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;

¼ root

Root development - MOORREES et al.

½ root ¾ root • Root completely • develped Apex open • Apex ½ closed • Apex closed 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: M

1 • •  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 PERMANENT T.

1. Molars 1. incisos Lateral incisor Canine 1. and 2. Praemolars 2. Molar 3. Molar Hidasi 6 8 8 11 9-10 12 Fehér 6-7 6-8 7-9 9-12 10-12 11-13 17-21 Upper

♂ ♀

Eruption sequences

4→5→3 3→4→5 vagy 4→3→5

Lower Eruption sequences

♂, ♀ 3→4→5

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%; Gábris et al.: I 2 ˃pm 2 ˃ PM 2 ˃i 1 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

MESIODENS

•

DENS SUPERNUMERARIUS

•

DENS SUPPLEMENTARIUS

17

Early primary teeth extraction

Physiological root resorption



Genetical code!

PATHOLOGY

 TIME  SPACE 

THE PATHOLOGICAL TRIAS:

   Perturbance of the rootresoption; Persisting primary models; Retained permanent teeth.

PATHOLOGY

 DENTITIO PRAECOX  DENTITIO TARDA  DENTITIO DIFFICILIS

INFRAOCCLUSIO SECUNDARIA

 Partialis retentio; reinclusio;  Submergentia;  „Halbretention”  „submerged deciduous teeth”

Eruption cyst/haematoma

Importance of the distal plane in primary dentition