The purpose of this article is to outline an achievable treatment solution to a problem we may increasingly see with older restored dental implants which have experienced a tough tour of duty.
Biomechanical complications of implant treatment include marginal bone loss, prosthodontic material fractures, loosening or fracturing of abutment screws and, uncommonly, implant failure. The incidence of dental implant fracture is reported to be between 0.16–1.5 per cent for restored cases over varying periods. In the aetiology of implant fracture, many studies confirm occlusal overloading, para functional habits and bruxism to be the identifiable clinical factors. In simple terms, mechanical overload from whatever cause must be ultimately responsible for the failure. This area of research is inherently difficult to firstly understand (quantify) the loading cycles placed on the successfully integrated and restored implants and secondly, to determine the relevant mechanical, biological and restorative factors contributing to the overall restorative failure. It is a serious concern that recent estimates for Implant-supported Fixed Complete Dental Prosthesis (IFCDPs) ‘free of complication’ could be as low as 8.6 per cent over 10 years and technical failure complications (largely mechanical screw fracture) over the same period is 20.8 per cent. Selection of the most suitable dental implant, both for the clinical outcome and the long term mechanical/biological stability remains with the dental surgeon.
Case report
The patient attended in October 2013 with what appeared to be a loose 22 implant retained crown. Initial diagnosis was that the abutment screw had loosened and the cement retained crown now had 10-20 degrees freedom of rotation. The appearance on the intra oral dental radiograph illustrated an area of radiolucency in the coronal third of the implant 22 and a similar radiolucency on implant 23.
At the appointment to remove the crown and tighten the abutment, the upper third of the dental implant 22 detached completely from the socket. This outcome was not expected.
Investigations
Interpretation of both the CBCT (fig 2) and further radiographs suggested both implants 22, 23 may be similarly affected. At the change in the threaded regions of the 23 implant, a similar fracture and the possible cause for the radiolucency mid length of both implants was interpreted. Measurement of the implant diameter on the CBCT suggested the apical component was approximately 3.5mm in diameter.
Treatment plan
After discussion with the patient, it was thought best to attempt to remove the apical component of the implant 22 and anticipate a similar procedure with implant 23. The alternative of leaving the apical components buried and constructing a new prosthetic superstructure was rejected on the grounds of:
- leaving two infected foreign objects in the maxilla.
- the potential physical load a future prosthodontic structure would be expected to receive. If occlusal loadings could fracture two adjacent dental implants, then these extreme loadings would risk any cantilever type restorations based on adjacent dental implants.
A trephine technique was chosen and, providing there was adequate bone, immediate ‘replacement’ dental implants were to be placed.
An Immediate placement technique with a non-loading osseointegration phase and the use of a removable acrylic partial denture 22-23 was planned.
Surgery
Removal and implant placement was performed under local anaesthetic (Bartonest 10mls 1:100000 epinephrine):
- Muco-periosteal flap raised.
- Fractured coronal component 23 removed.
- 22 apical implant component trephined (Straumann explantation medium drill, internal diameter 4.2mm, external diameter 4.8mm 044 341 ) under chilled saline (900 RPM).
- 23 coronal implant component removed (fig 4).
- 23 apical implant component trephined (Straumann explantation medium drill, internal diameter 4.2mm, external diameter 4.8mm 044 341) under chilled saline (900 RPM).
The peri-implant bone loss in the alveolar area aided access. A rose-head bur was used to debride fibrous tissue in the area of the fractures and the trephine prepared bone circumferential to the integrated component. With care, the trephine was able to core both apical components. The cored apical portion was then fractured off the apical attached bone, allowing each component to be removed entirely.
Implant selection and placement measurements of the osteotomy suggested that primary stability could be achieved using a 5mm diameter implant body. For strength, the internal octagonal connection was considered appropriate. For implant 23 I chose Southern Implants’ ITST 5mm diameter, 12 degree co-axis, length 14mm. For implant 22, Southern Implants’ ITT 5mm diameter, length 12mm.
The 5mm diameter (fig 9) was considered to be sufficient to take up most of the trephined osteotomy and engage apical bone with sufficient torque.
To assist with guided bone regeneration, small particulate xenograft (Bio-Oss, Geistlich) and resorbable collagen membrane (conFORM, Ace Surgical Supplies) was selected to infill the larger jump gap spaces (fig 13). A 10 week period for osseointegration and soft tissue maturation was chosen before impressions.
Restoration
The impression copings (Southern Implants) were both torqued to 15Ncm and picked up in a custom acrylic tray. The patient’s bruxist and clenching history suggested that a screw retained restorative solution would be ultimately stronger and, if the crowns were connected, the overall strength would be enhanced with the effect of bracing. Care with the final functional occlusal platform in all centric and lateral excursion movements would further help prevent porcelain fractures and ultimately prevent a repeat of the implant failure.
Discussion
This was a case where the use of the trephine provided an oversized osteotomy. Successful osseointegration was dependent on achieving primary stability and this came from the replacement Implants engaging sufficient bone apical in the osteotomy site.
The patient has had a history of dental root, prosthesis and implant fractures. Protective splints are recommended with bruxist, parafunctional and grinding patients. Here the problem of the implant fractures may have been preventable. Historically, the patient was unable and unwilling to wear any form of splint. The response from the manufacturer of the fractured implants confirmed that failure was probably due to parafunctional bruxism. Treatment was completed in February 2014.
References available on request.