Dentists enrolled in the National Dental Practice-Based Research Network completed a study questionnaire about techniques and materials used for single-unit crowns and an enrollment questionnaire about dentist/practice characteristics. The objectives were to quantify dentists’ material recommendations and test the hypothesis that dentist’s and practice’s characteristics are significantly associated with these recommendations.
Surveyed dentists responded to a contextual scenario asking what material they would use for a single-unit crown on an anterior and posterior tooth. Material choices included: full metal, porcelain-fused-to-metal (PFM), all-zirconia, layered zirconia, lithium disilicate, leucite-reinforced ceramic, or other.
1777 of 2132 eligible dentists responded (83%). The top 3 choices for anterior crowns were lithium disilicate (54%), layered zirconia (17%), and leucite-reinforced glass ceramic (13%). There were significant differences (p < 0.05) by dentist’s gender, race, years since graduation, practice type, region, practice busyness, hours worked/week, and location type. The top 3 choices for posterior crowns were all-zirconia (32%), PFM (31%), and lithium disilicate (21%). There were significant differences (p < 0.05) by dentist’s gender, practice type, region, practice busyness, insurance coverage, hours worked/week, and location type.
Network dentists use a broad range of materials for single-unit crowns for anterior and posterior teeth, adopting newer materials into their practices as they become available. Material choices are significantly associated with dentist’s and practice’s characteristics.
Decisions for crown material may be influenced by factors unrelated to tooth and patient variables. Dentists should be cognizant of this when developing an evidence-based approach to selecting crown material.
Dentists have a wide variety of options when selecting a material to fabricate a single-unit crown . The dentist’s choice and recommendation to the patient can depend on various patient and tooth factors, such as tooth location, esthetics, patient desires, masticatory factors, and patient finances .
All-zirconia crowns have gained popularity due to their high strength and toughness , wear compatibility with natural dentition and low cost. However, some dentists may decide against this material due to its relative opaqueness and fear of long-term strength degradation from low temperature degradation . Zirconia layered with a translucent ceramic, such as porcelain, is considered a more esthetic crown option, but the relatively low coefficient of thermal expansion and thermal diffusivity of zirconia compared to traditional metal coping materials led to laboratory complications. These manifested as veneer chipping and delamination over time .
Lithium disilicate is another popular material choice for single-unit crowns. It is more translucent than zirconia , and can be used in the anterior region without adding a layer of veneering porcelain, which reduces the risk of porcelain chipping. Additionally, the glass matrix of lithium disilicate can be etched with hydrofluoric acid and chemically bonded to tooth structure with a silane primer and adhesive resin cement . Lithium disilicate is not as strong as zirconia, with approximately 40% of its strength and 57% its fracture toughness . A review done by Pieger reported that 5–10 years after cementation, the majority of failures of lithium disilicate crowns occurred in the posterior region .
Leucite-reinforced glass ceramic is more translucent than lithium disilicate ; however, it is more limited in use and is only recommended as a single-unit in the anterior region . In order to gain sufficient strength for function, leucite-reinforced glass ceramic should be bonded to tooth structure .
Porcelain-fused-to-metal (PFM) has been used for many years and studied extensively. Studies have demonstrated a 94% success rate over a 10-year period and good long-term clinical reliability .
Although chipping of veneering porcelain is a possible complication, fracture of the metal framework is uncommon . PFM restorations require sufficient tooth reduction to allow space for at least 0.3 mm of metal coping and 0.7 mm of veneering porcelain, and a minimum facial reduction of 1.2 mm according to Hobo and Shillingburg . When comparing PFM crowns to zirconia crowns, several points are noteworthy. Laboratory testing has determined that the fracture strength of a PFM crown using 1.5 mm reduction is similar to zirconia crowns with only 1 mm of reduction . Some manufacturers have even suggested a 0.6 mm minimum reduction for posterior zircona crowns, which has led some dentists to prescribe all-zirconia restorations to preserve tooth structure .
Metal crowns are among the strongest options, although their major disadvantage is esthetics. Full-metal restorations are often considered the gold standard in dentistry due to their excellent biocompatibility and strength. However, the increasing price of precious metals and patients’ demands for esthetics have limited the use of both PFM and full metal restorations , which could make profitability an important aspect in the dentists’ decision on crown material.
Previous studies have investigated the role that patient and dentist factors may have on material longevity , but none have focused on single-unit crown material selection and dentist characteristics. Therefore, the objectives of this study were to: (1) quantify dentists’ material recommendations; and (2) test the hypothesis that dentist/practice characteristics are significantly associated with these recommendations.