The Impact of Dental Probe Wear on Implant Health

Effective long-term implant health monitoring is crucial following the placement of a dental implant. Practitioners must possess a comprehensive understanding of how monitoring is used to direct the appropriate maintenance care.¹

Various clinical parameters are used to assess implant health, including mobility, radiography, gingival alterations, pain, occlusion, probing pocket depth, and bleeding on probing.^2-6 Probing around dental implants has been a subject of debate in the past, however, it is now widely recognized as one of the most valuable diagnostic tests for evaluating implant health. Clinically, bleeding on probing and probing depth measurements are the most beneficial when baseline measurements are used for comparison.^3,7-10

Probing around and adjacent to an implant will cause some frictional wear or tribological interaction between the probe and the implant and/or abutment material.¹¹ The science of tribology and frictional wear is complex and depends on factors such as loading forces, surface texture, rate of movement, hardness of the material, adhesion, lubrication and other factors.^11,12 Thus, the probing force and materials are important as is the environment.

Periodontal probes are made from either metal or plastic, and the choice between the two types continues to be a topic of debate.^13-17 Metal instruments, including titanium, have been criticized for producing scratches on implants and abutments, while plastic instruments have been associated with leaving debris deposits on dental implants and implant components.^13-17

Some plastic probes have colored, graduated depth markings (green and red) to aid in visualizing and measuring (Figure 1). The instructions for use indicate that the probes can be utilized up to 30 times and should be replaced when the colored markings become poorly visible or are removed. However, it is unclear how these color markings degrade — whether it’s during the sterilization process or through use. The biocompatibility of the paint is not disclosed other than it is a food grade-material registered with the United States Food and Drug Administration. If the color comes off as the probe moves against the implant or abutment surface, the resulting contamination may impact the peri-implant tissues.^18-20

In order to ascertain how probe markings degrade and the effects of color degradation on implant health, a study was initiated. The purpose of this study was to answer the following questions:

1. Do the color markers degrade as a result of cleaning and sterilization?
2. Is the colored paint removed during the action of probing the implant or abutment?
3. What is the force required for transfer of colored material onto different implant and abutment materials compared to clinically recommended peri-implant probing force?

Materials and Methods

Twenty new, unused plastic probes from two manufacturers (A and B) were selected for the study. Both sets of probes had similar proprietary color code graduations of green and red (Figure 1).

To assess if the color markings were being removed during the cleaning and sterilization processes, one probe from each manufacturer was chosen for a preliminary study. A standardized photographic setup was developed with the probe placed a specific distance from the camera.

Photos of the probes prior to cleaning and sterilization were taken. The cleaning sequence involved wiping the probes with isopropanol disinfection cloths and then placing them in sterilization pouches. The probes were heat sterilized following the manufacturer’s protocol. After every five cycles, images of the probes were taken, and visual examination was conducted. This process was repeated for a total of 30 cycles.

The remaining 18 colored probes, nine from each manufacturer A and nine from manufacturer B, were used to investigate if the color markings faded due to frictional wear between the implant or implant abutment during use. To control the force applied at the probe tip, a custom linear movement test probing model was developed. The sample implants and abutments were placed at a 90° angle to a clamp, which held the test plastic probe tip (Figure 2). The probe tips were then moved across the surfaces of four different implant types and five abutments in single, one-direction passes. The initial weight on the probe clamp was fixed at 10 g equivalent to a force of approximately 0.1 N.

Of the four implant types, one was made from zirconia, two were titanium grade 4, and one was titanium grade 5 alloy. The five abutment materials used were: zirconia, titanium nitride, titanium aluminum vanadium, titanium aluminum niobium, and gold alloy. Images (1:1 magnification) of the probes, implants, and abutments were obtained prior to testing to serve as controls.

Each probe was moved across the surface of either the implant or the abutment, and after each pass, photographs were taken. Testing stopped when the green color was visibly transferred to the implant or abutment, or when the green color was removed from the probe tip, exposing the underlying white plastic core. For further analysis, select implants and abutments were viewed using a scanning electron microscope (SEM).

Results

In the cleaning and sterilization study, no observable color alterations occurred on the probe tips even after 30 cycles. Both the A and B probes appeared identical to the new untouched control (Figure 3).

Color loss from the tips did occur when the probes passed across the implant materials. The titanium-based implants showed visible deposits of green debris. This occurred after just one pass with a force of 0.1 N on the probe tip (Figure 4). Although the green debris was present on the zirconia implant, it was relatively more challenging to detect due to the smoother, reflective surface (Figure 4D).

We also assessed the number of passes — made by the probe at 0.1 N across the implants — needed to remove the green paint and expose the underlying plastic core. The plastic base was evident with the three titanium implants after two passes from either probe A or probe B, while the zirconia implant required five passes for probe B and six for probe A (Figure 4). This was an indicator of how much colored paint was being removed during each probing.

The abutments exhibited varying results. The locator abutment with a titanium nitride, gold-colored coating exhibited green color on a single pass with both probe types (Figure 5A). The underlying probe core was exposed at 12 passes for probe A and eight for probe B. For the gold alloy abutment, probe A resulted in green debris after the first pass, with the probe’s core exposed after eight passes. Probe B showed green debris deposits on the second pass and exposed the core after 18 passes (Figure 5B).

The zirconia abutment displayed green debris with a single pass of either probe type, at 0.1 N, consistent with the zirconia implant (Figure 5C). Additionally, the tip of probe A exposed the probe’s core material after eight passes over the abutment surface, whereas probe B required 10 passes (Figure 6A-B and Figure 7A-B).

In contrast, the titanium aluminum vanadium and titanium aluminum niobium alloy abutments did not display any visible debris on their surfaces, even after 30 passes. This was mainly due to the difficulty in visualizing green paint on the smooth metal surface. The green paint did not adhere to the titanium alloy’s smooth surface in contrast to the other materials. However, both probe tips showed visible wear exposing the probe’s core after 30 tests.

To better understand the surface alterations on the titanium abutments in particular, SEM images were captured. They showed vertical streaks and debris present after 30 passes (Figure 8).

Discussion

Both probes appeared similar, however, probe A had a smoother surface and the green marker color appeared darker. This may be due to thicker paint or different paint material (Figures 6 and 7). According to the manufacturer’s information, the proprietary colors are food colorants.¹⁶ The colored probes exhibited excellent resistance to wiping with isopropanol and steam autoclaving, indicating their durability and robust nature. The resilience to dissolution both in alcohol and steam autoclaving suggests that the colorant may remain in situ if retained on any implant materials.

The 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions defined implant health as having an absence of visible signs of inflammation and bleeding on probing. Peri-implant mucositis, characterized by bleeding on probing and visual inflammation, is considered a precursor to peri-implantitis. However, the use of terms like “gentle probing” in the classification raises concerns, as it lacks quantifiability.¹⁰

Cha et al¹² conducted a study to determine the appropriate force for probing around dental implants, finding a desired pressure of 119 Ncm². This pressure equates to a plastic probe with a 0.6 mm tip and 0.34 N of force, or 3.4 times more force than that used in this study. During initial tests, it was observed that the green color was removed due to wear at the minimal force of 0.1 N. All the tests showed that the green pigment was being worn away, which was clearly visualized on the implants and most of the abutments. For the titanium-based abutments, which had a smooth surface, SEM images were necessary to detect minute deposits and the exposure of the white probe core material after multiple passes.

The tested implant surfaces all had rough textures designed to enhance integration. This is particularly relevant as remnants of color are likely to be retained even when probed with “gentle force” of around 0.1 N. It was apparent that the test materials were harder than the probe core material, as seen from the wear on the tip of the probe after the color had been removed. However, the degree of wear was not quantified. The absence of fluid lubrication may also have affected wear and debris transfer.

The study used a force of approximately 0.1 N directed toward the probe’s tip at 90°. Although this scenario might be uncommon in clinical situations, a calculation was performed to determine the glancing angle the probe could make to mimic a 0.1 N force. Any angle greater than 17° between the implant and probe would result in color transfer when using the recommended probing force of 0.34 N on the plastic probe.¹²

Further investigation is required to understand the composition of the debris and its potential impact on biocompatibility with host epithelial cell attachment. Contamination of abutment surfaces has been shown to compromise the epithelial attachment of the peri-implant mucosa and inhibit the adhesion of gingival fibroblasts, ultimately leading to apical migration of the junctional epithelium.¹⁹

The study had some limitations, including the design of the probing model, use in a dry field, lack of a host peri-implant environment, material limitations, and the challenge of mimicking human factors, such as controlling and maintaining probing pressures. The true minimum threshold of debris could not be measured due to the model used which was set at a minimum force of 0.1 N due to the weight of the holding apparatus. The hardness values and surface roughness were not measured for the materials used. Further investigation into the potential effects of these implant-retained remnants should be undertaken.

Conclusion

Within the limitations of this study, color markings on the plastic probes were not being degraded by the action of chemical cleaning and sterilization. At a force (0.1 N) deemed considerably lower than recommended for clinical probing, colored paint contamination occurred due to frictional wear on the implants and abutments. Further investigation is required to understand the composition of the paint and plastic debris and its potential interaction and biocompatibility with host epithelial cell attachment.

Acknowledgement

The authors wish to acknowledge Richard T. O’Brien, BSEE, for building the linear model used in this study.

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From Decisions in Dentistry. June/July 2024; 10(4):32-35