The Study Of The Average Tooth Wear Level In General Populations In China

In human history, it was a very long evolution course from ape to the modern man. Along with the changes of environment, the human organ of mastication has changed accordingly. So in a large scale, morphological and development aspects of chewing organ represent an important line of research in the study of human living condition and culture development, and what's more,the main changes of chewing organ are in teeth and jaws . Dental tissue is the hardest tissue in human body. It provides important insights into aspects of dietary habits,the ingestion of refined food, and socioeconomic status. With man's developed knowledge and usage of fire, cooked and refined food took place of the raw and rough food, which led to the gradual weakening of the functional stimulus and developmental potentiality of masticating apparatus, and what's more, the tooth wear changes accordingly .Tooth wear begins with tooth eruption and ends until death of man, it develops gradually and lasts all the lifetime. As for some certain time, for a certain district ,and population ,the tooth wear can reflect the age of people's death, the tooth wear is not the same in different times and different age groups, so it has a great significance. The amount of tooth wear seen nowadays is considerably greater than in the past due to the fact that more people are now retaining their natural teeth into old age, so people pay much attention to tooth wearOur study used the method of cross-sectional study of descriptive epidemiology. Observing tooth wear in incisal and occlusal surface by extensive survey of contemporary general population. The study aimed to know the grade of physiological tooth wear by studying the average tooth wear level of each age group. And by comparative analysis of tooth wear condition in contemporary population, we could find the differences of tooth wear along with changes of society environment and dietary structure.In our study we examined the sampling population aged above 15 years old ,the enrolled population were divided into four groups according to the age which is described in《Human Skeleton Measurement》(Wu Rukang, Wu Xinzhi, 1965),《Anthropometric Handbook》(Shao Xiangqing, 1985): the age below 23 ,23-35,24-35,36-55,the age above 56 , and the group of 36-55 and the group above 56 were divided into two groups.Tooth wear in incisal and occlusal surface using the grading standard according to Smith and Knight index TWI 5, the tooth with residual root ,large area of residual crown ,impaction and porcelain were excluded in this study. Every data of tooth wear was carefully noted. In the mean while, the questionnaire survey was carried out in the enrolled population .All the data were grouped and entered respectively. Statistical methods are used in the analysis of the above data. The results were discussed and showed as follows. 1. The study of tooth wear1.1 A group of 416 adults was enrolled in this study. Male 226,female 190, six age group samples: the≤23 age group contained 89 persons, the 24~35age group 85 persons, the 36~45 age group 44 persons,the 46~55 group 42 persons,the 56~65 age group 81 persons,the≥66 age group 75 persons. A total of 11395 teeth from the population were examined excluding the teeth with residual root, large area of residual crown, impaction and porcelain.1.2 According to different age groups and teeth types, we worked out medians and interquartiles of every grades of tooth wear respectively, so we could gain the average degrees of tooth wear in different age groups, and it was signified by median.1.3 In order to display the difference of individual tooth in each age group ,we use weighing mean to calculate the average gradation of tooth wear. the average of the teeth in general population was 1.51 .The ratio of severer tooth wear in a population aged above 56 is 4.3%。1.4 Using chi square test to exam the significance of every two age group. There was great significant variation on degree of tooth wear among different age groups (P<0.05). Tooth wear is synchronous with the increase of age1.5 No significant difference in the tooth wear between male and female (P>0.05)2 Comparative analysis of tooth wear gradation2.1 There were 9395 teeth show wear of different gradation.. Among all the worn teeth, the first grade wear take the largest proportion(45.7%), the second grade wear 35.6%.2.2 In the different grades of tooth wear constitution proportion of the six different age groups, the ratio of 0o and 1o decrease along with aging, but the ratio of 2o , 3o and 4o increase along with aging.2.3 There was great statistical significance between first ,second third molar ,the wear degree of the first molar was highest, contrasting with the lowest of the third molar. There was no significance between incisors and canines (P>0.05), while a great significance appeared between incisors and first molars (P<0.05).。2.4 There was no statistical difference between isonym tooth except incisors(P>0.05) ,while a great significance appeared between lower incisor and upper incisor(P<0.05) The average tooth wear of mandibular incisors was higher than that of maxillary incisor (P<0.05).2.5 The index of the difference in tooth wear between anterior and posterior. The ration of upper incisor and first molar is1.31/2.16=60.64%,the ratio of lower incisor and first molar is 1.575/2.16=72.92%,the ratio of three upper incisor and three molar is 79.11%,the ratio of three lower incisor and three molar is 81.3%。3 The research of factors which affect tooth wearAfter checking the degree of tooth wear for the examined population, and carrying out questionnaire for the factors of tooth wear, and excluding two people without normal cognition, we got 414 pieces of effective questionnaires in the end. We calculated the average wear grade of every individual, worked out the data, and analyzed every related factors.3.1 Acid, tough food ,soft drink bruxism malocclusion Gastric acid reflux (regurgitation) and so on have an effect on tooth wear(P<0.05),while other factors have little effect on tooth wear and there is no statistical difference. Acid food is closely related to tooth wear , and in order is tough food , malocclusion Gastric acid reflux (regurgitation). 3.2 The severity of tooth wear differs with the frequency of eating acidic foods ,nuts and soft drinks and how much they are consumed. There is statistical difference of tooth wear prevalence between the three groups.In a summary, tooth wear is a gradual irreversible course. The tooth wear grade of different times and different ages vary much accordingly. But to the same individual, there is obvious difference among different teeth. The bruxism is the effect of multi-factors, the average tooth wear value of different age groups has important significance for preventive dentistry and contrast research of different social stages, referring to the aging change of bruxism, we can objectively appraise whether the tooth has pathologic bruxism, it is beneficial for dentist to carry out effective prevention therapy for patients according to pathogeny. As the prolonging of life-span, the problem of bruxism will be a challenge for dentists.