Prosthodontic procedures for implant reconstruction. 2. Post-surgical procedures S. Lechner, MDS, FRACDS* N. Duckmanton, MDS, FRACDSt I. Klineberg, BSC, MDS, PhD, FDSRCS, FRACDS, FICDS
Key words Implants: framework fit, impressions, superstructure. Abstract There is essentially no flexibility in an osseointegrated implant system, so that the final fit of the prosthesis must be absolutely precise. A simple approach to this problem is presented with details as to impression taking, confirmation of accuracy of the master cast, fitting of the cast metal framework and construction of the superstructure. The information presented describes a full arch fixed restoration attached to mandibular implants, but may easily be followed for the maxilla or modified for quadrant restorations. (Received for publication May 1991. Accepted September 1991.)
Introduction The prosthodontic procedures required for developing a fmed bridge attached to implants must be carried out accurately, as the final fit of the prosthesis to the abutments must be absolutely precise. There is essentially no flexibility in the system, since the superstructure is rigid as are the implants in their attachment to bone. As a result,
*Senior Lecturer, Department of Prosthetic Dentistry, The University of Sydney. +Prosthodontic Co-ordinator, Implant Centre, United Dental Hospital, Sydney. $Professor, Department of Prosthetic Dentistry, The University of Sydney; Consultant, Implant Centre, United Dental Hospital, Sydney. Australian Dental Journal 1992;37(6):427-32.
greater precision is required than for conventional crown and bridge work attached to natural teeth. The following information follows pre-surgical procedures and briefly describes a simplified approach to post-surgical prosthodontic procedures that the writers have found effective in obtaining the degree of accuracy required. The details to follow are described for a fill-arch fixed restoration attached to mandibular implants. However, the procedures may be followed for maxillary and quadrant restorations incorporating implants.
Post-surgical procedures 1. Impression procedures At second stage surgery, healing abutments are usually preferred, particularly where abutment length is of special importance in optimizing aesthetics. Three to four weeks after suture removal and once soft tissue inflammation has resolved, the healing abutments are removed, soft tissue height assessed and abutments of appropriate length screwed to the fixtures. Following abutment placement, healing caps are attached to protect the abutment surface and gingival tissues. The healing caps are removed for impression procedures and the abutment face cleared of any debris (Fig. la). 1.1 Primary impression - Lower jaw An alginate impression is taken of the lower jaw using a stock perforated tray (Fig. Ib). Brass abutment replicas are placed in the impression and a cast is poured in plaster (Fig. lc). Accelerator (NaC1, K,SO,) or a plaster slurry is 427
Fig. la.-Healing caps are removed and the abutment face cleared of debris. Fig. 1b.-Alginate impression taken in stock tray. Note that the impression extends over the entire area covered by a conventional complete denture. Fig. 1c.-Brass abutment replicas are placed in the alginate impression. Fig. Id.-Plaster, weakened by the addition of slurry or accelerator, forms the primary cast.
used to reduce the setting time and also to weaken the plaster, so that later retrieval of the abutments will not be difficult (Fig. Id). Once the cast has set, impression copings are positioned on the abutment replicas and held in position firmly with guide pins. Each coping must be seated precisely and firmly on each replica. The abutment replica-impressioncoping interface is covered with wax which is extended onto the lower border of the square section of the impression coping (Fig. 2). The abutments may now be linked together with auto-polymerizing acrylic resin, ensuring that the resin holds each impression coping firmly. When the resin has set, the masking wax is removed and the resin is trimmed until it is box-form, approximately 5 mm high and 5 mm wide (Fig. 3a,b). 1.2 Impression tray A relief of one layer of baseplate wax is placed over the impression coping-acrylic block and the saddle areas. An impression tray is formed in auto420
polymerizing acrylic resin,§ and designed so that it is open and does not cover the implants or acrylic
blocks. This is essentially a complete denture secondary impression tray with an open ‘well’ over the implant area (Fig. 4). 1.3 Preparation for secondary impression The wax relief is removed from the acrylic attached to the impression copings, and the acrylic block is numbered from left to right on the labial side to indicate abutment position. The resin is then divided vertically, using a disc in a straight handpiece so that each coping is held in a separate block of acrylic following removal of a minimum amount of acrylic resin (Fig. 5a,b). The brass analogues may now be removed from the plaster cast, and the impression copings placed in cold sterilizing solution in preparation for secondary impressions.
§For example, Tray resin. (Kerr, Romulus, MN, USA.) Australian Dental Journal 1992:37:6.
Fig. 2.-Masking wax extended over abutmentkoping interface reaching to lower border of square section of coping. Fig. 3.-Acrylic resin links the copings and is trimmed to a 5 mm box form. The masking wax which protected the abutment/ coping interface has been removed. Fig. 3a: labial view. Fig. 3b: occlusal view. Fig. 4.-Impression tray. Note that the area above the implant site is left open.
1.4 Secondary impression
Impression copings are placed in the mouth in their correct position and alignment, with the numbers oriented to the labial face of the acrylic block and in numerical order. They are secured with their guide pins ensuring that the acrylic does not touch the approximating block. The blocks may now be joined with a minimum amount of resin I( to make a rigid assembly using a powder/liquid build up with a brush. Wax is then placed over the opening in the impression tray to contain the impression paste before taking the impression. While seating the impression tray, pressure is exerted on the wax so that the tops of the guide pins penetrate the wax layer (Fig. 6). When the impression material has set, the wax is removed and the guide pins are readily unscrewed and the impression removed from the mouth.
IDuralay. Reliance Dental Mfg Co., Ill, USA. Australian Dental Journal 1992;37:6.
The guide pins must be completely cleared of the machined surface. Brass abutment analogues are then fitted carehlly against the exposed machined surface of the impression copings and screwed into place. Following placement of all brass abutments, a cast is poured in die stone7 and once set, the guide pins are unscrewed and the impression removed. This is the master cast. 1.5 Checking the accuracy of the master cast Gold cylinders are placed on the abutment replicas and screwed firmly into place with guide pins. The cylinder-abutment interface is covered with wax to a point 1 mm above the interface of the gold cylinder - or to the machined groove (Fig. 7). The gold cylinders are linked together with autopolymerizing acrylic resin which is then contoured and sectioned between the cylinders. A minimum YFor example, Velmix. Kerr, Sybron Dental Division, Romulus MN, USA. 429
Fig. 5a.-Acrylic numbered on labial of each impression coping and then divided by a fine disk. Fig. 5b.-Note that the divided acrylic sections are almost touching. Fig. 6.-Tops of guide pins penetrate wax during impression taking procedures.
amount of new resin is then added to the cut edges of the resin to minimize the setting contraction which is clinically significant if the gold cylinders are linked in one procedure. The guide pins are now removed and the cylinders are examined to ensure that they have maintained a precise fit on the abutment analogues. This is referred to as a passive fit. 1.6 Checking the accuracy of the cylinder assembly in the mouth The cylinder assembly must fit precisely on the abutments, without the guide pins in position. The passive fit of the assembly is tested for rotation; any movement indicates the need for realignment. An absolutely precise contact fit is required. Once confirmed, the clinician is now confident that the master cast is a true and precise replica of the arrangement of the abutments in the mouth and may confidently proceed with clinical records.
2. Maxillo-mandibular transfer records For transfer recordings, an acrylic base is prepared that attaches to the abutments. Impression copings are placed onto the two most distal 430
abutments of the master cast. The coping-abutment interface is covered with wax which is extended to cover the other abutments to the level of their upper surface (Fig. 8). The exposed surfaces of the machined abutments are covered with foil and a hole is made through the foil over the screw hole of one of the central abutments. A guide pin is lubricated and screwed into this hole. A baseplate is made in autopolymerizing resin, which should incorporate the two impression copings and the lubricated guide pin, and accurately sit on the machined surface of the central abutments (Fig. 9). The baseplate should not cover the labial area as it is important to be able to examine the fit of the acrylic-abutment and abutment-coping interfaces. The acrylic resin is made as thin as is consistent with strength, so that it will not interfere with subsequent tooth placement. Wax occlusal rims are added to the baseplate. 2.1 Aa'justing the occlusal rim The occlusal rim is adjusted to have bilateral stops in the bicuspid region at the correct vertical dimension of occlusion. The rim is reduced in all other areas to provide Australian Dental Journal 1992;37:6.
Fig. 7. -Masking wax covers cylinderlcoping interface and extends to the inferior border of the machined groove.
rl Fig. 8. -Masking wax extends over abutmentlcoping interface on two distal abutments and to the upper surface of the other abutments.
2 mm clearance at the correct vertical dimension. The base is secured into place with three short guide pins and the maxillo-mandibular transfer registration made with registration paste.
3. Trial insertion The position of the teeth on the duplicate diagnostic denture is used as a guide for the setting of the teeth for trial insertion. If the implant fixtures have been aligned correctly there is likely to be little room for setting the artificial teeth and they will need to be reduced on the lingual side. The impression copings over the posterior abutments may also interfere with tooth placement and it is usually necessary to either grind the copings or omit those teeth for trial insertion. 3.1 Checking the trial insertion The vertical dimension, jaw relationship, tooth position, aesthetics and phonetics are carefully examined and verified at the trial insertion. 3.2 Preparation of cast framework Once the trial insertion is completed, a key,** is made relating tooth position to the lower cast. The base plate is no longer required. Grooves are cut into the lingual surfaces of the teeth which are secured in the key with sticky wax. The acrylic/gold cylinder assembly is replaced on the abutment analogues and screwed into place. This may be used as a base to prepare the acrylic-wax pattern to unite _____~
**Optosil. Bayer AG, Leverkusen, Germany. Australian Dental Journal 1992:37:6.
1
I
Fig. 9. -Acrylic base does not cover abutmentlcoping interface. It is held in position by copings on the two distal abutments, and a guide pin through acrylic on the central abutment.
the fixtures using the teeth in the key as a guide to the position of the waxing required (Fig. 10). The essential features in the design of the casting to support the superstructure are, as follows. 1. Undercut finishing lines are prepared on the labial and lingual aspects to prevent acrylic resin separating from the casting. 2. Retention for acrylic in the form of beads or loops are required. 3. The waxed form of the casting should be a minimum 6.5 mm high and 4.5 mm wide and extend to the area of the cantilevered section distal to the last fixture, to prevent flexing and breakage. 4. The length of the cantilevered section distal to the distal abutment must not be such that it will overload the implants. 5. The wax up is extended at least 2 mm above the abutment-gold cylinder interface. 6. The undersurface is convex and smoothly contoured to facilitate cleaning by the patient. 3.3 Trial insertion of casting The casting must fit precisely on the abutments (that is, without any rocking) without the guide pins in position, that is, it must have a passive fit. If it does not have passive fit, it may need to be sectioned and soldered. The casting together with the teeth waxed into position may then be trial-fitted clinically and a similar check made as before (see 3.1). Once trial insertion is completed the superstructure may be finalized. 3.4 Attaching teeth to the metal framework When attaching the teeth to the metal framework with acrylic resin, ensure that: 1. The machined edges of the gold cylinders are protected. 2. There are cylindrical openings in the acrylic to provide access to the gold screws. 431
Fig. 10.-Matrix used to establish tooth position while casting is waxed up.
When the Superstructure has been polished, it is replaced on the articulated master cast and the occlusion refined.
Fig. 11.-Completed denture bridge.
4. Primary issue
The superstructure is fitted in the mouth with three short guide pins and the occlusion assessed. If satisfactory, the superstructure is ready to be screwed into position. It is important to eliminate the ‘empty space’ between the abutment face and the gold cylinder by placing a small quantity of slow-setting (3 parts base to 1 part accelerator) rubber base or silicone impression material onto each abutment around the central screw hole thus forming a ‘gasket’. The gold screws are positioned and screwed into place. There should be no rubber base or silicone material visible at the cylinderabutment interface when the fixed bridge has been screwed home and tightened. T o close the screw holes of the superstructure, a cotton pellet is placed into each access hole over
432
the gold screw head and the remaining section of the access hole is filled with gutta percha initially. After one month, once all screws have been retightened to ensure long-term superstructure stability, the access channels to the screws are covered more securely with a base of cotton wool, a layer of gutta percha and composite restorative material. This allows re-exposure of screw heads and removal of superstructure for maintenance as required (Fig. 11). Address for correspondenceheprints: Department of Prosthetic Dentistry, The University of Sydney, 2 Chalmers Street, Surry Hills, New South Wales, 2010.
Australian Dental Journal 1992;37:6.
Key words Implants: framework fit, impressions, superstructure. Abstract There is essentially no flexibility in an osseointegrated implant system, so that the final fit of the prosthesis must be absolutely precise. A simple approach to this problem is presented with details as to impression taking, confirmation of accuracy of the master cast, fitting of the cast metal framework and construction of the superstructure. The information presented describes a full arch fixed restoration attached to mandibular implants, but may easily be followed for the maxilla or modified for quadrant restorations. (Received for publication May 1991. Accepted September 1991.)
Introduction The prosthodontic procedures required for developing a fmed bridge attached to implants must be carried out accurately, as the final fit of the prosthesis to the abutments must be absolutely precise. There is essentially no flexibility in the system, since the superstructure is rigid as are the implants in their attachment to bone. As a result,
*Senior Lecturer, Department of Prosthetic Dentistry, The University of Sydney. +Prosthodontic Co-ordinator, Implant Centre, United Dental Hospital, Sydney. $Professor, Department of Prosthetic Dentistry, The University of Sydney; Consultant, Implant Centre, United Dental Hospital, Sydney. Australian Dental Journal 1992;37(6):427-32.
greater precision is required than for conventional crown and bridge work attached to natural teeth. The following information follows pre-surgical procedures and briefly describes a simplified approach to post-surgical prosthodontic procedures that the writers have found effective in obtaining the degree of accuracy required. The details to follow are described for a fill-arch fixed restoration attached to mandibular implants. However, the procedures may be followed for maxillary and quadrant restorations incorporating implants.
Post-surgical procedures 1. Impression procedures At second stage surgery, healing abutments are usually preferred, particularly where abutment length is of special importance in optimizing aesthetics. Three to four weeks after suture removal and once soft tissue inflammation has resolved, the healing abutments are removed, soft tissue height assessed and abutments of appropriate length screwed to the fixtures. Following abutment placement, healing caps are attached to protect the abutment surface and gingival tissues. The healing caps are removed for impression procedures and the abutment face cleared of any debris (Fig. la). 1.1 Primary impression - Lower jaw An alginate impression is taken of the lower jaw using a stock perforated tray (Fig. Ib). Brass abutment replicas are placed in the impression and a cast is poured in plaster (Fig. lc). Accelerator (NaC1, K,SO,) or a plaster slurry is 427
Fig. la.-Healing caps are removed and the abutment face cleared of debris. Fig. 1b.-Alginate impression taken in stock tray. Note that the impression extends over the entire area covered by a conventional complete denture. Fig. 1c.-Brass abutment replicas are placed in the alginate impression. Fig. Id.-Plaster, weakened by the addition of slurry or accelerator, forms the primary cast.
used to reduce the setting time and also to weaken the plaster, so that later retrieval of the abutments will not be difficult (Fig. Id). Once the cast has set, impression copings are positioned on the abutment replicas and held in position firmly with guide pins. Each coping must be seated precisely and firmly on each replica. The abutment replica-impressioncoping interface is covered with wax which is extended onto the lower border of the square section of the impression coping (Fig. 2). The abutments may now be linked together with auto-polymerizing acrylic resin, ensuring that the resin holds each impression coping firmly. When the resin has set, the masking wax is removed and the resin is trimmed until it is box-form, approximately 5 mm high and 5 mm wide (Fig. 3a,b). 1.2 Impression tray A relief of one layer of baseplate wax is placed over the impression coping-acrylic block and the saddle areas. An impression tray is formed in auto420
polymerizing acrylic resin,§ and designed so that it is open and does not cover the implants or acrylic
blocks. This is essentially a complete denture secondary impression tray with an open ‘well’ over the implant area (Fig. 4). 1.3 Preparation for secondary impression The wax relief is removed from the acrylic attached to the impression copings, and the acrylic block is numbered from left to right on the labial side to indicate abutment position. The resin is then divided vertically, using a disc in a straight handpiece so that each coping is held in a separate block of acrylic following removal of a minimum amount of acrylic resin (Fig. 5a,b). The brass analogues may now be removed from the plaster cast, and the impression copings placed in cold sterilizing solution in preparation for secondary impressions.
§For example, Tray resin. (Kerr, Romulus, MN, USA.) Australian Dental Journal 1992:37:6.
Fig. 2.-Masking wax extended over abutmentkoping interface reaching to lower border of square section of coping. Fig. 3.-Acrylic resin links the copings and is trimmed to a 5 mm box form. The masking wax which protected the abutment/ coping interface has been removed. Fig. 3a: labial view. Fig. 3b: occlusal view. Fig. 4.-Impression tray. Note that the area above the implant site is left open.
1.4 Secondary impression
Impression copings are placed in the mouth in their correct position and alignment, with the numbers oriented to the labial face of the acrylic block and in numerical order. They are secured with their guide pins ensuring that the acrylic does not touch the approximating block. The blocks may now be joined with a minimum amount of resin I( to make a rigid assembly using a powder/liquid build up with a brush. Wax is then placed over the opening in the impression tray to contain the impression paste before taking the impression. While seating the impression tray, pressure is exerted on the wax so that the tops of the guide pins penetrate the wax layer (Fig. 6). When the impression material has set, the wax is removed and the guide pins are readily unscrewed and the impression removed from the mouth.
IDuralay. Reliance Dental Mfg Co., Ill, USA. Australian Dental Journal 1992;37:6.
The guide pins must be completely cleared of the machined surface. Brass abutment analogues are then fitted carehlly against the exposed machined surface of the impression copings and screwed into place. Following placement of all brass abutments, a cast is poured in die stone7 and once set, the guide pins are unscrewed and the impression removed. This is the master cast. 1.5 Checking the accuracy of the master cast Gold cylinders are placed on the abutment replicas and screwed firmly into place with guide pins. The cylinder-abutment interface is covered with wax to a point 1 mm above the interface of the gold cylinder - or to the machined groove (Fig. 7). The gold cylinders are linked together with autopolymerizing acrylic resin which is then contoured and sectioned between the cylinders. A minimum YFor example, Velmix. Kerr, Sybron Dental Division, Romulus MN, USA. 429
Fig. 5a.-Acrylic numbered on labial of each impression coping and then divided by a fine disk. Fig. 5b.-Note that the divided acrylic sections are almost touching. Fig. 6.-Tops of guide pins penetrate wax during impression taking procedures.
amount of new resin is then added to the cut edges of the resin to minimize the setting contraction which is clinically significant if the gold cylinders are linked in one procedure. The guide pins are now removed and the cylinders are examined to ensure that they have maintained a precise fit on the abutment analogues. This is referred to as a passive fit. 1.6 Checking the accuracy of the cylinder assembly in the mouth The cylinder assembly must fit precisely on the abutments, without the guide pins in position. The passive fit of the assembly is tested for rotation; any movement indicates the need for realignment. An absolutely precise contact fit is required. Once confirmed, the clinician is now confident that the master cast is a true and precise replica of the arrangement of the abutments in the mouth and may confidently proceed with clinical records.
2. Maxillo-mandibular transfer records For transfer recordings, an acrylic base is prepared that attaches to the abutments. Impression copings are placed onto the two most distal 430
abutments of the master cast. The coping-abutment interface is covered with wax which is extended to cover the other abutments to the level of their upper surface (Fig. 8). The exposed surfaces of the machined abutments are covered with foil and a hole is made through the foil over the screw hole of one of the central abutments. A guide pin is lubricated and screwed into this hole. A baseplate is made in autopolymerizing resin, which should incorporate the two impression copings and the lubricated guide pin, and accurately sit on the machined surface of the central abutments (Fig. 9). The baseplate should not cover the labial area as it is important to be able to examine the fit of the acrylic-abutment and abutment-coping interfaces. The acrylic resin is made as thin as is consistent with strength, so that it will not interfere with subsequent tooth placement. Wax occlusal rims are added to the baseplate. 2.1 Aa'justing the occlusal rim The occlusal rim is adjusted to have bilateral stops in the bicuspid region at the correct vertical dimension of occlusion. The rim is reduced in all other areas to provide Australian Dental Journal 1992;37:6.
Fig. 7. -Masking wax covers cylinderlcoping interface and extends to the inferior border of the machined groove.
rl Fig. 8. -Masking wax extends over abutmentlcoping interface on two distal abutments and to the upper surface of the other abutments.
2 mm clearance at the correct vertical dimension. The base is secured into place with three short guide pins and the maxillo-mandibular transfer registration made with registration paste.
3. Trial insertion The position of the teeth on the duplicate diagnostic denture is used as a guide for the setting of the teeth for trial insertion. If the implant fixtures have been aligned correctly there is likely to be little room for setting the artificial teeth and they will need to be reduced on the lingual side. The impression copings over the posterior abutments may also interfere with tooth placement and it is usually necessary to either grind the copings or omit those teeth for trial insertion. 3.1 Checking the trial insertion The vertical dimension, jaw relationship, tooth position, aesthetics and phonetics are carefully examined and verified at the trial insertion. 3.2 Preparation of cast framework Once the trial insertion is completed, a key,** is made relating tooth position to the lower cast. The base plate is no longer required. Grooves are cut into the lingual surfaces of the teeth which are secured in the key with sticky wax. The acrylic/gold cylinder assembly is replaced on the abutment analogues and screwed into place. This may be used as a base to prepare the acrylic-wax pattern to unite _____~
**Optosil. Bayer AG, Leverkusen, Germany. Australian Dental Journal 1992:37:6.
1
I
Fig. 9. -Acrylic base does not cover abutmentlcoping interface. It is held in position by copings on the two distal abutments, and a guide pin through acrylic on the central abutment.
the fixtures using the teeth in the key as a guide to the position of the waxing required (Fig. 10). The essential features in the design of the casting to support the superstructure are, as follows. 1. Undercut finishing lines are prepared on the labial and lingual aspects to prevent acrylic resin separating from the casting. 2. Retention for acrylic in the form of beads or loops are required. 3. The waxed form of the casting should be a minimum 6.5 mm high and 4.5 mm wide and extend to the area of the cantilevered section distal to the last fixture, to prevent flexing and breakage. 4. The length of the cantilevered section distal to the distal abutment must not be such that it will overload the implants. 5. The wax up is extended at least 2 mm above the abutment-gold cylinder interface. 6. The undersurface is convex and smoothly contoured to facilitate cleaning by the patient. 3.3 Trial insertion of casting The casting must fit precisely on the abutments (that is, without any rocking) without the guide pins in position, that is, it must have a passive fit. If it does not have passive fit, it may need to be sectioned and soldered. The casting together with the teeth waxed into position may then be trial-fitted clinically and a similar check made as before (see 3.1). Once trial insertion is completed the superstructure may be finalized. 3.4 Attaching teeth to the metal framework When attaching the teeth to the metal framework with acrylic resin, ensure that: 1. The machined edges of the gold cylinders are protected. 2. There are cylindrical openings in the acrylic to provide access to the gold screws. 431
Fig. 10.-Matrix used to establish tooth position while casting is waxed up.
When the Superstructure has been polished, it is replaced on the articulated master cast and the occlusion refined.
Fig. 11.-Completed denture bridge.
4. Primary issue
The superstructure is fitted in the mouth with three short guide pins and the occlusion assessed. If satisfactory, the superstructure is ready to be screwed into position. It is important to eliminate the ‘empty space’ between the abutment face and the gold cylinder by placing a small quantity of slow-setting (3 parts base to 1 part accelerator) rubber base or silicone impression material onto each abutment around the central screw hole thus forming a ‘gasket’. The gold screws are positioned and screwed into place. There should be no rubber base or silicone material visible at the cylinderabutment interface when the fixed bridge has been screwed home and tightened. T o close the screw holes of the superstructure, a cotton pellet is placed into each access hole over
432
the gold screw head and the remaining section of the access hole is filled with gutta percha initially. After one month, once all screws have been retightened to ensure long-term superstructure stability, the access channels to the screws are covered more securely with a base of cotton wool, a layer of gutta percha and composite restorative material. This allows re-exposure of screw heads and removal of superstructure for maintenance as required (Fig. 11). Address for correspondenceheprints: Department of Prosthetic Dentistry, The University of Sydney, 2 Chalmers Street, Surry Hills, New South Wales, 2010.
Australian Dental Journal 1992;37:6.
