Extended Abstract

Introduction
Dental caries is an infectious disease caused by acid-producing bacteria such as Streptococcus mutans and Lactobacilli. Various sociodemographic factors can influence dental caries; thus, calculating a valid dental caries index, known in dentistry as the DMFT (Decay, Missing, Filling Teeth) Index, can provide a comprehensive overview of an individual's and the community's dental health. The appearance of teeth, a beautiful smile, and their role in social interactions, absence of pain in the jaw and teeth, comfort in the mouth, and ease and pleasure in eating and speaking can all be affected by dental caries, reducing overall life satisfaction and quality of life. This study aimed to determine the relationship between the DMFT index and oral health-related quality of life.
Methods
This descriptive-analytical study was conducted on 61 patients (29 men and 32 women) aged 20-50 years, selected through convenience sampling. A specialist in oral, maxillofacial, and dental diseases performed oral examinations. Participants were divided into three age groups: 20-29 years, 30-39 years, and 40-50 years. The DMFT index, including decay (D), missing (M), and filled (F) teeth, was determined for each subject. The DIDL (Dental Impact on Daily Living) questionnaire was used to assess the quality of life. This 36-question survey evaluates five domains: appearance and aesthetics, oral comfort, general oral and dental function, eating restrictions, and tooth and jaw pain. Participants were asked to carefully complete the DIDL questionnaire after receiving the necessary explanations. The DIDL questionnaire was completed under the supervision of a specialist in oral and dental diseases. Scores were recorded based on positive (+1), neutral (0), and negative (-1) responses, with a total score range from -10 to 10. The DIDL responses were then categorized into three groups: dissatisfied (scores below 0), moderately satisfied (scores 0-7), and satisfied (scores above 7).
Results
The mean and standard deviation of the oral health-related quality of life score for the entire study population was 5.14±0.229. The overall satisfaction percentages based on the DIDL questionnaire were 31.14% dissatisfied, 57.37% moderately satisfied, and 11.47% satisfied. Patients satisfaction rate was 63.93%, 52.45%,45.90% ,45.90and39.43%  in the oral comfort domain, overall oral and dental function, eating limitations, (45.90), appearance and aesthetics and dental and jaw pain , respectively.
The mean and standard deviation of the DMFT index with ranges of 0-28 was 9.36±5.14, with the most frequent values being 7, 11, and 13, each comprising 11.5% of the sample. The mean and standard deviation for decay (D) with ranges of 0-12 was 3.44±3.15, for missing teeth (M) with ranges of 0-19 was 2.92±1.98, and for filled teeth (F) was 3.93±3.63.
A significant inverse moderate relationship was found between the DMFT index and oral health-related quality of life (P=0.005, Pearson correlation coefficient=-0.358). There was a significant difference in the mean DMFT index among dissatisfied, moderately satisfied, and satisfied individuals in the domains of appearance and aesthetics, oral comfort, and eating restrictions. Still, no significant differences were found in the general function and pain domains. The mean DMFT index was lower among those satisfied with their quality of life compared to those moderately happy and dissatisfied. Additionally, the mean DMFT index significantly differed among the three satisfaction groups across all five domains (P<0.05).
Conclusion
According to the results of this study, there is a moderate, inverse, and significant relationship between the DMFT index and oral health-related quality of life. In other words, as the total caries index (sum of decayed, missing, and filled teeth) increases, the quality of life (level of satisfaction) decreases. The correlation analysis indicated that men are more affected by oral and dental problems than women, which might be due to more accurate reporting of life quality by men or underreporting by women due to sample size limitations. However, the regression approach identified gender as a significant predictor.
The most significant impact of the DMFT index was observed in the 30-40 age group. This can be explained by the increasing overall effects of the DMFT index on quality of life with age. Still, in the 30-40 age group, the impact is more pronounced due to broader social interactions in professional, educational, and familial settings, as they constitute a segment of the younger workforce. Appearance, a satisfying smile, and the absence of pain and psychological discomfort are crucial criteria that can profoundly affect the quality of life in this age range.
In this study, the effect of the DMFT index decreased with higher education levels. In other words, with higher education and consequently better socioeconomic status, individuals place more importance on oral health and dental care access, reducing the DMFT index and improving quality of life. Tooth decay and loss had negative effects on quality of life, with tooth loss having a more significant impact than decay. However, an interesting point is the direct relationship between filled teeth and quality of life observed in this study. Well-restored teeth without clinical signs such as pain can function similarly to healthy teeth, fulfilling their roles in aesthetics, chewing, and speech.
The mean DMFT index was lower among those who were satisfied with their quality of life than among those who were moderately happy and dissatisfied.
Ethical Statement
The present study was approved by the Research Ethics Committees of Golestan University of Medical Sciences (IR.GOUMS.REC.1398.052).
Funding
This article is based on Hossein Khodabakhshi's thesis for obtaining a professional doctorate in dentistry from the Faculty of Dentistry, Golestan University of Medical Sciences, Gorgan, Iran.
Conflicts of Interest
The authors have no conflicts of interest.
Acknowledgement
We extend our gratitude to the study participants for their cooperation.

Key Message
An increase in the dental caries index decreases oral health-related quality of life. Appearance and aesthetics, oral comfort, and eating restrictions are crucial factors impacting quality of life and life satisfaction.