Editorial Type: CLINICAL DENTAL IMPLANT SCIENCE RESEARCH
 | 
Online Publication Date: 10 Oct 2024

In Vitro Comparison of Titanium Disc Surface Roughness and Bacterial Colonization After Ultrasonic Instrumentation With Three Different Tips

DMD, MSD,
PhD, MS,
DDS, MS, MPH, and
DDS, MSD
Article Category: Research Article
Page Range: 537 – 543
DOI: 10.1563/aaid-joi-D-24-00049
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During implant maintenance, preserving a smooth surface on the machined transmucosal abutment is critical to reduce biofilm attachment and colonization. The present study compared the surface roughness and bacterial colonization of machined titanium surfaces after instrumentation with various materials. Forty-four machined grade 23 titanium discs were instrumented with a round polyether ether ketone (PEEK) tip, a plastic curette tip, or a pure titanium curette tip with piezoelectric devices. Before and after instrumentation, the surface roughness (Ra and Rz) values were analyzed with a profilometer and scanning electron microscopy (SEM). Streptococcus sanguinis was cultured and incubated for 24 hours on the instrumented discs, and colony-forming units per milliliter were obtained for each group. Samples instrumented with the metal ultrasonic tip significantly increased surface roughness compared with the other groups. This resulted in greater colonization by S. sanguinis than surfaces instrumented with PEEK tips or the negative control. Samples instrumented with PEEK and plastic tips did not exhibit any statistically significant increase in surface roughness, and SEM analysis revealed a significantly rougher surface of discs instrumented with metal compared with discs instrumented with plastic or PEEK tips despite the possibility of debris from tip dissolution. Our results suggest that instrumentation with metal ultrasonic tips with piezoelectric devices significantly increased machined titanium’s surface roughness and elicited higher biofilm formation in vitro. Meanwhile, instrumentation of machined titanium with PEEK or plastic ultrasonic tips did not affect the surface roughness or bacterial adhesion.

Keywords: peri-implantitis; bacterial; peri-implant disease(s); dental materials

Introduction

Treating single- or multiple-tooth edentulism with the surgical placement and prosthodontic restoration of osseointegrated root-form implants has become commonplace. Peri-implantitis; peri-implant inflammation; and progressive, irreversible loss of the supporting bony architecture are common late complications that are observed in 10%–22% of implants1,2 and may be almost double that for patients without proper professional peri-implant maintenance.3 Peri-implant mucositis, which involves reversible peri-implant inflammation without loss of surrounding osseous architecture, precedes peri-implantitis and converts to the latter.4 Both peri-implant diseases appear to be caused by local bacterial biofilm-induced inflammation that is caused in part by poor plaque control via lack of professional peri-implant maintenance and/or inadequate patient home care.5 Poor plaque control is the most robust statistical indicator associated with peri-implantitis with an odds ratio of 5 to 14.6 Meanwhile, prospective studies indicate that patients who regularly comply with maintenance visits suffer from a lower incidence of peri-implantitis (18%) compared with noncompliers (44%).7 Thus, adequate dental implant maintenance is considered the most predictable method to reduce the cost, morbidity, and unpredictability of treating peri-implant mucositis and peri-implantitis.8

During implant maintenance, the preservation of a smooth surface on the machined collar or the transmucosal abutment of many implant systems is critical to promote fibroblast proliferation.9 The preservation of a smooth implant collar and/or transgingival abutment may also prevent microbial biofilm attachment to surface irregularities as it has been found that a surface roughness greater than 0.2 μm of restorative materials promotes biofilm adhesion.10–12 Multiple modalities, including conventional titanium, stainless steel, and plastic curettes, have been available for the clinician maintaining dental implants. Powered devices, such as magnetostrictive or piezoelectric scalers, have the added benefit of calculus removal, biofilm disruption, and debridement compared with hand instruments. However, using hand and powered instruments made from harder materials, such as steel, carbon, or titanium, can alter the pristine surface topography of machined implant and transmucosal abutment surfaces by producing scratches, gouges, or other irregularities.13 Conversely, plastic instruments are often ineffective in biofilm disruption and surface debridement.14 To our knowledge, a standardized peri-implant maintenance protocol is not available, and the choice of technique and instrument depends on the individual clinician’s assessment of the benefits and disadvantages of each method.

A novel material, polyether ether ketone (PEEK), was recently introduced to construct powered ultrasonic scalers; PEEK is a thermoplastic polymer that is biocompatible, fracture-resistant, wear-resistant, and stable under high pressure and temperature sterilization. It has been researched extensively in implant and prosthetic medicine and dentistry.15 These novel tips could minimize damage to the smooth abutment surfaces compared with traditional debridement methods while still adequately removing bacterial biofilm from the abutment and crown surfaces.

However, to our knowledge, studies have yet to be conducted to evaluate the surface roughness changes after instrumentation with these piezoelectric device attachments and the subsequent effect on bacterial colonization of machined titanium surfaces. Therefore, the primary purpose of this study was to compare the surface roughness of machined titanium after instrumentation with a piezoelectric device with PEEK, titanium, and plastic tips. The secondary aim was to compare the bacterial colonization of Streptococcus sanguinis in vitro to the machined titanium discs subjected to the preceding instrumentation protocols.

Materials and Methods

Samples and materials

Forty-four 10 mm (diameter) × 2 mm (thickness) grade 23 commercial titanium alloy discs with machined surfaces were prepared for instrumentation and profilometry by placement of a reference notch at the 6 and 12 o’clock positions. These notches were created with a 2 mm round diamond bur attached to a high-speed handpiece to standardize the directionality of profilometry measurements. Surface roughness was measured before and postinstrumentation using mean Ra and Rz values obtained with an optical profilometer (Proscan 2000, Scantron, Venture Way, Taunton, UK; S5/03 sensor, 0.3 mm measuring range). For each specimen, 4 separate scan areas of 1 (1 × 1 mm), 2, 4, 6, and 8 mm2 from the 12 o’clock reference notch (y-axis) were determined at the time of baseline measurements, and the same locations were also used for postinstrumentation surface roughness measurement. Each of the 4 scan areas was scanned 3 times for each specimen. After completion of the pretreatment scan, all specimens were ranked in order of surface roughness from smoothest to roughest, and group assignments were made sequentially to minimize intergroup variability of initial roughness measurements. Each of the control and test groups contained 11 discs and were randomized into 4 groups (Figure 1):

Figure 1.Figure 1.Figure 1.
Figure 1. Piezoelectric tips used for instrumentation in the current study. (a) Titanium universal piezo instrument tip. (b) Straight round PEEK-coated piezo instrument tip. (c) Plastic anterior curette-shaped piezo instrument tip.

Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00049

Group 1: No treatment group.

Group 2: Pure titanium universal implant protect piezo instrument tip (IP1: Acteon Satelec SP, Newtron. Mount Laurel, NJ).

Group 3: Straight, round PEEK-coated implant cleaning insert piezo instrument tip (IC1: Mectron, Hilliard, OH).

Group 4: Plastic anterior curette-shaped Periosoft piezo instrument tip (PH1: Acteon Satelec).

Instrumentations

All instrumentation protocols with the piezoelectric device followed the manufacturer’s instructions with 30% power for 1 minute with copious water irrigation. The instrumentation was completed by an American Board of Periodontology–certified periodontist. Each titanium disc was stabilized in a custom polyvinyl-siloxane mold during the instrumentation (Figure 2). A single specimen from each group was selected for scanning electron microscopy (SEM) after instrumentation to allow visual comparison of the changes in surface roughness. In preparation for SEM of the instrumented samples, the discs were disinfected by rubbing with 70% ethanol and gold sputtered (layer thickness: 10–25 nm). Subsequently, the samples were evaluated under an SEM (JOEL 7800f FESEM, Japan) operating at 5 kV with a working distance of 10 mm at ×500, ×1000, ×2000, and ×10 000 magnifications.

Figure 2.Figure 2.Figure 2.
Figure 2. Instrumentation of titanium disc with PEEK-coated piezoelectric tip within a custom polyvinyl-siloxane mold.

Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00049

Microbiological analysis

For the second portion of the experiment, the noninstrumented surface areas of the sample discs were painted with ethyl acetate to localize the bacterial adherence to only the zone of instrumentation. The titanium discs were disinfected by immersion in 70% ethanol for 30 minutes before microbial exposure. Subsequently, the discs were placed into sterile 24-well tissue culture plates with 1 mL of brain-heart infusion broth (BHI) bacterial growth medium and 50 μL of a Streptococcus sanguinis bacterial preparation (ATCC 10556) that was thawed from a frozen vial and cultivated anaerobically in BHI for 24 hours at 37°C. S. sanguinis is a well-studied, commensal, pioneer oral pathogen that is prevalent in healthy plaque biofilm16 as well as being present in healthy peri-implant sites.17 After incubation, the samples were rinsed 3 times in sterile saline and sonicated in 1 mL of saline to dislodge the attached biofilm, after which serial dilutions up to 1:100 000 were performed. The 1:1000 and 1:100 000 dilutions were plated on blood agar plates and incubated anaerobically for 24 hours, followed by counting the colonies using an automated colony counter. Colony-forming units (CFU) per milliliter were obtained for each group.

Statistical analysis

For surface roughness, with a sample size of 10 specimens per group, the study has 80% power to detect a difference of 0.66 µm for Ra. For bacterial colonization, with a sample size of 10 per group, the study has 80% power to detect a ratio of means of 2.5. Calculations assume 2-sided tests conducted at a 5% significance level, a within-group standard deviation of 0.5 µm for Ra, and a coefficient of variation of 0.8 for colony counts. Surface roughness changes (Ra and Rz) and CFU were analyzed with 1-way analysis of variance followed by pair-wise group comparisons using Fisher protected least significant differences. A Spearman correlation coefficient was calculated between posttreatment surface roughness and bacteria CFU. A 5% significance level is used for all tests, and all analyses were performed using software (SAS version 9.4, SAS Institute, Inc., Cary, NC). An independent statistician completed all sample size calculations and statistical analyses.

Results

No significant differences in surface roughness were noted by Ra and Rz preinstrumentation measurements between all groups (p = .967 for Ra, p = .878 for Rz) (Table). Surface roughness measurements conducted after instrumentation revealed that samples instrumented with the metal contributed to statistically significant roughness change from preinstrumentation (Ra change of 0.175 μm ± 0.046 μm [p = .004], Rz change of 0.896 μm ± 0.187 μm [p = .001]), whereas those instrumented by plastic or PEEK did not reach statistically significant differences (Figures 3 and 4). Samples instrumented with a metal tip had significantly higher posttreatment roughness than negative controls (p < .001 for Ra and Rz), samples instrumented with PEEK (p < .001 for Ra and Rz), and samples instrumented with plastic (p < .001 for Ra and Rz). No significant posttreatment roughness differences were found among negative controls and samples instrumented with PEEK or plastic tips.

Figure 3.Figure 3.Figure 3.
Figure 3. Mean Ra surface roughness of postinstrumented negative control and test group samples. Samples instrumented with a metal tip showed a statistically significant roughness change versus all other groups. No statistically significant roughness changes were observed between negative control, PEEK, and plastic-instrumented groups.

Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00049

Figure 4.Figure 4.Figure 4.
Figure 4. Mean Rz surface roughness of postinstrumented negative control and test group samples. Samples instrumented with a metal tip revealed a statistically significant roughness change versus all other groups. No statistically significant roughness changes were observed between negative control, PEEK, and plastic-instrumented groups.

Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00049

The 1:10 000 dilution of the attached biofilm was analyzed for all groups as this dilution showed an optimal colony count spread for enumeration. Titanium discs instrumented with the metal tip resulted in significantly higher bacterial colonization by S. sanguinis: a high average CFU/mL count (425 ± 71), which was almost double that of discs instrumented with a PEEK tip (219 ± 52), plastic tip (284 ± 70), or negative controls (129 ± 48) (Figure 5). Samples instrumented with the metal tip exhibited statistically significant higher colonization of S. sanguinis than surfaces instrumented with PEEK (p < .023) or negative controls (p < .002). Samples instrumented with a plastic ultrasonic tip yielded slightly higher bacterial colonization than those instrumented with PEEK even though the difference was not statistically significant.

Figure 5.Figure 5.Figure 5.
Figure 5. Mean colony-forming unit counts of S. sanguinis after 24-hour colonization of negative control and test group samples. Samples instrumented with a metal tip demonstrated statistically significant higher colonization than samples instrumented with PEEK or negative controls. Samples instrumented with a plastic tip yielded slightly higher bacterial colonization than those instrumented with a PEEK tip even though the difference was not statistically significant.

Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00049

In the SEM images of the negative control, the smooth surface of the noninstrumented disc was visualized in all magnifications along with concentric machining circles (Figure 6); SEM images of the disc instrumented with a metal tip revealed deep gouges, multiple peaks and valleys, and large amounts of possible debris at all magnifications, illustrating the increased surface roughness that metal tips impart on machined titanium, and SEM images of the plastic- and PEEK-instrumented discs maintained a continuous smooth surface at all magnifications with fewer machining circles visible versus the negative controls. In the ×500, ×1000, and ×2000 magnifications of the SEM images of plastic-instrumented discs, remnants of the machining circles smoothed by instrumentation were visible. At the same time, none could be discerned in PEEK-instrumented samples at any magnification. Finally, visible surface debris, most likely from respective piezoelectric tip dissolution during instrumentation, was observed in PEEK and plastic-instrumented discs.

Figure 6.Figure 6.Figure 6.
Figure 6. Scanning electron microscope imaging of 1 specimen each from negative control and postinstrumentation test groups at ×500, ×1000, ×2000, and ×10 000 magnification. The metal-instrumented specimen demonstrated deep gouges, multiple peaks and valleys, and large amounts of debris at all magnifications.

Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00049

Discussion

The present study sought to elucidate the differences in surface roughness and colonization by S. sanguinis of machined commercially available titanium alloy surfaces after instrumentation with metal, PEEK, and plastic tips in piezoelectric devices. We show that instrumentation of machined titanium with metal piezoelectric devices increased the surface roughness significantly compared with baseline, which led to higher bacterial adhesion and accumulation. Previous multiple studies corroborated the alteration of the smooth titanium surface after instrumentation with piezoelectric metal tips. Sahrmann instrumented titanium discs of surface roughness ∼0.4 μm and ∼0.04 μm, and the results showed a significantly enhanced roughness for both after instrumentation under standardized pressure.18 From studies conducted by Quirynen and Bollen, the concept of “threshold Ra” of 0.2 μm was suggested; values higher than 0.2 μm elicited an increase in biofilm attachment, and values below 0.2 μm did not result in any significant decrease in biofilm attachment.10,11 However, when abutment roughness was decreased to less than 0.2 μm, there were no changes in biofilm adherence.10,11 A positive correlation between increased surface roughness and bacterial accumulation was found with in vivo experimental models. Rimondini tested and analyzed microbial adhesions on titanium discs. A total of 16 subjects were wearing titanium discs stabilized with palatal stents in their mouth for 24 hours. For the study, the Ra of three different types of Ti discs were 0.088, 0.201, or 2.142 μm. The roughest discs, Ra was approximately 2 μm, contributed to significantly higher bacterial accumulation and density than on the surface of the smoothest ones (0.088 μm).19 Quirynen compared surface-roughened (Ra = 0.81 μm) clinical abutments to smooth ones (Ra = 0.35 μm) and demonstrated that the roughened abutments harbored 20 times more bacteria from the submucosal area after 3 months of regular oral hygiene.20 Wennerberg assessed the relationship between bleeding on probing and plaque accumulation in implants with stock abutments versus abutments that were turned and abraded. After 4 weeks of function, the roughest abutments accumulated 2.5 times higher amounts of plaque and biofilm.12 The initial roughness of the samples utilized in this experiment already exceeded the threshold of Ra = 0.2 μm with a mean Ra surface roughness of 0.405 μm. However, instrumentation with metal piezoelectric tips significantly increased the surface roughness by 0.175 ± 0.046 μm. A machined titanium surface would be required to have a maximal Ra of 0.025 μm not to cross the 0.2 μm threshold Ra after instrumentation with metal piezoelectric instruments. Meanwhile, commercially available transmucosal abutments demonstrate a Ra of 0.10 to 0.30 μm,11,21 anodized surfaces demonstrate a Ra of 0.15 μm,5 and hand-polished machined implant abutments demonstrate Ra surface roughness of 0.06 μm.10 Thus, instrumentation of most commercially available transmucosal abutments with metal piezoelectric tips could result in higher surface roughness and contribute to more biofilm accumulation.

In contrast, the instrumentation of samples in this experiment with a PEEK or plastic piezoelectric tip did not produce a significantly higher surface roughness. Thus, it can be inferred that the instrumentation of commercially available abutments with PEEK or plastic would not result in higher biofilm accumulation due to changes in surface roughness. Previous investigations by Shmage also found no significant differences in the surface roughness of titanium discs after instrumentation with PEEK and plastic piezoelectric tips compared with baseline.22 Schmidt also did not find any differences in bacterial colonization of machined implant necks after instrumentation with plastic-coated ultrasonic tips versus negative controls in vitro.23

The use of linear surface profilometry versus area surface profilometry limit this study’s findings. Surface profilometry could have detected more significant differences in surface roughness and the possible presence of debris that was not reflected in our postinstrumentation surface roughness analysis. The higher CFU counts for samples instrumented with plastic tips could have resulted from the presence of peripheral debris from instrumentation that was not picked up by linear profilometry measurements, which increased the surface area for bacterial colonization.

The SEM imaging performed during this study improved the visual confirmation. The sample instrumented with a metal piezoelectric tip results in significant changes in the surface morphology at all magnifications studied. The surface was deeply gouged and presented multiple peaks and valleys and large amounts of debris at all magnifications. Meanwhile, samples instrumented with PEEK and plastic were visually smooth with no peaks or valleys discernable, albeit with some debris from tip dissolution present on the surface. The dissolution of the PEEK tip and the subsequent deposition of its debris on polished titanium surfaces was previously observed after using a sonically driven tip.22 PEEK- and plastic-instrumented samples contributed to a lack of machining lines as visible on the negative control sample, which was most likely removed through the instrumentation process. This was most noticeable in the plastic-instrumented sample, in which flattened remnants of the machining lines could be discerned.

Using metal ultrasonic tips to maintain patients’ transmucosal implant surfaces is not recommended unless vital adhered calculus or residual cement is present. Still, these recommendations are tempered by the in vitro nature of this study. Although it can be inferred that using PEEK and plastic seems less traumatic on the titanium surface in a clinical scenario, the cleaning efficacy of these devices was not studied. Previous studies prove the good cleaning efficacy of ultrasonic-powered plastic, PEEK, and metal tips but a much lower cleaning efficacy for nonpowered plastic curettes.

Due to the nature of the in vitro study, several areas for improvement of this study need to be addressed. Some limitations include the sample material selection of grade 23 Ti alloy instead of pure titanium discs. The grade 23 Ti alloy’s surface has a different strength than the grade 4 titanium surfaces. The instrumentation on the Ti alloy is not directly translational to the clinical scenarios. In addition, the pressure of instrumentation cannot be fully standardized even if experienced periodontists complete the instrumentations. This study did not assess the effect of the pressure of instruments on the outcomes of surface change. Moreover, SEM imaging exhibits the visual assessment of surface characteristic changes. However, the selected area is a very small area of 1 specimen with each instrumentation.

Table Mean preinstrumentation surface roughness measurements of specimens in test and negative control groups showed no significant difference
Table

Conclusion

Instrumentation of machined titanium surfaces with PEEK or plastic piezoelectric tips did not significantly increase surface roughness or bacterial colonization. Meanwhile, instrumentation with a metal ultrasonic tip significantly increased surface roughness and bacterial colonization of machined titanium. It can be concluded that PEEK or plastic piezoelectrically driven tips for maintenance of machined titanium surfaces reduce surface topography changes and do not change bacterial colonization.

Abbreviations

CFU

colony-forming units

PEEK

polyether ether ketone

Ra

roughness average

Rz

height of irregularities

SEM

scanning electron microscope

Acknowledgments

This study was partially funded by the Graduate Student Research Committee fund at Indiana University School of Dentistry and Student Grant of American Academy of Implant Dentistry Foundation. The statistical analyses for this paper were completed by George Eckert, MAS, biostatistician supervisor at Indiana University.

Note

The authors do not have any financial interests in any of the products mentioned in this article.

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Copyright: 2024
Figure 1.
Figure 1.

Piezoelectric tips used for instrumentation in the current study. (a) Titanium universal piezo instrument tip. (b) Straight round PEEK-coated piezo instrument tip. (c) Plastic anterior curette-shaped piezo instrument tip.

Figure 2.
Figure 2.

Instrumentation of titanium disc with PEEK-coated piezoelectric tip within a custom polyvinyl-siloxane mold.

Figure 3.
Figure 3.

Mean Ra surface roughness of postinstrumented negative control and test group samples. Samples instrumented with a metal tip showed a statistically significant roughness change versus all other groups. No statistically significant roughness changes were observed between negative control, PEEK, and plastic-instrumented groups.

Figure 4.
Figure 4.

Mean Rz surface roughness of postinstrumented negative control and test group samples. Samples instrumented with a metal tip revealed a statistically significant roughness change versus all other groups. No statistically significant roughness changes were observed between negative control, PEEK, and plastic-instrumented groups.

Figure 5.
Figure 5.

Mean colony-forming unit counts of S. sanguinis after 24-hour colonization of negative control and test group samples. Samples instrumented with a metal tip demonstrated statistically significant higher colonization than samples instrumented with PEEK or negative controls. Samples instrumented with a plastic tip yielded slightly higher bacterial colonization than those instrumented with a PEEK tip even though the difference was not statistically significant.

Figure 6.
Figure 6.

Scanning electron microscope imaging of 1 specimen each from negative control and postinstrumentation test groups at ×500, ×1000, ×2000, and ×10 000 magnification. The metal-instrumented specimen demonstrated deep gouges, multiple peaks and valleys, and large amounts of debris at all magnifications.

Contributor Notes

* Corresponding author, e-mail: yusukehamada@dentistry.ucla.edu
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