Classification of dental arch defects
Dental arch defects are usually categorized by extent and location. Depending on the number of missing units, minor (up to 3 teeth), moderate (4–6 teeth), and major (more than 6 teeth) defects are distinguished.
For precise topographical evaluation in prosthodontics, author-specific systems are used (Betelman, Ilyina-Markosyan, etc.), among which the most demanded are:
- Kennedy classification (Kennedy): takes into account the location of the defect and abutment teeth. It includes four classes: bilateral and unilateral distal extension defects (Classes I and II), as well as bounded defects in the posterior (Class III) and anterior (Class IV) regions.
- Gavrilov classification: is based on the nature of the defect itself. It distinguishes distal extension (Group I), bounded (Group II), combined (Group III) defects, and jaws with single remaining teeth (Group IV).
Main orthopedic structures
To eliminate deformations, fixed and removable partial dentures, orthodontic appliances, and implant-supported structures are used.
Fixed partial denture (bridge) is a fixed appliance for replacing bounded defects. It consists of:
- Abutment elements (crowns, half-crowns, or Inlay/Onlay/Overlay microprostheses) fixed to the remaining teeth.
- Pontic (the body of the prosthesis), which directly replaces the missing teeth.
Removable dentures (partial and complete plate dentures) have a different structure. Their foundation is a base that accommodates artificial teeth and retaining elements (clasps, attachments, or telescopic crowns).
Features of fixed partial dentures
The pontic of a fixed prosthesis contacts the mucosa differently depending on the restoration zone:
- Tangential: used in the anterior region to ensure aesthetics and proper phonetics.
- Sanitary (ovate/hygienic): used in the posterior regions, leaving free space for hygienic care.
- Saddle: closely covers the alveolar ridge (rarely used, primarily in ceramic structures).
According to manufacturing technology, fixed partial dentures can be stamped-soldered, all-cast, milled (CAD/CAM technology), and adhesive. Materials include metal, acrylic, ceramics, and their combinations (porcelain-fused-to-metal, metal-acrylic).
Clinical stages of prosthetics
The fabrication and placement of a fixed partial denture require a strict sequence of steps:
- Preparation: separation of contact surfaces, reduction of the occlusal, buccal, and oral walls taking into account the thickness of the future restoration, formation of a cervical shoulder, and smoothing of sharp angles.
- Fitting (try-in): evaluation of the structure on the working model, placement on the abutment teeth in the oral cavity, control of marginal adaptation to the tooth neck, and checking of occlusal contacts using articulating paper.
- Cementation: isolation of the operational field from saliva, medical treatment and drying of the tooth preps and prosthesis, application of mixed cement into the crowns, firm seating, and removal of excess material after setting.
If the technique is violated, complications are possible: decementation, chipping of the facing material, fracture of the pontic, as well as the development of localized periodontitis or decubitus ulcers under the pontic.
Role of microflora and body reactivity
During orthopedic treatment, it is important to consider the risk of purulent-inflammatory complications. Their development is triggered by a decrease in immunological reactivity and impaired microcirculation in the tissues.
The main causative agents are opportunistic anaerobes: Fusobacterium and Bacteroides (melanogenicus and fragilis species). Infection often occurs at the outpatient stage of prosthodontics, leading to nosocomial infections in hospitals.
The course of inflammation depends on the microbial landscape and the patient's homeostasis state. The body's reactivity (the ability to respond to external influences) determines the type of inflammatory reaction. Three main types are distinguished: hyperergic, normergic, and hypoergic.
For quick memorization of Kennedy classes: Classes I and II are "ends" (bilateral and unilateral distal extension defects), and III and IV are "inclusions" (lateral and anterior).
Class and exam questions
In which cases is the placement of a fixed partial denture contraindicated?
The structure cannot be placed in cases of distal extension and extensive bounded defects, pronounced mobility of abutment teeth (severe periodontitis), presence of untreated inflammation foci in periapical tissues, and unsanitized oral cavity.
Why is a hygienic pontic design necessary for a dental bridge?
The sanitary (hygienic) form is used in the posterior jaw. It leaves a space between the pontic and the mucous membrane, which is necessary for adequate hygiene and prevention of pressure sores.
What instruments are used to remove old artificial crowns?
Metal crowns are cut with carbide burs, ceramic ones with diamond burs. For direct removal, a Kopp crown remover, special forceps, elevators, and ultrasonic devices for breaking down the cement structure are used.
What else to study on this topic
- Types of retaining elements for removable dentures (clasps, attachments, telescopic crowns)
- Complications when using fixed partial dentures and methods for their prevention
- Instruments and devices for safe removal of artificial crowns
- Factors determining macroorganism reactivity in infectious-inflammatory processes
- Classifications of dental arch defects according to Betelman and Ilyina-Markosyan
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