Influence of surface treatment by laser irradiation on bacterial adhesion on surfaces of titanium implants and their alloys: Systematic review

Abstract

Objective

The aim of this systematic review was to present the current knowledge on the influence of laser surface treatment on the adhesion of bacteria to titanium and its alloys.

Design

This review was structured according to PRISMA guidelines for systematic reviews and meta-analyses, and registered on the Open Science Framework platform (https://doi.org/10.17605/OSF.IO/FTA3W). Article searches were performed in 4 databases: PubMed, Scopus, Embase, and Science Direct. In addition, a manual search was performed in the reference lists of the selected articles. The selection of articles was performed by two reviewers. The articles found were screened for eligibility using the previously established inclusion and exclusion criteria. The methodological quality of the studies was assessed using the Joanna Briggs Institute (JBI) Critical Assessment Checklist for Quasi-Experimental Studies (non-randomized experimental studies).

Results

Most of the studies evaluated showed that surface treatment by laser irradiation can affect the adhesion of bacteria to titanium surfaces and that this is directly related to changes in surface properties such as chemical composition, morphology, roughness, and wettability, as well as the type of bacterial species involved.

Conclusions

The studies considered in this systematic review have shown that surface treatment by laser irradiation is a promising technique to reduce the adhesion of bacteria on the surface of titanium implants.

1. Introduction

The continuous development and improvement of titanium implant surfaces is the focus of many companies and research projects. In addition to optimizing the micro- and nanoscale properties that are critical to bone biology, (Calazans Neto et al., 2022, Souza et al., 2019, Zhang et al., 2021) implant surface treatment can decrease bacterial adhesion, colonization, and biofilm formation and prevent infections that affect implant survival. (Costa et al., 2021, Donaghy et al., 2019, Jeong et al., 2017, Komorowski et al., 2020, Yao et al., 2020) The modification of the topographic characteristics of implants through surface treatments significantly modifies the surface properties and, in this way, it is possible to limit bacterial adhesion or even create antibacterial topographies. (Papa et al., 2022)

Several factors affect bacterial adhesion to the implant surface, including bacterial species, implant material, and physicochemical properties of the surface, the regulation and modification of which increase implant survival, and even the fluid phase properties of the inoculation medium and the type of adhesion test evaluated, thus different species of bacteria can exhibit varying degrees of adhesion depending on all these factors as they have different sizes and affinities for surface characteristics. (Costa et al., 2021, Drago et al., 2016, Linklater et al., 2021, Lorenzetti et al., 2015, Luo et al., 2020, Nunes Filho et al., 2018).

Among the various types of surface modification, laser irradiation has attracted much attention in recent years because it offers advantages such as the ability to control the surface texture, it has a simple technique, low risk of contamination, and high reproducibility. (Costa et al., 2021, Souza et al., 2019) In addition, the use of the laser does not lead to bacterial resistance, as occurs in surface treatments with antimicrobial agents. (Fadeeva et al., 2011).

Several studies have investigated the antimicrobial potential of laser surface treatments (Chik et al., 2018, Donaghy et al., 2019, Drago et al., 2016, Eghbali et al., 2021, Luo et al., 2020, Orazi et al., 2019, Parmar et al., 2018, Shiju et al., 2019) because of the ability of laser to alter surface properties such as wettability, roughness, morphology, and chemical composition and to create surfaces with different types of nano- and micro textures, that can have varying width, periodicity (spacing) and height to which bacteria are sensitive^. (Costa et al., 2021, Eghbali et al., 2021, Linklater et al., 2021, Luo et al., 2020, Lutey et al., 2018, Meinshausen et al., 2021, Papa et al., 2022, Simões et al., 2021, Uhlmann et al., 2018) These modifications are reported to result in surfaces with fewer viable bacteria (Eghbali et al., 2021) and lower colonization, (Medvids et al., 2021) adhesion, (Donaghy et al., 2019, Du et al., 2022, Meinshausen et al., 2021, Zwahr et al., 2019) and adhesion strength than untreated surfaces. (Du et al., 2022).

Despite these results, laser treatment is still being refined (Calazans Neto et al., 2022) and the irradiation parameters have a direct influence on the result obtained since they are directly related to the surface modification produced, (Simões et al., 2021) so there are also studies that observe an increase in the amount of bacteria on laser-treated surfaces (Esfahanizadeh et al., 2018, Guastaldi et al., 2019, Singh et al., 2021) or that found no significant changes in bacterial adhesion. (Duarte et al., 2009, Hauser-Gerspach et al., 2014).

Given the importance of developing titanium surfaces that prevent bacterial adhesion for better dental implant survival, and given the benefits of laser treatment and discrepancies in the literature, the aim of this systematic review was to present the current knowledge on the effect of laser surface treatment on bacterial adhesion to titanium and its alloys. It was hypothesized that laser surface treatment makes it more difficult for bacteria to adhere to the implant surface.

2. Materials and methods

This review was structured according to PRISMA guidelines for systematic reviews and meta-analyses, and registered on the Open Science Framework platform. The PICOS strategy for this review was defined as follows: population - titanium surfaces; intervention - laser irradiation treatment; comparison - titanium surfaces not treated with laser irradiation; outcome - bacterial adhesion; study design - in vitro. Article searches were performed in 4 databases: PubMed, Scopus, Embase, and Science Direct. The keywords used in the search strategy of each database and the number of results found are described in Table 1. In addition, a manual search was performed in the reference lists of the selected articles.

Table 1.

Research strategies used.

Data base	Search strategy used	Records found
PubMed January	(“dental implant”[MeSH Terms] OR “dental implant”[All Fields] OR “dental implants”[MeSH Terms] OR “dental implants”[All Fields] OR (“dental”[All Fields] AND “implant”[All Fields]) OR “implant”[All Fields] OR “implant s”[All Fields] OR “titanium”[Mesh Terms] OR “titanium”[All Fields] OR (“titanium”[All Fields] AND “implant”[All Fields]) OR “implants”[All Fields] OR (“titanium implant”[All Fields] OR (“titanium implants”[All Fields]) AND (“laser s”[All Fields] OR “lasers”[MeSH Terms] OR “lasers”[All Fields] OR “laser”[All Fields] OR “lasered”[All Fields] OR “lasering”[All Fields] OR “laser treatment”[All Fields] OR “laser irradiation”[All Fields] OR (“laser” [All Fields] AND “treatment”[All Fields])) AND (“bacterial adhesion”[MeSH Terms] OR “bacterial adhesion”[All Fields] OR (“bacterial”[All Fields] AND “adhesion”[All Fields]) OR “bacterial adhesions”[All Fields])	137
Scopus	(“DENTAL IMPLANTS” OR “TITANIUM”) AND (“LASER” OR “LASER TREATMENT” OR “LASER IRRADIATION”) AND (“BACTERIAL ADHESION”)	109
Embase	'TITANIUM' AND ('LASER'/EXP OR LASER) AND ('BACTERIAL ADHESION'/EXP OR ‘BACTERIAL ADHESION’) AND 'ARTICLE'/IT	88
Science Direct	(“DENTAL IMPLANTS” OR “TITANIUM”) AND (“LASER” OR “LASER TREATMENT” OR “LASER IRRADIATION”) AND (“BACTERIAL ADHESION”)	582

Article selection was performed by two reviewers (IGS and MLCV), and a third reviewer (ACR) was consulted in case of disagreement. Manual selection of peer-reviewed articles was performed using the Rayyan software (Qatar Computing Research Institute, Doha, Qatar) by the two reviewers. The first selection was based on reading the title and abstract of all articles, and for studies with insufficient data, the manuscript was read in full. The articles selected from the reading of the titles and abstracts underwent a second selection in which the articles were read in full. The articles found had their eligibility assessed through the inclusion and exclusion criteria previously established and were finally selected for this systematic review.

Inclusion criterion was research articles that addressed in any way the effect of laser irradiation on bacterial adhesion to titanium surfaces, there was no restriction regarding language or publication period. The exclusion criteria were: articles that did not assess laser irradiation or assessed laser irradiation combined with other surface treatments; articles that did not assess bacterial adhesion; articles that evaluated surfaces other than titanium and its alloys; articles that assessed surface treatment for purposes other than dental or biomedical implants. Finally, in vivo studies, clinical trials, systematic reviews, book chapters, short communications, conference summaries, case reports, and personal opinions were excluded. Methodological quality of studies was assessed using the Joanna Briggs Institute (JBI) Critical Assessment Checklist for Quasi-Experimental Studies (nonrandomized experimental studies). This checklist consists of 9 items (Table 2) that can be scored as follows: yes, unclear, no, and not applicable.

Table 2.

Critical Assessment Checklist for Quasi-Experimental Studies (non-randomized experimental studies) of the Joanna Briggs Institute Critical Assessment Tools for use in JBI Systematic Reviews.

Question	Description
Q1	Is it clear in the study what is the ‘cause’ and what is the ‘effect’ (i.e. there is no confusion about which variable comes first)?
Q2	Were the participants included in any comparisons similar?
Q3	Were the participants included in any comparisons receiving similar treatment/care, other than the exposure or intervention of interest?
Q4	Was there a control group?
Q5	Were there multiple measurements of the outcome both pre and post the intervention/exposure?
Q6	Was follow up complete and if not, were differences between groups in terms of their follow up adequately described and analyzed?
Q7	Were the outcomes of participants included in any comparisons measured in the same way?
Q8	Were outcomes measured in a reliable way?
Q9	Was appropriate statistical analysis used?

The following data were extracted from the selected studies: (1) authors and year of publication; (2) titanium alloy evaluated; (3) laser used and parameters; (4) comparison group; (5) method used to evaluate bacterial adhesion and bacteria evaluated; (6) main results.

Due to the heterogeneity of the studies in terms of the titanium alloys investigated, the lasers and parameters used, and the methods used to evaluate bacterial adhesion, it was not possible to perform a meta-analysis. Therefore, a descriptive analysis of the data is presented.

3. Results

The initial search returned 923 results: 138 in PubMed, 110 in Scopus, 89 in Embase, and 586 in Science Direct. After removing duplicates, 740 studies remained, of which 710 were excluded after reading the title and abstract. Thirty articles were read in full, of which 5 were excluded because they used other surface treatments in conjunction with the laser treatment or because they used the laser for other purposes (Chan et al., 2017, Chan et al., 2021, Chang et al., 2020, Lubov Donaghy et al., 2020, Porrelli et al., 2021) and other 2 because they did not evaluate the treatment for use in dental or biomedical implants. (Truong et al., 2012, Vanithakumari et al., 2021) At the end of this selection process, 23 articles were selected for this systematic review. The details of the selection process are shown in Fig. 1.

Fig. 1.

Flow diagram summarizing selection process.

Among the articles included, 14 evaluated the adhesion of Staphylococcus aureus, (Chik et al., 2018, Costa et al., 2021, Doll et al., 2016, Donaghy et al., 2019, Drago et al., 2016, Du et al., 2022, Fadeeva et al., 2011, Guastaldi et al., 2019, Meinshausen et al., 2021, Orazi et al., 2019, Parmar et al., 2018, Shiju et al., 2019, Singh et al., 2021, Uhlmann et al., 2018) 5 of Escherichia coli, (Chik et al., 2018, Du et al., 2022, Eghbali et al., 2021, Luo et al., 2020, Zwahr et al., 2019) 4 of Porphyromonas gingivalis, (Drago et al., 2016, Esfahanizadeh et al., 2018, Hauser-Gerspach et al., 2014, Yao et al., 2020) 3 of Pseudomonas aeruginosa, (Drago et al., 2016, Fadeeva et al., 2011, Medvids et al., 2021) 3 of Streptococcus sanguinis, (Doll et al., 2016, Duarte et al., 2009, Hauser-Gerspach et al., 2014) and only 1 article evaluated Staphylococcus epidermidis, (Medvids et al., 2021) Prevotella intermedia, (Esfahanizadeh et al., 2018) Aggregatibacter actinomycetemcomitans, (Esfahanizadeh et al., 2018) and Streptococcus mutans. (Grössner-Schreiber et al., 2001).

Eight studies evaluated bacterial adhesion by the number of colony-forming units, (Duarte et al., 2009, Eghbali et al., 2021, Guastaldi et al., 2019, Hauser-Gerspach et al., 2014, Luo et al., 2020, Medvids et al., 2021, Orazi et al., 2019, Parmar et al., 2018) 7 evaluated adhesion by microscopy, (Donaghy et al., 2019, Du et al., 2022, Grössner-Schreiber et al., 2001, Meinshausen et al., 2021, Shiju et al., 2019, Souza et al., 2019, Chik et al., 2018) 3 used scanning electron microscopy, (Fadeeva et al., 2011, Singh et al., 2021, Zwahr et al., 2019) 3 used confocal laser scanning microscopy, (Doll et al., 2016, Drago et al., 2016, Fadeeva et al., 2011) 2 used the spectrophotometric assay, (Drago et al., 2016, Luo et al., 2020) 1 used the PMA-PCR method, (Esfahanizadeh et al., 2018) and 1 the OD595 method. (Uhlmann et al., 2018) The characteristics of the included studies are shown in Table 3.

Table 3.

Characteristics of the included studies.

Author	Titanium Alloy Evaluated	Laser and Parameters Used	Comparison Group	Bacteria Assessed and Assessment Method
DRAGO et al., 2016	Ti grade 4	Laser treatment (GEASS, Pozzuolo Del Friuli, Itália) Laser type and parameters not specified	Sandblasted modified titanium discs	Bacteria evaluated: Staphylococcus aureus methicillin resistant; Pseudomonas aeruginosa multi-resistant; Porphyromonas gingivalis. All isolated from peri-implantitis lesions. Evaluation method: The amount of biofilm was determined by spectrophotometric assay. Confocal laser scanning microscopy analysis was used to assess bacterial volume.
GUASTALDI et al., 2019	Ti-15Mo and cpTi grade 2	Yb:YAG Laser Fluency: 1.9 J/cm2 Sweep speed: 0–200 mm/s Pulse frequency: 20–35 kHz	Non-laser-irradiated polished Ti-15Mo and cpTi	Bacteria evaluated: Staphylococcus aureus methicillin resistant Assessment method: The initial adherence of Staphylococcus aureus methicillin resistant cells was assessed by counting CFU/mL.
CUNHA et al., 2016	Ti grade 2	Yb:KYW Laser, forming two types of different textures LIPSS (1) and nanopillars (2) Wave-length: 1030 nm Pulse duration: 500 fs Fluency: 0.30 J/cm2 (1) and 0.40 J/cm2 (2) Repeat rate: 1 kHz (1 and 2) Scan Speed: 5 mm/s (1) and 25 mm/s (2) Side shift: 0.1 mm (1) and 0.2 mm (2) Linear polarization: perpendicular (1) and perpendicular + parallel (2) Number of pulses: 192 (1) and 137 (2)	Non-laser irradiated polished titanium surfaces	Bacteria evaluated: Staphylococcus aureus Evaluation method: Quantification of adherent bacteria was performed using an epifluorescence microscope. The quantification of adherent bacteria was performed using Image J software.
PARMAR et al., 2018	Ti-6Al-4 V	Fiber laser Wave-length: 1064 nm Pulse width: 250 ns Pulse frequency: 50; 100; 150; 200; and 250 kHz Average power: 10; 15; 20; and 25 W Number of scans: 1; 3; 5; and 10	Surface without laser treatment	Bacteria evaluated: Staphylococcus aureus Evaluation method: To quantify viable bacterial cells, the number of CFU/ml was determined.
SHIJU et al., 2019	Ti-6Al-4 V	Femtosecond pulsed Nd:YAG Wave-length: 1064 nm Power: 40 W Scan speed: 25 mm/s Sample distance: 10 mm	Polished sample without laser irradiation	Bacteria evaluated: Staphylococcus aureus Evaluation method: Bacteria were observed using a fluorescence microscope.
DOLL et al, 2016	Ti grade 4	Ti-sapphire amplified femtosecond laser Wave-length: 800 nm	Non-laser-irradiated titanium	Bacteria evaluated: Staphylococcus aureus Evaluation method: Bacterial colonization was analyzed by confocal laser scanning microscopy. The percentage of surface coverage on structured and smooth titanium was calculated using ImageJ.
EGHBALI et al., 2021	Ti-6Al-4 V	Fiber laser Scan speed: 2000 mm/s Average power: 80 W Frequencies used: 20; 80; and 160 kHz Distances between the slots: 0.5; 1; 4; 10; 20; 50; and 100 µm	Laser untreated surface	Bacteria evaluated: Escherichia coli Evaluation method: bacterial adhesion was evaluated by the plate counting method,
ORAZI et al., 2019	Ti-6Al-7Nb	Picosecond laser Wave-length: 1064 nm Pulse: 8 ps Pulse energy: 16 µJ (1) and 32 µJ (2)	Untreated polished surface	Bacteria evaluated: Staphylococcus aureus Evaluation method: the number of UFC was determined.
CHIK et al., 2018	Ti grade 5	Ultra fast fiber laser Wave-length: 515 µm Average power: 0.11 W Pulse: 380 fs Repetition rate: 200 kHz Scan speed: 20 mm/s	AISI 316L stainless steel treated with the same parameters and polished surface	Bacteria evaluated: Staphylococcus aureus and Escherichia coli Evaluation method: Bacterial adhesion was evaluated with a fluorescence microscope and the surface area covered by adherent bacteria was calculated using ImageJ software.
SINGH et al., 2021	Ti-6Al-4 V	Yterbio fiber laser Wave-length: 1040 nm Power: 20 W Frequency: 5 kHz Scan speed: 0.37 mm/s	Samples without surface treatment	Bacteria evaluated: Staphylococcus aureus Evaluation method: Samples of cultured bacteria were coated with gold for scanning electron microscopy images. Five micrographs were evaluated and Image J software was used to quantify bacterial density.
MEINSHAUSEN et al., 2021	cpTi grade 4	Direct laser interference pattern technique Did not specify the type of laser used Fluency: 0.9 (1); 0.29 (2); 0.06 (3); 0.06 (4); 0.47 (5) J/cm−2 Space period (∼): 5 (1); 2.2 (2); 1.3 (3); 0.7 (4) µm; without periodicity (5)	Polished Ti-6Al-4 V sample	Bacteria evaluated: Staphylococcus aureus Evaluation method: the amount of adherent bacteria was quantified using a fluorescence microscope and the number of bacteria was determined with ImageJ software.
ZWAHR et al., 2019	Ti grade 4	Combination of Direct Laser Writing with Laser Direct Interference Patterning Parameters Direct Laser Writing: Nanosecond pulsed ytterbium fiber laser Wave-length: 1064 nm Focal distance: 254 mm Pulse duration: 100 ns and 200 ns Fluency: 2–8.1 J/cm2 Parameters Laser Direct Interference Patterning four beams: Nd:YAG laser Wave-length: 1064 nm Pulse duration: 70 ps Focal distance: 60 mm Fluency: 0.20 J/cm2 Number of pulses: 10 Accumulated fluency: 2 J/cm2	Samples not treated by laser	Bacteria evaluated: Escherichia coli Evaluation method: the samples were pulverized with a layer of gold and the unstructured and hierarchically structured part of the titanium surface was photographed with scanning electron microscopy. Four images per structured and unstructured part of each sample were evaluated with ImageJ by measuring the area covered with bacteria.
(GRÖSSNER-SCHREIBER et al., 2001)	Ti grade 2	Nd-YAG laser Wave-length 1.06 μm Pulse power: 50 W, Pulse length: 8.4 ms Point diameter: 0.8 mm	Polished titanium discs	Bacteria evaluated: Streptococcus sanguis and Streptococcus mutans Evaluation method: Quantitative analysis was performed using a fluorescence microscope.
HAUSER-GERSPACH et al., 2014	Ti grade 2	Er:YAG laser Wave-length: 2940 nm Pulse energy: 100 mJ (1) and 500 mJ (2) Pulse frequency: 10 Hz Pulse duration: 250–400 µs Sample distance:0.5–1 mm Energy density: 12.74 J/cm2 (1) and 63.69 J/cm2 (2)	Polished discs without surface treatment	Bacteria evaluated: Streptococcus sanguis and Porphyromonas gingivalis Evaluation method: The amount of bacteria adhered was determined by CFU.
DU et al., 2022	Ti TC4	Femtosecond laser Wave-length: 1030 nm Repeat frequency: 100 kHz Pulse width: 200 fs Pulse energy: 3 µJ Scan speed: 500 mm/s Irradiation point size: 30 µm	Polished sample without laser irradiation	Bacteria evaluated: Escherichia coli and Staphylococcus aureus Assessment method: Fluorescence microscopy was used to assess bacterial adhesion. The surface adhesion rate was assessed by gray analysis using ImageJ software.
ESFAHANIZADEH et al., 2018	Did not specify the league evaluated	No details were given about the laser treatment, only reported that the samples were laser treated.	Titanium without laser irradiation	Bacteria evaluated: Aggregatibacter actinomycetemcomitans, Prevotella intermedia and Porphyromonas gingivalis Evaluation method: the viable bacteria of the biofilm formed on the surfaces of the discs were quantified with PMA-PCR in real time. For this purpose, the bacteria that formed the biofilm on the disc surfaces were separated from the disc surface by sonification.
YAO et al., 2020	Ti grade 2	Er,Cr:YSGG Laser Wave-length: 2780 nm Power: 1.50 W Frequency: 20 Hz Sample distance: 2 mm	Samples without laser treatment	Bacteria evaluated: Porphyromonas gingivalis Evaluation method: The maximum absorbance of bacteria was inspected by scanning with a spectrophotometer, evaluating 1, 2, 3, 4 and 5 days of incubation.
DUARTE et al., 2009	Ti grade 4	Er:Yag Laser Wave-length: 2940 nm Fluency: 8.4 J/cm2 Repetition rate: 10 Hz Pulse energy: 120 mJ	Untreated samples	Bacteria evaluated: Streptococcus sanguis Evaluation method: the number of CFU was determined in a stereomicroscope.
UHLMANN et al., 2018	Ti-6Al-4 V	LMBS “Tricolore” laser machine (did not specify laser type) Wave-length: 355 nm Pulse: 10 ps Repetition rate: 200 kHz Scan speed: 75.4 mm/s for LIPSS and 400 mm/s for the other microtextures Fluency: 0.4 J/cm2 for LIPSS an 2.2 J/cm2 for the other microtextures	Two reference titanium surfaces: abrasive blast finish and chemical polish finish	Bacteria evaluated: Streptococcus mutans Evaluation method: the measurement method to evaluate bacterial adhesion was the OD595, which measures the optical density of the specimen by photometry at the wave-length of 595 nm.
MEDVIDS et al., 2021	Ti cp	Pulsed Nd:Yag laser Wave-length: 1064 nm Pulse: 6 ns Intensity: 52.8 W/cm2 Scan speed: 1 mm/s Irradiation distance: 700; 550; and 400 µm	Non-laser irradiated surfaces	Bacteria evaluated: Staphylococcus epidermidis and Pseudomonas aeruginosa Evaluation method: To quantify bacterial colonization, the colony forming units method was used.
LUO et al., 2020	Ti cp	Femtosecond Laser Wave-length: 1030 nm Pulse width: 300 fs Diameter of focal point: 63 µm Fluency: 0.49 J/cm2 Scan speed: 300 mm/s	Non-laser-treated polished titanium surfaces	Bacteria evaluated: Escherichia coli Evaluation method: to evaluate bacterial growth, the colony forming units method was used.
FADEEVA et al, 2011	Ti cp grade 2	Ti:sapphire amplified femtosecond laser Wave-length: 800 nm Pulse: 50 fs Fluency: 100 J/cm2 Repeat rate: 1 kHz	Ti polished not laser irradiated	Bacteria evaluated: Staphylococcus aureus and Pseudomonas aeruginosa Evaluation method: Bacterial cells were evaluated by scanning electron microscopy and by a confocal laser scanning microscope. To quantify the stacks of 3D biofilm images, Comstat computer software was used.
DONAGHY et al., 2019	Ti-35Nb-7Zr-6Ta	Continuous wave fiber laser Wave-length: 1064 nm Power: 30 W Sample distance: 1.5 mm Gas used: argon gas with a flow of: 30 L/min Scan speed: 100 mm/s and 200 mm/s Laser energy at each speed: 1.8 J and 0.9 J respectively	Base metal not laser treated	Bacteria evaluated: Staphylococcus aureus Evaluation method: Stained bacteria were observed using a fluorescence microscope. The surface areas covered by the adherent bacteria were calculated using ImageJ software.

Ti- titanium; cpTi- commercially pure titanium; CFU- colony forming units; LIPSS- laser-induced periodic structures; PMA-PCR- agent propidium monoazid- polymerase chain reaction.

Of the 23 studies included in the systematic review, 13 found that laser treatment was able to reduce bacterial adhesion on titanium surface compared with untreated surfaces, (Chik et al., 2018, Costa et al., 2021, Doll et al., 2016, Donaghy et al., 2019, Du et al., 2022, Eghbali et al., 2021, Luo et al., 2020, Medvids et al., 2021, Meinshausen et al., 2021, Parmar et al., 2018, Shiju et al., 2019, Yao et al., 2020, Zwahr et al., 2019) 3 found an increase in bacterial adhesion, (Esfahanizadeh et al., 2018, Guastaldi et al., 2019, Singh et al., 2021) and 3 found no difference between treated and untreated surfaces. (Duarte et al., 2009, Grössner-Schreiber et al., 2001, Hauser-Gerspach et al., 2014) One study found that one bacterial strain adhered more to treated surfaces and another strain adhered more to polished surfaces. (Fadeeva et al., 2011) One study found that bacterial adhesion was lower on the untreated surface after 2 h, but after 4 h, bacterial adhesion was lower on the treated surfaces. (Orazi et al., 2019) Among studies comparing laser surface treatment to other surface treatments, (Drago et al., 2016, Uhlmann et al., 2018) one study found lower bacterial adhesion on laser-treated surfaces compared to sandblasted surfaces, (Drago et al., 2016) and another study found lower bacterial adhesion compared with sandblasted surfaces, but higher adhesion than on chemically polished surfaces. (Uhlmann et al., 2018) The main results of each study are shown in Table 4.

Table 4.

Main results of included studies.

First Author and Year of Publication	Main results
DRAGO et al., 2016	Biofilm formation was observed in both materials and for all strains of microorganisms evaluated. The amount of biofilm and bacterial volume were significantly lower on the laser treated discs compared to the discs that had been sandblasted. Observing a reduction in biofilm formation of 79, 36 and 42 %, respectively, for Staphylococcus aureus, Pseudomonas aeruginosa and Porphyromonas gingivalis. Bacterial volume reduced about 32, 73 and 39 % for Staphylococcus aureus, Pseudomonas aeruginosa and Porphyromonas gingivalis, respectively.
GUASTALDI et al., 2019	Laser irradiation of the surfaces statistically increased the adhesion of bacterial cells to the surface of both titanium samples evaluated, when compared to the respective controls. When comparing the Ti-15Mo samples with the cpTi samples, both laser treated, it was observed that bacterial adhesion on the Ti-15Mo alloy was statistically lower than cpTi.
CUNHA et al., 2016	Less bacterial adhesion was observed in laser-irradiated samples compared to polished samples. The average fraction of surface area covered by bacteria is 7 % for the laser treated surfaces compared to 25 % for the polished specimen. Bacterial adhesion was similar for the two types of textures produced by the laser.
PARMAR et al., 2018	It was observed that the sample treated with the laser showed lower bacterial adhesion compared to the untreated samples. It was also observed that after 72 h after incubation there was a reduction in the number of viable bacteria compared to the number of viable bacteria immediately at the time of incubation, this reduction was greater for the laser treated samples (80 %) compared to the untreated samples (20 %).
SHIJU et al., 2019	It was observed that bacterial adhesion was lower on laser-textured surfaces compared to polished surfaces.
DOLL et al, 2016	Bacterial adhesion on laser-textured surfaces was statistically lower for the surfaces evaluated compared to surfaces without laser-texturing.
EGHBALI et al., 2021	Bacterial adhesion on laser-treated surfaces was lower than on untreated surfaces. The number of viable bacteria in all samples was increased by 2-fold increasing the storage time from 3 to 6 h. For samples recorded at a constant frequency of 20 kHz, increasing the slot distance from 0.5 to 50 μm leads to a reduction in the number of viable bacteria on the surface. For samples recorded with a fixed slot distance of 4 µm and varying the laser frequency, the number of viable bacteria in all samples tripled, increasing the storage time from 3 to 6 h.
ORAZI et al., 2019	After 2 h the polished surface without laser irradiation showed no bacterial adhesion while the laser irradiated surfaces did. However, after 4 h, bacterial adhesion of non-irradiated surfaces was greater than that of laser-irradiated surfaces, and samples treated with pulse energy of 16 µJ were the ones that showed the lowest bacterial adhesion.
CHIK et al., 2018	The adhesion of Staphylococcus aureus in titanium was almost 7 times greater than the adhesion of Escherichia coli. Bacterial adhesion to stainless steel was higher for Staphylococcus aureus and smaller for Escherichia coli compared to titanium surface. When comparing the bacterial adhesion of the laser-treated and untreated titanium surface, greater bacterial adhesion to the untreated laser surface was observed for both bacterial strains evaluated. When comparing the two laser-treated titanium surfaces, bacterial adhesion of Staphylococcus aureus was higher than that of Escherichia coli.
SINGH et al., 2021	Bacterial adhesion was higher on laser-textured surfaces (60 % average surface coverage) compared to those that were not surface treated (35 % average surface coverage).
MEINSHAUSEN et al., 2021	There was a significant reduction in bacterial adhesion in the laser treated samples compared to the control sample. Among the different fluences used, the one that showed the lowest bacterial adhesion was 0.06 J/cm−2 with a spatial period of 0.7 µm, however there was no statistical difference in bacterial adhesion of the different groups that underwent laser treatment.
ZWAHR et al., 2019	Bacterial adhesion after 24 h of colonization of laser treated surfaces was reduced by 30 % compared to untreated samples.
(GRÖSSNER-SCHREIBER et al., 2001)	After 1 h of incubation, there was no statistically significant difference for bacterial adhesion of both bacteria evaluated between the laser-treated and polished surfaces.
HAUSER-GERSPACH et al., 2014	Laser irradiation did not affect bacterial adhesion compared to polished discs, with no difference between the amount of bacteria adhered between the two groups.
DU et al., 2022	There was a large reduction in bacterial adhesion on laser-treated surfaces compared to polished surfaces. On the polished surface, the adhesion rate of Staphylococcus aureus was 33.2 ± 4.9 % and the adhesion rate of Escherichia coli was 23.1 ± 6.1 %. On the LIPSS surface, the adhesion rate of Staphylococcus aureus was 2.8 ± 1.4 % and that of Escherichia coli the adhesion rate was 2.1 ± 1.2 %.
ESFAHANIZADEH et al., 2018	In the evaluation, the bacterial count on the laser-treated surface was statistically higher than in the group without irradiation. The mean Aggregatibacter actinomycetemcomitans was 11.3163 (0.0869) and 9.6941 (0.1658) log CFU/mL in the laser and titanium groups, respectively. The mean count of Prevotella intermedia was 11.3437 (0.1972) and 10.0831 (0.2245) log CFU/mL and the mean count of Porphyromonas gingivalis was 12.1176 (0.1972) and 10.1213 (0.1843) log CFU/mL. The overall mean bacterial count was 11.59 (0.42) and 9.97 (0.27) log CFU/mL in the laser and titanium groups, respectively.
YAO et al., 2020	Bacterial adhesion was slightly lower for laser treated samples compared to untreated samples, being statistically significant on days 1, 3 and 5.
DUARTE et al., 2009	There was no statistically significant difference between the adhesion of laser-treated and untreated surfaces.
UHLMANN et al., 2018	Bacterial adhesion on laser treated surfaces was lower than adhesion on control surface with abrasive blast finish, but was greater than bacterial adhesion on control surface with chemical polish finish. Among the different micro-textures evaluated, the micro-channel ones showed greater bacterial adhesion compared to the other three micro-textures.
MEDVIDS et al., 2021	There was a great decrease in bacterial colonization on the surface of the laser-irradiated samples compared to the non-irradiated samples for both bacteria evaluated. The colonization of Staphylococcus epidermidis was greater than that of Pseudomonas aeruginosa on non-irradiated surfaces, after laser irradiation, bacterial colonization was similar for both surfaces.
LUO et al., 2020	Surface treatment by laser irradiation promoted antibacterial properties and less bacterial colonization on titanium surfaces compared to untreated samples.
FADEEVA et al, 2011	When evaluating the bacterial adhesion of Staphylococcus aureus, it was observed that the number of bacteria adhered was higher for the laser treated surface compared to the polished surfaces. On the other hand, when evaluating the microorganism Pseudomonas aeruginosa, the number of adhered bacteria was lower for the laser-treated surfaces compared to the polished surfaces.
DONAGHY et al., 2019	The images obtained using fluorescence microscopy showed a noticeably greater number of live bacteria on the untreated surface compared to the treated surfaces. Evaluation of bacterial adhesion showed statistically lower bacterial coverage on the laser treated titanium surface compared to the untreated surface which had bacterial adhesion 4 times greater than the treated surface.

Ti- titanium; cpTi- commercially pure titanium; LIPSS- laser-induced periodic structures; CFU- colony forming units.

All articles had a low risk of bias for items 1 and 7 of the JBI checklist. For items 2, 3, 4, and 5, 75 to 100 % of the articles had a low risk of bias. As for items 5 and 9, 50 % to 75 had a low risk of bias. The low percentage regarding item 5 was due to many articles not performing or not reporting multiple measurements and for item 9, many articles did not perform statistical analysis. Item 8 was marked as not applicable because it assesses evaluators reliability in the measurement and the articles considered did not have evaluators and most were evaluated using software (Fig. 1).

4. Discussion

The quantity and quality of bacterial adhesion on the surface of the implant are crucial in the development of peri-implant inflammatory processes, so several surface treatments are proposed with the aim of reducing the primary adhesion of bacterial cells and the formation of biofilm.(Al-Radha et al., 2012, Komorowski et al., 2020, Meinshausen et al., 2021, Nunes Filho et al., 2018) Most of the studies included in this review observed reduced adhesion of bacteria to laser-treated titanium surfaces than to non-treated surfaces, supporting the initial hypothesis of the study. (Chik et al., 2018, Costa et al., 2021, Doll et al., 2016, Donaghy et al., 2019, Du et al., 2022, Eghbali et al., 2021, Luo et al., 2020, Medvids et al., 2021, Meinshausen et al., 2021, Parmar et al., 2018, Shiju et al., 2019, Yao et al., 2020, Zwahr et al., 2019) This review article provided information on the properties of titanium surface modified by laser irradiation and the resulting decreased adhesion of bacteria.

Changes in roughness, surface free energy, chemical composition, and nanostructure formation have a direct effect on bacterial adhesion to the titanium surface, so appropriate modification of these properties is promising for increasing implant survival.(Costa et al., 2021, Drago et al., 2016, Jeong et al., 2017, Komorowski et al., 2020, Lorenzetti et al., 2015, Luo et al., 2020, Meinshausen et al., 2021, Nunes Filho et al., 2018) In this review, the antibacterial effect observed by most authors is due to the changes that laser treatment cause to the surface properties of the implant, making the environment inhospitable to bacteria by impairing or making impossible their adhesion and colonization. (Donaghy et al., 2019, Eghbali et al., 2021).

The alteration of topography by laser irradiation, resulting from the formation of various micro- and nano-surface textures, may influence bacterial colonization by selectively controlling adhesion, which appears to be one of the factors with the greatest influence on bacterial fixation. The surface pattern will determine the contact area and the adhesion force between the bacteria and the surface, these patterns can vary in several ways, such as the width of the nanoripple line, microgrooves or the diameter of the formed nanostructures (Costa et al., 2021, Fadeeva et al., 2011, Luo et al., 2020, Meinshausen et al., 2021, Yang et al., 2022).

In addition, the change in roughness promoted by laser treatment can also influence bacterial adhesion, with greater bacterial adhesion being observed on rough surfaces with cavities that are larger than bacteria. This happens because if these cavities are smaller than the size of the bacterial cells, the contact area available for their fixation is reduced, while in cavities larger than their size they can achieve greater adhesion strength due to the greater contact area available (Cunha et al., 2016, Lutey et al., 2018, Papa et al., 2022, Singh et al., 2021) There are also some studies that suggest that surfaces with low roughness with Ra in the nanometric range (less than 30 nm) and very high (more than 1–2 µm) are more conducive to bacterial adhesion than intermediate roughness. (Cunha et al., 2016, Linklater et al., 2021, Truong et al., 2012).

Thus, it is essential to understand how specific degrees of roughness, together with other properties, affect the adhesion of bacteria to surfaces, and it is important to consider a set of topographic standards such as average surface roughness, maximum height, cap width and skewness. (Al-Radha et al., 2012, Cunha et al., 2016, Linklater et al., 2021, Meinshausen et al., 2021, Singh et al., 2021) In addition to the size of the microcavities influencing the fixation of the bacteria, it is also possible with the laser treatment to create a surface pattern with bactericidal characteristics by producing a mechanism that breaks the membrane of the bacteria, inactivating them by contact, thus both the density, space period and depth in the micro and nanotextures influence this capacity. (Linklater et al., 2021, Papa et al., 2022) It has already been reported that nanopillar radius, when smaller than 5 nm, confer poor properties for effective adhesion to the surface. (Linklater et al., 2021).

In the case of surface free energy, the increase in hydrophilicity provided by irradiation of the titanium surface can promote the reduction of bacterial adhesion. There are so many works reporting that bacteria adhere more easily to hydrophobic surfaces, as well as to hydrophilic surfaces, and this interaction may also be influenced by the species of bacteria evaluated. (Esfahanizadeh et al., 2018, Jeong et al., 2017, Komorowski et al., 2020, Lorenzetti et al., 2015, Singh et al., 2021) This demonstrates that surface wettability, despite influencing it, is not determinant in bacterial adhesion, and the effect of other properties has a greater influence on bacterial adhesion. (Esfahanizadeh et al., 2018, Lutey et al., 2018, Singh et al., 2021, Yang et al., 2022) In addition, the laser also has an effect on the chemical composition of the surface, being able to make the surface oxide layer thicker, (Isadora Gazott Simões et al., 2021) This can directly influence bacterial adhesion on the surface, since the increase in thickness together with the anatase present, acts as a load barrier causing a decrease in bacterial adhesion on surfaces treated with laser. (Cunha et al., 2016, Singh et al., 2021).

In general, the results suggest that laser irradiation can decrease bacterial adhesion on the titanium surface, but this is directly related to the type of laser, different lasers produce different responses as they may have greater or lesser affinity to the treated surface, thus as the selected irradiation parameters also have a direct influence on the surface modification produced.(Simões et al., 2021) This explains why some studies included in this review found an increase in bacterial adhesion on the laser-treated surface (Esfahanizadeh et al., 2018, Guastaldi et al., 2019, Singh et al., 2021) or even no effect on adhesion. (Duarte et al., 2009, Grössner-Schreiber et al., 2001, Hauser-Gerspach et al., 2014) In these cases, the changes in some surface properties probably did not favor bacterial protection.

In studies in which greater adhesion of bacteria to the irradiated surface was observed, (Esfahanizadeh et al., 2018, Guastaldi et al., 2019, Singh et al., 2021) the increase in roughness may have had an effect because the grooves produced were larger than the size of the bacteria studied. The decrease in surface free energy (Esfahanizadeh et al., 2018) and, in the case of Guastaldi et al., 2019, the increase in surface wettability may also have had an effect because the bacterial species studied (methicillin-resistant Staphylococcus aureus) has a greateraffinity for hydrophilic surfaces. (Guastaldi et al., 2019).

As mentioned earlier, the species of bacteria studied is another factor that affects the results. Different species react differently depending on surface roughness and wettability. (Costa et al., 2021, Fadeeva et al., 2011, Guastaldi et al., 2019, Luo et al., 2020, Lutey et al., 2018) Fadeeva et al., 2011 observed contrasting results regarding adhesion on laser-treated surfaces when studying two different bacterial strains and found that the treatment decreased adhesion of Pseudomonas aeruginosa but not Staphylococcus aureus. Drago et al., 2016 also observed that Staphylococcus aureus formed more biofilm than Pseudomonas aeruginosa and Porphyromonas gingivalis on laser-treated surfaces. Since Pseudomonas aeruginosa has the shape of rods, this species was not able to colonize the entire surface, whereas Staphylococcus aureus requires less contact for its colonization due to its spherical shape and adheres more easily to the hemispherical porosities of the titanium surface. (Drago et al., 2016, Fadeeva et al., 2011).

Some studies also compared laser with other surface treatments (Drago et al., 2016, Uhlmann et al., 2018) and observed lower bacterial adherence on the laser-treated surface compared with surfaces that were sandblasted. Uhlmann et al., 2018 found that the laser-treated surface promoted less bacterial adhesion compared to the sandblasted surface, but exhibited greater adhesion compared to the chemically polished surface. The comparison between surface treatments may help determine the most efficient treatments for titanium implants.

Although it was observed that the laser frequency influenced the antibacterial properties of the surface, this is related to the effect that the modification of this parameter has on the micro topography of the surface, since by varying it it is possible to obtain greater or lesser roughness as well as different distances between grooves. (Eghbali et al., 2021) Likewise, other parameters such as wavelength, intensity, beam area and energy density also have a direct influence on the microstructure of the irradiated area. (Simões et al., 2021) However, it is still not possible to define the ideal parameters for each type of laser, requiring further studies to evaluate specific parameters on surface modification as well as the interactions of the bacteria of interest with these surfaces.

The studies included in this systematic review have shown that laser surface treatment has the ability to affect bacterial adhesion on titanium implants. However, this potential is directly related to the ability of the laser to alter surface properties. Although most articles found that the laser reduced bacterial adhesion, some articles found no change or an increase in adhesion. This suggests that there's a need to investigate and determine what types of lasers and what parameters are best suited to promote this surface change and reduce bacterial adhesion to the titanium surface.

5. Conclusions

Based on the results of this systematic review, the following conclusions could be drawn:

• •Laser surface treatment can affect the adhesion of bacteria to the surface of titanium implants, depending on the selected irradiation parameters.
• •The adhesion of bacteria to the surface is directly related to the change in surface properties of topography, roughness, wettability, and chemical composition caused by the laser, and thus to the irradiation parameters used.
• •Different bacterial species react differently to the generated nanotexture and surface properties resulting from laser treatment.

Funding

This work was supported by FAPESP - Foundation for Research Support of the State of São Paulo [Grant No 2019/09213-3 and 2021/11843–5], that funded the research from which the question investigated in this systematic review originated.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.