Tooth wear against ceramic crowns in posterior region: a systematic literature review
The objective of this systematic review was to assess tooth wear against ceramic crowns in posterior region in vitro and in vivo. An electronic PubMed search was conducted to identify studies on tooth wear against ceramic crowns in posterior region. The selected studies were analyzed in regard to type of crowns, natural antagonist, measuring protocol and outcome.
From a yield of 1 000 titles, 43 articles were selected for full-text analysis; finally, no in vitro and only five in vivo studies met the inclusion criteria. As there is heterogeneity in design, used measuring method, ceramics and analysis-form, a meta-analysis was not possible. Results of these studies are very controversial which makes a scientifically valid comparison impossible.
This review indicated that some all-ceramic crowns are as wear friendly as metal-ceramic crowns. Up to now, it has been impossible to associate tooth wear with any specific causal agent. The role of ceramic surface leather treatment that might be responsible for the changing in rate of tooth wear seems undetermined as yet through clinical trials.
The literature reveals that studies on this topic are subject to a substantial amount of bias. Therefore, additional clinical studies, properly designed to diminish bias, are warranted.Wear of tooth structure is a natural unavoidable process which occurs when tooth and tooth, or tooth and restoration are in contact and slide against each other.
However, this natural process may be accelerated by the introduction of restorations whose properties of wear differ from those of the tooth structure that they slide against. It has been shown that enamel may be subject to accelerated wear when opposed by ceramic. Therefore and despite the truth that a constant wear of the entire dentition is possible independent of dental restorations, it is desirable that wear behavior of restorative materials is similar to natural enamel, because excessive wear could lead to clinical problems such as damage of teeth occluding surfaces, loss of vertical dimension of occlusion, poor masticatory function associated with temporomandibular joint remodeling, dentine hypersinsivity or death of the tooth and at least may lead to esthetic impairment.
In the oral cavity, many factors contribute to the wear of enamel and dentin, such as the nature of the occlusal contacts with antagonist teeth (attrition), chewing of food items, tooth brushing with toothpaste, inhalation of dust (abrasion), acidic attack due to the consumption of certain fruits and beverages, inhalation of industrial acids or vomiting and regurgitation of gastric juice as in the case of bulimia and anorexia nervosa (corrosion).In order to observe and assess wear, it is necessary to understand tooth wear mechanisms and how it can be measured and evaluated, both clinically and in the laboratory. The terms abrasion, attrition and even corrosion were often used to identify the same thing which is the tooth wear caused mostly by alimentation and utilities use.
Contrary, nowadays there is an agreement that the terms, abrasion, attrition and corrosion describe different mechanisms.Attrition: tooth-to-tooth contact causes this form of wear, this occurs without the presence of food or foreign substances during deglutition and clenching; it is typically characterized by the facets on a tooth and the opposing tooth. It becomes more serious during bruxism.Abrasion: is the wear caused by friction between a tooth and an exogenous phone agent.
The 'masticatory abrasion', usually occurs by friction from the food and abrasion, which is a result of bad oral habits such as nail biting or hard objects such as pens, pencils or pipes, opening hair pins with teeth. Occupational abrasion may occur among hairdressers because of opening hair pins with their teeth, tailors through cutting thread with their teeth, shoemakers who hold nails between their teeth and musicians who play wind instruments.Tooth-cleaning, habits such as extreme tooth brushing, improper use of dental floss and toothpicks are the most common cause of abrasion.
Even normal tooth-cleaning practices produce some abrasion of dentine over a lifetime. In Western populations, the major abrasive agent is toothpaste, which affects dentine much more than enamel. Tooth brushing without paste has no effect on enamel and clinically negligible effects on dentine.
Corrosion: Is the loss of tooth surfaces caused by chemical dissolution without the involvement phone of plaque. Depending on the source of the acids causing the dissolution, there are two types of corrosion, intrinsic and extrinsic corrosion. The tooth corrosion caused by intrinsic sources such as bulimia and gastro esophageal reflux disease, shows enamel surfaces which appears to be translucent and thin; moreover bowel-shaped defects on the posterior occlusal surfaces and an enamel lost on the anterior palatal surfaces can be recognized.
It has been reported that consuming drinks and food with a pH value of less than 5.5 can cause corrosion and demineralize teeth. Corrosive damage to anterior teeth may affect workers in industries where they are continuously exposed to acid droplets and fumes.
Softened enamel exposed to saliva for an adequate time can regain mineral and thus re-acquire mechanical strength. On the other hand, it has been stated that fluoridated toothpaste had a protective effect on enamel corrosion progression.The observation of and studies show that individual wear mechanisms rarely act alone but interact with each other so that tooth wear is the result of three processes: abrasion, attrition and corrosion.
One of the most popular measuring methods of tooth wear is the direct measuring using clinical tooth wear indices; with this method, special equipment is not required, but the assessment is subjective and it takes a long time to get significant results. In addition, most tooth wear indices use unclear and complicated leather diagnostic criteria. Other limitations of these indices are no clear classification and quantification of tooth wear, besides the limited ability to determine the critical value of acceptable wear.
Also, there are a lot of tooth wear index which make it difficult to achieve standardized and reliable tooth wear quantification and that leads to difficulties by comparing the results of various studies.Indirect techniques for evaluation of tooth wear suggest measuring the loss of tooth surface using cast replicas. For more accurate quantification, image analysis, scanning electron microscopy, computer graphics, three dimensional (3D) scanner and profilometry were developed.
Disadvantages can be inaccurate replicas and repositioning problems, due to the fact that reproducing of tooth surfaces with impressions before scanning always adds a source of error.Various clinical studies applied these 3D measuring techniques, which allow 3D scanning of the entire tooth surface without affecting the tooth surfaces. These techniques are highly accurate, quantitative, applicable to both the clinic and the laboratory, and provides storable 3D databases that enable comparison to other 3D databases.
3D images can be obtained using contact profilers, non-contact white light, micro/cone computerized tomography (CT) scanners, laser scanners and computer-aided design/computer-aided manufacturing (CAD/CAM) systems leather such as Cerec and Cercon systems. However, 3D canning requires a specialized hardware and software and has the disadvantage of time-consuming, high cost and the limited availability to clinical investigators. Measurement accuracy of the cone-beam CT scanners approximates few hundred microns, and thus they have limited ability to determine tooth wear on the occlusal surfaces.
Direct intraoral 3D scanning of teeth, e.
g.
, intraoral digital camera of Cerec, is accurate and requires less number of steps when compared to the indirect scanning of models, but the need for spraying teeth with white powder might decrease the accuracy of measurement.Clinical studies which evaluate dental wear are very time-consuming, expensive and have the disadvantage that a lot of factors such as chewing forces cannot be controlled. Thus, laboratory mastication simulation has been used by a lot of investigators to study single parameters of the wear processes.
But even the wear simulations show considerable variability and do not simulate the clinical condition, because the loads, speeds and abrasives used are often more severe than the masticatory standards.As mentioned before, wear of teeth differs according to the different restorative materials used as antagonist. Ceramic reconstructions have become increasingly popular as a result of rising patient demands for more aesthetics.
But the main disadvantage of ceramics is their high abrasiveness to opposing enamel. Various types of ceramic crowns can be used as fixed dental prosthesis; some entirely made of the same ceramic material through out and others consist of high-strength ceramic substructure veneered with porcelain; in addition metal-ceramic crowns veneered with porcelain are still used. Recently, the high-strength zirconia ceramic (yttrium-oxide tetragonal zirconia polycrystal) was introduced for dental application; it has a high bending strength and fracture toughness.
The clinical use of this ceramic is increasing because of its chemical and dimensional stability, its higher fracture toughness, hardness and frictional resistance in comparison to conventional dental porcelain. But the weak point of a zirconia restoration is at this time veneer chipping or cracking, whereas other all-ceramic restorations show a percentage of framework fracture.Using CAD/CAM techniques, it has become possible to produce full-zirconia restorations with occlusal design that do not need to be veneered (Zirluna; ACF GmbH, Amberg, Germany; Zirkonzahn Prettau; Zirkonzahn GmbH, Bruneck, Italy; BruxiZir; Glidewell Laboratories, Newport Beach, CA, USA); and must have the advantage that no chipping of the veneering porcelain will occur because of the absence of this veneering layer.
Mono-block restorations could be also fabricated from glass ceramics; however, they are less stable in comparison to zirconia-based restorations and their indication range is clearly limited to single crowns and small fixed dental prostheses.At this point of research, some of the features of ceramic which affect enamel wear were evaluated:Hardness of ceramics was always associated with the greater abrasiveness against teeth, but some studies showed that the hardness of ceramics will not substantially lead to wear of the opposing teeth. On the other hand, the degree of wear is more affected by the surface structure and the roughness of the restoration or environmental factors.
Various investigations on the effect of ceramic hardness on the dental wear have supported this fact by their finding that soft ceramics caused more abrasion against enamel (enamel abrasion) in comparison with harder ceramics.Similarly, more wear was expected from zirconia, because zirconia has strong surface hardness, but certain investigations reported that less wear of antagonistic teeth was measured with zirconia than with the feldspathic dental porcelain. Rosentritt has no wear traces for enamel against zirconia using a chewing simulation.
It was also reported that the wear rate of zirconia is bad in water and even under dry sliding conditions, that suggests that the hardness of ceramics alone is not a reliable predictor of the wear of opposing teeth.Resistance to friction: Many factors may affect the frictional resistance of the both teeth and ceramic restorations when coming together in contact, e.g., morphology, properties and structure of tooth and restoration, as well as mastication movements.
With increased coefficient of friction, more wear of the tooth structure would be expected. It has been shown that high loads, rough surfaces and high sliding speed caused an increase in the coefficient of friction which leads to greater wear. Therefore, meticulously polished ceramic surfaces would lead to an decrease in the rates of wear of the opposing tooth surfaces.
Porosity: Undesirable characteristic of ceramic like decreased strength, reduced aesthetics and increased plaque accumulation can be impart by porosity. Furthermore, during the wear process, a subsurface porosity of ceramic may be exposed, then the sharp edge of the defect will cause increased wear in the opposing teeth; therefore, porosity of dental porcelain needs to be minimized.Some parameters are associated with increased porosity of dental ceramics such as particle size, higher sintering temperature and longer sintering time.
More porosity was showed in low-fusing porcelains with a fine grain size than in conventional feldspathic porcelain. It was also reported that aluminous porcelain has a higher viscosity than conventional feldspathic porcelain, which requires a higher firing temperature to increase the wetting of crystals and the glassy matrix and because of that, a higher porosity of aluminus porcelain is expected. Although a reduction of porosity is expected by longer sintering time, Piddock and Cheung reported an increase in porosity with increasing sintering time, because of the limited ability of air to escape during rapid firing.
During the building of porcelain layers in order to simulate the teeth tissues, the influence of mechanical vibration on the reduction of porosity is limited.Full-zirconia restorations without veneering are free from the problems associated with porosity, because they have no veneer layer and their microstructure shows no open porosity.Effect of roughness of ceramic surfaces: The surface treatment of all ceramic crowns may be responsible for the changing in the rate of enamel wear.
Glazing of ceramic restorations produces a smooth, aesthetic and hygienic surface and is considered as a step which reduces the amount of wear of opposing teeth and restorations, but this layer of glaze can be removed shortly after being in function or by a required occlusal adjustment that may lead to more abrasive wear of the opposing teeth because of the insufficiently polished exposed surface of the crown.Jagger suggested in his study that the amounts of wear of enamel caused by glazed and unglazed porcelain are similar. Some investigators found that the glazed ceramic surfaces are smoother than the polished ones.
However, other authors found no significant differences between glazed and polished ceramic surfaces. Contradictorily, some investigations confirmed the finding that the smoothness of polished ceramic surfaces is similar or better than the glazed surfaces. This conclusion was supported through various studies, which found that the glazed surfaces caused more teeth wear compared to polished surfaces.
Functional finishing of ceramic surfaces during the wear process was documented by Monasky, who reported in his study that the initially high rate of wear decreased over time, suggesting that the effect of surface roughness on wear may be self-limiting.However, it must be considered that the factors described above are results of studies depending on wear or chewing simulation device and these results are contradictory.The aim of this manuscript was to provide a literature review about the tooth wear against ceramic crowns in posterior region both and .
This systematic review was prepared following the preferred reporting items for systematic reviews and meta-analyses statement guidelines (). This article focuses as well on measuring methods of tooth wear available in dental literature and on factors related to ceramic materials
From a yield of 1 000 titles, 43 articles were selected for full-text analysis; finally, no in vitro and only five in vivo studies met the inclusion criteria. As there is heterogeneity in design, used measuring method, ceramics and analysis-form, a meta-analysis was not possible. Results of these studies are very controversial which makes a scientifically valid comparison impossible.
This review indicated that some all-ceramic crowns are as wear friendly as metal-ceramic crowns. Up to now, it has been impossible to associate tooth wear with any specific causal agent. The role of ceramic surface leather treatment that might be responsible for the changing in rate of tooth wear seems undetermined as yet through clinical trials.
The literature reveals that studies on this topic are subject to a substantial amount of bias. Therefore, additional clinical studies, properly designed to diminish bias, are warranted.Wear of tooth structure is a natural unavoidable process which occurs when tooth and tooth, or tooth and restoration are in contact and slide against each other.
However, this natural process may be accelerated by the introduction of restorations whose properties of wear differ from those of the tooth structure that they slide against. It has been shown that enamel may be subject to accelerated wear when opposed by ceramic. Therefore and despite the truth that a constant wear of the entire dentition is possible independent of dental restorations, it is desirable that wear behavior of restorative materials is similar to natural enamel, because excessive wear could lead to clinical problems such as damage of teeth occluding surfaces, loss of vertical dimension of occlusion, poor masticatory function associated with temporomandibular joint remodeling, dentine hypersinsivity or death of the tooth and at least may lead to esthetic impairment.
In the oral cavity, many factors contribute to the wear of enamel and dentin, such as the nature of the occlusal contacts with antagonist teeth (attrition), chewing of food items, tooth brushing with toothpaste, inhalation of dust (abrasion), acidic attack due to the consumption of certain fruits and beverages, inhalation of industrial acids or vomiting and regurgitation of gastric juice as in the case of bulimia and anorexia nervosa (corrosion).In order to observe and assess wear, it is necessary to understand tooth wear mechanisms and how it can be measured and evaluated, both clinically and in the laboratory. The terms abrasion, attrition and even corrosion were often used to identify the same thing which is the tooth wear caused mostly by alimentation and utilities use.
Contrary, nowadays there is an agreement that the terms, abrasion, attrition and corrosion describe different mechanisms.Attrition: tooth-to-tooth contact causes this form of wear, this occurs without the presence of food or foreign substances during deglutition and clenching; it is typically characterized by the facets on a tooth and the opposing tooth. It becomes more serious during bruxism.Abrasion: is the wear caused by friction between a tooth and an exogenous phone agent.
The 'masticatory abrasion', usually occurs by friction from the food and abrasion, which is a result of bad oral habits such as nail biting or hard objects such as pens, pencils or pipes, opening hair pins with teeth. Occupational abrasion may occur among hairdressers because of opening hair pins with their teeth, tailors through cutting thread with their teeth, shoemakers who hold nails between their teeth and musicians who play wind instruments.Tooth-cleaning, habits such as extreme tooth brushing, improper use of dental floss and toothpicks are the most common cause of abrasion.
Even normal tooth-cleaning practices produce some abrasion of dentine over a lifetime. In Western populations, the major abrasive agent is toothpaste, which affects dentine much more than enamel. Tooth brushing without paste has no effect on enamel and clinically negligible effects on dentine.
Corrosion: Is the loss of tooth surfaces caused by chemical dissolution without the involvement phone of plaque. Depending on the source of the acids causing the dissolution, there are two types of corrosion, intrinsic and extrinsic corrosion. The tooth corrosion caused by intrinsic sources such as bulimia and gastro esophageal reflux disease, shows enamel surfaces which appears to be translucent and thin; moreover bowel-shaped defects on the posterior occlusal surfaces and an enamel lost on the anterior palatal surfaces can be recognized.
It has been reported that consuming drinks and food with a pH value of less than 5.5 can cause corrosion and demineralize teeth. Corrosive damage to anterior teeth may affect workers in industries where they are continuously exposed to acid droplets and fumes.
Softened enamel exposed to saliva for an adequate time can regain mineral and thus re-acquire mechanical strength. On the other hand, it has been stated that fluoridated toothpaste had a protective effect on enamel corrosion progression.The observation of and studies show that individual wear mechanisms rarely act alone but interact with each other so that tooth wear is the result of three processes: abrasion, attrition and corrosion.
One of the most popular measuring methods of tooth wear is the direct measuring using clinical tooth wear indices; with this method, special equipment is not required, but the assessment is subjective and it takes a long time to get significant results. In addition, most tooth wear indices use unclear and complicated leather diagnostic criteria. Other limitations of these indices are no clear classification and quantification of tooth wear, besides the limited ability to determine the critical value of acceptable wear.
Also, there are a lot of tooth wear index which make it difficult to achieve standardized and reliable tooth wear quantification and that leads to difficulties by comparing the results of various studies.Indirect techniques for evaluation of tooth wear suggest measuring the loss of tooth surface using cast replicas. For more accurate quantification, image analysis, scanning electron microscopy, computer graphics, three dimensional (3D) scanner and profilometry were developed.
Disadvantages can be inaccurate replicas and repositioning problems, due to the fact that reproducing of tooth surfaces with impressions before scanning always adds a source of error.Various clinical studies applied these 3D measuring techniques, which allow 3D scanning of the entire tooth surface without affecting the tooth surfaces. These techniques are highly accurate, quantitative, applicable to both the clinic and the laboratory, and provides storable 3D databases that enable comparison to other 3D databases.
3D images can be obtained using contact profilers, non-contact white light, micro/cone computerized tomography (CT) scanners, laser scanners and computer-aided design/computer-aided manufacturing (CAD/CAM) systems leather such as Cerec and Cercon systems. However, 3D canning requires a specialized hardware and software and has the disadvantage of time-consuming, high cost and the limited availability to clinical investigators. Measurement accuracy of the cone-beam CT scanners approximates few hundred microns, and thus they have limited ability to determine tooth wear on the occlusal surfaces.
Direct intraoral 3D scanning of teeth, e.
g.
, intraoral digital camera of Cerec, is accurate and requires less number of steps when compared to the indirect scanning of models, but the need for spraying teeth with white powder might decrease the accuracy of measurement.Clinical studies which evaluate dental wear are very time-consuming, expensive and have the disadvantage that a lot of factors such as chewing forces cannot be controlled. Thus, laboratory mastication simulation has been used by a lot of investigators to study single parameters of the wear processes.
But even the wear simulations show considerable variability and do not simulate the clinical condition, because the loads, speeds and abrasives used are often more severe than the masticatory standards.As mentioned before, wear of teeth differs according to the different restorative materials used as antagonist. Ceramic reconstructions have become increasingly popular as a result of rising patient demands for more aesthetics.
But the main disadvantage of ceramics is their high abrasiveness to opposing enamel. Various types of ceramic crowns can be used as fixed dental prosthesis; some entirely made of the same ceramic material through out and others consist of high-strength ceramic substructure veneered with porcelain; in addition metal-ceramic crowns veneered with porcelain are still used. Recently, the high-strength zirconia ceramic (yttrium-oxide tetragonal zirconia polycrystal) was introduced for dental application; it has a high bending strength and fracture toughness.
The clinical use of this ceramic is increasing because of its chemical and dimensional stability, its higher fracture toughness, hardness and frictional resistance in comparison to conventional dental porcelain. But the weak point of a zirconia restoration is at this time veneer chipping or cracking, whereas other all-ceramic restorations show a percentage of framework fracture.Using CAD/CAM techniques, it has become possible to produce full-zirconia restorations with occlusal design that do not need to be veneered (Zirluna; ACF GmbH, Amberg, Germany; Zirkonzahn Prettau; Zirkonzahn GmbH, Bruneck, Italy; BruxiZir; Glidewell Laboratories, Newport Beach, CA, USA); and must have the advantage that no chipping of the veneering porcelain will occur because of the absence of this veneering layer.
Mono-block restorations could be also fabricated from glass ceramics; however, they are less stable in comparison to zirconia-based restorations and their indication range is clearly limited to single crowns and small fixed dental prostheses.At this point of research, some of the features of ceramic which affect enamel wear were evaluated:Hardness of ceramics was always associated with the greater abrasiveness against teeth, but some studies showed that the hardness of ceramics will not substantially lead to wear of the opposing teeth. On the other hand, the degree of wear is more affected by the surface structure and the roughness of the restoration or environmental factors.
Various investigations on the effect of ceramic hardness on the dental wear have supported this fact by their finding that soft ceramics caused more abrasion against enamel (enamel abrasion) in comparison with harder ceramics.Similarly, more wear was expected from zirconia, because zirconia has strong surface hardness, but certain investigations reported that less wear of antagonistic teeth was measured with zirconia than with the feldspathic dental porcelain. Rosentritt has no wear traces for enamel against zirconia using a chewing simulation.
It was also reported that the wear rate of zirconia is bad in water and even under dry sliding conditions, that suggests that the hardness of ceramics alone is not a reliable predictor of the wear of opposing teeth.Resistance to friction: Many factors may affect the frictional resistance of the both teeth and ceramic restorations when coming together in contact, e.g., morphology, properties and structure of tooth and restoration, as well as mastication movements.
With increased coefficient of friction, more wear of the tooth structure would be expected. It has been shown that high loads, rough surfaces and high sliding speed caused an increase in the coefficient of friction which leads to greater wear. Therefore, meticulously polished ceramic surfaces would lead to an decrease in the rates of wear of the opposing tooth surfaces.
Porosity: Undesirable characteristic of ceramic like decreased strength, reduced aesthetics and increased plaque accumulation can be impart by porosity. Furthermore, during the wear process, a subsurface porosity of ceramic may be exposed, then the sharp edge of the defect will cause increased wear in the opposing teeth; therefore, porosity of dental porcelain needs to be minimized.Some parameters are associated with increased porosity of dental ceramics such as particle size, higher sintering temperature and longer sintering time.
More porosity was showed in low-fusing porcelains with a fine grain size than in conventional feldspathic porcelain. It was also reported that aluminous porcelain has a higher viscosity than conventional feldspathic porcelain, which requires a higher firing temperature to increase the wetting of crystals and the glassy matrix and because of that, a higher porosity of aluminus porcelain is expected. Although a reduction of porosity is expected by longer sintering time, Piddock and Cheung reported an increase in porosity with increasing sintering time, because of the limited ability of air to escape during rapid firing.
During the building of porcelain layers in order to simulate the teeth tissues, the influence of mechanical vibration on the reduction of porosity is limited.Full-zirconia restorations without veneering are free from the problems associated with porosity, because they have no veneer layer and their microstructure shows no open porosity.Effect of roughness of ceramic surfaces: The surface treatment of all ceramic crowns may be responsible for the changing in the rate of enamel wear.
Glazing of ceramic restorations produces a smooth, aesthetic and hygienic surface and is considered as a step which reduces the amount of wear of opposing teeth and restorations, but this layer of glaze can be removed shortly after being in function or by a required occlusal adjustment that may lead to more abrasive wear of the opposing teeth because of the insufficiently polished exposed surface of the crown.Jagger suggested in his study that the amounts of wear of enamel caused by glazed and unglazed porcelain are similar. Some investigators found that the glazed ceramic surfaces are smoother than the polished ones.
However, other authors found no significant differences between glazed and polished ceramic surfaces. Contradictorily, some investigations confirmed the finding that the smoothness of polished ceramic surfaces is similar or better than the glazed surfaces. This conclusion was supported through various studies, which found that the glazed surfaces caused more teeth wear compared to polished surfaces.
Functional finishing of ceramic surfaces during the wear process was documented by Monasky, who reported in his study that the initially high rate of wear decreased over time, suggesting that the effect of surface roughness on wear may be self-limiting.However, it must be considered that the factors described above are results of studies depending on wear or chewing simulation device and these results are contradictory.The aim of this manuscript was to provide a literature review about the tooth wear against ceramic crowns in posterior region both and .
This systematic review was prepared following the preferred reporting items for systematic reviews and meta-analyses statement guidelines (). This article focuses as well on measuring methods of tooth wear available in dental literature and on factors related to ceramic materials
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