Telescopic dental prostheses (TDP) were introduced in the United States at the end of the 19th century and developed in Europe during the 20th century. The telescopic crown is defined as an artificial crown fabricated to fit over a coping (1).
Telescopic crowns have been used mainly in removable dental prostheses (RDP) to connect the dentures to the remaining dentition (2, 3). They may also be designated as retainers in completely abutment-borne detachable prostheses (4). In addition, telescopic crowns have been used successfully in removable and fixed dental prostheses supported by endosseous implants in combination with natural teeth including overdentures (5-7). The primary indications of a fixed telescopic dental prosthesis (FTDP) are the periodontally compromised abutment teeth that need splinting and cross arch stabilization (8-10).
Telescopic dental prostheses present multiple advantages such as minimization of destructive horizontal torque and enhancement of vertical long axis forces, achievement of parallelism of abutments using primary copings for common path of insertion, cross arch stabilization and retrievability due to the use of provisional cement (11).
Therefore, this procedure provides maximum flexibility because the superstructure can be removed, if needed, for additional periodontal therapy or additional surgery, repair and extraction of hopeless abutment teeth (12).
Telescopic dental prostheses present disadvantages such as aggressive tooth preparations, complex laboratory procedures, difficulty in achieving aesthetics (metal collar of primary telescopic coping present) and additional cost. Attempts have been made to overcome the aesthetic limitation resulting from the presence of the metal collar of the traditional gold copings by incorporating all-ceramic primary telescopic copings (13).
The primary telescopic coping needs to be fabricated with taper between 2-120 and that taper can be different for each abutment under the same restoration usually depending on its periodontal condition. Mean taper of 60 is suggested for standard use when teeth with reduced periodontal support that require cross arch stabilization are involved while the primary telescopic coping ends with a chamfered cervical design. Modifying the height or degree of taper of the copings may control the amount of retention for the superstructure on the copings (14, 15).
This article describes a full-arch maxillary telescopic prosthesis, employing milled base metal primary copings and base metal superstructure veneered with composite, designed to retrieve and convert to a fixed – removable prosthesis in case of posterior tooth loss. In the mandible, a conventional fixed ceramo-metal fixed dental prosthesis was constructed.
A white 58-year-old male patient came to us seeking a fixed maxillary and mandibular dental prosthesis due to intense gag reflex. The medical and dental examination revealed uncontrolled diabetes and severe periodontitis.
Maxillary molars presented severe furcation involvement, especially the maxillary second right molar. Osseous support was 40% for maxillary abutment teeth, resulting in an unfavourable crown to root ratio.
The existing maxillary restorations involved a fixed dental prosthesis with right second molar, right first premolar and right lateral incisor serving as abutments and the maxillary right first molar, the right second premolar and the right canine serving as pontics. A single crown was placed on the maxillary left second molar. Other maxillary teeth present were the left lateral incisor and left canine and were not restored in any way.
In the mandible, a fixed partial denture was present with the right second molar and first premolar serving as abutments, replacing the missing right second molar and premolar. This prosthesis had to be removed due to recurrent decay present in the abutment teeth. Mandibular incisors presented with poor periodontal prognosis and would have to be extracted (Figure 1A). Patient was classified as partial edentulism class IV according to the American College of Prosthodontists (ACP) (16).
Restorations employing implants were not included in the treatment options due to the cost and the uncontrolled diabetes. Removable dental prostheses were not included either since the patient had an intense gag reflex.
The prosthetic treatment employed a full-arch maxillary telescopic dental prosthesis using the maxillary right second molar, right first premolar, right lateral incisor, left lateral incisor, left canine and left second molar as abutments restored with primary telescopic copings. A full arch fixed superstructure was constructed over these primary copings and cemented with temporary cement.
In the mandible, the right fixed dental prosthesis was replaced and the four incisors that were extracted were replaced with a fixed prosthesis using the mandibular canines as abutment teeth. Base metal alloy was used due to finances along with composite for the maxilla and compatible veneering porcelain for the mandible. Composite was chosen over porcelain for the maxilla due to its resistance to chipping and excellent aesthetic appearance.
The periodontal disease was treated, the distal root of the second maxillary molar was resected and severely compromised teeth were extracted. All maxillary teeth were endodontically treated since the occlusal and axial reduction had to be sufficient for the fabrication of telescopic restorations. Access holes were sealed with composite material (Gradia Direct, GC America Inc., Alsip, Ill) (Figure 1B). Old maxillary and mandibular restorations were sectioned and removed, teeth preparations were refined along with the preparation for the mandibular canines for a fixed partial denture, and provisional restorations were placed (Figure 1C). The provisional restorations were used for a six month period in order to ensure that the patient complied with oral hygiene instructions and had his diabetes controlled through proper diet since he refused drug administration.
Maxillary fixed telescopic dental prosthesis fabrication
The prosthetic design employed a 60 taper and advocated a chamfered cervical line.
The milled maxillary primary telescopic copings along with the maxillary metal superstructures were fitted intraorally to verify passive seating (Figure 2A). The maxillary metal telescopic superstructure was designed, waxed and cast with underlying rest seats and milling surfaces that would transform the case to fixed-removable in case of posterior tooth loss (Figure 2B). Light cured composite resin (Gradia, GC America Inc., Alsip, Ill) was used to cover the maxillary metal superstructure (Figure 2C) whereas porcelain was used as a veneering material for the mandibular metal framework (Figure 3A).
Primary telescopic copings were cemented with reinforced glass ionomer luting cement (GC FujiCEM Automix; GC America, Inc) and the telescopic superstructure was cemented with provisional cement (TempBond NE; Kerr Corp, Orange, Calif) for retrievability reasons (Figure 3B). The permanent cementation protocol for the primary copings included one by one permanent seating, while the superstructure was seated each time over the all copings to ensure passive fit.
Oral hygiene instructions were given following final cementation, and three-month recall appointments were suggested.
This report describes the restoration of a partially edentulous maxilla with a fixed telescopic dental prosthesis (FTDP) using base metal alloy, and composite veneering material. The maxillary primary telescopic copings were milled in order to achieve ideal taper and parallelism and the telescopic superstructure was cemented with provisional cement.
Base metal alloy was utilized to reduce cost and composite was used for the maxillary telescopic restoration due to its resistance to chipping. In addition, composite can be easily repaired either intraorally or extraorally.
The main advantage of such prosthetic design would be retrievability since periodontal maintenance is often required. The use of the temporary cement would account for this, and would make periodontal treatment more effective since the superstructure could be detached and the abutments could be fully exposed. Convertibility is another advantage of such a prosthetic design. It can be removed easily, expose the underlined rest seats in the laboratory, cut the unsupported framework, and convert to a fixed-removable combination case.
However, the treatment presented disadvantages such as wear of the composite resin opposing mandibular ceramo-metal FDP, and staining.
The mandibular left side remained as a shortened dental arch since the patient was not a good candidate for dental implants or a removable prosthesis.
The main goal and clinical significance of such a treatment modality would be the recall factor and the treatment alteration in case of future tooth loss.
The recall issue was addressed through a 3 month recall evaluation, done more effectively with the superstructure removed.
The treatment alteration due to posterior abutment tooth loss was addressed by incorporating occlusal rest seats on the fixed telescopic dental prosthesis. In the case of extraction of the maxillary second right molar which presents as the weakest abutment with an already resected root, the temporarily cemented telescopic restoration will be detached and will be sectioned distally to the maxillary right first premolar, while the rest seats mesially to the maxillary first premolar, the maxillary left canine and the maxillary second left molar will be exposed. Then, the remaining telescopic dental prosthesis will be permanently cemented in order to support a unilateral distal extension partial removable dental prosthesis (PRDP) employing a short palatal plate as a major connector, offering the patient additional years of prosthetic treatment use.
The incorporation of underlined rest seats in fixed telescopic reconstructions offers the distinct advantage of converting to fixed-removable combination cases, offering the patient more years of prosthetic service. This treatment approach is especially useful for borderline periodontal cases with weakened abutments and requires patients who can comply with oral hygiene instructions and maintenance.