- Open Access
Development of a dental handpiece angle correction device
© The Author(s) 2018
- Received: 7 June 2018
- Accepted: 19 November 2018
- Published: 26 November 2018
Preparation of a uniform angle of walls is essential for making an ideal convergence angle in fixed prosthodontics. We developed a de novo detachable angle-correction apparatus for dental handpiece drills that could help the ideal tooth preparation.
We utilized a gyro sensor to measure the angular velocities to calculate the slope of an object by integrating the values, acceleration sensor to calculate the slope of an object by measuring the acceleration relative to gravity, and Kalman filter algorithm. Converting the angulation of the handpiece body to its drill part could be performed by a specific matrix formulation set on two reference points (2° and 6°). A flexible printed circuit board was used to minimize the size of the device. For convergence angle investigation, 16 volunteers were divided randomly into two groups for performing tooth preparation on a mandibular first molar resin tooth. All abutments were scanned by a 3D scanner (D700®, 3Shape Co., Japan), the convergence angle and tooth axis deviation were analyzed by a CAD program (SolidWorks 2013®, Dassault Systems Co., USA) with statistical analysis by Wilcoxon signed-rank test (α = 0.05) using SPSS statistical software (Version 16.0, SPSS Inc.).
This device successfully maintained the stable zero point (less than 1° deviation) at different angles (0°, 30°, 60°, 80°) for the first 30 min. In single tooth preparation, without this apparatus, the average bucco-lingual convergence angle was 20.26° (SD 7.85), and the average mesio–distal (MD) convergence angle was 17.88° (SD 7.64). However, the use of 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). The angle correction device showed a statistically significant effect on reducing the convergence angle of both directions regardless of the order of the directions.
The angle correction device developed in this study is capable of guiding practitioners with high accuracy comparable to that of commercial navigation surgery. The volume of the angle correction device is much smaller than that of any other commercial navigation surgery system. This device is expected to be widely utilized in various fields of orofacial surgery.
- Angulation correction device
- Convergence angle
- Tooth axis deviation
- Gyro sensor
Today, the needs for precise dental procedures have increased. In tooth preparation and implant placement, which are the two main axes of modern dental procedures, there have been a myriad of developments to meet those needs. Accuracy not only improves the quality of the dental procedures, but also reduces the time required, allowing for minimally invasive techniques to reduce postoperative complications . The accuracy of angulation is especially emphasized for tooth preparation of full-crowns and placement of implant fixtures [2, 3]. During patient functioning, in order to keep the fixed prosthesis stable on the tooth, proper resistance and maintenance of the abutment form are necessary. The maintenance of cast prosthesis is determined by convergence angle of the abutment, contact area, inner surface roughness of the structure, etc. [4, 5]. Among them, convergence angle is considered a primary factor and has been the main focus of most studies . The definition of convergence angle is ‘the angle between opposing axial walls and has been shown to affect crown retention’. It has also been determined that the optimal convergence angle ranges from 5 to 12° [7, 8].
The accuracy of angulation in dental procedures is important for minimizing adverse effects, ensuring ideal aesthetic results, and maintaining proper oral health. Ideally, the implant should be placed parallel to other adjacent implants or remaining teeth. This results in proper application of vertical occlusal forces to the implant. In particular, when more than one dental implant has been placed, the angle between them affects the maintenance of the upper prosthesis. A study on the relationship between retention of the prosthesis and inter-implant angle in 24 overdenture-wearing patients reported that, as inter-implant angle was increased, retention of the implant overdenture using locator attachments significantly decreased . In addition, when using the angled abutment to compensate for angulation error, the stress on the implant and surrounding bone has been found to increase. However, the increased stress did not exceed physiological limits . The ability to create the correct angulation is an important dental technique. However, there must be a discrepancy between reality and theory when performing this technique with a dental handpiece. This discrepancy is well-described in the studies about convergence angles for abutments for casting crowns. Analysis of the convergence angle of 478 clinically formed abutments reported that the actual average convergence angle was 21°, with a large variance among the dentists . Other studies also supported that finding by reporting the average convergence angle ranging from 14 to 20°, which is considerably deviated from the ideal value [6, 12]. An increase of convergence angle results in a reduction of the average retention force regardless of the type of cement used . Implant placement procedures have already reached a level of computer guidance that implements preoperative planning, surgical guiding, and uses an optical tracking device [4, 14, 15]. In addition, there is a method using an electromagnetic tracker and a direct surveying apparatus such as a Parallel-A-Prep [16, 17].
In this paper, a de novo detachable dental angulation correction device is proposed to overcome the disadvantages of conventional guiding devices and to achieve the requirements listed above.
Principle of angulation measurement
We used the MPU-6050® module containing a gyro sensor and acceleration sensor (TDK InvenSense®, Mouser Electronics Co., USA) commercialized in the field of mobile devices and drones to measure the three-dimensional angulation of the dental drill. The gyro and acceleration sensors measure the angular velocity and relative acceleration of gravity, respectively. When integrating the angular velocity measured from the gyro sensor, the angular deviation can be obtained from the original state. When using the acceleration sensor, it is possible to measure the extent of the device tilted from the original state by measuring acceleration relative to gravitational acceleration. Both sensors have complementary pros and cons. Although the stabilized value of the gyro sensor is sensitive to a single rotation, its reliability decreases over time because of the zero point shift. On the contrary, the acceleration sensor exhibits no zero point drift with the lapse of time, but its accuracy is variable due to translational movement. To compensate for the errors caused by these technical limitations, several algorithms such as the Kalman filter have been applied . For the device developed in this study, gyro and acceleration sensors are simultaneously utilized to calculate the angle of the drill while applying the Kalman filter algorithm.
Computation and display process
The computational process of the device can be divided into three phases. The first phase involves setting the reference angulation. This process begins by contacting the tip of drill to the tooth surface. At the contact point, the practitioner presses the pedal with her/his free foot to retain the spatial angle of the sensor and use that angle as the reference. After noting the reference angle, the second phase involves translation of the three axial angles of the handpiece body to the dental drill. Almost every commercially available handpiece has a drill-containing head part that is not parallel to the hand-holding body part.
The clinician is able to maintain the original angulation when he/she tilts the drill according to the flashing LED indicators. For instance, when the drill is tilted toward the + x direction by 3°, the LED indicator of − x will blink. If the clinician adjusts the angulation by tilting the drill toward the − x direction, the LED indicator for − x will be turned off. The indicators for the x and y axes of the dental drill operate independently. The second reference point is 6°, which is set by the user. The LED indicator for each axis is constantly lit when the dental drill is moved out of the second reference angle (by 6°) for each reverse axis. For example, when the drill is tilted toward the + x direction by 10°, the LED indicator of − x will be turned on. If the clinician adjusts the angulation of the dental drill to the proper position, the indicator will be turned off or blink.
Use of a flexible electronic circuit board (fPCB)
Effectiveness and efficacy of the device
Zero point drift
To evaluate the zero point drift of the device, we measured the x angulation at various angles (0°, 30°, 60°, 80°, and 90°) when the device was in a stationary state. Data was collected for 30 min. According to in vitro studies, the minimum security distance was recommended at 1 mm [19–21]. The ‘30 min’ criterion was established to allow sufficient time for each dental practice. Therefore, in this study, we defined the stabilized zero point as ‘less than 1 mm deviation for 30 min’.
Reduction of the convergence angle during single crown preparation
Sixteen volunteers were recruited to participate in the study. Volunteers were composed of 14 dental students (3rd and 4th years in Seoul National University School of Dentistry) and two prosthetics residents. They were divided randomly into 2 groups (1 and 2). The only difference between these groups was the timing of device use. A dental simulator (Nissim type 1®, Nissan Co., Japan), Dentiform (PRO2002-UL-SP-FEM-28®, Nissan Co., Japan), and #36 tooth model (A5A-200®, Nissan Co., Japan) were used.
When the volunteers used the apparatus, they created a 1.5-mm-deep punch out (at the reference angulation), which was parallel to the preferred tooth axis at the center of the occlusal plane. According to the instruction of the apparatus, the volunteers performed tooth preparation within the range of 2 to 6° of deviation from the reference angulation. When the volunteers did not use the apparatus, they performed usual tooth preparation for a full veneer gold crown without marking the reference angulation.
All abutments were scanned by a 3D scanner (D700®, 3Shape Co., Japan). The convergence angles were analyzed by a CAD program (SolidWorks 2013®, Dassault Systems Co., USA). The midline of each axial wall was selected to measure the convergence angle. Data was statistically analyzed by Wilcoxon signed-rank test (α = 0.05) using SPSS statistical software (Version 16.0, SPSS Inc.).
Reduction of convergence angle during 3-unit bridge crown preparation
Sixteen volunteers were years in Seoul National University School of Dentistry) and two prosthetics residents. They were randomly divided into 2 groups (1 and 2). The only difference between these two groups was the timing of device use. A dental simulator (Nissim type 1®, Nissan Co., Japan), Dentiform (PRO2002-UL-SP-FEM-28®, Nissan Co., Japan), #36 tooth mode l (A5A-200®, Nissan Co., Japan), and #34 ideal abutment mode l (A21A-LL42®, Nissan Co., Japan) were used to mimic real clinical situations.
Novel angle correction device
Zero point drift
Zero point drift at various angles
The effect of correcting device on convergence angle
(A) Convergence angle in the bucco-lingual direction
(B) Convergence angle in the mesio–distal direction
Tooth axis deviation between the 3-unit bridge abutments
The effects of correcting device on tooth axis deviation
(A) Tooth axis deviation in the mesio–distal direction
(B) Tooth axis deviation in the mesio–distal direction
In this study, a cylinder-shaped hollow detachable angle correction device was developed and tested on tooth preparations for a full veneer and a 3 unit-bridge prosthesis. Recently, several attempts utilizing gyro and acceleration sensors on dental handpieces have been made [22, 23]. However, those projects were only conceptual and therefore not commercialized because of numerous technical and clinical hurdles. Another main purpose of this study is to minimize inevitable human errors in various types of tooth preparations with sensor-mounted devices. In this aspect, this study is expected to have potential in improvement of technical accuracy in various types of dental practice. The convergence angle of the abutment largely affects the retention of restorative materials. Convergence angle can be defined as “the angle between opposing axial walls” and has been shown to affect crown retention. In addition, it has been demonstrated that the increase of convergence angle reduces the retentive force regardless of the type of cement [7, 13].
The practitioner group using the device developed in this study exhibited significantly decreased convergence angles (MD p = 0.009, BL p = 0.023). For the same practitioner group, the conventional handpiece resulted in convergence angle values of MD 17.88° and BL 20.26°, close to the values from previous studies of 21° and 14–20° [6, 12]. Another advantage of using this device is improved consistency. The distribution of the data collected in each trial decreased from MD 7.64° and BL 7.85° to MD 4.48° and BL 4.77°, respectively. For the #36 single crown full veneer preparation, there was a significant decrease in both average convergence angle and distribution at bucco-lingual and mesio–distal sides. This suggests that the device actually improves not only the accuracy, but also the precision of the practitioner’s work, allowing more credible results.
In preparation for a 3-unit bridge prosthesis, the axis of #34 tooth was set as the standard for the preparation of #36 tooth. After the preparations, the angle between the axes of each abutment was measured. For the bucco-lingual side, the average angle between the two axes decreased from 3.86° (SD 2.99) to 2.12° (SD 1.32) with statistical significance (p = 0.021). In preparation for the 3-unit bridge prosthesis, the angle between the two axes decreased from 2.00° (SD 1.47) to 1.71° (SD 1.33) at the mesio–distal side, but this change was not statistically significant (p = 0.081). Two possible explanations are discussed here; first, it is easier for the practitioner to perform accurate surgical procedures on the mesio–distal side versus the bucco-lingual side. Based on this result, it is possible to deduce that surgical procedures on the mesio–distal side require less technical skill than those on bucco-lingual side, and this difference is due to the spatial arrangement of the teeth. Therefore, improvement of clinical efficacy by using this device is less dramatic on the mesio–distal side. Secondly, since the mesio–distal length of the mandibular molar is longer than its bucco-lingual length, the same 0.5–1 mm preparation of different sides of the tooth might have resulted in a smaller amount of axial reduction on the mesio–distal side. As a result of the smaller amount of axial reduction, the smaller difference in angles between the two axes becomes not statistically significant.
The angle data collected from this device can be integrated and displayed to improve the practitioner’s accuracy in his/her dental procedures. The clinical efficacy of this device was tested in a dental simulator for the consideration of various clinical aspects. However, the data collected from the test cannot perfectly reflect real clinical situations because the patient’s head and mandible are not fixed as they are in the dental simulator. Therefore, the next generation of this device should be attachable to the relatively fixed anatomical structure of the patient. In addition, considering that angle detection by gyro and acceleration sensors is influenced by external forces such as tremors, use of vibration-proof materials for low speed handpieces or implant drills is highly recommended.
We developed a de novo detachable angle-correction apparatus for the dental handpiece drill for minimized volume and improved convenience. This angle correction device is capable of guiding practitioners with high accuracy comparable to that of commercial navigation surgery. This device can be utilized in various fields of dentistry such as tooth preparation, implant placement, orthodontics, esthetics surgery, and education for novice dental students.
YN read and wrote the manuscript, MYE corrected data as co-first author, and SMK designed and wrote the entire article. All authors read and approved the final manuscript
This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (2017R1D1A1B03036054).
The authors declare that they have no competing interests.
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- Greenstein G, Cavallaro J, Romanos G, Tarnow D. Clinical recommendations for avoiding and managing surgical complications associated with implant dentistry: a review. J Periodontol. 2008;79:1317–29.View ArticleGoogle Scholar
- Ertas H, Capar ID, Arslan H, Akan E. Comparison of cyclic fatigue resistance of original and counterfeit rotary instruments. Biomed Eng Online. 2014;13:67.View ArticleGoogle Scholar
- Hegazy MA, Cho MH, Lee SY. A metal artifact reduction method for a dental CT based on adaptive local thresholding and prior image generation. Biomed Eng Online. 2016;15:119.View ArticleGoogle Scholar
- Neugebauer J, Stachulla G, Ritter L, Dreiseidler T, Mischkowski RA, Keeve E. Computer-aided manufacturing technologies for guided implant placement. Expert Rev Med Devices. 2010;7:113–29.View ArticleGoogle Scholar
- Bernal G, Okamura M, Munoz CA. The effects of abutment taper, length and cement type on resistance to dislodgement of cement-retained, implant-supported restorations. J Prosthodont. 2003;12:111–5.View ArticleGoogle Scholar
- Ayad MF, Maghrabi AA, Rosenstiel SF. Assessment of convergence angles of tooth preparations for complete crowns among dental students. J Dent. 2005;33:633–8.View ArticleGoogle Scholar
- Chan DC, Wilson AH Jr, Barbe P, Cronin RJ Jr, Chung C, Chung K. Effect of preparation convergence on retention and seating discrepancy of complete veneer crowns. J Oral Rehabil. 2005;32:58–64.View ArticleGoogle Scholar
- Zidan O, Ferguson GC. The retention of complete crowns prepared with three different tapers and luted with four different cements. J Prosthet Dent. 2003;89:565–71.View ArticleGoogle Scholar
- Jabbour Z, Fromentin O, Lassauzay C, Abi Nader S, Correa JA, Feine J. Effect of implant angulation on attachment retention in mandibular two-implant overdentures: a clinical study. Clin Implant Dent Relat Res. 2014;16:565–71.View ArticleGoogle Scholar
- Cavallaro J Jr, Greenstein G. Angled implant abutments: a practical application of available knowledge. J Am Dent Assoc. 2011;142:150–8.View ArticleGoogle Scholar
- Nordlander J, Weir D, Stoffer W, Ochi S. The taper of clinical preparations for fixed prosthodontics. J Prosthet Dent. 1988;60:148–51.View ArticleGoogle Scholar
- Smith CT, Gary JJ, Conkin JE, Franks HL. Effective taper criterion for the full veneer crown preparation in preclinical prosthodontics. J Prosthodont. 1999;8:196–200.View ArticleGoogle Scholar
- Yun JH, Kim JH, Lee KW. Comparison of the retention of the full veneer casted gold crowns with varying convergence angle, crown length and dental cements. J Kr Pros. 2013;51:99–106.Google Scholar
- Kramer FJ, Baethge C, Swennen G, Rosahl S. Navigated vs. conventional implant insertion for maxillary single tooth replacement. Clin Oral Implants Res. 2005;16:60–8.View ArticleGoogle Scholar
- Tack P, Victor J, Gemmel P, Annemans L. 3D-printing techniques in a medical setting: a systematic literature review. Biomed Eng Online. 2016;15:115.View ArticleGoogle Scholar
- Wang J, Suenaga H, Yang L, Liao H, Kobayashi E, Takato T. Real-time marker-free patient registration and image-based navigation using stereovision for dental surgery. In: Liao H, Linte C, Masamune K, Peters T, Zheng G, editors. Augmented reality environments for medical imaging and computer-assisted interventions. Berlin: Springer; 2013. p. 9–18.View ArticleGoogle Scholar
- Marinello C, Soom U, Schaerer P. Tooth preparation in adhesive dentistry. Dent Today. 1991;10(46):48–51.Google Scholar
- Song MK, Park YJ. Multi-sensor data fusion methods based on the Kalman filter for attitude and vibration control of the biped Robot. Int J Precis Engineer Manufac. 2008;25:39–46.Google Scholar
- Fortin T, Champleboux G, Bianchi S, Buatois H, Coudert JL. Precision of transfer of preoperative planning for oral implants based on cone-beam CT-scan images through a robotic drilling machine. Clin Oral Implants Res. 2002;13:651–6.View ArticleGoogle Scholar
- Horwitz J, Zuabi O, Machtei EE. Accuracy of a computerized tomography-guided template-assisted implant placement system: an in vitro study. Clin Oral Implants Res. 2009;20:1156–62.View ArticleGoogle Scholar
- Watzinger F, Birkfellner W, Wanschitz F, Ziya F, Wagner A, Kremser J. Placement of endosteal implants in the zygoma after maxillectomy: a Cadaver study using surgical navigation. Plast Reconstr Surg. 2001;107:659–67.View ArticleGoogle Scholar
- Goodacre BJ. Method and device for reducing angulation error during dental procedures. US Patent 9,179,987 B2, 10 Nov 2015Google Scholar
- Hinckfuss S, Conrad HJ, Lin L, Lunos S, Seong WJ. Effect of surgical guide design and surgeon’s experience on the accuracy of implant placement. J Oral Implantol. 2012;38:311–23.View ArticleGoogle Scholar