Vitamin C affect the melanocytes function not the number while diode laser cause melanocytes destruction. Although diode laser and vitamin C have proved their effectiveness in depigmentation in previous studies, there are no published studies compared the effect of diode laser and vitamin C on melanocytes and melanosomes clinically and histologically.

Cosmetic dentistry is usually centered on aesthetic restorative procedures but it may also involve the appearance of the gingiva, especially when it is located in the anterior labial region. Oral pigmentation may be physiological or pathological in nature. Better esthetics results of depigmentation were achieved with diode laser than conventional scalpel and with rotary abrasion, also diode laser is effective and safe in removal of gingival hyperpigmentation and repigmentation doesn't occur.When choosing a depigmenting agent, it is important to differentiate between substances that are toxic to the melanocyte and substances that interrupt the key steps of melanogenesis. Vit. C interacts with copper ions at the tyrosinase-active site and inhibits action of the enzyme tyrosinase, thereby decreasing the melanin formation.

This randomized comparative clinical study was conducted on ten patients attending the outpatient clinic of the Oral Medicine and Periodontology department, Faculty of Dentistry, Ain Shams University and seeking treatment for their gingival hyperpigmentation for esthetic reason.

The study was conducted after receiving an ethical clearance from the Research Ethics Committee of Ain Shams University, Faculty of Dentistry; that the study follows the ethical guidelines of research. The patients clearly understood the purpose of this study and signed an informed consent.

According to the study results, vit C treated patients showed no or little repigmentation after six months post treatment. Conversely, diode laser treated patients showed significant recurrence of gingival pigmentation after six months post treatment. These could be attributed to the blocking effect of vitamin C on the existing melanocytes to form new melanoseomes, however diode laser cause removal of the existing melanocytes that may cause formation of new melanocytes (migrating from neighboring melanocytes from the adjacent area of the gingiva) with the ability of forming new melanosomes and causing repigmentation. Histopathological assessment revealed that both treatment modalities caused significant reduction in MAF after six months post treatment.

Inclusion Criteria:

• Male and female patients with age ranging from 18 years old to 40 years old.
• Bilaterally symmetric gingival hyperpigmentation on the maxillary and mandibular labial keratinized gingiva between canines.
• Patients free from any systemic diseases as evidenced by the health questionnaire, using modified Cornell medical index (Pendleton et al., 2004).
• Patients with thick gingival biotype ≥ 3 mm.

Exclusion Criteria:

• Presence of local condition that may cause gingival hyperpigmentation (traumatized epithelium caused by defective fixed prosthesis or restoration).
• Smokers.
• Pregnant or lactating females.
• Patients with poor oral hygiene, incompliance to treatment and persistence gingival inflammation after phase I periodontal therapy.
• Clinically diagnosed periodontitis (attachment and bone loss, presence of periodontal pockets, gingival recession and tooth mobility).
• Previous treatment to pigmentation.
• Patients taking supplementary vitamin C for any reason.
• Known sensitivity to ascorbic acid or any of its derivatives.
• Patients taking any drug that may cause gingival pigmentation.

when measuring the gingival brightness and MAF of melanosomes