Anatomical Features of Teeth and Their Development

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08/02/20 Medical Reference this

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DENTITION

INTRODUCTION

Throughout this essay, information regarding the formation, types of teeth, importance, practices, and disorders affecting dentition will be discussed.

FORMATION OF TEETH AND DISORDERS THAT AFFECT TOOTH DEVELOPMENT

The formation of teeth begins through dental lamina, in the sixth week of embryonic life. The oral epithelium thickens through the embryonic stage and grows to the underlying connective tissue in a descending manner. The epithelium develops into a ‘U’ shape for the future arrangement of maxillary and mandibular teeth. The stages of tooth development start with bud, cap, and bell stage. Bud stage is the first sign of the enamel organ. The buds enter the connective tissue and cause a minimal dip in the deepest area.

Cap stage has three processes in the development of teeth: outer enamel epithelium (OEE), Inner Enamel Epithelium (IEE) and the Stellate reticulum. OEE layer of the cap stage is the continuation of the oral epitheliums basal layer, IEE comes from the basal layer and is the concavity and deepest part of the cap. During development, the IEE and OEE cells are both in constant motion. The stellate reticulum combines IEE and OEE to advance to the next stage of development.

During the bell stage, an extra layer of epithelium and stratum intermedium is added to the development of the tooth. Stratum intermedium contains coatings of flattened squamous cells that are held in the IEE and stellate reticulum. The cell layers are expanded to outline the shape of the crown and changes to the IEE and other cells in the enamel organ (Brand and Isselhard). During this time, “formation of dentine from odontoblasts proceeds amelogenesis and the enamel formation for the incisal edges and cusp tips.” The cervical area of the enamel organ then gives rise to Hertwig Epithelial Root Sheath (HERS). HERS helps in the size, shape, and number of roots formed in each tooth. The expansion of the root begins with the IEE and OEE bonding to form a cervical loop. It lengthens and bends horizontally forming a diaphragm to convert to HERS (Varanasi). Developmental disorders can also affect tooth development. Disabilities such as autism, down syndrome, etc. are more prone to tooth decay, malocclusion, delayed tooth eruption, oral malformations, periodontal disease and trauma and injury (“Developmental Disabilities | National Institute Of Dental And Craniofacial Research”).

DIFFERENT TYPES OF DENTITION AND THE SIGNIFICANCE TO GROWTH AND DEVELOPMENT IN THE FACE.

When dental professions talk about dentition, it can be categorized into two sections. Primary dentition refers to 20 deciduous teeth (baby teeth) and secondary dentition refers to 32 permanent teeth. The teeth are spread out evenly in the oral cavity, one half in the maxillary (upper jaw) and the other in the mandible (lower jaw). The importance of teeth eruption is for the full development of muscles of mastication, formation of the bones of the jaw, future location, alignment, and occlusion of permanent teeth (Brand and Isselhard).

DIFFERENCES OF DECIDUOUS AND PERMANENT TEETH

The oral cavity only has two of the same teeth in the maxilla and the mandible. In the deciduous teeth, there are two central incisors, two lateral incisors, two canines, two 1st molars and two 2nd molars in the maxilla and mandible. Differences of Primary dentition: they are smaller in size, shorter crowns than their roots, bulbous crown due to teeth being wider mesio-distally, whiter in colour and opaquer, easily ground, a prominent cervical ridge in anterior teeth and many more (Varanasi). In the permanent dentition, there are two central incisors, two lateral incisors, two canines, two 1st premolars, two 2nd premolars, two 1st molars, two 2nd molars and two 3rd molars (Varanasi).

ERUPTION DATES OF DECIDUOUS AND PERMANENT TEETH

Citation: (“Baby Teeth Eruption Charts – American Dental Association”)

The eruption process for deciduous upper teeth begins with the:

  1. central incisors 8-12-month
  2. lateral incisors 9-13 months
  3. first molar 13-19 months
  4. canine 16-22 months
  5. second molar 25-33 months.

The lower teeth emerge start with:

  1. central incisor 6-10 months
  2. lateral incisor 10-16 months
  3. first molar 14-18 months
  4. canine 17-23 months
  5. second molar 23-31 months.

The sequence for the permanent teeth of the upper:

  1. first molar 6-7 years
  2. central incisor 7-8 years
  3. lateral incisor 8-9 years
  4. first premolar 10-11 years
  5. second premolar 10-12 years
  6. canine 11-12 years
  7. second molar 12-13 years
  8. third molar (wisdom tooth) 17-21 years

The lowers begin:

  1. first molar 6-7 years
  2. central incisor 6-7 years
  3. lateral incisor 7-8 years
  4. canine 9-10 years
  5. first premolar 10-12 years
  6. second premolar 11-12 years
  7. second molar 11-13 years
  8. third molar (wisdom tooth) 17-21 years

ANATOMICAL FEATURES OF TEETH AND FUNCTIONS

The tooth’s anatomical features consist of enamel, dentin, pulp chamber and cementum. Refer to figure 6. The tooth is a complex tissue that involves many cells working together inside each individual tissue. The enamel is the outer layer of the tooth and is the anatomical crown forming the tip. The enamel becomes thinner as it continues down the cervical line (Brand and Isselhard).

Dentin is the main tissue; it helps form the size and shape of each tooth. Dentin is calcified tissue that is hard and dense while being yellow in colour. The role of cementum is to cover the root with a small layer of tissue. Cementum is used to provide “a medium for the attachment of the tooth to the alveolar bone.” The cervical line has a thin layer of cementum which is thickened near the peak of the root. The pulp is the “nourishing, sensory, and dentin-reparative system.” It contains blood vessels, connective tissue, nerve tissue, lymph vessels, and odontoblasts. The pulp chamber is positioned in the middle of the tooth. The blood vessels nourish the tooth support and activate the formation of dentin. They also provide white blood cells that fight bacteria from entering the pulp and lymph fluids filter inside the tooth. The nerve tissue sends signals of pain but no hot or cold sensations (Brand and Isselhard).

In the oral cavity, each tooth anteriorly and posteriorly has a role. The incisors cut food on the biting edge (incisal edge). The teeth assist in guiding food through the depression on the lingual aspect. The canines hold or clasp food and aid/protect in stress-bearing jaw movements. The premolars 1 and 2 are a mixed tooth of a canine and a molar. Premolars have at least two cusps, the lingual cusp grinds whilst the buccal cusp holds food in the place. Molar teeth have at least 4 cusps and aid in the chewing and grind of food. The maxillary and mandibular molars occlude with each other to form an interlocking movement (Brand and Isselhard).

NOTATION SYSTEMS

Notation systems help identify a specific tooth, arch, quadrant, tooth name, and dentition. They are divided into quadrants: right and left, refer to figure 1. There are three methods: universal system, Palmer notation system and Federation Dentaire Internationale System (FDI) (Brand and Isselhard).

The Universal system uses numbers and letters. The permanent teeth consist of numbers 1-32. 1 is assigned to the most posterior molar on the upper right quadrant of the maxillary and the last number 32, is given to the most posterior tooth of the third right molar in the bottom right quadrant of the mandible. This is the same for the deciduous teeth except letters are used. A-T is the sequence with the letter A is the right second molar and T is the right second molar of the mandible (Brand and Isselhard). Refer to figure 2 and 3.

The Palmer Notation System is like the universal system except numbers 1-8 are used for permanent teeth and letters A-E are used for deciduous. The teeth are split into 4 quadrants: maxillary right, maxillary left, mandibular right, and mandibular left. The numbers are divided by a line in the middle, which represents the midline of the teeth. The number of teeth: 1 is the central incisor, 2 is the lateral incisor, 3 is the canine, and so on. Likewise, primary teeth have the same sequence, except letters are used (Brand and Isselhard). Refer to figure 4

The Federation Dentaire Internationale System (FDI) has similarities to the Palmer system except for the use of teeth identification. Each tooth is given a two-digit number, the first number identifies the tooth with quadrant numbers and can either be permanent or deciduous. The second number uses the Palmer 1-8 numbering. For example, the top right quadrant of the maxilla central incisor is quadrant 1 and is the first tooth in the sequence, so the number would be 11. The deciduous teeth use the same method, but the quadrants start with 5-8 (Brand and Isselhard). According to the RACGP, dentists in Australia use the FDI notation (Practitioners). Refer to figure 5.

NERVES

The nerves involved in the maxilla and mandible is branched from the trigeminal nerve. It is the sensory and motor nerve to the face. In the maxillary, the trigeminal is branched into the anterior superior alveolar through the infraorbital canal and supplies the maxillary incisors and canines. The middle superior alveolar nerve delivers the sensation to the maxillary premolars. Through the maxillary nerve, the pterygopalatine fossa branches to the posterior superior alveolar nerve, providing the posterior maxillary molars the response (Varanasi). The main trunk of the mandibular nerve divides into the posterior division sending the nerves to the inferior alveolar branch (Brand and Isselhard). The branch enters through the mandibular foreman and stretches towards the mandibular teeth and periodontal ligaments.

FLUOROSIS

Dental Fluorosis is a condition that affects teeth by fluoride. This is caused by overexposure of fluoride over the first eight years of life. The different forms of fluorosis are stained teeth from yellow to dark brown, surface anomalies, and pits in the teeth. Some reasons may be swallowing dental products such as toothpaste or mouth rinse (Cold et al.). Fluorosis can also affect the development of enamel and dentin in permanent teeth (“Fluorosis, Dental Fluorosis | Colgate® Oral Care”).The recommended intake of fluoride according to the Australian government varies for different ages and stages in life (pregnancy) (“Fluoride (Updated 2017) | Nutrient Reference Values”), refer to figure 7-10. In the community water system, fluoride provides advantages and disadvantages.

Fluoride was introduced to aid in reducing tooth decay and cavities in the tooth. Although a disadvantage of fluoride in the water system is that there is a connection between fluoride and certain cancers. This is especially true for people with kidney disease as they possess a health risk to fluoride (Reinagel).

During bone growth and development, if Fluorosis is present it can cause skeletal fluorosis. This is a condition that creates weak, stiff and painful joints to bones (VidaZohoori and Marsland Duckworth).

SYSTEMIC CONDITIONS FOR LOSS OR DELAYED ERUPTION OF TEETH

Research has shown that systemic conditions in the delayed eruption of teeth can be associated with nutrition, endocrine disorders, HIV infection, cerebral palsy, celiac disease, ichthyosis and vitamin D-resistant rickets (Muntasoot). A rare condition where teeth fail to form or erupt in the oral cavity is called Anodontia (subdivided into hypodontia, oligodontia, and anodontia). This is a genetic disorder and can cause primary or permanent teeth to be undeveloped (“Tooth Agenesis – NORD (National Organization for Rare Disorders)”).

DIFFERENCE BETWEEN HYPOPLASIA AND HYPOCALCIFICATION IN TEETH

The difference between hypoplasia and hypocalcification is that hypoplasia means the enamel is significantly less when compared to normal. Hypoplasia does not produce enough enamel leaving deficient areas (Pietrangelo).

Hypocalcification are white spots or stains that is caused by demineralization. Acids are required for calcium to be broken down into the enamel. Acids such as acidic foods, mouth bacteria or drinks help this process. If untreated future cavities may result (“What Is Hypocalcification? | Colgate® Oral Care”).

HISTORY, FABRICATION, AND MANAGEMENT OF DENTURES IN HYPOPLASIA, HYPOCALCIFICATION OR FLUOROSIS

Taking a history of hypoplasia or hypocalcification can help provide health professionals know specific areas of pain, side effects, and allergies. The history must include their past and present history as this helps dental professionals to make the correct judgment (Rahn, Ivanhoe, and Plummer). The referral for the dentist needs to include the prosthetists oral examination as this includes the issues that may occur during the fabrication of a denture. For example, placing pressure on the maxilla or mandibular bones when taking impressions on a skeletal fluorosis patient. When a denture is fabricated for a fluorosis patient, the colour of teeth and gums are to be coloured specifically to match their old teeth. Future check-ups would be organized after a few days to check whether any areas are inflamed or hurting the patient.

CONCLUSION

In conclusion, the essay has outlined the anatomical features of teeth, development, and growth, differences of permanent and deciduous teeth, tooth disorders, notation systems, nerves and eruption times.

FIGURE:


BIBLIOGRAPHY

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