Abstract
Several systematic reviews and meta-analyses have clearly showed a lack of properly designed controlled clinical trials comparing the outcome of a combined immediate implant placement and loading protocol with that of delayed placement in the molar region. Anatomical, occlusal and biomechanical considerations in molar sites were described as deterrent factors influencing positive outcomes of immediate protocols. Recently a novel implant design with moderately roughened surface was introduced to allow a safe and predictable immediate implant placement in molar extraction sockets. The implant has a strongly tapered body with a diameter of 8 or 9 mm, grit-blasted surface and a built-in platform switched implant-abutment connection. The wide-diameter implant body was proposed to be advantageous for engaging the molar socket walls during surgery, enhancing primary stability, minimizing the need for augmentation procedures, and facilitating immediate restoration/loading.
The main aim of this doctoral thesis was to report four-year quantitative and qualitative outcomes of this novel implant design when used for immediate restoration of single missing mandibular molar teeth. In a controlled clinical trial conducted at the School of Dentistry, University of Otago, an 8 or 9 mm diameter implant was placed into either a fresh molar extraction socket or a healed site. All the implants were immediately restored with provisional crowns within 48 hours. After eight weeks, the provisional crowns were replaced with full ceramic crowns on zirconia abutments. The overall implant success after one year of service for 24 participants in two treatment groups was 75.0%. Success rates were 83.3% for the delayed placement groups and 66.7% for the immediate placement group respectively, with no significant difference observed between the two groups (P = 0.35). After four years, six participants failed to attend the four-year recall visit but none of the implants of the remaining participants failed. The difference between the two placement groups remained insignificant (P = 0.16).
The marginal bone level changes were favourable after four years, with bone gain of 0.88 ± 1.56 mm for immediately placed implants and 0.70 ± 0.37 for delayed placed implants. No statistically significant differences were observed between the two placement groups (P = 0.79).
Implant stability measurements using resonance frequency analysis immediately after surgery identified a higher mean initial ISQ value for immediately placed implants (80.08 ± 5.07) compared with delayed placed implants (78.83 ± 3.69). In contrast, after eight weeks the mean ISQ value for delayed placed implants were higher than those placed in extraction sites (76.75 ± 10.24 vs. 75.10 ± 10.52) and this was also found after one year (83.90 ± 2.51 vs. 76.63 ± 10.65), and four years (84.40 ± 4.39 vs. 76.43 ± 13.15). The differences between the two treatment groups at different time points were not statistically significant.
Although peri-implant biological complications were noted, with bleeding on probing in at least one peri-implant site in 75.0% of the participants, the periodontal health status was generally considered fair at the four-year recall visit, with no significant differences in mean values of gingival bleeding index, plaque index and probing depth between the two placement groups. In terms of peri-implantitis, only one participant (8.5%) in the immediate placement group showed the clinical signs of peri-implantitis (bleeding on probing, probing depth > 5 mm, cumulative bone loss of > 2 mm extending beyond the third thread with circumferential peri-implant radiolucency) after four years of function.
The chipping of ceramic veneer was the most common prosthodontic complication with six event reported in the first year. Cooling rate and inadequate support for the ceramic veneers were identified as contributing factors influencing the rate of crown chipping. Nevertheless, only one event of ceramic chipping was observed in the following years of loading.
The qualitative study showed that the major factor in selecting implant treatment option was the cost of treatment rather than the potential advantages that an implant-supported prosthesis could offer. The findings emphasized the importance of providing implant patient with a realistic forecast of the outcome through establishing an effective verbal and non-verbal communication.
The rehabilitation of single missing mandibular molars by immediately-placed and restored wide-diameter implants was associated with a relative high failure rate in the first eight weeks even though the successful implants showed favourable bone changes and improvements in implant stability values after four years of function. The early implant failure rate should be weighed against the advantages of reduced treatment time and no requirements for bone grafting procedures. Further research to optimize the design of oral implants for immediate placement and/or restoration in molar sites is still needed.