From Volume 41, Issue 9, November 2014 | Pages 785-795
The aims of this second paper are to address the general principles involved in treatment planning precision attachment-retained dentures, with careful consideration of the whole patient rather than just the intra-oral aspects of planning. These principles are illustrated with four cases. The literature on maintenance and complications is also discussed in this paper.
Precision attachments potentially offer many advantages over conventional removable dentures. When these are used appropriately they can lead to increased patient satisfaction. There is also a vast number of different attachments available for use. This means that appropriateness has to be carefully assessed, not only by correct case selection, but also by clinical and technical experience, and patient compliance and dexterity.
Careful treatment planning is essential. Errors at this early stage may result in failure of the case. A clinical examination to assess for caries, periodontal disease, peri-apical disease, tooth surface loss, or infections of the oral mucosa should be completed. This should inform the clinician of the suitability of the mouth to receive complex restorations. In conjunction with this, it is fundamental that the patient is assessed as a whole as previous dental history and manual dexterity may impact on the decision process.
A patient's medical history can also influence the decision-making process. The construction of a precision attachment-retained denture is more time consuming than a conventional denture. Any component of the medical history that would preclude long appointment times may make this form of treatment an inappropriate choice. Owing to the very nature of their precise fit, patients would require sufficient manual dexterity to enable placement and removal of the prosthesis. For example, patients with severe arthritis affecting the hands, or neurological disorders such as Parkinson's disease, may find the placement and removal too difficult, without assistance. These problems can be overcome with the use of magnet-retained overdentures, as they may prove easier to remove.
Patients who suffer from xerostomia may be at a greater risk of caries. Whilst this would not preclude this group of patients, it would impact on home maintenance and the chosen recall period. Limitations of jaw opening may also influence this choice of treatment owing to the vertical path of insertion for these prostheses.
Teeth that are to receive precision attachments need favourable crown:root ratios, minimal mobility and healthy periodontal support. Teeth that are mobile are not necessarily unsuitable. For example, if a tooth has suffered loss of periodontal attachment, reduction of the crown height to gingival level improves the crown:root ratio, which in turn reduces the fulcrum point and reduces the mobility. It must be remembered that, in conjunction with this approach, stabilization of the periodontal disease is essential. In circumstances in which previously root-filled teeth are being considered as potential abutment teeth/roots for receiving attachments, then the quality of existing root canal treatments should also be assessed.
The impact of the prosthesis on the soft tissue profile also requires consideration. The retention of roots, especially the canines, retains the buccal plate of bone that can result in excessive upper lip support if a flange is placed on an overdenture.
Study casts mounted on a semi-adjustable articulator using a facebow and either centric relation or the retruded contact position (depending on the tooth/jaw relationships) will aid assessment of the occlusion and definitive treatment planning. As with any assessment, the following should be evaluated, where appropriate:
In addition, it is important to consider the amount of interocclusal clearance and if there is sufficient available space for the attachment system, surrounding framework and prosthetic tooth to give an aesthetic and durable restoration. This demands knowledge of the specific dimensions of the proposed attachment systems available. For extracoronal attachments, sufficient space beneath the attachment is also required to enable the patient to perform appropriate oral hygiene measures.
With an increased complexity to the treatment comes an associated need for repairs and maintenance of precision attachment-retained dentures. These may include minor adjustments, major adjustments, full replacement or removal. Patients need to be fully informed of this. Shaw followed 23 patients who received precision attachment-retained overdentures between 1964 and 1977. Of the teeth retaining the prostheses, 75% were functioning adequately after a mean period of 7 years, but only 5 patients out of 23 had received no technical maintenance after a mean period of 6 years.1 All other patients had required repairs, remakes or a combination of the above within this period. The most common repair involved a puncture fracture of the acrylic covering the patrix, thought to be produced by repeating impingement of the patrix during mastication or clenching activity. At the end of the study, a third of patients had carious abutment teeth (Figure 1). Oral hygiene was found to be generally poor in the group and periodontal disease ‘prevalent’. Overdentures opposing natural teeth were found to need more maintenance than full denture rehabilitations. A study by Öwall and Jönsson found that, out of a total of 57 precision attachment-retained denture patients, 63% needed attachment repairs, or experienced complications from abutment teeth or prostheses.2 This is significantly different from Öwall's first study, which reported 14% for the same complications in a specialist setting.3 These findings suggested the need for further research of long-term results in general practice.
Öwall and Jönsson, in their study2, showed that dentists and patients were satisfied with 94% of precision attachments placed over a two year period and, during the first 2 years, 22 of 57 constructions were complication free. There appeared to be a correlation between the frequency of complications, and the number of root-treated abutments. It seems that the most important part of treatment using precision attachments is case selection. Patients need to be well motivated with a high level of manual dexterity.4
In a retrospective study on combined fixed–removable prostheses by Studer et al, it was found that 38.5% needed to be remade or repaired after a follow-up period of 8 years.5 This study looked at rigid and semi-rigid retainers. The success for semi-rigid retained prostheses was reported as 98.1% at 5 years and 93.1% at 8 years. This was favourable compared with the studies on the survival of clasp-retained partial dentures.6,7 The results in the rigid group were very contrasting, with survivals of 53.6% at 5 years and only 30.1% at 8 years. This study also identified that the anatomical distribution of the abutment teeth was an influencing factor on survival. Bilateral free-end saddles influenced survival significantly. They also found that the older the patient, the greater the hazard rate for failure, although no explanation could be given for this.
Kennedy Class I and II situations require particular mention. Little is known on the action of the attachments on supporting structures for distal extension removable prostheses. Photoelastic analysis investigating the forces developed in the bone supporting the distal abutment teeth found that rigid type attachments had a tendency to torque the primary abutment tooth distally.8 They also reported that splinting abutment teeth together resulted in better force distribution and reduced torquing of the teeth involved. Similar results were shown by Shohet.9 They found that the greatest torquing forces were associated with rigid attachments and non-splinted single abutment teeth. Altay et al, in their in vitro study, demonstrated that splinting abutment teeth together resulted in significant reductions in mesiodistal and buccolingual movements of distal abutments when vertical loads were applied.10 There was no difference in the magnitude of the vertical movement. Similar results were found by El Charkawi and el Wakad in their in vitro study on the effects of splinting on load distribution.11 Resilient attachments are therefore favoured for Kennedy Class 1 situations.12
The use of selected attachments will be illustrated in four case reports.
A 90-year-old male patient presented complaining of repeated problems of retaining his previous loose upper denture. Clinical examination revealed two maxillary central incisors that had been retained as overdenture abutments. The residual alveolar ridge was severely reduced in height and the buccal sulcus depth was particularly shallow (Figure 2). The mandibular arch was partially edentulous with evidence of severe tooth surface loss affecting the anterior teeth. The patient was so dissatisfied with his denture that he did not wear it at all. Radiographic and clinical examination demonstrated root-treated central incisors with a fractured post present in the UR1 (Figure 3). Particular treatment planning considerations in this case included a lack of residual ridge to provide a stable and retentive conventional prosthesis, tooth surface loss affecting the lower incisors and the fractured post in the UR1. A plan was formulated to place post-retained stud attachments of the Rothermann (Preat, Grover Beach, CA, USA) variety on both central incisor roots and the provision of a complete maxillary overdenture with Rothermann eccentric clips. A mandibular partial overdenture to restore the occlusal vertical dimension was also planned. Preparatory work included the removal of the fractured post in the UR1 with ultrasonic instrumentation. To ensure that there would be sufficient interocclusal space for the attachment, a primary centric jaw relation was recorded taking into account the resting vertical dimension and freeway space (Figure 4). This identified that there was sufficient space to allow the placement of two Rothermann eccentric attachments. It also identified that there was sufficient space to overlay the mandibular canines which, although crowned, had been designed to conform to his worn dentition. Overlaying these would improve the aesthetic outcome of the mandibular partial denture. The attachments would be resilient rather than rigid to increase retention but limit stress to the rather short abutment teeth. The two central incisors were then prepared for parallel posts and an impression made (Figure 5). Titanium posts with cast on gold copings were constructed on the working model, the Rothermann stud attachments were soldered to the copings in the laboratory (Figure 6). At the next appointment the posts were cemented with Rely X Unicem (3M ESPE, Seefeld, Germany) and a secondary impression in medium-bodied silicone was made in a special tray (Figure 7). At this stage it was important to ensure accuracy of location of the eccentric clips and adaptation of the future denture base. To aid this process, a clear acrylic base-plate with eccentric clips in position was constructed on the secondary cast and this was tried in the mouth (Figure 8). This was satisfactory and so the denture was processed in the usual manner. The wax try-in is shown in Figure 9. This form of treatment provided a satisfactory outcome for the patient. It provided him with a retentive maxillary complete denture and a functional occlusion with the well tolerated mandibular overdenture.
A 52-year-old patient presented complaining about the appearance of his teeth and difficulty with eating. He also complained of a recent fracture of one of his anterior teeth and the subsequent loss of his bridge. Clinical examination revealed a subgingival crown/root fracture of the UR3 and a carious root face of the UR5 in the middle of an otherwise edentulous span from UR1 to UR5 (Figure 10). Assessment of the radiographs taken also indicated periapical periodontitis of the UL1 and the level of the fracture on the UR3 was close to the alveolar bone crest (Figure 11). The patient also had caries associated with a small number of other teeth. The treatment planning considerations in this case were dictated by a potentially large unilateral bounded edentulous space in the maxillary arch (Kennedy Class III) with potential abutment teeth UR6 and UL1. This space posed an aesthetic challenge and made gaining adequate direct and indirect retention more difficult. The UR3 was unrestorable at presentation owing to the likelihood of invasion of the biologic width with any restoration. Initially, the patient was keen for a fixed restoration, however, the UR3 was unsuitable as a distal abutment for a bridge, and extending a bridge from UR6 to UL1 with UR3 as a pier abutment was felt to be high risk. A plan was formulated to restore the carious lesions and stabilize the dentition, extract the unrestorable UR5, complete root canal treatment of the UL1 and retain the UR3 after surgical crown lengthening and root treatment. This tooth and the UR6 were planned to be used as abutments with precision attachments of the CEKA variety, along with a conventional clasp assembly around UL6 to provide a retentive partial overdenture. Once again, to confirm the appropriateness of this treatment plan, articulated casts were made and a primary centric jaw record was taken with a wax occlusal rim. This plan ensured preservation of a well positioned canine that could provide direct retention and aid in the aesthetic restoration of the space. The initial treatment involved surgical crown lengthening of the UR3, which included the raising of a full mucoperiosteal flap and osseous recontouring. This resulted in a supragingival root face that allowed root canal treatment of the UR3. Following primary impressions and the construction of special trays, the UR6 was prepared for a gold crown and extracoronal precision attachment, the UR3 was prepared to receive a parallel-sided post-retained radicular attachment and the UL1 prepared to receive a new porcelain-bonded crown (Figure 12). This was completed in the same visit and a secondary impression made of the preparations and potential denture-supporting tissue (Figure 13). This single impression would allow the fixed prosthodontic work and partial denture to be constructed on the same model, minimizing potential errors. One drawback of this technique is that each stage of construction requires placement and removal of the individual fixed restorations and subsequent temporization.
This technique was based on discussion of the planned fixed and removable components with the laboratory. Other methods of fabrication include having the fixed components made on removable dies then picked up in a further impression to give the master model for the construction of the removable component. Alternatively, following cementation of the fixed components, a further impression can be made for provision of the master model.
The provision of combined fixed and removable prosthodontics requires both the removable and fixed prosthodontic technicians to work together in the designing phase. The design of the fixed prosthodontic components must be done to enable retentive features to be incorporated as well as allow an appropriate path of insertion, particularly when combining conventional and precision attachment features. This highlights the importance of discussion with the technician prior to starting, as it is important for both clinician and technician to work closely together to avoid errors.
The gold crown with extracoronal CEKA attachment was fabricated for the UR6. A cast metal post with gold coping and radicular CEKA was fabricated for the UR3 and a porcelain-bonded crown (PBC) for the UL1. These were tried in the mouth. The fit was satisfactory and the restorations were returned to the model to allow construction of the partial denture (Figure 14). Following the usual stages for denture construction, the fixed restorations and partial denture were delivered to the patient on the same day (Figure 15). This provided the patient with a satisfactory outcome. The denture was found to be very retentive and the patient has found no problems with insertion and removal.
A 69-year-old lady presented complaining of loosening of her lower partial denture. The denture had been in place for approximately 10 years. Clinical examination revealed a bilateral free-end saddle denture (Kennedy Class I) that acted as an overdenture retained by the lower canines (Figure 16). Further examination of the remaining dentition revealed intra-radicular metal attachments in the mandibular canines. The maxillary arch was restored with a complete denture and the retention of this was poor. According to the patient, these attachments had been in place since 1985 and examination demonstrated that they were still satisfactory (Figures 17 and 18). The fitting surface of the prosthesis revealed that the patrix component of the attachment system was composed of nylon (Figure 19). The retention provided by the denture was poor. The attachment system was identified as a Zest Anchor (ZEST Anchors LLC, Escondia, USA), an example of which is shown in Figure 20. It was recognized that there were some technical inadequacies with the root canal treatment of the abutments, however, the risk benefit ratio for attempting removal of the metal matrix and re-treatment without compromising the abutment was considered unfavourable. A plan was formulated to construct a new precision attachment-retained lower prosthesis following the previous design using the existing overdenture abutments and matrices. A complete maxillary denture would also be constructed. All standard prosthodontic stages were completed until delivery of the dentures (Figure 21). At the delivery appointment, space had been made in the fitting surface of the prosthesis, by the technician, to allow direct chairside pick-up of the patrices with cold cure acrylic. It is important at this stage that a vent is left in the polished surface of the denture to enable escape of any excess acrylic resin. This intra-radicular case illustrates that, when abutment angulations preclude patrix placement on the root face, the use of the Zest Anchor attachment system allows matrix placement within the abutments.
A 41-year-old female patient with cleft lip and palate was referred by her GDP for restorative care. The patient unfortunately had a very compromised dentition. As well as presenting with carious teeth that were unrestorable, she also had advanced periodontal disease. In the maxilla, the only teeth that were deemed savable were the UL3,4 and the UR3. There was also a palatal defect that required obturation. The UR3 was grade two mobile at presentation with reduced bone support (Figure 22). The treatment plan was to root treat the UR3 and decoronate it and use it with a magnet-retained attachment. The planned prosthesis was a cobalt chrome partial denture with conventional clasping on the UL3,4 with extension of the denture base into the palatal defect and magnetic retention from the decoronated UR3. The decision to maintain those three teeth rather than consider a clearance was made because there was very little sulcus depth and a full clearance would have made construction of a successful complete denture difficult. Following root treatment of the UR3, it was decoronated to 2 mm supra gingivally. This provides sufficient height for a ferrule and sufficient occlusal space. Once again pre-operative assessment of intra-occlusal space was essential. Insufficient space would mean the magnet would be thinly covered in acrylic with the risk of fracture of the acrylic and loss of the magnet. An impression was made for a post-retained keeper on the root face. There are various systems available including pre-formed keepers. In this instance, a cast post was constructed using Dyna EFM alloy which consists of Pd/Pt/Co casting alloy. The Dyna System (Dyna Dental Engineering bv Netherlands) consists of the EFM alloy and four different types of magnets are available. Their size and magnetism vary from 1.7–2.8mm in height and 300–500 g of retentive magnetism, respectively. Assessment of the intra-occlusal space in this case identified that there was sufficient space to use the larger magnet. Once this was cemented, an overall impression was made and the usual stages of denture construction occurred (Figure 23). The final denture was inserted and has been satisfactory for over three years (Figure 24). This case highlights that, despite reduced bone support associated with the UR3 and its mobility, it could still be considered for an attachment. By decoronating the tooth, the fulcrum changed, the relative support became appropriate and the mobility reduced.
The introduction of dental implants has probably seen a reduction in the number of roots being maintained for retention of overdentures. Comparison between the two treatment modalities is difficult to do because of the differences in study designs and outcome parameters used.13 The decision to maintain roots for overdentures and the ensuing endodontics, periodontics and more complexprosthodontics, instead of placing implants, needs to be balanced against a number of factors: patient willingness and ability to undergo implant surgery, self motivation to maintain the teeth and economics.
There is no doubt that several precision attachment systems are relatively complex devices that will require continuing care and maintenance. This paper has focused on showing the benefits that precision attachments can bring to the provision of a removable partial denture. It is important to realize that precision attachments are not a panacea and their use can only be advocated in carefully selected cases. It is imperative that careful treatment planning, attachment selection and meticulous clinical and laboratory procedures are carried out. With all this in mind, precision attachments can be a useful part of the dentist armamentarium.
