Different types and forms of partial dentures

         The choice of various therapeutic choices to replace missed teeth is affected by health, and dental and patient factors. Replacement of missing teeth is one of the most significant needs to restore esthetics and/or work for patients attending clinics. Many treatment modalities are required to restore missing teeth; partial removable denture (RPD), partial fixed denture, or dental implant. Every modality is a potential treatment choice and has its own pros and cons.

Removable partial dentures had become common with the emergence of acrylic polymers and cobalt chrome alloys in dentistry many decades ago. Many patients opt for removable partial dentures due to cost-to-psychology factors. Dr. Walter Wright (1937) presented polymethyl methacrylate as a base material for the denture that became the main polymer to be used. Polymethyl methacrylate (PMMA) has been used for manufacturing the dentures for ages. Aluminum cast / metal frame / base metal dentures are also made to repair the defects. Some of the acrylic issues are difficult to tackle, such as placement in undercut regions, methyl fragility Methacrylate that contributes to fracture, and methyl methacrylate monomer allergy. Flexible removable part-dentures have become really common in recent times.

 A path of insertion which is nearly perpendicular to the current occlusal plane is used when designing a traditional removable partial denture. The cast is positioned in such a way that the occlusal plane is perpendicular to the surveyor's analyzing rod. Reasons for using this insertion path are (1) the contours of the abutment teeth surveyed in this position typically found beneficial retentive undercuts; (2) guiding planes could be easily incorporated; (3) the placement path can be easily repeated; and (4) because many patients sit under occlusal force, a lower incidence of permanent clasp distortion is likely to occur because of the occlusal force. Alterations from such an insertion path are often indicated to compensate for the lack of the ideal position of the dent or contours. The changed insertion direction is calculated by adjusting the lateral or anteroposterior tilt of the on-screen cast. 

Swing-lock RPD

In 1963, Simmons introduced the Swing-lock RPD to the dental profession. It consists of a labial / buccal holding bar hinged at one end and locked with a latch at the other, reciprocating the lingual plate together to achieve maximum retention and stability. [Figure 3]

Indications are: insufficient bone support, and insufficient retention. Often, mobility of teeth or economy when the main abutments are absent.

For people with poor oral hygiene, insufficient physical ability, deep vertical overbite with negligible horizontal overjet which does not allow a lingual plate for a maxillary prosthesis, a swing-lock RPD should not be used. Increased frenal attachment or Prominent labial alveolar ridge without any labial undercut. Short lip or small vestibular depth found .

Removable partial overdenture

Overdenture is a removable partial or complete denture which covers and rests on one or more remaining natural teeth, roots and/or dental implants; a dental prosthesis which covers and is partially supported by natural teeth, tooth roots and/or dental implants. It is also known as overlay denture, overlay prosthesis, and prothesis superimposed. [Figure 4]

Indication: patients with few remaining retainable teeth in an arch; as well as patients with ill-related ridge cases; patients requiring single denture, or unfavorable tongue positions, muscle attachments, and high palatal vault, making the stability and retention of the prothesis difficult.

Contraindications: patients with questionable oral prophylaxis, systemic complications and insufficient distance between arches.

Advantages

-- Alveolar bone preservation, proprioception, enhanced stability and vertical dimensional retention and maintenance of the occlusion.

-- Patients with congenital defects such as oligodontia, cleft palate, cleidocranial dysostosis, and Class III occlusion are also useful.

-- Overdenture can easily be converted over a period of time into full denture.

-- Arch-form harmony.

The disadvantages are: susceptibility to caries, over contour, under contour, Esthetics, Meticulous oral hygiene and costly approach with frequent patient recall checks compared to conventional removable complete denture [7].

Nesbit denture

      Nesbit dentures are a variation of the traditional RPDs used on the same side of the upper or lower arch to restore one – three missing teeth. They provide a low-cost option using development of new technology to replace missing teeth, whereby no metal clasps are fitted around supporting teeth on either side of the gap, to prevent the denture from settling into your oral mucosa. Compared to the regular partial denture, the result is a much smaller and more relaxed prosthetic.

Nesbit dentures are mostly used as a temporary replacement while patients are waiting for implant restoration, as there is no metal or plastic connection behind the lower front teeth or across the mouth roof to connect to the contrary direction of the jaw. This means that there is no bi-lateral support from the other sides of the mouth to stop the impact of the damaging forces Teeth backing Nesbit. Hence, avoiding damaging adjacent teeth should be short-term. [Figure 5]

 

Cu-Sil Partial Denture

      Cu-Sil dentures are meant to protect the few surviving natural teeth and also the alveolar bone. They get an impact on denture retention and stability. It also gives the patient sense of satisfaction of retaining the natural teeth just as they were. The retained natural teeth preserve vertical dimension and proprioception. Add-on devices are Evaded altogether. Cu-Sil is an appliance that carries tissue and has a soft elastomeric gasket. It clasps each natural tooth 's neck, sealing off food and fluids, padding and splinting each natural tooth from the base of the hard denture. By eliminating wear, torque and stress, it helps prevent tooth loss and improves the prognosis of loose, mobile, isolated, elongated or parodontally involved abutments.

They offer a solution for single or separated teeth that are present in the dental arch. They are not implied for patients with large amounts of teeth spread equally across the dental arch. There are also some disadvantages to consider with those dentures. The soft liner used has a limited performing duration of 3 years. [8] 

Implant-Supported RPD

The challenging problem with using standard RPDs is the distal rotation of the acrylic base in the RPDs distal free-end region to the last natural tooth. In effect, distal implants convert a Kennedy Class I or II denture into a Kennedy Class III denture. Because an implant is placed in a distal position, there is a need for fewer implants to achieve a successful distal extension RPD while preventing alveolar ridge bone loss over time. Use of dental implants has become widely accepted, and many studies have shown that combining RPDs with implants improves the biomechanics of prosthetics, resulting in greater patient satisfaction. Years have passed since the use of implants and RPDs combined. Discussing the differences associated with implant-assisted RPDs versus fixed prosthodontics is also worthy of note. Previously, Blum and McCord contrasted the long-term costs of both systems and found that the use of implants in RPDs is perceived as a less costly choice than fixed prothesis, where multiple implants will be needed with the requisite crowns during restorations. [Figure 7][9] 

Telescopic Denture

Though first described by Starr in 1886, at the beginning of the 20th telescopic copings were originally introduced as retainers for RPDs. Because of her resemblance to the collapsible optical telescope became recognized as the telescopic denture, this system of the double crowns which can be fitted into one another. Telescoping refers to the use of a quality system-cover casting (coping / male telescopic portion) lubricated to the prepared tooth with a secondary casting (superstructure / secondary crown / female telescopic portion), which is part of the denture framework and is retained over the primary casting by means of interfacial surface tension. They act by switching forces along the direction of the abutment teeth's long axis as well as provide guidance, support and protection against movements that could dislodge the RPDs. Telescopic crowns can also be used as indirect retainers to prevent dislodgement away from the edentulous ridge of the distal extension base. [Figure 8][10]

Benefits

-- Creation of a common insertion path, and easy oral hygiene routine.

-- Rigid splinting action, so the abutment teeth receive stress.

-- Provision of suitable abutments for RPDs, even when the remaining teeth are interfered with periodontally. A lot easier for the patient to put and extract. Have a room for future changes to treatment plan. Patients mentally well-tolerated.

The disadvantages are: increased cost, complex laboratory procedures, extensive tooth decrease and increased number of dental appointments required. Often, the accomplishment of esthetics and preservation is challenging.

Fixed RPD (Andrew’s Bridge)

Dr. James Andrews, from Amite, Louisiana, introduced the fixed removable Andrews Bridge System (Cosmetic Dentistry Institute, Amite, La.). [Fig. 9]

Proper cases

1. Patients whose residual ridge is related to the opposing dentition which would prohibit the esthetic placement of a fixed partial denture in the pontics.

2. Patients required to harmonize natural dentition with diastemas.

3. Patients suffering extensive loss of alveolar bone and tissue.

Advantages: Decreases denture size, taking reduced vertical and horizontal space with Four separate bar curvatures covering the ridge and allowing for anterior use of the rim. It also restores one – four teeth of varying lengths and the denture ensures strong preservation with no wear and high tensile strengths and yield strengths.

Drawbacks

-- Failure due to insufficient soldering, as it is technically sensitive procedures.

-- It should not be used in occupied patients where reconstruction may become loose jarred and swallowed or aspired. [11]

Flexible Denture

Flexible dentures are commonly used in situations where conventional dentures create patient pain. In nearly any partial edentulous condition, versatile RPDs are suggested as long as the patients are willing to hold a temporary implant in their mouth. Flexible denture uses material made from polyamide nylon. Flexible partial dentures use the undercuts in the surface for preservation, so they are shown on ridges where there are bilateral undercuts. Patients with tilted teeth (due to a long period of missing adjacent tooth) develop an undercut in which rigid partial denture is difficult to insert. [Figure 10]

Indications

-- Flexible partial dentures can solve the problem of casting partial dentures in patients who are allergic to nickel.

-- Patients with big, unremovable bony exostoses, versatile partial dentures display strong retention or with patients suffering from microstomia, systemic diseases such as scleroderma, or for any other reason where mouth opening is reduced. Flexible part-dentures have shown good success in such cases. [12]

Benefits

-- The flexibility of the material allows the undercut under the bony exostoses, that is, in rigid partial dentures it is not possible

-- Other perks, such as: Unbreakable, Lightweight, Improved esthetics and ease of manufacturing.

Disadvantages 

-- Only intended for temporary or provisional use.

-- Acrylic teeth debonding from nylon denture base.

-- Tend to absorb water content and become discolourated.

-- High surface roughness and low hardness, and sensitive to technical requirements.

Non-metal Clasp Denture

       Applying metal clasps to anterior teeth can cause esthetic problems. Methods to overcome this esthetic dilemma include painting tooth-colored resin clasps, using lingually positioned clasps, engaging mesial rather than distal undercuts, and using gingival clasps that approach. Unless clasps with precise attachments can be avoided, some of the RPD framework will always be visible. The possibility of the plasticizing resin being injected into the mold has opened up a new perspective for full denture and RPD technologies. A thermoplastic resin called acetal (Bio Dentaplast, Bredent, Senden, Germany) can be used as an alternative clasp material for the denture. Acetal was first proposed in 1971 as an RPD material from unbreakable thermoplastic resin. Rapid Injection Systems produced the first tooth-colored clasps using a thermoplastic fluoropolymer during this time. [Figure 11][13]

 

Light Polymerized Partial Denture

PMMA is also widely accepted as a material for temporary restorations, denture repairs and relays to dentures. While PMMA in prosthodontic practice is considered an indispensable polymeric material, an increasing number of patients present with hypersensitivity PMMA responses. The substance used in these patients for the denture base should be chosen from other polymeric products which are not allergic to the patient.[14] [Figure 12]