Metal ion release of titanium and titanium alloy dental implants with dissimilar abutment materials: A systematic review of in vitro studies

Abstract

The emerging concept of tribocorrosion including metal ion release and wear at the implant–abutment interface remains a challenge. This systematic review aims to investigate the differences in metal ion release at implant abutment interface when titanium/titanium alloy implants are coupled with dissimilar abutment materials as compared to titanium/titanium alloy abutments. A comprehensive search relevant to the predefined key terms was conducted across five databases (PubMed, Scopus, Web of Science, Embase, and Google Scholar) up to March, 2024 using the PECO framework. Inclusion criteria focused on in vitro studies on metal ion release at the implant–abutment interface. The eligibility and risk of bias of study was assessed using the QUIN tool. The data were extracted and based on the observed heterogeneity; only qualitative synthesis was performed. A total of 17 studies (477 specimens) were included for data analysis. The findings revealed significant variations in ion release depending on material combinations. Titanium implants paired with dissimilar abutment materials showed increased ion release over time, especially from days 43 to 84 as compared to Ti/Ti alloy abutment. Greater wear was also observed with dissimilar materials as compared to similar abutment material. Within the limitations of the analysis, metal ion release was substantially variable for Ti/Ti alloy abutments compared to other metal abutment materials coupled with Ti/Ti alloy implant and was found to be increased over time. Further clinical studies are needed to standardize metal ion detection and wear measurement methods and extend implant longevity.

INTRODUCTION

Dental implants have become a cornerstone of modern dentistry, offering patients a durable and functional solution for the replacement of missing teeth. Pioneering work by researchers such as Dr. Per-Ingvar Brånemark in the 1950s laid the foundation for the development of osseointegrated implants, which form a direct bond with the bone, ensuring stability and functionality. Since their introduction in the 1960s, dental implants have revolutionized oral rehabilitation and aesthetic dentistry.[1]

Central to the success of dental implants is the implant-abutment system. Abutments are intermediary components that connect the implant fixture to the prosthetic restoration, such as a crown, bridge, or denture. The implant fixture and abutments form a comprehensive implant system that mimics the structure and function of natural teeth or other biological structures within the body.[2,3,4,5]

The most commonly used materials for dental implants and abutment are commercially pure titanium (cpTi) grade IV and Titanium alloy. These materials are favoured for their biocompatibility in the oral environment, high resistance to chemical degradation, and mechanical properties well-suited for implant dentistry.[2,6,7] Titanium implants exhibit an inherent capability to spontaneously form a nanometric oxide layer on their surface upon exposure to atmospheric oxygen. This oxide layer functions as a corrosion-resistant and protective barrier, conferring passivity to the titanium implants within biological environments and furthermore, this oxide layer facilitates osseointegration. Despite the superiority of titanium-based implants, researchers have explored alternative materials for implant abutments to address specific clinical needs and patient preferences. Materials such as Zirconia, stainless steel, and various ceramics have been investigated for their potential in implant dentistry, each offering distinct advantages in terms of aesthetics, strength, and wear resistance.[8,9,10]

The dynamic oral environment subjects implants and their components to repeated mechanical stresses and exposure to corrosive agents, leading to material degradation and surface alterations. Tribocorrosion is defined as the degradation of materials resulting from the combined effects of mechanical wear and electrochemical reactions. Occlusal forces, oral fluids, and bacterial biofilm accelerate tribocorrosive processes at the implant-abutment interface. The complex oral environment, influenced by microbiome, pH levels, saliva composition, dietary habits, and oral hygiene, plays a crucial role in implant corrosion, necessitating comprehensive management of oral health in implant patients. This phenomenon not only compromises the mechanical stability of implants but also increases the risk of peri-implant diseases.[2,3,7,10,11,12,13,14,15]

Metal ion release at the implant-abutment interface is a consequence of tribocorrosion, with potential implications for systemic health and biocompatibility. High concentrations of metal ions have been shown to impair cellular viability, proliferation, and differentiation, ultimately compromising tissue regeneration and osseointegration around dental implants. The composition and surface characteristics of the implant materials, as well as the design of the implant-abutment interface, can impact corrosion susceptibility and ion release kinetics. While titanium and its alloys are known for their low toxicity, the release of metal ions into the oral cavity can influence local and systemic immune responses. Similarly, exposure to acidic or alkaline conditions, as well as the presence of saliva or peri-implant fluids, can alter the corrosion behavior of implant materials. Metal ions such as titanium, aluminium, vanadium, and nickel have been detected in peri-implant tissues and fluids, raising questions about their biocompatibility and inflammatory potential. While low levels of metal ion release may not elicit significant adverse reactions in most individuals, certain patient populations, such as those with metal allergies or compromised immune systems, may be more susceptible to adverse effects. Despite these concerns, limited research has specifically investigated metal ion release at the implant-abutment interface, highlighting the need for further investigation. The release of metal ions from dental implants has raised concerns regarding their potential adverse effects on peri-implant tissues, systemic health, and the overall longevity of implant restorations.[2,3,4,7,10,15,16,17,18,19]

In recent years, there has been growing interest in understanding the mechanisms underlying metal ion release from dental implants and its clinical implications. However, there remains a need for comprehensive synthesis and analysis of the existing literature to provide clinicians and researchers with a deeper understanding of this complex phenomenon.

Therefore, the aim of the present systematic review:

“Is there any difference in metal ion release of titanium or titanium alloys implants (Ti/TiaI) using dissimilar abutments material (DAM) as compared to titanium or titanium alloy abutments (Ti/TiaA)?”

MATERIALS AND METHODS

Study design

This systematic review was registered on the Open Science Framework (OSF) platform with registration no. of, osf.io/263ud and was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. An electronic search was performed across several databases, including PubMed, Scopus, Web of Science, and Embase, to collect all relevant literature pertaining to the research question. In addition, Google Scholar was used to search for gray literature to ensure comprehensive coverage of studies not indexed in the primary databases. The PECO ((Participants/Specimen; Exposure; Comparison; Outcome) framework, was employed to guide the search strategy which was as follows:

P: Participants/Specimen – titanium or titanium alloy dental implants

E: Exposure – dissimilar abutment materials

C: Comparator – titanium or titanium alloy abutments

O: Outcome – primary outcome - metal ion release at implant–abutment interface and secondary outcome - wear at implant–abutment interface.

Information sources and search strategy

The search strategy was developed with careful consideration of the study’s title and research question. Relevant keywords and MeSH terms were identified and combined to create the most effective search approach. Additionally, a manual search was also performed to ensure that no pertinent data related to the research question was overlooked [Table 1].

Table 1.

Search strategy

Database	Search stratergy	Search result
PubMed	(Titanium) OR (Titanium alloy) OR (Dental alloy) OR (yttria stabilized tetragonal Zirconia) AND (Dental Implants) AND (Dental Abutments) AND (Dental Implant-Abutment Design) AND (Corrosion) NOT (Caustic) ((“titanium”[MeSH Terms] OR “titanium”[All Fields] OR “titaniums”[All Fields] OR ((“titanium”[MeSH Terms] OR “titanium”[All Fields] OR “titaniums”[All Fields]) AND (“alloy s”[All Fields] OR “alloyed”[All Fields] OR “alloying”[All Fields] OR “alloys”[MeSH Terms] OR “alloys”[All Fields] OR “alloy”[All Fields])) OR (“dental alloys”[MeSH Terms] OR (“dental”[All Fields] AND “alloys”[All Fields]) OR “dental alloys”[All Fields] OR (“dental”[All Fields] AND “alloy”[All Fields]) OR “dental alloy”[All Fields]) OR (“yttria stabilized tetragonal zirconia”[Supplementary Concept] OR “yttria stabilized tetragonal zirconia”[All Fields])) AND (“dental implants”[MeSH Terms] OR (“dental”[All Fields] AND “implants”[All Fields]) OR “dental implants”[All Fields]) AND (“dental abutments”[MeSH Terms] OR (“dental”[All Fields] AND “abutments”[All Fields]) OR “dental abutments”[All Fields]) AND (“dental implant abutment design”[MeSH Terms] OR (“dental”[All Fields] AND “implant abutment”[All Fields] AND “design”[All Fields]) OR “dental implant abutment design”[All Fields] OR (“dental”[All Fields] AND “implant”[All Fields] AND “abutment”[All Fields] AND “design”[All Fields]) OR “dental implant abutment design”[All Fields]) AND (“caustics”[Pharmacological Action] OR “caustics”[MeSH Terms] OR “caustics”[All Fields] OR “corrosive”[All Fields] OR “corrosives”[All Fields] OR “corrosion”[MeSH Terms] OR “corrosion”[All Fields] OR “corrosions”[All Fields] OR “corrosiveness”[All Fields] OR “corrosivity”[All Fields])) NOT (“causticity”[All Fields] OR “caustics”[Pharmacological Action] OR “caustics”[MeSH Terms] OR “caustics”[All Fields] OR “caustic”[All Fields])	16
Web of Sciences	((((((ALL=(Titanium)) OR ALL=(Titanium alloy)) AND ALL=(Dental implant)) AND ALL=(Dental abutments)) AND ALL=(Dental implant abutment design)) AND ALL=(corrosion)) NOT ALL=(caustic)	11
Scopus	TITLE-ABS-KEY (titanium) OR TITLE-ABS-KEY (titanium AND alloy ) OR TITLE-ABS-KEY (dental AND alloy) OR TITLE-ABS-KEY (yttria AND stabilized AND tetragonal AND zirconia ) AND TITLE-ABS-KEY (dental AND implants) AND TITLE-ABS-KEY (dental AND abutments) AND TITLE-ABS-KEY (dental AND implant-abutment AND design ) AND TITLE-ABS-KEY (corrosion) AND NOT TITLE-ABS-KEY (caustic) OR TITLE-ABS-KEY (metal AND ion AND release) )	17

Eligibility criteria

This systematic review included in vitro and laboratory experimental studies that investigated metal ion release and wear at the implant–abutment interface, comparing various abutment materials to titanium and titanium alloy abutments. The literature search was conducted till March 2024. Inclusion criteria encompassed eligible studies evaluating metal ion release at the implant-abutment interface, specifically in vitro and laboratory studies. Exclusion criteria comprised animal studies, studies with insufficient data, studies published in languages other than English, and studies not directly related to the main topic.

Selection of studies

Three reviewers MM, VG and SS independently extracted information from each included article to minimize the risk of missing relevant literature and disagreements were clarified and resolved by the intervention of a fourth author AJ. Retrieved articles were imported into Endnote version 21, where duplicate articles were removed. The remaining articles underwent title and abstract screening. Subsequently, full-text articles were assessed for eligibility, and those not meeting the predefined inclusion criteria were excluded. The articles that met the criteria were used for qualitative synthesis of the data. The PRISMA flow diagram is illustrated in Figure 1.

Figure 1.

Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart illustrating selection process (n – number of articles)

Risk of bias analysis

The risk of bias for each selected study was independently assessed by two reviewers, with interexaminer agreement calculated using Cohen’s kappa (κ). The Quality Assessment Tool for In Vitro Studies (QUIN) was employed, comprising 12 criteria to evaluate the quality of reporting in each study. Each criterion was scored 2 points for adequately reported, 1 point for inadequately reported or 0 points for not specified; additionally, criteria could be marked as not applicable and excluded from the calculation. According to the author’s formula, studies scoring above 70% were categorized as low risk of bias, those scoring between 50% and 70% as medium risk, and those scoring below 50% as high risk of bias.[20,21]

Data extraction and data synthesis

A comprehensive review of all eligible articles was conducted, and the extracted data was organized under the following headings: author and year, study type, number of implant–abutment interfaces (n), fixture group, abutment group, medium in which metal ion release was detected, primary and secondary outcomes of metal ion release, surface wear, method of detection, and results, as presented in Table 2. The data were evaluated for both qualitative and quantitative synthesis; however, due to the heterogeneity in the collected data, the meta-analysis could not be conducted.

Table 2.

Study characteristics of all included studies

Author and year	N	Specimen(S) Fixture group	Test group Exposure(E) Abutment group	Control Group Comparator(C) Abutment group	Medium	Follow up	Method of detection	Result, Outcome(O)
Barros et al., 2021[3]	8	CpTi Ti6Al4V	NiCr	-	Fusayama Artificial Saliva pH 6 and 3	30 min before, 60 min during and 30 min after sliding	Confocal Microscope SEM images	Wear rate higher for cp-Ti compared to Ti6Al4V and NiCr Tracks aligned with sliding direction and Areas of plastic deformation
Silva et al., 2021[4]	48	Ti	(Au+Pt+Pd) cast Cast + Au fitting surface Au + Au fitting surface	-	1% Lactic acid	3, 5, and 12 months	ICP-MS (ppm) SEM/EDX Analysis	Ion release max when cast and Au fitting surface and Ti implant and min for (Au+Pt+Pd) cast abutment and Ti implant Black spots and scratch-like marks Most Ti particles located near the hex of the implants
Son et al., 2004[5]	3	Gold alloy	Gold/plastic coping Gold coping	-	Modified Fusayama artificial saliva	Before Casting 24 h after casting	SEM	Gold coping showed a greater extent of crevice corrosion and was observed to be concentrated at the interface between the coping and the suprastructure
Berbel et al., 2022[6]	6	Ti6Al4V	Stainless steel 316L	-	Phosphate buffer solution	24 h Observations after 1, 4, and 7 days.	SEM-EDS	SEM images show pits on the 3 and 5 strikes samples after 24 h SEM images after 7 days show fewer pits on 7 strikes sample
Pascale Corne et al., 2019[7]	8	Cp Ti4 Ti6Al4V	Y-TZP	Cp Ti4 Ti6Al4V	Rest saliva	16 h	TEM	A lamella from TEM microtome showing dislocations and damaged microstructure Ti/Y-TZP showed less microstructure modification than Ti-6Al-4V/Ti-6Al-4V
Arregui et al., 2021[8]	10	Type4 CpTi n=4 14 mm ×4 mm ×2.2 mm	Cr-Co n=4	Ti6Al4V n=2	Hanks’ solution 1% Lactic acid	1, 7, 14, and 21 days	ICP-EOS(ppm) Stereomicroscope	All groups showed increased ion release after 21 days, with lactic acid groups showing the highest increase Material transfer observed in groups with crown directly screwed to the implant (CrCo/cpTi), but not in groups with intermediate abutments (CoCr +Ti6Al4V /cpTi)
Lee et al., 2015[9]	30	Cp Ti n=15	NiCrBe n=5 NiCr n=5 Ni-highCr n=5	-	Dulbecco’s culture media 37 degree celsius	48 h	ICP-MS (ppm)	The amount of metal ions released was increased by galvanic corrosion in all of the groups in which Ni-Cr alloys were in contact with Ti
Sikora et al., 2018[10]	24	Ti n=6 Rox(TiZr) n=6	Zr n=6	Ti n=6	Artificial saliva at 37 degree c		SEM/EDX 3000×	Ti/Ti group showed rows of light grooving. Zr/Rox group, crack in the surface In Ti/Rox group, vanadium was detected on the Rox disc, showing the transfer of particles.
Stimmelmayr et al., 2012[11]	12	Ti n=6 3.8/13 mm	Zr n=3	Ti n=3	-	-	SEM CT	Zirconia Abutment: More wear and damage observed on the implant interface Scratches and undercuts vertical to the groove Coiled furrows on the implant shoulder and cam-groove due to micro-rotational movement
Taher and Al Jabab, 2003[12]	48	Ti n=24	CoCr n=6 NiCr n=3 AgPd n=3 Au n=3 Amalgam n=3	Ti n=3 Ti n=3	Modified artificial saliva	24 h	Corrosion Cell	Au/Ti= excellent couple AgPd/Ti=acceptable galvanic corrosion behavior. Co-Cr/Ti=good galvanic corrosion behavior CoCr (R2000)/Ti=least acceptable Ni–Cr/Ti = unstable galvanic corrosion Amalgam alloy/Ti=higher galvanic interaction Commercially pure Ti Grade 1 (SSTi) /Ti = unexpected galvanic corrosion behavior
Mehkri et al., 2021[13]	6	Ti6Al4V n=3	Yttria-stabilized zirconia YSZ n=1 Zirconia toughened Alumina ZTA n=1	Ti6Al4V=1	Artificial saliva	3600 s	Wear loss Wear Coefficient	ZTA | Ti6Al4V had lowest wear volume loss and lowest wear coefficient The YSZ | Ti6Al4V had the highest wear volume loss and wear coefficient
Queiroz et al., 2020[14]	80	Ti n=40 3.75 mm×13 mm	Zr n=10 (Neodent) Zr n=10 (Zirkozahn)	NiCrTi CoCr (pre machined) n=10 NiCrTi n=10	-		SEM	Zirconia abutments resulted in significantly more wear on implants and increased misfit on the abutment-implant interface than metal abutments Regardless of abutment materials, different degrees of misfit and wear on the external hexagon evident on all the implant specimens
Olander et al., 2022[15]	24	Ti n=6 TiZr n=6	Zr n=6	Ti n=6	Lactic acid 37°C	7 days	ICP-OES (ppm) SEM/EDS	low Ti or Zr ion release (< 0.1 mg/L) Wear at abutment base, inside the implant connecting surface, and on top of the implant head. No difference in surface wear between the different material couplings. Larger particles typically being composed of Ti and smaller particles composed of Zr, with varying particle morphologies/shapes
Niedermeier et al., 2020[16]	5	Grade 4 Ti	Au CoCrMo CoCrMo and Au	Ti	Lactic acid	1, 2–4, 5–7, 36–38 days	ICP-MS Surface discoloration	Total and Ti ion release was highest on day 1 diminishing thereby. Titanium surfaces showed an insignificant grey-yellowish and matte tan hue. Fine gold samples exhibited a brown-grey-violet discoloration which could be easily removed by acidification
Yamazoe 2010[17]	74	FTi n=27 FTi2 n=5 F64 n=6 17 mm×4 mm	PFM alloy n=12 Gold alloy n=12 Ag-Pd-Cu-Au alloy n=4 Silver alloy n=4 4.8 × 6 mm	Ti n=3 Ti6Al4V n=1	1% lactic acid 37°C	3 months	ICP-AES Scanning confocal laser microscope	The Ti release level was significantly lower in cement-fixed titanium/titanium and titanium/dental alloy combinations than in those directly fixed Regarding the combination with titanium alloy, the Ti and V release levels were higher when titanium alloy was used in combination with titanium than with titanium alloy and dental alloy Smaller grain sizes observed in the titanium alloy compared to titanium. Twinning was observed in all titanium samples
Kassapidou et al., 2020[18]	72	CpTi4 n=36	Co-Cr manufactured by 4 techniques 34 mm × 13 mm × 1.5 mm n=30	Ti6Al4V n=6	Artificial saliva 37°C n=114	1, 4, 7, 14, 21 days	ICP-MS	all tested materials (the controls included) had a lower total ion release 0.08−0.4(µg/cm2) and showed gradually reduced ion release over time with the highest decrease of 0.3(µg/cm2) for Zz
Tuna et al., 2009[19]	16	Ti Swiss Plus implant fixtures 10 mm ×4.1 mm ×4.8mm (n=8)	Co-Ni n=2 Co-Cr n=2 Pd n=2 Au n=2 UCLA type 6.5 mm ×4.8 mm (n=4)	-	Afnor type Artificial saliva at 37degree C	-	ICP-MS SEM Images	Co-Cr abutment when coupled with Titanium had max total ion release of 2.01 ppm and min of 0.002ppm when coupled with Au based abutment More structural breakdown for Co-Ni and Co-Cr

CpTi or Cp Ti4 – Commercially Pure Titanium Grade 4; Ti6Al4V – Titanium 6 Aluminum 4 Vanadium; NiCr – Nickel Chromium; SEM – Scanning Electron Microscopy; cp-Ti/ NiCr – Abutment/Implant; ICP-MS – Inductive Couple Plasma Mass Spectroscopy; SEM/EDX – energy-dispersive X-ray spectroscopy; ppm – Parts per million; Au – Aurum/Gold; Pt – Platinum; Pd – Palladium; N – Number of specimens; mV – milliVolt; C/cm² – Coulomb/centimeter square; µm – micrometer; OCP – Open Circuit Potential; SVET – Scanning vibrating electrode technique; SEM-EDS – Scanning electron microscopy and energy dispersive spectroscopy ; hrs – hours; Y-TZP – Yttria-Tetragonal Zirconia Phase (Y-TZP); Cr-Co – Chromium Cobalt; ICP-EOS – inductively coupled plasma mass spectrometry; NiCrBe – Nickel Chromium Beryllium; NiCr – Nickel Chromium; Ni-highCr – Nickel high Chromium; ICP-MS – inductively coupled plasma mass spectrometer; Rox – Roxolid TitaniumZirconia; EDX – Energy Dispersive X-ray Spectroscopy; CT – 3D-Computer Tomography; NiCr – NickelChromium; AgPd – SilverPalladium; ZTA – Zirconia toughened Alumina; YSZ – Yttria-stabilized zirconia ; NiCrTi – Nickel Chromium Titanium; ICP-OES – Inductively coupled plasma atomic emission spectroscopy; TEM – Transmission electron microscopy

RESULTS

A total of 44 studies were identified through electronic database search (PubMed: 16, Scopus: 17, Web of Science: 11), and 29 studies through manual searching. After removing 4 duplicate articles, 69 articles were screened, and 46 articles were excluded based on title and abstract screening. Of the 23 full-text articles assessed for eligibility, six were excluded as they were not found relevant to research questions and 17 articles were included for data synthesis. Due to heterogeneity in terms of different media used, methods of metal ion detection and wear detection, duration of metal ion and wear detection, quantitative synthesis could not be performed, and thus only qualitative results were summarized. The PRISMA flow diagram is illustrated in Figure 1.

A total of 477 specimens were used, of which 212 were implants, 71 were abutments made up of Ti or Ti alloy and 164 were abutments made up of different material. Of these, 182 cpTi, 14 Titanium 6 Aluminium 4 Vanadium (Ti6Al4V), four Nickel Chromium (NiCr),12 Roxolid Titanium Zirconia (TiZr) were implant materials and 47 cpTi, 14 Ti6Al4V, ten NiCr abutments were made of Ti or Ti alloy. For abutment made up of different material 45 gold alloy, 18 Yttria-Tetragonal Zirconia Phase (Y-TZP), three stainless steel 316L specimens,42 Chromium Cobalt (CrCo) abutment materials, five Nickel Chromium Beryllium (NiCrBe) abutments, five Ni-HighCr abutments, seven Silver Palladium (AgPd) abutment materials, three amalgam abutments, three ternary titanium abutment materials, one Zirconia-toughened alumina (ZTA) abutment, ten Zirconia (Neodent), ten Zirconia (Zirkonzahn), ten completely cast NiCrTi, ten overcast NiCrTi, one Cobalt Chromium Molybdenum (CoCrMo), one Cobalt Chromium Molybdenum Gold (CoCrMoAu), 12 Porcelain-fused-to-metal (PFM), four Silver Palladium Copper Gold (Ag-Pd-Cu-Au), two Cobalt Nickel (CoNi) , and two Palladium (Pd) were abutment materials.[3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] In all studies, abutments were screw retained except in one study where both screw and cement retained abutments were used.[3,18]

Of the 17 studies, seven used artificial saliva, 6 lactic acid, one used phosphate buffer solution, one Dubelcco’s culture media, one Hank’s balanced salt solution, one saliva as medium for detection, 2 studies did not specify a medium of measurement.[3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]

In studies quantity of metal ion release at implant abutment interface was recorded in terms of Ti ion release (Tir) and Total ion release (Toir), when Titanium or Titanium alloy implants were coupled with Titanium or Titanium alloy abutment Group A (Ti/TiaI-Ti/TiaA) and Titanium or Titanium alloy implants were coupled with different abutment materials Group B (Ti/TiaI-DAM). On data compilation variations were found in terms of method of detection, intervals of detection, units of values and distribution of metal ions. A total of 5 studies used Inductive Coupled Plasma Mass Spectrometry (ICP-MS) for metal ion release calculation, 2 used inductively coupled plasma mass spectrometry (ICP-EOS) and one used Inductively coupled plasma atomic emission spectroscopy (ICP-AES).[4,8,9,15,16,17,18,19] In all studies, the data were normally distributed except in one in which the data were presented in the form of median and interquartile ranges (Median[IQ1-IQ3]).[9]

In some studies, tribocorrosion was detected using tribometer which were, ball-on-plate tribometer, Ball-on-Disc, Pin-on-disc tribometer devices. Other methods identified were, Fretting-Corrosion Device, hydraulic testing machine (Dartec HC10), dynamic loading, Corrosion Cell, Electrochemical cell, Anodic polarization, Cyclic Potentiodynamic polarization test (CPPT), potentiodynamic polarization curves, Open Circuit Potential (OCP) and Galvanic current measurement.[3,4,5,6,7,10,11,12,13,15,19]

For the assessment of metal ion release, i.e. the primary outcome variable the data were divided into subgroups which were 1–7 days (Subgroup a), 8–21 days (Subgroup b), 22–42 days (Subgroup c), 43–84 days (Subgroup d). The maximum (max), minimum (min) of Tir for Group A Subgroup a was 254.7 ± 0.031 and 0.003 ± 0.001, respectively. For Group A Subgroup b the max and min was 1.531 + 0.650 and 0.007 ± 0.001, respectively, for Group A Subgroup c max and min was 0.037 ± 0.002 and 0.028 ± 0.002, respectively, and for Group A Subgroup d max was 1.419 ± 0.599 and min of 0.493 + 0.060.

Tir for Group B Subgroup a had a max value of 0.3 ± 0.039 and min of 0.003 ± 0.001, for Group B Subgroup b had max and min value of 2.405 + 0.236 and 0.007 + 0.001, respectively, for Group B Subgroup c max of 0.028 ± 0.003 and min of 0.004 ± 0.004 and for Group B Subgroup d max and min was 0.604 + 0.150, 0.186 + 0.062, respectively.

The Toir for Group A Subgroup a had a max value of 254.77 ± 0.010 and min 0.005 ± 0.002, for Group A Subgroup b the max and min value were 5.646 + 0.198 and 0.625 ± 0.020, respectively, for Group A Subgroup c max of 0.037 ± 0.001 and min 0.028 ± 0.002, for Group A Subgroup d days max and min was 1.419 ± 0.599 and 0.493 ± 0.06, respectively. For Group B Subgroup a, max and min value of 0.366 ± 0.036 and 0.169 ± 0.004 were present, respectively, for Group B Subgroup b the max and min value of 7.747 + 0.164 and 0.62 ± 0.016, respectively, for Group B Subgroup c max was 0.037 ± 0.001 and min 0.029 ± 0.001 and for Group B Subgroup d max and min was 117.827 ± 4.64 and 0.597 ± 0.051, respectively.

The overall max Tir value was 254.7 ± 0.031 and min was 0.003 ± 0.001 for Group A interface.[16] For Group B interface max Tir was 2.405 ± 0.236 and min was 0.003 ± 0.001.[8,9]

The overall max Toir for Group A interface was 254.77 ± 0.010 and min was 0.005 ± 0.002.[16] For Group B interface, max Toir was 117.827 ± 4.64 and min was 0.029 ± 0.001 [Tables 2 and 3].[16,17]

Table 3.

Quantitative characteristics

Author and year	Values form (units) (data presentation)	Minimum value (abutment material/implant material)	Maximum value (abutment material/implant material)
Silva et al., 2021[4]	Ti ion release (ppm) (median [IQ1–IQ3] Total ion release (ppm)	0.002 (0.001–0.006) (Au+Pt+Pd) cast/Ti 0.003 (0.001–0.004) Au+Au/Ti 0.003 (0.001–0.004) Au+Au/Ti 0.001 (0.001±0.002) (Au+Pt+Pd) cast/Ti 0.001 (0.001–0.001) Au+Au/Ti 0.001 (0.001–0.001) Au+Au/Ti	0.004 (0.002–0.008) Cast + Au /Ti 0.005 (0.003–0.009) Cast + Au /Ti 0.006 (0.004–0.017) Cast + Au /Ti 0.002 (0.001–0.003) Cast + Au /Ti 0.002 (0.002–0.002) Cast + Au /Ti 0.003 (0.002–0.004) Cast + Au /Ti
Arregui et al., 2021[8]	Ti ion release (ppm) (mean±SD) Total ion release (ppm)	0.007±0.001(CoCr/cpTi) 1.531±0.650 (CoCr+Ti6Al4V/cpTi) 0.620±0.016 (CoCr/cpTi) 5.646±0.198 (CoCr+Ti6Al4V/cpTi)	0.007±0.001 (CoCr+Ti6Al4V/cpTi) 2.406±0.236 (CoCr/cpTi) 0.626±0.020 (CoCr+Ti6Al4V/cpTi) 7.747±0.164 (CoCr/cpTi)
Lee et al., 2015[9]	Ti ion release (ppm) (mean±SD) Total ion release (ppm)	0.003±0.001 (Ni-Cr/ cpTi) 0.216±0.008 (Ni high Cr/ cpTi)	0.018±0.017 (Ni high Cr/cpTi) 0.265±0.011 (Ni-Cr-Be/cpTi)
Sikora et al., 2018[10]	Wear Volume Loss(µm³)	2.26×107±4.15×106 (Zr/Ti)	15.1×107±2.25×107 (Ti/Ti) P<0.001
Stimmelmayr et al., 2012[11]	Wear(µm) (mean±SD)	0.7±0.3 (Ti/Ti)	10.2±1.5 (Zr/Ti) P≤0.001
Mehkri et al., 2021[13]	Wear loss(µm) Wear rate(mm3) Wear depth(mm) Wear Coefficient	749.36 (ZTA/Ti6Al4V) 1.223×10−5(ZTA/Ti6Al4V) 2.78×10−6 (ZTA/Ti6Al4V) 0.131×10−3(ZTA/Ti6Al4V)	1536.54 (YSZ/Ti6Al4V) 1.433 ×10−4 mm3(YSZ/Ti6Al4V) 4.49×10−4 (YSZ/Ti6Al4V) 1.796×10−3 (YSZ/Ti6Al4V)
Queiroz et al., 2020[14]	initial marginal misfits (µm) final marginal misfits (µm) worn surface area (µm2)	2±4 (Zr/Ti) Neodent group 19±7(Zr/Ti) Zirkozahn group 201±125(NiCrTi/Ti) Overcast group	37±8(NiCrTi/Ti) Completely cast group 58±9(NiCrTi/Ti) Completely cast group 1313±315(Zr/Ti) Neodent group
Olander et al., 2022[15]	Displacement during mechanical cycling (mm) Particle size (nm) Particle size (µm)	0.068±0.004(Zr/TiZr) 258 (Ti/TiZr) Ti 8.42±6.976(Zr/Ti) Ti	0.081±0.009(Ti/Ti) 734±583.8 (Zr/TiZr) Ti & Zr particle 28.37±32.234(Ti/TiZr) TiZr and Ti
Niedermeier and Huesker, 2020[16]	Ti ion release (ppm) (mean±SD) Total ion release (ppm)	0.003±0.001(Ti/Ti) 0.164±0.013(Ti/Ti) 0.158±0.014 (CCM/Ti) 0.004±0.004(CCMAu/Ti) 0.005±0.002(Ti/Ti) 0.02±0.017(Ti/Ti) 0.169±0.004(CCM/Ti) 0.028±0.002(Ti/Ti)	254.7±0.031(TiAu/Ti) 0.34±0.032(CCMAu/Ti) 0.3±0.03(CCMAu/Ti) 0.037±0.002(TiAu/Ti) 254.77±0.010(Au/Ti) 0.38±0.005(TiAu/Ti) 0.364±0.006(TiAu/Ti) 0.037±0.001(CCMAu/Ti)
Masatoshi Yamazoe 2010[17]	Ti ion release (ppm) (mean±SD) Total ion release (ppm) Ti ion release (ppm) Total ion release (ppm)	0.186±0.062 (Pd+Ag+Sn+In/Ti) 0.493±0.06 (Ti/Ti) 0.058± 0.022(Au+Pt+Pd+Ag/Ti) 0.069±0.009 (Au+Pt+Pd+Ag+Cu/Ti)	1.158±0.963 (Ti6Al4V/Ti6Al4V) 117.827±4.64 (Pd+Ag+In+Zn/Ti) 0.168±0.034(Ti/Ti) 43.597±3.12 (Pd+Ag+In+Zn/Ti)
Tuna et al., 2009[19]	Ti ion release (ppm) Total ion release (ppm)	0.179(Pd/Ti) 0.227(Au/Ti)	0.184(CoNi/Ti) 2.01(CoCr/Ti)

Ni – Nickel; Cr – Chromium; cpTi – Commercially pure Titanium; Ti6Al4V-Titanium 6 Aluminum 4 Vanadium; ppm – Parts per million; IQ1-IQ3 – Interquartile range 1 and 3; Au-Aurum/Gold; Pt-Platinum; Pd – Palladium; SD-Standard Deviation; Co-Cobalt; Be-Beryllium; Zr-Zirconia; Rox-Roxolid or TiZr ; Ag-Silver; ZTA-Zirconia Toughened Alumina; YSZ – Yttria-stabilized zirconia; SCE – Single Calomel Electrode; SS – Stainless Steel; mm – Millimeter; mm³ – Millimeter cube; µm – Micrometer; µm² – Micrometer square; nm – Nanometer; CCM – Cobalt Chromium Molybdenum; Sn – Stannous or Tin; In – Indium; Cu – Copper

Wear at the implant–abutment interface was recorded using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (SEM/EDX), scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), scanning confocal laser microscope.[3,4,5,6,10,11,15,19]

The wear rate at the implant–abutment interface was calculated in 2 of the studies.[10,13] The max wear rate was 15.1 × 10⁷ ± 2.25 × 10⁷ μm³ for Group A, while the min was 1.223 × 10⁻⁸ μm³ for Group B.[10,13] Worn surface area, was calculated by one study with max value of 1313 ± 315 μm² for the Group B, and the min of 201 ± 125 μm² for the Group A interface.[14] Wear loss was evaluated by 2 studies with max value 1536.54 μm for Group B, and the min 0.7 ± 0.3 μm for the Group A interface [Tables 2 and 3].[11,13]

Quality assessment results

Among the 17 in vitro studies assessed, 15 studies presented a medium risk of bias, one study exhibited a high risk of bias, and one study had a low risk of bias [Figure 2 and Supplementary Table 1].[3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]

Figure 2.

Risk of bias assessment across all the included studies

Supplementary Table 1.

Risk of bias assessment (supplementary)

Study	Clearly stated aims/objectives	Detailed explanation of sample size calculation	Detailed explanation of sampling technique	Details of comparison group	Detailed explanation of methodology	Operator details	Randomization	Method of Measuring outcome	Outcome assessor details	Blinding	Statistical analysis	Presentation of results	Total score	Final score (%)
Barros et al., 2021[3]	2	0	0	1	2	1	-	2	1	-	2	2	13	65
Silva et al., 2021[4]	2	2	2	1	2	1	-	2	1	-	2	2	17	85
Son et al., 2004[5]	1	1	0	0	1	0	-	2	0	-	0	1	6	30
Berbel et al., 2022[6]	2	1	2	0	2	0	-	2	0	-	0	2	11	55
Corne et al., 2019[7]	2	0	1	1	2	0	-	2	0	-	0	2	10	50
Arregui et al., 2021[8]	2	1	2	2	2	0	-	2	0	-	2	2	15	75
Lee et al., 2015[9]	2	1	1	2	2	0	-	2	0	-	2	2	14	70
Sikora et al., 2018[10]	2	2	1	1	2	0	-	2	0	-	2	2	14	70
Stimmelmayr et al., 2012[11]	2	1	1	1	2	0	-	2	0	-	0	2	11	55
Taher et al., 2003[12]	2	1	1	0	2	0	-	2	0	-	0	2	10	50
Mehkri et al., 2021[13]	2	1	1	0	2	0	-	2	0	-	0	2	10	50
Queiroz et al., 2020[14]	2	0	1	1	2	1	-	2	1	-	2	2	14	70
Olander et al., 2022[15]	2	0	1	1	2	0	-	2	0	-	2	2	12	60
Niedermeier and Huesker, 2020[16]	2	0	2	1	2	0	-	2	0	-	2	2	13	65
Yamazoe 2010[17]	2	0	1	1	2	0	-	2	0	-	2	2	12	60
Kassapidou et al., 2020[18]	2	1	1	1	2	0	-	2	0	-	2	2	13	65
Tuna et al., 2009[19]	2	1	1	1	2	0	-	2	0	-	0	2	11	55

DISCUSSION

Tribocorrosion, the combined action of mechanical wear and corrosion, presents a significant challenge in dental implantology, particularly at the implant–abutment interface. This interface is crucial for the long-term success and stability of dental implants, as it directly influences the integrity of the implant system and its surrounding tissues. Tribocorrosion at the interface can lead to detrimental effects such as material loss, surface roughening, and the release of ions into the surrounding biological environment, all of which can compromise the performance and biocompatibility of dental implants.[22,23,24,25,26,27,28] Further the release of metal ions from dental implants has been implicated in the development and progression of peri-implantitis.[29,30,31,32] It can induce cytotoxicity, inflammation, allergic reactions, and promote bacterial colonization, all of which contribute to bone loss and implant failure.[30] This systematic review aimed to evaluate metal ion release and wear at the implant–abutment interface.

The analysis included 17 studies with a total of 477 specimens, of which 212 were implant materials and 265 were abutments materials.[3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] The primary outcome of the study was the comparison of metal ion release at the implant abutment interface when Ti or Ti alloy implants were utilized with different metal abutment as compared to Ti or Ti alloy abutments. The metal ion release has been studied in terms of Ti ion release and the total ion release at the interface. Due to comprehensive data and heterogeneity observed in the included studies, we categorized the study data for simplification and comparisons were made at different intervals of time, i.e. 1–7 days, 8–21 days, 22–42 days, 43–84 days.

Max Ti ion release was observed in the initial most interval, i.e. 1–7 days and was found to be 254.7 ± 0.031 where Ti alloy abutment was coupled with Ti implants.[16] However, interestingly min ion release of 0.003 ± 0.001 was also observed in the same interval when cpTi was used as an abutment.[16] The difference in metal ion release may be attributed to the alloying of Ti which owing to the use of different metals impurities can enhance the ionic release and interactions thereof.[33] Over 21 days observation, the metal ion release was increased in both the groups, though a greater increase was observed in the dissimilar metal abutments used with Ti/Ti alloy implants as compared to Ti/Ti alloy abutments. This essentially was because of initial passive layer disruption over Ti surface which has been experimentally demonstrated by Barros et al.[3] Another important information which was inferred from literature was the greatest ion release at the outset when similar implant abutment, i.e. Ti/Ti alloy were used. This characteristic finding plausibly may relate to the passive disruption of Ti oxide layer which may recapitulate later over a period of time.[8,9,10]

The total ion release values were observed to follow similar patterns of release of the metal ion at implant abutment interface when Ti or Ti alloy implants were coupled with Ti or Ti alloy abutment at 1–7 days interval. The max value of 254.77 ± 0.010 was obtained when abutment material was made up of Ti alloy and min of 0.005 ± 0.002 when cpTi was coupled with cpTi implant material.[16] These findings are strongly supported from previous observations by many researchers, i.e. Kitamura et al., Foti et al., Reclaru et al., and Grosgogeat et al., who observed in their respective studies that the use of Ti/Ti and Ti alloy/Ti alloy combinations were superior to Ti/Ti alloy and Ti/different abutment material alloy combinations in terms of corrosion resistance.[34,35,36,37] Another observation was that the max total ion release was more where lactic acid was utilized as analyzing medium for the experiment. This could have possible influence and serve as a contributing factor for increased metal ion release as acidic medium can hasten ion dissolution at implant abutment interface. These findings were also corroborated by Maria Arregui et al. and substantiated in the systematic review by Delgado-Ruiz et al., where they have studied the influence of the immersion medium on the release of ions and suggested the influence of pH changes on implant abutment interface.[8,31]

In observations of up to 21 days, there was an increase in total ion release, where abutment made up of Co-Cr was coupled with Ti/Ti alloy implant. Similar findings have been reported by Roppongi et al., who studied the corrosion behavior at the implant–abutment interface in case of Co-Cr abutment used with Ti implant in an animal study.[38] In addition according to study by Maria Arregui et al., the different abutment materials when coupled with Ti or Ti alloy implant can cause release of ions into surrounding media, more so in acidic environment.[8] With the passage of time the metal ion release reached equitable for both groups around 1–1.5 months, i.e. approximately 43 days. The total ion release reached a max value in case when Ti or Ti alloy implant was coupled with different abutment material and had a max value of 117.827 ± 4.64, which may be because of difference of potentials among dissimilar couples leading to formation of electrochemical cell and eventually leading to galvanic corrosion over time.[17]

In evaluating wear at the implant–abutment interface, it was observed that the worn surface area and wear particle loss were highest when Ti or Ti alloy implants were paired with Zr abutments, and lowest when Ti or Ti alloy implants were coupled with Ti or Ti alloy abutments. These findings align with a systematic review by Anne Karoline et al., who reported that Zr abutments resulted in significantly greater wear at the implant–abutment interface.[22] Similarly, a study by Sabeel Mehkri et al. demonstrated more favorable wear outcomes when both the implant and abutment were composed of Ti or Ti alloy. Interestingly, these results contrasted with the wear rate observations, where the lowest wear rate was noted when different abutment materials were used. This paradoxical finding could be explained by the “self-sacrificing effect” of Ti. At a pH of 6.5, Ti is enveloped by a thick oxide layer, which is continuously removed and reformed, leading to volume loss as the oxide layer regenerates. This cyclical process may contribute to the wear behavior observed in Ti or Ti alloy combinations.[13]

The findings of current analysis could not be translated as meta-analysis owing to the data heterogeneity, yet the analysis provides very clear, concise, systematic, organized data of published literature in this area. The findings of the paper enhance the knowledge and provide a detailed and structured analysis of the existing literature on metal ion release and wear at the implant–abutment interface and understanding of tribocorrosion behavior of implant abutment system for reader.

Limitations

Inspite of the above-mentioned strengths, the current work has its fair share of limitations as well. For instance, the variability in the techniques and instruments used for measuring wear and metal ion release (e.g., different types of tribometers, SEM configurations) has introduced inconsistencies and affected the reliability of comparative results, thereby restricting the development of standardized protocols and clear guidelines. Similarly, variability in study conditions, such as the use of different mediums (lactic acid, artificial saliva), pH levels, immersion durations, and environmental settings, further influences ion release and wear patterns, complicating cross-study comparisons. Moreover, owing to the paucity of in vivo studies regarding the defined research question, the current review is completely focused on in vivo studies. This analysis, though providing critical insights, may not fully replicate the complex and dynamic oral environment where factors such as saliva, oral microbiota, masticatory forces, oral hygiene, and patient-specific habits play significant roles; hence, the observations may not be entirely translatable to in vivo conditions. Finally, the time-dependent behavior of ion release, though reported to peak around 1–1.5 months, has not been adequately explored in the long term, which is critical for understanding implant longevity and clinical applicability.

CONCLUSION

Within the limitations of the present analysis, a significant variation in the metal ion release is observed, when Ti or Ti alloy implants are coupled with dissimilar abutment materials. Specifically, a high unusual metal ion release at implant abutment interface is observed, due to oxidation of Ti surface, which reduces over time upto 1 to 1.5 month. With further passage of time higher metal ion release is observed when different abutment materials were coupled with Ti or Ti alloy implants, which may be hugely impacted by environmental factors.

These findings underscore the need for clinical studies and randomized controlled trials that employ homogeneous methods for quantitative metal ion detection and wear measurement, along with long-term follow-ups. Gaining a deeper understanding of the behavior at the implant–abutment interface will help identify the most suitable implant–abutment material combinations for minimizing tribocorrosion, thereby enhancing the longevity of implants in the oral cavity.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.