In office bleaching menggunakan hidrogen peroksida 40% sering memberikan efek samping berupa linu baik selama maupun setelah perawatan tersebut dilakukan. Penelitian ini dilakukan dengan tujuan untuk mengetahui pengaruh waktu aplikasi dan kandungan fluor desensitizing agent pada metode in office bleaching terhadap kandungan mineral gigi. Delapan gigi masing-masing dipotong menjadi 4 bagian, 6 potong digunakan untuk pemeriksaan XRD awal. Gigi dikeringkan dalam oven suhu 50° selama 30 menit diserbuk, diambil 1 mg untuk diperiksa kandungan mineralnya dengan goniometer. Dua puluh empat potong yang lain dibagi dalam 4 kelompok perlakuan. Kelompok I: gigi diaplikasi bahan bleaching 0,5-1 mm hidrogen peroksida 40% selama 1 jam, dicuci, dikeringkan, diikuti aplikasi 0,1 ml desensitizing agent tanpa fluor (CPP-ACP) selama 30 menit, dicuci, dikeringkan. Kelompok II : gigi diaplikasi CPP-ACP 30 menit, dicuci, dikeringkan, dibleaching menggunakan hidrogen peroksida 40% selama 1 jam. Selanjutnya gigi diaplikasi CPP-ACP 30 menit lagi, dicuci, dikeringkan. Kelompok III gigi dibleaching menggunakan hidrogen peroksida 40% selama 1 jam, dicuci, dikeringkan, diikuti aplikasi desensitizing agent yang mengandung fluor (CPP-ACFP) selama 30 menit, dicuci, dikeringkan. Kelompok IV: gigi diaplikasi CPP-ACFP 30 menit, dicuci, dikeringkan, dibleaching menggunakan hidrogen peroksida 40% selama 1 jam. Selanjutnya gigi diaplikasi CPP-ACFP selama 30 menit, dicuci dikeringkan. Sesudah perlakuan, semua gigi dilakukan pemeriksaan kandungan mineral gigi dengan prosedur yang sama. Uji Mann Whitney menunjukkan penurunan mineral paling sedikit terjadi pada kelompok IV (4500). Desensitizing agent mengandung F sebelum dan sesudah perlakuan in office bleaching menunjukkan penurunan mineral paling kecil. The Effectiveness of Desensitizing Agent with and without Fluorine in Office Bleaching Method to Tooth Mineral content. Tooth sensitivity arises during or after an in-office bleaching was performed is usually overcome by using desensitizing agent with or without fluor. So far, desensitizing method applied only reduces tooth sensitivity but it had not overcome demineralization problem yet. This study was aimed to determine the influence of an application process and fluoride containing desensitizing agent in tooth mineral lossEight teeth were divided into four parts. Six specimens were smoothened using agate mortar. One mg of powder was inserted into the sample holder and mounted on goniometer heads to examine mineral content before treatment using X-Ray Diffraction (XRD). Twenty-four specimens were classified into four groups. In group I, 0,1 ml desensitizing agent without fluoride (CPP-ACP) was applied for 30 minutes after an in-office bleaching using 40% Hydrogen Peroxide was performed, while in group II, CPP-ACP was applied before and after an in-office bleaching was performed. In group III 0,1 ml fluoride containing desensitizing agent (CPP-ACFP) was applied for 30 minutes after in-office bleaching using 40% Hydrogen Peroxide was performed, while in group IV fluoride containing desensitizing agent was applied before and after an in-office bleaching was performed. Finally, all of the specimens were measured in their after-treatment mineral contain. Mann Whitney test showed that the lowest mineral lost was detected in group IV (4500). Fluoride containing desensitizing agent applied before and after an in-office bleaching effectively reduced mineral loss.