) were calculated and compared among teeth using two-way ANOVA with post-hoc Bonferroni correction.

Results

Significant differences were found among CI₄₀, CI₅₀, and CI₆₀ for all teeth (P < 0.01 for all). The largest changes in CI at vertically deviated reference points were found at the second molar (7.22 ± 3.58°) for the maxillary arch and at the second premolar (5.25 ± 2.77°) for the mandibular arch.

Conclusion

Deviations within 10% of the CCH of the vertical reference point were found to have a significantly greater adverse effect on Cl for the maxillary second molar and mandibular second premolar than other teeth.

Keywords:

• Crown inclination
• Clinical crown height
• FA point
• Bracket position
• Torque

Acknowledgement

The authors would like to thank Mr. Mutsuji Muramoto of UNISN, Osaka, Japan, for providing technical support, maintenance, and advice regarding the VMS Dental Plaster Model Shape Scanning System used in this study.