The root-supported overdenture using the Locator overdenture attachment
James Pavlatos, DDS
This article reviews the rationale for the use of overdenture in the partially edentulous and fully edentulous maxilla and mandible. Treatment options, prosthetic designs, indications, and fundamental principle for the successful applications of overdentures are discussed. A detailed step-by-step procedure and technique for the construction of overdentures is provided.
Most patients who have complete dentures are dissatisfied with the limited retention and stability of their prostheses.1 Bone loss and deterioration of the alveolar ridge in the maxilla and the mandible can lead to atrophy and lack of support for complete dentures.2 The area of bony support for a denture base is 1.8 times greater in the maxilla than it is in the mandible. The force on the mandible during mastication is greater than on the maxilla, creating a unique and considerable problem in overdenture design.3,4
Changes in muscle attachments may result in loss of facial form, decreased or impaired function, and compromised esthetics and phonetics.2 Changes occur in the residual ridge after tooth extraction with the size of the bony ridge decreasing as resorption continues, initially for up to two years. The resorption rate is the greatest in the anterior maxilla and mandible, with the resorption beginning on the buccal or labial surface of bone. The resorption rate is three to four times greater in the mandible than in the maxillary ridge.3
In data complied by Carlsson and Persson, the rate of residual bone resorption was 0.5 mm per year starting after the second year.3 Clinical research in 1975 by Crum and Rooney over a five-year period indicated that bone loss in the edentulous mandible in denture wearers was reduced by an average of 0.1-0.3 mm a year.2,5-7 Over a five-year period the bone loss averages 5.0 mm. In the same period, vertical bone loss in patients wearing overdentures was 0.6 mm.2,5-9 Alveolar bone resorbs at a faster rate without the support of natural dentition. Retained roots maintain alveolar bone, which will support an overdenture and prevent rapid bone loss.5
Root-supported or implant-supported overdentures can help to solve the problems created by a partially or completely edentulous maxilla or mandible. Root-supported overdentures are an alternative to extractions and complete dentures. The overdenture will increase the patient’s retention, stability, and resistance to denture displacement. Retaining the existing teeth also will preserve the alveolar ridge, prevent bone loss, and increase both proprioception and masticatory performance.7-9
Rissin and House analyzed the masticatory performance of three dental patient groups: those with natural dentition, those wearing complete dentures, and those wearing overdentures. Food was chewed by each patient, then passed through a No. 12 sieve. The chewing efficiency of patients with natural dentition was measured at 90%, complete denture wearers 59%, and patients with overdentures 79%.5,6 Chewing efficiency with a root-supported overdenture was 34% higher in patients who previously wore a complete denture. This increase in function, retention, and stability leads to better esthetics and phonetics in denture wearers. These factors elevate patients’ self-esteem and increase their confidence level.
Attachments
Root-supported overdentures gain their retention and stability from the use of attachments. Attachments are simple connectors consisting of two or more parts. One part connects to the root and the other part to the overdenture acrylic denture base. Attachments are either resilient or nonresilient (rigid). A resilient attachment has vertical, lateral, and hinging movements and 360 degree rotation at the attachment site. These movements allow the prosthesis to move up and down or vertically over the abutment as the patients chews, while the 360 degree rotation at the attachment site redirects or redistributes the load over the posterior mucosa and directs it way from the abutment. This action reduces the stress on the abutment tooth or implant. Only resilient attachments are used in the design of mucosal root-supported or implant-supported overdentures.1,2,10,11
There are three types of overdenture attachment designs: bar type, radicular type, and intraradicular type. The bar type spans an edentulous area and connects two or more teeth or implants with rigid fixation. Supraradicular type attachments are placed on top of the existing root structure or surgically placed implants. Intraradicular attachments are placed within the endodontically treated root structure of natural teeth or implants. All three designs are used in the construction of maxillary and mandibular overdentures.1,2,10,11
Complete diagnosis and treatment planning are most important for the success of overdentures. Evaluation of the existing limited abutments- for endodontic and periodontal treatment is the first step in a successful treatment plan. Teeth with advanced periodontitis having less than 6.0 mm of bone support, subgingival decay, and poor attached gingival tissue are contraindicated for overdentures.12
From Del Rio et al:
Overdentures require particularly careful accessment of vertical space. There must be sufficient room for roots, copings, and possible attachments, together with an adequate thickness of denture base material and artificial teeth, all this without jeopardizing the strength of the denture.13
Performing endodontic therapy on overdenture abutment teeth accomplishes a number of objectives, including retaining the natural tooth root in its alveolar bony environment for retention, support, and stability of the overdenture, preserving and maintaining the height of the alveolar bone and ridge: maintaining the proprioceptive quality and integrity of the periodontal ligament: and creating a favorable crown-to-root ratio for periodontally involved abutment teeth.12,14,18
The Locator root-retained attachment (Zest Anchors, Escondido, CA: (800) 262-2310) is classified as a supraradicular, universal hinge, resilient attachment for endodontically treated roots. It is indicated for use with overdentures or partial dentures, retained in whole or in part by endodontically treated roots in the mandible or maxilla. It is contraindicated where a totally rigid connection is required. The supraradicular attachments (self-locating design) allow patients to seat their overdenture easily without the need for accurate alignment of the attachment components. It is designed with a locating skirt that seats the attachment in the proper location every time, regardless of the patient’s ability or dexterity. It is ideal for stroke patients or arthritis patients who have compromised dexterity and difficulty in exact overdenture placement.
The Locator implant attachment also is manufactured for implant-supported overdenture retention. It has the same features as the root-supported overdenture attachment. With a total attachment height of 3.17 mm on an externally hexed implant, it is the lowest profile connector available.
The pivoting Locator male allows a resilient connection for the prosthesis. The retentive nylon male remains completely in contact with the female socket while its metal denture caps has a full range of rotational movement over the male. The unique dual retention (both inside and outside) provides the Locator attachment with a greater retention surface area than other attachments. A test was performed by the manufacturer to compare the retentive surface area of three dental attachments.19 The removable denture component for each type of attachment was measured by a comparator to determine the actual contacting retention surface area. The measured retentive surface area of the Locator attachment was 1.3-1.8 times greater than the other attachments, the ZAAG and the ERA.
Delsen Testing Laboraties, Inc. performed an insertion and extraction test of retention loss.20 The Locator attachment did not wear out until 110,000 cycles were completed. The ZAAG attachment wore out in 12,000 cycles and the ERA in 4,000 cycles.
This new Locator attachment creates a longer lasting, more retentive attachment for root-supported and implant-support overdentures. The supraradicular design includes a choice of a straight post or two angled posts (10 and 20 degrees) to accommodate divergent roots. Two different retentive males allow for the choice of regular retention (5.0 pounds) or light retention (1.0 pounds), according to the needs of the patient.
Locator male attachments are available in varying amounts of retention. The black male attachment provides the least amount of retention at 1.0 pound: the pink male attachment provides 3.0 pounds of retention; and the white male attachment provides 5.0 pounds of retention and is considered the regular or standard for this system. With two to four abutment teeth, the maximum retention should be used (the white male at 5.0 ponds per attachment). If more than four abutments are used, any combination of black, pink, and white attachments can be used to create the maximum retention for the overdenture (20 pounds is ideal). If there is too much retention with these attachments (six white attachments equals 30 pounds of retention), the overdenture cannot be removed easily. Choose the final Locator nylon retention liner based upon the maximum amount of retention needed to retain the overdenture.
Contraindications for use of the Locator root attachment
The width of the root surface must equal or exceed 4.0 mm. The length of root must equal or exceed 7.0 mm.
The Locator post has a length of 6.0 mm but can be shortened to as little as 3.0 mm. The Locator post is cemented in place, not threaded or screwed into the root. Care must be taken when drilling the post preparation not to perforate or fracture the root due to its small diameter. The Locator cannot be placed in mandibular incisor or lateral teeth or in maxillary lateral incisors (ZAAG mini attachments (Zest Anchors) are recommended for these teeth).
Te Locator cannot be used when a metal post already is present in the root canal (a cast-to-ZAAG can be cast in a coping above the post).
The crown-to-root ratio of leverage on the supporting root structure is affected by whether an attachment connection is intra-radicular or extra-radicular. The Locator is an extra-radicular attachment. Therefore, when the supporting root structure is short or compromised, the ZAAG attachment should be used because of its lower crown-to-root ratio, which will be a more gentle connection.1,2
Most patients who have poor oral hygiene, missing teeth, periodontal and endodontic problems, and appear to be candidates for full dentures can be ideal patients for maxillary or mandibular overdentures. Retained teeth or roots will maintain alveolar bone, which in turn will support an overdenture and prevent rapid bone loss.3 Instructions on overdenture care must be given at the time of insertion.
Diagnosis and treatment planning for these patients is essential for overdenture success. Extractions, periodontal surgery, and possible bone grafting with endodontic therapy must be accomplished at the start of treatment.21
Technique for placement of the Locator female in natural teeth
The crown of each tooth selected for an attachment is decoronated to within 1.0 mm supragingivally (Fig.1). Keep the top of the root surface as flat as possible from the mesial to the distal portion of the tooth, because the interdental papilla are the highest part of the crest of the ridge. This leaves the buccal and lingual portion of the tooth more than 1.0 mm supragingival. They will be reduced after placement of the Locator female attachment.
Set the white plastic reference ring on the pilot drill to a depth 1.0 mm longer than the length of the female post (Fig.2). Using the pilot drill in a straight root and following the canal, make the initial preparation to the depth previously selected (Fig.3).
In a nonparallel root, a 10 degree or 20 degree attachment can be used to correct the divergence (Fig.4). After preparation with the pilot drill, the countersink diamond bur is used. The preparation with the countersink diamond bur is only a very shallow recessed seat on the root surface (Fig.5). The major diameter o the Locator female must have at least half of its height above the root surface for the Locator cap male to snap all he way down in place without interference (Fig.6 and 7).
The Locator parallel post has a dual purpose. It acts as a paralleling pin when placing multiple attachments and as a handle for cementing the Locator attachment into the completed preparation (Fig.8 and 9). Cement the Locator in place with composite resin cement or a material of your choice (Fig.10-12). After the cement has set, complete the final root contouring of the buccal and lingual surfaces.
Place a Locator cap assembly with black processing male into each cemented female. When the black processing liner is in place for either an acrylic chairside pickup or an impression technique for laboratory placement, it sets up the vertical resiliency needed for the final male. It also allows the metal cap housing to pivot up to even degrees without contacting the surrounding surface of the root. Take an impression using a combination of light and heavy bodied vinylpolysiloxane impression material (GC America Inc., Alsip, Il: (800) 323-7063) or any firm body impression material. The impression is held in place with very little pressure so as not to compress the posterior soft tissue and lose the vertical resiliency built into the Locator attachment. Remove the impression, leaving the processing cap male in place (Fig.13).
Place the Locator analog into each of the recovered processing cap males attachments and reinsert into the impression (Fig.14). The impression is sent to the laboratory for the construction of the master cast, which is an exact duplication of the position of the Locator female in the patient. A soft rubber material (Gi-mask, Coltene/Whaledent Inc., Mahwah, NJ: (800) 221-3046) is poured in and around the impression copings at the gingival crest and the laboratory working cast is poured in blue stone (Fig.15). The black processing cap male is cured into the overdenture using normal laboratory processing techniques (Fig.16).
In the completed overdenture, the black processing male must be replaced with the final white retentive male attachment (Fig.17). A special hand tool with a hook is used to remove the black processing male. The final retentive male attachment is snapped into the metal denture cap using a seating tool (Fig.18). The overdenture now is complete for delivery to the patient (Ottawa Dental Laboratory, Ottawa, IL: (800) 851-8239).22,23



Fig 1. The crown of each tooth selected for an attachment is decoronated to within 1.0 mm supragingivally. Fig 2. Locator with pilot drill Fig 3. Make the initial preparation using the pilot drill to the depth selected previously. Fig 4. In a nonparallel root, a 10 or 20 degree attachment is useful to correct the divergence.




Fig 5. Preparation with the countersink diamond bur. Fig 6. Clinical preparation with the countersink diamond bur (tooth No. 6). Fig 7. Preparation in root prior to cementing Locator female attachment (tooth No. 6). Fig 8. Female Locator attachment cemented in place on teeth No. 6 and 11.




Fig 9. The Locator parallel post on teeth No. 6 and 11. Fig 10. Female Locator attachment cemented in place on tooth No. 6. Fig 11. Completed Locator female attachments cemented in place on teeth No. 4-6. Fig 12. Completed Locator female attachments cemented in place on teeth No. 4-6 and 11-13.




Fig 13. An example of the final impression from the mouth with processing cap males. Fig 14. Vinylpolysiloxane impression with impression coping/analog assembly. Fig 15. Laboratory working cast. Fig 16. An example of the intaglio surface of the denture with the black processing males.


Fig 17. An example of the intaglio surface of the denture with the final white retentive male attachments. Fig 18. An example of the intaglio surface of the denture with the male attachments.
Overdenture construction technique
Appointment No. 1: Preliminary impression
  • Use a stock tray
  • The attachments are placed on the natural teeth
  • The impression is taken in alginate and poured in plaster
  • The laboratory uses the impression to develop the preliminary working cast: it also is used to fabricate the custom tray for the master impression
  • Make temporary acrylic denture or modify existing denture for temporary use
Appointment No. 2: Master impression
  • Check fit of custom tray for overextension of borders and muscle attachments
Border mold the customs tray using a softened wax (Adaptal, Heraeus Kulzer,Inc., Armonk, NY; (800) 431-1785)
  • Snap on plastic impression copings to root attachments on the natural teeth
  • Take an impression with a vinylpolysiloxane impression material (GC America Inc.) or any firm-bodied material
  • Remove master impression from mouth, making sure the impression coping is picked up in the impression
  • Place the analogs onto the impression copings in the impression to form the impression coping/analog assembly
  • Send to the laboratory to pour up master cast which will duplicate the exact position of the attachments in the mouth
Appointment No. 3 (part one): Records
  • Receive the working model from the laboratory with the bite rim assembly completed
  • Establish the plane of occlusion using an occlusal plane plate (Dentsply Trubyte, York, PA: (800) 786-0085)
  • Establish the labial of the wax rim and the lip support
  • Establish the mid-line
  • Establish vertical dimension (2.0-4.0 mm freeway space)
  • Establish centric relation
  • Face bow transfer
Appointment No.3 (part two): Selection of teeth
  • Determine facial outline using a typal form
  • Determine the size of the maxillary central incisors
  • Determine facial profile using a tooth indicator assembly (Dentsply Trubyte)
  • Select denture teeth from mould guide (Portrait IPN (Dentsply Trubyte))
  • Face form as a guide to natural anterior arrangement of denture teeth (use chart for individualized anterior arrangements of Dentsply Trubyte teeth)
  • Preview the six anterior teeth as they will appear in the mouth (Truflex selection rim (Dentsply Trubyte))
  • Select denture base resin (Lucitone 199 denture base resin shade guide (Dentsply Trubyte))
Appointment No. 4: Wax try-in
  • Check esthetics of the denture setup for correct size, shape, and color and for the arrangement of the teeth
  • Check horizontal plane, lip support, and mid-line of the denture setup
  • Check the overbite and overjet and jaw relationship (Class I, II, or III)
  • Check the function: centric relationship and centric occlusion, freeway space, working and balancing occlusion, group function
  • Reset teeth in denture setup if needed for second wax try-in
Fig 19. Maxillary overdenture mandibular implant-supported 11-unit fixed bridge.


Appointment No. 5 Delivery of overdenture (Fig. 19)
  • Check all borders of the denture for overextension
  • Make sure the overdenture attachments provide retention and stability for the denture
  • Check for sore spots
  • Give patient instructions on placement and removal of the overdenture
  • If lack of proper retention from laboratory attachment placement occurs, a chairside pick-up may be needed to replace attachments and correct the retention problem
  • Oral hygiene instructions are given by the dental assistant or hygienist.24
Hygiene
The role of dental auxiliaries in the maintenance of overdentures is very important. Most candidates for full dentures or overdentures may not be in a daily habit of brushing and oral cleansing. Overdenture attachments must be kept clean and free from plaque and food debris. Careful instructions and a demonstration on overdenture care must be given at the time of insertion by the dental assistant or hygienist. Dailey brushing and placement of the overdenture in an antibacterial solution are most important. If tartar, calculus, or food debris builds on the surface of the attachments, the overdenture will not seat properly. In patients with root-supported overdentures, it is recommended by many dentists that overdenture abutments should be brushed at least once a day with gel toothpaste to remove plaque and to stimulate gingival tissues. A daily application of 1.1% neutral sodium fluoride (Prevident 5000 Plus, Colgate-Palmolive, New York, NY; (800) 763-0246) or 0.5% stannous fluoride (Zest Anchors, Inc.) should be placed on each exposed root surface. Poor oral hygiene has the potential for root or implant failure in overdenture cases.21,25
The patient should be instructed to visit the dentist periodically for professional cleanings and attachment evaluation. Use plastic instruments (Hu-Friedy, Chicago, IL: (800) 729-3743) for scaling the attachments. Do not use metal instruments that may create scratches.
If you are concerned that exposed dentin may re-decay, a special Locator cast-to-female is used in cases where a gold coping is desired to cover and protect the root surface.
Case Report
Fig 20. A 35-year-old patient prior to surgery.


A 35-year-old man was referred for a maxillary overdenture evaluation (Fig. 20). The maxilla contained 11 teeth with periodontal problems. The treatment plan was extraction of teeth No.3 and 7-10 with periodontal surgery on the remaining teeth (No. 4-6 and 11-13) and a bone graft on all extraction sites for possible future implant considerations. Osteograf LD-300 (CeraMed Dental, Lakewood, CO: (800) 426-7836 0 was used as the bone graft material on all surgical sites and cytoplast (Endopore, Innova Corporation, Toronto, ON: (800) 898-6261) as the barrier membrane. A temporary acrylic denture (flippers) was used to replace the missing teeth. Endodontic therapy was performed on teeth No. 4-6 and 11-13. The teeth were decoronated to within 1.0mm of the gingival crest and the Zest Locator attachment system for overdentures was cemented into each root (Fuji Plus, GC America Inc.). The patient requested a maxillary overdenture without a palate and an anterior flange. Retaining six teeth for retention of the overdenture would make this possible.
Six white males retentive attachments were used at 5.0 pounds per attachment for a total of 30 pounds of retention. Upon insertion of the maxillary overdenture by the patient, it became impossible to remove the denture because of the extreme retention. It was decided to remove the white male attachments on teeth No. 5 and 12 from the denture base and add two black male attachments at 1.0 pounds of retention each. This reduced the retention and allowed the patient easier insertion and removal.
It was evident that using the Locator white male attachment system on six teeth for retention of the maxillary overdenture was excessive. By using the black retentive males (1.0 pound) instead of the white retentive males (5.0 pounds). The retention was reduced. The use of any combination of black (1.0 pound), pink (3.0 pound), and white (5.0 pounds) retentive males also could be used to regulate the overdenture retention, with approximately 20 pounds being ideal.
Conclusion
All of us have a comfort zone in which we practice. To grow as people and to increase our knowledge as dentists, we must reach out to new ideas, solutions, and techniques. The root-supported overdenture is one solution to the problem created by an edentulous maxilla and mandible. Complete diagnosis and treatment planning are most important for the success of overdentures. This alternative treatment to extraction of natural teeth and complete dentures provides the patient with greater retention, stability, and comfort and improved function, esthetics, and phonetics. The Locator attachment is designed for patients who have difficulty seating their overdentures. Stroke and arthritis patients are ideal candidates for this attachment. The technique for constructing root-supported overdentures is easily within the skill level of most general dentist.
Disclaimer
The author has no financial interest in the products mentioned in this article.
Acknowledgements
The author thanks Zest Anchors, Inc. and Paul Zuest for his expertise and technical support and the center for continuing education and Ottawa Dental laboratory and Joe Jennings for his expertise and technical support.
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Reprinted from General Dentistry September/October 2002 www.adg.org