Zest Anchors
Root-supported Over-Dentures
by James Pavlatos, DDS with permission of Zest Anchors INC .
Most patients with complete dentures are dissatisfied with the limited retention and stability of their prosthetics. Rapid deterioration of the alveolar ridge is the source of the problem. Vertical bone in the edentulous mandible deteriorates at an average annual rate of 0.1 mm to 0.3 mm. In a five-year period, the bone loss averages 5 mm. The root-supported overdenture Root-supported over-dentures can solve the problems created by an edentulous mandible and maxilla. This alternative to extraction and complete dentures will increase the patient's retention, stability and resistance to denture displacement. It will also preserve the alveolar ridge and prevent bone loss. Periodontal status, endodontic potential, position considerations and oral hygiene must be evaluated when teeth are selected for use as over-denture abutments. Long term periodontal disease does not preclude most patents from being candidates for root-supported over-dentures. Loss of teeth from periodontal disease is one of the major reasons for over-dentures. It is important to select a repairable abutment tooth that has a healthy periodontal prognosis. Periodontal treatment may be required to retain teeth for abutments. The more root supported by bone, the more desirable the abutment will be. Most potential abutments require at least 6 mm of bone support. The Zaag abutment system is an exception to this rule, as it requires al little as 5 mm of root support. Teeth that have extreme horizontal and vertical displacement are poor choices for over-denture abutments. Teeth with a broad band of attached gingiva are more desirable than teeth with minimal attached gingiva. Patients with poor oral hygiene must be carefully evaluated as candidates for root-supported over-dentures. Endodontic therapy is indicated in the preparation of an over-denture abutment. It is essential for retention of the root in the alveolar ridge and as a housing for the attachment. This will allow over-denture retention and stability. By maintaining the root in its environment, we preserve the height of the alveolar ridge, and the proprioceptive qualities of the periodontal ligament. When reduction of the clinical crown occurs (to within 1 mm of the ridge crest) the crown-root ratio is changed to favor periodontal involved abutments. The success of the over denture is determined in the selection of abutment teeth during the diagnosis and treatment planning phases. Position considerations include determining how many tooth abutments should be retained, and where they should be located in the arch to create a desirable over denture. Two abutments (usually canines) are the most frequently used positions for an over denture. Three or four abutments can also be used, with abutments most commonly added in the bicuspid or central incisor regions. Zaar anchor system The Zaar anchor system provides retention and stability for full and partial dentures by utilizing non-vital roots of teeth.
The Zaag system is designed for direct placement into the root without a cast coping.
All Zaag components are uniquely designed to be at the lowest vertical height possible.
This low point of connection ensures decreased stress on the supporting structures and more flexibility with the placement and design of denture teeth. This system is highly successful, even with the minimum bone support of the remaining dentition with as little as 5 mm of bone remaining in the alveolar ridge.
Saving the questionable abutments will reduce bone loss associated with extractions and maintain the patient's periodontal ligament proprioceptor qualities. When bone support is lost, the reduction of the tooth's structure to the level of gingiva and utilization of the Zaag anchor attachment will greatly increase the probability of success. The Zaag anchor is suggested any time the prognosis of an abutment tooth is doubtful. It is recommended to save as many roots as possible to preserve the bone structure. Roots with the greatest support and most desirable location in the arch should be selected to receive the attachment. Two anchors will provide very satisfactory retention and good stability. As I wrote in a previous article, "Root-supported over dentures gain their retention and stability from the use of attachments, which are simple connectors consisting of two or more parts. One part connects to the root and the other part to the over denture. Attachments are classified as either resilient or nonresilient. A resilient attachment is one where the prosthesis can move up and down or vertically over the abutment as the patient chews. This allows the prosthesis to come in maximum contact with the oral mucosa. It distributes the load over the mucosa and directs it away from the abutment. It is also most important for over denture attachments to have a hinging motion that permits the prosthesis to rotate over the abutment and allow greater distal compression of the mucosa. Root-supported over denture attachments are resilient they are not solid and rigid, as the nonresilient types. Attachments for over dentures are generally the intraradicular (stud) type and are connected or retained directly into the free-standing roots." The Zaag anchor, an intraradicular or stud type subgingival universal hinge resilient attachment, is not appropriate if a totally rigid connection is required or a load-bearing system is indicated. Increased wear areas on both plastic males and metal females allow longer attachment life.
The surgical stainless steel Zaag female is coated with titanium nitrate, which is three times harder than the base metal. It will not wear as quickly as other attachments. The Zaag male pivots in its permanent metal housing to allow for function up to 15 degrees from a parallel path of insertion and can be changed in 30 seconds when necessary.
The Zaag standard male comes in two heights, the standard height, 3.1 mm (Figure 4) and the short type, 2.2 mm above the female (Figure 5). The short type is recommended for situations when occlusal space is very limited. The Zaag female comes in two sizes. The Zaag standard female has a 2.5 mm primary diameter and an overall diameter of 3.8 mm, with a depth of 4.0 mm (Figure 3). Always determine the space available in the root for the standard size Zaag female. Space must equal or exceed 4.0 mm. The Zaag mini-female has a 2.0 mm diameter and an overall dimension of 3.3 mm, with a depth of 2.3 mm. Determine the space available in the root for the mini-size Zaag female. Space must equal or exceed 3.5 mm. The mini-Zaag attachment is available to fit into very small lateral or central incisor roots, or non-parallel abutment teeth.
Placing the standard-size female
Measure mounted study casts to determine the space available in the root to receive the standard size Zaag female. Space must equal or exceed 4.0 mm in width. It is best to use the standard size Zaag female whenever possible because of its stronger, longer lasting male component. Obtain occlusal records before initiating tooth reduction. Complete the endodontic and periodontic procedures. Partial reduction of the teeth simplifies the endodontic technique and allows better access to the canal. Decoronate with complete reduction of non-vital teeth to within 1 mm of gingiva . The Zaag one-step drill is self starting and creates an accurate preparation for the Zaag female without the need for a pilot hole (Figure 2). Drill a hole to a depth where a full 360-degree recessed seat is created on the occlusal surface of the root. This will assure firm and accurate seating of the female and facilitate a proper seal. A built-in stop prevents drilling past the required depth. When more than one attachment is used, make the preparations as parallel to each other as possible. The preparation does not have to follow the canal. Divergence of the female component will limit the degree of rotational freedom of the male anchors and could contribute to the premature wear or breakage of the males. Keep in mind that the smaller size mini-female may be the one to use when placing the Zaag anchors in divergent roots. When using the Zaag parallel post as a handle, try in the metal female to check for a proper fit. The first attachment with a parallel post can be used as a guide for placing the following attachment as parallel as possible. The pivoting Zaag male allows for some leeway in parallelism (15 degrees) between multiple attachments. Keep in mind also, that the closer to parallel they are, the easier it will be for the patient to insert the prosthesis. Using the parallel post as a handle, cement the metal female component into place, with a strong resin reinforced glass ionomer like Fugi Plus. Some restorative dentists will bond the female into the non-vital root, but either method is acceptable (Figure 8). The parallel post will keep the inside of the Zaag female clean and free of cement. It is very important that the root surface surrounding the Zaag female be finished down to the exact level or lower than the top of the female (Figure 9). This will allow the Zaag male with centering sleeve to seat completely. Round off and polish the root surface from the metal flange to the tissue. (Bonding the exposed dentin surface is also acceptable.) After cementing the Zaag female and contouring the final root, the dentist or the dental laboratory can process the Zaag denture cap male attachment into the over denture. A chairside pick-up of the male attachment (direct method) can be done when the patient's existing prosthesis is a well-fitting denture. A Zaag impression male (coping) (Figure 10) and analog is used for the indirect method of placing the male attachments by the dental laboratory. A vinyl polysiloxane impression material such as EXOMIX by GC America will easily pick up the Zaag impression males (Figure 11). If a new over denture is being made, take a preliminary impression of the edentulous ridge and make a custom tray. Prepare the custom tray with attachment recesses and proceed to border-mold the tray. Take a vinyl polysiloxane impression of the edentulous ridge and prepare to send it to the dental laboratory. A metal substitute model female is used by the dental laboratory as an analog in the master cast to replicate the Zaag female in the oral cavity (Figure 12). Snap a substitute model female onto each impression male, making sure they are completely seated. Pour the master cast, incorporating the model female in an exact duplication of the position of the Zaag female in the patient. Place the Zaag cap male with centering sleeve into each model female and process the denture.
The centering sleeve is removed from the male component before delivering the finished over denture to the patient (Figures 13-15). Changing the male Using the coring and seating tools, a nylon Zaag male can be replaced in about 30 seconds without removing any acrylic from the over denture. The coring tool fits into a straight lab hand piece. Using a medium speed, quickly core out the nylon male. The nylon male will be cored out, leaving a thin band of plastic material in the cap. Use an explorer to remove the remaining band of plastic material. Make sure the inside of the cap is completely clear before snapping in a replacement male. The seating tool is used to place a new Zaag male into the metal cap. Insert a replacement male into the tip of the tool. The seating tool will hold the male while delivering it to the sight. While supporting the denture, use firm pressure to snap the replacement male into the metal cap. It is mechanically retained in an undercut and will not pull out. The Zaag male can be changed very quickly without altering the original fit of the over denture.
Conclusion
The "denture face" syndrome can be eliminated with root-supported over denture therapy. Complete diagnosis and treatment planning are most important for the success of over dentures. Through careful selection of abutment roots, the prosthesis can be retained and stabilized. This alternative treatment to extraction of natural teeth and complete dentures provides greater retention, stability, comfort, improved function, aesthetics and phonetics for the patient. This relatively simple technique for fabrication of root-supported over dentures is easily within the skill level of most general and restorative dentists.