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Anatomy and Physiology
Muscles of the Head and Neck
Muscles of Mastication: These muscles are responsible for chewing and moving the jaw. You need to know: Masseter : o Action: Elevates the mandible (closes the jaw). o Location: From the zygomatic arch to the mandible. o Innervation: Mandibular division (V3) of the trigeminal nerve. Temporalis : o Action: Elevates and retracts the mandible. o Location: Temporal fossa to the coronoid process of the mandible. o Innervation: Mandibular division (V3) of the trigeminal nerve. Medial Pterygoid : o Action: Elevates the mandible and assists in closing the jaw. o Location: Pterygoid plate of the sphenoid bone to the mandible. o Innervation: Mandibular division (V3) of the trigeminal nerve. Lateral Pterygoid : o Action: Depresses the mandible, allowing the mouth to open, and helps in side-to-side movements of the jaw. o Location: Lateral pterygoid plate of the sphenoid bone to the condyle of the mandible. o Innervation: Mandibular division (V3) of the trigeminal nerve. Muscles of Facial Expression: These muscles control facial expressions. Focus on: Orbicularis Oris : o Action: Closes and puckers the lips. o Location: Around the mouth. o Innervation: Facial nerve (CN VII). Zygomaticus Major : o Action: Elevates the corners of the mouth (as in smiling). o Location: Zygomatic bone to the corners of the mouth. o Innervation: Facial nerve (CN VII). Buccinator : o Action: Compresses the cheek to help keep food between the teeth during chewing. o Location: Between the maxilla and mandible, forming the muscular portion of the cheek. o Innervation: Facial nerve (CN VII). Key Concepts: Know that muscles of mastication are innervated by the mandibular division of the trigeminal nerve (CN V3). Muscles of facial expression are controlled by the facial nerve (CN VII).
Bones of the Skull
Key Bones: Maxilla : o Forms the upper jaw, holds the upper teeth, and forms part of the orbit of the eye. o Contains the infraorbital foramen , which transmits the infraorbital nerve (branch of CN V2). Mandible : o The lower jawbone, holding the lower teeth. The largest and strongest bone of the face. o Features include: Mental foramen : Transmits the mental nerve (branch of CN V3). Mandibular foramen : Transmits the inferior alveolar nerve (branch of CN V3). Zygomatic Bone : o Commonly known as the cheekbone, it articulates with the maxilla and temporal bone. o Foramen of interest: Zygomaticofacial foramen (transmits the zygomaticofacial nerve, branch of CN V2). Frontal Bone : o Forms the forehead and the upper part of the orbital cavities. o Contains the supraorbital foramen or notch, through which the supraorbital nerve (branch of CN V1) exits. Sphenoid Bone : o Complex bone located at the base of the skull. o Key foramina: Foramen ovale : Transmits the mandibular nerve (CN V3). Foramen rotundum : Transmits the maxillary nerve (CN V2). Key Concepts: Focus on foramina through which the cranial nerves (CN V and VII) exit. Understand how these bones and their landmarks relate to dental anesthesia and nerve blocks (e.g., inferior alveolar nerve block in the mandible).
Cranial Nerves: Trigeminal Nerve (CN V) and Facial Nerve (CN VII)
Trigeminal Nerve (CN V): The trigeminal nerve is the primary sensory nerve for the face and motor nerve for the muscles of mastication. It has three divisions:
- Ophthalmic (V1) : o Sensory to the upper face (forehead, scalp, upper eyelids). o Passes through the superior orbital fissure.
- Maxillary (V2) : o Sensory to the middle face (cheeks, upper lip, maxillary teeth). o Passes through the foramen rotundum and exits the skull through the infraorbital foramen.
- Mandibular (V3) :
Muscles of Mastication (masseter, temporalis, medial and lateral pterygoid) are innervated by the Mandibular division (V3) of the Trigeminal nerve (CN V). Muscles of Facial Expression (orbicularis oris, zygomaticus major, buccinator, etc.) are innervated by the Facial nerve (CN VII). Bony Landmark Foramen Structures Passing Through Clinical Relevance (Nerve Block) Maxilla Infraorbital foramen Infraorbital nerve (branch of CN V2), artery, vein Infraorbital nerve block : anesthetizes upper lip, cheek, side of nose, and maxillary teeth
Bony Landmark Foramen Structures Passing Through Clinical Relevance (Nerve Block) Mandible Mental foramen Mental nerve (branch of CN V3), artery, vein Mental nerve block : anesthetizes chin, lower lip, and anterior mandibular teeth Mandible Mandibular foramen Inferior alveolar nerve (branch of CN V3), artery, vein Inferior alveolar nerve block : anesthetizes mandibular teeth and lower lip Sphenoid Bone Foramen ovale Mandibular nerve (CN V3) Key exit point for V3 division of CN V (trigeminal) affecting the mandible Sphenoid Bone Foramen rotundum Maxillary nerve (CN V2) Key exit point for V2 division of CN V (trigeminal) affecting the maxilla Frontal Bone Supraorbital foramen Supraorbital nerve (branch of CN V1), artery, vein Supraorbital nerve block : anesthetizes forehead and upper eyelid Zygomatic Bone Zygomaticofacial foramen Zygomaticofacial nerve (branch of CN V2) Sensory innervation to cheek area, important in maxillary region blocks Palatine Bone Greater palatine foramen Greater palatine nerve (branch of CN V2), artery Greater palatine nerve block : anesthetizes posterior hard palate and adjacent gums Incisive Canal (Maxilla) Incisive foramen Nasopalatine nerve (branch of CN V2), artery Nasopalatine nerve block : anesthetizes the anterior hard palate behind the maxillary incisors Sphenoid Bone Superior orbital fissure Ophthalmic nerve (CN V1), cranial nerves III, IV, VI, and veins Important for sensation in upper face (forehead, scalp) via CN V
Key Points:
Focus on the maxilla and mandible for relevant nerve blocks in dentistry (e.g., infraorbital , mental , and inferior alveolar nerve blocks). The sphenoid bone houses important foramina for the passage of the trigeminal nerve branches (CN V2 and V3) , critical in maxillary and mandibular innervation. Understanding the foramina and nerves passing through them will help in locating precise areas for anesthesia during dental procedures.
Cranial Nerve V (Trigeminal Nerve)
The trigeminal nerve (CN V) is the largest cranial nerve and has both sensory and motor components. It is crucial for: Sensation in the face, oral cavity, and teeth. Motor control of the muscles of mastication (chewing). The trigeminal nerve splits into three major divisions:
- Ophthalmic (V1) : Purely sensory, supplying the forehead, scalp, upper eyelids, and parts of the nose.
- Maxillary (V2) : Sensory, supplying the middle part of the face, maxillary teeth, and maxillary sinus.
- Mandibular (V3) : Both sensory and motor, supplying the lower part of the face, mandibular teeth, and muscles of mastication. Relevance to Dental Procedures and Anesthesia
FDI (International) Numbering System : Teeth are numbered in quadrants (e.g., 11, 21 for upper incisors). Be familiar with these systems for identifying specific teeth in clinical records.
Eruption Patterns
Understanding eruption timelines for both primary and permanent teeth is critical for diagnosing developmental abnormalities and planning treatment, especially in pediatric patients. Primary Teeth Eruption Pattern (deciduous or baby teeth): Erupt between 6 months to 2½ years. Order of eruption : o Central incisors: 6–10 months o Lateral incisors: 9–16 months o First molars: 13–19 months o Canines (cuspids): 16–23 months o Second molars: 23–33 months Permanent Teeth Eruption Pattern: Erupt between 6 years to early 20s. Order of eruption : o First molars: 6–7 years o Central incisors: 6–8 years o Lateral incisors: 7–9 years o Canines: 9–12 years o First premolars: 9–11 years o Second premolars: 10–12 years o Second molars: 11–13 years o Third molars (wisdom teeth): 17–21 years
Key Concepts to Focus On for the NBDHE
Tooth Morphology : Know the detailed anatomy of different types of teeth (cusp shapes, root structures, grooves, and ridges). Tooth Identification : Be able to identify teeth based on their position, form, and function. This includes recognizing whether a tooth is primary or permanent. Developmental Issues : Understand common abnormalities like delayed eruption , impaction (especially of third molars), and retained primary teeth. Anomalies : Familiarize yourself with anomalies like extra teeth ( supernumerary teeth ) or missing teeth ( anodontia ). Eruption Sequence and Timing : Be ready to identify if a tooth has erupted out of sequence or if an eruption is delayed. Clinical Applications: Pediatric Dentistry : Identifying the eruption sequence and timelines helps in monitoring the normal development of primary and permanent teeth. Orthodontics : Understanding the eruption sequence is vital when planning braces or other interventions.
Tooth Identification and Charting : Knowing the anatomy and numbering system helps in accurate dental charting during exams. Tooth Type Cusp Shapes Root Structures Grooves Ridges Incisors Flat, sharp edges One conical root for maxillary incisors; one or two for mandibular incisors Mesiolabial and distolabial grooves; developmental grooves Marginal ridges; incisal ridge Canines Single prominent cusp One long, single root Developmental groove on the labial surface Cusp ridge; mesial and distal cusp ridges Premolars (Bicuspids) Two or more cusps (buccal and lingual) One or two roots (maxillary premolars often have two roots) Central and mesial/distal grooves; developmental grooves Marginal ridges; buccal and lingual cusp ridges Molars Multiple cusps (usually 4 or more) Typically two or three roots for maxillary molars; one or two for mandibular molars Major grooves (buccal, lingual, central, and oblique grooves) Cusp ridges; transverse ridges; marginal ridges
Detailed Anatomy:
1. Incisors Cusp Shapes : Incisors have sharp, flat edges for cutting food. Root Structures : Usually have a single conical root. Maxillary incisors may have wider roots than mandibular ones. Grooves : Two main grooves (mesiolabial and distolabial) run along the facial surface; developmental grooves may be present. Ridges : Marginal ridges (along the mesial and distal edges) and an incisal ridge. 2. Canines Cusp Shapes : Feature a prominent single cusp that is pointed for tearing food. Root Structures : One long, strong single root that provides stability. Grooves : A developmental groove runs vertically down the labial surface. Ridges : Mesial and distal cusp ridges extend from the cusp tip to the cervical area. 3. Premolars (Bicuspids) Cusp Shapes : Typically have two major cusps (buccal and lingual) and may have a third minor cusp. Root Structures : Usually one root, but maxillary first premolars may have two roots (buccal and palatal). Grooves : Central groove runs down the center; mesial and distal grooves may also be present. Ridges : Marginal ridges and buccal/lingual cusp ridges. 4. Molars Cusp Shapes : Have multiple cusps (4 or more) for grinding; maxillary molars often have a larger, additional cusp (cusp of Carabelli). Root Structures : Maxillary molars typically have three roots (two buccal, one palatal), while mandibular molars usually have two roots. Grooves : Major grooves include the central groove, buccal groove, and lingual groove; there are often more complex patterns. Ridges : Cusp ridges connect the tips of the cusps; transverse ridges and marginal ridges are also present.
o Third Molars (Wisdom Teeth) : Erupt between ages 17-21, if at all. Function can vary; often extracted if impacted.
Summary:
Primary Teeth : Total of 20, including 8 incisors, 4 canines, and 8 molars. Permanent Teeth : Total of 32 (if all third molars are present), including 8 incisors, 4 canines, 8 premolars, and 12 molars. Understanding the position, form, and function of each tooth type is crucial for diagnosis, treatment planning, and providing effective dental care. Abnormality Description Causes Potential Effects Management Options Delayed Eruption Eruption of teeth occurs later than the expected timeline. Genetic factors, systemic health issues, nutritional deficiencies, or mechanical obstruction. Misalignment, malocclusion, increased risk of cavities. Monitoring, orthodontic evaluation, possible extraction of primary teeth. Impaction A tooth fails to erupt properly into the dental arch. Insufficient space, abnormal tooth position, or obstruction by adjacent teeth or bone. Pain, infection, crowding, potential cyst formation. Surgical removal, orthodontic intervention, pain management. Retained Primary Teeth Primary teeth that do not fall out as expected. Absence of permanent successor, root resorption issues, or mechanical blockage. Misalignment, malocclusion, delayed eruption of permanent teeth. Monitoring, extraction if necessary, orthodontic evaluation. Detailed Breakdown:
- Delayed Eruption : o Description : Teeth take longer than the normal eruption timeline (e.g., central incisors typically erupt at 6-8 months). o Causes : Can be caused by genetic factors (family history), systemic health issues (like hormonal disorders), poor nutrition, or physical obstruction (e.g., supernumerary teeth). o Effects : Misalignment of teeth, malocclusion, and increased risk of cavities due to improper spacing. o Management : Regular monitoring, orthodontic assessment for alignment issues, and possibly extracting retained primary teeth to allow permanent teeth to erupt.
- Impaction : o Description : Teeth, particularly third molars, are unable to erupt due to lack of space or blockage. o Causes : Insufficient arch space in the jaw, abnormal positioning of the tooth, or neighboring teeth blocking the eruption pathway. o Effects : Pain, swelling, infections (pericoronitis), crowding of other teeth, and potential development of cysts. o Management : Surgical extraction of impacted teeth, orthodontic treatment to create space, and pain management.
- Retained Primary Teeth : o Description : Primary teeth that persist beyond the expected age of exfoliation. o Causes : Absence of the permanent tooth (agenesis), failure of the primary tooth roots to resorb, or physical blockage preventing exfoliation. o Effects : Malalignment of subsequent teeth, malocclusion, and delayed eruption of permanent teeth, leading to possible crowding or spacing issues. o Management : Regular monitoring, possible extraction of retained primary teeth, and orthodontic consultation if alignment issues arise. Anomaly Description Causes Potential Effects Management Options Supernumerary Teeth Extra teeth that develop in addition to the normal dentition. Genetic factors, syndromic conditions, or developmental disturbances. Crowding, misalignment, potential for impaction of adjacent teeth. Extraction if causing issues; monitoring if asymptomatic. Anodontia Complete absence of teeth, either primary or permanent. Genetic mutations, syndromic conditions (e.g., ectodermal dysplasia), or environmental factors. Difficulty in chewing, speech issues, facial aesthetics. Dentures, dental implants, or orthodontic treatment for prosthetic solutions. Hypodontia Missing one or more teeth, but not all teeth. Genetic predisposition, associated with certain conditions. Crowding, spacing issues, malocclusion. Monitoring, prosthetic replacements (implants, bridges) as needed. Hyperdontia Presence of more than the normal number of teeth (including supernumerary teeth). Genetic factors or associated with syndromes. Crowding, dental malposition, increased risk of caries. Extraction of extra teeth if causing functional or aesthetic issues. Detailed Breakdown:
- Supernumerary Teeth : o Description : Additional teeth that can appear anywhere in the dental arch, often seen in the midline of the maxilla or between incisors. o Causes : Can result from genetic factors or associated with syndromic conditions (e.g., Gardner syndrome). o Effects : May cause crowding or misalignment of adjacent teeth, and can potentially become impacted. o Management : If symptomatic or causing functional problems, extraction may be required; otherwise, monitoring may be sufficient.
- Anodontia : o Description : A rare condition characterized by the complete absence of teeth. o Causes : Often linked to genetic mutations or developmental conditions like ectodermal dysplasia.
Probing Depths : Knowledge of how to measure periodontal probing depths and what various depths indicate. Clinical Signs of Disease : Be able to identify signs such as bleeding on probing, recession, and mobility of teeth.
6. Risk Factors for Periodontal Disease
Systemic Factors : Understand how conditions like diabetes, smoking, and stress can influence periodontal health. Local Factors : Be aware of local factors such as plaque accumulation, calculus, and tooth position.
7. Treatment and Management
Non-Surgical Treatment : Scaling and root planing, dental hygiene instructions, and maintenance. Surgical Treatment : Familiarity with periodontal surgical procedures (flap surgery, bone grafts) when necessary. Role of Dental Hygienists : Understanding the dental hygienist's role in periodontal assessment, treatment, and patient education.
