Gingival recession is a common defect among the American population. It is also a major cause for root decay, hypersensitivity, contributes to tooth mobility and low self-esteem. Acellular dermal matrix, a human-derived grafting material has been put on the market for the treatment of gingival recession. Treating gingival recession with this material has been a validated treatment option for years.

However, treatment outcomes in two patient populations, namely those with thin biotypes and those with thick biotypes, has not been investigated. This study will observe the primary treatment outcomes in the two patient groups at 5 time points - 3 months, 6 months and 12 months post-surgery to observe short term outcomes; additional 24 months and 48 months post-surgery to observe long term outcomes.

The study aim is to evaluate and compare the use of acellular dermal matrix, a material used for treating gum recession, in two study populations, namely thin or thick gingival biotype. Short term outcomes and the long term stability of ADM in recession repair between thick and thin biotypes will be evaluated.

There will be two study groups, namely thin and thick groups. The included subjects will be divided in two groups according to gingival thickness: Thin gingival biotype group (TnB): < 0.8 mm, thick gingival biotype group (TkB) ≥ 0.8 mm. Each subject will be in one of the two groups only.

Randomization will not be used to assign the subjects to the study groups, because the intervention will be the same for both groups, namely ADM applied beneath a coronally advanced flap.

The short term (3 months, 6 months post-surgery) outcomes and the longer term (12 months, 24 months and 48 months post-surgery) outcomes will further be compared within the groups and between the groups.

Inclusion Criteria:

• Subjects must be current patients of Tufts University School of Dental Medicine
• Subjects with two Miller class I or class II adjacent recessions with a recession height ≥ 2 mm and < 4 mm
• Affected tooth/teeth are anterior- incisors, canines or premolars (except the mandibular central and lateral incisors)
• Healthy subjects with no contraindications to root coverage surgery
• Subjects with full-mouth plaque index<1 and gingival index<1, calculated as the average value of plaque index and gingival index

Exclusion Criteria:

• Presence of adjacent defects, whose gingival thickness values place them in a different category other than thick or thin biotype
• Areas that have previously been treated with root coverage surgeries
• Subjects with a known hypersensitivity to polysorbate 20 (contraindicated with the use of Alloderm®)
• Subject smokes more than 5 cigarettes per day
• Subjects with systemic conditions which influence wound healing
• Subjects that are pregnant or lactating
• Subjects with a condition causing immunosuppression, or currently taking immunosuppressant medications
• Teeth with severe occlusal interferences, deep cervical lesions, or large restorations whose margins impinge on the cement-enamel junction or make identification of this landmark impossible