Significance of keratinized mucosa in maintenance of dental implants with different surfaces

Background: The need for keratinized mucosa (KM) or immobile keratinized mucosa (i.e., attached mucosa [AM]) for the maintenance of osseointegrated endosseous dental implants has been controversial. The purpose of this study was to investigate the significance of KM in the maintenance of root-form dental implants with different surfaces. Methods: A total of 339 endosseous dental implants in place for at least 3 years in 69 patients were evaluated. The width of KM and AM, modified plaque index (mPI), gingival index (GI), modified bleeding index (mBI), probing depth (PD), and average annual bone loss (ABL) were measured clinically and radiographically by a masked examiner. Based on the amounts of KM or AM, implants were categorized as follows: 1) KM < 2 mm (KL); 2) KM >= 2 mm (KU); 3) AM < 1 mm (AL); and 4) AM >= 1 mm (AU). Implants were further subdivided into the following four subgroups based on their surface configurations: 1) smooth surface implants (SI) with KM < 2 mm (SKL); 2) SI with KM >= 2 mm (SKM); 3) rough surface implants (RI) with KM < 2 mm (RKL); or 4) RI with KM >= 2 mm (RKM); or 1) SI with AM < 1 mm (SAL); 2) SI with AM >= 1 mm (SAM); 3) RI with AM < 1 mm (RAL); or 4) RI with AM >= 1 mm (RAM). The effect of KM or AM on clinical parameters was evaluated by comparing the different KM/AM groups. In addition, the significance of the presence of KM on implant prostheses types (i.e., fixed versus removable) and on implant locations (i.e., anterior versus posterior) was evaluated. Results: Comparison of ABL among the four subgroups in KM or AM failed to reveal statistically significant differences (P > 0.05); however, statistically significantly higher GI and mPI were present in SKL or SAL compared to the other three subgroups (P < 0.05). GI and mPI were significantly higher in KL (0.94 and 1.51) than KU (0.76 and 1.26) and higher in AL (0.95 and 1.50) than AU (0.70 and 1.19) (P < 0.05), respectively. The difference in GI between posterior implants with or without an adequate amount of KM was also significant (P < 0.05). Conclusions: The absence of adequate KM or AM in endosseous dental implants, especially in posterior implants, was associated with higher plaque accumulation and gingival inflammation but not with more ABL, regardless of their surface configurations. Randomized controlled clinical trials are needed to confirm the results obtained in this retrospective clinical study.