Five-year evaluation of the influence of keratinized mucosa on peri-implant soft-tissue health and stability around implants supporting full-arch mandibular fixed prostheses

Abstract

Background: The question of the importance of keratinized mucosa around dental implants for the prevention of peri-implant disease could not be answered in the relevant literature so far.

Objective: To investigate the influence of peri-implant keratinized mucosa on long-term peri-implant soft-tissue health and stability over a period of 5 years.

Material and methods: A total of 386 mandibular dental implants were placed in 73 completely edentulous patients, and subsequently restored with fixed full-arch prostheses. At prosthesis delivery (baseline) and after 3, 6, 12, 18, 24, 36, 48 and 60 months, modified plaque index (mPlI), modified sulcus bleeding index (mBI), distance between implant shoulder and mucosal margin (DIM) and width of peri-implant keratinized mucosa (KM) were recorded. Statistical analysis included multivariate logistic regression, multivariate ordinal logistic regression, generalized estimating equations and Bonferroni's correction.

Results: Fifty-eight patients with 307 implants completed the 5-year study. Statistically significantly higher plaque accumulation on lingual sites (mean mPlI 0.67, SD 0.85), bleeding tendencies on lingual sites (mean mBI 0.22, SD 0.53) and larger soft-tissue recession on buccal sites (mean DIM -0.69 mm, SD 1.11 mm) were found when the width of KM was <2 mm, compared to sites with>or=2 mm of KM (mean mPlI 0.40, SD 0.68, P=0.001; mean mBI 0.13, SD 0.41, P<0.01; mean DIM -0.08 mm, SD 0.86 mm, P<0.001). The width of keratinized mucosa had no effect on bleeding tendency or plaque accumulation on buccal sites (P>0.05).

Conclusion: In patients exercising good oral hygiene and receiving regular implant maintenance therapy, implants with a reduced width of <2 mm of peri-implant keratinized mucosa were more prone to lingual plaque accumulation and bleeding as well as buccal soft-tissue recession over a period of 5 years.

Fig. 1

Prosthodontic treatment protocol. (a) All patients were treated with five to six one-stage dental implants placed in the symphysis of edentulous mandibles. (b) Semi-precious metal frameworks and acrylic resin prostheses with distal cantilevers were fabricated and screw-retained 4–7 months after implant placement.

Fig. 2

Clinical parameters affected by the width of keratinized mucosa. (a) Plaque accumulation (mPlI) at lingual sites: Lingual sites with < 2 mm of lingual KM presented with significantly more plaque accumulation compared to sites with at least 2 mm of lingual KM (P = 0.001). (b) Bleeding tendency (mBI) at lingual sites: Lingual sites with < 2 mm of lingual KM presented with significantly higher mBI scores compared to sites with at least 2 mm of lingual KM (P < 0.01). (c) Soft-tissue recession (DIM): Sites with < 2 mm of buccal KM presented with significantly greater soft-tissue recession compared to sites with at least 2 mm of buccal KM throughout the 5-year observation period (P < 0.001, DIM was measured at buccal sites only). mPlI, modified plaque index; KM, width of peri-implant keratinized mucosa; DIM, distance between implant shoulder and mucosal margin; mBI, modified sulcus bleeding index.

Fig. 3

Outcome parameters according to different widths of KM. (a) Increasing mPlI scores on lingual sites with decreasing widths of KM can be seen. Statistically significant changes in outcome primarily occurred between 1 and 2 mm of lingual KM (P < 0.01 Bonferroni adjusted; n-median exposure level over follow-up). (b) Increasing mBI scores on lingual sites with decreasing widths of KM are evident. Statistically significant changes in outcome primarily occurred between 0 and 1 mm of lingual KM (P < 0.001 Bonferroni adjusted; n-median exposure level over follow-up). (c) Increasing soft-tissue recession on buccal sites with decreasing widths of buccal KM are evident. Changes in outcome primarily occurred between 1 and 2 mm of buccal KM (P < 0.001 Bonferroni adjusted; n-median exposure level over follow-up). mPlI, modified plaque index; KM, width of peri-implant keratinized mucosa; mBI, modified sulcus bleeding index.