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Dental anatomy Assis. Lec. Zainab Abid Ali Lecture Fourteen 1st Stage Tooth Development The development of the crown and the root of the tooth takes place within the bone in the jaw. The toot...

Dental anatomy Assis. Lec. Zainab Abid Ali Lecture Fourteen 1st Stage Tooth Development The development of the crown and the root of the tooth takes place within the bone in the jaw. The tooth passes through stages named according to their shapes: 1. Bud stage. 2. Cap stage. 3. Bell stage. Dental development can be considered to have two components: (1) The formation of crowns and roots and (2) The eruption of the teeth. After the crown of the tooth is formed, development of the root portion begins. After the root and crown are formed, the tooth penetrates the mucous membrane and enters into the mouth by a process called {Eruption}. The eruption of a tooth stops when it occluded with a tooth in the opposing jaw and contacts the adjacent teeth. 1 Dental anatomy Assis. Lec. Zainab Abid Ali Lecture Fourteen 1st Stage Sequential order of deciduous teeth according to their eruption times: Primary Tooth Time of Eruption (in months) Mandibular central incisors 6.5 Mandibular lateral incisors 7 Maxillary central incisors 7.5 Maxillary lateral incisors 8 Mandibular first molars 12-16 Maxillary first molars 12-16 Mandibular canines 16-20 Maxillary canines 16-20 Mandibular second molars 20-30 Maxillary second molars 20-30 Deciduous Teeth The deciduous teeth are 20 in number. They start erupting at the age of 6.5 months (mandibular central incisor), and they finish at the age of 20-30 months (mandibular and maxillary second molars). The Importance of Deciduous Teeth 1. Allow proper mastication. 2. Prevents malocclusion. 3. Guide the eruption of the permanent teeth. 4. Esthetics. 5. Phonetics. 2 Dental anatomy Assis. Lec. Zainab Abid Ali Lecture Fourteen 1st Stage The deciduous teeth roots are fully formed after eruption, then after a while resorption to these roots starts until exfoliation of the deciduous teeth occurs, followed by the eruption of the permanent successor teeth. Maxillary Deciduous Teeth Central and Lateral Incisors: 1. The mesio-distal width is more than the labiolingual dimension. 2. The root: crown ratio is increased. 3. From the mesial aspect, the crown appears thicker because of the short crown’s length. Canine: 1. From the labial aspect, the crown is more constricted at the cervical area, so the cusp and the slopes are seen more developed. 2. The mesial slope of the cusp is longer than the distal slope. 3. The mesial and distal contact areas are at the same level. 4. The root: crown ratio is increased. 5. From the mesial aspect, the crown appears thicker labio-lingually because of the short crown’s length. 3 Dental anatomy Assis. Lec. Zainab Abid Ali Lecture Fourteen 1st Stage First Molar: 1. There are four cusps: mesio-lingual (largest), mesio-buccal, disto-buccal and disto-lingual (smallest) 2. There are three roots: lingual, mesio-buccal, and disto-buccal. Second Molar: 1. There are five cusps (four well developed and one supplemental) which are the mesio-lingual (largest), mesio-buccal, disto-buccal, disto- lingual and the fifth cusp (supplemental cusp). 2. There are three roots: lingual, mesio-buccal, and disto-buccal roots. Mandibular Deciduous Teeth Central and Lateral Incisors: 1. They are wider mesio-distally in relation to their length more than the permanent mandibular incisors. 2. The root: crown ratio is increased. 3. The labiolingual width appears more due to the short crown’s length. 4 Dental anatomy Assis. Lec. Zainab Abid Ali Lecture Fourteen 1st Stage Canine: 1. The labiolingual dimension is much less than the maxillary deciduous canine. 2. The cervical ridge is less pronounced than the maxillary deciduous canine. 3. The distal slope of the cusp is larger than the mesial slope. First Molar: 1. There are four cusps: mesio-lingual (largest), mesio-buccal, disto-buccal and disto-lingual (smallest). 2. There are two roots: mesial and distal roots. Second Molar: 1. There are five cusps: mesio-lingual, mesio- buccal, disto-buccal, disto-lingual and distal cusp). 2. There are two roots: mesial and distal roots. Principal Differences between Deciduous and Permanent Teeth General Differences: 1. The deciduous teeth are (20) in number while the permanent teeth are (32) in number. 2. The deciduous teeth are smaller in all dimensions. 5 Dental anatomy Assis. Lec. Zainab Abid Ali Lecture Fourteen 1st Stage 3. The deciduous teeth show less morphology variations. 4. The enamel of the deciduous teeth is whiter, and more opaque so they are whiter than the permanent teeth. 5. The enamel of the deciduous teeth is thinner (0.5-1cm), while in the permanent teeth it is (1.5-2.5 cm). Crown Differences: 1. The crowns of the deciduous teeth are more constricted at the cervix. 2. The cervical ridges in all deciduous teeth are more prominent. 3. The intercuspal distance of the deciduous teeth is more constricted bucco- lingually. 4. The crowns of the deciduous anterior teeth are wider mesio-distally as compared with the crown’s length. Root Differences: 1. Lack of root trunk in the deciduous molars. 2. The roots of the deciduous teeth are shorter, weaker, and narrower. 3. The roots of the deciduous teeth are longer in proportion to the crown. 4. The roots of the deciduous molars are wider than the crown, to allow more room for the development of the successor permanent teeth. 6