Tooth Morphology Primary Teeth and mixed dentition - Dr Casper Jonker (2024-25).pdf

Tooth morphology: Primary teeth and the mixed dentition Casper Jonker B.Ch.D, PGDip.Dent (Odont), MSc (Odont), PGCert (ClinEd), MAcadMed, PhD  Learning outcomes At the end of this session students will be able to: Compare the root and crown anatomy of the...

Tooth morphology: Primary teeth and the mixed dentition Casper Jonker B.Ch.D, PGDip.Dent (Odont), MSc (Odont), PGCert (ClinEd), MAcadMed, PhD  Learning outcomes At the end of this session students will be able to: Compare the root and crown anatomy of the primary and permanent teeth. Describe exfoliation dates of the primary dentition and subsequent eruption dates of the permanent dentition. Describe the development of permanent teeth between 7- 21 years, including calcification and root formation. Describe the mixed dentition with relevance appropriate restoration. Chart the mixed dentition appropriately. Features distinguishing primary teeth from permanent teeth Smaller than the corresponding permanent successors. Primary teeth crowns appear bulbous with pronounced labial/buccal cingulae. Cervical margins more pronounced than those of the successional teeth.  Cusps more pointed. Enamel softer, more opaque with a more prominent aprismatic layer: whiter appearance. The enamel layer is thinner and of a more consistent Image: Dreamstine.com depth (0.5-1.0mm) than in permanent teeth (approx. 2.5mm). The pulp chambers are correspondingly relatively larger. Image: van Beek (1983) Image: Berkovitz et al. (2010) Image: van Beek (1983)  The enamel is softer and more easily worn than permanent tooth enamel. All primary teeth start to calcify before birth: ALL will exhibit neonatal lines. Image: Wheeler’s Dental Anatomy, Physiology, and Occlusion Contrast this with the permanent dentition where only the first permanent molars are calcifying at birth so only these teeth will have neonatal lines. Image: Canva  The roots tend to be shorter and more delicate than permanent teeth. The roots of the primary incisors and canines are longer in proportion to their crown height than corresponding permanent teeth. The roots of the primary molars are widely divergent and usually extend beyond the dimensions of the crown. Image: Wheeler’s Dental Anatomy, Physiology, and Occlusion Comparison of maxillary, primary, and permanent second molars, linguo-buccal cross section A. The enamel cap of primary molars is thinner and has a more consistent depth. B. A comparatively greater thickness of dentine is over the pulpal wall at the occlusal fossa of primary molars. C. The pulpal horns are higher in primary molars, especially the mesial horns, and pulp chambers are proportionately larger. Image: Clinical pedodontics, Saunders D. The cervical ridges are more pronounced, especially on the buccal aspect of the first primary molars. E. The enamel rods at the cervix slope occlusally instead of gingivally as in the permanent teeth. F. The primary molars have a markedly constricted neck compared with the permanent molars. G. The roots of the primary teeth are longer and more slender in comparison with crown size than those of the Image: Clinical pedodontics, Saunders permanent teeth. H. The roots of the primary molars flare out nearer the cervix than do those of the permanent teeth. Images: Peninsula Dental School Wheeler’s Dental Anatomy, Physiology, and Occlusion  Primary teeth facts summary Thinner enamel and dentine layers. Pulp horns closer to the outer surface. Mesial pulp horn much higher. Relatively larger pulps. Enamel rods direct slightly occlusally in the cervical area. Cervical area is constricted significantly. Roots flare as they approach the apex. More tortuous and irregular pulp canals. Charting: primary teeth Images: courtesy Nicky Kilpatrick Image: Brand and Isselhard, 7th edition Charting: permanent teeth Image: Brand and Isselhard, 7th edition  Dental age Dental age is defined by a combination of: Which teeth have erupted. The amount of resorption of the roots of the primary teeth. The amount of development of the permanent teeth.  General observations The transition from the primary to the mixed dentition begins at about the age of 6 years. The permanent teeth erupt in groups. Be aware of the most common eruption sequence to calculate the expected timing of these eruption groups. Teeth usually emerge when about 75% of their roots are completed. It takes 2-3 years for root completion after a tooth has erupted into occlusion.  Age 6 years Teeth erupting at about 6 years: Mandibular central incisor Mandibular 1st permanent molar Maxillary 1st permanent molar  These teeth erupt at about the same time. Biological variation: unrealistic to determine a precise eruption order. Primary incisors are smaller than the permanent incisors: spacing prior to the eruption of the permanent successors is normal at this stage. Parents may need some reassurance about this. Images: Peninsula Dental School  Age 7 years Teeth erupting at 7 years: Maxillary central incisors Mandibular lateral incisors Root formation of the maxillary lateral incisors: well advanced but are still a year from eruption. Canines and premolars are still at the stage of crown completion or the commencement of root formation.  Following eruption of the upper central incisors, a diastema may persist. Characteristic ‘goofy’ or “ugly duckling” appearance. This will close as the laterals erupt and the canines form and begin to descend along their eruptive path. This is a normal feature and will close naturally but parents may require some reassurance. A larger space may require specialist orthodontic intervention. Images: Peninsula Dental School Image: Brand and Isselhard, 7th edition  Age 8 years Teeth erupting at 8 years: Maxillary lateral incisors * Following eruption of the maxillary lateral incisors there is a delay of 2 to 3 years before further permanent teeth appear. Images: Peninsula Dental School Image: Brand and Isselhard, 7th edition Images: Peninsula Dental School  Age 9 years Primary canines are present. Primary first and second molars are present. Approximately 1/3 of the root of the mandibular canines and mandibular first premolars are complete. Root development has just started (if at all) on the mandibular 2nd premolar. Root development of the maxillary 1st premolar has begun and is just beginning for the 2nd maxillary premolar. Image: Brand and Isselhard, 7th edition Image: Berkowitz et al, 2017 Images: Peninsula Dental School  Age 10 years Greater amount of root resorbtion in both the primary canines and molars. Approximately half of the roots of the mandibular canine and mandibular first premolar have been completed. Nearly half the root of the maxillary first premolar is complete. Significant root development of the: Mandibular 2nd premolar Maxillary canine Maxillary 2nd premolar Amongst the most useful indicators of a dental age of 10 years are: Completion of the roots of the mandibular incisors. Near completion of the roots of the maxillary lateral incisors. Image: Brand and Isselhard, 7th edition  Age 11 years The roots of all the permanent incisors and first permanent molars should be complete. Only primary teeth remaining should be: The maxillary canine The maxillary second molar The mandibular second molar Mandibular arch Mandibular canine, mandibular first premolar and maxillary first premolar erupt more or less simultaneously. The mandibular canine most often appears just ahead of the first premolar. Important: time of eruption rather than the eruption sequence is the most important feature. Maxillary arch The first premolar usually erupts well ahead of the canine. Image: Brand and Isselhard, 7th edition Image: Berkowitz et al, 2017  Age 12 years The remaining permanent successors erupt. These include: Maxillary canine Maxillary second premolar Mandibular second premolar * Often possible to spot the earliest radiographic signs of 3rd molar formation. Image: Brand and Isselhard, 7th edition  Age 13 - 15 years Completion of the roots of the permanent teeth. Eruption of the second molars. The third molars should become increasingly apparent on radiographs. Image: Brand and Isselhard, 7th edition Image: Berkowitz et al, 2017 Images: Peninsula Dental School  Age 18 - 21 years The third molar teeth erupt into the dental arches. Image: Brand and Isselhard, 7th edition Eruption/exfoliation primary Eruption dates permanent Clinical implications Important normal variations with clinical significance Eruption of the second molars ahead of the premolars in the mandibular arch. This sequence may decrease the space available for the latter leading to them being crowded out of the arch. Eruption of the canines ahead of the premolars in the maxillary arch. Maxillary canine erupts at about the same time as the maxillary first premolar the canine may be forced labially out of the arch.  Asymmetries in eruption between the right and left sides. Teeth on one side of the arch should erupt within 6 months of those on the other. A small degree of asymmetry is normal - any large discrepancy is not normal and warrants further investigation.  The progress of caries is much faster in the primary dentition, so incipient lesions. Should be restored sooner than later! Thinner enamel and dentine. Chemical composition and their physical properties differ from permanent teeth including softer Image: Prof Nicky Kilpatrick enamel. Vulnerable to dissolution by cariogenic acids. Mesial pulp horn higher. Flat contact points. Important preventative considerations The effect of behaviour should not be overlooked. It must be an integral part of treatment strategies. Good oral hygiene habits needed at an early age. These habits can translate into benefits for the permanent teeth. Permanent dentition can last a lifetime if cared for properly.  The permanent teeth are at high risk of caries during this period of mixed dentition. Erupting teeth is difficult to clean. They are not yet fully aligned with their neighbour. Cleaning is usually avoided completely because of tender gums. Primary teeth are important for guiding the erupting permanent teeth. Primary teeth play a role in the development of speech. Procedures in Primary Teeth: Restorative Dentistry Enamel is thinner, therefore modifications are necessary in the cavity prep. Broad contacts need to be restored. Beware of the mesio-buccal Image: Ahmed et al., 2020 pulp horn. May need to do SSC if both proximal surfaces involved. Images: Nicky Kilpatrick  Implications of primary tooth morphology Procedures in Primary Teeth: Surgical Procedures Conical anterior roots facilitate easy removal. Flared roots of the molars. Due caution as premolar buds are located between the roots. Image: Steenkamp et al., 2018: A female cheetah dentition Procedures in Primary Teeth: SSC Images: SDLE presentations and Prof. Nicky Kilpatrick  Loss of primary teeth Growth of the jaws, sequential exfoliation of the primary teeth and eruption of the permanent teeth allow movement into predictable positions in the dental arches. The primary second molars are exceptions: they have a greater mesio-distal dimension than the second premolars. They are retained in the dental arches until the eruption of these teeth at 10-12 years and serve to maintain space for the second premolars.  Premature loss consequences Where crowding is absent Early loss little or no effect on the permanent dentition. Where crowding is present Space loss is always greater in the upper arch than the lower. Loss of second primary molars leads to a greater loss of space than loss of the first primary molars. Very early loss of second primary molars, before the eruption of the first permanent molars, can lead to almost complete loss of the second premolar space. Extractions after the age of 10 can cause relatively little space loss.  Early loss causes mesial drift of the dentition into the ensuing space may lead to crowding or occlusal irregularities. In the canine region, it can also be due to distal drift of anterior teeth. Images: Peninsula Dental School  Sources Berkovitz B.K.B., Holland G.R.. Moxham B.J. (2002) Oral Anatomy, Histology, and Embryology. 3rd Edition. Mosby. Berkovitz, B., Moxham, B. J., Linden, R. W. A., Sloan, A. J. (2010). Master dentistry volume 3 oral biology : Oral anatomy, histology, physiology and biochemistry. Elsevier Health Sciences. Berkovitz, B. K. B., Holland, G. R. R., & Moxham, B. J. (2017). Oral anatomy, histology and embryology e-book. Elsevier. Managing the developing occlusion: a guide for dental practitioners (British Orthodontic Society). Profit W. R., Fields H. W., Sarver D. M. Contemporary Orthodontics. (2007) Mosby (2nd Edition), Chapter 3, 93-100. van Beek G.C. (1983) Dental Morphology: an illustrated guide.. 2nd Ed’n. Wright. Brand and Isselhard. Anatomy of Orofacial structures: a comprehensive approach, 7th edition, Elsevier. Ahmed H.M.A., Musale P.K., El Shahawy O.I., Dummer P.M.H. (2020). Application of a new system for classifying tooth, root and canal morphology in the primary dentition. International Endodontic Journal, 53, 27–35. Steenkamp G., Boy S.C., van Staden P.J., Bester M.N. (2018) Oral, Maxillofacial and Dental Diseases in Captive Cheetahs (Acinonyx jubatus). Journal of Comparitive Pathology, 158, 77-89. Clinical pedodontics, second edition, Philadelphia, 1957, Saunders.  Sources Wheeler’s Dental Anatomy, Physiology, & Occlusion, tenth edition, Saunders Youtube link: https://www.youtube.com/watch?v=TBW4BQT_P-U Youtube link: https://www.youtube.com/watch?v=4xdAFJBabhY Please go to Mentimeter Thank you Any questions?