A detailed examination of the smile characteristics is an essential part of treatment planning in restorative dentistry especially when anterior dentition is involved and the patient has high aesthetic demands. The present study has explored common features of a posed smile among a sample of Pakistani students. Posed smile was employed in the present study mainly because it’s readily reproducible. The common findings were: average smile line, consonant smile arcs, cuspid-type smile, an upward lip curvature, with a not-touching relationship of maxillary anterior teeth with lower lip and teeth displayed up to first premolars.
Consideration of smile line has a clinical application in treatment of the patients, great care should be taken to avoid excessive display of gingiva during restoration of anterior teeth in patients with high smile lines. Average smile line was observed to be the most frequent among participants in the present study. Other studies such as Tjan et al.2 and Nold et al.3 have also reported similar findings. Tjan and Miller2 also reported that high smile line were least common in their study, this too is in agreement with the present study. Contrary to this, Nold et al.3 revealed low smile line to be least common among their study participants. Furthermore, aforementioned studies showed statistically significant differences between male and female participants for the position of smile line. However, no such difference has been observed in the present study. Clinically, it is known that low smile lines are more tolerant to inadequacies in the anterior restorations and hence it is easier for the dentist to satisfy these patients with the restorative dentistry work.12
The term smile arc has different definitions in literature of Prosthodontics, Orthodontics and Cosmetic dentistry.9 In the present study, smile arc has been defined as described by Sarver.9 A consonant smile arc is considered to be more attractive than a non-consonant smile.6 Consonant smile arc was most commonly observed among the participants of this study whereas reverse smile arc was least frequent. These findings are in agreement with Tjan and Miller,2 Nold et al.,3 and Desai et al.13 Statistically significant difference existed regarding smile arc between the two genders, this was also testified by Nold et al.3 On the other hand, Maulik and Nanda14 reported that straight smile arc was the most common finding observed in 49% of their participants followed by consonant and reverse smile arc in 40% and 10% subjects, respectively. Their methodology involved capturing spontaneous smiles by making video of orthodontically treated and untreated subjects. This may be the reason of different results from our study which involved posed smile of otherwise healthy subjects.
A large proportion of the subjects had cuspid smile in the present study, whereas previous studies10,15,16 have reported the commissure smile pattern as the most common. Liang et al. in their study on Chinese subjects reported that more female subjects were found to have commissure smile pattern while complex smile being primarily a male feature.15 The recent study did not show any gender based differences regarding the smile pattern. These differences may be attributed to the difference in population studied.
According to Hulsey;8 an upward lip curvature was the most prevalent feature in subjects of his study, which is similar to the present study. Contrary to this, Liang et al.15 showed large number of individuals with straight lip curvatures, followed by downward and upward. These contradictory results stem out to demographic variation. Dong et al.11 reported that straight to upward lip curvatures are considered more appealing than downwards. It has been documented that curvature of the upper lip cannot be altered by orthodontic treatment, thus attaining an ideal smile in a patient with downward lip curvature is limited.7
Majority of the participants in the present study, had a non-touching labiodental relationship followed by relatively few participants with covering and slightly touching relationships (with no gender based difference statistically); these results are similar to that reported by Nold et al.3 This is contradictory to the findings of Tjan et al.2. They have observed a higher percentage of touching labiodental relationship in their studies. Moreover, significant differences in males and females were also recorded. Desai et al.13 reported that with increasing age, people usually cover their maxillary incisal edges with their lower lip during smile. Dong et al.11 concluded that greater aesthetic scores were obtained for patients whose lower lips slightly touched or did not touch the maxillary anterior teeth than those whose teeth were covered by lower lip. Moreover, everted lower lip is usually seen with excessive proclination of incisors, while upright and retroclined incisors are partially covered by the lower lip.7
Data of the present study suggest that individuals usually display six maxillary anterior teeth along with the first premolars during posed smile. Dong et al and Maulik and Nanda observed teeth display upto second premolars during smile.11,14 Similar to our study, teeth display upto first premolar was also reported by Tjan et al.2 However, Nold et al.3 showed that only 24% participants (all Caucasians) showed teeth up to the first premolar on posed smile. Both these studies showed no gender based differences for extent of teeth visible during smile. And, the present study suggests that males have wider smiles, exposing more teeth than females. Greater smile width among males requires consideration during treatment planning of anterior restorations.
A correlation between pattern of smile design and upper lip curvature was observed in the present study. Most participants with upward lip curvature had a commissure smile type whereas subjects with cuspid smiles showed predominantly straight lip curvatures. Downward upper lip curvature was primarily seen in individuals with gummy smiles. A similar association was reported by Liang et al.15 where straight or upward upper lip curvatures were seen predominantly with commissural smiles, and downward upper lip curvature among subjects with cuspid type and gummy smiles.
This study also proposes a relationship between consonant smile arcs and upward lip curvature, which suggests that curvature of the upper lip may affect the position of smile arc. More research is needed to confirm if such an association among different characteristics of smile can be established. One limitation of the present study lies in its lack of generalizability. As this study was conducted in only one dental school located in the largest city of the country but it limits the generalizability of the results to the whole population. In addition, there was no information on occlusion, cephalometric/ anthropometric measurements of maxilla and mandible. A large sample size comprising of ethnically diverse group of subjects are warranted with inclusion of some other components contributing to smile such as occlusal plane, symmetry, lip length, lip thickness and smile width and gingival zenith etc.