THE STUDY BY X-RAY CONTRAST ON CENTRAL INCISOR ERUPTION AND ELONGATION OF CLINICAL DENTAL CROWN

Abstract

The report about growth and development, calcification and eruption year of teeth had been made and published by many investigators but mutual relation between teeth and paradentium was not understood accurately.Upper and lower central incisors had been continuously observed for 17.5 months (upper 48 samples, lower 11 samples) by contrast radiography, originally, developed for the purpose.Clinical teeth crown length before and after dental completion is measured and change from clinical dental crown length to anatomical crown length after dental emergence was observed in 526 samples (upper 279, lower 247) in association with continuous observation groups.Obtained results were as follows :1. Rider was set on the cutting-edge of incisor and labial surface of dental crown and gingival boundary line were plastered with contrast medium. Approximately value of clinical dental crown length and teeth length from radiography were found.2. When the teeth in jaw attained three-quarters of completed teeth length, their eruption was found in oral cavity.3. Judging from continuous observation groups, growth velocity of clinical dental crown length and teeth length in upper or lower jaws fast, 4 or 5 months after eruption but slower late after its time.4. Clinical dental crown length attained one-half of anatomical crown length in upper jaw about a year after emergence and in lower jaw about a year and 2.5 months.5. From the result of statistical analysis, the developmental relation between clinical dental crown length and teeth length was of high correlation.(r=0.97, Y=-15.92 + 0.94 X, in upper; r =0.98, Y=-11.014-0.76 X, in lower)6. Judging from continuous observation groups and other observation groups, the root was complet 27.17 months in upper and 30.93 months in lower after emergence.7. Clinical dental crown length was in upper about 60.9 % and in lower about 58 % of anatomical crown length at the time of root completion.8. After root completion, clinical dental crown length was linear in semi-logarithmic table. Clinical dental crown length increased in propotion to a logarithm of months.9. Clinical dental crown length was in accord with anatomical crown length in upper 822 months (approximately 69 years) and in lower 619 months ( approximately 52 years) after emergence.