title: Clinical outcomes of three different crown systems with CAD/CAM technology.
abstract: BACKGROUND
  Computer-aided design and computer-aided manufacturing (CAD/CAM) generated restorations are gaining popularity. However, limited clinical evidence is available for single-unit posterior CAD/CAM restorations fabricated with established and newer crown materials.
  
  
  OBJECTIVE
  The purpose of this clinical study was to assess the restoration quality of and gingival response to CAD/CAM fabricated posterior single-tooth restorations with different processing technologies.
  
  
  METHODS
  Twenty-two individuals in need of posterior complete coverage crowns were recruited under an institutional review board approved protocol. Teeth were randomized to 1 of 3 groups: metal ceramic, lithium disilicate, and monolithic zirconia. An unprepared or minimally restored tooth on the contralateral side was chosen as a control tooth for gingival measurements with each participant. Teeth were prepared and scanned intraorally by 1 of 3 experienced practitioners. A total of 32 restorations were digitally designed and fabricated with either milling technology or rapid-prototype printing and casting with conventional porcelain application. Restorations were evaluated with modified United States Public Health Service criteria for contour, marginal adaptation, occlusion, and shade. Gingival crevicular fluid volume and bleeding on probing were recorded preoperatively, at 1-month and 6-month postcementation visits. Polyvinyl siloxane impressions were made of the buccal margin of cemented restorations and evaluated with microcomputed tomography to assess marginal adaptation (horizontal discrepancy). The Mantel Haenszel row mean score was used to assess whether the crown systems differed with respect to the modified United States Public Health Service criteria. Linear mixed models were used to assess whether the average gingival volumes were affected by the explanatory variables (crown system, tooth status [treated vs control], or visit). A generalized estimating equation approach was used to assess whether bleeding on probing was affected by the explanatory variables. One-way ANOVA was used to assess marginal discrepancy values among the crown systems (α=.05 for all tests).
  
  
  RESULTS
  Twelve metal ceramic, 10 lithium disilicate, and 10 zirconia restorations were fabricated for 22 participants. Zirconia restorations were significantly different from the other 2 crown systems (P<.001) with respect to occlusion. No occlusal adjustment was needed on 80% of the zirconia restorations. The average gingival crevicular fluid volumes did not differ among crown systems, between treated and control groups, or over time. The average horizontal marginal discrepancy was significantly different between lithium disilicate and zirconia crowns (P=.027), with zirconia crowns having the least amount of horizontal marginal discrepancy.
  
  
  CONCLUSIONS
  Given the small sample size and limitations of this study, CAD/CAM-generated restorations for posterior teeth made from different materials had acceptable clinical results.
authors: Former Resident, Department of Prosthodontics, University of North Carolina at Chapel Hill School of Dentistry, Private practice, Colorado Springs, Colo. Electronic address: drbatson@pickledental.com.
authors: Emily R
authors: ER
authors: Batson
authors: Director and Stallings Distinguished Professor, Graduate Prosthodontics, University of North Carolina at Chapel Hill School of Dentistry, Chapel Hill, NC.
authors: Lyndon F
authors: LF
authors: Cooper
authors: Clinical Assistant Professor, Department of Prosthodontics, University of North Carolina at Chapel Hill School of Dentistry, Chapel Hill, NC.
authors: Ibrahim
authors: I
authors: Duqum
authors: Clinical Assistant Professor, Department of Prosthodontics, University of North Carolina at Chapel Hill School of Dentistry, Chapel Hill, NC.
authors: Gustavo
authors: G
authors: Mendonça
mesh_terms: D017076:Computer-Aided Design; D003442:Crowns / Q000592:standards*; D003760:Dental Impression Materials / Q000737:chemistry; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design / Q000592:standards; D005500:Follow-Up Studies; D005881:Gingiva / Q000033:anatomy & histology; D005883:Gingival Crevicular Fluid / Q000737:chemistry; D006801:Humans; D016876:Metal Ceramic Alloys / Q000737:chemistry; D019558:Occlusal Adjustment; D010512:Periodontal Index; D011145:Polyvinyls / Q000737:chemistry; D066330:Printing, Three-Dimensional; D011446:Prospective Studies; D017797:Prosthesis Coloring; D016628:Replica Techniques; D012833:Siloxanes / Q000737:chemistry; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic / Q000379:methods; D016896:Treatment Outcome; D055114:X-Ray Microtomography / Q000379:methods; D015040:Zirconium / Q000737:chemistry
chemical_list: D003760:Dental Impression Materials; D003764:Dental Materials; D016876:Metal Ceramic Alloys; D011145:Polyvinyls; D012833:Siloxanes; C493120:lithia disilicate; C034183:vinyl polysiloxane; D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide