Materials and Methods: 100 patients with lower flat ridge were included in the study. A questionnaire was used to record the data of each patient which include; the gender, the age of the patient, the presence or the absence of a previous denture, and the date of the last tooth extraction (the period of complete edentulism). The patients were informed that the recorded information was required for a research purpose, and it will be used in a survey, and their consents and agreements were taken verbally. All the collected data were checked and assessed by a prosthodontic specialist. The patients age were divided into four groups; (40-50 years), (51-60 years), (61-70 years), (more than 71 years). The period of complete edentulism were divided into two groups; (up to 4 years), and (more than 4 years). The data were correlated and descriptive statistic of tables, numbers and percentages along with Chi-Square, were used to analyze the data.

Results: The results of the study showed that; 64 (64%) of the patients were males and 36 (36%) of the patients were females. The majority of the patients were from the age group (51-60) and (40-50) years in male and female respectively. The occurrence of the lower flat ridge was significantly higher in patients with previous dentures 75(75%) than those without dentures 25(25%) in both genders. Finally, the results revealed that patients who were completely edentulous for up to four years had significantly higher numbers of lower flat ridge 55(55%) comparing to those who were completely edentulous for more than four years 45(45%).

Conclusions: The presence of a previous denture, the longevity period of complete edentulism, the age, and the gender of the patient has an effect on the resorption of the lower residual ridge, and on the height of the lower residual ridge.