5.1 Dental Occlusion & Angle's Classifications of Malocclusion

Dental Occlusion & Angle's Classifications of Malocclusion

Quick Answer: Dental occlusion describes how the maxillary and mandibular teeth contact during static closure and dynamic masticatory movements. Under Angle's Classification System, the mesiobuccal (MB) cusp of the permanent maxillary first molar serves as the primary anatomical benchmark. In Class I (Neutroclusion), this cusp occludes in the buccal groove of the permanent mandibular first molar. In Class II (Distoclusion), the mandibular molar is positioned distal (posterior) to normal, presenting as either Division 1 (proclined maxillary incisors, large overjet) or Division 2 (retruded central incisors, deep overbite). In Class III (Mesioclusion), the mandibular molar is positioned mesial (anterior) to normal, resulting in a prognathic facial profile and frequent anterior crossbite.

Mastery of dental occlusion and malocclusion is essential for dental assistants across restorative dentistry, orthodontics, prosthodontics, and comprehensive clinical examination. Dental assistants must accurately recognize occlusal relationships when taking diagnostic records, mounting study casts, assisting during orthodontic consultations, and evaluating post-operative restorations with articulating paper.

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1. Foundational Occlusal Terminology & Joint Relationships

Occlusion refers to the functional and resting contacts between the incising or masticating surfaces of the maxillary and mandibular teeth.

                    OCCLUSAL RELATIONSHIP DEFINITIONS
   =========================================================================
   Centric Relation (CR)   --> Bone-to-bone joint position (condyle in fossa)
   Centric Occlusion (CO)  --> Tooth-to-tooth habitual maximum intercuspation
   Working Side Contact    --> Side toward which the mandible moves
   Non-Working (Balancing) --> Side opposite the direction of mandibular movement
   =========================================================================

Primary Occlusal Positions

• Centric Relation (CR): A reproducible maxillomandibular relationship in which the condyles articulate in an anterior-superior position against the posterior slopes of the articular eminences, independent of tooth contact. It is a bone-to-bone relationship that is entirely independent of tooth contact and is clinically reproducible.
• Centric Occlusion (CO) / Maximum Intercuspation (MIP): The voluntary, habitual position of maximum contact and intercuspation between the occlusal surfaces of the maxillary and mandibular arches. In roughly 90% of the population, Centric Occlusion does not coincide perfectly with Centric Relation, typically lying approximately 1 to 2 mm anterior to CR.
• Functional Occlusion: The dynamic contacts of teeth during active mastication, swallowing, and speech.

Dynamic Guidance Schemes

• Canine Guidance (Canine-Protected Occlusion): During lateral mandibular movements, the maxillary and mandibular canines contact, causing immediate disclusion (separation) of all posterior premolars and molars on both the working and non-working sides. This protects posterior teeth from destructive horizontal lateral forces.
• Group Function (Unilateral Balanced Occlusion): During lateral movement, multiple posterior teeth on the working side (canines, premolars, and molars) share contact simultaneously, while the non-working (balancing) side discludes completely.
• Working Side vs. Non-Working (Balancing) Side: When the mandible shifts to the right, the right side is the working side (the side executing mastication), and the left side is the non-working / balancing side.

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2. Anatomical Curves of the Occlusal Plane

The occlusal surfaces of natural teeth do not sit on a flat, two-dimensional plane. Instead, they form physiological curves that allow efficient mastication and prevent interferences during mandibular excursion.

                    CURVES OF THE OCCLUSAL PLANE

         Curve of Spee                          Curve of Wilson
     (Anteroposterior Curve)                  (Mediolateral Curve)

     Maxillary Anterior Teeth                 Left Molar      Right Molar
         \                                       \               /
          \  (Concave Mandible)                   \_           _/
           \___________                             \_________/ 
                       \                            Lingual Tilt of
                        Ramus                      Mandibular Molars

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3. Spatial Occlusal Relationships & Alignment Deviations

In addition to molar classification, clinicians evaluate anterior and posterior tooth relationships across sagittal, vertical, and transverse dimensions.

             OVERJET (HORIZONTAL) vs. OVERBITE (VERTICAL)

          OVERJET (Horizontal Gap)            OVERBITE (Vertical Overlap)
             Maxillary Incisor                     Maxillary Incisor
                  |    |                                |   |
                  |    |                                |   |
                  |    |                                |   | <--- Overlap
                  |____|                                |___|      Amount
                     <---> Measured in mm                 |    Mandibular
                     |   |                                |    Incisor
                     |   | Mandibular                     |    |
                     |___| Incisor                        |____|

Definitions of Occlusal Relationships

• Overjet (Horizontal Overlap): The horizontal distance between the labial incisal edge of the maxillary incisors and the labial surface of the mandibular incisors. Measured in millimeters using a periodontal probe. Normal physiological overjet is 1 to 3 mm.
• Overbite (Vertical Overlap): The vertical distance that the maxillary incisors overlap the crowns of the mandibular incisors when the posterior teeth are in centric occlusion. Recorded as a percentage or in millimeters (Normal: 20% to 30% or 2 to 3 mm). Severe vertical overlap is termed a deep bite (closed bite).
• Open Bite: A lack of vertical contact or overlap between opposing teeth when the posterior teeth are fully occluded in centric occlusion. May occur anteriorly (anterior open bite, frequently caused by digit-sucking habits or tongue thrusting) or posteriorly (posterior open bite).
• Crossbite (Transverse Discrepancy):
  • Anterior Crossbite: One or more maxillary anterior teeth occlude lingual to the mandibular anterior teeth (negative overjet / underjet).
  • Posterior Crossbite: Maxillary posterior teeth occlude lingual to the mandibular posterior teeth (lingual crossbite) or entirely buccal without occlusal contact (buccal crossbite / scissor bite / Brodie bite).
• Edge-to-Edge Occlusion: Maxillary and mandibular anterior teeth meet incisal edge to incisal edge with 0 mm overjet and 0 mm overbite.
• End-to-End Occlusion (Cusp-to-Cusp): Posterior teeth meet cusp tip to cusp tip instead of interlocking in normal cusp-fossa relationships.

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4. Angle's Classification of Malocclusion

Developed in 1899 by Dr. Edward H. Angle, this system classifies malocclusion based on the relationship of the permanent maxillary first molar (the "key to occlusion") to the permanent mandibular first molar, supplemented by the maxillary and mandibular canine relationships.

                      ANGLE'S MOLAR CLASSIFICATIONS

     CLASS I (Neutroclusion)        CLASS II (Distoclusion)        CLASS III (Mesioclusion)

        Maxillary Molar                Maxillary Molar                Maxillary Molar
         [ MB Cusp ]                    [ MB Cusp ]                    [ MB Cusp ]
              |                              |                              |
              v                              v                              v
         [Buccal Groove]                [Buccal Groove]                [Buccal Groove]
        Mandibular Molar               Mandibular Molar               Mandibular Molar
     (MB Cusp in Groove)             (Groove is DISTAL)             (Groove is MESIAL)

Detailed Breakdown of Angle's Classes

Subdivisions in Angle's Classification

When an asymmetry exists between the right and left sides of the dental arch (for example, Class I on the left side and Class II on the right side), the condition is designated as a Subdivision (e.g., Class II, Division 1, Subdivision Right).

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5. Primary Dentition Occlusion & Terminal Plane Relationships

In children prior to the eruption of the permanent first molars (ages 2 to 6), occlusion is evaluated by the relationship of the distal surfaces of the second primary molars (known as the Terminal Plane):

                  PRIMARY DENTITION TERMINAL PLANES

     FLUSH TERMINAL PLANE            MESIAL STEP                  DISTAL STEP
     Max. 2nd Primary Molar      Max. 2nd Primary Molar      Max. 2nd Primary Molar
          |-------|                   |-------|                   |-------|
          |       |                   |       |                   |       |
          |-------|                   |-------|                   |-------|
          |-------|                      |-------|             |-------|
          |       |                      |       |             |       |
          |-------|                      |-------|             |-------|
     Mand. 2nd Primary Molar     Mand. 2nd Primary Molar     Mand. 2nd Primary Molar
     (Distal surfaces flush)     (Mandible stepped mesial)   (Mandible stepped distal)

• Flush Terminal Plane: The distal surfaces of the maxillary and mandibular primary second molars are vertically flat and flush with each other. This is the most common primary relationship and usually transitions into an Angle Class I permanent molar relationship via late mesial shift (utilizing primate and leeway spaces).
• Mesial Step: The distal surface of the mandibular second primary molar is mesial (anterior) to the distal surface of the maxillary second primary molar. This relationship almost always develops into an Angle Class I or Angle Class III permanent relationship.
• Distal Step: The distal surface of the mandibular second primary molar is distal (posterior) to the distal surface of the maxillary second primary molar. This relationship usually persists and commonly develops into an Angle Class II permanent molar relationship; unlike a flush or mesial step, it does not normally self-correct to Class I.
• Primate Spaces: Natural physiological spaces in primary dentition located:
  • Maxillary arch: Between the primary lateral incisor and primary canine.
  • Mandibular arch: Between the primary canine and first primary molar.

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6. Clinical Assessment, Articulating Paper & Chairside Responsibilities

During operative and prosthodontic procedures, the dental assistant assists the clinician in verifying occlusal harmony:

Articulating Paper & Marking Protocols

• Articulating Paper: Used to mark occlusal contact points. Available in blue, red, thick, and ultra-thin varieties. Typically held with articulating paper forceps (Miller forceps).
• Two-Color Technique: Blue paper is commonly used to record static centric contacts (tapping straight up and down), while red paper is placed over the blue marks while the patient grinds side-to-side and forward-to-back to reveal dynamic excursive interferences.
• Shimstock Foil: A high-precision, metallic polyester film (8 to 12 microns thick) used to verify whether teeth or restorations hold firm contact when occluded.

Holding Cusps vs. Non-Supporting Cusps

• Centric Holding (Supporting) Cusps: Cusps that occlude directly into the central fossae and marginal ridges of opposing teeth to maintain the vertical dimension of occlusion:
  • Maxillary Lingual Cusps
  • Mandibular Buccal Cusps
• Guiding (Non-Supporting) Cusps: Cusps that overlap the opposing arch to protect the buccal mucosa and tongue from being bitten:
  • Maxillary Buccal Cusps
  • Mandibular Lingual Cusps
  • Mnemonic: BULL Rule (Buccal of Upper, Lingual of Lower are non-supporting/guiding cusps adjusted during occlusal equilibrium in working excursion).

Clinical Manifestations of Primary Occlusal Trauma

When a newly placed restoration is left in "hyperocclusion" (high spot):

• Fremitus: Palpable or visible functional vibration/movement of a tooth when the patient taps into centric occlusion.
• Tooth Soreness: Localized sensitivity to mastication and percussion.
• Radiographic Changes: Widening of the periodontal ligament (PDL) space and thickening of the lamina dura around the root.

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7. DANB NELDA Clinical Traps & Exam Pearls

[!CAUTION] DANB Exam Trap #1: Overjet vs. Overbite Measurement Units Questions frequently try to confuse overjet and overbite. Overjet is the horizontal protrusion of maxillary incisors past mandibular incisors and is measured in millimeters (mm). Overbite is the vertical overlap of incisal edges and is typically expressed as a percentage (%) or in millimeters. Remember: "Jet flies horizontally across the sky (overjet = horizontal)."

[!WARNING] DANB Exam Trap #2: Class II Division 1 vs. Division 2 Incisor Angulation Both divisions share the identical Class II molar relationship (mandibular molar distal). The sole distinguishing factor is anterior tooth angulation:

• Division 1: Central incisors are proclined / flared labially, producing a large overjet.
• Division 2: Central incisors are retroclined / tipped lingually, and lateral incisors overlap them, producing a deep overbite.

[!NOTE] DANB Exam Trap #3: Primary Distal Step Outcome A common question asks which primary terminal plane relationship never self-corrects into Class I. A distal step usually persists and commonly transitions into a permanent Class II malocclusion; avoid treating this developmental tendency as an absolute prediction for every child.