Converting conventional mandibular denture prosthesis into overdenture supported by two endosseous implants with ball attachments

Headnote

Abstract

The conventional complete mandibular dentures are often associated with problems in j aws with advanced ridge resorption. The aim of oral implantology has been to improve the retention of such mandibular dentures and also improve patient's satisfaction. In this article a simple process to convert existing conventional denture into an implant supported overdenture is described and illustrated. The retentive elements for the implant abutment were housed directly into the fitting surface of the denture with the help of auto polymerizing resin through a simple chair side technique. It represents a case of an edentulous patient looking for low-cost improvement of denture retention.

Key words: Overdenture, implant, O ring attachments.

Introduction

A successful long term use of osseointegrated implants in treating edentulous subjects has wide range of application. Like all dental restorative procedures a complete remov¬able denture requires extensive attention to detail if an excellent clinical resultis to be achieved. Depending on the shape of the residual ridge, the denture may be unstable or inadequately retained, leaving the patient dissatisfied with the functional result. The most important aim of oral implantologist is to improve retention of complete mandi¬bular dentures, which are often associated with problems in jaws with advanced ridge resorption and in the process improve patient's satisfaction.14 The treatment is more expensive as compared to the conventional treatment plan for edentulous patients, van Steenbergheet al., were among the pioneers to propose placement of only 2 implants in the edentulous mandible.5 Their 98% success rate, with up to 52 months of observation was remarkable. Naert et al., compared the clinical outcome of different overdenture anchorage systems and found 100% implant success after 5 years for all groups.6 Nevertheless, the controversy regard¬ing the treatment concept and indications persist.

In this article a simple technique to convert existing conve¬ntional complete denture prosthesis into implant supported overdenture prosthesis has been described and illustrated. The patient did not undergo surgical procedures for impro¬ving the implantation bed before the implant placement, but insteadrepresents a case of an edentulous patient look¬ing for low-cost improvement of denture retention.

Case report

A 65-year-old patient reported to the clinic with chief complaint of loose lower complete denture prosthesis. The patient had been wearing denture for past one year and had the complaint of loose mandibular complete denture. On intraoral examination, the mandibular ridge was found to be resorbed. However, the ridge was U shaped, smooth withnoirregularities.Athoroughmedicalanddentalhisto-ry of the patient was recorded. Maxillary and mandibular study models were made, a panoramic radiograph and Denta Scan ((Figure 1,2) were taken to assess the bone for selection of implants.

Clinical Procedure

1. The existing denture of the patient was recently fabricated and was found to be satisfactory in stability and aesthetics. Hence, the same prosthesis was used for the conversionintoimplantsupportedoverdenture prosthesis.

2. With the help of lower complete denture prosthesis radiographic stent (by duplicating the lower complete denture) was fabricated (Figure 3). Denta scan was used to identify the sites for the implant placement and the sites were marked on the surgical stent((Figure 4,5).

3. The implants (XIVE, Dentsply Lot No. M060010303 and M060010315) of size 3.8mm x 9.5mm were placed in the two sites identified.

4. The patient was asked not to wear the lower denture for two weeks. The patient was recalled and the lower prosth¬esis was relieved from the area where the implants were placed and was later lined by a soft reliner (Coe-Soft Reliner, Dentsply).

5. Periodic clinical and radiological investigations (Figure 6) were carried out to establish if osseointegration was achieved.

6. After three months of implant placement the cover screw of the implants were exposed and healing abutments were put in place.

7. After two weeks the healing abutments were replaced by the ball bearing attachments (Figure 7).

8. The liner placed on the tissue surface of the prosthesis was removed. A wax spacer was placed in that area and the prosthesis was put in place. The site of ball attachment was marked on the tissue surface of the prosthesis.

9. The sites for the retentive housings of the ball attach¬ments were identified and the wax spacer was removed.

10. The retentive elements for the implant abutment were housed directly into the fitting surface of the denture (Figure 8) with the help of auto polymerizing resin (Dentsply Repair Material). The final prosthesis was an excellent blend of retention, stability and support.

Discussion

This procedure allows for the conversion of existing conventional complete denture prosthesis into implant supported overdenture prosthesis at a comparatively low cost without compromising aesthetic and function. A screw retained implant supported fixed prosthesis would require placement of more number of implants and hence, the cost of the treatment increases. Also with this procedure, the prosthesis can be fabricated with materials that are readily available and familiar. In a study done by Li Chen et al., the patients in the comparative masticatory efficiency test restored with implant-supported overdentures and tooth-supported overdentures showed higher comparative masticatory efficiency than those restored with conventio¬nal complete dentures.7

The implant supported overdenture prosthesis helps in preservation of alveolar bone. Cram and Rooney have found that the reduction in the height of anterior part of the mandible in those patients wearing complete upper and lower dentures amounted to 5.2 mm as compared with 0.6 mm for the overdenture patients.8 The anterior mandible bone under an implant overdenture may resorb as little as 0.5mm over a 5 year period, and long term resorption may remain at 0.1mm annually.9" Same is true for fixed implant complete denture.1 LoCascio and Salinas12 for a conventi¬onal implant supported mandibular complete denture, recommended 15 mm of space measured from the crest of the mandibular ridge to the opposing dentition at a correct vertical dimension of occlusion, whereas, William et al., recommended 17mm space for an overdenture supported by framework, this is an additional 2mm (for the fixed frame).13 The case presented in this article had 15mm of interarch space available.

Bulent et al., described a pressure free technique to provide the accurate relation of the implant components and the supporting tissues without finger pressure.14 However, it is technique sensitive and the clinician must assure the accurate placement of the locator attachments on the implant abutments during the impression process. Bulent and Volkan described a 2-stage impression technique that records the alveolar mucosa in a functional state and implant components accurately15 The disadvantage of this technique is that it is time consuming compared with single stage techniques. The pick-up technique described in this article is less technique sensitive and less time consuming provided the implants are placed accurately parallel to each other.

A photo elastic analysis done by Kenney and Richards indicated that the ball/O-ring attachment transferred less stress to the implants.16 It appears that the O-ring performed as it was intended, allowing the overdenture to rotate around the ball connected to the implant body. As rotation occurred, stress was transferred perpendicularly to the posterior edentulous area providing optimal broad stress distribution to the ridge and minimal stress to the implants. Thus, the mandibular overdenture retained by implants in the interforaminal region appears to maintain bone in ante¬rior mandible and appeared to improve retention, stability and chewing ability When two implants are used in the anterior mandible to retain an overdenture, solitary ball attachments appear to be less costly, less technique sensi¬tive and more accommodating for tapered arches. However, ball attachments seem to be less retentive than thebar design.

Conclusion

The mandibular overdentures retained by two ball attach¬ments supported by two endosseous implants can be used in cases of reduced space for attachment placement. It not only provides retention for the loose mandibular denture prosthesis but also improves the oral health related quality of life of the edentulous subject.

References

References

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Disclosure: The authors report no conflicts of interest.