Restorative dentistry, which

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1 Practitioner, patient and carious lesion characteristics associated with type of restorative material Findings from The Dental Practice-Based Research Network Sonia K. Makhija, DDS, MPH; Valeria V. Gordan, DDS, MS, MS-CI; Gregg H. Gilbert, DDS, MBA; Mark S. Litaker, PhD; D. Brad Rindal, DDS; Daniel J. Pihlstrom, DDS; Vibeke Qvist, DDS, PhD, DrOdont; for The Dental Practice-Based Research Network Collaborative Group Restorative dentistry, which includes the placement and replacement of restorations, constitutes the majority of the workload in daily clinical practice. 1-3 With the increasing availability of new dental materials, choice of material is an important part of a dentist s decision-making process. At one point, amalgam was the material of choice for posterior tooth restorations, 4,5 but across time, materials have changed such that amalgams are being phased out in favor of more esthetic choices This change is a result of various patientrelated and dentist-related factors For esthetic reasons, patients may choose to receive restorations composed of direct resin-based composites (RBC) instead of amalgams. 6-9,15 Patients also may opt for RBC restorations because of the public perception of mercury toxicity associated with amalgams, 7,9-11 although results of numerous studies have shown no adverse health effects Alternatively, patients may request amalgams because they are less expensive than RBCs; this may be especially true of patients who do not have dental insurance coverage. 19,20 Dentists may choose to place amalgam because they consider it ABSTRACT Background. The authors conducted a study to identify factors associated with the materials that dentists in The Dental Practice-Based Research Network (DPBRN) use when placing the first restoration on permanent posterior tooth surfaces. Methods. A total of 182 DPBRN practitioner-investigators provided data regarding 5,599 posterior teeth with caries. Practitionerinvestigators completed an enrollment questionnaire that included the dentist s age, sex, practice workload, practice type and number of years since graduation. When patients who had provided informed consent to participate in the investigation sought treatment for a previously unrestored carious surface, the practitionerinvestigator recorded patient and tooth characteristics. Results. Practitioner-investigators used amalgam more often than they used direct resin-based composite (RBC) for posterior carious lesions. Practitioner and practice characteristics (years since graduation and type of practice); patient characteristics (sex, race, age and dental insurance status); and lesion characteristics (tooth location and surface, preoperative and postoperative lesion depth) were associated with the type of restorative material used. Conclusions. Several practitioner and practice, patient and lesion characteristics were associated significantly with use of amalgam and RBC: geographical region, years since dentist s graduation, patient s dental insurance status, tooth location and surface, and preoperative and postoperative lesion depth. Clinical Implications. Despite advances in esthetic dentistry, U.S. dentists still are placing amalgam on posterior teeth with carious lesions. Amalgam was used more often than RBC in older patients, who may have had deeper carious lesions. Key Words. Direct resin-based composite; dental amalgam; practice-based research; multicenter studies; clinical research. JADA 2011;142(6): C O N T J I N U A I N G D A ARTIC LE 2 I O N E D U C A T Dr. Makhija is an assistant professor, Department of General Dental Sciences, School of Dentistry, University of Alabama at Birmingham, rd Ave. South, SDB 111, Birmingham, Ala , smakhija@uab.edu. Address reprint requests to Dr. Makhija. Dr. Gordan is a professor, Department of Operative Dentistry, College of Dentistry, University of Florida Health Science Center, Gainesville. Dr. Gilbert is a professor and the chair, Department of General Dental Sciences, School of Dentistry, University of Alabama at Birmingham. Dr. Litaker is an associate professor and the director of biostatistics, Department of General Dental Sciences, School of Dentistry, University of Alabama at Birmingham. Dr. Rindal is a clinical investigator and dental health care provider, HealthPartners Dental Group and HealthPartners Research Foundation, Minneapolis. Dr. Pihlstrom is the associate director, Evidence-Based Care and Oral Wellness Research, and a practitioner, Permanente Dental Associates, Portland, Ore. Dr. Qvist is an associate professor, Department of Cariology and Endodontics, School of Dentistry, University of Copenhagen, Denmark. 622 JADA 142(6) June 2011

2 an effective low-cost restorative treatment with a long clinical life. 15,21-25 In the early 1990s, results of one study showed that the typical life span of posterior RBC was three to 10 years, with large restorations lasting fewer than five years. 26 However, the quality of RBC material has since improved, 27 and results of a longitudinal study regarding RBC restorations demonstrated a success rate of 76 percent after 17 years, with success being defined as color matching, no marginal discoloration, marginal integrity and no loss of surface texture or anatomical form. 28 On the one hand, amalgams are not as technique sensitive 29,30 and are associated with less postoperative sensitivity than are RBCs, 5 and results of a longitudinal study showed that complex amalgam restorations had a better survival rate than did complex RBC restorations. 31 On the other hand, with RBC restorations, greater retention may be achieved with a smaller cavity preparation, which might lead to greater conservation of tooth structure. 6 Therefore, certain characteristics of practitioners, practices, patients and carious lesions likely influence whether a practitioner restores a tooth with a carious lesion with amalgam or RBC. As participants in The Dental Practice-Based Research Network (DPBRN), we conducted a study regarding the placement of restorations on previously unrestored tooth surfaces in daily clinical practice. 32,33 Dentists in this study recorded information about certain patient and carious lesion characteristics during the study. DPBRN is a consortium of dental practices whose purpose is to answer questions raised by dental practitioners in everyday clinical practice and to evaluate the effectiveness of current strategies to prevent, manage and treat oral diseases and conditions. 31,34 The DPBRN includes dental practitioner-investigators (dentists and hygienists) from the United States and Scandinavia, mainly from five regions: dalabama/mississippi (AL/MS); dflorida/georgia (FL/GA); ddentists in Minnesota, either employed by HealthPartners (Bloomington, Minn.) or in private practice (MN); dpermanente Dental Associates, in cooperation with Kaiser Permanente s Center for Health Research in Portland, Ore. (PDA); ddenmark, Norway and Sweden (SK). DPBRN represents substantial diversity of both dentists and patients with regard to practice types (large group, small group, public), treatment philosophies, race, ethnicity, workload, age and sex. Results from previous analyses demonstrated that DPBRN dentists have much in common with dentists at large. 35 The purpose of this study was to test the hypothesis that certain factors (practitioner and practice, patient and carious lesion characteristics) are associated with use of restorative material types (amalgam and RBC) that DPBRN practitioners in the United States used to place the first restoration on permanent posterior tooth surfaces. PARTICIPANTS, MATERIALS AND METHODS Selection and recruitment process. To become a member of DPBRN, practitioners must first complete a DPBRN enrollment questionnaire. This questionnaire, which is publicly available at supplement.aspx under the heading DPBRN Enrollment Questionnaire, collects information about practitioner, practice and patient characteristics. DPBRN regional coordinators recruited practitioners to become members of the network through continuing dental education courses sponsored by the DPBRN; they also sent letters to licensed dentists from the participating regions. To be eligible for the DPBRN study Reasons for Placing the First Restoration on Permanent Tooth Surfaces, practitioners had to complete both the DPBRN enrollment questionnaire and a questionnaire regarding how they diagnose and treat dental caries (also available at www. dpbrn.org/users/publications/supplement.aspx under the study title), attend a DPBRN orientation session or watch a video of it, and complete their training in human participants protection. Study design. Details of the DPBRN study Reasons for Placing the First Restoration on Permanent Tooth Surfaces are available elsewhere. 33 Briefly, this study was a cross-sectional study that DPBRN practitioner-investigators conducted in their offices. The institutional review boards of the universities in each region that have agreed to work with the DPBRN, as well as HealthPartners and Kaiser Permanente, approved the study. All patients who took part in this investigation provided informed consent after dentists or members of dentists staffs provided them with a full explanation of the nature of the procedures. The practitioners recorded data regarding ABBREVIATION KEY. AL/MS: Alabama and Mississippi. DPBRN: Dental Practice-Based Research Network. FL/GA: Florida and Georgia. LGP: Large group practice. MN: Minnesota. PDA: Permanente Dental Associates. PHP: Public health practice. RBC: Resin-based composite. SGP: Small group practice. JADA 142(6) June

3 consecutively seen patients who had provided informed consent and had received a restoration on a previously unrestored permanent tooth surface. The practitioner could enroll as many as four restorations per patient and continued to collect data until information regarding 50 restorations had been collected. We established this limit in the study design phase, with the goal of reducing varianceinflation due to patient-level clusters of observations and, thus, increasing the study s precision. This approach also provided a larger number of patients for a given total sample size, thus improving the generalizability of the study results. We defined primary caries as the first carious lesion on a surface not related to an existing restoration. Practitioners also recorded the technique used to diagnose the lesion: clinical assessment, radiography and transillumination or optical technique. Each practitioner maintained a consecutive patient log in which to record information about each eligible restoration regardless of whether the lesion was enrolled. Practitioners enrolled 95 percent of eligible patients in the study. Copies of all data collection forms are available under the study title at users/publications/supplement. aspx. Table 1 shows factors tested for their association with restorative material used. We grouped these factors into three categories: dpractitioner and practice characteristics; dpatient characteristics; dcarious lesion characteristics. Practitioner and practice characteristics. We col- TABLE 1 Frequency distributions of potential predictors of type of restorative material used.* CHARACTERISTIC NO. PERCENTAGE Regional Participation Practitioner-investigators, according to DPBRN region Alabama/Mississippi Florida/Georgia Minnesota PDA TOTAL Restorations, according to DPBRN region Alabama/Mississippi 1, Florida/Georgia 1, Minnesota 1, PDA 1, TOTAL 5, Patients, according to DPBRN region Alabama/Mississippi 1, Florida/Georgia Minnesota PDA TOTAL 3, Practitioner and Practice Characteristics Male Female TOTAL Years Since Graduation Data missing 7 4 TOTAL Type of Practice Large group practice (four or more practitioners) Small group practice (three or fewer practitioners) Public health practice 2 1 TOTAL Practice Workload Too busy to treat all patients 17 9 Provided care to all patients, but overburdened Provided care to all patients, but not overburdened Not busy enough Data missing 7 4 TOTAL * Includes only restorations involving the use of amalgam or resin-based composite. DPBRN: Dental Practice-Based Research Network. Minnesota: Area encompasses dentists either employed by HealthPartners (Bloomington, Minn.) or working in private practice. PDA: Permanente Dental Associates, in cooperation with Kaiser Permanente s Center for Health Research (Portland, Ore.). SD: Standard deviation. # Percentages of 3,672 posterior one-surface restorations. 624 JADA 142(6) June 2011

4 TABLE 1 (CONTINUED) CHARACTERISTIC NO. PERCENTAGE Patient Characteristics Male 1, Female 1, Data missing 7 0 TOTAL 3, Race White 2, Black or African American Other (American Indian/Alaska Native/Asian/Pacific Islander) Data missing TOTAL 3, Hispanic or Latino ethnicity Hispanic or Latino Not Hispanic or Latino 2, Data missing TOTAL 3, Dental Insurance Yes 2, No Data missing 9 0 TOTAL 3, Mean (± SD ) age in years (n = 3,407) 31.1 (16.4) Carious Lesion Characteristics Tooth location Molar 3, Premolar 1, TOTAL 5, Posterior tooth surface Multisurface 1, One surface 3, One occlusal surface 1, # One mesial or distal surface 1, # One buccal or lingual surface # Depth as estimated preoperatively E1, outer one-half of enamel E2, inner one-half of enamel D1, outer one-third of dentin 2, D2, middle one-third of dentin 1, D3, inner one-third of dentin Uncertain 32 1 Data missing 65 1 TOTAL 5, Depth as determined postoperatively E1, outer one-half of enamel E2, inner one-half of enamel D1, outer one-third of dentin 2, D2, middle one-third of dentin 1, D3, inner one-third of dentin Data missing 34 1 TOTAL 5, lected practitioner-level variables from the DPBRN enrollment questionnaire. In addition to DPBRN region, this form also included questions related to dentists sex, year of graduation, type of practice and practice workload. We recategorized the graduationyear variable to enable us to identify the number of years since graduation: five years or less, six to 15 years, 16 to 19 years and 20 or more years. We characterized type of practice as large group practice (LGP), solo or small group practice (SGP) and public health practice (PHP). We defined LGPs as practices consisting of four or more practitioners, SGPs as those consisting of three or fewer practitioners and PHPs as those receiving the majority of their funding from public sources. In the AL/MS region, 98 percent (62 of 63) of the practitioners worked in SGPs and 2 percent (one of 63) in a PHP. In the FL/GA region, 97 percent (36 of 37) of the practitioners were in SGPs and 3 percent (one of 37) in a PHP. In the MN region, 90 percent (28 of 31) of practitioners were in LGPs and 10 percent (three of 31) were in SGPs. All practitioners (51 of 51) in the PDA region were in LGPs. Table 1 shows the responses. Patient characteristics. If the patient consented, the practitioner completed a data collection form regarding the tooth or teeth being restored. This included information regarding the patient s race, ethnicity, age and sex, as well as whether the patient had dental insurance. Table 1 shows the responses to these questions. Carious lesion characteristics. The practitioner also provided information about the carious lesion itself. JADA 142(6) June

5 This included dtooth number (we used only premolars and molars for our analyses in this report); dthe surface(s) restored; dthe main reason for placing the restoration: carious or noncarious (we confined analyses in this report to restorations placed mainly because of primary caries); dlesion depth as estimated preoperatively; dlesion depth as determined postoperatively. For the purposes of these analyses, we categorized the treated tooth surface as either multisurface or one surface (occlusal, mesial or distal, and buccal or lingual). To classify the preoperative and postoperative lesion depth, we used the following categories: de1, outer one-half of enamel; de2, inner one-half of enamel; dd1, outer one-third of dentin; dd2, middle one-third of dentin; dd3, inner one-third of dentin. Because restorations completed with materials other than amalgam or RBC were relatively uncommon (4 percent; 247 of 5,846), we limited our analyses to amalgam and RBC restorations. Table 1 shows responses to these questions. Statistical methods. We analyzed data by using statistical software (SAS Version 9.2, SAS Institute, Cary, N.C.). We considered P <.05 to be statistically significant. We calculated descriptive statistics as numbers and percentages of restorations composed of amalgam rather than RBC; we present numbers and percentages for each level of the predictor variables. We evaluated statistical significance by using generalized estimating equation modeling to implement logistic regression analysis, which helped us account for correlated observations owing to multiple restorations placed by the same dentist and as many as four restorations within the same patient. Table 2 shows associations between each of the potential predictor variables and each of the materials. We used three blocks of potential predictors to develop multivariate models to predict use of TABLE 2 Associations of individual potential predictor variables with use of amalgam or resin-based composite (RBC) restorations.* CHARACTERISTIC 626 JADA 142(6) June 2011 TYPE OF RESTORATION, NO. (%) Amalgam (n = 3,028) Regional Participation RBC (n = 2,571) Restorations, according to DPBRN region Alabama/Mississippi 663 (36.2) 1,171 (63.8) Florida/Georgia 283 (26.5) 785 (73.5) Minnesota 814 (75.7) 262 (24.3) PDA 1,268 (78.2) 353 (21.8) Practitioner and Practice Characteristics Male 2,250 (50.8) 2,180 (49.2) Female 778 (66.6) 391 (33.4) Years since graduation (60.8) 346 (39.2) (68.9) 337 (31.1) (56.1) 387 (43.9) 20 1,175 (45.9) 1,386 (54.1) Type of practice Large group practice (four or more 2,064 (79.0) 548 (21.0) practitioners) Small group practice (three or 947 (32.2) 1,993 (67.8) fewer practitioners) Public health practice 17 (36.2) 30 (63.8) Practice workload Too busy to treat all patients 346 (58.3) 248 (41.8) Provided care to all patients, but 497 (52.7) 447 (47.3) overburdened Provided care to all patients, but 1,727 (55.9) 1,362 (44.1) not overburdened Not busy enough 357 (44.9) 439 (55.1) P VALUE < < * P values from individual regression models account for clustering within practitioner. All numbers are at the restoration level. DPBRN: Dental Practice-Based Research Network. Minnesota: Area encompasses dentists either employed by HealthPartners (Bloomington, Minn.) or working in private practice. PDA: Permanente Dental Associates, in cooperation with Kaiser Permanente s Center for Health Research (Portland, Ore.). # SD: Standard deviation. ** The association between tooth location and material was confounded by clustering in the data set because of unequal numbers of restorations and varying proportions of material usage for different dentists. Appropriately accounting for clustering in the analysis demonstrated a significant association that was not apparent from the raw percentages. amalgam versus RBC: practitioner and practice characteristics, patient characteristics and carious lesion characteristics (Table 3, page 628). We conducted separate analyses for each block. We then included variables showing significant association at P <.10 in a multiple logistic regression model. To avoid excluding variables that might become more significant in the mul-

6 TABLE 2 (CONTINUED) CHARACTERISTIC TYPE OF RESTORATION, NO. (%) Amalgam (n = 3,028) Patient Characteristics RBC (n = 2,571) Male 1,516 (58.8) 1,064 (41.2) Female 1,500 (49.9) 1,506 (50.1) Race White 2,123 (51.0) 2,037 (49.0) Black or African American 381 (53.4) 332 (46.6) Other (American Indian/Alaska 205 (72.9) 76 (27.1) Native/Asian/Pacific Islander) Hispanic or Latino ethnicity Hispanic or Latino 172 (49.0) 179 (51.0) Not Hispanic or Latino 2,581 (52.8) 2,304 (47.2) Dental Insurance Yes 2,657 (56.4) 2,055 (43.6) No 367 (41.9) 508 (58.1) Mean (± SD # ) age in years 30.5 (15.2) 27.5 (15.3) <.001 Carious Lesion Characteristics Tooth location Molar 2,108 (54.3) 1,778 (45.8) Premolar 920 (53.7) 793 (46.3) Posterior tooth surface Multisurface 1,104 (57.3) 823 (42.7) One surface 1,924 (52.4) 1,748 (47.6) One occlusal surface 765 (41.0) 1,101 (59.0) One mesial or distal surface 796 (78.3) 220 (21.7) One buccal or lingual surface 363 (45.9) 427 (54.1) Depth as estimated preoperatively E1, outer one-half of enamel 53 (25.1) 158 (74.9) E2, inner one-half of enamel 212 (33.7) 417 (66.3) D1, outer one-third of dentin 1,697 (56.6) 1,300 (43.4) D2, middle one-third of dentin 783 (59.6) 531 (40.4) D3, inner one-third of dentin 214 (61.0) 137 (39.0) Uncertain 13 (40.6) 19 (59.4) Depth as determined postoperatively E1, outer one-half of enamel 40 (31.5) 87 (68.5) E2, inner one-half of enamel 143 (32.4) 299 (67.7) D1, outer one-third of dentin 1,399 (56.7) 1,069 (43.3) D2, middle one-third of dentin 1,007 (55.2) 816 (44.8) D3, inner one-third of dentin 425 (60.3) 280 (29.7) tivariate model, we included in a final predictive model the variables that were significant. RESULTS Table 1 shows the overall frequency results. A total of 229 practitioner-investigators participated in the study, but because amalgam is being phased out or already banned in Denmark, Norway and Sweden, 4,7 we did not include the Scandinavian DPBRN practitioners in these analyses. P VALUE Therefore, the final number of practitioners, for the purpose of this analysis, was 182. Although a total of 9,980 lesions were enrolled in the study, we excluded from our report any restorations <.001 placed on teeth with noncarious lesions (n = 1,539), placed on anterior teeth (n = 2,087), consisting of a material other than amalgam or.026 RBC (n = 930) or placed in non- U.S. regions of the DPBRN (Scandinavia) (n = 1,312); this resulted in an enrollment of 5,599 restorations in 3,421 patients. Note that.783 the exclusion categories are not mutually exclusive..040 Regional participation. The highest percentage of practitionerinvestigators was from the AL/MS region, followed by PDA, FL/GA and MN (Table 1). About one-third of the restorations were placed in.001 ** patients from the AL/MS region, followed by PDA, with the MN and FL/GA regions each representing 19 percent (1,076 of 5,599 and <.001 1,068 of 5,599, respectively) of the restorations (Table 1). Practitioner and practice characteristics. With regard to practitioners characteristics (Table 1), 81 percent (147 of 182) of the practitioner-investigators <.001 who participated in this study were male, 47 percent (86 of 182) had graduated 20 or more years previously, and a majority of the practitioner-investigators worked in an SGP (56 percent; 101 of 182). When asked about practice workload, 56 percent (101 of 182) of the <.001 practitioners responded that they were able to provide care to all of their patients but were not overburdened, and only 9 percent (17 of 182) said they were too busy to treat all of their patients. Patient characteristics. Fifty-four percent (1,850 of 3,421) of the patients enrolled in the study were female, and 75 percent (2,561 of 3,421) were white (Table 1). Patients mean age JADA 142(6) June

7 was 31.1 years ± standard deviation (SD), 16.4 years, and 6 percent (205 of 3,421) were of Hispanic or Latino ethnicity. With regard to dental insurance, 84 percent (2,859 of 3,421) of the patients reported having some type of dental insurance. Carious lesion characteristics. As Table 1 shows, a majority of the restorations placed were located in molars (69 percent; 3,886 of 5,599) and were onesurface restorations (66 percent; 3,672 of 5,599). Of the onesurface restorations, more than one-half (51 percent; 1,866 of 3,672) were on the occlusal surface. Before preparing the tooth, practitioners assessed the depth of the lesion in the tooth to be restored. The most common estimated preoperative depth was in D1 (54 percent; 2,997 of 5,599), which coincided with the postoperative (actual) depth (44 percent; 2,468 of 5,599). Table 2 describes the associations of individual potential predictor variables with amalgam (n = 3,028) and RBC (n = 2,571) restorations. The region with the highest percentage of amalgam restorations was PDA (78 percent; 1,268 of 1,621), followed by MN (76 percent; 814 of 1,076) and AL/MS (36 percent; 663 of TABLE 3 Multivariate predictive models of use of amalgam versus resin-based composite.* CHARACTERISTIC Restorations, according to DPBRN region Alabama/Mississippi Florida/Georgia Minnesota PDA Univariate Model Regional Participation Practitioner and Practice Characteristics P VALUE Block Model Final Model <.001 NA NA Male NA Female Years since graduation Type of practice Large group practice (four or more practitioners) Small group practice (three or fewer practitioners) Public health practice Practice workload Too busy to treat all patients Provided care to all patients, but overburdened Provided care to all patients, but not overburdened Not busy enough Patient Characteristics NA <.001 <.001 < NA NA Male <.001 <.001 <.001 Female Race White Black or African American Other (American Indian/Alaska Native/ Asian/Pacific Islander) Hispanic or Latino ethnicity Hispanic or Latino.783 NA NA Not Hispanic or Latino Dental Insurance Yes No Mean (± SD # ) age in years <.001 <.001 <.001 * Variables showing significant association at P <.10 in the univariate model were included in the block model, and variables showing significant association at P <.10 in the block model were included in the final model. DPBRN: Dental Practice-Based Research Network. Minnesota: Area encompasses dentists either employed by HealthPartners (Bloomington, Minn.) or working in private practice. PDA: Permanente Dental Associates, in cooperation with Kaiser Permanente s Center for Health Research (Portland, Ore.). NA: Not applicable. # SD: Standard deviation. ** Because of high correlation with tooth location, this variable was excluded from the final model. Because of high correlation with preoperative depth, this variable was excluded from the final model. 628 JADA 142(6) June 2011

8 TABLE 3 (CONTINUED) CHARACTERISTIC Tooth location Molar Premolar Tooth surface ** Multisurface One surface One occlusal surface One mesial or distal surface One buccal or lingual surface Depth as estimated preoperatively E1, outer one-half of enamel E2, inner one-half of enamel D1, outer one-third of dentin D2, middle one-third of dentin D3, inner one-third of dentin Uncertain Depth as determined postoperatively E1, outer one-half of enamel E2, inner one-half of enamel D1, outer one-third of dentin D2, middle one-third of dentin D3, inner one-third of dentin Univariate Model Carious Lesion Characteristics 1,834), with the smallest percentage being in FL/GA (27 percent; 283 of 1,068). Practitioner and practice characteristics. The association between restorative material and practitioner s sex was significant. Male practitioners placed as many RBC restorations (51 percent; 2,250 of 4,430) as amalgam restorations, but a majority of the restorations that female practitioners placed in their patients were amalgam (67 percent; 778 of 1,169) (Table 2). The number of years since graduation was associated with the type of restorative material used, with a tendency to increased use of RBC among older dentists (P =.02). Of restorations placed by practitioners who had graduated five or fewer years previously, 61 percent (536 of 882) were amalgam; of restorations placed by dentists who had graduated 20 or more years previously, 46 percent (1,175 of 2,561) were amalgam. The type of practice also was associated with the type of material used. A large percentage of amalgam restorations were placed in LGPs (79 percent; 2,064 of 2,612). Alternatively, a large percentage of RBC restorations were placed by practitioners who were in an SGP (68 percent; 1,993 of 2,940) or a PHP (64 percent; 30 of 47). Practice workload was not statistically significant. A little more than one-half of the amal - Final Model gam restorations (58 percent; 346 of 594) were placed by practitioners who indicated they were too busy to treat all of their patients. Patient characteristics. Among patients, sex was associated with type of restorative material used (Table 2). Male patients were more likely than were female patients to receive amalgam restorations (59 percent; 1,516 of 2,580). Amal - gam and RBC restorations were distributed approximately equally among female patients. The patient s race also was associated significantly with the material used. The proportion of amalgam restorations placed in white (51 percent; 2,123 of 4,160) and black or African American (53 percent; 381 of 713) patients was almost equal; however, 73 percent (205 of 281) of the restorations placed in patients of other race (American Indian/AlaskaNative/Asian/ Pacific Islander) were amalgam. Ethnicity was not associated with the material used, with amalgam and RBC placement distributed approximately equally among Hispanic and non- Hispanic patients. With regard to dental insurance status, practitioners placed amalgam restoration (56 percent; 2,657 of 4,712) rather than RBC restorations more often in patients who had insurance. A larger percentage of patients who did not have dental insurance received RBC restorations (58 percent; 508 of 875) rather than amalgam restorations. Carious lesion characteristics. All variables regarding lesion characteristics were significantly related to the type of material used (Table 2). More than one-half of the restorations placed in either molars (54 percent; 2,108 of 3,886) or premolars (54 percent; 920 of 1,713) were amalgam. In addition to tooth location, more than one-half of the restorations placed on P VALUE Block Model.001 <.001 <.001 <.001 <.001 NA < <.001 < NA JADA 142(6) June

9 multiple surfaces (57 percent; 1,104 of 1,927) or on one surface (52 percent; 1,924 of 3,672) also were amalgam. Of the restorations placed on one surface, only 41 percent (765 of 1,866) of those placed on the occlusal surface were amalgam, 78 percent (796 of 1,016) placed on the mesial or distal surface were amalgam and 46 percent (363 of 790) placed on the buccal or lingual surface were amalgam. The greater the preoperative lesion depth was estimated to be, the more likely amalgam was to be used. For lesions perceived preoperatively to be limited to E1, practitioners used amalgam in one-fourth (53 of 211) of the restorations, and for those limited to D3, practitioners used amalgam in 61 percent (214 of 351) of the restorations. For postoperative depth (actual depth), we noted a similar pattern. On average, more RBC than amalgam restorations were placed in younger people. The mean age of patients receiving RBC restorations was 27.5 years (± SD, 15.3 years) compared with 30.5 years (± SD, 15.2 years) for patients receiving amalgam restorations. Patients with both amalgam and RBC restorations. Only a small percentage of patients received both amalgam and RBC restorations (3 percent; 107 of 3,421), all of which were placed during the same visit on different teeth. A majority of these patients were enrolled from the PDA region (57 percent; 61 of 107), followed by AL/MS (19 percent; 20 of 107), FL/GA (15 percent; 16 of 107) and MN (9 percent; 10 of 107). More than one-half of these patients were female (54 percent; 58 of 107), white (82 percent; 88 of 107) and non-hispanic (90 percent; 96 of 107). Most of these patients had dental insurance (89 percent; 95 of 107). Block model for practitioner and patient characteristics. Table 3 shows the block model for practitioner and patient characteristics. Practitioner and practice characteristics included sex, years since graduation and type of practice. Only type of practice was significant (P <.001) in the block model. The patient characteristics model included sex, race, Hispanic or Latino ethnicity, age and dental insurance status. All of these except Hispanic or Latino ethnicity remained significant in the block model. We included tooth location, tooth surface, preoperative lesion depth and postoperative lesion depth in the lesion characteristics model, and all were significant in the block model. The block models led to the development of a final model including type of practice; patient s sex, race, age and dental insurance status; tooth location; tooth surface; preoperative lesion depth; and postoperative lesion depth. Owing to strong association between tooth location and tooth surface (contingency coefficient = 0.308, P <.001) and between preoperative and postoperative lesion depth (contingency coefficient = 0.768, P <.001), we excluded tooth surface and postoperative lesion depth from the final model. Thus, the final model included type of practice; patient s sex, race, age and dental insurance status; tooth type; and preoperative lesion depth, with all variables significant (P <.05). DISCUSSION These results suggest that many factors are associated with material use when a dentist is placing the first restoration on a tooth surface. Although many materials are available, amalgam and RBC were the materials used for most of the first-time restorations in posterior teeth with carious lesions. There is an increasing trend in the use of esthetic materials in the United States, 6-11 but amalgam still is being used in the United States for many restorations, including those placed in dentists themselves. Results of an Internet survey of more than 700 dentists indicated that of the 5,908 molar restorations present in the dentists own mouths, 36 percent (2,104 of 5,908) were amalgam, compared with just 7 percent (400 of 5,908) that were RBC. 9 Regional differences. Selection of restorative material differed significantly among regions. For the AL/MS region, in which 98 percent (62 of 63) of dentists were in SGPs, 64 percent (1,171 of 1,834) of the restorations placed were RBC. In the FL/GA region, in which 97 percent (36 of 37) of dentists were in SGPs, 74 percent (785 of 1,068) of the restorations placed were RBC. In the MN region, in which 90 percent (28 of 31) of dentists were in LGPs, only 24 percent (262 of 1,076) of the restorations placed were RBC. In the PDA region, in which all 51 of 51 dentists were in LGPs, only 22 percent (353 of 1,621) of the restorations placed were RBC. Dentists in LGPs (the PDA and HealthPartners [MN] practices) tended to place amalgam restorations rather than RBC restorations, which may be due to the fact that practitioners in LGPs are not compensated solely according to production, but rather according to a mix of fixed base salary and pay-for-performance measures. In a study involving Norwegian clinicians, researchers found that salaried dentists used RBC less often, 9 which is consistent with our findings that salaried dentists are less likely to use RBC compared with those in private-practice settings. Researchers in a 2009 study regarding the selection of dental materials in public health clinics in Sweden found that 93 percent of all the restora- 630 JADA 142(6) June 2011

10 tions placed because of primary caries consisted of RBC and less than 1 percent consisted of amalgam. 6 Although these findings are in contrast to those of both the 1999 Norwegian study 9 and our study, this Swedish investigation was more recent than those studies and its findings may reflect the fact that amalgam is being phased out or already banned in Denmark, Norway and Sweden. 4,7 Years in practice. The most recent graduates (those out of dental school five years or fewer) placed amalgams in 61 percent (536 of 882) of their restorations. This finding is in contrast to reports that numerous schools do not teach students how to use amalgam and that older dentists are not as experienced in placing RBC. 36,37 One possible reason for the high proportion of amalgam restorations is that recent graduates may work in LGPs rather than SGPs. We found that PDA s practitioner-investigators were the youngest compared with those in the other DPBRN regions, with many of them having graduated less than five years previously. 38 Alternatively, we found that older clinicians may work in SGPs, with private insurance or cash services, and may receive higher compensation for placing RBCs. Characteristics. For patients, we found that sex, race and dental insurance status were associated significantly with material use. Results of one study of Norwegian clinicians also showed a sex difference in the selection of materials; female patients were more likely than male patients to have received RBC than amalgam restorations (73 percent versus 65 percent, respectively). 9 For restorations, all variables were significant: tooth location, tooth surface, preoperative lesion depth, postoperative lesion depth and patient s age. Our finding that younger patients were more likely to have received RBC restorations is consistent with those of another study in which investigators found that older patients received more amalgam than RBC restorations, which they noted could be related to the size of the restoration placed. 9 Limitations. This study had some limitations. The sample size for individual predictors varied owing to nonresponses. Also, the data collection form did not allow respondents to record other reasons, such as patient request, for placement of certain materials. In this study, we investigated treatment as delivered in everyday, real-world clinical practice and therefore made no attempt to standardize or calibrate treatment. However, we chose dentists from each of the regions, and recent publications by DPBRN researchers suggest that although DPBRN dentists are substantially diverse, they have much in common with dentists at large. 35 CONCLUSION To our knowledge, this is the first study in recent years in which investigators have tested whether certain factors are associated with the type of material that dentists in the United States use to restore carious posterior teeth. The results suggest that several characteristics of practitioners and practices, patients and carious lesions are associated with practitioners use of amalgam and RBC. Disclosure. None of the authors reported any disclosures. The investigation described in this article was funded by grants U01-DE and U01-DE from the National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Md. Opinions and assertions contained herein are those of the authors and are not to be construed as necessarily representing the views of the respective organizations or the National Institutes of Health. The authors obtained informed consent from all human participants involved in this investigation after fully explaining the nature of the procedures. The Dental Practice-Based Research Network (DPBRN) Collaborative Group comprises practitioner-investigators, faculty investigators and staff investigators who contributed to this DPBRN study, titled Reasons for Placing the First Restoration on Permanent Tooth Surfaces. Lists of these people are available at uploadeddocs/reasons%20for%20placing%20first%20restorations_ pdf. 1. Traebert J, Marcenes W, Kreutz JV, Oliveira R, Piazza CH, Peres MA. Brazilian dentists restorative treatment decisions. Oral Health Prev Dent 2005;3(1): Braga SR, Vasconcelos BT, Macedo MR, Martins VR, Sobral MA. 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