Occlusion | Primate Spaces | Gum Pads | Flush Terminal Plane

Occlusion Stages and Definitions
📌 Occlusion is defined as the contact relationship of teeth in function or parapunction, a dynamic concept involving the teeth, temporomandibular joint, and mastication muscles.
🦷 The journey of dentition is divided into four stages: Gumpad (Pre-dented), Primary Dentition (6 months to 6 years), Mixed Dentition (6 to 12 years), and Permanent Dentition (12 years and beyond).
👶 The initial Gumpad stage (0–6 months) features a horseshoe-shaped maxillary gum pad and a U-shaped mandibular gum pad, contacting only in the posterior region.

Primary Dentition Characteristics (6 Months to 6 Years)
📏 Overjet is the horizontal distance between the maxillary and mandibular anterior teeth (normally 0 to 4 mm in primary teeth), while Overbite is the vertical overlap.
🧩 Physiological/Developmental spaces are crucial; localized spaces, known as Primate spaces (or Simian spaces), occur between the lateral incisor/canine (maxilla) and canine/first molar (mandible).
🔗 The relationship between the distal surfaces of the maxillary and mandibular second primary molars is the Terminal Plane Relationship, which normally presents as a flush terminal plane (straight alignment).

Clinical Implications Across Dentition Periods
🦷 Thumb-sucking habits during the primary dentition period can lead to an increased overjet (increased horizontal distance) and an anterior open bite.
😟 Lack of physiological spacing in primary teeth can result in crowding of the teeth, negatively impacting the accommodation of larger permanent teeth.
⬆️ The terminal plane relationship—whether flush, mesial step, or distal step—guides the eruption of the permanent first molars and influences the development of permanent occlusion.

Key Points & Insights
➡️ Viva questions often focus on the horseshoe shape of the maxillary gum pad and the U-shape of the mandibular gum pad in the pre-dented period.
➡️ The general rule is that mandibular primary teeth erupt before maxillary, with the exception being the maxillary lateral incisors erupting before mandibular lateral incisors.
➡️ Primate spaces are critical for permanent tooth accommodation; their absence leads to crowding, with incidence rates cited as 70% in the maxilla and 63% in the mandible for localized spacing.

📸 Video summarized with SummaryTube.com on Nov 25, 2025, 20:28 UTC