Journal of Oral Rehabilitation 2004 31; 562–567 The bitewing radiograph as an assessment tool in fixed prosthodontics D. G. PURTON, B. P. NG, N. P. CHANDLER & B. D. MONTEITH Department of Oral Rehabilitation, University of Otago School of Dentistry, Dunedin, New Zealand SUMMARY Molar crown preparations, as described in the literature, have standard forms dictated by the demands of retention, resistance and the physical properties of materials. Standard designs may not be appropriate for all patients because of ethnic variations in tooth shape, pulp size and dentine thickness. Accurate data on these features could assist clinicians to minimize the risk of accidental pulpal injury. The aim of this study was to compare the first molar crown and pulp dimensions between Asian (Chinese, Korean, Malay) and other ethnic groups, using measurements from the bitewing radiographs of 121 subjects. Comparisons revealed the following significantly different features of Asian first molars: larger total pulp areas in uppers (P < 0Æ0005); shorter crowns (P < 0Æ0005); narrower upper teeth at the cervix (P < 0Æ0005); wider pulps at Introduction Anthropological studies describe differences in molar tooth crown morphology between ethnic groups (1). Little information is available on the subject of coronal pulp morphology in different ethnic groups. The combination of crown and pulp dimensions defines the hard tissue structure of the crown, and is directly relevant to operative dentistry and fixed prosthodontics. Shillingburg and Grace (2) measured the dentinal thickness at several levels in horizontally sectioned first molars from Caucasian subjects of unspecified age and sex. They reported on 22 maxillary first molars and 20 mandibular first molars. Stambaugh and Wittrock (3) similarly reported on four upper and four lower first molars without documenting the race or sex of the subjects. Informal, undocumented accounts from colleagues had drawn the authors’ attention to the possibility ª 2004 Blackwell Publishing Ltd the cervix of lowers (P < 0Æ02); more bulbous crowns (P < 0Æ0005 for uppers; P < 0Æ01 for lowers), and finally significantly thinner dentine interproximally at the cervix (P = 0Æ001 for uppers; P = 0Æ011 for lowers). Preparations with wide shoulders could pose hazards to the pulps in Asian subjects. This study emphasizes the value of bitewing films in assessing crown and pulp size and shape before making crown preparations. The experienced practitioner may intuitively include tooth and pulp morphology in treatment planning, but this appears not to be taught or documented in textbooks. KEYWORDS: pulp size, dentine thickness, bitewing, ethnicity Accepted for publication 27 November 2002 that Asian (Chinese, Korean, Malay) patients are at a greater risk than others of suffering pulp exposure during the preparation of teeth for crowns or bridges. Accurate data on tooth shape, pulp size and dentine thickness in ethnic groups could guide clinicians during treatment planning and tooth preparation, to minimize the risk of accidental pulp exposure or inflammatory changes. The aim of this study was to compare the first molar crown and pulp dimensions between Asian and other ethnic groups, using data from bitewing radiographs. Materials and methods Bitewing radiographs were taken of 121 University of Otago undergraduate dental students up to 25 years of age, over three successive years, as part of a teaching exercise. Ethical approval was gained for the study and 562 BITEWING RADIOGRAPH AS AN ASSESSMENT TOOL IN FIXED PROSTHODONTICS the students signed a consent form which also provided details of their age, sex and the ethnicity of their parents and grandparents. The subjects were grouped into two ethnic groups: Asian and others. Kodak Ektaspeed Plus E speed film*, supported in a Rinn bitewing holder and beam alignment device† was exposed using the same X-ray machine for all subjects. Processing was automatic using Kodak GBZ developer and fixer solutions. The 242 bitewing films were mounted in slides, coded and digitally scanned using a Nikon Scan 2 scanner‡. A radiograph of a standard measuring grid with 1-mm squares was also taken and scanned. An operator, who was unaware of the origin of the images, measured the maxillary and mandibular first molars using Scion Image software§ on a desktop computer. The reliability of his measurements using this method had been checked in three pilot tests, revealing a high correlation of his repeat measurements (r ¼ 0Æ90, 0Æ92 and 0Æ92, respectively) with regression slopes not differing significantly from 1Æ00. The software was calibrated from the digital image of the measuring grid film. A baseline was drawn between the mesial and distal cemento-enamel junctions, the area above this line being termed the clinical crown. The following were measured (Fig. 1): crown width and crown height, crown width at the cervix (the baseline) and pulp area in the clinical crown (above the baseline). The total pulp area above a line drawn across the most superior part of the pulpal floor (parallel to the baseline), the pulp width at the cervix (along the baseline) and the heights of the mesial and distal pulp horns were also measured (Fig. 2). Statistical analysis of the results was performed using SPSS release 11 statistical software¶. Student’s t-test was used to test for equality of means and Levene’s test for equality of variances. When data were found not to be normally distributed, the non-parametric Mann– Whitney U-test was employed. Results From the 242 bitewing films, data were available from 445 first molars. Thirty-nine teeth were not available *Kodak Co., Rochester, NY, USA. Dentsply Rinn, Weybridge, UK. ‡ Nikon Corp., Tokyo, Japan. § Scion Corp., Frederick, MD, USA. ¶ SPSS Inc., Chicago, IL, USA. † Fig. 1. Measurements made on bitewing films; 1, crown width; 2, crown height; 3, crown width at the cervix; 4, pulp area in the clinical crown. because they had been extracted, crowned, endodontically treated or because one of the required measurements could not be accurately made. The distributions of the teeth by ethnic group, sex and jaw are shown in Table 1. Pulp areas For upper molar teeth, Asian subjects had a mean total pulp area of 8Æ04  2Æ02 mm2 compared with 6Æ95  1Æ91 mm2 in the other subjects. The difference was statistically significant. There were no significant differences between groups in either total pulp area of lower molars or pulp area in the clinical crowns of uppers or lowers (Table 2). The presence of restorations led to a significant reduction in pulp area. For all subjects, the mean pulp area in the clinical crowns of the 302 unrestored teeth was 3Æ61  1Æ54 mm2 and of the 143 restored teeth was 3Æ13  1Æ50 mm2 which was a significant reduction (P < 0Æ001). ª 2004 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 31; 562–567 563 564 D . G . P U R T O N et al. 7Æ76  0Æ54 mm for the other subjects. The difference was statistically significant. The mean values for lower molars were 7Æ05  0Æ56 mm for Asian subjects and 7Æ32  0Æ56 mm for the others. This difference was also statistically significant. Asian subjects thus had significantly shorter upper and lower molar crowns. Crown widths were not significantly different between groups (Table 2). Crown and pulp widths at the cervix The upper molar crowns of Asian subjects had a mean width at the cervix of 8Æ59  0Æ66 mm compared with a mean of 8Æ94  0Æ83 mm in the other subjects. The difference was statistically significant. For lower molars the Asian group had a mean pulp width at the cervix of 4Æ28  0Æ59 mm compared with 4Æ06  0Æ83 mm for the other subjects. The difference was statistically significant. There were no other significant differences between groups for these measurements (Table 2). Fig. 2. Measurements made on bitewing films; 5, total pulp area; 6, pulp width at the cervix; 7, mesial pulp horn height; 8, distal pulp horn height. Table 1. Distributions of the first molar teeth by ethnic group, sex and jaw Upper Lower Total Asian male Asian female 72 68 n ¼ 229 43 46 Other male 63 60 n ¼ 216 Other female Total 47 46 225 220 There were too few carious lesions into dentine (n ¼ 11) to draw any conclusions about the effect of caries on pulp area. Pulp horn heights Student’s t-tests revealed that there were no significant differences in mesial or distal pulp horn heights between the two groups (Table 2). Crown heights and widths The upper molars in Asian subjects had a mean crown height of 7Æ39  0Æ56 mm compared with Crown bulbosity Subtracting crown widths at the cervix from the crown widths provided further information about crown shapes. This difference defines the bulbosity of the teeth (Table 3). For upper molars the Asian subjects had a mean difference of 2Æ77  0Æ45 mm and the other subjects had a mean of 2Æ50  0Æ51 mm. The upper molars were significantly more bulbous in the Asian subjects. For lower molars the Asian subjects had a mean difference of 2Æ38  0Æ52 mm and the other subjects had a mean of 2Æ21  0Æ40 mm. The lower molars were also significantly more bulbous in the Asian subjects. Dentine thickness at the cervix The thickness of dentine at the cervix of the teeth was derived by subtracting the pulp width at the cervix from the crown width at the cervix. Halving this difference defines the dentine stock available at the mesial and distal aspects of the teeth for operative procedures such as class II cavities or full-crown preparations. For upper molars the Asian subjects had a mean dentine thickness of 2Æ77  0Æ30 mm and the other subjects had a mean of 2Æ92  0Æ29 mm. The difference was significant. For lower molars, Asian subjects had a mean dentine thickness of 2Æ67  0Æ23 mm and the ª 2004 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 31; 562–567 BITEWING RADIOGRAPH AS AN ASSESSMENT TOOL IN FIXED PROSTHODONTICS Table 2. Mean values for pulp and crown dimensions Asian Other Asian Upper Lower Total pulp area (mm2; s.d.) 8Æ04  2Æ02* 8Æ82  2Æ14 6Æ95  1Æ91* 8Æ52  2Æ33 Pulp area in the clinical crown (mm2; s.d.) 3Æ32  1Æ46 3Æ23  1Æ48 3Æ61  1Æ37 3Æ66  1Æ83 Upper Lower Mesial pulp horn height (mm; s.d.) 1Æ48  0Æ55 1Æ40  0Æ53 1Æ76  0Æ52 1Æ74  0Æ54 Distal pulp horn height (mm; s.d.) 1Æ00  0Æ51 1Æ03  0Æ50 1Æ09  0Æ44 1Æ20  1Æ14 Upper Lower Crown height mm; (s.d.) 7Æ39  0Æ56* 7Æ05  0Æ56* Crown width mm (s.d.) 11Æ36  0Æ66 12Æ04  0Æ57 Upper Lower Crown width at the cervix (mm; s.d.) 8Æ59  0Æ66* 8Æ94  0Æ83* 9Æ66  0Æ58 9Æ69  0Æ58 7Æ76  0Æ54* 7Æ32  0Æ56* Other 11Æ44  0Æ78 11Æ90  0Æ66 Pulp width at the cervix (mm; s.d.) 2Æ96  0Æ58 2Æ86  0Æ72 4Æ06  0Æ83† 4Æ28  0Æ59† *Significant difference between Asian and others at the P < 0Æ0005 level. † Significant difference between Asian and others at the P < 0Æ02 level. Table 3. Mean values for crown bulbosity and dentine thickness Asian (mm; s.d.) Other (mm; s.d.) Table 4. Crown and pulp dimensions that were significantly larger in male subjects than in females, with P-values for the comparisons Crown bulbosity ¼ crown width minus crown width at the cervix Upper 2Æ77  0Æ45* 2Æ50  0Æ51* Lower 2Æ38  0Æ52† 2Æ21  0Æ40† Dentine thickness ¼ (crown width at the cervix minus pulp width at the cervix)/2 Upper 2Æ77  0Æ30‡ 2Æ92  0Æ29‡ § Lower 2Æ67  0Æ23 2Æ74  0Æ20§ *Significant difference at P < 0Æ0005. † Significant difference at P < 0Æ01. ‡ Significant difference at P ¼ 0Æ001. § Significant difference at P ¼ 0Æ011. other subjects had a mean of 2Æ74  0Æ2 mm. The difference was significant. The Asian subjects thus had significantly less dentine stock at the cervix of upper and lower teeth (Table 3). Asian Upper Total pulp area Pulp area in clinical crown Mesial pulp horn height Distal pulp horn height Crown height Crown width Crown width at the cervix Pulp width at the cervix Crown bulbosity Dentine thickness Other Lower Upper 0Æ01 Lower 0Æ039 0Æ037 0Æ001 0Æ000 0Æ010 0Æ000 0Æ000 0Æ05* 0Æ010 0Æ014 0Æ000 0Æ000 Student’s t-test for all comparisons, except ‘*’ which was Mann– Whitney U-value because of non-normal distribution of data. Pulp horn height and bulbosity were not related to the sex of the subjects. Sexual dimorphism Male subjects were found to have significantly larger tooth and pulp dimensions for some of the measurements made. The significance levels of these differences appear in Table 4. In summary, the lower molar crowns, pulps and cervical dentinal stock of Asian males were wider than those of Asian females. In the other subjects, the males had wider upper and lower crowns, thicker dentine in the uppers, and the lowers were taller with larger pulps. Discussion Molar tooth preparations for prosthetic crowns, as described in the dental literature, have standard forms dictated by the demands of retention, resistance and the physical properties of materials. The application of such standard designs may not be appropriate for the treatment of all patients. The requirement to provide adequate height for retention in a crown preparation could create problems ª 2004 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 31; 562–567 565 566 D . G . P U R T O N et al. in the first molar teeth of Asian patients. These teeth have significantly shorter natural crowns, which means that other features being equal, crown preparations on these teeth will provide less retention than preparations in other patients. Maximizing the gingival extension of the proximal walls to gain height will bring the gingival margin into the cervical region where the Asian teeth become significantly narrower. To maintain shoulder width and avoid undercuts the operator must place the proximal preparation walls more centrally in the tooth bringing the preparation closer than ideal to the pulp chamber. This threat to the pulp is thus an effect of tooth shape not of pulp area. The pulp areas in the clinical crowns of the teeth in Asian subjects were not different from those in the other subjects, nor were the pulp horns different in height. This problem of proximity to the pulp will be most acute with preparations for all-ceramic crowns. Allceramic crowns require gingival shoulders in the preparations of at least 1 mm uniformly around their periphery, with up to 1Æ5 mm recommended for some systems (4). Such a preparation encroaches heavily on the dentine stock at the cervical area of the tooth. Because the density and diameter of dentinal tubules increase with proximity to the pulp, the prospects of creating more pronounced hydrodynamic effects and pathways for bacterial penetration of the pulp will be greatest with these preparations in bulbous, Asian teeth. Ceramo-metal crowns requiring 1Æ2–1Æ5 mm of shoulder width in areas of porcelain coverage may similarly endanger the pulps of bulbous teeth. However compromises are possible with these crowns because metal alone may be acceptable in the interproximal cervical regions, depending on the aesthetic demand of the case. In the present study the mean thickness of interproximal cervical dentine, measured from the radiographs of non-Asian subjects was 2Æ92 mm in upper first molars and 2Æ74 mm in lowers. Shillingburg and Grace (2) recorded mean values of 2Æ53 mm and 2Æ59 mm for upper and lower first molars, respectively, in Caucasian subjects. Stambaugh and Wittrock (3) reported 2Æ67 mm and 2Æ60 mm, respectively, in subjects not specified by ethnic group. The differences between the studies no doubt reflect the different populations studied and the different techniques used. However, the thinner dentine apparent in the sectioned teeth of these two earlier studies further highlights the need for care in planning preparation designs. Shilling- burg et al. (5) cautioned against the indiscriminate use of full coverage ceramo-metal crowns when more conservative designs in metal could be used. Cast metal crowns would seem to offer the least threat to pulps, as they require the least occlusal reduction and the narrowest marginal shoulder width. This applies to all patients but may be rather more strongly indicated in Asian patients. Class II cavities for plastic restorations are also invasive of proximal dentine. The extent of the lesion largely dictates the form of the preparations. The acceptability or even desirability of undercuts makes these preparations more adaptable to individual tooth forms and thus less threatening to pulps than crown preparations. The present study considered the first molars in young adult patients. Older adults would be expected to have smaller pulps and thicker dentine. However it is unlikely that this would be clinically significant. Murray et al. (6) found that the mean rate of increase in dentine thickness was 6Æ5 lm year)1. Thus the subjects in this study would expect to gain only 0Æ065 mm of dentine by their early thirties. Deferring crown preparation solely on the basis of age does not seem appropriate. Most teeth being crowned will previously have had restorations placed, many interproximally. As described in the results this will have affected pulp size. However the reduction will be unpredictable and asymmetrical making it difficult to factor this effect into crown preparation designs. This study emphasizes the value of bitewing films in assessing crown and pulp size and shape before making crown preparations. It is noteworthy that no authoritative textbooks on operative dentistry or fixed prosthodontics could be found which referred to this use of the bitewing film. In general, this film is recommended for detecting caries, assessing restorations, determining bone levels and so on. The experienced practitioner may use bitewing films and intuitively include tooth and pulp morphology in treatment planning, but such use appears not to be taught or at least not documented in textbooks. Prosthetic crowns are known to be associated with a high incidence of post-operative sensitivity and a significant incidence of pulpal necrosis. In reporting a prospective study, Johnson et al. (7) reported that one quarter of crowned teeth were sensitive to cold 3 months after cementation. From a radiographic study Valderhaug et al. (8) estimated that after ª 2004 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 31; 562–567 BITEWING RADIOGRAPH AS AN ASSESSMENT TOOL IN FIXED PROSTHODONTICS 10 years, 8% of teeth that were vital at crowning would have signs or symptoms of pulpal deterioration. The use of bitewing radiographs to assess tooth and pulp morphology when treatment planning for crowns on molars, especially in Asian patients, may help to reduce these problems, and the possibility of unexpected pulp exposures. References 1. Kieser JA. Human Adult Odontometrics. Cambridge: Cambridge University Press; 1990: 128. 2. Shillingburg HT, Grace CS. Thickness of enamel and dentin. J South Calif Dent Assoc. 1973;41:33–52. 3. Stambaugh RV, Wittrock JW. The relationship of the pulp chamber to the external surface of the tooth. J Prosthet Dent. 1977;37:537–546. 4. Pröbster L. Survival rate of In-Ceram restorations. Int J Prosthod. 1993;6:259–263. 5. Shillingburg HT, Jacobi R, Brackett SE. Fundamentals of Tooth Preparations for Cast Metal and Porcelain Restorations. Chicago, IL: Quintessence Publishing Co; 1987: 13. 6. Murray PE, Stanley HR, Matthews JB, Sloan AJ, Smith AJ. Age-related odontometric changes of human teeth. Oral Surg Oral Pathol Oral Med Oral Radiol Endod. 2002;93: 474–482. 7. Johnson GH, Powell LV, Derouen TA. Evaluation and control of post-cementation pulpal sensitivity: zinc phosphate and glass ionomer luting cements. J Am Dent Assoc. 1993;124:39–46. 8. Valderhaug J, Jokstad A, Ambjørnsen E, Norheim PW. Assessment of the periapical and clinical status of crowned teeth over 25 years. J Dent. 1997;25:97–105. Correspondence: David G. Purton, Department of Oral Rehabilitation, University of Otago School of Dentistry, PO Box 647, Dunedin, New Zealand. E-mail david.purton@stonebow.otago.ac.nz ª 2004 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 31; 562–567 567