| Sign In to gain access to subscriptions and/or personal tools. |
Modulation of Clinical Expression of Plaque-induced Gingivitis: Effect of Incisor Crown Form
1 Research Center for the Study of Periodontal Diseases, University of Ferrara, Corso Giovecca 203, 44100 Ferrara, Italy; and Correspondence: * corresponding author, l.trombelli{at}unife.it
Evidence indicates that incisor crown form correlates with clinical periodontal features. It was hypothesized that incisor crown form may explain subject differences in gingivitis expression. The present experimental gingivitis study aimed to assess the effect of incisor crown form on plaque accumulation and gingival inflammation, and on individual susceptibility to plaque-induced gingivitis. Eighty-five periodontally healthy subjects were evaluated. A negative correlation was found between incisor crown width/crown length ratio and bleeding score (p = 0.045). From the 85 subjects, two groups of subjects with either ‘long-narrow’ or ‘short-wide’ incisor form were identified. The ‘long-narrow’ group had a significantly higher bleeding score than the ‘short-wide’ group (p = 0.014). No significant differences were found in the incisor crown width/crown length ratio between previously identified ‘high responder’ and ‘low responder’ subjects (Trombelli et al., 2004a). In conclusion, incisor crown form appears to affect the bleeding response of inflamed gingival tissues, while it exerts no influence on explaining differences in individuals’ susceptibility to plaque-induced gingivitis.
Key Words: periodontal disease/gingivitis • dental plaque/diagnosis • gingivitis/diagnosis • tooth crown/anatomy
The clinical anatomical characteristics of the periodontium may vary greatly among individuals. Two markedly different anatomical types of periodontium have been recognized: the ‘flat-thick’ type, characterized by slightly scalloped and bulky marginal gingiva, associated with short and wide incisor crown form; and the ‘scalloped-thin’ type, characterized by highly scalloped and thin gingiva and associated with long and narrow incisor crown form (Olsson and Lindhe, 1991; Olsson et al., 1993; Müller and Eger, 1997; Müller et al., 2000). Studies have shown that certain clinical manifestations of plaque-induced periodontal lesions may vary among subjects with different anatomical types of periodontium. Specifically, subjects with a ‘scalloped-thin’ periodontium, i.e., long and narrow incisor crown form, exhibit greater gingival recession (Olsson and Lindhe, 1991) and shallower probing depth (Müller et al., 2000) than subjects with a ‘flat-thick’ biotype. The only reported study to examine the possible association of bleeding on probing with gingival anatomical characteristics in chronic gingivitis subjects found that, after adjustment for smoking status and tooth type, gingival dimensions (either thickness or width) did not influence bleeding tendency (Müller and Heinecke, 2002). There appear to be no studies in the literature addressing the possible association between anatomical characteristics, and specifically tooth crown form, and clinical parameters in experimental gingivitis. It was hypothesized that incisor crown form is a host-dependent factor that modulates the clinical expression of plaque-induced gingivitis. Severity of gingival inflammation is primarily dependent on quantitative (Löe et al., 1965; Breuer and Cosgrove, 1989) and interrelated qualitative (Theilade et al., 1966; Moore et al., 1982) characteristics of the accumulated bacterial plaque. However, several host-related factors, e.g., hormonal status and smoking, could modify the clinical expression of plaque-induced gingivitis (Mariotti, 1999; Tatakis and Trombelli, 2004). Severity of gingivitis in response to plaque accumulation may also be an individual trait (Wiedemann et al., 1979; Abbas et al., 1986), possibly dependent on genetically determined factors (Tatakis and Trombelli, 2004). As a first step toward characterizing such factors, we identified, from among a large pool of volunteers participating in a 21-day experimental gingivitis trial, two groups of individuals with significantly different levels of severity of gingival inflammatory response to plaque accumulation, expressed as gingival crevicular fluid levels, without any difference in either amount of plaque deposits or plaque accumulation rate (Trombelli et al., 2004a). These were described as ‘high responders’ (HR) and ‘low responders’ (LR). The aim of the present randomized, split-mouth, localized experimental gingivitis trial was to assess the impact of incisor crown form on gingivitis expression. Specifically, the study examined the effect of incisor crown form on clinical parameters of plaque accumulation and gingival inflammation. The possible association of incisor crown form with individual susceptibility to plaque-induced gingivitis, i.e., HR and LR, was also investigated.
Experimental Design and Study Population The study design was approved by the local ethics committee and was found to conform to the requirements of the ‘Declaration of Helsinki’ as adopted by the 18th World Medical Assembly in 1964 and subsequently revised (www.wma.net/e/policy/17-c_e.html). All participants provided written informed consent. The overall experimental design has been previously described (Tatakis and Trombelli, 2004; Trombelli et al., 2004a,b), and the clinical analysis of the examined population—consisting of 96 systemically and periodontally healthy non-smokers, 46 males (mean age, 23.9 ± 1.7 yrs) and 50 females (mean age, 23.3 ± 1.6 yrs)—has been detailed (Trombelli et al., 2004a,b). Briefly, a randomized split-mouth localized experimental gingivitis clinical trial was conducted in volunteers. In each subject, one maxillary quadrant was randomly assigned as ‘test’ (experimental gingivitis) and the contralateral quadrant as ‘control’. According to GCF values, as recorded on day 21 in test quadrants and standardized on cumulative plaque exposure (CPE), we were able to identify 2 sets of individuals, defined as HR (n = 24) and LR (n = 24), with significantly different levels of severity of gingivitis and similar amounts of plaque deposits. The HR group was comprised of 13 males and 11 females (mean age, 24.1 ± 1.6 yrs), and the LR group was comprised of 11 males and 13 females (mean age, 23.4 ± 1.9 yrs) (Trombelli et al., 2004a).
Clinical Parameters
Determination of Incisor Crown Form All cast measurements were made to 0.01 mm by one calibrated examiner, blinded as to any clinical data, using an electronic digital caliper (LTF, Bergamo, Italy). To assess intra-examiner reproducibility, we measured 16 randomly selected cast models twice with an interval of at least 1 hr. Measurement error was evaluated according to the standard deviation of the differences (SDD) in repeated tooth measurements. SDDs were 0.1 for CL and 0.1 for CW. P-value for the paired t test between first and second CL and CW recordings was 0.5 and 0.2, respectively.
Statistical Analysis To investigate the relationship between clinical parameters, assessed on day 21 in both test and control quadrants, and incisor crown form, we used Pearson and Spearman correlation analysis for parametric and non-parametric variables, respectively. Comparisons between subjects grouped according to crown form shape (‘short-wide’ or ‘long-narrow’) and between subjects from HR and LR groups were performed by unpaired t test and the Mann-Whitney U-test. The level of significance was set at 5%.
Study Population Incisor Crown Form Eleven of 96 cast models (1 from HR subject) presented incisal attrition or imperfections, such as fractures or bubbles, on both central incisors. Therefore, casts from 85 subjects, 41 males and 44 females (mean age, 23.6 ± 1.7 yrs), were suitable for the analysis. The CW/CL ratio for the 85 subjects displayed a normal distribution (data not shown). Mean CW/CL ratio was 0.80 ± 0.09.
From the 85 subjects, two sub-populations of subjects, representing the two extremes of the CW/CL ratio distribution (Olsson and Lindhe, 1991), were arbitrarily selected as having a ‘short-wide’ (CW/CL ratio
Relationship between Incisor Crown Form and Clinical Parameters
Comparison of Clinical Parameters between ‘Long-Narrow’ and ‘Short-Wide’ Groups Clinical parameters were recorded on day 21 in ‘long-narrow’ and ‘short-wide’ groups (Table 2  ). At the completion of the experimental gingivitis period, no significant differences in PlI, CPE, GCF, and GI were found between groups in either test or control quadrants. However, test quadrant AngBS was significantly higher in the ‘long-narrow’ group compared with the ‘short-wide’ group (p = 0.014) (Table 2).
Comparison of Incisor Crown Form in HR and LR Subjects CW/CL ratios were 0.80 ± 0.08 for HR subjects (n = 23) and 0.78 ± 0.09 for LR subjects (n = 24). No significant difference in incisor crown form was detected between HR and LR subjects (p = 0.399).
The aim of the present randomized, split-mouth, controlled trial was to determine: (1) the effect of incisor crown form on clinical parameters of plaque accumulation and gingival inflammation following a 21-day experimental gingivitis trial, and (2) the association of incisor crown form with individual susceptibility to plaque-induced gingivitis. Results from the present study indicate that subjects with a ‘long-narrow’ incisor crown form (low CW/CL ratio) present a substantially higher evoked bleeding response of inflamed gingival tissues compared with subjects with a ‘short-wide’ incisor crown form (high CW/CL ratio). Moreover, the incisor crown form seems to have no influence in explaining the different susceptibilities to plaque-induced gingivitis as detected in LR and HR subjects. Evidence indicates that incisor crown form correlates with anatomical gingival characteristics (Olsson et al., 1993; Müller and Eger, 1997; Müller et al., 2000). Individuals with ‘long-narrow’ incisor crowns present smaller width of keratinized gingiva, greater height of interdental papilla, and more pronounced scalloping of the gingival margin compared with individuals with ‘short-wide’ incisor crowns (Olsson et al., 1993). Furthermore, subjects with the ‘long-narrow’ tooth form have thin gingiva, whereas ‘short-wide’ form is associated with thicker gingiva (Müller and Eger, 1997; Müller et al., 2000). Therefore, it was hypothesized that various incisor tooth forms (CW/CL ratio) may explain subject differences in the inflammatory responses of gingival tissues to plaque, due to the associated various anatomical characteristics of the gingiva. In the present material, a significant negative correlation was found between CW/CL ratio and bleeding score assessed following 21 days of experimental gingivitis. Specifically, in test (inflamed) quadrants, subjects with low CW/CL ratio (‘long-narrow’ group) had an AngBS three-fold higher than that of subjects with a high CW/CL ratio (‘short-wide’ group). It is noteworthy that the AngBS difference between the two incisor crown form groups was not paralleled by differences in amount of plaque, plaque accumulation rate, or other parameters of gingival inflammation (GI and GCF), measured in either test or control quadrants. Consistently with previous reports (Olsson and Lindhe, 1991), the present results suggest different levels of vulnerability of inflamed marginal gingival tissues to mechanical stimuli in subjects with various incisor crown forms. These observations suggest that bleeding index data analysis in gingivitis trials should take into account the incisor crown form of participants, unless the study design (e.g., crossover studies) inherently controls for subject factors. The present findings are in contrast to the reported lack of influence of gingival dimensions on bleeding tendency, as assessed by bleeding on probing in subjects with chronic gingivitis (Müller and Heinecke, 2002). The discrepancy may be ascribed to several methodological differences between the studies. In the present study, we determined AngBS by running a periodontal probe, held approximately at an angle of 60° to the longitudinal axis of the tooth, along the marginal gingiva (Trombelli et al., 2004a; van der Weijden et al., 1994). AngBS is considered the bleeding index of choice for determining tissue changes in the experimental gingivitis model, since it is a more sensitive indicator of early changes in the gingiva (van der Weijden et al., 1994). The present study utilized incisor crown form as a substitute criterion for the determination of gingival anatomical variations, while the previous report on chronic gingivitis (Müller and Heinecke, 2002) utilized direct ultrasonic measurements of gingival thickness. In a recent study, we identified two sub-populations of individuals (HR and LR) with different levels of susceptibility to plaque-induced gingival inflammation (Trombelli et al., 2004a). HR and LR subjects were characterized by similar CW/CL ratios. This result suggests no effect of incisor crown form on individual variabilities in levels of gingivitis susceptibility. The apparent contradiction between the reported association of high AngBS with low CW/CL ratio and the lack of effect of incisor crown form on gingivitis susceptibility may be explained by two facts. First, identification of HR and LR subjects was based on GCF levels and not on bleeding index. Second, although HR and LR subjects exhibited significantly different AngBS, the difference in AngBS between the two groups (Trombelli et al., 2004a) was much less than the difference in AngBS observed here between the ‘long-narrow’ and ‘short-wide’ groups.
We express our gratitude to Drs. Marina Tosi, Elisa Orlandini, and Sabrina Bottega, University of Ferrara, for their notable service in clinical procedures, and Dr. Chiara Scapoli for her assistance in statistical analysis. This study was supported by the Ministry of Education, University and Research of Italy (grant ‘ex 60% 2000’), by the Ohio State University Section of Periodontology, and by GABA International AG, Münchenstein, Switzerland. Received for publication October 28, 2003. Revision received June 23, 2004. Accepted for publication June 29, 2004.
Journal of Dental Research, Vol. 83, No. 9,
728-731 (2004)
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|
|
 |
|
Sign In to gain access to subscriptions and/or personal tools.
TOP
ABSTRACT
INTRODUCTION
coefficient (
0.91) and a ‘long-narrow’ (CW/CL ratio 
0.70) incisor crown form. Eleven subjects (mean age, 23.5 ± 2.0 yrs; six males, five females) were included in the ‘long-narrow’ group, while 12 subjects (mean age, 23.6 ± 1.7 yrs; six males, six females) were included in the ‘short-wide’ group. CW/CL ratios for the ‘long-narrow’ and ‘short-wide’ groups were 0.67 ± 0.02 and 0.95 ± 0.03, respectively (p < 0.001).