For some clinicians and technicians there is no bigger challenge than to achieve a natural result with ceramics to restore a single tooth, especially a central incisor, or to provide a nice smile using bonded restorations in a patient with discolored teeth. Success in these situations depends both on the abilities of the two professionals involved and the protocols they can use. Taking advantage of the tooth’s sound structure by using partial bonded restorations instead of preparing the teeth for full-coverage restorations is the way to work for many practitioners around the world. By being as conservative as possible, neither the tooth nor the restoration is weakened, and subsequently, the tooth-restoration complex may last longer. Dentists don’t need their patient’s restorations to last forever, but they do want their patient’s teeth to last forever. Bonding, especially to enamel, will make fragile restorations strong and reliable even in extreme situations.
Articles have been written regarding the most adequate coping material for full-coverage restorations in different clinical situations, such as an ideal-shade abutment versus a discolored abutment. Materials and thicknesses have been discussed; a minimum of 1.4 mm reduction has been suggested for metal-ceramic restorations and a minimum thickness of 0.7 mm is required for the veneering ceramic to develop a correct shade. With bonded ceramic restorations there are still many trends but usually no guidelines for material selection or layering. Only recently, Calgaro et al assessed different material selection and layering technique options for one clinical situation. On the other hand, preparation has been widely discussed, both related to its design and tooth reduction.
The aim of this article is to present the different tooth preparation demands, material selections, and layering techniques for different clinical situations.
TOOTH PREPARATION DESIGN
There are three basic preparation designs for veneers, specifically related to the incisal reduction: the butt joint, preparation with no incisal reduction, and the palatal over- lap/chamfer (Fig 1).
Of these three designs, the incisal butt joint is the most extensively used by clinicians and accepted as best. It is not technically demanding, provides space for the technician to produce adequate incisal effects, allows easy laminate positioning during cementation, and produces the most resistant tooth-restoration complex. The preparation with no incisal reduction also is not technically demanding and provides strong restorations. However, bonding is not easy in some situations, since positioning a relatively “flat” veneer can be difficult and may disrupt the cementation process of many restorations. This design does not provide space for the technician to emulate the incisal effects. Fially, the palatal chamfer is the least resistant design, more prone to fracture of the restoration in the palatal aspect. It is the most complex to prepare properly and requires more reduction than its counterparts, since this design is more retentive and has a more restrictive path of insertion. For these reasons, the basic incisal butt joint design is the authors’ preferred design.
Based on the average enamel thickness and given the fact that preparations should be limited to enamel, if possible, the authors suggest a maximum enamel reduction of 0.3 mm at the gingival level to 2 mm of incisal reduction to keep restorations within the boundaries of the enamel remaining and an adequate percentage of enamel surface in the preparation (Fig 2).
This may be complicated, as enamel thickness diminishes with age. In the adult patient, enamel can be as thin as 0.17 mm in the apical third, averaging 0.31 mm in thickness. In the midfacial third, the enamel is 0.75 mm thick on average. Therefore, dentin exposure in the adult patient is very common, especially in the apical third. Keeping a thin enamel rim is key in such cases. No preparation (prep-less) is another option.
Regarding tooth reduction, LeSage proposed a classification for veneer preparations based on facial reduction, dentin exposure, and remaining enamel. Class I and II are basically addition veneers, for which very little or no enamel reduction is performed. Class III and IV are more conventional preparations for veneers and all-ceramic restorations with more dentin exposure and less enamel re- maining. LeSage32 designed this veneer classification system to help clarify professional communication and allow patients to better understand how much tooth structure will need to be removed. Most times the enamel reduction is not based on the actual thickness of the restoration but on the needs for veneer fitting, future position, and final color. Veneers are typically based on the “additive contouring” concept, in which reduction is thinner than the restoration that will be bonded, since the goal is to restitute the tooth structure lost over the years. If the tooth is labially positioned, how- ever, the reduction will need to be larger than the thickness of the restoration. A decision tree is useful for determining what type of preparation to use based on the space it requires, the remaining enamel available, the shade of the stump, and location of the finishing lines (Fig 3).
RESTORATION THICKNESS AND SHADE
The restoration thickness is key for shade matching. If the stump is the same shade as the surrounding dentition, then the restoration only needs to “transmit” that color through it. A very translucent restoration (contact lens), not more than 0.5 mm in thickness, must be fabricated. If the restoration cannot be too translucent due to an unfavorable stump shade, or there is lack of sufficient tooth structure (coronally, interproximally, or labially), a “self-colored” restoration should be fabricated. This restoration needs more thickness for correct ceramic layering. Figure 4 presents a decision tree for material selection based on restoration thickness and stump shade
CLINICAL SITUATIONS
Single Central Incisor with Adequate Substrate and Shade (Case 1)
When a patient needs an indirect restoration for a central incisor, both clinician and technician need to have clear protocols. If the situation does not require a change of tooth shade and there is enough sound tooth structure, shade will not be a problem and only shape and texture will need to be assessed.
The patient in Case 1 had a fractured right central incisor—the second fracture in that tooth. The more facial position of the right central incisor compared to the surrounding incisors caused the tooth to suffer the impact when the patient hit the area by chance. Therefore, the treatment involved more than just replacing the fractured area with a ceramic fragment. A minimal preparation of the entire facial surface was needed to create a fully aligned facial aspect.
By preparing the tooth minimally, enough space was created for the technician to place a 0.3-mm ceramic restoration with the same profile of the intact left central incisor. By making a very thin veneer, the tooth’s shade could be exploited and the shape remained almost intact. The only challenge was to match the incisal translucent area in the nonsupported area.
Very thin veneers provide what is referred to as a “contact lens effect.” Color does not change, and the cement, or just water, “connects” both surfaces, producing the color transmission through the restoration.
For a full facial ceramic veneer, the authors recommend a 0.3-mm chamfer and a gradual increment in thickness from 0.3 mm in the gingival third to 0.8 mm in the incisal third in order to have space to mask the transition area, where there is no tooth support. Generally a 1.5- to 2-mm incisal free space is created to allow the technician to re- produce the incisal effects of the surrounding dentition. This incisal preparation ends with a butt joint with no palatal overlap.
In any ceramic restoration, the preparation color is a determining factor. This color can be evaluated as favorable, unfavorable, or very unfavorable. The patient in this case has a very favorable tooth color, the only difficulty being the lack of substrate at the incisal third due to a trauma. The choice of the proper dentin (it must have the same color and opacity as the substrate) is necessary in order not to perceive any chromatic discrepancy in the transition area. The remaining layering was done according to a traditional chromatic map by taking the shade zonally. Opalescent Transparent 1 (d.SIGN, Ivoclar Vivadent) was the only ceramic powder applied to the area where there was a favorable substrate. This allows the light to circulate and the substrate color to provide the dentin color for the restoration.
Single Central Incisor with Not Enough Substrate and Slight Discoloration (Case 2)
When the substrate is not ideal, the case is much more challenging. There are two situations in which the substrate is not ideal: when there is not enough tooth structure optically and when the abutments are discolored. In both situations, the “contact lens effect” is not possible. Therefore, color becomes an issue. Shape may be easy to copy, but reproducing the color is more difficult. Porcelain layering is complex because all the color characteristics have to come from the restoration itself. This is referred to as a “self-colored restoration.”
When restoring central incisors with feldspathic porcelain, the chance of error is high, especially in a clinician’s first cases and particularly in cases with discolored abutments. There are no second chances with feldspathic porcelain veneers other than redoing the restoration. Some technicians may fabricate two or three veneers to increase the chance for success with feldspathic porcelain, but they still may not have success. Therefore, using a material that allows try-ins, such as lithium disilicate, is best.
Lithium disilicate (e.max, Ivoclar) not only allows try-ins but also permits use of the classic bonding technique, with only a change of the etching time of the ceramic portion. The restoration needs more space (minimal thickness is 0.6 to 0.8 mm), so it may look slightly bulky in the cervical aspect, where the average enamel thickness is 0.4 mm.
The patient in Case 2 presented with a fracture of almost half of the tooth, and the remaining tooth structure did not have a desirable shade. A lithium disilicate coping and fluorapatite-reinforced ceramic (e.max Ceram) were therefore used.
Achieving the correct translucency is key in the anterior segment. Blending of the nonsupported area and the tooth-supported area with a lithium disilicate coping is helpful and provides the adequate substrate on which to work. Using a pressed ceramic framework allows a bisque bake try-in, so mistakes made in the first bake can be corrected. Then a conventional ceramic layering can be per- formed.
Although the shade of the substrate in this case would allow the use of an LT ingot, to better control opacity an MO1 ingot was used with a complete ceramic layering.
Diastema Closure (Case 3)
When a patient desires spaces to be closed, the situation is similar to having insufficient tooth structure—instead of a vertical lack of structure, it is a horizontal lack of structure. These situations demand a precise degree of ceramic layering, as beautifully depicted in the article by Calgaro et al. Layering has to be done in order to block some of the light transmitted through the restoration and thus eliminating the excessive translucency that will produce an unfavorable outcome.
The patient in Case 3 presents a favorable substrate color, which allows a minimally invasive preparation in the facial aspect that will provide the space needed for suit- able translucency and at the same time allow the natural substrate to give the dentin color to the restoration. The ceramic layering will be similar to that presented in Case 1. In the interproximal aspect, the preparation has to be more aggressive because the margin must be subgingival in or- der to alter the tooth emergence profile to close a very noticeable diastema. When layering the interproximal area, opaque dentin powder substitutes for the absence of natural dentin.
Discolored Teeth: Tetracycline Stains + Diastemata (Case 4)
Tetracycline stains are usually a challenge for the restor- ative dentist. Many patients try whitening treatments, but the success rate is low and the recurrence high. For this reason, patients with tetracycline staining often ultimately request veneers.
The problem with tetracycline staining is that it comes from within the tooth. The closer dentin is approached during preparation, the darker the tetracycline-stained tooth will be. It is also necessary to remain within the boundaries of enamel in order to achieve and maintain a successful bond of the restoration to the tooth surface. Therefore, a layering strategy is needed to block light within tenths of a millimeter. This means that while the preparation has to be thin, the restoration also needs to be thick enough to block the dark substrate. Therefore, the restoration will need to be overcontoured. The patient in Case 4 has a very unfavorable substrate color. There is no pressed ceramic color with the capability to opaque 100% of the substrate with minimal thickness that also will provide acceptable translucency in this situa- tion. The only option is an opaqued ceramic veneer.39 This ceramic veneer allows opaque to be placed as a wash, as is done with metal-ceramic crowns. A conventional layer- ing procedure can be used, except that opaque/deep den- tin will substitute for the conventional dentin layer to obtain a dentin color with minimal thickness.
CONCLUSIONS
Care must be used in all the steps described. Planning is important, but proper execution of the blueprint is required. The proper tooth preparation, correct margin position, and appropriate material selection with the indicated ceramic layering will make all the difference in the outcome. As the great German architect Ludwig Mies van der Rohe said, “God is in the details".
Articles have been written regarding the most adequate coping material for full-coverage restorations in different clinical situations, such as an ideal-shade abutment versus a discolored abutment. Materials and thicknesses have been discussed; a minimum of 1.4 mm reduction has been suggested for metal-ceramic restorations and a minimum thickness of 0.7 mm is required for the veneering ceramic to develop a correct shade. With bonded ceramic restorations there are still many trends but usually no guidelines for material selection or layering. Only recently, Calgaro et al assessed different material selection and layering technique options for one clinical situation. On the other hand, preparation has been widely discussed, both related to its design and tooth reduction.
The aim of this article is to present the different tooth preparation demands, material selections, and layering techniques for different clinical situations.
TOOTH PREPARATION DESIGN
There are three basic preparation designs for veneers, specifically related to the incisal reduction: the butt joint, preparation with no incisal reduction, and the palatal over- lap/chamfer (Fig 1).
Of these three designs, the incisal butt joint is the most extensively used by clinicians and accepted as best. It is not technically demanding, provides space for the technician to produce adequate incisal effects, allows easy laminate positioning during cementation, and produces the most resistant tooth-restoration complex. The preparation with no incisal reduction also is not technically demanding and provides strong restorations. However, bonding is not easy in some situations, since positioning a relatively “flat” veneer can be difficult and may disrupt the cementation process of many restorations. This design does not provide space for the technician to emulate the incisal effects. Fially, the palatal chamfer is the least resistant design, more prone to fracture of the restoration in the palatal aspect. It is the most complex to prepare properly and requires more reduction than its counterparts, since this design is more retentive and has a more restrictive path of insertion. For these reasons, the basic incisal butt joint design is the authors’ preferred design.
Based on the average enamel thickness and given the fact that preparations should be limited to enamel, if possible, the authors suggest a maximum enamel reduction of 0.3 mm at the gingival level to 2 mm of incisal reduction to keep restorations within the boundaries of the enamel remaining and an adequate percentage of enamel surface in the preparation (Fig 2).
This may be complicated, as enamel thickness diminishes with age. In the adult patient, enamel can be as thin as 0.17 mm in the apical third, averaging 0.31 mm in thickness. In the midfacial third, the enamel is 0.75 mm thick on average. Therefore, dentin exposure in the adult patient is very common, especially in the apical third. Keeping a thin enamel rim is key in such cases. No preparation (prep-less) is another option.
Regarding tooth reduction, LeSage proposed a classification for veneer preparations based on facial reduction, dentin exposure, and remaining enamel. Class I and II are basically addition veneers, for which very little or no enamel reduction is performed. Class III and IV are more conventional preparations for veneers and all-ceramic restorations with more dentin exposure and less enamel re- maining. LeSage32 designed this veneer classification system to help clarify professional communication and allow patients to better understand how much tooth structure will need to be removed. Most times the enamel reduction is not based on the actual thickness of the restoration but on the needs for veneer fitting, future position, and final color. Veneers are typically based on the “additive contouring” concept, in which reduction is thinner than the restoration that will be bonded, since the goal is to restitute the tooth structure lost over the years. If the tooth is labially positioned, how- ever, the reduction will need to be larger than the thickness of the restoration. A decision tree is useful for determining what type of preparation to use based on the space it requires, the remaining enamel available, the shade of the stump, and location of the finishing lines (Fig 3).
RESTORATION THICKNESS AND SHADE
The restoration thickness is key for shade matching. If the stump is the same shade as the surrounding dentition, then the restoration only needs to “transmit” that color through it. A very translucent restoration (contact lens), not more than 0.5 mm in thickness, must be fabricated. If the restoration cannot be too translucent due to an unfavorable stump shade, or there is lack of sufficient tooth structure (coronally, interproximally, or labially), a “self-colored” restoration should be fabricated. This restoration needs more thickness for correct ceramic layering. Figure 4 presents a decision tree for material selection based on restoration thickness and stump shade
CLINICAL SITUATIONS
Single Central Incisor with Adequate Substrate and Shade (Case 1)
When a patient needs an indirect restoration for a central incisor, both clinician and technician need to have clear protocols. If the situation does not require a change of tooth shade and there is enough sound tooth structure, shade will not be a problem and only shape and texture will need to be assessed.
The patient in Case 1 had a fractured right central incisor—the second fracture in that tooth. The more facial position of the right central incisor compared to the surrounding incisors caused the tooth to suffer the impact when the patient hit the area by chance. Therefore, the treatment involved more than just replacing the fractured area with a ceramic fragment. A minimal preparation of the entire facial surface was needed to create a fully aligned facial aspect.
By preparing the tooth minimally, enough space was created for the technician to place a 0.3-mm ceramic restoration with the same profile of the intact left central incisor. By making a very thin veneer, the tooth’s shade could be exploited and the shape remained almost intact. The only challenge was to match the incisal translucent area in the nonsupported area.
Very thin veneers provide what is referred to as a “contact lens effect.” Color does not change, and the cement, or just water, “connects” both surfaces, producing the color transmission through the restoration.
For a full facial ceramic veneer, the authors recommend a 0.3-mm chamfer and a gradual increment in thickness from 0.3 mm in the gingival third to 0.8 mm in the incisal third in order to have space to mask the transition area, where there is no tooth support. Generally a 1.5- to 2-mm incisal free space is created to allow the technician to re- produce the incisal effects of the surrounding dentition. This incisal preparation ends with a butt joint with no palatal overlap.
In any ceramic restoration, the preparation color is a determining factor. This color can be evaluated as favorable, unfavorable, or very unfavorable. The patient in this case has a very favorable tooth color, the only difficulty being the lack of substrate at the incisal third due to a trauma. The choice of the proper dentin (it must have the same color and opacity as the substrate) is necessary in order not to perceive any chromatic discrepancy in the transition area. The remaining layering was done according to a traditional chromatic map by taking the shade zonally. Opalescent Transparent 1 (d.SIGN, Ivoclar Vivadent) was the only ceramic powder applied to the area where there was a favorable substrate. This allows the light to circulate and the substrate color to provide the dentin color for the restoration.
Single Central Incisor with Not Enough Substrate and Slight Discoloration (Case 2)
When the substrate is not ideal, the case is much more challenging. There are two situations in which the substrate is not ideal: when there is not enough tooth structure optically and when the abutments are discolored. In both situations, the “contact lens effect” is not possible. Therefore, color becomes an issue. Shape may be easy to copy, but reproducing the color is more difficult. Porcelain layering is complex because all the color characteristics have to come from the restoration itself. This is referred to as a “self-colored restoration.”
When restoring central incisors with feldspathic porcelain, the chance of error is high, especially in a clinician’s first cases and particularly in cases with discolored abutments. There are no second chances with feldspathic porcelain veneers other than redoing the restoration. Some technicians may fabricate two or three veneers to increase the chance for success with feldspathic porcelain, but they still may not have success. Therefore, using a material that allows try-ins, such as lithium disilicate, is best.
Lithium disilicate (e.max, Ivoclar) not only allows try-ins but also permits use of the classic bonding technique, with only a change of the etching time of the ceramic portion. The restoration needs more space (minimal thickness is 0.6 to 0.8 mm), so it may look slightly bulky in the cervical aspect, where the average enamel thickness is 0.4 mm.
The patient in Case 2 presented with a fracture of almost half of the tooth, and the remaining tooth structure did not have a desirable shade. A lithium disilicate coping and fluorapatite-reinforced ceramic (e.max Ceram) were therefore used.
Achieving the correct translucency is key in the anterior segment. Blending of the nonsupported area and the tooth-supported area with a lithium disilicate coping is helpful and provides the adequate substrate on which to work. Using a pressed ceramic framework allows a bisque bake try-in, so mistakes made in the first bake can be corrected. Then a conventional ceramic layering can be per- formed.
Although the shade of the substrate in this case would allow the use of an LT ingot, to better control opacity an MO1 ingot was used with a complete ceramic layering.
Diastema Closure (Case 3)
When a patient desires spaces to be closed, the situation is similar to having insufficient tooth structure—instead of a vertical lack of structure, it is a horizontal lack of structure. These situations demand a precise degree of ceramic layering, as beautifully depicted in the article by Calgaro et al. Layering has to be done in order to block some of the light transmitted through the restoration and thus eliminating the excessive translucency that will produce an unfavorable outcome.
The patient in Case 3 presents a favorable substrate color, which allows a minimally invasive preparation in the facial aspect that will provide the space needed for suit- able translucency and at the same time allow the natural substrate to give the dentin color to the restoration. The ceramic layering will be similar to that presented in Case 1. In the interproximal aspect, the preparation has to be more aggressive because the margin must be subgingival in or- der to alter the tooth emergence profile to close a very noticeable diastema. When layering the interproximal area, opaque dentin powder substitutes for the absence of natural dentin.
Discolored Teeth: Tetracycline Stains + Diastemata (Case 4)
Tetracycline stains are usually a challenge for the restor- ative dentist. Many patients try whitening treatments, but the success rate is low and the recurrence high. For this reason, patients with tetracycline staining often ultimately request veneers.
The problem with tetracycline staining is that it comes from within the tooth. The closer dentin is approached during preparation, the darker the tetracycline-stained tooth will be. It is also necessary to remain within the boundaries of enamel in order to achieve and maintain a successful bond of the restoration to the tooth surface. Therefore, a layering strategy is needed to block light within tenths of a millimeter. This means that while the preparation has to be thin, the restoration also needs to be thick enough to block the dark substrate. Therefore, the restoration will need to be overcontoured. The patient in Case 4 has a very unfavorable substrate color. There is no pressed ceramic color with the capability to opaque 100% of the substrate with minimal thickness that also will provide acceptable translucency in this situa- tion. The only option is an opaqued ceramic veneer.39 This ceramic veneer allows opaque to be placed as a wash, as is done with metal-ceramic crowns. A conventional layer- ing procedure can be used, except that opaque/deep den- tin will substitute for the conventional dentin layer to obtain a dentin color with minimal thickness.
CONCLUSIONS
Care must be used in all the steps described. Planning is important, but proper execution of the blueprint is required. The proper tooth preparation, correct margin position, and appropriate material selection with the indicated ceramic layering will make all the difference in the outcome. As the great German architect Ludwig Mies van der Rohe said, “God is in the details".
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