The experienced Cerec user can manufacture high-quality, esthetic anterior and posterior bridges from IPS e.max CAD in a manageable 3-hour chairside session. On the basis of over 8 years of experience, it can be said that these restorations are clinically very well proven, provided they are used within the range of recommended indications. Experimental retainer bridges with extensions can be seen as highly interesting alternatives, although more clinical data are required for further confirmation.
Keywords: all-ceramic, Cerec, chairside treatment, bridge prosthetics, adhesive cementation, retainer bridges with extensions
Author: Oliver Schneider
Access to this Content is provided by Ivoclar Vivadent
More Information about IPS e.max CAD:
Diplom-Stomatologist Oliver Schneider
CAD/CAM systems have become firmly established in dental laboratories and dental practices in the course of the past few years. The manufacture of highly precise substructures with a morphologically detailed design made of high-performance ceramics is not possible without digital technology and computer-controlled milling machines. This technology has a history of over 30 years of development. In 1985, the first successful seating of an all-ceramic chairside inlay took place. This was achieved with the aid of the Cerec I technology. The Cerec system has seen rapid development since then, with the result that inlays, onlays, partial crowns, anterior and posterior crowns, and veneers are today established in, and form a standard part of, the daily working routine of Cerec users. Statistic investigations that have been running for about the past 18 years confirm that Cerec inlays have become clinically established to a degree similar to that of cast gold inlays.1
It was the long-held wish of Cerec users to have the capability to also manufacture larger, multiunit restorations such as bridges at chairside. The hardware and software capability was, however, not sufficient to permit this until 2006. Neither could industry come up with materials of sufficient strength prior to that time.
There was an abrupt change for the better in the context of the IDS 2007, when Sirona presented the inLab 3D software version 3.00 and the Cerec MC XL milling unit to the dental world. The Cerec 3 Redcam scanner could at that point be used for the imaging of three-unit bridges. Likewise, the then new CAD-Temp (Vita Zahnfabrik, Bad Säckingen) made it possible for the first time for dentists to manufacture temporary three-unit bridges.2 This enabled the dental anatomy of crowns and bridge units to be biometrically digitized. The biogeneric design technique was introduced initially for use with inlays only.3
Before 2007, there were no ceramics suitable for fully anatomical chairside bridges as a permanent solution for closing small gaps in the dental arch. Lithium disilicate ceramics, such as those offered by Ivoclar Vivadent AG (Schaan, Liechtenstein) under the name of IPS e.max CAD LT, posed a solution to this problem from 2007 onwards.4 These could be processed into fully anatomical and highly esthetic all-ceramic restorations.4,5 Compared to traditional feldspathic ceramic (Vita Mark II, Vita Zahnfabrik) and leucite-reinforced glass ceramics (IPS Empress CAD, Ivoclar Vivadent AG), this material shows a considerably higher three-point flexural strength.6
The figure quoted on the basis of tests performed by the manufacturers is 360 MPa (Table 1). Moreover, fracture resistance tests had demonstrated that similar values were achieved with adhesive cementation using IPS e.max CAD as with conventional cementation.7
Lithium disilicate ceramic had already been available to users of the ceramic press technology for several years in the form of IPS e.max Press. According to the manufacturer, by means of the ceramic press technology this material reaches an average flexural strength of 400 MPa, with the values varying according to the measurement method used.8,9 In vitro studies revealed that under permanent load, IPS e.max Press achieves values considerably above the expected load values occurring under natural conditions in the anterior area.10 The highest fracture strength values obtained for three-unit posterior bridges made of IPS e.max Press were achieved with anatomically pressed restorations.11
On the basis of these insights, the material manufacturer, in collaboration with the Technical University of Aachen (RWTH) and five dental practitioners – including the author – with many years of clinical experience as Cerec users, demonstrated in a controlled clinical study that IPS e.max CAD LT chairside bridges represent a viable solution, and can be said to ensure clinical success.12 It was a question of defining the key points of the clinical procedure.
In the course of experimental studies over the past several years, a further 58 three-unit bridges were manufactured in IPS e.max CAD LT in the author’s practice; the method was further perfected, and the limits of this technology pushed further. Moreover, the Cerec system has seen vast developments in both hardware and software. The aim of this article is to show the extremely high degree of safety with which the well-versed Cerec user can produce esthetic bridges from lithium disilicate ceramic at the chairside today.
Materials and methods
Definition of the task
In the scope of a prospective clinical study in 2008, at least 12 all-ceramic IPS e.max CAD LT bridges were produced and seated in the anterior and premolar areas via a chairside or semi-chairside workflow (with the cutback technique).
To this purpose, Ivoclar Vivadent produced a small series of bridge blocks with a length of 32 mm from IPS e.max CAD LT in the shades A1 to A3,5 (Fig 1).
General clinical conditions:
- The bridge was to be used, at the most, for the replacement of the anterior and the first premolar teeth.
- The clinical procedure had to be in accordance with the manufacturer’s current working instructions.
- No tooth mobility (degree of tooth mobility > 1).
- Connector thickness: 16 mm3.
- Adhesive cementation with Multilink Automix (Ivoclar Vivadent).
Subsequent recall visits were scheduled for every 6 months over the next 5 years. For this follow-up period, events were defined which would constitute a sign of clinical failure; these included fractures, irreparable chipping, delamination, marginal gaps, caries, tooth mobility, and decementation. The periodontal parameters, such as OHI (oral hygiene instruction), GVI (gingival index), and PBI (periodontal bleeding index) were likewise recorded. Both patient and dentist subsequently rated the seated restorations according to school grades in Germany (ie, between 1 and 6, with 1 being the highest and 6 the lowest grade). In 2013, the authors of the study12 agreed to continue to check all seated bridges in an annual follow-up. In terms of the authors’ clinical practice, this means that the patients concerned are examined at least twice a year, and the results documented once a year on the clinical findings sheet; as an additional record, clinical photographs are taken.
Building on the initial results and clinical experience, the authors manufactured a further total of 60 bridges during the period lasting until 29 March 2016. At the same time, the defined area of indications of the clinical study was further extended. The authors then fabricated bridges to replace the second premolar and the first molar. In addition, cantilever bridges were seated. The first retainer bridges with extensions came onto the market in autumn 2008 (Tables 2 and 3). The patients were all from the authors’ patient base. Thanks to their well-functioning recall system, checkups are guaranteed every 6 months. In the period between 1 October 2015 and 29 March 2016, a control rate of 92% was observed for bridges in the study. A total of 90% of all other patients attended regular checkups in the dental office.
After 8 years, however, the design procedure used by the Cerec unit is comparable only to a limited extent. Both the hardware and the software have seen a rapid development in the meantime. The measuring accuracy increased markedly following the introduction of the Cerec Bluecam, and later the Cerec Omnicam, which came onto the market in 2009 and 2012, respectively. With values of 19 µm, this technology already reaches the level of high-precision extraoral reference scanners.13 As from version 3.4.0 of the Cerec 3D software, it was already possible to manufacture fully anatomical bridges with up to two pontics.14 This was followed by the introduction of the biogeneric software for crowns (2009), the virtual articulator (2013), and the Biojaw (2015). The authors consider the continuous monitoring of the connector thicknesses on the computer screen to be of particular importance. In the clinical study phase, the connector thicknesses were determined in the cut window.
For the design of all permanent bridge restorations made of IPS e.max CAD LT, the authors use the current inLab software with the Cerec AC unit in daily practice. Besides reasons relating to the development of Cerec up to software version 4.0, there still remain two further decisive reasons today:
- inLab permits the connectors to be designed as individual (anatomically contoured) components. The software features various tools for processing. This enables larger-dimensioned connector cross-sections to be effectively concealed even in the esthetically sensitive anterior region (Fig 2).
- Only with the inLab software is it possible to utilize in practice the possibility of four-axis milling with the Cerec MC XL milling unit. This enables minor adjustments of the abutment teeth to be made (Figs 3 and 4).
The clinical study included the results obtained with 12 bridges for the treatment of eleven patients in 2007 and 2008. These bridges were mostly used as a substitute in the case of older patients with metal-ceramic bridges needing replacement.
These and all following bridges were manufactured exclusively at chairside in one treatment session following an optical scan and without the use of a master model. In five cases, the authors collaborated with a dental technician to perform the cutback technique in the anterior region. The authors manufactured simple silicone models for the technicians to use.
The treatment was likewise performed each time in one sitting. Models were used only in the case of two implant-supported bridges.
After local anesthesia during treatment in the author’s practice, a pronounced chamfer preparation with a width of 0.8 to 1 mm was made. To this purpose, after a preliminary phase, the authors used diamond grinding instruments with short guide pins (MDS Medical & Dental Service, Höhr-Grenzhausen). In this way it is possible, after a familiarization phase, to define ideal preparation borders.15 The authors’ preferred position is slightly supragingival in the posterior region, and tendentially epigingival or subgingival in the anterior region. Since the material manufacturer requires 1.5 mm both circumferentially and occlusally (anterior tooth 1.2 mm circumferentially), the corresponding amount of hard tooth substance must be removed (Fig 5).
To ensure that the preparation borders are clearly marked, the authors refrain from using retraction cords, and instead use Expasyl retraction paste (Acteon Germany GmbH, Mettmann) prior to scanning. After an application time of at least 90 s, ideal conditions are reached for optical impression taking (Fig 6).
The authors always use the intraoral optical impression technique. If the dental assistants are familiar with the material and are instructed accordingly, even full jaw scans can be completed during the time required by classical impression taking. In order to benefit from the virtual articulator function of Cerec, the scan is generally extended at least up to the canine/premolar area of the opposite side of the jaw. Using the Omnicam AC unit, it is possible, after the initial scan of the treatment area, to copy the data into different folders; all that is then required is to cut out the area to be altered, and then to modify this with subsequent brief scans. This enables the rapid recording of the clinical situation prior to preparation (in the “BioCopy” folder), an FGP (Functionally Generated Path) (in the bite record folder), and the actual preparation. The authors recommend beginners in particular to record the relevant information in the “BioCopy” folder. Cross-fading the images facilitates the positioning of the design elements and contains directions pertaining to their size, as well as information on the articulation technique.
The precise alignment of the model axis (LJ, interincisal point, Camper’s line) is necessary, both to enable the system to provide excellent initial design proposals and to ensure the accurate operation of the average-value articulator (Fig 7).
After marking the preparation borders on the abutment teeth, the baseline for the pontic is outlined (Fig 8). This can be drawn on the mucosal surface with an electrosurgical unit, or as a small groove that is carved using a gingival trimmer. In this way, the pontic is made to look as if it were growing out of the gingival tissue like a natural tooth. Setting the parameters of the pontic – distance to gingiva: 0 mm; lingual opening angle: 0 degrees.
In the next step, the axis of insertion is determined. Not only the occlusal view should be taken into account; the lateral view is also important. This is the only way to ensure a clean-cut design of the approximal areas mesially and distally. Additionally, the insertion axis can be optimized buccolingually by utilizing the fourth axis of the Cerec MC XL for each abutment crown. The initial biogeneric design proposal calculated by the machine can be further optimized and adapted to the clinical situation using the various tools.
The authors begin each time with the crowns. If necessary, the alignment, size, inclination of the tooth row, and static occlusion are checked and modeled, first using coarse-grained and subsequently finer-grained tools. Adjacent to these is the pontic.
In the next step, the connectors are processed. With the inLab software, the individual components of the future restoration can be displayed and processed using the various tools (for scaling, designing, forming, and shifting), with simultaneous live monitoring of the cross-section. To conclude, the static – and in particular the dynamic – contacts are verified once more in the articulator (Fig 9).
The Cerec MC XL requires approximately 25 min for milling in the dental practice, provided that fresh abrasives are used. As standard procedure, the authors use IPS e.max CAD B32 bridge blocks in LT.
After separating the body of the bridge from the block, the first intraoral try-out is performed on the patient. The static and dynamic occlusion is checked and, if necessary, adjustments are made using fine-grained (red) diamond abrasives (Fig 10). Further extraoral corrections can be made for an optimum shape and surface texture. Especially in the anterior area, ridges and perikymata are appropriate features. It is recommended that separating discs are not used. This is a good opportunity to check all details intraorally while the patient is in the dental office. If the patient agrees, the bridge is then prepolished. It has been shown that such an ultrafine, homogeneous surface structure can be achieved with IPS e.max CAD.
Bridges in the esthetically demanding anterior region are crystallized first, and in a second firing, colored and characterized from the dentin core to the enamel with IPS e.max Shades and Stains. In the case of posterior bridges, the authors perform both these tasks in a single step. To finish off, the glazed surfaces are polished with diamond polishing paste (Fig 11).
All restorations were adhesively cemented by the authors, who have been using Multilink Automix for this purpose in all cases since 2007. The restorations were etched for 20 s with hydrofluoric acid (Vita Ceramics Etch, Vita Zahnfabrik) and then silanized with Monobond-S (Ivoclar Vivadent AG), and as from 2013, with Monobond Plus (Ivoclar Vivadent AG). The dies are treated for 30 s with Multilink Primer A and B (Ivoclar Vivadent AG). Before light curing, the bonded joint is always sealed with Airblock (Dentsply DeTrey GmbH, Konstanz). Excess material is removed using a scalpel, an abrasive disc, and rubber polishers (Eve Diapol, Eve Ernst Vetter GmbH, Pforzheim) (Fig 12).
A special case: retainer bridges with extensions
The authors gained their first clinical experience with IPS e.max CAD retainer bridges with extensions in the treatment of patients after implant insertion. In the course of the healing phase (maximum 6 months), they observed no failures in temporary restorations of this type. These encouraging results led the authors to also use this method for definitive restorations. If the first bridges were made with two extensions, the authors later restricted themselves to using only one. Depending on the occlusal relationships, the minimally invasive technique was used for preparations in the enamel only if required. In the mandible, this was not usually necessary; in the maxilla, however, a suitable palatal veneer preparation was required. Approximal preparations were mostly only made to ensure good seating of the restoration. Furthermore, sometimes a slight approximal box cavity preparation is recommended for permanent bridges to ensure precise positioning and dimensional accuracy of the connector.
The pontic, the anatomical connector, and a veneer are stored in the inLab software administration. This is carried out intraorally on the abutment tooth (Figs 13 and 14). Prior to seating, the bridge extensions are usually conditioned in the same way as for IPS e.max CAD. Variolink II, Variolink Veneer, and Multilink Automix were used for adhesive cementation.
All 12 bridges manufactured by the authors in the period from 2007 to 2008 in the context of this clinical study are currently in situ. Patients and dentists have rated the esthetic appearance of the restorations, awarding a rating of “1” to eleven restorations, and a rating of “2” in the case of one restoration (Figs 15 and 16). Apart from one exception, no negative results were obtained for any of the patient cases.
In the exceptional case, the authors observed chipping in an anterior bridge on teeth 11 to 22 in the vicinity of the incisal edge on tooth 11. The cutback procedure was used here to achieve particularly outstanding esthetic results. The problem occurred 37 months after seating in the vicinity of the subsequently applied IPS e.max Ceram. Some adjustments were made in this area using abrasive discs, rubber polishers, and diamond polishing paste to avoid having to renew the bridge, which is still in situ in the patient’s mouth today (Figs 17 to 19).
It is particularly noteworthy that no cracks, fractures or decementation were observed among the authors’ patients. A further positive point is that no marginal gaps or discolorations were observed in the vicinity of the bonded joint. Good to excellent GVI and PBI values can be observed among the authors’ patient population.
This also applies to all further bridges seated. Only in two cases was endodontic treatment necessary. After this was completed, the trepanation openings (for endodontic access) were successfully sealed with small inlays.
One retainer bridge with extension became detached after 5 months because, contrary to instruction, the patient had been chewing on a lip piercing. After appropriate cleaning and conditioning, the restoration was reseated.
The patients reported being satisfied that, in this author’s city center practice, the bridges were manufactured in a single sitting of around 2.5 to 3 h. This does away with the need for a second appointment, no time is lost in traveling and parking, and waiting time is saved. The patients take a lively interest in the manufacture of their restorations. Furthermore, the patients’ individual wishes can be directly taken into account.
With the IPS e.max CAD LT B32 block, the experienced Cerec user can manufacture esthetic bridge restorations in the anterior and premolar areas with a high probability of success. Over a period of 8 years, the authors observed only one case of chipping; this did not occur in the IPS e.max CAD substructure but in the border layer to the IPS e.max Ceram veneering material, perhaps due to incorrect axial loading that went unnoticed during the mandibular protrusion movement. This is yet another example of why it is vital to precisely monitor the static and dynamic occlusion. The authors perform this routinely around a week after the seating of the bridges.
The authors do not wish to associate the endodontic treatment required in the case of two bridges with the material used in the chairside procedure. The occurrence of preparation trauma during crown and bridgework treatment is known from the literature.16
The conditions for successful clinical procedures for the manufacture of chairside bridges can be defined as follows:
- Strict adherence to the area of indications; replacement of one tooth at the most.
- Anterior area: maximum width of bridge unit should be 11 mm.
- Premolar area: maximum width of bridge unit should be 9 mm.
- No loosening of the abutment teeth: maximum 1st degree tooth mobility (according to Fogge).
- The connectors should have a minimum wall thickness of 16 mm2; no reworking (no separating discs!).
- Bridges should be adhesively cemented (Multilink Automix).
The chairside method is to be recommended if it can be neatly integrated into the dentist’s clinical routine. At the beginning, there is likely to be more tension in the team. Nevertheless, this is more than balanced out by the time saved for both patient and dentist, how easily the restoration can be continuously monitored, the fact that there is no need for provisionalization, and ultimately by the very high level of patient satisfaction.
For restorations intended to close gaps in the distal portion of the posterior region, or which exceed the recommended width for the respective bridge units, the authors use semi-chairside bridges made of translucent zirconium oxide (InCoris TZI or TZI C; Sirona). The amount of material and time used is considerably higher compared to IPS e.max CAD, and requires collaboration with dental technicians well versed in the use of these materials.17
In 44% of all cases, the authors have manufactured bridges made of IPS e.max CAD that do not correspond to the range of indications recommended by the manufacturer. The patients were briefed accordingly. All these restorations were closely monitored in recall visits. The long-term clinical results of the retainer bridges with extensions are sure to be of particular interest. These save time and effort for both the dentist and patient as well as ensuring a highly esthetic appearance. The authors recommend this treatment in the case of congenital hypodontia in young people. After completion of endodontic treatment, these can serve as a long-term restoration in the anterior area. The authors hope that implant therapy will not be necessary until after these patients reach the age of 25 (Figs 20 and 21). Likewise, during the implant healing phase, and in older patients when other forms of restoration are not recommended and/or desired by the patient, retainer bridges with extensions made of IPS e.max CAD ought to be an appropriate solution.
The requirements for these should be:
- Utilization of the entire available retention surface on the abutment tooth.
- In preparation for attaching the retainer bridge extensions, it can be necessary to also utilize the entire space between the incisal edge and the tubercle.
- Connectors should be modeled as robustly as possible, depending on the individual clinical situation.
- Use of a dental dam during seating of the restoration.
- Exclusion of parafunctions and habits.
- No loading of the bridge unit in static and dynamic occlusion.
The results of treatment using retainer bridges with extensions made of IPS e.max CAD look encouraging to date. However, even though the authors can look back on 5 years of clinical experience, the fact is that these restorations are of an experimental nature. Also interesting is the comparison with all-ceramic adhesive bridges made of zirconium oxide, which have already been clinically established on the basis of 15 years of clinical experience.18
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