Assessment of Exact Working Length Determination Method by Comparison between Grossman Formula and Ingle's Method

Background: Determination of appropriate or exact working length measurement method during root canal treatment is a necessary factor for the long-term success of root canal treatment. The use of the radio-visiographical methods as an aid to measure root canal length has been most prevalent methods. Although, different methods have been recommended, reviewed and discussed, but Grossman formula and Ingle’s methods are mostly preferred methods. In addition, there are several controversies with these two methods which is more exact or better.

Methods: In -vitro study was conducted at Dept. of Conservative Dentistry and Endodontics, BSMMU. Total 20 human premolar teeth were selected based on inclusion and exclusion criteria. Purposive sampling technique was used to select the study samples. The Grossman formula was considered as Group-I and Ingle’s method was considered as Group-II. Extracted teeth samples were collected from the orthodontic patient who was indicated for tooth extraction. Acrylic base was made to support the tooth sample during the RVG image taking. Then the tooth sample was imaged by the radio-visiography to take diagnostic initial measurement of the radiological working length root canal. Then working length measurement was recorded by RVG with reamer insertion within root canal. Then the actual tooth length was measured with endo-scaler and architectural scaler. Data were calculated and collected with the help of a pretested semi-structured check list with Grossman formula and Ingle’s method individually. Level of coincidence was assigned as evaluation index according to predetermined evaluation criteria. The recorded data for coincidence scoring, radiological working length with Grossman formula, Ingle’s method and actual working length were analyzed statistically using descriptive analysis and T-test. Tables were used to present the results.

Results: The mean value of difference between actual tooth length and working length with Grossman Formula (.40 mm) greater than difference (.22 mm) between actual tooth length and working length with Ingle’s Method. The study results revealed that for 2 samples, the level of coincidence was not acceptable in case of Grossman formula. In contrast, in case of Ingle’s method, for 2 samples, the level of coincidence was exact. There was also statistically significant difference between two methods (p-value=.001). 

Conclusion: To conclude, though both the Grossman Formula and Ingles Method are applicable for working length measurement nearly as accurately as the actual root canal length, but among two methods, Ingles Method in determining the working length being more accurate to the actual root canal length compared to Grossman Formula.