Effect of Preparation Surface Area on the Clinical Outcome of Full Veneer Crowns in Dogs
Jessica Riehl, DVM; Jason W. Soukup, DVM; Caitlyn Collins, MS; Sarah Siverling; Heidi-Lynn Ploeg, MS, PhD; Christopher J. Snyder, DVM Summary:
Crown therapy is commonly used in veterinary medicine to provide support to teeth which have previously fractured, received root canal therapy, have significant wear, or experienced other detrimental removal of tooth substance. As with several aspects of veterinary medicine, many of the recommendations or guidelines for crown therapy originate from human dentistry, which are then transferred to veterinary patients. Due to the significant difference in the anatomy of teeth and function of the oral cavity between humans and dogs, these guidelines need to be studied to determine the appropriateness of their use in veterinary patients. This article evaluates the relationship between surface area of the preparation and clinical outcome of full veneer crown therapy of the canine tooth in dogs. Although there appeared to be a positive relationship between preparations with greater surface area and successful clinical outcome, it was not found to be statistically significant. J Vet Dent 31(1); 22-25, 2014
Introduction
Therapy with full veneer crowns is often performed in veterinary patients to restore or protect existing tooth structure. Maintaining functionality and protection of a tooth are the most common indications for crown therapy. A veterinary dentist may recommend full veneer crown therapy in order to return the tooth to normal function, protect it from further damage, or help maintain proper appearance in teeth which have experienced significant wear, previous fracture, previous root canal therapy, or other loss of tooth material (e.g. enamel hypocalcification).1 The clinical outcome of a full veneer crown depends on the physical dimensions of the preparation, and the performances of the restoration material and the luting cement.2,3 In most situations, the variable that the clinician has greatest control of is the tooth preparation design. The availability of veterinary literature is minimal and the paucity of set guidelines has led to adaptation of recommendations from human operative dentistry for use in veterinary patients. Concepts generally adhered to include: preservation of tooth structure, retention and resistance forms, structural durability, marginal integrity, and preservation of the periodontium.4 Retention and resistance involves consideration of the convergence angle, the height to diameter ratio (H/D), and freedom of displacement (limiting the number of paths along which a restoration can be removed).4 Many of these factors are also directly related to the surface area of the tooth preparation. The preparation should be designed in a way as to maintain the greatest possible surface area.4 The goal of this study was to evaluate the effect preparation surface area has on the clinical outcome of full veneer crowns of the canine 22
AAA379.indd 22
tooth in dogs. It was our hypothesis that the clinical outcome would improve with an increase in preparation surface area.
Materials and Methods
Stone dies of 32 maxillary and mandibular canine teeth from the collection of the University of Wisconsin-Madison Veterinary Medical Teaching Hospital Dentistry and Oral Surgery Service were used in this study. The dies were from single unit full veneer preparations of clinical patients, performed by either residents in dentistry and oral surgery or a board-certified veterinary dentist between the years of 2002-2008. These stone dies were previously used in a study evaluating the clinically achievable convergence angle and the effect of other physical parameters on clinical outcome.5 The clinical outcome associated with each die was obtained from the medical record or from a telephone interview with the owners regarding restoration presence or absence. Clinical outcome was classified as “adhesive/cohesive failure,” “tooth fracture failure,” or “success (or non-failure)” as previously defined.5 All clinical crowns were cemented with the same resin-based cement. Three-dimensional computer generated models of each die were acquired using a 3-D laser scannera with a high resolution of 0.05-mm (Fig. 1). Each die was scanned eight to ten times, rotating the die on the long (vertical) axis approximately o 45 between each scan. The axial wall of the die was placed approximately perpendicular to the detector. The scans were then imported into a dedicated software programb. Scans were initially aligned manually, followed by an automatic alignment function using the software. After alignment, the scans were merged to form a three-dimensional computer generated model of the die (Fig. 2). The surface area of each die was then calculated from the computer-generated models using measurement softwarec (Fig. 3). The surface area for each die was entered to the nearest thousandth cm2 and recorded on a spreadsheet. The data were evaluated and the mean, median, and range values for each outcome category were calculated. One-way analysis of variance (ANOVA) was utilized to evaluate any association between the die surface area and the clinical outcome of the full veneer crowns. A value of p ≤ 0.05 was considered statistically significant.
Results
Of the 32 full veneer crowns evaluated, 5 had an unsuccessful clinical outcome (15.625 %). Fracture of the tooth accounted for 40.0 % (2/5) and adhesive/cohesive failure accounted for 60.0 % (3/5) of the negative clinical outcomes. The range of surface area for all crowns was between 0.866 cm2 to the largest being 3.360 cm2. The overall mean surface area was 1.781 cm2 (Table 1). Twenty-seven of the 32 crowns were successful as
J VET DENT Vol. 31 No.1 Spring 2014
4/3/14 7:49 AM
Figure 1
Figure 2
Photograph of the three-dimensional laser scanner used to acquire computer-generated models of the stone dies used in this study.
Image of a three-dimensional computergenerated model of a stone die from a canine tooth.
Table 1
Individual dies with corresponding surface area (cm2) and clinical outcome data.
Figure 3
Image of a three-dimensional computergenerated model of a die from the study in the software program used to calculate surface area.
Die 100 101 102 103 104 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131
Surface Area (cm2) 2.17 1.48 1.64 3.36 1.62 1.19 1.47 2.43 1.50 1.80 1.52 2.08 2.04 1.59 1.16 0.99 2.68 1.34 1.83 1.61 2.33 1.60 3.01 2.30 1.36 1.86 1.40 2.05 2.30 2.50 0.87
Outcome N N N N F N N N A N N N N N N N N A F N N N N N N N N N N N A
N = Success; F = Fracture failure; A = Adhesive/cohesive failure
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Table 2 Preparation surface area (cm2) according to clinical outcome.
Mean
STD
Median
Range
Success
1.9
0.58
1.83
0.99-3.36
Adhesive/Cohesive Failure
1.23
0.33
1.34
0.87-1.50
Fracture
1.73
0.11
1.73
1.62-1.83
Figure 4 Box plot depicting the relationship between preparation surface area (y-axis) and clinical outcome (x-axis).
3.0
determined by medical records or contact with the owners. The mean +/- SD and median surface areas of these preparations were 1.916 +/- 0.585 cm2 and 1.829 cm2, respectively (range 0.990 - 3.360 cm2) [Table 2]. Three of the 32 crowns failed by adhesive/cohesive type failure. The mean +/- SD and median surface area for these preparations was 1.234 +/0.329 cm2 and 1.336 cm2, respectively (range 0.87 - 1.50 cm2) [Table 2]. Tooth fracture was the cause of failure for 2 of the 32 crowns. The mean +/- SD and median surface areas for these preparations were 1.728 +/- 0.105 cm2 and 1.728 cm2, respectively (range 1.624 - 1.833) [Table 2]. Comparison of the clinical outcomes and association with preparation surface area revealed a trending positive correlation between increasing surface area and the likelihood of clinical success. Teeth with a successful clinical outcome had a higher mean surface area compared to those with a non-successful clinical outcome (Fig. 4). However, this association was not statistically significant (p = 0.137).
24
AAA379.indd 24
2.0 1.5 1.0
Evidence-based research with respect to full veneer restorations is lacking in the veterinary literature. As with much of veterinary dentistry, most clinical guidelines for crown preparation are adapted from human applications. General principles for tooth preparation are often valid with translation to our patients. However, given the differences in the structure, anatomy, and function of the tooth and oral cavity between veterinary and human patients, it is not appropriate to assume these principles are necessarily applicable in veterinary patients. These principles require scientific evaluation and verification in veterinary patients. Studies evaluating the direct relationship between surface area and clinical outcome are scarce in the human literature and non-existent in the veterinary literature. In an in vitro study, the specific factors of preparation design that lead to retention in humans were evaluated and demonstrated a positive correlation between increased surface area and increased unseating force.3 The main conclusions that can be drawn from this research is that 1) surface area changes with changes in underlying variables (height, diameter, convergence angle), and 2) when surface area increases, the force needed to unseat a crown also increases. By evaluating the clinical outcome of full veneer crown restoration of the canine tooth in dogs, our study supports, albeit not in a statistically significant manner, these findings regarding the relationship between preparation surface area and crown retention. Abundant studies exist comparing different classes of luting cements. The choice of cement contributes to the clinical outcome and can compensate for some discrepancies in the framework of the preparation design.2 However, no cement compatible with tooth structure and the oral cavity has adequate adhesive properties to hold a restoration in place based solely on adhesion.4,5 This places further emphasis on the configuration of the tooth preparation to provide necessary retention and resistance.4 The inter-relationship between tooth preparation and cement becomes more co-dependent when consideration is given to the theory that increased surface area promotes increased resistance and retention due to an increase in available mechanical
2.5
Discussion
A
F
N
(N = Success; F = Fracture failure; A = Adhesive/cohesive failure)
interlocks for cement bonding.2,4 Therefore, the larger the surface area, the greater the number of mechanical interlocks available for cement bonding, increasing the retentiveness of the prepared surface. The results of the present study and those in a previous report3 lend support to the utilization of techniques to increase preparation surface area. Multiple sources in the veterinary literature indicate that a preparation should possess adequate height for adequate retention.1,5-10 While we believe most references make recommendations that are too simplistic, the concept is useful in that preparation height, for a given preparation diameter and convergence angle, contributes to the overall surface area. The most current information available in the veterinary literature is a study that defined and evaluated the relationship of convergence angle and other physical dimensions of preparations with clinical outcome of full veneer crowns on canine teeth.5 This study concluded that an increase in height, for a given preparation diameter and convergence angle, generally improves the clinical outcome of full veneer crown therapy in dogs. More specifically, it showed that using the height to diameter ratio (H/D) of a preparation was more useful in determining adequate resistance/retention form than using height alone. An increase
J VET DENT Vol. 31 No.1 Spring 2014
4/3/14 7:49 AM
in the H/D led to an increased likelihood of a positive clinical outcome. Based on this research, a logical conclusion could be made that positive physical dimensions of a preparation also lead to an increase in surface area. The present study supports that logic, while adding to the body of evidence-based guidelines in the veterinary literature. The recommendation can be made that tooth height should be maintained when possible. Another method for increasing preparation surface area that has been suggested is the utilization of a subgingival preparation margin.1,11 While this method will increase preparation height and thus preparation surface area, it is not without potential consequences. Subgingival margins are associated with increased plaque accumulation12, gingival inflammation13-18, deep pocket formation13,14,17,19, attachment loss13,14 and gingival recession20. The decision to utilize a subgingival margin must be considered carefully. The potential quantitative gain in surface area that this method will provide must be considered in light of the negative consequences to a patient’s periodontal health. Although the success of crown therapy relies on characteristics of the preparation, restoration, and the cement, the clinician has the most control over the physical dimensions of the preparation.3.4 One such physical dimension that can increase surface area is the introduction of axial grooves into the preparation design. Axial grooves positively decrease the “effective” convergence angle to improve the resistance/retention form.21,22 Axial grooves also increase the preparation surface area. It was found that axial grooves placed into dies with unfavorable preparation design properties provided complete resistance to dislodgement, whereas, without the grooves, the same design failed to provide adequate resistance/retention form.21 Based on the concept of increasing surface area, our study potentially supports the use of axial grooves. This is a technique that requires future research efforts to validate its use in dogs. A limiting factor of this study was its retrospective nature. At the time of crown preparation, future evaluation of the crowns was unknown to the clinician, which introduced an inherent lack of standardization in preparation design. Additionally, the conditions of the full veneer crowns after cementation have no uniformity based on the patient’s purpose/function, lifestyle, chewing habits, and continued dental care. Any of these factors may have played a role in the clinical outcome. The low number of negative clinical outcomes may also have contributed to the lack of statistical significance. Given the irregular shape of the canine tooth and the associated preparations, geometric equations to calculate surface area were not completely reliable. For this reason, 3-D laser scanning and geometric data software were used. In addition, using the laser scanner to obtain the surface area of the stone dies was a practical way to avoid the impracticalities of obtaining the surface area of the tooth in an anesthetized patient. The use of the 3-D laser scan has been previously validated as an accurate measurement of surface area in replicated computer simulated models.23 Our study revealed that teeth with a successful clinical outcome had a higher mean surface area, however this trend was not statistically significant. Although the current study did not evaluate force specifically, it implied a positive correlation between preparation surface area and the amount of force required to unseat a full veneer crown.3 This study supports the concept that surface area plays an important role in the retention of full
veneer crowns in dogs and provides the basis for further research on possible methods to increase preparation surface area. ___________________________________________________ a b c
ShapeGrabber 102, Shape Grabber Inc, Ottawa, Ontario, Canada Geomagic Studio 2011, Geomagic Research, Triangle Park, NC Solidworks 2011, Dassault Systems, Waltham, MA
Author Information
From the Dentistry and Oral Surgery Section, School of Veterinary Medicine, 2015 Linden Drive; and, the Bone and Joints Biomechanics Lab (Collins, Siverling, Ploeg), 1513 University Avenue, University of Wisconsin-Madison, Madison, WI, 53706. Email: [email protected]
References 1. Grove, TK. Functional and esthetic crowns for dogs and cats. Vet Med Rep 1990; 2:409-420. 2. Carnaggio TV, Conrad R, Engelmeier RL, et al. Retention of CAD/CAM all-ceramic crowns on prefabricated implant abutments: an in vitro comparative study of luting agents and abutment surface area. J Prosthodont 2012; 00:1-6. 3. Kaufman EG, Coelho DH, Colin L. Factors influencing the retention of cemented gold castings. J Prosthet Dent 1961; 11:487-502. 4. Shillinburg HT, Hobo S, Whitsett LD, et al. Principles of tooth preparation. In: Schillinburg HT, Hobo S, Whitsett LD, et al eds. Fundamentals of fixed prosthodontics. 3rd ed. Chicago: Quintessence, 1997; 119-137. 5. Soukup JW, Snyder CJ, Karls TL, et al. Achievable convergence angle and the effect of preparation design on the clinical outcome of full veneer crowns in dogs. J Vet Dent 2011; 28: 72-82. 6. van Foreest A, Roeters J. Evaluation of the clinical performance and effectiveness of adhesively bonded crowns on damaged canine teeth of working dogs over a two- to 52-month period. J Vet Dent 1998; 15:13-20. 7. Holmstrom SE, Fitch PF, Eisner ER. Restorative dentistry. In: Holmstrom SE, Fitch PF, Eisner ER, eds. Veterinary dental techniques for the small animal practitioner. 3rd ed. Philadelphia: Saunders, 2004; 415-497. 8. Visser CJ. Restorative dentistry: crown therapy. Vet Clin North Am Sm Anim Pract: Canine Dentistry 1998; 28:1273-1284. 9. Wiggs RB, Lobprise HB. Operative dentistry: crowns and prosthodontics. In: Wiggs RB, Lobprise HB, eds. Veterinary dentistry principles and practice. 1st ed. Philadelphia: Lippincott-Raven, 1997; 395-434. 10. Harvey CE, Emily PP. Restorative dentistry. In: Harvey CE, Emily PP, eds. Small animal dentistry. 1st ed. St. Louis: Mosby, 1993; 213-265. 11. Karger K, Bloom B. Crown preps: Debunking the myth. From the Proceedings of 25th Annual Veterinary Dental Forum, November 2011, Boston, MA. 12. Kosyfaki P, del Pilar Pinilla Martin M, et al. Relationship between crowns and the periodontium: a literature update. Quintessence Int 2010; 41:109-122. 13. Valderhaug J, Birkeland JM. Periodontal conditions in patients 5 years following insertion of fixed prostheses. Pocket depth and loss of attachment. J Oral Rehabil 1976; 3:237-243. 14. Valderhaug J. Periodontal conditions and carious lesions following the insertion of fixed prostheses: a 10-year follow-up study. Int Dent J 1980; 30:296-304. 15. Gemalmaz D, Ergin S. Clinical evaluation of all-ceramic crowns. J Prosthet Dent 2002; 87:189-196. 16. Bader JD, Rozier RG, et al. Effect of crown margins on periodontal conditions in regularly attending patients. J Prosthet Dent 1991; 65:75-79. 17. Kancyper SG, Koka S. The influence of intracrevicular crown margins on gingival health: preliminary findings. J Prosthet Dent 2001; 85:461-465. 18. Larato DC. Effects of artificial crown margin extension and tooth brushing frequency on gingival pocket depth. J Prosthet Dent 1975; 34:640-643. 19. Orkin DA, Reddy J, et al. The relationship of the position of crown margins to gingival health. J Prosthet Dent 1987; 57:421-424. 20. Padbury Jr A, Eber R, et al. Interactions between gingiva and the margin of restorations. J Clin Periodontol 2003; 30:379-385. 21. Woolsey GD, Matich JA. The effect of axial grooves on the resistance form of cast restorations. J Am Dent Assoc 1978; 97:978-980. 22. Proussaefs P, Campagni W, et al. The effectiveness of auxillary features on a tooth preparation with inadequate resistance form. J Prosthet Dent 2004; 91:33-41. 23. Piller, Geoffrey. “Geometric accuracy of physical and surface models created from computed tomography data.” MA thesis. University of Wisconsin-Madison, 2012. Print.
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Jessica Riehl, DVM; Jason W. Soukup, DVM; Caitlyn Collins, MS; Sarah Siverling; Heidi-Lynn Ploeg, MS, PhD; Christopher J. Snyder, DVM Summary:
Crown therapy is commonly used in veterinary medicine to provide support to teeth which have previously fractured, received root canal therapy, have significant wear, or experienced other detrimental removal of tooth substance. As with several aspects of veterinary medicine, many of the recommendations or guidelines for crown therapy originate from human dentistry, which are then transferred to veterinary patients. Due to the significant difference in the anatomy of teeth and function of the oral cavity between humans and dogs, these guidelines need to be studied to determine the appropriateness of their use in veterinary patients. This article evaluates the relationship between surface area of the preparation and clinical outcome of full veneer crown therapy of the canine tooth in dogs. Although there appeared to be a positive relationship between preparations with greater surface area and successful clinical outcome, it was not found to be statistically significant. J Vet Dent 31(1); 22-25, 2014
Introduction
Therapy with full veneer crowns is often performed in veterinary patients to restore or protect existing tooth structure. Maintaining functionality and protection of a tooth are the most common indications for crown therapy. A veterinary dentist may recommend full veneer crown therapy in order to return the tooth to normal function, protect it from further damage, or help maintain proper appearance in teeth which have experienced significant wear, previous fracture, previous root canal therapy, or other loss of tooth material (e.g. enamel hypocalcification).1 The clinical outcome of a full veneer crown depends on the physical dimensions of the preparation, and the performances of the restoration material and the luting cement.2,3 In most situations, the variable that the clinician has greatest control of is the tooth preparation design. The availability of veterinary literature is minimal and the paucity of set guidelines has led to adaptation of recommendations from human operative dentistry for use in veterinary patients. Concepts generally adhered to include: preservation of tooth structure, retention and resistance forms, structural durability, marginal integrity, and preservation of the periodontium.4 Retention and resistance involves consideration of the convergence angle, the height to diameter ratio (H/D), and freedom of displacement (limiting the number of paths along which a restoration can be removed).4 Many of these factors are also directly related to the surface area of the tooth preparation. The preparation should be designed in a way as to maintain the greatest possible surface area.4 The goal of this study was to evaluate the effect preparation surface area has on the clinical outcome of full veneer crowns of the canine 22
AAA379.indd 22
tooth in dogs. It was our hypothesis that the clinical outcome would improve with an increase in preparation surface area.
Materials and Methods
Stone dies of 32 maxillary and mandibular canine teeth from the collection of the University of Wisconsin-Madison Veterinary Medical Teaching Hospital Dentistry and Oral Surgery Service were used in this study. The dies were from single unit full veneer preparations of clinical patients, performed by either residents in dentistry and oral surgery or a board-certified veterinary dentist between the years of 2002-2008. These stone dies were previously used in a study evaluating the clinically achievable convergence angle and the effect of other physical parameters on clinical outcome.5 The clinical outcome associated with each die was obtained from the medical record or from a telephone interview with the owners regarding restoration presence or absence. Clinical outcome was classified as “adhesive/cohesive failure,” “tooth fracture failure,” or “success (or non-failure)” as previously defined.5 All clinical crowns were cemented with the same resin-based cement. Three-dimensional computer generated models of each die were acquired using a 3-D laser scannera with a high resolution of 0.05-mm (Fig. 1). Each die was scanned eight to ten times, rotating the die on the long (vertical) axis approximately o 45 between each scan. The axial wall of the die was placed approximately perpendicular to the detector. The scans were then imported into a dedicated software programb. Scans were initially aligned manually, followed by an automatic alignment function using the software. After alignment, the scans were merged to form a three-dimensional computer generated model of the die (Fig. 2). The surface area of each die was then calculated from the computer-generated models using measurement softwarec (Fig. 3). The surface area for each die was entered to the nearest thousandth cm2 and recorded on a spreadsheet. The data were evaluated and the mean, median, and range values for each outcome category were calculated. One-way analysis of variance (ANOVA) was utilized to evaluate any association between the die surface area and the clinical outcome of the full veneer crowns. A value of p ≤ 0.05 was considered statistically significant.
Results
Of the 32 full veneer crowns evaluated, 5 had an unsuccessful clinical outcome (15.625 %). Fracture of the tooth accounted for 40.0 % (2/5) and adhesive/cohesive failure accounted for 60.0 % (3/5) of the negative clinical outcomes. The range of surface area for all crowns was between 0.866 cm2 to the largest being 3.360 cm2. The overall mean surface area was 1.781 cm2 (Table 1). Twenty-seven of the 32 crowns were successful as
J VET DENT Vol. 31 No.1 Spring 2014
4/3/14 7:49 AM
Figure 1
Figure 2
Photograph of the three-dimensional laser scanner used to acquire computer-generated models of the stone dies used in this study.
Image of a three-dimensional computergenerated model of a stone die from a canine tooth.
Table 1
Individual dies with corresponding surface area (cm2) and clinical outcome data.
Figure 3
Image of a three-dimensional computergenerated model of a die from the study in the software program used to calculate surface area.
Die 100 101 102 103 104 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131
Surface Area (cm2) 2.17 1.48 1.64 3.36 1.62 1.19 1.47 2.43 1.50 1.80 1.52 2.08 2.04 1.59 1.16 0.99 2.68 1.34 1.83 1.61 2.33 1.60 3.01 2.30 1.36 1.86 1.40 2.05 2.30 2.50 0.87
Outcome N N N N F N N N A N N N N N N N N A F N N N N N N N N N N N A
N = Success; F = Fracture failure; A = Adhesive/cohesive failure
J VET DENT Vol. 31 No. 1 Spring 2014
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Table 2 Preparation surface area (cm2) according to clinical outcome.
Mean
STD
Median
Range
Success
1.9
0.58
1.83
0.99-3.36
Adhesive/Cohesive Failure
1.23
0.33
1.34
0.87-1.50
Fracture
1.73
0.11
1.73
1.62-1.83
Figure 4 Box plot depicting the relationship between preparation surface area (y-axis) and clinical outcome (x-axis).
3.0
determined by medical records or contact with the owners. The mean +/- SD and median surface areas of these preparations were 1.916 +/- 0.585 cm2 and 1.829 cm2, respectively (range 0.990 - 3.360 cm2) [Table 2]. Three of the 32 crowns failed by adhesive/cohesive type failure. The mean +/- SD and median surface area for these preparations was 1.234 +/0.329 cm2 and 1.336 cm2, respectively (range 0.87 - 1.50 cm2) [Table 2]. Tooth fracture was the cause of failure for 2 of the 32 crowns. The mean +/- SD and median surface areas for these preparations were 1.728 +/- 0.105 cm2 and 1.728 cm2, respectively (range 1.624 - 1.833) [Table 2]. Comparison of the clinical outcomes and association with preparation surface area revealed a trending positive correlation between increasing surface area and the likelihood of clinical success. Teeth with a successful clinical outcome had a higher mean surface area compared to those with a non-successful clinical outcome (Fig. 4). However, this association was not statistically significant (p = 0.137).
24
AAA379.indd 24
2.0 1.5 1.0
Evidence-based research with respect to full veneer restorations is lacking in the veterinary literature. As with much of veterinary dentistry, most clinical guidelines for crown preparation are adapted from human applications. General principles for tooth preparation are often valid with translation to our patients. However, given the differences in the structure, anatomy, and function of the tooth and oral cavity between veterinary and human patients, it is not appropriate to assume these principles are necessarily applicable in veterinary patients. These principles require scientific evaluation and verification in veterinary patients. Studies evaluating the direct relationship between surface area and clinical outcome are scarce in the human literature and non-existent in the veterinary literature. In an in vitro study, the specific factors of preparation design that lead to retention in humans were evaluated and demonstrated a positive correlation between increased surface area and increased unseating force.3 The main conclusions that can be drawn from this research is that 1) surface area changes with changes in underlying variables (height, diameter, convergence angle), and 2) when surface area increases, the force needed to unseat a crown also increases. By evaluating the clinical outcome of full veneer crown restoration of the canine tooth in dogs, our study supports, albeit not in a statistically significant manner, these findings regarding the relationship between preparation surface area and crown retention. Abundant studies exist comparing different classes of luting cements. The choice of cement contributes to the clinical outcome and can compensate for some discrepancies in the framework of the preparation design.2 However, no cement compatible with tooth structure and the oral cavity has adequate adhesive properties to hold a restoration in place based solely on adhesion.4,5 This places further emphasis on the configuration of the tooth preparation to provide necessary retention and resistance.4 The inter-relationship between tooth preparation and cement becomes more co-dependent when consideration is given to the theory that increased surface area promotes increased resistance and retention due to an increase in available mechanical
2.5
Discussion
A
F
N
(N = Success; F = Fracture failure; A = Adhesive/cohesive failure)
interlocks for cement bonding.2,4 Therefore, the larger the surface area, the greater the number of mechanical interlocks available for cement bonding, increasing the retentiveness of the prepared surface. The results of the present study and those in a previous report3 lend support to the utilization of techniques to increase preparation surface area. Multiple sources in the veterinary literature indicate that a preparation should possess adequate height for adequate retention.1,5-10 While we believe most references make recommendations that are too simplistic, the concept is useful in that preparation height, for a given preparation diameter and convergence angle, contributes to the overall surface area. The most current information available in the veterinary literature is a study that defined and evaluated the relationship of convergence angle and other physical dimensions of preparations with clinical outcome of full veneer crowns on canine teeth.5 This study concluded that an increase in height, for a given preparation diameter and convergence angle, generally improves the clinical outcome of full veneer crown therapy in dogs. More specifically, it showed that using the height to diameter ratio (H/D) of a preparation was more useful in determining adequate resistance/retention form than using height alone. An increase
J VET DENT Vol. 31 No.1 Spring 2014
4/3/14 7:49 AM
in the H/D led to an increased likelihood of a positive clinical outcome. Based on this research, a logical conclusion could be made that positive physical dimensions of a preparation also lead to an increase in surface area. The present study supports that logic, while adding to the body of evidence-based guidelines in the veterinary literature. The recommendation can be made that tooth height should be maintained when possible. Another method for increasing preparation surface area that has been suggested is the utilization of a subgingival preparation margin.1,11 While this method will increase preparation height and thus preparation surface area, it is not without potential consequences. Subgingival margins are associated with increased plaque accumulation12, gingival inflammation13-18, deep pocket formation13,14,17,19, attachment loss13,14 and gingival recession20. The decision to utilize a subgingival margin must be considered carefully. The potential quantitative gain in surface area that this method will provide must be considered in light of the negative consequences to a patient’s periodontal health. Although the success of crown therapy relies on characteristics of the preparation, restoration, and the cement, the clinician has the most control over the physical dimensions of the preparation.3.4 One such physical dimension that can increase surface area is the introduction of axial grooves into the preparation design. Axial grooves positively decrease the “effective” convergence angle to improve the resistance/retention form.21,22 Axial grooves also increase the preparation surface area. It was found that axial grooves placed into dies with unfavorable preparation design properties provided complete resistance to dislodgement, whereas, without the grooves, the same design failed to provide adequate resistance/retention form.21 Based on the concept of increasing surface area, our study potentially supports the use of axial grooves. This is a technique that requires future research efforts to validate its use in dogs. A limiting factor of this study was its retrospective nature. At the time of crown preparation, future evaluation of the crowns was unknown to the clinician, which introduced an inherent lack of standardization in preparation design. Additionally, the conditions of the full veneer crowns after cementation have no uniformity based on the patient’s purpose/function, lifestyle, chewing habits, and continued dental care. Any of these factors may have played a role in the clinical outcome. The low number of negative clinical outcomes may also have contributed to the lack of statistical significance. Given the irregular shape of the canine tooth and the associated preparations, geometric equations to calculate surface area were not completely reliable. For this reason, 3-D laser scanning and geometric data software were used. In addition, using the laser scanner to obtain the surface area of the stone dies was a practical way to avoid the impracticalities of obtaining the surface area of the tooth in an anesthetized patient. The use of the 3-D laser scan has been previously validated as an accurate measurement of surface area in replicated computer simulated models.23 Our study revealed that teeth with a successful clinical outcome had a higher mean surface area, however this trend was not statistically significant. Although the current study did not evaluate force specifically, it implied a positive correlation between preparation surface area and the amount of force required to unseat a full veneer crown.3 This study supports the concept that surface area plays an important role in the retention of full
veneer crowns in dogs and provides the basis for further research on possible methods to increase preparation surface area. ___________________________________________________ a b c
ShapeGrabber 102, Shape Grabber Inc, Ottawa, Ontario, Canada Geomagic Studio 2011, Geomagic Research, Triangle Park, NC Solidworks 2011, Dassault Systems, Waltham, MA
Author Information
From the Dentistry and Oral Surgery Section, School of Veterinary Medicine, 2015 Linden Drive; and, the Bone and Joints Biomechanics Lab (Collins, Siverling, Ploeg), 1513 University Avenue, University of Wisconsin-Madison, Madison, WI, 53706. Email: [email protected]
References 1. Grove, TK. Functional and esthetic crowns for dogs and cats. Vet Med Rep 1990; 2:409-420. 2. Carnaggio TV, Conrad R, Engelmeier RL, et al. Retention of CAD/CAM all-ceramic crowns on prefabricated implant abutments: an in vitro comparative study of luting agents and abutment surface area. J Prosthodont 2012; 00:1-6. 3. Kaufman EG, Coelho DH, Colin L. Factors influencing the retention of cemented gold castings. J Prosthet Dent 1961; 11:487-502. 4. Shillinburg HT, Hobo S, Whitsett LD, et al. Principles of tooth preparation. In: Schillinburg HT, Hobo S, Whitsett LD, et al eds. Fundamentals of fixed prosthodontics. 3rd ed. Chicago: Quintessence, 1997; 119-137. 5. Soukup JW, Snyder CJ, Karls TL, et al. Achievable convergence angle and the effect of preparation design on the clinical outcome of full veneer crowns in dogs. J Vet Dent 2011; 28: 72-82. 6. van Foreest A, Roeters J. Evaluation of the clinical performance and effectiveness of adhesively bonded crowns on damaged canine teeth of working dogs over a two- to 52-month period. J Vet Dent 1998; 15:13-20. 7. Holmstrom SE, Fitch PF, Eisner ER. Restorative dentistry. In: Holmstrom SE, Fitch PF, Eisner ER, eds. Veterinary dental techniques for the small animal practitioner. 3rd ed. Philadelphia: Saunders, 2004; 415-497. 8. Visser CJ. Restorative dentistry: crown therapy. Vet Clin North Am Sm Anim Pract: Canine Dentistry 1998; 28:1273-1284. 9. Wiggs RB, Lobprise HB. Operative dentistry: crowns and prosthodontics. In: Wiggs RB, Lobprise HB, eds. Veterinary dentistry principles and practice. 1st ed. Philadelphia: Lippincott-Raven, 1997; 395-434. 10. Harvey CE, Emily PP. Restorative dentistry. In: Harvey CE, Emily PP, eds. Small animal dentistry. 1st ed. St. Louis: Mosby, 1993; 213-265. 11. Karger K, Bloom B. Crown preps: Debunking the myth. From the Proceedings of 25th Annual Veterinary Dental Forum, November 2011, Boston, MA. 12. Kosyfaki P, del Pilar Pinilla Martin M, et al. Relationship between crowns and the periodontium: a literature update. Quintessence Int 2010; 41:109-122. 13. Valderhaug J, Birkeland JM. Periodontal conditions in patients 5 years following insertion of fixed prostheses. Pocket depth and loss of attachment. J Oral Rehabil 1976; 3:237-243. 14. Valderhaug J. Periodontal conditions and carious lesions following the insertion of fixed prostheses: a 10-year follow-up study. Int Dent J 1980; 30:296-304. 15. Gemalmaz D, Ergin S. Clinical evaluation of all-ceramic crowns. J Prosthet Dent 2002; 87:189-196. 16. Bader JD, Rozier RG, et al. Effect of crown margins on periodontal conditions in regularly attending patients. J Prosthet Dent 1991; 65:75-79. 17. Kancyper SG, Koka S. The influence of intracrevicular crown margins on gingival health: preliminary findings. J Prosthet Dent 2001; 85:461-465. 18. Larato DC. Effects of artificial crown margin extension and tooth brushing frequency on gingival pocket depth. J Prosthet Dent 1975; 34:640-643. 19. Orkin DA, Reddy J, et al. The relationship of the position of crown margins to gingival health. J Prosthet Dent 1987; 57:421-424. 20. Padbury Jr A, Eber R, et al. Interactions between gingiva and the margin of restorations. J Clin Periodontol 2003; 30:379-385. 21. Woolsey GD, Matich JA. The effect of axial grooves on the resistance form of cast restorations. J Am Dent Assoc 1978; 97:978-980. 22. Proussaefs P, Campagni W, et al. The effectiveness of auxillary features on a tooth preparation with inadequate resistance form. J Prosthet Dent 2004; 91:33-41. 23. Piller, Geoffrey. “Geometric accuracy of physical and surface models created from computed tomography data.” MA thesis. University of Wisconsin-Madison, 2012. Print.
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