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Influence of oscillating and rotary cutting instruments with electric and turbine handpieces on tooth preparation surfaces
Influence of oscillating and rotary cutting instruments with electric and turbine handpieces on tooth preparation surfaces Alessandro Geminiani, DDS, MS,a Tamer Abdel-Azim, DDS,b Carlo Ercoli, DDS,c Changyong Feng, PhD,d Luiz Meirelles, DDS, MS, PhD,e and Domenico Massironi, DDSf Eastman Institute for Oral Health, University of Rochester, Rochester, NY; University of Louisville, Louisville, Ky Statement of the problem. Rotary and nonrotary cutting instruments are used to produce specific characteristics on the axial and marginal surfaces of teeth being prepared for fixed restorations. Oscillating instruments have been suggested for tooth preparation, but no comparative surface roughness data are available. Purpose. To compare the surface roughness of simulated tooth preparations produced by oscillating instruments versus rotary cutting instruments with turbine and electric handpieces. Material and methods. Different grit rotary cutting instruments were used to prepare Macor specimens (n¼36) with 2 handpieces. The surface roughness obtained with rotary cutting instruments was compared with that produced by oscillating cutting instruments. The instruments used were as follows: coarse, then fine-grit rotary cutting instruments with a turbine (group CFT) or an electric handpiece (group CFE); coarse, then medium-grit rotary cutting instruments with a turbine (group CMT) or an electric handpiece (group CME); coarse-grit rotary cutting instruments with a turbine handpiece and oscillating instruments at a low-power (group CSL) or high-power setting (group CSH). A custom testing apparatus was used to test all instruments. The average roughness was measured for each specimen with a 3-dimensional optical surface profiler and compared with 1-way ANOVA and the Tukey honestly significant difference post hoc test for multiple comparisons (a¼.05). Results. Oscillating cutting instruments produced surface roughness values similar to those produced by similar grit rotary cutting instruments with a turbine handpiece. The electric handpiece produced smoother surfaces than the turbine regardless of rotary cutting instrument grit. Conclusion. Rotary cutting instruments with electric handpieces produced the smoothest surface, whereas the same instruments used with a turbine and oscillating instruments achieved similar surface roughness. (J Prosthet Dent 2014;112:51-58)
Clinical Implications Because surface roughness affects the retention of self-etching luting agents and possibly the fit of fixed restorations, the selection of handpiece type and cutting instrument grit provides control over the surface characteristics of the preparations and possibly the retention provided by selected luting agents. During tooth preparation, periodontal structures must be respected and sufficient space must be created to a
allow for the fabrication of a restoration with adequate esthetics, strength, and longevity.1,2 To create a less visible
transition between the restoration and the underlying tooth structure, the marginal area of the preparation can be
Assistant Professor, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester. Assistant Professor, Division of Prosthodontics, University of Louisville. c Professor and Chair, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester. d Associate Professor, Department of Biostatistics and Computational Biology, School of Medicine and Dentistry, University of Rochester. e Assistant Professor, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester. f Private practice, Milan, Italy. b
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Volume 112 Issue 1 placed within the gingival sulcus.3 The definitive preparation of the marginal area of the tooth preparation is generally achieved with rotary cutting instruments of varying grit sizes. The choice depends on the clinician’s preference and the control of these instruments, which theoretically can be enhanced by adopting finer grit instruments and slow-speed handpieces. However, regardless of the instruments used, minimizing trauma to the gingival tissue and avoiding any violation of the biologic width is important for the long-term health and dimensional stability of the soft tissue.4 A major disadvantage of rotary instruments is that, despite the use of slow-speed handpieces and the insertion of gingival displacement cords, the gingival tissues could be injured. Any trauma or immediate bleeding at the site could hinder the efficiency and accuracy of impression procedures and materials.5 Oscillating instruments were originally developed for finishing the interproximal boxes of inlay tooth preparation.6 They were then gradually adopted for finish-line placement in complete coverage restorations, allegedly because they caused less damage to the sulcular and gingival tissues.7,8 For the aforementioned applications, sonic and ultrasonic devices, such as piezoelectric and pneumatic instruments, are used in conjunction with diamond cutting instruments of varying grits.9-11 The surface obtained by using oscillating instruments is characterized by an irregular pitted appearance, unlike the regular groovy surface that is produced by a rotating diamond instrument. In theory, such a surface may provide better adhesion by permitting the luting agent to cover more area. According to Ayad et al,12 the ideal degree of roughness of dental preparations, which can be measured with a roughness profilometer, is between 5 and 10 mm. Below this value, bonding systems adhere less effectively to the surfaces of the prepared tooth, whereas, above 12 mm, the cement does not achieve an even contact with the tooth surface, which leaves spots that are
devoid of luting agent. The roughness of the tooth preparation axial walls also may influence the wettability of luting agents and thus restoration retention.13 Indeed, Ayad et al14 found that tungsten carbide burs produced increased dentin roughness compared with that produced by finishing burs or diamond rotary instruments. The authors of the present study concluded that surface texture differences after preparation may significantly influence adhesion. Similarly, Al-Omari et al15 showed that instrument selection for tooth preparation may influence the retention and adhesion of resin-based restorative materials. The retention of artificial crowns has been shown to vary not only with the mechanical properties of the luting medium16 and the surface characteristics of the prepared teeth17 but also with the geometric relationship of the prepared tooth axial walls and definitive restoration.18 These factors can influence the stress distribution within the interposed cement layer,13 the bonding efficiency of cement to both surfaces, and the durability of the cement, including the long-term resistance to mechanical deterioration.19 Moreover, in the past few years, the use and marketing of self-etching cements has increased over luting agents that require multiple steps. The adhesion of the self-etching agents to dentin, especially those with a mildly acidic primer, is clearly affected by the thickness of the smear layer, which is, in turn, is influenced by the grit20-25 and type of the rotary cutting instrument used.20,26,27 In addition to affecting the cement’s ability to retain the restoration, the surface roughness of a tooth preparation also can affect its marginal accuracy and seating. A reproducible, precise, and smooth marginal surface of the preparation may positively affect the marginal accuracy of the restoration.28-33 The surface roughness of a tooth preparation can affect the seating, marginal accuracy, and retention of a crown, and the use of sonic and electric handpieces is gaining
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popularity. However, no studies have compared the surface roughness generated by conventional rotary cutting instruments used with electric handpieces with that generated by oscillating diamond-coated instruments used with sonic handpieces. The objectives of this study were to compare the surface roughness of the marginal area of a simulated tooth preparation produced by oscillating diamond-coated instruments with that obtained by fine- and medium-grit rotary cutting instruments used with either turbine or electric handpieces. The null hypotheses were that no difference would be found in surface roughness created by oscillating and rotary cutting instruments, no difference would be found in surface roughness produced by rotary cutting instruments when used with either electric or turbine handpieces, and no difference would be found in surface roughness produced by medium- or fine-grit rotary cutting instruments.
MATERIAL AND METHODS Tangential tooth preparations were simulated on Macor blocks (10 10 10 mm). Macor is a material that has physical and thermal properties34 similar to enamel and that has been used in previous studies to simulate tooth structure.35-39 It is a white nonporous, porcelain-like material composed of approximately 55% fluorophlogopite mica and 45% borosilicate glass, with a hardness (250 Knoop) and elastic modulus (66.9 GPa) similar to those of tooth enamel (300-340 Knoop and 84 GPa).40 The following 6 combinations of grits, handpieces, and power levels were used (Table I): group CFT, coarsegrit (Komet USA) followed by a fine-grit (Komet USA) rotary cutting instruments used with a turbine handpiece; group CFE, coarse-grit (Komet USA) followed by fine-grit (Komet USA) rotary cutting instruments used with an electric handpiece; group CMT, coarse-grit (Komet USA) followed by medium-grit (Komet USA) rotary cutting instruments used
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Table I.
53 Description of cutting instruments
Instrument
Shape
Grit
Size (mm)
Rotary (T)
Parallel chamfer
Coarse
0.16
6881.314.016
Rotary (T)
Parallel chamfer
Fine
0.16
8881.314.016
Rotary (E)
Parallel chamfer
Coarse
0.16
6881.314.016
Rotary (E)
Parallel chamfer
Fine
0.16
8881.314.016
Rotary (T)
Parallel chamfer
Coarse
0.16
6881.314.016
Rotary (T)
Parallel chamfer
Medium
0.16
881.314.016
Rotary (E)
Parallel chamfer
Coarse
0.16
6881.314.016
Rotary (E)
Parallel chamfer
Medium
0.16
881.314.016
CSL
Rotary (T)
Parallel chamfer
Coarse
0.16
2979.314.016
Sonic (L)
Parallel chamfer
Medium
0.16
SF979.000.016
CSH
Rotary (T)
Parallel chamfer
Coarse
0.16
2979.314.016
Sonic (H)
Parallel chamfer
Medium
0.16
SF979.000.016
Group CFT CFE CMT CME
Reference No.
CFT, coarse, then fine-grit rotary cutting instruments with turbine; T, turbine; CFE, coarse, then fine-grit rotary cutting instruments with electric handpiece; E, electric; CMT, coarse, then mediumgrit rotary cutting instruments with turbine; CME, coarse, then medium-grit rotary cutting instruments with turbine electric handpiece; CSL, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at low-power setting; L, low power; CSH, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at high-power setting; H, high power.
with a turbine handpiece; group CME, coarse-grit (Komet USA) followed by medium-grit (Komet USA) rotary cutting instruments with an electric handpiece; group CSL, coarse-grit (Komet USA) rotary cutting instrument used with a turbine handpiece followed by the use of oscillating diamond-coated (Komet USA) cutting instruments at a low-power setting; and group CSH, coarse-grit rotary (Komet USA) cutting instrument used with a turbine handpiece followed by the use of oscillating diamond-coated (Komet USA) cutting instruments at a high-power setting. The cutting actions were performed with a computer-controlled, dedicated testing apparatus used in previous studies.41,42 This apparatus allows a dental handpiece to perform controlled cutting actions for which preset values of load or displacement can be precisely and continuously monitored. As in previous studies, a high-speed turbine (Midwest Quiet-Air; Midwest Dental Products Corp) was connected to a compressed air tank with a regulator to provide a free maximum instrument rotation rate of 400 000
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2000 rpm. The revolutions per minute were monitored by an infrared tachometer (Model IRS; Monarch Instruments) mounted on the handpiece head. The handpiece head was modified with the rotor painted half black and half white to allow for the tachometer reading.41,42 Moreover, in this study, an electric handpiece (EWL 4890-Intra K-Lux 196 motor; KaVo) and a sonic handpiece (Sonicflex; KaVo) also were mounted on the testing apparatus. For the electric handpiece, no real-time rotation values were measured as the chuck button mechanisms on the back the handpiece head prevented modification of the handpiece rotor as described earlier for the turbine. The sonic handpiece also was not modified to monitor the kinetics of the oscillation. Each handpiece was mounted on a low-friction ball-bearing slider (MA-25 1500 stepper-driven UniSlide; Velmex Corporation) with an included linear variable differential transducer (SD20 LVDT; Metrolog Ltd) to measure the position and/or displacement and was positioned so that the rotary
instrument or oscillating insert was parallel to the surface of the substrate to be cut. In this manner, a tangential cutting action was used to simulate margin placement during crown preparation. A single operator (TAA) performed all cutting procedures as described later, and a computer software program (LabView 7.1; National Instruments) was used to monitor all sensors and control the testing apparatus. The testing unit applied a nominal arbitrary load of 1.5 N for the coarse-grit rotary cutting instrument initially used in each group and 0.5 N43,44 for the rotary cutting instrument or the oscillating instrument used for the second part (margin placement and/or finishing) of the cutting action. Based on the characteristics of the software used, “the software varied the rate of advancement according to the following program: if the load exceeded the nominal value, the rate of advancement was reduced. Instead, if the load was less than the nominal value, the rate was increased, in this way simulating the action of a clinician during tooth preparation.”41,42 Each Macor block was mounted on a stainless-steel plate, and the plate was mounted on a custom-made water bath, in which the level of the water was controlled with a combined water bathewater pump system (Haake D3L). The water bath was mounted on a sliding device (Manual slider system B90; Velmex Corp) so that the position of the specimen (itself fixed in the water bath) could be adjusted (x,y coordinates) during testing. The position of the Macor block could also be finely adjusted in a vertical direction (z coordinate) by moving the metal plate along threaded posts incorporated in the design of the water bath.41,42 According to the methods used in previous studies,41,42 the cutting procedure was divided into different steps as follows. From a fixed starting position, the computer software moved the handpiece forward until the cutting instrument contacted the Macor block to establish a baseline position. The software then slightly retracted the
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Volume 112 Issue 1 handpiece to allow it to be powered without touching the Macor block. The rotary or oscillating instrument then was allowed to reach free maximum instrument rotation or oscillation rate before the cutting action began. Water spray irrigation was activated. After the specimen was cut for its entire length (10 mm), the handpiece moved back to the starting position. This cutting procedure was repeated for each rotary cutting or oscillating instrument. When the finishing instrument was used (fine grit, medium grit, or oscillating instrument), the Macor specimen was moved approximately 0.3 mm in the x and z coordinates (toward the rotaryoscillating instrument) to allow the engagement of the finishing instruments. To control for possible inconsistencies of the Macor43 blocks, each block was cut along the 4 axial surfaces with 4 of the 6 different combinations of instruments specified in the 6 groups. For the first block, groups CFT, CFE, CMT, and CME were used to cut 1 surface each. Then, for the second blocks, groups CSL, CSH, and, then again, CFT and CFE were used. For the third blocks, groups CMT, CML, CSL, and CSH were used. This rotating sequence was continued until each group performed 36 cutting actions. Topographic analyses were performed with optical interferometry (NewView 7300; Zygo Corp). Optical interferometry has a nominal vertical resolution of <0.01 nm and is suitable for evaluating microstructures numerically. The analysis was performed on a measurement area of 280 210 mm (50 objective; zoom factor, 0.5) and a Gaussian filter (size 60 60 mm) selected to remove errors of form. Measurements were further analyzed with a software processor package (Scanning Probe Image Processor; Nanoscience Instruments Inc) to characterize the surface roughness parameters: average roughness (Sa), developed interfacial area ratio, summit density, reduced valley depth, core roughness depth), reduced peak height, skewness, and kurtosis. However, for the purpose
of this study, only the Sa values are reported as they relate to the outcome of interest of the study, namely average roughness. The reliability of the measuring instrument was assessed by 10 repeated measurements of the same area of a Macor specimen, which revealed a mean (SD) Sa value of 0.62385 0.0021 mm. To ensure the homogeneity of the Macor blocks used in the study, baseline surface roughness values also were obtained in 10 randomly selected blocks (a random number generated with statistical software). Marginal areas were measured for each specimen. To standardize the imaged area, data acquisition was performed 1 mm inside the marginal line angle of each specimen and in the middle of the prepared area (each prepared side of the block was 9-mm long after preparation). Consistent identification of the measured area and of the direction of incident light of the profilometer was ensured with the use of a custom-made positioning device. The specimen size was based on the 1-way ANOVA used to compare the mean values of the 6 groups. The significance level and proposed power were set at .05 and .80, respectively. The calculation showed that 216 cuttings (36 in each group) achieved an 82% power to detect differences among the means with an effect size of 0.24. One-way ANOVA was used to compare Sa values among the 6 groups. The Tukey honestly significant difference test was used for post hoc pairwise comparisons to control the overall type I error (a¼.05). All statistical analyses were implemented with SAS 9.2 (SAS Institute Inc).
RESULTS The 10 Macor specimens analyzed before the study began showed a mean (SD) Sa value of 0.4 0.144. Mean (SD) Sa values were 1.34 0.284 for CFT, 0.868 0.12 for CFE, 1.671 0.343 for CMT, 0.97 0.144 for CME, 1.63 0.357 for CSL, 1.578 0.33 for CSH, and are reported in
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Table II.
Descriptive statistics
Sa Group
No.
Mean (SD) (mm)
CFT
36
1.34 0.284
CFE
36
0.868 0.120
CMT
36
1.671 0.343
CME
36
0.97 0.144
CSL
36
1.63 0.357
CSH
36
1.578 0.33
Sa, average roughness; CFT, coarse, then finegrit rotary cutting instruments with turbine; CFE, coarse, then fine-grit rotary cutting instruments with electric handpiece; CMT, coarse, then medium-grit rotary cutting instruments with turbine; CME, coarse, then medium-grit rotary cutting instruments with turbine electric handpiece; CSL, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at low-power setting; CSH, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at high-power setting.
Table II. A statistically significant difference for Sa was found for all the between-group comparisons except for group CFE versus group CME, group CMT versus group CSL and CSH, and group CSL versus group CSH (Table III). The 1-way ANOVA showed significant group effects (P value for Sa, P<.05). The top panel in Figures 16 presents a 3-dimensional map of the surface (scale: x- and z-axis 50 mm per mark, y-axis 2 mm per mark), whereas the bottom panel is the profilometer read-out (scale: x-axis 50 mm per mark, y-axis 2 mm per mark). The sonic handpiece at low (Fig. 1) or high (Fig. 2) power setting produces roughness that is greater than that obtained with fine-grit rotary cutting instruments used with a turbine handpiece (Table III, Fig. 3). When a medium grit rotary cutting instrument was used with a turbine (Fig. 4) or the sonic handpiece, the difference in surface roughness was not significant (Table III).
DISCUSSION The 3 null hypotheses investigated in this study were that no difference would be found in finish-line surface
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Table III.
Sa pairwise group effect comparison
P Values Group
CFE
CMT
CME
CSL
CFT
<.001
<.001
<.001
<.001
.001
<.001
.12*
<.001
<.001
CFE
<.001
CMT CME
CSH
.54*
.16*
<.001
<.001
CSL
.43*
Sa, average roughness; CFE, coarse, then fine-grit rotary cutting instruments with electric handpiece; CMT, coarse, then medium-grit rotary cutting instruments with turbine; CME, coarse, then mediumgrit rotary cutting instruments with turbine electric handpiece; CSL, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at low-power setting; CSH, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at high-power setting; CFT, coarse, then fine-grit rotary cutting instruments with turbine. *Nonsignificant difference.
1 Three-dimensional and 2-dimensional surface profile of group CSL (sonic, low-power setting).
2 Three-dimensional and 2-dimensional surface profile of group CSH (sonic, high-power setting). roughness achieved by sonic versus rotating diamond instruments, no difference would be found in the finishline surface roughness achieved by a
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conventional high-speed handpiece versus an electric handpiece versus a sonic handpiece, and no difference would be found in the surface
roughness produced by medium- or fine-grit rotary cutting instruments. According to the results of this study, the first null hypothesis was rejected as the type of cutting instrument (sonic vs rotating) affected finishline surface roughness. The second null hypotheses was rejected as the type of handpiece (turbine vs electric vs sonic) had a significant effect on the recorded roughness values. The third null hypothesis also was rejected because instrument grit significantly affected the surface roughness of the finish line. In the present study, the roughness of the prepared Macor surface was analyzed with a 3-dimensional surface profilometer. This technology is based on scanning white-light interferometry. It is a precision vertical scanning transducer and a camera put together to generate a 3-dimensional interferogram of the model surface. After the acquisition of the model is completed, the computer analyzes each pixel for its height data, and the results are calculated based on the equation for each surface roughness parameter. The sonic handpiece used in this study had an amplitude of oscillation with a peak-to-peak range of 120 to 250 mm. With its nominal 64-mm-grit diamond layer, pneumatic feed and grip-regulated intensity, the sonic tool was claimed to “effectively finish margin surfaces.”7 Whereas this initial claim was based on expert opinion, the present study quantified the actual roughness produced by this handpiece and dedicated diamond-coated insert experimentally. The sonic handpiece, despite its power setting, produces roughness greater than that obtained with fine-grit rotary cutting instruments and a turbine handpiece. Therefore, the finding of the present study does not support the claim that using the sonic handpiece for finish-line preparation produces a smoother surface than using turbine handpieces. However, in the clinical setting, factors such as tactile feedback and vibration might also affect surface roughness and the accurate placement of finish lines; such
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Volume 112 Issue 1
3 Three-dimensional and 2-dimensional surface profile of group CFT (turbine, coarse and fine grit).
4 Three-dimensional and 2-dimensional surface profile of group CMT (turbine, coarse and medium grit).
5 Three-dimensional and 2-dimensional surface profile of group CFE (electric handpiece, coarse and fine grit). variables were not assessed in this study. The quantitative results of this study also are corroborated by a qualitative examination of the surface (Figs. 1, 2, 4).
It appears that the surface roughness achieved by the sonic handpiece with a medium-grit diamond-coated insert was not different from that obtained by medium-grit rotary cutting instruments.
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Indeed, in the illustrations, the peaks and valleys created by these diamond instruments are clearly visible. The experimental design used in this study, namely, a single pass of the sonic instruments, may not have significantly modified the surface achieved by the coarse rotary cutting instrument. Although the authors have not tested oscillating instruments after multiple passes on the cut surface, they believe that this is not the main reason for the surface characteristics achieved by the sonic instrument in this study. Indeed, Figures 3, 5, and 6 show that fine-grit rotary cutting instruments used with a turbine and both medium and fine instruments used with an electric handpiece were able, in a single pass, to distinctly modify the surface characteristics of the specimen. The current results that oscillating instruments generated a rougher surface than diamond rotary instruments disagree with those of Laufer et al11 and with Sous et al,8 who reported an increase in surface roughness with oscillating instruments at high power compared with low power. The electric handpiece produced the smoothest surface regardless of the grit of the rotary cutting instrument (Table III; Figs. 5, 6). Although the authors cannot explain these results, they may be related to the greater ability of this handpiece to limit the eccentricity of the cutting rotary instrument. Coupled with results from previous studies that showed that medium- and coarse-grit rotary cutting instruments have similar cutting efficiency,41,42 analysis of the present findings suggests that using medium-grit rotary cutting instruments with an electric handpiece could be a replacement for the use of multiple rotary cutting instruments in the clinician’s armamentarium, at least for the purpose of crown preparation. Once again, the clinical reality may prove these assumptions to be irrelevant and that other clinical factors may play a major role. A smoother preparation surface has been associated with improved seating and a decreased marginal opening of
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6 Three-dimensional and 2-dimensional surface profile of group CME (electric handpiece, coarse and medium grit). fixed restorations.33 Use of a specific combination of a handpiece and a rotary cutting instrument for tooth preparation could lead to the fabrication of a restoration with improved marginal adaptation. Although this study did not directly investigate the fit of a crown restoration because of the use of rotary cutting instruments with 5 different grits, the use of the electric handpiece with either medium- or finegrit instruments achieved a smoother surface than the same instruments used with a turbine or oscillating instruments. Moreover, the surface characteristics of prepared teeth function with the luting agents used for cementation to retain the definitive restoration. Luting agents that rely on micromechanical retention, such as zinc phosphatebased cements, provided increased retention as the roughness of the tooth surface increased.17 Resin luting agents behaved differently, depending on the adhesive and the thickness of the smear layer produced by the abrading (rotary cutting or oscillating) instrument. Both the type20,26,27 and the grit20-25 of the rotary cutting instruments used for tooth preparation clearly influence the amount of the residual smear layer. Although the thickness of the smear layer does not seem to affect the bond strength of luting agents that use 2and 3-step adhesives, self-etch adhesives generally behave quite differently, depending on the acidity of their
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primer.20 As a result, the bond strength of self-etch adhesive is generally affected by the use of rotary cutting instruments, with finer grits producing a thinner smear layer and, therefore, achieving greater bond strength. The use of sonic instruments also seems to reduce the amount of smear layer produced during tooth preparation.20,26,27 This could, at least in theory, increase the bonding strength of self-etch bonding systems and cements. However, a cause-effect relationship between the use of oscillating diamond instruments and an increase in the bond strength of crown restorations has not been demonstrated and should be the focus of further research. The present study demonstrated that the average surface roughness generated with an oscillating handpiece and/or diamond inserts is not different from that obtained with a turbinerotary cutting instrument. However, this remains an in vitro study, and its findings may be modified by intervening clinical factors not tested, for example, the ease of control of the different handpieces. The other advantage claimed for oscillating instruments is their lack of rotation, which theoretically allows better control during margin placement and reduces the risk of gingival lacerations.7 Although this claim deserves further investigation, the present study did not include simulated soft tissues in the experimental setup. In a previous study, differences have been
reported in cutting efficiency between turbine and electric handpieces,42 in this study, the electric handpiece achieved a smoother surface than all the other handpiece-instrument combinations. Lastly, Macor blocks were used as the substrate in place of whole extracted teeth because the complex tridimensional geometry of the tooth makes it virtually impossible to prepare the tooth in a standardized fashion with the testing apparatus used.43 However, as previously recognized,36,37,41,43 this machinable glass ceramic can behave differently from enamel and dentin during cutting; therefore, caution is necessary in interpreting experimental results.
CONCLUSIONS Within the limitations of this study, the following conclusions were drawn. Oscillating diamond-coated (medium grit) instruments used at a low- and/ or high-power setting produced surface roughness similar to that produced by rotary cutting (medium grit) instruments with a turbine handpiece. An electric handpiece with medium-grit rotary cutting instruments produced smoother surfaces than turbine and oscillating instruments with similar grit rotary instruments. An electric handpiece with fine-grit rotary cutting instruments produced smoother surfaces than a turbine instrument with similar grit rotary instruments. An electric handpiece with medium-grit rotary cutting instruments produced smoother surfaces than a turbine instrument with fine-grit rotary cutting instruments. Although fine-grit rotary cutting instruments in a turbine handpiece produce a smoother surface than medium-grit rotary cutting instruments, an electric handpiece produces similar surfaces, regardless of the grit of the rotary cutting instrument.
REFERENCES 1. Shillingburg HT Jr, Jacobi R, Brackett SE. Fundamentals of tooth preparation: for cast metal and porcelain restorations. Chicago: Quintessence; 1987. p. 61-79.
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Volume 112 Issue 1 2. Blair FM, Wassell RW, Steele JG. Crowns and other extra-coronal restorations: preparations for full veneer crowns. Br Dent J 2002;192:561-71. 3. Kois JC. New paradigms for anterior tooth preparation. Rationale and technique. Oral Health 1998;88:19-22, 25-27, 29-30. 4. Knoernschild KL, Campbell SD. Periodontal tissue responses after insertion of artificial crowns and fixed partial dentures. J Prosthet Dent 2000;84:492-8. 5. Ackerman MB. The full coverage restoration in relation to the gingival sulcus. Compend Contin Educ Dent 1997;18:1131-8. 6. Hugo B, Stassinakis A. Preparation and restoration of small interproximal carious lesions with sonic instruments. Pract Periodontics Aesthet Dent 1998;10:353-9. 7. Massironi D, Pascetta R, Romeo G. Precision in dental esthetics: clinical and laboratory procedures. Chicago: Quintessence; 2005. p. 151-73. 8. Sous M, Lepetitcorps Y, Lasserre J, Six N. Ultrasonic sulcus penetration: a new approach for full crown preparations. Int J Periodontics Restorative Dent 2009;29:277-87. 9. Kocher T, Plagmann HC. The diamond coated-sonic scaler tip. Part II: loss of substance and alteration of root surface texture after different scaling modalities. Int J Periodontics Restorative Dent 1997;17: 484-93. 10. Devall R, Lumley PJ, Waplington M, Blunt L. Cutting characteristics of a sonic root-end preparation instrument. Endod Dent Traumatol 1996;12:96-9. 11. Laufer BZ, Pilo R, Cardash HS. Surface roughness of tooth shoulder preparations created by rotary instrumentation, hand planing, and ultrasonic oscillation. J Prosthet Dent 1996;75:4-8. 12. Ayad MF, Maghrabi AA, Saif RE, GarcíaGodoy F. Influence of tooth preparation burs on the roughness and bond strength of adhesives to human dentin surfaces. Am J Dent 2011;24:176-82. 13. Ayad MF, Johnston WM, Rosenstiel SF. The influence of dental rotary instruments on the roughness and wettability of human dentin surfaces. J Prosthet Dent 2009;102:81-8. 14. Ayad MF, Rosenstiel SF, Salama M. Influence of tooth surface roughness and type of cement on retention of complete cast crowns. J Prosthet Dent 1997;77:116-21. 15. Al-Omari WM, Mitchell CA, Cunningham JL. Surface roughness and wettability of enamel and dentin surfaces prepared with different dental burs. J Oral Rehabil 2001;28:645-50. 16. Rosenstiel SF, Gegauff AG. Mixing variables of zinc phosphate cement and their influence on the seating and retention of complete crowns. Int J Prosthodont 1989;2:138-42.
17. Oilo G, Jørgensen KD. The influence of surface roughness on the retentive ability of two dental luting cements. J Oral Rehabil 1978;5: 377-89. 18. Felton DA, Kanoy BE, White JT. The effect of surface roughness of crown preparations on retention of cemented castings. J Prosthet Dent 1987;58:292-6. 19. Ayad MF. Effects of tooth preparation burs and luting cement types on the marginal fit of extracoronal restorations. J Prosthodont 2009;18:145-51. 20. Cardoso MV, Neves AD, Mine A, Coutinho E, Landuyt KV, Munck JD, et al. Current aspects on bonding effectiveness and stability in adhesive dentistry. Aust Dent J 2011;56(suppl): 31-44. 21. Ogata M, Harada N, Yamaguchi S, Nakajima M, Pereira PN, Tagami J. Effects of different burs on dentin bond strengths of self-etching primer bonding systems. Oper Dent 2001;26:375-82. 22. Pangsrisomboon B, Harnirattisai C, Nilsri K, Burrow MF. Microtensile bond strength of self-etching adhesive systems to differently prepared dentin. Am J Dent 2007;20:259-62. 23. Dias WRL, Pereira PNR, Swift EJ. Effect of surface preparation on microtensile bond strength of three adhesive systems to bovine enamel. J Adhes Dent 2004;6:279-85. 24. Yiu CKY, Hiraishi N, King NM, Tay FR. Effect of dentinal surface preparation on bond strength of self-etching adhesives. J Adhes Dent 2008;10:173-82. 25. Ermis RB, de Munck J, Cardoso MV, Coutinho E, Van Landuyt KL, Poitevin A, et al. Bond strength of self-etch adhesives to dentin prepared with three different diamond burs. Dent Mater 2008;24:978-85. 26. Pioch T, Garcia-Godoy F, Duschner H, Koch MJ, Staehle HJ, Dörfer CE. Effect of cavity preparation instruments (oscillating or rotating) on the composite-dentin interface in primary teeth. Dent Mater 2003;19:259-63. 27. Banerjee A, Kidd EA, Watson TF. Scanning electron microscopic observations of human dentine after mechanical caries excavation. J Dent 2000;28:179-86. 28. Hung SH, Hung KS, Eick JD, Chappell RP. Marginal fit of porcelain-fused-to-metal and two types of ceramic crown. J Prosthet Dent 1990;63:26-31. 29. Weaver JD, Johnson GH, Bales DJ. Marginal adaptation of castable ceramic crowns. J Prosthet Dent 1991;66:747-53. 30. Naert I, Van der Donck A, Beckers L. Precision of fit and clinical evaluation of allceramic full restorations followed between 0.5 and 5 years. J Oral Rehabil 2005;32:51-7. 31. May KB, Russell MM, Razzoog ME, Lang BR. Precision of fit: the Procera AllCeram crown. J Prosthet Dent 1998;80:394-404.
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32. Tuntiprawon M, Wilson PR. The effect of cement thickness on the fracture strength of allceramic crowns. Aust Dent J 1995;40:17-21. 33. Zena RB, Khan Z, von Fraunhofer JA. Shoulder preparations for collarless ceramic crowns: hand-planing as opposed to rotary instrumentation. J Prosthet Dent 1989;62: 273-7. 34. International Organization for Standardization. ISO-7785-1. Dental handpieces. Part I: high-speed air turbine handpieces. Geneva: ISO; 1997. Available at: http://www.iso.org/ iso/catalogue_detail.htm?csnumber¼22723. Accessed July 23, 2012. 35. Siegel SC, von Fraunhofer JA. Assessing the cutting efficiency of dental diamond burs. J Am Dent Assoc 1996;127:763-72. 36. Taira M, Wakasa K, Yamaki M, Matsui A. Dental cutting behaviour of mica-based and apatite-based machinable glass-ceramics. J Oral Rehabil 1990;17:461-72. 37. Tanaka N, Taira M, Wakasa K, et al. Cutting effectiveness and wear of carbide burs on eight machinable ceramics and bovine dentin. Dent Mater 1991;7:247-53. 38. Siegel SC, von Fraunhofer JA. The effect of handpiece spray patterns on cutting efficiency. J Am Dent Assoc 2002;133:184-8. 39. Siegel SC, von Fraunhofer JA. Cutting efficiency of three diamond bur grit sizes. J Am Dent Assoc 2000;131:1706-10. 40. von Fraunhofer JA, Siegel SC, Feldman S. Handpiece coolant flow rates and dental cutting. Oper Dent 2000;25:544-8. 41. Ercoli C, Rotella M, Funkenbusch PD, Russell S, Feng C. In vitro comparison of the cutting efficiency and temperature production of ten different rotary cutting instruments. Part I: turbine. J Prosthet Dent 2009;101:248-61. 42. Ercoli C, Rotella M, Funkenbusch PD, Russell S, Feng C. In vitro comparison of the cutting efficiency and temperature production of ten different rotary cutting instruments. Part II: electric handpiece and comparison with turbine. J Prosthet Dent 2009;101:319-31. 43. Liao WM, Taira M, Ohmoto K, Shintani H, Yamaki M. Studies on dental high-speed cutting. J Oral Rehabil 1995;22:67-72. 44. Siegel SC, von Fraunhofer JA. Dental cutting with diamond burs: heavy-handed or lighttouch? J Prosthodont 1999;8:3-9. Corresponding author: Dr Alessandro Geminiani 625 Elmwood Ave Rochester, NY 14620 E-mail: [email protected] Copyright ª 2014 by the Editorial Council for The Journal of Prosthetic Dentistry.
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Clinical Implications Because surface roughness affects the retention of self-etching luting agents and possibly the fit of fixed restorations, the selection of handpiece type and cutting instrument grit provides control over the surface characteristics of the preparations and possibly the retention provided by selected luting agents. During tooth preparation, periodontal structures must be respected and sufficient space must be created to a
allow for the fabrication of a restoration with adequate esthetics, strength, and longevity.1,2 To create a less visible
transition between the restoration and the underlying tooth structure, the marginal area of the preparation can be
Assistant Professor, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester. Assistant Professor, Division of Prosthodontics, University of Louisville. c Professor and Chair, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester. d Associate Professor, Department of Biostatistics and Computational Biology, School of Medicine and Dentistry, University of Rochester. e Assistant Professor, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester. f Private practice, Milan, Italy. b
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Volume 112 Issue 1 placed within the gingival sulcus.3 The definitive preparation of the marginal area of the tooth preparation is generally achieved with rotary cutting instruments of varying grit sizes. The choice depends on the clinician’s preference and the control of these instruments, which theoretically can be enhanced by adopting finer grit instruments and slow-speed handpieces. However, regardless of the instruments used, minimizing trauma to the gingival tissue and avoiding any violation of the biologic width is important for the long-term health and dimensional stability of the soft tissue.4 A major disadvantage of rotary instruments is that, despite the use of slow-speed handpieces and the insertion of gingival displacement cords, the gingival tissues could be injured. Any trauma or immediate bleeding at the site could hinder the efficiency and accuracy of impression procedures and materials.5 Oscillating instruments were originally developed for finishing the interproximal boxes of inlay tooth preparation.6 They were then gradually adopted for finish-line placement in complete coverage restorations, allegedly because they caused less damage to the sulcular and gingival tissues.7,8 For the aforementioned applications, sonic and ultrasonic devices, such as piezoelectric and pneumatic instruments, are used in conjunction with diamond cutting instruments of varying grits.9-11 The surface obtained by using oscillating instruments is characterized by an irregular pitted appearance, unlike the regular groovy surface that is produced by a rotating diamond instrument. In theory, such a surface may provide better adhesion by permitting the luting agent to cover more area. According to Ayad et al,12 the ideal degree of roughness of dental preparations, which can be measured with a roughness profilometer, is between 5 and 10 mm. Below this value, bonding systems adhere less effectively to the surfaces of the prepared tooth, whereas, above 12 mm, the cement does not achieve an even contact with the tooth surface, which leaves spots that are
devoid of luting agent. The roughness of the tooth preparation axial walls also may influence the wettability of luting agents and thus restoration retention.13 Indeed, Ayad et al14 found that tungsten carbide burs produced increased dentin roughness compared with that produced by finishing burs or diamond rotary instruments. The authors of the present study concluded that surface texture differences after preparation may significantly influence adhesion. Similarly, Al-Omari et al15 showed that instrument selection for tooth preparation may influence the retention and adhesion of resin-based restorative materials. The retention of artificial crowns has been shown to vary not only with the mechanical properties of the luting medium16 and the surface characteristics of the prepared teeth17 but also with the geometric relationship of the prepared tooth axial walls and definitive restoration.18 These factors can influence the stress distribution within the interposed cement layer,13 the bonding efficiency of cement to both surfaces, and the durability of the cement, including the long-term resistance to mechanical deterioration.19 Moreover, in the past few years, the use and marketing of self-etching cements has increased over luting agents that require multiple steps. The adhesion of the self-etching agents to dentin, especially those with a mildly acidic primer, is clearly affected by the thickness of the smear layer, which is, in turn, is influenced by the grit20-25 and type of the rotary cutting instrument used.20,26,27 In addition to affecting the cement’s ability to retain the restoration, the surface roughness of a tooth preparation also can affect its marginal accuracy and seating. A reproducible, precise, and smooth marginal surface of the preparation may positively affect the marginal accuracy of the restoration.28-33 The surface roughness of a tooth preparation can affect the seating, marginal accuracy, and retention of a crown, and the use of sonic and electric handpieces is gaining
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popularity. However, no studies have compared the surface roughness generated by conventional rotary cutting instruments used with electric handpieces with that generated by oscillating diamond-coated instruments used with sonic handpieces. The objectives of this study were to compare the surface roughness of the marginal area of a simulated tooth preparation produced by oscillating diamond-coated instruments with that obtained by fine- and medium-grit rotary cutting instruments used with either turbine or electric handpieces. The null hypotheses were that no difference would be found in surface roughness created by oscillating and rotary cutting instruments, no difference would be found in surface roughness produced by rotary cutting instruments when used with either electric or turbine handpieces, and no difference would be found in surface roughness produced by medium- or fine-grit rotary cutting instruments.
MATERIAL AND METHODS Tangential tooth preparations were simulated on Macor blocks (10 10 10 mm). Macor is a material that has physical and thermal properties34 similar to enamel and that has been used in previous studies to simulate tooth structure.35-39 It is a white nonporous, porcelain-like material composed of approximately 55% fluorophlogopite mica and 45% borosilicate glass, with a hardness (250 Knoop) and elastic modulus (66.9 GPa) similar to those of tooth enamel (300-340 Knoop and 84 GPa).40 The following 6 combinations of grits, handpieces, and power levels were used (Table I): group CFT, coarsegrit (Komet USA) followed by a fine-grit (Komet USA) rotary cutting instruments used with a turbine handpiece; group CFE, coarse-grit (Komet USA) followed by fine-grit (Komet USA) rotary cutting instruments used with an electric handpiece; group CMT, coarse-grit (Komet USA) followed by medium-grit (Komet USA) rotary cutting instruments used
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Table I.
53 Description of cutting instruments
Instrument
Shape
Grit
Size (mm)
Rotary (T)
Parallel chamfer
Coarse
0.16
6881.314.016
Rotary (T)
Parallel chamfer
Fine
0.16
8881.314.016
Rotary (E)
Parallel chamfer
Coarse
0.16
6881.314.016
Rotary (E)
Parallel chamfer
Fine
0.16
8881.314.016
Rotary (T)
Parallel chamfer
Coarse
0.16
6881.314.016
Rotary (T)
Parallel chamfer
Medium
0.16
881.314.016
Rotary (E)
Parallel chamfer
Coarse
0.16
6881.314.016
Rotary (E)
Parallel chamfer
Medium
0.16
881.314.016
CSL
Rotary (T)
Parallel chamfer
Coarse
0.16
2979.314.016
Sonic (L)
Parallel chamfer
Medium
0.16
SF979.000.016
CSH
Rotary (T)
Parallel chamfer
Coarse
0.16
2979.314.016
Sonic (H)
Parallel chamfer
Medium
0.16
SF979.000.016
Group CFT CFE CMT CME
Reference No.
CFT, coarse, then fine-grit rotary cutting instruments with turbine; T, turbine; CFE, coarse, then fine-grit rotary cutting instruments with electric handpiece; E, electric; CMT, coarse, then mediumgrit rotary cutting instruments with turbine; CME, coarse, then medium-grit rotary cutting instruments with turbine electric handpiece; CSL, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at low-power setting; L, low power; CSH, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at high-power setting; H, high power.
with a turbine handpiece; group CME, coarse-grit (Komet USA) followed by medium-grit (Komet USA) rotary cutting instruments with an electric handpiece; group CSL, coarse-grit (Komet USA) rotary cutting instrument used with a turbine handpiece followed by the use of oscillating diamond-coated (Komet USA) cutting instruments at a low-power setting; and group CSH, coarse-grit rotary (Komet USA) cutting instrument used with a turbine handpiece followed by the use of oscillating diamond-coated (Komet USA) cutting instruments at a high-power setting. The cutting actions were performed with a computer-controlled, dedicated testing apparatus used in previous studies.41,42 This apparatus allows a dental handpiece to perform controlled cutting actions for which preset values of load or displacement can be precisely and continuously monitored. As in previous studies, a high-speed turbine (Midwest Quiet-Air; Midwest Dental Products Corp) was connected to a compressed air tank with a regulator to provide a free maximum instrument rotation rate of 400 000
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2000 rpm. The revolutions per minute were monitored by an infrared tachometer (Model IRS; Monarch Instruments) mounted on the handpiece head. The handpiece head was modified with the rotor painted half black and half white to allow for the tachometer reading.41,42 Moreover, in this study, an electric handpiece (EWL 4890-Intra K-Lux 196 motor; KaVo) and a sonic handpiece (Sonicflex; KaVo) also were mounted on the testing apparatus. For the electric handpiece, no real-time rotation values were measured as the chuck button mechanisms on the back the handpiece head prevented modification of the handpiece rotor as described earlier for the turbine. The sonic handpiece also was not modified to monitor the kinetics of the oscillation. Each handpiece was mounted on a low-friction ball-bearing slider (MA-25 1500 stepper-driven UniSlide; Velmex Corporation) with an included linear variable differential transducer (SD20 LVDT; Metrolog Ltd) to measure the position and/or displacement and was positioned so that the rotary
instrument or oscillating insert was parallel to the surface of the substrate to be cut. In this manner, a tangential cutting action was used to simulate margin placement during crown preparation. A single operator (TAA) performed all cutting procedures as described later, and a computer software program (LabView 7.1; National Instruments) was used to monitor all sensors and control the testing apparatus. The testing unit applied a nominal arbitrary load of 1.5 N for the coarse-grit rotary cutting instrument initially used in each group and 0.5 N43,44 for the rotary cutting instrument or the oscillating instrument used for the second part (margin placement and/or finishing) of the cutting action. Based on the characteristics of the software used, “the software varied the rate of advancement according to the following program: if the load exceeded the nominal value, the rate of advancement was reduced. Instead, if the load was less than the nominal value, the rate was increased, in this way simulating the action of a clinician during tooth preparation.”41,42 Each Macor block was mounted on a stainless-steel plate, and the plate was mounted on a custom-made water bath, in which the level of the water was controlled with a combined water bathewater pump system (Haake D3L). The water bath was mounted on a sliding device (Manual slider system B90; Velmex Corp) so that the position of the specimen (itself fixed in the water bath) could be adjusted (x,y coordinates) during testing. The position of the Macor block could also be finely adjusted in a vertical direction (z coordinate) by moving the metal plate along threaded posts incorporated in the design of the water bath.41,42 According to the methods used in previous studies,41,42 the cutting procedure was divided into different steps as follows. From a fixed starting position, the computer software moved the handpiece forward until the cutting instrument contacted the Macor block to establish a baseline position. The software then slightly retracted the
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Volume 112 Issue 1 handpiece to allow it to be powered without touching the Macor block. The rotary or oscillating instrument then was allowed to reach free maximum instrument rotation or oscillation rate before the cutting action began. Water spray irrigation was activated. After the specimen was cut for its entire length (10 mm), the handpiece moved back to the starting position. This cutting procedure was repeated for each rotary cutting or oscillating instrument. When the finishing instrument was used (fine grit, medium grit, or oscillating instrument), the Macor specimen was moved approximately 0.3 mm in the x and z coordinates (toward the rotaryoscillating instrument) to allow the engagement of the finishing instruments. To control for possible inconsistencies of the Macor43 blocks, each block was cut along the 4 axial surfaces with 4 of the 6 different combinations of instruments specified in the 6 groups. For the first block, groups CFT, CFE, CMT, and CME were used to cut 1 surface each. Then, for the second blocks, groups CSL, CSH, and, then again, CFT and CFE were used. For the third blocks, groups CMT, CML, CSL, and CSH were used. This rotating sequence was continued until each group performed 36 cutting actions. Topographic analyses were performed with optical interferometry (NewView 7300; Zygo Corp). Optical interferometry has a nominal vertical resolution of <0.01 nm and is suitable for evaluating microstructures numerically. The analysis was performed on a measurement area of 280 210 mm (50 objective; zoom factor, 0.5) and a Gaussian filter (size 60 60 mm) selected to remove errors of form. Measurements were further analyzed with a software processor package (Scanning Probe Image Processor; Nanoscience Instruments Inc) to characterize the surface roughness parameters: average roughness (Sa), developed interfacial area ratio, summit density, reduced valley depth, core roughness depth), reduced peak height, skewness, and kurtosis. However, for the purpose
of this study, only the Sa values are reported as they relate to the outcome of interest of the study, namely average roughness. The reliability of the measuring instrument was assessed by 10 repeated measurements of the same area of a Macor specimen, which revealed a mean (SD) Sa value of 0.62385 0.0021 mm. To ensure the homogeneity of the Macor blocks used in the study, baseline surface roughness values also were obtained in 10 randomly selected blocks (a random number generated with statistical software). Marginal areas were measured for each specimen. To standardize the imaged area, data acquisition was performed 1 mm inside the marginal line angle of each specimen and in the middle of the prepared area (each prepared side of the block was 9-mm long after preparation). Consistent identification of the measured area and of the direction of incident light of the profilometer was ensured with the use of a custom-made positioning device. The specimen size was based on the 1-way ANOVA used to compare the mean values of the 6 groups. The significance level and proposed power were set at .05 and .80, respectively. The calculation showed that 216 cuttings (36 in each group) achieved an 82% power to detect differences among the means with an effect size of 0.24. One-way ANOVA was used to compare Sa values among the 6 groups. The Tukey honestly significant difference test was used for post hoc pairwise comparisons to control the overall type I error (a¼.05). All statistical analyses were implemented with SAS 9.2 (SAS Institute Inc).
RESULTS The 10 Macor specimens analyzed before the study began showed a mean (SD) Sa value of 0.4 0.144. Mean (SD) Sa values were 1.34 0.284 for CFT, 0.868 0.12 for CFE, 1.671 0.343 for CMT, 0.97 0.144 for CME, 1.63 0.357 for CSL, 1.578 0.33 for CSH, and are reported in
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Table II.
Descriptive statistics
Sa Group
No.
Mean (SD) (mm)
CFT
36
1.34 0.284
CFE
36
0.868 0.120
CMT
36
1.671 0.343
CME
36
0.97 0.144
CSL
36
1.63 0.357
CSH
36
1.578 0.33
Sa, average roughness; CFT, coarse, then finegrit rotary cutting instruments with turbine; CFE, coarse, then fine-grit rotary cutting instruments with electric handpiece; CMT, coarse, then medium-grit rotary cutting instruments with turbine; CME, coarse, then medium-grit rotary cutting instruments with turbine electric handpiece; CSL, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at low-power setting; CSH, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at high-power setting.
Table II. A statistically significant difference for Sa was found for all the between-group comparisons except for group CFE versus group CME, group CMT versus group CSL and CSH, and group CSL versus group CSH (Table III). The 1-way ANOVA showed significant group effects (P value for Sa, P<.05). The top panel in Figures 16 presents a 3-dimensional map of the surface (scale: x- and z-axis 50 mm per mark, y-axis 2 mm per mark), whereas the bottom panel is the profilometer read-out (scale: x-axis 50 mm per mark, y-axis 2 mm per mark). The sonic handpiece at low (Fig. 1) or high (Fig. 2) power setting produces roughness that is greater than that obtained with fine-grit rotary cutting instruments used with a turbine handpiece (Table III, Fig. 3). When a medium grit rotary cutting instrument was used with a turbine (Fig. 4) or the sonic handpiece, the difference in surface roughness was not significant (Table III).
DISCUSSION The 3 null hypotheses investigated in this study were that no difference would be found in finish-line surface
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Table III.
Sa pairwise group effect comparison
P Values Group
CFE
CMT
CME
CSL
CFT
<.001
<.001
<.001
<.001
.001
<.001
.12*
<.001
<.001
CFE
<.001
CMT CME
CSH
.54*
.16*
<.001
<.001
CSL
.43*
Sa, average roughness; CFE, coarse, then fine-grit rotary cutting instruments with electric handpiece; CMT, coarse, then medium-grit rotary cutting instruments with turbine; CME, coarse, then mediumgrit rotary cutting instruments with turbine electric handpiece; CSL, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at low-power setting; CSH, coarse-grit rotary cutting instruments with turbine handpiece and oscillating instruments at high-power setting; CFT, coarse, then fine-grit rotary cutting instruments with turbine. *Nonsignificant difference.
1 Three-dimensional and 2-dimensional surface profile of group CSL (sonic, low-power setting).
2 Three-dimensional and 2-dimensional surface profile of group CSH (sonic, high-power setting). roughness achieved by sonic versus rotating diamond instruments, no difference would be found in the finishline surface roughness achieved by a
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conventional high-speed handpiece versus an electric handpiece versus a sonic handpiece, and no difference would be found in the surface
roughness produced by medium- or fine-grit rotary cutting instruments. According to the results of this study, the first null hypothesis was rejected as the type of cutting instrument (sonic vs rotating) affected finishline surface roughness. The second null hypotheses was rejected as the type of handpiece (turbine vs electric vs sonic) had a significant effect on the recorded roughness values. The third null hypothesis also was rejected because instrument grit significantly affected the surface roughness of the finish line. In the present study, the roughness of the prepared Macor surface was analyzed with a 3-dimensional surface profilometer. This technology is based on scanning white-light interferometry. It is a precision vertical scanning transducer and a camera put together to generate a 3-dimensional interferogram of the model surface. After the acquisition of the model is completed, the computer analyzes each pixel for its height data, and the results are calculated based on the equation for each surface roughness parameter. The sonic handpiece used in this study had an amplitude of oscillation with a peak-to-peak range of 120 to 250 mm. With its nominal 64-mm-grit diamond layer, pneumatic feed and grip-regulated intensity, the sonic tool was claimed to “effectively finish margin surfaces.”7 Whereas this initial claim was based on expert opinion, the present study quantified the actual roughness produced by this handpiece and dedicated diamond-coated insert experimentally. The sonic handpiece, despite its power setting, produces roughness greater than that obtained with fine-grit rotary cutting instruments and a turbine handpiece. Therefore, the finding of the present study does not support the claim that using the sonic handpiece for finish-line preparation produces a smoother surface than using turbine handpieces. However, in the clinical setting, factors such as tactile feedback and vibration might also affect surface roughness and the accurate placement of finish lines; such
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3 Three-dimensional and 2-dimensional surface profile of group CFT (turbine, coarse and fine grit).
4 Three-dimensional and 2-dimensional surface profile of group CMT (turbine, coarse and medium grit).
5 Three-dimensional and 2-dimensional surface profile of group CFE (electric handpiece, coarse and fine grit). variables were not assessed in this study. The quantitative results of this study also are corroborated by a qualitative examination of the surface (Figs. 1, 2, 4).
It appears that the surface roughness achieved by the sonic handpiece with a medium-grit diamond-coated insert was not different from that obtained by medium-grit rotary cutting instruments.
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Indeed, in the illustrations, the peaks and valleys created by these diamond instruments are clearly visible. The experimental design used in this study, namely, a single pass of the sonic instruments, may not have significantly modified the surface achieved by the coarse rotary cutting instrument. Although the authors have not tested oscillating instruments after multiple passes on the cut surface, they believe that this is not the main reason for the surface characteristics achieved by the sonic instrument in this study. Indeed, Figures 3, 5, and 6 show that fine-grit rotary cutting instruments used with a turbine and both medium and fine instruments used with an electric handpiece were able, in a single pass, to distinctly modify the surface characteristics of the specimen. The current results that oscillating instruments generated a rougher surface than diamond rotary instruments disagree with those of Laufer et al11 and with Sous et al,8 who reported an increase in surface roughness with oscillating instruments at high power compared with low power. The electric handpiece produced the smoothest surface regardless of the grit of the rotary cutting instrument (Table III; Figs. 5, 6). Although the authors cannot explain these results, they may be related to the greater ability of this handpiece to limit the eccentricity of the cutting rotary instrument. Coupled with results from previous studies that showed that medium- and coarse-grit rotary cutting instruments have similar cutting efficiency,41,42 analysis of the present findings suggests that using medium-grit rotary cutting instruments with an electric handpiece could be a replacement for the use of multiple rotary cutting instruments in the clinician’s armamentarium, at least for the purpose of crown preparation. Once again, the clinical reality may prove these assumptions to be irrelevant and that other clinical factors may play a major role. A smoother preparation surface has been associated with improved seating and a decreased marginal opening of
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6 Three-dimensional and 2-dimensional surface profile of group CME (electric handpiece, coarse and medium grit). fixed restorations.33 Use of a specific combination of a handpiece and a rotary cutting instrument for tooth preparation could lead to the fabrication of a restoration with improved marginal adaptation. Although this study did not directly investigate the fit of a crown restoration because of the use of rotary cutting instruments with 5 different grits, the use of the electric handpiece with either medium- or finegrit instruments achieved a smoother surface than the same instruments used with a turbine or oscillating instruments. Moreover, the surface characteristics of prepared teeth function with the luting agents used for cementation to retain the definitive restoration. Luting agents that rely on micromechanical retention, such as zinc phosphatebased cements, provided increased retention as the roughness of the tooth surface increased.17 Resin luting agents behaved differently, depending on the adhesive and the thickness of the smear layer produced by the abrading (rotary cutting or oscillating) instrument. Both the type20,26,27 and the grit20-25 of the rotary cutting instruments used for tooth preparation clearly influence the amount of the residual smear layer. Although the thickness of the smear layer does not seem to affect the bond strength of luting agents that use 2and 3-step adhesives, self-etch adhesives generally behave quite differently, depending on the acidity of their
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primer.20 As a result, the bond strength of self-etch adhesive is generally affected by the use of rotary cutting instruments, with finer grits producing a thinner smear layer and, therefore, achieving greater bond strength. The use of sonic instruments also seems to reduce the amount of smear layer produced during tooth preparation.20,26,27 This could, at least in theory, increase the bonding strength of self-etch bonding systems and cements. However, a cause-effect relationship between the use of oscillating diamond instruments and an increase in the bond strength of crown restorations has not been demonstrated and should be the focus of further research. The present study demonstrated that the average surface roughness generated with an oscillating handpiece and/or diamond inserts is not different from that obtained with a turbinerotary cutting instrument. However, this remains an in vitro study, and its findings may be modified by intervening clinical factors not tested, for example, the ease of control of the different handpieces. The other advantage claimed for oscillating instruments is their lack of rotation, which theoretically allows better control during margin placement and reduces the risk of gingival lacerations.7 Although this claim deserves further investigation, the present study did not include simulated soft tissues in the experimental setup. In a previous study, differences have been
reported in cutting efficiency between turbine and electric handpieces,42 in this study, the electric handpiece achieved a smoother surface than all the other handpiece-instrument combinations. Lastly, Macor blocks were used as the substrate in place of whole extracted teeth because the complex tridimensional geometry of the tooth makes it virtually impossible to prepare the tooth in a standardized fashion with the testing apparatus used.43 However, as previously recognized,36,37,41,43 this machinable glass ceramic can behave differently from enamel and dentin during cutting; therefore, caution is necessary in interpreting experimental results.
CONCLUSIONS Within the limitations of this study, the following conclusions were drawn. Oscillating diamond-coated (medium grit) instruments used at a low- and/ or high-power setting produced surface roughness similar to that produced by rotary cutting (medium grit) instruments with a turbine handpiece. An electric handpiece with medium-grit rotary cutting instruments produced smoother surfaces than turbine and oscillating instruments with similar grit rotary instruments. An electric handpiece with fine-grit rotary cutting instruments produced smoother surfaces than a turbine instrument with similar grit rotary instruments. An electric handpiece with medium-grit rotary cutting instruments produced smoother surfaces than a turbine instrument with fine-grit rotary cutting instruments. Although fine-grit rotary cutting instruments in a turbine handpiece produce a smoother surface than medium-grit rotary cutting instruments, an electric handpiece produces similar surfaces, regardless of the grit of the rotary cutting instrument.
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