Changes in mucogingival junction after an apically positioned flap with collagen matrix at sites with or without previous guided bone regeneration: A prospective comparative cohort study

Aim: To assess changes in the position of the mucogingival junction (MGJ) after an apically positioned flap (APF) with collagen matrix performed at sites with or without previous guided bone regeneration (GBR). Materials and methods: Dental implants were placed with or without GBR (group GBR or non-GBR) depending on the available ridge width in 30 patients with a limited width of keratinized mucosa (MGJ placed more coronally than the expected prosthetic margin). An apically positioned flap with collagen matrix was performed in both groups. Changes in the position of the MGJ from the day of an apically positioned flap up to 1, 3, and 12 months thereafter were assessed on digital scans (primary endpoint). Secondary endpoints were the width and thickness of the keratinized mucosa, and the position of the mucosal margin. Results: The position of the MGJ changed significantly from baseline to the first month, by 5.25 ± 2.10 and 4.40 ± 1.41 mm in groups GBR and non-GBR, respectively. Thereafter, the position remained stable in both groups up to 1 year (changes from baseline of 5.46 ± 2.28 and 4.58 ± 1.92 mm, respectively; p = .34). The position of the mucosal margin did not differ between groups GBR and non-GBR (-1.57 ± 2.04 and -1.75 ± 2.08 mm, respectively; p = .84), nor did the width of the keratinized mucosa (1.20 ± 1.03 and 0.99 ± 0.66 mm, p = .91) or its thickness (1.28 ± 0.44 and 1.40 ± 0.78 mm, p = .87). Conclusion: Apically positioned flap combined with a collagen matrix results in a more apical position of the MGJ at sites with or without GBR. Following a coronal shift during the first month after the apical positioning of the flap, the level of the MGJ remained stable.restrictio