Although Modern Standard Arabic (MSA) has three different interdental fricatives /θ/, /ð/, and the emphatic interdental /ðˤ/, most Egyptian Arabic (EA) speakers do not pronounce these interdental fricative sounds in MSA, and instead substitute them with the sibilant /s/ and /z/, respectively (Schmidt, 1987). The factors which influence the pronunciation of interdentals by EA speakers vary from one study to another. For instance, Ahmed Ali (2014) and El Zarka (2013) refer to dialect interference in the second language acquisition of phonology, while other studies indicate some sociolinguistic variables such as a socioeconomic background variable (Labov, 1970) or a stylistic variable (Schmidt, 1987) as influencing the EA speakers’ pronunciation of interdental fricatives. This study examines the interdentals of 16 Egyptian Arabic speakers through an interview and several tasks, including reading samples, in order to determine which variables (e.g., phonological, sociolinguistic, or stylistic) are the most salient in the acquisition of interdentals in MSA. In addition, this study tests several new variables (the effect of pronunciation teaching and formality of the topic) that may influence the EA speakers’ pronunciation of interdentals. Learning how to read the Qur’an has a great influence on the participants’ reading as well. The collected data also supports the same results in reading the interdentals in English as a second language. Through analysis of the collected data, this study demonstrates that the pronunciation of interdentals by EA speakers is in fact due to a combination of these factors.