4 SDA + RPD SDA SDA previous RPD Complete dentition Wear on anterior teeth SDA + RPD SDA SDA previous RPD Complete dentition Wear on premolars SDA + RPD SDA SDA previous RPD Complete dentition Table 3: Mean scores (SD) for reported awareness of bruxism. Observations International Journal of Dentistry 6-year 0.7 (0.6)b∗c∗ 0.4 (0.6) 0.2 (0.4)b 0.3 (0.5)c 6-year 1.8 (0.1) 1.9(0.1) 1.8 (0.1) 1.7 (0.1) 1.5 (0.1)h∗∗ 1.4 (0.1)i∗∗ 1.4(0.2)j∗∗ 1.1(0.1)hij 9-year 0.5 (0.6) 0.5 (0.7) 0.3 (0.4) 0.4 (0.7) 9-year 1.9 (0.1) 1.9 (0.1) 1.8 (0.1) 1.8 (0.1) 1.6 (0.2)k∗∗ 1.4 (0.1)l∗ 1.6 (0.2)m∗ 1.1(0.1)klm Baseline 0.6 (0.7)a∗∗ 0.4 (0.7) 0.4 (0.7) 0.2 (0.4)a Baseline 1.7 (0.1) 1.5 (0.1) 1.5 (0.1) 1.4 (0.1) 1.3 (0.1)c∗∗ 1.0 (0.1)d∗ 1.0 (0.1) 0.8 (0.1)cd 3-year 0.3 (0.6) 0.4 (0.6) 0.3 (0.6) 0.3 (0.5) 3-year 1.8 (0.1) a∗∗ 1.7 (0.1)b∗ 1.7 (0.1) 1.5 (0.1)ab 1.4 (0.1)e∗∗∗ 1.2 (0.1)f∗∗ 1.3 (0.1)g∗∗ 0.9 (0.1)efg Same letters indicate signiﬁcant diﬀerence comparing the four dental groups at the same observation. ∗ : .01 < P ≤ .05; ∗∗ : .001 < P ≤ .01; ∗∗∗ : P ≤ .001 SDA: shortened dental arch, RPD: mandibular distal extension removable partial denture. Table 4: Mean scores (SE) of occlusal tooth wear of lower anterior teeth and upper and lower premolars at the right side of the dentition. Observations same letters indicate signiﬁcant diﬀerence comparing the four dental groups at the same observation. ∗: .01<P ≤.05; ∗∗ := .001 < P ≤ .01; ∗∗∗: P ≤ .001. SDA: shortened dental arch, RPD: mandibular distal extension removable partial denture. eﬀect, showing increase of both vertical (P < .0001) and horizontal overlap (P = .04). Regarding occlusion on denture teeth, the more distal the location, the lower the number of occlusal contacts in Intercuspal Position (Table 7). The percentage of potential possible contacts decreased from 70% for second premolars via 50% for ﬁrst molars to 30% for second molars. 4. Discussion This longitudinal study deals with a relative small conve- nience sample of subjects with diﬀerent periods of times that the shortened dental arch existed and diﬀerent times of wearing or having worn a distal extension removable partial denture at baseline. Matching of the study groups was not perfect. For example, elder subjects with complete dentitions were scarce; consequently the mean age of subjects in the shortened dental arch groups was older than for subjects with complete dentitions. Also, the mean number of occluding units amongst the shortened dental arch groups and gender distribution diﬀered slightly. Nevertheless, we consider the study groups as suﬃciently homogeneous to compare with the control group. Awareness of bruxism was reported in all groups at all observations in almost similar frequencies. We cannot explain the irregular course in awareness of bruxism in the “SDA + RPD group”. A possible explanation could be the relative frequent interventions in this group [2]. Given the relative small sample size, this high incidence could well have aﬀected the outcome, meaning that awareness could be more associated with these interventions rather than with wearing a removable partial denture as such. Moreover, of the 25 subjects with distal extension removable partial denture, ﬁve stopped wearing the device during the observation period for various reasons. However, we were not able to substantiate this possible association on the basis of our data. In conclusion, the hypothesis that subjects with moderate shortened dental arches with mandibular distal extension removable partial dentures report more often awareness of bruxism than subjects without such dentures or than subjects with complete dentitions should be rejected. On the whole, diﬀerences in occlusal wear between the shortened dental arch groups and complete dentitions were only found in the premolar regions. This might be explained by the ﬁnding that, although the total maximum bite force of subjects with shortened dental arches is lower compared to that of subjects with complete dentitions [21, 22], the center of occlusal forces has shifted mesially. Consequently, maxi- mal occlusal forces on each individual premolar are higher when molar support is absent [21, 23]. Referring to our hypothesis, as the “SDA + RPD group” did not show signiﬁ- cantly more occlusal tooth wear compared to the other short- ened dental arch groups, the hypothesis should be rejected.