ABSTRACT
Maxillary arch rehabilitations can be clinically challenging. Because of the fundamental differences between implants and teeth, as related to their differing degrees of micro-movement within bone, the issue of combining them in fixed prostheses has been controversial. A case is presented demonstrating the clinical steps involved in a ‘retrofit/salvage’ of an existing implant supported bridge to a natural tooth abutment, utilizing a precision attachment, following the loss of a Central Incisor.
Maxillary arch rehabilitations involving crowns, bridges and implants can be challenging clinical procedures. Clinicians are increasingly being called upon to provide these types of dental modalities to restore masticatory function, and esthetics. In addition, clinicians will increasingly be called upon to repair/salvage existing restorations, as many patients have (or will have) medical or financial barriers to replacing their existing dentistry. By incorporating established functional and esthetic principles1 the clinician can have a tremendous impact on the physical and psychological well-being of the patient.2,3 How stress distribution occurs when tooth supported and implant supported abutments are connected, and whether the dissimilar mobility patterns affect the stability and fracture strength and survival of the superstructure is still being investigated.4-6 The use of a precision attachment in the case described below, allows for some stress-breaking within the prosthesis superstructure, and allows for retrievability should the prosthesis require any repair or further conversion in the future. Following an orderly protocol, with the end results in mind, we can create predictable functional, durable and esthetic results for our patients.
CASE REPORT HISTORY
The patient is a 79-year-old male, retired commercial airline pilot, who has been a long-time patient in the author’s practice. He attends regularly for prophylaxis and restorative care. He is partially edentulous, and has had implant, fixed crown and bridge, removable partial denture and endodontic treatments. He presented with central incisor #21 fractured at the gingival level (Fig. 1). While he demonstrates advanced wear on his mandibular anterior teeth, TMJ evaluation shows normal ranges of opening/closing, with no movement deviations or joint sounds. The joints are symptom free under bi-manual load testing.1 The patient does admit to clenching and grinding his teeth when he sleeps. He wears a bruxism appliance at night. He is an occasional pipe smoker and plays the clarinet as a hobby. As well, he reports a past history of GERD (gastro esophageal reflux disorder), no longer occurring, which has been implicated as a causative factor in tooth erosion. In 2006, Biohorizons external hex implants were placed in the #22 and #24 sites to restore the maxillary left anterior quadrant. The implant in the #22 site is angled towards #21, and there is insufficient space for an implant to be placed in the #21 site as a restorative solution, without risk to the adjacent central incisor.
The central incisor #21 was extracted in an atraumatic manner, using a periotome and Misch-Golden Physics Forceps, preserving the buccal plate, and the site was grafted (Mineross and a resorbable Memlock membrane Biohorizons Birmingham, AB), and allowed to heal for three months prior to beginning the case (Figs. 2-3). Some of the existing porcelain fused to metal crowns show evidence of wear and porcelain fracture, and some gingival recession, but are otherwise they are functional and not in need of replacement . His periodontal condition is stable and he is seen every four months for prophylaxis.
Treatment options presented to the patient included: fabricating a removable partial denture, extracting the right central incisor, and placing an implant, and then joining it to the previously placed #22 and #24 implants with a new fixed bridge spanning #’s 11-24, or replacing the crown on #11 and joining it to the implant bridge on #’s 22-24 with the use of a precision attachment. After numerous consultations with the patient, the decision was made to restore his maxillary central incisor with the combination approach utilizing crown and bridge, and a precision attachment, to ‘retro-fit’ to his existing implant supported bridge. The patient decided to rehabilitate his mouth in this fashion, considering his current financial situation and overall health, and the faster treatment times it afforded. It was explained to the patient that if the right central incisor were to require extraction in the future, the site could be restored with a dental implant, and the case similarly converted/retrofitted, as with the natural tooth.
PRE-OPERATIVE AND LABORATORY STEPS
Pre-operative casts, mounted on a Denar Combi- semi-adjustable articulator along with centric relation records, and lateral check bites, existed from the prior fabrication of a Bruxeese appliance. These were used to fabricate a putty matrix incisal guide, to be used during the porcelain application phases. A triple tray polyvinyl impression was taken of the pre-operative state after the #21 extraction site had healed, and set aside to be used at the preparation appointment. The lab was asked to fabricate a custom tray, from the pre-operative casts, with an open window corresponding to the #24 and #22 sites for an ‘open tray’ implant impression.
OPERATIVE AND LABORATORY STEPS
Following local anesthetic administration, a crown remover/bridge tapping instrument was gently used to loosen the provisional cement seal between the implant bridge and the abutments (Fig. 4). The PFM on 11 was removed by preparing a thin slot, mid buccally and lingually through the porcelain and metal, exposing the cement line. A crown spreader was used to spread the crown and loosen the cement seal (Fig. 5). Following the PFM’s removal, significant recurrent caries was noted on the lingual, and a core build-up was completed using Clearfil (KURRAY) and Grandio composite resin (VOCO) and the existing preparation was refined using carbide and diamond burs in a Kavo electric handpiece. Margin placement was supra-gingival and/or equi-gingival. Supra-gingival margin placements have the advantages of minimizing gingival tissue irritation and/or biologic width violations, and are easier to record in the final impression. Retraction cord (Ultradent OO and OOO cord) was placed according to a two cord technique, and allowed to gently retract the tissue for approximately 10 minutes, while the next steps took place (Fig. 6).
Cotton pellets and Fermit, which had been placed in the screw access openings, were removed with an explorer. The abutment screws were loosened and removed using a Biohorizons torque driver and ratchet. Transfer impression copings were installed, and a radiograph taken to verify complete seating. An ‘open-tray’ polyvinyl siloxane impression was taken, and carefully evaluated (Fig. 7). Healing abutments were placed over the implants and tightened using finger pressure. It was felt, in prior consultation with the dental laboratory that an implant level impression would yield a more accurate result than a pick up impression of the #22-24 bridge superstructure would. As well, the lab would have no way of knowing the condition of the bridge, and whether or not it could be ‘retro-fitted’, until it was examined in the laboratory. The central incisor was dried and a thin mixture of Provilink (Ivoclar) was applied to the tooth. Using the polyvinyl triple tray fabricated at the records appointment, Luxatemp (Zenith DMG) was injected into the guide, taking care not to incorporate any air bubbles, and the stent was fully seated over the prepared tooth and allowed to set for 120 seconds. Once polymerization was complete, the triple tray was removed,
with the temporary crown staying on the tooth. The temporary crown was trimmed of any flash or overhangs and polished, and the embrasures opened up to allow for oral hygiene procedures and overall gingival tissue health. The occlusion was checked, and instructions given in oral hygiene, and the patient dismissed. Closys II stabilized chlorine dioxide rinse was given to the patient and daily rinsing advised, to aid in maintaining gingival health and marginal stability. The patient was informed prior to beginning the case that he would be without the implant bridge during new bridge’s fabrication.
The laboratory was provided with all the records obtained, as well as detailed instructions regarding the desired occlusal scheme, tooth shade and mold, ovate pontic design and type of precision attachment etc….7,8 and proceeded to fabricate the new #11-24 prostheses (Figs. 8,9). As well, the lab was instructed to fabricate a Duralay seating jig to assist in the correct seating of the implant abutments.
It was decided in the interim laboratory fabrication period, based on the recurrent caries found when the #11 PBM was removed, that the tooth should have a prophylactic endodontic treatment completed prior to the bridge being cemented, to prevent having to access and damage the new prostheses should endodontic symptoms develop in the future, and the patient was referred to an Endodontist for the procedure. Following the endodontic treatment, and completion of the laboratory fabrication, the patient was appointed.
The metal framework sections were returned from the laboratory and inspected both singly and together on the models. The temporary crown and Cavit temporary seal were removed from #11, and a direct pattern post and core was fabricated chair side, using Duralay pattern resin and a plastic burnout post. Full seating of the #11-21 section of the bridge, over the post and core build-up was confirmed. The temporary crown was recemented with Temp-bond cement and a cotton pellet in the pulp chamber. The post pattern was sent to the lab to be cast in precious metal.
One week later, the patient was appointed. Local anesthesia was administered to minimize any discomfort during the seating and cementation procedures and the modification of the ovate pontic site for #21 (if the bridge didn’t fully seat and tissue modification was needed). The soft tissues appeared to be in good health. The healing abutments were removed from #22 and #24. The abutments were placed in their correct orientations using a lab fabricated seating jig (Fig. 10), and tightened using finger pressure and a radiograph was taken to verify complete seating prior to final torquing down of the abutments according to Biohorizon’s specifications. The temporary crown on #11 was removed, any Temp-bond cement removed, and the cotton pellet removed from the post space. The cast post and core was tried in and cemented using Zinc Oxide cement (Fleck’s Mizzy) with a lentulo carrier. The intaglio of #11 was lightly lubricated with Vaseline and seated over the post and core, to ensure complete seating while the cement set. The #22-24 segment of the bridge was also tried in, and the patient instructed to bite down on a cotton roll for approximately ten minutes to gently expand the tissues around the abutments and allow for complete seating of the #22-24 segment of the bridge, while the cement for the post and core was setting. The #11-21 crown- pontic and #22-24 sections were tried in the mouth both singly and together and the marginal fit, shade, shape and occlusion evaluated. The intaglio portions of the bridge were cleaned of any cement and contaminants using alcohol.
The two segments of the bridge were cemented simultaneously using Fuji cement (Shofu) for the right central incisor and Temp-bond mixed with Vaseline for the #22 and #24 implant abutments. Both sections of the bridge were seated at the same time to ensure that everything seated correctly relating to the precision attachments and that the bridge fully seated. Following cement set, meticulous cement clean up was performed. Occlusion was carefully evaluated and lightly refined. The composite bonding on the right lateral incisor was partially removed with a diamond bur and a new composite resin veneer overlay was fabricated using Scotchbond adhesive and Estelite composite (Tokuyama), to more closely match the new bridge’s shade. The patient was seen the following week and two weeks later for follow up examination and slight further refinement of the occlusion. He reported great satisfaction with the esthetics and occlusion. As is evident from the post-op photos and radiographs, a very esthetic result was achieved (Figs. 11-16). The patient is thrilled with the result, which has greatly exceeded his expectations.
DISCUSSION
Today implants are a widely accepted solution to replacing missing teeth. Successful osseointegration results in the close apposition of, and strong union between, the bone and implant surfaces. Because of this connection, implants exhibit very little if any micro movement (typically in the range of 10 microns when loaded), and any movement is thought to be due to bone flexure. Natural teeth show quite a different mobility pattern when loaded. Unlike the bony union seen between an implant and bone, natural teeth are separated from the bone by the periodontal ligament (PDL), a complex arrangement of connective tissues and blood vessels which act as compressive shock absorbers during mastication. Natural teeth can move in the range of 50-200 microns when loaded. Because of these fundamental differences between implants and teeth, the issue of combining them in fixed prostheses has been controversial. How stress distribution occurs when differently supported abutments are connected, and whether the dissimilar mobility patterns affect the stability and fracture strength and survival of the superstructure is still undetermined.9 The restoration of masticatory function with a combination implant-to-natural-tooth fixed partial denture can be associated with a variety of undesirable clinical sequelae, including the breakage of implant components, damage to the abutment teeth, or intrusion of the abutment teeth. Several theories are presented to explain the intrusion of natural teeth in association with implant-to-natural-tooth fixed partial dentures. One theory proposes the idea that a lack of normal stimulation of the periodontal ligament produces atrophy of the periodontal ligament and intrusion of the tooth. Other theories relate to excessive forces being placed on the natural tooth, resulting in movement of the tooth to a less stressful position. These forces are placed on the tooth by differential energy dissipation, mandibular flexion and torsion, flexion of the fixed partial denture framework, impaired rebound memory, debris impaction or microjamming, or ratchet effect related to the use of precision attachments.10
For several years, it has been suggested that implant-to-tooth interconnected restorations behave like a cantilever, with the implant bearing the higher load. Various complications have also been reported for partial dentures with implant-to-tooth fixation, such as hypo-function, disuse atrophy, intrusion of the abutment teeth, peri-implantitis, and failure of osseointegration, bone fracture, implant fracture, loosening of screws, and failure of luting cements. It has been suggested that splinting natural teeth to implants should be avoided.11-16 However, there have been recent reports of the combination of natural teeth with implants, reporting good survival data on the implants and no adverse effects on the prostheses.17,18 Christensen suggests that using resin cement under the natural tooth abutment may be a way to prevent it from separating from the bridge as a result of these dissimilar forces.19 Numerous longitudinal studies have demonstrated that teeth can be successfully connected to implants with no evidence of tooth intrusion and with stable bone levels at both teeth and implants.3
A p
recision attachment (Tube-Lock Sterngold Dental Attleboro, MA) was selected to help overcome some of the potential problems associated with the connecting of natural teeth and implant abutments. As the patient has historically demonstrated bruxism and shows advanced wear, it was felt that the prostheses should have some sort of ‘stress-breaking’ component built into it to help dissipate stresses to it and the natural tooth. The slight micromovement allowed by the tube-lock attachment should also help prevent any disuse atrophy from occurring in the periodontal ligament of the central incisor. As well, the ‘interlock’ allows for future repairs/retrofits should the right central incisor require extraction in the future and conversion to a fully implant supported bridge from #11-24, or if the porcelain requires repair. Furthermore, this design allows the implant portion of the prostheses to be removed, as needed, to obtain access to the implant components. Similar designs have been described in the literature as showing long term success. When implants and natural teeth are combined, forces on the abutments need to be controlled so that neither the teeth nor the implants sustain excessive amounts of force. The technique described addresses reduction of potentially harmful cantilever effects in a fixed prosthesis. This relationship limits cantilever forces exerted on the natural-tooth abutment. The non-rigid connection of the tooth-supported retainer limits cantilever forces and directs occlusal loads axially in a direction along the long axis of the implant.20,21 Some complications reported in the literature when natural teeth are splinted to implant teeth include a small percentage of natural abutment teeth undergoing intrusion and survival rates of both implants and reconstructions in combined tooth-implant-supported fixed partial dentures were lower than those reported for solely implant-supported fixed partial dentures.22 It seems from the present literature that tooth-implant-supported fixed partial dentures have not been studied to any great extent and hence, there is a definitive need for more longitudinal studies examining these reconstructions. The issue of connecting with rigid or non-rigid connectors remains unresolved with a growing body of information favouring retrievable short-span rigid connection to non-mobile teeth.11 Some have suggested that implants and natural teeth should not be splinted together, and that it is preferable to extract a tooth in order to place an implant in its stead. Hence, planning of prosthetic rehabilitation may preferentially include solely implant-supported fixed bridges.22
However, anatomical aspects, patient centered issues and risk assessments of the residual dentition may still justify combined tooth-implant-supported reconstructions. Lindh showed that there was no support for extracting teeth in favour of placing implants. On the contrary, the healthy tooth had a survival that was life-long, which is yet to be shown for the dental implant. Also the use of teeth as abutments in combination with dental implants for support of fixed dental prostheses could be endorsed in certain situations with solid albeit limited scientific support. In a wider sense, such prostheses could be used as a reliable therapy in all regions of the jaws. However the status of the abutment teeth in terms of periodontal support, pulpal status and risk for carious lesions and biomechanical complications should always be considered in relation to the long-term prognosis of the prosthesis. The conclusion was that teeth should not be extracted in favour of placing dental implants without a specific indication, and that tooth-implant supported prostheses should be considered as a viable prosthetic option.23 It seems then, that careful patient selection and regular follow–up monitoring will ensure that these reconstructions last as long as possible.
CONCLUSION
The concept of connecting natural teeth and implants together remains controversial, and further research is required. However; clinicians are often faced with treatment decisions relating to cost, the patient’s health, length of time to complete treatment, and the desires of our patients. The use of a precision attachment in this case allowed for dissipation of stresses on the prostheses and natural abutment tooth, and an element of retrieveability in the future, if required A Maxillary arch rehabilitation involving a natural tooth, a pre-existing implant bridge, and a precision attachment was demonstrated, resulting in an esthetic and functional result for the patient, and personal satisfaction for the clinician.OH
Dr. Michael Pollak graduated from the University of Toronto in 1989. He is a Past-President of the Toronto Academy of Cosmetic Dentistry. He maintains a general dental practice in Markham, Ontario, with an interest in cosmetic, restorative and implant dentistry. He is a graduate of the Misch Implant Institute, The Dawson Center for Advanced Studies, and the SUNY post-graduate program in Esthetic Dentistry. He is a Fellow in the International Congress of Oral Implantologists (ICOI).
Oral Health welcomes this original article.
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