International Journal of Dentistry Reasons for drop-out were: (1) no further treatment at the dental school clinic for personal reasons (e.g. moving to another area), (2) resignation for other reasons (e.g. not keeping treatment or payment appointments), (3) deceased, and (4) no longer meeting criteria for the dental groups (e.g. due to extraction of teeth). The numbers of dropouts for the dental groups after 9 years for the reasons mentioned were respectively: “SDA + RPD group”: 5, 0, 0, 3; “SDA group”: 12, 9, 1, 3, “SDA previous RPD group”: 2, 1, 0, 4; “CD group”: 18, 8, 2, 3. 2.2. Assessments and Scores. Following a structured ques- tionnaire, subjects were asked for awareness of brux- ing habits, tempromandibular joint (TMJ) pain/muscle pain/muscle stiﬀness, restricted mandibular mobility, and clicking/crepitus. (i) Bruxism: score 0 = sometimes; 2 = often. no or not aware; 1 = (ii) TMJ pain: score 0 = no pain; 1 = mild and sometimes pain; 2 = heavy and /or often pain. (iii) Restricted mandibular mobility: 0 = no; 1 = yes. (iv) TMJ noises: 0 = no; 1 = yes. Occlusal tooth wear, vertical and horizontal overlap, maximal mouth opening, TMJ clicking/crepitus and occlu- sion on denture teeth were assessed clinically: (i) Occlusal tooth wear (teeth at right side only): score 0 = no wear facets visible; 1 = facets in enamel; 2 = wear in dentine; 3 = wear in secondary dentine (teeth with artiﬁcial crowns were excluded from analysis) [19]. (ii) Vertical and horizontal overlap: measured at the right central incisors by means of a compass and a ruler (in mm). (iii) Active (unforced) maximal mouth opening (MMO), measured at the right central incisors by means of a compass and a ruler) added by the vertical overlap (in mm): 0 ≥ 45; 1 ≥ 40 and ≤ 45; 2 ≤ 40. (iv) TMJ clicking/crepitus: audible or palpable by bilat- eral palpation during several exercises of opening and closing movements: 0 = no; 1 = dubious; 2 = yes. (v) occlusion on denture teeth: recorded in Intercuspal Position using Artus Occlusal Registration strips [20] (13 µm thickness; Artus, Englewood, NJ, USA): yes/no contact with opposing natural tooth. Contacts between mandibular denture teeth and the teeth of the 3 maxillary removable partial dentures were not considered. 2.3. Statistical Analyses. For all statistical analyses, a mixed longitudinal model was applied using SAS version 6 software. For “awareness of bruxism” the model (based on a skewed (Poisson) distribution of the scores) analyzed the eﬀects of (1) dental group, (2) time of observation, (3) gender, 3 (4) the period the shortened dental arch existed at baseline observation, and (5) the interaction between observation time and dental group. For “occlusal tooth wear”, the model (based on a normal distribution of the scores) analyzed the eﬀects of (1) dental group, (2) time of observation, (3) age, (4) reported bruxism, (5) interaction between dental group and time of observation, and (6) interaction between reported bruxism and time of observation. For signs and symptoms related to temporomandibular dysfunction, and for anterior vertical and horizontal overlap the model (based on a normal distribution of the scores) analyzed the eﬀects of (1) dental group, (2) time of observation, and (3) interaction between dental group and observation time. 3. Results Mean scores for reported awareness of bruxism (Table 3) revealed a few signiﬁcant diﬀerences amongst the groups. At baseline and at 6-year observation, subjects of the “SDA + RPD group” reported signiﬁcantly more frequently awareness of bruxism than those of the Complete Dentition group. However, diﬀerences within the shortened dental arch groups were statistically not signiﬁcant except at 6- year observation (“SDA+RPD” more often reported bruxism than “SDA previous RPD”). The mixed model revealed no signiﬁcant eﬀects on awareness of bruxism for time of obser- vation, gender, nor an interaction between observation time and dental group. The model showed only one signiﬁcant eﬀect in the ‘SDA previous RPD’ the period the shortened dental arch existed at baseline had a signiﬁcant inﬂuence on awareness of bruxism (P =.03). Occlusal wear scores for the lower anterior teeth (Table 4) did not diﬀer signiﬁcantly amongst the dental groups with two exceptions at the 3-year observation. However, time of observation (P < .0001), awareness of bruxism (P = .002), and age (P = .002) showed signiﬁcant inﬂuence on occlusal wear scores. Also occlusal wear increase over time did not diﬀer signiﬁcantly amongst the four dental groups. In addition no interaction was found between occlusal wear increase and awareness of bruxism. Occlusal wear scores for the premolars did not diﬀer amongst the three shortened dental arch groups but were signiﬁcantly higher than in the complete dentition group. The model revealed a signiﬁcant dental group eﬀect (P = .001), observation time eﬀect (P < .0001), and age eﬀect (P = .02) but no relation between occlusal wear and reported awareness of bruxism. No signiﬁcant interactions were found. Signs and symptoms related to temporomandibular dysfunction were independent from dental group and observation time (Table 5). The only associations found for these variables were interactions between dental group and observation time for the variables restricted mandibular mobility (P = .02) and palpated clicking (P = .04). The means of the vertical overlap for the diﬀerent groups ranged from 2.6 to 3.6 mm, those of the horizontal overlap from 2.7 to 4.0 mm (Table 6). The mixed model demonstrated no dental group eﬀect, but an overall time