Before initiation of any esthetic restorative treatment procedure, the clinician should determine interdental spacing and tooth size by using an appropriate instrument such as a caliper (Fig. 8.3). Maxillary central incisors are the most dominant teeth in an esthetic restorative treatment procedure, therefore, the clinician can primarily begin with the measurement of these teeth to correct median and/or polydiastemas. In addition, a detailed analysis can be performed by the orthodontist using “Bolton analysis,” which compares the overall tooth measurements in one arch relative to the other (please see below) [3].

Creating an ideal single tooth proportion is essential in diastema correction since imbalance in the restored tooth proportion may occur after diastema closure [4]. Single tooth proportion is defined by the ratio of width to length of a tooth. A pleasing and natural width to length tooth ratio is therefore important for creating an esthetically pleasing final outcome in diastema closure. It has been reported previously that a pleasing tooth proportion for maxillary central incisor should be 80 % within the acceptable esthetic range of 75–85 % (Fig. 8.4) [2, 4]. Increasing or decreasing these proportions would produce square or rectangular form (Fig. 8.5) for a single tooth and would create an unaesthetic appearance. Changes in width-length ratio can be seen frequently in diastema closure especially in direct technique and affect the proportion, size, and shape of a single tooth appearance and consequently affect the overall esthetic outcome of the final restoration. There have been different reports regarding the length of the maxillary central incisors in the literature. In previously published literature, it has been reported that the length of the maxillary central incisors measured from the gingival margin to the incisal edge should be approximately 10.5–11.0 mm for an esthetic appearance (Fig. 8.6) [5–7]. In another report, it has been stated that the average length of the maxillary central should be 10 mm, with the maximum and minimum lengths being 12 and 8 mm, respectively [8]. Another article reported that the average length of the unworn maxillary central incisors should be 12 mm ranging from 11 to 13 mm [7]. Magne et al. [9] have also reported that the average length of maxillary unworn central incisors measured from the cementoenamel junction to the incisal edge is slightly over 11 mm. For an esthetically pleasant smile, the length of the maxillary central incisors should be between 10.5 and 12 mm, with the average being 11 mm, a good starting point in the esthetic zone according to these authors [9]. In addition, for a natural and perfect appearance, ideal length of the lateral incisors should be 1 mm to 2.5 mm shorter than that of maxillary central incisors (Fig. 8.7) [10, 11]. Maxillary canines should also be slightly shorter than the central incisors ranging between 0.5 mm and 1 mm [10, 11]. The width of the ideal maxillary central incisors should be approximately 8–8.5 mm (Fig. 8.6) for accepted dimensions to create naturally esthetic form [5, 6]. The clinician should always bear in mind that maxillary central incisors are approximately 2–3 mm wider than the lateral incisors and 1–1.5 mm wider than the canines in the esthetic zone (Fig. 8.8) [12]. In addition, maxillary canines should be 1–1.5 mm wider than the laterals, and maxillary central incisors and canines should be positioned 1–1.5 mm incisally than the lateral incisors [12]. Maxillary lateral incisors and canines are also essential clinical evaluation parameters in smile analysis as they play an important role in a pleasing smile. In general, maxillary lateral incisors seem asymmetric in the arch and influence the gender characterization [2, 13]. Maxillary canines are also critical teeth since they are located at the corner of the dental arch. Only the mesial half of these teeth are visible from the frontal aspect when the patient smiles; they can support the upper lips, and position, size, and the shape of these teeth greatly affect the buccal corridor characteristics [2, 13]. In addition, canines and central incisors present gender-specific anatomical differences where feminity is characterized by roundness and smoothness, leading to an oval tooth form with round edges. On the other hand, masculinity is determined by a square shape [2, 13]. The length of the maxillary central incisor shows individual variability depending on the incisal display [8], and patients can have a pleasant smile despite the disproportionate teeth [13]. It has been previously stated that 2 mm tooth size discrepancies in the esthetic zone should be considered as a clinically significant threshold [3, 14]. If the tooth size discrepancy is less than 2 mm, the diastema can be successfully treated with orthodontic treatment [3]. If the tooth size discrepancy exceeds 2 mm, which is confirmed by the tooth size analysis, then a multidisciplinary treatment approach should be considered to enhance the size of the anterior teeth and close the space for an esthetically pleasant outcome [3]. If necessary, the clinician canprepare a diagnostic wax setup (please see Fig. 4.​3a, b) for subsequent multidisciplinary evaluation and reconsider the treatment plan [3].

According to Andrews, “six keys of the occlusion” are the prerequisites of a normal occlusal relationship [15]. These parameters include molar interarch relationship, mesiodistal crown angulation, labiolingual crown inclination, rotation, tight proximal contacts, and occlusal plane. The inability to achieve proximal contact between all teeth in an arch while maintaining ideal molar intercuspation may indicate a tooth size-arch size discrepancy or a size discrepancy between the maxillary and mandibular teeth. There are several methods of determining the cause of this discrepancy. In this chapter, the most commonly used space and tooth size analysis will be explained. For this purpose, digital models and a software program are most accurate, though standard dental models and a caliper are sufficient.