Titanium Grade V vs Titanium-Zirconium: what real impact on the viability of gingival fibroblasts?

While titanium alloys dominate modern implantology, their propensity for metal ion release remains a clinical concern. This phenomenon can induce local cytotoxicity and deleterious inflammatory responses in peri-implant tissues. This in vitro study directly addresses this issue by comparing two common prosthetic configurations: Grade V titanium associated with titanium abutments, versus titanium-zirconium coupled with lithium disilicate (Emax) abutments.

The specific objective was to quantify the ionic release of titanium (Ti), aluminium (Al) and vanadium (V) and to measure its impact on the survival of human gingival fibroblasts (HGF). To achieve this, the researchers analysed 6 implants, divided between Group A (Grade V Titanium / Ti Abutment) and Group B (Titanium-Zirconium / Emax Abutment), immersed in a culture medium over an experimental period of 7, 14 and 21 days.

The authors tested the hypothesis that an alternative choice of materials, such as the titanium-zirconium and ceramic combination, would reduce metallic toxicity compared to the Grade V titanium standard. Measurements were performed using mass spectrometry (ICP-MS) and MTT cell viability assays to determine whether this configuration optimises the biological response of soft tissues.

A rigorous in vitro protocol

This in vitro experimental study evaluates the biological impact of two combinations of implant materials on 6 samples, divided into two distinct protocols:

• Group A: Grade V titanium implants coupled with titanium abutments.
• Group B: Titanium-zirconium implants coupled with lithium disilicate abutments (Emax).

The research team immersed these assemblies in a cell culture medium for periods of 7, 14 and 21 days. This design allows the observation of ionic release kinetics over time. To test biocompatibility, the authors exposed human gingival fibroblasts (HGF) to these different eluates.

The analytical methodology is based on two specific axes:

• Inductively coupled plasma mass spectrometry (ICP-MS) precisely quantifies the concentrations of titanium (Ti), aluminium (Al) and vanadium (V) ions.
• The MTT colourimetric assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) measures the viability and proliferation of fibroblasts.

Finally, analysis of variance (ANOVA) and effect size calculation ensure the statistical validity of the comparisons between the two groups.

Ion release: a marked superiority of Ti-Zr

Mass spectrometry (ICP-MS) analyses reveal significant disparities in metal release kinetics between the two experimental groups. Group A (Grade V Titanium / Titanium Abutment) exhibits a markedly higher release of titanium (Ti) and vanadium (V) than that of Group B (Titanium-Zirconium / Emax Abutment).

• Titanium (Ti) and Vanadium (V): Concentrations were significantly higher in Group A (p < 0.001).
• Temporal kinetics: For both groups, the ionic release rates showed a decreasing trend between the 7th and 21st day.
• Aluminium (Al): Conversely, Group B released higher concentrations of aluminium on the 21st day compared to Group A, a point that could influence the long-term cellular response.

Cytological impact on gingival fibroblasts (HGFs)

The evaluation of cytotoxicity via the MTT assay demonstrates that the nature of the materials directly influences peri-implant cell survival. The results highlight a correlation between ionic release and soft tissue health:

• Cell viability: Group A induced significantly lower gingival fibroblast viability, suggesting a cytotoxic effect related to the ions released by the Grade V titanium alloy.
• Proliferation: Group B maintained higher cell proliferation rates, confirming better biocompatibility of the titanium-zirconium and lithium disilicate combination.

In summary, the use of titanium-zirconium coupled with Emax abutments drastically reduces fibroblast exposure to cytotoxic Ti and V ions, promoting a more stable biological environment for soft tissue integration.

Tissue biocompatibility analysis

The results of this study highlight a marked biological superiority of the titanium-zirconium combination with lithium disilicate abutments (Group B) compared to conventional Grade V Titanium (Group A). The significantly higher release of titanium (Ti) and vanadium (V) ions in Group A (p < 0.001) is directly correlated with a decrease in the viability of human gingival fibroblasts. Clinically, this suggests that the chemical corrosion of standard titanium alloys may alter peri-implant soft tissue homeostasis within the first few weeks.

Ion kinetics and experimental limitations

A point of interest lies in the release kinetics: while Ti and V levels decrease over time in the pure titanium group, Group B shows a higher release of aluminium (Al) at 21 days. Although this group maintains better cellular proliferation, the long-term impact of this aluminium on tissues remains to be monitored. However, the study has limitations inherent to its in vitro design: the small sample size (six implants in total) and the absence of biomechanical constraints or oral biofilm do not allow the complexity of the clinical environment to be perfectly replicated.

Implications for material selection

These data confirm that the choice of the implant-abutment combination is a determining factor in the cellular response. The use of titanium-zirconium combined with an aesthetic Emax connection reduces ionic cytotoxicity and promotes an environment conducive to fibroblastic attachment. For the practitioner, these results validate the value of alternative materials to Grade V titanium to optimise biological integration and limit the risks of chronic inflammation related to metal release.

Summary of results

This in vitro study demonstrates that the combination of titanium-zirconium implants and lithium disilicate abutments releases significantly fewer titanium and vanadium ions than conventional Grade V titanium (p < 0.001). MTT assays confirm that this reduction in metallic load preserves the viability and proliferation of human gingival fibroblasts over 21 days, despite a more pronounced aluminium release at the end of the period.

In practical terms, for the practitioner:

• Mucosal attachment optimisation: favour lithium disilicate abutments combined with titanium-zirconium implants to limit local cytotoxicity and promote peri-implant soft tissue health.
• Alternative to Grade V: as Grade V titanium releases more vanadium and titanium ions, its replacement with titanium-zirconium reduces the risks of early inflammatory responses associated with metallic debris.
• Biological selection: the choice of abutment material is as critical as that of the implant; ceramic (Emax) offers superior biocompatibility here compared to pure titanium prosthetic components.

Technical glossary of the study

Titanium Grade V: Alloy composed of titanium, aluminium and vanadium (Ti-6Al-4V), used as a reference material for implants and abutments in Group A of the study.

Titanium-Zirconium (Ti-Zr): Alternative metal alloy used for Group B implants, having demonstrated in this study a lower release of cytotoxic ions (Ti and V) than conventional titanium.

Lithium Disilicate (Emax): Ceramic material used for the fabrication of Group B prosthetic abutments, promoting better biocompatibility with peri-implant soft tissues.

ICP-MS (Inductively Coupled Plasma Mass Spectrometry): High-resolution chemical analysis method used to quantify the ultra-low concentrations of titanium, aluminium, and vanadium ions released into the culture medium.

MTT test: Colorimetric cell viability assay measuring the metabolic activity of fibroblasts, enabling the quantification of the cytotoxic effect of released metal ions.

Human Gingival Fibroblasts (HGFs): Specific cell type of the oral connective tissue used in this study to model the biological response of the soft tissues surrounding the implant-abutment junction.

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