January 2013, Volume 34, Issue 1
Published by AEGIS Communications
New Method for Improving the Accuracy of Bite Registrations in Restorative Implant Dentistry
Mark W. Wilhelm, DMD, MSD
Recording accurate bite registrations over edentulous ridges has long been a difficult aspect of dental implant therapy. Implants form a more rigid connection in the bone than natural teeth, and, therefore, a method of acquiring a rigid bite record is needed. This case study describes a new method that has been proposed to treat edentulous areas of the mouth using dental implants and fixed prosthodontic concepts to register secure and accurate bites. This method incorporates the use of solid titanium implant bite posts that screw directly into the implants, creating a rigid connection.
Throughout the history of modern dentistry a huge effort has been made to save teeth to avoid the necessity for removable prostheses. While able to provide reasonable esthetics and acceptable, yet reduced, function,1,2 removable prostheses are usually a second choice to fixed prosthetic options. A major challenge to obtaining excellent fixed prostheses is registering accurate bite records. Different approaches to recording dentate bites have been suggested3 and while they may be useful, similar techniques fall short when attempting bite records with multiple missing teeth. To deal with these edentulous situations, dentists have relied on techniques used in removable prosthetics. A new method has been proposed to treat edentulous areas of the mouth using dental implants and fixed prosthodontic concepts to register secure and accurate bites.
Bite Record Considerations
Assuming that meticulous laboratory protocols can be used to create well-fitting esthetic restorations, the occlusion can make or break the clinical outcome. Results that make the occlusion high require dentists to spend chairtime adjusting the surface, ruining the fine anatomical detail the technician worked hard to create. Open occlusal contacts result in wasted time re-performing clinical steps to add to the occlusal surface. Both outcomes result in another appointment for patient, doctor, and technician. Clinical efficiency demands that dentists provide their laboratory technicians with accurate bite records with which they can mount casts and produce extremely accurate restorations. Upon completion of the restoration, occlusal adjustments can be as simple as polishing the occlusal contacts with a brownie point or as disastrous as having to redo the case.
Traditional crown-and-bridge reconstruction uses a closed-mouth bite record placed directly between the teeth.3 When performed properly, the inter-dental bite record can produce mountings that accurately recreate the same bite relationship in the dental laboratory. There are three layers to an occlusal bite registration. The first layer is the upper arch, including prepared teeth, unprepared teeth, and any soft-tissue edentulous ridges; the second layer is the corresponding lower arch, and the third is the bite record itself. The fewer missing teeth there are, the easier it is to create an accurate bite record. Solid occlusal stops of prepared and non-prepared teeth aid in orienting the maxillary and mandibular casts into the bite record or index. The bite record must be capable of detailed reproduction and be rigid enough to resist deformation when indexing the casts.
Occlusal stops are needed to support the opposing cast. Principals of tripodization require three stops to ensure stable referencing. Because the geometry of a dental arch forms a horseshoe, a tripod can only be formed when each posterior segment can be joined by a stop near the midline. More than three stops provide greater opportunity for stability. Distribution of the stops can make a significant difference in the ease with which indexing of the casts takes place. Missing teeth eliminate these stops, creating fewer solid landmarks for orientation of the cast into the bite index. Secondly, when missing teeth are the most distal in the jaw, the only landmark present is that of the soft tissue or edentulous ridge, which, similar to complete denture prosthetics, considerably diminishes the 3-dimensional (3-D) accuracy of the bite record.4
Dental implants have changed the landscape of tooth replacement therapy. Whether the clinician replaces a single tooth, quadrant of teeth, or entire arches, the resultant restoration will be more rigid than the natural teeth it is replacing.5,6 Consider, for instance, that a failed fixed partial denture leaves a patient with no teeth distal to the canine. Conventional fixed prosthodontic methods are not practical to restore this quadrant. Traditionally, a removable partial denture might be used. Today, implants are often selected as the treatment of choice. Although after the impression for the implant prosthesis is taken, what technique is employed to record the bite? Since this clinical situation has never been faced in conventional fixed prosthodontics, dentists resort to what they know best, removable techniques. By definition, implants replace missing teeth, and yet the prosthetic connection between abutment and implant body is more rigid than natural teeth. Capturing bite records on implants creates a significant dilemma. Edentulous areas pose challenges similar to removable prosthetics, yet they present intolerance to error because of the rigidity of the implant/bone interface.7 Errors made while recording the bite in these cases can result in costly remakes and loss of valuable chairtime. Because of this lack of flexion of the implant connection to the bone, the bite record must be equally rigid and accurate. Some operators say that recording bites over implants in these situations can employ the same methods used for removable prostheses. If this were true, why do errors in implant prosthesis occlusion result in higher remakes for implant dentistry compared to conventional tooth-borne fixed prostheses? (Denis Lemke, CDT, oral communication, October 2011)
Various methodologies have been employed to compensate for the lack of teeth while performing bite records in edentulous regions.8 The traditional closed-mouth record used in completely dentate arches demands the use of the recording medium to record the soft tissue of any edentulous area. Direct soft-tissue recordings do not transfer from the mouth to the cast,9 thus necessitating a prefabricated removable baseplate with occlusal rim. Baseplates are fabricated on the working cast made from the final impression. The base is made of acrylic or light-cured composite materials, is removable, and fits against the soft tissue. When placed in the mouth, there is space where the base touches the tissue and gaps where it does not touch. During the bite registration, the baseplate moves in the mouth by various means, including compression of the soft tissue, torsional distortion of the base material under load, and sliding across the soft tissue. Historically, this method has been used for complete-removable and partial-removable prosthodontics. The final bite record is reasonably accurate. As a result, it is necessary to perform clinical remount procedures to further refine the occlusal relationship of the final prostheses. The above-mentioned methods make adjusting the occlusion of removable prostheses feasible, especially complete dentures, when occlusal errors are limited to polymerization shrinkage of the acrylic. But when cast, removable partial denture frameworks are seated on supporting teeth, and the prosthetic system becomes more rigid. Inaccurate bite recordings cause the possibility of open occlusal contacts. Such a result requires redoing the bite record, teeth set-up, occlusal verification, and processing. In the end, some form of error is tolerable because of the mobility of the prostheses themselves. Movement decreases stress and the moments of force on the dentition.10,11
While it is possible to mount single-tooth restorative cases using simple inter-arch dental bite records, mounting cases with edentulous quadrants or missing molars poses accuracy concerns likened to removable prosthetics. The rigid connection of implant abutments necessitates extremely accurate bite records. Use of baseplates creates too much 3-D error. A form of rigid implant connection is mandatory. Some clinicians and laboratory technicians have proposed using tall secondary healing caps, modified stock implant abutments, or some other prosthetic component attached to the implant to simulate such a connection. These components are removed from the mouth, disinfected, and returned to the laboratory to be placed on corresponding implant analogs acting as teeth. Additionally, another step to ensure occlusal accuracy prior to porcelain application entails a framework try-in over the final abutments, along with a new bite record and clinical remount. While safe or conservative, this step is redundant and consumes precious chairtime.
New Approach to Bite Records in Implant Patients
Dentists can avoid the chairtime involved in the final step mentioned above—ie, the framework try-in over the final abutments, plus new bite record and clinical remount—with a novel solution offered by the use of Implant Bite Posts (IBP™, Lebeau Dental, www.lebeaudental.com). These titanium components seat completely into the implant, providing a rigid connection whose spatial relationship can be accurately transferred to the laboratory technician via a highly accurate addition reaction vinyl polylsiloxane (VPS) bite registration material.
After the final impression for the working cast fabrication is taken, the inter-arch space is evaluated for height. Then a tall or short IBP™ is selected to match the specific implant platform (Figure 3) and inserted into the appropriate implant site (Figure 4). The posts are designed to be seated in three simple turns using gentle finger pressure. A standard 0.50-inch hex opening is provided to facilitate removal with a universal driver, if desired (Figure 3). The IBPs contain a circle at their coronal aspect and a second circle apical to this, creating an undercut designed to capture the bite material. Due to the relatively parallel nature of multiple implants, the IBP undercuts create 360 degrees of diametric opposition to firmly hold the bite registration material in place, even after generous laboratory trimming (Figure 5). Once installed, a high-viscosity, softer memory-perfect VPS material is injected over the teeth and IBPs, and the patient closes into maximum intercuspation or according to the clinician’s chosen jaw position technique (Figure 6). Note that use of rigid or crumble-prone materials will fracture upon removal and laboratory manipulation and will ruin the record. When the bite material is set, the record and IBPs are removed. Then both are disinfected and sent with the impression and other documentation to the laboratory.
When installing IBP in the laboratory, it is necessary to trim any gypsum around the analogs that may impinge on the complete seating of the IBPs (Figure 7). Removal of a silicone gingival moulage around the implants will also permit complete seating of the IBPs (Figure 7). The technician should seat the IBPs with gentle finger pressure and assemble the bite record. As is normal, the technician should trim the bite record to guarantee visible seating of all record components. The bite record will snap onto the IBPs.
Single-Tooth or Quadrant Restorations
The IBPs can be used for both single-tooth or quadrant restorations. They replace the need for baseplates with wax rims. Tripodization is restored to quadrants with missing teeth. IBPs simulate prepared teeth in conventional crown-and-bridge procedures. By providing rigid occlusal stops to all areas where implants are present, the bite record can be easily indexed to areas with greater distribution. IBPs also save chairtime by making the registration process similar to the conventional bite procedures with which most dentists are already familiar.
When used in whole-arch reconstruction, analogous dentate crown-and-bridge techniques can be employed. First, a bite record is taken over the entire arch provisional restoration. Next, a posterior quadrant section of the temporary is removed and the patient is instructed to close into the bite, after which the VPS bite material is injected into the open space over the quadrant of the IBPs. The procedure is repeated over the opposite posterior segment. Last, the clinician should remove the anterior segment and complete the bite record to create a full-arch registration. In the case of a patient wearing a removable complete denture (Figure 8) the clinician should begin the procedure by using a baseplate with a wax rim. Following a bite taken over the wax rim (Figure 9), the rim should be removed and the IBPs placed. Next, the practitioner should cut a window into the baseplate and have the patient bite into the original record (Figure 10). PVS material is then injected into the bite over the top of the IBPs (Figure 11). When the bite is reassembled in the laboratory, there will be rigid occlusal stops in the segments incorporated into the IBPs (Figure 12). Figure 13 through Figure 15 demonstrate the final implant-supported removable complete denture over a milled titanium bar with attachments.
Since the integration of dental implant therapy into modern dentistry, recording accurate bite registrations over edentulous ridges has been problematic. Implants form a more rigid connection in the bone than natural teeth and thus necessitate a method of acquiring a rigid bite record. Techniques borrowed from removable prosthodontics do not lend themselves to the demands of fixed implant restorations.
A new method has been introduced that incorporates the use of solid titanium IBPs that screw directly into the implants, creating a rigid connection. Conventional crown-and-bridge bite recordings can now be performed to make more accurate records, reducing the need for extra steps and increased chairtime. Incorporation of these timely and ingenious components to the restorative implant arsenal will generate more predictable clinical outcomes by saving time with more accurate bite registrations.
About the Author
Mark W. Wilhelm, DMD, MSD
University of Minnesota School of Dentistry
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