Written by Dr. Ian Shuman
Long-term chairside fabricated crowns and bridges offer clinical possibilities that were previously unavailable. Innovative new materials and techniques are designed to make the fabrication of provisional crowns and bridges more efficient and precise. There is now a long-term fabricated crown or bridge that can be created chairside that will last approximately five years. What’s more, an updated process of the cordless H&H technique that perfectly captures deep subgingival margins using advanced new materials can be used for nearly all impression manners.
Here we explore all steps of fabrication from prep to provisional while applying a variety of techniques and materials to several cases. The article will discuss the importance of a well-fabricated chairside crown, describe the materials and steps needed to create a long-term prosthesis, and examine the theory and steps needed for the H&H cordless final impression technique.
Pre-prep impressions for provisional fabrication
Polyvinyl siloxane (PVS) is an ideal material choice for the fabrication of provisional impressions. Unlike traditional alginate, it is accurate and reusable, and impressions made with PVS material can be kept for many years.
If a tooth has a guarded prognosis such as the one in this first case, it is best to perform a procedure that will attempt to solve the problem chairside. If no endodontic work occurred or is required at the time of preparation, a long-term provisional crown is an excellent treatment choice in order to evaluate the health of the tooth and the gingiva, and to determine if the tooth requires root canal therapy. Moreover, because of potential endodontic work in the future, or if the tooth eventually fractures and becomes non-restorable afterwards, a small amount of time is invested into the restoration of the tooth.
Patient presented with a failing restoration on tooth #18, and deep proximal caries on both mesial and distal sides (Figures 1-2).
The impression for the provisional prior to preparing the tooth is made with StatusBlue (DMG), a medium-body polyvinyl material.
Fill the pre-preparation impression with LuxaCrown (DMG), a chairside long-term bisacryl composite material designed to be long-lasting. Be sure to fill the impression all the way up to the margin to avoid any insufficient material coverage or thin spots. (Figure 3).
After a mere two minutes the material has set, and is ready for trimming, placement in the mouth, and cementation (Figure 4).
Final impression: H&H technique (aka the cordless impression)
The Hydraulic and Hydrophobic (H&H) Technique uses impression materials and hydraulic pressure to drive a low viscosity polyvinyl siloxane (PVS) impression material deep into the sulcus to capture a perfect impression of the subgingival margin.1
Here we have a prepped tooth prior to the impression (Figure 5). Due to its thixotropic nature, a heavy body base impression material is not designed to fully capture fine marginal detail (Figure 6).
With no hydraulic compression, the heavy body material is simply not light enough to fill in critical marginal areas.
Following the complete set of the base material, a wash is added to the impression (Figure 7). Using a triple tray under occlusal force, the wash material is hydraulically forced into the marginal areas (Figure 8). Because of its hydrophobic nature, it displaces the fluids, allowing the wash to closely capture margins and the sulcus without the need to pack cord.
A final impression is made using a triple tray and Honigum Pro Heavy QuadFast (DMG) impression material (Figure 9). Honigum Pro Heavy QuadFast has a very rapid set time, taking a mere 2 minutes to set.
The heavy body impression is removed out of the mouth, rinsed and dried thoroughly, and then wash material is added to the entire surface (Figure 10). Adding it only to the prepped tooth will create an imbalance between the base impression – a bit of remaining wash offsets the impression so, be sure to add the wash material to the entire surface of the impression (Figure 11).
Because the heavy body impression material has to be strong enough to push the light body material up into the sulcus, a shore hardness of at least 50-55 is required to qualify for this type of technique. In this case, Honigum Pro has a shore hardness of 62-74.
When doing full arch or quad bridge work, always use separate impression trays with a bite registration for both upper and lower arches. After the impression base is set (Figure 12), use a lab blade, trim any excess material to allow easy entrance into the mouth. Cut off any overhang as well, but not so much as to encroach on the margins of any of the teeth.
Teeth #s 3-6 are prepped for a full-coverage four-unit bridge (Figure. 11). Honigum Pro Light Quad Fast is used for step two of the final impression (Figure 12). A thick ribbon of the material is placed to fill all teeth (Figure 13).
Since this impression technique is typically performed with a triple tray, adequate force must be applied to the single trays being used. Therefore, have the patient bite down on two cotton rolls on each side for adequate occlusal pressure to allow the light body material to push up its way up into the sulcus (Figure 14).
Due to excellent penetration depth, the final impression displays exquisite detail of the sulcus, and crisp sharp margins of the prepped teeth necessary when doing full arch or quad bridge work. Conversely, the light body material also has extremely high toughness when compared with similar products on the market (Figure 15).
Proper core preparation
A core is required for sufficient cuspal coverage and can be accompanied by a ferrule for maximum stability. To demonstrate the importance of sufficient cuspal coverage, here is an image of an endodontically-treated maxillary molar restored with a bonded composite restoration (Figure 16). Because the tooth was solely protected with the bonded composite restoration, the tooth eventually became fractured and non-restorable.
What is a ferrule?
A ferrule is ring or a cap, typically made of metal, that str
engthens the end of a handle, stick, or tube and prevents it from splitting. A comparative example of a crown ferrule is a metal eraser tube. The metal tube located on the end of the pencil prevents the wood from splitting and allows an eraser to be plugged into the other end. The ferrule should have the same effect when applied to crowns.
The ferrule provides a bracing action to protect the integrity of the root
while offering even distribution of forces to the root. When used, restorations have a subgingival collar that acts by a “hugging” action and prevents vertical fracture of the tooth.
For maximum ferrule effect, the margin should
be 1.5-2mm of tooth structure. Here we have a tooth colored in silver amalgam, and below is the ferrule. This shows how much of the ferrule is needed beyond the core restoration to provide a successful effect (Figure 17).
A study by Sorenson and Engelman evaluated the fracture resistance of pulpless teeth with various ferrule designs and amounts of coronal tooth structure. They determined that only one millimeter of coronal tooth structure above the crown margin substantially increased the fracture resistance of endodontically-treated teeth.2 Therefore, according to this study, a successful ferrule effect can actually be achieved with at least 1-1.5mm of coronal tooth structure.
Preparing a crown with an adequate ferrule
Pin Diamonds (Komet) allow depth-controlled preparation, preventing users from going too deep into the tooth to achieve a proper step-down margin. Pin diamonds come in a wide variety of shapes and styles including shoulder, chamfer, and feather in order to create different effects depending on the kind of margin preferred.
The guide pin acts as “horizontal or vertical distance keeper” (Figure 18-19). Using a circular material reduction mechanism, the guide pin guarantees controlled preparation with an even cutting depth, creating a uniform preparation and avoiding the “gutter” effect. Using a guide pin ensures the same thickness and depth of preparation throughout the entire tooth.
During the preparation of the subgingival margin, the 0.5 mm long guide pin assures a pre-defined distance to the periodontium (Figure 20). Use of the guide pin allows exact measurement of spacing, helping to prevent any damage to the biological width (Figure 21).
Root fracture is one of the most serious complications following restoration of endodontically-treated teeth.3 A study was recently conducted that compared fracture strengths using posts and cores, and variable quantities of coronal dentin located apical to core foundations with corresponding ferrule designs incorporated into cast restorations. It concluded that an increased amount of coronal dentin significantly increases the fracture resistance of endodontically-treated teeth. In short, the more coronal dentin that can be preserved, the better the outcome.
Traditional composite resin vs. hybrid composites for core build-up
Composite resin materials have many advantages including: high compressive strength, they are easy to manipulate, they polymerize rapidly, and are easily bonded to dentin. However, there are some key disadvantages when using composite resin as a core material. They are prone to polymerization shrinkage and have poor dimensional stability. When building a core, a material is needed that will stack up and stay stacked without drooping.
Today, those disadvantages have been eliminated with the use of universal nano-composite materials. These hybrid composite materials appear to be the most reliable material for core buildup. According to studies, prepared core buildups using a hybrid composite material provides the highest fracture resistance.4
Matrix systems for core build-ups
The ReelMatrix (Garrison Dental) includes instruments and matrices ideal for posterior procedures. It contains material very well, avoiding any spilling into the adjacent teeth. The reels are inserted into the handle and retracting the grippers lock the reel in place, eliminating the need for a tofflemire.
This particular case has a loss of tooth structure, previous amalgam, and recurrent caries. Because of the recurrent caries and the deep margin at the gingiva, a crown is the preferred treatment (Figure 22).
After initial gross preparation, a wedge is made, and the matrix band is placed for stabilization (Figure 23). In figure 24 the core buildup is seen prior to curing showing the stackability, no-slumping and how very well contained it is.
The pocket is then measured on the distal aspect. There was no violation of biological width and did not require crown lengthening (Figure 25).
Enamel Peel Technique
The enamel peel technique is effective, safe, and saves an enormous amount of time. Using a carbide bur, preparation is conducted in a counterclockwise direction to efficiently remove the enamel. Peeling away the enamel and dentin circumferentially performed in a counterclockwise fashion allows the bur to work without effort.
There is a small fracture in this tooth from the amalgam towards the lingual, as well as caries. Amalgam has a very poor marginal barrier once it has been breached, allowing decay to readily invade under the margins. Prior to prepping the tooth, if an impression was taken of the crown as is, there would be a lump in the polyvinyl which would have to be cut in order to look like the full tooth. To avoid that difficulty, an orthodontic wax is used (Figure.26).
The fracture defect is rebuilt with orthodontic wax solely for making the pre-preparation impression of the provisional crown (Figure 27). Orthodontic wax is inexpensive, quick, easy, and maintains its shape. It can then be sculpted as needed, and the impression made. Moreover, when the patient occludes using a triple tray, the orthodontic wax will descend even further, forming an extremely precise occlusion.
The bulk of reduction is then performed with the carbide bur, making a depth cut into the enamel just at the dentin (Figure 28). Moving the bur in counterclockwise fashion will effortlessly peel the enamel away. Then, it is a simple matter of finishing the margins and dropping the occlusal table (Figure 29).
Always be sure to remove all old restorative material in case there is underlying caries.
When dropping margins during preparation, it is critical not to violate the biological width to avoid a crown lengthening procedure.
The biological width zone of the root surface includes the space coronal to the alveolar crest which contains the sulcus (1-3mm), the junctional epithelium (1mm) and the connective tissue attachment (1-2mm)
Cord packing especially on the distal (specifically in this case because of the depth) can potentially tear the PDL ligament, often requiring palatal anesthesia.
In alignment with the cordless concept, a gel hemostatic drying agent is applied (Exposil) (Figure 30).
Comprecaps (Roeko), tightly wound cotton rolls with small concavities, are placed on the tissue and the patient is instructed to bite for no longer than two minutes. Biting for any longer than two minutes can cause muscle fatigue that can result in incorrect occlusion when the patient closes for the final impression. The concavities fit into the sulcus and allow the tooth to drop inside the Comprecap (Figure 31).
After the Comprecap is taken off and the drying agent is removed, there are clean margins, no bleeding, and everything is almost exposed (Figure 32). The H&H technique using Honigum Pro then completes the effect.
Here we have a very precise impression of the anterior tooth using Honigum (Figure 33). Another way to manage the sulcus is using electro-surgery, or diode lasers. If the tissue is managed correctly with lasers, they can remove tissue at the margin at a fine cellular level and amount, but because of the innovative Honigum material, lasers are no longer required for an extremely precise impression.
Fabrication of a long-term provisional bridge prior to extraction
It is difficult to remove bridges made with heavy-body materials. Although very durable, there is a high risk of breakage in any thin areas upon removal. A monophase polyvinyl material lends flexibility upon removal of the provisional, and StatusBlue was an ideal solution for this case.
Swelling on the gingiva is indicative of a fracture in the tooth from buccal to lingual and the radiograph showed a large radiolucency between the roots and the isthmus. The crown on the 2nd molar is removed. The crown on the 1st molar, which is to be extracted, is prepped by cutting it off to the gingiva to create a pontic space. The root surface, what’s left of the occlusal table, is then ditched using a football diamond bur. At this point a long-term bridge can be fabricated (Figure 34).
The long-term provisional, LuxaCrown (DMG), is fabricated and allowed to bench set for 3 minutes (Figure 35).
Because of undercuts in the polyvinyl, restorations made with the material may be difficult to remove. It helps to move the polyvinyl back and forth in order to release, or an instrument can also be used to push it through. A tremendously accurate representation of the occlusion, teeth, and morphology prior to preparation has been captured (Figure 36).
LuxaCrown is a glass filled material in a matrix of multi-functional methacrylates. It contains catalysts, stabilizers, and additives but, more importantly, it does not contain methyl methacrylate. Methacrylate resins have a very strong odor and tend to burn the oral tissue.
Prior to extraction of the molar roots, the provisional can be tried in the mouth and any adjustments, additions, or changes can be made at this time (Figure 37). This avoids introducing foreign bodies into the extraction socket, including polyvinyl and bisacryl composite that can cause a reaction and delay healing.
After removing the provisional the molar roots are extracted, and the bridge cemented.
Over time, LuxaCrown consistently maintains its original color. Throughout a study of thermocycling using distilled water and grape juice, LuxaCrown measured well below the 1.8 acceptable threshold for color detection with the human eye.
Core Buildups and Fiber Reinforced Provisionals
Prior to LuxaCrown, long-term provisionals had to be reinforced with a fiber such as ribbon.
This image is of a preparation (Figure 38). The core-buildups were done, and the amalgam was replaced with composite (Figure 39). In the tooth to be extracted, a pontic space was created using a football diamond (Figure 40).
The ribbon was measured (Figure 41), and in order to have proper fiber reinforcement, the material needed to be laminated. This required two pieces of ribbon that took up quite a bit of room in the provisional (Figure 43) causing weak spots that led to failure. A full fracture typically does not occur due to the ribbon holding it together, but the longevity of the case was compromised.
Because LuxaCrown was unavailable at the time, Luxatemp (DMG) was used. To avoid air bubbles, the tip is placed and kept in the material when dispensing it (Figure 42).
Once placed and laminated, the ribbon will disappear into the tooth (Figure 44).
Once completed, a few pieces of the flaked material had to be removed, but the Luxatemp captured beautiful and precise anatomy of the area (Figure 45).A mosquito diamond was then used to open the interproximal areas to enable cleaning (Figure 46).
LuxaCrown and Luxatemp
This is an image of a bridge with a void (Figure 47). A fistula is present which is why the tooth was fractured, non-restorable and had to be extracted. The provisional can be seen prior to extracting the tooth.
The bridge is tried in to ensure proper fit and patient comfort, and at this time the occlusion can also be evaluated as well as the anatomy, and any additions or changes can be made to the composite. A flowable material is used in order to adhere to the surface. There is virtually no comparison to time spent using methyl methacrylate versus LuxaCrown and a flowable material. As opposed to mixing a monomer, polymer, and hot water, the user simply injects LuxaFlow material and cures it with light.
LuxaCrown is superior to most other materials regarding flexural and compressive strength, and fractural toughness.
Correcting Poor Occlusion using LuxaCrown and Ecosite Bulk Fill
LuxaCrown and Ecosite (DMG) are compatible materials that can be added or used together. Here is a case where Ecosite Bulk Fill composite is added to an existing LuxaCrown bridge to improve esthetics and function.
Here is a case of a 4-unit LuxaCrown bridge that completely lacks occlusion (Figure 49). The patient wore his anteriors down, so they had to be opened up quite a bit.
Once a LuxaCrown bridge is fabricated, do not touch or rub the occlusal surface (or any of the surfaces), as there is an air inhibition layer that allows other composites such as flowables or paste to adhere to it. Without removing the air inhibition layer, add the Ecosite Bulk Fill to the occlusal aspect of the cured LuxaCrown provisional bridge to improve the occlusion (Figure 50).
Prior to curing, a celluloid strip is placed over the Ecosite Bulk Fill composite (Figure 51).
The patient is instructed to close into maximum intercuspation, and then the added composite is light cured (Figure 52).
Additional Ecosite Bulk Fill is added to the facial aspects of the bicuspid and molar to bring them out buccally and ensure that the patient is able to function properly (Figure 53).
Final images show the before and after prior to adding composite to the facials (Figures 54, 55). The overall occlusion was greatly improved by using LuxaCrown and Ecosite while waiting for his bridge to be fabricated in the laboratory.
Ecosite Bulk Fill is manufactured with DMG’s innovative nanotechnology filler. It is a mixture of quality fine glass and nanofiller particles (0.02 – 0.7 um). Compared to similar technologies, Ecosite has an even homogeneous distribution of particles when analyzed under a scanning electron micrograph, presenting a homogenized image of the nanofillers within the composite matrix. This consistency in particle sizes makes the composite material strong and durable.
The University of Iowa conducted a study that concluded that Ecosite bulk fill showed the highest depth of cure when compared to other composite materials.5 It is also ideal for direct restorations and sculpts very well.
With a 5mm depth of cure, Ecosite Bulk Fill requires just one 20-second light cure. It is a packable material with excellent adaptation. Due to its small and consistently-shaped particle sizes, it exhibits excellent polishability for superior esthetics. Ecosite Bulk Fill is part of an easy- to-use system with Ecosite Bond.
- Hoos J, Kaplowitz G. Hydraulic and hydrophobic impressions. Dent Today. 1998 Oct;17(10):77-9.
- Ferrule design and fracture resistance of endodontically treated teeth. Sorensen JA, Engelman MJ. J Prosthet Dent. 1990 May;63(5):529-36.
- Pereira JR, et al. Effect of a crown ferrule on the fracture resistance of endodontically treated teeth restored with prefabricated posts. J Prosthet Dent. 2006 Jan;95(1):50-4.
- Fracture resistance of five pin-retained core build-up materials on teeth with and without extracoronal preparation. Burke FJ, et al. Oper Dent. 2000 Sep-Oct;25(5):388-94.
- Teixeira, M, Vargas, S. Armstrong. IADR 2019 Poster – Performance of different bulk fill dental composite materials. University of Iowa, Department of Operative Dentistry