1 Introduction

Nonsurgical surface debridement is the gold standard in managing periodontal disease [1]. Unfortunately, there is no gold standard in the decontamination of dental implants. Still, mechanical debridement might have to be combined with surface decontamination treatment to improve the hygiene in the deeper groove of the implants [2, 3]. In patients with periodontitis, the most commonly used method for root surface debridement is using the curettes to remove the calculus and dental plaque. However, when used inadvertently, these stainless-steel curettes produce implant surface irregularities [4, 5] and produce plaque retention and causes initiation or progression of the disease.

In a study by Polizzi and co-workers the complex calculus formed on the surface of the dental implants is shown to be adherent and penetrate the micro irregularities and the grooves of the acid-etched surface of the implant. Removing this residual calculus is a challenge and can result in refractory periodontal disease even after the treatment of the surface of the dental implant [6]. A study [7] on the presence of plaque/calculus and peri-implant health showed that plaque/calculus results more often in patients with an unhealthy peri-implantitis state than in the absence of it. Prophylaxis should aim at controlling persistent hard residue, such as calculus that converts the tooth to a foreign object hampering the attachment of the soft and hard tissues to the surface of the dental implants [6].

One of the most critical problems that can result from the removal of plaque from the surface of the dental implant is the damage to its surface. The loss of the surface oxide layer can result in the corrosion of the metal and impaired attachment of the fibroblasts to the dental implant surface. Hence, a more conducive approach is to treat the implant surface using an instrument that seldom results in surface roughness loss and eradicates the surface biofilm [8]. The survival rate of a moderately rough implant is about 98.4% compared to highly rough and minimally rough that were 96.4% and 97.6%, respectively [9]. In an another review the peri-implant bone loss in minimally rough was less (0.86 mm) in comparison to the moderately rough (1.01 mm) and highly rough surface (1.04 mm) [10].

The primary treatment modalities are surgical or nonsurgical treatment combined with mechanical debridement. Several instruments are used for mechanical debridement such as plastic, metal or ultrasonic scalers, rubber polishers, air-powder abrasive devices, and rotating titanium brushes [11, 12]. A study comparing a plastic curette, implantoplasty using the titanium brushes, and an air-abrasive system showed that these were valid approaches that eliminate the plaque and improves the implant’s biocompatibility [13]. As a commercialized medical instrument, titanium brushes have been used in treating peri-implantitis and have achieved satisfactory results in previous investigations. The advantage of these brushes during decontamination is the access and in turn being effective in smaller thread pitch and thread depth improving their effectiveness. In one of the studies it was notice that Implants with smaller thread pitch and thread depth values appeared to have less residual staining compared to deeper thread pitch. But, these brushes can lead to wearing of the implant with deeper thread depth. On the other hand, the most followed methods for treating peri-implantitis that have shown favorable results as assessed by systematic reviews are air abrasion and the titanium brush [8].

Hence the study aimed to evaluate the efficiency of artificial dental calculus (ADC) removal of four different types of scaling instruments from the surface of dental implants. The objectives of the present study were to compare the complete removal of the artificial dental calculus (ADC) from the surface of a dental implant by different prophylactic methods and to compare and evaluate the surface roughness of the new dental implants created by various types of surface treatment methods.

2 Material and Method

2.1 Materials

Twenty-four surfaces on twelve sandblasted and acid-etched dental implants (MIS narrow-diameter implants) were chosen for this study. Four instruments included were the titanium curette, titanium-coated curette, air abrasion unit (Pyrax®), and Titanium thread Cleaning Brush (Rotobrush—Salvin®). In addition, a styrofoam mandible model base was used for implant stabilization. The model helped provide a firm base during the implant placement.

Before the commencement of the study, SLA-coated implants were inserted into the Styrofoam base up to half of its length, maintaining adequate primary stability and simulated peri-implant disease (Fig. 1a).

Fig. 1
figure 1

a Dental implants inserted in to a Styrofoam model up to half of its length, b titanium curette (Ti), c titanium-coated curette (TiC), d Treatment using air abrasion unit, e Titanium brush (Rotobrush®)

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2.2 Artificial Dental Calculus (ADC) Application

Each of the exposed surfaces of the dental implant was coated with artificial dental calculus (ADC). The coating was done to submerge the implant threads (Fig. 1a). Artificial dental calculus (ADC) (Nakagyoku, Kyoto 604-0847 Japan) consisting of light grey and dark grey colored powders and a self-curing liquid resin was applied in two coats on the surface of the implant. The amount of ADC was comparable in all the implants, as it covered only the threads.

2.3 Grouping the Dental Implant Surfaces

Twenty-four surfaces of the twelve dental implants were divided into four groups. Surfaces in Group 1 were treated by titanium curettes (Ti), group 2 was treated by titanium nitride coated universal curettes (TiC), group 3 was treated by Air abrasion unit (Ap), and the group 4 was treated by titanium brushes (Tib) (Fig. 2) [14].

Fig. 2
figure 2

Flowchart of the division of the implant surfaces into different groups and various treatment modalities

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2.4 Titanium Curettes (Ti) and Titanium-Coated Curettes (TiC)

The titanium curette was made out of titanium alloy (Medical grade – Ti6-Al4-V) and was designed identical to the universal curette (Columbia 2R-2L). The titanium-coated curette was a coated curette designed out of stainless-steel metal and the coating of 1 – micron thickness of titanium nitride using the cathode arc evaporation PVD technique.

In the titanium curette (Fig. 1b) treatment group, the root surface covered with the artificial calculus was removed using the titanium curettes following the principles of instrumentation as applied to an invitro situation. The strokes were vertical and traversed from the apical to the coronal part of the implant. A single examiner performing the procedure was calibrated such that the force was within (3-4N). In the titanium-coated instruments group, the ADC-covered titanium surface was treated using the titanium-coated curettes (Fig. 1c).

2.5 Air Abrasion Unit (Ap)

In the Air abrasion (Fig. 1d) group, the treatment was done using the air prophy unit. The unit was filled with sodium bicarbonate (particle size of 40–65 µm), the air abrasion unit was held close to the titanium implant surface, and the treatment was done in a zigzag manner in a mesiodistal direction from the apical to the coronal end of the implant.

2.6 Titanium Brush (Tib)

The titanium brush (Rotobrush®) comprises titanium bristles with a central stainless-steel shaft. The brush was fitted to a slow-speed contra-angled handpiece (NSK), which oscillates in a clockwise/counter-clockwise direction. The handpiece was connected to a portable Coreless Micromotor System. The Tib shaft was placed parallel to the implant surface to give the brush adequate contact. It was moved until the required implant surface was free of the artificial calculus. The procedure was performed by a single examiner (Fig. 1e).

2.7 Determination of the Endpoint of the Treatment

All the procedures were done by a single examiner (SK) to minimize the bias. Other examiners visually explored the residual calculus remnants on the surface of the dental implants, and the instrumentation time was kept constant for all the groups. The procedure was followed by applying H2O2 (3% by Vol) using sterile cotton gauze. The surface roughness and the change in the morphology of the dental implants were determined and calculated.

2.8 Measurement of the Surface Roughness and Statistical Analysis

The roughness of the dental implant surface and complete removal of the artificial calculus was assessed using the Scanning electron microscope and surface roughness was evaluated using a Confocal laser scanning microscope (Olympus LEXT OLS4100 Confocal microscope) (Fig. 3). It achieves a 0.12-micron lateral resolution the accuracy of the measurement value is ± 2% all the measurement values were repeatable.

Fig. 3
figure 3

Output from a Confocal Laser microscope showing the Ra and Rz values of a Air abrasion, b Titanium curette, c Titanium-coated curette and d Titanium brush

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The images of the dental implant surface were checked using the image analysis software (Mountainslab software®) to measure the islands of surface loss.

3 Results

3.1 Determination of the Cleaning Efficacy of the Instruments

The calibrated examiner (SK, MY) determined the complete removal of ADC using visual examination. Examiners considered complete absence of the ADC on the implant surface as effective to maintain the treatment uniformity in all the groups.

3.2 Gross Morphology

The gross morphology under the low magnification of 27× to 30× showed the surface of the implants treated with all four methods. Ti and TiC curettes had residues in the grooves of the threads. The Ap had lesser residue than the other groups (Fig. 4).

Fig. 4
figure 4

Showing the gross morphology of the implant surface under scanning electron microscopy at 27×–30× magnification

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3.3 Ultrastructure View

The ultrastructure view at 1000× had regions of surface changes due to the instrumentation. The ultrastructural view shows (Fig. 5) the surface of implants treated with Ti, TiC, and Tib to have more significant regions of loss of the implant surface roughness.

Fig. 5
figure 5

Showing the regions of surface loss following the use of a Titanium curette (Ti), b Titanium-coated curette (TiC), c Air abrasion unit (AiP) and d Titanium brush (Tib)

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3.4 The Mean Surface Roughness (Ra), the Roughness Depth (Rz), and the Surface Area Loss (SL)

The descriptive group table (Table 1) shows the Ra value to vary between 0.29 to 1.08 µm and the Rz value between 10.3 to 70.5 µm. The mean surface loss area showed variation between 154 and 9410µm2. The homogeneity of variance was checked using Levene’s test (Table 2), and it showed a p > 0.05 for the mean surface roughness and the roughness depth values. Hence, the one-way ANOVA analysis (Fisher’s) was carried out to measure the Mean surface roughness (Ra) and roughness depth (Rz).

Table 1 Descriptive of the Ra, Rz and SL values showing mean, standard deviation (SD) and the standard error (SE)
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Table 2 Homogeneity of variances test (Levene’s)
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3.5 ANOVA Analysis

For the surface area loss (SL), one-way ANOVA (Welch’s) was carried out. The results showed a statistically significant difference between the four groups (P < 0.05) for all three parameters (Table 3).

Table 3 One-way ANOVA analysis
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The air abrasion unit showed the highest mean roughness value of 1.08 ± 0.14 µm (Table 4), a mean roughness depth of 70.5 ± 2.21 µm (Table 5), and a minor surface area loss of 154 ± 132 µm2 (Table 6) (Figs. 6 and 7).

Table 4 Tukey post—hoc test—arithmetic mean roughness (Ra)
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Table 5 Tukey Post—Hoc Test – Mean Roughness depth (Rz)
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Table 6 Post Hoc Games-Howell surface loss assessment
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Fig. 6
figure 6

Showing the regions of surface loss a and b following the use of titanium (Ti); c and d titanium-coated (TiC) curettes at 1000× magnification

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Fig. 7
figure 7

Showing the regions of surface loss a and b following the use of Air abrasion. (Aip); c and d titanium brush (Tib) at 1000× magnification

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In comparison, the titanium brushes showed the least Ra and Rz of 0.29 ± 0.05 µm and 10.3 ± 2.32 µm, respectively, whereas the titanium-coated curettes showed the highest loss of surface area (SL) 9410 ± 91.6 µm2 (Fig. 8).

Fig. 8
figure 8

Box plot with error bar of Arithmetic mean roughness, mean roughness depth and surface loss assessment

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3.6 Energy Dispersive X-ray Spectroscopy (EDS)

The elements on the surface of the treated titanium implants were analyzed for the weight percentage of oxygen and titanium elements using energy-dispersive X-ray spectroscopy (EDS). It revealed that the concentration ranged from 54.63% to 11.45% (Fig. 9), and the surface of new implants revealed the weight percentage of Oxygen to be 54.3% (Fig. 10) (Table 7).

Fig. 9
figure 9

a EDS spot 1 on the surface of titanium with high Ti and high O2 concentration, b EDS spot 2 with low Ti and high O2 concentration and c Surface of the impurity showing high O2 concentration but no Ti concentration

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Fig. 10
figure 10

a EDS of spectrum 1 with low Ti concentration and moderate oxygen concentration, b EDS spectrum 2 with minimal Ti concentration and high O2 concentration c EDS spectrum 3 with High Ti concentration and moderate O2 concentration

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Table 7 Elements found on the surface of the implants in the treated and non-treated groups
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But when the titanium element was check on the surface of the treated implant that had the debris/ impurities (in cases of failed implant surface), artificial dental calculus or the material that was left on the surface after air-polishing it was noticed that there was minimal to complete absence of titanium element. On the specified surface of treated implants, the maximum weight percentage of titanium was 2.15%. The weight concentration decreased to even as low as zero percentage (Fig. 11) (Table 7).

Fig. 11
figure 11

a EDS spectrum 1 with high Ti concentration and moderate O2 concentration, b EDS spectrum 2 with moderate O2 concentration and no Ti concentration c EDS spectrum 3 Minimal O2 concentration and no Ti concentration

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4 Discussion

Non-surgical periodontal therapy is aimed at removing dental plaque and calculus from the surfaces of dental structures. Several studies have shown the significance of the rotary, hand, and air abrasives to be significantly effective in treating the surface of the implants and rendering them biocompatible [15]. Dental plaque adhered to the implant surface accounts for the progression of peri-implant mucositis to peri-implantitis [16]. The plaque mineralization occurs and forms the dental calculus. Dental calculus formed on dental implant surfaces presents a challenge for complete removal. The thorough removal of hard & soft deposits from implant surfaces represents the basis for treating peri-implantitis [17]. Many cleaning instruments are available and recommended for personal oral hygiene and professional recall; they include air-polishing abrasive systems, rubber prophy cups with or without abrasives, toothbrushes with soft bristles, interproximal brushes, gauze strips, and plastic or metal scalers [18]. However, during implant surface treatment, the instruments may leave the implant surface more irregular and rougher [19].

Regarding implant roughness, previous in vivo studies have shown that ultrasonic or metallic instruments leave a rough surface and can harbor plaque. In a study by [20], the procedure that increased the roughness of the Ra values was 0.68 to 2.08 Rz 4.68 to 11.92; the unaltered surface had Ra of 0.44–0.57 and Rz 0.42 to 3.46; methods that smoothened the implant surface had Ra of 0.36 to Rz of 2.15 in our study the air-polishing showed a surface roughness (Ra) of 1.08 ± 0.14 µm and Rz of 70.5 ± 2.21 µm similar to the increased roughness value of the surface. The titanium brush used titanium surface had a Ra of 0.29 ± 0.05 µm and Rz 10.3 ± 2.32 µm, identical to the smoothened implant surface. The roughness value following the air abrasion was similar to a study [21] where it showed the value to be 1.31 ± 0.14 µm, and in our research, it was 1.08 ± 0.14 µm. However, the Ti-Brush Ra value was 1.22 ± 0.31, but in our study, the surface was smoother with a Ra value of 0.29 ± 0.05. The air abrasion and the Tib fulfilled the intended objective, and both removed the ADS from the implant surface. Nevertheless, air abrasion provides a biologically acceptable rough surface as it does not interfere much with the implant surface; hence, the surface oxide layer critical for Osseo integration and implant success could be retained [22].

The different material compositions and differing methods for using the cleaning instruments may adversely affect the surface quality of the implant. They could increase plaque and calculus retention and accumulation. They may also contaminate the surface of the titanium implant and could alter the oxide layer, thus increasing the possibility of implant surface corrosion [8]. The oxide layer on the surface of the titanium trans mucosal abutment is thought to be critical for the success of implant restoration. Studies shows that the surface oxygen content of > 5% [23] is biocompatible and can cause migration of the cells that make the surface conducive for Osseo integration. We have noted that the surface showed an oxygen content > 20% in our study. However, the surface of the failed and the surface treated with titanium brush showed similar oxygen content. We have seen the absence of titanium element on the EDS analysis of the surface of the foreign object, indicating a deterrent to the migrating osteoblast seeking a biocompatible titanium element to house itself. There are several studies done [11, 19, 24,25,26] to show that the air-powder polishing caused lesser surface loss compared to other instruments and was similar to our research but the biocompatible appearance of the implant surface after treatment with titanium brush was not identical to the one after air-polishing but resembled that of a failed implant. Hence, removing the implant surface impurities [27, 28] such as debris or calculus, is necessary, but it should be done without compromising the rough surface [23]. Further, there is a need to assess the limit value for the biological contaminants that can cause adverse reaction [29].

In a systematic review [30], the titanium rotary brushes show improvement in the decontamination of titanium implant surfaces. However, the studies only show efficiency by removing plaque-simulated ink but do not describe the detrimental effect on the surface caused by the instruments. Hence, the present study attempted to check the influence of various instruments on the implant surface during the removal of the artificial dental calculus (ADC).

Several limitations must be considered during the interpretation of the presented data of the study. First, the amount of artificial dental calculus deposited could not be quantified. Second, the attachment dynamics of the calculus on the implant surface could not be established which could affect the amount of force required to remove the ADS using different instruments. Third, the access to the site of treatment, since in clinical situation there can be variations in the access to the site where the usage of abutments could hinder the cleaning procedure. These could be overcome by measuring the amount of ADC used, use of atomic force microscopy to determine the attachment dynamics and using a subgingival invitro model. In the present study, more emphasis was given on the amount of calculus that could be removed even though plaque is the etiology and calculus is a predisposing factor. The surface roughness of the dental implants is an essential factor to determine the biocompatibility and osseointegration. If this portion of the dental implant is exposed due to bone loss and gets contaminated by plaque and calculus then it must be treated. The methods used in this study include curettes, rotary, and air abrasion devices; the air abrasion device has been shown to have a minor surface irregularity compared to other treatment methods. Maximum surface loss was observed after using the titanium brush.