RESEARCH AND EDUCATION Maxillary lateral incisor agenesis and its relationship to overall tooth size Jane Wright, DDS, MS,a Jose A. Bosio, BDS, MS,b Jang-Ching Chou, DDS, MS,c and Shuying S. Jiang, MSd Prosthodontists, orthodontists, ABSTRACT and general dentists frequently fi Statement of problem. Agenesis of the maxillary lateral incisor has been linked to differences in encounter dif culties when the size of the remaining teeth. Thus, the mesiodistal space required for definitive esthetic resto- attempting to restore the oc- ration in patients with missing maxillary lateral incisors may be reduced. clusion if unilateral or bilateral Purpose. The purpose of this study was to determine whether a tooth size discrepancy exists in maxillary lateral incisors are orthodontic patients with agenesis of one or both maxillary lateral incisors. congenitally missing. Restora- tion of the missing lateral Material and methods. Forty sets of dental casts from orthodontic patients (19 men and 21 women; mean 15.9 years of age; all of European origin) were collected. All casts had agenesis of one incisor using an implant- or both maxillary lateral incisors. Teeth were measured with a digital caliper at their greatest supported crown, a partial mesiodistal width and then compared with those of a control group matched for ethnicity, age, and fi xed dental prosthesis, or sex. Four-factor ANOVA with repeated measures of 2 factors was used for statistical analysis (a=.05). mesial movement of the Results. Orthodontic patients with agenesis of one or both maxillary lateral incisors exhibited canine are treatment options. smaller than normal tooth size compared with the control group. The maxillary arch had a larger In order to establish the tooth size difference between the control and test groups than the mandibular arch (there was a optimal amount of space significant Jaw×Group interaction [F=4.78, P=.032]). required for an ideal restora- Conclusions. Agenesis of one or both maxillary lateral incisors is significantly associated with tion, the contralateral lateral tooth size discrepancy, which may affect the space remaining for restoration of the remaining incisor size can be used as a teeth. (J Prosthet Dent 2016;115:209-214) guide for determining the size of the missing lateral incisor.1 However, the contralateral where midlines are coincident, canines are in a class I tooth is frequently peg shaped or also missing.2 In order relationship, and an ideal vertical and horizontal overlap to determine the appropriate size, 2 methods have been is present, the space required to restore the maxillary suggested: use of the golden proportion, which indicates lateral incisor may still be insufficient. A tooth size that the lateral incisor should be approximately 62% of discrepancy in the mandibular, maxillary, or both arches the width of the central incisor; and the Bolton analysis, could explain this clinical situation. which is used to determine the required space for a Numerous studies have evaluated tooth size and missing lateral incisor.3,4 malocclusion,4-11 but no firm conclusions have been A minimum of 6 mm, but ideally 7 mm of space, is drawn as to whether tooth size can determine or affect usually recommended for an implant in the area of the malocclusions. One study found the mesiodistal dimen- lateral incisor.5,6 However, in many clinical situations, sion of the maxillary lateral incisor to be the most Supported, in part, by the American Association of Orthodontists and American Association of Orthodontists Foundation (to J.A.B.). This article is based on the Master’s thesis (J.W.) presented in 2011 in partial fulfilment of requirements for the degree of Master of Science, Marquette University School of Dentistry, 2011. aAdjunct Professor, Department of Developmental Sciences, Marquette University School of Dentistry, Milwaukee, Wis. bAssociate Professor, Department of Orthodontics, Rutgers School of Dental Medicine, Newark, N.J. cAssistant Professor, Department of Oral Health and Rehabilitation, University of Louisville School of Dentistry, Louisville, Ky. dResearch Associate I, Department of Institutional Assessment and Quality Improvement, Rutgers School of Dental Medicine, Newark, N.J. THE JOURNAL OF PROSTHETIC DENTISTRY 209 210 Volume 115 Issue 2 the maxillary lateral incisor have the same sized teeth in the Clinical Implications maxilla and mandible as those in a matched control sample. Because maxillary and mandibular teeth are smaller The secondary hypothesis was that sex, arch, and tooth type than normal in patients missing one or both affect tooth size in the missing lateral incisor group. maxillary lateral incisors, the space created or MATERIAL AND METHODS remaining for the definitive restorations may be smaller than ideal. Thus, clinicians should plan This research was approved by the Institutional Review accordingly. Board. Forty sets of dental casts (21 women, 19 men, mean 15.9 years of age), with missing maxillary lateral incisors (22 unilateral, 18 bilateral) (Fig. 1), were collected significant variable affecting tooth size arch size from local orthodontic practices. For comparison, an discrepancy compared with the mesiodistal and bucco- equal number of dental casts were collected from the lingual dimensions of other teeth.10 Graduate Orthodontics program at the Marquette Uni- Research has demonstrated that genetic factors may versity School of Dentistry to form a control group contribute to agenesis and tooth size discrepancies.12-19 matched for ethnicity, age, and sex. Inclusion criteria for Specifically, MSX1 and PAX9 mutations have been asso- the test population were: white individuals with unilat- ciated with tooth agenesis.12,15 PAX9 gene mutation has eral or bilateral agenesis of the maxillary lateral incisors, also been associated with smaller than normal teeth.19 with the other permanent teeth (except for third molars) Although individuals of different ethnic origins in both arches fully erupted; and with no evidence of experience dental agenesis, those of European origin are extreme wear, breakdown, or interproximal reduction of more often missing maxillary lateral incisors, with a any teeth. Pretreatment and post-treatment dental casts higher incidence in women.16,20,21 Men generally have were used for measurement. Post-treatment dental casts larger teeth than women within any given ethnicity. To were examined only to confirm that no interproximal minimize ethnic variations within the sample population, enamel reduction or enameloplasty had been conducted this study focused on the agenesis of maxillary lateral during treatment. Dental casts with crowns or mesio- incisors of individuals of European origin. distal restored teeth were rejected because of the modi- Few studies have discussed the relationship between fication of tooth structure and size. tooth size and agenesis.22-26 However, some studies have The mean age for the test group was 15.9 years suggested that newer implants require smaller spaces for (SD=7.12), ranging from 11 to 47 years of age, and the implant placement, leading to size reduction in tooth mean age for the control group was 15.9 years (SD=6.7). replacement.27-30 Thus, the purpose of this study was to The orthodontic program’s computerized charting system evaluate whether tooth size discrepancy is observed in (axiUm; Exan Group) was used to search for the matching white orthodontic patients with agenesis of one or both sample. Mesiodistal widths of each tooth were measured maxillary lateral incisors. Thenullhypothesiswasthator- with a high-precision digital caliper (Digital Calipers; Masel, thodontic patients with unilateral or bilateral agenesis of Henry Schein Orthodontics), with measurements rounded Figure 1. A, Patient cast showing unilateral agenesis of left maxillary lateral incisor, retained left primary canine, left permanent canine in position of lateral incisor, and peg-shaped right lateral incisor. B, Cast of patient with agenesis of both maxillary lateral incisors. Maxillary canines moved mesially into lateral incisor space. THE JOURNAL OF PROSTHETIC DENTISTRY Wright et al February 2016 211 As expected, tooth size in the maxillary arch was larger than in the mandibular arch (F=680.84, P<.001), and the maxillary arch had larger tooth size differences between control and test groups than the mandibular arch (there was a significant arches×group interaction [F=4.818, P=.031]) (Table 2). Central incisors presented the largest tooth size differ- ences between the maxillary and mandibular arches (there was a significant tooth number×jaw interaction [F=1879.67, P<.001]). The mean width for maxillary central incisors was 8.51 mm, and the mean for mandibular incisor was 5.24 mm (Table 1). First premolars had the smallest tooth size difference between maxillary and mandibular arches (Fig. 3C). The Shrout-Winer intrarater reliability test found a consistency of 0.994, confirming the excellent Figure 2. Digital caliper measuring mesiodistal widths of maxillary teeth. Teeth were measured at their widest points. reliability of the test. to the nearest hundredth of a millimeter (Fig. 2). One DISCUSSION investigator (J.W.) collected all dental cast measurements. Although clinicians discuss the minimum necessary For each combination of arches and teeth number, space for an implant when one or both maxillary lateral except for maxillary lateral incisor teeth, the left and right incisors are missing, they should focus on determining tooth sizes were averaged and used as an outcome var- the appropriate space for the implant/restoration. The iable for the tooth size in the data analysis. Because the golden proportion for the anterior teeth can be consid- maxillary lateral incisor was missing in one or both sides ered when they determine the size for the missing lateral of the arch, all lateral incisors were excluded from data incisor.3 Patients with smaller than normal maxillary and analysis. Tooth sizes were compared between the test mandibular teeth, as shown in the test sample of this and control groups and also compared for tooth study, may require a smaller than necessary 6.5-mm or numbers, both jaws, and sex.