Understanding the Mechanism of Second Dentition in Humans

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Second dentition is a natural process involving the development of a second set of teeth in humans. This complex phenomenon includes factors like root development, periodontal changes, and functional occlusion. The process is crucial for normal craniofacial development and has implications for orthodontic treatment and cariology. The eruption timetable for permanent teeth is also highlighted, emphasizing the importance of recognizing and monitoring the stages of dental development.

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MECHANISM OF SECOND DENTITION

Diphyodont and Heterodont humans homodont: all tooth are alike; heterodont: teeth have diferent shapes; poliphyodont: changing of teeth for the whole lifetime diphyodont : 2 sets of teeth mammals;

Root development - MOORREES et al. Root completely develped Apex open Apex closed Apex closed root root root MOORREES CF, FANNING EA, HUNT EE Jr. AGE VARIATION OF FORMATION STAGES FOR TEN PERMANENT TEETH. J Dent Res. 1963 Nov-Dec; 42:1490-1502.

SECON DENTITION - MECHANISM Mechanism several factors responsible for normal second dentition process Primary teeth period, after development of primary teeth transitory period: maxillary bones are preparing for the permanent teeth arrival.

SECOND DENTITION Physiological developmental phenomenon; Dynamic process: root development, periodontal development, functional occlusion.

SECOND DENTITION - IMPORTANCE Normal develpment of the craniofacial complex; Treatment planing, timing - orthodontics; Cariology.

6 years: M1 First permanent molars: at the end of the line; Sechsjahrmolaren ; There are no changing of teeth, so it goes often unnoticed by the parents!

ERUPTION - TIMETABLE Eruption sequences 4 5 3 3 4 5 vagy 4 3 5 PERMANENT T. Hidasi Feh r Upper 1. Molars 6 6-7 1. incisos 8 6-8 Eruption sequences Lower Lateral incisor 8 7-9 , 3 4 5 Canine 11 9-12 1. and 2. Praemolars 9-10 10-12 2. Molar 12 11-13 3. Molar - 17-21

CHARACTERISTICE Percentil presence of permanent teeth: prevalence of a particular tooth at a given moment in the population. dierences between the arches; sexual dimorfizm; Dental age determination!; dental status or the given age.

CHARACTERISTICS Average eruption time: the age when the percentil presence of the tooth is 50%. IMPORTANCE: describes the second dentition process; comparative studies between populations; acceleratio: comparison with older data!; Percenti presence: tooth type 15-40% Average eruotion time: tooth type 1-1,5 years.

BONE MATURATION Second dentition is paralell with bone maturation: Tanner-Whitehouse method TW2 (Tanner et al. 1975); Orthodontic diagnostic value!

GROWTH- TANNER End of secondary dentition Chronological age

SECOND DENTITION CRITERIA Presence of the permanent toothgerm Optimal position of the toothgerm Sufficient space Physiological root resorption

PRESENCE OF THE PERMANENT TOOTH GERM Aplasia prevalence: 3-4%; G bris et al.: I2 pm2 PM2 i1 Persisting primary teeth Bolk s terminal reduction theory

APLASIA: 35; 31; 41; 45. Persisting primary teeth: 75; 71; 72; 85 Bolk s terminal reduction theory: EXEPTION LOWER PERMANENT FIRST INCISORS 15

OPTIMAL POSITION OF THE PERMANENT TOOTHGERM Lower incidors: lingual eruption, erupting often in the presence o the primary incisors; Extraction of the primary teeth; Upper canines: Ectopia; Retentio/Impactio