Occurrence of Malocclusion in Attritive Environment: a Study of a Skull Sample from Southwest Finland

Occurrence of malocclusion in attritive environment: a study of a skull sample from southwest Finland

JUHA VARRELA

Department of Oral Development and Orthodontics, Institute of Dentistry, University of Turku, Turku, Finland

Varrela J: Occurrence of malocclusion in attritive environment: a study of a skull sample from southwest Finland. Scand J Dent Res 1990; 98: 242-7. Abstract - Occlusal variation atid occurrence of malocclusion were examined in a Finnish skull sample derived from the 15th and 16th centuries. The material consisted of 207 adult individuais; 141 maxilias and 159 mandibles, including 93 pairs, were in observable condition. In the skull sample, only dental anomalies were observed; no skeletal malocclasions were fonnd. The frequency of an Angle Class I lateral relationship was 97.7%. Tbe mean values for overjet and overbite were 1.6 and 1.4 tnm, respectively. A comparison with present-day Finns revealed that the skull sample showed less variation in all occlusal variables studied. An Angle Class 11 type occlusion, deep bite, crowding, spacing, and lateral crossbite occurred with significantly lower frequencies in the skull sample than in the present-day Finns. Advanced dental wear in the skull sample shows that a hard and attritive diet was eaten at that time. It is suggested that a dietary transition from hard to soft food is the most probable cause of the increased occlusal variation and bigh frequency of malocclusion in present-day Finns.

Key words: malocclusion; masticatory function; occlusal variation; paleopathoiogy. Institute of Dentistry, University of Turku, Lenmminkaisenkatu 2, SF-20520 Turku, Finland. Accepted for publication 29 December 1989.

Low occlusal variability is a typical finding Traditionally, clinical orthodontics has in preindustrialized populations (1), In emphasized genetics in the etiology of occlu- Scandinavia, a comparison of the recent epi- sal variation. Accordingly, genetic theories demiologic studies and investigations of me- have been presented to explain the develop- dieval materials indicate a considerable in- ment in prevalence of malocclusion; there is crease in occlusal variation during the last not much evidence, however, to support centuries (2-3). Mild dental and occlusal these theories (4). On the contrary, recent anomalies, including impaction, tipping, ro- twin and family data indicate that only a low tation, crowding and spacing, are found in portion, if any, of the occlusal variation can the skeletal samples but more extreme forms be ascribed to genetic variance (5-7). As of malocclusion seem to be rare.: an alternative, CORRBQCINI (1) has suggested MALOCCLU,SION IN A FINNISH SKULL SAMPLE 243

that the increase in occlusal variation is acteristics was based on visual inspection. In the caused by factors relating to a change from registration, the definitions given by MYLLARNIEMI preindustrialized food of a coarse and attri- (14) were used. The examination included rota- tive texture to a soft modern diet. According tion, crowding and spacing of teetb, impaction of to this hypothesis, malooclusions mainly re- tbe canines, overjet, overbite, sagittal jaw relationship, crossbite, scissors bite and open bite. Rota- sult from insufficient jaw size to tooth size, tion was measured using 5-degree intervals. masticatory hypofunction being the most im- Crowding and spacing were recorded as tbe differ- portant cause of the inadequate growth of ence between space available and space required the jaws (1). This hypothesis is supported by by the teetb. Overjet and overbite were measured animal experiments which show that occlusal to tbe nearest 0.1 mm for central incisors on tbe variation is increased in animals raised on right side or, if either was missing, on the left soft food (8—10). It has been suggested that side. Sagittal occlusal reiationsbip of tbe Jaws was approximal wear may be an additional ad- classified on tbe basis of the intermaxillary relation justing factor (11), although its role is con- of tbe molars and canines. If molars were missing, tbe relation of premolars was considered. In uni- troversial (1, 12). lateral cases, the general type of the occlusion was There are still few studies of occlusal varia- used as a criterion. Intermaxillary registrations tion in genetically stable populations before were only made if enough teetb were present to and after a dietary transition. In the present allow proper occlusal positioning of the jaws. Sex investigadon, a Finnish skeletal sample, de- determination was possible only in a small portion rived from the 15th and 16th centuries, is of tbe ,skeletons. As there seems to be only slight compared with present-day Finns with re- differences between tbe sexes in the frequency of malocclusion (14), no attempt was made in the gard to occlusal charcteristics and occur- present study to analyze the sexes separately. In rence of malocclusion. Marked dental attri- the comparisons witb present-day Finns, the val- tion in the skulls indicates that a hard and ues reported hy MYLLARNIEMI (14) were used by attritive diet was eaten at that titne. The aim copibining the frequencies given for the girls and of the study is to examine whether a change boys (n = 453) in the permanent dentition. Differ- from hard to soft diet does significantly affect ences between the study sample and present-day the frequency of malocclusion. Finns were statistically tested hy Fisber's exact test.

Material and methods Results The material consisted of tbe skulls and jaws of 207 adult individuals. Tbe total number of maxil- The frequencies of rotated teeth are indicated las and mandibles in observable condition were in Table 1. Of the 27 teeth rotated more than 141 and 159, itjcluding 93 pairs. The skeletal sam- 15°, 11 were maxillary and 16 mandibular ple was excavated from a medieval graveyard in teeth. In the maxilla, the majority were inci- the middle of the city of Turku. Tbe main part of sors (82%)j in the mandible, premolars tbe sample is derived from tbe 15th and 16tb (75%). Impacted maxillary canines were centuries. According to bistoric documents, the found in two, or 1.4%, of the individuals burials included mainly Finnish-speaking ddzens (n= 141); nO' impacted mandibular canines from middle and lower socioeconomic classes. were observed. The fmdings on crowding While tbe sample itself may not be fully represen- tative of tbe entire population of Turku, it provides and spacing with a space anomaly of more suitable data for examination of the relation be- than 2 mm are summarized in Table 1. tween occlusion and diet. The attritiora of the teetb Crowding occurred more frequently in the in the skulls was comparable to that reported for mandible than in the maxilla. In contrast, medieval samples froni Scandinavia (13). spacing was more frequent in the maxilla The examination of dental and occlusal cbar- than in the mandible. ^Crowding in both 244 VARRELA

Table 1 temporomandibular joint. Scissors bite was Frequency of rotation, crowding, and spacing of teeth. observed in one individual. Frequencies are given separately for the maxillary denti- The occlusal anomalies found were all tions, the mandibular dentitions, and for individuals with dental; among the present 86 individuals ohsemable maxillary and mandibular dentitions with complete occlusions, no skeletal maloc- Rotation Crowding Spacing clusions were found. In one individual, the (>15'') (>2 mm) (>2 mm) occlusal fmdings included crowding of the n Percent Percent Percent mandibular incisors and canines with space deficiency of 3.0 mm, overjet of 4.5 mm, Maxillas 141 4.4 3.5 4.3 and overbite of 3.1 mm. In addition, the Mandihies 159 7.! 10.1 0.6 Sktills with mandibular incisors were lingually inclined both jaws 93 14.0 11.8 5.4 and were not in contact with the maxillary incisors. As a result, anterior open bite result- ed in spite of positive overbite. Furthermore, a primary mandibular second molar was persisting and, on the eontralateral side, arches was observed only in two, or 2.1%, space excess of 1 mm was observed between ofthe 93 skulls with both jaws present. Two the premolars. However, in this as well as in eases were found with crowded mandibular the single cases with Angle Class II and An- premolars; in all others, either incisors or gle Class III molar occlusion, the skeletal canines or both were involved. relationship between the maxilla and the Incisal relationship was measurable in 49 mandible was harmonious. individuals. The mean value for overjet was A comparison of occlusal findings in the 1.6 mm (SD 1.2) and for overbite 1.4 mm study sample and in present-day Finns is (SD' 1.4). An edge-to-edge bite was observed shown in Table 2. As evident, variation was in several individuals: there were nine, or much lower in the skull sample than in pre- 18.4%, with both zerO' overjet and zero over- sent-day individuals. Angle Class I occlusion bite, and an additional 7, or 14.3%, with was significantly more common and Angle zero overbite only. The sagittal occlusal rela- Class II occlusion significantly rarer, tionship of the lateral segments was observ- 40'0—500 yr ago than today. In addition, deep able in 86 individuals. In 84, or 97.7%, an overbite, crowding, spacing and lateral eross- Angle Class I relationship was noted. An bite occurred with significantly lower fre- Angle Glass II relationship was found in one quencies in the skull sample. No statistically (1.2%) and an Angle Class III relationship significant difference was found in the occur- also in a single individual (1.2%). In the rence of Angle Class III occlusion, anterior former, the incisors were missing; in the lat- crossbite, anterior open bite, or scissors bite. ter, there was an edge-to-edge incisal relationship. Crossbite was found in 11, or 12.8%, of Discussion the individuals (n — &%), involving one tooth The marked increase in the frequency of in eight individuals, two teeth in one individ- malocclusion in Finland during the last few ual, and three teeth in two individuals. hundred years is in line with the earlier re- Asymmetrical attrition ofthe teeth and ar- sults which have indicated that an epidemi- thritic changes in the eondyles or articular logic transition has recently taken place in tubercles were found in three individuals the occlusion (1, 2). As discussed by CoR- with crossbite. These findings indicate func- RUCCINI & WHITLEY (4), attempts to explain tional disturbances in occlusion and in the the increased variation by genetic factors MALOCCLUSION IN A FINNISH SKULL SAMPLE 245

Table 2

Comparison of occlusal iiariability between 15th-Wth century Finns (study sample) and present-day Finns. The criteria and the figures for the present-day Finns (n = 453) are adapted from MYLLARNIEMI (14) 15th-16tb century Finns Present-day Finns (Present study) (MYLLAENIEMI (14)) Percent Percent Angle I 97.7 77.2*** Angle II 1.2 21.8*** Angle III 1.2 0.4 Overjet (< 3 mm) 8.1 16.3 Overbite (> 5 mm) 2.0 24.2*** Crowding {> 3 mm) maxilla 2.1 14.1*** mandible 6.9 17.7*** Spacing (> 2 mm) maxilla 4.3 9.9* mandible 0.6 3.9* Crossbite (> 3 teeth) anterior 1.2 2.7 lateral - 4.0* Anterior open bite 1.2 3.1 Scissors bite (> 2 teeth) - 0.8 *F<0.05, ***/><0.001 (Fisher's exact test). cannot be substantiated. Instead, CORRBC- in present-day individuals (20). A tendency CINI (1) suggested that the intensity of masti- to anterior rotation of the mandible in the cation is the most important single factor skull sample may have contributed to the affecting occlusal variation. In preindustrial- low frequency of Angle Class II type occlu- ized poptilations, the extensive wear of mo- sion. Other functional factors such as inade- lars and premolars results predominantly quate nasopharyngeal airways with altered from the effects of a coarse diet and vigorous head posture aiso seem to affect the rotation- mastication; the attrition of the anterior al growth ofthe mandible (21, 22). However, teeth, on the other hand, also seems to reflect while the dietary transition, which accompa- numerous non-dietary functions such as nies industrialization, is well documented, holding and manipulating (12, 13). The in- there is no data to indicate secular changes crease in the occurrence of malocclusion can in breathing or head posture. be explained by dietary factors if it is as- According to the hypothesis proposed by sumed that bone growth is affected by func- GoRRUcciNi (l)j malocclusion. in modern tional stimulation of chewing forces. This as- man results from insufficient jaw size to tooth sumption is supported by several studies size. This view was also shared by BEOG (11) which indicate an association between crani- who suggested that approximal attrition is ofacial morphology and size and activity of the primary factor in the adjustment of the the masticatory muscles (16-19). teeth into the dental arches. The wear of the A recent cephalometric analysis of 32 com- approximai surfaces of the teeth may indeed plete crania from the present skeletal sample have a beneficial effect on crowding in the showed that an anterior rotation ofthe man- later stages of dental development. It may dible was more common in the crania than also contribute to successful eruption of the 246 VARRELA

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