Objectives: To evaluate the discoloration of the peri-implant mucosa caused by titanium (Ti), titanium nitride (TiN), and zirconia (ZrO2) with and without ceramic veneering and to establish the influence of mucosal thickness on the resulting color.

Material and Methods: For the present in vitro investigation a pig maxilla was used. In the region disto-palatally to the last molar on the right side of the palate a partial-thickness trap-door-type flap was prepared with a thickness of 0.5 mm and dimension of 5 x 5 mm (width x length). To simulate different mucosa thicknesses, multiple connective tissue grafts (CTG) with a thickness of 0.5 mm were harvested on the left side of the palate. To provide grafts of uniform thickness, a mucotome instrument (GB270, Aesculap, Tuttlingen, Germany) was used for the harvesting process. Thus, test-mucosa-layers with a thickness of 1.5, 2.0, or 3.0 mm resulted. To test a variety of clinical situations, different abutment and crown materials were evaluated. The following test specimens were prepared in dimensions of 5 x 5 mm and a thickness of 1.0 mm (Non-veneered) to 2.0 mm (Veneered): titanium (Ti alloy, Dentsply Sirona Implants, Mannheim, Germany), titanium veneered with veneering ceramic (Color A3), (GC Initial Ti, Leuven, Belgium), titanium nitride (GoldHue, Dentsply Sirona Implants, Mölndal, Sweden), titanium nitride veneered with veneering ceramic (Color A3) (GC Initial Ti, Leuven, Belgium), zirconia (Zirlux, Henry Schein Dental, Langen, Germany), and zirconia veneered with veneering ceramic (Color A3) (GC Initial Zr-FS, Leuven, Belgium). Color differences (ΔE values) were measured and calculated comparing the measurements of the native tissue, and the measurements with ascending mucosal thickness by spectrophotometric assessment (ShadePilot, Dentsply DeguDent, Hanau, Germany). Three consecutive images were captured to be used for data analysis. The ΔE E values were compared to the clinically visible ΔE threshold of 3.1 for intraoral color distinction as perceived by the bare eye (Sailer et al. 2014).

Result: The results of the in vitro study confirm that all tested restorative materials lead to a discoloration of the mucosal tissue, diminishing with increasing mucosal thickness. In terms of metal-based abutment materials, the results indicate that in cases of thin soft tissues of 1.5 mm, the use of titanium nitride (mean ΔE 1.93) was superior compared to titanium alloy (mean ΔE 4.07), and revealed comparable ΔE values to the tested zirconia material (mean ΔE 2.13). At 3 mm mucosa thickness overlying the tested material, the differences in ΔE values became negligible.

Impact of abutment material and soft tissue thickness on mucosa discoloration- a spectrophotometric in vitro study