Fixed Prosthodontics Lecture 10: Interocclusal Record

Interocclusal Record (Bite Registration Record)

• Bite registration is a technique to transfer the relationship between the upper and lower jaw from the patient's mouth to the articulator.
• It allows the dentist to observe tooth contact, occlusal discrepancies, and fabricate restorative procedures without changing the patient's occlusion.

Requirements of Bite Registration Materials

• The material should be stable with little or no dimensional change during setting.
• It should give an accurate record of the occlusal surface and incisal edges of the teeth.
• It should not affect normal closing of the mandible.
• The material should remain rigid after setting.

Bite Registration Materials

• Pink base plate wax or compound
• Bite registration paste (ZOE, Silicone)
• Bite rim or occlusal rim

Centric Relation

• The physiological position of the condylar head of the mandible (without stress) from which all other movements are initiated.
• Taken when no enough occlusal stops are left after teeth preparation, especially in cases of full mouth rehabilitation of fixed partial denture.

Centric Occlusion

• The maximum occlusal contact or intercuspation, irrespective of condylar position.
• Maxillary and mandibular teeth should contact in a harmonious manner, allowing optimum function, minimum trauma to the supporting structure, and even distribution of load through the dentition.

Dowson's Technique

• Patient's chair is reclined, and the head is fixed by the dentist standing behind the patient.
• The dentist applies gentle downward pressure with thumbs and upward pressure on the fingers to bring the patient's mandible into centric relation.

Methods of Inter-occlusal Record

• If enough teeth are present in both upper and lower arches, no bite registration is needed, and the relation can be transferred by hand articulation.
• If the remaining teeth are insufficient, bite registration materials such as pink base plate wax, bite registration paste, or occlusal rims can be used.

Glass Bite Material

• Introduced between the dental arches with a special cannula and can be applied ideally between the dental arches much faster and more easily than other materials.
• Stable and transparent.

Luxa Bite Rigid Bite Registration

• Highly accurate to the models
• Can be used with or without bite registration trays
• No interference with closure of teeth
• Fast setting and easy to trim
• Resist normal temporary variations better than wax
• No compression on mounting

Bite Registrations for CAD/CAM Procedures

• Bite registration can be digitally recorded in the same way as digital impression, both procedures are employed in conjunction with computer-aided design/computer-aided manufacturing (CAD/CAM).
• Digital bite registration can be taken indirectly using an extra oral scanner (in lab) or directly in the mouth at chairside using an intraoral digital camera (in office).

Fluid Control and Isolation in Fixed Prosthodontics

• Control of fluids and appropriate displacement of the gingiva are essential during tooth preparation to obtain accurate impressions and for cementation.

Sources of Fluid in the Oral Cavity

• Saliva from parotid, submandibular, and sublingual glands
• Inflamed gingival tissues and iatrogenic soft tissue damage
• Water and dental materials
• Gingival crevicular fluid (sulcular fluid)

Objectives of Fluid Control

• To obtain a dry, clean operating field
• For easy access and visibility
• To improve the properties of dental materials
• To protect the patient and the operator
• To improve operating efficiency

Methods of Fluid Control and Isolation

• Rubber dam: used to isolate the tooth during restorative procedures
• Cotton roll: simplest method of fluid control and isolation
• Mechanical method of retraction: physically displaces the gingiva
  • Examples: retraction cord, rubber clamp, temporary crown with a long margin
• Chemo-mechanical method: combination of mechanical and chemical methods
  • Examples: impregnated retraction cord with hemostatic agents, displacement polymer and paste
• Surgical method: radical or surgical means or technique
  • Examples: electrosurgery, laser

Retraction Cords

• Classification:
  • According to chemical treatment: plain or impregnated with hemostatic agents
  • According to configuration: twisted, knitted, or braided
• Advantages of knitted cord:
  • Affords greater inter-thread space than braided cord
  • Forms an interlocking chain of tiny loops, making it easy to pack below the gingival margin
  • Compresses upon packing, then expands for tissue displacement

Gingival Retraction

• Definition: deflection of the marginal gingiva away from a tooth
• Indications:
  • To provide adequate reproduction of finish lines
  • To expose the prepared finish line and evaluate the depth and uniformity of it
  • To control the gingival crevicular fluid
  • To provide access for the impression material to record accurately
• Objectives:
  • To obtain accurate marginal fit
  • To prevent periodontal disease
  • To fabricate accurate restorations
  • To help obtain accurate marginal fit, reducing marginal leakage and subsequent deterioration of the tooth