Comparison of Early Implant Failure Rates Between Subjects With and Without Orthodontic Treatment Before Dental Implantation

Restoring a missing tooth or multiple teeth with dental implants is a highly predictable treatment.^1–3  To create ideal implant-supported prostheses, dental malalignment induced by a missing tooth usually necessitates orthodontic correction before dental implant placement can be performed. Bone density may decline after orthodontic therapy, and decreases in bone density can occur as early as 7 months after orthodontic treatment.^4–9  In addition, bone density changes are associated with the direction of tooth movement.^4,10  Bone density is associated with implant osteointegration time and failure rates,¹¹  and surgical protocols and loading schemes are also performed according to bone density.¹²  With longer osteointegration periods, implant rates are expected to be higher in soft bone than in hard bone.

Results of our preliminary study¹³  revealed that orthodontic treatment induced more changes in bone density of the maxilla than that of the mandible.¹³  Greater changes in bone density occur in the maxilla than in the mandible because of greater bone remodeling activity in the maxilla.⁵  In addition, the maxilla is weaker than the mandible, which induces higher levels of strain. This, in turn, results in more microcracks and microdamage to the maxilla when there is stress.⁵  However, to the best of our knowledge, no published studies have focused on the effect of orthodontic treatment on early dental implant failure rates because of changes in bone density. We hypothesized that orthodontic treatment prior to dental implantation may be associated with early dental implant rates. Therefore, the present study aimed to compare dental implant failure rates between patients with and without orthodontic treatment before dental implantation.

This retrospective study analyzed the data of adults who had undergone dental implant treatment by the same surgeon in our department at Chang Gung Memorial Hospital between January 2007 and December 2016. The exclusion criteria for subjects were as follows: implant surgery performed in patients aged >50 years, patients with a systemic condition such as diabetes or osteoporosis, and patients who smoked or had a history of taking a medication, such as bisphosphonates, known to affect bone density. Further, the exclusion criteria for implant sites included sites that underwent ridge preservation or ridge augmentation before dental implant placement and that had severe trauma.¹³ 

Subjects were divided into two groups: a treatment group (group T) that had undergone orthodontic treatment within 2 months before implant placement (between January 2007 and December 2016) and a control group (group C) that had not undergone orthodontic therapy before implant surgery (between January 2011 and December 2016). However, if the implant site was not within the orthodontic treatment area, the implant site was placed in the control group (group C) rather than the treatment group (group T). For example, if orthodontic therapy was performed on only the upper arch, the implant site of the lower arch was included in group C.

This study was conducted in accordance with the Helsinki Declaration of 1975 as revised in 2000. The protocol was approved by the hospital institutional board (Chang Gung Memorial Hospital No. 201700042B0).

All patients received 2-staged implant therapy, including stage I and stage II surgeries. Orthodontic wires were removed before implant surgery in group T. The implants used were the 3i system (Osseotite or Certain Taper, Biomet 3i, Palm Beach Gardens, Fla). All procedures were performed after flap elevation under dental local anesthesia. Primary wound closure was used with resorbable suture. Postoperative antibiotics and analgesics were prescribed for 3 days (nongrafting cases) or 7 days (grafting cases and sinus lift cases). The sinus lift method used the crest approach with osteotome technique. The used grafts included autograft, allograft, and xenograft. The suture was removed after 2 weeks (Figure).

Patients' baseline demographic and clinical data were recorded, including sex, age and along with the other parameters for the implant sites were recorded. The implant sites were divided into either the maxillary area or mandibular area. Detailed locations also were analyzed as follows: upper anterior (UA), upper premolar (UP), upper molar (UM), lower anterior (LA), lower premolar (LP), and lower molar (LM). The site conditions before, during, and after implant placement surgery (stage I surgery) were also included. Classification of bone density was carried out accorded to Misch's classification system.^14–16  Soft bone was defined as D4 bone, and the other bone types were included in the non–soft bone group. Primary stability of the dental implant was measured using the implant insertion torque (N/cm) as reference, and 30 N/cm was established as the cutoff point. In addition, the timing, including stage I, stage II, and prosthetic treatment finish, were recorded. Implants that failed before permanent crown fabrication were defined as failure cases.

Categorical variables are presented as counts and percentages, and chi-square or Fisher exact test were performed to compare differences between groups T and C, as appropriate, as each tooth was independent in this study. Age is presented as mean ± SD (standard deviation), and an independent t test was performed for group comparisons. Duration between two timepoints is presented as medians and interquartile ranges, and the Mann-Whitney U test was performed to compare differences between groups T and C. Statistical analyses were performed using IBM SPSS statistical software, version 22 for Windows (IBM Corp, Armonk, NY), and a two-tailed P value of <.05 indicated statistical significance.

A total of 124 subjects (52 women and 72 men, with a mean age of 40.1 years) with 255 implants were included in this study, and 46 subjects with 85 implants were included in the treatment group (group T). No significant differences were found between groups T and C in gender or age (both P > .05; Table 1).

A total of 255 implants were included in this study, with 85 implants in group T and 170 teeth in group C. The median duration from extraction to Stage I was significantly higher in group T than in group C (841.5 vs 130.5 days, respectively; P < .001), but the duration from stage I to stage II was significantly higher in group C than group T (188 vs 155 days, respectively; P = .006). Bone density was significantly different between groups T and C; a higher percentage of group C patients had non–soft bone than group T patients (P = .003). No significant differences in any other parameters were found between the two groups (Table 2).

In the maxilla, group T had 27 implants and group C had 61 implants. The median duration from extraction to stage I was significantly higher in group T than in group C (738 vs 147 days, respectively; P = .004). Bone density was significantly different between groups, with a higher percentage of non–soft bone (density of D1, D2, and D3) demonstrated in group C than in group T (both P = .001). Implant insertion torque <30 N/cm was higher in group T than in group C (58.38% vs 25%, respectively; P = .022; Table 3).

In the mandible, group T had 58 implants and the control group had 109 implants. The median duration from extraction to stage I was significantly higher in group T than in group C (859.5 vs 130 days, respectively; P < .001). No significant differences were found in any other parameters between groups T and C (all P > .05; Table 4).

No significant differences in failure rates for maxilla implants were found between the treatment group receiving preimplant orthodontic treatment and the control group, which did not receive orthodontic treatment; however, the implant failure rate in the treatment group was higher than that in the control group. For mandible implants, no significant differences in any parameter were found between the two groups.

The main risk factors reported previously for early implant failure included smoking, shorter implant, implant inserted in the posterior area of the jaw, implants placed in small-volume bone or soft bone, and implants placed in the maxilla.^17,18  Low implant insertion torque and implant insertion into soft bone were associated with an increased implant failure rate in the maxilla.¹⁸  In the present study, the group receiving orthodontic treatment had a higher percentage of soft bone and implant insertion torque <30 N/cm than found in controls; therefore, soft bone and higher implant insertion torque may be important contributing factors to the higher implant failure rate in the treatment group.¹³  In the present study, 4 implant failures occurred in treatment group patients. All 4 implant sites were placed in the first molar area; in addition, a sinus lift using an osteotome technique was performed in all 4 cases. Three poor osteointegration cases and one sinus infection were included in the above failures. Previous studies reported a survival rate for the osteotome technique ranging from 85.1% to 100%, which was comparable to that found in traditional implantology.^19–21  The survival rates of sinus lift (total teeth: 49/54 = 90.74%) in the present study were similar to the rates shown above. However, the osteotome technique in the treatment and control groups had survival rates of 75% (12/16) and 97.4% (37/38), respectively. The difference may be associated with inadequate volume and soft bone quality in the upper first molar sites of the treatment group, which was induced by bone density change in the maxilla derived from orthodontic treatment.

Shifts in the balance between bone formation and bone resorption are influenced by many factors, including aging, postmenopausal status, chronic inflammation, and a number of other factors. To avoid such factors in this study, we excluded subjects who were older than age 50 years, which should decrease the confounding effects of aging and menopause on bone density.^22,23 

Bone density changes observed during orthodontic treatment persist until the orthodontic treatment has been completed. For this reason, more time may be needed for osteointegration before functional loading.¹²  However, no study has shown precisely how long bone density improvement will take.⁶  Therefore, delaying implant placement until the bone density recovers is not suggested.¹³ 

A major limitation of this study was the small sample size, especially the number of upper teeth in the treatment group. Any space in the maxilla can usually be closed during orthodontic treatment; the treatment group actually had fewer maxillary teeth than mandibular teeth. Therefore, further investigation of the effects of other confounding factors based on a larger sample size and clinical trial study is necessary.

No significant differences were found in failure rates of either jaw between patients receiving orthodontic treatment prior to implant surgery and controls not receiving preimplant orthodontic treatment. However, the implant failure rate in the maxilla was higher for patients receiving orthodontic treatment than for those who did not receive preimplant treatment, especially in patients receiving implant surgery combined with sinus lift. Additional study with a larger sample size and longer follow-up period is necessary to confirm the results of the present study and to identify other confounding factors.

Abbreviations

LA

lower anterior teeth

LM

lower molars

LP

lower premolars

UA

upper anterior teeth

UM

upper molars

UP

upper premolars

The authors declare no conflict of interest.