Development of angle correction apparatus for dental handpiece drill

Abstract

The preparation of uniform angle of wall is essential in fixed prosthesis. It has been known that the ideal convergence angle for prosthesis is ranged from 5°to 12°. However the average convergence angle formed in clinical field was ranged from 14°~ 20°. Increase in convergence angle is the major cause of reduced retention and may lead to the adhesive failure, the second most frequently occurring problem in fixed prosthesis. In this study, we developed a de novo detachable angle-correction apparatus for dental handpiece drill which could help preparation of tooth successfully. We would like to introduce its efficiency on full veneer tooth preparation in single crowns and 3-unit bridges. To measure the angulation of dental handpiece, we utilized gyro sensor, acceleration sensor, and Kalman filter algorithm. Gyro sensor can measure angular velocities to calculate slope of an object by integrating them. Acceleration sensor can also calculate slope of an object by measuring acceleration relative to gravity. However, accuracy of acceleration sensor is vulnerable to translational movement and shows inconsistent values. In case of gyro sensor zero point shifting occurs as the time goes by. To compensate those problems Kalman filter algorhythm is used in this study. The device developed in this study is directly attached to handpiece body thus a specific matrix equation is used to convert the angle of handpiece body to handpiece drill. Various handpieces can be used in this system by simply put the cervical angle of them. Converting the angulation of handpiece body to its drill part could be gained by a specific matrix formulation set on two reference points (2°, 6°). Flexible printed circuit board(FPCB)was used to minimize the size of device, improving clinical usefulness

the maximum diameter of this apparatus is 26 mm. Zero point error, convergence angle, tooth axis deviation analysis were performed to examine the efficiency of de novo detachable angle correction apparatus. We measured angulation values from various angles (0°, 30°, 60°, 80°, 90°) for x-axis in stationary state to evaluate a zero point error of the device. Sixteen volunteers were recruited to participate in this study. Fourteen of them were dental students (third and fourth grade, school of dentistry, Seoul National University) and two of them were residents in the department of dental prosthetics. They were divided randomly into two groups(group 1, 2). The only difference between these two groups was the point of time of using the device. For the convergence angle investigation, each practitioner performed tooth preparation on mandibular first molar resin tooth. 1.5 mm punch-out on occlusal plane was used as a reference. For the tooth axis deviation, commercially available ideal abutment model of mandibular first premolar tooth was used as a reference. All abutments were scanned by 3D scanner (D700, 3Shape Co.). The convergence angle and tooth axis deviation were analyzed by CAD program (Solidworks 2013, Dassault systems Co.). Statistical analysis was performed using paired t-test. Statistical significance was defined as P<0.05 (SPSS 21.0, IBM Co.). This device successfully maintained stable zero point (less than 1°deviation) at different angles (0°, 30°, 60°, 80°) for the first 30 minutes. However, after 30 minutes, zero point moved for 1.16°at 90°. In single tooth preparation, without this apparatus, the average bucco-lingual (BL) convergence angle was 20.26° (SD 7.85) and the average mesio-distal (MD) convergence angle was 17.88° (SD 7.64). However, using this apparatus improved the average BL convergence angle to 13.21°(SD 4.77) and the average MD convergence angle to 10.79°(SD 4.48). Furthermore, the angle correction device showed a statistically significant effect on reducing convergence angle of both directions regardless of the order of the direction (p = 0.005, 0.001 for bucco-lingual, mesio-distal, respectively). In addition, in 3-unit bridge tooth axis deviation, without this apparatus, the average BL tooth axis deviation was 3.86°(SD 2.99) and the average MD convergence angle was 2.12°(SD 1.32). However, using this apparatus improved the average BL convergence angle to 2.00°(SD 1.47) and the average MD convergence angle to 1.71°(SD 1.33). The angulation correction device had a statistically significant effect on reducing BL tooth axis deviation regardless of the order of using the device (p = 0.039). Although there was a reduction of tooth axis deviation on MD direction, it was not statistically significant. The angle correction device developed in this study is capable of guiding practitioner with high accuracy comparable to commercial navigation surgery. However by succinctly minimizing the operative mechanism, volume of the angle correction device is much smaller than any other commercial navigation surgery system. This device is expected to be widely utilized in the various fields of orofacial surgery. For instance, when a practitioner does abutment preparation, multiple implant placement, or orthodontic bracket attachment the angle correction device will provide accurate guidance to achieve maximal clinical output. In addition, this device can be used to educate and train dental students by helping them to learn the proper sense of angle and position. In the field of OMFS, the angle correction device will help surgeon to maintain a certain degree of precision